A frequency offset compensation method for ultra narrowband digital wireless modems

We evaluate the performance of the digital modulation schemes described in the APCO Project 25 FDMA specifications which can be used for applying the ultra-narrowband technology to the simple two-way radio systems, and discuss difficulties in the DSP implementation of the systems. We analyze the effect on the systems´ BER performance of the frequency-offset between the transmitter and receiver oscillators. And we present a frequency offset compensation method for improving the system performance. With the frequency offset compensation method implemented in the systems using DSP, the Eb/No performance degradation of about 1.0 dB was occurred at the BER of 10^-3 for 10 % of frequency offset.