The Personal Access Communications System (PACS) is an American National Standards Institute common air interface standard developed for the 1.9 GHz PCS band in the United States. PACS uses frequency division duplexing technology and is optimized to support low-mobility pedestrian outdoor usage and uireless local loop applicaiioni in a medium-range environment. PACS-Unlicensed B (PACS-UB) is a version of PACS using time division duplexing. PACS-UB has been optimized for private, indoor wireless PBX applications and cordless telephony. Both modes of operation are supported using the same portable hardware and the same signaling protocol.
Two authentication schemes (AS's) have been proposed in the Electronic Industry Association/Telecommunications Industry Association's (EIA/TIA) Telecommunications Systems Bulletins (TSB's) 51 for incorporation in the cellular industry Interim Standard IS 41 Revision C. In the first scheme, which we refer to as the WS scheme, a unique secret key [also known as shared secret data (SSD)] is shared only between the authentication center (AC) and handset. In the second scheme, referred to as the S scheme, the SSD is also shared with the visited system. The performance of the two schemes can be compared by using the expected number of call originations/terminations between two consecutive registrations or call-to-mobility ratio (CMR). Based on the message flow (accesses to databases), it is apparent that the S scheme outperforms the WS schemes if the CMR ratio is large. The CMR's of users will likely span a wide range and, even for the same user, will perhaps vary from time to time. It is therefore desirable to switch between the AS's based on the users' CMR to reduce the signaling network traffic. We propose two adaptive algorithms to determine how and when to switch between the AS's for a given user. Our performance study indicates that as the CMR of a user changes, the adaptive algorithms automatically select the best AS in real time.
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