Comparison of duobinary and 4-level continuous phase frequency shift keying signals for narrowband land mobile radio applications

Abstract

The bit error rate performance of partial-response duobinary continuous-phase frequency shift keying (CPFSK), and full-response 4-level CPFSK are compared under the condition of equal RF spectral occupancy and equal data rate, for both Gaussian and Rayleigh fading channels. Incoherent limiter-discriminator detection is assumed for all cases. The spectral efficiency requirements of the FCC, for the allocated 220-222 MHz band for land mobile communications, are used to establish the system specifications. It is shown that 4-level CPFSK system significantly outperforms the 3-level duobinary CPFSK. This is due to the fact that the receiver bandwidth may be lowered for 4FSK thereby higher frequency deviation can be achieved resulting in higher SNR at the receiver which outweighs the noise margin advantage of duobinary system. Simulation systems are designed to measure the performance for both static and Rayleigh-fading narrowband channels.