Irreducible BER Research Articles

On the application of decorrelating receiver to multicode system

AbstractIn this letter a novel decorrelating detector for multicode system is proposed and analysed. Multicode transmission is an alternative technique for providing multirate data to multiple users. However, it suffers from an inter‐channel‐interference when the signal is transmitted over a multipath channel. The proposed receiver processes the received message in a symbol‐by‐symbol fashion, which reduces the computational complexity of the decorrelating receiver considerably comparing to the more traditional approach, where the full frame is processed at a time. Simulation results show that the performance improvement is substantial using the proposed receiver, e.g. the irreducible BER can be lowered as much as 2 orders of magnitude @ 20 dB. Copyright © 2009 John Wiley & Sons, Ltd.

Error performance of narrowband and spread-spectrum modulation with diversity in frequency-selective channel

Abstract The analysis of irreducible average bit error of narrowband and direct sequence spread-spectrum modulation using BPSK, QPSK, DPSK and DQPSK in Rayleigh and Rician frequency-selective channels is presented. The analysis for narrowband modulation shows a substantial improvement in irreducible BER at moderate normalized delay spread when a specular component (K) is present in the channel. This improvement decreases rapidly as normalized delay spread increases. However, with the use of direct sequence spread-sprectrum, this improvement can be maintained even at high values of normalized delay spread. With selection diversity, the irreducible BER in Rayleigh fading is less than 10−5with normalized delay spread of up to 0-7 and 0-2 for DPSK and DQPSK, respectively. When equal-gain combining is used, BER of less than 10−4 is obtained under Rayleigh fading with normalized delay spread of up to 1.0 for DPSK, whereas BER of less than 10−4is obtained with normalized delay spread of up to 0-4 for DQPSK.

The Effects of Time Delay Spread on Portable Radio Communications Channels with Digital Modulation

Frequency-selective fading caused by multipath time delay spread degrades digital communication channels by causing intersymbol interference, thus resulting in an irreducible BER and imposing a upper limit on the data symbol rate. In this paper, a frequencyselective, slowly fading channel is studied by computer simulation. The unfiltered BPSK, QPSK, OQPSK, and MSK modulations are considered first to illustrate the physical insights and the error mechanisms. Two classes of modulation with spectral-shaping filtering are studied next to assess the tradeoff between spectral occupancy and the performance under the influence of time delay spread. The simulation is very flexible so that different channel parameters can be studied and optimized either individually or collectively. The irreducible BER averaged over fading samples with a given delay profile is used to compare different modulation/detection methods, while the cumulative distribution of short-term BER is employed to show allowable data symbol rates for given values of delay spread. It is found that both GMSK and QPSK with a raised-cosine Nyquist pulse are suitable for a TDM/TDMA digital portable communications channel.

Switched-diversity FSK in frequency-selective Rayleigh fading

This paper presents the measured performance of a 64 kbit/s switched-diversity FSK receiver subjected to simulated frequency-selective Rayleigh fading. The single receiver input is switched between two, three, or four uncorrelated Rayleigh-fading signals whenever the instantaneous receiver output falls below a threshold. The optimum level of this threshold relative to the mean signal level is relatively insensitive to frequency selectivity and vehicle speed. A nearly optimum threshold may be determined using an AGC amplifier and fixed comparator. Switched diversity is a powerful tool for combating frequency selectivity and Rayleigh fading. Two-branch switched diversity can achieve 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> BER, with 6 dB lower SNR than that needed without diversity. In the absence of frequency selectivity, two-branch switched diversity can perform within 3 dB SNR of maximal-ratio diversity and within 1 dB of selection diversity. Switched diversity can achieve BER's lower than the irreducible single-channel BER produced by frequency selectivity. Four-branch switched diversity typically requires 4 dB lower SNR to achieve a given BER than does two-branch switched diversity.

Switched-Diversity FSK in Frequency-Selective Rayleigh Fading

This paper presents the measured performance of a 64 kbit/s switched-diversity FSK receiver subjected to simulated frequency-selective Rayleigh fading. The single receiver input is switched between two, three, or four uncorrelated Rayleigh-fading signals whenever the instantaneous receiver output falls below a threshold. The optimum level of this threshold relative to the mean signal level is relatively insensitive to frequency selectivity and vehicle speed. A nearly optimum threshold may be determined using an AGC amplifier and fixed comparator. Switched diversity is a powerful tool for combating frequency selectivity and Rayleigh fading. Two-branch switched diversity can achieve 10-2BER, with 6 dB lower SNR than that needed without diversity. In the absence of frequency selectivity, two-branch switched diversity can perform within 3 dB SNR of maximal-ratio diversity and within 1 dB of selection diversity. Switched diversity can achieve BER's lower than the irreducible single-channel BER produced by frequency selectivity. Four-branch switched diversity typically requires 4 dB lower SNR to achieve a given BER than does two-branch switched diversity.