Wireless Communications & Networking

APPENDIX D Spreading Codes Used in CDMA

In this appendix, we discuss Walsh codes, PN sequences, and Gold codes [1-9].

D.1 Walsh Codes

Walsh codes are used in direct sequence spread spectrum (DSSS) systems (such as IS-95, cdma2000, etc.). They are also used in frequency hopping spread spectrum (FHSS) systems to select the target frequency for the next hop (see Chapter 11).

Walsh codes are orthogonal codes. As such, if two Walsh codes are correlated, the result is intelligible only if these two codes are the same. As a result, a Walsh-encoded signal appears as random noise to a CDMA-capable mobile terminal, unless that terminal uses the same code as the one used to encode the incoming signal. We denote W(k, n) as Walsh code k in the n-length ...