mohatta2015.pdf

CHAPTER 7
ADVANCED TOPICS
In the previous chapter we considered MLSD, which provides one way to account for
ISI rather than removing it and minimizes sequence error rate. In this chapter we
consider another such approach, maximum a posteriori symbol detection (MAPSD),
which minimizes symbol error rate. Next we introduce the notion of coding, in
which additional symbols are transmitted to provide error detection and/or error
correction at the receiver. To do this well, generation of soft information (reliability
or confidence measures) in the equalization process is needed. Finally, we explore
ways of performing equalization and decoding together, taking better advantage of
the structure that the coding gives the received signal.
7.1 THE IDEA
We start with an introduction to MAP symbol detection. Extracting soft information
from different equalization approaches is discussed. The section ends with a
discussion of joint demodulation and decoding.
7.1.1 MAP symbol detection
In the previous chapter, we took advantage of the fact that symbols can be only
+1 or —1, allowing us to hypothesize symbol sequences and find the sequence that
best fits the received data samples. Such an approach minimizes the chance of
Channel Equalization for Wireless Communications: From Concepts to Detailed 151
Mathematics, First Edition. Gregory E. Bottomley.
© 2011 Institute of Electrical and Electronics Engineers, Inc. Published 2011 by John Wiley L· Sons, Inc.