1. A speech signal encoding decoding method using A-b-S vector quantization comprising the steps of: generating basic vectors having a predetermined vector dimension size by applying an arbitrary shift to a code sample retrieved from a random series of code samples; and generating code vectors constituting a code book, by extending said basic vectors according to a structuring process; and storing the random series in a ring buffer memory, and generating the basic vectors from the random series stored in the ring buffer memory, according to an overlapping vector generation process.