Spectrum Sensing & Availability of White Spaces

Abstract

Cognitive radios [4], [5], in the recent past have been extensively researched for opportunist spectrum access, which is potentially a new paradigm in spectrum access where licensed spectrum is being shared by unlicensed devices. These available spaces in spectrum are called white spaces (TVWS), the spectrum which is available after digital switchover. Cognitive radios in this mode acts as spectrum scavenger, it senses the spectrum over the whole range and identifies the unused spectrum and operates in this band when it is not being used by any other device. There are two types of opportunist spectrum access, temporal and spatial. In temporal opportunist access, cognitive radio monitors the activity of licensee at any given location and use the spectrum when it’s idle, use of cognitive radio in Radar & UMTS band is example of this type of operation. In spatial opportunist access, cognitive radio identifies the geographical location where certain licensed bands are unused and access them without causing interference to the devices in nearby region. TV stations operate in licensed band of radio spectrum. Use of licensed spectrum by unlicensed devices is strictly prohibited in most of the countries except remote controls, medical devices and wireless microphones. In developed countries regulators are in process of requiring TV channel to switch from analog to digital. Due to higher spectrum efficiency of Digital TV (DTV), a portion of TV analog channels becomes vacant; this vacant portion is then reallocated to other services. These vacant spaces can’t be used by DTV as they operate at maximum power, however transmitter operating at a low level would be able to operate without causing any adjacent or co channel interference, these vacant channels are known as TV White Spaces (TVWS).operation of cognitive radio in these bands is based on the ability of these devices to operate without causing interference to the licensed users of this band. In November 2008, FCC adopted a report setting out rules allowing unlicensed devices to operate in licensed bands. These rules require cognitive devices to use a combination of sensing and geo-location. These devices must be able to sense down to -114dBm, and must be locate themselves within 50 meters accuracy and then consult a database that will inform about the available spectrum at that place. In order to protect the system from interference different spectrum sensing techniques are used .In this paper we will implement a sensing prototype which senses for any incumbent device operating in the vicinity.