Method and apparatus for reliable intersystem handoff in a cdma system

In a communications network, a network user communicates through a remote unit via at least one base station. The communications network includes a first mobile switching center for controlling communications through a first set of base stations and a second mobile switching center for controlling communications through a second set of base stations. The network also includes a service providing base station controlled by the first mobile switching center and providing service to a first transition coverage area using a first pseudorandom noise code. The first transition coverage area defines a boundary between a first system controlled by the first mobile switching center and a second system controlled by the second mobile switching center. The network further includes a passage providing base station controlled by the second mobile switching center for providing service to the first transition area using a second pseudorandom noise code offset in time by a first amount from the first pseudorandom noise code. The passage providing base station provides service to a remote unit only if the remote unit is entering the first transition coverage area while exiting the second system or is about to exit the first transition coverage area while entering the second system.