[Paper Review] Resource Allocation in Heterogenous Full-duplex OFDMA Networks: Design and Analysis

Peyman Tehrani, Farshad Lahouti+1 more|arXiv (Cornell University)|Feb 8, 2018

Full-Duplex Wireless Communications18 references3 citations

TL;DR

This paper proposes a joint sub-channel and power allocation algorithm for heterogeneous full-duplex OFDMA networks to maximize the weighted sum-rate of femto users while protecting macro users' rates. It accounts for imperfect full-duplex operation, self-interference, and mixed HD/FD user deployments, showing that throughput can double only if self-interference cancellation exceeds a critical threshold, otherwise gains are limited by residual interference.

ABSTRACT

Recent studies indicate the feasibility of full-duplex (FD) bidirectional wireless communications. Due to its potential to increase the capacity, analyzing the performance of a cellular network that contains full-duplex devices is crucial. In this paper, we consider maximizing the weighted sum-rate of downlink and uplink of an FD heterogeneous OFDMA network where each cell consists of an imperfect FD base-station (BS) and a mixture of half-duplex and imperfect full-duplex mobile users. To this end, first, the joint problem of sub-channel assignment and power allocation for a single cell network is investigated. Then, the proposed algorithms are extended for solving the optimization problem for an FD heterogeneous network in which intra-cell and inter-cell interferences are taken into account. Simulation results demonstrate that in a single cell network, when all the users and the BSs are perfect FD nodes, the network throughput could be doubled. Otherwise, the performance improvement is limited by the inter-cell interference, inter-node interference, and self-interference. We also investigate the effect of the percentage of FD users on the network performance in both indoor and outdoor scenarios, and analyze the effect of the self-interference cancellation capability of the FD nodes on the network performance.

Motivation & Objective

• To design a resource allocation framework that maximizes weighted sum-rate in heterogeneous full-duplex OFDMA networks with imperfect FD base stations and mixed HD/FD users.
• To analyze the impact of self-interference cancellation capability on network performance, especially in indoor vs. outdoor scenarios.
• To determine the minimum self-interference cancellation level required to achieve throughput gains over half-duplex systems.
• To evaluate how the percentage of FD users affects spectral efficiency in both single-cell and multi-cell settings.

Proposed method

• Formulates a joint sub-channel assignment and power allocation problem for a single-cell FD OFDMA network with mixed HD and FD users.
• Uses convex optimization techniques to solve the power allocation subproblem under quality-of-service constraints for macro users.
• Applies an iterative algorithm to jointly optimize sub-channel assignment and power allocation in heterogeneous multi-cell networks, accounting for intra-cell and inter-cell interference.
• Introduces a threshold-based analysis for self-interference cancellation, deriving a critical cancellation level below which FD gains vanish.
• Employs a path loss model and simulation setup with macro and femto cells to evaluate performance under realistic propagation conditions.
• Validates theoretical findings via simulations comparing FD-FD, FD-HD, and HD-only configurations across varying self-interference levels and user ratios.

Experimental results

Research questions

• RQ1 What is the minimum level of self-interference cancellation required for full-duplex networks to outperform half-duplex networks in terms of spectral efficiency?
• RQ2 How does the percentage of full-duplex users affect the overall network throughput in indoor and outdoor environments?
• RQ3 To what extent do inter-cell and inter-node interference limit the capacity gain of full-duplex OFDMA networks with imperfect FD nodes?
• RQ4 Can the proposed resource allocation algorithm achieve significant spectral efficiency gains in heterogeneous networks while ensuring minimum rate constraints for macro users?
• RQ5 How does the trade-off between macro cell rate requirements and femto cell sum-rate performance manifest in a multi-cell FD OFDMA setting?

Key findings

• When all users and the base station are perfect full-duplex nodes, the network spectral efficiency can be doubled, achieving a theoretical capacity gain of 100%.
• With imperfect full-duplex operation, the actual throughput gain is limited by residual self-interference, inter-node interference, and inter-cell interference.
• In indoor environments, equipping just 10% of nodes with full-duplex capability leads to a significant throughput increase due to reduced inter-node interference.
• In outdoor scenarios, increasing the percentage of FD users yields only marginal gains, as path loss and propagation conditions limit the benefit of FD operation.
• A critical self-interference cancellation threshold exists; if the cancellation level is below approximately -90 dB to -120 dB (depending on scenario), the FD network cannot outperform a half-duplex network.
• The simulation results confirm the theoretical analysis of the self-interference cancellation threshold, showing strong agreement between analytical predictions and observed performance.