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TOTAL Bandwidth Bit Assignment Algorithm for Multi-User Frequency-Domain Speech Coders

IP.com Disclosure Number: IPCOM000047232D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 4 page(s) / 79K

Publishing Venue

IBM

Related People

Irvin, DR: AUTHOR

Abstract

Channel efficiency in a group of frequency-domain speech coders may be increased by statistical multiplexing. In statistical multiplexing, bits defining portions of bandwidth are assigned to each individual coder. An algorithm for effective bit assignment is essential for reaching a high degree of compression. This disclosure provides an effective bit assignment algorithm for use with such a group. It concerns the overall or "global" bit assignment that divides the available bits among active coders. Only the active coders are considered. Each active coder will use more or less than its proportional fixed rate share of the channel bandwidth, as needed, in order to meet a signal quality criteria.

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TOTAL Bandwidth Bit Assignment Algorithm for Multi-User Frequency- Domain Speech Coders

Channel efficiency in a group of frequency-domain speech coders may be increased by statistical multiplexing. In statistical multiplexing, bits defining portions of bandwidth are assigned to each individual coder. An algorithm for effective bit assignment is essential for reaching a high degree of compression. This disclosure provides an effective bit assignment algorithm for use with such a group. It concerns the overall or "global" bit assignment that divides the available bits among active coders. Only the active coders are considered. Each active coder will use more or less than its proportional fixed rate share of the channel bandwidth, as needed, in order to meet a signal quality criteria. The basic algorithm given is a bit assignment method for distributing the encoding bit algorithm allocations among a group of frequency-domain speech coders. The distribution is made in a time-domain multiplex configuration on a common outgoing channel. A pool of active coders is defined among the total group of coders available to use the channel. Those which currently have voice activity traffic are deemed to be active. Each coder is assigned more or less of its proportional fixed rate share of the total channel bandwidth, as needed, to meet a signal quality criterion based on signal-to-noise ratio. The average signal-to-noise ratio of all of the active coders is determined, and the individual signal-to-noise ratio for each active coder is also determined. Those coders having better than average signal-to-noise ratio will have bits taken away from their allocations to form a pool of available bits. The pool of available bits is reassigned or allocated to those coders having less than average signal-to-noise ratio. If C represents the total channel capacity of available bits per frame and A(j) represents the number of coders which are active during a frame j, operation begins at a fixed rate by equally partitioning the available channel bandwidth between the active coders. Each coder will thus receive a number of bits N(i,j) which represents the number of bits assigned to the ith coder during a frame j. Equation (1) represents the partitioning. N(i,1) = C/A(1) (initial frame) (1) A second constraint is that the total sum of the N bits assigned for each coder must equal the total C. This is set forth in Equation (2). SUM N(i,j) = C sum from i = 1 to A(j) (2) Bit assignments to a coder i in a frame j+1 will be based on an estimate of the performance of coder i during the preceding frame j, as assessed by locally operating monitor device. Each coder submits a request for bits for frame j+1 through an arbiter circuit. The function of the arbiter is to ensure that constraint 2 in Equation (2) above is met. The arbiter's decision is a set of changes in bit assignments signalled to each coder and decoder denoted by a delta(i,j) with the following constraints:...