1、 CEA Bulletin Mobile/Handheld DTV Implementation Guidelines CEA-CEB26-A October 2013 Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-NOTICE Consumer Electronics Association (CEA) Stan
2、dards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum del
3、ay the proper product for his particular need. Existence of such Standards, Bulletins and other technical publications shall not in any respect preclude any member or nonmember of CEA from manufacturing or selling products not conforming to such Standards, Bulletins or other technical publications,
4、nor shall the existence of such Standards, Bulletins and other technical publications preclude their voluntary use by those other than CEA members, whether the standard is to be used either domestically or internationally. Standards, Bulletins and other technical publications are adopted by CEA in a
5、ccordance with the American National Standards Institute (ANSI) patent policy. By such action, CEA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard, Bulletin or other technical publication. This document does not purport t
6、o address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this document to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. This document is co
7、pyrighted by the Consumer Electronics Association (CEA) and may not be reproduced, in whole or part, without written permission. Federal copyright law prohibits unauthorized reproduction of this document by any means. Organizations may obtain permission to reproduce a limited number of copies by ent
8、ering into a license agreement. Requests to reproduce text, data, charts, figures or other material should be made to CEA. (Formulated under the cognizance of the CEA R4 Video Systems Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2013 Technology Phone 800.854.7179; Fax 303.397.2740; Inte
9、rnet http:/ ; Email ATSC Standards: Advanced Television Systems Committee (ATSC), 1776 K Street N.W., Suite 200, Washington, DC 20006-2304; Phone 202.872.9160; Fax 202.872.9161; Internet http:/www.atsc.org/standards.html IETF Standards: Internet Engineering Task Force (IETF), c/o Corporation for Na
10、tional Research Initiatives, 1895 Preston White Drive, Suite 100, Reston, VA 20191-5434 USA; Phone 703-620-8990; Fax 703-758-5913; Email ietf-infoietf.org ; Internet http:/www.ietf.org/rfc/rfc0791.txt?number=791 and http:/www.ietf.org/rfc/rfc1071.txt?number=1071 OMA Documents: Open Mobile Alliance,
11、4330 La Jolla Village Dr., Suite 110 San Diego, CA 92122, USA; Fax: 1 858 623 0743; Internet www.openmobilealliance.org ECIG Documents: http:/www.eas-cap.org/documents.htm FIPS Publications: http:/www.nist.gov/itl/fips.cfm 3 System Overview The reader is referred to ATSC A/153 Part 1 10, for an intr
12、oduction to A/153. However, from the receiver developers point of view, there are some important considerations when porting a mobile video stack from another technology to A/153. This Section is an overview of the most important areas of interest that should be considered by developers. 3.1 Softwar
13、e Stack Overview The A/153 standard for ATSC mobile DTV is defined in eight Parts. Part 1 (Overview the SSC and FIC provide only the current running content information. Therefore, the receiver tunes to the appropriate frequency and selects the appropriate M/H Service, after which the physical layer
14、 can be treated as an abstract pipe that simply delivers bytes. 3.2.5 Data Structure, Logical Pipes, and Physical Layer Abstraction Besides the physical tuning elements mentioned above, another aspect of A/153 which makes a pure stack abstraction difficult is the structure of data in the emitted sig
15、nal. The structure is a consequence of the flexible way that A/153 uses Forward Error Correction (FEC). A/153 provides for multiple logical pipes within each emission, each pipe having independent FEC settings. An M/H emission may include one or more M/H Ensembles. An M/H Ensemble is a collection of
16、 M/H Services which all have the same Forward Error Correction (FEC) coding. Each Ensemble may be coded to a different level of FEC to meet different application requirements. For example, a FLUTE 11 data carousel may not require as strong an FEC code as audio or video streams. Each Ensemble is enco
17、ded using a dedicated sequence of Reed-Solomon (RS) Frames with particular attendant FEC configurations, as a result of this requirement for independent FEC settings. Note that although the A/153 standard permits carrying components of a service across multiple Ensembles, decoding of components from
18、 more than one Ensemble at a time is not expected to be a feature of all receivers, at least in early implementations. Implementation of such a multi-Ensemble Service requires consideration on the part of broadcasters and receiver manufacturers of the required or optional nature of the various Servi
19、ce components, and the capabilities of fielded receivers, especially the possible need for dual tuners in some cases. 3.2.6 A/153 Packet Format Before transmitting bytes over the A/153 physical layer, data are formatted as datagrams. Datagrams are carried within RS Frames, and the basic datagram for
20、mat is UDP/IPv4 (User Datagram Protocol / Internet Protocol version 4). This leads to an important difference with other physical layers for mobile video. Since this is a broadcast technology, Transmission Control Protocol (TCP) is not used because it requires a bidirectional link. User Datagram Pro
21、tocol (UDP) (Part of Internet Protocol (IP) is used in this technology because it is an unacknowledged unidirectional protocol and therefore can be used over a simplex link. The Real-time Transport Protocol (RTP) provides datagrams with defined order and timing. Network Time Protocol (NTP) “tics” an
22、d RTP Sender Report packets are used in order to keep audio and video streams synchronized. This results in datagrams having defined playback timing and location. 3.2.7 Video and Audio Codecs, and File Delivery Protocol Once RTP packets arrive, the video and audio decoders can go to work. In A/153,
23、the video compression used is AVC, with optional CEA-708 closed captions, and optional (Active Format Description (AFD) (for optimal cropping of a 16:9 image for a 4:3 screen). Certain constraints are used to ensure that the source compression is compatible with mobile chipsets; see Part 7 of A/153
24、for details. The audio compression used is HE AAC v2 (High-Efficiency Advanced Audio Coding version 2); source audio is mono or stereo. Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,
25、-CEA-CEB26-A 9 Surround sound is possible, but not standardized. That is, A/153 does not indicate how to code multichannel sound and it does not have a method for signaling what type of surround is being used. In theory, the “dynamic range” payload type or RTP payload type can be used to signal mult
26、ichannel sound, but this is not standardized. Instead, multichannel detection is embedded in the various surround decoders; that is, the surround demultiplexer/decoder for a given technology will recognize that technology and act accordingly. However, multichannel technology is generally outside the
27、 scope of A/153. Files are delivered using File Delivery over Unidirectional Transport (FLUTE). This may be for Service Guide (SG) (see A/153 Part 4), application presentation data encoded as Rich Media Environment (RME) (see A/153 Part 5), or Non-Real-Time services. It is also possible to receive a
28、 Rights Object by file delivery, but not through the broadcast medium; that requires a use of the Interactivity Channel. In addition, a Service Guide may be delivered by the Interactivity Channel. Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo repr
29、oduction or networking permitted without license from IHS-,-,-CEA-CEB26-A 10 3.3 A/153 Terminal Block Diagram Figure 4 below shows the functional blocks of an example receiver device, which are dealt with in this implementation guideline document. Each block is represented at a very high level. Some
30、 blocks shown are necessary for basic receiver functionality, i.e., unidirectional video/audio reception, and some provide optional functionality. C h a n n e l S y n c h r o n i z e rC h a n n e l E q u a l i z e rC h a n n e lD e c o d e rR S F r a m eD e c o d e rS i g n a l i n gD e c o d e rM /
31、 H T P I n t e r f a c eB a s e b a n dO p e r a t i o n C o n t r o l l e rF I C - S e g m e n t the characteristics and position of which are specified in the “M/H Group” section of ATSC A/153 Part 2 2. This M/H system provides burst transmission of the M/H data, which allows the M/H receiver to c
32、ycle power in the tuner and demodulator for energy saving. The M/H system also includes added signaling of various signal details that are unique to the presence of the M/H system. Detailed specification of the M/H Transmission system can be found in ATSC A/153 Part 2 2. 4.2 Receiving Antennas The c
33、hoice of an antenna system is an important consideration in the design of the receiver system and the implementation is often an optimization between the requirements for performance, aesthetics, and complexity. Some design considerations for the antenna system are briefly discussed below. 1 The the
34、 audio/video decryption process is not explicitly shown but may be a function of the AV Processor. Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-CEA-CEB26-A 12 4.2.1 Reception Envir
35、onment Special consideration should be given to the dynamic conditions of the RF propagation channel (multipath, Doppler), potentially large variations in the RF input power as the receiver moves relative to the transmitting tower, and interference levels (either in-band or out-of-band) that could o
36、ccur during routine operation. The simplest channel model consists of an unimpaired desired signal in a static channel with a small amount of random Gaussian thermal noise generated within the receiver system. In this case, the BER will be determined by the RF input power of the desired signal and i
37、s limited by the equivalent receiver system input noise power (typically specified as the receiver Noise Figure). This can be considered as the noise-limited receiver system sensitivity. Generally, the environment that will be encountered is much more complex. Typically, the channel is subject to mu
38、ltipath distortion, Doppler shift, or extraneous interfering signals on other frequencies; and therefore the required RF input power to produce the same BER will generally be greater compared to that of the Gaussian channel model. Additionally, the channel characteristics are time-variant and change
39、 with receiver movement. To optimize the system performance, the receiver should have not only adequate sensitivity in a Gaussian channel, but also should have a wide dynamic range to minimize overload or desensitization under high field-strength conditions. 4.2.2 Antenna Gain and Radiation Pattern
40、U.S. DTV stations broadcast on VHF channels 2-13 (54 MHz 88 MHz, 174 MHz 216 MHz) and UHF channels 14-51 (470 MHz 698 MHz), with most stations operating on the UHF channels. Stations are required to have a horizontally polarized component of their signal, but some have a vertically polarized compone
41、nt as well. Ideally, the polarization of the receiving antenna should match that of the transmitter, but due to reflections and scattering, the polarization at the receiver is difficult to accurately predict. From a practical perspective, the received signal should be considered to be randomly polar
42、ized, with varying amounts of power contained in both the vertical and horizontal planes. The simplest implementation could consist of a single antenna element that is used for reception in both the VHF and UHF frequency bands. However, optimizing the antenna gain and obtaining a suitable impedance
43、match over a wide frequency range may require the use of multiple elements. For reception in the UHF band, it should be possible to achieve about 0dBi gain with a relatively small antenna. Achieving this amount of gain on the VHF channels becomes more problematic as the antenna becomes physically la
44、rger (for example, a /4 whip is about 55” long 54 MHz). Expected antenna gain and efficiency values for Mobile Handheld and Personal Player receiver antennas can be found in Section 4.1.2.4 of ATSC A/174 16. 4.2.3 Active versus Passive Design An active antenna typically has a low-noise amplifier (LN
45、A) integrated at the feedpoint of the antenna element(s) and provides the advantage of minimizing the coaxial cable loss between the antenna and the receiver. DC power is typically provided to the LNA through the coaxial cable using RF isolated biasing circuitry in the receiver. The feedline loss, w
46、hich is dependent on the cable type, cable length, and operating frequency, will result in a corresponding reduction of the RF input power to the receiver and a subsequent reduction in the service range from the transmitting tower. For example, for properly terminated cable (VSWR=1), the loss Copyri
47、ght Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-CEA-CEB26-A 13 of 5 feet of RG-58 coax 600 MHz is approximately -0.6 dB, while the loss of 20 feet of RG-174 cable is about -4.2 dB. These lo
48、sses will increase with higher mismatch and VSWR values. Active antenna designs typically use a fixed gain amplifier with a high compression point to minimize the generation of IMD (Intermodulation Distortion) products under high field-strength conditions. Excessive LNA gain should be avoided and sh
49、ould only be high enough as to negate the effects of the anticipated cable loss and the receiver Noise Figure. Non-amplified passive antenna designs are generally less complex to implement, may require a smaller packaging space (since the LNA circuitry is not required), and may reduce the likelihood of receiver overload in high field-strength areas due to the overa
