Multiple HARQ Processes based on Network Coding in LTE Downlink

In 3GPP 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 terminals. 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.