Here we
see each user receives multiple signals or replicas of the same information that has traversed different
propagation paths.
Generally speaking, a RAKE receiver has individual despreading functions called fingers [3]. One
typically assigns a finger to each arriving multipath. An example of a two-finger RAKE for User 1 is
shown in Fig. 7.14.
Above we have decided to have two entirely separate receiver chains to start a discussion on spectral
down conversion. In practice, a single spectral down-conversion operation is needed for all the
arriving multipaths. In doing so, a phase offset term is introduced since a single phase reference is
used for all the arriving multipaths. In fact, this term can be lumped together with the channel hj,k(t)
to produce an overall channel response.
If we remove the separate spectral down converters, then we have the simplified block diagram in
Fig. 7.15.
354 CHAPTER SEVEN
FIGURE 7.14 Two-finger RAKE receiver for User 1.
X X LPF
X X LPF
X1(t)
BS
#1
b(t ??“ t11) . h11(t) ?† ?†
b(t ??“ t12) . h12(t) ?† ?†
C1(t ??“ t11) ?†
C1(t ??“ t12) ?†
2P . cos[2pfct ??“ f11]
2P . cos[2pfct ??“ f12]
PG. Tc
dt
0
??«
PG
. Tc
dt
0
??«
FIGURE 7.15 Two-finger RAKE receiver block diagram.
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