Analysis of the LTE Access Reservation Protocol for Real-Time Traffic

TL;DR

This paper analyzes the LTE access reservation protocol for real-time M2M traffic, focusing on throughput under realistic conditions where resources are limited and collision detection may fail, impacting timely data transmission.

Contribution

It provides a novel analysis of LTE's two-phase reservation protocol considering resource variability and collision detection limitations, which are often overlooked.

Findings

Throughput decreases with limited data resources.

Collision detection limitations affect successful transmissions.

Real-time M2M traffic may face missed deadlines due to protocol constraints.

Abstract

LTE is increasingly seen as a system for serving real-time Machine-to-Machine (M2M) communication needs. The asynchronous M2M user access in LTE is obtained through a two-phase access reservation protocol (contention and data phase). Existing analysis related to these protocols is based on the following assumptions: (1) there are sufficient resources in the data phase for all detected contention tokens, and (2) the base station is able to detect collisions, i.e., tokens activated by multiple users. These assumptions are not always applicable to LTE - specifically, (1) due to the variable amount of available data resources caused by variable load, and (2) detection of collisions in contention phase may not be possible. All of this affects transmission of real-time M2M traffic, where data packets have to be sent within a deadline and may have only one contention opportunity. We analyze the features of the two-phase LTE reservation protocol and derive its throughput, i.e., the number of successful transmissions in the data phase, when assumptions (1) and (2) do not hold.