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Abstract
Some new unidigit, viz. SQ-PCM, HU-PCM, and multidigit, viz. Δ-ΔM, Feedback-PCM and Δ-PCM, PCM systems have been developed and their performances evaluated and compared with those of other similar systems, viz. Δ-M, conventional PCM and D-PCM. It is shown that among all the unidigit systems, HU-PCM has the best coding characteristics and of the multi-digit systems, Δ-ΔM is the best. For RF transmission, PSK-mode has the greatest communication efficiency. HU-PCM is superior to conventional PCM up to a transmission rate of 60 Kbits/sec. and the Δ-ΔM, with a closed loop compandor at a transmission rate of 60 Kbits/sec. is equivalent to a 9-digit PCM system. In an n-digit ΔM, the rate of decrease of the quantizing noise is exponential as in the conventional PCM, moreover the optimum SNR's in n-ΔM are much better than in any other PCM system.