[Paper Review] Integrated Access and Backhaul Optimization for Millimeter Wave Heterogeneous Networks

Yilin Li, Jian Luo+2 more|arXiv (Cornell University)|Jan 15, 2019

Millimeter-Wave Propagation and Modeling27 references17 citations

TL;DR

This paper proposes a joint scheduling and resource allocation algorithm combined with a dynamic routing scheme for millimeter wave heterogeneous networks with integrated access and backhaul (IAB), leveraging directional beamforming to maximize spatial reuse and data rate. The approach achieves near-theoretical optimum performance with lower latency, supports flexible uplink/downlink slot allocation, and enhances both half- and full-duplex operation for point-to-point and point-to-multipoint communications.

ABSTRACT

By allowing a large number of links to be simultaneously transmitted, directional antenna arrays with beamforming have been envisioned as a promising candidate to reach unprecedented levels of spatial isolation. To achieve the high efficiency of spatial reuse in improving system performance, an optimization problem that maximizes the achievable data rate of a multihop heterogeneous network, which incorporates the concept of integrated access and backhaul and supports both downlink and uplink transmissions on access and backhaul links, is formulated. The optimization problem is then systematically decomposed and demonstrated as NP-hard, and a heuristic joint scheduling and resource allocation algorithm is proposed to maximize the achievable data rate. In addition, an efficient dynamic routing algorithm is proposed to further enhance the data rate. With extensive system-level simulations, it is demonstrated that the proposed algorithms achieve significant gain over benchmark schemes, in terms of data rate, and closely approach the theoretical optimum, yet with lower latency. Besides, the proposed algorithms enable a flexible adjustment of downlink and uplink transmission duration allocation and support both half- and full-duplex modes with considerable performance enhancement. In particular, the proposed algorithms are capable of fulfilling different performance requirements for both point-to-point and point-to-multipoint communications.

Motivation & Objective

• To address the challenge of maximizing data rate in millimeter wave heterogeneous networks with integrated access and backhaul (IAB), where backhaul links are wireless and subject to blockage and pathloss.
• To optimize spatial reuse in multi-hop mmWave networks by jointly scheduling transmissions and allocating resources while accounting for directional beamforming and interference constraints.
• To design a dynamic routing algorithm that adapts to real-time network load and traffic to further improve data rates.
• To support flexible downlink/uplink slot allocation and both half- and full-duplex operation for diverse communication scenarios.

Proposed method

• Formulates an NP-hard optimization problem to maximize the achievable data rate in a multihop mmWave IAB heterogeneous network with downlink and uplink transmissions on both access and backhaul links.
• Decomposes the problem into joint scheduling and resource allocation, and proposes a heuristic algorithm to maximize data rate under power and interference constraints.
• Introduces a dynamic routing algorithm that greedily selects optimal paths between base stations and user equipment based on real-time network conditions and traffic load.
• Uses a modified KKT-based power allocation approach to solve the relaxed optimization problem, with optimal power allocation derived from Lagrangian multipliers and channel gains.
• Incorporates beamforming gain and pathloss models to model realistic mmWave propagation, including directional link isolation and interference.
• Employs system-level simulations to evaluate performance against benchmarks, validating the algorithm's near-optimal performance and low latency.

Experimental results

Research questions

• RQ1 How can joint scheduling and resource allocation be optimized in mmWave IAB heterogeneous networks to maximize data rate while accounting for directional beamforming and interference?
• RQ2 What is the impact of dynamic multihop routing on data rate performance in mmWave IAB networks with variable traffic and load?
• RQ3 To what extent can flexible uplink/downlink slot allocation improve system performance in mmWave IAB networks with asymmetric traffic demands?
• RQ4 How does the proposed algorithm perform in both half-duplex and full-duplex transmission modes, and what is the gain in spectral efficiency?
• RQ5 Can the proposed heuristic algorithm closely approach the theoretical optimum in terms of data rate while maintaining low computational latency?

Key findings

• The proposed joint scheduling and resource allocation algorithm achieves significant data rate gains over benchmark schemes in extensive system-level simulations.
• The algorithm closely approaches the theoretical optimum in terms of achievable data rate, with substantially lower latency compared to exhaustive search methods.
• The dynamic routing algorithm further enhances data rates by adaptively selecting optimal multihop paths based on real-time network load and traffic conditions.
• The system supports flexible downlink and uplink slot allocation, enabling performance adaptation to varying user demand patterns.
• The proposed algorithms achieve considerable performance enhancement in both half-duplex and full-duplex modes, particularly benefiting point-to-multipoint and point-to-point communications.
• The solution demonstrates strong scalability and adaptability, effectively managing interference and leveraging spatial reuse in dense mmWave HetNets.