Performance of punctured convolutional codes in asynchronous CDMA communications under perfect phase-tracking conditions

In this paper, the performance of punctured convolutional codes of short constraint lengths is discussed. The punctured codes are used to provide error protection to a particular user in an asynchronous code division multiple access (A-CDMA) system. Perfect channel estimation is assumed at the receiver. A slow fading Rician or Rayleigh channel is assumed. Maximum likelihood decoding through a Viterbi algorithm is used to decode the received symbols. Soft decision decoding for perfect phase tracking of the received signal is considered. Analytical bounds, which are useful in predicting the performance of the A-CDMA system are derived and plotted for the cases of infinite and finite channel memory. The upper bounds with Viterbi decoding are derived and plotted for the various punctured codes considered. The simulated results are found to agree very well with their upper bounds and predicted results.     

Simple rateless error-correcting codes for fading channels

This paper introduces a new class of rateless forward error correction(FEC) codes,which are called semi-random Kite(SR-Kite) codes.By introducing fixed patterns to an original purely random sparse parity-check matrix,the proposed code can lower down the error floors.We present a simulation-based greedy optimization algorithm to design the degree distribution of SR-Kite codes for independent Rayleigh fading channels.The performances of SR-Kite codes under maximum likelihood decoding are analyzed for both AWGN and independent Rayleigh fading channels via union bound.Both the analysis and simulation results show that the proposed codes perform well over AWGN and fading channels within a wide range of signal-to-noise-ratios.Moreover,we combine SR-Kite codes with high-order modulation schemes to obtain a continuously variable spectral efficiency in a large range of SNRs.     

Performance of multiuser CDMA system with space-time block coding in MIMO Rayleigh fading channels

In this paper, by introducing orthogonal space-time coding scheme, the multiuser CDMA systems with different space time codes are given, and corresponding system performance is investigated over Rayleigh fading channel. A low-complexity multiuser receiver scheme is developed for space-time coded CDMA systems. The scheme can make full use of the complex orthogonality of space-time coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, average bit error rate (BER) of the system is derived in detail, and tight closed-form approximation expressions of BER are attained. Simulation results on average BER are in agreement with the theory analysis. The results show that the proposed scheme can achieve almost the same performance as the existing scheme. Moreover, on the condition of same system throughput and concatenation of channel code, the given full-rate space-time coded CDMA system has lower BER than the full-diversity space-time coded CDMA systems.     

Performance of Haar wavelet based scale-code division multiple access (HW/S-CDMA) using decorrelating multi-user detector

Recently, we have proposed a new multi-rate/multi-media system called wavelet based scale-code division multiple access (W/S-CDMA) that depends on the code, time and scale orthogonality introduced by pseudo-noise (PN) sequences, and wavelets. Wavelets are used as an orthogonal set of symbols for signaling, and their orthogonality is exploited over scale and time. In this system, the channel is divided into different scales, and each scale into time slots. In addition, the PN sequences are used in each scale to accommodate multiple users. In other words, each user encodes its successive information symbols with time-shifted replicas of the same basic wavelet in a specific scale and spreads its scaled and translated wavelets with its PN sequence. The finer the scale used, more symbols are transmitted. In this paper, we analyze the performance of Haar wavelet based S-CDMA (HW/S-CDMA) over a synchronous additive white Gaussian noise (AWGN) channel using a decorrelating multi-user detector. Results reveal that HW/S-CDMA holds promise since the users of HW/S-CDMA can achieve variable and higher data rates than those of direct sequence (DS)-CDMA for a similar bit error rate performance when real-valued PN sequences are used. However, HW/S-CDMA achieves better performance than DS-CDMA when complex-valued PN sequences are used. In addition, for all rates the same performance is achieved in HW/S-CDMA and the multi-user detector has no processing delay for different rates and has the same features as the standard decorrelating detector. Because of the reuse capability introduced by the scales, HW/S-CDMA is also capable of employing many available PN sequences from the optimal PN sequence families with limited number of sequences such as Kasami, Bent, etc.     

The design and analysis of unequal error protection fountain coding for multiple source networks over binary erasure channels

A novel network model of multiple source fountain coding is developed and a novel class of generic multiple source fountain codes with unequal error protection(UEP)property is proposed.The And–Or tree analysis technique is generalized to analyze the asymptotic performance of the proposed codes and a joint optimization method employing both linear and nonlinear programs is developed to optimize the degree distributions.Furthermore,we propose three basic methods to achieve UEP property and the performance of each method is discussed.We employ these analytical results and optimization method to design and discuss several UEP codes with two and four sources for different application scenarios.Simulation results verify that the proposed codes can be applied to the networks with any number of sources and can provide strong UEP property in various ways based on the proposed three basic methods.