MBMS Technology Introduction

MBMS Technology and Application Analysis

To effectively use mobile network resources, the global Organization for Standardization (3GPP) proposed two broadcast services: one is to use the residential broadcast service, which was developed on the GSM system, therefore, only the text-based broadcast service can be provided. The other is the multimedia broadcast multicast service (MBMS: MultimediaBroadcastMulticastService), where one Data Source sends data to multiple users for point-to-point services, network resource sharing, including sharing resources of mobile core networks and access networks, especially empty port resources. The 3GPP-defined MBMS not only enables low-speed message multicast and broadcast for plain text, but also enables high-speed multicast and broadcast for multimedia services, this undoubtedly conforms to the development trend of mobile data in the future.

Technical Features

 
The major changes of the original WCDMA network in MBMS are: adding the network element of the Broadcast multicast business center (BM-SC: Broadcast-MulticastServiceCentre), and upgrading the function of MBMS for the existing PS domain-related network elements, it supports MBMS-specific interface functions (such as Gmb), special channels (such as MICH, MTCH/MCCH/MSCH), special physical layer processes (FACH channel selective merge, PTM and PTP switching) and special business processes (such as subscription ).

In terms of terminals, MBMS still inherits the existing 3GPP standards to the maximum extent. While the technologies of terminals such as power consumption, storage, multimedia processing, and display are improved, the original baseband processing function is also enhanced. Therefore, MBMS terminals carrying broadband multimedia services maintain a good uniformity with existing terminals.

In terms of bandwidth, MBMS can use a maximum of 256 kbit/s for download and streaming media transmission. In terms of interaction, MBMS does not define a special uplink channel, but it can use an existing uplink control channel for business subscription, business addition, and other business control processes, at the same time, the uplink service channel is used to implement interactive services that work with downstream broadcast/multicast.

In terms of capacity, MBMS provides a multimedia sending mechanism from point to multiple points, and a business model called "SendOnce, ChargeManytimes". resource consumption is irrelevant to the increase in the number of users, in this way, we can find a fundamental solution to save space port resources and Iub port transmission resources in 3G networks, and avoid the disadvantages of mobile network capacity.

Technical Principles and network structure of MBMS

1. Network Structure

Based on the WCDMA/GSM network, MBMS adds some new functions entity-broadcast multicast business center BM-SC, to the existing group domain functional entities such as SGSN (ServingGSN), GGSN (GatewayGSN) add MBMS functions such as RadioNerwork Controller and UE (User Equipment) to implement the broadcast multicast service, and define a new logical sharing channel to achieve empty port resource sharing.

The business Implementation of MBMS is mainly realized through the UE on the user side and the BM-SC on the network side:

● On the user side, MBMS uses a specific Qos to distribute multicast packets to the UE through the Gi port.

● On the control plane, the Business provision mechanisms include: managing the activation status (in multicast mode) of the business carried by the MBMS service of UE, and determining the outsourcing copyright of the business (in multicast mode) provides session trigger and stop control and manages the bearer resources of data distribution (in multicast and broadcast modes ).

Figure 1 MBMS Network Architecture

2. function implementation

The new feature of MBMS is the entity broadcast business center (BM-SC), a content provider portal that authorizes and initiates MBMS to carry businesses on the mobile network, and transmits MBMS content as scheduled. Its functions include:

● Authentication, authorization, and billing of third-party content providers;

● Provide MBMS transmission parameters, such as QoS and multicast broadcast areas;

● Initiate and terminate MBMS transmission resources;

● Receive and transmit MBMS content from external data sources, arrange MBMS session transmission, notify users, and re-transmit sessions;

● Service declaration, including media description and session description, such as the Business ID, address, and transfer time of multicast.

MBMS functions and processes must be added for existing WCDMA/GSM network-based entities, such as GGSN, SGSN, RNC/BSC, and UE. Its new functions for MBMS include the following four parts.

● GGSN is the IP multicast service node of MBMS data. It establishes or releases the user plane bearing for broadcast or Multicast Transmission Based on the notification request of the BM-SC; receives IP multicast content from a BM-SC or other data source, and routes through the GTPs tunnel; and Message notification, Billing Data mobile phone, business (QoS) negotiation.

● SGSN controls the network of users, supports the movement of MBMS receivers between SGSN, and charges for multicast services, including post-paid and pre-paid users; establish or release the Iu and Gn bearer based on the notifications sent by GGSN.

● The RAN transmits MBMS data in the pre-defined multicast or broadcast business area. In the multicast mode, the RAN selects an appropriate wireless Bearer Based on the number of current service users and available wireless resources in the residential area, that is, select a shared channel or VPC channel. Support for starting and ending MBMS transmission from the core network; support for moving MBMS receivers between RNC, which may cause some data loss; supports the transmission of MBMS service declarations, paging information, and parallel MBMS services, such as receiving MBMS video content, and simultaneous voice call and messaging services.

● UE supports activation/deactivation of MBMS services; MBMS security functions, such as content encryption and consistency protection; receives MBMS service statements, paging information, or supports synchronous services; determines whether to ignore the mbms session based on the mbms session ID.

3. Main link layer Technologies

When introducing MBMS, you must make the following changes to the physical layer:

● Add a new MBMS notification indicator channel (MICH) similar to PICH );

● Add S-CCPCH operation in the residential area, as far as possible with the adjacent residential area to maintain synchronization.

MBMS data is sent to UE through the Uu interface, which can be transmitted from point to point. For example, the existing PDCH function can also be used for point to multiple points.

Point-to-point transmission is used to transmit MBMS-specific control/user information and dedicated control/user information. This information is transmitted between UE and network in RRC connection mode. This mode is only applicable to the MBMS multicast mode. For an UE, if it is on the CELL_FACH, CELL_DCH, DCCH, or DTCH channel, the existing ing relationships can be used to map to the transmission channel. Point-to-point transmission is used to transmit control/user information unique to MBMS. This information is transmitted between the network and several UE in idle or RRC connection mode in RRC connection or idle mode. This mode applies to the broadcast and multicast modes of MBMS.

The UE end can be combined to improve the receiving performance:

● Selective merge: UE combines TTIs in L2 re-sorting buffer to allow longer time shifting between different wireless links. The time shifting allowed by selective merge can reach several TTI. 3.7 ~ 4.8dB gain;

● Soft merge: The sending time of the Current and adjacent cells is kept within 1 TTI + one time slot, and the UE can soft merge the received information on the physical layer. Soft merge can be used to further obtain 2 ~ 3 dB gain.

To support the transmission of MBMS user planes and control planes, a new functional entity MAC-m is added to MAC-c/sh entities on the MAC layer, this entity is mainly used to map the logical channels MTCH, MCCH, and MSCH to the transport channel FACH in the point-to-point transmission mode. In the point-to-point mode, the logical channels DTCH and DCCH are used.

Business Process of multicast mode and broadcast mode

1. Business Process in multicast Mode

The MBMS multicast service provides the following specific processes. The individual behaviors of signing, adding users, and exiting users are initiated by users. Other processes are completed by the system.

Contract: establish the relationship between the user and the business provider, contract information is recorded by the BM-SC.

Business statement: the business statement mechanism of MBMS enables users to obtain information about the business of MBMS, such as geographical range, IP multicast address, and business start time. Operators may consider using multiple methods to implement business declarations, such as through community broadcast, MBMS broadcast, MBMS multicast, and PUSH (WAP, SMS, and MMS), URL (HTTP, FTP ).

User joining and user exiting: A User joining or exiting a Multicast group can be achieved through the IGMP (InternetGroupManagementProtocol) protocol or the MLD (Multicast Listener disener) protocol.

Session start and session end: initiated by the BM-SC of the broadcast multicast business center, triggering MBMS data transfer to establish or release the corresponding network resources, including the GTPs user plane, Iu interface, and air bearer. This process is completely independent from the process of adding or exiting a multicast group.

MBMS notification: indicates that the network-side notification UE will transmit MBMS data.

Data transmission: MBMS transfers data to UE.

2. Broadcast Business Process

Unlike multicast services, in broadcast mode, you do not need to join multicast groups. When receiving and exiting the broadcast business, you need to activate and deactivate the business locally without interaction between the network and UE.

3. Implementation of multicast services

Business and Application Based on MBMS Technology

MBMS provides a set of broadcast/Multicast Transmission Channels fully operated and controlled by WCDMA mobile operators, and can use the existing two-way channel of the cellular network for interaction. Therefore, carriers can provide a wide range of mobile multimedia services over MBMS.

In terms of implementation methods, in addition to broadcast services, MBMS can also provide more abundant multicast services. Thanks to the point-to-point repair mechanism, it can also implement highly reliable download services. MBMS can be used not only to carry the services subscribed by users, but also to provide users with a variety of "PUSH" services, such as mobile advertisements and announcement information.

Different media types also require different speeds. In the 3GPP user business specification, the rate information of various businesses is provided.

As shown in table 1, the speed requirements of typical MBMS applications are related to the media type used, and the maximum bandwidth is required for video-based services.

A business combination may take the following forms:

● Live video programs: about 10 ~ 15 channels, such as news, entertainment, TV series, cartoons, and finance;

● Live audio programs: about 8 ~ 10 channels;

● On-demand video service: short videos, cartoon cartoons, and special on-demand videos for mobile terminals and users' preferences;

● Data service.

The basic method of business combination: based on the user demand market survey results, users are divided into several types. Based on different user types, various programs provided above are combined to form multiple program packages, it can be used together with the data service and VOD service for users to choose from, thus simplifying the program customization process and user management.

● 2 ~ Three video channels (such as news channels, integrated entertainment channels, and financial channels) and several audio programs are used as basic program packages and provided to users at preferential prices, other video programs and audio programs are charged by channel;

● The VOD service is billed on a per-use or monthly basis;

● Data and video and on-demand video services are provided at the same time. You can also select data services separately.

Comparison between MBMS and other multimedia broadcast Multicast Technologies

The realization technology of mobile multimedia broadcast is mainly divided into three types: one is based on mobile network technology, MBMS belongs to this type of technology; the other is based on the ground of digital broadcast network technology, such as DVB-H in europe, third, satellite broadcast-based technologies, such as South Korea's S-DMB. These three types of technologies have their own characteristics. Next we will make a simple comparison between the implementation technologies of MBMS, satellite, and terrestrial digital broadcast networks.

According to the comparison and analysis in table 2, although mobile network-based implementation technology can effectively implement mobile video broadcast services, it also has some advantages in user personalized operations and interactions, however, the frequency is relatively cost-effective. The Implementation Technology Based on the terrestrial digital broadcast network can provide mobile video broadcast only after a simple upgrade based on the digital broadcast network, due to its comprehensive broadcast-based downlink transmission and its huge advantages in network construction and operation costs, the Implementation Technology Based on terrestrial digital broadcast networks is a better downstream transmission technology for mobile video broadcast businesses. However, as a whole, such technologies must be combined with the uplink technology of mobile networks to achieve bidirectional communication between networks and users.