Reducing the probability of detection, improving jamming resistance and security for broadband wireless systems

Commercial radio systems, including the broadband wireless communications systems based on OFDM technology such as those of the IEEE standard 802.16, are designed from the outset to operate in protected spectrum channels with low interference and noise. This paper outlines some techniques whereby the commercial radio signal waveform may be modified to reduce its probability of detection, the communication is made more robust to jamming, and the signalling and control information is protected against eavesdropping. The techniques applied include reduction of the spectral signature through changes in the data and pilot signals and the symbol timing. The modulation of the data and pilot/guard sub-carriers is also modified to disguise the signal characteristics. Protection techniques are also applied to the signalling information flows used to administer the radio operations and to prevent the identity of terminals from being revealed to hostile receivers. There are advantages to developing radio systems based on commercially derived systems that are also suitable for communications use in hostile environments. The use of commercially based systems provides the opportunity to lower costs for the military and public safety users through the economies of manufacturing scale that are applied to the commercial systems and terminals. The use of systems with a commercial base also facilitates interworking between the military/public-safety radio systems and commercial devices and networks. The modifications to the commercial waveform discussed in this paper have the advantage that they may be added as functional blocks to the standard chip-sets for processing the commercial waveforms.