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The key innovation of this proposal is the use of Time Modulated Ultra-Wideband (TM-UWB) technology to develop a low cost radio system that allows both voice communication and tracking positions of fire fighters inside buildings. This radio has several characteristics which make it ideal for tracking multiple individuals without line-of-sight. During Phase I we have performed many tests, including basic ranging, 3-D position determination, communication through fire, smoke, steam, and different kinds of walls. We have developed a new system architecture to track the location of a fire fighter, which is more scalable, less sensitive to errors due to multipath and wall penetration than the multilateration based scheme, and does not require clock synchronization. This scheme uses a two-antenna array which transmits two consecutive TM-UWB pulses. The fire fighter carries a receive-only TM-UWB tag which will receive these pulses. By measuring the Time Difference of Arrival (TDOA) of these pulses, the mobile unit can calculate the Angle of Arrival (AOA), which in turn gives the 3-D location. During Phase II, we will conduct more extensive tests to characterize the multipath effects, noise problem, material penetration, etc. We will implement the AOA architecture and construct prototype tags and a base unit.