Research On The HARQ Techniques In IEEE802.16e Systems

The rapidly developing WiMAX (Worldwide Interoperability for Microwave Access) is a broadband wireless access technology based on IEEE 802.16 series protocol. As the global communication industry displays the traits of Mobility, Broadband and IP-based Architecture, IEEE 802.16e has been proposed to support fast mobile environment. Its appearance and development enhances the mobility of broadband wireless access, as well as speeds up the process from mobile to broadband, which makes it a promising wireless access technology.HARQ (Hybrid Automatic Repeat Request) is now the most effective error control technology in guaranteeing reliable transmission, and is essential to the high-speed data rate, high QoS (Quality of Service) and high reliability mobile broadband systems. It is one of the key technologies of the physical layer of IEEE 802.16e. Therefore, based on the IEEE 802.16e protocol and focusing on HARQ, the following issues are addressed, HARQ and its performance in IEEE 802.16e protocol, cross-layer optimization method combining HARQ, AMC (Adaptive Modulation and Coding) and adaptive sub-packet scheme, the integration strategy of HARQ and power control, and the joint control mechanisms of HARQ and adaptive subcarrier allocation.Firstly, the HARQ scheme in IEEE 802.16e was investigated and a system simulation platform was built up using MATLAB. The performance of Chase combining and IR (Incremental Redundancy) HARQ were compared and the results showed that IR is better than Chase combining, the performance gain depends on the modulation size and coding rate.Thereafter, a cross-layer optimization method was proposed. The proposed method efficiently combined sub-packet transmission scheme at data link layer and AMC at physical layer. The number of sub-packets and the scheme of modulation and coding were jointly optimized to maximize the system throughput. Meanwhile, a novel criterion on the SNR threshold of AMC was given, taking the HARQ protocol into consideration. Simulation results showed that the optimization method can efficiently improve the system throughput dramatically at a very tiny cost of implementation complexity.Next, the thesis focused on the integration of HARQ and power control in OFDMA (Orthogonal Frequency Division Multiple Access) systems. A compromise solution between power and delay was proposed. By introducing a retransmission ratio factor, the total transmission power was reduced effectively while satisfying the signal-to-noise ratio and delay demand. It is validated that HARQ and power control integration strategy can greatly reduce the transmission power, as the delay increases. And a convenient compromise solutioncan be realized according to the integration strategy.Finally, in order to improve the QoS support ability, HARQ and dynamic subcarrier allocation (DSA) were joined and a HARQ-DSA joint strategy was proposed. The joint strategy considered retransmission packets previously in subcarrier allocation. It is disclosed the HARQ-DSA joint strategy reduced the packets drop rate significantly. And by comparing to the traditional HARQ/DSA independent control mechanism, an important conclusion was derived that while signal-to-noise is low, the HARQ/DSA independent control should be used and while signal-to-noise is high, the HARQ-DSA joint control strategy should be adopted.