Future wireless connectivity is envisioned to accommodate functionalities far beyond broadband data transmission over point-to-point direct links, enabling novel scenarios, such as communication behind blockers and around corners, and innovative concepts, such as situational awareness, localization, and joint communications and sensing. In this landscape, beams that are able to propagate on bent paths are ideal candidates for dynamic blockage avoidance, interference management in selected regions, and user connectivity on curved trajectories. In this work, we study beam shaping for applications in near-field wireless connectivity. We explain the underlying mechanism of beam bending and we present the design principles for tailoring the curvature of the propagation trajectory. We discuss design aspects for the generation of such beams with large arrays and analyze the impact of several parameters on their performance, including the beam’s footprint shape, the aperture size, the inter-element spacing, the sub-array selection of active elements, the available phase levels of the array elements and the operating frequency. We introduce the concept of near-field virtual routing (NFVR) and we demonstrate that such beams are able to address challenges of high-frequency communications, such as dynamic routing, blockage avoidance, and energy-efficiency more efficiently than conventional beamforming.

It is true that medical diagnosis and treatment have always been at the top of research activities. Recently, a very promising area that combines the operation of human body with the principles of wireless communications has arisen and given birth to the field of bio-photonics. Although the deployment of nano-networks inside the human body seems to be an achievable goal, the implementation of optical wireless nano-networks remains a very challenging field due to the lack of accurate channel modeling. Therefore, in this paper, we comprehensively investigate the optical wireless nano-communication channels by considering the deterministic geometric losses (e.g., optical absorption and scattering in human tissues), and modeling the impact of nano-node disorientation and misalignment in in-body nano-networks. To this end, we analytically study the stochastic nature of disorientation and misalignment coefficient in terms of the position and orientation of the nano-node with reference to the out-of-body optical receiver. In particular, we study the statistics of the joint disorientation and misalignment coefficient in terms of the probability density function, which is given in closed-form expression, whereas its cumulative distribution function is introduced as a semi-infinite series expression. Building upon them, we extract novel analytical expressions for the average signal-to-noise-ratio and the outage probability, and a thorough study on the impact of the human tissues on the above performance metrics is conducted. The analytical results are corroborated and cross-compared by means of Monte Carlo simulations, which reveal the importance of accounting for the joint impact of disorientation and misalignment of nano-node when designing optical wireless nano-networks.

A Reconfigurable Intelligent Surface (RIS) redirects and possibly modifies the properties of incident waves, with the aim to restore non-line-of-sight communication links. Composed of elementary scatterers, the RIS has been so far treated as a collection of point scatterers with properties similar to antennas in an equivalent massive MIMO communication link. Despite the discrete nature of the RIS, current design approaches often treat the RIS as a continuous radiating surface, which is subsequently discretized. Here, we investigate the connection between the two approaches in an attempt to bridge the two different perspectives. We analytically find the factor that renders the two approaches equivalent and we demonstrate our findings with examples of RIS elements modeled as antennas with commonly used radiation patterns and properties consistent with antenna theory. We analyze the equivalence between the two theoretical approaches with respect to design aspects of the RIS elements, such as gain, directivity and coupling between elements, with the aim to provide insight into the observed discrepancies, the understanding of which is crucial for assessing the RIS efficiency.

The design of Reconfigurable Intelligent Surfaces (RISs) is typically based on treating the RIS as an infinitely large surface that steers incident plane waves toward the desired direction. In practical implementations, however, the RIS has finite size and the incident wave is a beam of finite k-content, rather than a plane wave of$\delta $-like k-content. To understand the implications of the finite extent of both the RIS and the incident beam, here we treat the RIS as a spatial filter, the transfer function of which is determined by both the prescribed RIS operation and the shape of the RIS boundary. Following this approach, we study how the RIS transforms the incident k-content and we demonstrate how, by engineering the RIS shape, size, and response, it is possible to shape beams with nontrivial k-content to suppress unwanted interference, while concentrating the reflected power to desired directions. We also demonstrate how our framework, when applied in the context of near-field communications, provides the necessary insights into how the wavefront of the beam is tailored to enable focusing, propagation with invariant profile, and bending, beyond conventional beamforming.

This paper presents a quantified assessment of the physical layer security capabilities of reconfigurable intelligent surface (RIS)-aided wireless systems under eavesdropping. Specifically, we derive a closed-form expression for the ergodic secrecy capacity (ESC) that is adaptable to different types of fading and RIS size. The channels between the transmitter (TX) and RIS, the RIS and legitimate receiver as well as the TX and eavesdropper are assumed to follow independent mixture Gamma (MG) distributions. Note that MG is capable of modeling a large variety of well-known distributions, including Gaussian, Rayleigh, Nakagami-m, Rice, and others. The results reveal that as the RIS size increases, although the legitimate links diversity order increases, the ESC gain decreases.

Targeting ultra-reliable and scalable connectivity of extremely high data rates, in the 100 Gbps to Tbps range, at almost “zero-latency” in 6G systems would require taking advantage of breakthrough novel technology concepts, including THz wireless links, broadband and spectrally efficient RF-frontends for a variety of different bands, the employment of intelligent materials (e.g., reconfigurable intelligent surfaces) and the design of machine learning-based models, protocols, and management techniques. To materialize the 6G vision, novel system techniques will need to be devised, including channel modeling and estimation, waveforms, beamforming, and multiple-access schemes, all tailored to the particularities of the adopted breakthrough technologies. As challenging Tbit/s usage scenarios are becoming ever more relevant for 6G systems, including non-line of sight connectivity based on intelligent surfaces and ad hoc connectivity in fast-moving network topologies, e.g., based on drones or V2X links, performance targets need to be reassessed. In such scenarios, apart from the high data rates in the order of Tbit/s other critical parameters may arise as more relevant: range, reliability, adaptability, reconfigurability, and agility, to name just a few.

Reconfigurable intelligent surface (RIS)-assisted unmanned areal vehicles (UAV) communications have been identified as a key enabler of a number of next-generation applications. However, to the best of our knowledge, there is no generalized framework for the quantification of the throughput performance of RIS-assisted UAV systems. Motivated by this, in this paper, we present a comprehensive system model that accounts the impact of multi-path fading, which is modeled by means of mixture gamma, transceiver hardware imperfections, and stochastic beam disorientation and misalignment in order to examine the throughput performance of a RIS-assisted UAV wireless system. In this direction, we present a novel closed-form expression for the systems throughput for two scenarios: i) in the presence and ii) in the absence of disorientation and misalignment. Interestingly, our results reveal the importance of accurate modeling the aforementioned phenomena as well as the existence of an optimal transmission spectral efficiency.

In this paper, we analyze the performance of holographic surface assisted wireless systems that employ non-orthogonal multiple access (NOMA) approaches. In this direction, we present a comprehensive system model that captures the particularities of holographic surfaces as well as the impact of multipath fading. Building upon the system model, we quantify the outage performance of the downlink scenario, by providing novel closed-form expressions for its outage probability. Simulation results validate the authenticity of the presented analysis, illustrate the performance gain of the proposed NOMA scheme over conventional orthogonal multiple access schemes and reveal the feasibility and efficiency of the proposed approach.

In this paper, we introduce a theoretical framework for analyzing the performance of multi-reconfigurable intelligence surface (RIS) empowered terahertz (THz) wireless systems subject to turbulence and stochastic beam misalignment. In more detail, we extract a closed-form expression for the outage probability that quantifies the joint impact of turbulence and misalignment as well as the effect of transceivers’ hardware imperfections. Our results highlight the importance of accurately modeling both turbulence and misalignment when assessing the performance of multi-RIS-empowered THz wireless systems.

This contribution aims at experimentally validating the suitability of Gaussian mixture (GM) distributions to capture the stochastic characteristics of outdoor terahertz (THz) wireless channels. In this direction, we employ a machine learning enabled approach, based on the expectation maximization algorithm, in order to identify the suitable number of Gaussian distributions as well as their corresponding parameters that result to an acceptable fit. The fitting accuracy of the GMs to the empirical distributions is evaluated by means of the Kolmogorov-Smirnov (KS), Kullback-Leibler (KL), root-mean-square-error (RMSE) and R2fitting accuracy tests. These tests verify the suitability of GMs to model the small-scale fading channel amplitude of outdoor THz wireless links. In addition, the fitting accuracy results indicate that as the number of mixtures increases the resulting GMs achieve a better fit to the empirical data.

In this paper, we examine the potential for a reconfigurable intelligent surface (RIS) to be powered by energy harvested from information signals. This feature might be key to reap the benefits of RIS technology’s lower power consumption compared to active relays. We first identify the main RIS power-consuming components and then propose an energy harvesting and power consumption model. Furthermore, we formulate and solve the problem of the optimal RIS placement together with the amplitude and phase response adjustment of its elements in order to maximize the signal-to-noise ratio (SNR) while harvesting sufficient energy for its operation. Finally, numerical results validate the autonomous operation potential and reveal the range of power consumption values that enables it.

This paper presents an analytical pathloss model for reconfigurable intelligent surface (RIS) assisted terahertz (THz) wireless systems. Specifically, the model accommodates both the THz link and the RIS particularities. Finally, we derive a closed-form expression that returns the optimal phase shifting of each RIS reflection unit. The derived pathloss model is validated through extensive electromagnetic simulations and is expected to play a key role in the design of RIS-assisted THz wireless systems.

This work investigates the suitability of α–µ distribution to model line-of-sight (LoS) and non-line-of-sight (NLoS) multi-path fading in terahertz (THz) wireless systems. The goodness of fit of α–µ to the small-scale fading of the measured channels is evaluated in terms of the Kolmogorov-Smirnov (KS) test. The KS test revealed the capability of α–µ distribution to capture the fading characteristics of THz wireless channels. To highlight the importance of this study and the applicability to the theoretical analysis of THz wireless systems, for indicative values of α and µ, the ergodic capacity of THz wireless systems is assessed.

Future wireless networks are expected to be highly assisted by reconfigurable intelligent surfaces (RIS) in non-line-of-sight links. The role of the RIS is to redirect the incident beam from the transmitter to the receiver and possibly modify its characteristics, in order to maximize the signal power at the receiver and optimize the beamforming efficiency. Therefore, it is crucial to understand what are the bounds imposed on the received power and how these bounds depend on the system design parameters. In this paper we show that there is an interplay between the transmitter beamwidth and the RIS size that leads to a maximum power at the receiver. We demonstrate our findings with numerical examples that provide insight on the effect of the RIS size on the received signal power.

The primary role of a reconfigurable intelligent surface (RIS) is to restore the propagation path between the access point (AP) and the user equipment (UE) in a non-line-of-sight communication link. Depending on the RIS placement with respect to the AP and UE positions, different power levels can reach the UE, thus affecting the quality of the communication. Particularly when the UE moves freely, the RIS position that maximizes the received signal will depend strongly on the UE location. In this context, we use an analytical model to assess the decisions that have to be made concerning the positioning of the RIS, which are determined by the interplay of three crucial quantities, namely (a) the available AP gain, (b) the available positions for the AP and RIS placement, and (c) the minimum desired power levels at the UE. The impact of the AP antenna gain tunability on the RIS placement selection is assessed and illustrated in D-band indoor scenarios.

This paper focuses on quantifying the outage performance of terahertz (THz) relaying systems. In this direction, novel closed-form expressions for the outage probability of a dual-hop relaying systems, in which both the source-relay and relay-destination links suffer from fading and stochastic beam misalignment, are extracted. Our results reveal the importance of taking into account the impact of beam misalignment when characterizing the outage performance of the system as well as when selecting the transmission frequencies.

This paper presents the theoretical framework for the performance evaluation of terahertz (THz) wireless fiber extender in the presence of misalignment and multipath fading. In more detail, after providing the appropriate system model that incorporates the different operation, design, and environmental parameters, such as the operation frequency, transceivers antenna gains, the level of misalignment as well as the stochastic behavior of the channel, we extract novel closed-form expressions for the ergodic capacity. These expressions are expected to be used as useful tools for the analysis and design of such systems. Moreover, several insightful scenarios are simulated. Their results highlight the importance of taking into account the impact of misalignment fading when analyzing the performance of the THz wireless fiber extender.

In this paper, we provide the mathematical framework to evaluate and quantify the performance of wireless systems, which employ beamforming, in the presence of hardware imperfections at both the basestation and the user equipment. In more detail, by taking a macroscopic view of the joint impact of hardware imperfections, we introduce a general model that accounts for transceiver impairments in beamforming transmissions. In order to evaluate their impact, we present novel closed form expressions for the outage probability and upper bounds for the characterization of the system's capacity. Our analysis reveals that the level of imperfection can significantly constraint the ergodic capacity. Therefore, it is important to take them into account when evaluating and designing beamforming systems.

In this paper, a novel cooperation-aided localization and tracking approach, suitable for terahertz (THz) wireless systems is presented. It combines an angle of arrival (AoA) tracking algorithm with the two-way time of arrival method, in order to accurately track the user equipments (UE) position and reduce the deafness caused by the estimation errors of the tracking algorithms. This algorithm can be used by one base station (BS) to estimate the UEs position, or by multiple BSs, that cooperate with each other to increase the accuracy of the estimations, as well as the probability of successful estimations and guarantee low-estimation overhead. The efficiency of the algorithm is evaluated in terms of deafness and probability of successful AoA estimation and is compared with the corresponding performance of the fast channel tracking algorithm.

In this paper, we present a novel two-path channel model for wireless terahertz (THz) systems operating in the range of 275 to 400 GHz, which accommodates both the channel particularities and the transceivers parameters. The channel particularities include the frequency selectivity, path-loss, as well as the atmospheric conditions, namely temperature, relative humidity and pressure, while the transceiver parameters, which are taken into account, are the antenna gains as well as the power of the transmitted signal. Finally, we evaluated the THz system performance in terms of average signal to noise ratio and ergodic capacity.

In this paper, we establish an appropriate system model for the terahertz (THz) wireless links in the range of 275 to 400 GHz, which accommodates the channel particularities and transceivers parameters. The former includes the frequency selectivity, pathloss, as well as the atmospheric conditions, namely temperature and pressure, whereas the latter are assumed to be consisted of the antenna gains as well as the power allocation of the transmitted signal. Moreover, we present analytical expressions of low computational complexity, for the evaluation of the average SNR, and capacity of the line of sight wireless THz links. These expressions are expected to be the key tools for the design of the THz link.

Advances in cellular networks such as device-to-device communications and full-duplex radios, as well as the inherent elimination of intra-cell interference achieved by network-controlled multiple access schemes, motivate the investigation of the cross-mode interference properties under a guard region corresponding to the Voronoi cell of an access point (AP). By modeling the positions of interfering APs and user equipments (UEs) as Poisson distributed, analytical expressions for the statistics of the cross-mode interference generated by either APs or UEs are obtained based on appropriately defined density functions. The considered system model and analysis are general enough to capture many operational scenarios of practical interest, including conventional downlink/uplink transmissions with nearest AP association, as well as direct communication between UEs that do not necessarily lie in the same cell. Analysis provides insights on the level of protection offered by a Voronoi guard region and its dependence on type of interference and receiver position. Numerical examples demonstrate the validity/accuracy of the analysis in obtaining the system coverage probability for operational scenarios of practical interest.

Recent trends in wireless networking such as small cells and network function virtualization, strongly suggest that the future cellular network will consist of many sub-networks controlled by self-interest operators competing for a share of the revenues associated with the high demand for service. This paper attempts to analyze the future network performance under these new market conditions, taking into account not only engineering properties of the sub-networks, e.g., spectral efficiency, but economic properties as well, i.e., service pricing. Going beyond previous related works, large scale infrastructure deployments over wide geographical areas, targeting a large number of users, are explicitly considered. The focus of the analysis is on the effects of different deployment densities (in units of average number of small cells per unit area) among competing operators as well as random placement of small cells. A game-theoretic system analysis is employed with market equilibrium characterization obtained analytically for the practical cases of two competing operators with arbitrary network characteristics and multiple competing operators with similar network characteristics. Closed form expressions for user and operator utilities at equilibrium are provided, revealing, among others, that extreme infrastructure densification, even though desirable from a purely engineering perspective, may not lead to stable market conditions under the considered competition model.

An important enabler towards the successful introduction of any new element/feature to the cellular network, such as the ability to allow for direct, device-to-device (D2D) communications, is the investigation and characterization of the operational conditions, e.g., density of users, where its deployment will enhance performance. This paper attempts to provide a mathematically rigorous characterization of the set (region) of operational conditions, for which overlay D2D communications enhance performance in terms of average user rate. Using tools from stochastic geometry, and for the practically interesting case of a heavy loaded network, the operational region is identified in closed form as a function of a variety of parameters reflecting a wide range of operational conditions. It is shown that, under the appropriate deployment scheme, D2D communications can be beneficial not only in the typically assumed regime of “proximal communications” but to a wide range of operational conditions that include D2D link distances comparable to the distance from the cellular access point(s) as well as significantly large user densities.

An important enabler towards the successful deployment of any new element/feature to the cellular network is the investigation and characterization of the operational conditions where its introduction will enhance performance. Although there has been significant research activity on the potential of device-to-device (D2D) communications, there are currently no clear indications of whether D2D communications are actually able to provide benefits for a wide range of operational conditions, thus justifying their introduction to the system. This paper attempts to fill this gap by taking a stochastic geometry approach on characterizing the set (region) of operational conditions for which D2D communications enhance performance in terms of average user rate. For the practically interesting case of a heavy-loaded network, the operational region is provided in closed form as a function of a variety of parameters such as maximum D2D link distances and user densities, reflecting a wide range of operational conditions (points). It is shown that, under the appropriate deployment scheme, D2D communications can indeed be beneficial not only for the usually considered regime of “proximal communications” but to a wide range of operational conditions that include D2D link distances comparable to the distance to the cellular access point and considerably large user densities.

This paper examines the efficiency of spatial and frequency dimensions in serving multiple users in the downlink of a small cell wireless network with randomly deployed access points. For this purpose, the stochastic geometry framework is incorporated, taking into account the user distribution within each cell and the effect of sharing the available system resources to multiple users. An analysis of performance in terms of signal-to-interference-ratio and achieved user rate is provided that holds under the class of non-cooperative multiple access schemes. In order to obtain concrete results, two simple instances of multiple access schemes are considered. It is shown that performance depends critically on both the availability of frequency and/or spatial dimensions as well as the way they are employed. In particular, increasing the number of available frequency dimensions alone is beneficial for users experiencing large interference, whereas increasing spatial dimensions without employing frequency dimensions degrades performance. However, best performance is achieved when both dimensions are combined in serving the users.

This paper examines the impact of system parameters such as access point density and bandwidth partitioning on the performance of randomly deployed, interference-limited, dense wireless networks. While much progress has been achieved in analyzing randomly deployed networks via tools from stochastic geometry, most existing works either assume a very large user density compared to that of access points, which does not hold in a dense network, and/or consider only the user signal-to-interference-ratio as the system figure of merit, which provides only partial insight on user rate as the effect of multiple access is ignored. In this paper, the user rate distribution is obtained analytically, taking into account the effects of multiple access as well as the SIR outage. It is shown that user rate outage probability is dependent on the number of bandwidth partitions (subchannels) and the way they are utilized by the multiple access scheme. The optimal number of partitions is lower bounded for the case of large access point density. In addition, an upper bound of the minimum access point density required to provide an asymptotically small rate outage probability is provided in closed form.

Network densification with universal resources reuse is regarded as a possible solution to increase capacity and deal with the “1000x” mobile data challenge in future 3GPP radio access networks. Interference is the major performance limitation is such networks, and global coordination of coexisting transmissions comprises the technology enabler for achieving high performance levels. In this work we consider large distributed networks of low-cost infrastructure nodes, such as small-cells or simply access points. We explore optimal and efficient strategies for selecting the serving access point for each user (access point/user pairing) and tuning the transmission power per communication link, in order to achieve uniform quality-of-service levels across the whole network. For this purpose, we reformulate the original intractable joint pairing and power optimization problem, leveraging the powerful integer linear programming optimization framework. We also propose lower-complexity coordination algorithms by decoupling the pairing and power allocation sub-problems. We evaluate the proposed algorithms performance in large dense access networks and we demonstrate how to guarantee specific rates over increased user population by infrastructure densification and network resources coordination.

In this paper, we present a machine to machine (M2M) communication scheme, where the source communicates with the corresponding destination node with the help of one or more relay nodes. The objective is to minimize the total consumed power at the relays under specific performance constraints, while also considering the individual power limitations of each relay. In order to solve the original problem, we transform into an equivalent convex optimization problem. Simulations results are provided to validate the theoretical analysis and to illustrate the desired tradeoff between error performance and total energy consumption.

In the evolution of wireless systems to the next generation, it is becoming increasingly important to offer substantial improvements, not only in terms of peak and average cell rates but also in terms of outage performance. To this end, interference management by means of coordination between different base stations and coverage/capacity improvements by means of cooperation with relays are considered potential candidate technologies. The introduction of multiuser MIMO processing principles and cross-layer optimized resource allocation may offer promising performance gains for coordination and cooperation but their feasibility depends on overhead signaling constraints and system deployment assumptions. In this paper, we present two realistic approaches for coordination and cooperation, analyze their performance merits and discuss their complexity requirements.

In this paper we propose a two-step distributed scheduling algorithm for relay-assisted cellular networks where a given user can be either served by the base station or by a relay, in a opportunistic way. Such a distributed approach allows a reduced feedback signaling with respect to the centralized case, especially when a simple scalar feedback is not sufficient for estimating the channel quality. As a result of the reduced feedback signaling requirements the system becomes more scalable, as new relays can be deployed where required without need of a careful network planning. We study the effectiveness of the proposal by means of a multicell simulator.

Herein, we present a novel approach for decode-forward relay transmissions using multiple antennas. In this approach, multiple independent spatial data streams are sent to the destination directly and/or through different relays simultaneously, where the relays are selected in an opportunistic way. We show the efficiency of the proposed approach through simulations.

In this paper, the design of a highly efficient and flexibly deployable wireless backhaul is addressed as a promising alternative to the typical wired solutions. To this end, a novel approach for relay transmissions with multiple antennas is proposed in the framework of wireless meshed backhaul system design optimization. The link and system level performance are assessed and different mesh topologies and relaying protocols are investigated. The optimality of the approach relies on the reconfigurable /adaptive use of the degrees of freedom offered by the combination of multiple antennas and relays and is promising for both wireless backhaul and access applications.

Future wireless systems are expected to support high data rates of 1 Gbit/s or more in a variety of scenarios. A key technology in order to achieve the required high spectral efficiency is the application of multiple input multiple output (MIMO) techniques, which exploit spatial diversity, array gain or spatial multiplexing gain. Another source of diversity - inherent to wireless systems- is that of the multiuser diversity. Multiuser (MU) MIMO algorithms combine both MIMO gains with multiuser diversity benefits. Although MU MIMO techniques have been extensively studied and were shown to provide considerable average cell throughput gains, they often prove inadequate to cope with intercell interference and can only offer poor cell edge performance. Network coordination (multisite MIMO) can be applied in this case, which can achieve significant improvements for the users including those at the cell edge, based on coordinated transmission and reception by multiple base stations. In this paper we present an overview of the most promising MIMO technologies and discuss their relative merits and requirements.

We consider the problem of designing the vector quantizer for a multiuser eigenmode transmission applied to a MIMO broadcast channel with limited feedback. We propose a hierarchical vector quantization method based on the idea that the CDI can be refined by permitting multiple feedback steps between receivers and transmitter. At each new quantization level a new codebook is built based on the codebook and on the best codeword at the previous level. We firstly give a general definition of a hierarchical quantizer. Then we build a hierarchical quantizer based on the Fourier codebook. Finally, we propose an algorithm for implementing the hierarchical quantization principle. The proposed algorithm improves the channel quantization quality if the channel vector remains almost constant during different feedback steps, whereas allows backward steps to lower levels, in order to track channel variations. Simulations comparison with respect to the Fourier codebook and to the random vector quantization technique, confirm the effectiveness of the proposed approach.

Herein, we present a novel approach for high data rate transmission in a wireless relay network. The system include a source, a destination and multiple relays. All nodes are equipped with multiple antennas. A half-duplex transmission protocol and a decode-forward transmission mode are deployed in the system. Our approach splits the data at the source into multiple independent data streams, and send them to the destination via some selected relays at the same time. The relays are selected using an opportunistic approach based on spatially decomposing the channels and accessing the best modes. Simulation results show the benefits of our technique, particularly with correlated channels.

In order to account for spatial correlation in a multiple input multiple output (MIMO) channel using precoding over space-time block codes (STBC), an approach was proposed for the design of a linear precoder (H. Sampath and A. Paulraj, 2002). This approach works well for orthogonal STBC but fails in the case of non-orthogonal STBC. Based on a min-max problem formulation, a new design of the linear precoder is proposed in this paper. Simulation results in the case of quasi-orthogonal STBC (ABBA) are presented in order to show the gain over the conventional design approach and the non-precoded system

Packet scheduling techniques exploiting multiuser diversity have been proposed in order to improve the throughput of high speed packet systems. However, the use of techniques that take the scheduling decisions based only on the channel conditions, may fail to provide the desired QoS, as the maximum allowable delay is an important parameter, and therefore algorithms aiming at providing QoS should combine QoS related parameters with the channel conditions. In this paper we consider two algorithms that address this issue. One algorithm has been developed D. Avidor et al., (2004) to improve the opportunistic beamforming technique by tying the sequence of radiation patterns with the waiting times of the served mobiles, while the other weights the waiting times and channel reliability to schedule the packets while using beamforming to spatially reuse the radio resources in a CDMA scheme. We show through simulations that such schemes lead to reduced probability of excess delay while keeping a high throughput

This paper gives an overview of some so-called link performance models used in system level simulations to determine the link packet error rate (PER) at reduced complexity. A subset of link performance models is evaluated in terms of PER prediction accuracy focusing on a single receive and transmit antenna OFDM link with different coding options and channel characteristics. The results demonstrate that a mutual-information based metric which accounts for the modulation alphabet is preferable in the considered cases and, furthermore, applicable to the large class of MIMO-OFDM transmission techniques with linear pre- and post-processing.

The presence of strong channel correlations reduces the amount of the available diversity in the multiple input multiple output (MIMO) channel, leading to performance degradation. These correlations are long-term statistics that the transmitter can obtain either by exploiting channel reciprocity or by low-rate feedback from the receiver. In order to account for this correlation, a linear precoding technique has been proposed for the adaptation of space-time block codes (STBC). This technique works well for orthogonal STBC but fails in the case of non-orthogonal STBC. In this paper, we present the adaptation of linear precoding to non-orthogonal STBC. Simulations in the case of ABBA codes are provided and comparisons are performed with respect to beamforming

Abstract Coexistence of different access technologies, hierarchical cellular deployment, a wide variety of data services, requirements for transparent operation across different technologies, adaptivity to varying network conditions and mobility and quality of service (QoS) constraints introduce a number of challenges in the design of future generation systems and the specification of new air interfaces, such as efficiency and flexibility in the utilization of spectrum, dynamic resource allocation and exploitation of the multiuser diversity and reconfigurable interference management and inter‐cell coordination. In this paper, three critical issues for the design of next generation systems are addressed: (i) duplexing, (ii) scheduling and resource allocation and (iii) interference and inter‐cell coordination. A number of research directions are presented, which constitute promising potential candidates for next generation systems specification. Copyright © 2005 John Wiley & Sons, Ltd.

In this paper the system level performance of an HSDPA (high speed downlink packet access) MIMO network, which combats the effects of antenna correlation by applying novel reconfigurable techniques is investigated. Reconfigurability is achieved at the link level by applying a linear precoding scheme at the transmitter space-time block encoder. An appropriate link to system interface has been developed, taking into account the linear precoding technique. The system level performance metrics of interest are the average system throughput and the number of satisfied users. Simulation results are presented in order to demonstrate the performance enhancements achieved by the application of reconfigurable techniques compared to the conventional ones.