Frequency-selective Rician Fading Channels Research Articles

Interference Cancellation in CDMA Systems Employing Complementary Codes Under Rician Fading Channels

The ideal correlation properties of single user code division multiple access (CDMA) systems with complementary codes (CC) are lost by multiple access interference and near–far effects in downlink frequency selective fading channels. This severity in interference has motivated to develop ways to overcome the threats with suitable suboptimal interference cancellation schemes. In this paper, we propose successive interference cancellation (SIC) for downlink CDMA systems with CC to improve the system capacity and reduce error rate under near–far situations. Theoretical study and extensive simulations were conducted to verify the effectiveness of proposed SIC under frequency selective Rician fading channels in achieving frequency diversity gain, close to theoretical lower bound in complementary coded CDMA (CC-CDMA) systems.

Information theoretical performance analysis and optimisation of cooperative underwater acoustic communication systems

In this study, the authors investigate the information theoretical limits on the performance of single-carrier cooperative underwater acoustic communication systems in the presence of intersymbol interference. The authors assume decode-and-forward relaying and consider orthogonal half-duplex cooperation. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise, the authors derive expressions for bounds on the individual and achievable rates for both cases where channel state information is available at the transmitter or not. Using these expressions, the authors optimise input signalling and relay location to maximise average achievable rates.

Information theoretical performance limits of single‐carrier underwater acoustic systems

In this study, the authors investigate the information theoretical limits on the performance of point-to-point single-carrier acoustic systems over frequency-selective underwater channels with intersymbol interference. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise, the authors derive an expression for channel capacity and demonstrate the dependency on channel parameters such as the number, location and power delay profile of significant taps, as well as environmental parameters such as distance, temperature, salinity, pressure and depth. Then, the authors use this expression to determine the optimal carrier frequency, input signalling and bandwidth for capacity maximisation.

Maximum-likelihood receivers for synchronous fast frequency-hopped multiple-access M -ary frequency-shift-keying systems over frequency-selective Rician-fading channels

In this study, the performance of a synchronous fast frequency-hopped multiple-access (MA) M-ary frequency-shift-keying system employing maximum-likelihood (ML) method over either frequency-selective Rician- or Rayleigh-fading channels is investigated. The ML receiver structures are derived and analysed. It is assumed that all the signals arrive at a receiver with the same power strength and all the users operating in the system undergo independent frequency-selective fading. The performance of the ML receivers is compared with that of the linear-combining and the product-combining receivers. The bit-error rate results of the two conventional receivers are obtained via simulation. The proposed analysis, validated by simulation results, shows that the proposed ML receivers can suppress the MA interference more effectively than other existing receivers under different fading conditions. Moreover, the proposed ML receivers are shown to be robust against the inaccuracy in estimation of the required side information.

Statistical Characteristics of OFDM Systems over Frequency-Selective Rician Fading Channels and Its Application to BER Study

Some statistical characteristics, including the means and the cross-correlations, of frequency-selective Rician fading channels seen by orthogonal frequency division multiplexing (OFDM) subcarriers are derived in this paper. Based on a pairwise error probability analysis, the mean vector and the cross-correlation matrix are used to obtain an upper bound of the overallbit-error rate (BER) in a closed-form for coded OFDM signals with and without inter-carrier interference. In this paper, the overall BER is defined as the average BER of OFDM signals of all subcarriers obtained by considering their cross-correlations. Numerical examples are presented to compare the proposed upper bound of the overall BERs and the overall BERs obtained by simulations.

Appropriate Algorithms for Estimating Frequency-Selective Rician Fading MIMO Channels and Channel Rice Factor: Substantial Benefits of Rician Model and Estimator Tradeoffs

The training-based channel estimation (TBCE) scheme in multiple-input multiple-output (MIMO) frequency-selective Rician fading channels is investigated. We propose the new technique of shifted scaled least squares (SSLS) and the minimum mean square error (MMSE) estimator that are suitable to estimate the above-mentioned channel model. Analytical results show that the proposed estimators achieve much better minimum possible Bayesian Cramér-Rao lower bounds (CRLBs) in the frequency-selective Rician MIMO channels compared with those of Rayleigh one. It is seen that the SSLS channel estimator requires less knowledge about the channel and/or has better performance than the conventional least squares (LS) and MMSE estimators. Simulation results confirm the superiority of the proposed channel estimators. Finally, to estimate the channel Rice factor, an algorithm is proposed, and its efficiency is verified using the result in the SSLS and MMSE channel estimators.

BER Analysis of OFDM Systems Impaired by Phase Noise in Frequency-Selective Fading Channels

In this paper, we study the effect of finite-power, phase-locked loop based phase noise on the bit-error-rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems in frequency-selective fading channels. It is well known the impact of phase noise on the performance of an OFDM system can be divided into a multiplicative term called common phase error (CPE) and an additive term called intercarrier interference (ICI). Based on the conditional Gaussian approximation technique, we first derive the BER formulas for BPSK, QPSK, 16-QAM, and 64-QAM modulated OFDM signals in frequency-selective Rayleigh fading channels. To further quantify the individual influence of the CPE and the ICI on system performance for different phase noise spectra, we derive the BER expressions for perfect CPE compensation cases. The analytical results obtained for frequency-selective Rayleigh fading channels are then generalized to frequency-selective Rician fading channels. Simulation results not only validate the accuracy of our analysis but also show the dependency of BERs on the shapes of phase noise spectra.

Doppler Spread Estimation for Broadband Wireless OFDM Systems Over Rician Fading Channels

In this paper, we present a new Doppler spread estimation algorithm for broadband wireless orthogonal frequency division multiplexing (OFDM) systems with fast time-varying and frequency-selective Rayleigh or Rician fading channels. The new algorithm is developed by analyzing the statistical properties of the power of the received OFDM signal in the time domain, thus it is not affected by the influence of frequency-domain inter-carrier interference (ICI) introduced by channel variation within one OFDM symbol. The operation of the algorithm doesn’t require the knowledge of fading channel coefficients, transmitted data, or signal-to-noise ratio (SNR) at the receiver. It is robust against additive noise, and can provide accurate Doppler spread estimation with SNR as low as 0 dB. Moreover, unlike existing algorithms, the proposed algorithm takes into account the inter-tap correlation of the discrete-time channel representation, as is the case in practical systems. Simulation results demonstrate that this new algorithm can accurately estimate a wide range of Doppler spread with low estimation latency and high computational efficiency.

Error probability analysis of FFH/MFSK receivers over frequency-selective Rician-fading channels with partial-band-noise jamming

An optimum maximum-likelihood (ML) receiver structure for a fast frequency-hopped M-ary frequency-shift keying system over frequency-selective Rician-fading channels against partial-band-noise jamming and additive white Gaussian noise is proposed. In addition, we propose two suboptimum ML receivers and derive their corresponding analytical bit-error rate expressions.

EXACT PERFORMANCE MEASURES FOR DIRECT-SEQUENCE CODE SYNCHRONIZATION IN FADING CHANNELS

This paper presents an exact performance analysis for the evaluating a mean acquisition time in a cellular code division multiple access system. New expressions for the probabilities of detection, miss, and false alarm are derived in a frequency-selective Rician fading channel. From the numerical results, it is shown that our formula gives the accurate results of the mean acquisition time in the performance analysis of the parallel acquisition system with the reference filter.

Pairwise error probability of space-time codes in frequency selective Rician channels

In this letter, we investigate the performance of space-time codes in frequency selective correlated Rician channels. An exact expression has been derived for the pairwise error probability (PEP) of space-time trellis codes over frequency selective Rician fading channel, which is in the form of a single finite range integral. We also obtain a closed form expression for the PEP when the signal matrices are drawn from some special design and the performance upper bound.

BER Performance for Downlink MC-CDMA Systems over Rician Fading Channels

We consider downlink multicarrier code-division multiple-access (MC-CDMA) systems using binary phase-shift keying (BPSK) modulation scheme and maximal ratio combining (MRC) in frequency-selective Rician fading channels. A time-domain method to obtain bit error rate (BER) by calculating moment generating function (MGF) of the decision variable for a tapped-delay-line channel model is proposed. This method does not require any assumption regarding the statistical or spectral distribution of multiple access interference (MAI), and it is also not necessary to assume that the fading encountered by the subcarriers is independent of each other. The analytical formula is also verified by simulations.

A Simple Method of BER Calculation in DPSK/OFDM Systems over Fading Channels

In orthogonal frequency division multiplexing (OFDM) systems with differential phase shift keying (DPSK), it is possible to apply differential modulation either in the time or frequency domain depending on the condition of fading channels, such as the Doppler frequency shift and the delay spread. This paper proposes a simple calculation method, that is, an approximate closed-form equation of the bit error rate (BER) in DPSK/OFDM systems mentioned above over both time and frequency selective Rician fading channels. The validity of the proposed method is demonstrated by the fact that the BER performances given by the derived equation coincide with those by Monte Carlo simulation.

Nonparametric PN code acquisition using the signed-rank statistic for DS/CDMA systems in frequency-selective Rician fading channels

In this paper, signed-rank based nonparametric detectors are used for pseudonoise (PN) code acquisition in frequency-selective Rician fading channels. We first derive the locally optimum rank detector and then propose the locally suboptimum rank (LSR) and kth order modified signed-rank (MSR/sub k/) detectors using approximate score functions. We compare the hybrid parallel double-dwell scheme using the LSR and MSR/sub k/ detectors with that using the conventional squared-sum (SS) and modified sign (MS) detectors. From the simulation results, it is shown that the LSR and MSR/sub k/ detectors perform better than the SS detector using the cell averaging constant false-alarm rate processor and the MS detector by about 2-3 dB.

Decision feedback equalization of frequency-selective Rician fading channels

The time-varying tap coefficients of the frequency-selective Ricain fading channels are typically modeled as complex Gaussian stochastic processes. This study proposes a novel design method of optimal decision feedback equalizer (DFE) for such fading channels. In the proposed design method, based on the estimated dynamic characteristics of Rician fading channel, a realizable DFE, which is constructed to minimize the mean square error from the perspective of frequency domain, is designed to recover the transmitted sequence. The main advantage of the proposed design method is that only a fixed equalizer is required to treat the equalization problem of Rician fading channels. Furthermore, since the dynamic characteristics of Rician fading channels are considered in the design procedure, the proposed DFE possesses better tracking ability as compared to the conventional adaptive equalizer. Consequently, the proposed DFE exhibits a better reconstruction performance than the conventional adaptive equalizer. To illustrate the superior performance of the proposed design method, two simulation examples are presented.

Error probability analysis for 16 STAR-QAM in frequency-selective Rician fading with diversity reception

The bit-error rate (BER) performance of differential 16 STAR-QAM in frequency-selective Rician fading channels with diversity reception is theoretically analyzed for three different types of delay profiles: double-spike, one-sided exponential, and Gaussian profiles as well as two kinds of pulse-shaping filtering: a raised cosine (RC) Nyquist signaling pulse and the rectangular pulse. The effect of time delay between line-of-sight (LOS) and multipath components is also included in the analysis and shown to degrade the system performance significantly.

Approximate maximum likelihood differential phasedetection with diversity reception

Diversity reception is incorporated into the structure of approximate maximum likelihood differential phase detection (MLDPD) for M-ary DPSK. The bit error rate (BER) performance improvements obtained with MLDPD are evaluated by computer simulation for 4DPSK in frequency selective Rician fading channels.

Diversity reception of 16 STAR-QAM infrequency-selective Rician fading

Bit error rate (BER) performance of differential 16 STAR-QAM in frequency-selective Rician fading channels with diversity reception is theoretically analysed for three different types of delay profiles: double spike, one-sided exponential and Gaussian profiles. The effect of time delay between line-of-sight (LOS) and multipath components is also included in the analysis, and is shown to degrade the system performance significantly.

Orthogonal frequency division multiplexing with BFSK modulation in frequency selective Rayleigh and Rician fading channels

The performance of noncoherent reception with orthogonal frequency division multiplexing (OFDM) and binary frequency-shift-keying (BFSK) modulation over multipath fading channels with noise is investigated. This analysis demonstrates that it is possible to transmit information in selective channels with no symbol interference. Expressions of the bit error probability (BEP) are derived in the context of frequency selective Rayleigh and frequency selective Rician fading channels with and without convolutional coding. >

Direct-sequence spread-spectrum parallel acquisition in nonselective and frequency-selective Rician fading channels

This work presents the performance of the direct-sequence spread-spectrum (DS-SS) parallel acquisition system, previously proposed by the authors (1989, 1990), for nonselective and frequency-selective Rician (i.e. specular plus Rayleigh) fading channels. The acquisition system utilizes a bank of parallel I-Q noncoherent matched filters for the search mode, and a coincidence detector for the verification mode. The probabilities of detection and false alarm are derived and the mean and variance of the acquisition time are evaluated as a measure of the system performance. The nonselective channel is a Rayleigh fast fading channel, while the frequency-selective channel model is the so-called wide sense stationary uncorrelated scattering (WSSUS), selective only on frequency. These channels are typical for aircraft-satellite and line-of-sight (LOS) communications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>