Turbo synchronization for group-blind multiuser detection

研究了在多径衰落信道下的码分多址系统中Turbo多用户检测(MUD)的同步和信道估计问题，其目的是在一般Turbo原理的基础上研究如何使用估计的同步和信道参数。具体地说，我们认为同步单元是另一个译码单元，它将被用于Turbo方案中。同步器不是传递同步信号，而是将每个编码比特的外部信息传递到下一阶段。最后，在本项目中，我们提出了一种同时考虑所有必要的信号处理操作的接收器结构。换言之，所提出的迭代接收机可以联合执行同步、信道估计、信道均衡、盲/群盲多用户检测和信道译码。本文提出的快速迭代(Turbo)信号处理方法允许接收机(例如，同步器和信道估计器)的前两级(或子模块)基于从后期(例如，信道解码器)获得的软信息来改进它们的处理，以提供一些信号参数的精确估计。本工作的预期结果如下：申请人和他的研究小组可以开发一个数学框架来设计Turbo接收机，该Turbo接收机可以根据最大后验(MAP)准则与多用户检测联合执行同步和信道估计，使用期望最大化(EM)算法或空间交替广义期望最大化(SAGE)算法，所提出的Turbo接收机的性能可以预期比传统(或非迭代)接收机好得多，但非常接近理想接收机的性能，后者假设系统中的同步和信道参数以及所有活跃用户的签名都是完全已知的。

This proposal considers the problem of synchronization and channel estimation for turbo multiuser detection (MUD) in CDMA systems operating over multipath fading channels.The aim of this project is to investigate using the estimated synchronization and channel parameters in a manner motivated by the general turbo principle. Specifically, we consider the synchronization unit to be another decoder, which will be employed in a turbo scheme. Instead of passing a synchronized signal, the synchronizer passes extrinsic information for each of the coded bits to the next stage.Finally, in this project we propose a receiver structure that takes all the necessary signal processing operations into account simultaneously. In other words, the proposed iterative receiver can jointly perform synchronization, channel estimation, channel equalization, blind/group-blind MUD, and channel decoding. The  proposed  iterative (turbo)  processing  approach  allows  earlier  stages  (or submodules) of a receiver (e.g. the synchronizer and the channel estimator) to refine their processing based on soft information obtained from later stages (e.g., the channel decoder) to provide a refine estimate of some signal parameters.The expected results in this work are as follows: the applicant and his research group can develop a mathematical framework for the design of turbo receivers that can perform jointly synchronization and channel estimation with muliuser detection according to the maximum a posteriori (MAP) criterion, using the expectation-maximization (EM) algorithm or the space alternating generalized expectation and maximization (SAGE) algorithm.The performance of the proposed turbo receivers can be expected to be much better than that of the conventional (or non-iterative) receivers but very close to that of the ideal receiver which assumes perfect knowledge of synchronization and channel parameters as well as all the signatures of active users in the system.