WCDMA technology is being deployed worldwide to provide third-generationmobile systems and services. The WCDMA standard continues to evolve with HSDPA and EUL.
Receiver technology is also evolving. Today's terminals and base stations employ Rake receivers, which collect signal energy that has been dispersed in time by the multi-path radio channel. In the future, however, besides collecting signal energy, advanced receivers will be used to suppress interference. In this regard, G-Rake receivers show great promise.
To understand the G-Rake receiver, let us briefly review WCDMA transmission. Figure 1 shows the transmission and reception of a single stream of information. Information bits are encoded with a forward error correction (FEC) encoder, such as a convolutional encoder or turbo encoder. The encoded bits are used to create modulation symbols, such as quadrature phase-shift keying (QPSK) symbols. These are then spread so that each symbol is represented by a sequence of "chips." Next, the spread-spectrum signal is mixed up to a radio frequency and transmitted. At the receiver, the radio signal is mixed down to baseband for demodulation and decoding.
