ber measurement of qpsk, qam and cofdm modulated · pdf filebeing in the ber measuring screen,...

OPT-103-81/82/83/85/86 INSTRUCTION MANUAL

BER measurement of QPSK, QAM andCOFDM modulated signals

OPT-103-81/82/83/85/86

1

1 GENERAL

1.1 Description

This appendix contains the operating instructions for the following options belongingto the PROLINK-3 range:

OPT-103-81 BER measurement for DVB-Satellite signals (QPSK modulation)OPT-103-82 BER measurement for DVB-Cable signals (QAM modulation)OPT-103-83 BER measurement for DVB-Terrestrial signals (COFDM modulation)OPT-103-85 BER measurement for DVB-Satellite and DVB-Cable signals (QPSK

and QAM modulations)OPT-103-86 BER measurement for DVB-Satellite and DVB-Terrestrial signals

(QPSK and COFDM modulations)

By means of these options it is possible to make Bit Error Rate measurements ondigital signals. Besides, these options incorporate the DCI2 function (DVB ChannelsIdentifier) which provides information on the tuned channel, in this way it is possible toidentify it with total certainty with no need to decode the digital signal.

(1) Trade Mark of the DVB Digital Video Broadcasting Project (1830 to 1832)

(2) DCI, Device and Procedure patented by PROMAX ELECTRONICA, S.A. (Patent 9901632)

January 2000


1.2 Specifications

RF INPUTFrequency range

QAM signals 47 MHz to 862 MHzQPSK signals 950 MHz to 2150 MHzCOFDM signals 470 to 862 MHz

Level range QAM signals 45 dBµV to 110 dBµVQPSK signals 44 dBµV to 99 dBµVCOFDM signals 45 dBµV to 100 dBµV

Impedance 75 Ω

MEASUREMENTSQAM signals

Measurement BER before FEC (Forward Error Correction).Number of wrong packets received in themeasurement time.

Reading Numerical and level bar.

QPSK signalsMeasurement BER before Viterbi

BER after ViterbiNumber of wrong packets received in themeasurement time.


COFDM signalsMeasurement BER after Viterbi

CSI (Channel Status Information). Qualitativemeasurement about channel quality. Readoutbetween 0 and 100%, the 0 % valuecorresponds to maximum quality.Number of wrong packets received in themeasurement time.


DCI FUNCTION DVB Channel Identifier. It provides informationabout the channel we are making themeasurement.

January 2000


QAM SIGNAL PARAMETERSDemodulation 16/32/64/128/256 QAMSymbol rate 1000 to 7000 kbaudsSymbol Rate acquisition range ± 240 ppmCarrier frequency offset ± 0.08 x Symbol rateNyquist filter roll-off (α) 0.15Spectral inversion Selectable: On, OffEquivalent noise degradation < 1.5 dB

QPSK SIGNAL PARAMETERSIF bandwidth 55 MHzSymbol rate 23000 to 30000 kbauds

4000 to 30000 kbauds for channel spacingfrequency ≥ 29.5 MHz

Symbol Rate acquisition range ± 70 ppmCarrier frequency offset ± 0.1 x Symbol rateNyquist filter roll-off (α) 0.35Code rate 1/2, 2/3, 3/4, 4/5, 5/6, 6/7, 7/8, 8/9 and AutoSpectral inversion Selectable: On, Off and Auto except for the

following values of Code Rate: 4/5, 5/6, 6/7and 8/9.

Equivalent noise degradation < 1 dB

COFDM SIGNAL PARAMETERSCarriers 2k / 8k (user definable)Guard Interval 1/4, 1/8, 1/16, 1/32 (user definable)Code Rate 1/2, 2/3, 3/4, 5/6, 7/8Modulation QPSK, 16QAM, 64QAMSpectral inversion On/offHierarchyFEC Reed-Solomon (204,188) and Viterbi

January 2000


January 2000


2 OPERATING INSTRUCTIONS

The following operating instructions assume the user's knowledge in operatingthe PROLINK-3, as described in its instructions manual.

2.1 BER measurement mode selection

To select the BER measurement mode:

1) Select the TV operating mode. If present operating mode is the spectrum analyser

mode press key [21].

2) Select the terrestrial band for the measurement of QAM or COFDM modulatedsignals or the satellite band for the measurement of QPSK modulated signals.Available frequency ranges are:

QAM signals 47 MHz to 862 MHzQPSK signals 950 MHz to 2150 MHzCOFDM signals 470 to 862 MHz

3) Select the DIGITAL operating mode by means of the key [20].

4) Select the BER measurement mode: to do this press key [22] and turn therotary selector [4] to select the BER measuring mode, next, to activate it press the

rotary selector [4] or key [22].

January 2000


2.2 QAM modulation

The equipments including any of the following options permit to makemeasurements of the BER for digital QAM modulated channels:

OPT-103-82 BER measurement for DVB-Cable signals (QAM modulation)OPT-103-85 BER measurement for DVB-Satellite and DVB-Cable signals

(QPSK and QAM modulations)

Before to measure the BER it is necessary to define some parameters concerningthe digital signal, which are described next. To see its present value or to modify it,being in the BER measuring screen, press the rotary selector, a multiple-choice menushowing the functions relative to the BER measurement will appear on the screen:

1) Modulations It defines the modulation type. When selecting this function and pressing the rotaryselector a multiple-choice menu will appear on the screen, this menu permits tochoose one of the following modulations: 16, 32, 64, 128 and 256.

2) Symbol RateWhen selecting this function and pressing the rotary selector a multiple-choice menuwill appear on the screen, this menu permits to choose one of the following values:6875, 6111, 5000, 4443, 1528, 1500, 1408, 1333, 1266, 1000 kbauds, or well todefine any other value by means of the Other option.

When selecting the Other option, a screen titled QAM SYMBOL RATE will appear,

this screen shows present Symbol Rate value, to modify it press key [31] ,enter the new value (four figures) and finally press the rotary selector to activate it.

3) Spectral Inv.If necessary, activate the Spectral inversion. If the spectral inversion is not correctlyselected, reception will not be correct.

4) AttenuatorIt permits to select attenuation between 0 and 30 dB. It is advisable to activate the30 dB attenuator under that measurement conditions where the signal level is nearto the maximum input level (approximately starting from 20 dB under the maximumlevel) and it is possible that the tuner becomes saturated. Under no-saturationconditions, when increasing the attenuation value the BER measure must tomaintain or to increase (insufficient signal level) but never to decrease.

January 2000


Once you have defined the QAM signal parameters, it will be possible to measurethe BER.

When the BER measuring mode is selected, the monitor will show a picture like thefollowing:

Figure 1.- BER measuring screen for QAM modulated signals.

First of all it is shown the BER before FEC (Forward Error Correction).

In a digital reception system for cable signals, after the QAM decoder an errorcorrection method called Reed-Solomon is applied (see figure 2). Obviously, the errorrate after the corrector is lower to the error rate at the QAM decoder output. This is thereason because this screen provides the BER measurement before FEC (Forward ErrorCorrection) and the number of non correctable errors (W.P., Wrong Packets) receivedafter Reed-Solomon in the measuring time.

Figure 2.- Digital reception system via cable.

January 2000


The BER measurement is provided in scientific notation (i.e. 1.0 E-5 means 1.0x10-5

that is to say one wrong bit of every 100,000) and through an analogue bar (as itslength is smaller the signal quality will be better). The analogue representation is doneon a logarithmic scale (not linear).

With the aim to have a reference about the signal quality, it is considered that asystem has a good quality when it decodes less than one non-correctable error forevery transmission hour. This border is known as QEF (Quasi-Error-Free) and itcorresponds approximately to a BER before FEC of 2.0E-4 BER (2.0x10-4, that is to saytwo incorrect bits of every 10,000). This value is marked on the measurement bar of theBER and therefore, BER for acceptable signals must be at the left side of this mark.

Below the BER analogue bar it is shown the tuned frequency (or channel) and thefrequency deviation in kHz between the tuned frequency and the one which optimizesthe BER (i.e. 800.00 MHz + 1.2 kHz).

In the next line it is shown the number of noncorrectable packets received 'wrongpackets' (up to a maximum of 126) in the time detailed on its right. A packet isconsidered wrong when one, at least, noncorrectable bit is detected. To reset thismeasurement just modify the measurement conditions: for example change the tunedfrequency.

Finally it is shown a status line which displays information about the detected signal.The possible messages that can appear and its meaning are shown in the following list.The messages are exposed from less to more fulfilment of the MPEG-2 standard:

No signal receivedAny signal has been detected.

Signal receivedA signal is detected but it can not be decoded.

Carrier recoveredA digital carrier has been detected but it can not be decoded.

MPEG-2 Correct detection of a MPEG-2 signal. The BER is showed.

In case of detecting a DVB signal, message MPEG-2 DVB-C will appearand the DVB Channel Identifier function will be automatically activated. Seesection 2.5 DVB Channel Identifier.

January 2000


IMPORTANT REMARK

DVB-C channels tuning may require an adjusting process. It is recommended tofollow next procedure:

1.- From the spectrum analyser mode, tune the channel at its centralfrequency.

2.- Switch to TV mode, BER measuring mode.3.- If in the lower line of the screen does not appear MPEG-2 message

(and consequently BER is unacceptable), by turning the rotary selectordeviate the tuning frequency until MPEG-2 message appears. Finallytune channel again to minimize the frequency deviation which optimizesthe BER and therefore minimize the BER.

If it is not possible to detect any MPEG-2 channel, make sure that digital signalparameters are correctly defined and if signal level is too low, check that the30 dB attenuator is not activated (Attenuator 0 dB).

2.3 QPSK modulation

The equipments including any of the following options permit to makemeasurements of the BER for digital QPSK modulated channels:

OPT-103-81 BER measurement for DVB-Satellite signals (QPSK modulation)OPT-103-85 BER measurement for DVB-Satellite and DVB-Cable signals

(QPSK and QAM modulations)

Before to measure the BER it is necessary to define some parameters concerningthe digital signal, which are described next. To see its present value or to modify it,being in the BER measuring screen, press the rotary selector, a multiple-choice menushowing the functions relative to the BER measurement will appear :

1) Code Rate Also known as Viterbi ratio. It defines the ratio between the number of data bits andactual transmission bits (the difference corresponds to the control bits for errordetection and correction). It permits to choose between 1/2, 2/3, 3/4, 4/5, 5/6, 6/7, 7/8, 8/9 and Auto. If CodeRate parameter is not known it is possible to assign the Auto option.

January 2000


2) Symbol Rate It is possible to choose between the following values : 30000, 27500, 22000, 20000,19995, 6110, 6000, 5998, 5632, 5062, 4340, 4000 kbauds, or well to define anyother value (Other).

When selecting the Other option, a screen titled QPSK SYMBOL RATE will appear.

This screen shows present value, to modify it press key [31] and enter thenew value through the keyboard. The unit accepts any number with 5 figuresbetween 2000 and 35000 kbauds (fifth figure acts as validation). For example, toselect a symbol rate of 8200 kbauds it must be entered : 08200.

3) Spectral Inv. Finally, if necessary, activate the Spectral inversion. The Auto mode permits toautomate this selection except for the following Code Rate: 4/5, 5/6, 6/7 and 8/9. Ifthe spectral inversion is not correctly selected, reception will not be correct.

4) Attenuator It permits to select attenuation between 0 and 30 dB. It is advisable to activate the30 dB attenuator under that measurement conditions where the signal level is nearto the maximum input level (approximately starting from 20 dB under the maximumlevel) and it is possible that the tuner becomes saturated. Under no-saturationconditions, when increasing the attenuation value the BER measure must tomaintain or to increase (insufficient signal level) but never to decrease.

Once you have defined the QPSK signal parameters, it will be possible to measurethe BER.

When the BER measuring mode is selected, the monitor will show a picture like thefollowing:

Figure 3.- BER measuring screen for QPSK modulated signals.

January 2000


Two BER measurements are shown:

1) BER before FEC (Forward Error Corrections)2) BER after Viterbi

In a digital reception system for satellite signals, after the QPSK decoder twodifferent correction methods are applied (see figure 4). Obviously, each time we applyan error corrector to a digital signal, the error rate changes, therefore if we measure ina digital satellite television system, for example, the error rate at the output of the QPSKdemodulator, at the output of the Viterbi decoder, and at the output of the Reed-Solomon decoder, we obtain nothing more than different error rates. This is the reasonbecause the BER measurement is provided before FEC, after Viterbi and the numberof non correctable errors (W.P. - wrong packets-) received after Reed-Solomon for themeasuring time.

Figure 4.- Digital reception system via satellite.

The BER measurement is provided in scientific notation (i.e. 2.0 E-3 means 2.0x10-3,that is to say two incorrect bits of every 1,000) and through an analogue bar (as itslength is smaller the signal quality will be better). The analogue representation is doneon a logarithmic scale (not linear).

With the aim to have a reference about the signal quality, it is considered that asystem has a good quality when it decodes less than one non-correctable error forevery transmission hour. This border is known as QEF (Quasi-Error-Free) and itcorresponds approximately to a BER after Viterbi of 2.0E-4 BER (2.0x10-4). This valueis marked on the measurement bar of the BER after Viterbi and therefore, BER foracceptable signals must be at the left side of this mark.

Next it is shown the tuning frequency and the frequency deviation in MHz betweenthe tuned frequency and the one which optimizes the BER (i.e. Freq: 1777.0 + 1.2 MHz).

Next it is shown the number of noncorrectable packets received W.P. -wrongpackets- (up to a maximum of 126) in the time detailed on its right. A packet isconsidered wrong when a bit is received incorrectly. To reset this measurement justmodify the measurement conditions: for example change the tuning frequency.

January 2000


Finally it is shown a status line with information about the detected signal. Thepossible messages that can appear and its meaning are shown in the following list. Themessages are exposed from less to more fulfilment of the MPEG-2 standard:

No signal received Any signal has been detected.

Signal receivedA signal is detected but it can not be decoded.

Carrier recoveredA digital carrier has been detected but it can not be decoded.

Viterbi synchronizedA digital carrier has been detected and the Viterbi algorithm is synchronized, buttoo many frames arrive with non correctable errors. It is not possible to quantifythe BER.

MPEG-2Correct detection of a MPEG-2 signal.

In case of detecting a DVB signal, message MPEG-2 DVB-S will appearand the DVB Channel Identifier function will be automatically activated. Seesection 2.5 DVB Channel Identifier.

IMPORTANT REMARK

DVB-S channels tuning may require an adjusting process. It is recommended tofollow next procedure:

1.- From the spectrum analyser mode, tune the channel at its centralfrequency.

2.- Switch to TV mode, BER measuring mode.3.- If in the lower line of the screen does not appear MPEG-2 message

(and consequently BER is unacceptable), by turning the rotary selectordeviate the tuning frequency until MPEG-2 message appears. Finallytune again channel to minimize the frequency deviation which optimizesthe BER and therefore minimize the BER.

If it is not possible to detect any MPEG-2 channel, make sure that digital signalparameters are correctly defined and if signal level is too low, check that the30 dB attenuator is not activated (Attenuator 0 dB).

January 2000


2.4 COFDM modulation

The equipments including any of the following options permit to makemeasurements of the BER for digital COFDM modulated channels:

OPT-103-83 BER measurement for DVB-Terrestrial signals (COFDM modulation)OPT-103-86 BER measurement for DVB-Satellite and DVB-Terrestrial signals

(QPSK and COFDM modulations)

Before to measure the BER it is necessary to define some parameters concerningthe digital signal, which are described next. To see its present value or to modify it,being in the BER measuring screen, press the rotary selector, a multiple-choice menushowing the functions relative to the BER measurement will appear. The parametersthat must be defined by the user are the following:

1) Carriers It defines the number of modulation carriers between 2k and 8k. To modify its value,place the marker over the Carriers field by turning the rotary selector and then pressit: a menu will appear on the screen. Turning the rotary selector select the desiredvalue for the Carriers parameter and finally press it again to validate.

2) Guard interval The Guard Interval parameter corresponds to the time between symbols, its purposeis to permit a correct detection in multi-path situations. This parameter is definedaccording to the symbol length: 1/4, 1/8, 1/16, 1/32. To modify its value, by turningthe rotary selector, place the marker over the Guard Interval field and then press it: a menu with the available values will appear. Turning the rotary selector select thedesired value and finally press it to validate.

3) Attenuator

It permits to select attenuation between 0 and 30 dB. It is advisable to activate the30 dB attenuator under that measurement conditions where the signal level is nearto the maximum input level (approximately starting from 20 dB under the maximumlevel) and it is possible that the tuner becomes saturated. Under no-saturationconditions, when increasing the attenuation value the BER measure must tomaintain or to increase (insufficient signal level) but never to decrease.

This configuration menu shows, besides the user definable COFDM signalparameters, the value of the rest of COFDM signal parameters detected automatically:

January 2000


Code Rate Also known as Viterbi ratio, defines the ratio between the data bitsnumber and the total number of bits transmitted (the differencecorresponds to the number of control bits for the error detection andrecovery).

Modulations Carriers modulation. It also defines the system noise immunity.(QPSK, 16-QAM and 64-QAM).

Spectral Inv. Defines the state of the spectral inversion.Hierarchy The DVB-T norm contemplates the possibility to make a TDT

transmission with hierarchical levels, it is to say a simultaneoustransmission of the same program with different image qualities andnoise protection levels, in order the receiver decodes the signal inthe best conditions.

Once you have defined the COFDM signal parameters, it will be possible tomeasure the BER. When the BER measuring mode is selected, the monitor will showa picture like the following:

Figure 6.- COFDM signals BER measuring screen.

Two measures are shown :

1) CSI: Channel status information2) BER after Viterbi

The CSI measure (Channel Status Information) is a qualitative measure aboutchannel state, between 0 and 100%. The optimum value corresponds to 0%. Thismeasure permits to look for the best situation even in those measuring conditions wherethe measured BER is best than the minimum readout (in this way, in the example of theprevious figure, the measured BER is lower that the minimum readout, 1.0x10-7, but theCSI measurement, 27%, still can be improved).

January 2000


Next it is shown the BER after Viterbi measurement both in numeric and graphic barformat.

In a reception system of terrestrial digital signal, after the COFDM decoder two errorcorrection methods are applied. Obviously, each time we apply an error corrector to thedigital signal, the error rate changes, therefore if we measure the error rate at the outputof the COFDM demodulator, at the output of the Viterbi decoder, and at the output ofthe Reed-Solomon decoder, we obtain nothing more than different error rates. This isthe reason because of the OPT-103-83 and 86 options provide the BER after Viterbiand the number of Wrong packets received after Reed- Solomon.

Figure 7.- COFDM reception system.

The BER measurement is provided in scientific notation (i.e. 3.1 E-7 means 3.1x10-7,that is to say 3.1 wrong bits of each 10000000) and through a graphic bar (as its lengthis smaller the signal quality will be better). The analogue representation is done on alogarithmic scale (not linear), that is to say, the bar divisions correspond to the exponentof the measurement.

With the aim to have a reference about the signal quality, it is considered that asystem has a good quality when it decodes less than one non-correctable error forevery transmission hour. This border is known as QEF (QUASI-ERROR-FREE) and itcorresponds approximately to a BER after Viterbi of 2.0E-4 BER (2.0x10-4, that is to say2 wrong bits of each 10000). This value is marked on the measurement bar of the BERand therefore, BER for acceptable signals must be at the left side of this mark.

In the lower line of the screen it appears the W. P. counter (Wrong Packetscounter). This counter shows the number of wrong packets received after Reed-Solomon during the measuring time. This counter is automatically activated when theunit detects an MPEG-2 signal.

If at any time, the received signal stops to satisfy the requirements of the MPEG-2standard, this counter will deactivate, that is to say it will keep the number of wrongpackets received and the measuring time, later, if an MPEG-2 signal is received again,it will activate with no reset.

January 2000


When during any measuring time interval the counter has been deactivated, in otherwords the signal has not satisfied the MPEG-2 requirements, the presentation of thiscounter will alternate with another counter titled FAIL. This second counter shows thetime that the detected signal has not fulfilled the MPEG-2 standard requirements (12seconds in the example of the following figure) and the number of signal cuts (2 in theexample of the following figure). To reset the counter it is necessary to change any of

the detection parameters, for example tune again the signal or push twice the [22]key.

Figure 8.- Signalling two MPEG-2 signal cuts with a total length of 12 seconds.

Finally it is shown a status line with information about the detected signal. Thepossible messages that can appear and its meaning are showing the following list. Themessages are exposed from less to more fulfilment of the MPEG-2 standard:

No signal receivedNo signal has been detected.

Timing recoveredOnly it is possible to recuperate the symbol time.

AFC in lockThe system automatic frequency control can identify and lock a digital transmission(TDT) but its parameters can not be obtained. It can be due to a transitory situationprevious to the TPS identification (Transmission Parameter Signalling) or well to a TDTtransmission with an insufficient C/N ratio.

January 2000


TPS in lockThe TPS (Transmission Parameter Signalling) are decoded. The TPS are carriers (17in the 2k system and 68 in the 8k system) modulated in DBPSK, containing informationrelated to the transmission, modulation and codification: Modulation type (QPSK,16-QAM, 64-QAM), Hierarchy, Guard Interval, Viterbi Code Rate, Transmission mode(2k or 8k) and Number of the received frame.

MPEG-2Correct detection of a MPEG-2 signal.

In case of detecting a DVB signal, message MPEG-2 DVB-T will appear and theDVB Channel Identifier function will be automatically activated. See section 2.5 DVBChannel Identifier.

2.5 DVB Channels Identifier: DCI3 function

This function permits to identify DVB channels with no need to have a digital signaldecoder which permits to see transmitted TV channels.

The DVB group recommends to digital TV service operators the codification on theTransport Stream of some particular fields containing data information. The TransportStream is a sequence of packets, of constant length, which carry video or audioinformation or data.

Data packets can be grouped to constitute TABLES, some of these tables contentinformation defined by the network operator and which show the type of service that isbeing supplied to the users. Among the different data defined in these tables, the mostfrequently used data for channel identification purposes are:

Network: It contents the name given to the set of all the Transport Streammanaged inside the same communication channel.

Bouquet: It contents the name given to the set of all the services commercializedas one entity.

Service: It contents the names of services that, under the control of oneoperator, can be shown at each moment on the Transport Stream, asa function of current programming.

In case the operator includes this information, the three fields are not transmittedat the same time but they appear alternatively in different packets. Besides, the cadenceof presentation of each one of these packets may vary from one operator to another.

(3) DCI, Device and Procedure patented by PROMAX ELECTRONICA, S.A. (Patent 9901632)

January 2000


When tuning a DVB compatible transponder, the DCI function (DVB ChannelsIdentifier) detects those data packets including service information relative to these threefields and shows on the lower line on the screen the information contained in themautomatically.

Figure 5.- DCI function. In this example the information coded by the operator on the Service and Network fields is the same.

January 2000


The information that appears in the Network, Bouquet and Service fields isresponsibility of the Operator in charge of the tuned transponder. ThePROLINK-3 only decodes this information, if it is present, and shows it on thescreen.

January 2000


January 2000


TABLE OF CONTENTS

1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 OPERATING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.1 BER measurement mode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2 QAM modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3 QPSK modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.4 COFDM modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.5 DVB Channels Identifier: DCI function . . . . . . . . . . . . . . . . . . . . . . . . . 17

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