Level Of Error Probability Research Articles

Near-optimal symbol-by-symbol detection schemes for flat Rayleigh fading

The optimal MAP detection algorithm for demodulation of M-QAM signaling in the frequency flat Rayleigh fading channel is proposed. A recursive structure is derived which allows for symbol-by-symbol metrics to be computed and data decisions to be made in an efficient manner. The complexity problem inherent to optimal detection schemes is addressed and approximations to optimal detection are considered which reduce complexity to practical levels yet still provide near-optimal performance levels. Reduced complexity algorithms are obtained through the use of decision feedback and thresholding which allow for higher order modulations such as 16-QAM to be implemented. Performance characterization of the algorithms presented are obtained via Monte Carlo simulation and results show that near-optimal bit error probability levels can be achieved. Extensions of the algorithms to include diversity combining techniques are also developed and shown to provide improved performance. Some theoretical derivations for optimal detection of 16-QAM in fading with diversity are also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental realization of ASK underwater digital acoustic communications system using error correcting codes

An ASK digital underwater acoustic communications system has been designed and tested to investigate the influence of error correcting codes on the performance of the system. The underwater communications channel is a multi-path fading channel and has been modelled accordingly, and the error probability was estimated under varying operating conditions. This paper describes the experimental investigations which confirm the presence of certain error probability levels. An improvement in the system performance when using error correcting coding techniques has been achieved. The ASK modulation scheme has been used in the system for ease of implementation. The tests were carried out in an outdoor swimming pool to simulate short range channels with severe multi-path effects.

A comparison of wife abuse between two cultures: perceptions, attitudes, nature, and extent

The purpose of this study was to explore the similarities and differences between Anglo-American and Mexican-American battered women. This descriptive study compared a group of 25 Anglo-American and 25 Mexican-American women over age 18 who had been physically abused by their husbands at least two times and had resided in shelters for battered women. This study addressed the nature, severity, and frequency of wife abuse; women's perception of what they consider wife abuse; and their attitudes toward wife abuse. Respondents were matched for age and socioeconomic status. Data were collected through personal interviews, using a semistructured interview schedule consisting of three instruments. Data were analyzed using descriptive statistics. Comparisons between the two groups were done using t test and chi-square procedures. A Type I error probability level of less than .05 was used to determine statistical significance. Results showed that there were more similarities than differences in the manifestation of wife abuse between the two groups. However, Anglo-American women perceived more types of behavior as being abusive and exhibited a less tolerant attitude toward wife abuse than did Mexican-American women. The t test results indicated no significant difference in the severity and frequency of wife abuse between Anglo-Americans and Mexican-Americans.

Error probability analysis for continuous phase modulation with Viterbi detection on a Gaussian channel with multiple signal interference

The effects are studied on the symbol error probability of the Viterbi detector for continuous phase modulations with constant amplitude, when the desired signal is received in multiple interfering signals and white Gaussian noise. The detection is assumed to be coherent and, furthermore, perfect timing in the detector is also assumed. An upper bound on the symbol error probability is derived for the Viterbi detector. The bound is based on the union bound technique, and it is shown to be tight for small error probability levels. It is found that the smoothed binary and all quaternary modulations sustain much larger interference power in adjacent channel interference than minimum-shift keying (MSK) does and, thus, the adjacent channels can be spaced closer in frequency for these modulations, In particular, the smoothed quaternary modulations seem to be significantly more efficient than MSK. In cochannel interference the difference in error performance between the schemes is relatively small.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A statistical approach to station discontinuance

The sequential probability ratio test (SPRT) is developed and applied to the station discontinuance problem. The decision whether to discontinue a station is dependent upon statistical considerations that include the error probabilities of accepting a model when it is incorrect as well as rejecting it when it is correct. Both error probabilities can be explicitly set by using the SPRT approach so that the decision rules are: accept model 1, accept model 2, continue to sample (cannot accept either). The error probability levels are a decision variable that depends upon the use of the data and the cost of collection. Procedures are developed for determining the expected benefits from sampling one additional time within the SPRT framework. The SPRT approach was applied to the Susquehanna River at Harrisburg, Pennsylvania.

Optimum Weighted PCM for Speech Signals

Weighted digital modulation schemes which provide bit error probabilities matched to the PCM bits with respect to their sensitivity to digital errors are analyzed. The channel is additive, white Gaussian. The PCM system has arbitrary code, companding law and input signal density function. Especially optimum weighted PSK/PCM and QAM/PCM are given for speech signals. The average channel signal to noise ratio is kept constant when schemes are compared. We obtain a channel signal to noise ratio gain in threshold extension of 2 dB for standard 8 bit PCM. The performance of suboptimum schemes, where the number of different bit error probability levels are smaller than the number of PCM bits are also studied. Two levels per 8 bit PCM word yield more than half of the achievable gain (in dB) and 4 levels is almost equal to optimum.