Permutation Spreading for Asynchronous MIMO-CDMA Systems Using Hadamard Codes and Gold Scrambling Sequences

Permutation spreading has been proposed as an alternative technique for assigning spreading codes to the different transmit antennas of a user in a multiple input multiple output-code division multiple access (MIMO-CDMA) system. In this paper, we propose the use of the permutation spreading technique using Hadamard codes for antenna separation and gold scrambling codes for user separation. All users are assigned the same set of Hadamard sequences, thus our proposed technique reduces the overall number of spreading sequences required by the system. In the example shown in the paper, the proposed spreading combination allows both an increase in spectral efficiency and a four-fold decrease in the number of spreading codes needed by the system. Moreover, permutation spreading shows more than 7 dB advantage over conventional MIMO-CDMA system in a heavily loaded environment.