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This paper proposes a novel parallel detection scheme for enhancing the sensitivity of coherent optical time domain reflectometry (C-OTDR). The proposed scheme is based on frequency-division multiplexing using a phase modulator and software processing. The performance advantages of the proposed method are clarified experimentally by comparison with a conventional C-OTDR. The detection sensitivity performance with the proposed method, operating at 40 frequency-division multiplexing, was improved by about 8 dB compared with the conventional method. We also clarified that the 3 dB resolution and Rayleigh dead zone of conventional C-OTDR and the proposed method were almost the same at a spatial resolution of 1 km.