| openaire: EC/HE/101169042/EU//FOCAL

With the commercialization of Fifth-Generation (5G) technologies, the emergence of data-intensive applications has driven the need for future-generation networks to support seamless, immersive and high bandwidth services while ensuring enhanced quality of service for mobile users. To address this, Millimeter Wave (mmWave) frequency bands offer substantial potential for delivering high data rates, though, prone to blockages due to clutter, particularly in dense urban environments. Thus, Integrated-Access-and-Backhaul (IAB) deployment enables network densification by improving the line-of-sight condition to the serving node, replacing part of the optical fibre backhaul links with mmWave wireless links. This paper evaluates the IAB-enhanced cellular network performance in a Manhattan-like urban setting, across four potential network deployment scenarios, comprising candidate locations for mobile User Equipment (UE) placement. The mobile UEs can connect to the serving node, either gNodeB (gNB) that may take the role of IAB donor or IAB node, enabling the best link performance. Simulation results demonstrate significant Signal-to-Interference-plus-Noise-Ratio (SINR) gains of 10dB at the 50th percentile across all IAB deployment scenarios when using the optimal path selection approach compared to forcing UEs to connect to a specific serving node, besides the best option. These SINR gains translate into improved spectral data rates, in the order of 0.11- 2.72 bps/Hz. This study emphasizes the strategic placement of IAB nodes and optimized path selection in dense urban mmWave networks to enhance the end-user experience.

Ultra-reliable low-latency IoT communications (URLLC-IoT) has recently gained a growing interest. Here the challenge in reliable low-latency uplink transmission results from the transmission power limitations and lack of multiple antennas. However, in many IoT services the data volumes are small and sensor deployments may include massive number of devices. In this work we consider a coordinated uplink transmission of clustered IoT devices. The focus is on scenarios where location-based channel knowledge map (CKM) can be applied to enable cooperation. We model and analyse the impact of hardware impairments and erroneous CKM information. In the performance evaluation we focus on the recently introduced dataoriented approach that has gathered significant attention in the context of short-packet transmissions. Specifically, it introduces a transient performance metric for small data transmissions, where the amount of data and available bandwidth play crucial roles. Results show that cooperation between clustered IoT devices may provide notable benefits in terms of increased range. Yet, the performance of the coordinated transmission system is heavily depending on the strength of the static channel component in the CKM based cooperation, the level of hardware impairments and the quality of CKM information. Analytic results are verified against simulations, showing only minor differences between analytical and experimental results.

5G New Radio (NR) is the de facto global standard for 5G mobile networks. 5G NR was developed by 3GPP and designed to provide new kinds of mobile services across very large geographical areas. One of the main challenges that evolutions of 5G NR must face is the limited radio frequency resources that are available for Beyond-5G mobile connectivity. Optical wireless bands have been already considered for Wireless Local Area Network (WLAN) technologies, where they are denoted as Light Fidelity (Li-Fi). However, and in order to make optical wireless an integral part of Beyond 5G mobile standards, it is convenient to first assess the performance that is feasible when an actual 5G NR waveform is transmitted over an optical wireless frequency band. This paper presents the first experimental proof-of-concept for the transmission of a 5G NR frame over an LED-based optical wireless link. The obtained results are very motivating, as the 5G NR data rates that would be feasible over optical wireless links are very similar to the ones observed nowadays over the n78 RF band (centered around 3.5 GHz, with 100 MHz bandwidth). However, the most important difference is that the spectrum of the optical wireless signal will be reusable in very small cells of radius not larger than few meters, with the possibility of deploying many remote optical units for ultra-densification in indoor service areas without notable inter-cell interference.

Ambient backscatter communication (AmBC) is a key enabler for green Internet of Things (IoT) employing ambient radio frequency (RF) signals for low-power communication. The AmBC devices discussed in the literature so far harvest light to power their microcontrollers for controlling RF modulation and reflection circuits. The ubiquitous presence of configurable light-emitting diodes (LEDs) based luminaires can also leverage such control functionalities by involving visible light communication (VLC). In this paper, we propose a visible light-enabled AmBC system that integrates VLC and AmBC for future ambient power-enabled IoT. We design LiBD, a backscatter device (BD) that uses visible light signals for both modulation control and energy supply. We demonstrate the real-time end-to-end data transmission with a proof of concept experiment. Evaluation results show that the LiBD supports multiple sub-6 GHz RF bands and can receive modulated light at frequencies up to 250 kHz. The investigations verify the feasibility of integrating the VLC and AmBC for future green IoT systems.

As wireless information transmission (WIT) progresses into its sixth generation (6G), a challenge arises in sustaining terminal operations with limited batteries for Internet-of-Things (IoT) platforms. To address this, wireless power transfer (WPT) emerges as a solution, empowering battery-less infrastructures and enabling nodes to harvest energy for sustainable operations. Thus, the eclectic integration of WPT with WIT mechanisms becomes crucial to mitigate the need for battery replacements while providing secure and reliable communication. A novel protocol that amalgamates WIT and WPT calledInformation Harvesting (IH)has recently been proposed to effectively handle challenges in wireless information and power transfer (WIPT) by employing index modulation (IM) techniques for data communication atop the existing far-field WPT mechanism. This paper presents a unified framework for IM-based IH mechanisms and evaluates their energy harvesting capability, bit error rate (BER), and ergodic secrecy rate (ESR) performance for diverse IM schemes. The findings indicate the significant potential of the IM-based IH mechanism in facilitating reliable data communication within existing far-field WPT systems while underscoring promising refinements in green and secure communication paradigms for next-generation IoT wireless networks.

Considering the current capability in hardware design, the wireless power transmission (WPT) enables the next stage in the current consumer electronics revolution by prolonging the lifetime of devices powered by batteries. Recently, Information Harvesting (IH) introduced a novel mechanism for wireless power and information transfer which differs from existing far-field wireless power transfer and simultaneous transmission of power and data protocols. In this paper, a new IH mechanism which relies on quadrature spatial modulation (QSM) is proposed and the simulation results demonstrate that the proposed mechanism improves the secrecy at information receiver and provide more harvested energy to the harvester.

Vertical sectorization introduces considerable gain to particular scenarios where user equipment (UE) are distributed in 3D domain, i.e. high-rise buildings, in terms of coverage and network capacity thanks to availability of active antenna systems. However, due to the huge varieties in distribution of UEs and different physical environments, presenting a comprehensive analytical framework is quite challenging. From this aspect, most available studies on vertical sectorization are limited to present only empirical results. In this paper, we introduce a novel methodology to forecast the performance of NB-IoT systems over urban scenarios. In particular, a logistic distribution-based analytical framework is exploited in order to calculate the group probabilities for each available UE. Based on these probabilities, we propose a scheduling framework with beamforming which improves physical resource block (PRB) utilization by over 50% compared to the case with no scheduling.

The integration of Radio Frequency (RF) and Visible Light Communication (VLC) technologies has been considered an enabler to achieving the Key Performance Indicators (KPIs) in Beyond 5G (B5G). Apart from higher data rates for enhanced Mobile Broadband applications, Ultra-Reliable and Low-Latency Communications and massive Machine-Type Communications must be also supported. This poses notable challenges in the design of a mobile communication system that relies exclusively on the use of licensed RF spectrum. In order to cope with the requirements of B5G services, the complementary benefits that RF and VLC bands have in terms of communication bandwidth, signal propagation characteristics, and ultra-densification feasibility, can be exploited. For this purpose, this paper studies the performance of two integration approaches, namely RF - VLC selection (Layer-3 or network-layer) and RF-VLC aggregation (Layer-2 or MAC-layer). Based on the obtained simulation results, it is possible to conclude that RF - VLC aggregation outperforms RF - VLC selection in terms of data rate performance, especially when ultra-reliable communication services are required to connect a large number of user terminals placed in an indoor scenario.

In this study, we focus on the cell individual offset (CIO) parameter in the handover process, which represents the willingness of a cell to admit the incoming handovers. However, it is challenging to tune the CIO parameter, as any poor implementation can lead to undesired outcomes, such as making the neighboring cells over-loaded while decreasing the traffic load of the cell. In this work, a reinforcement learning-based approach for parameter selection is introduced, since it is quite convenient for dynamically changing environments. In that regard, two different techniques, namely Q-learning and SARSA, are proposed, as they are known for their multi-objective optimization capabilities. Moreover, fixed CIO values are used as a benchmark for the proposed methods for comparison purposes. Results reveal that the reinforcement learning assisted mobility load balancing (MLB) approach can alleviate the burden on the overloaded cells while keeping the neighboring cells at some reasonable load levels. The proposed methods outperform the fixed-parameter solution in terms of the given metric.

Visible Light Communication (VLC) systems provide not only illumination and data communications, but also indoor monitoring services if the effect that different events create on the received optical signal is properly tracked. For this purpose, the Channel State Information (CSI) that a VLC receiver computes to equalize the OFDM subcarriers can be reused to train an unsupervised learning classifier. This way, different clusters can be created on the collected CSI data, which could be then mapped into relevant events, such as the position of an object in the sensing area. When compared to supervised learning algorithms, the proposed approach does not need tags in the training data, simplifying notably the implementation. The validation of this monitoring approach was done using a software-defined VLC transmission based on OFDM, in which a reflected copy of the intensity modulated signal coming from a white LED was captured by a pair of photodetectors. The experimental evaluation of the VLC-based monitoring demo achieved a positioning accuracy in the few-centimeter-range, without the necessity of deploying a large number of sensors and/or adding a sensor on the object to-be-tracked.

Industrial Internet of Things (IIoT) and Industry 4.0 are used interchangeably while talking about the revolution in the field of manufacturing and logistic industries. IIoT is a digital ecosystem of connected devices, machines, equipment, and robots that communicate with each other without or with minimum human intervention. The 28 GHz band and 60 GHz band are two lucrative Millimeter Wave (mmWave) bands for 5G, and are getting popular since they enable standalone private network for IIoT. To ensure the successful deployment of IIoT in practice, we need to revisit our understanding of the radio channel characteristics at target frequencies in Indoor Factory (InF) environments. In this paper, we have considered three operating frequencies i.e., 3.5 GHz, 28 GHz and 60 GHz, and we investigate the performance of several Distributed Antenna System (DAS) and non-DAS layouts in 3GPP specified InF environment that is characterized by high density of blockers. The performance of the system is quantified in terms of received power, SINR, outage ratio, application layer throughput, and system capacity. The system performance is analyzed with Three-Dimensional (3D) Ray Tracing (RT) simulations. The acquired simulation results and related discussion provided in this paper gives insightful information about the communication properties in an indoor industrial environment.

We propose the use of adaptive optimized irregular constellation to enhance the performance of full duplex (FD) wireless radio systems which suffer from residual self-interference (RSI). Specifically, an error performance expression which takes into account the RSI level and signal-to-noise ratio is first derived for a single FD relay link. During the search for optimal constellation for a given parameter set, there are no predefined assumptions on symbol point locations. The optimization framework yields adaptive irregular constellations depending on RSI levels and power budget values. It is shown that the proposed adaptive transmission along with optimized irregular constellations achieves better error performance than the conventional$M$-QAM constellations and other$M$-ary improper Gaussian signaling (IGS) constellations.

This paper studies a novel way to estimate the position of an object in an indoor environment, using the Channel State Information (CSI) that a Visible Light Communication (VLC) system collects to maintain the link-level connectivity. First, supervised learning is applied to characterize, the effect that an object in variable but known positions has on the received optical wireless signal. Second, the trained classifier is used to estimate the new unknown positions that the object may take, making use of the instantaneous CSI that is used to equalize the data-carrying signal samples in reception. The practical validation of the proposed positioning approach was done with the aid of a software-defined VLC link based on OFDM, in which a copy of the intensity modulated signal coming from a Phosphor-converted LED is captured by Photodetectors (PDs) in different room locations. Then, the CSI of the VLC receiver is used to train a Random Forest classifier, which will predict the position of the object during the assessment phase. The performance evaluation of our experimental setting shows that the proposed VLC-based positioning approach can reach a few centimeter accuracy, provided that a proper training is executed, without the necessity of deploying a large number of PDs in the room, or adding a VLC receiver on the object to be tracked.

Visible light communication (VLC) systems should be designed to provide illumination and wireless data services simultaneously. To achieve this goal at a reasonable cost, the use of Phosphor-Converted (PC) LEDs for indirect illumination should be favored to provide a homogeneous and reliable coverage in the whole service area. Unfortunately, PC-LEDs found in the market so far have not been designed for data transmission; moreover, the response of the other (electro-) optical components of the VLC link are far from ideal. In this paper, we estimate the data rate that is feasible with VLC when indirect illumination is used. For this purpose, the end-to-end response of the VLC link is first modeled using actual measurements of the spectral power distribution of a PC-LED lamp and the ceiling reflectance. Then, different power allocation schemes are studied assuming an optical OFDM waveform. As commercial LEDs have a relatively slow time response, the equivalent VLC channel that results has strong frequency selectivity; therefore, notable data rate gains are achievable when waterfilling power allocation is applied.

Visible Light Communication (VLC) systems are designed to provide illumination and data services simultaneously. To achieve this goal, LED lamps are usually deployed on the ceiling of the rooms, in order to maximize the chances of having Line-of-Sight (LoS) connectivity between the VLC transmitter and the random locations that the VLC receiver can take. In an early stage of adoption, where the cost of LED lighting fixtures incorporating VLC technology will be high to enable ultra-dense deployments, it is expected that only one VLC transmitter is placed per room. In this situation, the use of direct illumination may have serious problems to satisfy the illumination constraints and provide a homogeneous data rate coverage. Moreover, the use of a single powerful LED lamp per room may create discomfort glare effect to users and over-exposure problems in areas of the room at which the light beam is directed. In order to address these problems, this paper studies the data rate that VLC technology can achieve with indirect illumination. That is, when the LED lamp is pointing upwards, and the VLC user receives the optical signal that is reflected back from the ceiling. Obtained simulation results show that indirect illumination provides a more homogeneous data rate coverage when compared to the direct case, while simultaneously verifying the illumination constraints in most of the places that the VLC receiver may take in the room.

We study low-overhead uplink multi-access algorithms for massive Internet-of-Things (IoT) that can exploit the MIMO performance gain. Although MIMO improves system capacity, it usually requires high overhead due to Channel State Information (CSI) feedback, which is unsuitable for IoT. Recently, a Pseudo-Random Beam-Forming (PRBF) scheme was proposed to exploit the MIMO performance gain for uplink IoT access with uniform channel and load, without collecting CSI at the BS. For non-uniform channel and load, new adaptive beamselection and random-access algorithms are needed to efficiently utilize the system capacity with low overhead. Most existing algorithms for a related multi-channel scheduling problem require each node to at least know some information of the queue length of all contending nodes. In contrast, we propose a new Low-overhead Multi-Channel Joint Channel-Assignment and Random-Access (L-MC-JCARA) algorithm that reduces the overhead to be independent of the number of interfering nodes. A key novelty is to let the BS estimate the total backlog in each contention group by only observing the random-access events, so that no queue-length feedback is needed from IoT devices. We prove that L-MC-JCARA can achieve at least `0.24`` of the capacity region of the optimal centralized scheduler for the corresponding multi-channel system.

This paper demonstrates the feasibility of using supervised learning algorithms to identify the presence of different objects, taking advantage of the effect that they create on the VLC channel gains. For this purpose, a software-defined VLC link is implemented using a Phosphor-converted LED, whose light intensity is modulated by an Optical OFDM frame that includes synchronization words and pilot sequences for channel estimation. Actual estimated channel gains are collected in the receiver, which are used to train and assess the performance of the Random Forest classifier. The accuracy of the monitoring system is evaluated using three different objects, showing an accuracy in the order of 90% in detecting the objects, even when they take different positions when obstructing the VLC link.

Channel models are routinely used for evaluating the performance of wireless technologies and cellular networks. An appropriate channel model is necessary for a credible system analysis, and the shortcomings in the channel model may lead to erroneous conclusions. In this paper we characterize the impact of Interference Suppression (IS), Interference Cancellation (IC) and interference management on the system performance when using a) the 3rd Generation Partnership Project (3GPP) street canyon model (TR 38.901, Release 14), b) Shoot and Bouncing Ray (SBR) method based Ray Tracing (RT) model, and c) a proposed large scale path loss model in an urban, so-called Manhattan building grid environment. Simulations are performed using the 28 GHz carrier frequency that has been recently considered for the 5thGeneration (5G) networks. Simulation results indicate that the 3GPP channel model provides slightly pessimistic path loss values than RT in Line of Sight (LOS) conditions, whereas in Non-LOS (NLOS) situation it gives a considerable pessimistic path loss estimation as compared with the deterministic RT approach. The difference between channel models is notable especially for the estimation of Signal to Interference plus Noise Ratio (SINR). Since RT provides realistic results due to accurate radio environment and signal modeling and, on the other hand, the correct SINR estimation is crucial for the wireless system evaluation. Our proposed path loss model is based on RT simulations. The performance of the proposed model for different performance metrics matches well with the RT results.

A pseudo-random beamforming (PRBF) based random access (RA) system is proposed to enable uplink (UL) machine-type communications (MTC) with ultra low signaling overheads. Specifically, a pseudo random (PR) sequence is used as public information to coordinate the beamforming vectors used at the base station (BS) and the devices. Within the coherence time window, each device distributively determines in advance the ''good'' time slots and receiving beams for transmission. This UL protocol reduces the overheads due to the feedback of channel state information and the control signals for centralized scheduling. This paper derives the throughput and user scaling of the proposed M- PRBF-CA protocol for achieving spatial multiplexing gain, under both an i.i.d. slow fading channel and a correlated slow fading channel. Our simulation results confirm the analysis in both fading channel models.

Cellular vehicle-to-network (V2N) communication will be the backbone of the connected vehicles of future. One of the key requirements of the connected vehicles is a near universal coverage on the streets. Traditional radio network planning for cellular coverage is done with raster format whereby all pixels in a network area have equal weighting. Whereas, for V2N communication the target is to primarily ensure continuous network coverage on the streets. In this work, a route-based methodology which is pertinent for V2N coverage analysis is presented. This method adds another key parameter into consideration, namely, the base stations (BS) deployment schema. Existing cellular networks, whereby, small base stations (BSs) are deployed at the macro BS cell-edge, at traffic hotspots or to compensate for coverage holes, may not be sufficient for V2N coverage especially at millimeter wave (mmWave) carrier frequencies. Herein, we perform the coverage analysis for an existing small BS deployment as well as for an ultra-dense deployment at 2 GHz, 5 GHz and 28 GHz carriers. The statistics for signal-to-noise-plus-interference ratio (SINR) and achieved rate are aggregated by a large number of realistic vehicular routes from Google Directions application programming interface (API).

Recently, an active discussion on the feasibility of Millimeter Wave (mmWave) frequencies for the Vehicle-to-Vehicle (V2V) communication have been carried out in research community. We contribute to this discussion by providing a comparison between explicit three-dimensional ray-tracing simulations and field trial measurements on 39 GHz frequency. Three basic practical and relevant cases for V2V communications are considered covering several important scenarios of daily life traffic. A close match between the measured and simulated results is found through explicit ray tracing simulations; thus validating the feasibility of the simulation model and underlying assumptions. Moreover, these outcomes also shed light on the potential and challenges of using mmWave frequencies for V2V communication. The acquired results indicate that the Reference Signal Received Power (RSRP) levels are sufficiently above the noise level even up to 100 m distance between TX and RX in case of a single obstructing car. Results also reveal the impact of moving vehicle intersecting the LOS between the TX and RX vehicle at road intersection, and they indicate a notable blockage loss in case of short TX-RX separation.

In cellular networks, users are grouped into different cells and served by different access points (base stations) that provide wireless access to services and applications. In general, the service demand is very heterogeneous, non-uniformly distributed, and dynamic. Consequently, radio access networks create veryirregulartopologies with more access points, where service demand is concentrated. While this dynamism requires networks with the ability to adapt to time-varying conditions, the non-uniformity of the service demand makes the planning, analysis, and optimization difficult. In order to help with these tasks, a framework based on canonical domains and spatial mappings (e.g., conformal mapping) have recently been proposed. The idea is to carry out part of the planning in a canonical (perfectly symmetric) domain that is connected to the physical one (real-scenario) by means of a spatial transformation designed to map the access pointsconsistentlywith the service demand. This paper continues the research in that direction by introducing additional tools and possibilities to that framework, namely the use of centroidal Voronoi algorithms and non-conformal composite mappings. Moreover, power optimization is also introduced to the framework. The results show the usability and effectiveness of the proposed method and its promising research perspectives.

In vehicle-to-vehicle (V2V) channels, roadside scatterers (RSSs), such as houses, buildings, trees, and many more, play a crucial role in the determination of the Doppler power spectral density (DPSD) characteristics. However, the relevant research results are scarce due to the lack of computationally tractable analytic DPSD solutions. To fill this gap, we investigate an indirect method for the DPSD analysis of a generic 2-D RSS model for V2V channels. The indirect method, based on Hoeher's theorem, employs successive transformations of random variables to obtain the DPSD. Compared with the conventional methods, leading to impractical multiple integral solutions, our method yields a single integral form, more useful for analytic studies, model validation/parameter estimation, and fading simulator design. Using the new DPSD solution, the impact of different RSS layouts on the DPSD characteristics is further investigated, and several new insights are provided. The joint probability density function (PDF) of the angle-of-departure and the angle-of-arrival (AoA) and the joint Doppler-AoA PDF are newly presented in closed forms and analyzed with respect to the DPSD shape. Comparisons with the DPSDs measured in highway and urban canyon environments demonstrate not only the validity of the generic 2-D RSS model but also the significant contribution of RSSs to V2V channels.

The Rayleigh product channel model is useful in capturing the performance degradation due to rank deficiency of MIMO channels. In this paper, such a performance degradation is investigated via the distribution of mutual information assuming the block fading channels and the uniform power transmission scheme. Using techniques of free probability theory, the asymptotic variance of mutual information is derived when the dimensions of the channel matrices approach infinity. In this asymptotic regime, the mutual information is rigorously proven to be Gaussian distributed. Using the obtained results, a fundamental tradeoff between multiplexing gain and diversity gain of Rayleigh product channels under the uniform power transmission can be characterized by the closed-form expression at any finite signal-to-noise ratio. Numerical results are provided to compare the outage performance between the Rayleigh product channels and the conventional Rayleigh MIMO channels.

From its origins, cellular networks have been in constant evolution. Nowadays, real-world deployments admit very irregular network topologies in order to satisfy nonuniformly distributed service demands, i.e., there are small cells in areas where users are concentrated. This makes the planning, analysis, and optimization of such irregular topologies difficult. Methods based on stochastic geometry have been proposed and successfully used to capture some characters of this heterogeneity; and recently, the analysis based on canonical domains and spatial transformations has also been proposed as a complementary tool to aid in network planning and optimization tasks. The key idea is to simplify the analysis by using a dual/canonical domain that is perfectly symmetric and homogeneous. Unfortunately, yet expected, these synthetic models have fallen into disuse as they cannot capture the heterogeneity of the increasingly complex real-world deployments. However, the introduction of the aforementioned framework creates an opportunity to revisit these reference models and to study them from several new points of view. In addition, the one-dimensional network model fits with several relevant study items, such as Intelligent Transportation Systems and road-side deployments. The contribution of this paper is to present the analysis of the one-dimensional canonical domain (and several applications of it) as an initial effort to pave the way towards further generalizations, such as the challenging two-dimensional case.

The pursuit of more bandwidth and more efficient spectrum usage has led to consider the use of Long Term Evolution (LTE) technology in unlicensed frequency bands, a concept known as LTE-Unlicensed (LTE-U). This feature would be especially useful in hot-spots and indoors, where short-range pico-base stations could be used. However, indoor WiFi on unlicensed bands calls for coexistence mechanisms between LTE and WiFi. Accordingly, methods including listen-before-talk, advanced channel selection, duty-cycle, and variations of them, have been proposed. While these protocols are of great importance, we are approaching the coexistence issue from the radio access planning/optimization point of view by presenting a statistical system model for LTE-U indoor planning. The proposed optimization framework allows to obtain network topologies that maximize the benefits from the LTE-U deployment and fulfill coverage criteria. The performance of the statistically-optimized network topologies has also been validated by means of system level simulations.

Machine-to-machine (M2M) communication represents a new paradigm for mobile cellular networks, where a massive number of low-cost devices request the transfer of small amounts of data without human intervention. One option to tackle this problem is obtained by combining random beamforming (RBF) with opportunistic scheduling. RBF can be used to induce larger channel fluctuations, and opportunistic scheduling can be used to select M2M devices when their overall channel quality is good. Traditional RBF does not fulfill M2M requirements, because overall channel quality needs to be tracked continuously. In order to tackle this limitation, a novel codebook-based RBF architecture that identifies in advance the time instants in which overall channel quality should be reported, within a coherence time window, is proposed. This opportunistic feedback mechanism reduces signaling overhead and enables energy saving at M2M devices. A simplified methodology is presented to evaluate the system mean data rate, using for this purpose closed form formulas derived from SNR distribution approximations. Results reveal that the performance loss that is experienced for introducing the proposed modifications to traditional RBF scheme is negligible. The concepts analyzed in this paper provide useful insights, and show that codebook-based RBF with simplified opportunistic scheduling algorithms is an excellent combination to provide wide-area M2M services with low-cost devices and limited signaling overhead.

In order to cope with the rapidly increasing service demand in cellular networks, more cells are needed with better resource usage efficiency. This poses challenges for the network planning since service demand in practical networks is not geographically uniform, and to cope with the nonuniform service demand, network deployments are becoming increasingly irregular. This paper introduces a new idea to deal with the nonuniform network topology. Rather than capturing the network character (e.g., load distribution) by means of stochastic methods, the proposed novel approach aims at transferring the analysis from the physical (irregular) domain to a canonical/dual domain that simplifies the work due to its symmetry. To carry out this task, physical and canonical domains are connected using conformal (Schwarz-Christoffel) mapping, a rich and mature theory from complex analysis. Thus, the main contribution of this paper is to introduce the analysis through canonical domains and validate the usability of conformal mapping as a feasible solution approach for this problem.

Opportunistic scheduling exploits the multiuser diversity to improve the performance of wireless communications. The scheduling gain is enabled by the channel feedback sent from the receiver to the transmitter. In this paper, we consider the so-called opportunistic cumulative distribution function (CDF) scheduling with threshold-based selective feedback in the orthogonal frequency division multiple access downlink system. Among opportunistic scheduling techniques, the CDF scheduling is known to provide multiuser diversity gain while maintaining fair radio resource sharing among users. We first derive the exact and asymptotic average sum rates assuming antenna selection at transmitters. The expressions are valid for arbitrary number of inter-cell interference and number of transmit antennas. Moreover, a closed-form approximation for the user rate distribution is calculated using the exact moments of the user sum rate. The approximation is shown to provide an accurate estimate for the rate distribution, and the results can be utilized in rate adaptation at the transmitter.

The Diversity-Multiplexing Tradeoff (DMT) is studied for the large Rayleigh product channel at non-asymptotic SNRs. The first result is that, as matrix dimensions growing to infinity, the channel capacity converges to a Gaussian random variable. Based on this, we derive a compact expression for the finite-SNR DMT. From the analytical and numerical results, we gain useful insight into the fundamental tradeoff of the considered channel model in the realistic SNR regime.

The fifth generation (5G) of wireless networks will connect not only persons but also things, in a massive and previously unheard-of scale. Therefore, engineers and researchers need to develop methods and solutions to 1) satisfy the increasing demand, and 2) plan, maintain, and optimize networks that are envisioned to provide services to a highly dynamic, diverse, and heterogeneous traffic, both in time and space. This paper makes a contribution to the second goal by introducing an idea for planning and/or optimization of cellular networks based on the use of Centroidal Voronoi Tessellations. The framework allows obtaining (deterministically) network topologies that are compatible with the service demand, described statistically in terms of its spatial distribution and volume. While the method provides by itself a first network performance assessment, site locations and cell areas, are key references for planning and optimization.

The analysis of cellular systems has been carried out modeling the access network by means of deterministic and stochastic methods. Deterministic models include hexagonal geometries or real-world data. Stochastic methods, given their nature, capture (in a statistical manner) the inhomogeneities found in realistic deployments. Beyond pros and cons of each approach, the notion of ‘topology’ associated to these models is either geometric (regular or non-regular) or architectonic (heterogeneous or not), but it is not enough to describe many aspects of real-world deployments. Despite the term is widely used in the context of cellular communications, there is no precise (mathematical) definition for it. In the light of this situation, this paper presents a set of proper definitions to describe network topology and its compatibility with service demand distribution in a way that is useful from the planning and optimization perspective. In addition, a novel view of ‘irregularity’ is also introduced. Due to its generality, this statistical framework is timely for 5G where 1) hyper-dense and hierarchical deployments are foreseen, and 2) more complex performance indicators such as energy, spectral, and deployment efficiency per area unit need to be accurately estimated. In addition, operator-specific criteria such as QoS can be taken into account in the model presented herein.

A simple quantization scheme is proposed to adjust separately the amplitudes and phases of signals in a codebook-based Transmit Beamforming (TBF) scheme. The proposed quantization scheme is valid for both desired signal power maximization (egoistic TBF) and co-channel interference mitigation (altruistic TBF), and does not require an exhaustive search to find the optimal TBF vector. Performance results are presented when variable numbers of bits for amplitude and phase feedback resolutions are used for both egoistic and altruistic TBF schemes.

Spatially distributed transmissions in coordinated multipoint (CoMP) systems can lead to mean channel power imbalance (CPI) at the receiver. Similar imbalance also occurs in distributed antenna and co-located multi-antenna systems due to inaccurate antenna calibration. This paper studies performance impact of power imbalance on some practical CoMP methods with limited feedback. We derive approximate analytical expressions of asymptotic capacity, optimal amplitude weights, as well as signal-to-noise ratio gain for a few methods under analysis. Numerical results validate the analysis and show impacts of erroneous feedback under CPI. Results demonstrate that CPI has significant negative impact on the CoMP performance. Furthermore, our results reveal that amplitude information at transmitter is crucial and detrimental effect of CPI can be effectively compensated by using long-term amplitude information at transmitter. Moreover, additional short-term amplitude feedback shows insignificant gain when a large number of diversity antennas in base stations or CoMP suffer from feedback errors. In fact, a sparsely quantized phase and long-term power information feedback can lead to performance very close to the use of full channel state information at the transmitter.

Relay node cell area is limited by low transmission power and limited antenna capabilities, which may not allow it to carry a significant share of the traffic load, thus reducing its efficiency. Cell range extension is thus expected to better balance the load in the network, hence, improving the performance of relay deployments. Herein, we investigate two relay cell range extension techniques, introducing a bias to cell selection and handover thresholds along with reduction in donor enhanced Node B transmission power. The study focuses on inband half-duplex relaying where resource partitioning among the two relay hops is jointly considered with cell range extension. As opposed to picocell deployments, extending the relay cell range offloads only partially the macrocell as newly admitted users increase the resource demand of the relay on its wireless backhaul link from its donor enhanced Node B. Hence, joint optimization of the decisive parameters for different key performance metrics is performed. Comprehensive analysis was carried out for both the downlink and the uplink in urban and suburban scenarios within the LTE- Advanced framework. Results reveal that the investigated solution yields significant gains. Finally, we discuss on the realization of cell range extension as part of network planning and offline optimization.Copyright © 2013 John Wiley & Sons, Ltd.

Urban (and suburban) informal settlements in emerging markets will be the fastest growing population hotspots in the next few decades. This presents a significant challenge in delivery of services, including affordable mobile Internet access. Operator-led upgrades through network densification (rollout of additional operator-maintained sites) are difficult to sustain in those areas due to low revenues, lack of fixed lines, energy scarcity, insecurity, and so on. This calls for alternative approaches in mobile network upgrades and operation. In this paper, we present capacity enhancement approach using user-deployed shared-access small cells in the dense informal settlements. To that end, we consider leveraging macro Long Term Evolution (LTE) networks to backhaul High Speed Packet Access (HSPA) small cells. As a case study, we present comparative network simulations based on an example informal settlement. The results of the study highlight the possibilities for cost-effective capacity upgrades for users in dense settlements for even a limited number of unplanned end-user small deployments and self-backhauling via existing macro sites. In the study, we also note possible system performance enhancements of the small cell backhaul link through improved antenna design, scaling of carrier bandwidth and introduction of traffic steering across HSPA and LTE layers.

Wireless networks are evolving continuously and expected to provide seamless experience for multiple real-time internet applications. Quality-of-service is one of the major component associated with user experience. In this paper, we have considered the provisioning of desired QoS to mobile users that are capable of running multiple internet applications in parallel. For this purpose, a three-step iterative downlink scheduler is proposed for resource management at per-userper-service level. The scheduler performs sorting in multiple iterations on the basis of three weights. In the first iteration, the scheduler performs sorting based on the throughput weight. The second iteration latency weight and followed by buffer weight in the third iteration. The allocation of resources is done to satisfy the promised QoS to all the services of every user. A comparison is carried out with traditional scheduling algorithms in terms of system throughput, fairness index and percentage of satisfied guaranteed bit-rate users. Results show that the proposed algorithm outperforms existing schemes and the performance is more closer to theoretical system throughput.

The emerging Long Term Evolution-Advanced (LTE-A) standard promises improvements in throughput and reduction in costs-per-bit, through use of techniques, such as, relaying and coordinated multipoint (CoMP) transmission and reception. The inherent self-backhauling of relays nodes makes them an attractive solution in areas where backhaul is either unavailable or costly. However, the performance of the backhaul relay link limits overall performance of relay systems, particularly for relays deployed in the cell edge. In this paper, we propose CoMP-enhancements in order to relax the relay link bottleneck. We study this proposed approach through system simulations of a selected realistic deployment scenario. The results demonstrate that use of a quantized co-phasing (QCP) CoMP technique provides significant signal- to-interference-plus- noise-ratio (SINR) gains and end-to-end throughput improvements for user equipment connected to the relays, even with simple scheduling techniques.

Mobile devices have evolved remarkably over the last decade and are now being utilized to access much broader range of internet applications. Moreover, their capability to simultaneously run many applications has significantly transformed the traffic characteristics of mobile networks. Quality of service (QoS) is a fundamental component associated with these applications and network should be able to support multiple QoS requests from the same user at same time. This requires complex buffer management and simultaneous scheduling of resources to multiple users with multiple services. In this paper, we propose a framework with pre-processor for MAC-layer scheduler including two-dimensional buffer management (users × services) that enable more efficient allocation of resources to users running multiple internet applications in parallel. The framework will enhance the performance of existing scheduling algorithms by increasing the resolution of scheduling. A comparative analysis of traditional scheduling algorithms is provided to show the gains of proposed framework.

This work studies constrained rate maximization problem for clustered device-to-device (D2D) communication in cellular networks. In the cluster, only one capable user equipment (cluster head) downloads data from the base station. D2D communication is used for local data sharing between the cluster head and other user equipments in the cluster. When sharing and reusing cellular spectrum resources, D2D links must control the potential impact of mutual interference. In a scenario that D2D is only allowed by eNB when the cochannel cellular QoS constraint can be achieved, we investigate joint precoding strategy of D2D and cochannel cellular transmission subject to the cellular outage probability constraint. Based on estimated cellular channel state information (CSI), we analyze the feasibility and optimality of the constrained rate maximization problem and provide optimized solutions for different scenarios. Our simulation demonstrates the advantage of the proposed precoding strategy in satisfying cellular QoS and improving D2D rate.

In this paper, we study the impact of cross-layer interference in a two-tier Heterogeneous Network (Het-Net), where the assumption of a single dominant interferer is not always valid. We investigate the improvements that can be achieved when Transmit Beamforming (TBF) is utilized to mitigate the interference originating from multiple interference sources. For this purpose, closed-form expressions are presented to model the outage capacity of a heavily interfered Macro User Equipment (MUE), when a variable number of Femto Base Stations (FBSs) substitute their current beamforming vectors that maximize own-user performance (i.e., egoistic TBF) with those that minimize emitted interference (i.e., altruistic TBF). Our analysis reveals that application of altruistic TBF is most efficient when performed in clusters of interferers, ranked from strongest to weakest according to the level of interference that is observed at the MUE. Determination of the optimal number of participating clusters is strongly connected to the type of feedback algorithm used, and the resolution of the feedback message to be exchanged.

A novel closed-form approximation is derived for the statistics of cascaded Nakagami-m channels with integer and half-integer m. The adopted approximation generalizes the prior results by incorporating cross-correlations between each pair of component channels. The approximative probability density function is constructed by an easily computable log-normal density and its associated orthogonal polynomials. The proposed approximation shows good agreement with numerical simulations under light fading condition and yields improved accuracy compared with the well-known lognormal distribution. To illustrate the usefulness of the derived result, we apply it in performance analysis involving the cascaded Nakagami-m channels.

Relay deployments promise to alleviate the limitations of conventional macrocell networks, such as poor indoor penetration and coverage holes in a cost-efficient way. In this context, the capacity of the wireless relay link between a relay node (RN) and its serving base station (BS) has a crucial role in the achievable end-to-end performance. The deployment flexibility of RNs, which mainly stems from the wireless relay link, compact physical characteristics, and low-power consumption, can be exploited by relay site planning (RSP) to overcome the limitations of the relay link and, thus, enhance the system performance. To this end, RSP is carried out via selecting an RN deployment location from a discrete set of alternatives considering the signal-to-interference-plus-noise ratio (SINR) on the relay link as the selection criterion. In practice, the so-called coarse RSP takes into account only large-scale fading due to shadowing. Nevertheless, as RNs are stationary, the wireless channels pertaining to relay deployments are subject to simultaneous impairments by both shadowing and multi-path fading, i.e., composite fading/shadowing. In this paper, we present the performance of coarse RSP that can be used for planning and dimensioning of two-hop cellular relay networks in composite fading/shadowing environments, where co-channel interference is also present. The relay link is modeled by Nakagami-lognormal distribution while the access link between a mobile terminal (MT) and its serving RN is modeled by Rician-lognormal distribution. Furthermore, we provide an accurate analytical framework through closed-form expressions for relay link SINR, link rates, and end-to-end rate. Results show that coarse RSP can still yield high performance improvements considering composite fading/shadowing channels.

In this paper, we analyze the downlink performance of a multi-user system consisting of mobile users with wide range of velocity. We categorize these users into different groups on the basis of their velocity range and study the impact of feedback delay on each group for closed-loop transmit beamforming. Based on this analysis, we propose an adaptive feedback-scheduling algorithm to minimize the effect of feedback delay on the performance of the system. We derive generalized performance measuring expressions for the proposed algorithm and carry out simulations to validate the analysis.

Green radio has attracted much attention currently, and among the many factors to be considered, power consumption reduction is of great significance. In this paper, we consider a power minimization problem with rate requirement and power constraints for downlink multi-cell cooperative MIMO(Co-MIMO) systems. A transmit signal covariance design scheme is proposed, and an integrated algorithm is developed to search the optimal covariance for power minimization. Numericalsimulations verify the optimality of our proposed transmit signal covariance scheme. A significant performance gain is observed over the uniform power allocation (UPA) and the noncooperative geometric mean decomposition (GMD)-based schemes.

Multi-user MIMO communication can provide significant gains by exploiting spatial multiplexing. However, it requires better feedback to provide accurate channel state information at the transmitter (CSIT) for minimizing the multiuser interference. 3GPP LTE provides support for MU-MIMO, but it is not sufficient to extract sizable gains. In this paper, our primary goal is to efficiently exploit the system's resources for MU-MIMO in LTE. In the existing 3GPP LTE standard (Rel. 8), we observed that the transmission mode 5 (TM5) dedicated for MU-MIMO utilizes wideband feedback method for providing channel directional information/ precoding matrix indicator (CDI/PMI). The standard supports finer granularity feedback i.e. sub-band feedback method, but it's not utilized for MU-MIMO and restricted only to SU-MIMO. Therefore in this work, we propose to exploit the sub-band feedback for providing more frequent update of PMI. However, in order to support this feedback method, we need to propose a new downlink control information (DCI) format for TM5 that will contain additional fields in comparison to the existing DCI format 1D. Furthermore, to extract optimal performance at the system level, we also propose a MAC-layer scheduling algorithm that deals with resource management on sub-band basis. Utilizing these proposed methods, we show considerable gains in MU-MIMO for 3GPP LTE at the system level.

A blind target detector using the time reversal transmission is proposed in the presence of channel correlation. We calculate the exact moments of the test statistics involved. The derived moments are used to construct an accurate approximative Likelihood Ratio Test (LRT) based on multivariate Edgeworth expansion. Performance gain over an existing detector is observed in scenarios with channel correlation and relatively strong target signal.

Opportunistic resource allocation for multiple users utilizing multiple-input multiple-output (MIMO) channel in orthogonal frequency division multiple access (OFDMA) is used to attain the spectral efficiency required in future wireless communications networks. In this paper, we express analytical outage capacity results and average capacity results with optimal rate adaptation for MIMO-OFDMA systems with limited feedback. A resource block (RB)-wise SNR quantization feedback scheme and a best-M feedback method are studied for RB allocation. Feedback based transmit antenna selection (AS) is considered in the analysis. An imperfect feedback channel has a significant impact on the performance of practical feedback based communication. The proposed analysis also considers imperfect feedback in the RB allocation and AS.

This work studies femtocell resource allocation in shared spectrum heterogeneous networks. We propose an enhanced shadow chasing method for femtocell resource allocation to achieve interference mitigation in heterogeneous networks serving both Macrocell User Equipments (MUEs) and Home User Equipments (HUEs). Shadow chasing home eNB (HeNB) uses Downlink Control Information (DCI) together with over-heard macrocell user ACK/NAK feedbacks and CQI reports to assign its own downlink resources to mitigate downlink interference to MUEs. Since the HeNB receives outdated DCI due to backhaul delay, we derive a likelihood metric for each resource unit being either empty or assigned to a (low-interference) outdoor MUE based on a finite-state Markov chain model for each resource unit. By dynamically separating MUE and HUE assignments, the enhanced shadow chasing can better control the downlink interference to MUEs for QoS assurance. It effectively reduces the probability of resource collision and MUE interference compared to schemes not considering backhaul delay effect or user feedbacks.

In this paper, we propose an enhancement to a resource allocation scheme known as shadow chasing for interference mitigation in heterogeneous networks composed of Macrocell User Equipments (MUEs) and Home User Equipments (HUEs). In shadow chasing, the Home eNB (HeNB) uses Downlink Control Information (DCI) together with the overheard ACK/NAK feedback and CQI reports to assign its HUEs the Physical Resource Blocks (PRBs) that are assigned to outdoor MUEs. Since the HeNB receives an outdated DCI due to backhaul delay, our solution is to derive a likelihood metric for each PRB being either empty or assigned to an outdoor MUE by using a MC model for the state of each PRB. By dynamically separating the MUE and HUE PRB assignments, enhanced shadow chasing can better constrain the downlink interference to the MUE. Our results show effective reduction of probability of PRB assignment collision and MUE interference compared to schemes that do not integrate the delay effect or exploit user feedbacks.

Deploying relay nodes is foreseen a cost-efficient solution to combat the severe propagation loss at cell edge. However, relay cell coverage is limited by the low transmit power, limited antenna capabilities and wireless backhaul link bottleneck which may lead to load imbalances and hence low resource utilization efficiency. Further challenges in relay deployments are attributed to increased interference levels in the network compared with macrocell-only deployments, causing degradation of the user throughput. In this context, relay cell coverage expansion and interference coordination techniques are expected to improve the performance of relay deployments. In this study, we analyze the impact of the additional interference due to the relay node transmissions. Jointly with our previous study on cell expansion, we show how the interference coordination mitigates the interference from relays and hence optimizes the system performance. Comprehensive system level simulations are carried out within the LTE-Advanced framework. Results confirm that the interference imposed by relay nodes can be reduced. Furthermore, both cell edge throughput gains and cell average throughput gains are observed.

As wireless communications experience tremendous growth, energy consumption is becoming a crucial problem in the wireless industry. Energy saving mechanisms are important for supporting the mobility and extending the battery life of a user equipment, reducing the operation costs of a network operator, enhancing corporate image of operators and vendors alike, and providing a lower total energy consumption which reflects in a lower environmental impact. Herein, we evaluate the energy efficiency of different small node deployments, namely relay nodes and Picocells, within the 3GPP LTE-Advanced framework. The energy efficiency of small node deployments is considered on both the uplink and downlink of 3GPP-defined urban and suburban models. In specific, the work investigates the impact of deploying different numbers of small nodes on reducing area power consumption, or alternatively, on enhancing the throughput power consumption of access networks.

Relaying is a promising enhancement to existing radio access networks and is currently being standardized in 3GPP to be part of the LTE-Advanced Release 10. Relays promise to alleviate the limitations of conventional macrocell-only networks such as poor indoor penetration and coverage holes in a cost-efficient way. Yet, to fully exploit the benefits of relaying, the inter-cell interference which is increased due to the presence of relays should be mitigated. Besides, a high receiver dynamic range should be avoided to retain the orthogonality of the SC-FDMA system. In this manner, uplink power control is an effective tool to address such challenges. However, in order to enhance the overall system performance, power control optimization should be jointly done on all links, i.e. on eNB-relay node, eNB-UE and relay node-UE links. In this paper, we propose a joint optimization strategy of power control parameters based on Taguchi's method that exploits the mutual dependencies of the different links without a priori knowledge. The proposed joint parameter optimization is compared with a reference study that comprises a four-step optimization. The evaluation of the optimization strategies within the LTE-Advanced uplink framework is carried out by applying the standardized LTE Release 8 power control scheme both at eNBs and relays. Simulations show that the proposed optimization yields similar or better performance relative to the reference strategy depending on the considered performance metric.

Various low-power node technologies such as relays and femtocells are considered an integral part of the heterogeneous fourth generation radio access networks. However, due to different transmit power levels, antenna configurations, and network planning strategies of such nodes, the interference characteristics in heterogeneous deployments can be significantly different than the conventional macrocell-only deployments. The variations in experienced co-channel interference levels could affect the convergence of numerical interference modeling methodologies and significantly decrease their convergence rates. In this paper, different preconditioning approaches are proposed and their impact on the convergence of numerical co-channel interference approximations is analyzed. The evaluations are performed utilizing a flexible MGF-matching method which approximates the lognormal sum distribution by a lognormal random variable, a well-known approach to model the co-channel interference in mobile cellular networks. Simulations show that the proposed preconditioning approaches can substantially increase the computational efficiency of the MGF-matching method while ensuring the convergence of the method.

In this paper, a mathematical framework for the Random Access Channel (RACH) modeling in Long-Term Evaluation (LTE) technology is presented on the basis of probability theory and statistics. The framework is exemplified by basic investigations on the self-optimization of RACH resource unit allocation and preamble split. Evaluations are performed by modeling a stochastic process in which outputs of a dynamic LTE network simulator are taken as inputs.

LTE-Advanced Type 1 inband relays support a two-hop decode-and-forward relaying mode where the relay link reception is time-division multiplexed with the access link transmission on different subframes. Thus, any misalignment in the subframe configurations of different relays may cause overlapped reception and transmission on both links generating a new type of interference, referred to as relay-to-relay interference. In this work, we propose a novel divide-and-conquer technique to mitigate such interference; the approach exploits the localized nature of the effect of the relay-to-relay interference and hence avoids the need to perform a network-wide subframe configuration. In particular, we propose a two-step scheme, namely grouping of RNs in exclusive groups and then aligning the subframe configurations within each group. Such an approach can be realized in a centralized manner by a proposed self-organizing network interference management entity within the Operation and Maintenance system. The proposed scheme is evaluated via comprehensive system-level simulations of relay deployments within the LTE-Advanced downlink framework. Results show that the divide-and-conquer approach can effectively mitigate relay-to-relay interference in all of the considered scenarios.

Type 1 inband relaying, as being standardized in 3GPP LTE-Advanced, supports a relaying mode where the backhaul link transmission is time-division multiplexed with the access link transmission, whereas macro users share the same resources with the relays. Hence, system performance depends strongly on the resource sharing and allocation strategy among and within the different links. Moreover, the set of subframes assigned for the backhaul transmission is semi-statically configured and thus a dynamic reconfiguration to adapt to fast-changing system conditions, e.g. relay cell load, is not viable. In order to tackle the above issues, we propose a statistic-based over-provisioned backhaul subframe allocation to be utilized for flexible co scheduling of relays and macro users at the donor eNB. In addition, a power control optimization is investigated to enhance overall system performance and to reduce the donor eNB receiver dynamic range. Performance evaluation is carried out within the LTE Advanced uplink context in urban and suburban scenarios. Results as well show that the proposed scheme achieves significant throughput gains.

In this paper, we study the performance of a LTE-A relay-aided system with limited buffer size at the relay node. In presence of a link quality mismatch between the backhaul and access links of the relay node, we analyze the impact of the buffer size on the occurrence of undesirable events such as buffer overflows or underflows. Based on simulations, we find out that the size of the buffer at the RN can positively influence the throughput performance of the served users. Finally, we observe that in different relaying conditions, the buffer size setting plays an important role on the overall system performance, especially in terms of underflow and overflow occurrence.

In this paper, we propose a simple decentralized frequency-domain resource allocation strategy combined with uplink power optimization for Long Term Evolution (LTE) femtocell base stations (FBSs). We consider femtocells as an underlay network that reuse the existing macrocell spectral bands. The objective of this work is to maximize the uplink throughput of femtocell user equipments (FUEs) without causing performance degradation to macrocell user equipments (MUEs). System-level simulations are carried out to investigate the power optimization problem by extensive search over the power control (PC) parameter space. Based on the parameters selection, the FUEs uplink throughput is evaluated using the resource allocation scheme which roughly separates the macro- and femtocell users in frequency by imposing different allocation probabilities on different parts of the spectrum. Results show a significant FUE throughput improvement compared with an uniform allocation scheme.

ABSTRACT The long term evolution (LTE) is being designed to enhance third generation radio access technologies, and it represents a major step towards high‐performance mobile data networks that are fully optimized for packet‐switched connections. In an initial access, the LTE user equipment executes the random access (RA) procedure while searching for serving base station and initiating services. For a good cell coverage to be obtained, feasible uplink data rate and low delays in, for example, call setup, the optimal random access channel (RACH) performance is essential. Although manual tuning of procedures can be very costly, it is important to design self‐organizing network (SON) algorithms that optimize procedures such as RA. In this paper, a mathematical framework for the RACH modeling in LTE technology is presented on the basis of probability theory and statistics. A self‐optimization algorithm for RACH preamble sequence allocation and preamble split is then examined using the deduced mathematical framework and system‐level simulations. Performance analysis is semi‐analytical: First, RACH performance results are produced using analytical model, and second, outputs are fed into a dynamic LTE network simulator. Results show that the proposed optimization approach clearly improves uplink performance and ensures a certain success rate at the first RA attempt so that shorter handover durations and call setup delays can be achieved. Copyright © 2011 John Wiley & Sons, Ltd.

Decode-and-forward relaying is a promising enhancement to current radio access networks and is now being standardized in the 3GPP work item on LTE-Advanced. Relay enhanced networks are expected to fulfill the demanding coverage and capacity requirements in a cost-efficient way. However, due to the low transmit power characteristic of relay nodes, their coverage areas will be relatively small in the overlaying macro cell. Therefore, the performance of relay deployments may be limited by load imbalances, unless system parameters are properly selected. In this paper, we propose a practical solution for this problem by introducing a bias to cell selection and handover thresholds. By applying the bias, the relay cells can be extended and an appropriate load balance can be achieved. Via a comprehensive system level simulation campaign, it is shown that biasing results in significant user throughput improvements in both the uplink and the downlink.

The capacity and coverage area of a cell may vary due to changed environment, insertion or deletion of base stations, or malfunctioning base stations, and wrong parameter selection in the network planning phase. Suboptimal capacity and coverage area leads to the waste of network resources and the lower quality. Reacting on the changed situation manually is very expensive and time consuming. Therefore, 3GPP introduces Coverage and Capacity Optimization (CCO) use case for LTE and LTE-Advanced technologies. In this paper, we focus on the self-optimization of remote electrical tilt from the perspective of CCO. Simulation studies are performed for best-effort traffic, and resource fair scheduling by using LTE snap-shot simulator where propagation and uneven user distribution is modeled in three dimensions for a realistic macro-cellular network scenario.

Relaying is considered a promising cost-efficient solution in 3GPP LTE-Advanced for coverage extension and throughput enhancement. Due to compact physical characteristics and low power requirements of the relay nodes, the relay deployment has a high degree of freedom. In this paper, the impact of site planning on the backhaul performance of relay networks within the LTE-Advanced framework is investigated. The site planning strategies are formulated in terms of SNR and SINR based selection criteria. 3GPP compliant simulations are performed comparing relay site planning strategies. It is shown that proper site planning yields significant SINR gain on the eNB-RN link along with a clear reduction in the shadowing standard deviation compared to random deployment.

Relaying is a promising enhancement to current radio technologies, which has been investigated in the 3GPP LTE-Advanced study item and has been recently agreed to be standardized during the work item. Relay enhanced networks are expected to fulfill the demanding coverage and capacity requirements in a cost-efficient way. Yet, in order to fully exploit the benefits of relaying, the inter-cell interference which is increased due to the presence of relay nodes should be limited. Moreover, large differences in the received power levels from different users should be avoided. The goal is to keep the receiver dynamic range low in order to retain the orthogonality of the SC-FDMA system. In this paper, an evaluation of the relay based deployment within the LTE-Advanced uplink framework is carried out by applying the standardized LTE power control scheme both at eNBs and relay nodes. The power control is shown to be a crucial means to increase the cell edge and system capacity, to mitigate inter-cell interference and to adjust the receiver dynamic range.

This paper studies the performance of a two-hop infrastructure-based relay link. The relay operates in a half-duplex mode using an amplify-and-forward protocol. Considering transmission of OFDM signals with nonlinear power amplifiers (PAs), we determine exact closed-form expressions for end-to-end bit error probabilities (BEPs). The expressions allow us to analyze the effect of nonlinear distortion as well as the special case of linear PAs. Furthermore, we derive asymptotic BEP floor values which illustrate how the end-to-end performance is limited by both the nonlinear PA distortion and the weakest hop. Our discussion indicates that the influence of the nonlinear distortion can be mitigated by properly adjusting the PA back-offs.

This paper studies the resource allocation for orthogonal frequency division multiple access (OFDMA) in a fixed amplify-and-forward (AF) relay link. We express closed-form average capacity results for the system when frequency allocation is based on limited and imperfect feedback information and multiple antennae are assumed at the relay node (RN) and the user equipment (UE). Feedback strategies based on the best-M method and resource block (RB)-wise one bit quantization are analyzed and compared. Capacity expressions are presented for space-time block coding (STBC) and transmit antenna selection (AS) schemes. The capacity results with imperfect feedback path are of particular interest. The results illustrate that promising tradeoff between the system performance, feedback overhead, and robustness against feedback errors can be achieved by using AS and limited feedback in frequency allocation.

Relaying concept has been proposed to satisfy the demanding requirements of LTE-Advanced which was recently agreed by 3GPP as an evolution of LTE. Relay enhanced networks are expected to enhance the coverage and capacity in a cost efficient way. Yet, transmit power of UE should be optimized in a relay based scenario where interference increases by additional RNs. New cell edges introduced by RNs increase the number of users that transmit with high power. This leads to severe interference, in particular when a large number of RNs are deployed in a cell with reuse one. In this paper, performance evaluation of relay based deployment within the LTE-Advanced uplink framework is carried out by applying the standardized LTE power control scheme both at eNBs and RNs. The importance of power control parameter settings is examined to achieve optimal performance in relay scenarios.

This paper investigates the uplink performance of LTE-Advanced cellular networks upon relay node deployment. The uplink interference upon deploying relays is analyzed, and a resource partitioning scheme based on user grouping is proposed to mitigate the interference and improve system performance. Simulation results for the proposed resource partitioning scheme reveal that the throughput experienced by the user equipment upon relay deployment is clearly better than the throughput in conventional macro cellular deployments. Also, an improvement in the user equipment's battery life is foreseen.

Current broadband wireless networks are characterized by large cell sizes. Yet, even in advanced networks that will be built using 3 GPP Long Term Evolution (LTE), also referred to as 3GPP LTE-Advanced, or mobile WiMAX radio interface, users on the cell edge will face relatively low signal-to-interference-plus-noise-ratio (SINR). An attractive solution for this problem is provided by multihop technologies. In this paper we consider the feasibility of Decode and Forward (DF) Relay Nodes (RNs) from 3GPP LTE-Advanced perspective. We propose a novel evaluation methodology that can be used to find a relation of RN transmission power, ratio between number of Base Stations (BSs) and RNs, and performance of the system. Evaluation of DF relays in 3GPP LTE-Advanced framework indicates a good performance gain.

Relaying is one of the most important novel elements in 3GPP LTE-Advanced study item. It promises to offer significant gain for system capacity or coverage depending on the deployment prioritization. In this paper, we investigate the feasibility of relay node deployments in terms of system throughput and cell coverage area extension as compared to pico node deployments and traditional homogeneous single-hop macro cells. Relay backhaul link overhead is taken into consideration as a limiting factor in a relay deployment; nevertheless, results show that its effect on coverage extension is in most cases negligible. While the effect of relay backhaul overhead is small in coverage limited scenarios, the limitations on throughput due to relaying are evident, in particular, for 500 m ISD scenarios. This study also demonstrates that both relay and pico node deployments outperform clearly traditional macro cell deployment in terms of coverage and network capacity.

Current broadband wireless networks are characterized by large cell sizes. Yet, even in advanced networks, users on the cell edge will face relatively low Signal-to-Interference-plus-Noise-Ratio (SINR). An attractive solution for this problem is provided by multi-hop technologies. In this paper, we consider the performance of full duplex Amplify-and-Forward (AF) and half duplex Decode-and-Forward (DF) Relay Nodes (RNs) from 3G LTE-Advanced perspective. The comparison between AF and DF relaying is important because both approaches are currently under consideration in LTE-Advanced study item in 3GPP. Performance evaluation considers AF RN loop back signal interference and concurrent DF RN transmissions on the access link. Results show that the concurrent transmissions improve the spectral efficiency for DF RN over performing AF RN.

Abstract-The aim of this paper is to evaluate the impact of various antenna parameters to the down-link performance of the 3GPP Long Term Evolution (LTE) networks. The network performance impacts of horizontal and vertical half-power beamwidths (HPBW) as well as downtilt angle of antenna systems are investigated. Cell coverage and capacity in different macro-cellular network scenarios for various combinations of antenna parameter configurations have been studied in terms of signal to interference plus noise ratio (SINR) performance and cell throughput. Simulation studies are performed for uniform UE distribution and full-buffer traffic by using LTE snap-shot simulator where propagation is modeled in three dimensions.

The aim of this paper is to evaluate and compare impacts of mechanical and electrical downtilt angles of antenna systems to the downlink performance of the 3GPP Long Term Evolution (LTE) networks. Cell coverage and capacity in different macro-cellular network scenarios for various combinations of antenna parameter configurations have been studied in terms of signal to interference plus noise ratio (SINR) performance. Simulation studies are performed for uniform UE distribution and full-buffer traffic by using LTE snap-shot simulator modeling electrical and mechanical antenna tilt in details and propagation in three dimensions.

This paper considers usage of a single-frequency mode for cell coverage extension in infrastructure-based relay links. We provide new closed-form expressions for outage probability by taking into account practical constraints such as interference due to frequency reuse and signal leakage between the relay transmitter and receiver. The analysis covers both decode-and-forward and amplify-and-forward protocols both in downlink and in uplink. For amplify-and-forward relaying, variable gain and fixed gain methods for transmit power normalization are discussed. Simulations show excellent agreement with theory and confirm that the single-frequency mode can be applied at the cost of tolerable signal degradation.

Opportunistic resource allocation in orthogonal frequency division multiple access (OFDMA) with limited feedback improves the performance of wireless networks and it has been considered in several studies. However, the performances of reduced feedback schemes have not been characterized analytically. In this paper, the analysis of the resource allocation in downlink OFDMA with limited feedback is presented. OFDMA system with a practical resource fair round robin allocation and erroneous feedback channel is considered. The performances of the resource allocation based on three feedback methods are analyzed and compared. A resource-wise signal-to-noise ratio (SNR) quantization based feedback method is considered and two feedback strategies are based on the best-M method, where the M best resource blocks are informed to the transmitter. Analytical bit error probability (BEP) expressions are derived for binary phase-shift keying (BPSK) modulation for each feedback strategy. Furthermore, an asymptotic BEP performance for large SNR values is derived for the best-M feedback schemes. The outage capacity results are derived for the considered feedback schemes to illustrate performance with slow link adaptation. Numerical results based on the analysis are compared to those obtained by computer simulations to validate the correctness of the proposed analysis.

Opportunistic user allocation and multiple antenna transmission provide significant performance enhancement in future wireless communication systems. In this paper, theoretical outage capacity analysis of user allocation in downlink orthogonal frequency division multiple access (OFDMA) with multiple antenna transmission and limited feedback is presented. Several multiple antenna transmission schemes are considered in OFDMA system, where resources are allocated according to the resource-wise signal-to-noise ratio (SNR) quantization. Performance results show that the resource-wise one bit feedback from few uncorrelated resources provides significant allocation gain. Numerical results based on the analysis are compared to those obtained by computer simulations to validate the correctness of the proposed analysis.

We propose a closed-loop scheme that combines opportunistic beamforming (OBF) and closed-loop (CL) transmit-diversity (TD) techniques. This quantized OBF scheme is compatible with CL TD algorithms, and allows to adaptively control the amount of feedback overhead according to the number of participating users. Closed-form expressions for the SNR gain of the quantized OBF proposal are derived. Important reductions in the amount of feedback overhead are observed without affecting the SNR gain considerably, when compared to CL TD techniques.

Opportunistic user allocation based on limited feedback information has been shown to offer significant enhancement for wireless multiple access communications. In this paper, theoretical analysis of user allocation in downlink orthogonal frequency division multiple access (OFDMA) with limited feedback is presented. The performances of resource allocation based on two feedback methods are analyzed and compared. We consider feedback based on the resource-wise SNR quantization and the ordered best-M feedback strategy, where the M best resources are informed to the transmitter. Exact bit error probability (BEP) expressions and analytical outage capacity calculus are presented for the both feedback strategies. Results indicate that significant allocation gain can be achieved with very limited feedback in wideband OFDMA systems. To achieve this allocation gain, we combine multiple resource selection and feedback strategies.

Theoretical outage capacity analysis for resource allocation in a downlink orthogonal frequency division multiple access (OFDMA) with limited feedback is presented. OFDMA system with practical resource fair round robin scheduler and erroneous feedback channel is considered. Two feedback methods are analyzed and compared. In the set best-M feedback method, the feedback word indicates the group of the M best resource units. The other feedback method is based on the resource-wise signal-to-noise ratio (SNR) quantization. Results indicate that the set best-M feedback scheme is attractive due to the low feedback overhead and significant allocation gain when few resource units are used and M les 3. The allocation based on the resource-wise one bit feedback outperforms the set best-M schemes especially with erroneous feedback at the cost of the larger feedback overhead.

We study the performance of fair physical layer schedulers that select a pair of orthogonal users for simultaneous transmission. The schemes rely on partial channel state information compatible with 3GPP specifications and differ with respect to their usage of channel quality indicator in scheduling decisions. Closed-form expressions for the achievable sum-rate of three practical scheduling algorithms are derived.

This work analyzes the outage probability of fair physical layer schedulers that select a pair of orthogonal users for simultaneous transmission. These schemes rest on finite-rate channel state information compatible with 3GPP specifications and differ with respect to their usage of channel quality indicator in scheduling decisions. Closed-form approximations for the outage probability of these practical transmission schemes are derived. Important outage capacity gains are observed when these multiuser scheduling strategies are compared to the scheme that transmits sequentially to only one user at a time.

Assuming a single bounce scattering geometric channel model with circularly symmetric scatter density we deduce a general integral relation between angle of arrival (AOA) and scatter density function. Then we show that this relation can be expressed in terms of an integral equation that admits an accurate numerical solution provided that AOA is known. Furthermore, we show that similar integral equation relation between time of arrival (TOA) and scatter density function can be efficiently solved numerically for a given TOA. Results indicate that the scatter density can be numerically computed for a given AOA or TOA. Since these marginal distributions can be directly fit in channel measurements, the method provides means to adjust the applied geometrical channel model through field measurements. Hence, we follow the idea of inverse scattering theory where the far field pattern of scattered waves is known and the aim is to define the structure of the scattering medium. We consider two example AOA distributions, Gaussian and Student's t-distribution, found in literature. Our results show that scatter densities as well as the corresponding TOAs greatly vary depending on the assumed AOA

We consider a Gaussian parallel relay network where multiple wireless relays forward cooperatively so that a destination receives a superposition of signals propagated through multiple distinct relay paths. Previous research often assumes that the relayed signals arrive synchronously in the receiver. This is not feasible in practical wireless networks, because spatial separation causes different propagation delays for the signal components and the destination observes a multipath channel. We model the effect of signal delays by introducing spatial separation to the network geometry and present trade-off analysis between diversity, signal bandwidth, relay density, and the number of relays for both narrowband and wideband reception at the destination

We show that channel-aware scheduling can significantly improve the capacity of CDMA uplink when compared to round robin scheduling. Using both analysis and simulations we quantify the capacity increase due to channel-aware scheduling in terms of reduction in intercell interference. The scheduling approaches can be used, e.g., within the current cdma2000 and WCDMA systems. Finally, we demonstrate that soft handover reduces the benefit from channel-aware scheduling and base station antenna gain properties are important for the scheduling performance

Previous works have shown that in case of multiple transmit antenna broadcast channels, the total system throughput can be greatly improved by combining spatial prefiltering (SP) with multiuser scheduling (MS) [G. Caire et al., 2003], [D. Samardzija et al., 2003]. However, most of the studies assume full channel state information at the transmitter (CSIT). In this paper, we study the achievable data rates within the current WCDMA HSDPA specification and present different schemes based on the WCDMA closed-loop transmit diversity (CLTD) modes. Although the achievable throughput is interference limited at high SNR due to partial CSIT, we show that at moderate power regimes a significant performance gain can be achieved by the proper combination of SP and MS concepts, compared to the systems that only transmit to the user with the best channel condition in each transmission time interval (TTI).

We compare the performance of three physical layer scheduling algorithms: round robin; transmit time selection diversity (TTSD); maximum SNR. With TTSD, downlink transmission is suspended if the instantaneously received SNR in the mobile station falls below a given threshold, which requires only one feedback bit per user; this considerably decreases the overhead of the feedback signaling when compared with a maximum SNR scheduler. In the case of FDD systems, TTSD and maximum SNR schedulers require a fast feedback channel from mobile to base station, like the one in the FDD WCDMA system. It is shown that, while the maximum SNR scheduler outperforms the other two schedulers when the feedback signaling is error-free, TTSD is better in the case of feedback bit errors. Furthermore, while orthogonal space-time coding does not improve the performance with channel aware schedulers when compared to single antenna transmission, it is shown that space-time coding makes the system more robust and gives gain in the case of feedback errors.

Several diversity techniques employing multiple antennas in the base station have been developed for mobile communication systems. However, the performance of diversity methods strongly depends on the correlation between antenna elements. When multiple copolarized antennas are used in base station, the practical factor limiting the number of diversity branches is the required antenna separation, because large antenna separation makes the antenna array unfavourable large while small antenna separation may result in high correlations between the antennas. Therefore, dual-polarized antennas are commonly used to implement two diversity branches. If more than two diversity branches are needed, spatially separated dual-polarized antennas provide an attractive solution alternative. In this paper we propose a model for calculating the correlations between the cross and copolarized antennas when employing spatially separated dual-polarized antennas with nominal /spl plusmn/45/spl deg/ inclination to vertical linear polarization. Results are of theoretical nature and show the relationship between base station antenna correlations and the properties of the physical channel, base station, and mobile station antennas.

We examine a two-rate communication system where the transmission is suspended if the received SNR falls below a given threshold. We assume an FDD system and derive novel closed-form bit error probabilities in the presence of feedback errors in flat Rayleigh fading environment for single antenna transmission, orthogonal space-time block coding and transmit antenna selection. A single-user two-rate system would result in an infrequent use of the channel and long delays, but combined with a physical layer multiuser scheduler like in the high speed downlink packet access scheme included in the 3GPP WCDMA Release 5 specification the overall channel utilization can be improved.

We examine site selection diversity transmission (SSDT) for 3GPP WCDMA forward link by means of analytical tools. Hard handover (HHO), soft handover (SHO) and SSDT are compared by using the receiver bit error probability as a performance measure taking into account the effect of feedback bit errors as well as the shadow fading. Results show that without fast transmission power control the performance gain from SSDT can be seriously degraded by feedback bit errors.

Transmit diversity techniques have received a lot of attention recently, and open-loop and closed-loop downlink transmit diversity modes for two transmit antennas have been included in the 3GPP WCDMA Release 5. System capacity can be increased from that of open-loop modes if the transmitter can be provided additional side information of the downlink channel. In a frequency division duplex (FDD) system this requires a separate feedback channel. Quantization of the feedback messages in closed-loop transmit diversity schemes reduces the performance of the system. However, this effect has not been usually taken into account in the analysis. In this paper we analyze the effect of quantization and deduce an analytic formula for the asymptotic bit error probability of the closed-loop transmit diversity schemes defined in 3GPP WCDMA specification.

Transmit diversity techniques have received a lot of attention recently, and open-loop and closed-loop downlink transmit diversity modes for two transmit antennas have been included in 3GPP WCDMA release 4. System capacity can be increased from that of open-loop modes if the transmitter is equipped with additional side information of the downlink channel. In a frequency division duplex system, this means that the receiver has to provide the information through a feedback mechanism. We study the performance loss caused by feedback errors using the bit error probability as a performance measure. It is shown that the asymptotic diversity of closed-loop schemes is reduced to one in the presence of feedback errors, i.e., the performance is similar to a single transmit antenna system with some SNR gain. The proof is given in a very general manner and it is valid for a large variety of feedback schemes. Two example schemes, selection and cophasing algorithms, are discussed in more detail to verify the results.

Transmit diversity techniques provide attractive solutions for increasing downlink capacity in 3G systems within low-mobility environments. Open-loop and closed-loop transmit diversity modes with two transmit antennas have already been included in 3GPP WCDMA Release 4, and at the moment schemes exploiting a larger number of transmit antennas are being developed. This paper analyzes the performance of a simple closed-loop transmit diversity scheme suitable for 3GPP WCDMA. The goal is to study the effect of different feedback delays on the performance of the given closed-loop scheme. Although the analysis applies only in the case of the specific algorithm (phase-only feedback) it is expected that the performance of the more general magnitude and phase feedback shows similar properties. We use signal-to-noise ratio (SNR) gain as a performance measure, which corresponds to the gain in expected received SNR in a mobile terminal when feedback information from the receiver is applied in the transmitter.