Modulation and Coding Techniques in Wireless Communications

7

Coded Modulation

Andrey Trofimov

St. Petersburg State University of Aerospace Instrumentation, Russia

7.1 Principle of Coded Modulation

For uncoded M-ary transmission using signals, belonging to a signal set, or signal alphabet S, M = |S|, M = 2m, m is integer, data transmission rate is equal to:

(7.1)

where T is signalling interval. Hereafter the narrowband signalling is assumed, for example, PSK and QAM as most important cases. For such signal sets the bandwidth W used for transmission does not depend on number of signals M in signal set S, and it can be evaluated as:

(7.2)

where α is a pulse shape dependent constant. In particular, for signals of duration T with a constant envelope α = 2, for signals with envelope of sinc(·), transmitted with period T, α = 1. In further consideration we assume that the pulse shape is chosen and remains unchangeable, hence the value of α is constant for all cases of uncoded and coded systems considered in this chapter.

Ratio of transmission rate to bandwidth is called spectral efficiency. For uncoded transmission the spectral efficiency is equal to:

(7.3)

and as it follows from (7.1) and (7.2):

(7.4)

For coded data transmission the structure ...