Improved interference cancellation for downlink DCT‐MC‐CDMA systems

Abstract

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]:

Improved Interference Cancellation for Downlink Wavelet Based Multi-Carrier CDMA System

“…A downlink single cell CDMA system with K active users over a frequency selective fading channel plus additive white Gaussian noise (AWGN) is proposed. For the DWT-MC-CDMA system, the steps are the same as the conventional DFT-MC-CDMA system in [11] except using IDWT and DWT instead of IFFT and FFT. Each user transmits binary phase shift key (BPSK) information symbols.…”

“…On the receiver side, DWT is applied to the received signal to de multiplex the multicarrier signal, and then descrambling and despreading are applied. The channel impulse response can be stated as follows [11]:…”

“…The received signal can be formulated as follows [ 11 ] : (16) Where r is the received signal, t is an NM 1 vector that representing the transmitted chip block, is an 2NM 2NM multipath channel circulant matrix and n is AWGN.…”

An approach to compare the developments in performance of multicarrier CDMA system

“…2013 [28] Presented effect of Cyclic Prefix on MC-CDMA System. 2013 [30] Analyzed DCT performance for subcarrier realization instead of FFT, DCT has excellent spectral energy compaction property, hence has good performance as compare to FFT 2014 [31] Investigated BER performance of MC-CDMA system with pseudo-chaotic sequence instead of conventional PN sequence, obtained good result.…”

“…Al-fuhaidi & M.M. Salah[30] presented, Improved interference cancellation for downlink DCT-MC-CDMA systems. They used Discrete Cosine Transform (DCT) instead of FFT.…”