DIGITAL DOWNCONVERTER/DESPREADER FOR DIRECT SEQUENCE SPREAD SPECTRUM CDMA COMMUNICATIONS SYSTEM

摘要

A digital despreader and downconversion technique useful for spread spectrum communications receivers digitally tracks a timing phase of a PN sequence without the need for steering an external hardware clock. An additional benefit of the technique is the use of a receive filter (408) matched to the bandlimited transmit chip sequence prior to despreading which reduces the amount of noise present after despreading. A narrowband filter (404) also permits the use of a single A/D converter (406) in the receiver, IF sampling at a relatively low sample rate compared to other techniques. A method for reducing a total number of computations required thereby facilitating implementation in a single custom digital integrated circuit is also described. The inventive technique also is applicable to multi-channel implementations; method and apparatus for multi-channel applications also are described.