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We investigate multiuser detection under uplink asynchronous scenario, where the triangular successive interference cancellation (T-SIC) detection scheme is exploited. As the existing analysis was conducted under some ideal assumptions for simplicity, the asynchronous scenario is analyzed under rigorous assumptions in this paper so that important insights are revealed for practical systems. Specifically, the average symbol error rate (SER) formulas are derived for a two-user system with arbitrary $M$ -ary quadrature amplitude modulation ($M$ -QAM) over Rayleigh fading channels. These solutions are shown to have higher accuracies compared to the existing solutions. Furthermore, a novel iterative detection algorithm is proposed, i.e., the parallel T-SIC method, which is more efficient and effective compared to the iterative T-SIC method. Insightful discussion is conducted in terms of the potentials of the concerned iterative detection method. Simulation results show that the most significant improvement of the iterative detection reflects on the SER for the strongest user, and the reduction is always within 50% of the SER compared to the primary detection. The gains obtained by the iterative detection is negligible for higher order $M$ -QAM cases. [ABSTRACT FROM AUTHOR]

Analysis on the exact error rate of jointly optimal (JO) maximum likelihood (ML) multiuser detection is limited in the existing literature owing to its high computational complexity. In this paper, the JO ML detection of two quadrature phase-shift keying (QPSK) signals with an arbitrary relative phase offset is investigated. Exact, analytical symbol error rate (SER) and bit error rate (BER) formulas are derived for two users with no less than 3 dB power difference between them. Closed-form union bounds on the user SER and BER with an arbitrary phase offset and an arbitrary user power ratio are also given as a simpler approach to acquire the asymptotic error rate performance. Furthermore, insights on the potentials and properties of the JO ML detector regarding its error rate behaviors for each user are revealed through comparisons with the successive interference cancellation receiver. The accuracies of the obtained formulas are demonstrated through simulation. The results show the error rates for the two-user QPSK case no longer follow the classic knowledge on the error rate behaviors in the single signal detection. In addition, the performance and dB penalty employing different modulation types are also compared and discussed. [ABSTRACT FROM AUTHOR]

Determining tractable analytical expressions for the probability density functions (PDFs) of correlated Rayleigh random variables (i.e., the multivariate Rayleigh joint PDF) is a longstanding problem in wireless communications. Recent results have reported simpler forms for the 3-D and 4-D Rayleigh joint PDFs. Yet, the new solutions are still mathematically complex. New representations for the general 3-D Rayleigh and the general 4-D Rayleigh fading PDFs are derived. An advantage of the new representations is that only a single-integral computation is needed to compute the 3-D Rayleigh PDF and only double integral computation is needed for the 4-D Rayleigh PDF, where the integrals are proper and definite on $[0,\pi )$ and {[0,2\pi )} , respectively. The new expressions for the 3-D and 4-D Rayleigh PDFs are used to determine several special, “best” placements in the 2-D plane for three and four antennas. Closed-form solutions are found for three antennas with two or three independent antenna pairs, and four antennas with four or five independent antenna pairs. [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]

An efficient cooperative spectrum sensing (SS) scheme based on Cholesky decomposition of the covariance matrix is proposed. The maximum eigenvalue (ME) of the matrix obtained by Cholesky decomposition is used as a test statistic. Analytical expressions for the false alarm probability and the decision threshold are derived. The effects of noise uncertainty on the ME SS algorithm and on the Cholesky ME cooperative SS scheme are assessed. It is proved that the proposed SS scheme is more robust than the conventional ME SS scheme in terms of noise uncertainty. Simulation results show that the performance of the proposed scheme is better than that of existing ME SS scheme in some conditions. [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]

The biproduct correlation coefficient matrix structure has gained acceptance and application in wireless communications. Yet, the set of correlation matrices that has this structure has not been fully identified. It is known that the positive equicorrelated matrix satisfies the biproduct condition, but little else is known. The set of admissible correlation matrices having the special biproduct structure is investigated. Constraints on the signs of the correlation coefficients that define the admissible set are revealed. Additional constraints on the magnitudes of the correlation coefficients for admissibilty are also identified. The set of matrices satisfying the required structure is much more restricted than previously thought. The constraints are shown to become increasingly restrictive as the dimension $N$ of the correlation matrix increases. The constraints also become more restrictive as the values of the correlation coefficients increase to approach 1. Previously, only the equicorrelated matrix has been identified as having the biproduct structure. Two additional correlation matrix structures satisfying the biproduct structure are identified. Tests that exclude a correlation matrix from having the biproduct structure are derived. [ABSTRACT FROM AUTHOR]

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]

The communication channel power gain to the nearest neighbor of a node in a wireless communication network is not necessarily the largest among all neighbors due to fading. The probability that the $k$th nearest neighbor of a node has the best communication channel with the highest power gain in a 2-D network with homogeneous Poisson distribution of nodes is derived for a general fading environment. The result is specialized to the case where the communication links are modeled as generalized-gamma fading channels. The analytical results are verified and illustrated by computer simulations and numerical results. Some applications of the new theory are also presented. A novel criterion that represents the fading severity, i.e., the generalized amount of fading (GAF) , is defined, and its value as an important measure for fading channels is justified. [ABSTRACT FROM PUBLISHER]

The exact average bit error probability (BEP) performance of decode-and-forward (DF) cooperative systems with multiple relays for binary phase-shift keying (BPSK) signals in Rayleigh fading channels is derived. Two types of receivers, i.e., a $\lambda$-maximal ratio combining ( $\lambda$-MRC) receiver and a piecewise linear (PL) receiver, are examined. The characteristic functions (CFs) of the decision statistics are derived and used for the derivation of the BEPs. Closed-form integral-free solutions for the BEPs are obtained. [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]

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]

Two optimal frameworks for multichannel spectrum sensing in cognitive radio networks are presented. Both frameworks search for multiple secondary transmission opportunities over a number of narrowband channels, enhancing the secondary network performance while respecting the primary network integrity and keeping the interference limited. Considering a sequential periodic sensing scheme with non-uniform channel sensing durations, the original sensing problems are formulated as optimization problems to maximize the throughput capacity of the secondary network subject to some bounds/limits on the interference to the primary network. The first framework, referred to as sequential multichannel joint detection, considers the aggregate (weighted) interference on the primary network as the constraint. The second framework, known as decoupled sequential multichannel joint detection, assumes that interference is limited in each channel separately (i.e. independently). The non-convex sensing problems are transformed into convex optimization problems under certain practical conditions. Simulation results demonstrate the effectiveness of both the proposed frameworks and attest to their superior performances compared to contemporary strategies. [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]

Novel single-integral representations for the multivariate probability density functions and cumulative distribution functions of Gaussian class distributions (Rayleigh, Rician, Weibull, Nakagami-m, and generalized Rician) are derived. The solutions are expressed in terms of well-known functions which are available in common mathematical software. The marginal random variables are not necessarily identically distributed as is the case for some past solutions. A generalized correlation structure based on a special linear transformation of independent Gaussian random variables is used in this study. The advantage of the new representation is that only a single-integral computation is needed to compute an N-dimensional distribution. [ABSTRACT FROM AUTHOR]

An optimal wideband spectrum sensing framework which identifies secondary transmission opportunities over multiple nonoverlapping narrowband channels is presented. The framework, which is referred to as multiband sensing-time-adaptive joint detection, improves the overall secondary user performance while protecting the primary network and keeping the harmful interference below a desired low level. Considering a periodic sensing scheme, the detection problem is formulated as a joint optimization problem to maximize the aggregate achievable secondary throughput capacity given a bound on the aggregate interference imposed on the primary network. It is demonstrated that the problem can be solved by convex optimization if certain practical constraints are applied. Simulation results attest that the proposed wideband spectrum sensing framework achieves superior performance compared to contemporary frameworks. An efficient iterative algorithm which solves the optimization problem with much lower complexity compared to other numerical methods is presented. It is established that the iteration-complexity and the complexity-per-iteration of the proposed algorithm increases linearly as the number of optimization variables (i.e., the number of narrowband channels) increases. The algorithm is evaluated via simulation and is shown to obtain the optimal solution very quickly and efficiently. [ABSTRACT FROM AUTHOR]

The article explores the performance limits of optimum combined with dense multiple correlated antennas. The authors' evaluation of the asymptotic performance of optimum combining was done with the use of derived expression and eigenvalues of dense correlation matrices' asymptotic analysis. They revealed that in the fixed average received power per antenna, average output signal-to-interference-plus-noise ratio is asymptotically a linear function of the number of antennas.

The bit error rate performance of Rake reception of impulse radio ultra-wide bandwidth signals over the IEEE 802.15.3a channel models is evaluated. Instead of using Gaussian approximation for the probability density function of the total disturbance which includes the multi-user interference and the background additive white Gaussian noise, two new models dubbed the "composite lognormal-Gaussian" and the "composite lognormal-Laplacian" are proposed for modeling the multi-user interference and shadowing in ultra-wide bandwidth multipath fading channels. Tractable formulae for bit error rate evaluation of Rake reception in ultra-wide bandwidth multipath channels are derived for both models. Numerical results indicate that these formulae predict the bit error rate performance with good accuracy, and can be rapidly and easily evaluated using commonplace computer resources. [ABSTRACT FROM AUTHOR]

The performance of multi-hop diversity transmission systems in Rayleigh fading is studied. Simple closed-form approximations for the outage and bit error probabilities of multi-hop diversity systems employing fixed amplify-and-forward relaying are derived. An exact closed-form expression for calculating the outage probability of a multi-hop diversity transmission scheme employing fixed decode-and-forward relaying is obtained. In addition, a selective relaying protocol for multi-hop diversity transmission systems, which adapts transmissions at the source and relays based on the instantaneous received signal-to-noise ratio at each relay, is developed and analyzed in terms of outage probability and bit error rate. The mathematical analyses show that multi-hop diversity transmission systems with fixed decode-and-forward relaying offer no diversity order gain, while those employing the other relaying schemes achieve diversity order equal to the number of hops. It is also shown that multi-hop diversity transmission systems employing fixed amplify-and-forward relaying attain the best outage probability and bit error rate performances, despite the noise amplification at the relays. [ABSTRACT FROM AUTHOR]

A more appropriate statistical model for the multiple access interference than the generally used Gaussian approximation is proposed to reflect the heavy-tailed nature of the multiple access interference in ultra-wide bandwidth systems. Novel receiver structures which surpass the performance of the conventional matched filter receiver are studied for ultrawide bandwidth multiple access communications in both AWGN and fading multipath channels. A proposed Rake receiver is advantageous over the conventional Rake receiver when multiuser interference dominates ambient Gaussian noise and originates from a small to moderate number of interferers. Explanation is provided for the inaccuracy of a Gaussian approximation with regard to the multiple access interference, and the heavy-tailed nature of the probability density function of the multiple access interference is also discussed. [ABSTRACT FROM AUTHOR]

We propose the Hadamard matrix as a codebook for multiple-input multiple-output (MIMO) beamforming systems, and show that a quantized equal gain transmission (QEGT) scheme using the Hadamard codebook has the same symbol error probability performance as a receiver selection diversity combining scheme operating in independent generalized Rayleigh fading channels. We show that a MIMO beamforming system using quantized feedback over Rician fading channels can be analyzed by considering a corresponding receiver selection combining scheme operating in single-input multiple-output (SIMO) systems over correlated generalized Rician fading channels. Also, we propose a greedy cophasing scheme for MIMO beamforming systems using quantized feedback. The greedy cophasing scheme provides 3.2 dB power gain over an orthogonal space-time block code when the number of transmit antennas is four, the number of receive antennas is one, and the number of feedback bits is three. [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]

New exact single-integral expressions for the evaluation of the average error probability of a wireless communication system are derived for a variety of modulation schemes in terms of the momentgenerating function (MGF) of the reciprocal of the instantaneous received signal-to-noise ratio (SNR). The expressions obtained form a framework for performance evaluation of wireless communication systems for which the well-known MGF-based performance analysis method cannot be used, that is, systems for which the MGF of the instantaneous received SNR is not known or cannot be derived in closed-form. Using the framework obtained, the error probability performance in general fading of an amplifyand-forward (AF) multihop relaying system with both variable-gain and fixed-gain relays is then evaluated. In particular, a new expression for the MGF of the reciprocal of the instantaneous received SNR of an AF multihop system with fixed-gain relays is derived. Numerical examples show precise agreement between simulation results and theoretical results. [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]

An integrated cross-noise component frequently arises in communications and in signal processing. One typical example is the autocorrelation receiver. Integrated cross-noise generally appears when a noisy signal is recovered (detected) using correlation techniques with a noisy signal as the reference. The statistics of the integrated cross-noise component are analyzed in general for both the cases of uncorrelated and correlated noise terms in the integrand. The exact 2nd order statistics of the integrated cross-noise are derived, and new improved expressions are derived for an approximate probability density function. Accurate computer simulations are performed to evaluate the actual probability density function of the integrated cross-noise component and these results are compared with the approximations. The convergence of the approximation to a Gaussian distribution is also discussed. [ABSTRACT FROM AUTHOR]

The effect of noise on the switching rate of a dual branch selection diversity combiner in noisy fading channels is examined. A closed-form solution is derived for independent and identically distributed (i.i.d.) and independent and non-identically distributed (i.n.d.) fading channels. The switching rate in noisy fading channels is compared to that in noise-free conditions. [ABSTRACT FROM AUTHOR]

Selection amplify-and-forward (SAF) relaying, which has been shown to be optimal under the constraints of localized channel information at the relays and a constant relay power allocation (PA) template, is shown to be globally strictly suboptimal. A necessary condition for the outage optimality of the SAF PA, and an exponentially vanishing upper bound on the probability of the SAF optimality are derived. [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 a dual-branch decorrelator receiver operating in correlated Rayleigh and Rician fading channels in conjunction with selection combining (SC) and switch-and-stay combining (SSC) is analyzed and compared to the performance of a conventional SC and SSC receiver. For each combining scheme, analytical expressions for the average bit error rate (BER) of several modulation techniques of practical interest, the mean output signal-to-noise ratio (SNR) and the outage probability are derived. It is shown that the decorrelator receiver has superior performance over the conventional receiver by as much as 2.83 dB in average SNR. The effects of modulation order, correlation coefficient and the severity of fading on the performance of the decorrelator receiver are studied. [ABSTRACT FROM AUTHOR]

The average bit-error rate performance of one-stage and two-stage diversity combining schemes operating over correlated fading channels is investigated. Two channel models that can significantly simplify the performance analysis are considered. In particular, a linear correlation channel model having equal branch variances can be decorrelated at the receiver, so that the branches become independent. It is shown that, in general, employing diversity combining schemes for decorrelated or orthogonalized branches can recover some of the diversity gain lost due to the branch correlations. This is observed, for example, for the case of hybrid selection/maximum ratio combining operating over decorrelated and orthogonalized non-zero mean Gaussian fading channels. Furthermore, a fading amplitude channel model is proposed assuming vector norm superposition of the impinging plane waves. This channel model is well-suited for the performance analysis of maximum ratio and equal gain combining schemes operating over correlated fading channels. Finally, the average bit error rates of several diversity combining schemes are evaluated analytically using the Prony approximation method as well as using computer simulation. [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]

Maximum likelihood (ML) receivers for space-time coded multiple-input multiple-output (MIMO) systems with Gaussian channel estimation errors are proposed. Two different cases are considered. In the first case, the conditional probability density function (PDF) of the channel estimate is assumed Gaussian and known. In the second case, the joint PDF of the channel estimate and the true channel gain is assumed Gaussian and known. In addition to ML signal detection for space-time coded MIMO with ML and minimum mean-squared-error channel estimation, ML signal detection without channel estimation is also studied. Two suboptimal structures are derived. The Alamouti space-time codes are used to examine the performances of the new receivers. Simulation results show that the new receivers can reduce the gap between the conventional receiver with channel estimation errors and the receiver with perfect channel knowledge at least by half in some cases. [ABSTRACT FROM AUTHOR]

Analytical results for the symbol error rate (SER) of M-ary phase shift keying (MPSK) in a slow, flat Rayleigh fading channel for a multiple-input multiple-output (MIMO) system using an Alamouti transmission scheme and generalized selection combining (GSC) scheme are given. Two new receiver selection schemes, generalized space-time sum-of-squares (GSTSoS) selection diversity and generalized space-time sum-of-magnitudes (GSTSoM) selection diversity are proposed. The first provides the same performance as conventional GSC, and the second provides slightly poorer performance, but neither requires channel state information and both have much simpler implementations. The SER of MPSK in Rayleigh fading using these two selection schemes is studied and compared to that of conventional GSC. The effects of channel estimation errors on each selection scheme are examined. [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]

Four new moment-based estimators are proposed for the shape parameter of the generalized Gaussian distribution. The new moment-based estimators have simple structures. They also outperform previous known moment-based estimators when the true value of the shape parameter is small. Simulation results show that in some cases, the estimation error in the proposed moment-based estimators is less than half of the error observed in current moment-based estimators. [ABSTRACT FROM AUTHOR]

A novel ultra-wide bandwidth receiver structure dubbed the "zonal" receiver is based on the qualitative nature of the probability density function of the multiple access interference. It is proposed for time-hopping ultra-wide bandwidth wire- less signal detection in multiple access interference channels. In ideal free-propagation channels, the zonal receiver always meets or outperforms the conventional matched filter UWB receiver, the recently proposed soft-limiting UWB receiver and its enhanced version, the adaptive threshold soft-limiting UWB receiver. A new Rake receiver design based on the zonal receiver is proposed for signal detection in multipath fading channels. Simulation results and analysis show that this new Rake receiver can achieve larger signal-to-interference-plus-noise ratio than the standard matched filter Rake receiver when multipath components are resolvable in UWB channels. [ABSTRACT FROM AUTHOR]

Statistical moments of the inter-path interference, the inter-chip interface and the intersymbol interference in a direct-sequence binary phase shift keying ultra-wide bandwidth (UWB) system are analyzed for the IEEE UWB channel models. Exact expressions for the first- and second-order moments are derived. The effects of the duration of the monocycle pulse, the spreading gain, and the number of interfering symbols on the average powers of the interference are examined. [ABSTRACT FROM AUTHOR]

Exact closed-form expressions are derived for the bit error rate of binary phase shift keying in Rayleigh fading channels with maximal ratio combining diversity in the presence of cochannel interference and additive white Gaussian noise. The desired signal and the interferer signals are subject to correlated Rayleigh fading and binary phase shift keying modulation is used by all users. [ABSTRACT FROM AUTHOR]

A new selective time-domain filtering scheme for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems is proposed. The proposed scheme not only relies on conventional pilot symbol channel estimation and demodulation techniques to recover the data in OFDM systems but also uses additional pilot symbols. The proposed scheme has greatly reduced complexity compared with the selective mapping (SLM) scheme and only slightly poorer performance than the SLM scheme. The new scheme achieves significant PAPR reduction at a cost of typically 0.1-0.75 dB in signal-to-noise ratio (SNR) relative to pilot symbol OFDM not having PAPR reduction. [ABSTRACT FROM AUTHOR]

A novel and simple semianalytical method for evaluating the average probability of transmission error for digital communication systems that operate over slow-fading channels is presented. The proposed method applies a sum of exponentials fit known as the Prony approximation to the conditional probability of error. Hence, knowledge of the moment-generating function of the instantaneous signal-to-noise ratio (SNR) at the detector input can be used to obtain the average probability of error. Numerical results show that knowledge of the conditional probability of error at only a small number of points and the sum of only two exponentials are sufficient to achieve very high accuracy; the relative approximation error of the exact average probability of error is less than 6% in most of the cases considered. Furthermore, a piecewise polynomial approximation of the conditional probability of error is investigated as an alternative to the sum of exponentials fit. In this case, knowledge of the partial moments of the instantaneous SNR at the detector input can be used to obtain the average probability of error. Numerical results indicate that, to achieve good accuracy, the method based on the polynomial approximation requires that the product of the polynomial degree and the number of approximation subintervals be larger than 10. [ABSTRACT FROM AUTHOR]

The generalized Gaussian probability density function is shown to better approximate the probability density function of the multiple access interference in ultra-wide bandwidth systems than the Gaussian approximation and the Laplacian density approximation. Two ultra-wide bandwidth receiver structures based on this new approximation using a p-order metric receiver decision statistic are investigated for the detection of time-hopping ultra-wide bandwidth wireless signals in multiple access interference channels. The first receiver outperforms both the conventional matched filter ultra-wide bandwidth receiver and the soft-limiting ultra-wide bandwidth receiver when only multiple access interference is present in UWB channels. The second new receiver with adaptive limiting threshold outperforms the conventional matched filter ultra-wide bandwidth receiver, the soft-limiting ultra-wide bandwidth receiver, and the adaptive threshold soft limiting ultra-wide bandwidth receiver in all multiple access interference-plus-noise environments. In multipath channels, a new Rake receiver based on the p-order metric receiver is proposed for signal detection. Mathematical analysis and numerical results show that this new Rake receiver can achieve larger signal-to-interference-plus-noise ratio than the standard matched filter Rake receiver when multipath components are resolvable in UWB channels. [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]