PHY-Layer Resiliency in OFDM Communications: A Tutorial

This tutorial paper addresses the physical layer security concerns and resiliency of Orthogonal Frequency Division Multiplexing (OFDM) communications; the de facto air-interface of most modern wireless broadband standards including 3GPP Long Term Evolution (LTE) and WiMAX. The paper starts with a brief introduction to the OFDM waveform and then reviews the robustness of the existing OFDM waveform in the presence of noise, multipath fading, and interference. The paper then moves on to build comprehensive adversarial models against OFDM waveforms. Robustness of OFDM is first investigated under AWGN noise and noise-like jamming attack scenarios, then under uncorrelated yet colored interferences from modulated sources (both intentional and unintentional). Finally, the paper explores some of the more recent developments in the field of energy efficient correlated jamming attacks that can disrupt communication severely by exploiting the knowledge of the target waveform structure. Potential countermeasures against such jamming attacks are presented, in an attempt to make a robust and resilient OFDM waveform.

I. Introduction

MODERN wireless broadband communication systems require extremely high throughput using a limited bandwidth, to accommodate the ever increasing mobile data demand. Orthogonal Frequency Division Multiplexing (OFDM) modulation technique and associated Orthogonal Frequency Division Multiple Access (OFDMA) channel access mechanism have become a major element in modern wireless broadband communication systems. This is due to OFDM's spectral efficiency, achievable data rates, and robustness in multipath fading environments. Wireless Local Area Network (WLAN) technologies based on the IEEE 802.11a, 802.11g, 802.11n, 802.11ac, and 802.11ad standards all use OFDM. It is also used in Wireless Metropolitan Area Network (WMAN) technologies based on the IEEE 802.16d, 802.16e, and 802.16m standards. In addition, Long Term Evolution (LTE), the leading cellular broadband technology, relies on OFDM for its air-interface.