Iterative Equalization Techniques In The Hierarchical Modulation System

The core activities in wireless communication systems is to provide reliable transmission for high rate data, modulation and channel coding are crurial techniques to achive this goal. Due to non-linear sensitivity to channels and huge signal constellation, which increase the difficulty to equalize and demodulate transmit signal, high order modulation has received relatively little attention in wireless communication. Meanwhile, in the fiels of wireless communications, the most problem is intersymbol interference because of multipath transmission and the limited channel bandwidth. To improve communication's quality and decrease ISI, equalizers are ofen used to combat the influence of channels in receivers. Iterative equaliztion has received enough attention, a number of important advances have been made in the areas of iterative equalization, which is a powerful method to perform joint equalization and decoding.Hierarchical modulation is a practical way of achieving unequal error protection. Howerer, it has received relatively little attention to data. With the present of some equaling methods for iterative equalization, iterative equalization has been widely used in different kinds of communication systems, so it is meaningful to research it.This thesis focuses on the iterative equalization for high order modulation.Summary of the fundamental theory of hierarchical modulation and iterative equalization is finished in this paper. For sinle-carrier sysytem, using MMSE criteria, we combine LDPC codes with iterative equalization, thus forming the combined iterative equalization receiver. This method is expanded in high order modulation to implement data transmission of high quality.A communication system using hierarchical modulation is introduced to detail the basic principles of hierarchical combined LDPC codes and equalization based on MMSE algorithm. A simplified hierarchical equalizer's extrinsic information of base-layer for 4QAM hierarchical modulation is presented. A new hierarchical equalization method of base layer is applied to hierarchical modulation. A lot of work in this topic is available but the complexity of the system in these works is too high or the performance of the system is not so good. Simulation results show that compared with conventional equalization method, the proposed hierarchical equalization method works effectively for hierarchical coded modulation and the simplified equalizer's extrinsic information algorithm is able to reduce the calculation complexity degrees of equalizer's extrinsic information without the loss of BER performance.