Vector search method

Abstract

Each of the M basic vectors in a noise code bookis multiplied by a factor ±1 in a sign adderand combined in an adderto create 2noise signed vectors. The characteristic of the binary Gray code is utilized as follows. A change ΔGobtained 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 ΔGfrom 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.