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In this Tech Topic, we return to consider some of the basic precepts of public safety communications systems while at the same time advocating the potential strengths of software defined radio (SDR) in meeting the demands of public safety communications.
The Bureau recently established a web page elucidating the core concepts in public safety communications.1 These concepts include operability, interoperability, reliability, resiliency, redundancy, scalability, security, and efficiency. This Topic considers the application of software defined radio characteristics within the framework of the core concepts.
In addressing these demanding core concepts for public safety, future networks would benefit from being dynamically adaptable and close to real-time reconfigurable in order to insure interoperability. The implementation and operational costs of public safety radios and networks are high and improvements can be made in interoperability among segmented public safety communities. The US military is facing similar challenges and they have confronted the problems with dynamic new communications technologies that employ the advanced and developing technologies embodied in SDR and Cognitive Radio (CR). We introduce cognitive radio here and will expand our discussion in the next Tech Topic.
In general, SDRs provide software control of the radio frequency operating parameters such as choice of modulation, transmit frequency, bandwidth, and transmit power level. An SDR system can include multiple layers in the OSI hierarchy, but it primarily involves the physical link and often part of the network layer. A CR provides different functionalities such as sensing and monitoring, tracking changes in the RF environment, and autonomously adapting its access to the communications channel. Although the terms SDR and CR are defined slightly differently by different industry sectors, SDR implies implementation aspects using software control, while CR includes extra functionalities other than the basic features of a radio system. Often these two technologies are quoted interchangeably and intermixed in usage with some qualifications in certain cases. For example, a cognitive radio capability is an obvious application to implement a software controllable feature in an SDR.
Supporting adaptive functionalities and reconfigurability in a radio system is quite challenging. SDR and CR are complex paradigms that involve underlying technologies implemented in various types of hardware and software platforms as suggested in our previous Topics. These underlying technologies involve generic hardware implementations of general purpose processors, RF components, digital signal processing (DSP) chips, A/D converters, and smart antennas – among other things – to provide multiple functionalities such as reconfigurability, interoperability, flexibility, upgradeability and cognition capability. SDR also involves new implementations of system and device architectures assembled from RF components, hardware, software and networks. All of these diverse technologies need to be harmonized to implement SDR systems. Because of the magnitude of the diverse and varied technologies involved, progress on their implementation in a practical system is following a path that increases in complexity and functionality for each phase of development. In order to give direction and standardization to the SDR development process, a new IEEE Standards Coordinating Committee (Dynamic Spectrum Access Networks) (IEEE SCC41), was established along with IEEE 1900, a standard for the development of next generation radios4. These standards will provide a technology roadmap for SDR development.
The evolution of multi-band, multi-mode and multi-protocol radios has already contributed to the adoption of SDR technologies in various industry sectors. For example, some functions that are used in SDR/CR technologies now, such as dynamic frequency selection (DFS) and transmit power control (TPC) have already been adopted by FCC rules and implemented in various systems and equipments.
As the precepts mentioned above suggest, the ultimate goal of a public safety network is to provide assured, secure, and seamless communications that are accessible anytime and anywhere with maximum interoperability and adaptability. SDR-based systems are an obvious choice to overcome these challenges in radio design. In the next Tech Topic, the key advances in cognitive radio technologies will be considered along with the potential impact that these technologies may have on the public safety communications environment.
1 See http://www.fcc.gov/pshs/clearinghouse/core-concepts/.
2 See http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=159342.
3 See http://ieeexplore.ieee.org/Xplore/defdeny.jsp?url=/iel1/2752/1441/00035033.pdf&code=2.
4 "The IEEE P1900 Standards Committee was established in the first quarter 2005 jointly by the IEEE Communications Society (ComSoc) and the IEEE Electromagnetic Compatibility (EMC) Society. The objective of this effort is to develop supporting standards dealing with new technologies and techniques being developed for next generation radio and advanced spectrum management. On March 22, 2007 the IEEE Standards Board approved the reorganization of the IEEE 1900 effort as Standards Coordinating Committee 41 (SCC41), Dynamic Spectrum Access Networks (DySPAN). The IEEE Communications Society and EMC Society are sponsoring societies for this effort, as they were for the IEEE 1900 effort." See http://www.scc41.org/.