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It is challenging to realize ultra-reliable and low latency communications (URLLC) under severe shadow fading and imperfect channel state information (CSI). However, reliability can be increased by exploiting space diversity from multiple receive antennas rather than retransmission with limited latency. Massive multi-user multiple-input-multiple-output (MU-MIMO) is studied to enable URLLC with imperfect CSI from least-square channel estimation. The linear minimum error probability (MEP) detector with a given length of pilots (LoP) is derived. Further, the LoP is optimized to minimize the error probability of the uplink with a limited number of channel uses, using the finite blocklength information theory and one-dimensional search methods. Numerical results verify that the proposed linear MEP detection incorporated in massive MU-MIMO improves reliability with limited latency and imperfect CSI. [ABSTRACT FROM AUTHOR]

Energy efficiency (EE) optimization of wireless systems has attracted increasing attention recently due to its beneficial impacts on the environment and operational savings. Max-min user energy-efficient precoding for multicell multiple-input–multiple-output (MIMO) cooperative networks is investigated. The optimization problem is a nonconvex fractional programming problem, and optimal solutions are hard to find. Two different local optimization methods, namely, block coordinate descent and sequential convex approximation, are proposed to transform the original problem into a series of convex subproblems. In the former method, the relationship between the user rate and the minimum mean square error (MMSE) is utilized, and optimization of the transmitter matrix is formulated as a semidefinite program; the latter method is based on the convex approximation of the nonconvex rate function. The fractional subproblem is transformed into a parameterized subtractive form by exploiting the generalized fractional programming theorem in both methods. Two iterative-fairness-based energy-efficient algorithms are proposed with proved local convergence. Numerical results illustrate that the proposed max-min EE algorithms can improve EE with a performance loss in terms of the sum rate at a high signal-to-noise ratio (SNR) and achieve EE fairness among base stations with different transmit power levels. [ABSTRACT FROM PUBLISHER]

We show that an L-branch maximal ratio combining (MRC) receiver with an average signal-to-noise ratio (SNR) \bar{\gamma} in Nakagami- m fading channels is equivalent to an mL-branch MRC receiver with average SNR \bar{\gamma}/m in Rayleigh fading channels in terms of symbol error probability (SEP) when mL is an integer. Moreover, the orthogonal space–time block code (OSTBC) employing M_\mathrmt transmit antennas and M_\mathrmr receive antennas with the average SNR \bar\gamma in Nakagami- m fading channels is shown to be equivalent to an mM_\mathrm{t}M_\mathrm{r}-branch MRC single-input–multiple-output (SIMO) receiver with the average SNR \bar{\gamma}/mM_\mathrm{t}$ in Rayleigh fading channels. [ABSTRACT FROM AUTHOR]

Spatial point processes are commonly used to model the placement and the number of interferers in modern wireless networks, where the ad hoc deployment of transmitters is common. The homogeneous Poisson point process (PPP) is the most popular spatial point process used to model co-channel interference. Optimum combining (OC) is the diversity combining technique that maximizes the signal-to-interference-plus-noise ratio at the receiver. The performance of OC in cooperative relaying in an interferer field modeled by a homogeneous PPP is analyzed. Both decode-and-forward (DF) and amplify-and-forward (AF) relay protocols are studied. Multirelay transmission and relay selection techniques are considered. Accurate approximations for the outage probability are derived for DF and AF relaying when the destination is able to estimate the noise-plus-interference correlation matrix (NICM) perfectly. An approximation for the outage probability of DF relaying is obtained when the destination only estimates the channel state information of the closest interferer. Relay selection outperforms multirelay transmission in both DF and AF relaying protocols. The interference correlation at the relays significantly degrades the outage performance. Limited estimation of the NICM results in better performance than conventional maximal-ratio combining, although it fails to achieve diversity gains. [ABSTRACT FROM AUTHOR]

Cooperative communication through relaying can improve the performance of communication systems under multipath fading conditions. Increasing the number of relays will also boost the performance of the system, but since relays transmit through orthogonal channels, this improvement is at the cost of bandwidth or rate of the system. A two-hop multi-relay decode-and-forward cooperative system is proposed in which selected relays transmit simultaneously in the same band, and therefore, there is no rate or bandwidth loss. To mitigate the error propagation due to incorrect decoding of symbols at the relays, we use a selection relaying method in which a relay transmits in the second hop if the channel quality between the relay and the source exceeds a minimum threshold regardless of the relay–destination link. In our proposed beamforming scheme, the phase of selected relays for transmission in the second hop is adjusted to compensate for the channel between the relay and the destination and achieve the best performance at the destination using only a simple MRC receiver. The relays use only two-bit quantized phase information of the channel gain between the relay and the destination, which can be sent to the relays by the destination. The general family of M-QAM modulation constellations is considered in the performance and diversity analysis. It is proved that the scheme achieves full diversity order, and closed-form expressions for the thresholds that achieve full diversity are found. [ABSTRACT FROM AUTHOR]

The exact average bit error probability (BEP) of decode-and-forward (DF) cooperative systems with relay selection for binary phase-shift keying (BPSK) signals in Nakagami- $m$ fading channels is derived. Two types of relay selection schemes, i.e., signal-to-noise ratio (SNR)-based relay selection and log-likelihood-ratio-based relay selection, are investigated, assuming that there are no feedback channels from the destination to the relays. Two types of receivers, i.e., a $\lambda$-maximal ratio combining receiver and a piecewise linear receiver, are examined. The BEP analysis for DF cooperative systems employing BPSK signals is used to derive symbol error probability upper bounds of DF cooperative systems with SNR-based relay selection for quadrature phase-shift keying and 16-quadrature amplitude modulation (16-QAM) signals. [ABSTRACT FROM PUBLISHER]

The outage probability of a two-hop coordinated decode-and-forward relay network is investigated. The case of two interfering cells is considered. This is analogous to the case when network coordination is performed with the dominant cochannel interfering cell. Different levels of network coordination are studied and their performances are compared. Exact expressions are derived for of the system for each coordination method. The impact of user location randomness on the outage probability is investigated. [ABSTRACT FROM PUBLISHER]

The downlink performance of a two-cell relay enhanced wireless network is investigated. A single relay is shared by the two base stations in the system. The relay is assumed to be placed in a geographic region covered by both base stations. The relay station is operating in the decode-and-forward mode. Closed-form approximations which estimate the exact results extremely closely are derived for the outage probability and the ergodic rate of the system. The impact of finite rate channel state information feedback on the user ergodic rate is examined. [ABSTRACT FROM PUBLISHER]

ABSTRACT The channel capacity and the bit error rate of ultra-wide bandwidth transmitted-reference systems are optimized with respect to time delay between the reference and the adjacent data pulses. Approximate and theoretical expressions for the signal-to-interference-plus-noise ratio are derived. Numerical results show that optimizing the receiver can provide a significant capacity improvement of up to 2.2 bits/s/GHz and a bit error rate performance gain of up to 2 dB in effective signal-to-noise ratio. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The outage probability of a multiuser two-hop amplify-and-forward relaying system employing opportunistic scheduling is investigated. A practically important case where there are cochannel interference signals present at the network is considered for the analysis. Exact expressions and closed-form lower bounds are derived for the outage probability. Exact closed-form expressions are derived for the system outage probability when interference signals are present at the relay and at the destination separately. A closed-form lower bound is derived for the outage probability when the relay and the destination nodes are affected by interference simultaneously. The effects of channel state information feedback delay are investigated for special cases. In addition, asymptotic outage probability results are derived to obtain useful insights on the effects of interference and feedback delay. The novel expressions can be used by practicing engineers to obtain reliable and realistic performance estimates for dual-hop multiuser relay networks. The results are useful for understanding the capabilities of the feedback channel required in this system. [ABSTRACT FROM AUTHOR]

The performance of opportunistic relaying in a dual-hop amplify-and-forward relay network where the relaying nodes are distributed according to a homogeneous two-dimensional Poisson point process with fixed density is analyzed. Largely ignored in the literature, this assumption leads to more realistic results, as in a typical practical scenario neither the number of relays nor their distances from the source and destination are known. An exact expression for the outage probability of this cooperative system for general fading environments and different types of relaying is derived. The expression is then simplified under an assumption that the radius of the relay deployment region is sufficiently large, and specialized to additive white Gaussian noise (no fading), Rayleigh fading and severe (half-Gaussian) fading environments. Simple and tight upper and lower bounds on the outage probability are also derived. Simulation results validate the theoretical analyses and verify the accuracies of the proposed bounds. [ABSTRACT FROM PUBLISHER]

New, exact closed-form expressions are derived for the probability density function and the cumulative distribution function of the end-to-end signal-to-noise ratio (SNR) of opportunistic dual-hop amplify-and-forward (AF) relaying systems with relay selection. The expressions are used to obtain the first exact integral solutions for the ergodic capacity and average symbol error probability, and the first exact closed-form solution for outage probability of an opportunistic AF relaying system where the best node is selected from a number of candidate intermediate nodes to relay the data signal between the source and the destination. The selection follows a maximum end-to-end SNR policy, based on the available channel state information. The results are precise for any number of candidate relays and Rayleigh, Nakagami-m or Rician fading distributions. The effects of different channel fading parameters and the number of relays in the relay selection pool are studied. The system performance is compared to that of dual-hop AF systems without relay selection and to dual-hop AF relaying systems with maximum relay-to-destination SNR relay selection. The adopted selection method provides diversity gain over dual-hop AF relaying systems without relay selection and over maximum relay-to-destination SNR relay selection. The diversity gain is proportional to the relay selection pool size. [ABSTRACT FROM AUTHOR]

A new theoretical method, the generalized transformed characteristic function (GTCF) approach gives an exact, integral solution for the probability density function of the end-to-end received signal-to-noise ratio in multihop amplify-and-forward relaying systems. In turn, the GTCF approach is used to obtain exact integral solutions for the ergodic capacity, outage probability and average symbol error probability of multihop amplify-and-forward relaying systems. The results are precise for any number of hops and can accommodate any channel fading distribution. The theory provides the first exact theoretical solutions for numbers of hops larger than 2. [ABSTRACT FROM AUTHOR]

New and improved energy detectors for cognitive radios are derived by considering the effect of the primary user traffic on spectrum sensing. The new energy detectors are designed based on the assumption that the primary user randomly arrives or departs during the sensing period. Numerical results show that the new energy detector outperforms the conventional energy detector in all the cases examined. The performance gain depends on the operating signal-to-noise ratio as well as the sample size used. [ABSTRACT FROM PUBLISHER]

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]

The capacity of amplify-and-forward multi-hop relaying systems under different adaptive transmission schemes over Nakagami-m fading channels is considered. Accurate theoretical approximations for the capacity of these systems are derived in terms of the characteristic function of the reciprocal of the instantaneous received signal-to-noise ratio. An accurate theoretical approximation for the probability of outage is also obtained. The accuracy of the expressions obtained is verified by Monte Carlo simulation. It is shown that a system with optimal power and rate adaptation outperforms the system with truncated channel inversion adaptive technique. Systems employing optimal rate adaptation with constant power achieve almost the same capacity as those with optimal rate and power adaptation at large values of signal-to-noise ratio. However, the capacity performance of a system with the truncated channel inversion adaptive technique is better than the corresponding system employing optimal rate adaptation with constant power for small values of signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

A signal-plus-noise (S + N) energy selection combining (S + N-ESC) scheme and a weighted S + N-ESC scheme for binary phase shift keying (BPSK) signaling are studied. The S + N-ESC selects the branch with the maximum S + N energy for detection. The advantage of the S + N-ESC and the weighted S + N-ESC is that they require no explicit channel estimation for diversity branch selection. The bit error rate (BER) performances of the S + N-ESC and the weighted S + N-ESC are analyzed for BPSK signaling in independent and nonidentically distributed (i.n.d.) Rayleigh fading channels. We show that the average error rate performance of the S+N-ESC is the same as classical signal- to-noise ratio selection combining (SNR-SC), which requires the estimation of fading amplitudes for branch selection, in independent and identically distributed (i.i.d.) Rayleigh fading channels. We also show that the weighted S + N-ESC has the same BER performance as the classical SNR-SC for i.n.d. Rayleigh fading channels. [ABSTRACT FROM AUTHOR]

The optimal linear Rake receiver for the detection of signals contaminated by symmetric alpha stable noise is derived for 1 < α ⩽ 2. Although this structure is suboptimal, it is optimal among the class of linear Rake receivers in the sense of minimizing the bit error rate. The proposed receiver is a very simple form of diversity combiner for signal detection in symmetric alpha-stable noise. The bit error rate improvements of the optimal linear Rake receiver over the maximal ratio combiner and the equal gain combiner are also derived in the form of signal-to-noise ratio advantage. [ABSTRACT FROM AUTHOR]

A framework for analyzing the performance of coded OSTBC-OFDM systems over arbitrary correlated generalized Ricean fading channels is established. The moment generating function of the signal-to-noise ratio at the input to the channel decoder is derived assuming correlated transmitter and receiver antennas and correlated paths in frequency selective channels. The probability of outage, the pairwise error probability, and the bit error rate are then evaluated. Bit-interleaved and iteratively decoded turbo product codes, Gray encoded M-ary quadrature amplitude modulation, and other parameters of the IEEE 802.16 Standard are used to illustrate numerical results. [ABSTRACT FROM AUTHOR]

The performance of collaborative spectrum sensing for cognitive radio in a lognormal shadowing and Rayleigh fading channel is investigated. Unlike previous works that assume perfect knowledge of the average channel signal-to-noise ratio, this paper considers the realistic case where estimation of the average channel signal-to-noise ratio has error. Furthermore, while previous works have designed and examined estimators based on assuming that the channel samples used in the average signal-to-noise ratio estimators are noiseless, the present work assumes that the channel samples are noisy, as is the case in practical systems. Numerical results show that the probability of missed opportunity decreases as the estimation error decreases, as expected. Perhaps unexpectedly, the results also show that in the presence of noise, there exists a threshold phenomenon for the noise level. Below a particular threshold, the probability of missed opportunity increases as the noise level increases. Yet above this threshold, the probability of missed opportunity decreases as the noise level increases. [ABSTRACT FROM AUTHOR]

The performance of non-data-aided feedback-loop symbol timing synchronization operating with the raised-cosine (RC) and the "better than" raised-cosine (BTRC) pulses is investigated. The individual effects of additive channel noise, self- noise, and their product on the variance of the jitter are studied for the two pulses. The BTRC pulse is shown to have better synchronization performance than the conventional RC pulse, except when the signal-to-noise ratio is very large and the excess bandwidth is large. Furthermore, in the case where a prefilter removing self-noise is employed, the BTRC pulse always has a performance gain over the RC pulse. The gain is, for example, as much as 1.4 dB for excess bandwidth of 0.35 without a prefilter and is larger when the excess bandwidth is smaller or a prefilter is employed. [ABSTRACT FROM AUTHOR]

Optimum selection combining using the maximum energy (OSC-ME) criterion for M-ary noncoherent frequency shift keying signaling in independent and nonidentically distributed fading channels is examined. A weighted maximum energy selection combining (WMESC) scheme is proposed and found to provide virtually the same symbol error probability as OSC-ME in Rician fading channels. The WMESC always provides power gain over the classical selection combining regardless of diversity order and signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Asymptotic error rate expressions are derived for equal gain combining and selection combining on dual-branch correlated Rician channels. The asymptotic error rate performances of three popular, diversity combining techniques are compared and some insights are obtained. The impacts of various channel parameters on the asymptotic performances of these diversity combining techniques are studied comprehensively. Some previous observations on diversity performances on correlated Rician channels are unified and further extended. [ABSTRACT FROM AUTHOR]

A novel receiver structure based on soft-limiting is proposed for detecting a time-hopping ultrawide-bandwidth (UWB) signal in the presence of multiple-access interference (MAI). The proposed structure contains a nonlinear limiter for suppressing the MAI. Simulation results show that the pro- posed receiver achieves better bit-error-rate performance than the conventional matched receiver when operating in MAI. When operating in an MAI-plus-Gaussian-noise environment, the receiver structure outperforms the conventional matched-filter receiver for moderate to large values of signal-to-noise ratio (SNR). A receiver structure with adaptive limiting threshold is further proposed to ensure that the performance of the soft-limiting receiver always meets or surpasses the performance of the conventional UWB receiver for all values of SNR. Application of the soft-limiting structure in the fingers of a Rake receiver is shown to enhance the signal-to-noise-plus-interference ratio. [ABSTRACT FROM AUTHOR]

The outage probability of maximal ratio combining diversity with an arbitrary number of antennas in the presence of an arbitrary number of cochannel interferers and thermal noise is derived when the branch gains of the desired user signal and interfering signals experience Rayleigh fading and have the same correlation matrix. Two special cases, when the correlation matrix is equicorrelated and when the correlation matrix has different eigenvalues, are considered for both the equal-power cochannel interference case and the unequal-power cochannel interference case. Further, the average bit-error rate of a coherent binary phase-shift keying (BPSK)-modulated cellular system using maximal ratio combining diversity in cochannel interference and correlated Rayleigh fading is derived. The effects of the average signal-to-noise ratio (SNR) and the average signal-power-to-interference-power ratio on the system performance are examined. [ABSTRACT FROM AUTHOR]

The question of how many receiver antennas to employ in a diversity system operating in cochannel interference is examined. The long-term signal-power-to-interference-power ratio, the long-term signal amplitude to the square root of the interference power ratio, the average instantaneous signal-to-interference ratio, and the average bit-error rate of a maximal ratio combining diversity system in the presence of an arbitrary number of cochannel interferers are evaluated when the desired user signal and the interfering user signals are independent, and each of them experiences correlated Ricean fading at the receiver antennas. The best number of antennas required for a fixed-size antenna array to achieve a good compromise between system performance and system cost is investigated. The results show that, in general, the performance of a fixed-size antenna array containing the maximum number of independent antennas cannot be significantly improved by adding more than one additional antenna. Some special cases where particular gains can be achieved by adding additional correlated antennas are also discussed. [ABSTRACT FROM AUTHOR]

The exact performance of selection combining, hybrid selection/maximal-ratio combining (H-S/MRC), and threshold-based H-S/MRC in correlated Nakagami-m fading for positive integer values of fading parameter m, is analyzed for a particular correlation structure. This correlation model, though not general, is much more general than the equal-correlation case, and includes equal correlation as a special case. The symbol-error rate and outage probability of the three combining schemes are obtained by transforming the correlated branch gains into a set of conditionally independent branch gains. Numerical and simulation results show excellent agreement with theoretical results. [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]

A useful integral, representing the average over Rayleigh fading of the product of two Gaussian Q-functions, is solved in closed-form. A closed-form solution for the symbol-error probability of general rectangular quadrature amplitude modulation in Rayleigh fading is derived. [ABSTRACT FROM AUTHOR]

Time variation on fading channels hinders accurate channel estimation in differential space-time modulation and deteriorates the performance. Decision-feedback differential detection is studied for block differential space-time modulation, and compared with conventional differential space-time modulation. It is observed that the proposed scheme does not suffer effective fading bandwidth expansion, as does the conventional scheme. An improved effective signal-to-noise ratio approach is proposed for analyzing the performance of the proposed scheme in time-varying flat Rayleigh fading. Theoretical analysis and simulations show the improved performance of the proposed scheme over the conventional scheme. [ABSTRACT FROM AUTHOR]

The performances of general M-ary and binary orthogonal noncoherent frequency-shift keying signal-plus-noise (S + N) receiver structures in slow, flat Rician fading channels are examined. The fading on the diversity branches is assumed to be independent, but not necessarily identically distributed. For each receiver, a symbol-error probability expression is derived as a single integral with finite integration limits. Extensive Monte Carlo simulation results are presented to validate the analytical expressions. The results indicate that, unlike previously published results, the performance of S + N selection combining (SC) is not always superior to that of classical SC in fading and is dependent on the value of the signal-to-noise ratio (SNR), the modulation order, the diversity order, the multipath intensity profile, and the fading parameter. It is further shown that increasing the number of diversity branches in a S + N SC receiver does not necessarily decrease the probability of error if the system is operating in the low-SNR region. The performances of S + N SC schemes are also compared with the performances of equal-gain combining and square-law combining receivers. [ABSTRACT FROM AUTHOR]

The bit-error rate (BER) of binary phase-shift keying in Rayleigh fading, using the Alamouti transmission scheme and receiver selection diversity in the presence of channel-estimation error, is studied. Closed-form expressions for the BER of log-likelihood ratio selection, signal-to-noise ratio (SNR) selection, switch-and-stay combining selection, and maximum ratio combining are derived in terms of the SNR and the cross-correlation coefficient of the channel gain and its corrupted estimate. Two new selection schemes, space-time sum-of-squares combining selection diversity and space-time sum-of-magnitudes selection diversity, are proposed and proven to provide almost the same performance as SNR selection, but with much simpler implementations. The effects of channel-estimation errors on each selection scheme are examined. [ABSTRACT FROM AUTHOR]

An accurate approximation to the average symbol-error rate of hybrid selection/maximal-ratio combining (H-S/MRC) in correlated Nakagami-m fading with positive integer values of m is obtained by using a Green's matrix approximation. This approach is valid for different M-ary linear modulation schemes. We illustrate our methodology using M-ary phase-shift keying as an example. [ABSTRACT FROM AUTHOR]

In two recent papers, the performances of dual-branch postdetection switch-and-stay combining (SSC) for non-coherent orthogonal binary frequency-shift keying (BFSK) and noncoherent orthogonal M-ary frequency-shift keying (MFSK) operating in the present of slow flat fading modeled by Rayleigh, Nakagami-m, and Rician distributions have been analyzed. In this paper, we show that these previous analyses for the Nakaga mi-m fading model, which are restricted to integer values of m, are incorrect, and we derive the correct bit-error rate (BER) performances of BFSK and MFSK with dual-branch SSC in Nakagami-m fading for all values of m. Optimum switching thresholds that minimize the BER of BFSK and MFSK with postdetection SSC in Nakagami-m fading are obtained. The performance of postdetection SSC is compared with the performance of predetection SSC, and it is shown that postdetection SSC outperforms predetection SSC for all values of signal-to-noise ratio (SNR). We also show that for a given BER, the performance gain of postdetection SSC over predetection SSC has been overestimated by several decibels in SNR in previous publications. [ABSTRACT FROM AUTHOR]

An exact analysis is derived for precisely calculating the bit error probability of time-hopping and direct-sequence ultra-wideband systems with multi-user interference in an additive white Gaussian noise environment. The analytical expressions are validated by simulation and used to assess the accuracy of the Gaussian approximation proposed for estimating the performance of ultra-wideband communication systems. The Gaussian approximation is shown to be inaccurate for predicting the bit error rate for medium and large signal-to-noise ratio values. The performances of time-hopping and direct-sequence modulation schemes are accurately compared for different numbers of users and frame widths. It is shown that direct-sequence binary phase-shift keying outperforms time-hopping binary phase-shift keying for medium and large values of signal-to-noise ratio, which contradicts some previous results obtained using a Gaussian approximation. [ABSTRACT FROM AUTHOR]

It is known that the "better than" raised-cosine pulse has several advantages over the conventional raised-cosine pulse. In addition to the advantages previously reported, this letter reports that the "better than" raised-cosine pulse enables better performance of symbol timing estimation than the raised-cosine pulse. Both Cramer-Rao lower bounds and simulations of practical synchronizers show the superiority of the new pulse. The performance gain can be as much as 3.4 dB for a practical system. [ABSTRACT FROM AUTHOR]

Weighted sums of Rayleigh random variables occur in diverse problems in wireless, and particularly in interference systems. Previous work has reported upper bounds on the cumulative distribution function of weighted Rayleigh sums. New lower bounds to the cumulative distribution function of weighted Rayleigh sums are derived. The new lower bounds to the cumulative distribution function are used as an intermediate result in deriving a new upper bound on the ratio of a Rayleigh random variable to a weighted sum of Rayleigh random variables shifted by a nonnegative constant. Special cases of this ratio occur in the context of cognitive radio systems and synchronization components. Novel approximations, that are tighter than any known bounds, to the cumulative distribution function of weighted Rayleigh sums are also presented. [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]

The Nakagami—0.5 distribution is an important special case of the Nakagami distribution as it represents a worst case fading scenario. This scenario is of particular significance for wireless applications with high quality of service requirements. The bit error probability (BEP) performances of three basic diversity combining schemes in Nakagami—0.5 fading are considered. It is shown that the error rate performances of dual branch equal gain and selection combining (SC) diversity are identical regardless of modulation format. It is also shown that L—branch maximal ratio combining diversity in Nakagami—0.5 fading has the same BEP performance as single branch reception in Nakagami—L/2 fading with L times the transmission power of each branch. A useful upper bound for the BEP of L—branch SC diversity in Nakagami—0.5 fading is also derived. The performance degradation for the worst case Nakagami—0.5 fading relative to Rayleigh fading can be as much as 24.6 dB for a dual-diversity receiver at target BEP of 10^-6. The additional resources required to restore a specified performance level, as increased channel signal-to-noise ratio and as number of additional diversity branches, are quantified. It is concluded that worst case Nakagami channels can result in dramatically poorer performance than Rayleigh channels, making proper system design and evaluation essential to achieve a required transmission quality. [ABSTRACT FROM AUTHOR]

Novel single-integral representations for the multivariate probability density functions (PDFs) and cumulative distribution functions (CDFs) of the Gaussian class Weibull distribution are derived. The solutions are expressed in terms of familiar mathematical functions which are available in common mathematical software. The well known equal (constant) correlation model is considered. A special linear transformation of independent Gaussian random variables is used to generate correlated Weibull random variables. The advantage of the new representation is that only a single integral computation is needed to compute a N-dimensional distribution. The new representation of the CDF is used for the performance evaluation of a selection diversity combiner operating in equally correlated Weibull fading channels. The new PDF representation is also used for an analysis of the moments of the output signal-to-noise ratio of an equal-gain diversity combiner operating in equally correlated Weibull fading channels. [ABSTRACT FROM AUTHOR]

Multiple-symbol differential detection (MSDD) of differentially encoded phase-shift keying (PSK) signals in the presence of random frequency variation and additive white Gaussian noise is studied. It is shown that frequency variation distorts the transmitted signal through attenuating its amplitude and introducing a time-varying phase shift to the information symbols. A double differential PSK (DDPSK) modulation scheme is then introduced and a MSDD for detecting DDPSK signals in the presence of frequency offset is proposed. It is shown that the proposed receiver is robust to the distortions caused by the random frequency variation. A lower bound on the error probability of the proposed MSDD receiver is also derived and compared to that of an autocorrelation demodulator for the case where the observation interval approaches infinity. [ABSTRACT FROM PUBLISHER]

A signal-plus-noise (S+N) energy selection diversity combining (S+N-ESC) scheme for M-ary phase shift keying (MPSK) in Rayleigh fading channels is mathematically analyzed. Also, the S+N-ESC scheme for MPSK and 16-quadrature amplitude modulation (16-QAM) signaling in Nakagami-m and Rician fading channels is studied by computer simulations. The S+N-ESC selects the branch with the maximum S+N energy for detection. The advantage of the S+N-ESC scheme is that it requires no explicit channel estimation for diversity branch selection. We show that the symbol error probability (SEP) of the S+N-ESC is the same as that of classical selection combining (SC) for MPSK signaling in independent and identically distributed (i.i.d.) Rayleigh fading channels. Also, we show that the SEP of a weighted S+N-ESC scheme is the same as that of classical SC for MPSK signaling in independent and nonidentically distributed (i.n.d.) Rayleigh fading channels. It is shown by computer simulations that the S+N-ESC scheme provides a smaller SEP than classical SC for MPSK signaling in nondispersive fading channels such as Nakagami-m fading channels with Nakagami parameter m > 1 and Rician fading channels with Rician parameter K > 0. On the other hand, the S+N-ESC scheme is shown by computer simulations to have a larger SEP than classical SC for 16-QAM signaling in Nakagami-m and Rician fading channels. [ABSTRACT FROM AUTHOR]