Frequency and time division duplex techniques for CDMA cellular radio

A time division duplex (TDD) technique for use in code division multiple access (CDMA) cellular radio systems is investigated and compared with the performance results for frequency division duplex (FDD) CDMA systems. The TDD base station measures the impulse response of the channel (on the uplink) and uses a matched filter to the channel. It then pre-matches the signal it wishes to transmit on the downlink since its impulse response is identical. This eliminates any channel matched filter operations in the mobile unit and so reduces its complexity, although the base station complexity is increased slightly. Results indicate that FDD techniques provide a higher cell capacity than the equivalent TDD techniques. The advantage of a reduction in mobile station complexity, by using TDD, is offset by the poor error rate and cell capacity performances found for high speed mobile operation