Age of Information of Dual-Sensor Information Update System With HARQ Chase Combining and Energy Harvesting Diversity

A novel status update information system is designed by jointly considering wireless energy harvesting diversity, status update transmission diversity, and hybrid automatic repeat request with chase combining (HARQ-CC) diversity, which consists of two sensors and one destination. The two sensors, which have finite-sized batteries, harvest energy from a Bernoulli process, and cooperatively deliver the status update to the destination by sharing a common information source. In addition, the two sensors synchronously operate in half-duplex (HD) mode and are triggered by a common control center. We first propose the sensor energy harvesting model that can be represented by Markov chain (MC) and develop the construction method of the transition matrix of sensor battery energy states as well as the stationary distributions. Secondly, the average age of information (AoI) of the proposed dual-sensor status update system is derived in terms of a closed-form expression by accurately calculating the statistical descriptions of the maximal number of the retransmissions of an update packet and the service time of one packet. Compared with traditional single-sensor system, the proposed dual-sensor system not only harvests more energy, but also has a smaller average AoI.