Cross-Band Interference Considered Harmful in OFDM Based Distributed Spectrum Sharing

TL;DR

This paper analyzes the causes and effects of cross-band interference in OFDMA-based distributed spectrum sharing, proposing mitigation strategies and emphasizing the importance of guardband sizing for effective dynamic spectrum access.

Contribution

It is the first systematic analysis of cross-band interference in distributed OFDMA networks, identifying key artifacts and evaluating mitigation methods.

Findings

Guardband placement effectively reduces interference.

Inter-link frequency offset and sampling mismatch significantly impact interference.

Power heterogeneity influences optimal guardband size.

Abstract

In the past few years we have witnessed the paradigm shift from static spectrum allocation to dynamic spectrum access/sharing. Orthogonal Frequency-Division Multiple Access (OFDMA) is a promising mechanism to implement the agile spectrum access. However, in wireless distributed networks where tight synchronization is infeasible, OFDMA faces the problem of cross-band interference. Subcarriers used by different users are no longer orthogonal, and transmissions operating on non-overlapping subcarriers can interfere with each other. In this paper, we explore the cause of cross-band interference and analytically quantify its strength and impact on packet transmissions. Our analysis captures three key practical artifacts: inter-link frequency offset, temporal sampling mismatch and power heterogeneity. To our best knowledge, this work is the first to systematically analyze the cause and impact of cross-band interference. Using insights from our analysis, we then build and compared three mitigating methods to combat cross-band interference. Analytical and simulation results show that placing frequency guardband at link boundaries is the most effective solution in distributed spectrum sharing, while the other two frequency-domain methods are sensitive to either temporal sampling mismatch or inter-link frequency offset. We find that the proper guardband size depends heavily on power heterogeneity. Consequently, protocol designs for dynamic spectrum access should carefully take into account the cross-band interference when configuring spectrum usage.