The G-Rake receiver, which resides in the demodulator, produces estimates of the
modulation symbols from the received signal. Because the G-Rake receiver is similar
to a traditional Rake receiver, let us also briefly review Rake reception.
Signal energy is collected from different delayed versions of a transmitted signal. As seen in Figure 2, the channel response creates multiple images of the transmitted signal (that is, the dispersive, multipath channel gives rise to different versions). The “fingers” of the Rake receiver extract signal energy from delayed signal images by despreading and combining them – the Rake receiver coherently combines the finger outputs using complex conjugates of estimated channel coefficients to estimate the modulation symbol. Figure 3 shows a simple example
in which two despread values are combined (x1 and x2, which correspond to
two signal paths). Each despread value consists of a signal component (s), an interference component (i), and a noise component (n). When combining the values, the Rake
