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Our last Tech Topic introduced the technologies of software defined radios (SDR) that allow for dynamic and adaptive software implementations of radio functionality. With SDR as an implementation strategy, the concept of cognitive radio (CR) technology was then introduced. The potential inherent in CR technology has given rise to rapidly emerging radio developments being pursued by the defense and commercial communities with the promise of inexpensive adaptable radio architectures in the future.1 CR devices can sense, detect, and monitor the surrounding radio frequency (RF) conditions including interference, assess frequency availability and reconfigure their own operating characteristics to best match those conditions. A cognitive capability that can make real-time autonomous decisions for radio operations can increase spectrum efficiency leading to higher bandwidth services as well as reduce the burdens of centralized spectrum management by public safety communications officials.
The flexibility and rapid growth of SDR implementations is apparent in two recently released equipment packages that capitalize on SDR technologies. The first is from Thales Communications, Inc., and is called the Liberty radio.2 Designed for the homeland security segment, this radio is intended to operate in the public safety frequency bands 136-174 MHz, 380-520 MHz, 700 MHz, and 800 MHz and operate in several modes including Project 25 (P25), P25 trunked, and conventional frequency modulation (FM).
The second piece of new equipment is the RF-1033M radio from Harris Corporation.3 This radio is designed to operate in the VHF low (30-50 MHz) and high (136-174 MHz) bands as well as the UHF (380-512 MHz) band. It is intended to operate in P25 modes and analog AM and FM modes.
These software-based radios represent only a first step, however, on the road to true cognitive technologies. Although these two radios are reconfigurable, they are not completely compatible with each other because they do not have the same operating frequency bands and operational modes. Accordingly, there remains much potential for dynamically reconfigurable radios but much work still needs to done to achieve true interoperability. So what advantage does reconfigurability provide?
As noted in our last topic, the DARPA XG and WNAN Programs are investigating much more dynamic frequency selective radios based on agile radio architectures that can respond dynamically to the radio's surrounding environment. The real value of this type of radio and network architecture is the efficiency of operation in establishing an interoperability environment over a flexible frequency range and over reconfigurable operating modes. Based on an assessment of their operating environment, that may also include an evaluation of location identification information and any particular operating rule set, i.e. a "policy-based" rule set. In this manner, these devices can modify their operational parameters such as frequency, modulation schemes, and transmit power, in order to capitalize on available spectrum or other resources.
Perhaps the key to the success and the future development of cognitive radio lies in the ability of developers and practitioners, that is, the first responder community, to establish the policy rule set by which the radios will operate - and this harkens back to Tech Topic #1 and to the fundamental premise of interoperability. There must be a priori agreement at the HUMAN LEVEL to establish the rule set for the operation at the MACHINE LEVEL. In this regard, several issues form the basis for a policy rule set - a few of these are addressed below.
These are a few of the myriad of issues that must be resolved before cognitive radio will be able to meet its potential. The first hints are now obvious though that CR can meet the expectations. In our next topic, we'll take a look at how license exempt spectrum use, one aspect of CR, is already benefiting the public safety community.
1 The Defense Advanced Research Projects Agency (DARPA) XG Program has evolved and morphed into the DARPA Wireless Network After Next (WNAN) Program that is intended to create a flexible and adaptable radio architecture for self-forming ad hoc military networks. See http://www.darpa.mil/sto/smallunitops/xg.html.
2 See http://www.thalesliberty.com/.
3 See http://www.harris.com/view_pressrelease.asp?act=lookup&pr_id=2353.
4 See Jesuale, Nancy and Eydt, Bernard C. "Spectrum Paradigm Shift", RadioResource Mission Critical Communications Magazine, Volume 23, No. 3, March 2008, pp. 83-91.