We propose an iterative multiuser detector for turbo-coded synchronous and asynchronous direct-sequence CDMA (DS-CDMA) systems. The receiver is derived from the maximum a posteriori (MAP) estimation of the single user's transmitted data, conditioned on information about the estimate of the multiple-access interference (MAI) and the received signal from the channel. This multiple-access interference is reconstructed by making hard decisions on the users' detected bits at the preceding iteration. The complexity of the proposed receiver increases linearly with the number of users. The proposed detection scheme is compared with a previously developed one. The multiuser detector proposed in this paper has a better performance when the transmitted powers of all active users are equal in the additive white Gaussian noise (AWGN) channel. Also, the detector is found to be resilient against the near-far effect
We investigate the performance of turbo interference cancellation receivers in the space time block coded (STBC) direct-sequence code division multiple access (DS-CDMA) system. Depending on the concatenation scheme used, we divide these receivers into the partitioned approach (PA) and the iterative approach (IA) receivers. The performance of both the PA and IA receivers is evaluated in Rayleigh fading channels for the uplink scenario. Numerical results show that the MMSE front-end turbo space-time iterative approach receiver (IA) effectively combats the mixture of MAI and intersymbol interference (ISI). To further investigate the possible achievable data rates in the turbo interference cancellation receivers, we introduce the puncturing of the turbo code through the use of rate compatible punctured turbo codes (RCPTCs). Simulation results suggest that combining interference cancellation, turbo decoding, STBC, and RCPTC can significantly improve the achievable data rates for a synchronous DS-CDMA system for the uplink in Rayleigh flat fading channels.
A new approach that characterised satellite mobile transmission system is proposed and described in this paper. This paradigmatic agent-based system is required for the future wireless communication system for effectiveness and robustness. We examine adaptive BPSK/QPSK for Rice-lognormal mobile satellite channel. We compare the behaviour of the fixed modulation transmission with adaptive schemes and present the visual results of the data generated.
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