With DSA, multiple available spectrum bands discovered via CR can be aggregated dynamically to fulfill the service requirement.
On the other hand, SUs accessing the spectrum of PUs makes the power control in CRNs difficult to operate, especially when multiple frequency spectrum bands are considered.
Another method is to use channel aggregating technique, which allows one radio to operate on multiple discontinuous spectrum bands simultaneously (e.g., orthogonal frequency division multiplexing access (OFDMA)).
As there are multiple available spectrum bands in the distributed CWNs, the multi-channel hidden terminal problem, which is a challenge for the traditional distributed multi-channel wireless networks and first proposed in [18], is also an important issue in the distributed CWNs.
Prior work used randomized spectrum sensing to spread multiple SUs over different spectrum bands [7, 8].
In this article, we consider a system with multiple wireless service providers (WSPs) where multiple SUs are allowed to access the unused licensed spectrum bands without conflicting with PUs.
It is likely, however, that a new flagship iPhone from Apple would resolve these banding issues — either by supporting multiple spectrum frequencies, or by Apple offering multiple versions of the device for different carriers' network.
A space discovery protocol is designed to find multiple space disjoint paths, and a spectrum discovery protocol is designed to guarantee spectrum bands which are used by nodes in selected paths that are independent to neighbor nodes.
While the iPad supports LTE spectrum bands used only in the U.S. and Canada, the new iPhone will apparently work with multiple bands, making it compatible with networks in Europe and Asia as well.
