An empirical assessment of Quasi-permanently vacant channels in mobile communication bands for cognitive radio

Basis of cognitive radio is to exploit unused frequency channels in licensed band. Recently standardized IEEE 802.22 set of cognitive radio protocols envisages fixed and nomadic receivers at below 800 MHz bands. Radio link design for this cognitive radio consider that the channels are available only dynamically to secondary users. Scanning period is thus embedded in link layer control as overhead and reduces overall efficiency of cognitive radio technology. For mobile receivers, availability of permanent channels for radio link control is essential for in-band signaling. Existing mobile communication system uses CDMA 800, GSM 900, GSM 1800 and WCDMA 2000 MHz bands for which approximately l/8^th of the band capacity is used for in-band signaling. Present work provides an assessment of vacant channels in mobile communications range which were permanently available at the time of measurement. The study used conventional Radio frequency scanners available for different bands and dedicated engineering handsets for tracking active frequencies. The tests were performed with assemblies carried in a vehicle and across the length and breadth of each city. The allotment of frequencies by Frequency Regulatory Authority to local mobile operators along with the frequency bands reserved for further distribution were also considered. The experimentally collected data were analyzed using RF analysis software and spread sheet database. An analysis of the collected data lead to arrive at the conclusion that more than l/8^th part of resources of each band are nearly permanently vacant which is enough to design in-band common control signalling methods for cognitive radio. Also, with the help of collected data of eight cities, an empirical relationship has been established which can be taken as a thumb rule for projection of channel occupancy from densely populated core areas of big cities to less populated township areas when population is known.