We present a UWB two-way communication system with novel PHY and MAC layers, for low-rate communications with multitude of low-cost devices in ultra low power consumption. The system features a novel multiple access protocol called interleaved impulse radio. In this simple protocol the transmission is done in short bursts of about 100ns with large gaps between them. During the gaps other users can send their own bursts. This multiple access mechanism is easy to implement, ad-hoc (no central control needed) and provides immunity from near far problem and multipath. The wide bandwidth of the UWB provides frequency diversity and accurate ranging. Reliable & robust communication is achieved in a variety of multi-path environments. High level of reliability is provided by mesh networking the tags, i.e. using other tags to transfer information to the destination in case no direct link is possible. The system design targets Active RFID and sensor networks for wide area of applications ranging from asset management and tracking applications in industrial environments, to military and security applications. In order to achieve "Total Asset Visibility", the system can read information from devices, write information, and locate tagged objects. The single chip tag is fabricated in 0.13um CMOS technology, and tags are able to operate for 5 years from a coin battery.