This performance
improvement is a direct result of exploiting the time diversity present in the wireless channel.
In Fig. 7.70, we present some uncoded BER simulation results for the downlink. The performance
curves are plotted against Eb/No, which is derived below, assuming QPSK modulation (generally
speaking).
(7.87)
Ec
No
S
N
Eb
No
# 1
PG
# 2
So(t) d(t) # aK
j1
Zhj(t) Z2
398 CHAPTER SEVEN
FIGURE 7.69 RAKE block diagram using K fingers.
Finger 1 Output
X
Despread
CCH
Despread
DCH
Depilot
& Gating
WMSA
Memory
+
Finger 2
Finger K
..
.
Received
Signal
RAKE
Output
So(t)
Combiner
@ t1
FIGURE 7.70 Receiver block diagram showing signal energies.
Despread
Symbols
to Bits
Ec
Es Eb
We can provide a more accurate definition in the sense of relating this to what was previously
defined earlier for the figure of merit. On the downlink, this is given as
(7.88)
Eb
No
Ec
Ior
# Ior
Ioc
# PG # 1
2
where fraction of the total power allocated to the DPCH channel of interest, form of SNR
or SIR using the total (common plus dedicated channels) for the transmitted power value, PG processing
gain of the channel of interest, and the factor of 1/2 is for conversion from the symbol-to-bits factor.
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