On the spectral efficiency of CDMA with multiple antennas

We consider the impact of transmit diversity on the capacity of synchronous, randomly-spread code-division multiple-access, in the presence of frequency-flat fading. For large user populations, we characterize the spectral efficiency (capacity per chip) of two systems that use different spreading sequences on each antenna: a theoretically optimal system in which each transmit antenna is fed by independent data streams, and a code sequence diversity scheme that transmits the same data on each antenna.