Long range wireless sensor networks using transmit-only nodes

Wireless sensor networks for environmental monitoring and agricultural applications often face long-range requirements at low bit-rates together with large numbers of nodes. Most existing wireless sensor networks use nodes with a short-range radio and use software protocols to schedule the nodes and co-ordinate multi-hop routing in order to minimise power usage. Nodes have a relatively small radio range up to a few hundred meters that is also affected by the crop growth stage and vegetation density [2]. Disadvantages of this approach include the complexity of software protocols required to co-ordinate the nodes' behaviour and the unreliable nature of the short range radio links that requires sophisticated fault tolerance mechanisms. An alternative design solution is to use low frequency, long-range radios to build a single-hop network of a base station with satellite sensing nodes [4]. This approach has the benefits of much simpler software protocols, and that transmissions in the 40 MHz band are expected to be more reliable in outdoor settings than short range transmission in the 433 MHz or 915 MHz band used by most existing sensor network radios.