Importance

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Abstract

Each of the M basic vectors in a noise code book 260 is multiplied by a factor .+-.1 in a sign adder 270 and combined in an adder 280 to create 2.sup.M noise signed vectors. The characteristic of the binary Gray code is utilized as follows. A change .DELTA.G.sub.u obtained between a noise signed vector based on a signed word i of the binary Gray code and a noise sign vector based on a sign word u adjacent to the sign word i and different from the sign word i only in a predetermined bit position v is used in such a manner that a sign word u' which is next to reverse the bit position v on the Gray code sequence can express a change .DELTA.G.sub.u' from the noise signed vector by utilizing the fact that the sign word u' differs from the sign word u only in one bit position w excluding the bit position V. Thus, calculation is simplified, increasing the vector search speed.

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First Claim