In this paper, a channel-adaptive random access transmission scheme is presented for time-division-duplex (TDD)-based wireless systems. In a TDD-based wireless system, using the channel reciprocity, the channel gain of an uplink (UL) can be estimated from that of a downlink. The channel-adaptive random access scheme allows the transmission of a random access packet only when the channel gain of the UL is higher than a predetermined threshold. With channel-adaptive random access, it is possible to reduce the power required for random access transmission drastically at the cost of slightly larger transmission delay. If the threshold is set to zero, the presented channel-adaptive scheme is exactly the same as the conventional random access scheme. Therefore, channel-adaptive random access provides system design flexibility with the tradeoff between transmission power and transmission delay.
