Adaptive Cross-Packet HARQ

Abstract

In this work, we investigate a coding strategy devised to increase the throughput in hybrid ARQ (HARQ) transmission over block fading channel. In our approach, 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joint coding can vary and may be based on the negative acknowledgment (NACK) provided by the receiver or, on the past (outdated) information about the channel states.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 significant gains can be obtained using the proposed coding strategy, particularly notable when the conventional HARQ fails to offer throughput improvement even if the number of transmission rounds is increased. The new cross-packet HARQ is also implemented using turbo codes where we show that the theoretically predicted throughput gains materialize in practice, and we discuss the implementation challenges.

Effective Capacity for Renewal Service Processes With Applications to HARQ Systems

“…Nevertheless, the optimal design of transmission rates for HARQ schemes is out of the scope of this paper due to the non-convexity of the objective function. Similarly to [12], we conduct an exhaustive search over the space of following available transmission rates: FR-HARQ-IR and VR-HARQ adopt R , R k ∈ {1.5, 1.75, 2, · · · , 3.75}bps/Hz, while XP-HARQ adoptsȒ 1 ∈ {1.5, 1.75, 2, · · · , 3.75}bps/Hz for the initial round andȒ k ∈ {0, 0.25, 0.5, · · · , 3.75}bps/Hz for the others. Fig.…”

“…It is worth noting that both FR-and VR-HARQ do not include new information bits into retransmissions, they may yield the waste of mutual information. To overcome this issue, VR-HARQ is proposed to add new information bits to retransmissions for possible redundant mutual information [12].…”

“…1) Maximum Arrival Rate: In [8], the effective capacity is used to assess the maximum arrival rate of HARQ schemes. To do so, by putting (46) into (45) and then combining with (12) and (13), the effective capacities of the three HARQ schemes can be calculated as C e = ln ζ/θ, where K k=1 q k ζ kL = e θb . By introducingζ = ζ L andθ = Lθ, the effective capacity can be obtained as…”

“…conditions of XP-HARQ studied in [12], the outage event takes place after k HARQ rounds if and only if the accumulated mutual information is below the number of the delivered information bits in the current and previous HARQ rounds. Therefore, the outage probability of the XP-HARQ scheme can be obtained as [12] p k = Pr k κ=1 κ l=1…”

AMC and HARQ: How to Increase the Throughput

“…To make the multi-packet approach practical, we will use L-HARQ, studied in [2], [3] and implemented via a two-step (or, layered) approach, where the joint coding is implemented in two independent steps: the binary packet mixing is followed by the conventional channel coding. From the theoretical perspective, when compared to a more general joint coding/decoding scheme [21], [30], L-HARQ does not impose any throughput penalty [30,Th. 3].…”