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This paper studies the performance of a multiuser mixed radio frequency (RF)/free space optical (FSO) relay network with transmit opportunistic scheduling. The outdated channel information (OCI) on the first relaying hop and its effect on the system performance is also studied in this paper. Furthermore, a power allocation scheme is proposed for optimizing the overall system performance. The considered system includes $K$ sources (users), one amplify-and-froward relay and one destination. The users are connected with the relay node through RF links and the relay is connected with the destination through an FSO link. In the analysis, the first hop channels are assumed to follow Rayleigh fading model and the second hop channel is assumed to follow Gamma–Gamma fading model with considering the effect of pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability, and ergodic channel capacity. Furthermore, the system performance is studied at high signal-to-noise ratio regime, where the diversity order and coding gain are derived and analyzed. Using the asymptotic results, the power of users and relay are determined to minimize the system outage probability under a total power constraint. Monte–Carlo simulations are provided to validate the achieved exact and asymptotic results. Main results show that under weak atmospheric turbulence conditions, the system performance is dominated by the RF channels and a diversity order of $K$ is achieved by the system, whereas under severe atmospheric turbulence conditions, the system is dominated by the FSO channel and the diversity order is determined by the minimum value of the turbulence fading and pointing error parameters.

This letter proposes a low-complexity antenna selection scheme based on large-scale fading to enhance the secrecy performance in independent and non-identical generalized- $\mathcal{K}$ fading channels. New analytical results for the secrecy outage probability and the probability of non-zero secrecy capacity are derived when the receiving terminals employ the maximum ratio combining scheme. In addition, simple and insightful approximations are obtained for the secrecy outage probability in the high signal to noise ratio regime, which shed light on the impact of key system parameters on the secrecy performance. Simulation results are provided to validate the analytical expressions.

This paper studies power allocation for performance constrained dual-hop variable-gain amplify-and-forward (AF) relay networks in Nakagami-$m$ fading. In this context, the performance constraint is formulated as a constraint on the end-to-end signal-to-noise-ratio (SNR) and the overall power consumed is minimized while maintaining this constraint. This problem is considered under two different assumptions of the available channel state information (CSI) at the relays, namely full CSI at the relays and partial CSI at the relays. In addition to the power minimization problem, we also consider the end-to-end SNR maximization problem under a total power constraint for the partial CSI case. We provide closed-form solutions for all the problems which are easy to implement except in two cases, namely selective relaying with partial CSI for power minimization and SNR maximization, where we give the solution in the form of a one-variable equation which can be solved efficiently. Numerical results are then provided to characterize the performance of the proposed power allocation algorithms considering the effects of channel parameters and CSI availability.

This paper studies generalized single-stream transmit beamforming employing receive array co-channel interference reduction algorithms under slow and flat fading multiuser wireless systems. The impact of imperfect prediction of channel state information for the desired user spatially uncorrelated transmit channels on the effectiveness of transmit beamforming for different interference reduction techniques is investigated. The case of over-loaded receive array with closely-spaced elements is considered, wherein it can be configured to null specified interfering sources. Both dominant interference reduction and adaptive interference reduction techniques for statistically ordered and unordered interferers powers, respectively, are thoroughly studied. The effect of outdated statistical ordering of the interferers powers on the efficiency of dominant interference reduction is studied and then compared against the adaptive interference reduction. For the system models described above, new analytical formulations for the statistics of combined signal-to-interference-plus-noise ratio are presented, from which results for conventional maximum ratio transmission and single-antenna best transmit selection can be directly deduced as limiting cases. These results are then utilized to obtain quantitative measures for various performance metrics. They are also used to compare the achieved performance of various configuration models under consideration.

Femtocells can be employed in cellular systems to enhance the indoor coverage, especially in the areas with high capacity growing demands and high traffic rates. In this paper, we propose an efficient resource utilization protocol, named as shared access protocol (SAP), to enable the unauthorized macrocell user equipment to communicate with partially closed-access femtocell base station to improve and enhance the system performance. The system model considers a femtocell that is equipped with a total of N separated antennas or channels to multiplex independent traffic. Then, a set of N1 channels is used for closed access only by the authorized users, and the remaining set of channel resources can be used for open access by either authorized or unauthorized users upon their demands and spatial locations. For this system model, we obtain the signal-to-interference ratio characteristics, such as the distribution and the moment generating function, in closed forms for two fading models of indoor and outdoor environments. The signal-to-interference ratio statistics are then used to derive some important performance measures of the proposed SAP in closed form, such as the average bit error rate, outage probability, and average channel capacity for the two fading models under consideration. Numerical results for the obtained expressions are provided and supported by Monte Carlo simulations to validate the analytical development and study the effectiveness of the proposed SAP under different conditions. Copyright © 2013 John Wiley & Sons, Ltd.

This letter studies the ergodic capacity of channel state information (CSI)-assisted two-hop amplify-and-forward (AF) relaying system, in which the relay and the destination undergo independent sources of co-channel interference. The fading envelopes associated with the desired and interfering users are assumed to follow independent but non-identically distributed (i.n.d.) Nakagami-m fading models. Through the analysis and by assuming the fading parameter m of the two hop channels being integer, exact and approximate results for the system average ergodic capacity under different conditions are derived. They are valid for arbitrary numbers of interfering signals, and can be used to study the case of independent and identically distributed (i.i.d.) channels as a limiting application. Simulation results are provided to validate the analytical development, and to clarify the average ergodic capacity under different conditions.

This paper investigates an adaptive scheduling algorithm for multiuser environments with statistically independent but nonidentically distributed (i.n.d.) channel conditions. The algorithm aims to reduce feedback load by sequentially and arbitrarily examining the user channels. It also provides improved performance by realizing postexamining best user selection. The first part of the paper presents new formulations for the statistics of the signal-to-noise ratio (SNR) of the scheduled user under i.n.d. channel conditions. The second part capitalizes on the findings in the first part and presents various performance and processing complexity measures for adaptive discrete-time transmission. The results are then extended to investigate the effect of outdated channel estimates on the statistics of the scheduled user SNR, as well as some performance measures. Numerical results are provided to clarify the usefulness of the scheduling algorithm under perfect or outdated channel estimates.

This letter studies the outage probability of fixed-gain amplify-and-forward dual-hop relaying system in the presence of co-channel interference (CCI). Assuming that the relay and the destination terminals are subject to both CCI and additive white noise, and the envelopes of the channels follow dissimilar Nakagami-m distributions, an exact expression for the outage probability of the system is derived. The result is applicable for arbitrary numbers of interfering signals at receiving terminals and can be efficiently evaluated. In addition, it enables us to study the effect of CCI at either the relay or the destination as special cases. The analytical results are validated by simulations. The simulated results show that the outage performance of the system is less sensitive to the interference at the destination.

This paper investigates the performance of two low-complexity combining schemes, which are based on one- or two-phase observation, to mitigate multipath fading in dual-hop amplify-and-forward relaying systems. For the one-phase-based combining, a single-antenna station is assumed to relay information from a multiple-antenna transmitter to a multiple-antenna receiver, and the activation of the receive antennas is adaptively performed based on the second-hop statistics, regardless of the first-hop conditions. On the other hand, the two-phase-based combining suggests using multiple single-antenna stations between the multiple-antenna transmitter and the single-antenna receiver, where the suitable set of active relays is identified according to the precombining end-to-end fading conditions. To facilitate comparisons between the two schemes, formulations for the statistics of the combined signal-to-noise ratio and some performance measures are presented. Numerical and simulation results are shown to clarify the tradeoff between the achieved diversity-array gain, the processing complexity, and the power consumption.

The performance of multiple-antenna diversity systems in which the receiver combines signal replicas per threshold-based maximal ratio combining (MRC) and transmitter uses only a single antenna according to receive combined signal strength is studied. The impact of imperfect channel estimation and the effect of phase and time misalignments between desired and undesired signals are implicitly investigated. It is assumed that the desired signal replicas and interfering signals undergo statistically independent flat Rayleigh fading. The analysis is applicable for arbitrary transmit antenna selection, based either on receive combined signal-to-noise ratio (SNR) or receive combined signal-to-interference-plus-noise ratio (SINR). For the scenario of identical multiple-antenna channels, closed-form analytical results for the combined SNR statistics and some performance measures are first presented. The SNR-based and SINR-based selection algorithms are then employed to obtain expressions for the distribution of combined SINR and outage probability performance, which are applicable for different statistical models of interfering signals. The adopted system models herein as well as the analytical development add enhancements on many existing results, and can be used to study the performance of different architectures under various channel conditions when the implementation complexity is of interest.

This paper studies the performance of adaptive transmit selection with co-channel interference suppression in multipath fading channels. The adaptive selection algorithms are configured for single-antenna bandwidth-efficient or power-efficient transmission with as low transmit channel estimations as possible. Due to the fact that the number of active co-channel interfering signals and their corresponding powers experience random behavior, the adaptation to channels conditions, assuming uniform buffer and traffic loading, is proposed to be jointly based on the transmit channels instantaneous signal-to-noise ratios (SNRs) and signal-to-interference-plus-noise ratios (SINRs). Two interference cancelation algorithms are considered. The first algorithm assumes that the receiver eliminates the impact of the strongest subset of interferers, whereas the second algorithm suggests random cancelation of interferers to further reduce processing complexity. The impact of outdated ordering of interferers powers on the efficiency of interference cancelation, and the effect of imperfect prediction of transmit channels for desired user adaptation are investigated. Analytical formulations for various performance measures and comparisons between the performance and processing complexity of different adaptation schemes are presented.

The impact of co-channel interference on the performance of adaptive generalized transmit beamforming for low-complexity multiple-input single-output (MISO) configuration is investigated. The transmit channels are assumed to be sufficiently separated and undergo Rayleigh fading conditions. Due to the limited space, a single receive antenna is employed to capture desired user transmission. The number of active transmit channels is adjusted adaptively based on statistically unordered and/or ordered instantaneous signal-to-noise ratios (SNRs), where the transmitter has no information about the statistics of undesired signals. The adaptation thresholds are identified to guarantee a target performance level, and the adaptation schemes with enhanced spectral efficiency or power efficiency are studied and their performance are compared under various channels conditions. To facilitate comparison studies, results for the statistics of instantaneous combined signal-to-interference-plus-noise ratio (SINR) are derived, which can be applied for different fading conditions of interfering signals. The statistics for combined SNR and combined SINR are then used to quantify various performance measures, considering the impact of non-ideal estimation of the desired user channel state information (CSI) and the randomness in the number of active interferers. Numerical and simulation comparisons for the achieved performance of the adaptation schemes are presented.

This paper studies the effect of non-ideal estimation of channel state information (CSI) on the performance of output-threshold maximal-ratio combining (OT-MRC) diversity scheme in the presence of co-channel interference as well as white noise. The channel fading envelopes are assumed to follow slowly varying flat Rayleigh model. New closed-form expressions for the combined signal-to-interference-plus-noise ratio (SINR) distribution and outage probability performance are presented. Performance comparisons between the conventional MRC and OT-MRC for the system model described above are provided.

This paper studies the performance of Rake receivers with maximal ratio combining (MRC) in the presence of cochannel interference over slowly varying frequency-selective fading channels with combined spatial receive antenna diversity and temporal multipath diversity. Two models for the instantaneous powers of the residual multipath components and the resolved cochannel interfering signals, which represent the overall interfering signals, are employed. The first model considers the phase asynchronism between the desired signal replicas and interfering signals, whereas the second model assumes that the instantaneous powers of interfering signals incoherently add up. The desired signal replicas and interfering signals are assumed to experience statistically independent Rayleigh fading processes with arbitrary statistics. For the system model previously described, new closed-form expressions for the probability density function (pdf) of the combined signal-to-interference-plus-noise ratio (SINR) are derived. These expressions are then used to obtain formulas for various performance measures. The case study under consideration and the corresponding derived expressions for the statistical measures generalize many previous results and can usefully be employed to investigate the impact of various system and channel parameters on the performance of Rake receivers with MRC in the presence of cochannel interference.

This paper studies the performance of cellular mobile systems employing a signal-to-noise ratio (SNR)-based generalized selection combining (GSC) algorithm in the presence of background white noise and multiple cochannel interfering signals. Closed-form expressions are derived for the received signal-to-interference-plus-noise ratio (SINR) distribution and outage probability, considering the case when the interfering signals experience mixed Rayleigh and Nakagami-q fading conditions, and the desired signal replicas are attenuated by flat Rayleigh fading. These expressions are obtained via the new representation of the total interference-to-noise ratio (INR) distribution for the mixed mode of fading experienced by different interferers. The derived expressions for the aforementioned statistical measures are valid for an arbitrary number of interferers and system diversity order and can be employed to investigate the impact of various system and fading parameters on the performance measures. Several case studies can be deduced from the results presented in this paper, including interference-limited systems, wherein the impact of white noise can be neglected.

This paper analyzes the average bit error rate (BER) of noncoherent M-ary frequency-shift keying (FSK) signals over multichannel nonidentically distributed Nakagami-q (Hoyt) fading employing diversity combining. The first part of the paper considers the conventional postdetection noncoherent equal-gain combiner (NC-EGC), in which a Fourier series inversion formula is employed to derive a simple and rapidly converging series-based expression for the system average BER. This expression is valid for arbitrary values of received average signal-to-noise ratios (SNRs) and fading parameters. The derived expression is then compared with some existing ones in the literature, and the results show a large reduction in computational complexity, particularly when M and/or the diversity order increases. In the second part, a new noncoherent combiner is proposed to achieve improvements over the conventional NC-EGC. It is also shown that this new combiner results in a simple closed-form expression for the system average BER that is given in terms of elementary functions; hence, it can be easily numerically evaluated with noticeable computation efficiency.

This paper presents simple and exact expressions for the average bit error rate (BER) of M-ary orthogonal signals with noncoherent diversity combining in independent as well as arbitrarily correlated nonidentically distributed Nakagami-m fading channels. The expressions are given in terms of elementary functions, and they do not involve numerical integrals or complicated functional operations. In addition, they are valid for the generalized case when the channels have arbitrary average signal- to-noise ratios (SNRs) as well as nonidentical fading parameters. Simulation results are provided to validate the analytical results.

Exact results are presented for infinite integrals that consist of higher-order powers of the one dimensional Gaussian Q-function averaged over Rayleigh fading envelopes in multi-branch diversity reception with maximal ratio combining (MRC). Some known results for the average of the 1st and 2nd powers are shown as special cases. The results obtained in this paper are utilized to study the average symbol error probability (SEP) performance of differentially encoded quadri-phase shift-keying (DE-QPSK) in Rayleigh fading channels employing MRC, and new exact expressions are presented for different fading scenarios. The derived mathematical expressions are verified using Monte Carlo simulations.

This paper derives exact expressions for the average error performance of M-ary orthogonal signals with noncoherent equal-gain diversity combining over nonidentical generalized Rician, Nakagami-m, Nakagami-g, and implicitly Rayleigh fading channels. The assumption of generalized distributed fading envelopes implies that the received average signal-to-noise ratios (SNRs) and/or the fading parameters can have arbitrary nonidentical values. The derived expressions are precisely given in terms of either one-fold integral or rapidly convergent infinite series, which can be readily evaluated numerically. In addition, they can be usefully used to study the impact of arbitrary correlation among diversity branches on the system average error performance.

This paper presents simple tight upper bound expressions for the average symbol error probability and bit error probability of coherent M-ary biorthogonal signals over fading channels with diversity reception. The upper bounds, which do not involve numerical integration and are expressed with only elementary functions, can be efficiently evaluated. In addition, they are valid for different diversity-combining techniques, as well as for arbitrarily correlated and/or nonidentically distributed channels. The tightness of the derived upper bounds is clarified under various channel conditions. Numerical results are also provided to demonstrate the impact of nonidentical channels on the system average error performance.

This paper investigates the performance of multiuser mixed radio frequency (RF)/free space optical (FSO) relay network with transmit opportunistic scheduling. The outdated channel information (OCI) on the first relaying hop and its effect on the system performance is also studied. Furthermore, a power allocation scheme is proposed. The considered system includes K sources (users) that communicate with the relay node through RF links and the relay is connected with the destination through an FSO link. In the analysis, the first hop channels are assumed to follow Rayleigh fading model and the second hop channel is assumed to follow Gamma-Gamma fading model with pointing errors. Closed-form expressions are derived for the outage probability, average symbol error probability (ASEP) and ergodic channel capacity. Furthermore, the system performance is studied at high signal-to-noise ratio (SNR) regime. Using the asymptotic results, the power of users and relay are determined to minimize the system outage probability under a total power constraint. Monte-Carlo simulations are provided to validate the achieved exact and asymptotic results.

Constrained switching rate imposes practical limitations on the effectiveness of selection combining diversity algorithms. This paper investigates the impact of delayed arbitrarily ordered transmit antenna selection on the average symbol error probability (SEP) performance of arbitrary rectangular quadrature amplitude modulation (QAM) with receive maximal ratio combining (MRC) diversity. New closed form expression is presented for the system average SEP considering the case of statistically independent diversity branches over which the instantaneous fading-to-noise power ratios follow Gamma distributions.

This letter presents an exact-form expression for the average symbol error probability (SEP) of general rectangular quadrature amplitude modulation (QAM) in Rayleigh fading channels with generalized selection combining (GSC). Expressions for the system average SEP with maximal ratio combining (MRC) and selection combining (SC) are obtained as limiting cases. It is shown that the results herein reduce to some existing ones as special cases.

Presented are exact-form expressions for the average error performance of various coherent, differentially coherent, and noncoherent modulation schemes in Nakagami-q (Hoyt) fading channels. The expressions are given in terms of the Lauricella hypergeometric function, FD (n); for nges1, which can be evaluated numerically using its integral or converging series representation. It is shown that the derived expressions reduce to some existing results for Rayleigh fading as special cases

This letter presents a closed form expression for the average error performance of noncoherent M-ary orthogonal signals over nonidentically distributed Rayleigh fading channels with postdetection equal-gain diversity combining (EGC). The derived expression can be easily evaluated numerically, and is valid for the general case in which the received average fading powers over diversity branches are arbitrary and not required to be distinct. In addition, it reduces to some existing results in the literature as special cases

It is well-known that noncoherent equal-gain combining (NC-EGC) is the simplest combining technique for noncoherent and differentially coherent communication systems. However, for nonidentical Nakagami-m channels (channels having nonuniform multipath intensity profile (MIP) and/or arbitrary non-integer fading parameters), the use of NC-EGC has three main disadvantages. First, its performance serves as a lossy upper bound to that of the optimum diversity combiner. Second, it results in complicated expressions for the system average error performance. Third, it incurs noncoherent combining loss (does not aid the use of diversity) at relatively low average signal-to-noise ratio (SNR). In this letter, we propose a modified version of the NC-EGC, which is a noncoherent combiner with weighting coefficients, to overcome the disadvantages of the conventional one. We show that this alternative combiner does provide improvements over the conventional N.C-EGC for all values of average SNRs, it does not incur any noncoherent combining loss, and it leads to a design of the receiver whose average error performance can be evaluated easily.

In this paper, we study power allocation strategies for a fixed-gain amplify-and-forward relay network employing multiple relays. We consider two optimization problems for the relay network: 1) optimal power allocation to maximize the end-to-end signal-to-noise ratio (SNR) and 2) minimizing the total consumed power while maintaining the end-to-end SNR over a threshold value. We investigate these two problems for two relaying protocols of all-participate relaying and selective relaying and multiple cases of available channel state information (CSI) at the relays. We show that the SNR maximization problem is concave and the power minimization problem is convex for all protocols and CSI cases considered. We obtain closed-form expressions for the two problems in the case for full CSI and CSI of all the relay-destination links at the relays and solve the problems through convex programming when full CSI or CSI of the relay-destination links are not available at the relays. Numerical results show the benefit of having full CSI at the relays for both optimization problems. However, they also show that CSI overhead can be reduced by having only partial CSI at the relays with only a small degradation in performance., Comment: 8 figures, 28 pages. Journal paper

In this paper, we analyze the performance of a dual-hop system with partial relay selection and feedback delay over Nakagami-m fading channels in the presence of multiple identical interferers at the destination. Based on the new closed-form expressions for the cumulative distribution function of the effective signal-to-interference plus noise ratio, we present closed-form expressions for the outage probability and average symbol error rate (SER) for both fixed and CSI-assisted gain relaying systems. To gain further insights, the asymptotic outage probability and average symbol error rates at the high signal to noise ratio regimes are examined. Our results reveal that increasing the number of relays does not provide any extra diversity gain due to the presence of the feedback delay. Specifically, we show that feedback delay as well as CCI only affect the coding gain of the system. The accuracy of the analytical results are supported Monte-Carlo simulations.

We investigate the performance of a multiuser downlink access scheme based on a post-selection switch and examine algorithm. The studied scheme sequentially switches over the users that experience independent and non-identically distributed fading conditions, and selects a single user with an acceptable channel quality as compared to a pre-selected signal-to-noise ratio (SNR) threshold. If no one of the users can satisfy the target channel quality, the base station (BS) takes the advantage of the knowledge of all users channels and serves the user with the best channel quality among all users. This scheme reduces considerably the feedback load but offers a lower average spectral efficiency (ASE) as compared to that of the full feedback system with instantaneous best user selection. On the other hand, it improves the system performances, such as outage probability and average bit error rate (BER), as compared to a system that is based on a standard switching scheme without post-selection. Numerical results for the ASE average BER, and average feed back load, are presented for the cases of outdated and non-outdated rate-adaptive modulation scheme operating over independent and non-identically distributed users.

Minimum selection generalized selection combining(MS-GSC) scheme has been proposed as a generalized power-saving variant of the conventional generalized selection combining(GSC) scheme. Previous analysis of the performance of MS-GSC has focused on interference-free environments. This paper aims to investigate the performance of adaptive signal-to-noise ratio (SNR)-based MS-GSC in the presence of co-channel interference over multipath fading channels. The adaptation thresholds are selected to enhance either the spectral efficiency or power efficiency of discrete-time rectangular signaling system. New closed-form expressions for the statistics of combined signal-to-interference-plus-noise ratio (SINR) are presented, which are then used to obtain analytical formulations for various performance measures. Numerical and simulation comparisons for the performance of the adaptation scheme are provided.

This paper investigates the performance of different low-complexity combining schemes in the context of dual-hop amplify-and-forward relaying networks. It is assumed that the relay uses single transmit (receive) antenna due to space limitation and to reduce the processing complexity. On the other hand, the transmitter and the receiver use antenna arrays to improve the overall diversity gain. However, this gain is achieved at the expense of increased processing complexity and power consumption. To this end, some combining schemes aiming at reducing the processing complexity and decreasing the number of active receive channels are investigated. Through the analysis, new formulas for the end-to-end signal-to-noise ratio statistics in slowly varying and frequency flat Rayleigh fading channels are derived, which are then used to present some performance measures. Numerical and simulation results are presented to clarify the trade-off between the achieved diversity gain and the receive processing complexity.

This paper investigates the effect of different switched diversity configurations on the implementation complexity and achieved performance of dual-hop amplify-and-forward (AF) relaying networks. A low-complexity model of the relay station is adopted, wherein single-input single-output antenna configuration is employed. Each of the transmitter and the receiver however employs multiple antennas to improve the overall link performance. Single-phase and two-phase based receive switching strategies are investigated assuming optimum first hop signal-to-noise ratio (SNR). Moreover, the simple scheme in which the switched diversity is applied independently over the two hops is studied using tight upper bounds. Thorough performance comparisons and switching thresholds optimization for the aforementioned strategies are presented. Simulation results are also provided to validate the mathematical development and to verify the numerical computations.

The performance of a generalized single-stream transmit beamforming scheme employing receive co-channel interference null-steering algorithms in slowly varying and flat fading channels is analyzed. The impact of imperfect prediction of channel state information (CSI) for the desired user spatially uncorrelated transmit channels is considered. Both dominant interference cancelation and adaptive arbitrary interference can-celation algorithms for closely spaced receive antennas are used. The impact of outdated statistical ordering of the interferers instantaneous powers on the effectiveness of dominant interference cancelation is investigated against the less complex adaptive arbitrary cancelation scheme. For the system models described above, new exact formulas for the statistics of combined signal-to-interference-plus-noise ratio (SINR) are derived, from which results for conventional maximum ratio transmission (MRT) and best transmit channel selection schemes can be deduced as limiting cases. The results presented herein can be used to obtain quantitative measure for various performance metrics, and in addition to investigate the performance-complexity tradeoff for different multiple-antenna system models.

This paper proposes an adaptive co-channel interference null-steering algorithm for highly correlated receive antenna channels with an aim of reducing the power consumption at the receiver. With this algorithm, the receiver activates as many antennas as necessary to maintain the residual total interference instantaneous power within a tolerable range, which can be set to guarantee a target performance level. The mode of operation does not require perfect knowledge of the statistical ordering of interfering signals instantaneous powers, which further reduces the complexity of implementation. It is shown that the arbitrary interference cancelation technique and no cancelation scenario can be studied as limiting cases of the proposed scheme. Analytical expressions for the statistics of the residual total interference instantaneous power are derived, which are then used to obtain results for the average number of active antennas and system outage performance. Numerical studies supported by simulations are presented to clarify the usefulness of the proposed scheme.

The impact of co-channel interference and non-ideal estimation of the desired user channel state information (CSI) on the performance of an adaptive threshold-based generalized transmit diversity for low-complexity multiple-input single-output configuration is investigated. The adaptation to channel conditions is assumed to be based on the desired user CSI, and the number of active transmit antennas is adjusted accordingly to guarantee predetermined target performance. To facilitate comparisons between different adaptation schemes, new analytical results for the statistics of combined signal-to-interference-plus-noise ratio (SINR) are derived, which can be applied for different fading conditions of interfering signals. Selected numerical results are presented to validate the analytical development and to compare the outage performance of the considered adaptation schemes.

The performance of transmit antenna selection for threshold-based maximal ratio combining (MRC) diversity receivers in the presence of multiple co-channel interfering signals is studied. The impact of imperfect channel estimation of desired user signals is considered, and the effect of phase and time misalignments between desired and undesired signals is incorporated in the analysis. Precise formulation for Nakagami-m faded interfering signals is presented. The analysis is applicable for arbitrary transmit antenna selection, which is based on the receiver combined signal-to-noise ratios (SNRs) or combined signal-to-interference-plus-noise ratios (SINRs) for different transmit channels. New expressions for the distribution of combined SINR and outage probability performance are derived considering SNR-based as well as SINR-based selection algorithms. The results can be used to study the performance of different system architectures under various channel conditions when the implementation complexity is of interest.

The performance of multiple-antenna diversity systems in which the receiver combines signal replicas per threshold-based maximal ratio combining (MRC) and the transmitter uses only a single antenna according to receive combined signal strength is studied. The impact of imperfect channel estimation is considered when the received signal replicas undergo independent and flat multipath fading. The analysis is applicable for arbitrary transmit antenna selection when the multiple-antenna channels experience identically distributed and non-identically distributed Rayleigh fading conditions. New closed-form expressions for the combined SNR statistics and some performance measures are presented. The system models adopted herein and the presented analytical results can be used to study the performance of different system architectures under various channel conditions when the implementation complexity is of interest.

This paper studies the performance of adaptive transmit channel selection in multipath fading channels. The adaptive selection algorithms are configured for single-antenna bandwidth-efficient or power-efficient transmission with as low transmit channel estimations as possible. Due to the fact that the number of active co-channel interfering signals and their corresponding powers experience random behavior, the adaptation to channels conditions, assuming uniform buffer and traffic loading, is proposed to be jointly based on the transmit channels instantaneous signal-to-noise ratios (SNRs) and signal-to-interference-plus-noise ratios (SINRs). Two interference cancelation algorithms, which are the dominant cancelation and the less complex arbitrary cancelation, are considered, for which the receive antenna array is assumed to have small angular spread. Analytical formulation for some performance measures in addition to several processing complexity and numerical comparisons between various adaptation schemes are presented.

Exact-form results are presented for integrals involving higher-order power of the one dimensional Gaussian Q-function over identical and nonidentically distributed multichannel Rayleigh fading with maximal ratio combining (MRC). The formulas known in the literature for the average of the 1st and 2nd powers are shown as special cases. The derived results herein are then used to obtain new expressions for the average error performance of differentially encoded quadri-phase shift-keying signals over identical as well as nonidentically distributed multi-channel Rayleigh fading.

This paper presents simple, exact, and closed-form expressions for the average bit error rate (BER) of M-ary orthogonal signals with noncoherent diversity combining over independent as well as arbitrarily correlated nonidentically distributed Nakagami-m fading channels. The fading channels are allowed to have arbitrary average signal-to-noise ratios (SNRs) as well as arbitrary fading parameters. The derived expressions are given in terms of elementary functions, they do not involve numerical integrals or complicated functional operations, and can easily be evaluated numerically. The results show that the system average BER can be estimated using the derived expressions herein with large computational time savings as compared with those taken by the ones addressed perviously.

Square-law combining is the traditional linear combining scheme used in conjunction with noncoherent and differentially coherent modulation/detection systems. For fading scenarios other than identical Rayleigh channels, such as nonidentical Nakagami-m channels, the square-law receiver is suboptimum, and in fact it incurs combining loss (does not aid the use of signal diversity) at relatively low average signal-to-noise ratios (SNRs). To overcome these disadvantages, this paper presents a receiver design with postdetection weighting for differentially coherent phase-shift keying (DPSK) and noncoherent orthogonal frequency shift-keying (NCFSK) signals over nonidentical Nakagami-m channels. It is shown that the proposed receiver is capable of eliminating the noncoherent loss associated with the square-law receiver, and providing improvements on the average error performance, as compared with the square-law receiver, over the whole range of the average (SNRs).

In this paper, we derive a closed-form expression for the average bit error rate (BER) of multi-level (M-ary) orthogonal signals with noncoherent diversity combining in nonidentical Nakagami-m fading channels. The assumption of nonidentical fading channels means that the average received signal-to-noise ratio (SNR) over the diversity branches are distinct and the amount of fading severity among different branches is not necessarily to be identical. The derived expression for the average BER does not involve either special functions or time-costly numerical integrations. Numerical examples are provided to demonstrate the validation of the analytical results in this paper for different transmission conditions.

In this paper, we consider the performance eval- uation of M -ary frequency shift keying (M -ary FSK) with postdetection equal-gain diversity combining over multi-link AWGN and generalized fading channels, in which the diversity branches are arbitrarily correlated and not necessarily to be identically distributed (having non-uniform power delay profile, fading parameters, and statistical distributions). New expressions for the conditional and average bit error probabilities of M - ary FSK system are derived. The average bit error probability is expressed in terms of a one-fold finite-range integral and considers the impact of non-identical and correlated fading branches on the system performance. I. INTRODUCTION

We analyze the performance of multiple carrier M-ary orthogonal signals (M-ary frequency shift keying signals) with postdetection equal-gain frequency diversity combining (EGC) over nonidentically distributed and/or arbitrarily correlated fading channels. The frequency diversity is satisfied using fast frequency hopping (FFH) technique, thereby achieving redundant reception of the same information-bearing signal. Multiple carrier M-ary frequency shift keying (MC-FSK) modulation in this paper can be classified as bandwidth and power efficient modulation, in which the multiple carrier assignment is achieved based on the Steiner system design; a case of the balanced incomplete block design (BIBD) from the combinatorial theory. Comparisons between the performance of FFH BIBD-based MC-FSK and that of the FFH conventional M-ary frequency shift keying (M-ary FSK) system are performed to verify the impact of the nonidentically distributed and arbitrarily correlated fading channels on the systems performance. In addition, the available channel bandwidth is efficiently utilized by optimizing the frequency hopping rate that provides the minimum average bit error probability (BEP), considering the effects of nonuniform power delay profile and fading parameters

We evaluate the performance of the multiple carrier M-ary frequency shift keying (MC-FSK) system over generalized fading channels. MC-FSK system represents each transmitted signal by a series of orthogonal components, which are activated based on the balanced incomplete block (BIB) design from the combinatorial theory. The performance is quantified in terms of the system power efficiency, by deriving an upper bound expression on the average bit error probability (BEP), and calculating the system bandwidth efficiency. The average BEP expression considers the case where the fading envelopes are not identically distributed and/or statistically described by the same statistical distribution family. Furthermore, we compare between the performance of the MC-FSK and that of the conventional M-ary FSK system. The results show that both systems achieve the same power efficiency when their combined diversity orders are equal, but at the same time, MC-FSK system does provide better bandwidth efficiency, which is proportional to the number of orthogonal carriers per transmitted signal. We show that MC-FSK system can simultaneously provide the same power efficiency at different bandwidth efficiencies depending on the number of orthogonal components per transmitted signal.

This study investigates different receive single-branch switch-based diversity schemes for dual-hop amplify-and-forward relaying networks. Specifically, three receive processing algorithms are adopted, in which the receive branch is selected using the arbitrary selection algorithm, the switching algorithm, or the switching algorithm with post-examining best branch selection. The identification of the receive branch is carried out for two different system models. For the first model, a single-antenna relaying station is used in conjunction with a multiple-antenna transceiver, where the processing is performed independently of the first hop-fading conditions. The second model suggests the use of parallel deployment of single-antenna relays to transfer information from a multiple-antenna transmitter to a single-antenna receiver, where the active relaying station is determined based on the pre-combining end-to-end fading conditions. Performance comparisons for various transmission scenarios on the first hop are presented using new formulations for the statistics of the combined signal-to-noise ratio. Simulation results are also provided to validate the mathematical development and to verify the numerical computations.

The performance of selection combining (SC) diversity in the presence of additive white Gaussian noise as well as multiple co-channel interfering signals over fading channels is analysed. The analysis considers two SC algorithms, namely, the signal-to-noise ratio-(SNR) based SC algorithm and the signal-to-interference-plus-noise ratio (SINR)-based SC algorithm. Closed-form expressions for the distribution of the resulting SINR and the outage probability performance are derived for both SC algorithms. The derived expressions are valid for arbitrary number of interfering signals, and when the desired signal replicas experience independent Rayleigh fading with generalised statistics. In addition, they are applicable for the general case when the interfering signals are subject to arbitrary fading models, which include the cases of identical, non-identical, correlated and mixed-mode fading scenarios. Numerical results are presented to examine the impact of different fading conditions and system parameters on the outage performance for both SC algorithms under consideration.

The use of transmit antenna selection algorithms in multiple-antenna systems enables significant reduction in implementation cost and complexity while maintaining acceptable performance. An attractive and quite flexible selection algorithm is to allow the receiver to pick any of the transmit antennas that can satisfy a predetermined performance target. Such an algorithm is referred to as the arbitrarily ordered transmit antenna selection algorithm. However, the effectiveness of transmit antenna selection is decreased by several propagation impairments over the feedback channel from the receiver to the transmitter. Of these impairments, the feedback channel time delay may impose a significant impact on the achieved performance. This paper aims to investigate the impact of this time delay on the performance of receive maximal-ratio combining (MRC) diversity employing the arbitrarily ordered transmit antenna selection algorithm. In order to obtain quantitative measures for this impact, new expressions for various performance criteria are obtained by using the new derived formulas for the probability density function (pdf) and the moment generating function (MGF) of the combined signal-to-noise ratio (SNR). Numerical and simulation results are presented to illustrate the effect of delayed (i.e. outdated) feedback information on the system performance for various transmit antenna selection scenarios.

The average symbol error probability (SEP) performance of arbitrary rectangular quadrature amplitude modulation in the context of arbitrarily ordered transmit antenna selection and receive maximal ratio combining diversity system is analysed. The channel gains are assumed to follow Nakagami-m fading distribution with in general arbitrary fading parameters. Exact expressions for the average SEP performance are derived for the general case of unequal in-phase and quadrature decision distances as well as distinct in-phase and quadrature modulation orders. The results generalise many previous case studies, and can be used to investigate the impact of various diversity-combining schemes and different modulation and channel parameters on the system average SEP performance.