Outage-Optimal Power Allocation for Hybrid ARQ with Incremental Redundancy

Abstract

Abstract-We consider the optimization of power in incremental redundancy (IR) based hybrid automatic repeat request (HARQ) schemes when the maximum number of (re)transmissions is fixed. We formulate two optimization problems: (i) minimizing the packet drop probability (PDP) under a total average transmit power constraint, and (ii) minimizing the average transmit power under a fixed PDP constraint. We consider in detail the special case of only two allowed transmissions, and we prove that the two optimization problems are equivalent. For this special case, we also provide a suboptimal root-finding solution and compare its performance with the optimal solution obtained through an exhaustive search. The results show that the optimal power allocation can provide significant gains over the equal power solution in terms of average transmit power spent. The performance of the proposed rootfinding solution is practically the same as that of the optimal solution.Index Terms-Hybrid ARQ, incremental redundancy, optimal power allocation, outage probability.

Optimal Power Allocation for Hybrid ARQ with Chase Combining in i.i.d. Rayleigh Fading Channels

“…In [14], [15], the optimization problem of minimizing the PDP under an average transmit power constraint was considered for IR-HARQ schemes, and the results were presented for the special case of L = 2. An optimal power allocation scheme for a space-time coded HARQ scheme was presented in [16].…”

“…It can be easily proved that the average power constraint and the PDP constraint in (23) and (24) are active at their respective optimal solutions, from which we can deduce that (23) and (24) are also equivalent. We can use GPP toolboxes like GGPLAB [26] to solve (23) and (24) efficiently even for large values of L. Note that for the case of L = 2, the optimization problems (23) and (24) resemble the optimization problems for IR-HARQ presented in [14]. This is because, for both CC-HARQ and IR-HARQ schemes with L = 2, p drop ∝ 1 P1P2 .…”

Optimal resource allocation for IR-HARQ

“…In this work, we generalize the results of [5] to the case when the number of channel uses may differ for different ARQ rounds. We specifically provide an exact closed-form expression for the PDP of IR-HARQ schemes when the total number of transmissions is limited.…”

“…However in [4], the authors assumed that the same number of channel uses as well as the same transmission power is used in different transmission rounds. In our previous work [5], and in [6], the optimization problems of minimizing the packet drop probability (PDP) and the bit error rate (BER) under an average transmit power constraint for IR-HARQ schemes were considered, respectively. In the works of [2], [5] and [6] …”

“…In the later part, we extend our work in [5], and consider the optimal resource allocation problem of minimizing the PDP under the constraints of an average transmit power and total number of channel uses. We provide two approaches to solve this optimization problem and compare their performance with the solution given in [5]. …”