ise. In our S-CDMA system, however, we are limited not by noise but rather by interference caused by other Commercial Applications spread-spectrum signals. Here, we consider an alternative to the matched fil- ters based on Ruprecht [26]. Rather than assign a unique orthogonal codeword to each mobile unit in a microcell, an alternative S-CDMA scheme is to assign to each mobile unit a common codeword with a unique time slot. Suppose we have three mobile units, each using a common spreading codeword. As illustrated in Figure 3.5, if each mobile radio uses a different time offset from the basic reference derived from the base station's broadcast signals, then the common inphase and quadrature codeword-matched filters will have at their outputs differ- ing peaks, owing to the different offset transmissions of each mobile unit. As shown in Figure 3.5 with the in-phase matched filter, signals from the different mobile unit signals can then be separated at the output of the com- mon matched filter. This method for achieving a set of orthogonal signals is referred to as the time-slotted S-CDMA technique. Recall that the RAKE processor in Qualcomm's system is designed to separate the different mul- tipath signals from a mobile unit if the multipath delays are longer than the chip time. Such a RAKE processor combines the outputs to take advantage of this path diversity. Note that this time-slotted S-CDMA technique also requires time syn- chronization and that orthogonality is provided by time-slot assignment sim- ilar to that in TDMA. The output of the matched filter is essentially a TDMA signal at the bit level. Thus, in a microcell, there are as many S-CDMA orthogonal signals as TDMA signals. The important difference is that in a high-density application with many microcells in a network, S-CDMA can MATCHED FILTER Figure 3.5. Time-slotted S-CDMA with matched filters. Spread-Spectrum CDMA for PCS and PCN tolerate more interference from other microcells and thus allow greater fre- quency of reuse, which results in an overal