On the Information Loss of the Max-Log Approximation in BICM Systems
Journal article, 2016

We present a comprehensive study of the information rate loss of the max-log approximation for M-ary pulse-amplitude modulation (PAM) in a bit-interleaved coded modulation (BICM) system. It is widely assumed that the calculation of L-values using the max-log approximation leads to an information loss. We prove that this assumption is correct for all M-PAM constellations and labelings with the exception of a symmetric 4-PAM constellation labeled with a Gray code. We also show that for max-log L-values, the BICM generalized mutual information (GMI), which is an achievable rate for a standard BICM decoder, is too pessimistic. In particular, it is proved that the so-called harmonized GMI, which can be seen as the sum of bit-level GMIs, is achievable without any modifications to the decoder. We then study how bit-level channel symmetrization and mixing affect the MI and the GMI for max-log L-values. Our results show that these operations, which are often used when analyzing BICM systems, preserve the GMI. However, this is not necessarily the case when the MI is considered. Necessary and sufficient conditions under which these operations preserve the MI are provided.

Author

Mikhail Ivanov

Signals and Systems, Kommunikationssystem, informationsteori och antenner, Communication Systems

Christian Häger

Signals and Systems, Kommunikationssystem, informationsteori och antenner, Communication Systems

Fredrik Brännström

Signals and Systems, Kommunikationssystem, informationsteori och antenner, Communication Systems

Alexandre Graell i Amat

Signals and Systems, Kommunikationssystem, informationsteori och antenner, Communication Systems

Alex Alvarado

UCL

Erik Agrell

Signals and Systems, Kommunikationssystem, informationsteori och antenner, Communication Systems

IEEE Transactions on Information Theory

0018-9448 (ISSN)

Vol. 62 3011 - 3025 7436797

Areas of Advance

Information and Communication Technology

Subject Categories

Communication Systems

DOI

10.1109/TIT.2016.2543740