The multi-carrier code division multiple access (MC-CDMA) is becoming a very attractive multiple access technique for high-rate data transmission in the future wireless communication systems. MC-CDMA systems transmitting over multipath channels suffer from inter-symbol interference (ISI) and multiple access interference (MAI). Recently, MC-CDMA with equalisation has attracted much attention for its ability to obtain an excellent performance even in strong frequency-selective fading channels. In this study, the proposed architecture uses the minimum mean-square error (MMSE) with parallel interference cancellation (PIC) for downlink MC-CDMA system and compared with another system based on the rake receiver with PIC for downlink MC-CDMA system. A comparison between such architectures is presented. The effect of the tentative decision functions and the effect of the loading users on the performance of the two proposed receivers are discussed and presented in this study. Simulation results show that the combination of tentative decisions with PIC and equalisation provides an efficient solution to suppress the MAI and ISI in downlink MC-CDMA systems over frequencyselective fading channels.

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The low complexity receiver structure based on discrete cosine transform for a downlink multicarrier code division multiple access (DCT-MC-CDMA) system is proposed. It employs an interference cancellation scheme with a linear equaliser to suppress the multiple access interference and interference caused by the multipath fading channel The performance of the proposed receivers is analysed and compared to the conventional downlink DFT-MC-CDMA system. Simulation results show a large performance improvement when using such an interference cancellation scheme relative to the DCT equalisation receiver, and interference cancellation for the downlink DFT-MC-CDMA system. Introduction:The multicarrier code-division multiple-access (MC-CDMA) system has been proposed as one of the candidates for the future generations of wireless communications because of its attractive features such as high data rate, high capacity, and low complexity of implementation due to using fast-Fourier transform (FFT)-based carrier modulation [1][2][3]. The downlink DCT-MC-CDMA system is not studied in the literature. Recently, the DCT-OFDM system has received much attention, because it offers certain advantages over the 5]. The main advantage of the DCT lies in its excellent spectral energy compaction property [4]. Unlike the conventional DFT, a single set of co-sinusoidal functions cos(2pnf D t), where n = 0, 1, N − 1 and 0 < t < T is used in the DCT. f Δ is the subcarrier spacing. T is the symbol period. The minimum f Δ , required to satisfy the orthogonality condition [5]:

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