 inbound. Hence, for inbound channels, typically only one mobile laptop can transmit at any given time, using car- rier-sensed multiple access (CSMA) protocols. With S-CDMA on the more critical outbound channel, a much higher overall capacity can be achieved. The S-CDMA channel is limited by the multipath conditions in the propagation paths from the cell site on the wired LAN to the mobile laptop units. 3.5.5 Frequency of Reuse and Antenna Sectorization The primary advantage of direct-sequence spread-spectrum radios is that they allow reuse of the same frequency in adjacent cells in a multicellular network. Because narrowband radios are not designed to withstand much interference, narrowband radios in adjacent cells cannot share the same fre- quency band. If, as discussed above, the number of mobile users per cell is roughly the same for the same bandwidth per cell, a direct-sequence spread- spectrum radio system can employ frequency of reuse to attain a higher over- all network capacity. Figure 3.3 illustrates an idealized array of cells in a high-density network of many cells. In this configuration, each cell has six neighboring cells. For narrowband radios, each cell would have available only one-seventh of the total available bandwidth, while the direct-sequence spread-spectrum radios with 100 percent frequency of reuse would have available the entire bandwidth available in each cell. If a spread-spectrum system has as many mobile radios per bandwidth in each cell as a narrowband radio system, its overall capacity would be 7 times greater than that of the narrowband system. The actual achievable capacity depends on the tradeoff between many parameters in a network of direct-sequence radios. These parameters include the type of direct-sequence spread-spectrum modulation, processing gain, coding gain, level of network synchronization, data rates, use of power con- trol, specific code selection, and voice activation. Environmental issues include cell size and multipath/propagation conditions. In Section 3.6, we 