742 IEEE TRANSACTIONS ON BROADCASTING, VOL. 55, NO. 4, DECEMBER 2009 Multicast Delivery of File Download Services in Evolved 3G Mobile Networks With HSDPA and MBMS David Gómez-Barquero, Ana Fernández-Aguilella, and Narcís Cardona Abstract—This article presents and analyzes the multicast transmission problem of file download services to several users simultaneously in 3G mobile networks with MBMS (Multimedia Broadcast Multicast Services). MBMS is the second major en- hancement in the downlink of the 3G standard after HSDPA (High-Speed Downlink Packet Access). Whereas HSDPA supports high speed point-to-point (p-t-p) transmissions up to several Mb/s, with MBMS the same content can be transmitted with a point-to-multipoint (p-t-m) connection to multiple users in a unidirectional fashion. Reliable delivery of files is a challenging task, as an error-free reception of the files is required. In order to increase the robustness of the p-t-m transmission, MBMS adopts new diversity techniques to cope against fast fading and to combine transmissions from multiple cells, and an additional Forward Error Correction (FEC) mechanism at the application layer based on Raptor coding. Moreover, users not able to receive the file after the initial transmission can complete the download in a post-delivery repair phase, in which it is possible to employ both p-t-p and p-t-m connections. The article focuses on the efficient multicast delivery of files in future 3G mobile networks with HSDPA and MBMS. Delivery configurations studied include: only p-t-p transmissions with HSDPA (one for each active user), a single p-t-m transmission with MBMS, and using both jointly in a hybrid approach employing HSDPA for error repair of the MBMS transmission. The approach of minimizing the transmission en- ergy (product of the transmit power times the transmission time) to achieve a target file acquisition probability (percentage of users that successfully receive the file) has been adopted. Radio network simulations have been performed in a typical urban scenario under full background load conditions. This way by minimizing the energy the system capacity is maximized. We investigate the optimum HSDPA and MBMS transmission configurations as a function of the time to deliver the file when used separately, and the optimum trade-off between the initial MBMS file transmission and the HSDPA error repair for the hybrid delivery. Index Terms—Application layer FEC, HSDPA, hybrid multi- cast-unicast delivery, MBMS, raptor codes, 3G. Manuscript received August 18, 2008; revised July 14, 2009. First published October 20, 2009; current version published November 20, 2009. This work was supported in part by the Spanish Ministry of Industry, Tourism and Commerce under the project FURIA (Futura Red Integrada Audiovisual). The authors are with the iTEAM Research Institute, Universidad Politéc- nica de Valencia, 46022 Valencia, Spain (e-mail: dagobar@iteam.upv.es; an- ferag@iteam.upv.es; ncardona@iteam.upv.es). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TBC.2009.2032800 I. INTRODUCTION A FTER a slow start, third-generation (3G) mobile networks are now being deployed on a broad scale all over the world, and mobile operators have started to provide multimedia services, such as video clips from sports events or live TV pro- grams. However, the capabilities of the first release of the 3G standard are considerably limited, from both a cost and a tech- nical viewpoint. In order to offer a viable business model, and to not overload the network capacity to the point of preventing subscribers from placing voice calls (which is the main function and value of the cellular networks), only short video clips with a low resolution can be offered (e.g., 2 minutes at 128 kbps) [1]. To meet the increasing demands for high-speed data ac- cess, the 3G standard was initially enhanced with HSDPA (High-Speed Downlink Packet Access) [2], which supports higher peak data rates (up to several Mb/s), increasing consid- erably the network capacity. HSDPA introduces a new channel shared by all users in the cell, and it relies on a fast scheduling at the base station every 2 ms to control the allocation of the shared resources (transmission power and channelization codes), the use of link adaptation (variable modulation and coding rate, the transmit power is kept constant), and feedback from the terminals. All this leads to both higher data rates for users in favorable reception positions and reduced interferences. Another important bottleneck of the first release of the 3G standard not solved with HSDPA is the fact that it was optimized for unicast services delivered through dedicated point-to-point (p-t-p) connections for each individual user, even if the same content should be delivered to many users. Traditionally, cel- lular systems have focused on the transmission of data intended for a single user employing dedicated p-t-p radio bearers, not addressing the distribution of popular content to a large number of users. Unicast systems can easily support a wide range of services, as each user can consume a different service, being possible to optimize the transmission parameters for each user individually. The main drawback of unicast is its unfavorable scaling when delivering the same content to many users at the same time. This limits the maximum number of users cellular systems can handle, since both radio and network resources are physically limited. Multicast and broadcast 1 are more appropriate transport tech- nologies to cope with high numbers of users consuming simulta- neously the same service compared to unicast. Multicast/broad- cast wireless transmissions employ a common point-to-multi- 1 Multicasting and broadcasting describe different, although closely related, scenarios. Whereas broadcast transmissions are intended for all users in the ser- vice area, multicast transmissions are addressed to a specific group of users (usu- ally called the multicast group). 0018-9316/$26.00 © 2009 IEEE Authorized licensed use limited to: UNIVERSIDAD POLITECNICA DE VALENCIA. Downloaded on November 24, 2009 at 11:46 from IEEE Xplore. Restrictions apply.