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 study, the authors design and implement a real‐time hardware‐in‐the‐loop (HIL) wideband high‐velocity channel emulation platform for the performance evaluation and verification of 5G mmWave systems. A novel spectral splitting & stitching method and channel partitioning algorithm are developed to synchronously combine up to eight 160 MHz sub‐channels. The HIL platform was calibrated in the time and frequency domains and then validated using back‐to‐back results from a pair of experimental 60 GHz mmWave modems. The emulated path loss was generated for an additive white Gaussian noise channel to characterise the data throughput versus signal‐to‐noise ratio for a fixed point‐to‐point deployment. The wideband emulator was then used to introduce the Doppler shifts and spreads observed in a high velocity (up to 600 km/h) mmWave channel. For a Ricean channel ( K ‐factor greater than or equal to 10 dB), negligible data throughput losses were observed for velocities up to 293.9 km/h. Using the emulator, they show that the 5G modems can achieve continuous connectivity (albeit with some throughput loss) at velocities up to 587.8 km/h. Tests were also conducted in Rayleigh channels with uniformly distributed spatial multipath. In the Rayleigh case, the maximum vehicular velocity dropped to 51.4 km/h.

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.

Millimeter Waves (mmWaves) will play a pivotal role in the next- generation of Intelligent Transportation Systems (ITSs). However, in deep urban environments, sensitivity to blockages creates the need for more sophisticated network planning. In this paper, we present an agile strategy for deploying road-side nodes in a dense city scenario. In our system model, we consider strict Quality-of-Service (QoS) constraints (e.g. high throughput, low latency) that are typical of ITS applications. Our approach is scalable, insofar that takes into account the unique road and building shapes of each city, performing well for both regular and irregular city layouts. It allows us not only to achieve the required QoS constraints but it also provides up to 50\% reduction in the number of nodes required, compared to existing deployment solutions.

Connected and Automated Vehicles (CAVs) are expected to constantly interact with a network of processing nodes installed in secure cabinets located at the side of the road - - thus, forming Fog Computing-based infrastructure for Intelligent Transportation Systems (ITSs). Future city-scale ITS services will heavily rely upon the sensor data regularly off-loaded by each CAV on the Fog Computing network. Due to the broadcast nature of the medium, CAVs' communications can be vulnerable to eavesdropping. This paper proposes a novel data offloading approach where the Random Linear Network Coding (RLNC) principle is used to ensure the probability of an eavesdropper to recover relevant portions of sensor data is minimized. Our preliminary results confirm the effectiveness of our approach when operated in a large-scale ITS networks.

Future Connected and Automated Vehicles (CAVs) will be supervised by cloud-based systems overseeing the overall security and orchestrating traffic flows. Such systems rely on data collected from CAVs across the whole city operational area. This paper develops a Fog Computing-based infrastructure for future Intelligent Transportation Systems (ITSs) enabling an agile and reliable off-load of CAV data. Since CAVs are expected to generate large quantities of data, it is not feasible to assume data off-loading to be completed while a CAV is in the proximity of a single Road-Side Unit (RSU). CAVs are expected to be in the range of an RSU only for a limited amount of time, necessitating data reconciliation across different RSUs, if traditional approaches to data off-load were to be used. To this end, this paper proposes an agile Fog Computing infrastructure, which interconnects all the RSUs so that the data reconciliation is solved efficiently as a by-product of deploying the Random Linear Network Coding (RLNC) technique. Our numerical results confirm the feasibility of our solution and show its effectiveness when operated in a large-scale urban testbed.

Fifth generation (5G) networks will utilise the large bandwidth available in millimetre wave (mmWave) frequency bands up to 100 GHz in order to meet the ever-increasing high data rate demands. Efficient communications system design for such networks requires a thorough understanding of the propagation properties of the electromagnetic signals at such high frequencies. This paper presents the results of a polarimetric channel measurement campaign at 26 GHz and 60 GHz showing that diffuse scattering can be a dominant propagation mechanism for mmWave links. The use of a wide bandwidth provides a detailed insight into the multipath structure of the channel. It is shown that in a diffuse scattering scenario, nearly co-incident signals create small scale fading that affects the flatness of the channel significantly even when directional antennas are used. This also results in large co-to-cross polarisation ratio (XPR) variations across the channel bandwidth.

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.

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.

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.

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.

Millimeter wave (mmWave) communication is a key enabling technology with the potential to deliver high capacity, high peak data rate communications for future railway services. Knowledge of the radio characteristics is of paramount importance for the successful deployment of such systems. In this paper mmWave channel measurements are reported for a railway environment using a wideband channel sounder operating at 60GHz. Highly directional antennas are deployed at both ends of the link. Data is reported for path loss, root mean square (RMS) delay spread and K-factor. Static and mobile measurements are considered. Analysis shows that the signal strength is strongly dependent (up to 25dB) on the azimuth orientation of the directional transmit and receive antennas. A path loss exponent of n = 2. 04 was extracted from the Line-of-Sight measurements with optimally aligned antennas. RMS delay spreads ranged from 1ns to 22ns depending on antenna alignment. 50% of the measured K-factors were found to be less than 6dB. We conclude this is the result of ground reflections in the vertical Tx-Rx plane.

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 presents the analysis and characterization of the surface scattering process for both specular and diffused components. The study is focused on the investigation of various building materials each having a different roughness, at a central frequency of 60GHz. Very large signal strength variations in first order scattered components is observed as the user moves over very short distances. This is due to the small-scale fading caused by rough surface scatterers. Furthermore, it is shown that the diffused scattering depends on the material roughness, the angle of incidence and the distance from the surface. Finally, results indicate that reflections from rough materials may suffer from high depolarization, a phenomenon that can potentially be exploited in order to improve the performance of mm-Wave systems using polarization diversity.

Millimetre Waves (mmWave) systems have the potential of enabling multi-gigabit-per-second communications in future Intelligent Transportation Systems (ITSs). Unfortunately, because of the increased vehicular mobility, they require frequent antenna beam realignments - thus significantly increasing the in-band Beamforming (BF) overhead. In this paper, we propose Smart Motion-prediction Beam Alignment (SAMBA), a MAC-layer algorithm that exploits the information broadcast via DSRC beacons by all vehicles. Based on this information, overhead-free BF is achieved by estimating the position of the vehicle and predicting its motion. Moreover, adapting the beamwidth with respect to the estimated position can further enhance the performance. Our investigation shows that SAMBA outperforms the IEEE 802.11ad BF strategy, increasing the data rate by more than twice for sparse vehicle density while enhancing the network throughput proportionally to the number of vehicles. Furthermore, SAMBA was proven to be more efficient compared to legacy BF algorithm under highly dynamic vehicular environments and hence, a viable solution for future ITS services.

The successful deployment of safe and trustworthy Connected and Autonomous Vehicles (CAVs) will highly depend on the ability to devise robust and effective security solutions to resist sophisticated cyber attacks and patch up critical vulnerabilities. Pseudonym Public Key Infrastructure (PPKI) is a promising approach to secure vehicular networks as well as ensure data and location privacy, concealing the vehicles' real identities. Nevertheless, pseudonym distribution and management affect PPKI scalability due to the significant number of digital certificates required by a single vehicle. In this paper, we focus on the certificate revocation process and propose a versatile and low- complexity framework to facilitate the distribution of the Certificate Revocation Lists (CRL) issued by the Certification Authority (CA). CRL compression is achieved through optimized Bloom filters, which guarantee a considerable overhead reduction with a configurable rate of false positives. Our results show that the distribution of compressed CRLs can significantly enhance the system scalability without increasing the complexity of the revocation process.

A critical issue facing millimeter wave (mmWave) cellular systems is channel dynamics. MmWave signals are extremely susceptible to blocking and thus may vary rapidly with motion, orientation of the handset and local blockages. In this work, we derive a Finite State Markov Channel (FSMC) model of the mmWave channel from the statistics of ray tracing simulation data, which are based on channel measurements in an urban environment. The FSMC tracks the mutual information effective SINR (MI-ESNR), which can then be used in network simulations. The FSMC model is applied to analyze queue behavior and obtain the latency, throughput, packet error and droppage statistics for mmWave links at the MAC layer, making it useful for higher-layer analysis, as well. We evaluate the accuracy of the channel model for various model complexities and packet arrival rates and show that the model performance closely matches the empirical ray tracing data.

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.

Due to spectrum congestion in the commonly used mobile sub-6GHz frequencies, research and measurements in the Millimetre Wave (30-300GHz) bands are required to better understand the medium for 5G and beyond wireless connectivity. In this paper corner diffraction is investigated for an indoor environment in a modern building using a wideband (2GHz) channel sounder at 60GHz. Corner diffraction was measured at five different distances from the corner of interest, with parallel tracks at distances of 0.5m, 1m, 1.5m, 2m and 10m. These measurements were then compared with a Knife Edge Diffraction (KED) model where a `good-fit' was observed. Results showed that for 2m parallel tracks the power fell by 30dB as the user moved just 0.5m into the shadow region. For a 10m parallel track, the same effect was observed after moving 1.2m into the shadow region. Such rapid changes in received power can adversely affect the performance of link adaptation and beam tracking algorithms as well as the efficiency of the higher layer network protocols.

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.

This paper explores the possibility of opportunistic cognitive radio based offloading for infotainment services in future autonomous vehicles. With the goal of a truly intelligent vehicle, research into the potential of vehicular communications intends to facilitate a wide range of services from safety aspects such as collision prevention to in-car information and entertainment (infotainment) services. With such a broad remit, future vehicles will likely have to rely on multiple communication technologies to successfully service their needs. In this paper we identify the benefits of offloading to WiFi via Drive-thru Internet in vehicular applications but note the damaging handover overheads introduced by such schemes. Instead we propose a method of opportunistic access based on Beacon Interval Whitetime to macro-cellular WiFi access points as a means of sustaining an active connection whilst moving through an urban environment. This will reduce the inefficiencies of successive handovers and enable increased volumes of content to be delivered to the vehicle. We perform an empirical study of the potential for offloading in a representative urban environment and find periods of upto 100 ms per second are available for opportunistic use throughout the test. Additionally we find semi-deterministic opportunities for cognitive access occur following 35% of beacons observed on a WiFi channel.

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.

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.

This paper presents a wideband channel sounder for mmWave radiowave propagation measurements. Three test environments are described and a number of channel sounding validation techniques are proposed. The temporal performance of the sounder is assessed through real-time wideband measurements using two metallic reflectors placed within an anechoic chamber. Furthermore, high directional antennas are employed for the purpose of power validation, as well as for measuring the received signal strength reflected by various building materials. Finally, the depolarization of the building materials is assessed by means of measuring and characterizing the received cross-polar components.

The demand placed on wireless networks operating within fixed allocations of licensed or unlicensed spectrum has introduced the development of cognitive radios, capable of intelligently utilising spare resource whenever it is available. Since WiFi is an ubiquitous method for localized high speed mobile internet access it exists in almost all typical radio environments however the spectrum in which it operates is not exploited to its full potential. This paper introduces a concept called Whitetime to describe the free time between frame transmissions on a typical WiFi channel and across all networks. Initial measurements of real environments indicate that more than 85% of time on a channel is unused however this predominantly consists of short interframe spaces. Detailed analysis reveals periods of inactivity greater than 10ms are synchronised with the beacon interval from observable access points on the channel. For applications that require opportunistic network access such as non deterministic machine to machine (M2M) communication, Whitetime presents a reliable opportunity to transmit packets as long as 1500 bytes using standard physical layer techniques.

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.

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.

In the past few years, extensive research has focused its attention on interference alignment (IA) methods that are aimed at improving the interference networks potential. However, the channel state information (CSI) precision has a correlation with the functionality of IA. When the CSI is completely outdated then there is a possibility that performance effectiveness and gain of IA could be lost. In the current study, a completely outdated source-to-relay CSI within multi-user network is considered followed with the introduction of a collaborative relay system within such a situation to assist in improvement of the networks freedom levels. By examining various outdated CSI situations at transmitter (CSIT), the trade-off involving relay-aided IA (RIA) alongside non-relay-aided IA (NRIA) is obtained. Additionally, the total RIA rate alongside covariance-supported channel estimator is examined.

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.

This paper presents a path-loss prediction analysis and a performance evaluation of the 60GHz IEEE 802.11ad standard. Received signal strength measurements were performed in indoor locations and the decay coefficients were estimated over a number of measured routes. Furthermore, real world maps were incorporated into a 3-D mm wave ray- tracing tool for the purpose of employing realistic channel matrices into an 802.11ad bit level simulator. Finally, performance metrics for various MCS modes are presented and analyzed for both Orthogonal Frequency Division Multiplexing (OFDM) and Single Carrier (SC) transmissions.

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 presents a practical demonstration of the benefits of limited feedback beamforming for mmWave applications. Different beamforming strategies are presented, analysed and compared. Compressive sensing (CS) is investigated to accurately estimate the sparse Power Angular Profile (PAP) of the mmWave channel. This information is then used to estimate the antenna array weights required to steer the beam to maximise received SNR. This scheme is particularly attractive for outdoor mmWave networks where large antenna arrays are necessary to mitigate high observed pathloss. Codebook based beamforming strategies are also analysed. Using a practical mmWave antenna away, measurements are reported for a controlled multipath channel that compare the performance of the proposed beamforming strategies. In terms of received SNR CS based beamforming was shown to outperform more traditional codebook based solutions by to 5dB.

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.

Diffraction is known to have a major influence on the propagation performance of a wireless communications link especially in lower frequency bands and hence the diffraction in millimetre wave band needs to be emphasized. In this paper, we propose a single material characterisation measurement in a controlled indoor environment at the centre frequency of 40GHz. In addition, measurement results are presented in three distinct regions, line of sight (LOS), penumbra and umbra for a more comprehensible observation. Different materials with approximately same dimension are tested. The movement of the material under test through a direct ray path is investigated. Analysis shows that concrete experiences the greatest attenuation compared to other materials under test. The proposed results show significant agreement with the Knife Edge Diffraction theory. It also can be concluded that there is a significant diffracted field in umbra regions.

A novel fast blind equalizer is obtained by using the direct calculations from a channel matched filter decision feedback equalizer (CMF-DFE). The proposed technique converts the inverse convolution operations of an equalizer into a linear finite impulse response estimation filter, which is more suitable for blind training. A novel error function is introduced for blind training which enables the use of fast algorithms such as LMS or RLS. The required auto-regression values for the CMF-DFE equalizer are calculated from the incoming data. The resulting performance with LMS training is close to that of non-blind techniques.

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.

The non-orthogonal multiple access (NOMA) is regarded as a promising multiple access technique for 5G network. In this research, comparing with the joint transmission (JT) NOMA in Coordinated Multi-Point (CoMP) system, we propose a novel opportunistic NOMA (ONOMA) scheme, which aims to improve the efficiency of the successive interference cancellation (SIC) decoding in conventional NOMA. Besides, by comparing with the JT-NOMA in CoMP system, the data rate of the ONOMA is shown in the numerical results under the ideal and non-ideal scenarios.

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.

This paper evaluates the theoretic performance of single-user multi-stream beamforming for heterogeneous LTE-A urban deployments (i.e. Macro and Pico cells). The work investigates the impact of six different Base Station (BS) antenna configurations on system level capacity. Our standard configuration assume 8 BS and 8 User Equipment (UE) antenna elements. To enhance capacity the BS antenna number was increased to 12 and 16. A 3D laser-scanned database for the city of Bristol (UK) was used as input to the 3D channel propagation model along with measured 3D complex voltage and polarimetric antenna patterns for the individual BS and UE antenna elements. More than 50,000 ray-traced Pico and Macro cellular links per BS configuration were investigated to ensure statistical relevance. Our analysis quantifies the capacity of an 8×8 Single-User Multiple-Input-Multiple-Output (SU-MIMO) solution in realistic urban heterogeneous environments. Results address the system level benefits of increasing the number of BS antenna elements as well as the sensitivity of capacity to vertical and horizontal spatial element configurations.

This paper proposes novel Raptor-aware link adaptation (LA) when application layer Forward Error Correction (AL-FEC) with Raptor codes is used for live, high quality, video unicast over mobile broadband networks. The use of Raptor code AL-FEC is taken into account for the adaptation of the modulation and coding scheme (MCS) used in the physical layer. A cross-layer optimization approach is used to select the Raptor code parameters and the MCS mode jointly, in order to maximize transmission efficiency. The proposed methodology takes into consideration the channel resources required to accommodate the Raptor overheads. Simulation results show that packet loss is eliminated and the amount of radio resource required is reduced significantly. Automatic repeat request (ARQ) based unicast systems require up to 115.6 percent more channel resources, by comparison to the proposed Raptor-aware LA system without retransmissions. Furthermore, the Raptor-aware LA system can enhance the link budget by up to 4 dB, increasing coverage in LoS locations, and can improve total goodput by 46.7 percent compared to an ARQ-based system.

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 analyses the potential of polarimetric filtering to mitigate interference in a 60 GHz WPAN. A 3D ray tracing model is developed to simulate realistic propagation scenarios in a dense indoor environment and a Received Bit Mutual Information Rate (RBIR) abstraction technique is used to evaluate link level performance. Subsequently, the spatial reuse gain and the fairness between users at system level are evaluated and are shown to be considerably enhanced by the use of polarimetric filtering. In particular, the paper demonstrates the benefits of nulling the interference, maximising the signal power and optimising the SINR. An improvement of more than 80% in network throughput and 20% in fairness is observed among the users when optimal filtering is applied.

In this paper the use of compressive sensing (CS) to accurately estimate the sparse Power Angle Profile (PAP) of a mmWave propagation channel has been investigated. This scheme is especially attractive for outdoor mmWave applications where large antenna arrays are more likely to be deployed to compensate for high pathloss. Current analogue beamforming techniques such as the codebook based 802.11ad beamforming manifest large beamforming overhead for large antenna arrays of typically 16×16 elements. Measurements in an anechoic chamber were performed to demonstrate the applicability of CS to mmWave PAP estimation. The impact of noise on the estimation of Directions-of-Departure (DoD) using CS theory is analysed and finally the benefit of exploiting the reconstructed PAP in beamforming is assessed and compared to the beam searching algorithm adopted in the IEEE 802.11ad standard.

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.

A 2×2 60 GHz MIMO solution combined with polarisation diversity is proposed for high throughput WLAN applications. In addition to a PHY throughput of more than 12 Gbps, this scheme is robust against polarisation mismatch and antenna tilting due to the adoption of circular polarisation. It also offers the possibility to detect LOS/NLOS conditions for antenna adaptation. A fast beamforming ability that exploits the MIMO architecture is presented. Results show that the proposed beam switching procedure outperforms existing prior art schemes in terms of its ability to track a time varying channel.

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.

This paper evaluates the impact of antenna patterns in heterogeneous LTE-Advanced networks. The propagation channel between each BS and UE is modelled as the spatial and polarimetric convolution of the antenna patterns with the spatial and temporal multipath components from a 3D outdoor ray-tracer. An LTE-Advanced physical layer simulator is used to determine the user performance in pico-cells and macro-cells for non-line-of-sight links. The received bit mutual information rate abstraction method is employed to determine the optimal physical layer throughput based on analysis of all available modulation and coding schemes. Packet error rate, throughput, link correlation and channel capacity are studied for pico-cellular and macro-cellular users. Results show that measured antenna patterns along with their orientations strongly influence user performance in an LTE-A network.

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.

Recently there have been proposals to extend MIMO processing to the elevation dimension in addition to the azimuth direction. To accurately assess the promised gains of these "3D-MIMO" techniques, a channel model is needed that accurately accounts for the elevation angles of the rays. In addition it would be desirable for the 3D channel model to be a simple extension of an already defined 2D channel model to allow for ease of implementation and to assist the 3GPP standardization effort in the 3D MIMO area. In this paper we propose an extension of the ITU 2D channel model to 3D by adding a distance dependent elevation spread based on observations from ray tracing. Through system-level simulations we observe that the behavior of 3D MIMO is greatly impacted by the modeling of the 3D channel.

Conventional video compression relies on interframe prediction (motion estimation), intra frame prediction and variable-length entropy encoding to achieve high compression ratios but, as a consequence, produces an encoded bitstream that is inherently sensitive to channel errors. In order to ensure reliable delivery over lossy channels, it is necessary to invoke various additional error detection and correction methods. In contrast, techniques such as Pyramid Vector Quantisation have the ability to prevent error propagation through the use of fixed length codewords. This paper introduces an efficient rate distortion optimisation algorithm for intra-mode PVQ which offers similar compression performance to intra H.264/AVC and Motion JPEG 2000 while offering inherent error resilience. The performance of our enhanced codec is evaluated for HD content in the context of a realistic (IEEE 802.11n) wireless environment. We show that PVQ provides high tolerance to corrupted data compared to the state of the art while obviating the need for complex encoding tools.

Video encoders such as H.264 and VC-1 rely on variable length coding, motion estimation and intra prediction to achieve high compression ratios but, as a consequence, produce an encoded bitstream that is extremely sensitive to channel errors. Pyramid Vector Quantisation, which generates fixed length codes, has been shown to provide excellent error resilience for wireless transmission of HD video. This paper presents an efficient rate distortion optimisation algorithm for PVQ which yields impressive intra coding performance with low complexity. The compression performance of PVQ is comparable with intra-H.264 and intra-VC-1. The error resilience of PVQ is also compared with H.264 and VC-1 in a representative MIMO Wireless LAN environment, showing the superior performance of PVQ.

In this paper the throughput and packet error rate for an in-home 802.11n network is theoretically derived for two different types of 3x3 antenna configurations. Our first configuration assumes the use of three low directivity omni-dectional elements. The second arrangement makes use of three orthogonally orientated directional elements. The spatial and temporal characteristics of the in-home channels are modelled using 3D ray tracing and combined with appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is computed for all modulation and coding schemes using a received bit information rate abstraction technique. The theory shows that directional antennas outperform the omni-directional devices in most cases. Directional elements show increased sensitivity to orientation, however for 83% of locations and orientations they still result in throughput enhancement. Directional antennas provide a 33% improvement in average data rate for random client orientations, improving to 52% with optimum alignment to the multipath.

This paper explores rules and defines cross layer parameters that enhance the received video quality per unit bandwidth while observing strict video QoS for unicast video transmission over mobile WiMAX. Channel capacity and goodput are estimated using a detailed MAC/PHY simulator. The simulator supports link adaptation of the PHY layer Modulation and Coding Scheme (MCS) alongside MAC layer Automatic Repeat Request (ARQ). A new performance indicator, PSNR per Hz, is defined to capture the video PSNR attained for a given effective bandwidth. For the 3GPP urban micro channel, MCS and MAC layer block lifetime are jointly determined as a function of average channel SNR in order to enhance video PSNR and goodput. At low SNR higher level QAM is inefficient (as a result of excessive MAC layer ARQ or high packet error rate) for video transfer. Results show that video efficiency improves for block lifetimes up to 100ms, since the greater use of ARQ enables more spectrally efficient MCS modes to be applied.

This paper presents results from a novel OFDMA multi-cell mobile broadband system-level simulator. The tool is used to statistically characterize uplink and downlink inter-cell interference. Fully loaded interference studies cannot be performed on real-world networks until they have been fully deployed. As such, interference analysis and management must be accurately performed pre- deployment using detailed network simulators. This paper discusses our simulator architecture and the steps necessary to reduce computational complexity inherent in such simulations. The paper then demonstrates the impact of inter-cell interference in OFDMA networks. The results demonstrate that it is the frame-to-frame fluctuations in interference, and not the received signal level, that dominate inaccuracy in the Channel Quality Index (CQI). CQI errors lead to the wrong MCS mode being chosen by the AMC algorithm and this leads to throughput reduction. Results show that this problem is exacerbated by high vehicular speeds and the absence of interference randomization. Compared to ideal MCS selection, throughput reductions of up to 45% are reported.

Throughput and packet error rate are analysed in a home environment for two different 3×3 wireless LAN solutions. A 3×3 EBF approach (using three radio chains) is compared with a reduced cost 2×2 architecture (using two radio chains). In the 2×2 solution the optimum antenna pair is selected from the same set of three antennas at the AP and client. The impact of directional, as well as omni- directional, antenna elements is considered. The spatial and temporal characteristics of the in-home channels are modelled using 3D ray tracing and combined with appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is calculated for all modulation and coding schemes and (for the 2×2 case) all possible antenna combinations using a novel received bit mutual information rate abstraction technique. Results show that antenna number, pattern and orientation all play a key role in determining the performance of an 802.11n system. As expected, 3×3 EBF outperforms the 2×2 solution; however, with optimum antenna selection the performance of 2×2 EBF is competitive, especially when directional antennas are used at low signal to noise ratios. For distant rooms, 3×3 EBF is only 15% better (in terms of throughput) than 2×2 EBF when directional antennas and dynamic antenna selection are applied. 2×2 EBF with omni antennas results in a 45% reduction in throughput (compared with 3×3 EBF).

This paper presents results from a novel OFDMA multi-cell mobile broadband system level simulator. The tool is used to statistically characterize uplink and downlink inter-cell interference. Without suitable interference management, multi-billion dollar networks can collapse under the strain of heavy traffic loads. Fully loaded interference studies cannot be performed on the network until it has been fully deployed. As such, interference analysis and management must be accurately performed pre-deployment using detailed network simulators. System level simulation is a highly computationally intensive procedure. This paper discusses the simulator architecture (and steps taken to reduce computational complexity) and then demonstrates the impact of inter-cell interference in OFDMA networks. In an interference limited scenario the results demonstrate that it is the frame-to-frame fluctuations in interference, and not the received signal level, that dominate inaccuracies in the Channel Quality Index (CQI) prediction. CQI is used in the fast link-adaptation process to select the MCS mode for each user on a frame-by-frame basis. Results show that incorrect Modulation and Coding Scheme (MCS) modes are chosen up to 40% of the time when the CQI is delayed by 3 frames and the user is interference limited. Perfect MCS selection is then shown to improve user throughput by up to 50%.

Video Source encoders such as H.264 and VC-1 are in common use today and provide impressive compression performance. These use variable length coding and predictive coding to achieve high compression ratios but as a consequence render the encoded bitstream extremely sensitive to channel errors. In this paper we revisit an alternative technique, Pyramid Vector Quantisation, which generates fixed length codes. Intra mode PVQ is presented as a means of robustly compressing and wirelessly transmitting HD Video. The paper shows that PVQ is an effective codec for indoor wireless transmission of HD video. Comparing the required channel SNR for an H.264 based system with a PVQ based system shows that PVQ can operate at a much lower SNR (with gains of up to 11 dB) while still providing excellent video quality and compression performance.

An automatic method for rapid and optimised surveillance camera deployment is proposed for outdoor settings. Given a target scene. potential camera locations are generated taking account of real-world camera parameters and environmental constraints. For example, each point on a target must be viewed by at least two cameras. We employ ray tracing to determine the visibility of any point from a given camera and camera-to-point viewing angle is used to measure visibility quality. Gradient ascent is used to optimise camera orientation for maximum quality coverage. Camera network optimisation was also addressed, and a new combinatorial algorithm is proposed. A comparative study showed that our approach significantly outperforms competing techniques providing solutions which better cover the search space, while offering multiple alternative solutions.

Single-Carrier Frequency Division Multiple Access (SC-FDMA) has been selected as the uplink transmission scheme in the 3GPP Long Term Evolution standard. SC-FDMA is a form of Single-Carrier Frequency Domain Equalization (SCFDE) with flexibility in its resource allocation. In this paper we investigate the performance of SC-FDMA with Frequency-Domain Linear Equalization (FD-LE) with optimized transmit power allocation. We derive the optimum power allocation for both Zero-Forcing (ZF) and Minimum Mean-Square Error (MMSE) FD-LE receivers in order to maximize the achievable data rate subject to total transmit power constraint. Results show that optimum transmit power allocation given knowledge of the FD-LE receiver results in a better achievable transmission rate compared to the information theoretic optimum transmit power allocation, which assume an ideal receiver. Results show that the proposed power allocation scheme offers significant increases in the operating range and cell throughput of SC-FDMA system.

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.

Practical frequency domain equalization (FDE) systems generally require knowledge of the channel and the noise variance to equalize the received signal in a frequency-selective fading channel. Accurate channel estimate and noise variance estimate are thus desirable to improve receiver performance. In this paper we investigate the performance of the denoise channel estimator and the approximate linear minimum mean square error (A-LMMSE) channel estimator with channel power delay profile (PDP) mismatch and noise variance estimation errors for a single carrier frequency division multiple access (SC-FDMA) system. A windowed DFT-based noise variance estimator is also presented in this paper to improve A-LMMSE channel estimation as well as to facilitate the MMSE-FDE design. Results show that the proposed noise variance estimator remains unbiased up to a SNR of 50dB.

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.

Single-Carrier Frequency Division Multiple Access (SC-FDMA) has been selected as the uplink transmission scheme in the 3GPP Long Term Evolution standard. SC-FDMA has reduced sensitivity to phase noise and a lower Peak-to-Average Power Ratio (PAPR) compared to Orthogonal Frequency Division Multiple Access. In this paper we propose joint Tomlinson-Harashima Precoding and transmit power allocation for SC-FDMA. We derive the optimum power allocation for SC-FDMA transmission for both Zero-Forcing (ZF) and Minimum Mean-Square Error (MMSE) LE receivers in order to maximize the achievable data rate subject to constant transmit power. Although this improves the system's performance and offers a 1-2 dB improvement over Frequency-Domain Decision Feedback Equalization (FD-DFE), when the proposed transmit power allocation scheme is combined with decision feedback equalization the system incurs a performance degradation due to error propagation. In this paper we propose a joint implementation of the derived power allocation scheme with THP. Here we show that the system's performance is further improved over both FD-LE and FD-DFE when transmit power allocation is applied.

Single-Carrier Frequency Division Multiple Access (SC-FDMA) has been selected as the uplink transmission scheme in the 3GPP Long Term Evolution standard. SC-FDMA is a form of Single-Carrier Frequency Domain Equalization (SC-FDE) with a flexibility in resource allocation, thus it has reduced sensitivity to phase noise and a lower Peak-to-Average Power Ratio (PAPR) compared to Orthogonal Frequency Division Multiple Access. This, consequently, makes it more attractive for low cost devices with limited transmit power. In this paper we propose an optimum power allocation scheme for SC-FDMA transmission considering Frequency-Domain Linear Equalization (FD-LE). We derive the optimum power allocation for the SC-FDMA transmission for both a Zero-Forcing (ZF) and a Minimum Mean-Square Error (MMSE) receiver in order to maximize the achievable rate subject to a constant transmit power. Results show that the optimum power allocation for the MMSE FD-LE results in greater improvement in the achievable transmission rate compared to ZF FD-LE.

This paper investigates OFDMA downlink resource (spectrum and power) sharing algorithms for fixed relay stations. Iterative waterfilling is used in the power allocation process and shown to result in an optimal power allocation solution for multiple-relay networks. Iterative waterfilling is then developed with a power reallocation process to achieve more efficient spectrum utilization. Furthermore, joint subcarrier and power allocation algorithms are proposed with and without consideration for multiuser fairness. Simulation results show that iterative waterfilling can significantly improve the system capacity. The proposed joint allocation algorithm achieves gains of up to 21% in system capacity compared to iterative waterfilling. The joint allocation algorithm with fairness is shown to degrade system capacity, however fairness is important in a multiuser network.

A new class of iterative block decision feedback equalizer (IB-DFE) was pioneered by Chan and Benvenuto. Unlike the conventional DFE, the IB-DFE is optimized according to the reliability of the feedback (FB) symbols. Since the use of the training sequence (TS) for feedback reliability (FBR) estimation lowers the bandwidth efficiency, FBR estimation without the need for additional TS is of considerable interest. However, prior FBR estimation is limited in the literature to uncoded M-ary phaseshift keying (PSK). In this paper we investigate FBR calculation methods for uncoded and coded M-ary quadrature amplitude modulation (QAM) systems. Results show that our newly proposed method has similar or better error rate performance than the TS method without the associated loss of bandwidth efficiency.

There is considerable interest in the use of single carrier frequency division multiple access (SC-FDMA) as the uplink transmission scheme in the 3GPP Long Term Evolution standard. This interest is justified by the inherent single carrier structure of SC-FDMA, which results in reduced sensitivity to phase noise and a lower peak-to-average power ratio (PAPR) compared to orthogonal frequency division multiple access. This, consequently, makes it more attractive for low cost devices with limited transmit power. In this paper we demonstrate how precoding the uplink transmission is an alternative signal processing technique to equalization in order to combat the frequency selective nature of the propagation channel. The frequency-domain implementation of Tomlinson-Harashima precoding (THP) for uplink SC-FDMA is proposed. We investigate the BER performance and the PAPR characteristics of the preceded SC-FDMA waveform for ZF and MMSE based THP. Results reported here show that the MMSE-THP outperforms the ZF-THP in terms of BER performance and PAPR.

Recently there has been considerable interest in the use of single carrier frequency division multiple access (SC-FDMA) as the uplink transmission scheme for the 3GPP long term evolution (LTE) standard. This paper investigates different multiple input multiple-output (MIMO) techniques for uplink SC-FDMA. Here we demonstrate how the transmitter can exploit the available channel information, through precoding and pre-equalization, in order to combat the frequency selective nature of the propagation channel and improve the system's performance under fading. In this work we investigate the achievable system capacity, and the peak-to-average power ratio (PAPR) characteristics of the precoded and pre-equalized SC-FDMA waveform. We consider unitary preceding for MIMO, as well as pre-equalization for a multiple-input single-output (MISO) system with maximum ratio combining (MRC), equal gain combining (EGC), zero forcing (ZF), and minimum mean square error (MMSE) algorithms. Results reported in this paper show that ZF pre-equalization for SISO SC-FDMA is capable of achieving the Shannon Capacity limit for faded channels, with a BER performance that is identical to an AWGN channel, and that pre-equalized increases the capacity of MIMO SC-FDMA systems.

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.

SC-FDMA (Single-Carrier Frequency Division Multiple Access) is employed in the 3GPP LTE (Long-Term Evolution) standard as the uplink transmission scheme. The SC-FDMA signal has a low PAPR. This makes it well-suited to power efficient transmission at the mobile terminal. Although it is a common assumption to use frequency-domain linear equalization in SC-FDMA, a decision feedback equalizer (DFE) composed of a frequency-domain feedforward filter and a time-domain feedback filter can provide enhanced performance. Even when error propagation is taken into account, results show that a DFE still offers a significant performance gain over the conventional LE for uncoded SC-FDMA. This paper demonstrates that SC-FDMA with DFE is capable of increasing the throughput in a power limited channel by up to 41% compared to LE. Alternatively, for a given peak transmit power, the use of a DFE can achieve a 14% coverage extension in NLOS and 19% in LOS.

In this paper, algorithms on distributed resource (spectrum and power) sharing for relay stations are investigated for downlink transmissions in an OFDMA-based relay-aided cell. Both system capacity and user fairness are considered. By grouping the relay stations into coalitions according to the set of users they are relaying, the optimal resource allocation can be solved by considering resource allocation within and among the coalitions. The algorithm for intra-coalition resource allocation is proposed by utilizing the key observation: for each data symbol transmitted from the base station to a user (in a subcarrier), only one among all the available relay stations is required to relay the symbol. The inter-coalition resource allocation is modeled by both a non-cooperative and a cooperative game, where the cooperative game is solved by a nonsymmetric Nash bargaining solution. Simulation results show that the non-cooperative algorithm outperforms random allocation by approximately 50% in system capacity with 3 relay stations in each coalition. The cooperative algorithm has approximately 5% loss in system capacity comparing with the non-cooperative algorithm, but achieves a significant gain in terms of fairness performance.

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 addresses the downlink performance of mobile WiMAX operating at 2.3 GHz in an urban environment. The analysis includes a comparison of simulated and experimental results. Simulated packet error rate (PER) versus signal to noise ratio (SNR) graphs are generated on a per link-speed basis using a fully compliant 512 carrier mobile WiMAX simulator. Experimental data is gathered using a carrier-class basestation, a mobile-WiMAX enabled laptop, and a suite of application layer logging software. An H264 AVC encoder and IP packetisation unit is used to transmit video to a mobile client. Results show strong agreement in terms of simulated and captured PER. Using this data, the downlink operating range is evaluated as a function of the Effective Isotropic Radiated Power (EIRP) and path loss exponent. Results indicate that at low EIRP (32 dBm) the expected outdoor operating range is around 200-400 m. Applying the UK OFCOM regulations for licensed operation in the 2.5 GHz band, downlink operation in excess of 2 km can be achieved.

The performance of a mobile WiMAX system is highly dependent on the application environment. Local clutter has a significant impact on the path loss exponent and the observed multipath statistics. The spectral efficiency of a WiMAX network can be enhanced if channel quality information is included as part of the system optimization process. This paper presents a comprehensive study of such a scenario, with numerical analysis of mobile WiMAX presented for a multi-cell deployment. In order to achieve high coverage and throughput to a large number of users, handover (HO) and link adaptation (LA) strategies are addressed. Interference is spatially separated through the use of dynamic channel allocation and WiMAX user assignment. Results show that coverage to 98% of the service area is achieved with an average throughput of 3.88 Mbps per sector. This is based on a 5MHz (512-FFT) OFDMA TDD profile (using one-third fractional reuse) deployed in licensed 3.5 GHz spectrum.

In this paper, we focus on the design of efficient resource allocation algorithms for a multihop cellular network, with orthogonal frequency division multiple access (OFDMA) as downlink transmission technique and utilizing decode-and- forward cooperation strategy. Our objective is to maximize the total capacity based on the constraint of individual transmission power at each transmitter. We also consider users' QoS requirements by maximizing the total capacity while giving users proportional fairness weights according to their data requirements. We show that for each data symbol (at each subcarrier) transmitted by base station, the best relaying strategy is to let only one among all the relay stations perform the relaying task. This is true for both objectives of maximizing total capacity and maximizing capacity with proportional fairness constraint. We then propose efficient greedy algorithms for both centralized and distributed resource allocations based on our analysis. Simulation results indicate that our proposed algorithms effectively enhance the total capacity.

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.

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.

"Single Carrier Frequency Division Multiple Access" (SC- FDMA) is a strong candidate for uplink transmissions in the 3G Long Term Evolution (LTE) standard. SC-FDMA is a multiple access scheme that uses DFT spreading prior to OFDM modulation to map the signal from each user to a subset of the available subcarriers. SC-FDMA has a significantly lower peak-to-average power ratio (PAPR) compared to OFDM/OFDMA. This greatly improves its RF power amplifier efficiency and also the mean power output from a battery driven mobile terminal. In this paper, the impact of radio resource allocation and pulse shaping on the PAPR of SC-FDMA signals are investigated, especially for localized FDMA (LFDMA) signals. It is shown that distributed FDMA (DFDMA) signals with raised cosine filtering experience reduced PAPR as a increases. However, for LFDMA signals the PAPR increases with increasing α and further varies according to the allocated resource unit.

The high demand for unlicensed spectrum mandates the use of higher frequencies, such as the 60 GHz band, where large amounts unlicensed bandwidth exists. In this paper, the results from Power Azimuth Spectrum (PAS) measurements in a home and an office environment are presented with a view of revealing the amount of scattering power at that frequency and its relative power to the Line-of-Sight (LoS) signal. Moreover, a tractable scheme is proposed for the estimation of the Power Azimuth Spectrum from absolute power measurement data which produces a very close fit with the measured PAS. A discussion is made on the accuracy of this method which is dependent on the directionality of the antenna elements, the fading in the channel and the presence of noise.

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.

Over the years peer-to-peer (P2P) multi-hop relays have been studied for mobile ad-hoc networks (MANETs) to overcome poor signal coverage and to improve connectivity. However, for an urban environment, particularly with a sparse mobile distribution, a ground relay is not able to achieve significant benefits, mainly due to the extremely high pathloss and shadowing encountered. Dedicated airborne relay nodes, at a height of hundreds or thousands of meters, can provide much better coverage, and hence improve the connectivity, decrease the number of hops, reduce the power consumption, and support co-operative relays when integrated into mobile ad-hoc networks. An air node can also act as the sink for current wireless sensor networks (WSNs). Despite these potential advantages, the coverage from an air node located directly above an urban operating environment has not been adequately investigated in the literature. This paper compares the advantages of airborne relaying compared to more conventional peer-to-peer mobile relays. Three channel types are considered, i.e. line-of-sight (LoS), obstructed LoS (OLoS), and non-LoS (NLoS), each with their own likelihood, pathloss, and shadowing models. The practical gain pattern of a hemispheric antenna, or a directional antenna, is also carefully considered for the air node. Comparisons of the air-to-ground (A2G) channel and the mobile P2P channel demonstrate that airborne relays can enhance the coverage and reduce the power consumption significantly.

In this paper, the channel capacity of MIMO communication systems is evaluated from measurements in a home environment at 5.2 GHz. The capacity performance of a novel line-of-sight (LoS)-optimised antenna array architecture is investigated and compared to that of standard MIMO antenna arrays with one-wavelength inter-element spacing. Several transmit/receive locations are taken into account including LoS, non-LoS and obstructed-LoS areas. The results reveal that the proposed architecture can offer a significant capacity increase (more than 50%) in LoS environments compared to standard MIMO arrays. On the other hand, in non-LoS scenarios the performance of the proposed array is similar to the standard architecture.

The latest mobile WiMAX standard promises to deliver high data rates over extensive areas and to large user densities. More specifically, data rates are expected to exceed those of conventional cellular technologies. The IEEE 802.16e WiMAX standard enables the deployment of metropolitan area networks to mobile terminals in non-line-of-sight radio environments. Current concerns include leveraging high data rates, increasing area coverage, and competing with beyond 3G networks. Based on the IEEE 802.16e wirelessMAN-OFDMA (orthogonal frequency division multiple access) physical (PHY) layer air-interface, this paper presents a physical layer study of MIMO enabled mobile WiMAX in an urban environment. The radio channels are based on those developed in the European Union IST-WINNER project. Results are given in terms of system throughput and outage probability with and without relays for a range of SISO, MISO and MIMO architectures. Results show that satisfactory performance cannot be achieved in macrocells unless radio relays are used in combination with MIMO-STBC.

Multiple-input multiple output (MIMO) techniques can be applied to radio systems to enhance performance in fading channels, to exploit spatial and temporal diversity, and to increase the potential transmission rate. Here we investigate the combination of decision feedback equalizers (DFE's) with Alamouti space-time block codes (STBQ) in time-varying wideband channels. Most prior work considers the use of STBC in flat-fading channels. However, for many mobile applications, time and frequency selectivity in the wireless channel must be included in the analysis. As a result of delay spread and terminal mobility, the transmitted data stream can suffer from severe time varying inter symbol interference (ISI) which requires a form of channel equalization. For a quasi-static environment Alamouti's linear combining scheme provides a reliable and low complexity MIMO solution when perfect channel state information (CSI) is available. In this paper we address the mitigation of wideband channels effects on Alamouti STBC codes. The study considers the minimum mean square error (MMSE) performance as a function of channel estimation error for maximum likelihood (ML) and DFE equalizers.

The likelihood of line-of-sight (LoS) is an essential component in any radio channel model. It is particularly useful for radio network planning and urban coverage prediction. Empirical LoS models are hard to derive due to a strong dependency on local topology and the need for large measurement datasets. Since buildings are the major obstructions in a dense urban environment, we propose a new theoretical model to determine the LoS probability for air-to- ground channels based on local building geometry and knife-edge diffraction theory. The model takes into account key statistical parameters such as building height, building size, building coverage, street width and street angle distribution. The theoretical model is shown to agree well with ray tracing simulation results. The statistical parameters, such as mean building height, percentage of area covered by buildings (building coverage) and building density, can all be easily obtained for a specific location. We also derive equations for the likelihood of LoS for a direct slant path. These equations can be used in the analysis of air-to-ground channels.

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.

The directional dispersion of multipath energy arriving at the receiver is an important quantity, as increasing it leads to lower correlation between spatial diversity elements. The `RMS angular spread' metric, commonly used to measure this, is only applicable for relatively small angles in the 2-D plane. The quantification of the 3-D directional spread is not straighforward, and must be justified analytically by showing its relation to spatial selectivity, and hence spatial correlation. In this paper, an analysis of the second order moments of spatial fading has been used to define a spatial covariance matrix, which fully describes the second order moments of the directional energy distribution. An eigenvalue decomposition of this matrix has been used to propose a concise quantification of directional spread that is applicable for arbitrary distribution of multipath rays or clusters in 3-D directions. The effect of array orientation has also been investigated.

This paper uses a detailed site-specific channel model to analyze the impact of path loss and co-channel interference (CCI) in a multi-base station broadband fixed wireless access (BFWA) network. The base stations are deployed in an urban setting and make use of sectorised multi-element arrays to suppress CCI from other cells/sectors. Customer premises equipment (CPE) is mounted at rooftop level on a number of surrounding buildings. Spatially correlated multiple input multiple output (MIMO) channels are produced for each link using channel data generated from the ray-tracing model. The tool predicts MIMO correlation based on radiowave propagation and antenna array geometries. The paper considers the use of uniform linear arrays (ULA) and Uniform circular arrays (UCA) with a number of different element spacings. The results provide a unique insight into the deployment of multi-element WiMAX networks in an urban setting.

This paper provides new statistical models for air-to-ground channels in an urban environment. The model is derived to operate at frequencies from 200MHz to 5GHz. Issues such as path loss and shadowing are evaluated as a function of the elevation angle to the airborne platform, rather than the more usual separation distance used for terrestrial mobile communications. Results demonstrate the advantages of an air-to-ground channel for urban communication, and relayed peer-to-peer links in particular.

In this paper, the results of an on-body, line-of-sight (LOS), multiple-input, multiple-output (MIMO) channel sounding investigation are reported. Transmission takes place between on-body antennas and a uniform linear array, positioned at close range and within line-of-sight of each other. Due to the on-body location of the antennas, the influence of actual radio channel can no longer be separated from the effects of user behaviour and body proximity. This paper therefore argues that the composite channel must be considered. Post-processing of the recorded channels shows that their capacities outperform those from equivalent Rayleigh channels. Taking into account the clear LOS in the experiment, this appears counter-intuitive to the well-known fact that uncorrelated scattering results in high capacity. An analysis of the results highlights some less familiar facts and leads to an overview of capacity generating mechanisms in MIMO systems. The paper adds an analysis of the sensitivity of the capacity to the properties of the channel matrix, which is used for a discussion of the practical use of MIMO in personal and body area networks

The authors present an investigation on the capacity of line-of-sight (LoS) optimised and conventional (narrow-spaced) multiple-input multiple-output (MIMO) communication systems in outdoor environments. Under a LoS scenario, the channel is normally rank deficient due to the linear dependence of the LoS rays' phases on the receive elements. To overcome this problem, specifically designed antenna arrays can be employed, where the antenna elements are positioned to preserve the orthogonality of the LoS signal at the receiver; hence maximising the channel rank. A previously derived maximum capacity criterion is employed in the design of the proposed LoS-optimised MIMO system. The performance of this system is then assessed by means of a ray-tracing simulation and compared with that of a conventional MIMO system. It is shown that the proposed system exhibits a significant capacity enhancement (45.3 %) in the deployment area. Moreover, the capacity was found to be higher than that predicted by the i.i.d. Rayleigh fading model due to non-fading nature of the LoS signals.

This paper examines how the capacity of three multiuser multiple-input multiple-output (MIMO) algorithms is affected by a delay in computing and feeding back the transmit (and receive) weighting matrices used by the algorithms. Iterative schemes determining transmit weights that achieve the system-wide Nash equilibrium (NE) or block-diagonalization (BD) of the overall system channel matrix are compared as is a scheme applying successive diagonalization (SD) among users. The NE is found to be far the most robust to out-of-date channel information, whilst SD is found to suffer badly at even the shortest delay considered here (about 0.9 ms); BD's losses vary over a wide range depending on the delay. For the two iterative algorithms we also examine the tradeoff between better convergence and less delay. In both cases, the loss in capacity for weaker convergence is very small, and so it is desirable to minimize the delay and thus the capacity loss caused by it

This paper presents a new hybrid geometrical optics (GO) and radiance based rough surface scattering model for use in ray tracing propagation models. The reflectance model includes the effects of both specular and diffuse reflection. The specular component is modelled using GO Fresnel reflections, while the diffuse components are modelled using radiance reflectance. The hybrid scattering model is then developed and implemented within an existing three-dimensional microcellular ray tracing model. Comparisons of predicted path loss and rms delay spread are made at 1.92 GHz using site specific measurements in an urban environment. The results demonstrate that scattering can be an important mechanism at this frequency. Significant improvements in prediction accuracy are demonstrated with the new hybrid scattering model.

Multiple antenna systems can enhance wireless communication links by improving their capacity and/or reliability. Multiple input multiple output (MIMO) communications are the most common exploitation of this property. When applied to deterministic ray modelling, the computational cost of MIMO predication is a major drawback. Two MIMO modelling approaches are investigated. Both methods make use of an enhanced deterministic ray-tracing propagation model. The first method relies on point-to-point prediction for each of the multiple element-to-element links. The second approach estimates the MIMO link matrix from a single point-to-point ray tracing study. A comparison of normalized capacity and path loss is performed for the two methods in an outdoor city centre environment. For a single input multiple output (SIMO) case, the two modelling approaches are presented and compared with measured array data. Result show that the single point-to-point approximation works well and can significantly reduce run-time when compared with full element-to-element ray tracing.

A novel stochastic wideband dynamic spatio-temporal indoor channel model which incorporates both the spatial and temporal domain properties as well as the dynamic evolution of paths when the mobile moves is proposed based on the concept of a Markov process. The derived model is based on dynamic measurement data collected at a carrier frequency of 5.2 GHz in typical indoor environments. Multipath components are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization algorithm prior to identification of path "birth" and "death" using a new data analysis method. Analysis shows that multiple births and deaths are possible at any instant of time. Furthermore, correlation exists between the number of births and deaths. Thus, an M-step 4-state Markov channel model (MCM) is proposed in order to account for these two effects. The spatio-temporal variations of paths within their lifespans are taken into consideration by the spatio-temporal vector which was found to be well modeled by a Gaussian probability density function while the power variation can be modeled by a simple low-pass filter. In addition, the methodology used to extract the MCM parameters from the measurement data is also presented. Due to the distinction in the birth-death statistics, the model is generalized through segmentation of the measurement runs and can be completely parameterized by several sets of Markov parameters associated with the type of environment and scenario under consideration. The implementation of the model is also detailed and, finally, the model is evaluated by comparing key statistics of the simulation results with the measurement results.

This paper investigates the point-to-point PHY layer performance of two newly proposed IEEE 802.11n candidate solutions by suggesting extensions to 802.11a. The new solutions incorporate a MIMO architecture for the wireless links between the network terminals. The FEC block in the PHY layer chain is enhanced with a turbo encoder to provide interleaving gains for the larger sized PSDUs (1-4095 bytes). Due to the ambitious data rate targets identified in 802.11n, where 'on-air' data rates of 108-320 Mbit/s are quoted, a large MIMO architecture comprising of 6 transmit and 6 receive antenna elements is adopted. ML detection using such large configurations is often prohibitively complex due to an unrealistic enumerated symbol list. In this paper we propose ZF-GIS and MMSE-GIS solutions to ease complexity at the receiver. The PER performance offered by both proposals is compared together with the added computational requirements in constructing their matrices. Link throughputs are compared to demonstrate the viability of the chosen solutions.

The challenge at millimeter-wave frequencies is that the propagation characteristics approximates to that of light. In a nonline-of-sight scenario, when even the mobile station (MS) is near the base station, the attenuation may be tens of dBs due to shadowing and obstructions. Increasing the number of base stations reduces such effects but at the expense of cost and complexity. An attractive method to mitigate such shadowing effects is to use dedicated active or passive relay stations. Proposed here is a network infrastructure in the form of a 3D pyramid. It consists of a single access point with four (but not restricted to) active relays operating in parallel in a medium sized room of 400 m/sup 2/. Simulation is performed in a sophisticated 3D ray tracing tool. Human shadowing densities of 1 person/400 m/sup 2/ up to 1 person/1 m/sup 2/ are set to test the robustness of such a system. Results show that comparing to a normal system with just a single access point either mounted on the ceiling or at the same level as a MS; the pyramid relaying system provides superior coverage and capacity.

The paper presets the performance of two newly proposed IEEE 802.11n candidate solutions by suggesting extensions to 802.11a. The new solutions incorporate a MIMO architecture for the wireless links between the network terminals. The FEC block in the PHY layer chain is also enhanced with a Turbo encoder to provide interleaving gains for the larger sized PSDUs (1-4095 bytes). Due to the ambitious data rate targets identified in 802.11n, where 'on-air' data rates of up to 320 Mbit/s are quoted, a large MIMO architecture comprising 6 transmit and 6 receive antenna elements is adopted. ML detection using such large configurations is often prohibitively complex due to an unrealistic enumerated symbol list. In this paper we propose zero-forcing and MMSE-GIS solutions to ease complexity at the receiver. PER results for these new schemes are presented and Link throughputs are compared to demonstrate the viability of the chosen solutions and their benefits over the existing 802.11a standard.

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.

Recent developments in orthogonal frequency division multiplexing (OFDM) and single-carrier frequency-domain equalization (SCFDE) have sparked debate about the superiority of one method over the other. In this paper, we further this debate by comparing the theoretical performance of OFDM and SCFDE when each is implemented in one of two different multiple-input multiple-output (MIMO) architectures: spatial multiplexing and space-time block codes. This study focuses on the use of MIMO-OFDM and MIMO-SCFDE in wireless local area network (WLAN) applications. Performance is given in terms of the packet error rate (PER) and the throughput of the systems.

In this paper an iterative channel estimation technique for a mobile fourth generation coherent orthogonal frequency division multiplexing (OFDM) system is proposed. Coherent detection dictates that a per-subband estimate of the frequency response of the channel is generated for each OFDM symbol. This is often achieved by inserting pilot symbols amongst the data symbols in the OFDM modulation grid and interpolating accordingly. This paper proposes a lower complexity channel estimation method that exploits coding gain to achieve a channel estimate that yields an overall system performance that is shown to be comparable to the scattered pilot system, but with only one initial training sequence. A tracking algorithm is proposed which improves performance at high mobile velocities.

The paper reports on a new class of equalisation/detection for wideband multiple input-multiple output (MIMO) communications systems. The proposed scheme is somewhat akin to a multi-carrier MIMO system, and more precisely, builds upon a single carrier frequency domain equalised (SCFDE) MIMO system. At the core of our system lies a novel concept of iterative self-reused equalisation/detection (bootstrapping) combined with semi-hard decision making. The bootstrapping concept is derived from a new formulation of Tikhonov regularisation. The proposed scheme achieves a remarkable performance/complexity trade-off. In particular we show that our system approaches the performance of ML-MIMO-OFDM while being only slightly more complex than MMSE-MIMO-OFDM. The coded version achieves virtually the same performance as turbo MIMO-OFDM at a fraction of the complexity. The resulting system is termed zero tailed bootstrap frequency equalised (ZTBFE) MIMO system.

A novel multi-user detection (MUD) technique for CDMA systems is introduced. The new method is well suited for cases in which the code cross correlation matrix is ill-conditioned. In practice, this case coincides with having code lengths approximately equal to the number of users - a desirable condition in terms of bandwidth efficiency. Our approach employs an iterative formulation of a well-known regularization method for linear inverse problems, which is suited to the MUD problem. The technique allows knowledge of the finite set in which the solution belongs to be exploited in a computationally efficient manner in order to improve the quality of the estimate iteratively.

The paper considers a multiple-input multiple-output (MIMO) communication system, which uses space-time trellis coding (STTC). A novel method of decoding STTC without a need to transmit training sequences is developed. The technique uses only a single channel estimate to acquire a complete set of the channels' estimates while performing STTC detection. The method is akin to blind trellis search techniques (per-survivor processing - PSP) and adaptive Viterbi. Our solution consists of the deployment of a bank of Kalman filters. The bank of Kalman filters is coupled with Viterbi type decoders, which produce tentative decisions based on Kalman channel predictions. In return, the Kalman filters use the tentative decisions to update and track the MIMO channels corresponding to a number of tracked hypotheses. The proposed technique is particularly applicable to space-time systems operating in rapidly fading environments, where STTC can be decoded and MIMO channels efficiently tracked without relying on periodic pilot sequences.

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.

This paper considers an OFDM system with a multiple-input multiple-output (MIMO) configuration, which uses space-frequency trellis coding (SFTC). A novel method of decoding SFTC without a need to transmit separate training sequences is developed. The technique uses only a single frequency tone to acquire a complete set of the channels' estimates while performing SFTC detection. The method is akin to blind trellis search techniques (per-survivor processing - PSP) and adaptive Viterbi. Our solution consists of the deployment of a bank of Kalman filters. The bank of Kalman filters is coupled with Viterbi type decoders, which produce tentative decisions based on Kalman channel predictions. In return, the Kalman filters use the tentative decisions to update and track the MIMO channels corresponding to a number of tracked hypotheses.

In this paper, a new statistical wideband indoor channel model which incorporates both the clustering of multipath components (MPCs) and the correlation between the spatial and temporal domains is proposed. The model is derived based on measurement data collected at a carrier frequency of 5.2 GHz in three different indoor scenarios and is suitable for performance analysis of HIPERLAN/2 and IEEE 802.11a systems that employ smart antenna architectures. MPC parameters are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization (FD-SAGE) algorithm and clusters are identified in the spatio-temporal domain by a nonparametric density estimation procedure. The description of the clustering observed within the channel relies on two classes of parameters, namely, intercluster and intracluster parameters which characterize the cluster and MPC, respectively. All parameters are described by a set of empirical probability density functions (pdfs) derived from the measured data. The correlation properties are incorporated in two joint pdfs for cluster and MPC positions, respectively. The clustering effect also gives rise to two classes of channel power density spectra (PDS)-intercluster and intracluster PDS-which are shown to exhibit exponential and Laplacian functions in the delay and angular domains, respectively. Finally, the model validity is confirmed by comparison with two existing models reported in the literature.

In this paper, the serial interference cancellation (SIC) technique and the frequency domain SAGE (FD-SAGE) algorithm are jointly used to detect and estimate the radio channel parameters of interest. The implementation of the SAGE algorithm in the frequency domain is novel. Furthermore, the parallel interference cancellation (PIC) technique in the standard SAGE algorithm is replaced by the SIC technique. The SIC technique demonstrates more stable performance especially in a multipath rich environment. The two-dimensional (2-D) FD-SAGE algorithm and the SIC technique are introduced and their performance demonstrated by using real indoor channel measurement data to jointly estimate the number of multipath components (MPCs), their time-of-arrivals (TOAs), angle-of-arrivals (AOAs) and complex amplitudes. Their performance is evaluated and compared using synthetic data and results using 2-D unitary ESPRIT (another form of super-resolution algorithm).

Coded orthogonal frequency division multiplexing (COFDM) is currently specified in all three of the world's 5 GHz wireless LAN standards (HIPERLAN/2, IEEE 802.11a and MMAC HiSWANa). This technology was chosen due to its robustness at high data rates in a frequency selective multipath channel. Each standard operates using adaptive subband quadrature amplitude modulation (QAM) and offers a maximum data rate of 54 Mbits/s over a 20 MHz channel. This paper describes a real-time DSP implementation of an asynchronous OFDM based high speed WLAN system. The software reconfigurable OFDM based platform is developed around the Texas Instruments fixed point TMS320C6201 DSP. The physical layer DSP performance is evaluated and compared for an indoor channel against floating point C++ based simulations. Data throughput and complexity estimates are generated from the resulting hardware platform. Finally, a video based communications application is developed to operate over the demonstrator. Results indicate that the fixed point DSP solution can operate within 0.5 dB of the floating point simulation in an AWGN channel. For the indoor fading channel, an implementation loss of around 2.5 dB was observed.

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.

A novel technique for inserting basestations on an ad-hoc basis is investigated. Sector retraction and extension is used to reshape the network coverage area. Basestations are generally added to the network whenever there is a need to meet an increasing capacity demand. The replanning exercise can be both costly and time consuming. Situation awareness (SA) is the enabling functionality that allows a network redesign without a drain on resources. The simulation involves loading the network to capacity and evaluating the performance of adding a basestation 'on the fly'. Spectrum efficiency is the measure of performance used. Reconfiguration of the network area is performed by controlling the power level of the downlink pilot channel through the use of a genetic algorithm (GA). The performance of the algorithm is determined by its ability to reconfigure and redistribute the traffic. The technique is shown to offer a flexible and simple solution to the problem of UMTS network replanning for additional capacity.

The aim of this paper is to discuss and explore the impact of practical impairments such as timing error, frequency offset and phase noise on the physical layer performance of IEEE 802.11a and ETSI HiperLAN/2. Standard compliant correction techniques are identified or developed to exploit the allocated preambles and pilot symbols embedded in these standards. The paper includes physical layer performance results in the presence of each form of degradation. These results are presented in terms of packet error rate and bit error rate versus signal to noise ratio for IEEE/ETSI standard indoor channel models of A and E. The performance gain of the corrected receiver is then compared to that of an unaided device. Results indicate that an acceptable level of performance can be achieved over the full range of practical impairments given careful receiver design.

Adapting a modem's modulation scheme can significantly enhance the resulting performance over a wireless communications link. Non-adaptive modems are generally designed conservatively for worst-case channel conditions. Adaptive modems are able to exploit the higher channel capacity when good conditions are encountered. A number of different metrics can be used to drive the adaptation process (i.e. automatic repeat request (ARQ) or segment error rate (SER)). Not surprisingly, certain metrics are far more successful than others. This paper presents an investigation of adaptive modulation in the presence of interference. In particular, the case of non reciprocal interference is studied (i.e., cases where the level of interference is different on the forward and reverse links). Research results have shown that if adaptation is performed assuming a reciprocal channel, then poor performance will result for the link experiencing a higher level of interference. In this study, an algorithm is used to calculate a measure of the link quality. This value is then fed back to the other end of the link to adapt subsequent transmissions. Results indicate that the throughput of such a system can be considerably improved when transmitting adaptively using any one of DBPSK, DQPSK or 8DPSK modulation schemes. It is proposed that this simple approach be adopted for short range, ad hoc, wireless personal area networks (WPAN).

This paper examines the implementation of an automated W-CDMA microcellular deployment and coverage reconfiguration algorithm based on the concepts of situation awareness (SA). A deterministic microcellular propagation model (Citrus) is used to provide the detailed site-specific propagation data. An initial network deployment is performed over one square kilometre of central Bristol using the combination algorithm for total optimisation (CAT). Buildings are then added or removed from the microcell to represent realistic time variations in the geographic environment. A new situation awareness (SA) algorithm is developed and applied to the modified W-CDMA microcell to automatically reconfigure the network's coverage and capacity based on the new propagation environment. Optimisation of coverage and capacity is achieved through the use of a genetic algorithm (GA). This paper presents the details of the underlying SA algorithm and the results obtained for the above scenario. These new algorithms are shown to automatically sustain a high grade of service as the microcellular environment evolves over time. Gains of up 203% in spectral efficiency were observed for the 144 kbps service.

This paper begins by highlighting key features of the Bluetooth baseband standard. Software simulated results for the transmission of symmetric asynchronous data link (ACL) packets are used to discuss bit rate capabilities of various time-bounded and non-time bounded Bluetooth enabled consumer electronic devices. The investigation considers Bluetooth data medium (DM) and data high (DH) packet types. To meet the bit rate needs of future consumer electronic devices, BPSK, QPSK and 16-QAM are proposed as possible enhancements to the current GFSK modulation. The relative merits and demerits of using coherent modulation and linear receive architectures versus non-linear differential detection are discussed. Although adding considerably to the unit cost, the former is shown to significantly improve radio sensitivity. Results indicate that although the use of QAM modulation facilitates higher data rates, PSK schemes are more likely candidates for a low cost, high data rate Bluetooth extension due to the fact that they have less demanding hardware requirements.

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.

Standards for the operation of wireless local area network (WLAN) technology in the 5 GHz band have been developed in Europe, North America and Japan. These systems employ orthogonal frequency division multiplexing (OFDM) technology, and utilize forward error correction (FEC) coding, based on a 1/2-rate convolutional encoder, to combat frequency selective fading caused by multipath channels. This paper examines methods, based on the popular Viterbi algorithm, for maximum-likelihood (ML) decoding of this convolutional code within the WLAN baseband receiver. Although the paper focuses on the European HIPERLAN/2 standard, because of international physical (PHY) layer harmonization, the work is equally applicable to the North American and Japanese WLAN systems. Received error rate results, based on a software simulation of the HIPERLAN/2 PHY layer, are presented for both hard and soft decision decoding strategies. In addition, the effect of quantization on soft decision decoding is investigated. The results highlight the importance of the decoder design on the performance of the WLAN.

This paper addresses a number of key issues that affect the modelling of propagation in mobile-to-mobile communications. Current examples of such systems include intelligent relaying, Bluetooth and other ad-hoc solutions. The key difference in mobile-to-mobile communications is that both transmit and receive antennas are likely to be closer to the ground than those in conventional cellular networks. In addition, they may also be located in less favourable propagation positions, such as in users' pockets, bags or desk drawers. Two measurement programmes have been performed to investigate the propagation issues relating to intelligent relaying in the 2 GHz band. The first campaign concerns path loss measurements in an indoor environment where the heights of the antennas are lower than those in conventional cellular networks. The second set of data was taken to determine variations in the terminal radiation pattern given the close proximity of the human body. A number of single ray illumination measurements were performed inside an anechoic chamber. The results indicate that for the environments under consideration, an additional attenuation factor should be added to the path loss model to compensate for the unfavourable location of the terminals in a mobile-to-mobile propagation environment. This attenuation is dependent on the heights of the antennas involved, and is in the range 0-8 dB.

This paper describes a newly developed three dimensional ray launching model for complex indoor environments. The model is capable of predicting detailed temporal and spatial multipath. To investigate and evaluate the accuracy of this model, predictions are compared with detailed measurements taken in an office environment. Power delay and power azimuth spectra are measured using a multielement Medav channel sounder operating with 120 MHz of bandwidth in the 5 GHz band. Prediction accuracy was found to be sensitive to the accuracy of the basestation height, the permittivity of the surrounding materials and the number of reflections permitted in the model. Overall, the results indicate that with careful modelling and well calibrated measurements, good site specific spatial and temporal multipath agreement can be achieved.

To effectively dimension and rollout a cellular network, accurate site-specific field strength predictions are required. Traditionally, operators make use of high-speed statistical propagation models for each proposed base site. Today's advanced cellular networks place a greater emphasis on urban microcellular deployment. It is well known that statistical models perform poorly in such environments. To overcome these limitations, the use of deterministic propagation modelling is common. However, although such models enhance prediction accuracy, they also require excessive computation time. A new hybrid statistical/deterministic field strength prediction model is proposed that combines the speed of a statistical model with the site-specific accuracy of a deterministic ray model. Results indicate that the new hybrid model can produce very accurate field strength prediction grids with computing times reduced by one to two orders of magnitude. For the example considered, the computing time for a one square kilometer grid comprising 10000 points (100 by 100) has been reduced from 20 mins to just over 4 minutes (running on an 800 MHz Pentium III). For more complex ray models and/or higher grid densities, even higher speed-up factors can be achieved.

We examine the performance of a space-time coded (STC) OFDM system. As an example, two emerging WLAN standards (IEEE 802.11a and ETSI HIPERLAN/2) are modified to accommodate the STC technique. Performance results using statistical multi-element channel models are compared with those using state-of-the-art indoor MIMO channel measurements. We conclude that the gap between the ideal setting and our measured channel is 4, 5 and 6 dB for 1, 2 and 3 receive antennas respectively. We observe also that STC with (2Tx, 3Rx) over the measured channels doubles the capacity as compared to the equivalent mode of HIPERLAN/2.

Matching pursuits over a basis of separable Gabor functions has been demonstrated to outperform DCT methods for low bit rate video coding. This paper introduces an error resilient implementation of the matching pursuits algorithm, based on the error resilient positional code. Coded video is transmitted using the simulated HIPERLAN/1 air interface standard, which recommends ARQ as a means of overcoming channel errors. This may be unsuitable for real time and broadcast applications. Therefore, a modified HIPERLAN/1 receiver is proposed in this paper, which does not use ARQ to retransmit erroneous packets but instead passes them to the video decoder to exploit error resilience. This strategy provides an acceptable reconstruction quality for average bit error rates equal to 1 in 1000 and is superior to a standard compliant system in the absence of ARQ. This confirms that wireless LAN standards should support a transparent mode for video applications.

This paper investigates the performance of a number of direction-of-arrival (DOA) estimation algorithms in a wideband macrocellular channel using a dual-polarised antenna array. The signal data is obtained from a new spatial-temporal three-dimensional deterministic propagation model. The model was developed to meet the hierarchical network planning needs of third generation (3G) networks. Results show that a three-fold theoretical and two-fold practical improvement in DOA estimation accuracy can be achieved by exploiting information from a dual-polarised array.

The efficiency of a coded orthogonal frequency division multiplexing (COFDM) receiver can be improved by use of a pre-FFT equaliser (PFE). This technique is known as combined OFDM-equalisation. This paper considers the noise amplification effect of the PFE and its effect on the performance of a combined COFDM-equalisation modem and proposes a method to improve this performance. It first reviews and compares the conventional COFDM and combined COFDM-equalisation techniques. The PFE is then described and the conditions required to allow it to take the form of a decision feedback equaliser (DFE) are discussed. It is shown that these conditions often cannot be met. In these cases the PFE must take the form of a linear transversal equaliser (LTE). The performance of the LTE is inferior to that of the DFE due to significant noise amplification. Hence, if the performance of combined COFDM-equalisation is to match that of conventional COFDM, a method for mitigating the noise amplifying effect of an LTE type PFE is required. One such method is proposed. This technique exploits channel state information (CSI) available in a COFDM receiver in order to enhance the performance of a Viterbi convolutional decoder. This 'CSI modified' Viterbi algorithm is capable of mitigating the noise amplification occurring in the equaliser. To demonstrate this, the performance of conventional COFDM and combined COFDM-equalisation are compared by means of software simulation using both standard and CSI modified Viterbi decoding. The results for the standard Viterbi decoding illustrate the performance penalty due to noise amplification. The results for the CSI modified Viterbi algorithm demonstrate the effective mitigation of noise amplification and the comparable performance of conventional COFDM and combined COFDM-equalisation.

The combination algorithm for total optimisation (CAT) solves the problem of optimised base-station location and density for different cellular configurations and environments. The algorithm relies on two main user supplied databases for its operation. The first is an over specified list of possible base-station locations and the second is a database of control nodes. Coverage is defined by a distribution of control nodes in the area of study. The control nodes represent the operator's capacity and coverage requirements at those points. This paper discusses the importance of control node distribution and density. A new approach based on introducing different classes of control node is proposed to improve the efficiency of the CAT algorithm. Results indicate that 400 control nodes per km/sup 2/ are required to ensure satisfactory operation. Introducing control node prioritisation is also shown to improve the quality and interpretation of the final solution.

This paper investigates the potential capacity improvements made possible through the use of dynamic cell sizing in a cellular network. The purpose of dynamic cell sizing is to reduce cell radii and thus enable in-cell users to increase their transmit powers. The use of higher transmit powers suppresses intercell interference and leads to an overall increase in capacity. This paper discusses the degree of capacity enhancement that can be achieved in this manner. The analysis indicates that the capacity of a single cell can be increased by as much as 38%. However, under uniform traffic conditions, this results in a ratio of supported-to-offered traffic of just 0.2, which is clearly unsatisfactory. Dynamic cell sizing performs significantly better in hot-spot conditions, where the in-cell traffic follows a normal distribution with the highest density in close proximity to the base station. The ratio of supported-to-offered traffic under these conditions was found to rise to 0.6 to 1.0 depending on the traffic standard deviation and the location of the hot spot.

This paper compares the performance of pilot tone aided (PTA) and pilot symbol aided (PSA) BPSK, QPSK, 8QAM, 16QAM, 32QAM and 64QAM over a narrowband radio channel. This set of modems is capable of achieving 14, 28, 48, 56, 70 and 84 kbit/s respectively in a 20 kHz channel bandwidth. Computer simulations in a Rayleigh fading channel show that PTA modems have almost the same performance as PSA modems. However PTA signals have a higher peak to mean power ratio (/spl eta/) and this translates into greater amplifier linearity requirements in the transmitter. In the PSA modems, /spl eta/ is independent of the pilot symbols, however in the PTA modems it depends upon the pilot tone to data power ratio (R). An optimisation of R in an AWGN channel gives a value of 0.2 for QAM. A comparison of /spl eta/ between PSA and PTA transmitted signals show differences of 3.38, 5.1, 4.8, 4.25, 4.45 and 3.9 dB for 99.9% of the time (based on the above mentioned list of modulation schemes).

Due to the site specific nature of microcellular operational environments, propagation models are required to take into account the exact position, orientation and electrical properties of individual buildings, and hence, ray-tracing techniques have emerged as the dominant methods to predict propagation in such environments. A novel hybrid three-dimensional (3-D) ray-tracing algorithm which can evaluate scenarios incorporating many thousands of objects by utilising the concept of "illumination zones," is presented. In order to evaluate the accuracy of the presented model, comparisons of narrow-band and wide-band predictions with measurements are performed for a variety of scenarios. First, power comparisons show that very accurate predictions can be achieved (RMS errors less than 3.7 dB). Then, wide-band analysis shows that since the RMS delay spread for systems with finite bandwidth is a function of the multipath phase, only average measured and predicted RMS delay spread values can be compared and as a result, limited averaging can produce large RMS errors. With sufficient averaging the achieved wide-band accuracy in terms of the predicted RMS delay spread, is adequate for most planning purposes.

This paper presents the results of a series of evaluation trials undertaken in the scope of the ACTS project AWACS in order to investigate the feasibility of the use of directional antennas to support high bit rate transmissions using a single carrier unequalised modem. The relationship between the antenna directivity, propagation statistics and modem performance are reported here. The results illustrate the effectiveness of correctly aligned, high gain antennas in reducing the undesired effects of multipath propagation. Further, the transceiver trials indicate the need for balancing antenna directivity at both ends of the link.

This paper discusses some aspects of self-organisation in future cellular communications. In particular the effect sub-optimal base station positioning has on the overall interference level in the network. It is shown that the interference level. Increases with base station positioning error resulting in unacceptable dropping probability. With the incorporation of a simple power control algorithm, the network's sensitivity to error in base station positioning is reduced and an improvement in the performance is achieved. The results also show that a considerable tighter re-use pattern can be used in order to accommodate more users in the same spectrum.

Frequency hopping spread spectrum (FH-SS) has found a number of applications in both CDMA and TDMA cellular systems, wireless local loop, and wireless local area networks. The effect of FH-SS on mobile channel characteristics is evaluated. Employing propagation studies, statistical analysis and simulation models, it is shown that the frequency-hopped channel displays improved characteristics when compared to the non-hopped case. The short term fading statistics are improved, which can be exploited to provide an overall increase in quality-of-service. The short term statistics of the frequency-hopped channel are derived, enabling prediction of the performance of an FH system.

This paper presents a selection of wideband channel sounding measurements performed as part of the ACTS AWACS (ATM Wireless Access Communications System) project. The results were obtained for two different indoor operating environments (mainly in line-of-sight conditions) at a carrier frequency of 19.37 GHz. The paper discusses the configuration of the wideband channel sounder and its connection to the prototype ATM transmission system. Measurements concentrate on average power, RMS delay spread and K-factor for a number of different antenna configurations and beamwidths. Mixed antenna configurations are also analysed with a directive antenna at the base station and an omni antenna at the mobile station. In particular, the results demonstrate the improvement in K-factor and the reduction in RMS delay spread that can be achieved with correctly oriented high gain antennas.

This paper investigates the nature of the indoor radio channel at 60 GHz, with regard to its use for future high bit-rate broadband wireless networks. It is proposed that, for operation in the millimetre-wave indoor channel, directional antennas can be used to mitigate multipath effects, thus reducing the need for complex equalisation or multi-carrier techniques. An image based, ray-tracing prediction model is used to study the channel characteristics and to analyse the variation in received power, RMS delay spread and k-factor within a typical operating environment. The performances of different antenna combinations are investigated and narrowbeam, suitably aligned antennas are shown to reduce received delay spread for both LOS and non-LOS locations. The effects of non-optimal antenna alignment are observed, and system outage is determined for certain system design criteria. The results suggest that it will feasible to combat multipath effects using switched-beam directional antennas.

A three dimensional `image-based' ray tracing algorithm for indoor environments is presented. The model is capable of predicting wideband as well as narrowband propagation information for single floor scenarios. To show the practicality of such a model, the ray tracing engine has been used to investigate a typical indoor environment. The influence of internal objects such as windows, doors and partitions is considered. Since externally reflected and diffracted rays are supported, the impact of external building structures on the received power and RMS delay spread is examined. The channel characteristics were also studied for different receiver antenna orientations.

The European Telecommunications Standards Institute (ETSI) is currently defining a European standard for high performance radio LANs (HIPERLAN). To operate as wired LAN replacements, these systems will need to offer data rates as high as 20 Mb/s. To counteract the time dispersive nature of the indoor radio channel, adaptive equalisation is proposed at the receiver. In this paper a number of possible modulation and equalisation techniques are presented and, in particular, the BER performance of quasi-coherent GMSK detection is investigated. Important issues such as frame and symbol synchronisation, frequency offset correction and equaliser implementation are also addressed from a practical standpoint.

Standardisation bodies in Europe and North America are currently developing standards for high data rate packet radio LANs. Radio LANs will have two main applications: wired LAN replacement and ad-hoc networking. In contrast to wired LAN replacement, ad-hoc networks will operate without control from a central node. As a consequence, no central synchronisation is provided and nodes must have the capability of acquiring all synchronisation from a received packet. This synchronisation can be achieved by matched filtering synchronisation codes inserted into each data packet. This paper discusses these synchronisation requirements and outlines synchronisation sequence selection criteria.>