Design Articles

Putting Intelligence in ‘Bricks’

Cognitive radio technology can provide more robust, effective public safety communications capabilities and tools.

By Fred Frantz, Director, Law Enforcement Programs, Advanced Research Division, Global Security & Engineering Solutions, a division of L-3 Services Incorporated

emcomm radio

The size and weight of early public safety portable radios led them to often be referred to as “bricks”; while that reference had more to do with the physical characteristics of a radio, it also implied that the radios were not all that sophisticated.

Today’s public safety radios, however, incorporate a significant amount of software that processes RF signals. In fact, most high-end portables fit typical engineering definitions of software defined radios. (The SDR Forum’s most recent definition for software defined radio is a radio in which the physical layer’s operating functions are implemented using software.) For example, typical public safety portable radios today can support multiple protocols, can be reprogrammed for different protocols, channel assignments, talk groups (for trunked radio systems), and so on.

While software defined radios have added significant flexibility to public safety portable radios, the next step in the progression of capabilities is to add cognitive capabilities to public safety portables. A radio is considered cognitive if it is aware of its environment and internal state and can make decisions about its radio operating behavior based on that information and predefined objectives.

Much of the initial research into cognitive radio occurred through military research that was focused on dynamic spectrum access. The concept of dynamic spectrum access is to identify available spectrum that is not utilized and use it as needed to avoid interference, maintain connectivity, expand capacity, and so on. A successful demonstration conducted under the DAPRA xG program proved the viability of the overall concept. However, dynamic spectrum access is often associated with accessing unlicensed spectrum or spectrum outside that licensed to the user, neither of which is likely to provide immediate value to public safety users. The key for public safety is to develop cognitive radio technology beyond the concepts of dynamic spectrum access.


Interoperability has been a long-standing challenge in public safety communications; numerous examples have been cited over the past several years in which responders with incompatible radios have been unable to communicate. While there have been significant improvements in deploying shared systems, shared channels, and gateways, the problem still exists that responders to an incident can have incompatible radios. The ultimate interoperability solution (from a technical standpoint) would be for a responder’s radio to configure itself to meet the requirements and the capabilities of the communications established for an incident.

The Software Defined Radio (SDR) Forum identified the potential for SDR technology to support interoperability in a 2006 report on SDR Technology for Public Safety [1]:

“This capability improves interoperability by further enabling radios to be reconfigured to meet the requirements of the incident to which the subscriber is responding. This seamless interoperability with minimal user intervention is a model that could be achieved as multi-band, multi-service SDRs become well-established in the public safety community.”

Researchers are developing prototype capabilities to recognize waveforms to allow radios to reconfigure to the communications capabilities in place (for incident or disaster response). For example, researchers at Virginia Tech and Cognitive Radio Technologies are developing a Public Safety Cognitive Radio design to provide interoperability by first sensing the environment to identify frequency and waveforms in use, then provide the user with the option of reconfiguring the radio accordingly. [2]

The London Bombing Scenario

While researchers are developing prototype capabilities to address the interoperability challenge, the SDR Forum is looking at other applications of cognitive radio technology for public safety to encourage further research. The Forum’s Public Safety Special Interest Group is conducting a series of analyses to identify use cases for cognitive capabilities for public safety. The first of these analyses reviewed the events, the response to, and the communications challenges of, the terrorist bombings in London on July 7, 2005 [3]. The analysis approach looked at a real scenario as inspiration for ideas on how cognitive radio could enhance public safety communications.

One such concept involves the ability to extend network coverage beyond the coverage envelope of network infrastructure using multiple hops from radios outside the coverage envelope to a radio configured as a repeater. In the London scenario, responders at the scene of explosions inside the subway tunnels were unable to communicate to their above-ground networks. Cognitive radio capabilities could be used to automatically reconfigure radios to include a repeater capability to extend network coverage to areas where radios are otherwise cut off from their infrastructure, particularly during initial response to an incident before additional communications resources can be deployed.

As explained in the SDR Forum report, this network extension would allow transmissions to be passed back and forth from the incident site along a network of individual responder radios operating in peer-to-peer mode to a radio which can communicate with the main radio system/network. A radio would be positioned where it could maintain connectivity with the above-ground infrastructure (such as at an opening to the tunnel) and function as a repeater to bridge between the otherwise disconnected radios and the infrastructure. Depending on distribution of radios in the tunnels, additional radios could also be automatically reconfigured to act as repeaters among the disconnected radios.

While this particular example was derived from the London scenarios, there is more general applicability. For example, in a scenario in which there significant infrastructure loss (such as a major hurricane), the proposed capability could provide the ability to maintain connectivity where there are coverage holes, or where temporary and mobile network capabilities create dynamic coverage footprints.

This particular use case is the basis of a research challenge sponsored by the SDR Forum. It was defined as one of the problem areas of the Forum’s Smart Radio Challenge, in which university student team compete to demonstrate technical solutions to research problems.

Dynamic Prioritization

Another concept identified in the SDR Forum’s report involves dynamic prioritization. Land mobile radio trunking systems today have prioritization capabilities that allow certain talk groups to be granted access to the network more readily than others. However, such prioritizations are statically defined.  One of the observations about the London scenarios (although not in the context of trunked radio system) is that the dynamic nature of an incident response changes the priority that should be given to communications from an individual responder—the report thus introduces the concept of dynamically assigning priorities based on evolving aspects of an incident. Such aspects can include, but are not limited to, the role that a particular responder is performing in the incident, the type of data being communicated, or the physical location of the responder.

The role of cognitive capabilities here is in the ability to adjust in real time those priorities based on the unfolding events of the incident, communications resources demands and availability, and the changing roles of individual responders over the course of an event.  Implementation of this cognitive capability will likely require functionality at both the subscriber unit and within the network infrastructure. The subscriber unit provides input based on responder role, type of data being communicated, and location information, while the network cognitive capabilities include load balancing and resource management.

Cognitive capabilities with a portable radio can also improve radio performance in terms of parameters such as transmission quality and battery life. For example, cognitive radio algorithms could be implemented to adjust waveform bandwidths and frequency selections based on the geolocation and relative positions of the users. Waveform parameter adjustments allow the radio to tradeoff parameters such as data rates, coverage, and interference based on the dynamic RF environment, location of devices, and so on.

700 MHz Approaches

Another application of cognitive radio technology in subscriber performance is outlined in a recent SDR Forum report on the application of technologies to the newly auctioned 700 MHz spectrum. “Transmit power control, which is employed today in many commercial cellular systems, can improve the efficiency of the system. Currently implemented techniques are focused primarily on maximizing battery life by controlling transmit power as a function of distance from the cell site. This is generally performed by an individual handset as a function of its location.

A more sophisticated cognitive radio approach could be implemented that incorporates the locations and activities of multiple users to improve performance of multiple users and multiple links. For example, frequency selection for one link could be selected to minimize adjacent channel interference to another user, allowing that user to maintain a lower transmit power which in turn maximizes battery life. Cognitive capabilities in such scenarios are likely to be distributed among subscribers and the network; subscriber devices may provide information about the RF environment while decision logic relating to multiple links and subscribers would likely be performed at the network.” [4]

Next Steps

While the technology is promising, and there are demonstrable capabilities from both the research community and the military, there are still some steps that must occur before such devices will be available for public safety use.  In addition to the ongoing research and development, there are some regulatory considerations that must be addressed. While none of the capabilities proposed above require public safety radios to operate outside licensed frequencies, the capabilities may require some adjustments to the type acceptance processes currently required for public safety radios.

The other major area that will need to be addressed is development of policies and procedures, and subsequent training of users, to best exploit new capabilities. While much of the cognitive radio capability would be transparent to a public safety officer, understanding of additional capabilities will be important to maximize their impact and value.

A new generation of radios for public safety is rapidly approaching the marketplace, capable of far more than simply receiving and transmitting on a specific frequency defined by the user or programmed into the radio.  By reconfiguring to meet the needs and circumstances of each incident, such portable radios can provide significant tools and capabilities to support public safety end users, network managers, and communications unit leaders.  They will be the most sophisticated “bricks” around.

L-3 Communications Corporation
Chantilly, VA
(703) 708-1400

[1] SDR Forum, Software Defined Radio Technology for Public Safety,” SDR Forum Report No. SDRF-06-P-0001-V1.0.0, April 2006, available at

[2] B. Le, F. Rodriguez, Q. Chen, B. Li, F. Ge, M. ElNainay, T. Rondeau, and C. Bostian. “A Public Safety Cognitive Radio Node,” SDR ’07, Denver, CO, November 2007.

[3] SDR Forum, Use Cases for Cognitive Applications in Public Safety Communications Systems,
Volume 1: Review of the 7 July Bombing of the London Underground, SDR Forum Report No. SDRF-07-P-0019-V1.0.0, November 2007, available at

[4] SDR Forum, Considerations and Recommendations for Software Defined Radio Technologies for the 700 MHz Public/Private Partnership, SDR Forum Report No. SDRF-07-R-0019-V1.0.0, December 2007, available at

This article originally appeared in the March, 2008 issue of Portable Design. Reprinted with permission.

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