Prerake diversity combining in time-division duplex CDMA mobile communications

A prerake system is proposed for the time-division duplex (TDD) code-division multiple-access (CDMA) systems for portable communications, Since the up and down links are time slots on the same carrier frequency, they have the same channel impulse response during a short period of time. Instead of building a rake receiver in the portable unit, the base station (BS) can prerake the signal before transmission in the down link using the channel impulse response estimated from the up link. When the preraked signal is convolved with the channel impulse response, the function of the rake receiver is automatically performed. The mobile or portable unit uses a conventional receiver and still achieves the diversity gain of a rake receiver.