An algebraic approach to generate super‐set of perfect complementary codes for interference‐free CDMA

This paper introduces an algebraic approach to generate the super‐set of perfect complementary (PC) codes suitable for new generation CDMA applications, characterized by isotropic multiple access interference (MAI) free and multipath interference (MI) free properties. The code design methodology proposed in this paper takes into account major impairing factors existing in real applications, such as MAI, MI, asynchronous transmissions, and random signs in consecutive symbols, such that a CDMA system using the generated codes can insure a truly interference‐free operation. Two important facts will be revealed by the analysis given in this paper. First, implementation of an interference‐free CDMA will never be possible unless using complementary code sets, such as the PC code sets generated in this paper. In other words, all traditional spreading codes working on an one‐code‐per‐user basis are not useful for implementation of an MAI‐free and MI‐free CDMA system. Second, to enable the interference‐free CDMA operation, the flock size of the PC codes should be made equal to the set size of the codes, implying that a PC code set can support as many users as the flock size of the code set. A systematic search has been carried out to generate the super‐set of various PC codes with the help of carefully selected seed codes belonging to distinct sub‐sets. This paper will also propose an implementation scheme based on multi‐carrier CDMA architecture and its performance is compared by simulations with the ones using traditional spreading codes. Copyright © 2006 John Wiley & Sons, Ltd.     

Performance bounds for optimum and suboptimum reception under Class-A impulsive noise

The transmission over the memoryless additive white Class-A noise (AWCN) channel is considered. For uncoded transmission, an exact expression for the symbol error rate is derived. For coded transmission, the Chernoff bound on the pairwise error probability is calculated and the performance achieved on the real and the complex AWCN channels is compared. Moreover, a low-complexity, suboptimum decoding metric is derived and analyzed employing the cutoff rate as a performance criterion.     

Multi-variant analysis of otoacoustic emissions and estimation of hearing thresholds: transient evoked otoacoustic emissions

Evaluation of cochlear hearing loss by means of transiently evoked otoacoustic emissions is already established in clinical practice. However, accurate prediction of pure-tone thresholds is still questioned and is still regarded as troublesome. Both click- and tone-burst-evoked otoacoustic emissions at several intensity levels were measured and analysed in 157 ears from normally hearing and 432 ears from patients with different degrees of pure sensory hearing loss using the ILO88/92 equipment. Results of otoacoustic emissions (OAE), elicited by clicks and tone-bursts at centre frequencies from 1 to 5 kHz, were analysed using two different statistical methods. Both multivariate discriminant analysis and forward multiple regression analysis were used to determine which OAE variables were most discriminating and best at predicting hearing thresholds. We found that a limited set of variables obtained from both tone-burst and click measurements can accurately predict and categorize hearing loss levels up to a limit of 60 dB HL. We found correct classification scores of pure-tone thresholds between 500 and 4000 Hz up to 100 per cent when using combined click and tone-burst otoacoustic measurements. Prediction of pure-tone thresholds was correct with a maximum estimation error of 10 dB for audiometric octave frequencies between 500 and 4000 Hz. Measurements of multiple tone-bursts OAEs have a significant clinical advantage over the use of clicks alone for clinical applications, and a good classification and prediction of pure-tone thresholds with otoacoustic emissions is possible.     

Generalized pairwise complementary codes with set-wise uniform interference-free windows

This paper introduces an approach to generate generalized pairwise complementary (GPC) codes, which offer a uniform interference free windows (IFWs) across the entire code set. The GPC codes work in pairs and can fit extremely power efficient quadrature carrier modems. The characteristic features of the GPC codes include: the set size is 2K, the processing gain is 4NK, and the IFW's width is 8N identically for all codes in a set, where K is the times to perform Walsh-Hadamard expansions and N is element code length of seed complementary codes. Therefore, by using different N, the IFW width of a GPC code set can be adjusted with its set size unchanged. Each GPC code set consists of two code groups, with each having K codes, and they have sparsely and uniformly distributed autocorrelation side lobes and cross-correlation levels outside the IFWs.     

Coding and signal space diversity for a class of fading and impulsive noise channels

The transmission over the Gaussian mixture noise channel with perfect channel state information at the receiver side is considered. Lower and upper bounds on the achievable pairwise error probability (PEP) are derived for finite and infinite codeword lengths. It is shown that diversity codes, i.e., unitary transforms, can be applied to achieve a diversity gain. A large class of diversity codes is determined for which-if the codeword length is increased-the PEP between any two codewords approaches either zero or the lower bound on the PEP.     

Application of cross-correlation function in the evaluation of objective MLR thresholds in the low and middle frequencies

In this study, the cross-correlation function was applied in the evaluation of MLR thresholds in the low and middle frequencies. The parameters of the cross-correlation function consist of the correlation coefficient at a lag-time of zero (RO), the maximum correlation coefficient (RM), and the latency delay on the lag-time axis at the point of the maximum correlation coefficient (DL). The normal limits of the parameters of cross-correlation at the MLR threshold level, which was identified by visual detection across frequencies, were obtained in normal-hearing and hearing-impaired subjects. The cross-correlation functions for two traces were also performed below threshold level. All cross-correlation parameters (RO, RM and DL) below threshold level were outside normal limits in 91% of all the subjects. The incidence of the only RM or DL parameter value within normal limits was 6% or 3% of all cases at the subthreshold level. Correlation data allow precise measurements of the MLR threshold and enhance the sensitivity of the definition of the MLR threshold. In addition, our study provides quantifiable information for estimating MLR threshold.     

Coding Schemes for Crisscross Error Patterns

This paper addresses two coding schemes which can handle emerging errors with crisscross patterns. First, a code with maximum rank distance, so-called Rank-Codes, is described and a modified Berlekamp–Massey algorithm is provided. Secondly, a Permutation Code based coding scheme for crisscross error patterns is presented. The influence of different types of noise are also discussed.

A convolutional single-parity-check concatenated coding scheme forhigh-data-rate applications

The coding scheme uses a set of n convolutional codes multiplexed into an inner code and a (n,n-1) single-parity-check code serving as the outer code. Each of the inner convolutional codes is decoded independently, with maximum-likelihood decoding being achieved using n parallel implementations of the Viterbi algorithm. The Viterbi decoding is followed by additional outer soft-decision single-parity-check decoding. Considering n=12 and the set of short constraint length K=3, rate 1/2 convolutional codes, it is shown that the performance of the concatenated scheme is comparable to the performance of the constraint length K=7, rate 1/2 convolutional code with standard soft-decision Viterbi decoding. Simulation results are presented for the K=3, rate 1/2 as well as for the punctured K=3, rate 2/3 and rate 3/4 inner convolutional codes. The performance of the proposed concatenated scheme using a set of K=7, rate 1/2 inner convolutional codes is given     

Bilateral threshold frequency weighting in hearing disability predictions

The growing size of world cities and ever more competitive working conditions are thought to cause subjective stress, anxiety and depression, with a resulting decrease in the quality of life, sleep disturbances, drug and alcohol abuse and poor productivity. Acute stress may suppress immune function, leading to an increased incidence of infections, and chronic stress may predispose to a number of ailments, including digestive disturbances, hypertension, ischaemic heart disease and neoplasia; jointly, these factors cause a substantial shortening of life expectancy. The control of stress thus makes an important contribution to health. Stress levels can be reduced by anxiolytic drugs, or by a variety of psychological techniques; however, an appropriate programme of physical activity may be the preferred option, since exercise has many positive effects on health that are unrelated to stress. If exercise is to be effective in inducing relaxation, it must be noncompetitive, moderate in intensity, and pursued in pleasant surroundings.     

Delay analysis for single server queues

A discrete-time single server queue with FIFO discipline and general independent service times is studied. The authors present a relationship between the distribution of the delay of an arbitrary customer and the joint distribution of the buffer occupancy during an arbitrary (non-empty) slot, and the remaining service time for the customer in service at the beginning of such a slot