编码同步CDMA系统中的Turbo DFD多用户检测

Turbo DFD with implementation in coded synchronous code-division multiple-access systems

Turbo处理方法可以充分利用编码冗余信息,因此自从提出以来在通信各个领域得到广泛采用。这一方法应用于多用户检测中时,则可从MMSE的判决反馈多用户检测器的近似概率密度出发,推导出编码符号的对数似然比信息,然后把该信息作为先验信息输入到采用修正BCJR算法信道解码器中。经信道解码输出的外部信息给多用户检测器进行干扰抵消。然后采用Turbo原理进行迭代,多次迭代后利用MAP解码算法得到解码符号。最后的仿真结果证明这种方法具有较高的效率和接近于单用户的性能。

Turbo principle is a broadlyused technique in CDMA systems because of its effectiveness in handling redundant information gleamed from other coded bits. In this paper this principle is implemented in synchronous CDMA channels with multiuser detection technique. First an MMSEbased decisionfeedback parallel interference canceller is proposed, and then after approximating its probability distribution as Gaussian, soft output is calculated and relevant information is put into a succeeding channel decoder. Channel decoder calculates each symbol's LLR as well as corresponding channel bit estimation, using the BCJR algorithm. Output is then fed back into the MUD detector. The whole process is iterated and simulation results see a closer singleuser performance with this method.