Exploiting Frequency-Selectivity in Real-Time Multicast Services over LTE Networks M. Condoluci, G. Araniti, A. Molinaro, A. Iera ARTS Lab., DIIES Dep., University Mediterranea of Reggio Calabria, Italy e-mail: [massimo.condoluci, araniti, antonella.molinaro, antonio.iera]@unirc.it Abstract—Long Term Evolution (LTE) is considered the most promising cellular system able to support the growing demand of multicast services (e.g., IPTV, video streaming) over mobile terminals. The design of effective strategies for the manage- ment of these applications is still an open issue, especially in scenarios where several multicast streams are simultaneously transmitted in a cell. In this paper we propose different resource allocation policies for the delivery of multicast scalable video flows. Such policies efficiently exploit the multi-user diversity and the frequency selectivity in order to match the requirements of both users and providers. The performance of the proposed strategies is analyzed through simulations by evaluating different cell deployment and user load environments and by focusing on spectral efficiency, throughput, fairness, and amount of resources needed for multicast service delivery. The last parameter is important in practical scenarios where multicast services share the available resources with other flows, e.g., unicast services. Index Terms—LTE, LTE-A, MBMS, Multicast, RRM, IPTV. I. I NTRODUCTION L ONG Term Evolution (LTE) [1] represents the wireless technology that will lead the growth of mobile broadband services in the next years. In this scenario characterized by a growing proliferation of mobile devices and applications, LTE is very appealing for network providers in order to support a wide range of multicast services (e.g., IPTV, news forecast, video conferencing), expected to be massively accessed by mobile users for commercial and other purposes [2]. Although the Multimedia Broadcast Multicast Service (MBMS) [3] improves the LTE capability of supporting multicast services, it is well known [4] that the radio resource management (RRM) on a per-group basis is challenging and limited in performance due to the presence of cell-edge users which experience poor channel conditions. Moreover, the delivery of typical multicast applications (e.g., mobile TV) requires a large amount of radio resources and this further challenges the spectrum efficiency and the coexistence with other services (e.g., unicast flows). In this paper, we focus on the resource allocation when multiple scalable video streams [5] are managed through the subgrouping technique [6]. This is an effective solution for video transmission that exploits the multi-user diversity by The research of Massimo Condoluci is supported by European Union, European Social Fund and Calabria Regional Government. This paper reflects the views only of the authors, and the EU, and the Calabria Regional Government cannot be held responsible for any use which may be made of the information contained therein. guaranteeing a “basic” quality to all receivers and by offering improved quality to users with better channel conditions. In this work we address the design and analysis of RRM policies for the efficient management of multicast streams in LTE and LTE-Advanced (LTE-A) systems. The main contri- bution of this paper is to propose different subgroup-based schemes exploiting the frequency selectivity [7] besides the multi-user diversity in resource allocation strategies by taking into account, for the selection of the portion of users to allocate each video layer, which are the best resources (i.e., sub- bands) to assign to the selected users. The proposed resource allocation scheme can be tailored in order to achieve different objectives, such as fairness maximization and proportional fair allocation. Finally, concerning the key aspect of the amount of resources needed for multicast stream delivery, we also proposed a strategy for multicast radio resources minimization. The remainder of this paper is organized as follows. Section II provides an overview on multicasting over LTE systems. In Section III we discuss the related work. We introduce the proposed policies in Section IV and analyse their performances in Section V. Conclusive remarks can be found in Section VI. II. MULTICASTING OVER LTE The MBMS [3] defines the network architecture with the related procedures (e.g., service announcement) for supporting group-oriented communications in LTE networks [1]. Orthog- onal Frequency Division Multiple Access (OFDMA) is used in the radio access as it offers high spectral efficiency and robustness against fading phenomena. The channel bandwidth varies from 1.4 to 20 MHz, and it can be extended up to 100 MHz with LTE-A [1] through the aggregation of five LTE carriers. The spectrum is managed in terms of Resource Blocks (RBs). Each RB is a sub-channel of 180 kHz and lasts 0.5 ms. The base station (i.e., the eNodeB) assigns the RBs in both time and frequency domains. In the time domain, the scheduler selects the flows to serve in order to fulfil their Quality of Service (QoS) requirements. In the frequency domain, link adaptation is performed every 1ms-long Transmission Time Interval (TTI), according to the Channel Quality Indicator (CQI) feedbacks transmitted by the terminals to the eNodeB. The CQI indicates the maximum modulation and coding scheme (MCS) allowed by the experienced channel conditions. Different CQI reporting schemes are defined in LTE [1]. In this work we refer to the eNodeB-configured scheme that, by dividing the spectrum into several sub-bands and estimating a 978-1-4577-1348-4/13/$26.00 ©2013 IEEE 978-1-4577-1348-4/13/$31.00 ©2013 IEEE 2013 IEEE 24th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC) 2013 IEEE 24th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC) 1799