In this paper, space-time coding schemes with full transmit diversity are investigated for unequal error protection (UEP). Effective performance indicies are proposed to measure the intrinsic UEP capability of space-time codes, based on which we demonstrate that space-time trellis codes and superorthogonal space-time trellis codes can be used for UEP as long as the corresponding encoders are properly designed. In addition, UEP convolutional codes are concatenated with space-time block codes to construct another full-diversity UEP scheme which can provide more choices of UEP levels. Finally, good UEP codes are given by a computer search.

This paper proposes and compares three multi- rate receiver structures with post-fast Fourier transform (FFT) type and the pre-FFT type for orthogonal frequency division multiplexing code-division multiple access (OFDM-CDMA) communication systems. In multipath fading channel, the transmitted signal suffers from the effects of inter-chip interference (ICI) and multiple access interference (MAI). In order to solve these problems and support multimedia traffic, we propose three multi- rate methodologies- variable processing gain (VPG), variable chip rate (VCR) and multi-code systems to investigate the performance of the OFDM-CDMA communications in multipath fading environments. Simulations confirm the good performance of the proposed receiver structures.

Most investigations on the effect of channel memory on the performance of block codes use a two-state Gilbert-Elliott (GE) model to describe the channel behavior. As there are circumstances that the channel of concern can not be properly described by the GE model, there are some recent works on coded performance that characterize the channel behavior by a general finite-state Markov chain. This letter presents a new efficient systematic approach to analyze the performance of block codes in such a hidden Markov channel (HMC). An application example is given to predict codeword error probability performance of an RS-coded system in a channel with memory. Numerical results are also provided to validate our analytic results.

Frequency-hopping spread-spectrum (FH-SS) is an efficient technique to combat jamming. Previous works in jamming channels pay more attention to partial band noise jamming (PBNJ). In this paper, Low-Density Parity-Check (LDPC) coded fast frequency hopping binary frequency shift keying (FFH/BFSK) spread-spectrum (SS) systems are investigated under band multitone noise jamming (BMTJ). We take the advantage of both diversity gain and coding gain for enhancing the system performance. We consider maximum-likelihood (ML) diversity combing and square-law with equal gain combing schemes which are used to compute the codeword bit decision reliability. The sum-product algorithm (SPA) based on belief propagation is exploited for iterative decoding. Simulation results reveal that our proposed system provides excellent performance against band multitone noise jamming.

The performance of low-density parity-check (LDPC) codes is investigated for fast frequency hopping / binary frequency shift keying (FFH/BFSK) in partial-band noise jamming channels. We employ different diversity combining schemes to compute the codeword bit decision reliability. In this paper, we consider the maximum-likelihood (ML) diversity combining scheme and two low-complexity suboptimal diversity combining schemes: square-law with adaptive gain control (AGC) combining and square-law with equal gain combining. Simulation results show that, by combining both of the diversity and coding gain, our proposed system can provide excellent performance against partial-band noise jamming.

OFDM is a promising scheme for multicarrier (MC) transmission, since it has the advantage of high spectral efficiency, robustness to frequency selective fading, and feasibility of low-cost transceiver implementation. The combination of OFDM and CDMA, referred to as OFDM-CDMA, recently attracted most research interests in wireless communications. In this paper, adaptive receivers for OFDM-CDMA communication systems are developed based on the least mean square (LMS) algorithm. We evaluate the down-link performance for two forms of OFDM-CDMA schemes which are MC-CDMA and MC-DS-CDMA in multipath fading channels. A drawback of OFDM schemes is the rate reduction due to the cyclic prefix (CP) overhead, which significantly affects the channel utilization in MC-DS-CDMA systems. Thus we propose adaptive receiver structure that exploits both frequency-domain and time-domain equalization to improve the performances of MC-DS-CDMA systems with shorter or no CP. Simulation results show performance comparisons between MC-CDMA and MC-DS-CDMA systems, which also verify the performance improvement of our proposed receiver for MC-DS-CDMA systems exploiting shorter or no CP.

In code division multiple access (CDMA) mobile communication systems with time-varying multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) must be considered. The multipath effect usually change the characteristics of the spreading codes. Modification of the conventional receiver structure is needed to account for the interference of the multipath fading. This paper proposes an adaptive receiver for such multiuser direct sequence (DS) CDMA systems in multipath fading. We also analyze the mean square error (MSE) performances of the proposed receiver and the conventional receiver. Both the MSE analysis and simulation results show that the performance of the proposed receiver are better than that of the conventional receiver.

The application of Reed-Solomon codes in slow frequency-hopped systems has been extensively studied. Earlier investigations assumed an infinite interleaving length and considered partial-band noise jammers only. This paper extends previous efforts by analyzing the effect of finite interleaving length and the impact of band multitone jammers. We also explain why two-threshold (2T) erasure-insertion methods (EIM) are needed and examine their performance. Numerical results are presented to compare the effectiveness of the EIM and jammer types and to study the relationships among the hop rate, the interleaver size, and the code rate. The use of 2T-EIM necessitates the estimation of several additional channel and signal parameters. Simple and effective estimation algorithms are provided as well.