Parity bit selected spreading for MIMO-CDMA using Hadamard codes and Gold scrambling sequences

Parity bit selected spreading has been proposed for use in code division multiple access (CDMA) systems as a means of allowing the spreading to provide an added measure of coding gain. The technique has been extended to CDMA systems operating in multiple input multiple output (MIMO) channels. In previous work, Hadamard codes are used for spreading. In this paper, we propose assigning each user the same set of Hadamard sequences while employing a unique Gold scrambling code. This reduces the overall number of codes required while making the system more robust to frequency selective fading. Compared to a conventional MIMO-CDMA system, the proposed combination of spreading codes allows both increase in data rates and decrease number of needed spreading codes by a factor of 4. Moreover, parity bit selected spreading shows more than 8 dB advantage over the conventional MIMO-CDMA system in a loaded frequency selective channels at BER=10^-3.