Отчет мсэ-r bt. 2140-1 (05/2009)



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1.5.2 ATSC-M/H System Overview


The ATSC Mobile/Handheld service (M/H) shares the same RF channel as a standard ATSC broadcast service described in ATSC A/53. M/H is enabled by using a portion of the total available 19.4 Mbit/s bandwidth and utilizing delivery over IP transport. A block diagram representation of the broadcast system is shown in Fig. 17.

Central to the M/H system are additions to the physical layer of the ATSC transmission system that are easily decodable under high Doppler rate conditions. Extra training sequences and forward error correction (FEC) are added to assist reception of the enhanced stream(s). Consideration has also been given to the many system details that make such a signal compatible with legacy ATSC receivers, particularly audio decoder buffer constraints; but also such constraints as MPEG transport packet header standards, requirements for legacy PSIP carriage, etc. These changes do not alter the emitted spectral characteristics. The ATSC-M/H system broadcast protocol stack is illustrated in Fig. 17.

FIGURE 17



ATSC-M/H broadcast protocol stack


1.5.2.1 Description of A/153 Parts


The following sections provide an over view of the Parts that make up the ATSC-M/H system.

1.5.2.1.1 Part 2 - RF/ Transmission


M/H data is partitioned into Ensembles, each of which contains one or more services. Each Ensemble uses an independent RS Frame (an FEC structure), and furthermore, each Ensemble may be coded to a different level of error protection depending on the application. M/H encoding includes FEC at both the packet and trellis levels, plus the insertion of long and regularly spaced training sequences into the M/H data. Robust and reliable control data is also inserted for use by M/H receivers. The M/H system provides bursted transmission of the M/H data, which allows the M/H receiver to cycle power in the tuner and demodulator for energy saving.

1.5.2.1.2 Part 3 - Service Multiplex and Transport Subsystem


In the ATSC-M/H physical layer system, the M/H data is transferred by a time-slicing mechanism to improve the receiver’s power management capacity. Each M/H Frame time interval is divided into 5 sub-intervals of equal length, called M/H Subframes. Each M/H Subframe is in turn divided into 4 sub-divisions of length 48.4 ms, the time it takes to transmit one VSB frame. These VSB frame time intervals are in turn divided into 4 M/H Slots each (for a total of 16 M/H Slots in each M/H Subframe).

The M/H data to be transmitted is packaged into a set of consecutive RS Frames, where this set of RS Frames logically forms an M/H Ensemble. The data from each RS Frame to be transmitted during a single M/H Frame is split up into chunks called M/H Groups, and the M/H Groups are organized into M/H Parades, where an M/H Parade carries the M/H Groups from up to two RS Frames but not less than one. The number of M/H Groups belonging to an M/H Parade is always a multiple of 5, and the M/H Groups in the M/H Parade go into M/H Slots that are equally divided among the M/H Subframes of the M/H Frame.

The RS Frame is the basic data delivery unit, into which the IP datagrams are encapsulated. While an M/H Parade always carries a Primary RS Frame, it may carry an additional Secondary RS Frame as output of the baseband process. The number of RS Frames and the size of each RS Frame are determined by the transmission mode of the M/H physical layer subsystem. Typically, the size of the Primary RS Frame is bigger than the size of Secondary RS Frame, when they are carried in one M/H Parade.

The Fast Information Channel (FIC) is a separate data channel from the data channel delivered through RS Frames. The main purpose of the FIC is to efficiently deliver essential information for rapid M/H Service acquisition. This information primarily includes binding information between M/H Services and the M/H Ensembles carrying them, plus version information for the M/H Service Signaling Channel of each M/H Ensemble.

In ATSC-M/H, an “M/H Service” is similar in general concept to a virtual channel as defined in ATSC A/65C [10]. An M/H Service is a package of IP streams transmitted through M/H Multiplex, which forms a sequence of programs under the control of a broadcaster which can be broadcast as part of a schedule. Typical examples of M/H Services include TV services and audio services. Collections of M/H Services are structured into M/H Ensembles, each of which consists of a set of consecutive RS Frames.

In general, there are two types of files that might be delivered using the methods described in this standard. The first of these is content files, such as music or video files. The second type of file that may be transmitted is a portion of the service guide. This includes long- and short-term keys for service protection, logos, and SDP files. In either case, the delivery mechanisms are the same and it is up to the terminal to resolve the purpose of the files.

1.5.2.1.3 Part 4 - Announcement


In an M/H system, the Services available on that system (or another system) are announced via the Announcement subsystem. Services are announced using a Service Guide. A Service Guide is a special M/H Service that is declared in the Service Signaling subsystem. An M/H receiver determines available Service Guides by reading the Guide Access Table for M/H (GAT-MH). This table lists the Service Guides present in the M/H broadcast, gives information about the service provider for each guide, and gives access information for each guide.

The ATSC-M/H Service Guide is an OMA BCAST Service Guide, with constraints and extensions as specified in this standard. A Service Guide is delivered using one or more IP streams. The main stream delivers the Announcement Channel, and zero or more streams are used to deliver the guide data. If separate streams are not provided, guide data is carried in the Announcement Channel stream.

1.5.2.1.4 Part 5 - Application Framework


The primary objective for the M/H platform is to deliver a set of audio and/or video services from a transmission site to mobile or portable devices. The Application Framework for enables the broadcaster of the audio-visual service to author supplemental content to define and control various additional elements to be used in conjunction with the M/H audio-visual service. It enables one to define auxiliary (graphical) components, layout for the service, transitions between layouts and composition of audio-visual components with auxiliary data components. Furthermore, it enables the broadcaster to send remote events to modify the presentation and to control presentation timeline. The Application Framework further enables coherent rendering of the service and its layout over a variety of device classes and platforms, rendering of action buttons and input fields, and event handling and scripting associated with such buttons and fields.

1.5.2.1.5 Part 6 - Service Protection


Service Protection refers to the protection of content, be that files or streams, during its delivery to a receiver. Service Protection assumes no responsibility for content after it has been delivered to the receiver. It is intended for subscription management. It is an access control mechanism, only.

The ATSC-M/H Service Protection system is based on the OMA BCAST DRM Profile. It consists of the following components:

− Key provisioning

− Layer 1 registration

− Long-Term Key Message (LTKM), including the use of Broadcast Rights Objects (BCROs) to deliver LTKMs

− Short-Term Key Messages (STKM)

− Traffic encryption.

The system relies on the following encryption standards:

− Advanced Encryption Standard (AES)

− Secure Internet Protocol (IPsec)

− Traffic Encryption Key (TEK)



In the OMA BCAST DRM Profile there are two modes for Service Protection—interactive and broadcast-only mode. In interactive mode, the receiver supports an interaction channel to communicate with a service provider, to receive Service and/or Content Protection rights. In broadcast-only mode, the receiver does not use an interaction channel to communicate with a service provider. Requests are made by the user through some out-of-band mechanism to the service provider, such as calling a service provider phone number or accessing the service provider website.

1.5.2.1.6 Part 7 - AVC and SVC Video System


The M/H system uses MPEG-4 AVC and SVC video coding as described in ISO/IEC 14496 Part 10, with certain constraints.


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