Discontinuous Reception with Adjustable Inactivity Timer for IIoT

TL;DR

This paper describes the DRX process departing from a semi-Markov chain modeling and detail two ways to set DRX parameters to minimize the device power consumption while meeting a mean delay constraint, and proposes a more efficient method in which the transmit base station explicitly indicates restarting the timer through the control channel only when appropriate.

Abstract

Discontinuous reception (DRX) is a key technology for reducing the energy consumption of industrial Internet of Things (IIoT) devices. Specifically, DRX allows the devices to operate in a low-power mode when no data reception is scheduled, and its effectiveness depends on the proper configuration of the DRX parameters. In this paper, we characterize the DRX process departing from a semi-Markov chain modeling. We detail two ways to set DRX parameters to minimize the device power consumption while meeting a mean delay constraint. The first method exhaustively searches for the optimal configuration. In contrast, the second method uses a low-complexity metaheuristic to find a sub-optimal configuration, thus considering ideal and practical DRX configurations. Notably, within the DRX parameters, the inactivity timer (IT) is a caution time that specifies how long a device remains active after the last information exchange. Traditionally, a device implementing DRX will restart the IT after each data reception as a precedent to a low-power mode. The usual approach lies in restarting the IT whenever new data is received during this cautious period, which might sometimes needlessly extend the active time. Herein, we propose a more efficient method in which the transmit base station (BS) explicitly indicates restarting the timer through the control channel only when appropriate. The decision is taken based on the BS's knowledge about its buffer status. We consider Poisson and bursty traffic models, which are typical in IIoT setups, and verify the suitability of our proposal for reducing the energy consumption of the devices without significantly compromising the communication latency through extensive numerical simulations. Specifically, energy-saving gains of up to 30% can be obtained regardless of the arrival rate and delay constraints.

Figures (7)

• Figure 1: DRX mechanism. There are three states: (green) high consumption state in continuous reception, (yellow) high consumption state during $\text{T}_{\text{on}}$, and (red) low-power state where the interface does not read the downlink control channel. Note that the number of TTIs associated with the low-power state in the DRX long cycle is greater than that associated with that state in the DRX short cycle.
• Figure 2: Semi-Markov chain model for DRX. The continuous reception and $\text{T}_{\text{on}}$ are high-consumption states and appear with green and yellow color, respectively, while the low-power states are colored in red. Short and long cycles are distinguishable by the size of the colorbar (longer for long cycles).
• Figure 3: a) Poisson traffic model where dashed line means instantaneous return (left), and b) bursty traffic model (right) for traffic generations. Every TTI in the active state means a packet arrival.
• Figure 4: Proposed inactivity timer handling linked to transmitter (Tx) buffer state (per-TTI scheduling buffer at the Tx).
• Figure 5: Performance analysis of power consumption for Poisson traffic (bars with dotted line edges) and bursty traffic model (bars with straight line edges) when the TTI is equal to a) 0.125 ms (top left), b) 0.25 ms (top right), c) 0.5 ms (bottom left), and d) 1 ms (bottom right). The traffic rate is adjusted within the range of 5 to 50 pkt/s.