A time diversity CDMA scheme employing orthogonal modulation for time varying channels

In order to increase the channel capacity of CDMA (code division multiple access) mobile and personal communication systems, a new time diversity CDMA scheme that employs orthogonal modulation is proposed. The time diversity CDMA scheme with orthogonal modulation reduces the required Eb/(No+Io) by 5 dB at Pe = 10/sup -2/ in Rayleigh fading environments with fDT (the product of Doppler frequency and one symbol duration) values ranging from 0.002 to 0.02. This improvement in required Eb/(No+Io) significantly increases the channel capacity of CDMA communication systems that have time varying channels. Computer simulation results show that the required time delay values of the time diversity scheme are resonably short (20-100 symbols for 10 kbps transmission) for fDT values ranging from 0.002 to 0.02.