Considering a multi-user Downlink scenario, this paper studies transmit antenna selection (AS) for uniform rectangular arrays (URA). A key contribution of this work is the investigation of the trade-off between AS and the array directivity (or gain), and its impact on spectral efficiency (SE) and energy efficiency (EE). In this context, to improve EE of the system, a directivity-aware transmit AS and power allocation problem is formulated and solved using a sequential approach. For AS, two schemes are proposed: Block selection (BS) and L´evy flight based binary particle swarm optimization (LFBPSO), while for power allocation, an iterative quadratic transform method is employed in combination with Dinkelbach algorithm for EE maximization. The performance of the AS schemes is evaluated with respect to SE, EE and computational complexity. The results show that the array directivity varies with the subset of selected antennas and has a direct impact on the performance of the AS schemes in terms of achievable SE and EE. Furthermore, AS without considering the directivity can incur a loss in the array gain of up to 2 dB in a λ/2 spaced array. The results also show that LFBPSO outperforms other AS schemes with respect to SE and EE. Finally, another important contribution of this work is the experimental validation of the impact of array directivity on the AS process. This is demonstrated by replacing the isotropic antenna array with a measured 4×8 uniform rectangular array of patch antennas in the simulation framework.

This paper investigates the block error rate (BLER) of three encoding schemes: joint encoding (JE), separate encoding (SE), and rate splitting (RS) in low-throughput massive multiple input and multiple output (mMIMO) networks with finite blocklength transmission. To reduce pilot overhead, we first partition users via k-means clustering based on their spatial coordinates, by which the pilot sequences can be reused among different groups. Then, we apply a minimum mean square error (MMSE) estimator to examine their instantaneous signal-to-interference-plus-noise ratios (SINRs). In particular, a local successful interference cancellation is proposed to mitigate co-channel interference for the RS scheme. Then, we formulate min-max problems for optimizing the error performance, with power control coefficients, combining vectors, and blocklength being their variables. Additionally, we employ the iterative MMSE combiner as the combining vector and then transform the problem for minimizing the BLER to a max-min problem maximizing the SINR at each iteration based on the monotonicity of the BLER expression with respect to the SINR. Power control coefficients are then updated by solving the reformulated geographic programming (GP) problem. Furthermore, the golden-section and bisection methods are applied to optimize the blocklength allocation strategy for the SE scheme and to search for the achievable BLER for the RS scheme. Simulation results, using network availability as the performance metric, demonstrate the comparable performance of the JE and RS schemes when combined with the proposed solving methods, whereas the SE scheme exhibits moderate performance.

This paper proposes a closed-form low-complexity method for RIS configuration in a multi-user cell-free massive MIMO (maMIMO) network. Leveraging the large-scale fading (LSF) distribution and spatial diversity of the distributed network architecture, the proposed method jointly enhances the end-to-end channel gain and the degrees of freedom for interference suppression. An LSF-based algorithm is introduced to maintain fairness among user equipment (UEs). We have analysed the proposed method under short-term and long-term RIS configuration schemes and different CSI acquisition strategies. A closed-form channel estimation error variance for$b$-bit digital RIS is derived, and the non-negligible impact of digital RIS on pilot contamination is quantified. To explore different trade-offs between spectral efficiency (SE) maximisation and fairness, we also propose an element-selection based RIS configuration method. To verify the performance, we derive three achievable SE equations for perfect CSI and imperfect CSI scenarios with a fully centralised cell-free maMIMO operation. Numerical results show that the proposed schemes outperform the baseline under three linear uplink combining methods and non-linear successive interference cancellation (SIC).

Reconfigurable Intelligent Surfaces (RIS) have emerged as a promising technology for enabling seamless wireless connectivity, particularly in environments characterized by non-line-of-sight (NLoS) propagation and signal blockages. To enhance performance in such scenarios, densely deployed RIS configurations is a promising solution. In this context, this paper investigates the impact of inter-element spacing on the gain and the energy efficiency (EE) of RIS-assisted communication system. Unlike previous works, we formulate the received signal model that incorporates the array directivity and show how the array gain varies with the change in the inter-element spacing. The performance of the standard (where the spacing is half of the wavelength) and dense RIS (where the spacing is less than half of the wavelength) configurations is compared in terms of, 1) beam pattern and array gain while considering quantized and unquantized phase shifts, 2) variation in the number of RIS elements, and 3) the trade-off between EE and array gain. Results reveal that while dense RIS offers slightly improved array gain compared to standard RIS, it incurs higher power consumption and reduced EE.

This paper investigates point-to-point uplink rate-splitting (RS) transmission in the finite blocklength (FBL) regime. The system is configured with a dual-polarized (DP) multiple-input and multiple-output (MIMO) antenna array at the receiver and a pair of DP antennas at the transmitter. During transmission, vertically and horizontally polarized antennas at the transmitter are employed to transmit two independent data streams partitioned via RS. At the receiver, a successive interference cancellation (SIC)-free detection scheme is adopted to exploit the polarization-domain degree of freedom (DoF), thereby eliminating the need for SIC. To validate the efficacy of the proposed RS-DP scheme, we optimize the combining vectors for both vertical and horizontal data streams to maximize the sum spectral efficiency under FBL constraints. Simulation results demonstrate that the RS-DP scheme achieves performance comparable to the conventional RS-SIC approach, thereby corroborating its effectiveness in balancing system performance and decoding complexity.

Joint Communication and Sensing (JCAS) integrates communication and sensing (C&S) functions into a single system by sharing the same transmit signal. This paper focuses on a radar-centric JCAS system that transmits probing signals to detect targets while delivering communication data to users on the downlink. We aim to design a joint waveform that achieves three objectives: minimizing the mismatch between the desired and actual JCAS beam patterns, reducing multi-user interference (MUI), and adhering to per-antenna power constraints. We propose a waveform design based on multiobjective optimization to address the challenges associated with waveform design, highlighting the trade-offs between sensing and communication performance. To establish a balance between C&S performance, we introduce a trade-off control parameter. Initially, we reformulate the waveform design problem as an unconstrained problem and then present a new low-complexity waveform synthesis algorithm using gradient descent (GD). Finally, numerical results demonstrate the impact of the trade-off control parameter and demonstrate the effectiveness of our proposed algorithm compared to state-of-the-art techniques, ensuring optimal performance for both C&S in JCAS systems.

Uniform planar arrays (UPAs) are widely employed in practical systems, yet the study of antenna selection for UPAs remains limited. In particular, the interplay between selected antenna subsets and directivity has been overlooked in the existing literature. This paper addresses this by exploring how different subsets of selected antennas affect directivity and developing effective antenna selection strategies for UPA with a rectangular lattice. Our findings reveal that different subsets of selected antennas can lead to significantly different values for directivity, influencing selection outcomes compared to scenarios where directivity is not considered. Furthermore, we propose and compare four antenna selection strategies: 1) Column Selection (RS), 2) Row Selection (CS), 3) Full Aperture Greedy Selection (FAGS), and 4) Hybrid Initialization Binary Particle Swarm Optimization (HBPSO). With careful initialization of the particles, HBPSO achieves a spectral efficiency performance close to exhaustive search and surpasses other strategies. Moreover, incorporating directivity into the selection process significantly affects the performance of these strategies.

In this paper, we focus on the energy efficiency (EE) optimization and analysis of reconfigurable intelligent surface (RIS)-assisted multiuser downlink near-field communications. Specifically, we conduct a comprehensive study on several key factors affecting EE performance, including the number of RIS elements, the types of reconfigurable elements, reconfiguration resolutions, and the maximum transmit power. To accurately capture the power characteristics of RISs, we adopt more practical power consumption models for three commonly used reconfigurable elements in RISs: PIN diodes, varactor diodes, and radio frequency (RF) switches. These different elements may result in RIS systems exhibiting significantly different energy efficiencies (EEs), even when their spectral efficiencies (SEs) are similar. Considering discrete phases implemented at most RISs in practice, which makes their optimization NP-hard, we develop a nested alternating optimization framework to maximize EE, consisting of an outer integer-based optimization for discrete RIS phase reconfigurations and a nested non-convex optimization for continuous transmit power allocation within each iteration. Extensive comparisons with multiple benchmark schemes validate the effectiveness and efficiency of the proposed framework. Furthermore, based on the proposed optimization method, we analyze the EE performance of RISs across different key factors and identify the optimal RIS architecture yielding the highest EE.

This paper investigates the uplink power control scheme for massive multiple-input and multiple-output non-orthogonal multiple access (mMIMO-NOMA) in massive ultra-reliable and low-latency communications (mURLLC) for Industrial Internet of Things (IIoT) applications. By the proposed NOMA scheme, the connected sensors are divided into several groups, and only group-level successive interference cancellation (GL-SIC) is considered at the receiver to reduce the decoding complexity and processing delay. Two schemes, i.e., mMIMO-NOMA with and without pilot sharing, are developed to fully explore the superiority of mMIMO-NOMA in mURLLC with a finite blocklength. For both schemes, the closed-form expressions of the achievable rate are obtained for the minimum mean square error (MMSE) estimator and zero-forcing (ZF) detector. Next, to address the formulated sum rate maximization problem, we develop a successive condensation approach (SCA)-based algorithm to jointly optimize pilot and data power. Besides, the max-min fairness (MMF) rate is also analyzed by verifying the feasibility of the problem. Finally, the simulation results demonstrate the effectiveness of the proposed SCA power control scheme. In addition, the advantages of the proposed two NOMA schemes in both sum rate and sum MMF rate are verified compared to traditional multi-user MIMO systems in mURLLC scenarios.

Beamforming techniques have a significant impact on the capacity of downlink transmission in cellular systems. Beamforming can offer significant performance enhancements for wireless systems by allowing directional signal transmission which can improve the Signal to Noise Ratio (SNR), co-channel interference, and network capacity. These benefits can be substantial in Massive MIMO systems but there are costs associated with the large number of antenna elements. In this paper, the trade-off between spectral efficiency and energy efficiency of digital and hybrid beamforming of Massive MIMO are analyzed for different numbers of RF chains. Based on simulation results, suitable ratios for the number of RF chains to the number of antennas are determined for the base station in order to achieve a good trade-off between spectral and energy efficiency.

Reconfigurable intelligent surface (RIS) is considered one of the most promising technologies for beyond 5G and 6G communications with its potential to redefine the propagation environment and the simplicity of implementation. This paper proposes a closed-form low-complexity scheme for RIS configuration in a distributed multi-user MIMO (MU-MIMO) network and introduces a joint initial access and grouping scheme for RIS assignment. By leveraging the eigenvalue distribution of the access point-side channel, the proposed method aligns signals at orthogonal subspaces and effectively increases the degree of freedom for interference suppression. To verify the performance, we derive two achievable spectral efficiency (SE) equations for centralised and distributed operations. Numerical results show that the proposed scheme outperforms the baseline obviously under three different uplink combining methods.

This study delves into the radiation pattern syn-thesis of reconfigurable intelligent surfaces (RIS) / reflection metasurfaces. Through superimposing multiple single-reflection profiles, which comprise the amplitude and/or phase settings of all constituent elements, a single incident wave can be effectively reflected in multiple asymmetric directions. However, some mismatch and interference between adjacent reflection beams may be caused by this superposition as well. Additionally, it is constrained by the inherent limitation that achieving linear and continuous amplitude adjustments and phase shifts in real-world designs is challenging. Consequently, the reconfigurable amplitude and phase must be approximated to discrete values, necessitating the arrangement of reflection profile before and after optimization based on integer. Therefore, in this paper, we adapt the traditional particle swarm optimization (PSO) algorithm to discretized integer-based PSO by proposing the concepts of ‘discard rate’ and ‘knowledge.’ With the enhancement of the integer-based programming, the multiple asymmetric reflection pattern can be synthesized with suppressed sidelobe levels within limited iterations and time cost.

This paper presents an achievability bound that evaluates the exact probability of error of an ensemble of random codes that are decoded by a minimum distance decoder. Compared to the state-of-the-art which demands exponential computation time, this bound is evaluated in polynomial time. This improvement in complexity is also attainable for the original random coding bound that utilizes an information density decoder. The general bound is particularized for the binary symmetric channel, the binary erasure channel, and the Gaussian channel.

The channel estimation techniques for intelligent reflecting surface (IRS)-assisted communication are investigated in this paper. IRS-aided communications rely on the accurate and efficient channel estimation of IRS component-related channels. But conventional channel estimation methods are inefficient due to the sequential estimations of pilot signals. This paper proposes a hybrid coding method, which changes the amplitude and phase of the signal over time and generates two pilot signals at the required frequencies to estimate the channel using interpolation. By using this method, a new send-and-reflect estimation scheme is proposed for separated channel estimation. The method is evaluated based on discrete and continuous coding, respectively. Numerical results show that the proposed method significantly reduces the channel estimation time with a trivial penalty on transmitting accuracy. Besides, the feasibility of discrete hybrid coding is also validated through simulations.

In reconfigurable intelligent surface (RIS)-assisted wireless communication systems, the pointing accuracy and intensity of reflections depend crucially on the ’profile,’ representing the amplitude/phase state information of all elements in a RIS array. The superposition of multiple single-reflection profiles enables multi-reflection for distributed users. However, the optimization challenges from periodic element arrangements in single-reflection and multi-reflection profiles are understudied. The combination of periodical single-reflection profiles leads to amplitude/phase counteractions, affecting the performance of each reflection beam. This paper focuses on a dual-reflection optimization scenario and investigates the far-field performance deterioration caused by the misalignment of overlapped profiles. To address this issue, we introduce a novel deep reinforcement learning (DRL)-based optimization method. Comparative experiments against random and exhaustive searches demonstrate that our proposed DRL method outperforms both alternatives, achieving the shortest optimization time. Remarkably, our approach achieves a 1.2 dB gain in the reflection peak gain and a broader beam without any hardware modifications.

Beam alignment accuracy is critical for millimeter wave communications employing beamforming techniques. However, due to the high cost and complexity of the traditional solutions, especially beam sweeping, learning-based methods that use contextual data to select optimum beam orientations are emerging as a desirable technology for mobility applications such as vehicle to everything. However, the majority of available systems involve supervised learning, in which the training data is acquired ahead of time. In this study, we create an online learning algorithm for beam pair selection using a multi-armed bandit framework. The learning machine recognizes beam directions in a specified codebook separated by 3 dB beamwidths and makes recommendations for a set of beam combinations to complete beam training. In vehicular communication applications, the learning algorithm’s robustness to location inaccuracy provides a trade-off between overhead and alignment efficiency.

In response to the rise of crime in short-range communication systems, a novel method for authenticating co-located devices is presented. Our method, Channel Randomness Yields Secure Proximity (ChRYSP) exploits the fundamental properties of the wireless RF channel to protect against relay attacks and replay attacks - the two most common impersonation attacks in short-range communication systems. ChRYSP is based on the fact that two devices in close proximity - typically a couple of wavelengths - experience correlated fading on a received RF signal. ChRYSP is facilitated by the employment of a helper node and can be implemented by low-cost, narrowband transceivers. Numerical results demonstrate high accuracy in detecting both relay attacks and replay attacks.

Cell-free massive multiple-input multiple-output (MIMO) is considered as a promising network architecture for beyond-5G communications with its potential of supporting the exponentially increasing mobile connections and resolving the inherent disadvantage of canonical cellular networks. This paper proposes a scalable pilot assignment algorithm for user-centric cell-free massive MIMO systems. The proposed scheme considers the eigenspace of channel vectors and minimizes the sum pilot contamination caused to all the serving APs of the currently considered UE. Interference-suppressing combining schemes are utilized in both centralized and distributed operations to evaluate the performance of the proposed algorithm. Furthermore, max-min SE fairness is considered by applying fractional power control. Numerical results show that the proposed scheme outperforms previous methods while providing the scalability to the network.

Measuring customer experience on mobile data is of utmost importance for global mobile operators. The reference signal received power (RSRP) is one of the important indicators for current mobile network management, evaluation and monitoring. Radio data gathered through the minimization of drive test (MDT), a 3GPP standard technique, is commonly used for radio network analysis. Collecting MDT data in different geographical areas is inefficient and constrained by the terrain conditions and user presence, hence is not an adequate technique for dynamic radio environments. In this paper, we study a generative model for RSRP prediction, exploiting MDT data and a digital twin (DT), and propose a data-driven, two-tier neural network (NN) model. In the first tier, environmental information related to user equipment (UE), base stations (BS) and network key performance indicators (KPI) are extracted through a variational autoencoder (VAE). The second tier is designed as a likelihood model. Here, the environmental features and real MDT data features are adopted, formulating an integrated training process. On validation, our proposed model that uses real-world data demonstrates an accuracy improvement of about 20% or more compared with the empirical model and about 10% when compared with a fully connected prediction network.

Setting the transmit power setting of 5G cells has been a long-term topic of discussion, as optimized power settings can help reduce interference and improve the quality of service to users. Recently, machine learning (ML)-based, especially reinforcement learning (RL)-based control methods have received much attention. However, there is little discussion about the generalisation ability of the trained RL models. This paper points out that an RL agent trained in a specific indoor environment is room-dependent, and cannot directly serve new heterogeneous environments. Therefore, in the context of Open Radio Access Network (O-RAN), this paper proposes a distributed cell power-control scheme based on Federated Reinforcement Learning (FRL). Models in different indoor environments are aggregated to the global model during the training process, and then the central server broadcasts the updated model back to each client. The model will also be used as the base model for adaptive training in the new environment. The simulation results show that the FRL model has similar performance to a single RL agent, and both are better than the random power allocation method and exhaustive search method. The results of the generalisation test show that using the FRL model as the base model improves the convergence speed of the model in the new environment.

Channel-State-Information (CSI)-based Key Generation (KG) is an attractive technique for generating symmetric cryptographic keys due to low memory and processing power requirements. CSI-based KG protocols also promise high key rates for vehicular communication channels due to the rich entropy inherited in such dynamic channels. However, as a relatively new field, physical layer security is often limited to idealistic scenarios. The assumption that the channels decorrelate at a half-wavelength distance brings secrecy vulnerabilities that are quantified and brought to attention. This paper convinces that, even in rich scattering environments, the distance of half-wavelength is not perfectly secure, and it may be disastrous under non-idealistic antenna gain patterns. Aiming to bring CSI-based KG a step closer to practical implementation, this paper drops one of the most common idealistic assumptions in the field of PLS and redefines secure distance.

Orthogonal Multiple Access, or OMA, schemes have been widely adopted in microwave mobile networks to reduce interference. In the sub-6GHz spectrum, current LTE and 5G systems exploit the orthogonal communication resources in terms of time, frequency or code in order to improve the Signal-to-Interference ratio, leading to fast and reliable links. However, the low spectral usage of OMA schemes make them unsuitable for use in future generation mobile networks, especially in the mmwave spectrum. The high propagation losses at mmwave frequencies and the use of M-MIMO antennas allow experimentation with new techniques that allow a highly aggressive spectrum utilization. In this paper, a beam-based Non-orthogonal Multiple Access scheme is combined with Spectrum Sharing as a potential solution for successfully meeting the requirements set for the future generation mmwave networks. Single captures of a network were ray-traced under multiple access strategies and network performance was evaluated in terms of SINR and throughput.

This paper investigates the impact of spectrum sharing and network densification through sectorization in a local mmwave mobile network. Channel propagation was ray-traced in a real world environment while antenna radiation patterns were generated based on measurements of a real patch antenna. Network performance was quantified in therms of SINR (Signal-to-Interference-and-Noise-Ratio) and throughput using SINR-CQI (Channel Quality Indicator) mapping and formulas found in 3GPP (3rd Generation Partnership Project) Rel.15. Comparisons between the same `captures' of the network were made under different sectorization and spectrum access conditions. Simulation results support that the benefits of combining spectrum sharing and sectorization are multifold but the higher sectorization strategies do not always translate to better network performance. The impact of interference should be taken into account when aggressively re-using the spectrum in a non-orthogonal manner, even at mmwave frequencies.

We present a novel scheme for testing the proximity of an Ultra-high frequency (UHF) Radio Frequency Identification (RFID) transponder, based on the fact that two co-located devices experience correlated channel fluctuations on a reference signal. When the interrogator requests data from the transponder, the latter performs backscattering modulation on the carrier-wave provided by a helper node. The interrogator applies signal processing techniques on the backscattered signal to extract the channel characteristics of the channel between itself and the helper, and the channel between the transponder and the helper. If the two channels are correlated, then the proximity of the transponder is validated by the fundamental properties of spatial channel correlation. The proposed scheme can be employed seamlessly in RFID systems from the transponder's point of view and is resilient to distance-fraud attack.

Improved coverage, high data rates and Quality of Service (QoS) constitute important features of 5G networks. The spectrum limitations, currently faced in 4G, will be resolved by adopting millimeter-Wave (mmWave) frequencies technologies, which will also result in high throughput. High mobility scenarios will pose additional challenges in 5G communications, due to the rapid change in the environment, i.e. channel coefficients and Doppler effect. In this paper, we introduce our research on the achievable throughput, coverage and Signal-to-Noise-Ratio (SNR), considering a High-Speed Train (HST) in a simulated rail scenario in the UK. The paper's premises are that the line-of-sight (LOS) rays dominate the mmWave links and the sectors with the highest antenna gains are the ones around the LOS ray direction. With the proposed non-Uniform configurations, we aim to find the sectors which cover the LOS ray in fewer search steps. This reduces the BF setup time significantly and saves power while at the same time keeping throughput stable. Link performance evaluation of the proposed scheme is provided, and the number search steps are then compared to standard search algorithms.

This paper studies the indoor localisation of WiFi devices based on a commodity chipset and standard channel sounding. First, we present a novel shallow neural network (SNN) in which features are extracted from the channel state information (CSI) corresponding to WiFi subcarriers received on different antennas and used to train the model. The single-layer architecture of this localisation neural network makes it lightweight and easy-to-deploy on devices with stringent constraints on computational resources. We further investigate for localisation the use of deep learning models and design novel architectures for convolutional neural network (CNN) and long-short term memory (LSTM). We extensively evaluate these localisation algorithms for continuous tracking in indoor environments. Experimental results prove that even an SNN model, after a careful handcrafted feature extraction, can achieve accurate localisation. Meanwhile, using a well-organised architecture, the neural network models can be trained directly with raw data from the CSI and localisation features can be automatically extracted to achieve accurate position estimates. We also found that the performance of neural network-based methods are directly affected by the number of anchor access points (APs) regardless of their structure. With three APs, all neural network models proposed in this paper can obtain localisation accuracy of around 0.5 metres. In addition the proposed deep NN architecture reduces the data pre-processing time by 6.5 hours compared with a shallow NN using the data collected in our testbed. In the deployment phase, the inference time is also significantly reduced to 0.1 ms per sample. We also demonstrate the generalisation capability of the proposed method by evaluating models using different target movement characteristics to the ones in which they were trained.

Improved coverage, high data rates and Quality of Service (QoS) constitute important features of 5G networks. The spectrum limitations, currently faced in 4G, will be resolved by adapting millimeter-Wave (mmWave) frequencies technologies, which will also result in high throughput. High mobility scenarios will pose additional challenges, in 5G communications, due to the rapid change in the environment, i.e. channel coefficients and Doppler effect. In this paper, we introduce our research on the achievable throughput, coverage and Signal-to-Noise-Ratio (SNR), considering a High-Speed Train (HST) traveling on two different rail scenarios in the UK. Applying two beamforming (BF) techniques (maximum ray selection and codebook based) and employing a fixed beam pattern in the antennas, we compare the performance of the different schemes, considering different distances between the Access Points (APs) at the rail track, looking also at the minimum network requirements to maintain connection. We show that overall the employment of BF improves the achievable throughput and SNR, with the codebook based approach achieving constant coverage with stable throughput in a 300m radius mmWave cell.

In this work we propose a fronthaul compression scheme for distributed MIMO systems with multi-antenna receivers, in which, prior to signal quantisation, dimension reduction is performed at each receiver by matched filtering the received signal with a subset of the local user channel vectors. By choosing these matched filter vectors based on global channel information, a high proportion of the potential capacity may be captured by a small number of signal components, which can then be compressed efficiently using local signal compression. We outline a greedy algorithm for selecting the matched filtering vectors for each receiver, and a local transform coding approach for quantising them, giving expressions for the resulting system sum and user capacities. We then show that the scheme is easily modified to account for imperfect CSI at the receivers. Numerical results show that with a low signal dimension the scheme is able to operate very close to the cut-set bound in the fronthaul limited regime, and demonstrates significant improvements in rate-capacity trade-off versus local compression at all operating points, particularly at high SNR.

In this study, multi‐user (MU) underwater acoustic communication is investigated using massive multiple‐input multiple‐output (MIMO) orthogonal frequency division multiplexing (OFDM)‐based orthogonal time frequency space modulation (OTFS) systems. The performance of a 4‐user scenario is evaluated over a simulated 1 km vertically‐configured time‐varying underwater acoustic channel (UAC) in terms of bit error rate and maximum achievable bit rate. Considering 64‐QAM and frequency‐domain pilot‐based channel estimation, it is shown that the underwater vehicles employing the OFDM‐based OTFS modulation outperform those using the conventional OFDM modulation in a dynamic UAC. The application of massive MIMO allows the four underwater vehicles to use the same time and frequency resources to transmit their information reliably to a surface station. Furthermore, it is shown that each underwater vehicle in the MU‐massive MIMO transmission scenario can achieve an effective bit rate as high as 198.7 kbps over the 1 km UAC using four transmitting transducers.

Low delay and high reliability of safety broadcast messages are critical to future intelligent transport systems (ITS). The main objective of this paper is to propose a novel safety broadcast system model to satisfy the latency and reliability requirements of vehicle-to-vehicle (V2V) applications. Second, using this proposed model, a comprehensive performance evaluation is conducted under different technologies (cellular and IEEE 802.11p) for different vehicle densities in rural and urban scenarios based on a realistic system-level simulator. The performance is further improved by using application layer raptor Q codes as compared to the standard repetition codes proposed in the literature. Results show a coverage improvement of 144 m (rural) and 45 m (urban) using cellular V2V with raptor Q codes as compared to IEEE 802.11p for a target end-to-end delay of 5 ms. This is because IEEE 802.11p suffers from preamble channel estimation especially in urban areas with high collision rate due to the hidden terminal problems. In case of a traffic jam, with higher vehicle density, full duplex (FD) operation is needed for cellular V2V to achieve the target delay. FD operation satisfies the latency requirements even when half the resources are available for V2V transmissions.

We propose practical sets of rules for adapting Clear Channel Assessment (CCA) and Transmit Power (TP) parameters by simulating ensembles of randomly generated wireless networks and collecting throughput statistics. The rules' performances depend strongly on network topology, with increases in throughput in many cases. However, networks with a high clustering coefficient are often adversely effected by the adaptations. But simulations of small-scale networks show that apparently adverse adaptations may still yield benefits for uneven demand combinations. Finally, we have found that throughput is not usually correlated with the number of hidden or exposed nodes in any non-trivial network set-up.

In this work we analyse the capacity of the distributed MIMO uplink when transform coding is applied locally at each remote radio head (RRH) to compress fronthaul traffic. Assuming the use of optimal scalar compression, we derive a closed form capacity expression for the distributed MIMO uplink under Gaussian signalling, which is shown to be a function of both local and global channel eigendecompositions. We then outline two rate allocation schemes for efficiently allocating the available fronthaul to the compressed scalars, based on either local or global channel state information (CSI). Numerical results under Rayleigh fading conditions are presented which show that transform coding can provide a significant compression gain relative to direct signal quantisation, which grows as the number of antennas deployed at each RRH increases. Results also show that allocating fronthaul based on global CSI significantly improves performance, especially as the number of RRHs deployed increases.

Signal to interference plus noise ratio (SINR) is a widely common performance metric used in the majority of massive multiple-input, multiple-output (Ma-MIMO) research. This metric requires prior knowledge of the user channel vectors and the interference caused by inaccurate channel state information (CSI). However, the interference caused by inaccurate CSI can't be calculated for real-world scenarios. On the other hand, a comprehensive performance indicator can be achieved by the Error Vector Magnitude (EVM) metric in real-world scenarios. This considers all impairments upon the transmitted symbol as seen at the receiver. However, measuring the EVM values for a subset of users requires each user to retransmit data symbols. This paper presents an estimation method with high accuracy by associating EVM to SINR values for Ma-MIMO with zero-forcing (ZF) and Minimum Mean Square Error (MMSE). Also introduced is a novel EVM prediction method for subset of users taken from the original set of simultaneous users in a single cell Ma-MIMO. This method jointly relies on the channel correlation between users and the EVM performance to predict the EVM values for a subset of the available users without the need to retransmit data symbols. This method considers the user channel vector and the interference caused by inaccurate CSI, which makes it suitable for Ma-MIMO algorithms, such as user grouping and power control. Real-world experimental data-sets with real-time results are carried out to validate the EVM prediction method using software-defined radio Ma-MIMO testbed.

To examine complex cellular networks, system-level simulation is one possible approach used by various radio planning tools. There is thus an opportunity to provide a comprehensive study including building blocks and simulation flow. In this article, the heterogeneous cellular network in downlink transmissions is simulated by means of system-level approach. Not only small cell deployments but also scheduling techniques are investigated in this simulation. The user throughput distribution is evaluated when varying the small cell placement, number of small cells and scheduling algorithms. Due to the use of small cells and proper scheduler, the user throughput could be significantly enhanced.

Because of a significant increase in heterogeneous user demands, carrier aggregation has been widely proposed to provide higher data rates. Due to a variety of carrier aggregation implementations, the question is what the efficient resource allocation with carrier aggregation could be. Therefore, in this paper, a homogeneous cellular network is modelled using a system-level simulation of the downlink. The resource allocation, including component carrier selection and resource block scheduling, is investigated under different carrier aggregation types and operating frequency bands. The performance is then evaluated in terms of user throughput. By using the proper combination of carrier selection and scheduling, not only can the load across all carriers be balanced but also higher throughput is obtained. However, the use of resource allocation with carrier aggregation should be adapted since there is a trade-off of user performance and implementation complexity.

Seamless broadband connectivity and high data rates are a prerequisite for 5G networks, especially for connectivity to moving platforms. The H2020 5G-PICTURE project considers a complete network solution that supports operational and end-user services, for both Information and Communications Technology and vertical industries such as 5G rail. Targeting wireless access communication to High Speed Trains (HST), this paper presents an overview of both LTE-A and millimeter-Wave (mmWave) solutions. Moreover, we present a performance evaluation, considering a train, equipped with two mmWave antennas (front and rear), traveling along two 1.4km rail tracks, with several mmWave Access Points (APs) placed at the trackside. With the aid of a ray-tracing tool, to obtain realistic channels, and an IEEE 802.11ad simulator, assuming receive diversity, we investigate the impact of beamforming, frequency band (26GHz and 60GHz) and cell radius on the achievable throughput. Based on our results, the employment of beamforming considerably increases the system's throughput. Moreover, we show that even when APs on the trackside are placed 800m apart, the coverage is almost seamless. Finally, investigating the angular profile of each beam, we suggest a beamwidth of 20° to maintain connection to a distance greater than 30m from the APs, for the considered scenarios.

This paper investigates the connectivity of vehicles to road-side infrastructure (V2I) using a mmWave system at 60 GHz. Two highways in the UK were selected as virtual test drive routes. Detailed 3D geographic data of the city are incorporated into a 3D mmWave ray-tracing tool for the purpose of generating realistic channel matrices for use in an IEEE 802.11ad physical layer (PHY) simulator. The spatial and temporal multipath components of the radio channel between a road side unit (RSU) and the vehicles are modelled. Up to half million point-to-point ray tracing simulations were performed. Important parameters such as delay and angular spread for channel modelling have been extracted from the results. Statistical analysis for each route is presented. Spatial and polarimetric convolution between the multipath ray data and the appropriate beam pattern is performed in order to generate throughput predictions using a link level abstraction simulator. The throughput performance along the routes is presented for the Single Carrier (SC) transmission scheme of IEEE 802.11ad. A comparison between isotropic antennas and phased array beamforming is presented. It was found that three 60 GHz RSUs provided full coverage for a 2 km highway route. The simulation results provide a useful insight on the RSU deployment requirements.

Orthogonal Time Frequency Space (OTFS) is a recently proposed modulation scheme for doubly-dispersive channels in which symbol multiplexing and processing is performed in the Doppler-delay domain, rather than conventional time-frequency domain. In this paper, the performance of OTFS is compared to orthogonal frequency division multiplexing (OFDM) for line-of-sight mobility automotive channels. Ray launching is used to simulate the channel for two different dynamic 3D vehicle to infrastructure transmission environments, using a Kirchhoff model for diffuse scattering from rough surfaces. Bit level simulations for transmission from a transmitter moving at speeds of 13 m/s and 31 m/s are then carried out, for both OFDM and OTFS. We find that with short length block codes OTFS outperforms OFDM in all simulated scenarios, reducing the block error rate by more than 50% on average. Unlike previous work, simulations are performed in the time domain using practical rectangular pulse shapes, rather than theoretical `ideal pulses'. We provide an analysis of these pulses, and derive relevant expressions for the doubly dispersive channel in terms of the multipath delays and Doppler shifts.

In this paper we investigate the application of the non-orthogonal multiple access (NOMA) technique for multiuser underwater acoustic (UWA) communication. The NOMA scheme can be implemented using either orthogonal frequency division multiplexing (OFDM) or filterbank multicarrier (FBMC) modulation for waveform shaping. In order to boost the throughput over a 1 km time-varying underwater acoustic channel (UAC), spatially multiplexed multiple-input multiple-output (MIMO) systems are considered. We evaluate the bit error rate (BER), packet error rate (PER) and maximum bit rate performances of Turbo-coded NOMA-OFDM and NOMA-FBMC systems for a 2-user scenario where both users utilize the same frequency bandwidth. It is shown that while both the NOMA-OFDM and NOMA-FBMC systems show comparable performance in terms of BER and PER, the MIMO NOMA-FBMC system however achieves higher bit rates than the OFDM-based system.

The present paper considers the application of massive multiple-input multiple-output (MIMO) to a multi-user (MU) underwater acoustic (UWA) communication system. In the scope to achieve a high throughput within a limited acoustic bandwidth, we consider filterbank multicarrier (FBMC) modulation for waveform shaping instead of the widely used orthogonal frequency division multiplexing (OFDM). We assess the performance of the system in a 1 km simulated time-varying underwater acoustic channel (UAC) in terms of bit error rate (BER), packet error rate (PER) and maximum achievable throughput. The transmission scenario consists of four users, each one equipped with multiple transmitting hydrophones. We show that the implementation of massive MIMO at the receiver allows all the users to use the same frequency bandwidth to transmit their information reliably to the receiver. Therefore, a high spectral efficiency and throughput can be achieved, making the transmission of multimedia data such as high quality real-time video a reality.

This paper evaluates the impact of spatially multiplexing more users within a massive multiple- input, multiple-output (MIMO) system. Recent works on massive MIMO show that there is a peak value for sum spectrum efficiency (SE) achieved by serving a certain number of users. It was shown that until the sum SE reached its peak value, the maximum sum SE is achieved by serving all users simultaneously. These results were based on perfect channel state information (CSI) or Shannon capacity calculations or using very large number of antennas at the base station (BS). As opposed to the aforementioned results, we show that the maximum sum SE with practical number of antennas could be achieved by decreasing number of users before the sum SE reached its peak value. This is shown by calculating the sum SE based on the Error Vector Magnitude (EVM) performance. Sum SE with zero- forcing (ZF) and matched filtering (MF) is presented for uplink (UL) data transmission in a single-cell. Channel matrices formed from both independent and identically distributed (IID) Rayleigh samples and measured data from a real massive MIMO system were used for performance evaluation. The impact of adding more users is also demonstrated by real constellations captured from an indoor massive MIMO trail.

Enhanced network capacity and reduced overhead will be some of the future communication networks requirements. In the absence of Channel State Information (CSI) at the transmitter, Blind Interference Alignment (Blind IA) has shown that optimal Degrees of Freedom (DoF) can be achieved, minimizing network's overhead. Limited spectrum is a basic issue that millimeter-Wave (mmWave) frequencies can resolve in 5G systems. Our contribution is an interference management scheme, based on Blind IA that can be employed in multi-cell, slow-fading, mmWave networks. Blind IA manages inter-and intra-cell interference by antenna selection and appropriate message scheduling. We show that our proposed scheme achieves considerably higher sum rate than TDMA, and overall outperforms TDMA in terms of Degrees of Freedom (DoF) in most cases. Also, Blind IA provides better Bit Error Rate (BER) performance and fairness, in terms of scheduling, to the network users.

Low delay, high reliability and fast exchange of safety broadcast messages are critical to future Intelligent Transport Systems (ITS) systems. This paper presents a cross layer analysis based on Raptor Q codes for transmitting emergency DENM (Decentralized Environmental Notification Message) messages with interference from other vehicles transmitting periodic CAM (Cooperative Awareness message) safety messages. The performance is compared for Cellular Vehicle to Vehicle (C-V2V) Communications and IEEE 802.11p technologies in a realistic highway environment. The end-to-end delay and Packet Reception Ratio (PRR) are used as the performance metrics to demonstrate the latency and reliability problems of standard repetition codes that are addressed using raptor Q codes. Coverage improvements of up to 240m is seen by using C-V2V with raptor Q codes for higher density of vehicles as compared to standard IEEE 802.11p/WAVE with repetition codes. IEEE 802.11p suffers from preamble channel estimation which effects the reliability.

The cost and power consumption associated with the large number of linear power amplifiers required at the base station in a massive MIMO-OFDM system present a significant challenge when deploying systems commercially. In this paper, we show that capacities of up to 4 bits per channel use (bpcu) per user can be achieved in the massive MIMO downlink whilstonly transmitting the phase component of the precoded OFDM signals. This significantly reduces the peak-to-average power ratio (PAPR) of the transmit signals and relaxes the peak power and linearity requirements of the power amplifiers. Using Bussgang's theorem, it is shown that discarding the envelope information causes each OFDM subcarrier to be corrupted by an uncorrelated additive Gaussian error, which is received non-coherently by the users and asymptotically disappears as the number of transmit antennas is increased. SINR expressions are derived for linear precoders, and Monte Carlo simulations are performed with both Rayleigh and measured massive MIMO propagation channels. Under practical numbers of transmit antennas, we show that this phase-only OFDM scheme gives similar performance to other constant envelope precoding schemes described in the literature, and can achieve capacities of 2 bpcu per user with a 1-2 dB increase in mean transmit power (or 50% more transmit antennas) and 4-5 dB decrease in peak transmit power, compared to standard OFDM.

In this paper we propose to use massive multiple-input multiple-output (MIMO) systems in order to boost the throughput over a 1000 m vertically-configured time-varying underwater acoustic channel (UAC). We compare the bit error rate (BER) performance of un-coded and Turbo-coded massive MIMO systems based on filter bank multicarrier (FBMC) modulation and Orthogonal Frequency Division Multiplexing (OFDM). A modified FBMC system is considered whereby complex data symbols are transmitted instead of real-valued ones. This is made possible by spreading the data symbols in time while still ensuring maximum bandwidth efficiency and low complexity. It is shown that the coded FBMC systems outperform the coded OFDM systems both in terms of error performance and bit rate for similar massive MIMO configuration. Video transmission is evaluated over the UAC with the systems that achieve the highest bit rates and it is shown that real-time transmission is possible with acceptable video quality over the long range acoustic link.

This study considers the effects of inter‐cell interference (ICI) on the LTE‐Advanced physical layer downlink channel for different macro‐cell diameters and base station (BS) antenna heights with a frequency reuse factor of one and three sectors per site. A site‐specific three‐dimensional (3D) ray‐tracing tool is used to model the communication channel between the BSs (main and interfering links) and user equipment (UE) terminals. System performance is evaluated in terms of average spectrum efficiency, cell edge throughput and outage probability. Two 3D analogue beamforming algorithms are proposed to mitigate the harmful effects of ICI. These are applied at the BS and/or the UE and compared with a more traditional fractional frequency reuse deployment. Simulations demonstrate that the proposed beamforming algorithms provide significant system level improvements, especially for low BS antenna heights. With 10 × 10 and 2 × 2 antenna arrays at the BS and the UE, respectively, the proposed MaxMin‐BF algorithms can provide an average spectrum efficiency of 3.6 bps/Hz and a cell edge throughput of 0.56 bps/Hz up to a cell diameter of 1250 m. Importantly, these results satisfy the IMT‐Advanced requirements for candidate fourth generation and beyond radio interface technologies. Furthermore, the performance of proposed beamforming algorithms outperforms those achieved using fractional frequency reuse.

Responding to the unprecedented challenges imposed by the 5G technologies, mobile operators have given significant attention to Heterogeneous Cloud Radio Access Networks (H‐CRAN) due to their beneficial features of performing optimization, cost effectiveness, and improving spectral and energy efficiency performance. H‐CRAN inherits the attractive benefits of Heterogeneous Networks (HetNet) and the cloud computing by facilitating interference mitigation, scalability, and radio resource control. Consequently, H‐CRAN is proposed in this article as a cost‐effective potential solution to alleviate intertier interference and improve cooperative processing gains in HetNets by employing cloud computing. H‐CRAN can provide efficient resource sharing at the spectrum, network, and infrastructure levels. Therefore, this article proposes H‐CRAN cooperative interference mitigation method that enhances the time sharing among Radio Remote Heads (RRH) users. The study proposes an enhanced Almost Blank Subframe (ABSF) technique to increase the SINR and throughput of the small‐cell (low power base station) and macrocell users. Simulation results show that the proposed Dynamic P rogramming‐ D iverse A lmost Blank Subframe ( A BSF ) P attern ( DP-D A P) scheme improved the macro‐ and small‐cell users up to 56% and 35%, respectively, as compared to other state‐of‐the‐art ABSF schemes.

Deployment of low power base-stations (referred to as HetNet) within cellular systems can improve system capacity, coverage and enhance users experience. However, the inter-tier and intra-tier interference in such systems can significantly impact overall system performance, which makes interference and spectral resource management more complex. To build, operate HetNet networks, mobile operators have given significant attention to cloud radio access networks, C-RANs, due to their beneficial features of performance optimization and cost effectiveness. In C-RAN cooperated networks, the macro base-stations can operate cooperatively with small base-stations as advanced wireless access network paradigm, where cloud computing is used to fulfill the centralized large-scale cooperative processing. In this paper, such cooperated HetNet and C-RAN architecture is deployed to achieve effective spectral resources and interference management. The study proposes a user weighted probability-based algorithm, which divides the spectrum into shared and dedicated partitions, given that the amount of each partition is calculated efficiently based on the proposed methodology. The algorithm allocates each BS to the appropriate spectrum partition in order to meet certain QoS requirements and optimize overall users throughput in each tier.

Recent works on the future 5G cellular communication proposed that the enormous raw bandwidth availability of the millimeter-wave (mmWave) frequencies is an excellent opportunity to increase data capacity and channel capacity. However, mmWave transmission requires beamforming to overcome the high path loss, as well as other losses due to rain and oxygen absorption and higher noise floor associated with larger bandwidth. This paper presents a comparison on the channel statistics of a mmWave systems operating using isotropic antenna against phased array beamforming in the 60GHz IEEE 802.11ad standard. Real world maps are incorporated into a 3-D mmWave ray-tracing tool for the purpose of employing realistic channel matrices into an 802.11ad bit level simulator. Different environments such as dense urban, urban, highway and residential area in Bristol and Malaysia are considered. Besides that, the throughput performance considering various MCS modes are also presented for both Orthogonal Frequency Division Multiplexing (OFDM) and Single Carrier (SC) transmissions.

5G systems aim to achieve extremely high data rates, low end-to-end latency and ultra-low power consumption. Recently, there has been considerable interest in the design of 5G physical layer waveforms. One important candidate is Generalised Frequency Division Multiplexing (GFDM). In order to evaluate its performance and features, system- level studies should be undertaken in a range of scenarios. These studies, however, require highly complex computations if they are performed using bit-level simulators. In this paper, the Mutual Information (MI) based link quality model (PHY abstraction), which has been regularly used to implement system-level studies for Orthogonal Frequency Division Multiplexing (OFDM), is applied to GFDM. The performance of the GFDM waveform using this model and the bit-level simulation performance is measured using different channel types. Moreover, a system-level study for a GFDM based LTE-A system in a realistic scenario, using both a bit-level simulator and this abstraction model, has been studied and compared. The results reveal the accuracy of this model using realistic channel data. Based on these results, the PHY abstraction technique can be applied to evaluate the performance of GFDM based systems in an effective manner with low complexity. The maximum difference in the Packet Error Rate (PER) and throughput results in the abstraction case compared to bit-level simulation does not exceed 4% whilst offering a simulation time saving reduction of around 62,000 times.

Orthogonal Frequency Division Multiplexing based M-ary Frequency Shift Keying (OFDM-MFSK) is a non- coherent modulation scheme that was proposed for robust transmission over fast fading environments. It combines the MFSK modulation scheme with OFDM. In this paper, the Generalised Frequency Division Multiplexing (GFDM) waveform is considered to use with MFSK to take the advantages of the low out of band radiation and relaxed synchronisation requirements. Different methods to combine MFSK and GFDM are proposed and their performances are evaluated and compared with OFDM-MFSK. The mixed sub-carrier and sub-symbol method, which is one of the proposed methods, is the most promising technique. Additionally, gain margin is also seen for MFSK modulation scheme compared to ordinary OFDM or GFDM. This gain can be used to radically improve the performance for some 5G applications, such as IoT, at low Signal to Noise Ratio (SNR) values.

In this paper, a Virtual Drive Testing (VDT) methodology for a MIMO LTE Vehicle to Infrastructure (V2I) urban scenario is proposed and compared with actual road drive tests. We have developed a unique and generic radio performance analysis process based on 3D ray traced channel models, theoretic or measured antenna patterns, RF channel emulation and hardware-in-the-loop radio measurements. A 3D ray-tracing channel model is used to predict the spatial and temporal multipath ray components of the radio propagation channel between an LTE BS and the vehicle. Measured LTE vehicular antenna patterns were then applied using a spatial and polarimetric convolution process. The resulting channels were streamed into a Keysight PropSim F8 channel emulator, which was programmed to communicate with the multi-channel LTE BSs emulator and a Samsung S5 mobile client performing a handover procedure. The VDT emulation method proposed in this paper is shown to be reliable and repeatable and the accuracy of the emulated throughput agreed well with real measurements for MIMO operation.

This paper proposes a novel uplink power control scheme in a single cell for massive MIMO (Multiple-Input-Multiple-Output). The proposed algorithm exploits the spatial degrees of freedom provided by massive MIMO to achieve the highest signal to interference-plus-noise ratio (SINR) for each user by considering the mutual spatial correlation arising from other users. It also minimizes the required uplink transmit power to achieve the highest possible uplink SINR per user without increasing the complexity at the user equipment. The base station (BS) controls the user transmit power using only two bits in a Transmission Power Control (TPC) command and the newly introduced algorithm is expected to increase both the energy efficiency (EE) and single cell spectral efficiency (SE) with reduced transmission overhead, latency and complexity in the receiver. Through recent preliminary trials, a 0.9 dB average SINR increase was achieved, and transmit power was decreased by up to 2.5 dB in the uplink. The proposed algorithm supports several popular linear MIMO decoders and precoders including Minimum Mean Square Error (MMSE), Zero-Forcing (ZF) and Matched Filtering (MF).

Wireless mesh networks, utilizing the IEEE 802.11s standard, can provide an efficient communication architecture and large coverage as well as reliable data transmission for the Smart Grid applications in low voltage data collection networks. In this paper, we propose a traffic differentiated hybrid wireless mesh protocol for supporting the Smart Grid neighbourhood area networks. The proposed scheme aims to improve the quality of service of the 802.11s based Smart Grid networks by applying two methods, based on the extended airtime link metric and differentiated route selection algorithm. A simulation study of the proposed scheme using the ns-3 simulator is conducted. The simulation results indicate that the proposed scheme can differentiate the route according to the communication requirements of the applications as well as improved performance.

To improve reliability in vehicular communications Application Layer Forward Error Correction (AL-FEC) based on Raptor codes is explored for multimedia broadcast. This paper considers a novel cross-layer simulator based on the latest RaptorQ codes for transmitting high data rate video and investigates packet recovery for cooperative mobile devices and vehicle receiver. Multiple Input Multiple Output (MIMO) channels in a realistic outdoor environment for a user moving at 50kmph in an LTE-A system are considered. Results show that transmission efficiency and reliability can be significantly improved when Systematic RaptorQ Codes with user cooperation is employed. Enhanced throughput and improved outage along the route were also achieved.

Limited wireless spectrum in future networks is an issue that millimeter-Wave (mmWave) frequencies can resolve. Beamforming is a challenging operation for mmWave systems. Both analogue and hybrid solutions have been proposed. Apart from Orthogonal Multiple Access (OMA) systems, the Non-Orthogonal Multiple Access (NOMA) scheme has been recently considered as an alternative and can outperform OMA in many cases. Our contribution is the application of NOMA to a hybrid precoder design in mmWave indoor scenarios with multiple users. Introducing to our system appropriate user grouping and scheduling schemes, we show that the NOMA outperforms, in terms of spectral efficiency, OMA by providing a 17.1% improvement for high SNR values. Finally, applying NOMA with fair power allocation improves the rate of users with weak channel conditions by around 1 bps/Hz for SNR>5dB, without degrading the overall spectral efficiency in the cell.

Cloud Radio Access Network (C-RAN) has attracted a worldwide attention in both academia and industry. This network architecture re-forming has been considered as a potential solution to meet the increasing capacity demands for future mobile data traffic. In addition, Network Virtualisation is a promising technique for efficient resource utilisation. This paper proposes a customisable resource virtualisation algorithm for multi user data scheduling in a Long Term Evolution (LTE) C- RAN deployment. The algorithm is based on the hypervisor specific assignment of air resources allocation between the virtual operators (VOs) dynamically, based on either joint scheduling or per cell schemes. The objective is to improve the resource allocation mechanism based on traffic conditions and a database of pre-defined services priorities. Two distinctive scenarios are considered and evaluated against standard Round Robin (RR) C-RAN scheduling technique. Simulation results show improvements in the overall traffic throughput and reduction in end-to-end delay for delay sensitive applications. In addition, an assessment of fairness guarantee is considered across all users.

Smart grid neighbourhood area networks (NANs), supporting the communications for the power distribution system, involve high density of devices and massive volume of dates. A valid communication architecture for NANs has to guarantee the required date delivery for smart grid applications. In this paper, we propose a hybrid multi channel wireless network, combining wireless local area network and wireless mesh network, for smart grid NANs. The proposed architecture divides the NANs into two layers with different communication technologies that are connected by data aggregation points. A simulation study was carried out by using the ns-3 simulator, and the results indicate that the proposed network architecture fulfils the requirements of most applications in the smart grid with proper configurations. The simulation also provides quantitative analysis into the tradeoff between the number of data aggregation points and performance of the proposed architecture.

This paper evaluates Massive MIMO (Multiple-Input- Multiple-Output) at 2.6 GHz in urban macro-cellular and pico-cellular environments. Massive MIMO is a key 5G technology with the potential to deliver a step change in bandwidth and energy efficiency. Building on experimental results from our Massive MIMO testbed, this paper explores the potential to further enhance capacity via the application of novel power control and user scheduling algorithms. This study makes use of a 3D ray-tracing channel model. The Massive MIMO BS drives 128 antenna elements and simultaneously supports up to 48 single-antenna user terminals (or 24 dual-antenna terminals). Realistically achievable throughput is quantified in terms of cell size, number of user terminals, rank of the users and implementation of user grouping and power control.

This paper presents initial results for a novel 128-antenna massive Multiple-Input, Multiple- Output (MIMO) testbed developed through Bristol Is Open in collaboration with National Instruments and Lund University. We believe that the results presented here validate the adoption of massive MIMO as a key enabling technology for 5G and pave the way for further pragmatic research by the massive MIMO community. The testbed operates in real-time with a Long-Term Evolution (LTE)-like PHY in Time Division Duplex (TDD) mode and supports up to 12 spatial streams, providing an excellent basis for comparison with existing standards and complimentary testbeds. Through line-of-sight (LOS) measurements at 3.51 GHz in an indoor atrium environment with 12 user clients, an uncoded system sum-rate of 1.59 Gbps was achieved in real-time using a single 20 MHz LTE band, equating to 79.4 bits/s/Hz. To the best of the author's knowledge, this is the highest spectral efficiency achieved for any wireless system to date.

The vast growth in mobile data traffic with its increasing capacity demands necessitates investigating future solutions to cope with these challenges. Network Virtualisation is considered one potential solution to simplify the current wireless networks. Recently efforts have been made to show the performance gains of different resource allocation schemes in legacy LTE air interface virtualization. Moreover Cloud - based mobile networks are anticipated to play a significant role for next generation mobile networks. This paper investigates the potential deployment benefits of a novel resource virtualization algorithm (Traffic Aware Joint Scheduling) in Cloud-RANs (C-RAN). Air interface resources are coordinated and allocated dynamically by a hypervisor among different virtual operators (VOs). Three distinctive schemes are proposed and evaluated against standard Round Robin (RR) C-RAN scheduling. Simulation results show improvements in the throughput of the mobile video traffic and reduction in end-to-end delay for delay sensitive applications. In addition, an assessment of fairness guarantee is considered across all users. Note that this paper considers the impact of the proposed schemes on the transmission/data plane.

This paper examines the performance of filter bank multicarrier (FBMC) systems for underwater acoustic communications. We evaluate the performance of Filtered Multitone (FMT) and Orthogonal Frequency Division Multiplexing-Offset Quadrature Amplitude Modulation (OFDM-OQAM) and compare it to that of traditional OFDM. OFDM-OQAM is found to be the most suitable multicarrier technique that can be applied to underwater acoustic communications as it achieves maximum bandwidth efficiency and provides a higher bit rate than its OFDM counterpart due to the absence of a cyclic prefix (CP). We also present a bit error rate (BER) performance evaluation of coded and un-coded OFDM-OQAM for both horizontally and vertically configured acoustic channels.

In this paper, a novel user selection algorithm is proposed for downlink multiuser mmWave systems. The base station exploits hybrid precoding and communicates with multiple users simultaneously via spatial multiplexing. The system performance degrades when the spatially multiplexed users are angularly close and thus results in residual interference which is hard to be cancelled out by the hybrid precoding. To obtain an efficient and computably tractable solution, a novel formulation of the user selection problem and the associated algorithm is presented in this paper. The proposed algorithm enables an optimal spatial multiplexing at the base station, where a predefined number of users is selected and simultaneously served to maximise the averaged spectral efficiency per user. Simulation results show that implementing the multiuser hybrid precoding with the proposed user selection algorithm achieves a performance close to the interference-free limit.

This paper is the first to evaluate the realistic performance of Massive MIMO using real-time channel measurements conducted at 3.51GHz. Our testbed consists of 64 National Instruments Universal Software Radio Peripheral Reconfigurable Input and Output (NI USRP RIO) software defined radios (SDRs) with 128 dipole antennas at the Base Station (BS) side, and 6 USRPs configured as 12 single-antenna User Equipment (UE) nodes. The system operates in a Time Division Duplex (TDD) fashion with a Long Term Evolution (LTE) like Physical Layer framework which, when fully deployed, will enable instantaneous throughput measurements on the Uplink (UL) and Downlink (DL) according to a user-defined frame schedule. In this paper we present real-time UL channel measurements at all BS antenna ports simultaneously, which allows the temporal characteristics of the Massive MIMO channel to be recorded. Eigen-beamforming precoding and a Received Bit-level Mutual Information Rate (RBIR) abstraction simulator are then used to predict the theoretic DL performance. We quantify the co-located Massive MIMO throughput for differing numbers of BS antennas (i.e. 32, 64 and 112 elements) and UE locations for an indoor environment.

The current LTE network architecture experiences high level of signalling traffic between control plane entities. As a result many innovative architectures have been proposed including SDN to simplify the network. Cloud RAN on the other hand proposes a pioneering paradigm in terms of sustaining the profitability margin with unprecedented surge of mobile traffic and providing better performance to the end users. Schemes have been proposed to compute and analyse the signalling load in the new SDN LTE architecture; however in our best understanding, none of them consider future CRAN architectures. Thus in this paper we propose a new SDN CRAN architecture and present an analysis of the signalling load, evaluate the performance and compare it against existing architectures in the literature. Evaluation results show significant improvement of the proposed schemes in terms of reduction in the signalling load when addressing several network metrics.

The vast growth in mobile data traffic requires future mobile network infrastructure to support fast overall growing mobile devices while improving the cost and the energy efficiencies. Many recent studies in this context have focused on proposing solutions for end-to-end architectural designs based on flexible allocations of functions, network function virtualization and software-defined implementations (SDN). It's also of upmost importance to introduce a 5G End-to-End architecture that support low latency RAN with joint design of programmable and software's driven networks that can adapt dynamically to the fluctuating traffic demands. This study contributes in this area by providing innovative joint Cloud-RAN-SDN network designs which are expected to reduce operational cost and overall control signaling load. The paper proposes two architectural schemes called C-RAN.C-MME and C-RAN.D-MME. We demonstrate the associated signaling load analysis, evaluate the performance and compare it against existing literature architectures. Evaluation results indicate a substantial improvement in terms of reducing the signaling load taking into account several network metrics. It's worth mentioning that this study shows the impact of the proposed architectures on the signaling plane only, while their benefits for the transmission/data planes is considered in future work.

Application Layer Forward Error Correction (AL-FEC) based on Raptor codes has been employed in Multimedia Broadcast/Multicast Services (MBMS) to improve reliability. This paper considers a cross-layer system based on the latest Raptor Q codes for transmitting high data rate video. Multiple Input Multiple Output (MIMO) channels in a realistic outdoor environment for a user moving at 50kmph in an LTE-A system is considered. A link adaptation model with optimized cross-layer parameters is proposed under different channel conditions and quality of service requirements. The system investigates throughput performance for Spatial Time Block Coding (STBC) and Spatial Multiplexing (SM) MIMO with and without raptor codes. Improvements of up to 4dB SNR are seen by using raptor codes with SM depending upon the channel conditions and chosen Modulation and Coding Scheme (MCS). Results also show that at low SNR and low spatial correlation, the performance of AL-FEC with SM is better than STBC even when the user is moving at high speeds.

While obtaining the channel state information (CSI) required to perform Interference Alignment (IA) in a centralised MIMO network is a challenge, this is compounded in unplanned wireless networks that may be decentralised - not to mention composed of devices with varying degrees of complexity and capability. This is of particular interest to heterogeneous networks and the Internet of Things (IoT). The disparity in antenna number caused by this variation in capability can be taken advantage of, increasing the sum rate of the network providing the users are aware of the capabilities of their neighbours. This paper presents a method for estimating with a high degree of certainty the number of antennas each user possesses, endowing the receiver with the vital CSI required before channel equalisation or estimation can take place. The method is correlation based and so is not restricted to full rank channels where the receiving device has an equal or greater number of antennas than the transmitter. This permits the use of the method in situations where the rank of the channel is restricted, either by design or by nature (e.g. 'keyhole' channels).

One of the research activities in 5G communication systems is the extension of the MIMO processing from the 2D to the 3D plane by exploiting the elevation dimension which gives an additional degree of freedom to meet the high capacity demands. Despite the growing researches concerning 3D space propagation, there are few studies that evaluate the impact of 3D propagation on MIMO performance at the PHY level and the capacity gained from exploiting the elevation component. The aim of this paper is to evaluate, quantify and compare the downlink BER performance experienced by users in an urban environment in cases of 2D and 3D channel models, where the impact of the 3D component on MIMO performance is evaluated. Results indicate that 3D modelling implies lower correlation between MIMO spatial streams and consequently lower BER. Therefore, the full benefits of MIMO cannot be accurately predicted in 2D model where high correlated MIMO spatial streams are observed. The study also compares two different orientations of linear MIMO arrays (horizontal and vertical). In this study, we are also implementing our enhanced 3D channel model which is an extension of the well-known 3GPP/ITU channel model. The proposed channel model is made available to the public through SourceForge.

An efficient codebook-based beam training technique is proposed for mmWave communication systems operating under non-line-of-sight (NLoS) channel conditions. Using convex optimization theory, this technique formulates the beam training process as a combinational optimization problem. It finds the best transmit-receive beam pair that maximizes the received signal power by iterating the Nelder-Mead simplex method through a multi-stage formulation of the training process. Compared with beamforming protocols adopted by 60 GHz WLAN/PAN systems, the proposed technique is robuster in NLoS scenarios. Simulation results demonstrate that the proposed technique achieves the same selection performance as the exhaustive search with a possibility of 87.6% while requiring moderate measurement steps.

WLANs currently do not provide a robust solution for reliable data multicast. Multicast packets are delivered to multiple users as a simple broadcast service without support for Automatic Repeat Request. Hence, a fixed low speed transmission mode is generally used to improve the reliability of multicast files. However, this results in the inefficient use of bandwidth. This paper proposes a reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. We proposed an adaptive Application Layer Forward Error Correction (AL-FEC) enabled data carousel for reliable multicast transmission over standard 802.11 WLANs. To quantify the benefits of the proposed system, results are presented from a cross-layer simulator combining novel outdoor ray-tracing, a physical layer abstraction simulator and a RaptorQ enabled multicast data carousel simulator. The simulation results demonstrate that adaptive FEC carousels significantly reduce the average download time, increase the percentage of satisfied users and bandwidth efficiency in a multicast network.

This paper evaluates the theoretic performance of multi-user multiple-input-multiple-output (MU- MIMO) systems in heterogeneous LTE-Advanced urban environments (i.e. Macrocells and Picocells) using classic Eigen-Beamforming (EBF) and Block Diagonalisation (BD) precoding methods. The work quantifies the realistically achievable improvement of MU-MIMO compared with traditional single-user (SU) MIMO schemes. In addition, the impact on system level capacity of different Base Station (BS) antenna numbers and array geometries are investigated. A 3D ray-tracing channel propagation model of the City of Bristol (UK) was used along with measured 3D polarimetric antenna patterns for the individual BS and UE elements. More than one million ray-traced Pico and Macro cellular links were evaluated to ensure statistical relevance. Our analysis quantifies the capacity of an 8×8 Full-Dimension MU-MIMO solution in realistic urban heterogeneous environments addressing single-antenna and dual-antenna UEs. Results address the system level benefits of increasing the number of BS and UE antenna elements as well as the sensitivity of capacity to vertical and horizontal spatial element configurations at the BS.

In order to alleviate the mobile data explosion problem, a Wi-Fi offloading strategy has been proposed. Given the recent deployment of Wi-Fi like systems in the TVWS (TV White Space), the mobile offloading to White-Fi networks is an attractive solution to mobile operators to provide full broadband coverage in dense urban environments. To quantify the amount of throughput and coverage gain achieved from users offloading, this paper conducts a simulation-based analysis for a range of carrier class access points (AP) densities considering practical deployment of the IEEE 802.11af and 802.11g networks. The study takes into account a realistic modelling of the TV channels availability and wireless channel propagation. The interference from co-channel operation and DVB-T systems are also considered. The paper shows that the opportunistic deployment of White-Fi networks generally results in high throughput gain and coverage probability at various AP densities as compared to Wi-Fi only networks. It also grants a higher fraction of users with high throughput capability as compared to 802.11g only networks. In addition, the study provides the mobile operators with a range of performance statistics that can help them to select the suitable range of AP deployment to meet certain performance thresholds.

A key challenge for Machine to Machine (M2M) communication over the Long term Evolution-Advanced (LTE-A) is the performance of Random Access Channel (RACH) in interference-limited scenarios. This paper presents results of a Radio Access Network (RAN) evaluated for the macro-cell where the interference from M2M devices (M2M-Ds) is considered. The paper shows that considering an interference free scenario will result in inaccurate estimation of access success probability and average access delay in the 800MHz and 2.4GHz frequency bands. This will consequently affect the design and the evaluation of the M2M network. The effect of different values of the backoff timer is also analyzed.

This paper explores the benefits of application layer forward error correction (AL-FEC) based on Raptor codes for high quality video multicasting over 802.11n multiple-input multiple-output (MIMO) channels. A cross-layer Wi-Fi simulator in combination with a state-of-the-art ray tracing propagation tool was used to analyse the performance of spatial multiplexing (SM) and space time block coding (STBC) MIMO techniques under different channel conditions. Simulation results showed that with the use of Raptor code AL-FEC, the operation range of the SM system was increased, i.e., the outage probability was driven to zero even though the MIMO channels were highly correlated. Furthermore, the spectral efficiency was also increased since the SNR gain can be increased up to 10 dB depending on the channel conditions. This results in a higher MCS mode to be selected for the transmission of data. We also presented a MIMO switching algorithm which implements Raptor codes as a means to improve the SM performance and then we evaluated the system under realistic wireless channel conditions.

An efficient and low-complexity codebook-based beam training technique is proposed for mmWave communication systems. To identify the pair of beam patterns maximizing the received signal power with a given beam resolution, the proposed technique formulates the beam training process as a combinational optimization problem. It considers all of the beam pairs as a set of feasible solutions and the received signal power as the objective function. The main idea is to implement the Nelder-Mead simplex algorithm iteratively and recursively, each time finding the best beam pair with beam patterns of increased resolution. This technique benefits from the efficiency of the Nelder-Mead algorithm whilst avoiding its drawbacks, such as sticking in a local optimum near the optimum solution. Simulation results show that, for short-range indoor communications with line-of-sight (LoS) multipath components, the proposed technique achieves the same beam selection compared to the exhaustive beam training algorithm while requiring around 28% of the search steps needed by the two-level training mechanism adopted in IEEE 802.15.3c when 32 antenna elements are adopted at both the transmitter and the receiver.

Spectrum shortage in the conventional microwave bands coupled with the need for multi-gigabit per- cell capacities has motivated the use of the mmWave bands in future 5G networks. In this paper 3D ray tracing is used to derive key statistical parameters for the mmWave channel. These include path loss, LoS probability, K-factor, RMS delay spread and angular spreads. The mmWave parameters are directly compared to the microwave channel present in LTE-A. Cellular deployment in both bands is then simulated for a 500 m by 500 m regqasion of central Bristol. The impact of different antenna geometries is also studied. Due to the trade-offs between the number of required BSs and the cost of network deployment, we propose a converged mmWave/microwave network for improved user experience.

The regulatory framework for secondary utilization of TV white spaces (TVWS) is well underway in the United Kingdom, while important steps in this direction are taken within the European Union and elsewhere. Mobile network operators are interested in the use of TVWS for cellular extension and rural access, where TVWS is seen as a significant new opportunity for operators to provide new wireless services. The government's plan to close the digital divide between the urban and rural communities has motivated the efforts to develop Wi-Fi like operation in TVWS for better coverage in rural areas. The IEEE currently has a working group developing 802.11af amendment which will allow for WLAN operations in the TVWS. This paper presents a quantitative analysis of downlink throughput performance of IEEE802.11af, also known as White-Fi in a rural environment while taking into account realistic modelling of TV channel availability, wireless channel, AP density, and the effect of co-channel interference caused by secondary APs and DVB-T transmitters. The paper shows that the low operating frequency of White-Fi offers a wide coverage in a rural environment, where there is limited cellular coverage due to the cost-inefficiency of base stations deployment. The presented results also show that there are more available TVWS channels and less co-channel interferers in a rural environment, resulting in a significant throughput performance even in high mobility if suitable channel estimation is considered, making it ideal for vehicular communications with White-Fi.

This paper introduces a novel 128-element sub-6 GHz Massive MIMO (Multiple-Input Multiple-Output) testbed being developed by the University of Bristol in collaboration with National Instruments and Lund University as part of the BIO (Bristol is Open) city testbed. Distributed Massive MIMO systems avoid large single-piece antenna facets and their associated windage problems and also offer greater spatial diversity, but node synchronization and phase alignment becomes more challenging. Simulated network performance of a co-located 128-element 3D Multi-User MIMO system at a possible test site in Bristol are presented based on our 3D channel propagation model.

A neighbourhood area network (NAN) connects all the end users with energy suppliers and/or distributed generation. In this paper, we propose an IEEE 802.11af based NAN for Smart Grid applications in Low Voltage electricity networks and analyze its packet delivery and delay performance against the Smart Grid requirements. The IEEE 802.11af is implemented in ns3 and its performance for carrying Smart Grid traffic is simulated and analyzed. The simulation results show that the proposed NAN achieves over 99% PDR and below 200ms end-to-end delay for normal smart metering-like traffic, which adequately fulfils the requirement of best-effort applications in the Smart Grid. The results also provide quantitative insight into the tradeoff between coverage and performance, which can serve as guidelines for IEEE 802.11af NAN designs for Smart Grid deployment. To the best of our knowledge, this is the first work that provides specific results for IEEE 802.11af performance as the last mile access network technology in a Smart Grid scenario.

This paper analyses the theoretic throughput and coverage for a multi-element in-home Wireless Local Area Network (WLAN) in the 5 GHz band. In particular we study the impact of regulatory transmit power constraints on the relative performances of beamforming and antenna selection at the access point. A novel methodology is applied based on part measurement and part simulation. In home results are provided for standard 802.11n multiple-input multiple-output (MIMO) deployments. Results show that beamforming is particularly affected by regulatory transmit power constraints. For long-range links beamforming data throughputs are reduced by more than 50%. The average data rate in our test home reduces by 14.3% when regulatory constraints are applied to the beamforming system. For antenna selection the regulatory limits result in an 8.9% reduction in average throughput. Furthermore, we show that for long range links the average data rate is improved by 50% when the antenna selection is used in place of beamforming. Although antenna selection uses single stream MIMO more frequently than beamforming, the latter performs better when multiple spatial streams are used. Beamforming is shown to work best in the easy and medium-range channels.

This paper considers infrastructure to vehicle communications using Advanced-LTE. The paper compares the downlink throughput performance experienced by mobile users in an urban-macro-cell in cases of 2D and 3D channel models, where the impact of the 3D component on MIMO performance is investigated. Recently there has been strong interest in extending the MIMO processing from the azimuth dimension to include the elevation plane. Therefore, a 3D channel model is required in the evaluation of elevation MIMO performance. Bit level simulation is performed for the downlink physical shared channel (PDSCH) in LTE-A operating at 2.6GHz. Results indicate the accuracy of the 3D channel model and implies correct estimation of the 3D channel. The difference in the small scale parameters for the SISO case and the lower spatial correlation parameters for the MIMO case result in higher predicted capacity for the 3D channel model. The study has been carried out for different mobility speeds, packet sizes and MCSs modes.

802.11 WLANs do not provide any standardized solution for reliable data multicast. Multicast packets are delivered to multiple clients as a simple broadcast service without support for Automatic Repeat Request. Hence, a fixed low speed (robust) transmission mode is generally used to improve the reliability of multicast files. However, this results in the inefficient use of bandwidth. This paper details a reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. We propose an Application Layer Forward Error Correction enabled data carousel for reliable multicast transmission over standard 802.11 WLANs. To quantify the benefits of the proposed system, results are reported from a cross-layer simulator combining novel outdoor ray-tracing, a Physical layer abstraction simulator (to rapidly quantify the radio performance), a RaptorQ enabled multicast data carousel simulator and an optimal access point deployment tool. The simulation results demonstrate that RaptorQ enabled carousels (compared to standard carousels) significantly reduce the average response time and increase the percentage of satisfied users in a multicast network.

In this study, linear transceiver designs are proposed based on modified definitions of signal‐to‐leakage‐plus‐noise ratio (mSLNR) for multi‐cell coordinated beamforming scenarios. Two mSLNR definitions are presented, one of which modifies the computation of leakage and noise powers, while the other applies the modified procedure to the desired power calculation in addition to the computation of leakage and noise powers. The proposed mSLNRs are generally valid for any receiver types. Various linear receivers are studied, several of which, when applied with the first mSLNR definition, are shown to be equivalent. Moreover, a special case of the proposed scheme is shown to be equivalent to an existing algorithm. Iterative precoding algorithms are also presented with a discussion on their convergence properties. The proposed transceiver designs are further extended to incorporate scheduling functionalities. A weighted sum rate maximisation problem is formulated and is solved by two separate approaches, namely power allocation and data‐substream selection methods. Simulation results show that, for multiple users per cell, the proposed algorithms can effectively integrate user and substream selections and achieve multi‐user diversity gain.

In this paper we evaluate and compare the end-to-end performance of different multipath TCP (MPTCP) congestion controllers when run in conjunction with different TCP packet reordering recovery algorithms. The paper answers the following questions: what is the impact of out-of-order events on the end-to-end throughput when using MPTCP, how do out-of-order recovery algorithms that have been proposed for single-path TCP perform with multi-path TCP, and how sensitive this performance is against the delay difference between the paths used. The paper compares three different MPTCP congestion control algorithms used in conjunction with four current TCP packet reordering solutions: D-SACK, Eifel, TCP-DOOR, and F-RTO. Simulation results show that whilst TCP-DOOR and, second, D-SACK perform generally better across all congestion control MPTCP implementations, the choice of packet reordering algorithm is not always fixed and straightforward - when MPTCP is used with some form of coupled congestion control the performance degrades towards that of single-path usage when the delay difference of the paths is over 200ms. The paper identifies combinations of congestion control and packet reordering algorithms that give better aggregate throughput performance for different path delay differences.

LTE-Advanced is a promising technology for a higher spectral efficiency and reliable transmission. This paper compares the downlink throughput experienced by mobile users in a macro-cell in an interference limited scenario with a frequency reuse of one. Bit accurate link level simulations are performed for the downlink physical shared channel (PDSCH). The study is performed for a single antenna system in specific routes at two different carrier frequencies (800 MHz and 2.6 GHz), for two urban environments in the United Kingdom, and two cell sizes. The paper also considers the carrier aggregation technique which has been proposed since it is difficult to ensure a single wide frequency band for operators. A state-of-the-art 3D ray tracer tool is used to generate 3D channel models for accurate modelling of channel statistics. The study shows that the 800 MHz band has no greater effect on the downlink throughput as compared to 2.6 GHz band, which leads to no additional advantages of inter-band aggregation (considering 800 MHz) compared to intra- band aggregation. It is also observed that a range of speeds can be handled while maintaining good performance in LTE-Advanced. We have clearly shown that the choice of cell size by mobile operators for optimum coverage depends mainly on the propagation characteristic of the environment.

The digital switch-over has triggered the development of new wireless standards which are expected to use unoccupied TV channels known as TV white space. Wi-Fi like systems in TVWS are foreseen as cost effective high data rate communication systems which might provide significant coverage compared to existing 802.11 Wi-Fi systems. This paper presents a quantitative analysis of downlink throughput of three 802.11 standards, namely 802.11af in the TV band, 802.11g in the 2.4GHz band and 802.11p in the 5.9GHz band. The study is the first to compare the three standards considering realistic conditions such as availability of TV channels, realistic modelling of wireless channels and considering the effect of AP and DVB-T interference in rural and urban environments in the United Kingdom. We have shown that the overall benefit of operation in TVWS is mainly governed by the AP density, number of available TV channels and the AP transmission power.

This paper evaluates coverage prediction and radio performance for automotive infotainment applications. The work compares IEEE 802.11af operating in the TV White Space (TVWS) bands with LTE operating at 800MHz and 2.6GHz. Real world rural and urban databases are incorporated into a 3D ray tracing tool for the purposes of exploring signal coverage and data rates along with virtual drive tests. Results are presented as a function of radio standard, operating band, vehicle speed, user location and packet size. LTE is shown to outperform 802.11af since it is less affected by the multipath channel and the significant levels of Doppler Spread experienced by vehicular users. Results also indicate that 802.11af systems provide superior coverage, especially in rural environments.

This paper investigates the effectiveness of dynamic resource allocation scheme in WiMAX (Worldwide Interoperability for Microwave Access) system following to the WiMAX standard. Simulation experiments are performed for the case of MAC PDU (Media Access Control packet data unit) without fragmentation and numerically expanded for the fragmentation case. We used a technique called Dynamic Burst Mapping (DyPBM) to allocate the resources to mobile users, and this is then compared to other non-dynamic resource allocation techniques. Numerical study shows that the dynamic technique (DyPBM) achieves the highest goodput increment of up to 0.7 Mbps when the MAC PDUs are fragmented. Nevertheless, dynamic technique is less effective in the case of without MAC PDU fragmentation since it achieves low channel utilisation over the other non-dynamic techniques. This is because the available slots in some frames are insufficient to support the big PDU sizes as these PDUs (Packet Data Units) are not split into small fragments. This study thus concludes that the dynamic resource allocation is only significant when PDU fragmentation is applied in the WiMAX networks; nevertheless, there is a trade-off in terms of the complexity.

Recently many cellular and WLAN standards are considering operation in the TV bands due to enhanced coverage and access to additional bandwidth. To accurately assess the performance of wireless communication systems operating in the TeleVision White Space (TVWS) spectrum, a new channel model is required that accounts for the unique propagation characteristics in the UHF band. This paper proposes an extension to the existing 3GPP/ITU channel model for operation at frequencies from 400 MHz (bottom of the TVWS band) up to 5 GHz (top of the WLAN band). The channel model is suitable for urban environments and the raw propagation data was generated using a state-of-the-art 3D ray-tracing tool. Results are presented as cumulative distribution functions of total received power, RMS delay spread, K-factor and RMS angular spread (azimuth and elevation). The probability of line-of-sight as function of distance and best-fit parameters for large and small scale fading are also presented.

To maintain a high quality of service to the increasing number of smartphone users, additional spectrum is required. The TV white space bands provide a good opportunity to achieve this goal. They can be used as standalone spectrum or aggregated with other licensed bands to increase the total available bandwidth. This paper compares the downlink throughput performance of LTE-Advanced in two different frequency bands. It also addresses the impact of smartphone orientation, with results quoted for three different elevation angles. We consider the higher LTE-Advanced band at 2.6 GHz and the TV white space band at 800 MHz. The radio channel is modelled using a state-of-the-art 3D ray-tracing tool combined with measured 3D radiation patterns for the base station and handset antennas. The throughput performance for a large number of base station and mobile terminal locations is investigated in two different UK cities. We use the computationally efficient received bit information rate algorithm to compute packet error rate as a function of channel structure and SNR. The approach reduces simulation run time by a factor of more than 300. Similar average throughput vs SNR results are observed in both frequency bands. However, higher K-factor and total received power levels are observed when the user equipment is tilted to 45oin elevation. Throughput results show that the efficiency of carrier aggregation between LTE and TVWS bands depends on the cell size and the type of urban environment.

Data carousels are a traditional way of providing reliable multicast transmission without the need for per-user feedback channels. Application Layer Forward Error Correction (AL-FEC) codes (in the form of Reed-Solomon codes) have previously been used to improve the performance of data carousels. However, until now, their joint design has only been investigated analytically with unrealistic random packet loss values. In this paper we investigate the joint design of an AL-FEC enhanced data carousel for use in an outdoor 802.11 multicast wireless LAN. We use an advanced end-to-end system level simulator to determine the optimal design parameters. Furthermore, we extend previous research in this area by combining data carousels with AL-FEC based on fountain codes. Our simulation results show that this new approach is more efficient than traditional Reed-Solomon block codes. More specifically, average download times are reduced, percentages of satisfied users are increased and valuable network resources are more efficiently utilized.

Recently, there has been considerable interest to utilize the power line infrastructure for broadband communications. Power Line Communications (PLC) operate in the frequency range between 1.8MHz to 30MHz defined by the IEEE 1901 standard. Within this frequency range, a number of organizations and users occupy their own specific spectrum. As a result, spectrum notching and interference avoidance need to be applied to enable co-existence between the primary users and secondary PLC transmissions. Instead of employing a notch filter, this paper presents an effective spectrum notching technique to provide multiple deep notches in the PLC band. The performance and complexity of this notching technique is investigated.

This paper proposes a modified definition of signal-to-leakage-plus-noise ratio (SLNR) as a criterion for linear transmit filter design in Multi-user MIMO systems. The proposed metric incorporates receiver structures into the precoder design, which can potentially exploit unused receive signal subspaces in cases where the available eigenmodes are not fully transmitted. The improvement in terms of the degrees of freedom of the precoder is also elaborated. In addition, an iterative precoding algorithm is proposed and is studied with two linear receivers, namely the matched filter (MF) and the minimum mean square error (MMSE) receivers. Simulation results show that the proposed scheme outperforms the conventional SLNR scheme and can achieve further improvement with an MMSE receiver, at the expense of increased computational complexity and slow convergence rate. Moreover, the proposed scheme is shown to reduce its form to the conventional scheme when full-eigenmode transmission is assumed.

This paper analyses the throughput and coverage of an in-home wireless LAN in the 5GHz band. A novel approach is proposed based on part measurement, part simulation. The spatial and temporal characteristics of typical in-home channels are modelled using 3D ray tracing and combined with measured and appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is computed across 10 rooms in a virtual test house for all modulation and coding schemes. To accelerate the simulation process a received bit information rate abstraction technique is applied. Results are given for a standard 802.11a deployment. The benefits of 3x3 MIMO are then compared against the deployment of a Wireless Mesh Network (WMN). In the latter case meshing is performed using low cost single antenna radios. Relative to the benchmark SISO system, 3x3 MIMO is shown to improve the average throughput by 123%. Given four randomly deployed mesh points, the mesh solution improves the average throughput by 31%. Importantly, for the test house under consideration the MIMO solution improves connectivity by just 3%, while the mesh network offers 100% (whole home) connectivity. The mesh network (using 4 additional mesh points) is shown to support high definition video for 90% of the links, compared to 71% with 3x3 MIMO. Results confirm that mesh networks benefit the weaker links, while MIMO boosts the stronger links.

60 GHz wireless personal area networks (WPANs) are bringing a new wave of high data rate applications because they promise multi-Gbps level communications. This paper exploits the spatial reuse of location information aided 60 GHz multi- user beamforming systems. When the location information is available at the network coordinator, the scheduler chooses a set of maximum angularly separated links to share the same time slot simultaneously. If additional feedback of signal-to- interference and noise ratio (SINR) is known, a location-assisted scheduler is employed to increase the system overall performance. The position error sensitivity is also discussed. The results show that significant enhancement can be achieved by the proposed schedulers for 60 GHz WPAN systems and we observe an accuracy of 98% compared with the error free transmission with ultra-wideband (UWB) localization systems.

Even though the main motivation behind wireless access for vehicular environments was to support time‐sensitive safety applications, typical Internet applications are also required to attract private investment that would help expand the network and reduce the cost of implementing the systems. It is well known that the Automatic Repeat reQuest scheme used in the current IEEE 802.11p standard is highly inefficient for vehicular applications. Therefore a raptor‐coded decode‐and‐forward relaying scheme with an efficient feedback channel, named the ‘r‐DF scheme’ for infrastructure‐to‐vehicle infotainment applications is proposed in this study. The scheme is evaluated using a multi‐layered simulator combining a realistic IEEE 802.11p physical and MAC layer design considering the presence of interference in a highway and an urban scenario. The simulation shows that the scheme achieved up to double the average aggregate throughput and tens of decoding time improvements over the state‐of‐the‐art.

In an urban environment, vehicle mobility is limited by road structure and obstacles. This gives rise to extremely challenging network design for large data transfers due to unpredictable network dynamics, limited connection lifetime and unstable channel conditions. Conventional approaches using retransmission schemes do not perform well in these conditions due to nodes leaving the network in the middle of the download. Rateless codes have been identified as a solution to address interrupted downloads with minimal handshaking and overhead requirements. Varying channel conditions calls for the need of multi-rate vehicular communications, where low rate robust communication is used when bad channel is experienced and higher rate modulation is used in good channel conditions. This paper presents a novel coding scheme based on systematic raptor codes for multihop data dissemination that is based on multi-rate vehicular communications. With this scheme, even vehicles which are outside the roadside infrastructure coverage can be provided with reliable access to infrastructure services.

WiMAX promises an advanced framework to support Quality-of-Service (QoS) requirements of different types of applications and scheduling is a key part in its QoS provisioning. The scheduling algorithms used in this paper are based on our proposed Greedy-Latency scheduler, a modified form of Greedy algorithm which can guarantee delay requirements of real-time applications while optimising the system throughput. Our study of TCP performance in WiMAX shows that unlike UDP traffic, there are fluctuations in TCP throughput even for low traffic loads. It is seen that employing Automatic Repeat reQuest (ARQ) and setting the right TCP window size are crucial for a stable optimal TCP performance. WiMAX QoS mechanism can successfully maintain the inter-class priority between TCP traffic in Best Effort (BE) class and UDP in higher priority Real-Time Polling Service (rtPS) class. For intra-class scenarios, it is observed that TCP flows in general need a protection mechanism as the UDP traffic tend to seize the channel. The proposed Greedy-Scheduler can provide better intra-class protection for TCP flows due to its packet dropping policy.

In cases when system load approaches capacity (>;90% of capacity), scarce radio resources are wasted when a scheduler serves video packets that exceed a required latency, as the decoder will ultimately discard any such packets. In this paper, we introduce a combination of a packet-dropping policy with a modified Greedy-based scheduler to guarantee meeting maximum latency requirements under heavy load conditions, whilst optimising the system goodput for the WiMAX real-time Polling service (rtPS) class. Results of the comparison with existing schedulers show that they all can successfully guarantee the required maximum latency after they have been extended by the same packet- dropping policy, with average latency values well below the required maximum latency. The proposed channel- and delay-aware scheduler results in the lowest number of packet drops. Results also show that mobility does not have significant impact on the system performance across the schedulers compared to the number of users in the cell.

When the location information is available, this paper presents the PHY strategies which can be applied to improve the performance of a beamforming system and support multiple access with low feedback requirement. Based on a system providing real-time 3D coordinate information of all terminals in the environment, feedback-free and low feedback multi-user schedulers are considered. The location-based schedulers are evaluated with both perfect and imperfect position information and the sensitivity of the system to location errors are measured in terms of both rate and fairness performance based on statistics of commercial GPS receivers.

60 GHz wireless personal area networks (WPANs) offer multi-Gbps throughput, which will provide for a new wave of high data rate applications. This paper exploits the use of location information to improve the performance and enhance range of 60 GHz multi-user beamforming systems. When the location information is available at the transmitter, the scheduler chooses a set of maximum angularly separated users to share wireless resources simultaneously. If additional feedback of signal-to-interference and noise ratio (SINR) is known, a location-assisted scheduler is employed to increase the system overall performance. Both numerical and simulated results show that significant enhancement can be achieved by the proposed schedulers for 60 GHz WPAN systems.

This paper investigates the user scheduling strategy of multi-user MIMO (MU-MIMO) systems using a transmit precoding scheme based on maximum signal to leakage and noise ratio (SLNR). When users are equipped with multiple antennas, joint user and receive antenna selection may be performed and is shown to potentially provide superior performance to user selection schemes where users utilise all available antennas, especially at high SNR. To overcome the impractical computational burden of exhaustive methods, two suboptimal algorithms are presented in this paper. The simulation results show that the proposed suboptimal algorithms perform very close to the exhaustive joint user and antenna selection algorithm.

The performance of an OFDM system can be improved by performing per-subcarrier antenna selection, which facilitates the exploitation of frequency and spatial diversity in the wireless channel. In this paper, we extend the concept of per-subcarrier antenna selection to a multiuser cognitive radio environment and present a practical subcarrier and antenna selection algorithm that exploits the multiuser, frequency and spatial diversities inherent in such systems while requiring only limited channel knowledge. The problem is formulated as an integer programming (IP) problem. We demonstrate that a linear relaxation of the problem still leads to an optimal solution, thus reducing the computational complexity relative to other approaches found in the literature. Simulation results demonstrate that the proposed resource allocation problem leads to an improvement in secondary users' link qualities, compared to a single-input single-output system and, at the same time, limits the interference to the primary user.

In a cognitive radio system, the accuracy of spectrum sensing is critical for both primary and secondary systems. Both cooperative sensing and single-user multiple-antenna techniques have been proposed in the literature to enhance the accuracy of spectrum sensing. However, these techniques may require additional signaling and hardware costs, and can lead to user reliability problems or energy consumption issues. To avoid these problems, we propose a scheme that requires no extra signaling and low hardware costs, while still offering substantial diversity gains for enhancing the sensing performance. This is achieved by combining antenna selection with the spectrum sensing mechanism. We analyze the diversity order of the proposed scheme and show that no loss occurs relative to the case of single-user multiple-antenna sensing. This benefit is achieved while keeping a low implementation complexity as only a subset of RF chains are used in a given time period. Simulations show that a substantial sensing gain can be obtained compared to using other traditional multiple-antenna techniques in some practical cases.

The IEEE 802.11ad task group has published its first draft to cope with the characteristics in 60 GHz millimeter-wave (mmWave) wireless communications. In this paper, three different 2×2 multiple-input multiple-output (MIMO) techniques are considered to enhance the performance of 60 GHz wireless personal networks (WPANs). Packet Error Rate (PER) and link throughput performance are simulated under different channel conditions. In addition, the system throughput over operation range is presented in the paper. Results show that significant enhancements in both coverage and capacity can be achieved by employing space-time block codes (STBC), spatial multiplexing (SM) and three different configurations of beamforming.

Car-to-car safety applications that demand real-time and reliable communications in vehicular ad hoc networks (VANETs) requires a new paradigm of coding techniques. In this paper, we propose a novel coding approach using a systematic Raptor code for car-to-car post-crash warning broadcast applications. A cross-layer simulator model is developed to evaluate the performance of Raptor codes against repetition codes using also multiple antennas spatial diversity techniques. The end-to-end delay and packet delivery ratio are used as performance metrics to demonstrate the latency and reliability problems of repetition codes that are addressed using Raptor codes.

One of the important applications to be available in vehicular ad-hoc networks are value-added or infotainment services. However, vehicular communication suffers from high packet loss due to challenging channel characteristics such as huge Doppler spread and multipath fading. This makes current IEEE 802.11p standard for vehicular network based on the ARQ scheme inefficient. Therefore, the highly scalable and fault-tolerant properties offered by rateless code makes this a promising area of research. This paper investigates the implementation of a systematic Raptor codes for a broadcast service in infrastructure-to-vehicular communications. The code performance in terms of the decoding probability of success, mean decoding time and mean aggregate throughput are presented.

Link Adaptation (LA), adopted by many emerging standards, such as WCDMA, LTE and WiMAX is a key element for providing improved data rates and performance guarantees under specified Quality of Service (QoS) requirements. Link Adaptation can dynamically adjust a number of transmission parameters, most often modulation and coding, to reflect the characteristics of the wireless link to improve throughput and maintain link reliability. Most LA algorithms require only an estimate of the signal-to-noise ratio (SNR) to select an appropriate PHY mode, relying on the assumption of an AWGN channel. For channels experiencing frequency selective fading however, the conventional approach fails to accurately represent the stochastic variability across independent channels, resulting in inaccurate prediction of the current channel state and failure in selecting appropriate transmission parameters. A new channel quality metric is proposed in this paper that attempts to estimate the likelihood of packet errors in a fading channel and adjust Modulation and Coding Scheme (MCS) selection across each fading realisation independently. Results show improved mode selection efficiency over the conventional LA approach with added flexibility, as this approach is independent of the channel environment, providing a universal solution to LA.

Recently, the development and requirement for ultra-high data rate wireless communication applications has increased dramatically. The 60 GHz millimeter-wave wireless technology is getting increasing attention, and the IEEE 802.11 Task Group AD is making standardization efforts for multi-gigabit data rate communications on both the physical (PHY) and medium access control (MAC) layers. This paper presents a performance evaluation of the PHY and MAC layers of IEEE 802.1 lad. Packet error rate and PHY throughput are presented for different modes, and the theoretical MAC throughput is analyzed for different bit error rates, packet sizes and modes. In addition, 2×2 space-time block coding (STBC) is employed for range extension. The cross layer results show our approach enhance the throughput and coverage compared to the case of single antenna.

The joint use of opportunistic scheduling and orthogonal frequency division multiple access (OFDMA) provide significant gains in environments of low mobility and scatter for which channel variations are low. The downside of opportunistic scheduling in multicarrier systems such as OFDMA, lies in the substantial uplink overhead required to feed back by the mobile stations (MSs) describing users’ instantaneous link conditions. This study presents a novel approach towards multicarrier opportunistic scheduling for a multi-input multi-output configuration that promises major overhead reductions with only minor degradations on downlink throughput performance. The conventional channel quality indicator, in the form of instantaneous signal-to-noise ratio (SNR) is replaced by an alternative metric, in the form of the strongest cluster indices of each MS, which imposes a significantly reduced overhead. This study examines the performance of the proposes metric for random beamforming and examines the benefits in terms of throughput and feedback overhead over existing schemes. The results show that the proposed scheduling approach maintains performance within 1 dB of a full SNR based feedback scheme, while achieving feedback overhead reduction up to a factor of 24 and also providing improved fairness among users experiencing different channel gain levels.

WiMAX, based on the IEEE 802.16 standard, is designed to support a variety of applications, including voice and multimedia services, through scalable OFDMA, advanced antenna techniques supporting MIMO, and well-defined quality of service classes. This paper presents WiMAX downlink achievable user goodput and operating range for different modulation and coding schemes for SISO and MIMO (both Space Time Block Code (STBC) and Spatial Multiplexing (SM)) connections. The achievable maximum goodput is shown to be between 94.5% and 97.0% of the theoretical data rates. The analysis is then expanded to multiple Subscriber Stations (SSs) and different packet sizes for a specific transmission mode, and also to multiple connections considering an additional real-time polling service (rtPS). The maximum goodput of Unsolicited Grant Service (UGS) is dropped to 51% and 58% when an rtPS is used for multiple connections due to the scheduling type.

In this paper we discuss the application of multiple-wireless technology to a practical context-enhanced service system called ViewNet. ViewNet develops technologies to support enhanced coordination and cooperation between operation teams in the emergency services and the police. Distributed localisation of users and mapping of environments implemented over a secure wireless network enables teams of operatives to search and map an incident area rapidly and in full coordination with each other and with a control centre. Sensing is based on fusing absolute positioning systems (UWB and GPS) with relative localisation and mapping from on-body or hand-held vision and inertial sensors. This paper focuses on the case for multiple-wireless capabilities in such a system and the benefits it can provide. We describe our work of developing a software API to support both WLAN and TETRA in ViewNet. It also provides a basis for incorporating future wireless technologies into ViewNet.

Fourth Generation Networks will invariably adopt MIMO-OFDMA techniques, in order to cope with increased data rate demands and improved Quality of Service (QoS) requirements. OFDMA is a popular multiple access candidate, since it facilitates multi-user diversity by enabling two dimensional multiple access, in time and frequency domains. Random Beamforming enables exploitation of spatial multi-user diversity and spatial capacity multiplexing gain. Layered Random Beamforming is able to achieve further multiple access benefits by enabling different users to be scheduled on different spatial layers of the same time-frequency resource. This paper examines the QoS performance of SU-MIMO and MU-MIMO precoding schemes for a VoIP system under a realistic traffic and channel environment. A novel Link Adaptation algorithm operating under PER constraints for delay sensitive VoIP traffic that promises increased data rates, flexibility and improved QoS is proposed and examined in this paper.

The mobile WiMAX standard (802.16e) uses multiple-input multiple-output (MIMO) limited feedback linear precoding to exploit the channel state information at the transmitter. Although the performance of limited feedback linear precoding in relation to traditional open-loop MIMO-OFDM has been extensively studied in the literature, these studies commonly assume perfect channel estimation at the receiver. In a practical OFDM-based system, the estimated channel matrix often differs from the actual channel matrix due to errors incurred in the channel estimation process. This results in degraded performance relative to the case with perfect channel estimation. To date, few researchers have studied the impact of channel estimation error on the performance of an OFDM limited feedback linear precoding system. This paper investigates the channel estimation error using 1) an MMSE channel estimator that takes into account the subcarrier correlation when estimating the channel, 2) a Low Rank (LR) channel estimator that relaxes the requirement for a perfect channel covariance matrix in the MMSE receiver, and 3) a ZF estimator where this correlation information is ignored. Simulation results show that with the MMSE estimator the system suffers very little array gain loss with a performance degradation of 0.2dB SNR. Compared to the MMSE estimator, the LR estimator incurs a small performance loss of around 0.5dB. Finally, when the ZF estimator is implemented, a significant performance degradation is observed with approximately 4–5dB loss in array gain loss.

In this paper, we evaluate the performance of broadcast safety applications in a vehicular-to-vehicular (V2V) communication scenario using a BER-based reception model from a detailed IEEE 802.11p physical layer simulator for a more accurate interpretation of the vehicular communication system, instead of the prebuilt SNR threshold model available in a typical network simulators. Our main contribution is the spatial diversity analysis provided using MIMO-STBC, that is specific to modulation types, vehicular speeds and range of SNR values. To further improve the accuracy of the analysis, realistic vehicular traces from a bidirectional highway are used as the mobility model. Finally, we included post-crash warning message prioritization over periodic status updates by enabling a hybrid EDCA MAC. Our analysis shows that MIMO-STBC achieves up to 80% range extension of the 1-hop safety broadcast in a V2V when compared against single antenna system.

This paper aims to combine adaptive subcarrier allocation and bit loading with the transmission of the H.264 SVC (Scalable Video Coding) encoded video sequences in order to increase the number of supported users in the system and provide the best quality of service (QoS) to the subscribers. We initially assume that the number of calls at the base station can be supported, and present an integer program (IP) formulation of the problem that considers the frequency selective nature of the channel, bit error rate requirement and the discrete rate requirements of the different layers of the medium grain scalable (MGS) video. It is shown how the IP can be extended to perform call admission control (CAC). Due to the complexity involved with IP, a sub-optimal scheme is then presented. Results demonstrate that our proposed scheme performs better than systems with a fixed resource allocation strategy by supporting more users and by always achieving acceptable QoS. Furthermore, the low complexity of the proposed CAC schemes makes it suitable for practical application.

This paper presents a link level analysis of the rate and energy efficiency performance of the LTE downlink considering the unitary codebook based precoding scheme. In a multi-user environment, appropriate radio resource management strategies can be applied to the system to improve the performance gain by exploiting multi-user diversity in the time, frequency and space domains and the gains can be translated to energy reduction at the base station. Several existing and novel resource scheduling and allocation algorithms are considered for the LTE system in this paper. A detailed analysis of the performance gain of different algorithms in terms of throughput, rate fairness, and power efficiency is presented.

This paper exploits the use of location information of wireless terminals to improve the performance of a beamforming system and support multiple access. Based on a system providing real-time 3D coordinate information of all terminals in the environment, a novel feedback-free multi-user scheduler is proposed. It chooses a set of angularly separated wireless terminals for simultaneous transmission in order to reduce the impact of mutual interference on overall system performance. If additional feedback of signal-to-interference and noise ratio is available, a location-assisted multi-user scheduler is also suggested to further improve the overall system performance. Both multi-user schedulers are based on a rate-greedy approach. To improve the fairness in resource allocation without introducing additional feedback overhead, a modified proportional fair algorithm (PFA) based on location information can be applied to a beamforming OFDMA system. By scaling the window length of PFA, a range of trade-offs between fairness and rate can be achieved.

The mobile WiMAX standard (802.16e) uses multiple-input multiple-output (MIMO) limited feedback linear precoding to exploit the channel state information at the transmitter. Although the performance of limited feedback linear precoding in relation to traditional open-loop MIMO has been extensively studied in the literature, these studies commonly assume a zero-lag feedback channel. However, due to the mobile nature of the mobile station (MS), the channel feedback information at the base station (BS) is incorrect because of an inherent delay between the time the MS estimates the channel feedback information and the time it is used in the BS. This results in performance degradation compared to a zero-lag feedback channel. To date, few researchers have studied the impact of MS velocity and Doppler spread on the performance of limited feedback linear precoding. Simulation results show that the performance of the mobile WiMAX precoded system degrades significantly as the MS velocity increases. At a velocity of 3km/h the precoded system degrades by 0.1-0.2dB in terms of array gain. However, the performance drops considerably when the velocity exceeds 10 km/h. At high MS velocities (i.e., 120 km/h), the linear precoding technique fails to provide any benefits. In this high mobility case we show that a linear precoding MIMO system with more antennas experiences the same performance as an open-loop MIMO system with fewer antennas.

This paper proposes a new wireless scheduling methodology which takes advantage of future predictions of data rate for the several users competing for physical access. Based on a system which allows low-cost 3D mapping of an environment in real-time, the predictions are obtained via either low-resolution path-loss prediction given the physical structure of the surroundings or by reference to data rates achieved by previous visitors to a locality. The proportional fair scheduling (PFS) metric is extended to include measures of the future rates users may achieve, leading to a new family of schedulers. They show useful fairness improvements over PFS in exchange for a small capacity loss, and allow a number of configuration options and a range of trade-offs between fairness and capacity.

In this contribution, we consider design of distributed LT codes, i.e., independent rateless encodings of multiple sources which communicate to a common relay, where relay is able to combine incoming packets from the sources and forwards them to receivers. We provide density evolution formulae for distributed LT codes, which allow us to formulate distributed LT code design problem and prove the equivalence of performance of distributed LT codes and LT codes with related parameters in the asymptotic regime. Furthermore, we demonstrate that allowing LT coding apparatus at both the sources and the relay may prove advantageous to coding only at the sources and coding only at the relay.

LTE (Long Term Evolution) is a next major step in mobile radio communications, and will be introduced as Release 8 in the 3rd Generation Partnership Project (3GPP). The new evolution aims to reduce delays, improve spectrum flexibility and reduce cost for operators and end users [1]. To fulfil these targets, new enabling technologies need to be integrated into the current 3G radio network architectures. Multiple Input and Multiple Output (MIMO) is one of the crucial enabling technologies in the LTE system particularly in the downlink to achieve the required peak data rate. The unitary codebook based precoding technique is proposed in the standard to increase the capacity of the system. This paper presents a link level analysis of the LTE downlink and an investigation of the performance of both Single User (SU) MIMO and Multi User (MU) MIMO with codebook based unitary precoding.

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. The objective of the Green Radio research programme (Core 5) of Mobile VCE is to deliver reduced power consumption of radio access networks. This paper attempts to show that an efficient exploitation of multiple antenna techniques and multiuser diversity in both the time, frequency as well as the space domain can significantly ease the power requirements of a base station, whilst maintaining the same levels of service. Different MIMO transmission and preceding schemes proposed for LTE, achieving varying degrees of multiuser diversity are examined.

Fourth generation networks will almost invariably adopt OFDMA (orthogonal frequency division multiple access) and MIMO (multiple input-multiple output) technologies, in order to meet high data rate and quality of service (QoS) requirements. The worldwide interoperability for microwave access (WiMAX) MAC Layer, which is based on the IEEE 802.16 standard, is designed to support a variety of applications, including voice and multimedia services. The problem of providing QoS in broadband wireless systems is one of managing radio resources effectively. Efficient scheduling algorithms that balance the QoS requirements of each application and user with the available radio resources need to be developed. This paper considers a number of scheduling policies concentrating on real-time voice over IP (VoIP) traffic. Via numerical results we show that the conventional notion of fairness fails to guarantee service for low latency applications such as VoIP for an increasing traffic load. We show better QoS is achieved via a greedy scheduling approach that manages to serve packets faster.

The end-to-end performance of applications in broadband wireless networks is a key concern from the user perspective. Mobile WiMAX is designed to support a wide range of different applications including media streaming, voice-over- IP (VoIP), video conferencing, and web browsing. All of these applications require different levels of quality of service (QoS) and this imposes a variety of different performance requirements on the WiMAX physical (PHY) and medium access control (MAC) layers. For example, TCP-based applications such as FTP or Web-browsing use automatic-repeat-request (ARQ) to tolerate a relatively high PHY packet error rate (PER), whilst a UDP-based application such as video streaming requires very low PER due to the lack of ARQ. This means that the same WiMAX system configuration needs to be able to provide different performance levels for different types of applications in order to operate efficiently. This paper analyses and compares the performance of a multi-input multi-output (MIMO) mobile WiMAX system in terms of achievable throughput and operating range for different PHY PER requirements. The paper shows that TCP applications can achieve higher throughputs and operating ranges due to higher PER tolerance. It also shows that this important QoS parameter affects the AMC switching points. Cross-layer interaction is required between the PHY and the scheduler in the MAC layer in order to efficiently fulfil the various QoS requirements at the application layer.

For the radar spectrum to be shared efficiently a good sensing capability within a secondary cognitive communication system is required. In this paper, the swept radar's rotation mechanism is explored to improve the sensing performance. Several node teaming algorithms are proposed for cooperative sensing along with the use of weighted sensing algorithms in a swept radar scenario. These teaming algorithms are considered in respect of the mobile team node selection and the sensing task assignments of the team nodes. Performance results show that selecting appropriate sensing nodes to join the sensing-active team in different sensing cycles and exploring their frequency diversity (to perform the sensing task at the most suitable frequency subchannels), yields a substantial improvement in performance. In addition, it is illustrated that proper node teaming algorithms should be chosen based on several key factors, including the characteristics of the primary signal and the sensing team node's computational capabilities.

A novel approach to provide unequal error protection (UEP) using rateless codes over erasure channels, named Expanding Window Fountain (EWF) codes, is developed and discussed. EWF codes use a windowing technique rather than a weighted (non-uniform) selection of input symbols to achieve UEP property. The windowing approach introduces additional parameters in the UEP rateless code design, making it more general and flexible than the weighted approach. Furthermore, the windowing approach provides better performance of UEP scheme, which is confirmed both theoretically and experimentally.

Fountain codes are a robust solution for data multicasting to a large number of receivers which experience variable channel conditions and different packet loss rates. However, the standard fountain code design becomes inefficient if all receivers have access to some side information correlated with the source information. We focus our attention on the cases where the correlation of the source and side information can be modelled by a binary erasure channel (BEC) or by a binary input additive white Gaussian noise channel (BIAWGNC). We analyse the performance of fountain codes in data multicasting with side information for these cases, derive bounds on their performance and provide a fast and robust linear programming optimization framework for code parameters. We demonstrate that systematic Raptor code design can be employed as a possible solution to the problem at the cost of higher encoding/decoding complexity, as it reduces the side information scenario to a channel coding problem. However, our results also indicate that a simpler solution, non-systematic LT and Raptor codes, can be designed to perform close to the information theoretic bounds.

In this contribution, duals of fountain codes are introduced and their use for lossy source compression is investigated. It is shown both theoretically and experimentally that the source coding dual of the binary erasure channel coding problem, binary erasure quantization, is solved at a nearly optimal rate with application of duals of LT and raptor codes by a belief propagation-like algorithm which amounts to a graph pruning procedure. Furthermore, this quantizing scheme is rate adaptive, i.e., its rate can be modified on-the-fly in order to adapt to the source distribution, very much like LT and raptor codes are able to adapt their rate to the erasure probability of a channel.

In this contribution, we consider the application of digital fountain (DF) codes to the problem of data transmission when side information is available at the decoder. The side information is modelled as a "virtual" channel output when original information sequence is the input. For two cases of the system model, which model both the virtual and the actual transmission channel either as a binary erasure channel or as a binary input additive white Gaussian noise (BIAWGN) channel, we propose methods of enhancing the design of standard non-systematic DF codes by optimizing their output degree distribution based on the side information assumption. In addition, a systematic Raptor design has been employed as a possible solution to the problem.

Promising performance of multiple-description coding (MDC) as a suitable video decomposition for MIMO (multiple-input-multiple-output) wireless transmission, reported previously by a number of authors, is further enhanced in this paper by investigating power allocation in MIMO systems that employ singular value decomposition (SVD). Inspired by the water-filling power allocation strategy, results demonstrate that further improvements over conventional, single-description coding (SDC) are possible if, for low SNRs, stronger sub-channel is boosted at the expense of the weaker channel. For high SNR values, the converse is true. A simple yet effective power allocation strategy whereby the bulk of the transmit power - the highest value considered was nine tenths - was allocated to the stronger channel (weaker channel) for very low (very high) SNRs yielded improvements of up to 4 dB (1 dB) in average MDC PSNR over the nominal - equal power allocation - case. The PSNR gains for low SNR values even exceeded the gains arising from water-filling.

Demand for broadband services continues to grow. Conventional high-speed broadband solutions are based on wired-access technologies, such as digital subscriber line (DSL). This type of solution is difficult to deploy in remote areas, and furthermore it lacks support for terminal mobility. Broadband wireless access (BWA) offers a flexible and cost-effective solution to these problems. The WiMAX standard has emerged to harmonize the wide variety of different BWA technologies. The most recent WiMAX standard (802.16e) supports broadband applications to mobile terminals and laptops. This paper analyses the performance of a mobile WiMAX system operating in an urban microcell. As an extension to the basic SISO mode, a number of 2 times 2 MIMO extensions are analysed. Simulated packet error rate and throughput results are presented for each link-speed. The paper highlights the trade-off between peak error-free throughput and robust operation at low SNR.

This paper explores the potential gain of joint diversity in both frequency domain and time domain which can be exploited to achieve spectral efficiency gains whilst simultaneously facilitating QoS/fairness in an OFDMA system (particularly in 3GPP Long Term Evolution (LTE)). The performance of several joint time-frequency schedulers is investigated. Simulation results show that joint time frequency schedulers achieve significantly superior performance compared to a more conventional time domain (only) proportional fair scheduler. The joint schemes show promising throughput gain while meeting stringent fairness criteria.

This paper presents performance analysis of layered random beamforming (LRB) - MIMO-OFDMA employing various resource scheduling algorithms with feedback reduction in a realistic outdoor environment. LRB enables the exploitation of spatial multi-user diversity gain, spatial multiplexing capacity gain and layer spatial multi-user diversity gain, which is achieved by enabling the multiplex of data transmitted simultaneously to different destinations. Unlike a conventional beamforming system, an LRB system only requires an effective signal to interference and noise ratio (ESINR) based numerical data rate as feedback from every spatial layer of the MIMO channel and thus has potentially lower feedback requirements than a system which requires feedback of more detailed channel information. By combining the LRB technique with OFDMA, LRB-OFDMA can achieve an additional spectral multi-user diversity gain compared to the single carrier LRB system. Various scheduling algorithms are proposed for LRB-OFDMA and they show a trade-off between maintaining fairness and minimising delay. The performance of LRB-OFDMA is evaluated using some well-established statistical channel models as well as a propagation modeling tool, which represents a realistic outdoor environment.

Opportunistic beamforming (OB) relies on the transmission of channel state information (CSI) in the form of instantaneous signal to noise ratio (SNR) from mobile stations (MSs) back to the base station (BS) for scheduling purposes that increase throughput and/or maintain resource allocation fairness. OB is employed in environments of low mobility and low scatter, artificially inducing channel fluctuations that can better exploit multiuser diversity (MUD). Multiple antennas at the BS randomly alter the channel's response and generate peaks in gain where users can be scheduled on, maximising system throughput. Additional gains are achieved by transmitting multiple weighting vectors from the BS, but their use can significantly increase the load of the feedback channel and mitigate MUD gains. Selective multiuser diversity (SMUD) has been proposed for the original beamforming scheme as a technique that reduces feedback requirements substantially without any significant throughput degradations. This paper considers the joined use of multiple weights and SMUD in opportunistic beamforming, aiming to increase capacity while reducing feedback overhead. Results show that with an appropriate use of threshold levels, not only average throughput can be increased through the use of multiple weighting vectors but also a notable decrease in feedback load requirements compared to the conventional OB with SMUD design is achieved.

OFDM is an attractive solution for the design of future wireless communications due to its robustness to dispersion in multipath environments. Additional diversity gains can be realised by OFDMA by exploiting not only the temporal fading, but also spectral fading, that can result in higher rates due to increased diversity. A scheduler exploiting multiuser diversity imposes strict feedback requirements as channel quality information is required for every user's feedback unit with a feedback rate at least equal to the coherence time of the channel. The instantaneous signal to noise ratio is the most commonly used metric to quantify users' channel conditions. In OFDMA, the overhead due to feedback transmission increases significantly due to the fact that signal to noise ratio is required in the frequency domain, for every subcarrier of the OFDM symbol, which can potentially mitigate any multiuser diversity gains. This paper proposes a reduced feedback OFDMA design that requires very limited feedback information on a clustered subcarrier basis, whilst maintaining high downlink rates via opportunistic beamforming with multiple weighting vector transmission from the base station. This scheme is shown to be quite robust, as it can be easily adapted to variable channel conditions without any significant increase in complexity.

The demand for broadband mobile services continues to grow. Conventional high-speed broadband solutions are based on wired-access technologies such as digital subscriber line (DSL). This type of solution is difficult to deploy in remote rural areas, and furthermore it lacks support for terminal mobility. Mobile broadband wireless access (BWA) offers a flexible and cost-effective solution to these problems. In recent years the WiMax standard has emerged to harmonise the wide variety of different BWA technologies. The first WiMax version was based on the IEEE 802.16-2004 standard and offered wireless links to fixed subscribers. The most recent 802.16e standard supports broadband applications to mobile handsets and laptops. This paper analyses the performance of a mobile WiMAX system operating on all link-speeds in an urban microcell. The simulation results are generated using a fully compliant 802.16e simulator and cover important aspects such as link adaptation, packet error rate and throughput. The theory is supported by experimental data captured in an urban microcell environment using a mobile WiMax basestation. Predicted results are compared with measured data taken from a number of vehicular drive tests. Analysis shows that mobile WiMax is able to achieve a street-level range of 300-2100 m depending on the permitted EIRP level.

In this contribution, we construct two novel IR-HARQ (automatic repeat request) schemes based on fountain codes, which combine the punctured and rateless IR-HARQ schemes, in order to attain the advantageous properties of both: nearly optimal performance of the former at the high signal-to-noise ratio (SNR) region and ratelessness of the latter. The preliminary simulation results indicate that these schemes are particularly suitable for scenarios where the transmission is originally assumed to occur at the very high SNR region, but resilience to severe deterioration of channel conditions is required.

The feasibility of coexistence between radar and a communication system is investigated under log-normal shadowing conditions. A key element that enables coexistence is a sensing receiver to detect the presence of a radar system and prevent transmissions when interference may occur. Initial studies where each communication terminal does its own sensing and decision-making shows that while bandsharing is possible, under stringent interference requirements, communication efficiency can be limited. Analytical and simulation results illustrate that cooperative sensing leads to an improved detection range, higher detection probability and lower complexity of sensing nodes than that of single terminal sensing. It is concluded that cooperative spectrum sensing is able to enhance detection capabilities to maximise radar spectrum-sharing usage efficiency.

Previous research into MIMO systems has focused little on optimisation for video transmission. In terms of multimedia transmission, spatial multiplexing (SM) is commonly proposed as the most suitable MIMO technique. Most SM-based video transport schemes look to exploit the multiplexing gain, which comes at the expense of a relatively high SNR, unless the channel state is known at the transmitter. Space-time block coding (STBC) is an attractive technique that does not provide the mapping flexibility of SM techniques, but does dramatically reduce the packet-error rate. This paper compares these techniques in terms of decoded video quality through simulations based on practical transmission scenarios. The use of multiple-description coding (MDC) is further proposed to provide a new class of wireless video transmission algorithms.

Expectations and requirements for future wireless communication systems continue to grow and evolve. Thus, recently, the third generation partnership project (3GPP) has considered the long term evolution (LTE) of 3G - also known as super 3G - to ensure its competitiveness in the future. It is generally assumed that the downlink of the new air interface would be OFDMA based and that some form of hybrid ARQ (HARQ) might be employed. This paper aims to evaluate the performance of various HARQ schemes over the OFDMA downlink of the currently proposed 3GPP LTE specification. Schemes are compared in terms of throughput and PER in the context their differing memory requirements for implementation. Simulation results show that type II incremental redundancy offers the best throughput performance but at the cost of higher memory requirement. However, when the schemes are enhanced with subcarrier and constellation rearrangement techniques, the performance gap between the different HARQ types is reduced significantly.

This paper presents a downlink performance analysis of a layered random beamforming (LRB) - MIMO- OFDMA physical layer (PHY) with feedback reduction as applicable to future generation wireless communication systems. OFDMA is a popular multiple access candidate for future generation cellular communication systems which facilitates multi-user diversity by enabling multiple access in the frequency domain. LRB enables the exploitation of spatial multi-user diversity gain, spatial multiplexing capacity gain and layer spatial multi-user diversity gain, which is achieved by enabling the multiplex of data transmitted simultaneously to different destinations. Unlike a conventional beamforming system, an LRB system only requires effective signal to interference and noise ratios (ESINR) as feedback from every spatial layer of the MIMO channels and thus has potentially lower feedback requirements than a system which requires feedback of more detailed channel information. By combining the LRB technique with OFDMA, LRB-OFDMA can achieve an additional spectral multi-user diversity gain compared to the single carrier LRB system. However, in this case ESINR feedback on a per-sub-carrier basis is required in principle and the feedback requirements may thus increase substantially. This feedback requirement can be reduced by generating the feedback information on a cluster (group of sub-carriers) basis rather than on an individual sub-carrier basis. In this way, the system can exploit any correlation in the frequency response of the channel. The design of an LRB- OFDMA system is presented in this paper and the performance of the system is evaluated for different degrees of feedback reduction using various statistical channel models. A complete list of feedback requirements for various MIMO schemes is also presented.

This paper presents simulation results for the transmission of unicast MAC frames over 802.11a/g. Fading channel models at various Doppler frequencies are developed to generate time- correlated SNR waveforms. These are then used together with a bit accurate MAC/PHY simulator to estimate the frame loss rate, the transmission delay, and the jitter for a steady flow of transmit frames. Time correlated channels are required to correctly simulate the bursty nature of packet loss in a wireless channel. The Doppler spread is shown to have a strong effect on the performance of the ARQ mechanism in the MAC layer. Delay is computed as the sum of the transmission delay and the accumulated queuing delay in the MAC buffer. Delay and frame loss are compared for time correlated and time uncorrelated fading channels. Compared to the slow fading case, in a fast fading channel fewer retransmissions are required and the end-to-end delay is significantly reduced. When channel conditions are poor the simulated delay and frame loss rate are seriously underestimated when time uncorrelated fading is assumed. To analyze the performance of video codecs, we show that a time correlated channel model must be combined with a dedicated 802.11a/g MAC/PHY simulation.

This paper presents a performance evaluation of a WiMAX system (802.16-2004) employing directional antennas in highly mobile applications. A WiMAX physical layer simulator is used together with an appropriate mobile channel model to perform the analysis. Results show that mobile performance is significantly improved when directional antennas are utilised at the mobile end of the link. These antennas reduce the resulting Doppler spread, which in turn increases the channel's coherence time. In a time varying channel, irreducible errors occur as a result of an aging channel estimate. The structure of the channel estimation pilots has a strong impact on performance. Analysis reveals that results are relatively insensitive to the shape of the Power Doppler Profile, but strongly related to the value of the Doppler spread.

MIMO (multiple-input-multiple-output) systems offer potential for throughput increase and enhanced quality of service for multimedia transmission. The underlying multipath environment requires new error-resilience techniques if the obtained benefits are to be fully exploited. Different MIMO architectures produce error-patterns of somewhat diverse characteristics. This paper proposes the use of multiple-description coding (MDC) as an approach that outperforms the standard-based error-resilience techniques in the majority of these cases. Results obtained from the random packet-error generator are furthered through the use of realistic MIMO channel scenarios and argue in favour of the deployment of an MDC-based video transmission system. Singular value decomposition (SVD) is used to create orthogonal sub-channels within a MIMO system which provide, depending on their respective gains and fading characteristics, an efficient means of mapping video content. Results indicate improvements in average PSNR of decoded test-sequences of up to 3 dB (5dB in the region of high PERs) compared to standard, single-description video transmission. This is also supported by significant subjective quality enhancements.

This paper presents a downlink performance analysis of a layered random beamforming (LRB) - MIMO-OFDMA physical layer (PHY) as applicable to future generation wireless communication systems. OFDMA is a popular multiple access candidate for future generation cellular communication systems which facilitates multi-user diversity by enabling multiple access in the frequency domain. Random beamforming (RB) is a method which enables the exploitation of spatial multi-user diversity gain and a spatial multiplexing capacity gain. Unlike a conventional beamforming system, an RB system only requires effective signal to noise ratios (ESNR) as feedback and thus has potentially much lower feedback requirements than a system which requires feedback of more detailed channel information. The layered method (LRB) enables the spatial multiplex of data transmitted simultaneously to different destinations. As a result it is able to offer a further spatial multi-user diversity gain, referred to here as layer multi-user diversity gain to distinguish from that achieved by the RB technique. An LRB-OFDMA system is thus able to achieve the rich benefits of spatial multiplexing capacity gain in combination with spatial, layer and spectral multi-user diversity gains. In this paper, the design of both RB-OFDMA and LRB-OFDMA systems are proposed and the performance of the system is evaluated by software simulation using various statistical channel models

Recently, there has been an explosion of growth in research on MIMO systems, but little has been published characterising performance in realistic environments. This paper quantifies the performance of MIMO WLANs in outdoor environments, and compares performance between spatial multiplexing and space time block coding processing approaches. Packet Error Rate (PER) and throughput performance results are presented under different channel conditions. A WLAN physical layer simulator employing MIMO techniques and a propagation modelling tool are combined in order to evaluate the coverage and throughput enhancements of WLANs for the 2×2 and 4×4 MIMO cases.

This paper presents a downlink performance analysis of a link adaptation (LA) algorithm applied to a MIMO-OFDM physical layer (PHY) which is a popular candidate for future generation cellular communication systems. The new LA algorithm attempts to maximize throughput and adaptation between various modulation and coding schemes in combination with both space-time block codes (STBC) and spatial multiplexing (SM) is based on knowledge of SNR and H matrix determinant; the parameters which are found to have the most significant influences on the system throughput. By means of ray-tracing software, a detailed example coherent time-variant channel trace is generated. Subsequent application of physical layer simulation software to this channel trace yields throughput results for adaptive MIMO-OFDM for the cases of the proposed LA algorithm, an algorithm based on SNR only, an algorithm based on SNR and H matrix determinant with fixed threshold levels for different SM modes and the optimal case.

This paper presents a downlink performance evaluation of a candidate physical layer for future generation cellular communications systems employing link adaptive MIMO-OFDMA. Adaptation between various modulation and coding schemes in combination with both space-time block codes (STBC) and spatial multiplexing (SM) on the basis of channel knowledge is considered. By means of ray-tracing software, a detailed example coherent time-variant channel trace is generated. Subsequent application of physical layer simulation software to this channel trace yields PER and throughput results for all available link adaptation parameters. Various channel parameters are considered against this data and the SNR and H matrix determinant are found to have the most significant influences on the system throughput. Subsequently, LA algorithms are proposed whereby the system adapts according to SNR only and both SNR and H matrix determinant. The performance of these algorithms is compared to the optimal case.

Much of the work on wireless transmission over the past several years has focused on simulation and deployment of multiple-input-multiple-output (MIMO) systems. These systems provide benefits of improved robustness and enhanced throughput at relatively low cost. Despite the increased understanding of the performance of MIMO systems, little is known about which combination of channel and source coding yields the best results for video transport. It is clear that new ways of providing error-resilience that emerge from MIMO architectures need to be developed which can cope with the particularities of video content. This paper proposes a new scheme for video transmission using multiple-description coding (MDC). Two complementary MIMO techniques, space-time block coding (STBC) and spatial multiplexing (SM), are employed. The quality of the reconstructed video, already enhanced by the inherent MIMO systems' properties, is further improved through the use of MDC.

Medium access control (MAC) protocols have a large impact on the achievable system performance for wireless ad hoc networks. Because of the limitations of existing analytical models for ad hoc networks, many researchers have opted to study the impact of MAC protocols via discreteevent simulations. However, as the network scenarios, traffic patterns and physical layer techniques may change significantly, simulation alone is not efficient to get insights into the impacts of MAC protocols on system performance. In this paper, we analyze the performance of IEEE 802.11 distributed coordination function (DCF) in multihop network scenario. We are particularly interested in understanding how physical layer techniques may affect the MAC protocol performance. For this purpose, the features of interference range is studied and taken into account of the analytical model. Simulations with OPNET show the effectiveness of the proposed analytical approach.

In this paper the key design considerations and link parameters for a 4G coded OFDMA system are identified and physical layer performance results are presented for a number of transmission modes. Additionally, this paper investigates the problem of dynamic multiuser subcarrier allocation in a coded OFDMA system. A novel, near-optimal, low complexity algorithm is proposed that attempts to exploit multiuser diversity by allocating sub-carriers to users so as to achieve substantial increases in perceived channel gain which are approximately equal for all users. Performance results show that performance is significantly enhanced when this algorithm is employed. Gains up to 10 dB can be observed.

This work focuses on the throughput analysis of the IEEE 802.11 medium access control (MAC). In the IEEE 802.11 standard, the main access scheme is called the distributed coordination function (DCF) and is the basis for the other access schemes, such as the point coordination function (PCF) and the enhanced DCF (EDCF) of the new IEEE 802.11e MAC. Since the IEEE 802.11 MAC does not support quality of service (QoS), the IEEE is currently working on the final draft of an enhanced version known as the IEEE 802.11e. In this enhanced standard, QoS and service differentiations are supported. The throughput and delay performance of the DCF/PCF of the IEEE 802.11 MAC are presented for different packet lengths and different numbers of users. Throughput performances are also detailed for the EDCF.

At present, wireless local area networks (WLANs) such as HiperLAN2 and 802.11a are being developed and deployed around the world. In this letter, the use of sectorized antennas is considered as a means to improve the physical layer performance of WLANs. Results demonstrate that throughput and range can be enhanced and/or the transmit power can be reduced. However, these benefits are achieved with a small increase in multiple access protocol overhead. Simulations are performed using measured wideband channels in the 5-GHz band. In cases where the channel exhibits strong Rician characteristics, gains as high as 13 dB are demonstrated. These benefits substantially outweigh the associated medium access control overhead.

In recent years there has been considerable interest in the development of standards for wireless local area networks. In particular, IEEE's 802.11a and 802.11g both employ coded orthogonal frequency division multiplexing (COFDM) but operate in different frequency bands. In this paper, the performance and relative merits of 802.11a and 802.11g are compared for the scenario of a corporate office wireless LAN application. It is shown that for comparable scenarios 802.11g achieves superior range but that 802.11a achieves higher data rates. Thus the two standards are found to have complimentary strengths and weaknesses.

The exponential growth of cellular radio, WLANs and the Internet sets the context for a discussion on the, role and objectives of 4G. In this paper OFDM is proposed as a leading candidate for a 4G cellular communications standard. The key design considerations and link parameters for a 4G OFDM system are identified and initial physical layer performance results are presented for a number of transmission modes and channel scenarios. Additionally, space-time techniques are considered as a means of enhancing the performance of the coded OFDM system.

This paper explores the application of space-time diversity techniques to enhance the performance of 5 GHz WLAN. The analysis is based on systems conforming to either the IEEE 802.11a or ETSI HIPERLAN/2 standard. Two antennas are assumed at the access point (AP) with a single antenna at the mobile terminal (MT). Downlink (DL) improvements are offered via the application of one of two fully compliant diversity schemes. The first technique can be applied to time division duplex (TDD) OFDM systems (ie, HIPERLAN/2) and is based on adaptive sub-band phase compensation. The second technique can be applied to non-TDD systems (ie, 802.11a) and makes use of spatial transmit delay diversity. Uplink (UL) improvement is offered via the use of spatial receive diversity with maximal ratio sub-band combining. Software simulated physical (PHY) layer packet error rate (PER) results are presented for the various methods and compared with those of an unaided transceiver. Combining the enhanced link level results with an analysis of the 802.11a and HIPERLAN/2 protocols, the expected throughput and range enhancements for both standards are computed.