Joint coding/decoding for multi-message HARQ

Abstract

In this work, we propose and investigate a new coding strategy devised to increase the throughput of hybrid ARQ (HARQ) transmission over block fading channel. In our proposition, the transmitter jointly encodes a variable number of bits for each round of HARQ. The parameters (rates) of this joint coding can vary and may be based on the negative acknowledgment (NACK) signals provided by the receiver or, on the past (outdated) information about the channel states. The results indicate that significant gains can be obtained using the proposed coding strategy especially where the conventional HARQ fails to offer throughput improvement even if the number of transmission rounds is increased.

How to Boost the Throughput of HARQ With Off-the-Shelf Codes

“…where R [k] denotes the joint coding rate in the kth round. The throughput of such Cross-packet HARQ (XP-HARQ) is calculated as [14] η xp…”

“…where f k is defined by (5) To attain (10) two main venues are adopted in the literature: i) direct encoding/decoding [3], [12]- [14], and ii) layer encoding/decoding [3], [10], [11], which have different impact on the encoding/decoding complexity.…”

“…[12]- [14], and ii) layer encoding/decoding [3], [10], [11], which have different impact on the encoding/decoding complexity.…”

“…However, the throughput increase is obtained with variable-length channel blocks which may be a challenge in those systems which have to keep the block size constant. The second venue harnesses the channel coding to overcome this very difficulty: the works [3], [10]- [14] keep the block size constant but increase the coding rate, i.e., the number of bits encoded in each HARQ round. This may be seen as a joint encoding of various packets into a single channel block.…”

“…• We formulate and solve the problem of rate adaptation using a dynamic programming (DP) and compare the throughputs of L-HARQ to those of conventional IR-HARQ. While [13], [14] addressed the issue of rate optimization for idealized-decoding scenarios and explicitly joint (i.e., non layer) decoding, to the best of our knowledge, none of the previous works addressed the issue of rate optimization with off-the-shelf encoders/decoders. • We show the throughput achievable with L-HARQ based on (turbo)-codes, where the optimal solution is found using solely the empirical error-rate curves of the decoder.…”