Wireless Communication

Chapter: Network Concepts and Standards
Section: Cellular Systems, IS-95

Soft Handover in DS-CDMA

Figure: DS-CDMA system can perform a soft handover. Two base stations transmit the same wideband signal to a user.

The rake receiver is designed to optimally detected a DS-CDMA signal transmitted over a dispersive multipath channel. This receiver can also be used is the received CDMA signal comes from two different base stations, with slightly different delays. This can be used to support a soft handover from one base station to another. In the transition range, both base stations participate in maintaining the link with the user. This principle is used in the IS95 cellular CDMA system.

Figure: Rake receiver with 5 fingers. Two such fingers can be used for signals from two different base stations

Example and exercise

Assume that the channel between a single base station and the user is a non-dispersive line-of-sight channel. The signal from base station A is received with amplitude a and the signal from B is received with amplitude b. What are the optimum relative amplification/attenuation factors of the two fingers of the rake receiver in the user terminal. Assume Answer

JPL's Wireless Communication Reference Website Jean-Paul M.G. Linnartz, 1993, 1995.