Designing reliable home-automation networks based on unidirectional nodes

There has been an increasing interest in home automation over the last few years. In particular, applications such as intelligent illumination, heating, and ventilation, allow reducing the overall energy consumption and improve comfort in our everyday lives. To implement such applications, multiple sensors and actuators often need to be connected into networks typically communicating over radio signals. Since there may be a considerable amount of packet losses due to interference in the network, most available technologies are based on bidirectional devices or nodes with the capability of acknowledging packets, and performing retransmissions if necessary. On the other hand, bidirectional nodes are expensive and rapidly increase costs of a home-automation network, in particular, as the number of nodes increases. Alternatively, we can use unidirectional nodes, which can either send or receive data and, hence, are considerably less expensive. However, since unidirectional nodes are unable to perform carrier sensing or acknowledge packets, the resulting network is strongly unreliable. To overcome this predicament, we propose a design technique that allows guaranteeing a reliable communication based on unidirectional nodes. Our technique consists in making each transmit-only node in the system send a sequence of packets with constant inter-packet time or separation. We prove analytically that, with the proposed technique, it is always possible to guarantee that at least one packet of each sequence reaches its receiver on time. We further evaluate our approach with a simulation based on OMNeT++.