Adaptive Multicarrier CDMA Space-Time Receivers - Adaptive Signal Processing in Wireless Communications - page 293

Table 10.2 Simulation Parameters

Parameter Value Comment

BW max

5 MHz Maximum bandwidth

M 2 Number of antennas

f c 1.9 GHz Central carrier frequency

f D 8.8 Hz Doppier frequency (5 kmph)

Δ f 200 Hz Frequency offset

f PC 1,600 Hz Frequency of PC updating

Δ PC ±0.25 dB Power control adjustment

±30 dB Power control stage

PC min

max

BER PC 5% Simulated PC bit error rate

δτ/δ t 0.049 ppm Time-delay drift

Δτ 4 chips Delay spread

L g 0 Guard interval length

N s 2 Number of multistages

β 0.22 Roll-off factor

2 N src + 1 9 Number of pulse samples

10.4.2 Validation of the Performance Analysis
In this section, we investigate the accuracy of the analytical performance analysis in sec-
tion 10.3.3 under realistic channel conditions. Indeed, we do not assume perfect chan-
nel identification; instead, we use the channel estimate provided by MC-STAR [32]. We
validate the Gaussian approximation (GA) of the residual interference by comparison
with simulation results. Since the SUB (Ω) is not known explicitly in this case, it has
been obtained from extensive simulations. We consider two configurations: DBPSK
M T- C DM A ( L =64, N c = 3) and DBPSK MC-DS-CDMA ( L =32, N c = 3). Figure 10.5
shows the link-level performances. It is seen, not surprisingly, that the GA is accurate
in the presence of moderate background noise. The accuracy of GA increases at larger
loads or at lower Doppler situations (speed of V = 5 kmph). Despite the realistic channel
model employed and the channel estimate errors, there is a very good match between
the analytical and simulation results for both MT-CDMA and MC-DS-CDMA in the
target BER region (5%). This suggests that the analytical evaluation is accurate in a low
Doppler situation.

10.4.3 Advantage of Full Interference Suppression
The imperfect frequency downconversion due to the instability of local oscillators
combined with the multipath effect destructs the subcarriers' orthogonality and hence
causes ICI. In this section we evaluate the advantage of full interference suppression
on the link-level performance of MC-CDMA. We plot the link-level performances of
M T- C DM A ( L = 64, N c = 3, C = 8) and MC-DS-CDMA ( L = 32, N c = 3, C = 8) with
MC-MRC (i.e., multicarrier receiver with MRC combining) and MC-ISR in Figure 10.6 .
It is clear that MC-ISR performs better than MC-MRC. Indeed, in low Doppler (speed of