MIMO OFDM系统中基于物理层与链路层的跨层优化设计

A Cross-layer Design on Physical Layer and Data Link Layer in MIMO OFDM System

该文讨论了基于空时编码发射分集正交频分复用(OFDM)系统的跨层传输技术。该技术结合了传统物理层自适应调制和链路层自动请求重发,利用链路层的误包率和信道估计参数计算自适应调制门限,在系统给定时延和误包率约束的基础上最大程度地提高了频谱利用率。仿真结果表明,该算法相比传统物理层自适应传输,在频谱利用率性能上有1.5dB以上的增益。但随着最大重传次数的增加频谱利用率的提高越来越小,这就使得实际系统能以较小的时延代价换取足够的频谱利用率增益。

In this paper, a cross-layer design in OFDM （Orthogonal Frequency Division Multiplexing） systems with a space-time coded transmit diversity is provided, which combines the use of AM （Adaptive Modulation） at the physical layer and ARQ （Automatic Repeat reQuest protocol） at the data link layer. The packet error rate and channel estimation are used to compute the adaptive threshold in order to maximize spectral efficiency under given delay and error performance constraints. Simulation results show that this cross-layer design has 1.5dB gain in spectral efficiency comparing the traditional adaptive transaction at physical layer. Nevertheless, with the increasing of maximum number of retransmissions, the gain in spectral efficiency decreases, which suggest that enough spectral efficiency gain can be gotten by a desirable delay in practical systems.