In this study, the physical layer (PHY) security performance of orthogonal space‐time block coding (OSTBC) employing a coordinate interleaved orthogonal design (CIOD) is analysed and investigated using two metrics: average secrecy capacity and secrecy outage probability. It is shown that the CIOD system is superior than OSTBC in terms of secrecy outage probability. Closed‐form expressions for PHY security metrics in OSTBC as well as CIOD are presented and compared. Then, an extended model of CIOD with arbitrary number of antennas is considered. Furthermore, the effects of artificial noise and imperfect channel estimation on PHY security of OSTBC and CIOD systems are investigated. The validity of theoretical expressions is verified by simulation, and it is shown that in practical cases the CIOD system has a better secrecy outage performance than that of the OSTBC system.

The main objective of this study consists in reducing the correlated background radiations along with minimising the bit error rate (BER) for a multiple aperture free‐space optical (FSO) communication system based on differential signalling scheme. Instead of performing the conventional equal gain combining (EGC) of the two wavelengths, here, the authors propose to efficiently combine them at the receiver by using non‐equal channel‐dependent weighting factors. To this aim, they first derive the analytic expression of the BER of the considered system, which is necessary for optimising the background radiations. Second, by considering ON–OFF keying modulation, they optimise the decision threshold and the weighting factors of the two wavelength by minimising the BER. The performance merit of the proposed scheme is contrasted to the zero threshold scheme and to the EGC scheme in terms of the average BER, the average signal‐to‐noise ratio (SNR) and the background rejection at the receiver. They show that the proposed scheme can improve the SNR up to 17 dB, based on the correlation coefficient of the background radiations at two wavelengths. Moreover, simulation results confirm the superiority of the proposed scheme in terms of achievable BER compared to the aforementioned conventional methods.

Physical layer (PHY) security is an important issue in wireless communication systems. In this study, the authors investigate the interactions between the PHY security performance and the spectrum access technique in a cooperative cognitive radio (CR) network. In the classical spectrum access, if the measured energy on a given subchannel is less than a threshold, the subband is dedicated for CR transmission. Here, they consider a probabilistic spectrum access (PSA), which assigns to each primary subchannel a probability which is determined according to the measured energy on that subchannel. In addition, both spectrum access and CR power allocation are performed simultaneously. They formulate the general outage probability and some important PHY security performance metrics, such as average secrecy rate, secrecy outage probability, and probability of positive secrecy rate in terms of the spectrum access and optimal power allocation functions. The authors' numerical analysis indicates that the PSA method achieves a superior PHY security and outage performance compared to the classical threshold‐based spectrum sensing and power allocation method.

In this study, a fair user‐scheduling method is considered for an underlay cognitive radio system, in which the secondary users (SUs) are sharing the licenced frequency spectrum of a single primary user (PU), where the PU and SUs utilise Alamouti orthogonal space‐time block coding (OSTBC). The impacts of some important practical issues are investigated in the system. First, it is assumed that the signal‐to‐noise‐ratios of the SUs are independent non‐identically distributed. Second, the transmit antennas for OSTBC corresponding to the SUs are assumed to be equally correlated. Third, the interference from the PU to SUs as well as the interferences from SUs to the PU are taken into consideration. To investigate the outage performance of the SUs, a closed‐form expression for the cumulative distribution function of the SUs signal‐to‐interference‐noise‐ratio is obtained and then used to derive an expression for evaluating the secondary system outage performance. The numerically evaluated results, validated by computer simulations, provide insights about system outage performance under various practical situations on the impacts of the spatial antennas correlation and the PU interference on to SUs.

This study presents an analysis for evaluating the physical layer (PHY) security performance of a two‐hop amplify‐and‐forward cooperative relaying system employing Alamouti orthogonal space–time block coding (OSTBC) in the presence of an eavesdropper, where the transmit antennas for OSTBC are assumed to be spatially correlated. It is also assumed that the authorised main channels as well as the non‐authorised eavesdropper channels follow Rayleigh fading distribution. Closed‐form mathematical expressions are derived for three performance metrics for evaluating the PHY security, namely the probability of non‐zero secrecy capacity, the secrecy outage probability, and the average secrecy capacity. Using the extensive numerical results obtained from the derived mathematical expressions, the impact of antennas correlation on the PHY secrecy performance of the system is studied and evaluated under different parameters. It is also shown that the antennas correlation corresponding to the main channels has more impact than the antennas correlation corresponding to the eavesdropper channels.

Performance degradation in analog circuits due to layout dependent effects (LDEs) has become increasingly challenging in advanced technologies. To address this issue, LDEs have to be seriously considered as performance constraints in the physical design process. In this article, we have proposed an innovative LDE-aware retargeting methodology for analog layout migration from old technologies to new ones with LDEs optimized for performance preservation. The LDE constraints, which are first identified with the aid of a specialized sensitivity analysis scheme, are satisfied during the layout migration process. Moreover, optical proximity correction (OPC), as one of the most popular resolution enhancement techniques for subwavelength lithography in modern nanometer technology manufacturing, is also included in this study. We have developed an OPC-inclusive ILP-based analog router to route electrical nets for improving image fidelity of the final layout while the routability and other analog constraints are respected in the meantime. The experimental results show our proposed layout migration methodology along with the routing scheme is able to retarget analog layouts with better circuit performance and finer image quality compared to the previous works.

The authors propose an optimal joint power control and multi‐band spectrum sensing scheme for cognitive radio (CR) systems to increase the spectral efficiency and to overcome the spectrum‐sensing errors, in the presence of primary user emulation attacker (PUEA). This optimisation problem is solved to maximise the opportunistic CR data rate under interference and power budget constraints. To solve the formulated optimisation problem, they convert it to a convex problem, and then derive an optimal strategy for joint power control and spectrum access in the considered CR system. They show that the optimal strategy follows a quasi‐underlay signaling, which is equipped with spectrum sensing. They evaluate the performance of the optimised scheme for the CR system in the presence of PUEA, and compare it with the conventional underlay scheme. For more comparison, they compare the proposed approach to that of a similar system, which does not consider the PUEA in the formulation of the joint spectrum sensing and power allocation. They show that the proposed optimal joint power control and spectrum sensing can significantly improve the system performance in terms of average achievable CR data rates compared with the considered conventional methods.

This study presents an analysis for a cross‐layer design of a combined adaptive modulation and coding (AMC) with a truncated automatic repeat request (T‐ARQ) scheme in an underlay spectrum sharing cognitive radio employing an amplify‐and‐forward cooperative relaying system. The considered AMC employs a coded M‐ary quadrature amplitude modulation scheme combined with a T‐ARQ to improve the performance of the secondary user (SU) system in the considered cognitive radio. To establish the performance analysis, the cumulative distribution function (CDF) of the end‐to‐end signal‐to‐noise‐ratio at the receiver side of the SU system is derived. Then, using the derived CDF, closed‐form expressions are derived for three important performance metrics: the average spectral efficiency, the average packet‐error‐rate, and the outage probability. To evaluate the performance of the considered system, numerical results obtained from the derived closed‐form formulas are presented and compared. In addition, to verify the validity of the analysis, Monte–Carlo simulation results are also provided.

The hybrid cognitive radio (CR) system which combines the two classical interweave and underlay approaches has an improved spectrum efficiency compared to conventional CR systems. In this study, the authors apply the joint spectrum access and power control in a hybrid CR system in the presence of threshold estimation errors. They first formulate the performance metrics of the hybrid CR system under the optimal joint spectrum access and power control strategies by taking into account the threshold estimation errors. Then they show that the threshold estimation error decreases the probability of detecting the primary user (PU) while it increases the false‐alarm probability. Next, they show that the threshold estimation error degrades the performance of the hybrid CR system in terms of outage probability, average achievable data rate and the average interference introduced to the PU. To overcome these performance degradations, they propose a modified spectrum access formulation based on the probabilistic spectrum access scheme, which reduces the impact of threshold estimation uncertainty on the performance of the hybrid CR system. Simulation results indicate that the proposed spectrum access can compensate the performance degradation of a CR system up to 65% for a detection probability of 0.7.

Interconnect and via failures due to the electromigration (EM) effect have become very challenging in the advanced technology as a result of shrinking feature size of integrated circuit. The parasitic effects, which have to be normally represented as analog and radio frequency (RF) circuit constraints for effective suppression in practice, have also made the modern physical design more complicated. In this paper, we present a new integer-linear-programming (ILP) based electromigration- and parasitic-aware analog/RF router, which can effectively address the EM constraints as well as interconnect parasitics along the routing paths. The experimental results show that our proposed method is able to produce better circuit performance compared to the previous work while EM can be addressed for analog/RF circuits.

This study presents a performance analysis for a cognitive radio network with multi‐user scheduling in which a primary user can share its licenced spectrum with several secondary users (SUs), each employing Alamouti orthogonal space‐time block coding (OSTBC) with spatially correlated antennas over Rayleigh fading channels. Closed‐form formulae are obtained for the cumulative density function of the signal‐to‐noise‐ratio of SUs with multi‐user scheduling under correlated antennas. Closed‐form mathematical expressions are then derived for three important system performance metrics: the average channel capacity, outage probability, and the average bit error rate of the system. From the numerical results obtained from the derived mathematical expressions, the system performances with different parameters are studied, evaluated and compared showing the effects of spatial correlation on the performance of the system. It is observed that spatially correlated antennas can improve the average channel capacity of the cognitive radio system with user scheduling.

The shrinking design window and high parasitic sensitivity in advanced technologies have imposed special challenges on analog and radio frequency (RF) integrated circuit design. The state-of-the-art analog routing research tends to favor linear programming to achieve various analog constraints, which, although effective, fail to offer high routing efficiency on its own. In this article, we propose a new methodology to address such a deficiency based on integer linear programming (ILP) but without compromising the capability of handling any special constraints for the analog routing problems. Our proposed method supports hierarchical routing, which can divide the entire routing area into multiple small heterogeneous regions where the ILP can efficiently derive routing solutions. Distinct from the conventional methods, our algorithm utilizes adaptive resolutions for various routing regions. For a more congested region, a routing grid with higher resolution is employed, whereas a lower-resolution grid is adopted to a less-crowded routing region. For a large empty space, routing efficiency can be even boosted by creating more routing hierarchy levels. This scheme is especially beneficial to the analog and RF layouts, which are far sparser than their digital counterparts. The experimental results show that our proposed adaptive ILP-based router is much faster than the conventional ones, since it spends much less time in the areas that need no accurate routing anyway. The higher efficiency is demonstrated for large circuits and especially sparse layouts along with promising routing quality in terms of analog constraints.

As an indispensable portion in the modern system-on-chip designs, analog circuits are becoming more intractable and error prone in the time-consuming design process due to the nature of high parasitic sensitivity along with the shrinking design window in the advanced technology. Compared to the digital counterpart, analog circuits need to be designed more carefully taking into account special analog constraints besides the typical geometric requirements. Recent state-of-the-art analog routing research favors linear programming (LP) to satisfy various constraints, but leaving the routing efficiency as an open question. In this paper, we propose an integer linear programming (ILP) based algorithm to tackle the analog routing problem with a special focus on improving the routing efficiency. Hierarchical routing is developed to help the router to divide the entire routing area into multiple small regions, in each of which the ILP can derive a routing solution with speedy efficiency. Different from typical hierarchical methods, our proposed router deploys variant-grid resolution in different regions, that is, with a lower resolution for less crowded routing regions and a higher resolution for more congested regions. In this way, our proposed ILP-based router is much faster than any typical ones since it spends little time for the areas that do not need to be routed precisely. The experimental results show the high efficiency of our proposed method for both small circuits and especially big circuits without promising the routing quality.

In this study, the authors analyse the impact of spatial correlation on the average bit error‐rate (BER) performance of amplify‐and‐forward cooperative relay networks employing Alamouti orthogonal space‐time block coding (OSTBC) over Rayleigh fading channels. Closed‐form expressions are derived for the moment generating function of the total signal‐to‐noise‐ratio (SNR). The authors then obtain closed‐form expressions for the average BER of the system as well as asymptotic expressions for the average BER at high SNRs. To quantify the effects of antenna correlation on the system performance, numerical results are provided and compared for different cases.

A new approach for performance analysis of orthogonal space–time block coding systems with antenna selection is presented. Antenna selection has been performed at the transmitter and/or at the receiver sides. Closed‐form expressions are derived for the approximate average bit error rate (BER) of the considered system for M ‐ary quadrature amplitude modulation and phase‐shift keying schemes. Different from other approaches presented in the literature, analytical expressions are derived for the average signal‐to‐noise ratio (SNR) gain obtained from each antenna selection scheme, and then using those SNR gains closed‐form expressions are obtained for the approximate average BER performance. The system performances of several forms of the presented scheme are evaluated and compared. It is shown that the results obtained from the mathematical expressions match closely with simulation results.

This study analyses the impact of antenna correlation on orthogonal space–time block coding in amplify‐and‐forward cooperative relay networks in conjunction with different adaptive transmission techniques over Rayleigh fading channels. Closed‐form expressions are derived for the cumulative distribution function, and probability distribution function of the total signal‐to‐noise ratio. For each considered adaptive transmission technique, the authors derive closed‐form expressions for the average channel capacity, outage probability, average spectral efficiency and the average bit error rate of the system. Using numerical evaluations, the performances for different cases are compared in order to evaluate and quantify the effects of spatial correlation on the system performance.

The impact of outdated channel state information (CSI) on the performance of variable‐rate adaptive M ‐ary quadrature amplitude modulation in amplify‐and‐forward (AF) opportunistic relaying systems over time‐variant Rayleigh fading channels is analysed. Two rate‐adaptive modulation techniques are considered. In the first scheme, the relay and the transmission rate are selected according to the CSI at the receiver side. In the second scheme, whereas selection of the relay is based on the receiver's CSI, the transmission rate is selected based on the predicted CSI at the transmitter after the feedback delay. The impact of imperfect CSI prediction on the system performance is also evaluated. For each scheme, analytical expressions are derived for the average spectral efficiency, outage probability and the average bit‐error rate under outdated CSI. Using numerical evaluations the performances of the considered rate‐adaptive modulation schemes are analysed to illustrate the impact of outdated CSI on AF opportunistic relaying systems.

ABSTRACT In this paper, the performance of variable‐rate adaptive modulation schemes in the amplify‐and‐forward cooperative systems with relay selection is analyzed over Rayleigh fading channels. We consider constant power and discrete‐rate adaptive multi‐level modulation techniques. The switching levels required for discrete‐rate adaptive modulation have been determined for two schemes, namely fixed switching levels and optimum switching levels, both respecting a target bit error rate requirements, where in the later scheme, the switching levels are optimally determined in a way that the average spectral efficiency of the system is maximized. Two M‐ary modulation schemes, namely quadrature amplitude modulation and phase shift keying, are considered. Closed‐form expressions are derived for three performance metrics, namely average spectral efficiency, outage probability, and average bit error rate, for two cases: independent and identically distributed fading relay links and independent and non‐identically distributed links. It is shown that, compared with using fixed switching levels, employing optimum switching levels provides a slight improvement in the spectral efficiency and moderate improvements in the signal‐to‐noise ratio gain and in the outage probability of the system. It is also shown that compared with the independent and identically distributed links, independent and non‐identically distributed relay links yield a slight increase in the signal‐to‐noise ratio gain and a slight decrease in the diversity order of the system. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents an evaluation of the impact of channel time variations on performance of multiuser selection diversity systems employing orthogonal space-time block coding (OSTBC) over MIMO Rayleigh fading channels. A rate-adaptive M-QAM modulation along with the maximum signal-to-noise ratio (SNR) based user selection diversity is considered. Analytical expressions are derived for the average spectral efficiency, average bit error rate (BER), and bit error outage (BEO) of the system. Using the results obtained from the analytical expressions as well as from Monte-Carlo simulations, the impact of channel time variations on the system performance is evaluated.

In this article, the impact of outdated channel information on the average bit error rate (BER) performance of the opportunistic relay selection in amplify-and-forward cooperative systems is analysed and evaluated over Rayleigh fading channels. Using the moment generating function (MGF)-based approach closed-form analytical expressions are derived for the average BER performance of M-ary modulations and the average signal-to-noise-ratio (SNR) gain obtained from opportunistic relaying. Numerical evaluation results obtained from the analytical expressions are provided to study and quantify the deteriorating effects of outdated channel information on the BER performance and on the achievable diversity and SNR gain obtained from relay selection.

In this paper we consider an Interference Alignment (IA) approach for intercell interference coordination for the downlink of a MIMO multi-user cellular network. We determine the maximum degrees of freedom (DoF) of the network and give the feasibility proof of perfect IA. Furthermore, we consider the problem of approximate IA and the Mean-Squared Error (MSE) based optimization of the transmit and receive beamforming matrices with the orthogonality constraints and the per-antenna transmit power constraint. Iterative algorithms are presented to solve the corresponding MSE problems. Simulation results and convergence analysis of the algorithms are also discussed. The results indicate that it is feasible to significantly increase the network capacity using the proposed IA approach.

The impact of outdated channel state information (CSI) on the performance of variable-rate adaptive M-ary quadrature amplitude modulation (M-QAM) in an amplify-and-forward (AF) opportunistic relaying system over Rayleigh fading channels is analyzed. Closed-form expressions are derived for the average spectral efficiency, outage probability and the average bit error rate under outdated CSI. Using numerical evaluations, the performances of different cases are compared showing the impact of outdated CSI on the performance of the considered rate-adaptive modulation scheme in AF opportunistic relaying systems.

The system performance of the opportunistic relaying technique in amplify-and-forward cooperative systems with adaptive transmission over Rayleigh fading channels is analysed. Two rate-adaptive modulation techniques, continuous-rate and discrete-rate adaptive techniques, are considered. Closed-form expressions are derived for the average spectral efficiency, outage probability and the average bit error rate for two cases: independent and identically distributed (i.i.d.) fading links and independent and non-identically distributed (i.ni.d.) links. Using numerical evaluations, the performances of different cases are compared showing the advantages of each adaptive modulation technique in conjunction with the opportunistic relaying in a cooperative communication over both i.i.d. and i.ni.d. fading links.

In this study, the performance of user selection diversity for rate-adaptive multiuser multiple-input multiple-output (MIMO) systems employing orthogonal space time block coding (OSTBC) is analysed and evaluated. An antenna selection scheme is used to overcome the drawback of channel hardening effects in multiuser MIMO systems. Closed-form expressions for the average spectral efficiency and outage probability of the system are derived. Using numerical evaluations the considered schemes are compared in terms of outage probability and spectral efficiency. The effects of antenna correlation at the receiver ends on the performance of the system are analysed and evaluated, indicating that spatial correlation may be beneficial for the spectral efficiency of the multiuser OSTBC MIMO systems employing user selection.

In this letter, a performance analysis is presented for a joint multiuser scheduling and antenna selection in MIMO systems employing orthogonal space-time block coding (OSTBC) over Rayleigh fading channels under a general case of heterogeneous scenario. Using numerical evaluations the performance of different cases of the considered scheme are compared for heterogeneous and homogeneous scenarios.

In this paper, we derive probability density function (PDF) and cumulative distribution function (CDF) expressions for the end-to-end signal-to-noise ratio (SNR) of an opportunistic relaying amplify-and-forward (AF) cooperative diversity system over independent and non-identically distributed (i.ni.d.) Rayleigh fading links where outdated channel state information (CSI) is used for relay selection. Based on these expressions, we derive the analytical capacity and outage probability expressions for four classical adaptive transmission techniques, namely, optimal power and rate adaptation (OPRA), constant power with optimal rate adaptation (ORA), channel inversion with fixed rate (CIFR) and truncated channel inversion with fixed rate (TIFR). Numerical evaluations results are presented showing the impact of relay selection with outdated CSI and i.ni.d. links on the performance of each adaptive transmission technique in AF opportunistic relaying systems.

A performance analysis for cooperative diversity systems with best relay selection over Rayleigh fading channels is presented. The authors obtain analytical expressions for the probability density function (PDF), cumulative density function (CDF) and the moment generating function (MGF) of end-to-end signal-to-noise ratio (SNR) of the system under study for independent and non-identically distributed (i.ni.d.) fading links. Using these expressions the authors derive lower bound closed-form expressions for the average symbol error rate (SER), the outage probability, and an upper bound closed-form expression for the average channel capacity. Using numerical evaluation of the mathematical expressions, system performances of different cases are evaluated and compared for both non-identically and identically distributed links showing the impact of the relay selection in cooperative communication systems.

In this paper, we present a performance analysis for the user scheduling for the multiuser MRC MIMO systems exploiting the user and antenna diversities. We consider two scheduling schemes including absolute SNR-based scheduling and normalized SNR-based scheduling schemes. We propose the utilization of an antenna selection scheme to overcome the drawback of channel hardening in multiuser MIMO systems and to improve the system performance. We derive new closed-form expressions for the average bit error rate of the presented schemes for two scenarios: heterogeneous (independent nonidentically distributed SNRs-i.n.i.d.) and homogeneous (independent identically distributed SNRs- i.i.d.) cases. Using mathematical analysis and numerical simulations, we compare the presented schemes.

A performance analysis for cooperative diversity system with best relay selection over Rayleigh fading channels is presented. We obtain analytical expressions for the probability density function (PDF), cumulative density function (CDF), and the moment generating function (MGF) of end-to-end SNR of the system under study. Using these expressions we derive closed-form expressions for the average symbol error rate (SER), the outage probability and the average end-to-end SNR gain obtained form relay selection. Using numerical simulations and calculation of the mathematical expressions, the performances of different cases are evaluated and compared to show the significant advantages of the relay selection in a cooperative communication.

A performance analysis for the average channel capacity and average bit error rate (BER) of user scheduling schemes for multiuser MIMO systems exploiting the multiuser and antenna diversities over non-identically distributed Nakagami-m fading channels is presented. We consider different scheduling schemes including absolute SNR-based scheduling and normalized SNR-based scheduling schemes for both heterogeneous and homogeneous wireless networks. We derive expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the signal-to-noise-ratio (SNR) in non-identical Nakagami-m MIMO channels for each scheduling scheme. These expressions are used to obtain analytical expressions for the average channel capacity and average bit error rate (BER) of the system under study. Finally, the performances of different schemes are evaluated and compared.

In this paper, we consider a class of wireless ad hoc networks, namely two-hop MIMO interference relay network, where L M-antenna source-destination pairs communicate via K relay nodes each equipped with N antennas. Based on recent advances on characterizing the limits of MIMO X channel and the concept of interference alignment, we treat this network as the cascade of two MIMO X networks and decompose it into L non- interfering parallel MIMO relay channels. The rationale behind this approach can be justified by the information theory of MIMO X networks which reveals that they provide higher degrees of freedom than the conventional MIMO interference channels. Signaling, interference alignment, relay selection and simulation results will be presented. Compared to the well-known distributed interference cancellation technique, this approach offers higher capacity for small to medium number of relay nodes at the cost of feeding back CSI from the relays to the source nodes and more advanced signaling.

In this paper, we present a performance analysis of user scheduling for multiuser MIMO systems exploiting the multiuser and antenna diversities while maintaining the fairness among the users. We consider different scheduling schemes including absolute throughput-based scheduling, absolute SNR-based scheduling, and normalized SNR-based scheduling schemes. We also propose the utilization of an antenna selection scheme to overcome the drawback of channel hardening in multiuser MIMO systems. This also improves the system performance and reduces the system complexity. We derive closed-form expressions for the average spectral efficiency of the system under study for each scheduling scheme. Using the results obtained from the closed-form expressions, we compare the presented schemes and show their significant advantages in terms of fairness of scheduling and spectral efficiency.

In this paper, we present a multiuser scheduling technique for the MIMO-OFDM system over multipath frequency-selective fading channels to exploit the multiuser, space and frequency diversities. Two scenarios including full-feedback and limited-feedback channel information have been considered. A discrete-rate adaptive modulation is employed to increase the spectral efficiency of the system. Performance analysis and numerical simulation are conducted to evaluate the average bit error rate (BER) and average spectral efficiency (ASE) and to show the significant advantages of the proposed scheme. It is also shown that when the number of active users is moderately high and is above 30, even 10% feedback load is sufficient to get the benefits of the proposed scheme.

In this paper, we present a performance analysis of the user scheduling for the multiuser MIMO systems exploiting the multiuser and antenna diversities while maintaining the fairness among the users. We present different scheduling schemes including absolute throughput-based scheduling, normalized throughput-based scheduling, absolute SNR-based scheduling, and normalized SNR-based scheduling schemes. We use an antenna selection scheme to overcome the drawback of channel hardening in multiuser MIMO systems. This also improves the system performance and reduces the system complexity. Using mathematical analysis and numerical simulations, we compare the presented schemes and show their significant advantages.

In this paper, we present a multiuser scheduling technique for MIMO-OFDM system over multipath frequency- selective fading channels to exploit the multiuser, space and frequency diversities. A continuous-rate adaptive modulation is employed to increase the spectral efficiency of the system. A proportional fair scheduler is also considered to maintain the fairness among the users while exploiting the multiuser diversity. We also use a scheme to reduce the required feedback channel information. Using mathematical analysis and numerical simulations, the significant advantages of the proposed scheme have been shown. It is also shown that when the number of active users is moderately high and is above 30, even 10% feedback load is sufficient to get the benefits of the proposed scheme.

In this paper we consider a two-hop MIMO parallel relay channel where a source-destination pair both equipped with M antennas, communicate via K N-antenna half-duplex amplify-and-forward relays (K,N ges M). Multi-user beamforming techniques are jointly applied at the source and destination to respectively multiplex and recover the data streams. In order to further exploit the multi-relay diversity, we propose new relay selection criteria based on semi-orthogonality among spatial eigenmode and antenna pairs of the relays. The proposed algorithms have very low complexity, decrease the amount of feedback, and consume less power across the relays compared to previously proposed MIMO relaying strategies. Furthermore, for small to medium number of relay nodes, the proposed algorithms' capacity outperform the other strategies and in the asymptote of large number of relay nodes (K rarr infin), the capacity of the proposed algorithms scales as M/2 log log K.

Closed-form expressions for the bit error rate (BER) performance of space-frequency block coded OFDM (SFBC-OFDM) systems are derived and evaluated for frequency-selective fading channels. In the performance analysis, both M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) are considered, and the effects of channel estimation errors on the BER performance are studied. Numerical results and comparisons are provided for several forms of SFBC-OFDM. It is shown that the results obtained from the closed-form formulae are very close to the ones using the exact expressions and to simulation results of the SFBC-OFDM model. The BER deterioration that results from channel estimation errors in the SFBC-OFDM systems is also illustrated. Using the provided results, the amount of degradation can be quantified.

In this paper, a study of the effect of channel estimation error on the capacity, outage probability, and bit error rate (BER) performance of multiple-input multiple-output OFDM (MIMO-OFDM) systems, is provided. First, a lower bound for the mutual information of MIMO-OFDM in the presence of channel estimation error is derived. Then, we derive an outage probability expression under imperfect channel information for MIMO-OFDM systems in general and for space-frequency block coded OFDM (SFBC-OFDM) in particular. Furthermore, we consider SFBC-OFDM used in conjunction with adaptive modulation, and evaluate the spectral efficiency of the adaptive SFBC-OFDM system under imperfect channel information at the transmitter. Simulation results are provided to analyze the performance of the MIMO-OFDM systems under study, and quantify the amount of degradation that imperfect channel information yields on the channel capacity, BER, outage probability and system throughput.

A new scheme consisting of a combination of adaptive bit allocation, space-time block coded-OFDM and antenna selection is presented. The proposed scheme, exploits the benefits of space-time block codes, OFDM and adaptive bit allocation to provide high quality of transmission for wireless communications over frequency selective multipath channels with enhanced performance in terms of spectral and power efficiency. The system performance of non-adaptive OFDM, adaptive OFDM, non-adaptive STBC-OFDM, and the proposed adaptive STBC-OFDM are evaluated and compared. It is shown that the proposed scheme can greatly improve the performance of non-adaptive STBC-OFDM system.

This paper presents a new approach to adaptive modulation for OFDM using Space-Frequency Block Codes. In the proposed scheme, the benefits of adaptive modulation, space-frequency block codes (SFBC) and OFDM are exploited to provide high quality of data transmission over multipath fading channels. When the channel state information is known at the transmitter, a large gain over non-adaptive system can be obtained. The performance of the proposed system is eval- uated and compared with non-adaptive systems. We show that the proposed adaptive modulated SFBC-OFDM, has superior performance compared to non-adaptive systems.