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Thursday, December 23, 2010

Cognitive radio Spectrum Management: Aggregating Spectrum Demand and Use of Subleasing Methods

The immediate interest to regulators in fielding cognitive radios is to provide new capabilities that support new methods and mechanisms for spectrum access and utilization now under consideration by international spectrum regulatory bodies. These new methodologies recognize that fixed assignment of a frequency to one purpose across huge geographic regions (often across entire countries) is quite inefficient. Today, this type of frequency assignment results in severe underutilization of the precious and bounded spectrum resource.

This interest also has led to developing new methods to manage spectrum access in which the regulator is not required to micromanage every application, every power level, antenna height, and waveform design. Indeed, the goal of minimizing interference with other systems with other purposes may be reasonably automated by the cognitive radio. With a cognitive radio, the regulator could define policies at a higher level, and expect the equipment and the infrastructure to resolve the details within well-defined practical boundary conditions such as available frequency, power, waveform, geography, and equipment capabilities.

One method used to ensure spectrum management is the Aggregation of Spectrum Demand and Use of Subleasing Methods. Many applications for wireless service operate with their own individual licensed spectra. It is rare that each service is fully consuming its available spectrum. Studies show that spectrum occupancy seems to peak at about 14 percent, except under emergency conditions, where occupancy can reach 100 percent for brief periods of time. Each of these services does not wish to separately invest in their own unique infrastructure. Consequently, it is very practical to aggregate these spectral assignments to serve a user community with a combined system. The industry refers to a collection of services of this type as a trunked radio. Trunked radio base stations have the ability to listen to many input frequencies. When a user begins to transmit, the base station assigns an input and an output frequency for the message and notifies all members of the community to listen on the repeater downlink frequency for the message. Trunking aggregates the available spectrum of multiple users and is therefore able to deliver a higher quality of service while reducing infrastructure costs to each set of users and reducing the total amount of spectrum required to serve the community. Both public safety and public telephony services benefit from aggregating spectrum and experience fluctuating demands, so each could benefit from the ability to borrow spectrum from the other. This is a much more complex situation, however. Public safety system operators must be absolutely certain that they can get all the spectrum capacity they need if an emergency arises. Similarly, they might be able to appreciate the revenue stream from selling access to their spectrum to commercial users who have need of access during times when no emergency conditions exist.

Cognitive radio technology is the best means of using the available spectrum fully and thus realizing the highest possible data throughput with fixed and portable terminals.

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