A hybrid TDMA/CDMA mobile cellular system using complementary code sets as multiple access codes

Abstract

A method combining TDMA and CDMA in a digital cellular system is presented. This method makes use of complementary code sets. These codes have been selected due to their ideal autocorrelation and noninteracting characteristics. With these code sets orthogonality between users can be maintained even in the fading multipath channel which is a valuable property that cannot be provided with conventional multiple access codes. Bit error rate simulations have been made to test the link level performance of the system. Both AWGN and Rayleigh fading channels have been employed. Simulation results confirmed that complementary code sets are well adapted for use as multiple access codes in a mobile radio environment. Link level simulations pointed out that by using complementary code sets the number of non-interacting users in the Rayleigh fading channel on a single carrier can be increased. One clear advantage compared to the traditional CDMA systems is that power control is not necessary within a cell. Neither are the time synchronization requirements so strict as usual. The Erlang radio capacity was studied. The results indicated that approximately a twofold improvement over TDMA is possible with hybrid techniques.