d matrix M has the same call on two separate columns, and d; the coverage areas C and D have some overlap. 7 If a single call served nearly equally by two antenna faces uses capacity resources equivalent to two calls, then that same call in soft handoff is using the resources of four calls. And there is no reason the number of simultaneous signals is limited to two. Some wireless telephone systems al- low up to six simultaneous forward transmissions of the same call, so one of those calls would use the system resources of 36 calls. The reality of multiple-cell soft handoffs may not be this bad. The user terminal com- bines the soft handoff channel replications with its rake filter to get a clearer signal. The total resource consumption of a k-cell soft-handoff call is probably less than k2, but it still uses a lot of CDMA resources. Part of good CDMA design is avoiding large areas with multiple nearly equal serving cell sectors. 28.3.3 Orthogonal codes Orthogonal codes also can be put into the CDMA system of equations by increasing the Mbb terms. In Eq. (28.17) we saw that Mbb = a + 1 - Ob, where a is the spreading gain divided by Eb/No and is the number of calls served by antenna face b. If the orthogo- nality is perfect so that the base station and user terminal do a perfect job of filtering out the other forward channels, then Mbb = a for all serving antenna faces b, no mat- ter how many calls are being served up to the maximum number of orthogonal chan- nels. In cdmaOne, the maximum number of orthogonal calls is about 60, depending on how many codes are used for paging and access. This number is about 250 for cdma2000 or W-CDMA. 8 7In the CDMA equations without soft handoff, all the coverage areas are disjoint; the intersec- tion of C and D, C n D, is the empty set . Forward-direction soft handoff creates overlap, SO the intersection is not empty, C D # . 8The reason the number of calls is about 60 or 250 is that some of the codes are reserved for sig- naling, and the number reserved for signaling can vary. D