Tractable Model for Rate in Self-Backhauled Millimeter Wave Cellular Networks

Abstract: Millimeter wave (mmW) cellular systems will require high gain directional antennas and dense base station (BS) deployments to overcome high near field path loss and poor diffraction. As a desirable side effect, high gain antennas provide interference isolation, providing an opportunity to incorporate self-backhauling--BSs backhauling among themselves in a mesh architecture without significant loss in throughput--to enable the requisite large BS densities. The use of directional antennas and resource sharing between access and backhaul links leads to coverage and rate trends that differ significantly from conventional microwave ($\mu$W) cellular systems. In this paper, we propose a general and tractable mmW cellular model capturing these key trends and characterize the associated rate distribution. The developed model and analysis is validated using actual building locations from dense urban settings and empirically-derived path loss models. The analysis shows that in sharp contrast to the interference limited nature of $\mu$W cellular networks, the spectral efficiency of mmW networks (besides total rate) also increases with BS density particularly at the cell edge. Increasing the system bandwidth, although boosting median and peak rates, does not significantly influence the cell edge rate. With self-backhauling, different combinations of the wired backhaul fraction (i.e. the faction of BSs with a wired connection) and BS density are shown to guarantee the same median rate (QoS).

• The paper introduces a tractable stochastic geometry model to predict user rates in self-backhauled mmWave networks.
• It demonstrates that denser base station deployments improve spectral efficiency and mitigate urban blockage impacts.
• The analysis provides actionable design insights by balancing wired and wireless BS densities to optimize network performance.

Tractable Model for Rate in Self-Backhauled Millimeter Wave Cellular Networks

This paper explores a model for millimeter wave (mmWave) cellular networks focusing on the self-backhauling aspect, where base stations (BSs) can interlink in a mesh configuration to manage their backhaul requirements. These networks, characterized by high gain directional antennas and significantly denser BS deployments compared to traditional systems, aim to address the challenges posed by the considerable path loss and diffraction limitations inherent to mmWave frequencies.

Key Contributions and Methodology

The authors propose a stochastic geometry-based analytical model capturing the rate trends in self-backhauled mmWave networks. This model integrates aspects of blockage, path loss variability, and BS densification, providing insights beyond traditional ultra high frequency (UHF) cellular systems.

A notable aspect of this work is its inclusion of varying path loss parameters for line-of-sight (LOS) and non-line-of-sight (NLOS) conditions, validated against empirical data from urban environments such as New York and Chicago.

Numerical Results and Observations

The paper offers several strong numerical insights:

• Spectral Efficiency: Unlike interference-limited UHF networks, mmWave networks' spectral efficiency improves with BS density. This is particularly noted at the cell edge, suggesting that higher BS density can significantly boost the total rate.
• Bandwidth Influence: While increasing system bandwidth enhances median and peak rates, it affects the cell edge rates minimally, primarily due to power limitations at the edges.
• Interference Characteristics: The study finds that mmWave networks often operate in a noise-limited regime due to their high gain antennas and the isolation they provide from interference.

Self-Backhauling and Network Performance

Self-backhauling is highlighted as a potent approach due to its scalable nature. The analysis indicates that the same median rate can be achieved with different combinations of BS density and the fraction of BSs with a wired connection. This flexibility offers operators valuable design strategies, allowing them to vary the density of wired BSs versus total BS density to achieve desired performance benchmarks.

Practical and Theoretical Implications

The paper provides practical guidance on mmWave network deployments within urban landscapes, suggesting that dense BS deployments mitigate the detrimental effects of blockage. Theoretical implications extend to the modeling of these networks, as the findings demonstrate how blockage, path loss exponent variability, and user density converge to influence network performance.

Future Research Directions

The analysis sets the stage for further exploration in several key areas:

• Integration with UHF Networks: With hybrid mmWave-UHF networks emerging, understanding how offloading strategies can be optimized is crucial, particularly for users in challenging NLOS environments indoors.
• Multihop Backhaul Scenarios: Exploring the implications of multiple hops in backhaul systems for sparse deployments can further enhance network capabilities.
• Large-Scale Simulations: Continued validation using real-world data will help refine models, guiding optimal configurations for varying urban topologies and user demands.

This paper is a comprehensive contribution to understanding mmWave networks' complexities, specifically regarding self-backhauling and deployment strategies in dense urban contexts. It underscores the transformative potential of mmWave technologies while providing a solid foundation for advancing these networks' analytical models and practical implementations.