Friday, June 19, 2009

Cognitive Radio – Spectrum Monitoring is the Key to Practical Applications

The key to developing practical application with Cognitive Radio is a greater awareness of the spectrum and how it’s currently being used. A thorough monitoring of the spectrum over a period of time (say weeks and months) will create a database of date/time/frequency stats that can be used to more reliably predict the future use of the spectrum. In this article paints a picture of a world in which all spectrum users rely on cognitive radio techniques to find and use spectrum without much regard for pre assignment.

Part of the solution is to develop devices and practices that cooperate with each other. In other words all devices on the network should check the spectrum and monitor it so it can share spectrum cooperatively.

Best regards,
Hall T.

Friday, June 12, 2009

Spectral Awareness – How to Implement

Cognitive Radio promotes the concept of using unused spectrum to increase available bandwidth. The basic techniques for finding and managing a portion of spectrum are listed below:

Step 1: Find a frequency. Using Adaptive Frequency techniques, a series of frequencies are scanned.

Step 2: Find an unused time slot in between a periodic user. Typically an Adaptive TDMA technique is used to check the availability of the frequency by monitoring it through several cycles. Only measuring the energy in the channel doesn’t give an accurate reading as noise can appear to be a signal.

Step 3: Use spatial techniques to monitor the spectrum -= The two main techniques are - beam steering and null steering which changes the main lobe of the radiation pattern to focus in a specific area.

Step 4: Use Adaptive bit loading based on Signal to Noise Ratio to insert a signal into the unused spectrum. OFDM techniques can be used that fit the time-frequency/hole.

Step5: Perform interference suppression and multiuser decomposition.

Adaptive Power Control and Ad-Hoc Networks are important for managing the above steps.

Best regards,
Hall T.

Friday, June 05, 2009

Cognitive Radio – The Need it Fills

The need for Cognitive Radio techniques will always be with us as long as we’re short of RF bandwidth. In this article the author propose using licensed bandwidth while it is not currently being used. Game theory techniques can be used to monitor what the other users are doing. Of course, the licensed user gets first priority but if it’s not using the spectrum then others may be able to use it.

The FCC is actively studying Cognitive Radio to make better use of the spectrum and better devices that can adapt to the current conditions. In addition to increasing the spectrum, the FCC hopes to improve interoperability among public service units. Current systems give each public service a dedicated, full-time frequency band. Cognitive radio techniques could let one service use the unused bandwidth of another. It could also be used as a repeater between one public service to another. Cognitive radio could monitor and help translate signals to another public service.

The other advantage is increased reliability in terms of fewer dropped calls, blackout spots, and more. If the communication channel becomes noisy, a cognitive radio-based system could switch the call to a better channel.

Best regards,
Hall T.