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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. Index Terms--Diversity combining, fading channels, Rayleigh fading, Rician fading, selection combining, switch-and-stay combining.

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. Index Terms--Channel modeling, communications systems performance, correlation, diversity methods, fading channels.

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 ale 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. Index Terms--Collaborative spectrum sensing, cognitive radio, estimation errors.

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. Index Terms--Channel estimation, imperfect, maximum likelihood, MIMO.

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. Index Terms--Alamouti multiple-input multiple-output (MIMO) systems, error analysis, estimation error, generalized selection combining (GSC), selection diversity.

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 serf-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. Index Terms=Better than" raised-cosine pulse, non-data-aided symbol timing-error detection, raised-cosine pulse.

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 wireless 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. Index Terms--Bit error rate, demodulation, digital receiver, multiple access interference, multipath fading channel, Rake receiver, ultra-wide bandwidth.

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. Index Terms--Bit error rate, diversity, maximal ratio combining, cochannel interference, correlated Rayleigh fading.

Statistical moments of the inter-path interference, the inter-chip interference 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 interferences are examined. Index Terms--Average power, interference, moment, ultrawide bandwidth.

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 porder 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. Index Terms--Bit error rate, demodulation, digital receivers, multiple access interference, multipath channels, Rake receiver, ultra-wide bandwidth.

The switching rates of dual selection combining diversity and dual switch-and-stay combining diversity in Rayleigh, Rician and Nakagami-m (m half-integer or integer) fading are derived. Closed-form or single integral expressions are obtained for both the cases of balanced channels and unbalanced channels. Index Terms--Diversity, fading channels, Nakagami, Rayleigh, Rician, selection combining, switch-and-stay combining.

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. Index Terms--Diversity, fading, selection combining.

A characteristic function-based method is used to derive closed-form bit error probability (BEP) expressions for orthogonal frequency-division multiplexing (OFDM) systems in the presence of channel estimation error over frequency-selective Rayleigh fading channels and frequency-selective Ricean fading channels. Both single channel reception and diversity reception with maximal ratio combining (MRC) are examined. The BEP expressions are shown to be sums of several conditional probability functions which can be calculated by using proper complex Gaussian random variable theory and a characteristic function method. The closed-form BEP expressions can be used to accurately investigate the bit error rate performance degradation caused by channel estimation error under different wireless channel environment models. The performances of two interpolation methods, a sinc interpolator with Hamming windowing and a Wiener interpolator, are compared. Index Terms--Bit error probability analysis, channel estimation error, OFDM, orthogonal frequency-division multiplexing, pilot symbol-aided modulation.

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

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

An exact closed-form expression for the average bit error rate (BER) of coherent BPSK using maximal ratio combining (MRC) with correlated branches in the presence of cochannel interference (CCI) and noise is derived. This expression is valid for an arbitrary correlation structure under the assumption that the branch gains of the desired user signal and interfering signals experience correlated Rayleigh fading with the same correlation eigenvector matrix. Index Terms--Bit error rate (BER), cochannel interference (CCI), diversity, fading channels, maximal ratio combining (MRC).

Precise outage probability performance analysis of a microcellular system with selection and switched diversities is considered. The microcellular system is assumed to follow a flat, slow Nakagami/Rayleigh fading model wherein the fading channels from the desired transmitter to all the receiver antennas are independent and identically distributed Nakagami channels, and all the fading channels for the interfering signals are independent, identically distributed Rayleigh channels. Three selection and switching criteria, namely, desired signal power, signal-to-interference power ratio, and total output power are considered. Unlike previous results, the system model under investigation takes into account the pulse shaping, the random delays, and the phase offsets of the interfering users. Two Nyquist pulse shapes, spectrum-raised-cosine and Beaulieu-Tan-Damen pulse shapes, are considered. Analytical outage probability expressions are derived for an arbitrary number of interferers, arbitrary diversity order, and arbitrary value of desired user fading parameter. The outage performances of the selection criteria are compared. The optimum switching thresholds for different switching criteria are formulated. Index Terms--Cochannel interference, Nakagami fading, outage analysis, selection diversity, switched diversity.

The bit error rate of a binary phase shift keying (BPSK) signal in Ricean-faded cochannel interference is studied. A precise bit error rate expression is derived for a bandlimited BPSK signal corrupted by an arbitrary number of asynchronous Ricean-faded interfering signals. An error rate estimation based on a saddlepoint approximation is also provided. It is shown that this approximation is highly accurate. For the special case, when there is one synchronous Ricean-faded interfering signal in an interference-limited environment, an asymptotic error rate analysis based on the saddle point approximation reveals that fading in the cochannel interfering signal can have different impacts on the desired user's error rate performance. Our study shows that when the signal-to-interference ratio (SIR) is sufficiently large, the error floor of the desired user signal decreases with an increase of the Rice factor in the interfering user's fading channel. However, the opposite phenomenon can happen when the SIR is small. Index Terms--Cochannel interference, Ricean fading, saddlepoint approximation.

Optimum detectors for pilot symbol assisted modulation (PSAM) signals in Rayleigh and Rician fading channels are derived. Conventional PSAM as used on Rayleigh fading channels is also employed on Rician fading channels. It is shown that the conventional PSAM receiver is optimal for binary phase shift keying in Rayleigh fading but suboptimal for Rician fading and suboptimal for 16-ary quadrature amplitude modulation in Rayleigh fading. The optimum PSAM signal detector uses knowledge of the specular component and also jointly processes the pilot symbols and the data symbol. The performance of the optimum detector is analyzed and compared with that of the conventional detector. It is concluded that substantial gains can be achieved by exploiting knowledge of the specular component while joint processing of the data symbol with the pilot symbols may offer small benefits. Index Terms--Fading channels, optimum detection, pilot symbol assisted modulation (PSAM).

The performance of binary frequency-shift keying (BFSK) and M-ary frequency shift keying (MFSK) with dual-branch postdetection switch-and-stay combining (SSC) in correlated Rayleigh and Rician fading is studied. Two postdetection SSC receivers are considered and the performances of noncoherent BFSK and MFSK are analyzed. Closed-form expressions are derived for the average bit-error rate (BER) of BFSK and MFSK with postdetection SSC in correlated Rayleigh and Rician fading. Optimum switching thresholds that minimize the average BER are obtained. Extensive Monte Carlo simulations are presented to test the validity of the analytical results. The performance of dual-branch postdetection SSC is compared with the performance of dual-branch predetection SSC. The effects of correlation, fading parameter, average fading power imbalance, and switching threshold on the performances of postdetection SSC receivers are examined. Index Terms--Diversity combining, fading channels, postdetection diversity, predetection diversity, Rayleigh fading, Rician fading.

The symbol-error rate (SER) of a quadrature subbranch hybrid selection/maximal-ratio combining (QBHS/MRC) scheme for 1-D modulations in Rayleigh fading is examined. At the receiver, N diversity branches are split into 2N in-phase and quadrature subbranches. Traditional hybrid selection/maximal-ratio combining (H-S/MRC) is then applied over the 2N subbranches. M-ary pulse amplitude modulation, including coherent binary phase-shift keying, with QBHS/MRC is studied. The SER performances of QBHS/MRC and H-S/MRC are compared. Results show that QBHS/MRC systems outperform traditional H-S/MRC systems. Index Terms--Diversity combining, error rate, fading channel, hybrid selection/maximal-ratio combining (H-S/MRC).

An analytical expression for the bit-error rate (BER) of an individually optimal receiver in a two-user synchronous channel is derived. The desired signal is a binary phase-shift keying (BPSK) signal corrupted by a like-modulated interference and additive white Gaussian noise (AWGN). The BER expression decomposes into the probability of error of BPSK in AWGN plus an interference term which tends to zero when either the interferer power or the interferer signal correlation with the desired signal approaches zero. Index Terms--Cochannel interference (CCI), detection, error probability.

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

A precise method for calculating the bit-error probability (BEP) of a discrete cosine transform (DCT)-based orthogonal frequency-division multiplexing (OFDM) system on additive white Gaussian noise (AWGN) channels in the presence of frequency offset is derived. These accurate results are used to examine and compare the BEP performance of a DCT-OFDM system and the conventional discrete Fourier transform (DFT)-based OFDM system in an AWGN environment. Several signaling formats, such as binary phase-shift keying, quaternary phase-shift keying, and 16-ary quadrature amplitude modulation are considered. The performance of a DCT-OFDM with a zero-padding guard-interval scheme is then compared with a zero-padded DFT-OFDM with the employment of minimum mean-square error (MMSE) detection and MMSE decision-feedback detection with ordering scheme over frequency-selective fast Rayleigh fading channels. Analysis and simulation results show that the DCT-OFDM system outperforms the DFT-OFDM system in the presence of frequency offset, and in frequency-selective fast-fading environments. Index Terms--Bit-error probability (BEP) analysis, discrete cosine transform (DCT), fading channels, frequency offset, intercarrier interference (ICI), orthogonal frequency-division multiplexing (OFDM).

Accurate average bit-error rate analysis of asynchronous bandlimited binary direct-sequence code-division multiple-access (DS-CDMA) systems in Nakagami-m fading is studied. The fading is assumed to be flat and slow. The spectrum raised-cosine (SRC) and Beaulieu-Tan-Damen (BTD) pulse-shapes are employed. A new method which combines the characteristic function (CF) method with the improved Gaussian approximation (GA) is proposed for evaluating the BER of bandlimited DS-CDMA. A substantial computational complexity reduction is achieved. The well-known standard GA, Holtzman's simplified improved GA, and improved Holtzman's GA methods are also considered. The accuracies of the approximation methods are assessed using Monte Carlo simulation. For a system employing a deterministic sequence for the desired user and random sequences for the active interfering users, a CF method is employed to derive precise BER results. The new BTD pulse outperforms the SRC pulse in all situations. Index Terms--Bandlimited communication, bit-error rate (BER) analysis, code-division multiple access (CDMA), Gaussian approximation (GA), Nakagami fading channels.

An analysis is derived for calculating the bit-error probability of an ultra-wideband (UWB) communication system operating with binary phase-shift keying and quaternary phase-shift keying narrowband interference in additive white Gaussian noise. The analytical expressions are valid when phase transitions of the interfering symbols can be ignored. The accuracy of the Gaussian approximation is assessed, and several modulation schemes proposed for UWB communication are evaluated in terms of capability of interference suppression. Index Terms--Interference, multiaccess communication, orthogonal frequency-division multiplexing (OFDM), ultra-wideband (UWB), wireless.

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

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

A useful integral, representing the average over Rayleigh fading of the product of two Gaussian Q-functions, is solved in closed-form. A closed-form solution for the symbol-error probability of general rectangular quadrature amplitude modulation in Rayleigh fading is derived. Index Terms--Error function, fading channels, quadrature amplitude modulation (QAM), Rayleigh distribution, symbol-error probability (SEP).

A precise bit-error probability (BEP) analysis method is derived for a multicode direct-sequence code-division multiple-access (DS-CDMA) system in an additive white Gaussian noise channel. The method is applicable to a multicode DS-CDMA system with an arbitrary number of multiple code sequences, and any selection of multiple code sequences. The precise method gives results that discriminate the effect of the selection of different multiple code sequences on the BEP, whereas Gaussian approximations (GAs) do not. Thus, the new method can be used to select the best multicode set for a given system, a task that cannot be achieved using GAs. A two-step analytical procedure enables deriving an explicit, compact form for the CF of the receiver decision statistic in a DS-CDMA system with an arbitrary number of multiple code sequences, and for any selection of multiple code sequences. Index Terms--Bit-error probability (BEP), characteristic function (CF), code-division multiple access (CDMA), Gaussian approximation (GA), multicode, spread spectrum multiple access (SSMA).

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