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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136 MAXIMUM LIKELIHOOD SEQUENCE DETECTION<br />
POWER CONTROL<br />
It)" 1<br />
Œ<br />
LU<br />
ω<br />
IQ" 2<br />
10 3 -2 0 2 4 6 8 10 12 14<br />
avg Eb/NO (dB)<br />
Figure 6.14 BER vs. E b /N 0 for QPSK. root-raised-cosine pulse .shaping (0.22 rolloff),<br />
fading, two-tap, symbol-spaced channel, with relative path strengths 0 and —1 dB, target-C<br />
power control.<br />
an option of transmitting a speech frame by dividing it up into multiple time slots<br />
and sending each slot on a different carrier frequency, which hopefully experiences<br />
different fading and interference. The speech frame is recovered by collecting bits<br />
from multiple slots and passing them through an FEC decoder. The coding is<br />
designed so that the FEC decoder performance depends on the average SINR of<br />
the different slots. Thus, speech quality is directly related to average BER, averaged<br />
over different fading realizations.<br />
However, there are other applications and systems for which average BER isn't<br />
the best way to measure performance. For example, consider an indoor, LTE system<br />
in which a short packet (1 ms) is sent over a nondispersive channel. Rate adaptation<br />
is used, depending on the performance of the receiver. A convenient measure of<br />
output performance is the notion of output SINR, (we will define this shortly). So for<br />
the example considered, it makes more sense to examine the distribution of output<br />
SINR, which is related to the distribution of data rates that can be supported. For<br />
example, the median output SINR will determine the median data rate supported.<br />
The data rate supported translates into how fast data is transported, which impacts<br />
the overall delay experienced by the user (latency).<br />
How do we measure the output SINR of an equalizer? One approach is to use<br />
analytical expressions that relate performance to the input SNR, the channel coefficients,<br />
and the equalization approach. While such analysis is highly useful in<br />
gaining insight into the performance of a particular equalization approach, there<br />
are some limitations to such analyses. Analysis can be difficult, cumbersome, and