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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]

A multi-user multiple-input single-output simultaneous wireless information and power transfer full-duplex system with imperfect channel state information is considered. Under the assumption that the unknown channel estimation error is within a certain range, the self-interference cannot be suppressed completely at the base station and at the multi-user nodes. The proposed design problem is formulated as maximizing the average harvested energy of multi-user nodes and maintaining the signal-to-interference-plus-noise ratio requirement, which is proved to be non-convex. Utilizing semidefinite relaxation and S-procedure methods, a convex optimization problem of optimal beamforming vector for the multi-antenna transmitter is obtained. Moreover, semidefinite relaxation is proved to be tight by showing the existence of rank-one optimal solutions. Simulation results are presented to verify the robustness and effectiveness of the proposed algorithm compared with the non-robust design. [ABSTRACT FROM AUTHOR]

Packet collision is a well-known severe impairment in ALOHA-based networks and, more generally, in any random access network. As a consequence, several methodologies have been considered with the aim of lowering the resulting performance degradation. A novel multiuser detection scheme exploiting channel diversity to separate collided signals is proposed here to enable multiple packet reception capability in random access schemes. The performance of this approach is analytically derived and optimized in terms of network throughput, and compared with that of different alternatives. The overall performance in terms of throughput shows the effectiveness of the proposed scheme in different operating conditions. [ABSTRACT FROM AUTHOR]

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]

A MIMO two-hop relay network with power-splitting-based relaying is considered. Using a minimum mean-square-error criterion, the joint source-relay optimization problem with transmit power constraint and relay energy harvesting constraint is formulated. In order to address this non-convex problem, an iterative algorithm is proposed which converges to a local optimum. The Lagrangian dual function and successive convex approximation are used for solution. To reduce the computational complexity, a diagonalizing beamforming scheme is employed using singular value decomposition, water-filling and successive convex approximation. Results for MSE versus iterations and bit-error-rate versus signal-to-noise ratio demonstrate the good performance of the proposed schemes. [ABSTRACT FROM PUBLISHER]

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]

A cooperative network consisting of a source, one relay, and a destination is considered. The source and destination are both equipped with a single antenna. The relay is equipped with $N$ antennas and operates in decode-and-forward (DF) mode. At the relay, the detected symbols are retransmitted using a novel beamforming method proposed in this paper that assumes the relay has 2-bit quantized information about the phase of all links from the relay to the destination. At the destination, the detector combines the received signals from the source and the relay in the first and second phases of transmission, respectively. An upper bound for the bit error rate (BER) performance of the detector is derived, and it is shown that the proposed beamforming and detector achieve full diversity order. The detector is extended to a multicast system with one single antenna source, one $N$-antenna DF relay and $M$ single antenna destinations. It is assumed that the relay has 2-bit quantized phase information and exact signal-to-noise ratio (SNR) information at all the links from the relay to the destinations. An antenna selection algorithm based on a MAX-MIN criterion at the relay is proposed, and after beamforming, the detector is used at all destinations. By deriving a rigorous upper bound for BER performance at all destinations, it is shown that the proposed scheme achieves full diversity order at all destinations. Simulation results show that the BER performance of the proposed antenna selection algorithm outperforms the well known MAX-MIN antenna selection scheme. [ABSTRACT FROM PUBLISHER]

The performance of optimum combining (OC) in amplify-and-forward (AF) relaying systems in the presence of co-channel interference (CCI) is analyzed using a tight approximation for the signal-to-interference-plus-noise ratio (SINR) at the destination. Two types of relaying protocols are studied, all-relay transmission with OC and best-relay transmission with OC. When CCI is present only at the destination, both relaying protocols achieve diversity gains up to $M$ when interferer powers are scaled with the source and the relay powers, where $M$ is the number of relays. Best-relay transmission with OC maximizes the spectral efficiency as each communication consumes only two time slots. [ABSTRACT FROM PUBLISHER]

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]

Cognitive radio technology can significantly improve spectrum utilization efficiency by enabling SUs to access the licensed spectrum dynamically without causing excessive interference to PUs. Currently, most of the existing research on cognitive radio networks has been conducted based on an assumption that SUs can perfectly synchronize with PUs. However, when SUs are working with unknown behaviors of PUs, the synchronous assumption becomes invalid. To tackle this issue, we introduce several approaches for asynchronous spectrum sensing and asynchronous spectrum access, respectively, with which SUs can access the primary channels dynamically even without achieving synchronization with the PUs. In this article, we discuss the key techniques, corresponding solutions, and potential application scenarios of the asynchronous spectrum sensing and access schemes. Specifically, we present two asynchronous spectrum sensing schemes under non-cooperative and cooperative scenarios, respectively. Meanwhile, a distributed asynchronous spectrum access algorithm is also illustrated. Moreover, the proposed schemes are compared with existing works under the same framework, which enables readers to understand the motivation, problem formulation, methodology, and results of the asynchronous spectrum sensing and spectrum access schemes. [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]

An underlay cognitive multisource multirelay cooperative network is proposed and an analytical framework to evaluate the system performance is formulated. Under both maximum transmission power and interference power constraints, exact and asymptotic outage probabilities for proactive decode-and-forward relaying over Rayleigh fading channels are derived. Both multiuser diversity and cooperative diversity can be achieved with direct secondary links. [ABSTRACT FROM PUBLISHER]

The asymptotic performances of multibranch diversity reception systems employing the popular and important combining techniques over arbitrarily correlated Rician channels are studied. Based on an integral representation of the joint probability density function of multivariate Rician random variables with arbitrary correlations, closed-form expressions for asymptotic error rate and asymptotic outage probability are derived for multibranch receiver diversity receptions. The important diversity schemes studied are maximal ratio combining, equal gain combining, selection combining, and hybrid maximal ratio combining as well as hybrid equal gain combining. Numerical results indicate that these analytical solutions can provide accurate estimation of error rate and outage probability in large-signal-to-noise-ratio regimes. The analysis provides some important theoretical and practical results concerning the performance characteristics of multibranch diversity receivers operating on arbitrarily correlated Rician fading channels. [ABSTRACT FROM PUBLISHER]

Multiaccess interference (MAI)-plus-noise whitening for detecting impulse radio ultra-wide bandwidth (IR-UWB) signals transmitted over ideal free-space and the IEEE 802.15.3a channels is considered. IR-UWB signals are very sparse in time and, thus, MAI-plus-noise whitening cannot introduce intersymbol interference (ISI) in IR-UWB systems operating on an ideal free-space channel. In addition, ISI in UWB multipath fading channels can be eliminated by a proper choice of the frame duration. An analytical expression for the signal-to-interference-plus-noise ratio (SINR) of IR-UWB systems after MAI-plus-noise whitening is derived and the SINR improvement due to whitening is investigated. It is shown that whitening can improve the performance of a variety of the well-known IR-UWB receivers, viz., soft-limiting, P-order metric, optimal, and the conventional matched filter receivers. It is also observed that MAI-plus-noise whitening can improve the overall SINR of the system and, thus, decrease the complexity of Rake receivers through reducing the number of their processing branches. [ABSTRACT FROM PUBLISHER]

New infinite-series expressions are obtained for the probability density function (PDF) and the cumulative distribution function (CDF) of the instantaneous end-to-end signal-to-noise ratio (SNR) of dual-hop amplify-and-forward (AF) relaying systems operating over Rician fading channels and dissimilar dual-hop AF systems operating over mixed Nakagami- $m$/Rician fading channels. Precise analytical solutions for outage probability, as well as precise single-integral solutions for the ergodic capacity and the average symbol error probability, are obtained. Simulation results are used to verify the solutions obtained. It is shown that the limiting slopes of the average symbol error probability curves and the outage probability curves are not affected by the Rician fading parameter in contrast to the case of Nakagami- $m$ fading links. For the case of mixed fading links, the exact performance metrics are compared to performance bounds in the literature. It is shown that the existing performance bounds are not tight for medium ranges of SNR. The effects of the Rician and Nakagami- $m$ fading parameters on the system performance are also studied. It is shown that, while increasing the Rician parameter results in a notable SNR gain, increasing the Nakagami- $m$ parameter results in a negligible improvement in the system performance. [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]

Vehicular, military and industrial field wireless deployments take place in harsh environments affected by impulsive noise. This letter proposes the use of a selective automatic repeat request (SR-ARQ) scheme where the data transmission rate is optimized in order to minimize the mean delay. The optimization procedure is proposed in relation to the use of a soft-limiting detector that eliminates out-of-amplitude noise at the receiving end. The superiority of the optimized SR-ARQ scheme over different alternatives is clearly shown in the letter. [ABSTRACT FROM PUBLISHER]

A novel generalized framework for performance analysis of selection combining diversity in Rayleigh fading channels is derived. It is shown that the performance of arbitrary systems used with selection combining diversity can be expressed in terms of only the performance of the system on a single branch Rayleigh fading channel. The results are valid for coded and uncoded transmission as well as for balanced (equal power) diversity branches and unbalanced (unequal power) diversity branches. The generalized framework encompasses both general noise and general interference, and allows correlated noise and correlated interference sources. Applications of the generalized framework to analytical, semi-analytical and simulation based performance evaluation of digital modulation schemes are discussed. [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]

A new solution for evaluating the symbol error probability (SEP) of MPSK with arbitrary values of M is derived. Evaluation of the SEP for all values of M other than 2 and 4 currently requires numerical integration. It is shown that the SEP can be expressed in terms of the Gaussian Q-function and the bivariate Gaussian distribution for any value of M. [ABSTRACT FROM PUBLISHER]

The instantaneous end-to-end received signal-to-noise ratio (SNR) in K-hop amplify-and-forward (AF) relaying systems is commonly upper bounded by \frac1K of the harmonic mean of the individual per-hop instantaneous SNRs. It is shown that performance results in Nakagami-m fading of AF multihop relaying systems obtained based on this upper bound are not tight for small values of SNR or for larger values of the Nakagami parameter and, depending on certain channel conditions, these bounds may become looser as the number of hops increases. A new approximation to the instantaneous end-to-end received SNR is introduced in the form of a scaled version of the harmonic mean of the individual per-hop SNRs. The scaling factor is determined based on the average link SNRs. Performance results evaluated using the proposed approximation are more accurate than all performance bounds previously reported in the literature, even though they are obtained with the same computational complexity. Numerical results show that the approximate performance results are very close to the exact results especially in small SNR regimes or for larger values of the Nakagami parameter. [ABSTRACT FROM PUBLISHER]

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]

Three low complexity, single-parameter, selection cooperation protocols, called P-n, P-γ, and P-t, are introduced for dual-hop relaying networks. The protocols are based on information accumulation, and can potentially be implemented using rateless codes. The expected transmission time is analyzed for the three protocols for block fading channels. As a baseline for performance comparison, a rate optimal protocol, called P-o, is proposed. In the single-relay case, all the protocols, if used with their optimized parameter which is trivially obtained, coincide with P-o. Large signal-to-noise ratio (SNR) approximations to the optimal parameters in the multirelay case, which have good accuracy in large SNR regimes, and satisfactory accuracy for smaller values of SNR, are derived. The dependence of the optimal parameters on the network parameters is numerically studied for Rayleigh fading. The average rate and average source transmission time (ASTT) of the schemes are compared with one another and other comparable previous relaying schemes through numerical examples. It is observed that the suboptimal schemes exhibit near-optimal rate and ASTT performances. As a general rule, P-o and P-γ have the best performances. The P-n scheme has a larger rate, but a larger or smaller ASTT, compared to P-t. Increasing the number of relays ultimately causes diminishing returns in the average rate and ASTT. [ABSTRACT FROM PUBLISHER]

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]

Employing channel state information at the network layer, efficient routing protocols for equal-power and optimal-power allocation in a multihop network in fading are proposed. The end-to-end outage probability from source to destination is used as the optimization criterion. The problem of finding the optimal route is investigated under either known mean channel state information (CSI) or known instantaneous CSI. The analysis shows that the proposed routing strategy achieves full diversity order, equal to the total number of nodes in the network excluding the destination, only when instantaneous CSI is known and used. The optimal routing algorithm requires a centralized exhaustive search which leads to an exponential complexity, which is infeasible for large networks. An algorithm of polynomial complexity for a centralized environment is developed by reducing the search space. A distributed approach based on the Bellman-Ford routing algorithm is proposed which achieves a good implementation complexity-performance trade-off. [ABSTRACT FROM PUBLISHER]

Low complexity receivers for coherent amplify-and-forward (AF) cooperative diversity systems are developed. According to the availability of phase information at the relays and the destination, repetition-based and spectral-efficient distributed equal gain combining (DEGC) schemes are developed. In the former scheme, relays transmit over separate orthogonal subchannels, whereas in the latter scheme all relays transmit simultaneously. Analytical expressions for evaluation of the average output signal-to-noise ratio (SNR) and symbol error probability are derived and it is demonstrated that these schemes achieve full spatial diversity. In addition, upper and lower bounds on the ergodic capacity are obtained. The upper bound is tight in small-SNR regions whereas the lower bound is accurate for sufficiently large values of SNR. It is shown that the spectral-efficient DEGC scheme outperforms the repetition-based DEGC scheme especially by increasing the number of relays. The impact of combining loss on the performance of the proposed schemes is also studied. The average output SNR expression can be used as a simple theoretical tool for choosing the best number of relays that avoids the combining loss. [ABSTRACT FROM PUBLISHER]

Bandwidth efficient signaling requires using pulse-shaping that inherently has intersymbol interference (ISI) except when the timing is perfect. Several lower bounds to the mean-square-error (MSE) of non-data-aided bit-synchronizers are derived for this case. The optimal lower bound is derived using the maximum likelihood (ML) criterion for a sequence of binary pulse amplitude modulated pulses in the presence of ISI and Gaussian noise. This lower bound is used as a benchmark to evaluate the performance of other synchronizers in a practical scenario. It is shown that a previous lower bound based on the ISI-free ML synchronizer cannot be used to lower bound the MSE of bit-synchronizers. A detection theory bound (DTB) (also called Ziv-Zakai bound) is applied to the symbol timing recovery problem in the presence of ISI and it is shown that this bound is a tight lower bound on the MSE of the ML synchronizer. A simple lower bound on this DTB is derived and it is shown that the simple bound is almost as tight as the well known modified Cramer-Rao bound (MCRB) at moderate values of SNR, while it does not suffer from the shortcomings of the MCRB at small values of SNR. [ABSTRACT FROM PUBLISHER]

Novel non-data-aided near-maximum-likelihood estimators for the delays and the attenuations in an ultra-wide bandwidth channel are proposed by using an approximation to the maximum likelihood equation. Numerical results show that these new estimators outperform previous approximate non-data-aided maximum likelihood channel estimators reported in the literature. Moreover, in some cases, the performances of the new non-data-aided estimators approach those of the data-aided estimators, enabling a reduction in the overhead expense of pilot symbols. [ABSTRACT FROM PUBLISHER]