In general there are two ways to reach sensors that are at a great distance. First, it can be achieved using a high performance radio, such as ultra narrowband at a low radio frequency. Narrowband radio can also be combined with high transmission power and using a relatively low radio frequency, such as 169 MHz. The lower radio frequency will give a longer range as long as the antenna size is scales accordingly. One example is the RC1701HP-MBUS4 module for Wireless M-Bus at 169 MHz. Another example of ultra narrowband radio is the Sigfox modules operating at 868 MHz with direct access to the cloud via base stations. If the available space for an antenna is limited, a good tradeoff can be 433 or 868/915 MHz, where a smaller antenna will have comparably better performance. Regardless of the operating frequency, a narrowband radio will improve the range.
Second, greater coverage can be achieved using multi-hop or mesh technology. In these cases the communication is done by using other nodes as “step-stones”. This is an efficient way of increasing the coverage when there are many nodes in the network, and the nodes are powered such that they can listen and retransmit radio packets at any time. An example of mesh technology is Tinymesh used to control and monitor street lighting, where each light pole is a node in the mesh network. Another example is Zigbee, that use mesh routing to get better indoor coverage at 2.45 GHz.
Last Update: August 8, 2017