This paper introduces the work performed towards an Impulse Radio Wireless Sensor Network system. An overview of the fundamentals of the system is reported, from concept sections including applications and requirements, to the design and development of the hardware platform, networking protocols or routing algorithms. The low power, size and cost are key requirements influencing the whole system definition. An initial complete prototype has been designed, implemented and tested with Zigbee PHY. This has set the bases for the current Impulse Radio Sensor Network under development, for which the PHY has been designed and developed.