Energy spreading transform for down-link MC-CDMA

In this paper, we apply recently developed energy spreading transform (EST) technique to down-link MC-CDMA systems for frequency and spatial diversity. The performance of the proposed EST based MC-CDMA systems is independent of the number of active users, which is different from all current MC-CDMA systems. It is demonstrated by computer simulation that the BER for the EST based system is 1.1 times 110^-4 while it is 1.6 times 10^-3 for a MC-CDMA system without EST when the system is with full load and E_b/N_o = 12 dB. The EST based MC-CDMA system also facilitates transmit diversity and MIMO techniques when multiple transmit and receive antennas are available. In particular, we develop symbol shuffle and combined schemes for spatial diversity for a EST based MC-CDMA system with multiple transmit antennas at the base station. Compared with a MC-CDMA system without EST, the required E_b/N_o for 1% BER for the developed scheme is improved by about 4 dB.