Search

We investigate the error performance of opportunistic decode-and-forward (DF) relaying in Nakagami-m fading with arbitrary m≥ 0.5. In particular, we obtain exact moment generating function (MGF) expressions in terms of Lauricella hypergeometric function (LHF) for opportunistic DF relaying with maximal ratio combining (MRC) or selection combining (SC). In the case of SC, the cumulative density function (CDF) of the receive SNR is also derived and based on the CDF, two error probability expressions for opportunistic DF relaying with SC are provided. Further, we show that the MGF expressions can be greatly simplified when average SNRs become large. From asymptotic analysis, the diversity order of opportunistic DF relaying is identified.

Gaussian class multivariate distributions with single integral representations were recently proposed to obtain correlated fading channels with generalized correlation. In this letter, we focus on correlated generalized Rician fading channels, derived from Gaussian class multivariate distributions. We present a comprehensive investigation on the statistical properties of correlated generalized Rician fading channels. Specifically, closed-form expressions for joint probability density function (PDF), marginal PDF, power correlation, joint moment, and joint characteristic function are elaborated. These statistical characterizations help us have a better understanding of the correlated generalized Rician channels and allow for some new applications in performance analysis of diversity schemes and, particularly, maximal ratio combining over correlated fading channels with generalized correlation.

Lauricella hypergeometric function (LHF) FA is often used in the performance analysis of wireless communications, especially diversity systems. In this letter, FA is applied to solve two challenging problems: (1) a product of error functions averaged over generic fading channels and (2) error probability of BPSK modulation with equal-gain combining (EGC) in independent Nakagami-m fading channels. Closed-form expressions in terms of FA are obtained. In addition, a novel and efficient approximation to FA is presented.

Automatic modulation recognition is advantageous for wireless communication systems employing adaptive modulation, software-defined radio, and cognitive radio. In this paper, we consider a phase based maximum likelihood (ML) approach for identifying the modulation format of a linearly modulated signal. Since the optimal ML scheme is computationally intensive, we propose two approximate ML alternatives, which can offer close-to-optimal performance with reduced complexity. We then present a general performance analysis for classification of K types of modulation constellations. For K ;5, we obtain a set of upper bounds on Pcc, which provide a tradeoff between accuracy and complexity in calculating the Pcc. In addition, asymptotic behavior of phase based ML classification schemes is investigated.

We start with the computation of the Nuttall Q-function using Gauss quadrature rules. Since the integrand of the Nuttall Q-function is characterized by an exponential kernel function, the semi-infinite Gauss-Hermite quadrature is employed to efficiently calculate the tail probability involved. As such, with the help of the Gauss-Legendre quadrature, the Nuttall Q-function with arbitrary real orders can be accurately approximated in closed form. This methodology is then extended to provide closed-form approximations for other related semi-infinite integrals encountered in performance analysis of energy detection in fading channels.

This paper is concerned with classification of quadrature amplitude modulation (QAM) signals by using noncoherent maximum likelihood (ML) schemes, which are robust to frequency mismatch and phase shift. To reduce the high complexity involved in optimal noncoherent ML classification, we propose two suboptimal alternatives that perform well under various conditions. In particular, one suboptimal scheme, derived from high signal-to-noise ratio (SNR) approximation, is shown to provide close-to-optimal performance. We also present a general performance analysis for noncoherent ML classification of K types of QAM constellations, ending up with simplified integration for K ; 5. In addition, we investigate the asymptotic behavior of noncoherent ML classification assuming the number of samples used increases to infinity. The asymptotic performance of optimal as well as suboptimal noncoherent ML classification is established.

Based on frequency-domain oversampling and the Bayesian Gauss-Markov theorem, we propose a fractionally spaced frequency-domain minimum mean-square error (FSFDMMSE) receiver for orthogonal frequency-division multiplexing systems. It is shown that frequency diversity inherent in a frequency-selective fading channel can be extracted and exploited by the proposed FSFD-MMSE receiver. This diversity advantage outweighs the effect of intercarrier interference generated by frequency-domain oversampling, due largely to the MMSE receiver's interference suppression capability. Numerical results show that the FSFD-MMSE receiver outperforms the conventional MMSE receiver under both ideal and practical situations (i.e., with frequency offset, channel estimation errors, and even doubly selective channel fading). In addition, the FSFD-MMSE receiver only needs a fast Fourier transform size that is no larger than N + Q -1 (TV = number of data subcarriers, and Q = number of resolvable multipath components).

Based on the frequency-domain oversampling and minimum mean-square error (MMSE) principles, we propose three linear single-user detectors for downlink multicarrier codedivision multiple-access (MC-CDMA) systems. We begin with an optimal linear MMSE detector, which is computationally demanding. To reduce the complexity, a two-stage MMSE detector and a diagonal one-stage MMSE detector are developed subsequently. Simulation results show that the proposed detectors can efficiently suppress the multiple access interference (MAI) caused by frequency-selective fading, near-far effect, frequency offset, and nonlinear power amplification.

The constellation design for differential space-time modulation usually requires to construct L (constellation size) unitary matrices making the design complexity increasing rapidly with L. In this correspondence, we propose a new construction technique, which exploits the rotational invariance of unitary matrices and the property of MPSK modulation. The proposed constellations are derivable from a smaller set of D = L/M unitary matrices (via rotations defined by an M-ary PSK symbol) which, in turn, are parameterized by two unitary matrices U1 and U2. They share some good property of group constellations thereby considerably simplifying the optimization of U1 and U2. They also possess other good properties which allow for simplified maximum likelihood (ML) decoding. Extensive numerical examples are presented to demonstrate that the proposed constellations in general have larger diversity products than other constellations and thus, better error performance.

The minimum mean square error combining (MMSEC) scheme performs best among various equalization and combining schemes for downlink multicarrier code-division multiple access (MC-CDMA). However, it is also the most computationally complex to realize as it involves the complex matrix inversion operation of a large matrix. In this paper, a new method is proposed to calculate the equalizer coefficient for MMSEC based on reduced-size matrices. It is shown that as long as the number of users is even, the matrix inversion size is reduced to at least , where is the number of subcarriers.

M-ary orthogonal modulation with noncoherent detection is an attractive scheme for the reverse link of direct-sequence code-division multiple access (DS-CDMA). The performance analysis of such DS-CDMA systems with random spreading sequences has been thoroughly studied. However, little satisfactory work has been done for systems with deterministic spreading sequences, regardless of their importance from the viewpoint of multiple-access interference reduction. To fill this void, we consider deterministic spreading sequences in this paper. We first present a detailed error performance analysis for the reverse link of DS-CDMA with -ary orthogonal modulation on both additive white Gaussian noise (AWGN) and multipath Rayleigh-fading channels. Then, we formulate the design of spreading sequences for the DS-CDMA system as a nonlinear discrete optimization problem. Two steps are taken to complete the task of sequence optimization: (1) A large code space is generated by permutating a single binary code matrix and imposing a Kronecker product structure on candidate code matrices, and (2) an evolutionary algorithm is applied to efficiently perform optimization. Numerical examples show that the optimized sequences considerably improve the system performance, especially when the number of users is relatively small or an AWGN channel is considered. In addition, our proposed approach can make a good tradeoff between code performance and search complexity.

Orthogonality restoring combining (ORC) is appealing for the downlink of multicarrier code-division multiple- access (MC-CDMA) since it can eliminate multiple access interference (MAI) which would otherwise fundamentally limit the CDMA system performance. The ORC output instantaneous signal-to-noise ratio (SNR), however, takes the form of a harmonic mean of SNRs on different subcarriers, making its error performance difficult to analyze. In this paper, we tackle the problem in the framework of characteristic functions (CF) ending up with useful results for various modulation schemes including M-ary phase-shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM). The general solution for arbitrary real m can be evaluated numerically, and reduces to closed form for m being an odd multiple of half. Extensive simulations are conducted to verify the theoretical analysis. It is found that in general MQAM outperforms MPSK, and the error performance of MC-CDMA with ORC is insensitive to the number of subcarriers and to the correlation among subcarriers.

In the bit-error rate (BER) analysis of code-division multiple-access (CDMA) systems, a Gaussian approximation is widely used to tackle the multiple access interference (MAI), although it does not always offer satisfactory accuracy. This paper investigates the BER performance of synchronous multicarrier (MC) CDMA systems over Nakagami-m-fading channels in a different way. We present an accurate and unified BER analysis for synchronous MC-CDMA systems. To facilitate our analysis, we assume a synchronous uplink, whose BER performance can be intuitively viewed as a lower BER bound of the more realistic asynchronous MC-CDMA. The basic idea is that, by using the Gauss-Chebyshev quadrature (GCQ) rule to perform inverse Laplace transform, an accurate BER can be numerically obtained from the moment generating function (MAG) of the output decision variable at a receiver, without any assumption about the MAI distribution. First, signals on all subcarriers of MC-CDMA systems are assumed to experience independent fading. Two standard diversity combining techniques, equal gain combining (EGC) and maximal ratio combining (MRC), are employed. The BER performance in both downlink and synchronous uplink is analyzed. We then consider a more general system model, in which signals on different subcarriers undergo correlated fading. The asymptotic (error floor) performance of downlink MC-CDMA with MRC is studied. In particular, we investigate the effects of spreading sequences and the delay spread of the channel on the system performance. Numerical examples are provided to show the main results of this paper. The accuracy of the GCQ and MGF based solution is verified by different approaches such as Monte Carlo integration and the exact residue method. In addition, the accuracy of the commonly used Gaussian approximation is also examined.

The bit error rate (BER) of an asynchronous multicarrier code-division multiple-access system in an additive white Gaussian noise channel is evaluated using Monte Carlo integration and moment-generating function methods. The BER performance for different families of spreading sequences is investigated. Numerical results show that the approach of a recently published paper (see Popovic, B.M., IEEE Trans. Common., vol.47, p.918-26, 1999) cannot give an accurate BER because the interference from other subcarriers has been omitted. Some new findings about the performance of different sequences are also presented.

Based on the semi-infinite Gauss-Hermite quadrature rule defined in [0, ∞), we present an accurate and efficient approximation to the Gaussian Q-function, which is expressed as a finite sum of exponential functions. We then extend to address the problem of a product of Gaussian Q-functions averaged over Nakagami-m fading, ending up with a closed-form solution applicable for any real m ≥ 0.5. Numerical examples show that the proposed method with only N = 2 terms can give error probabilities (in closed form) that are virtually indistinguishable from the exact results obtained by numerical integration.

The error performance of M-ary frequency shift keying (MFSK) with square-law diversity combining (SLDC) on correlated Nakagami-m fading channels was previously analyzed in the literature. The results are either in the form of an integral, or a closed form involving the calculation of higher-order derivatives, or other closed forms subject to the constraint of integer-valued fading parameters. In this letter, we formulate the problem in the framework of Lauricellar hypergeometric functions leading to a simple symbol-error-rate formula involving only some elementary functions for generic correlated Nakagami fading environments

The bit error rate of a synchronous multicarrier code-division multiple-access system operating in a Rayleigh fading channel is calculated based on a moment generating function method, without any assumption on the distribution of multiple access interference. Two closed-form BER expressions are derived. Moreover, the BER can be accurately evaluated by using a Gauss-Chebyshev quadrature rule based numerical approach.

Downlink multicarrier code-division multiple access (MC-CDMA) with maximal ratio combining (MRC) in correlated Rayleigh fading channels is considered. An exact error floor in a closed-form expression is provided based on the characteristic function (CF) and residue calculation method. Numerical results show that orthogonal spreading sequences (Walsh and orthogonal Gold sequences) perform better than nonorthogonal sequences (Gold sequences) and Walsh codes have the best performance. In addition, downlink MC-CDMA is found to benefit from the correlation between subcarriers.