In this paper, we investigate a coding strategy devised to increase the throughput in hybrid ARQ (HARQ) transmission over a block fading channel. In our approach, the transmitter jointly encodes a variable number of bits for the each round of HARQ. The parameters (rates) of this joint coding can vary and may be based on the negative acknowledgment provided by the receiver or, on the past (outdated) information about the channel states. These new degrees of freedom allow us to improve the match between the codebook and the channel states experienced by the receiver. The results indicate that gains obtained using the proposed cross-packet coding strategy are particularly notable for the large values of the throughput. In this region, the conventional HARQ fails to offer throughput improvement even if the number of transmission rounds is increased. We implement the proposed cross-packet HARQ using turbo codes, where we show that the theoretically predicted throughput gains materialize in practice; the implementation challenges are also discussed.

In this paper, we propose a coding strategy designed to enhance the throughput of hybrid automatic repeat request (HARQ) transmissions over independent identically distributed block-fading channels with the channel state information unknown at the transmitter. We use a joint packet coding where the same channel block is logically shared among many packets. To reduce the encoding and decoding complexity, we use a two-layer coding where, first, packets are punctured, mixed, and then passed to the conventional channel encoder. We show how to optimize the puncturing rates on the basis of the empirical error-rate curves. We also discuss how the parameters of the practical turbo-codes may be modified to take advantage of the proposed HARQ scheme. Finally, simple and pragmatic rate adaptation strategies are developed. In numerical examples, our scheme is compared with the conventional incremental redundancy HARQ (IR-HARQ), which remains a strategy of choice in the region of small throughput; however, our scheme shows a notable gain of $1-2~\textrm {dB}$ in the region of high throughput, where IR-HARQ fails to provide any improvement.

In this work, we propose and optimize a new coding strategy designed to enhance the throughput of hybrid ARQ (HARQ) transmissions over i.i.d. block-fading channels where the channel state information (CSI) is unknown at the transmitter. Unlike in the conventional approach, where many blocks are exclusively assigned to carry the HARQ rounds of a single packet, we use a joint coding and the same channel block is logically shared among many packets. To reduce the complexity, we use a two-layer coding, where, first, packets are mixed on the binary level, and the resulting mixture is then passed for the conventional channel encoder. This allows us to decode packets on a block-by-block basis. Knowing the decoder error rate curves, the challenge is to find the optimal packets mixing that maximizes the total throughput. We show how to solve this problem using a dynamic programming (DP) approach, which we next apply to the off-the-shelf turbo-codes. We also discuss how the parameters of the practical turbo-encoder may be modified to take advantage of the proposed HARQ scheme. In numerical examples, our scheme is compared to the conventional incremental redundancy HARQ (IR-HARQ), and it yields a notable gain of 1 - 2dB in the region of high throughput, where IR-HARQ fails to provide any improvement.