码间干扰信道下叠加码系统的优化设计

Optimal design of superposition coded modulation systems over ISI channels

针对码间干扰(inter-symbol interference,ISI)信道下的单载波叠加码编码调制系统,提出了一种在频域内可以快速实现用于发射信号频谱整形的预编码方案。该预编码的引入并不增加频域均衡接收机额外的开销。从信息论的角度证明了当应用基于功率"注水"原理的预编码时,基于理想码构造的叠加码可以随着层数的增加渐近实现ISI信道容量。同时,针对基于实际码构造的叠加码系统,提出了预编码和功率分配的联合优化问题。基于卷积码的仿真结果表明,联合优化大大改善了系统的性能。

A precoding technique is proposed for superposition coded modulation （SCM） single-carrier systems over inter-symbol interference （ISI） channels. The precoder can be efficiently implemented in the frequency domain and is introduced to shape the spectrum of transmitted signals. When the receiver implements fre- quency domain equalization, the precoder does not incur extra cost to the equalizer. It is proved in information theory that the ideally coded SCM system with the precoder implemented based on the ＂water-filling＂ principle can asymptotically achieve the ISI channel capacity. For practically coded SCM systems, a joint optimization problem is introduced for the design of both the precoder and the power allocation of SCM. Simulation results based on convolutional codes show that the joint optimization can considerably improve the system performance.