Research On Downlink Power Control Scheme In CDMA Trunking

Trunking mobile communication system plays an irreplaceable role in dispatching. CDMA system, compared with FDMA and TDMA systems, is more accessible to a large capacity. The 3rd generation mobile communication system standards all use the CDMA technology, including TD-SCDMA standard, of which our country has intellectual property rights.. Because of the above reasons, the research on key technology of CDMA trunking has great strategic significance for China. CDMA is a power limited system, in which an appropriate downlink power control scheme can increase QoS of the mobile on the cell edge. But the CDMA trunking system adopts no downlink power control scheme, which diminishes the system capacity. Therefore, researching on the downlink power control scheme is necessary for the development of CDMA trunking system in China.Firstly, this paper reviews the literatures of basic theories and technology about CDMA power control, and constructs a model of the shared downlink channel technology, which is about the capacity of CDMA trunking multi-cells system. And then, an index based on the system capacity and the overhead is proposed to evaluate the CDMA trunking downlink power control schemes.Secondly, with the probability theory, calculus and other mathematical tools, system capacity is analyzed quantitatively, for CDMA trunking systems that adopt no downlink power control scheme and all downlink power control scheme respectively. A precise mathematical expression is reached, and the two downlink power control schemes are evaluated, based on the index including the system capacity and the overhead. Accordingly, the reason why the existing CDMA trunking system adopts the no downlink power control scheme, rather than follows the CDMA cellular system to use the all downlink power control scheme is analyzed,Thirdly, a compromise scheme, i.e. partial downlink power control scheme, is proposed, after analyzing the characteristic of the no downlink power control scheme and the all downlink power control scheme. The system capacity of partial scheme is quantitatively analyzed and its overhead is qualitatively analyzed.Finally, a simulation platform is built to verify the above theoretical results.