Long Code Mask

The long code mask is a 42-bit number that serves as a logical address for Reverse CDMA Channel spreading codes. It is used to select specific bits from the long code linear feedback shift register to be added, modulo-two, in order to produce the actual long code, at the proper phase. This method is taking advantage of one of the peculiar properties of maximal length shift register sequences (see the LFSR page). The logic is shown in Figure 1.

Figure 1. Long Code Mask logic.

When transmitting on an access channel, a mobile station constructs the mask from the base station identity, the paging channel number, and the access channel number. When transmitting traffic, a mobile station uses a mask constructed from its Electronic Serial Number.

Figure 2. Long code mask contents.

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Copyright © 1996-1999 Arthur H. M. Ross, Ph.D., Limited