Frame Structure for a Wireless Communication System

1. A wireless communication system in which a base station performs wireless communication with a plurality of fixed or mobile subscriber stations, the base station maintaining connections with each of the subscriber stations by performing wireless communication in units of frames, and within each frame, allocating resources for data transmissions and signalling in the wireless communication system, said frames being divided timewise into downlink subframes for transmissions from the base station to the subscriber stations, and uplink subframes for transmissions from the subscriber stations to the base station; characterized in that each frame has a plurality of downlink subframes and a plurality of uplink subframes including, in time order, a first downlink subframe containing a preamble for synchronization purposes, a first uplink subframe, a final downlink subframe and a final uplink subframe, and in that the subscriber stations comprise first type subscriber stations and second type subscriber stations, the base station allocating downlink resources to the first type subscriber stations within only the first downlink subframe, wherein the base station is further arranged to allocate uplink resources to the first type subscriber stations within only the final uplink subframe, wherein the base station is further arranged to allocate resources to the second type subscriber stations within at least the first uplink subframe and the final downlink subframe, and wherein the base station is operable to define a frame configuration in which the number of downlink subframes and uplink subframes in each frame is varied dynamically in accordance with the relative proportion of second type subscriber stations to first type subscriber stations currently being served by the base station.

2. The wireless communication system according to claim 1 wherein at least one other downlink subframe and uplink subframe, reserved for allocation of resources to the second type subscriber stations, is provided before the final downlink subframe and final uplink subframe.

3. The wireless communication system according to claim 2 wherein each second type subscriber station is arranged to return channel quality information to the base station during at least one uplink subframe within which it is allocated resources, the base station being responsive to said connection quality information when allocating resources to the same second type subscriber station in a later one of said plurality of downlink subframes or uplink subframes.

4. A base station forming a wireless communication system with a plurality of fixed or mobile subscriber stations which comprise legacy subscriber stations and enhanced subscriber stations, the base station maintaining connections with each of the subscriber stations by performing wireless communication in units of frames, and within each frame, allocating resources for data transmissions and signalling in the wireless communication system, said frames being divided timewise into downlink subframes for transmissions from the base station to the subscriber stations, and uplink subframes for transmissions from the subscriber stations to the base station, wherein the base station is arranged to: configure each frame with a plurality of downlink subframes and a plurality of uplink subframes including, in time order, a first downlink subframe containing a preamble for synchronization purposes, a first uplink subframe, a second downlink subframe and a second uplink subframe; allocate downlink resources to the legacy subscriber stations within only the first downlink subframe; and allocate resources to the enhanced subscriber stations within at least the first uplink subframe and the second downlink subframe, the base station which is responsive to connection quality information, fed back by each enhanced subscriber station in a said uplink subframe in which the base station has allocated it resources, when allocating resources to the same enhanced subscriber station in a later one of said plurality of downlink subframes or uplink subframes, wherein the legacy subscriber stations operate in accordance with a frame of predetermined length with a single downlink subframe and a single uplink subframe, and the base station is arranged to configure the frame such that the timing of said plurality of downlink subframes and uplink subframes allows the frame to include uplink resources for the legacy subscriber stations whilst including at least one downlink subframe and uplink subframe reserved for use by the enhanced subscriber stations, and wherein the base station is operable to define a frame configuration in which the number of downlink subframes and uplink subframes in each frame is varied dynamically in accordance with the relative proportion of enhanced subscriber stations to legacy subscriber stations currently being served by the base station.

5. The base station according to claim 4 wherein each downlink subframe is separated from its succeeding uplink subframe, and each uplink subframe is separated from its succeeding downlink subframe if any, by a respective time gap and the base station is arranged to set the duration of at least one such gap, which follows one of the subframes reserved for the enhanced subscriber stations, in accordance with said predetermined frame length to allow the frame to be decoded by the legacy subscriber stations.

6. The base station according to claim 5 arranged to configure each frame as a superframe which includes a plurality of said frames of predetermined length in accordance with which the legacy subscriber stations operate, and arranged to allocate resources to the enhanced subscriber stations in any of the subframes of the superframe.