Comparative Performance of Digital Data Transmission Systems in the Presence of CW Interference

During the last decade there has been a considerable amount of work done on the analysis of digital data transmissions in an interference environment. With few exceptions, the type of additive interference considered is normal noise. This paper treats the case where the interference consists of CW that falls within the pass band of the receiver. The results obtained can also be utilized to ascertain system performance in the presence of interference from similar systems and for certain classes of interrupted CW (ICW) interference. The performance of differential phase-shift, coherent phase-shift, amplitude-keyed, frequency-shift and time-shift binary digital data transmissions is determined. The average digit error probability is taken as the measure of system performance. The element of uncertainty involved in the CW interference analysis is due to random variation in the phase angle between the signal and interference. The performance of systems employing angle modulation is found to be independent of this phase angle for certain values of the interference frequency. In general, it is shown that the digit error probability varies as the arc cosine of a function of the signalto-interference ratio, the function being dependent on the system under consideration. It is shown that, of the systems investigated, coherent phaseshift keying is the best transmission technique in the face of CW interference. The digit error probability in a differential phaseshift-keyed transmission is found to be a sensitive function of the frequency of the interfering tone, and depending on this frequency, can be quite different from that obtained in a coherent phase-shiftkeyed transmission. Frequency-shift keying is found to exhibit the lowest threshold of the noncoherent systems considered, while time-shift keying is found to give an improvement of approximately 4 db over a simple amplitude-keyed system.