Opportunistic Cooperative Channel Access in Distributed Wireless Networks With Decode-and-Forward Relays

Abstract

This letter studies distributed opportunistic channel access in a wireless network with decode-andforward relays. All the sources use channel contention to get transmission opportunity. If a source wins the contention, the channel state information in the first-hop channel (from the source to its relay) is estimated, and a decision is made for the winner source to either give up the transmission opportunity and let all sources start a new contention, or transmit to the relay. Once the relay gets the traffic, it may have a sequence of probings of the second-hop channel (from the relay to the destination). After each probing, if the second-hop channel is good enough, the relay transmits to the destination and completes the transmission process of the source; otherwise, the relay decides either to give up and let all sources start a new contention, or to continue to probe the second-hop channel. The optimal decision strategies for the two hops are derived in this letter. The first-hop strategy is a pure-threshold strategy, i.e., when the first-hop channel signal-to-noise ratio (SNR) is more than a threshold, the winner source should transmit to the relay, and subsequently the second-hop strategy should let the relay keep probing the second-hop channel until a good enough second-hop channel is observed. Simulation results show that our scheme is beneficial when the second-hop channels have larger average SNR. Index TermsDecode-and-forward relaying, opportunistic transmission, optimal stopping, throughput maximization.DF relaying network is considered in [6], in which each source-destination pair is aided by a DF relay. If a source has traffic to send, it sends a probing packet, and based on reception of the probing packet, the information of channel SNR in the first hop (from the source to its relay and to the destination) is obtained. Then the source decides to 1) give up, or 2) transmit with direct link, or 3) continue to probe the second hop (from the relay to the destination). If the source decides to probe the second hop, then the channel SNR of the second hop is estimated, and it is decided either to give up or to transmit (by using direct link or relay link, whichever March 19, 2018 DRAFT

Two-Level Distributed Opportunistic Scheduling in DF Relay Networks

“…Each source-destination pair is pre-assigned a relay. As argued in [6], optimal DOS for the case with direct links can follow the same method in [1]. Thus, here we consider the case with no direct link between any source-destination pair.…”

“…DOS is also investigated in relay networks [4]- [6] with multiple pairs of sources and destinations. The work in [4] investigates amplify-and-forward relay networks.…”

“…The work in [5] focuses on whether or not to further probe the second hop. The work in [6] contention, its channel to its relay is probed, and a decision is made between two options: to give up the transmission opportunity; or to select a rate to transmit to the relay and let the relay wait for a good second-hop channel to transmit its received traffic to the destination (referred to as relay-waiting).…”

“…The further-probing option in [5] may be beneficial if the first hop and the second hop's instantaneous channel gains are both good. The relay-waiting option in [6] can be beneficial when the first hop and second hop's instantaneous channel gains are good and bad, respectively, since the source will first transmit to the relay (thus exploiting the good first-hop channel), and wait for the second hop to have a good channel. Motivated by these, we consider both further-probing and relay-waiting options.…”

“…Note that the combination of further-probing and relay-waiting in our work is not simple. A simple combination could be: the winner source has three options: give-up, further-probing, and relaywaiting; and if one of the latter two options is selected, just follow the same method as in [5] or [6]. Different from this simple combination, we propose that, if further-probing is selected by the winner source, relay-waiting is considered as one option in the second-level decision process.…”