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Bit Rate Compression for Modulation

IP.com Disclosure Number: IPCOM000081916D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Head, SM: AUTHOR [+3]

Abstract

This description relates to a method for the compression of delta coded sequences, especially those representative of speech waves. Relatedly, it should be appreciated that delta coding is a type of digital encoding, wherein only the variation in the analog level between two successive sampling instants is digitized. At any sampling instant, the sign of relative magnitude difference between a reference and the sampled value is representative as 1 or a 0, the reference being at the same time incremented or decremented by a unit amount correspondingly.

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Bit Rate Compression for Modulation

This description relates to a method for the compression of delta coded sequences, especially those representative of speech waves. Relatedly, it should be appreciated that delta coding is a type of digital encoding, wherein only the variation in the analog level between two successive sampling instants is digitized. At any sampling instant, the sign of relative magnitude difference between a reference and the sampled value is representative as 1 or a 0, the reference being at the same time incremented or decremented by a unit amount correspondingly.

If delta coded sequences are taken in groups of three bits at a time, then the 2/3/=8 possible codes (000, 001, 010, 011, 100, 101, 110, and 111) can be mapped into 2/2/=4 possible three-bit codes [000->000; 111->111; (001, 010, 100)->010; and (011, 101, 110)-> 101] with minimal information loss of transmission purposes. Also, the 8 codes can be mapped into 4 two-bit codes for storage purposes (000->00, 111->11; 101->10; and 010->01).

Central to the method is the fact that sequences of delta coded values (10111000) bear the same statistical properties as a run of independent events, such as a run of coin tosses (HTTHTT, etc.). In such runs, the probability of occurrence of a head (H) on the i/th/ toss is independent of the outcome of the prior i-1 tosses. Also, for any q bit string, the delta sum is equal to the algebraic sum of its transitions thus, a(i)+a(i-1)+a(i-2) =Epsilon is...