Abstract
Multi carrier code division multiple access (MC-CDMA) system is a promising multi carrier modulation (MCM) technique for high data rate wireless communication over frequency selective fading channels. MC-CDMA system is a combination of code division multiple access (CDMA) and orthogonal frequency division multiplexing (OFDM). The OFDM parts reduce multipath fading and inter symbol interference (ISI) and the CDMA part increases spectrum utilization. Advantages of this technique are its robustness in case of multipath propagation and improve security with the minimize ISI. Nevertheless, due to the loss of orthogonality at the receiver in a mobile environment, the multiple access interference (MAI) appears. The MAI is one of the factors that degrade the bit error rate (BER) performance of MC-CDMA system. The multiuser detection (MUD) and turbo coding are the two dominant techniques for enhancing the performance of the MC-CDMA systems in terms of BER as a solution of overcome to MAI effects. In this paper a low complexity iterative soft sensitive bits algorithm (SBA) aided logarithmic-Maximum a-Posteriori algorithm (Log MAP) based turbo MUD is proposed. Simulation results show that the proposed method provides better BER performance with low complexity decoding, by mitigating the detrimental effects of MAI.
Highlights
Multi carrier code division multiple access (MC-CDMA) system is the strongest candidate for generation wireless mobile communication systems due to its merits of high spectral efficiency and robustness against inter symbol interference (ISI) due to the presence of code division multiple access systems (CDMA) and orthogonal frequency division multiplexing (OFDM) systems [1]
It is demonstrated that the sensitive bits algorithm (SBA) aided logarithmic-Maximum a-Posteriori algorithm (Log Maximum a-Posteriori (MAP)) based turbo multiuser detection (MUD) improves the bit error rate (BER) performance with significantly reduce the computational complexity
Turbo MUD scheme is proposed for MC-CDMA system for improving the system performance in terms of BER
Summary
MC-CDMA system is the strongest candidate for generation wireless mobile communication systems due to its merits of high spectral efficiency and robustness against inter symbol interference (ISI) due to the presence of code division multiple access systems (CDMA) and orthogonal frequency division multiplexing (OFDM) systems [1]. In this paper a low-complexity iterative MUD approach for MC-CDMA systems is proposed This scheme effectively alleviates the harmful effects of MAI and confiscates the interference components from received signal by means of SOVA and Log MAP based turbo MUD Techniques. The following section describes the two major classes of turbo decoding algorithms currently used to implement SISO decoders such as the soft output viterbi algorithm [11] (VA / SOVA) and the maximum a posteriori algorithm (MAP) known as the BCJR algorithm, after Bahl, Cocke, Jelinek and Raviv Both solutions are based on trellis coding method. The MAP finds the probabilities of individual message bit being either 1 or 0 with the given noisy observation y It puts them into LLR form and this information is exchanged between the two decoders until the last iteration, at which point a hard decision is performed. The results of forward and backward recursions are used to find the LLR
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