[Paper Review] A Novel Cooperative Strategy for Wireless Multihop Backhaul Networks

Song-Nam Hong, Ivana Marić+1 more|arXiv (Cornell University)|Aug 1, 2015

Cooperative Communication and Network Coding29 references3 citations

TL;DR

This paper proposes a novel cooperative transmission scheme for 5G wireless multihop backhaul networks using group successive relaying and an optimized quantize-map-and-forward (QMF) coding scheme. By exploiting interference as a useful signal through interference-harnessing routing and a low-complexity successive MIMO decoder, the scheme achieves significant spectral efficiency gains—especially in dense networks—outperforming traditional decode-and-forward multihop routing with reduced relay transmit power and decoding complexity.

ABSTRACT

The 5G wireless network architecture will bring dense deployments of base stations called {\em small cells} for both outdoors and indoors traffic. The feasibility of their dense deployments depends on the existence of a high data-rate transport network that can provide high-data backhaul from an aggregation node where data traffic originates and terminates, to every such small cell. Due to the limited range of radio signals in the high frequency bands, multihop wireless connection may need to be established between each access node and an aggregation node. In this paper, we present a novel transmission scheme for wireless multihop backhaul for 5G networks. The scheme consists of 1) {\em group successive relaying} that established a relay schedule to efficiently exploit half-duplex relays and 2) an optimized quantize-map-and-forward (QMF) coding scheme that improves the performance of QMF and reduces the decoding complexity and the delay. We derive an achievable rate region of the proposed scheme and attain a closed-form expression in the asymptotic case for several network models of interests. It is shown that the proposed scheme provides a significant gain over multihop routing (based on decode-and-forward), which is a solution currently proposed for wireless multihop backhaul network. Furthermore, the performance gap increases as a network becomes denser. For the proposed scheme, we then develop energy-efficient routing that determines {\em groups} of participating relays for every hop. To reflect the metric used in the routing algorithm, we refer to it as {\em interference-harnessing} routing. By turning interference into a useful signal, each relay requires a lower transmission power to achieve a desired performance compared to other routing schemes. Finally, we present a low-complexity successive decoder, which makes it feasible to use the proposed scheme in practice.

Motivation & Objective

• Address the backhaul capacity bottleneck in dense 5G small cell deployments using wireless multihop relaying.
• Overcome the limitations of interference-aware routing and decode-and-forward multihop schemes in high-density networks.
• Develop a cooperative transmission scheme that leverages interference constructively rather than treating it as noise.
• Design an energy-efficient relay selection algorithm that exploits interference to reduce transmit power.
• Enable practical deployment by introducing a low-complexity successive MIMO decoder with near-optimal performance.

Proposed method

• Introduces group successive relaying, where all L sources transmit simultaneously, and L relays per hop forward a function of all received signals.
• Proposes an optimized QMF scheme that performs optimal quantization of received signals at relays to improve performance and reduce decoding delay.
• Develops interference-harnessing routing that selects relays based on maximum received power, turning interference into a constructive signal.
• Derives a closed-form achievable rate region for the proposed scheme in asymptotic network models.
• Designs a low-complexity successive MIMO decoder using linear receivers (e.g., interference-free (IF) receiver) that achieves near-ML performance with minimal complexity.
• Applies point-to-point channel codes (e.g., LDPC, Polar codes) to enable practical implementation with moderate complexity.

Experimental results

Research questions

• RQ1 How can interference in multihop backhaul networks be exploited rather than avoided to improve spectral efficiency?
• RQ2 What is the achievable rate gain of the proposed QMF-based scheme over traditional decode-and-forward multihop routing in dense networks?
• RQ3 How does the performance of the proposed scheme scale with increasing network density (i.e., number of sources L)?
• RQ4 Can a low-complexity successive decoder achieve near-optimal performance while maintaining practical feasibility?
• RQ5 To what extent does interference-harnessing routing reduce relay transmit power compared to interference-aware or conventional routing?

Key findings

• The proposed scheme achieves a significant spectral efficiency gain over multihop routing (decode-and-forward), with the performance gap increasing as network density (L) increases.
• In high-SNR regimes, the proposed scheme outperforms multihop routing due to its ability to exploit strong interference, while multihop routing is limited by interference on any single link.
• The energy efficiency of the proposed scheme improves with increasing network density, enabling lower relay transmit power for the same performance.
• Interference-harnessing routing reduces relay transmit power by selecting relays that benefit from constructive interference, unlike interference-aware routing that avoids interference.
• The successive MIMO decoder using an interference-free (IF) receiver achieves within 1 bit of the ML performance and outperforms multihop routing, especially for networks with fewer than four hops.
• The optimized QMF scheme significantly improves performance over conventional QMF and reduces decoding complexity, making the scheme practical for real-time deployment in 5G backhaul networks.