AN2251, Maximum Ratio Combining for a WCDMA Rake Receiver

Wideband CDMA (WCDMA), a widely accepted thirdgeneration interface, is based on direct-sequence (DS) CDMA technology. To minimize distortion of the signals in a DSCDMA system, a rake receiver is used. A signal transmitted through the wireless channel may be severely distorted due to co-channel interference, adjacent channel interference (or multiple access interference), thermal noise, and multipath fading. The most severe distortion comes from fading, which changes the bit error rate (BER) curve from an exponential to a linear curve. One technique the rake receiver employs to combat these distortions is diversity. There are different diversity techniques, including frequency, time, and space. This application note explains how the DS-CDMA rake receiver employs multipath diversity techniques to minimize distortion.