The Research Of HARQ Technique On Wireless Metropolitan Area Network

As an important part of future communication technologies, the Wireless Metropolitan Area Network (WMAN) access technology has gained an increasing interest. Anyway, in the WMAN communications system, the effects of multipath fading channel may cause to weaken the system performance,and lead into the co-existence of random errors and burst errors, but the end user applications often require low packet error rate and high throughput. Because Hybrid ARQ(HARQ) technology has been an effective mechanism for lowering packet error rate and promoting system throughput, so HARQ technology can be adapted in WMAN to ensure quality of service (QOS) and reduce the transmission delay. As a result, this thesis focuses on studies of critical technologies in the transmission system based on IEEE802.16 and the HARQ technique in Wireless Metropolitan Area Network. The main content as follows:(1) This thesis introduces and analyze main features, the agreement model, the physical layer air interface specification, the MAC layer and main applications of IEEE802.16 in detail, and describes the fundamental principles of varieties ARQ and mixed HARQ technologies, gives the steps to realize HARQ technology, analyze its strengths and weaknesses.(2) For the HARQ technology existed right now, when transmission quality in channel is poor, and decoding is unsuccessful, it need feedback and retransmit redundant information for many times, to increase the decoding rate, but the retransmission of redundant information increases retransmission frequency and transmission delay. To solve this problem, this paper propose two channel-based adaptive HARQ scheme: I1-HARQ and I2-HARQ. I1-HARQ reference on the times of retransmission of redundant information in the last frame success data transmission, to predict the current channel conditions, to determine retransmission number may be required of redundant information for the current frame transmission. I2-HARQ uses SNR estimator to estimate the signal-noise ratio to check the current channel conditions, thus to determine the retransmission number of redundant information that may be required for the current frame transmission. Through the redundancy check information that may be required in the first success transmission of data, to reduce the time of retransmission for redundant information, to reduce the transmission delay.(3) This thesis establishes a simulation model based on the principle of HARQ system, Simulation the Performance of Turbo code on the AWGN channel, Obtained the impactment of the parameters of Turbo code to the correctness of decoding. to simulate the average retransmission frequency of redundancy data and throughput in traditional HARQ and two improved HARQ schemes, by setting different system parameters, the improved schemes have improved the effectiveness of system performance, thus we know the improved schemes have better adaptability for different frame length, different generate polynomial, cutting length and constraint length, provides a theoretical reference for the actual application.