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The purpose of the Wireless Regional Area Networks (WRANs) is to allow the use of spectrum allocated for television broadcasting in areas with sparse users, ensuring no interference with licensed operators. Cognitive radios using the IEEE 802.22 standard should monitor the environment to not cause interference in primary operators. When multiple WRANs intend to operate on the same set of frequencies in overlapping areas, the 802.22 standard provides mechanisms for their co-existence and provides a temporal multiplexing scheme to solve this problem. We propose three channel allocation algorithms to support the co-existence of potentially interfering WRANs. The proposed algorithms are based on graph coloring, and the innovation is to consider the demand for bandwidth from each WRAN, maintaining proportionality between the demand for frequencies of each WRAN and what is actually allocated. The algorithms are evaluated and it is concluded that they can efficiently assign channels to WRAN taking into account the bandwidth needs of each network. [ABSTRACT FROM AUTHOR]