“…Thereafter, the ME-based DSAs cannot help the SUs further improve their rate performances since there is no extra idle spectrum for the PUs to lease. In such a situation, the PUs have the following two choices, i.e., (1) releasing some of the SUs through the user admission control mechanisms, e.g., [4], which may lead to the loss of the SUs, and, as a result, the long-term revenue loss of the PUs, and (2) resorting to the resource-exchange (RE) based DSAs, e.g., [5].…”