Frequency-nonselective Rayleigh Fading Channel Research Articles

Analysis of DPSK nonlinear combiner over fading channels with impulse noise

Analysis of performance of an L-diversity DPSK nonlinear combiner in frequency nonselective Rayleigh fading channels with impulse noise is presented. By employing the characteristic function, asymptotic and approximate bit error probabilities are derived. Analysis and simulation results indicate that by equipping a nonlinear element in the equal-gain combiner, the new detector can effectively combat impulse noise and fading.

Pilot-Symbol-Aided 16PSK and 16QAM for Digital Land Mobile Radio Systems

The paper proposes a novel pilot-symbol-aided (PSA) technique for fading compensation of digital signals in the mobile environments. In a PSA system, the data sequence at the transmitter is divided into frames of data. A pilot symbol from a known pseudoradom-symbol sequence is inserted periodically into a frame of data symbol for transmission. In a conventional PSA-receiver, these pilot symbols are extracted from the received signal and used to estimate the effects of signal distortion introduced in the fading channel. The resultant estimates are then used to correct the distortion effects in the received data frames. In the paper, a novel estimation technique that uses the data symbols as well as the pilot symbols is proposed. The technique has the major advantages of simple implementation and short storage-delay time. Results are presented in a series of computer-simulation tests. These assess the effectiveness of the estimation technique on the BER performances of a 16-ary phase-shift keyed (16PSK) and a 16-ary quadrature-amplitude modulated (16QAM) signals in the frequency-selective and frequency-nonselective Rayleigh fading channels. The channels are corrupted by co-channel interference or additive white Gaussian noise. Results of differential-detected 16PSK and star-16QAM signals are also presented for comparison. It has been shown that, the use of PSA technique can significantly improve the bit-error-rate performances of the systems, relative to those using differential detection.

Adaptive quantization and fast error-resilient entropy coding for image transmission

There has been an outburst of research in image and video compression for transmission over noisy channels. Channel matched source quantizer design has gained prominence. Further, the presence of variable-length codes in compression standards like the JPEG and the MPEG has made the problem more interesting. Error-resilient entropy coding (EREC) has emerged as a new and effective method to combat catastrophic loss in the received signal due to burst and random errors. We propose a new channel-matched adaptive quantizer for JPEG image compression. A slow, frequency-nonselective Rayleigh fading channel model is assumed. The optimal quantizer that matches the human visibility threshold and the channel bit-error rate is derived. Further, a new fast error-resilient entropy code (FEREC) that exploits the statistics of the JPEG compressed data is proposed. The proposed FEREC algorithm is shown to be almost twice as fast as EREC in encoding the data, and hence the error resilience capability is also observed to be significantly better. On average, a 5% decrease in the number of significantly corrupted received image blocks is observed with FEREC. Up to a 2-dB improvement in the peak signal-to-noise ratio of the received image is also achieved.

A stochastic importance sampling methodology for the efficient simulation of adaptive systems in frequency nonselective Rayleigh fading channels

We present an IS stochastic technique for the efficient simulation of adaptive systems which employ diversity in the presence of frequency nonselective slow Rayleigh fading and additive, white, Gaussian noise. The computational efficiency is achieved using techniques based on importance sampling (IS). We utilize a stochastic gradient descent (SGD) algorithm to determine the near-optimal IS parameters that characterize the dominant fading process. After accounting for the overhead of the optimization algorithm, average speed-up factors of up to six orders of magnitude [over conventional Monte Carlo (MC)] were attained for error probabilities as low as 10/sup -11/ for a fourth-order diversity model.

Performance of DPSK mobile receiver in impulse noise

The authors present a performance analysis of L-diversity DPSK receivers over frequency non-selective Rayleigh fading channels in Middleton's class A impulse noise. The analysis is exact and is shown by simulation to be accurate.

Error performance of circular 16-DAPSK with postdetection diversity reception in Rayleigh fading channels

A closed-form expression for the average error probability of circular 16-ary differential amplitude and phase shift keying with postdetection diversity combining is obtained for frequency-nonselective Rayleigh fading channels. The effect of random FM noise is also considered in the evaluation. Since both amplitude and phase are encoded and decoded independently, their detailed performances are analysed separately. System parameters such as the ring ratio and decision thresholds have been optimised for a number of fading conditions. The optimal and suboptimal decision thresholds are evaluated. The optimal ring ratio of the modulation is generally a function of Doppler frequency. The results have shown that postdetection diversity is a powerful technique for reducing the effects of random FM noise.

Differentially coherent multiuser detection in asynchronous CDMA flat Rayleigh fading channels

Presents a performance analysis of a decorrelating detector for differentially coherent transmission over a CDMA frequency-nonselective Rayleigh fading channel. While the correlation-type receiver is near-far limited in this channel, it is shown that the aforementioned multiuser detector eliminates the bit error rate floor and alleviates the near-far problem. >

Pilot symbol aided coherent decorrelating detector for up-link CDMA mobile radio communication

A new decorrelating arrangement for asynchronous up-link direct sequence code division multiple access communication, which employs coherent detection with pilot symbol aided channel estimation, is proposed. The proposed coherent scheme improves the bit error rate (BER) and exhibits no error floor compared to the previous noncoherent schemes. The BER performance for BPSK is obtained by simulations over a frequency-nonselective Rayleigh fading channel.

On the bit error probability of QAM modulation

This paper presents some closed-form bit error probability expressions for coherent demodulation of both Gray coded and differentially decoded Gray coded QAM modulations in nonfading and frequency nonselective Rayleigh fading channels. These results demonstrate that as QAM constellation sizes get larger the BEP degradation due to differential encoding and decoding becomes negligible.

Diversity improvement for 16-DAPSK in Rayleigh fading channel

Postdetection combining has been analysed together with fully differential 16-APSK (16-DAPSK) as a potential method for improving digital transmission in a frequency nonselective Rayleigh fading channel. Results are presented for the theoretical and computer simulated BER performance both with and without the use of diversity combining in the receiver.

Frequency domain equalisation of OFDM signals over frequency nonselective Rayleigh fading channels

In orthogonal frequency division multiplexing (OFDM) signal transmission via a frequency nonselective fading channel, multiplicative distortion in the time domain acts as intersymbol interference (ISI) in the frequency domain. The Letter proposes new compensation methods for the fading distortion in OFDM signals, in which compensation is achieved in the frequency domain. With the proposed methods, improved results can be obtained compared to previous schemes. The symbol error rate (SER) of each proposed scheme is obtained by baseband simulation.

Comparison of two ARQ protocols in a Rayleigh fading channel

Go-back-N (GBN) and selective repeat (SR) protocols for automatic repeat request (ARQ) are compared in a frequency-nonselective Rayleigh fading channel. Protocols implemented in software are used in a computer-simulated fading channel to study the throughput of these protocols as a function of fading parameters, such as the mean signal-to-noise ratio (SNR), maximum Doppler frequency number of diversity branches, time-out period and round-trip delay. The purpose is to complement well-documented theoretical work in (1) providing some design considerations and (2) investigating quantitatively whether data communications combining detection-only coding, diversity, and basic ARQ protocols can offer reasonable throughput in a fading channel. Although based on a set of assumptions, the following conclusions remain valid: (1) SR is significantly superior to GBN when the fading rate is high; this advantage decreases as fading becomes slower; and (2) error detection combined with ARQ and diversity selection can provide reliable data communications in a Rayleigh fading channel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>