In recent years, combining multiuser detection (MUD) and channel decoding has received considerable attention. The maximum a posteriori (MAP) criterion-based iterative multiuser detector greatly improves the system performance and can approach the performance of single-user coded systems. However, its complexity increases exponentially with the number of users and can become prohibitive for systems with a medium-to-large number of users. In this paper, a reduced complexity MAP-based iterative MUD based on the use of a soft sensitive bits algorithm is proposed for coded multicarrier code-division multiple-access systems. It is shown that it can greatly reduce the computational complexity with a minimal penalty in performance compared to the conventional optimal scheme.

A differential detection scheme for transmit diversity was proposed by Tarokh. which can achieve full diversity order without the requirement to estimate the channel state at the receiver. This paper investigates the potential of using multiple receive antennas for differential space time coded MPSK signals over correlated Nakagami fading channels. We also investigate the effect of the carrier frequency offset (CFO) and channel correlation on its performance and present some results on its maximal tolerable frequency offsets for different MPSK signals. The results have shown that the differential encoding transmit diversity is very robust to the CFO and channel correlation. Copyright

Non-binary type-II hybrid ARQ (HARQ), which combines shortened Reed–Solomon (RS) code with ARQ, is proposed. Its throughput is obtained by extending Lin and Yu’s analysis of binary type-II HARQ. The reliability and average delay are also obtained. The analytical results show that non-binary HARQ outperforms its binary counterpart in throughput, reliability and average delay when proper RS codes are selected. Non-binary HARQs are applied adaptively in a cellular phone system with uniformly distributed mobile terminals (MTs). MTs switch adaptively between two different hybrid schemes according to the average SNR of the received signals. The adaptive parameters include the size of the modulation constellation, the error-correction coding and their joint adaptation. Numerical results show that the adaptive scheme always outperforms its non-adaptive counterparts, and the adaptive modulation scheme is superior to adaptive coding and the joint adaptation scheme when the implementation complexity is a limiting factor. Robustness analysis shows that introducing a mixed modulation scheme in addition to QPSK and 8PSK in the adaptive modulation scheme is unnecessary, and HARQ with adaptive modulation is insensitive to deviations from the optimal threshold, thus facilitating its implementation. Copyright

In this paper, we consider the subchannel detection problem in forward links for the multicarrier DS-CDMA system when some different subchannel allocation policies are used. An optimal subchannel decision algorithm is proposed based on the maximum-likelihood (ML) criterion. Theoretical analysis and simulation results are presented. Furthermore, we discuss the parameter selection problem on the length of the training sequences in the subchannel allocation scheme in [8], [12] by using the proposed ML detection algorithm. The results show that the subchannel allocation scheme in [8], [12] is feasible since only a few symbols overhead is required.

Narrowband interference (NBI) is one of the mostimportant problems in an OFDM system, which not only degrades the signal performance on the overlapped subcarriers, but also affects the signal performance on the nearby subchannels due to the spectral leakage effect of DFT demodulation at the receiver. In this paper, we consider the NBI problem caused by narrow band digital communication systems, and propose a novel NBI cancellation method. We consider the NBI reconstruction problem including NBI central frequency and its bandwidth estimation. Simulation results show that this method can achieve about 6dB signal to interference plus noise ratio (SINR) gain if the interference bandwidth is about twice of that OFDM bins and the system SINR is about 0 dB. As the bandwidth of NBI decreases, more SINR gain will be obtained. Meanwhile, We also consider the system implementation problem, it has shown that its implementation complexity is not high based on the current digital signal processing techniques. If zoom FFT is employed in our system, the calculation complexity can be reduced considerably1.