Performance of OFDM-CDMA with Simple Peak Power Reduction

In this paper we propose simple schemes which reduce the peak-to-average power ratio (PAPR) of the OFDM-CDMA signals. The statistical behavior of the peak power in the OFDM-CDMA signals is first examined by computer simulations, employing the two orthogonal sets of spreading sequences, namely, Walsh-Hadamard sequences and Golay complementary sequences. It is shown that for small number of active users or uplink system, Golay complementary sequences yield much lower PAPR than Walsh-Hadamard sequences, and for large number of active users, Walsh-Hadamard sequences eventually becomes better. A simple scrambling scheme is introduced, which may result in considerable peak power reduction in the case of small number of the active users. For the downlink system, further reduction of the peak power can be achieved by a simple adaptive scheme based on the selection of the set of the spreading sequences.