The evolution of WiMAX, from 802.16-2004 to 802.16d and now toward 802.16e is an ongoing effort. However, from the beginning WiMAX layer 2 was designed based on licensed frequency operations in mind. At the heart of MAC protocol, polling is the mechanism by which the base station allocates bandwidth to individual users. In licensed-exempt operation, because of inference issues, polling can be the weakest point of operation. Inefficiency in polling mechanism can severely increase delay and make it impossible to support real time services. All of WiMAX products for 3.65 GHz licensed-exempt band is based on standard 802.16d licensed based MAC. For heavily utilized licensed-exempt, interference is going to be a big challenge.
The 802.16 standard defines two main grant-request methods, unicast polling and contention-based polling. While, unicast polling provides guaranteed method of access for users with high QoS needs, contention-based polling can support users with a best effort QoS type of services. It will provide the opportunity to build a portfolio of services based on different subscription rates. Different contentions resolution algorithms have already been proposed, but as it mentioned, more work is necessary to optimize the overall MAC performance for a license-exempt operation.
For future deployment it is important that either FCC releases more bandwidth for operations or standardizations bodies come up with new modified MAC for licensed-exempt WiMAX operations. At the moment, WiMAX MAC allocation is based on an individual subscriber or a group of subscribers. The use of polling simplifies the access operations and guarantees QoS for different subscribers.
All parties need to put their acts together in the next couple of months to make fixed wireless a success this time! FCC needs to release more spectrums to make wireless broadband deployment a reality. Standardization bodies and vendors need to optimize WiMAX for scalable license-exempt operations. And government needs to promote broadband deployment and usage as a necessity for an advanced twenty first century society.