A Cross-Layer Framework for Exploiting Virtual MISO Links in Mobile Ad Hoc Networks

Abstract

Space-time communications can help combat fading and, hence, can significantly increase the capacity of ad hoc networks. Cooperative diversity or virtual antenna arrays facilitate spatio-temporal communications without actually requiring the deployment of physical antenna arrays. Virtual MISO entails the simultaneous transmission of appropriately encoded information by multiple nodes to effectively emulate a transmission on an antenna array. We present a novel multilayer approach for exploiting virtual MISO links in ad hoc networks. The approach spans the physical, medium access control and routing layers, and provides 1) a significant improvement in the end-to-end performance in terms of throughput and delay and 2) robustness to mobility and interference-induced link failures. The key physical layer property that we exploit is an increased transmission range due to achieved diversity gain. Except for space-time signal processing capabilities, our design does not require any additional hardware. We perform extensive simulations to quantify the benefits of our approach using virtual MISO links. As compared to using only SISO links, we achieve an increase of up to 150 percent in terms of the end-to-end throughput and a decrease of up to 75 percent in the incurred endto-end delay. Our results also demonstrate a reduction in the route discovery attempts due to link failures by up to 60 percent, a direct consequence of the robustness that our approach provides to link failures.

Survey on Relay Selection Techniques in Cognitive Networks

“…An intuitive scheme of optimal relay assignment is using distance, either towards the source or the destination, as the criterion of optimal relay selection [29][30]. In [31][32], the authors proposed to choose the best relay depending on its geographic position, based on the geographic random forwarding (GeRaF) protocol.…”

On the performance of multi‐hop wireless relay networks

“…At the medium access control (MAC) layer, different protocols could be considered for the multi-hop WRN using distributed STBC. In [22,23], the authors explored a cross-layer protocol where centralized distributed STBC is used at the physical layer in a multi-hop fashion. The proposed MAC protocol adopts a hop-by-hop approach.…”

Cooperative Protocols Design for Wireless Ad-Hoc Networks with Multi-hop Routing

“…This design is more robust and practical for deployment than the commonly assumed time division multiple access (TDMA) or other orthogonal MAC relaying schemes in the literature. A system framework with similar design structure as ours is proposed in [14], where a comprehensive scheme across the physical, MAC and network layers is proposed for cooperative transmission in ad-hoc networks. In their work, only space-time coding is considered at the physical layer.…”

“…A primary route path is constructed using the dynamic source routing (DSR), and the relay nodes are selected at the MAC layer with an extensively modified 802.11 distributed coordination function (DCF) protocol where pilot tones are inserted after RTS frame transmission for channel estimation. Compared with [14], the proposed scheme in this paper is applicable to either repetition or space-time coding physical modules. More importantly, our relay selection is primarily carried out by the network layer with limited assistance from the MAC protocol and is based on average link signal-to-noise (SNR) estimation, so that no pilot tone is needed.…”