Near-far interference experiments using minimum cost hardware

Near-far interference is shown to be a potentially serious problem for low cost digital wireless communications systems. Low hardware cost implementations of both binary frequency shift keying (BFSK) and binary phase shift keying (BPSK) transmitters are evaluated. The near-far interference performances of these two modulations are compared. Path loss is the only propagation effect considered. Two significant results of these experiments are: (1) unfiltered BPSK is far more likely to cause near-far interference than unfiltered BFSK, and (2) to avoid near-far interference, modulations must be used that constrain the occupied spectrum within -70 dB to -100 dB relative (dBr) to the signal spectral peak.