CN1761221A - Method for building digital TV network - Google Patents

Abstract

Change of C/N, CSO/CTB indexes at any key connection point such as machine room, trunk amplifier, storied house amplifier etc. will affect stable transmission of QAM signal, causing index deterioration of PRO/POST BER, EVM, MER etc. When user receives signal, the said deteriorated index will induce mosaic phenomena, even up going interactive service is interrupted. The invention can measure transmission quality of QAM modulation signal effectively in complex network environment for digital cable TV.

Description

Method for building digital TV network

Technical field

The present invention relates to application of electronic technology, relate in particular to a kind of method for building digital TV network.

Background technology

Optical fiber/coaxial cable mixes (HFC) network

Optical fiber/coaxial cable mixes the main signal transfer mode of (HFC) network as cable television system, it develops rapidly and has driven the conversion of simulated television to digital cable TV, and itself is exactly the bidirectional multifunctional integrated information net of a labyrinth, its " at a high speed " performance not only makes cable television network may extend in the actual user family, and this network also has the unique function that other network can not replace.The appearance of hfc plant, the TV programme quality and quantity that cable TV station is transmitted has had the raising of matter, and service content exceeded simple TV programme and play, and various value-added services also occur in cable TV network.So " multi-functional once net " become the guiding theory of cable TV network development.

Cable television network and communication network difference

It is an asymmetric transmitted in both directions net, and the deal that downstream signal accounts for substantially exceeds upward signal.Mainly broadcast television signal in the downstream signal, its main task is to carry out the distribution of signal rather than the exchange of signal, and occupying bandwidth is 88MHz ~ 870MHz, and upward signal is used for the transmission of phone, data and signaling, the frequency band that occupies is much smaller, is generally 5MHz ~ 65MHz.In uplink band, various interference are very easy to invade, and form transmission error code, even cause signal transmission errors.

Digital modulation mode mainly contains following several at present:

(1). quadrature amplitude modulation (QAM): the modulation efficiency height, require the signal to noise ratio height of transmission approach, be fit to the cable of cable TV transmission.

(2). keying phase shift modulation (QPSK): the modulation efficiency height, require the signal to noise ratio of transmission approach low, be fit to satellite broadcasting.

(3). vestigial sideband modulation (VSB): anti-multipath propagation effect good (it is good promptly to eliminate ghost effect) is fit to terrestrial broadcasting.

(4). coded orthogonal division modulation (COFDM): anti-multipath propagation effect and co-channel interference are good, are fit to terrestrial broadcasting and net broadcasting with frequency.

Generally speaking, because the QPSK mode has stronger antijamming capability, so be used in the passback of two-way net more.And QAM passes so be used in down because of the code check height of its transmission more.The just many modulation systems of the signal of DVB-C with 64QAM.In the analog television channels bandwidth of a standard, can transmit the digital TV signal of 5 ~ 8 covers with the pattern of standard television.

Summary of the invention

Technical problem underlying to be solved by this invention provides a kind of method for building digital TV network, because at any crucial tie point, all can have influence on the transmission of QAM signal stabilization as the C/N of occasions such as amplifier between machine room, trunk amplifier, building, the variation of CSO/CTB index, cause indexs such as PRO/POST BER, EVM, MER to worsen, mosaic phenomenon appears when causing the user to receive, even the up interruption of interactive service.The present invention effectively measures the transmission quality of qam signal in complex network environment to digital cable TV.

The technical process that the present invention is detailed:

In numeral two-way net construction of CATV and the maintenance, the operating state that needs frequent test signal transmission quality and each node of network, the forward network needs test signal level, the modulation error rate (MER), noise allowance, signal to noise ratio, modulation error rate MER, bit error rate BER, the planisphere index, oppositely the main test noise of passback test converges situation, on the one hand be whether the overall noise that system is back to front end can control to certain level, be whole system on the other hand, whether the reverse operation level is operated in stable, rational operating state.Optical-fiber network is tested the luminous power of its each node, is used for installation, debugging and the maintenance of fiber optic network.

Process chart as shown in Figure 1

The present invention includes following equipment:

A. TV station's headend room signal testing is selected the digital signal measuring instrument for use:

(1) digital spectrometer, be suitable for the QAM of various bandwidth, the QPSK digital signal is measured, possesses cable analysis, Digital Signal Analysis two big professional analysis tools, CSO/CTB is provided, C/N, HUM, TILT, MOD, LEVEL, modulation degree, the sound accompaniment frequency deviation, digital power is measured and the QAM/QPSK modulation constellation, MER (the modulation error rate), EVM (vector error), PRO/POST BER key figure signal indexs such as (bit error rates) is measured, be comprehensive in the digital television engineering, measurement and analysis instrument can effectively be safeguarded CableModem fast reliably, key businesses such as DTV;

(2) DVB synthesis analyzer;

(3) Digital Television DVB tester except that the repertoire with simulated television, also has Measurement and analysis functions such as Digital Television average power, MER, BER, and simple and easy frequency spectrum function, support multiple DVB pattern, portable design, quick charge, is more suitable for multiple measurement needs at the overlength operating time;

(4) code stream analysis instrument can be to MPEG, and transmission code streams such as DVB (Transport Stream) provide the labor of data record under real-time analysis, record and the off-line state, finds and solve the mistake and the fault of digital television transmission system emerged in operation fast;

B. at network node or user side, mainly carry out the test of forward signal and reverse transfer, select for use tester as follows:

(1) spectrum analyzer,

(2) Digital Television DVB tester,

(3) digital DVB synthesis analyzer,

(4) have CATV " five in one " synthesis analyzer that there are line analysis, spectrum analysis, digital QAM power measurement, the function of televising in reverse signal source, CATV, be particularly suitable for the reverse channel transmission debugging,

(5) the reverse return path signal of digital modulation source, can carry out QPSK, DQPSK, QAM modulation to signal, support 320KB, 640KB, 1280KB, 2560KB to modulate code stream, the frequency transmission characteristic that its distinctive frequency sweep output function cooperates the DOCIS agreement can easily finish reverse passback path is measured

(6) reverse return path signal source;

C. light path is measured optional:

(1) optical time domain reflection analyzer (OTDR),

(2) light power meter;

D. for the monitoring of hfc plant the whole network running status, can select network management system for use, monitor in real time in each main node of network, and message transmission is carried out centralized monitor and management to Surveillance center.

The invention provides following method of testing and carry out bidirectional monitoring and uplink test:

(1) measurement result video modulation mode

Test connects sees figure two, select for use digital spectrometer as headend room test instrument, far-end selects reverse return path signal generator as the reverse signal source, or select for use and have that return path signal takes place and the TV functions field intensity meter, at far-end, by the return path signal generator or have that return path signal takes place and the TV functions field intensity meter in carrier signal of return path injection to cable television network.Digital spectrometer is measured the return path carrier signal at front end, and this measures picture and exports with video mode, and is modulated onto an idle channels, transmits by through path and goes back.At far-end, the engineer will receive one at the seen live signal measurement picture of front end.By level at reverse return path signal source adjusted frequency and variable carrier wave, can see the test result of headend room received signal as local test, it is simple unusually that network test and maintenance become.This system also allows to test simultaneously from different places, only different modulating frequencies need be set so that each engineer can differentiate its source easily.This method of testing is convenient and practical, is suitable for adopting in the construction of middle-size and small-size two-way net and monitoring, but owing to need take user channel, is unsuitable for using in the multinode complication system.

(2) multiplex's mode Auto-Test System of far and near end both-way communication

Be the monitoring of avoiding taking the family channel and realizing many working points (far-end), utilize up-downgoing pilot carrier frequency point to carry out communication (modulation and demodulation mode), carry out the simultaneous observation of reverse signal measurement result, can see the actual measurement situation of near-end machine room when being implemented in the far-end field adjustable equally synchronously.Utilize different recognition codings, can debug simultaneously or monitor by the dozens of far-end.

This system comprises reverse return path signal analyzer or digital spectrometer as headend room test instrument, the two-way catv analyzer takes place as the far-end reverse signal and the test instrument, the communication setting two ends are adjusted output synchronously and are measured, this mode is applicable to that the HFC complex network tests automatically, and the test connection layout is seen figure three.

Description of drawings

Fig. 1 is a process chart of the present invention

Fig. 2 is a test connection layout of the present invention

Fig. 3 is that the HFC complex network is tested connection layout automatically

Fig. 4 is the test planisphere

The present invention has following characteristics:

(1) the two-way catv analyzer transmits the swept-frequency signal of a 5 ~ 65MHz, arrive machine room by the return circuit, after oppositely return path signal analyzer or digital spectrometer receive this signal, its information package is modulated to a carrier signal, send by forward loop, the two-way catv analyzer receives this signal by forward path and unpacks, and can read and inject the measurement result of signal at machine room, and measuring process is simple and convenient.

(2) can change return circuit test into forward test, meet conventional test custom, also can carry out the test of forward signal simultaneously, the test of forward and reverse loop signal is once finished, convenient test, succinct, rapidly.

(3) each test all is to be center axis point with the machine room, and the light station is a reference zero, makes each level, each bar circuit return machine room, and level conforms to.

(4) this convergence type, normalizing formula method of testing meet Cable Modem upward signal and converge to the operation principle of machine room by different paths, can reduce the conventionally test error, and Fig. 4 is the test planisphere.

Embodiment

Embodiment 1

Present embodiment comprises following equipment:

A. TV station's headend room signal testing is selected the digital signal measuring instrument for use:

(1) digital spectrometer, be suitable for the QAM of various bandwidth, the QPSK digital signal is measured, possesses cable analysis, Digital Signal Analysis two big professional analysis tools, CSO/CTB is provided, C/N, HUM, TILT, MOD, LEVEL, modulation degree, the sound accompaniment frequency deviation, digital power is measured and the QAM/QPSK modulation constellation, MER (the modulation error rate), EVM (vector error), PRO/POSTBER key figure signal indexs such as (bit error rates) is measured, be comprehensive in the digital television engineering, measurement and analysis instrument can effectively be safeguarded CableModem fast reliably, key businesses such as DTV;

(2) DVB synthesis analyzer;

(3) Digital Television DVB tester except that the repertoire with simulated television, also has Measurement and analysis functions such as Digital Television average power, MER, BER, and simple and easy frequency spectrum function, support multiple DVB pattern, portable design, quick charge, is more suitable for multiple measurement needs at the overlength operating time;

(4) code stream analysis instrument can be to MPEG, and transmission code streams such as DVB (Transport Stream) provide the labor of data record under real-time analysis, record and the off-line state, finds and solve the mistake and the fault of digital television transmission system emerged in operation fast;

B. at network node or user side, mainly carry out the test of forward signal and reverse transfer, select for use tester as follows:

(1) spectrum analyzer,

(2) Digital Television DVB tester,

(3) digital DVB synthesis analyzer,

(4) have CATV " five in one " synthesis analyzer that there are line analysis, spectrum analysis, digital QAM power measurement, the function of televising in reverse signal source, CATV, be particularly suitable for the reverse channel transmission debugging

(5) the reverse return path signal of digital modulation source, can carry out QPSK, DQPSK, QAM modulation to signal, support 320KB, 640KB, 1280KB, 2560KB to modulate code stream, the frequency transmission characteristic that its distinctive frequency sweep output function cooperates the DOCIS agreement can easily finish reverse passback path is measured.

(6) reverse return path signal source

C. light path is measured optional

(3) optical time domain reflection analyzer (OTDR),

(4) light power meter,

D. for the monitoring of hfc plant the whole network running status, can select network management system for use, monitor in real time in each main node of network, and message transmission is carried out centralized monitor and management to Surveillance center.

Claims (1)

1. a method for building digital TV network is characterized in that, comprises following equipment:

A. TV station's headend room signal testing is selected the digital signal measuring instrument for use:

(1) digital spectrometer, be suitable for the QAM of various bandwidth, the QPSK digital signal is measured, possesses cable analysis, Digital Signal Analysis two big professional analysis tools, CSO/CTB is provided, C/N, HUM, TILT, MOD, LEVEL, modulation degree, the sound accompaniment frequency deviation, digital power is measured and the QAM/QPSK modulation constellation, MER (the modulation error rate), EVM (vector error), PRO/POSTBER key figure signal indexs such as (bit error rates) is measured, be comprehensive in the digital television engineering, reliable measurement and analysis instrument, can effectively safeguard CableModem fast, key businesses such as DTV

(2) digital DVB synthesis analyzer,

(3) Digital Television DVB tester except that the repertoire with simulated television, also has Measurement and analysis functions such as Digital Television average power, MER, BER, and simple and easy frequency spectrum function, support multiple DVB pattern, portable design, quick charge, the overlength operating time, be more suitable for multiple measurement needs

(4) code stream analysis instrument can be to MPEG, and transmission code streams such as DVB (Transport Stream) provide the labor of data record under real-time analysis, record and the off-line state, finds and solve the mistake and the fault of digital television transmission system emerged in operation fast;

B. at network node or user side, mainly carry out the test of forward signal and reverse transfer, select for use tester as follows:

(1) spectrum analyzer,

(2) Digital Television DVB tester,

(3) digital DVB synthesis analyzer,

(4) have CATV " five in one " synthesis analyzer that there are line analysis, spectrum analysis, digital QAM power measurement, the function of televising in reverse signal source, CATV, be particularly suitable for the reverse channel transmission debugging,

(5) the reverse return path signal of digital modulation source, can carry out QPSK, DQPSK, QAM modulation to signal, support 320KB, 640KB, 1280KB, 2560KB to modulate code stream, the frequency transmission characteristic that its distinctive frequency sweep output function cooperates the DOCIS agreement can easily finish reverse passback path is measured

(6) reverse return path signal source;

C. light path is measured optional:

(1) optical time domain reflection analyzer (OTDR),

(2) light power meter;

D. for the monitoring of hfc plant the whole network running status, can select network management system for use, monitor in real time in each main node of network, and message transmission is carried out centralized monitor and management to Surveillance center.

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