Performance tradeoff among spreading, coding and multiple-antenna transmit diversity for high capacity space-time coded DS/CDMA

The field of space-time coding has attracted interest as a means of improving link reliability in mobile environments. We evaluate the application of space-time forward error correction schemes in asynchronous direct-sequence code-division multiple-access (DS/CDMA) system over frequency selective multipath fading channels. The space-time system, employing either a convolutional or turbo coding scheme, combines coding (temporal diversity), with RAKE (multipath diversity) and maximal ratio combining (MRC) (spatial diversity) to realize high capacity DS/CDMA mobile communication systems. The receiver considered employs a L-branch space-path RAKE receiver, followed by a soft-input (soft-output) channel decoder. We analyze the bit error rate (BER) performance and capacity tradeoff between various system parameters under a fixed total bandwidth expansion and error correction codes' complexity constraint requirements. It is shown that compared to uncoded systems, the proposed space-time coding system dramatically decreases the BER and increases the system capacity.