Research On Multi-user Detection Technique In GSM System

As the number of GSM subscribers increase quickly, higher spectral efficiency is requested. GSM system uses compact frequency reuse technology to increase the spectral efficiency, which makes Co-channel Interference (CCI) in the cell increase seriously. A GSM system employing conventional detection techniques will be degraded in performance and limited in capacity because of CCI. Multi-user Detection technique applied for GSM is one of the most useful methods to suppress CCI, which makes for good receiver performance and larger system capability.This thesis investigates algorithms of Multi-user Detection in GSM system, the main work and contributions are described as follows:1. The principle of Multi-user Detection in GSM system is introduced. Then, the structure of multi-user system and signal model is given. Because of the need of Multi-user Detection, joint channel estimation algorithm is also presented.2. Three kinds of multi-user detection algorithms:JMLSE, JDDFSE and JDDFSE-ASA are analyzed and simulated. Joint Delayed-Decision Feedback Sequence Estimation (JMLSE) is the optimum algorithm, but its computational complexity is too high. Joint Delayed-Decision Feedback Sequence Estimation (JDDFSE) is a suboptimum algorithm, the performance of which can be increased by adaptive state allocation technique (ASA). Simulation results show that JDDFSE-ASA is valuable, which takes good compromise between performance and complexity.3. A new multi-user detection algorithm based on Turbo iterative procedure is proposed. The algorithm detects each co-channel signal with a soft-input soft-output (SISO) detector separately. The soft information provided by the decoders is used as the a priori information for the iterative cancellation of CCI. Simulation exhibits that the receiver employing the proposed algorithm outperforms conventional Turbo receiver for CCI dominated scenarios.4. To reduce the complexity of proposed algorithm, a new scheme is put forward, in which a soft interference cancellation algorithm based on MMSE is used for SISO equalization. Though MMSE-SIC algorithm is inferior to MAP equalization algorithm, the proposed receiver employing this scheme outperforms conventional Turbo receiver.