United States Patent [w]
Lee et al.
 INTER-SYSTEM CALLING SUPPORTING INTER-SYSTEM SOFT HANDOFF
 Inventors: Kuo-Chun Lee, 17161 Alva Rd. #2013, San Diego, Calif. 92127; Gadi Karmi, 1220 Cave St. #3, La Jolla, Calif. 92037; Bibhu Mohanty, 11553 Windcrest La. #257, San Diego, Calif. 92128; Todd R. Sutton, 11275 Caminito Rodar, San Diego, Calif. 92126; Noam A. Ziv, 10968 Corte Playa Barcelona, San Diego, Calif. 92124
 Appl. No.: 08/649,959  Filed: May 1, 1996
 Int. CI.6 H04Q 7/22
 U.S. CI 455/442; 455/439; 370/331
 Field of Search 455/442, 437,
455/453, 436; 370/331
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FOREIGN PATENT DOCUMENTS
9515665 6/1995 WIPO H04Q 7/24
US005940762A [ii] Patent Number: 5,940,762  Date of Patent: Aug. 17,1999
Ian F. Akyildizt et al., "Performance Analysis of the Anchor Radio System Handover Method for Personal Access Communications System", IEEE, Mar. 24,1996, pp. 1397-1404.
Primary Examiner—Edward F. Urban
Attorney, Agent, or Firm—Russell B. Miller; Brian S.
Edmonston; Christopher Edwards
A method and apparatus for performing an inter-system soft handoff is described. In accordance with the present invention, when a subscriber unit crosses from a first cellular system to a second cellular system, a base station controller determines if sufficient network resources are available to conduct a inter-system soft handoff. If so, the base station controller generates a set of signaling messages that cause call processing resource to be allocated and for the call to be processed at the second cellular system. The base station controller then perform data-selection and data-broadcast for the call by transmitting data to the subscriber unit by way of the second cellular system as well as via one or more base stations to which the base station controller is directly coupled. The determination as to whether sufficient network resources are available to conduct the inter-system soft handoff is based on the type of connection that exists between the first cellular system and the second cellular system, the number of inter-system calls being conducted, and the frame offset of the call currently being processed.
25 Claims, 11 Drawing Sheets