capacity, and the crowding of regulated radio fre- quency spectrum favors systems that offer not only high bit rates but also high bit rates concentrated in smaller physical areas. Given the latest trends toward the use of wireless and mobile communications, a new metric called spatial capacity has evolved. Spatial capacity is a measure of the number of bits per second per square meter that can be supported. Table 15.7 compares the spatial capacities of several commonly used short-range networking technologies. There are three key factors of interest in selecting a short-range technology: the range over which the technology can operate, how much power it consumes, and the spatial capacity. As you can see in Table 15.7, while 802.11b can operate over a larger coverage area, up to 300 feet (100 m), it can support only 1Kbps per square meter. In a well-attended cafe or hotel lobby, that is not going to provide hotspot users with the capacity needed to work in a multimedia environment. On the other hand, while UWB has a very short range, only 30 feet (10 m), it can support 1,000Kbps per square meter, and it also consumes very little power as an added bonus. Spatial capacity, which is a gauge of data intensity, will be critical to servic- ing growing number of users in crowded spaces such as airports, hotels, conven- tion centers, and workplaces. UWB is expected to achieve a data rate of 100Mbps to 500Mbps across dis- tances of 15 to 30 feet (5 to 10 m), and it is anticipated that these high bit rates will give birth to applications that are not possible today. It is also expected that UWB units will be cheaper, smaller, and less power-hungry than today's devices. Table 15.7 Comparison of Short-Range Spatial Capacities Technology Power Range Spatial Capacity IEEE 802.11b 50 mW 100 m 1Kbps/m2 Bluetooth 30Kbps/m² IEEE 802.11a 200 mW 55Kbps/m² 0.2 mW 1,000Kbps/m² WPANs Short-range technology is an ideal way to handle networks of portable (battery- powered) electronic devices, including PDAs, digital cameras, camcorders, 