mohatta2015.pdf
signal processing from power amplifier operation control point of view
signal processing from power amplifier operation control point of view
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THE MATH 133<br />
results, DFE and MLSD complexity have increased due to the need for most feedback<br />
taps and a larger state space, respectively. Compared to the previous figure,<br />
performance of each equalizer improves due to the lower delay spread of the channel.<br />
HALF-SYMBOL-SPACED CHANNEL<br />
IQ' 1<br />
LU<br />
m<br />
IQ 2<br />
10" 3 -2 0 2 4 6 8 10 12<br />
Eb/N0 (dB)<br />
Figure 6.11 BER vs. E b /N 0 for QPSK, root-raised-cosine pulse shaping (0.22 rolloff),<br />
static, two-tap, half-symbol-spaeed channel, with relative path strengths 0 and —1 dB, and<br />
path angles 0 and 90 degrees, 3 feedback taps.<br />
6.3.6.2 16-QAM results Let's return to the static, two-tap, symbol-spaced channel<br />
with relative path strengths 0 and —1 dB and path angles 0 and 90 degrees.<br />
Only now consider 16-QAM instead of QPSK. Modem BER is shown as a function<br />
oîE b /N t) (SNR) in Fig. 6.12. Both analytical (REF) and simulated (MFB) results<br />
are provided, the latter created through perfect subtraction of ISI from the previous<br />
and subsequent symbols.<br />
Relative to the QPSK results in Fig. 6.10, we see that all curves have shifted<br />
right. This is because 16-QAM pays a penalty in sending more than one bit on<br />
each orthogonal dimension. Otherwise, trends are similar.<br />
6.3.6.3 Fading results Now we consider fading channels. Consider the two-path,<br />
symbol-spaced fading channel (TwoTSfade). Each path experiences independent<br />
fading with average relative powers 0 and —1 dB. The phase angle settings are nó<br />
longer important, as the fading introduces a random, uniformly distributed angle. A<br />
block fading channel model is used, in which 2000 fading realizations are generated.<br />
For each realization, 200 symbols (plus edge symbols) are transmitted through the<br />
channel, noise is added, and the resulting signal is demodulated.<br />
Matched filter bound results were generated one of two ways. One is a semianalytical<br />
approach (labeled REF). For each fading realization, a channel gain is