51 research outputs found
Average age of information with hybrid ARQ under a resource constraint
Scheduling the transmission of status updates over an error-prone communication channel is studied in order to minimize the long-term average age of information (AoI) at the destination under a constraint on the average number of transmissions at the source node. After each transmission, the source receives an instantaneous ACK/NACK feedback, and decides on the next update without prior knowledge on the success of future transmissions. First, the optimal scheduling policy is studied under different feedback mechanisms when the channel statistics are known; in particular, the standard automatic repeat request (ARQ) and hybrid ARQ (HARQ) protocols are considered. Then, for an unknown environment, an average-cost reinforcement learning (RL) algorithm is proposed that learns the system parameters and the transmission policy in real time. The effectiveness of the proposed methods are verified through numerical simulations
Age-Energy Tradeoff in Fading Channels with Packet-Based Transmissions
The optimal transmission strategy to minimize the weighted combination of age
of information (AoI) and total energy consumption is studied in this paper. It
is assumed that the status update information is obtained and transmitted at
fixed rate over a Rayleigh fading channel in a packet-based wireless
communication system. A maximum transmission round on each packet is enforced
to guarantee certain reliability of the update packets. Given fixed average
transmission power, the age-energy tradeoff can be formulated as a constrained
Markov decision process (CMDP) problem considering the sensing power
consumption as well. Employing the Lagrangian relaxation, the CMDP problem is
transformed into a Markov decision process (MDP) problem. An algorithm is
proposed to obtain the optimal power allocation policy. Through simulation
results, it is shown that both age and energy efficiency can be improved by the
proposed optimal policy compared with two benchmark schemes. Also, age can be
effectively reduced at the expense of higher energy cost, and more emphasis on
energy consumption leads to higher average age at the same energy efficiency.
Overall, the tradeoff between average age and energy efficiency is identified
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