Optimal Timely Scheduling in Wireless Networks with Energy Constraints

Abstract

We investigate scheduling problems in wireless networks in which the nodes that send information have an average transmit-energy constraint, and the channels experience fading. The nodes observe a physical phenomenon, and send their observations to a base station (BS). The base station requires packets to be received from each node in a timely manner. Since each node has a transmit energy constraint, using a transmission opportunity at all times is not optimum, as it incurs more energy expenditure. Also, it may happen that a packet transmission is not successful due to channel fading, which requires retransmissions, and hence, more average energy. We are interested in studying problems of scheduling channel resources to the transmit-energy constrained nodes for communicating packets in a timely manner. newlineIn the first problem, we consider a single source that communicates packets to a BS. The packet arrivals follow an i.i.d. Bernoulli process, and each packet is expected to reach the destination before a delay deadline; otherwise, the packet is dropped. The delay deadline is used to drop the packets that are not fresh, and hence, plays a role of pushing the packets as early as possible. Time is slotted, and the channel undergoes finite state flat fading. The channel state information (CSI) is fed back to the transmitter at the end of every time-slot, and hence, there is a one-slot delayed CSI at the transmitter (CSIT). Since, the transmitter has (one time-slot delayed) CSIT, and knows the distribution of the fading gain, it chooses transmit-energy from a set of energies. Because of fading (which is known at the transmitter after a delay of one time-slot), the chosen transmit-energy may not be sufficient to achieve the required signal-to-noise ratio (SNR), and hence, the transmitter may be required to retransmit the packet again.