978-1-4244-2677-5/08/$25.00 ©2008 IEEE MILCOM 2008 1 A DYNAMIC SPECTRUM ACCESS MAC APPLIQUÉ FOR LEGACY MILITARY RADIOS Steven D. Jones, Naim M. Merheb, I-Jeng Wang The Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd.,Laurel, MD 20723-6099 {steven.jones, naim.merheb, i-jeng.wang}@jhuapl.edu Abstract – There is interest in dynamically allocating spectrum due to the high degree of usage and interference in DoD wireless communications bands. While all bands may not always exhibit high usage, there are times and locations where radio usage is interrupted due to inability to access spectrum. With this in mind, the DoD has undertaken programs such as DARPA neXt Generation (XG) and Wireless Network After Next (WNAN) to develop methods for dynamic spectrum access (DSA). In DSA, a radio or set of radios may select to use a frequency channel at any given time on the basis of the sensed signal activity (or interference temperature) in that channel. Currently fielded military radios do not have such a DSA capability. The situation among DoD radios is such that there exist a variety of means of introducing DSA. Among these are: development of entirely new DoD radios, modification of the software load of current software-defined DoD radios to give them DSA capability, and finally the addition of a hardware and/or software appliqué to interface with existing DoD radios, particularly those not software-defined. Of course there will also be a class of DoD radios that are not suited for the addition of DSA capability. The DARPA WNAN Program is pursuing the first method above, by developing a new radio. The second method above is being pursued in the DARPA XG Program by modifying radio software to add DSA protocols and sensing. In this paper we consider a military radio set (the AN/PRC-117F and the like) which has the necessary features to allow a hardware/software sensing appliqué to be integrated with it resulting in a radio/sensor suite with cognitive features. This paper describes the design and implementation of such an appliqué, along with controlling software and its integration with the PRC-117F in a prototype fashion. The appliqué has been developed and tested in a laboratory environment. Index Terms—dynamic spectrum access, XG, legacy radio. I. INTRODUCTION Recent study of cognitive radios has established the viability of dynamic spectrum access wherein a radio would sense the spectrum to find open bands which it may use for communications in a manner secondary to any primary users of that band. Current military radios do not have such a DSA capability. We consider any legacy military radio which has the necessary features to allow a sensing appliqué to be integrated with it resulting in a radio/sensor suite with cognitive features. There are efforts underway to incorporate DSA algorithms in new radio sets. The DARPA XG Program has demonstrated the ability to develop new radio protocols with the DSA capability as well as the ability to incorporate DSA software algorithms into existing SDRs [1]. The DARPA WNAN Program is also developing DSA-capable radios. In this paper we consider adding hardware and/or software appliqués to existing legacy radios so that they may be used in a DSA manner. The intention is to allow DoD users to gain the advantage of DSA while maintaining their existing inventory of radios. This approach would afford a cost savings while gaining a performance improvement over legacy operation. In many cases, the performance of the legacy radio plus appliqué will not match that of a new generation DSA radio or SDR with DSA capability due to slower sensing or channel switching; however it will be adequate to