哪位大虾帮我翻译下DVB测量指导这个标准
小弟痛苦中 4 GeneralThe Digital Video Broadcasting (DVB) set of digital TV standards specify baseline systems for various transmission
media: satellite, cable, terrestrial, etc. Each baseline system standard defined the channel coding and modulation
schemes for that transmission medium. The source coding was adapted from the MPEG-2 standard.
The design of these new systems has created a demand for a common understanding of measurement techniques and the
interpretation of measurement results.
The present document is an attempt to give recommendations in this field by defining a number of measurement
techniques in such detail that the results are actually comparable as long as the measurement is carried out in
compliance with the given definition.
Engineers seeking to apply the methods described in the present document should be familiar with the standards for the
respective baseline systems. Although most of the parameters specified in the present document are well known in
communications, most of them should be interpreted with respect to the new environment, especially the transmission
of digital TV signals or other related services.
The inclusion of each parameter in the present document is based on requirements from those who envisage having to
work alongside the defined procedures. This includes network operators and providers of equipment for network
installation, as well as manufacturers of Integrated Receiver Decoders (IRD) or test and measurement equipment.
The recommendations of the present document can be used:
- to set-up test beds or laboratory equipment for testing hardware for digital TV and other related services;
- to set these instruments to the appropriate parameters;
- to obtain unambiguous results that can be directly compared with results from other test set-ups;
- to form a potential basis for communicating results in an efficient way by using the definitions in the present
document as references.
They are not intended to describe a set of compulsory tests.
The recommendations are grouped in several clauses. Since the MPEG-2 TS is the signal format used for the inputs and
outputs of all baseline systems, clause 5 is devoted to the description of checking procedures for those parameters which
are accessible in the TS packet header, i.e. without decoding scrambled or encrypted data. The aim of these tests is the
provision of a simple and fast health check. It is meant neither as a MPEG-2 conformance test nor as a compliance test
for all DVB related issues.
Clause 6 contains the parameters which are commonly addressed by various transmission media. For example, the
measurement of the availability of transmission systems or links falls into this category, and it may be desirable to have
the same definition for availability independent of the actual system in use.
Clauses 7 and 8 address the parameters which are specific for cable and satellite, DVB-C and DVB-S, they are also
applicable to SMATV systems, DVB-CS, and possiblyMMDS systems such as DVB-MC and DVB-MS.
Clause 9 addressed parameters specific to the terrestrial DVB environment (DVB-T).
Clauses 6, 7, 8, and 9 of the present document follow the same structure. For each parameter there is a description of the
purpose of the recommended measurement procedure, the interface to which the measurement instrument should be
applied, and a description of the actual method of the measurement itself.
Apart from these clauses a number of annexes are included, containing recommendations for general aspects, examples
of test set-ups and certain requirements for the test and measurement equipment.
If the interfaces for a described measurement procedure are to be found within the transmitter, the notation is provided
in accordance with figures 4-1 and 9-1 for terrestrial. If the interfaces for the described measurement procedures are to
be found within the receiver (test receiver or IRD), the notation is provided in accordance with figures 4-2 and 9-2 for
terrestrial. These figures illustrate the general cases of a DVB transmitter and receiver, although certain functional
blocks only appear in certain systems.
Most of the parameters can be measured with standard equipment such as spectrum analysers or constellation analysers.
Other parameters are defined in a new way as a request to test and measurement equipment manufacturers to integrate
this functionality in their products. 5 Measurement and analysis of the MPEG-2 Transport
Stream
5.1 General
The MPEG-2 Transport Stream (TS) is the specified input and output signal for all the baseline systems, i.e. for
satellite, cable, SMATV, MMDS/MVDS and terrestrial distribution, which are defined in the DVB world so far.
Therefore these interfaces are accessible in the transmission chain. Direct access is given on the transmitter side at the
input of the respective baseline system. At other interfaces where the signal occurs in modulated form, access is
possible by an appropriate demodulator that provides the TS interface as an output for further measurements.
5.2 List of parameters recommended for evaluation
The present document recommends in this clause a set of syntax and information consistency tests that can be applied to
an MPEG-2 TS at the parallel interface, or either of the serial interfaces defined in EN 50083-9 .
The following assumptions and guiding principles were used in developing these tests:
- the tests are mainly intended for continuous or periodic monitoring of MPEG-2 TSs in an operational
environment;
- these tests are primarily designed to check the integrity of a TS at source; clause 5.3 covers other aspects of TSs
in networks including impairments created by transport systems;
- the general aim of the tests is to provide a "health check" of the most important elements of the TS. The list of
the tests is not exhaustive;
- the tests are consistent with the MPEG-2 Conformance tests defined in ISO/IEC 13818-4 , they do not replace
them;
- the tests are consistent with the DVB-SI documents (EN 300 468 , TR 101 211 ), they do not replace them.
MPEG-2 and DVB-SI reserved values in the TS do not cause a test error indication.
In general the tests are performed on TS header information so that they are still valid when conditional access
algorithms are applied, however a few of the tests may only be valid for an unscrambled or descrambled TS.
The tests are not dependant on any decoder implementation for consistency of results. The MPEG-2 T-STD model
constraints, as defined in ISO/IEC 13818-1 (MPEG-2 Systems), shall be satisfied as specified in
ISO/IEC 13818-4 (MPEG-2 Compliance).
Off-line tests are performed under stable conditions, no discontinuity or dynamic change can occur during an off-line
test process.
Other digital performance parameters such as BER are not considered in this clause.
This clause tabulates the parameters which are recommended for continuous or periodic monitoring of the MPEG-2 TS.
The tests are grouped into three tables according to their importance for monitoring purposes.
The first table lists a basic set of parameters which are considered necessary to ensure that the TS can be decoded. The
second table lists additional parameters which are recommended for continuous monitoring. The third table lists
optional additional parameters which could be of interest for certain applications.
Any test equipment intended for the evaluation of these parameters should report test results by means of the indicators
itemized in the second column of the tables under exactly the preconditions described in the third column of the tables.
If an indicator is set, then the TS is in error. However, since the indicators do not cover the entire range of possible
errors, it cannot be concluded that there is no error if the indicator is not set.
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