Multicast Delivery of File Download Services in Evolved 3G Mobile Networks With HSDPA and MBMS

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 enhancement 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 energy (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.