r attenuation factor assumed, the lower the mutual interference between radios. A 35 percent voice activation level was also assumed. Figure 3.9 shows a contour plot of the signal-to-interference ratio, SJR, for a mobile handset as a function of its location. As shown in Figure 3.9, the interference for mobile units derives from the cell sites of other micro- cells. The lack of symmetry is explained by the specific choice of codewords in each of the microcells in this model. Here, we assume six active voice chan- nels per microcell. Modified five-stage LFSR sequences were used. The prop- agation attenuation is assumed to be the inverse third power of distance. Figure 3.9. Three-dimensional contour SJR plot for handset. Commercial Applications Figure 3.10. SJR versus number of users per cell. For the mobile-to-cell-site channel, the SJR at the cell-site receiver depends on the particular distribution of mobile handsets throughout the network. Figure 3.10 illustrates a typical example as a function of the num- ber of randomly distributed mobile handsets per microcell for the inbound direction. 3.6.3.3 Other System Issues In the IS-95 digital cellular standard, mobile units synchronize on the cell site by locking onto the strongest pilot signal which is continuously trans- mitted by each of the cell sites. In this TDD structure, a similar broadcast pilot signal can be sent by each cell site at the beginning of its TDD burst. In this TDD design, the cell-site packetized bursts are longer than the mobile units' packetized bursts to accommodate the additional time needed to send a short common broadcast burst. This short burst serves as a pilot signal for the mobile units for maintaining a lock on the specific cell-site sig- nal. For initial acquisition, one of the cell-site signals is used for this purpose. As in IS-95, this signal aids in the initial acquisition and provides paging information to the mobile units. Cell sites using different codewords for this purpose are used instead of offsets of the same PN sequenc