Page 307 - Satellite Communications, Fourth Edition

Digital Signals 287

Figure 10.3 Encoding of 11010010 in (a) binary polar NRZ and (b)
quaternary polar NRZ.

symbol period is seen to be equal to twice the bit period, and the symbol
rate is
1
R sym (10.2)
T sym

The symbol rate is measured in units of bauds, where 1 Bd is one symbol
per second.
The periodic time of the squarewave having the greatest symbol
repetition frequency is 2T sym , which is equal to 4T , and hence the
b
bandwidth, compared with the basic binary waveform, is halved. The
bit rate (as distinct from the symbol rate) remains unchanged, and
hence the bandwidth utilization in terms of bits per second per hertz
is doubled.
In general, a waveform may have M levels (sometimes referred to as
an M-ary waveform), where each symbol represents m bits and
m log M (10.3)
2
The symbol period is therefore

T sym mT b (10.4)