Patent ID: 7822138
Filing Date: 2010-10-26
Classification: H03M

Abstract:
1. A calculating apparatus for use in a maximum likelihood detector, the calculating apparatus comprising: a receiver to receive convolution encoded data which may include added noise, the convolution encoded data having a constraint length; a first calculator to calculate a first component of a first path metric difference between two state sequences, each state sequence being a possible state sequence corresponding to a section of received data of length equal to said constraint length, the two state sequences starting at a common state and ending at a common state, said first calculator being adapted to calculate said first component using said received data and using convolution encoding parameters of said received data, wherein the first component is independent of the two state sequences; and a second calculator to calculate a second component of said first path metric difference using said two state sequences, wherein the second component is independent of said received data, and said second calculator is adapted to use the first and second components to determine a relative likelihood that each of the two state sequences corresponds to the section of received data, wherein: said second calculator is adapted to calculate a first component of a second path metric difference between a first of said two state sequences and a third state sequence having the same length as the first sequence, the third state sequence starting at a same state as a fourth state sequence and ending at a same state as the fourth state sequence, and the third sequence and the first sequence having one common end state, but the third sequence and the first sequence each having a different second end state, using said first path metric difference and using a path metric difference between the third and fourth state sequences; said first calculator is adapted to calculate a second component of said second path metric difference using said convolution encoded data, and to use the first component and the second component of the second path metric difference to obtain relative likelihoods that the first and third sequences correspond to the section of received data; and said first calculator is adapted to calculate a first part of the second component of said second path metric difference using the first and third sequences, said first part being independent of the convolution encoded data; and said first calculator is adapted to calculate a second part of the second component of said second path metric difference using the convolution encoded data, said second part being independent of said common end state of the first and third sequences.