Welcome to the World of CDMA
The long code is a period 242-1 LFSR sequence
that is used for spreading the reverse link. There is only one long code sequence.
Different stations are distinguished not by the sequence itself but by its relative
phase. The fact that the long code is added to each of the two (I and Q)
short code sequences ensures that cross correlations between the signals from
distinct stations are always small.
This addition property of LFSR sequences is exploited in the long code generation process for the reverse link spreading. A 42-bit number, the Long Code Mask, is used to select particular bits of the 42-bit long code generator register. The selected nodes are summed, modulo 2. The resultant of the sum, that is, the modulo-2 inner product of the generator state with the mask, is the generator output corresponding to that mask.
It can be shown that each distinct mask results in a distinct phase. The Long Code Mask thus serves as a reverse link address.
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