# Regarding Algebraic Codebook in CELP

Started by August 19, 2003
 Hi all, I need help in estimating the positions and pulses of algebraic codebook it is said in the standards (etsi 05.90) : "First, for each of the five tracks the pulse positions with maximum absolute values b(n) are searched.From global maximum value for all the pulse positions is selected.The first pulse i0 is always set into the position corresponding to the global maximum value. Next, four iterations are carried out. During each iteration the position of pulse i1 is set to the local maximum of one track. The rest of the pulses are searched in pairs by sequentially searching each of the pulse pairs {i2,i3}, {i4,i5}, {i6,i7} and {i8,i9} in nested loops. Every pulse has 8 possible positions, i.e., there are four 8x8-loops, resulting in 256 different combinations of pulse positions for each iteration. In each iteration all the 9 pulse starting positions are cyclically shifted, so that the pulse pairs are changed and the pulse i1 is placed in local maximum of different track. the rest of the pulses are searched also for the other position in the tracks. At least one pulse is located in position corresponding to the global maximum and one pulse is located in a position corresponding to one of the 4 local maxima." my confusions is around: 1. what is the different between global maximum and local maximum? what is a global maximum and a local maxima ? 2. after searching for the global maximum from each iteration of each track... is i0 replacing the pulse corresponding to the global maximum ? 3. what is the meaning of "The first pulse i0 is always set into the position corresponding to the global maximum value" ? 4. what is the meaning of "During each iteration the position of pulse i1 is set to the local maximum of one track" ? 5. what is the meaning of the 3rd paragraph? thanks alot regards, arida ---------------------------------