Walsh functions allow multiple access interference among users in the same cell to be
eliminated on the forward link using the transmitter/receiver combination shown. On the
forward link, all Walsh functions in the same cell are synchronized and have zero correlation between each other. The functions are orthogonal (correlation between two different function equal 0) and orthonormal (correlation between the same function equal 1).
•The input user data (e.g. speech) is multiplied by an orthogonal Walsh function.
•IS-2000 can use up to 128 (256 for 3G-3X) orthogonal Walsh functions.
•The user data is then spread by the base station PN code and transmitted on the carrier.
These Walsh functions are not used for user identification on the reverse link since each
mobile in the same cell experiences a different delay and the Walsh functions that are received would not be synchronized. Walsh functions that are shifted in time with respect to one another do not always produce zero correlation.