Enabling group communication for public safety in LTE-Advanced networks

Abstract

In this paper, we investigate public safety communications based on LTE-Advanced mobile networks. This work has a twofold aim, (i) to secure optimal radio resource efficiency using a mix of synchronous and asynchronous multicast traffic, and (ii) to provide public safety services with minimal interruptions due to mobility in a heterogeneous network environment.

To this end, we propose and evaluate three different options for multicast resource allocation: a synchronous scheme, where all multicast cells operate with the same modulation scheme as a single frequency network; an asynchronous scheme, where base stations can decide in a distributed fashion on the multicast configuration; and a coordinated scheme where a central network management entity selects the multicast configuration in a network.

For the performance evaluation, different network deployment alternatives and the impact on delay critical group communications using unicast and multicast bearers are analyzed. Different user distributions and mobility scenarios were also considered. We evaluate these schemes using system level simulations with 3GPP LTE-Advanced settings, analyzing the performance in terms of – resource efficiency, energy savings in macro-cellular networks, and optimization of signaling load in heterogeneous networks. From the numerical results, we observe significant gains in terms of resource efficiency as well as power consumption reductions for the multicast scheme over unicast, with minimal impacts due to mobility. The results also indicate that the scheme is flexible enough to handle different types of user distributions and mobility conditions, without compromising the resource utilization efficiency.

Introduction

The introduction of the 3rd generation of mobile networks known as Universal Mobile Telecommunications System (UMTS) in the 3rd Generation Partnership Program (3GPP), launched the initial support of multimedia communications. Such mechanisms are expected to be adopted widely with the deployment of LTE-Advanced networks that offer high capacity and data rates. Recent forecasts for data traffic growth (Cisco, June 2012) shows that video is the most popular application foreseeing over two-thirds of the mobile data globally to be video by 2018. For multimedia services such as streaming video or mobile TV where many users access the same content or service simultaneously, a unicast transmission of the data might be inefficient and have high resource requirements (Oyman et al., 2010).

In order to address this challenge, a multicast service for a point to multipoint transmission of data was developed by 3GPP to enable resource efficient service provisioning called Multimedia Broadcast and Multicast Service (MBMS) (Hartung et al., 2010). The service supports two different modes for the transmission – multicast and broadcast. Despite the research and standardization work conducted wide deployment of MBMS is not yet supported. This is due to the perceived inability to distribute audio and video media on demand, and thus the lack of attraction for the users. Also, broadcast technologies like DVB-T or DVB-H offer the possibility of video distribution to mobile devices (Ramacher, 2007). However, recent developments featured LTE-Advanced as the technology driver for the adoption of public safety as suggested in Ferrus et al. (2013) and Doumi et al. (2013). MBMS is considered to be a key enabler for providing resource efficient provisioning of such services. The work done in Song and Phung (2014) presents the challenges and limitations in provisioning multimedia capabilities for emergency public safety group calls using LTE-Advanced enhanced MBMS (eMBMS), and proposes an emergency group call mechanism over such a system.

The contribution of this paper is centered on the efficient radio resource provisioning for LTE by using different multicast transmission approaches, considering the attributes of utilization efficiency and power saving. In particular, this paper introduces mechanisms that address dynamically the process of setting-up of multicast cells considering the resource utilization efficiency by offering different Modulation and Coding Schemes (MCS) taking into account the link quality of users receiving unicast communication. It also tackles the issue of efficient resource allocation reflecting mobility not from the session continuity perspective, but in the context of adjusting the MCS in order to provide better resource utilization. In addition, we consider the use of a centralized management mechanism that can operate as a Self-Organized Network (SON) function (3GPP TS 32.500, 2011). This function should be responsible for collecting feedback from the RAN considering user positions in order to configure the MCS in a resource efficient way, while also adjusting the load and related power levels for saving energy. We also consider the mobility aspects of public safety UEs in a heterogeneous network environment and investigates mechanisms based on mobility state estimation and X2 data forwarding to enable service continuity and for signaling load reductions. In this work the scenario where commercial networks serving public safety users is considered. For such commercial eNBs, the non-public safety users can directly benefit from the resource efficient scheme.

The rest of the paper is structured as follows. Section 2 summarizes the related work considering the current state of the art in research and the advancements in 3GPP. Section 3 provides an overview of the system model used. Section 4 discusses the evaluated mechanism. Section 5 presents the simulation assumptions, system level parameters used, and performance results. Section 6 concludes this paper and provides further research directions.