Frequency-selective Fast Rayleigh Fading Channel Research Articles

RLS Channel Estimation with Adaptive Forgetting Factor for DS-CDMA Frequency-Domain Equalization

Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can increase the downlink bit error rate (BER) performance of DS-CDMA beyond that possible with conventional rake combining in a frequency-selective fading channel. FDE requires accurate channel estimation. Recently, we proposed a pilot-assisted channel estimation (CE) based on the MMSE criterion. Using MMSE-CE, the channel estimation accuracy is almost insensitive to the pilot chip sequence, and a good BER performance is achieved. In this paper, we propose a channel estimation scheme using one-tap recursive least square (RLS) algorithm, where the forgetting factor is adapted to the changing channel condition by the least mean square (LMS)algorithm, for DS-CDMA with FDE. We evaluate the BER performance using RLS-CE with adaptive forgetting factor in a frequency-selective fast Rayleigh fading channel by computer simulation.

Precise BER analysis of π/4-DQPSK OFDM with carrier frequency offset over frequency selective fast fading channels

An exact closed-form bit error rate (BER) expression is derived for an orthogonal frequency-division multiplexing system with π/4-shifted differentially encoded quadrature phase shift keying (π/4-DQPSK) in the presence of carrier frequency offset over frequency-selective fast Rayleigh fading channels. Different system configurations, including time domain differential modulation, frequency domain differential modulation, single channel reception, and multi-channel reception with maximal ratio combining diversity, are considered in the exact BER analysis. For a small number of subcarriers, the BER expression can be calculated directly. A Monte Carlo method is designed to evaluate the BER for a large number of subcarriers. The analytical expression can be used to investigate the effect of several channel parameters, including mean delay spread and maximum Doppler spread, on the system BER performance. Particularly, the effect of carrier frequency offset on the system performance, and the differences and opportunities to use frequency domain differential modulation or time domain differential modulation, can be studied in a quantitative way for a more realistic wireless channel environment model. By using the exact closed-form BER expression, an optimum number of subcarriers can be found, and the allowable carrier frequency offset, Doppler spread, and mean delay spread for given operating conditions can be determined.

A Comparison of DCT-Based OFDM and DFT-Based OFDM in Frequency Offset and Fading Channels

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

Transmission performance analysis of Multi-Carrier Modulation in frequency selective fast Rayleigh fading channel

In this paper, we discuss the transmission performance of Multi-Carrier Modulation (MCM) in frequencyselective fast Rayleigh fading channels. First, we optimize the transmission parameters of MCM withM-ary differential phase shift keying/differential detection (DPSK):the guard duration andthe number of sub-carriers for frequency-selective fast Rayleigh fading channels, and then show the bit error rate (BER) performance of the optimizedM-ary DPSK MCM. Next, we propose an MCM with pilot-assistedM-ary quadrature amplitude modulation/coherent detection (QAM), and discuss the BER performance when we reduce the number of pilot signals from the view-point of frequency-time utilization efficiency. Finally, we propose a two-stage frequency offset compensation method.

Pilot-symbol aided coherent M-ary PSK in frequency-selective fast Rayleigh fading channels

Pilot-symbol aided coherent M-ary PSK modems in digital cellular mobile radio systems are analyzed theoretically. The error-floors caused by the Doppler spread in a fast fading channel are removed in both flat and selective fading channels. However, the error-floors caused by the delay spread are lower-bounded by those that exist in the ideal coherent detection. The systems are modeled as frequency-selective fast Rayleigh fading channels, corrupted by co-channel interference (CCI) and additive white Gaussian noise (AWGN). In the proposed scheme, pilot symbols are inserted periodically to monitor the channel characteristics. The fading processes experienced by the pilot symbols are used to estimate those suffered by the data symbols using interpolation or filtering. The estimated fade characteristics are used to compensate the random phase variation caused by the Doppler spread, so that the signals can be demodulated coherently. The theoretical performances of the fade compensated coherent modems are evaluated. The results show that the fade compensated coherent demodulation with the least redundancy achieves the same performance as the ideal differential detection in a fading channel. The performance approaches that of the ideal coherent demodulation as more redundancy is allowed. The pilot-symbol-insertion (PSI) scheme is also applicable to M-ary QAM modems and Rician channels. The residual frequency offset can also be compensated by the PSI technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance of GMSK with two-bit differential detection in a land mobile radio channel

The performance of two-bit differential detection of Gaussian minimum-shift keying (GMSK) in a cellular mobile communication channel is theoretically analyzed. The channel is modelled to reflect those encountered in a practical system; i.e., a frequency-selective fast Rayleigh-fading channel corrupted by cochannel interference and additive white Gaussian noise. A two-ray model for the channel is used and a single cochannel interferer is considered in the analysis. The Doppler effect is included as well. A closed-form expression for the probability of error is obtained. Numerical computation is used to obtain GMSK bit-error-rate performance for various combinations of channel parameters. The results are compared with those for limiter-discriminator detection with the same channel parameters. The performance of limiter-discriminator detection is found to be superior to that of two-bit differential detection. As two-bit differential detection is generally simpler to implement, the choice of detection method involves a performance versus complexity trade-off. The results presented can be used to make this trade-off.

Bit error rate performance of pi /4-DQPSK in a frequency-selective fast Rayleigh fading channel

The bit error rate (BER) performance of pi /4-differential quadrature phase shift keying (DQPSK) modems in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). The probability density function of the phase difference between two consecutive symbols of M-ary differential phase shift keying (DPSK) signals is first derived. In M-ary DPSK systems, the information is completely contained in this phase difference. For pi /4-DQPSK, the BER is derived in a closed form and calculated directly. Numerical results show that for the 24 kBd (48 kb/s) pi /4-DQPSK operated at a carrier frequency of 850 MHz and C/I >

Performance of GMSK in a land mobile radio channel

Discriminator detection of Gaussian minimum shift keying (GMSK) in a cellular mobile-communication channel is analyzed. The channel is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). A closed-form expression for the probability of error is derived. Numerical computation is used to obtain the GMSK bit error rate (BER) performance for various combinations of channel parameters. These results show that GMSK gives slightly better performance compared to that for pi /4-quadrature phase shift keying (QPSK) previously reported in the literature. >