Application: Four different types of signals or channels may be transmitted on the for-ward link in IS-95 systems. These signal types are the pilot, and the Synchronization, paging, and traffic channels. There is one pilot, up to and typically just one Synchronization channel, up to seven paging channels, and typically between 55 and 61 traffic channels depending on the number of paging channels. The total power transmitted on the forward link is divided among the four channel types with the pilot usually allocated more power than any other signal. The total number of forward-link channels transmitted at one time cannot exceed 64, the number of Walsh words available. The Walsh words allow separation of the individual channels or signals at their designated receivers in spite of the fact that all the signals occupy the same physical channel. Walsh words are orthogonal or mutually non-interfering which allows them to be separated and distinguished from one another in the absence of multipath on the forward link. See Orthogonal from the GNL 170 key-word list and Logical Channel from this GNL 180 key-word list.

Each forward link channel from a given base station is spread by the same Pseudo-random Noise (PN) sequence. This spreading, along with the use of the Walsh words , produces wideband PN signals which allow universal reuse of the available frequencies with acceptable levels of interference. Universal reuse increases capacity and facilitates soft and softer handoffs. The wideband spread signals also allow some multipath paths to be resolved and combined constructively by the RAKE-receiver fingers. This provides IS-95 signals with multipath protection and actually uses multipath power to increase the signal strength.

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© 1999 DR. ERNEST SIMO - SPACE2000