Rate Adaptation for Secure HARQ Protocols

Abstract

This paper investigates the incremental-redundancy hybrid-automatic repeat request (IR-HARQ) transmission over independent block-fading channels in the presence of an eavesdropper, where the secrecy of the transmission is ensured via introduction of dummy-messages. Since the encoder only knows the statistics of the channel state, the secrecy and the reliability are defined in a probabilistic framework. Unlike previous works on this subject, we design a coding strategy tailored to IR-HARQ by splitting the dummy-message rate over several rate parameters. These additional degrees of freedom improve the match between the dummy-message rates and the realizations of the eavesdropper channels. We evaluate the performance in terms of secrecy outage probability, connection outage probability and throughput and we compare it with the benchmark paper by Tang et al. [2]. Numerical examples illustrate that, comparing to existing alternatives, splitting of the dummy-message rate provides higher throughput and lower expected duration/average delay.Index Terms-hybrid automatic repeat request, physical layer security, state-dependent wiretap channel, channel state information, secrecy outage probability and secrecy throughput.

Rate Adaption for Secure HARQ-CC System with Multiple Eavesdroppers

“…Hence, their slopes are positive when R B is less than its optimal valueR B , and negative when R B >R B . The maximum η s (R B ), using the parameterized close-form solution in Equations (21)- (23), are plotted in Figure 4. These results well match the maximum η s and maximum approximated η s without COP constraint.…”

“…The optimal rates are initialized asR B = 0 andR E = 0. Next, usingR E =R E , we solve the optimization of R B in Equation (14), while the optimal pointR B is obtained by Equations (21)- (23). Then, usingR B =R B , we solve the optimization of R E in Equation (33), while the optimal pointR E is obtained by Equation (40).…”

“…When a passive eavesdropper exists, it has been proven that retransmissions and combinations are capable of enhancing security, due to the diversity gain of the legitimate receiver [19]. In order to efficiently design secure HARQ, Tang et al [20] discussed SOP, secrecy throughput and their asymptotic properties; Tomasin [21] proposed a multiple-encoding HARQ scheme with statistics channel state information (CSI); Mheich et al and Treust et al [22,23] optimized secrecy throughput using multi-level feedback and rate adaption. However, most of them did not consider the influence of secrecy outage on secrecy throughput, which generally led to overestimated performance [24].…”

Quasi-concave optimization of secrecy redundancy rate in HARQ-CC system

“…Similar to the discussion above, we still consider a small COP and R B = R ⋆ B , as given in (22). Then η s , as expressed in (23), is proved to be quasi-concave. Let φ t be defined as in (26) again, and this optimization problem becomes…”

“…To efficiently use HARQ, Tomasin designed a multiple-encoding HARQ scheme with statistics channel state information (CSI). As channel capacity is not suitable for HARQ that combines retransmitted codewords, secrecy throughput was widely discussed with respect to PLS of HARQ [21][22][23]. Tang et al [21] analyzed SOP, secrecy throughput, and their asymptotic properties; Mheich et al [22] optimized secrecy throughput as extended; Treust et al [23] designed an adaptive rate transmission scheme to improve secrecy throughput.…”