Iterative Estimation Of The Wireless Signal Based On The Theory Of Information Exchange And Testing

As an important part of wireless communication system, wireless signal detection is faced with lots of new challenges in the next generation of mobile communication. Till now, a lot of algorithms have been proposed for the traditional single-input -single-output (SISO) system or the emerging multiple-input-multiple-output (MIMO) system. However, it is still a hot topic to obtain the optimal detection algorithm with a complexity as low as possible. Based on the existing work, this dissertation dedicates on research works on iterative detection algorithm for wireless communication by using factor graph under the information exchange theory frame.First, under the assumption of ideal channel estimation, iterative signal detection technology is studied in SISO system. By factoring of the likelihood function, the description of signal detection problem is achieved, and then iterative signal detection algorithm can be deduced by using sum-product algorithm. Furthermore, in order to reduce the complexity of sum-product algorithm, fast iterative signal detection algorithm based on SP-PDA (sum-product-probability-data-association) is proposed. Simulation results show that the iterative signal detection algorithm based on sum-product algorithm can approaching the optimal performance with computational complexity being reduced efficiently, while the fast iterative signal detection algorithm can obtain a tradeoff between performance and complexity, where computational complexity is reduced to being linear with the length of channel instead of being exponential with the length of channel.Second, optimal performance of channel equalization and signal detection relies on exact channel knowledge. Considering channel information is unknown and time-variant, joint channel estimation and signal detection based factor graph is studied. The factor graph for joint channel estimation and signal detection is set up according to the likelihood function and iterative rule is deduced by sum-product algorithm. To solve the integral of continuous variable of channel information, numerical method named as particle filter is considered to obtain its approximate result and the iterative algorithm for joint channel estimation and signal detection based on SP-PF (sum-product-particle-filter) is proposed.Furthermore, a unified iterative receiver of joint channel estimation and signal detection is designed in this dissertation. The receiver consists of two separate modules named channel estimation and signal detection, where signal detection is implemented by the iterative algorithm based on factor graph and is able to pass the soft information to help channel estimation and then the joint channel estimation and signal detection is achieved. Under the unified receiver structure, information passing between two modules can obviously improve the channel estimation performance whatever channel estimation technology is used; therefore, the signal detection performance of the whole receiver is improved.Based on the study of SISO system, the research of iterative signal detection using factor graph is extended to MIMO system. After the proposal of a new description of factor graph in MIMO system, sum-product algorithm is applied to obtain the iterative algorithm which can approximate the optimal performance. In order to reduce the complexity, PDA method is combined with the sum-product algorithm and a fast iterative signal detection algorithm based on SP-PDA is proposed.