, it requires more accurate timing and synchronization. But it can be predicted that the TDD technology will be used widely in the 4G and that these problems will be resolved. At the same time, the FuTURE TDD system is backward compatible with the TD-SCDMA (time division-synchronous code division multiple access) standard proposed by China, which is one of the international 3G standards in some aspects such as frame structure. Thus, the 3G system based on the TD-SCDMA standard can easily evolve to the FuTURE 4G system. 2.2.2 Promising Technologies Implemented in FuTURE TDD System In the research and development of the FuTURE TDD system, a series of innova- tions in basic theory has been proposed, such as flat wireless access network structure, which has been put into practice; group cell, which is a novel generalized cellular network architecture, and the slide handover strategy based on it; soft fractional frequency reuse to improve the spectrum efficiency; reliable end-to-end QoS (quality of service) mechanism; antenna array based on the generalized cellular network architecture to increase the system capacity, with a spectrum efficiency of 7 b/Hz; modular MIMO to support various environments; and scalable modular structure of the system, which can support data rates up to 330 Mb/s. The FuTURE TDD system provides an overall solution that can fulfill the requirements of E3G/4G and adopts lots of key technologies in many aspects, including cellular network architecture, physical layer, medium access control (MAC) layer, radio resource management, and hardware design. As a result, some positive effects have been brought out in the areas of system design, pivotal algo- rithm, and trial system development. 2.2.2.1 Network Architecture and Cellular Topology In the research of the FuTURE TDD system, the generalized distributed cellular architecture-group cell is brought out as a novel cellular network architecture; the slide handover strategy and the generalized distributed access network structure based on it are pro