1、 CEA Bulletin Mobile/Handheld DTV Implementation Guidelines CEA-CEB26 March 2012 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) Standard
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8、g 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 2012 Technology Phone 800.854.7179; Fax 303.397.2740; Internet
9、 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 Copyright Consumer Electronics Association Provided by IHS under license with CEA
10、Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-CEA-CEB26 8 IETF Standards: Internet Engineering Task Force (IETF), c/o Corporation for National Research Initiatives, 1895 Preston White Drive, Suite 100, Reston, VA 20191-5434 USA; Phone 703-620-8990; Fax 703-758-59
11、13; 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, 4330 La Jolla Village Dr., Suite 110 San Diego, CA 92122, USA;Fax: 1 858 623 0743; Internet www.openmobilealliance.org 3 System
12、 Overview The reader is referred to ATSC A/153 Part 1 10, for an introduction 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 a
13、reas of interest that should be considered by developers. 3.1 Software 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 an
14、d selects the appropriate M/H Service, after which the physical layer 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 st
15、ack abstraction difficult is the structure of data in the emitted signal. 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
16、include one or more M/H Ensembles. An M/H Ensemble is a collection of 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 a
17、s strong an FEC code as audio or video streams. Each Ensemble is encoded 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 component
18、s of a service across multiple Ensembles, decoding of components from 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
19、manufacturers of the required or optional nature of the various Service 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 datagram
20、s. Datagrams are carried within RS Frames, and the basic datagram format 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
21、 not used because it requires a bidirectional link. User Datagram Protocol (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
22、 with defined order and timing. Network Time Protocol (NTP) “tics” and 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 pa
23、ckets arrive, the video and audio decoders can go to work. In A/153, 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
24、 compression is compatible with mobile chipsets; see Part 7 of A/153 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 Resal
25、eNo reproduction or networking permitted without license from IHS-,-,-CEA-CEB26 14 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 “dynami
26、c range” payload type for RTP payload type can be used to signal multichannel 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 a
27、ccordingly. However, multichannel technology is generally outside the 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 Remote Method Execution (RME) (see A/15
28、3 Part 5), or Non-Real-Time services. It is also possible to receive a 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 As
29、sociation Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-CEA-CEB26 15 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 guid
30、eline document. Each block is represented at a very high level. Some 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
31、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 / 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 bu
32、rst transmission of the M/H data, which allows the M/H receiver to cycle 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 syst
33、em can be found in ATSC A/153 Part 2 2. 4.2 Receiving Antennas The choice 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 consider
34、ations for the antenna system are briefly discussed below. 1 The the 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 permitt
35、ed without license from IHS-,-,-CEA-CEB26 17 4.2.1 Reception Environment 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, an
36、d interference levels (either in-band or out-of-band) that could occur 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 wi
37、ll be determined by the RF input power of the desired signal and is 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 encount
38、ered is much more complex. Typically, the channel is subject to multipath 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. Add
39、itionally, the channel characteristics are time-variant and change 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 fi
40、eld-strength conditions. 4.2.2 Antenna Gain and Radiation Pattern 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 compo
41、nent of their signal, but some have a vertically polarized component 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 perspect
42、ive, the received signal should be considered to be randomly polarized, 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. Howeve
43、r, optimizing the antenna gain and obtaining a suitable impedance 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 chan
44、nels becomes more problematic as the antenna becomes physically larger (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 Passiv
45、e Design An active antenna typically has a low-noise amplifier (LNA) 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 R
46、F isolated biasing circuitry in the receiver. Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-CEA-CEB26 18 The feedline loss, which is dependent on the cable type, cable length, and o
47、perating 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 of 5 feet of RG-58 coax 600 MHz is approximately -0.6 dB, whil
48、e the loss of 20 feet of RG-174 cable is about -4.2 dB. These losses 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-
49、strength conditions. Excessive LNA gain should be avoided and should 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
