a large number of handoffs occurs among many small neighboring cells. An umbrella cell covers several microcells or picocells. The power level inside an umbrella cell is increased compared to the power levels used in the microcells that form the umbrella cell. When the speed of the mobile device is too high, the mobile device is handed off to the umbrella cell. The mobile device then stays longer in the same cell (in this case, the umbrella cell), reducing the number of handoffs and the work of the network. With FDMA, which is used in analog cellular systems, each user is assigned to a different frequency; everybody is speaking at the same time, but each conversation is on a different portion of the frequency band. FDMA is characterized as facilitat- ing what would today be called low capacity-approximately 60 users per cell. Given the number of users today, let alone what tomorrow will bring, FDMA alone can no longer handle the volume. The cost of FDMA handsets is low, as these are not smart devices. For example, an FDMA-based device does not know how to search for another frequency that has a better transmission quality associated with it. This approach is inexpensive for the user, but the service operator needs to have a transceiver for each channel, which means the base station cost is high. And because it's an analog technology, FDMA also consumes a great deal of power, and the cost associated with the power consumption is greater than with digital systems. The advantage of FDMA is that it doesn't need strict clocking devices to enable synchronization between the base stations, as would, for example, TDMA. As Fig- ure 13.5 shows, everybody uses the system at the same time, but each user is work- ing off a different frequency. Although analog FDMA systems are no longer common, with most analog sys- items having been decommissioned at this point, the FDM technique is still very important because it is required to divide the allocated spectrum into individual Spectrum Utilization User 1 User 2 User 3 Frequency 