  This work studies the average age of information (AoI) of a monitoring system
in which two sensors are sensing the same physical process and update status to
a common monitor using their dedicated channels. Generally, using redundant
devices to update the status of a process can improve the information
timeliness at the monitor, but the disordered arrivals of updates also make the
AoI analysis challenging. To that end, we model the system as two M/M/1/1
parallel status updating queues. By leveraging tools from stochastic hybrid
system (SHS), we provide a general approach to analyze the average AoI, whereas
a closed-form expression can be obtained when the status arrival rates and/or
the service rates are the same for the two sensors. Numerical results validate
the correctness of the theoretical analysis.
