LTE下行链路中基于网络编码的多进程联合HARQ

Multiple HARQ Processes based on Network Coding in LTE Downlink

长期演进系统的下行链路物理层采用了以传输块为基本单元的混合自动重传请求机制,保证移动终端在各种测试场景下都能获得较好的数据通过率。在对传输块的每次接收处理过程中,单个传输块中的多路独立码块数据解码结果差异较大。接收端可以通过对各个码块数据做循环冗余校验测试,标志各个码块的译码结果。然而由于传统重传机制中反馈链路的容量限制,即便只有一个码块解码错误,接收端也将反馈请求发送端重传整个传输块。网络编码技术通过对不同传输块数据做组合编码,可以有效地提高整个网络的传输效率。针对长期演进系统下行链路的传输机制,我们提出一种基于网络编码的多进程联合重传方案。新的重传方案联合多个传输块的重传进程,在每个传输块完成首次传输后,新增一个网络编码重传反馈比特,指示后续是否启动一个新进程传输多个传输块的网络编码数据包。我们给出了具体的重传协议流程,收发端都可以高效地根据网络编码重传反馈比特指示,完成相应的发送和接收操作。结合长期演进系统标准中的典型测试场景,我们给出了数据通过率的仿真结果比较。在仅新增一个反馈比特的条件下,采用网络编码技术的多进程联合重传方案在数据通过率方面有较为明显的性能增益。

In 3 GPP long term evolution （LTE） physical layer downlink, the hybrid automatic request （HARQ） based on the transmission block （TB） is utilized in order to obtain better data throughputs in various test cases for the mobile termi- nals. Since the different code blocks （CB） in one TB are turbo coded independently, the decoding status for individual CBs always vary considerably in the receiving process of TB. The receiver can set the decoding status for each CB according to the cyclic redundancy check. Due to the capacity limit of the uplink channel, the receiver can only feedback one bit for each TB and the all data in the TB will be retransmitted even though there is only one CB decoding failure. By the linear coding of the data in different TBs, the network coding technology can improve the data throughput efficiently. According to the characteristics of the LTE downlink transmissions, we propose a joint HARQ of multiple processes based on network coding. In the proposed HARQ schemes, the retransmissions of the multiple processes are scheduled jointly by an added feedback bits to indicate network coding process, after each TB has been transmitted once. The flowcharts for the proposed HARQ are given, where the transmitting, and receiving process both can work efficiently according to the added feedback bit for network coding indication. In the comparison of the throughput simulations, the new HARQ scheme based on network coding can achieve obvious performance gain over the LTE-HARQ schemes, while the only one feedback bit is added for the transmissions of multiple processes.