This article discusses software radio in a public safety application, but expand on the application to take advantage of the flexibility and adaptability of software defined radio (SDR). As previously suggested, the evolution of multi-band, multi-mode and multi-protocol radios has already contributed to the adoption of SDR technologies in various communications applications. The examples cited include dynamic frequency selection (DFS) and transmit power control (TPC); technologies that have already been adopted by FCC rules and implemented in various systems and equipments that are in common practice today. These technologies illustrate the dynamic and adaptive nature that software implementations bring to modern radio design. The key word now is flexibility based on software implementation of radio functionality.
With SDR as an implementation strategy, cognitive radio (CR) has become an emerging advanced radio technology that enables a radio device to monitor, sense, detect and autonomously adapt its communications channel access to the dynamic radio frequency (RF) environment in which it exists. In other words, CR devices can sense, detect, and monitor the surrounding RF conditions including interference and access availability and reconfigure their own operating characteristics to best match those conditions. 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, 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. 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 definition along with the potential of CR technology has been described in various industry sectors. Due to the complexity of CR technology, such descriptions are continuously evolving. The FCC previously defined CR as follows:2
A cognitive radio is, “a radio that can change its transmitter parameters based on interaction with the environment in which it operates.”
Although simply defined, the capabilities of cognitive radio technologies are much more complicated and involve leading edge technology developments ranging from nanoscale electronic devices for system hardware development to artificial intelligence techniques for advanced decision-making rule sets. The FCC describes these capabilities extensively in the NPRM and Order document, FCC 03-322. 3
Two applications of cognitive radio capabilities can be especially and directly applied to enhance public safety operations. The first is the ability of a public safety cognitive radio to recognize spectrum availability and reconfigure itself for much more efficient communications and spectrum use. This would allow public safety personnel to operate with the CR capability of dynamic spectrum selectivity. Secondly, cognitive radio is a prime application that may facilitate interoperability between communication systems that otherwise could not operate together. By adapting to the needs and conditions of another network the cognitive radio could identify the operating conditions and rules of the new network and reconfigure itself to either meet the new conditions, or in fact, configure itself to avoid the new network.
Historically, CR began with the limited purpose to provide flexible channels mainly for military radio applications over the platform of software defined radio (SDR). With SDR as a common enabler, CR functionalities have been advancing rapidly through such efforts as the Department of Defense Advanced Research Projects Agency (DARPA) Next Generation (XG) Program.4 This effort has lead to the development of a CR environment in which radios dynamically reconfigure their operating characteristics on a real-time basis for the purpose of maximizing effective use of available spectrum. This 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. 5
The enhancements in public safety communications indicate that narrow-band real-time voice communications will not be the only necessary mission critical application for public safety. This principal feature can easily be incorporated into broadband applications. Broadband multimedia services will extend the capabilities of the public safety system beyond voice to video, data, and visualized location-based services. The latter service is recognized as especially critical to first responders in emergency situations. Location and tracking of first responders in and around the crisis staging area, and more critically inside buildings or structures, can save lives and reduce the risks involved in their missions. Visualized location services are a priority to public safety organizations such that the ITU and National Emergency Number Association (NENA) are already developing the requirements for inclusion in next generation E-9-1-1 and public safety architectures.6 Such service requirements to exchange intensive video information will certainly require public safety communications capable of multimedia broadband operations. Thus, the CR’s cognitive capability of location awareness information can provide critical functions for future visualized location based applications for public safety.
Along with many other features, CR technology may also be useful to implement interoperability between different public safety wireless protocols. For example, the Association of Public-Safety Communications Officials, APCO, has developed a public safety system standard, Project 25 (P25), to respond to FCC requirements to move from 25 kHz voice channels to 12.5 kHz (and ultimately to 6.25 kHz, the timeframe for which is yet to be determined). 7 In some respects, the P25 standard helps in the move toward interoperability in public safety networks, however a fully CR-equipped system could enhance the effort by acting as an interoperable gateway between conventional public safety networks operating in incompatible channels and/or between:
- Different phase P25 networks,
- Between a conventional system and a P25 system,
- Among networks of legacy and P25 systems, and
- Among legacy, P25 systems and future systems.
A CR gateway system converts incompatible channels, operational modes and protocols into matching ones. Hence interoperability among a multitude of public safety network users can be achieved. Another way of achieving interoperability among incompatible public safety network users is to introduce a new CR-equipped user device that adapts its operating conditions to matching legacy modes of operation. In this way, a user equipped with new devices can act as a legacy or a P25 device when talking to a legacy or a P25 network user. Thus, the old devices can be used until their normal lifetime is exhausted.
In summary, CR can be viewed as a combined application of SDR and intelligent signal processing with functional elements of radio flexibility, spectral awareness and the intelligence of decision-making. Such cognitive capability allows rapid adaptability to an available communications channel and is an important feature for public safety radio devices to carry the operational requirements of anytime and anywhere communications in the case of an emergency. Also its adaptability to an optimal communications channel will help not only avoid interference to other users but also to improve spectrum efficiency for public safety communications. Thus, CR can greatly enhance spectrum accessibility without causing interference to others. CR devices can also access, and modify, the signal environment including spectrum estimation procedures, signal formats and location awareness information. Hence, CR technologies will enable new public safety systems to share spectrum and/or permit dynamically available spectrum use with existing legacy devices.
Over all, CR technology can help in many ways to enhance public safety services. These include:
- Avoiding spectrum congestion.
- Precedence service to higher priority users temporarily during the peak communications period of an emergency.
- Dynamic spectrum access to improve spectrum efficiency.
- Achieving interoperability among legacy and new devices and systems.
1 In an attempt to expand our horizons and in a spirit of collegiality in the Public Safety and Homeland Security Bureau, I have asked Mr. Yoon Chang of our Communications Systems Analysis Division to share in the preparation of this article. Hence, credit –and thanks - for many of the ideas expressed in this article go to him. Mr. Chang is currently an electronics engineer in the Public Safety and Homeland Security Bureau’s Communications Systems Analysis Division. He holds an MSEE Degree from Drexel University. In addition to his current position with the FCC, he has previously held positions with the National Institute of Standards and Technology, IBM Corp, AT&T/Bells Labs, and Hyundai Electronics America, Inc. He may be reached at 202-418-2140, or email@example.com.
2See https://www.fcc.gov/oet/cognitiveradio/. Further, it adds a supplementary description: “This interaction may involve active negotiations with other spectrum users and/or passive sensing and decision making (smart radio) within the radio. The majority of CRs will probably be SDRs, but a CR does not necessarily use software, nor does it need to be field programmable.”
3 See Facilitating Opportunities for Flexible, Efficient, and Reliable Spectrum Use Employing Cognitive Radio Technologies, ET Docket No. 03-108; Authorization and Use of Software Defined Radios, ET Docket No. 00-47, Notice of Proposed Rule Making and Order, 18 FCC Rcd 26859 (2003).
4 See http://www.darpa.mil/sto/smallunitops/xg.html. “The Next Generation (XG) Program goals are to develop both the enabling technologies and system concepts to dynamically redistribute allocated spectrum along with novel waveforms in order to provide dramatic improvements in assured military communications in support of a full range of worldwide deployments… The XG program approach is to develop the theoretical underpinnings for dynamic control of the spectrum, the technologies and subsystems that enable reallocation of the spectrum, and the system applique prototypes to demonstrate applicability to legacy and future DOD radio frequency emitters. The approach plans to investigate methods to leverage the technology base in microelectronics with new waveforms, and medium access and control protocol technologies to construct an integrated system. The proposed program goals are to develop, integrate, and evaluate the technology to enable equipment to automatically select spectrum and operating modes to both minimize disruption of existing users, and to ensure operation of U.S. systems. The result of the XG program will be to develop and demonstrate a set of standard dynamic spectrum adaptation [sic] technologies for legacy and future emitter systems for joint service utility.”
5 See Kenyon, Henry S., “Cognitive Radio Prepares for Action,” Signal Magazine, April, 2008, at http://www.afcea.org/signal/articles/templates/Signal_Article_Template.asp?articleid=1549&zoneid=231.
7 See http://www.tiaonline.org/standards/technology/project_25/ for a TIA Standards discussion and http://www.apco911.org/frequency/project25/information.html for an APCO discussion.