Like any other wireless network, LTE (long term evolution) is only as good as its components. This means delivery of services is extremely important. This is now achieved with LTE MBMS (multimedia broadcast multicast services). LTE MBMS is a point-to-multipoint interface that delivers broadcast and multicast services, both within a cell and the core network. When it comes to broadcast transmission across multiple cells, LTE MBMS utilizes single-frequency network configurations. This will ensure more efficient delivery of applications such as mobile TV, radio broadcasting, file delivery and emergency alerts.
Technical Description
The MBMS feature is split into the MBMS bearer service and the MBMS user service. As mentioned, the LTE MBMS bearer service provides delivery for two services: broadcast and multicast. The MBMS bearer service uses IP multicast addresses for the IP flows. The broadcast service can be received by any subscriber located in the area where the service is offered and multicast services can only be received by users who have subscribed to the service and have joined the multicast group associated with the service. Both services are unidirectional, point-to-multipoint transmissions of multimedia data and can be applied to broadcast text, audio, picture, video usually from a broadcast multicast service center to any user located within the designated service area.
Only the broadcast service providers can be charged based on the amount of data broadcasted, size of service area or broadcast service duration. Multicast, however, is subject to service subscription, and in order to receive the service, the end user must join that specific group. Because it is subject to subscription, the multicast service allows the operator to set specific user charging rules.
The MBMS user service is basically the MBMS service layer and, offering a streaming and a download delivery method. The streaming delivery method is used for continuous transmissions such as Mobile TV services. The download method is intended for “Download and Play” services. To increase the transmission reliability, an application layer FEC code may be used. Further, a file-repair service may be offered to complement the download delivery method.
Service Architecture
Based on the Packet Core domain the LTE MBMS service architecture is compatible with EPS, as well as 2G/GSM or 3G UMTS Packet Core nodes like the SGSN and GGSN. Inside the EPS networks, there are two additional logical network entities: MCE, MBMS GW. The MCE (Multi-cell/multicast Coordination Entity) handles time allocation and frequency resources for multi-cell MBMS transmission. The MCE actually does the scheduling on the radio interface. The MCE is a logical node which may be integrated as part of the eNodeB (in which case, the M2 interface becomes an internal eNodeB interface).
3GPP Parent
LTE MBMS was born as a result of the 3GPP Release 9, designed to further enhance the LTE network. In fact, LTE MBMS was one of the key features in that release. Though it was initially defined in 3GPP Release 6 for UMTS, the OFDM-based LTE structure now offers a characteristic better suited to these services.
3GPP has defined a control plane entity, known as the MBMS Coordination Entity (MCE) that ensures that the same resource block is allocated for a given service across all the eNodeBs within a specific MBSFN area. It is the task of the MCE to ensure that the RLC/MAC layers at the eNodeBs are appropriately configured for MBSFN operation.3GPP has currently assumed that header compression for MBMS services will be performed by the E-MBMS gateway.
The MBMS traffic will share the same carrier with the unicast traffic or will be sent via a separate carrier. MBMS data are carried on the MBMS traffic channel (MTCH) as a logical channel is mapped either on the MCH transport channel or on the DL-SCH downlink shared channel. In the case of mapping on the MCH channel, the physical channel associated is the PMCH. [1]
