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An Experimental Approach to CDMA and Interference Mitigation phần 6 docx
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128 Chapter 3
500
400
300
200
100
0
40x10 3
0 10 20 30
Normalized Time (Symbols)
L=64, K=32
C/I=-6 dB, P/C=6 dB
Eb/N0=2 dB
J BAID=2-15
Figure 3-37. CPRU acquisition sample.
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10
Eb/N0 (dB)
L=64, K=32
C/I=-6 dB, P/C=6 dB
J BAID=2-15
Figure 3-38. Accuracy of CPRU phase estimates.
3. Design of an All Digital CDMA Receiver 129
0.001
2
3
4
5
6
0.01
2
3
4
5
6
0.1
2
3
4
5
6
1
BER
0 2 4 6 8 10
Eb/N0 (dB)
L=64, K=32
C/I=-6 dB, P/C=6 dB
J BAID=2-15
AFC, PLL on
ideal
Figure 3-39. BER performance in the presence of frequency and phase errors.
where ˆ 'T T T () () () kkk is the residual phase error at step k, and
{±1±j} k c is the kth transmitted QPSK symbol on the useful traffic
channel. If we look at z k ( ) as a function of 'T( ) k we easily find that it is
not dependent on the particular value of k c , and it is periodic with period
S/ 2
zk A k k ª'T º ª'T º ^ cos sin ¬ ¼¬ ¼
ª'T º ª'T º cos sin ¬ ¼¬ ¼ k k ` (3.99)
(recall that A ! 0 by definition). As is seen from the plot of (3.99) in Figure
3-40, z k ( ) attains its maximum value 2A when the phase error is a multiple
of S/ 2 , i.e., when the phase loop is in lock. Re-considering noise and MAI,
z k ( ) needs filtering to yield a reliable lock metrics as in (3.97).
Before the AFCU and the CPRU have attained lock z k ( ) is affected by a
frequency offset. In such a condition 'T( ) k has a linear evolution with time,
and therefore the oscillating plot in Figure 3.40 is in a sense ‘swept’ on the
phase x-axis. If the forgetting factor is small, i.e., 1 L J , the lock metrics