Phase-swept and time-delay transmit diversity performance results for 1X RTT CDMA systems

With the evolution of CDMA (code division multiple access), increased capacity gain in terms of “voice” users is the foremost expectation. Initial estimates were that the utilization of fast power control would double the forward link capacity. However, detailed simulations have shown that this is not true. Therefore, the additional concept of transmit diversity is investigated. Of the many methods under scrutiny, two offer relatively simple implementation with the advantage that they can be implemented on an IS-95 network, today, without any impact on mobile design or need for standardization. This paper reports on results obtained from simulations, as well as laboratory trials investigating the comparative performance of PSTD (phase-swept transmit diversity) and TDTD (time-delay transmit diversity) using an actual IS-95 base station at 1.9 GHz. The experimental results obtained substantiate the simulation results. The results show that PSTD and TDTD perform equally well. These forms of transmit diversity offer several dBs of gain under Rayleigh fading conditions for vehicle speeds less than 20 kph. A description of a planned field trial intended to confirm these results is also included. Such transmit diversity techniques coupled with fast power control can provide up to double the IS-95 capacity