A Tractable Model of the LTE Access Reservation Procedure for Machine-Type Communications

TL;DR

This paper introduces a low-complexity, analytical model for LTE's access reservation protocol tailored for Machine-Type Communications, accurately estimating outage probability considering preamble and grant limitations.

Contribution

It provides a novel, closed-form model that captures key LTE access constraints and improves upon existing models by accurately predicting outage events for MTC devices.

Findings

Model accurately estimates outage probability

Supports large number of MTC devices

Matches well with LTE simulation results

Abstract

A canonical scenario in Machine-Type Communications (MTC) is the one featuring a large number of devices, each of them with sporadic traffic. Hence, the number of served devices in a single LTE cell is not determined by the available aggregate rate, but rather by the limitations of the LTE access reservation protocol. Specifically, the limited number of contention preambles and the limited amount of uplink grants per random access response are crucial to consider when dimensioning LTE networks for MTC. We propose a low-complexity model of LTE's access reservation protocol that encompasses these two limitations and allows us to evaluate the outage probability at click-speed. The model is based chiefly on closed-form expressions, except for the part with the feedback impact of retransmissions, which is determined by solving a fixed point equation. Our model overcomes the incompleteness of the existing models that are focusing solely on the preamble collisions. A comparison with the simulated LTE access reservation procedure that follows the 3GPP specifications, confirms that our model provides an accurate estimation of the system outage event and the number of supported MTC devices.