Pre-RAKE diversity combining in time division duplex CDMA mobile communications

A pre-RAKE system is proposed for the time division duplex code division multiple access systems for portable communications. Since the up and down links are time slots on the same carrier, 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 can pre-RAKE the signal before transmission in the down link using the channel impulse response estimated from the up link. When the pre-RAKE signal is convolved with the channel impulse response, the function of the RAKE receiver is automatically performed. The mobile or portable unit can use a conventional matched filter and still achieve the diversity gain of a RAKE receiver