Spectrum sharing has been proposed as a way to more efficiently use existing spectrum, and also to alleviate the spectrum scarcity that impedes new wireless services from being deployed. Cognitive radio is a promising technology that can allow users of spectrum to share spectrum with other users of the spectrum without causing harmful interference. Cognitive radio (CR) wireless devices perform spectrum (channel) sensing before accessing a channel.
Also, many spectrum allocation techniques utilize a centralized control. However, a centralized control has the disadvantage of presenting a single point of failure.
Further, even in a spectrum cleared of other users (e.g., cleared of incumbent users) achieving fair channel access among cooperating, yet independent, CR wireless devices can be problematic. The ability for a CR wireless device to quickly and efficiently join a CR system and access unused spectrum without having to undergo major changes to existing wireless networks has presented many challenges to designers of wireless communication systems. Particularly, in certain communication conditions CR wireless device data throughput can be reduced due to a particular CR spectrum allocation scheme used by a wireless communication system.
The term “spectral quantum” defines the smallest spectral bandwidth that a CR wireless device may occupy or, the smallest amount by which the bandwidth of a CR wireless device may be changed. When available spectrum is very wide relative to the size of a spectral quantum, a CR wireless device may take a long time to occupy the entire spectrum, even if there is no competition from other wireless devices. This access time may even exceed that needed to send all of the CR wireless device's available data. This problem occurs because of relatively slow growth (e.g., one quantum of spectrum per transmission) of the CR wireless device's occupied bandwidth. Because of this relatively slow growth, data throughput at the beginning of a communication session can be adversely affected.
As a second example, CR wireless devices operating on the edge of a spectrum band or adjacent to a fixed interferer, i.e., operating at a band-edge, can grow their signal only in one direction of spectrum (i.e., either higher or lower in frequency), away from the band-edge. That is, their signal growth is blocked in the direction of the band-edge. These CR wireless devices therefore grow their signal at half the rate of other unencumbered CR wireless devices' signals growing unencumbered by a band-edge, which can increase their signal occupied bandwidth toward both (high and low) sides into available spectrum. The band-edge CR wireless devices thus experience reduced bandwidth during their growth phase in comparison with that of unencumbered CR wireless devices, and, as a consequence, data throughput at the beginning of a communication session can be adversely affected.
As a third example, CR wireless devices operating next to a fixed limit, e.g., at a band-edge, may attempt spectrum growth next to such a fixed limit and therefore will maintain a fence quantum between the occupied signal bandwidth of the CR wireless device and the fixed limit. To maintain a fence quantum next to the fixed limit wastes available spectrum that could otherwise be used by CR wireless devices. This wasted spectrum can result in reduced data throughput for such CR wireless devices.
Therefore a need exists to overcome the problems with the prior art as discussed above.