n different transmit anten- nas increases by degrees in some predetermined order, detection order at receivers would execute at the same order. Consequently, the complexity of the conventional successive cancellation receiver of V-BLAST systems is greatly reduced. A simple way for the modified V-BLAST is to select a different modulation constellation for each transmit data stream. Then the first decoded stream will typically have the smallest constellation size because it is decoded first. Similarly, employing channel coding with different data rates would also be effective. In this case, the first stream to be decoded would adopt the channel-coding scheme of the lowest rate. Adaptive MIMO can guarantee system performance and throughput under various MIMO channel conditions and make full use of the MIMO channel. Adaptive MIMO is more convenient and needs less time delay in TDD mode. Adaptive antenna selection. As an effective technique to fulfill different service requirements of users, adaptive antenna selection should be considered in B3G-TDD systems. According to various kinds of services, the transmit antennas could be selected for transmission adaptively based on channel conditions and data rates required. Adaptive power allocation. The FuTURE TDD system should support adaptive power allocation. Different proportions of power could be allocated to different © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology subcarrier groups to exploit system performance optimization. In forward link, the scheme for power allocation can be adjusted according to channel information fed back from AT. In TDD mode, taking advantage of reciprocal radio channels, adap- tive power allocation can be carried out more flexibly with little time delay. 2.2.2.2.8 Random Access Procedure Scheduled access and contention-based access should be supported. The contention- based random access scheme is based on the contention windows (CWs) strategy. The length of the CW is decided by the number of