Physical Layer Firewall Design using Co-Channel Underlay-Based Watermark Authentication

The time-aligned injection of a co-channel underlay-based watermark for authentication at the receiver is an effective method to enhance physical layer security. While firewalls have traditionally been used to manage authorized traffic in wired networks, this paper provides the design and implementation of similar functions for wireless networks. The physical layer firewall only allows receiver access in cases where the valid watermark is detected concurrent to the incoming primary signal, and may be used with virtually any network waveform. Moreover, the use of non-repeating arbitrary-phase spread spectrum signals eliminates many common replay attacks. A hardware prototype is built to receive IEEE 802.11g primary signals with arbitrary-phase spread spectrum underlays, showing reliable authentication performance with only minor bit error rate degradation up to Modulation and Coding Scheme 5. Future prototypes are suggested to further optimize performance, for use with other data waveforms, and to demonstrate higher layer protocols.