Characterizing Energy-Delay Tradeoff in Hyper-Cellular Networks with Base Station Sleeping Control

IEEE Journal on Sel. Area Commun.,
Published Date:2015-2
Base station (BS) sleeping operation is one of the
effective ways to save energy consumption of cellular networks,
but it may lead to longer delay to the customers. The fundamental
question then arises: how much energy can be traded off by a
tolerable delay? In this paper, we characterize the fundamental
tradeoffs between total energy consumption and overall delay in
a BS with sleep mode operations by queueing models. Here, the
BS total energy consumption includes not only the transmitting
power but also basic power (for baseband processing, power
amplifier, etc) and switch-over power of the BS working mode,
and the overall delay includes not only transmission delay but
also queueing delay. Specifically, the BS is modeled as an M/G/1
vacation queue with setup and close-down times, where the BS
enters sleep mode if no customers arrive during the close-down
(hysteretic) time after the queue becomes empty. When asleep, the
BS stays in sleep mode until the queue builds up to N customers
during the sleep period (N-Policy). Several closed-form formulas
are derived to demonstrate the tradeoffs between the energy
consumption and the mean delay for different wake-up policies by
changing the close-down time, setup time, and the parameter N.
It is shown that the relationship between the energy consumption
and the mean delay is linear in terms of mean close-down time,
but non-linear in terms of N. The explicit relationship between
total power consumption and average delay with varying service
rate is also analyzed theoretically, indicating that sacrificing
delay cannot always be traded off for energy saving. In other
words, larger N may lead to lower energy consumption, but there
exists an optimal N* that minimizes the mean delay and energy
consumption at the same time. We also investigate the maximum
delay (delay bound) for certain percentage of service and find that
the delay bound is nearly linear in mean delay in the cases tested.
Therefore, similar tradeoffs exist between energy consumption
and the delay bound. In summary, the closed-form energy-delay
tradeoffs cast light on designing BS sleeping and wake-up control
policies which aim to save energy while maintaining acceptable
quality of service.

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