Performance of Biphase Digital FM Transmission

The observation by several investigators that the spectrum of a digital FM signal is concentrated near the carrier frequency for small frequency deviation ratios (
h
) led Tjhung and Wittke [1] to investigate the probability of error to determine the optimum bandwidth-bit period (
BT
) product and optimum
h
. Their results using discriminator demodulation showed that for a probability of error of 10
^-4
the optimum values are
h = 0.7
and
BT = 1.0
. Further, their results showed that in some narrow-band cases digital FM is superior to PSK. The purpose of this correspondence item is to extend Tjhung and Wittke's results by applying their method to a biphase [2] baseband signal. Such a signal has the well-known advantage of facilitating synchronization since a zero-crossing occurs during each bit.