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In this article, a new expression for the joint moment generating function (MGF) of the signal-to-noise ratio (SNR) considering correlated $\eta$ - $\mu$ fading is determined. Based on this result, a new closed-form expression is presented for the bit error probability (BEP) of the rectangular quadrature amplitude modulation ($R$ -QAM) scheme, considering frequency non-selective channel subject to cascaded double correlated $\eta$ - $\mu$ fading and a receiver with dual branch maximum ratio combining (MRC). The signal is received from two links with correlated cascaded double fading in the second link. In addition, a new expression for the outage probability (OP) is derived. All expressions determined in this paper are new and corroborated by simulations performed with Monte Carlo method. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) is considered as a promising technology, which can effectively control the phase of signals with low-cost reflective elements. In this paper, we investigate the RIS-assisted D2D communication system under Nakagami- $m$ fading. Overlay mode and underlay mode are discussed respectively. To characterize the performance of proposed communication system, we propose novel closed-form analytical expressions for outage probability under two modes, respectively. Based on the analytical results, we derive the diversity order of outage probability. We show that under overlay D2D mode, the diversity order depends on the number of elements and fading parameters. For the underlay D2D case, 0 diversity order is obtained due to the existence of interference. Furthermore, we study the ergodic achievable rate for each mode and the corresponding tight bounds are derived in closed form. High SNR slopes achieved by users under two modes are also discussed. We observe a high SNR slope of order 1 for overlay D2D mode and 0 for underlay D2D mode. In addition, we also investigate the energy efficiency (EE) of the considered system. Numerical results show that the optimal phase shift proposed in our paper enhance system performance effectively comparing to the traditional D2D communication and random phase shift scheme. Significant EE gains can be obtained for low to middle SNR region by passive reflectors with reconfigurable phase. Unlike relay system, the nearer RIS to the D2D transmitter/receiver, the better performance is obtained. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of wireless systems that employ finite-blocklength channel codes for transmission and operate under queuing constraints in the form of limitations on buffer overflow or delay violation probabilities. A block fading model, in which fading stays constant in each coherence block and changes independently between blocks, is considered. It is assumed that channel coding is performed over multiple coherence blocks. A simple ARQ scheme with error-free feedback without any delay is considered. The channel coding rate with given maximal error probability is considered as the service rate and is incorporated into the effective capacity formulation, which characterizes the maximum constant arrival rate that can be supported under statistical queuing constraints. Performances of variable-rate and fixed-rate transmissions are studied. The optimum error probability for variable-rate and fixed-rate transmissions is shown to be unique. The limiting performance as the number of blocks increases is characterized. The tradeoffs and the interactions between the throughput, the number of coherence blocks over which channel coding is performed, error probabilities, channel coherence duration, and queuing constraints are identified. [ABSTRACT FROM AUTHOR]

Multi-connectivity (MCo) is considered to be a key strategy for enabling reliable transmissions and enhanced data rates in fifth-generation mobile networks, as it provides multiple links from source to destination. In this paper, we quantify the communication performance of MCo in terms of outage probability and throughput. For doing so, we establish a simple, yet accurate analytical framework at high signal-to-noise ratio (SNR), in which the number of links, the spectral efficiency, the path loss, and the SNR are incorporated, giving new insights into the potentials of MCo as compared with the single-connectivity (SCo). These are our main contributions: 1) finding the exact coding gain of the outage probability for parallel block-fading channels; 2) quantifying the performance improvement of MCo over SCo in terms of SNR gain; and 3) comparing optimal and suboptimal combining algorithms for MCo at the receiver side, namely joint decoding, selection combining, and maximal-ratio combining, also in terms of SNR gain. In addition, we apply our analytical framework to real field channel measurements and thereby illustrate the potential of MCo to achieve high reliability and high data rates in real cellular networks. [ABSTRACT FROM AUTHOR]

This paper investigates the physical-layer security of the modify-and-forward (MF) protocol in multi-relay and multi-eavesdropper networks. Three relay selection critera are developed according to the channel state information (CSI) acquisition. Criterion I requires the CSI of all main channels for relay selection. Criteria II and III rely only on the CSI of the source-relay and relay-destination channels, respectively. We derive the exact secrecy outage probability (SOP), probability of nonzero secrecy capacity, and the ergodic secrecy rate in the closed forms. The $\epsilon$ -outage secrecy capacity is also evaluated. Asymptotic analysis of the SOP explicitly reveals that the secrecy diversity order of criterion I depends on the total number of relays, whereas those of criteria II and III are 2 and 1, respectively. The probability of nonzero secrecy capacity asymptotically decreases with the SNR of the wiretap channel as the eavesdropper is close to the source and relays. Criterion I is always superior to criteria II and III in terms of the ergodic secrecy rate and $\epsilon$ -outage secrecy capacity. Simulations results also demonstrated that the $\epsilon$ -outage secrecy capacity deteriorates as the SNR of the eavesdropper's channel increases. [ABSTRACT FROM AUTHOR]

Energy efficiency of three common hybrid automatic repeat request (HARQ) schemes, including Type I HARQ, HARQ with chase combining (HARQ-CC) and HARQ with incremental redundancy (HARQ-IR), is analyzed and joint power allocation and rate selection to maximize the energy efficiency is investigated in this paper. Unlike prior literature, time-correlated fading channels are considered and two widely concerned quality of service (QoS) constraints, i.e., outage and goodput constraints, are also considered in the optimization, which further differentiates this paper from prior ones. Using a unified expression of asymptotic outage probabilities, optimal transmission powers and optimal rate are derived in closed forms to maximize the energy efficiency while satisfying the QoS constraints. These closed-form solutions then enable a thorough analysis of the maximal energy efficiencies of various HARQ schemes. It is revealed that with low-outage constraint, the maximal energy efficiency achieved by Type I HARQ is $\frac{1}{4\ln 2}$ b/J, while HARQ-CC and HARQ-IR can achieve the same maximal energy efficiency as $\frac{\kappa _\infty }{4\ln 2}$ b/J, where $\kappa _\infty = 1.6617$. Moreover, time correlation in the fading channels has a negative impact on the energy efficiency, whereas large maximal allowable number of transmissions is favorable for the improvement of energy efficiency. The effectiveness of the energy-efficient optimization is verified by extensive simulations and the results also show that HARQ-CC can achieve the best tradeoff between energy efficiency and spectral efficiency among the three HARQ schemes. [ABSTRACT FROM AUTHOR]

In contrast to the traditional assumption of the independent and identically distributed fading channels, this paper studies the achievable rate of the multiuser two-way full-duplex (FD) relay system under the independent and nonidentically distributed (i.ni.d.) fading channels, which leads to the different selection probabilities and different weighted rates of different user pairs contributing to the overall system achievable rate as well. To be specific, we first derive the user pair selection probabilities of the max–min scheduling scheme for the i.ni.d. channels. Then, based on the selection probabilities, we solve the hard problem of the weighted rate derivation of each pair. Finally, according to the total probability theorem, the general expressions of the system achievable rate are obtained. In addition, theoretical evaluations and numerical simulations are conducted. The results verify the accuracy of the theoretical analysis and reveal the superiority of the FD mode especially within the low transmitting power regime. [ABSTRACT FROM PUBLISHER]

In this paper, we study the performance of a downlink non-orthogonal multiple access-based cooperative relay system with a single relay over Nakagami- $m$ fading channels, where both decode-and-forward (DF) and amplify-and-forward (AF) protocols are considered. We assume that only statistical channel state information is available to the system and used to determine the decoding order of cell-edge users’ data. For DF relaying, both ergodic sum rate and outage probability are solved in closed form. For AF relaying, closed-form asymptotic ergodic sum rate and outage probability are provided. Numerical results verify the accuracy of the analysis and demonstrate that the DF protocol significantly outperforms the AF one in terms of ergodic sum rate even the channel’s near–far effect weakens. In addition, the DF protocol exhibits better outage performance than the AF one at low signal-to-noise ratio (SNR), though the superiority becomes negligible with the increasing SNR. [ABSTRACT FROM PUBLISHER]

This paper investigates a distributed cyclic delay diversity (CDD) transmission scheme for cyclic-prefixed single carrier systems in non-identically and identically distributed frequency selective fading channels. The distinguishable feature of the proposed scheme lies in providing a transmit diversity gain while reducing the burden of estimating the channel state information, which is a challenging task in distributed and cooperative systems. To effectively use the distributed CDD scheme at the transmitters, two sufficient conditions are derived to eliminate the intersymbol interference at the receiver and leveraged to convert the multi-input single-output channel into a single-input single-output channel. These conditions allow the system to achieve the maximum diversity for frequency selective fading channels at a full rate. To achieve this maximum diversity, a fixed number of CDD transmitters are selected based on the channel conditions, symbol block size, and maximum time dispersion of the channel, and a new two-stage transmission mode is proposed. Based on the distributed CDD and the proposed selection schemes, a new expression for the signal-to-noise ratio at the receiver is obtained with the aid of order statistics, and then closed-form expressions for the outage probability and average symbol error rate (ASER) are derived. As far as the identically distributed frequency selective fading channel model is concerned, the achievable maximum diversity gain is proved, with the aid of asymptotic analysis, to be equal to the product of the total number of transmitters in the system and the number of multipath components. Link-level simulations are also conducted to validate the analytical expressions for outage probability, ASER, and maximum achievable diversity gain. [ABSTRACT FROM PUBLISHER]

We investigate the performance of three-node lossy-forward (LF) relaying over independent block Nakagami- $m$ fading channels. Based on the theorem of source coding with side information, the exact outage probability expression for arbitrary values of the shape factor $m$ is derived under the assumptions of both the Gaussian codebook capacity and the constellation constrained capacity. The difference in outage probability between the two codebook models of capacity is found to be very minor. Furthermore, an accurate high signal-to-noise ratio approximation for the outage probability is obtained. It clearly identifies the equivalent diversity order and coding gain of the LF relaying. It is shown that the LF relaying is superior to conventional decode-and-forward relaying in terms of the outage probability and the $\epsilon$ -outage achievable rate. Moreover, with the LF relaying, the optimal location for the relay (R), which minimizes the outage probability, is found to be the point having same distance to the source (S) and the destination (D) when the S-R and R-D links experience the same level of fading. The accuracy of the analytical results is verified by a series of Monte Carlo simulations. [ABSTRACT FROM PUBLISHER]

This paper quantifies the impact of correlated fading on secure communication of multiple amplify-and-forward (AF) relaying networks. In such a network, the base station (BS) is equipped with multiple antennas and communicates with the destination through multiple AF relays, while the message from the relays can be overheard by an eavesdropper. We focus on the practical communication scenario, where the main and eavesdropper’s channels are correlated. In order to enhance the transmission security, transmit antenna selection is performed at the BS, and the best relay is chosen according to the full- or partial-relay selection criterion, which relies on the dual-hop relay channels or the second-hop relay channels, respectively. For these criteria, we study the impact of correlated fading on the network secrecy performance, by deriving an analytical approximation for the secrecy outage probability and an asymptotic expression for the high main-to-eavesdropper ratio. From these results, it is concluded that the channel correlation is always beneficial to the secrecy performance of full relay selection. However, it deteriorates the secrecy performance if partial-relay selection is used, when the number of antennas at the BS is less than the number of relays. [ABSTRACT FROM PUBLISHER]

The outage probability (OP) of the signal-to-interference-plus-noise ratio (SINR) is an important metric that is used to evaluate the performance of wireless systems. One difficulty toward assessing the OP is that, in realistic scenarios, closed-form expressions cannot be derived. This is, for instance, the case of the Log-normal environment, in which evaluating the OP of the SINR amounts to computing the probability that a sum of correlated Log-normal variates exceeds a given threshold. Since such a probability does not admit a closed-form expression, it has thus far been evaluated by several approximation techniques, the accuracies of which are not guaranteed in the region of small OPs. For these regions, simulation techniques based on variance reduction algorithms are a good alternative, being quick and highly accurate for estimating rare event probabilities. This constitutes the major motivation behind this paper. More specifically, we propose a generalized hybrid importance sampling scheme, based on a combination of a mean shifting and a covariance matrix scaling, to evaluate the OP of the SINR in a Log-normal environment. We further our analysis by providing a detailed study of two particular cases. Finally, the performance of these techniques is performed both theoretically and through various simulation results. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel distributed cooperative sensing algorithm for connected vehicles. The adaptive energy detection threshold, which is used to decide whether the channel is busy, is optimized in this paper by using a computationally efficient numerical approach. The proposed optimization approach minimizes the probability of an incorrect detection as a function of both the probability of false alarm and the probability of missed detection. By considering both probabilities when computing the probability of incorrect detection, to the best of the authors' knowledge, the proposed approach is novel. During the energy detection process, large-scale fading, multipath fading, Doppler effect, and transmission errors affecting the control messaging process are accounted for in order to provide a practical solution for connected vehicles. Once the available channels have been detected, the vehicles share this information using broadcast control messages. Each vehicle evaluates the available channels by voting on the information received from one-hop neighbors, where the credibility of each neighbor is weighted during the voting process. An interdisciplinary approach referred to as entropy-based weighting is used to define the neighbor, as well as the vehicle's own credibility. The voting mechanism is switched between the proposed voting mechanism and the traditional voting approach obtained from the current state of the art in order to maintain a balance between the computational cost/latency and robust spectrum sensing. Experimental results show that by using the proposed distributed cooperative spectrum sensing mechanism, spectrum detection error converges to zero. [ABSTRACT FROM AUTHOR]

The Gamma–Gamma distribution has recently emerged in a number of applications ranging from modeling scattering and reverberation in sonar and radar systems to modeling atmospheric turbulence in wireless optical channels. In this respect, assessing the outage probability achieved by some diversity techniques over this kind of channels is of major practical importance. In many circumstances, this is related to the difficult question of analyzing the statistics of a sum of Gamma–Gamma random variables. Answering this question is not a simple matter. This is essentially because outage probabilities encountered in practice are often very small, and hence, the use of classical Monte Carlo methods is not a reasonable choice. This lies behind the main motivation of this paper. In particular, this paper proposes a new approach to estimate the left tail of the sum of Gamma–Gamma variates. More specifically, we propose robust importance sampling schemes that efficiently evaluates the outage probability of diversity receivers over Gamma–Gamma fading channels. The proposed estimators satisfy the well-known bounded relative error criterion for both maximum ratio combining and equal gain combining cases. We show the accuracy and the efficiency of our approach compared with naive Monte Carlo via some selected numerical simulations. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the performance of an overlay multiuser two-way relay network with $N$ th-user selection by employing a three-phase cooperative spectrum sharing (3PCSS) scheme. Hereby, a one-end primary user (PU) communicates with the arbitrary (which may be the $N$ th best) selected other-end PUs with the cooperation of a secondary user (SU) in three transmission phases. By splitting up its available power, the SU assists in bidirectional primary transmissions and accesses the spectrum for its own transmission, based on satisfying the primary system outage constraint. Considering the involved $N$ th-order statistics with correlation, we derive the outage probability expressions for both primary and secondary systems over general fading channels. Based on these expressions, we compute the total system throughput of the 3PCSS scheme and compare it with other competitive schemes. We illustrate that the 3PCSS scheme can effectively realize spectrum sharing by harnessing additional cooperative diversity and achieving spectral efficiency at par with the primary two-phase direct transmission system. Numerical and simulation results substantiate our theoretical findings. [ABSTRACT FROM PUBLISHER]

The incomplete moment generating function (IMGF) has paramount relevance in communication theory, since it appears in a plethora of scenarios when analyzing the performance of communication systems. We here present a general method for calculating the IMGF of any arbitrary fading distribution. Then, we provide exact closed-form expressions for the IMGF of the very general $\kappa $ - $\mu $ shadowed fading model, which includes the popular $\kappa $ - $\mu $ , $\eta $ - $\mu $ , Rician shadowed, and other classical models as particular cases. We illustrate the practical applicability of this result by analyzing several scenarios of interest in wireless communications: 1) physical layer security in the presence of an eavesdropper; 2) outage probability analysis with interference and background noise; 3) channel capacity with side information at the transmitter and the receiver; and 4) average bit-error rate with adaptive modulation, when the fading on the desired link can be modeled by any of the aforementioned distributions. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the achievable coverage and the information rate of an aerial base station. The air-to-ground link is analysed by considering random fading and shadowing effects impairing the wireless transmission, together with a homogeneous spatial distribution of the terrestrial users. The distribution of the buildings in the underlying coverage region is modeled using the International Telecommunication Union-Recommendation statistical city model. For a given urban environment/region, we analytically quantify the achievable coverage probability and the information rate of users on the ground at a particular base station altitude. Furthermore, we analytically find the optimal altitude of the aerial base station to maximise the terrestrial coverage given a certain service region. Simulations are conducted to verify our analysis, and a close match between the analytical and simulation results is observed. [ABSTRACT FROM AUTHOR]

In this paper, the secrecy performance of finite-sized cooperative cyclic prefixed single carrier systems with multiple eavesdroppers and unreliable wireless backhaul connections across multiple transmitters is investigated. For nonidentical frequency-selective fading channels between the relay and destination nodes, secrecy performance metrics including the secrecy outage probability, ergodic secrecy rate, and probability of nonzero achievable secrecy rate are derived. Furthermore, the existence of performance limits on the secrecy outage probability and probability of non-zero achievable secrecy rate are verified for various backhaul scenarios. These limits are found to be exclusively determined by the backhaul reliability. For imperfect backhaul connections, it is found that the diversity gain promised by cooperative cyclic prefixed single-carrier systems cannot be achieved in the conventional asymptotic high signal-to-noise ratio region. Link-level simulations are conducted to verify the derived impact of backhaul reliability on the secrecy performance. [ABSTRACT FROM PUBLISHER]

In this paper, we present a comprehensive framework for quadrature spatial modulation (QSM) in generalized fading channels. In particular, the performance analysis of QSM systems in the presence of imperfect channel knowledge and under correlated fading channels is presented. A simple and closed-form expression for the pairwise error probability (PEP) is provided. Based on the obtained PEP, a closed-form upper bound expression for the average bit error probability (BEP) is obtained. The analysis is unified in the sense that it is applicable for any fading channel once its envelope and phase distributions are available. As such, different generalized fading distribution models, namely, $\eta $ – $\mu $ , $\kappa $ – $\mu $ , and $\alpha $ – $\mu $ distributions, are considered. The obtained results clearly show the influence of the fading parameters on the average BEP. In the case of the $\alpha $ – $\mu $ fading channels, increasing $\alpha $ has larger negative impact on the average BEP compared with increasing $\mu $ . For the $\kappa $ – $\mu $ channels, increasing $\mu $ results in increasing the average BEP dramatically when compared with increasing $\kappa $ . In the same context, in $\eta $ – $\mu $ fading channels, as $\mu $ increases the average BEP degrades whereas increasing $\eta $ slightly improves the average BEP. In addition, it is demonstrated that transmit-antenna correlation significantly deteriorate the average BEP when compared with receive-antenna correlation. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of the point-to-point multiple-input–multiple-output (MIMO) systems in the presence of a large but finite numbers of antennas at the transmitters and/or receivers. Considering the cases with and without hybrid automatic repeat request (HARQ) feedback, we determine the minimum numbers of the transmit/receive antennas, which are required to satisfy different outage probability constraints. Our results are obtained for different fading conditions and the effect of the power amplifiers efficiency/feedback error probability on the performance of the MIMO–HARQ systems is analyzed. Then, we use some recent results on the achievable rates of finite block-length codes, to analyze the effect of the codewords lengths on the system performance. Moreover, we derive closed-form expressions for the asymptotic performance of the MIMO–HARQ systems when the number of antennas increases. Our analytical and numerical results show that different outage requirements can be satisfied with relatively few transmit/receive antennas. [ABSTRACT FROM PUBLISHER]

Prior results on exact error rates and outage probabilities of diversity receptions over arbitrarily correlated fading channels involve intractable nested integrals, which makes the performance analyses challenging to carry out. In this paper, we derive asymptotic expressions and asymptotically tight bounds for error rates and outage probabilities of diversity receptions (including maximal-ratio combining, selection combining, and equal-gain combining) over arbitrarily correlated Beckmann fading channels. These new asymptotic performance expressions reveal insights into the diversity systems over arbitrarily correlated Beckmann fading channels, and the accuracy of the asymptotic performance expressions is explicitly quantified by the performance bounds. Using these analytical tools, one can assess the performance of the diversity reception systems over arbitrarily correlated Beckmann fading channels without resorting to time-consuming Monte Carlo simulation or numerical multifold integration. [ABSTRACT FROM PUBLISHER]

SUMMARY An expression for the average symbol error probability of coherent orthogonal M-ary frequency shift keying in generalized fading was recently reported by Chandra, Poram, and Bose. We show that the expression is only exact for M = 2; it does, however, provide an accurate approximation for M > 2. By modifying the derivation of the reported expression, we derive a lower bound for M ⩽5 that has the same complexity as the reported expression, and we illustrate that, for M > 2, the expression of the derived bound provides an approximation that is also more accurate.Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper studies a multi-relay adaptive turbo-coded cooperative diversity scheme over Nakagami- m fading channels. In the underlying scheme, after receiving a fraction of the codeword determined by a tradeoff parameter denoted by f, all the relays decode, and only the reliable relays forward the rest of the codeword to the destination. We assume binary phase-shift keying modulation and analyze the scheme under study in terms of bit error rate (BER) and outage probability. Union bounds on the BER are derived using the transfer function bounding and the limit-before-average techniques. Furthermore, we examine the asymptotic behavior of the system in the high-signal-to-noise-ratio (SNR) regime using the derived pairwise error probability (PEP). We also derive a closed-form expression for the outage probability of the system and its high-SNR approximation to evaluate the achievable diversity order. Simulations are provided to assess the accuracy of our analytical work. [ABSTRACT FROM PUBLISHER]

We consider a single-input-multiple-output (SIMO) fading channel that can be assumed static over a duration of L symbols. We show that the generalized likelihood ratio test (GLRT) receiver for detecting a block of L uncoded symbols does not require channel-state information (CSI). By deriving an exact closed-form pairwise error probability expression for the detector over slowly time-varying Rayleigh fading, we show that its performance approaches that of coherent detection with perfect CSI when L becomes large. To detect a very long sequence of S symbols over a channel that can be assumed to remain static only over L symbols, where S ≫ L, while keeping computational complexity low, we consider three pilot-based algorithms, namely, the trellis search algorithm, pilot-symbol-assisted block detection, and decision-aided block detection. We compare them with the two existing block-by-block detection algorithms, namely, lattice decoding and sphere decoding, and show the former's advantages in complexity and performance. [ABSTRACT FROM AUTHOR]

Asymptotic error rate expressions are derived for multi-branch equal gain combining and selection combining operating on arbitrarily correlated Rayleigh fading channels. These closed-form solutions are used to provide rapid and accurate estimation of the error rates in large signal-to-noise ratio regions. More importantly, they reveal additional insights into the transmission characteristics of linear diversity combining schemes operating on correlated Rayleigh fading channels. It is shown that the asymptotic error rates over correlated branches can be obtained by scaling the asymptotic error rates over independent branches with a factor, det(M), where det( M) is the determinant of the normalized channel correlation matrix. This relationship is valid for both coherent and noncoherent signalings. A similar relationship is also established for the outage probabilities of fading wireless systems employing multi-branch diversity reception. [ABSTRACT FROM AUTHOR]

In this paper, the crossing statistics of phase processes and random frequency-modulation (FM) noise are studied for α-μ fading channels. Specifically, simple closed-form expressions for the probability density function (pdt) and the cumulative distribution function (cdt) of random FM noise as well as the generalized phase-crossing rate (GPCR) are derived. In addition, simple closed-form expressions for the conditional pdfs of the envelope and the random FM noise, which are conditioned on an arbitrary phase upward crossing level, are obtained and investigated. The formulations developed here are validated by means of Monte Carlo simulation and verified by comparison with results that are already known in the literature. These results correspond to special cases of the α-μ fading channels, such as Nakagami-m and Weibull channels. [ABSTRACT FROM AUTHOR]

It is well known that multipath fading significantly affects the performance of communication systems. In order to incorporate the impact of this random phenomenon on system analysis and design, in many cases, we need to calculate the probability density function (pdf) of the received signal envelope in multipath fading channels. In this paper, we consider a general multipath fading channel with arbitrary number of paths, where amplitudes of multipath components are arbitrary correlated positive random variables, independent of phases, whereas the phases are independent and identically distributed random variables with uniform distributions. Since the integral form of the envelope pdf for such a general channel model is too complicated to be used for analytic calculations, we propose two infinite expansions for the pdf: a Laguerre series and a power series. Based on the tight uniform upper bounds on the truncation error of these two infinite series, we show that the Laguerre series is superior to the power series due to the fact that for a fixed number of terms, it yields smaller truncation error. This Laguerre series with a finite number of terms, which expresses the envelope pdf just in terms of simple polynomial-exponential kernels, is particularly useful for mathematical performance prediction of communication systems in those indoor and outdoor multipath propagation environments, where the number of strong multipath components is small. [ABSTRACT FROM AUTHOR]

This paper considers the problem of minimizing outage probabilities in the downlink of a multiuser, multicell orthogonal frequency division multiple access (OFDMA) cellular network with frequency selective fading, imperfect channel state information, and frequency hopping. The task is to determine the allocation of powers and subcarriers for users to ensure that the user outage probabilities are as low as possible. We formulate a min-max outage probability problem and solve it under constraint that the transmit power spectrum at each base station is flat. In particular, we obtain a subchannel allocation algorithm that has complexity O(L log L) in L, the number of users in the cell. We also consider suboptimal but implementable approaches with and without the flat transmit power spectrum constraint. We conclude that the flat transmit spectrum approach has merit, and warrants further study. [ABSTRACT FROM AUTHOR]

This work analyzes the high-SNR asymptotic error performance of outage-limited communications with fading, where the number of bits that arrive at the transmitter during any timeslot is random but the delivery of bits at the receiver must adhere to a strict delay limitation. Specifically, bit errors are caused by erroneous decoding at the receiver or violation of the strict delay constraint. Under certain scaling of the statistics of the bit-arrival process with SNR, this paper shows that the optimal decay behavior of the asymptotic total probability of bit error depends on how fast the burstiness of the source scales down with SNR. If the source burstiness scales down too slowly, the total probability of error is asymptotically dominated by delay-violation events. On the other hand, if the source burstiness scales down too quickly, the total probability of error is asymptotically dominated by channel-error events. However, at the proper scaling, where the burstiness scales linearly with "Multiple line equation(s) cannot be represented in ASCII text " and at the optimal coding SNR duration and transmission rate, the occurrences of channel errors and delay-violation errors are asymptotically balanced. In this latter case, the optimal exponent of the total probability of error reveals a tradeoff that addresses the question of how much of the allowable time and rate should be used for gaining reliability over the channel and how much for accommodating the burstiness with delay constraints. [ABSTRACT FROM AUTHOR]

In this paper, closed-form expressions for the uncoded but error probability of closed-loop transmit diversity (CLTD) algorithms with two transmit and one receive antennas and noisy channel state information (CSI) in time-varying Rayleigh fading channels are derived. Two CLTD algorithms considered are the phase-amplitude CLTD (PA-CLTD), where the transmit antennas may transmit with different signal energy, and the phase-only CLTD (PO-CLTD), where the transmit antennas must transmit with the same signal energy. In addition to the uncoded bit error probability, this paper also derives the pairwise error probability when finite-depth interleaved convolutional codes are used with CLTD algorithms. However, due to the complexity of the coded system, the pairwise error probabilities are not in the closed-form expressions. The results have shown that PA-CLTD performs slightly better than PO-CLTD although PA-CLTD requires significantly more feedback information and that, when the Doppler spread is large, the performance of CLTD algorithms may degrade significantly. Moreover, a comparison between PA-CLTD, the Alamouti space-time code and the SISO system indicates that PA-CLTD outperforms the other two systems when the Doppler spread is small and the pilot SNR is large. Finally, the analytical results are compared with results from Monte Carlo simulation and the comparison shows that the analytical results match well with the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, we show that the cumulative and probability distribution functions (cdf and pdf, respectively) of small-scale wideband signal envelope fading in microcells can be very closely approximated by both the Rice and Nakagami distributions, which are already known to describe the cdfs and pdfs of small-scale narrowband signal envelope fading. Our results are obtained by means of an extensive Monte Carlo-based study of a wideband propagation model by Yan and Kozono, which is itself supported by extensive measurements. Over a comprehensive range of microcell propagation parameters, the average maximum error in the approximation is 1.65% and 1.78% for the Rice and Nakagami cdfs, respectively. The error in the approximation is 3.58% and 3.87% for the 95th percentile and does not exceed 7.61% and 7.80%, respectively, in the worst case. We propose an expression that maps the significant wideband small-scale signal envelope fading parameters to their narrowband counterparts for different standards like Dedicated Short Range Communication, WiMAX, Universal Mobile Telecommunications Service, and the family of the IEEE 802.11 standards. This mapping enables narrowband small-scale signal envelope fading statistical distributions, which are currently used, e.g., in fading simulators, link quality determination algorithms, and outage probability calculators, to be readily adapted to deal with small-scale wide-band signal envelope fading. As an application example of this proposed mapping, we derive the appropriate sample spacing and averaging interval (window size) that ought to be used to estimate the large-scale fading signal in an IEEE 802.11 receiver. [ABSTRACT FROM AUTHOR]

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 tipper 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. [ABSTRACT FROM AUTHOR]

This paper presents a unified analytical method for computing the average E [g(x/ (∑k=1κ=1 yk + b) )] of some arbitrary function g(.) when x is a gamma random variable and independent of the arbitrary random variables y1, y2,…, yκ. This leads to new explicit expressions for the averages of some specific functions including, erfc(√z), exp(-z), n, and ln(1 + z), in terms of the moment generating functions of y1, y2,… yκ. [ABSTRACT FROM AUTHOR]

Data transmission through frequency-selective block fading channels is considered in the case where neither the transmitter nor the receiver has any knowledge of the channel coefficients. Standard code design approaches for this scenario take channel uncertainty at the receiver into account by splitting the available channel coherence time into a part dedicated to training symbols utilized for channel estimation and a second part using an error-control coding scheme that is designed without channel uncertainty in mind. In contrast, in this correspondence joint codes are designed that are optimized for communication over the unknown channel and operate over the full coherence time. Using an approximation of the union bound on codeword error probability as design criterion, codes based on general complex-valued symbols are obtained with a gradient search optimization technique. Numerical examples for both single antenna as well as multiple-antenna systems illustrate that significant improvement over training-based schemes can be obtained. [ABSTRACT FROM AUTHOR]

This letter addresses the problem of energy detection of an unknown signal over a multipath channel. It starts with the no-diversity case, and presents some alternative closed-form expressions for the probability of detection to those recently reported in the literature. Detection capability is boosted by implementing both square-law combining and square-law selection diversity schemes. [ABSTRACT FROM AUTHOR]

The connection between the average codeword or frame error probability (FEP) of space-time codes and the outage probability over general block-fading multiple-input multiple-output (MIMO) channels is established. Three archetypal problems are considered under general fading distributions in a single framework wherein the receiver has channel state information whereas the transmitter knows a) the fading distribution but not the channel realization b) the channel realization but must follow a short term (per codeword) average power constraint, and c) the channel realization but is constrained only by a long-term average power constraint. Three telescoping sets of space-time codes are defined for a given rate and it is shown that average FEPs arbitrarily close to the respective outage probabilities for each of the three cases a)-c) can be achieved by codes in each set for sufficiently large frame lengths. For the smallest set among the three which contains codes with a spectral norm constraint that is stricter than the average or maximum energy constraints commonly assumed, firm sphere-packing lower bounds on the FEP are obtained, and, consequently, strong converse theorems are proved which assert that the respective outage probabilities also represent the best achievable FEP in the large frame-length limit. Moreover, the set of spectral norm constrained codes are also shown to be large enough to contain universal codes that can communicate reliably over any channel realization for which the mutual information exceeds the information rate of the code. [ABSTRACT FROM AUTHOR]

This letter presents infinite series expressions for the outage probability, the probability density function, the average error probability for binary modulations, and the average signal-to-noise ratio of dual selection combiners over correlated fading with arbitrary fading parameters at each input of the combiner. The outage probability is calculated for both thermal noise and interference-limited scenarios. The results obtained for the outage probabilities specified for identical fading parameters at both branches of the combiner are contrasted with the results of other studies in the literature. [ABSTRACT FROM AUTHOR]

The performances of dual-branch postdetection switch-and-stay combining (SSC) for noncoherent orthogonal binary frequency-shift keying and noncoherent orthogonal M- ary frequency-shift keying operating over slow, flat Rician fading channels are a topic of current interest. It is shown that recently published analyses obtain incorrect final results because some incorrect probability distribution parameters are used in the analyses. The previous results are corrected, and it is seen that the final results change significantly. The revised results are used to obtain optimum switching thresholds that minimize the average bit-error rate (BER) performance of these systems. Monte Carlo simulations are presented to verify the results, and it is shown that for a given BER, the signal-to-noise ratio difference of post-detection SSC and predetection SSC is much less than previously reported. [ABSTRACT FROM AUTHOR]

Lower and upper-bound expressions for the penalty of hybrid diversity used with any two-dimensional (2-D) signaling constellation with polygonal decision regions are derived. Using these bounds with well-known results for maximal ratio combining, the error probability performance of 2-D signaling with hybrid selection/maximal ratio combining can be approximated to a high accuracy. [ABSTRACT FROM AUTHOR]

Recent work has reported a lognormal limit theorem for sums of identically distributed equicorrelated lognormal random variables. An extended lognormal limit theorem for sums of nonidentically distributed correlated lognormal random variables having a particular correlation structure is derived. [ABSTRACT FROM AUTHOR]

Novel single-integral representations for the bivariate probability density function and cumulative distribution function of two correlated Rician random variables are derived. The solutions are expressed in terms of well known functions which are available in common mathematical software. The two random variables are not necessarily identically distributed as required by some past solutions. The new form of the bivariate Rician cumulative distribution function is applied to give a new expression for the outage probability of dual selection combining diversity operating in correlated Rician fading. [ABSTRACT FROM AUTHOR]

This letter advocates the performance of a multiuser relay network (MRN) equipped with a single amplify-and-forward (AaF) relay over Rayleigh fading environments. We derive new expressions for the cumulative distribution function (CDF) of the highest instantaneous end-to-end signal-to-noise ratio (SNR) taking into consideration the two cases of fixed gain relays and variable gain relays. Relying on these statistical results, we derive new expressions for the outage probability and symbol error rate (SER), both of which are obtained in exact closed form. Furthermore, we derive simple asymptotic outage probability and SER. Our asymptotic results confirm that opportunistic scheduling has no impact on the diversity order. We further prove that the array gain is what determines the SNR advantage of opportunistic scheduling over the single user scenario. [ABSTRACT FROM PUBLISHER]