Research On The Receiving Algorithms In Low SNR For Small Area Wireless Communication Networks

The study for the small area wireless communication networks is one of the hot points in the research and application of the wireless communication, which include Wireless Local Area Network (WLAN), Wireless Personal Area Network (WPAN), Bluetooth, Zigbee, Radio Frequency Identification (RFID), Wireless Sensor Network (WSN) and so on. Surrounding the key technologies of the small area wireless communication networks, the receiving algorithms in low Signal Noise Ratio (SNR) are studied deep in this dissertation. The emphases have been focused on the random construction for Low-Density Parity-Check (LDPC) codes, the synchronizations of carrier frequency, carrier phase and symbol timing.Firstly, based the MAP criterion, the factor graph is constructed for the joint channel decoding and the carrier frequency offset estimating. The corresponding joint algorithm of channel decoding and the carrier frequency offset estimating is proposed. Due to the high complexity of the joint algorithm of channel decoding and the carrier frequency offset estimating, the approximate realization of the joint algorithm is presented, where the long frame is divided to many short frames and the carrier frequency offset is quantified. So the application fields are enlarged. The simulation results show that the performance of the carrier frequency offset estimating is improved greatly by using the joint algorithm of channel decoding and the carrier frequency offset estimating.Secondly, a new adaptive iterative phase tracking algorithm is proposed for the carrier phase estimating of the receiver in low SNR. In this new approach, the phase tracking and the channel decoding are performed separately. The maximum- likelihood (ML) carrier phase estimator is completed, which the transmitted bits are considered as random variables. Due to the small scope of this adaptive iterative phase tracking, the data-aided carrier phase estimating is used before the adaptive iterative phase tracking and the large carrier phase error is eliminated. Simulation results show that this method not only eliminates the carrier phase error, but also improves the convergence rate of iterative carrier phase tracking.Thirdly,region effect and boundary effect are found in the simulation results, which worsen the timing synchronization algorithms. To eliminate them, two modified algorithm are proposed. And the modified algorithms are applied in the Lee, square, logarithm, and absolute timing synchronization algorithms. The simulation shows that the modified algorithms can greatly improve the performance of normal timing synchronization algorithms.And then, a new VR-HARQ (Variable Redundancy Hybrid-Automatic Repeat Request) scheme proposed. The channel is equivalent to a finite-markov process,...