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An analytical and numerical investigation of the performance characteristics of partially coherent system techniques which consist of 1) the squaring-tracking loop, 2) the pilot-tone tracking loop, and 3) the differential phase-shift keying (DPSK) technique is discussed. Performance characteristics (error probabilities) are obtained under a unified receiving systems framework, with commonality expressed in terms of the receiver data and reference acquisition channel bandwidths and equal total transmitted power conditions. The modulation addressed is binary phase-shift keying (PSK), operating over a Gaussian noise channel with nonstationary phase characteristics. System performance is expressed analytically, computed numerically, and illustrated graphically with the following conclusions. The squaring-tracking loop technique provides the best performance and closely approximates coherent PSK performance when reference smoothing over several bauds is employed. The performance of the squaringtracking loop system and the DPSK system are comparable within a decibel for tracking loop averaging over 1 baud. Performance of the pilot-tone system depends critically upon the tracking loop bandwidth and the power allocation between pilot carrier and information sidebands. In no case considered does the pilot-tone system outperform the squaring-tracking loop system. On the basis of minimum error rate, the systems can be ranked as follows: 1) the squaring-tracking loop system, 2) DPSK, and 3) the pilottone system. At large signal-to-noise ratios, pilot-tone systems can outperform DPSK.