Application: The logical channels, or means by which individual signals are separated, on the forward link are the Walsh words . After the PN chips common to the received forward-link signals have been removed, the resulting stream is the sum of time-aligned (or nearly so) Walsh words which may have different amplitudes and different polarities depending on the data symbols. Each of these individual Walsh words can be isolated or separated from this stream by using a correlator or a filter matched to the Walsh word assigned to that mobile. Ideally, there is no interference from any other Walsh word at the output of the correlators at the time the polarity of the data symbol is measured. Multipath and possible nonlinearities in the transmitter and receiver in practice produce some interference.

On the reverse link from a mobile to its base station, orthogonality or near orthogonality is achieved by the random nature of short segments of long PN code sequences. The Walsh-word symbols used on the reverse link are transmitted at a rate of 4800 per second. At the PN chipping rate of 1.2288 Mchips/sec, each Walsh word is spread by 256 random PN chips. The Walsh words from different mobiles are spread by different segments of 256 chips. At the base receiver, a signal is multiplied by a synchronized PN code which agrees in all 256 chips with the chips used to spread the Walsh word to which this channel of the receiver is tuned. Signals to which the receiver is not tuned also have their 256 PN chips multiplied by the receiver's 256 chips. Now, however, the two segments of 256 chips agree and disagree in about the same number of individual chip multiplications. Hence, the product of the two different 256-chip segments averaged over the Walsh-word is near zero; i.e., the segments are nearly orthogonal. For an example, see Correlators and Matched Filters in the GNL 170 key-word list.

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