Multi-segment vector quantizer for a speech coder suitable for use in a radiotelephone

A method of vector quantizing a reflection coefficient vector, the reflection coefficient vector having M elements, the reflection coefficient vector representing an input speech signal, the method comprising the steps of:

• a) providing a first array of predetermined vectors of reflection coefficients, each predetermined vector having a plurality of L elements, where L<M;
• b) correlating the input speech signal in order to form first segment correlations;
• c) selecting a first selected vector from the first array of predetermined vectors;
• d) calculating a first segment residual error corresponding to the first selected vector and the first segment correlations;
• e) repeating steps c) and d) for each predetermined vector of the first array of predetermined vectors;
• f) choosing a vector from the first array having lowest first segment residual error, forming a first chosen vector;
• g) defining, responsive to the first chosen vector and the first segment correlations, a set of second segment correlations;
• h) providing a second array of predetermined vectors of reflection coefficients, each predetermined vector having K elements, where L+K.ltoreq.M;
• i) selecting a second selected vector from the second array of predetermined vectors;
• j) calculating a second segment residual error corresponding to the second selected vector and the set of second segment correlations;
• k) repeating steps i) and j) for each predetermined vector of the second array;
• l) choosing a vector from the second array having lowest second segment residual error, forming a second chosen vector;
• and
• m) combining at least the first chosen vector and the second chosen vector to form a quantized reflection coefficient vector.