VSIM Modem and Telephony Simulator User Manual
Contents
1. MER gt I D r H I 1 r J DH 1 A D I Miller Engineering Services Inc e VSIM Modem and Telephony Simulator User Manual Miller Engineering Services Inc E mail sales mesi net Web www mesi net 1 1 1 1 2 VSINLUSAGE aaa ana 3 VEM COMMAND LINE OPTIONS vs nee lie ikea 3 ddd SV ODEON e e O eee e ee a 4 BU SE a 1 1 3 sleman p n A AA A BN sn 2 1 1 4 Duena me A eae ees ela a nal ila 6 1 4 5 AN Sa i MY rn 6 1 1 6 mode Mi Mode Options NN TN 6 Lay TR gi IA IP A ae i oe A Se ge eS 6 1 1 8 A DOW OCH ODA AAA ee ao ee 6 1 1 9 MAS TOO ODOM Ria 6 1 4 10 rata A eis aenea NN A talendi aa 6 14314 senat ODOT eest hon otra seas ails RM A den Aimakk er 2 20 FE ENAMORA iaa 7 180 00 A een en ee AU USM e re e E ES E 12 14 1 ODIO ia oo ib 12 MY es AA KR PAY KA DA KY MY 12 LL a PON On be A DR AD AAA AA nn A nn A AE 12 LAS Plevel GG Level ODIOS ld 12 1 13 redi level Op OR Sabet Maasika tad 12 1 120 ESOS CL OPIO LN IN ilast a sake illa te 12 1 127 BER Hlenome ODUOM asia sesinle MAN AA es ie e 13 E E 13 1 12 TON OT OA ANA SS INA aa a ei ee 13 1 124 E Mena ODILON eae on A A tana aatal aga aa eee 13 1 1 25 YA delay and YC delay OPIO ee 14 1 1 26 NAf delay and NC delay Option 14 E ES N OP ae LE EA al een A nek 14 1 1268 EE EE 14 1 5 29 ERA eain Ophon si sanal T innen 15 7 1 30 ed 72101 CGI Pp A e kaja BNN ARMY 15 1 1 31 SE2. 10 would correspond to a scale factor of 101020 applied to the Answer transmitter s samples or a gain factor of 3 16 Users should note that large positive values for T might result in excessive gain and saturation of the Answer transmitter signal Therefore it is advised to attenuate also using t For example v 32 with a CALL side transmit power of 16 dB and Answer side transmit power of 28 dB would be entered as VSIM v29 T 12 As another example v 32 with a CALL side transmit power of 28 dB and Answer side transmit power of 10 dB would be entered as VSIM v29 T18 1 1 11 r rate Option The option sets the bit rate for the modulator selected and 1s entered in bits sec For example v 29 at 9 600 bits sec would be entered as VSIM v29 r9600 1 1 12 c filename Option The c option selects the XY plot mode for the graphical display The Answer side is plotted in green and the ALL side is plotted in blue The constellation display or scatter plot can be observed using this option During execution the display can be toggled between XY plot and dual trace using the alt n key combination When a file name is supplied VSIM opens the specified file and displays the contents with even samples deflecting X and odd samples deflecting Y The file format is 4 character ASCII HEX samples one per line X or I sample first then Y or Q sample The user can generate an example of a suitable file b
3. is essential that the user set the Tx gt system delay to compensate for fixed near end delay or the near end echo canceller peak will slide toward the right side of the delay line and eventually out of the echo canceller s window This can be observed in the following 2 examples VSIM v32 EC plot taps NAQ VSIM v32 EC plot taps NA64 In example 1 the echo canceller main tap grows at about 1 4 of the EC coef length as it should leaving 3 4 of EC coeff for the echo tail In example 2 the near end path is 8 msec long 64 8000 and the echo canceller main tap has moved to about 3 4 of the EC coeff length leaving only 1 4 of the taps for the tail which will degrade the near end echo canceller performance In this case the user should compensate by setting Tx gt system delay 64 1 1 27 F delay Option The F option specifies the far path delay for both CALL and ANSWER modems and is entered in samples at 8 kHz The far path delay is the delay between the Answer side hybrid and the CALL side hybrid and it simulates the distance between the near end hybrid and the far end hybrid This is the actual far echo path The default far path is 0 samples so that there is no delay Far end echo cancellation can be seen in VSIM by using the F and ERLfarA options as in the following example for a far path distance of 12 5 msec and 6 dB far end return loss VSIM v32 EC plot taps F100 ERLfarA6 Users should note that the d
4. ANS near end Echo Return Loss dB default 0dB ERLfarAlgain gt ANS far end Echo Return Loss dB default infinite ERLnearC gain gt CALL near end Echo Return Loss dB default 0dB ERLfarC gain gt CALL far end Echo Return Loss dB default infinite C type gt write Coefficients to file coef dat default disabled It 2S Lai 3 5 C54xk 4esATTIGLX S ADSP21X 6 ADSP2106 Olfreg gt frequency Offset Hz default 0 h freg gt hum frequency Hz Hlratio gt signal to hum ratio dB S gt suppress banner display P gt XY plot persistence O accumulate max 2047 EC plot taps gt plot echo canceller taps V gt enable Tx and Rx test vector dump to txvector dat and rxvector dat IQ gt enable constellation I and Q dump to ig dat file nographics gt disable graphics YC delay gt CALL Tx gt system delay 8kHz samples default 0 1 1 1 v Option The v option configures the transmitter for the selected type of signal and sets up the receiver s detector mask as requires to enable detection of the selected signal The available v components available are v8 ITU T V 8 modem configured for use in a v 34 connection v17 ITU T V 17 fax modem v17TEP ITU T V 17 fax modem with 1800 Hz Talker Echo Protection signal enabled v21 ITU T V 21 configured for v 21 data modem v21hdlc or v21 fax ITU T V 21 channel 2 configured for fax HDLC flag tr
5. Frequency R1 signaling digits 0 9 11 12 KP KP2 ST vR2F ITU T Multi Frequency R2 Forward signaling digits 0 9 A E VR2B ITU T Multi Frequency R2 Backward signaling digits 0 9 A E VCAS or vCAS1 ETSI Type 1 Caller ID with preceding CPE Alert Signal vCID or vCID1 ETSI Type 1 Caller ID FSK vCID2 ETSI Type 2 Caller ID for Call Waiting with preceding CPE Alert Signal VCASIB Bellcore Type 1 Caller ID for with preceding CPE Alert Signal vCIDIB Bellcore Type 1 Caller ID FSK vCID2B Bellcore Type 2 Caller ID for Call Waiting with preceding CPE Alert Signal VCNG ITU T T 30 fax CalliNG 1100 Hz tone vdialtone ITU T North American dialtone 350 Hz 440 Hz tones vringback ITU T North American ringback 440 Hz 480 Hz tones 4 sec On 2 sec off vbusy ITU T North American busy 480 Hz 620 Hz tones 0 5 sec on 0 5 sec off vreorder ITU T North American reorder or fast busy 480 Hz 620 Hz tones 0 25 sec on 0 25 sec off 1 1 2 f filename Option The f option allows the user to read in samples from a file specified by filename for processing by the receiver enabled by the v option The file format is 4 characters ASCII HEX samples one per line and samples at 8 kHz The user can generate an example of a suitable file by running VSIM osamples dat to produce the file samples dat in the specified format Users are advised that full duplex modems will not correctly handshake when using sample files for in
6. I I I I I I I I I I I 0 35 LEI o P CC asu ABjag ANDIS 2000 2500 3000 3500 4000 Hertz 1500 1000 Frequency CONUS MV Continental US Mid Voice distortion Type 3 conus mid voice I I I I I I I I I I I I HA I I I I I I I I I I I I 4 I I I I I I LI L L IW my Op ssundsay apnyuhey 1500 2000 2500 3000 3500 4000 1000 Frequency Hertz 100 l l l l l l r l l l l l l ee eee EEN saa bap aseyj 1500 2000 2500 3000 3500 4000 1000 Frequency Hertz conus mid voice asw ABjag ANDIS 1500 2000 2500 3000 z500 4000 1000 Frequency Hertz CONUS PV Continental US Poor Voice distortion Type 4 conus poor volga al g I I I I I I HA I I I I I I I I I I I I 4 I I I I I I oo O O MU pi asuodsay apnpubejs 1500 2000 2500 3000 3500 4000 1000 500 al Frequency Hertz 200 dl va ii I I I I I I J I I I I I I 4 I I I I I I I I I I I I LI i saa bap aseyj 1000 1500 2000 2500 3000 3500 4000 500 Frequency Hertz conus Poor volga BEE LL 1 Lea dnog 1500 2000 2500 a000 3500 4000 1000 Frequency Hertz For example v 29 in CONUS Mid Voice would be entered as VSIM v29 13 1 1 14 d dir Option The d option selects the direction to be monitored betwe
7. LA CATA OPON asia klan akin T aatal aiandi abso E cena to 15 1432 C NCO ON rennen e A MEM e SEA 15 BESS AOLA SAJ AADO HO Md annad ee 16 1 1342 MITRE and PATO OPTIONS sssr na na nan al alla 16 IAr O Oea A RE BBm 16 21 30 A A A 16 1 137 EC DIO Tap Op TOR len mad a i ideal 16 1 10 AL 67 27 72 AAA A MK PL KM MAA A Ta e il 17 E E EE 17 1 1 40 sorap el ODOM eene 17 VS IM SIMULATION OPTIONS ee en en Aa 17 1 VSIM Usage The VSIM simulator runs under a DOS window that switches to full screen to support VGA graphics mode It 1s a DOS command line driven program that accepts a variety of command line configurations and run time controls that are described in the following sections VSIM implements a two channel telecom simulation that emulates a CALL channel and an Answer channel so that fax and data modems call progress dual tone digit signaling and miscellaneous telephony tones can be evaluated VSIM can be configured to display and or dump to file the Answer or CALL side receiver processor s operational status and the user can toggle the display and file mode between CALL and Answer during execution The channel simulation includes a variety of common telephony impairments that can be selectively enabled at run time and altered during execution The graphical display is a crude emulation of a 2 channel storage oscilloscope with dual trace and X Y plot modes again selectable at run time and during execution File I O includes a ge
8. ansmission and GenDet fax v21 channel 2 HDLC flag detection v22 ITU T V 22bis v23 ITU T V 23 data modem v23B ITU T V 26 75 baud backward channel v26 ITU T v 26 modem operating in the ALT B configuration transmitting all ones v26A or v26B ITU T V 26 ALT A or ALT B transmitting all ones v26P ITU T V 26bis ALT B transmitting P1800 alternations per FSVS 210 STU III mode v26fast ITU T V 26 ALT B transmitting all ones with reduced receiver synchronization time v27 ITU T V 27ter fax modem v27TEP ITU T V 27ter fax modem with 1800 Hz Talker Echo Protection signal enabled v29 ITU T V 29 fax modem with 1700 Hz Talker Echo Protection signal enabled v29TEP ITU T V 29 fax modem v32 ITU T V 32 without the TCM 9 600 mode v32bis ITU T V 32bis data modem v34 ITU T V 34 data modem vbell103 Bellcore Bell 103 300 baud modem in the FI channel vbell103F1 Bellcore Bell 103 300 baud modem in the F1 channel vbell103F2 Bellcore Bell 103 300 baud modem in the F2 channel vbell202 Bellcore Bell 202 FSK modem operating from 300 to 1350 baud vnoise Additive White Gaussian Noise AWGN only at SNR specified by nSNR vtone single tone oscillator at frequency specified by Ofrequency vCED ITU T T 30 fax CallED 2100 Hz tone VECSD ITU T V 25 Echo Canceller Suppressor Disable tone 2100 Hz with 450 msec phase reversals vDTMF ITU T Discrete Tone Multi Frequency digits 0 9 A B C D vR1 ITU T Multi
9. e One exception 1s that m8 selects a half duplex input mode for v32 and v34 so that the half duplex training signals can be processed using the f option 1 1 7 n ratio Option The n option sets the Signal to Noise Ratio and 1s entered as a floating point number in dB The default SNR is 1000 dB essentially no noise For example v 29 at 25 dB SNR would be entered as VSIM v29 n25 1 1 8 t power Option The t option sets the transmitter power level ratio and is entered as a floating point number in dBm0 The default transmitter power level is 16 dBm0 For example v 29 at 28 dBm0 would be entered as VSIM v29 t 28 1 1 9 twist ratio Option The twist option sets the high low tone power level ratio and is entered as a floating point number in dB The default twist is 0 dB For example DTMF at 8 dB twist would be entered as VSIM vdtmf twi st8 1 1 10 T ratio Option The T option sets the CALL transmit power ratio and is entered as a floating point number in dB The default ratio 1s 0 dB which corresponds to both CALL and Answer transmitter s operating without attenuation The channel model takes the value entered converts it to a linear number and multiplies the Answer transmitter samples by this number Therefore a T value of 10 would correspond to a scale factor of 10 applied to the Answer transmitter s samples or an attenuation factor of 0 316 Similarly Therefore a T value of
10. efault length of Tx sample is only 256 words which limits the bulk delay available to the far end echo canceller 1 1 28 ERLnearA gain Option The FRLnearA option sets the gain value for the ANSWER side near end Echo Return Loss gain block and 1s entered as a floating point number in dB The default value for the ERLnearA gain block is O dB unity gain so that VSIM normally runs with 100 of a channel s transmitted signal reflected back into its receiver A good analog hybrid design will typically provide 20 dB or more of attenuation of the near end echo For example v 32 with a near end echo return loss of 20 dB would be entered as VSIM v32 ERLnearA 20 EC plot taps In this example the user can clearly see the reduced echo return by the reduction in the main tap height plotted using the EC plot taps option 1 1 29 ERLfarA gain Option The ERLfarA option sets the gain value for the Answer side far end Echo Return Loss gain block and 1s entered as a floating point number in dB The default value for the ERLfarA gain block is infinity dB so that VSIM normally runs with no far end echo For example v 32 with a far end echo return loss of 10 dB at 10 msec would be entered as VSIM v32 ERLfarA 10 F80 EC plot taps In this example the user can clearly see the far end echo canceller tap grow in the far end green component of EC coef 1 1 30 ERLnearC gain Option The ERLnearC option sets the gain
11. en Call and Answer modems The dir options are Dir a Answer side monitoring Dir c CALL side monitoring For example v 32 CALL side display would be entered as VSIM v32 de 1 1 15 p Option The p option forces VSIM to pause between screen writes and is a method for slowing down the simulation 1 1 16 w Option The w option enables a watt meter display that shows the average power level of the signal as seen at the input to the currently enabled receiver direction For example to monitor the power for v 29 would be entered as VSIM v29 w 1 1 17 I delay Option The l option sets the path delays between the CALL and Answer modems and 1s entered in samples at 8 kHz For example v 32 with a path delay of 10 msec 8000 0 01 80 would be entered as VSIM v32 180 And would yield a round trip delay of 2 0 01 2400 8000 48 symbols 1 1 18 g level G level Options The g option specifies a gain hit level and is entered as a floating point number in dB and the G option specifies the amplitude deviation for a sinusoidal gain modulation and is entered as a floating point number in dB The g gain hit has a linear trajectory with a fixed time constant of 1 0 seconds for the transition time and 2 0 seconds for the level times The G sinusoid has a fixed frequency of 4 0 Hz 1 1 19 j freq J level Options The option sets the sinusoidal phase jitter impairment frequency and is entered as a f
12. graphics 1 2 VSIM Simulation Options There are several options available during a simulation These are printed to the screen when VSIM first starts to allow time for the screen to settle in VGA mode These options are alt x or esc terminate the program restore text mode and return to DOS space bar Pause program execution alt n toggle graphics screen between dual traces and XY plot alt d toggle the observation direction between Answer and CALL alt r force a re sync or re train if relevant alt c force a rate change or rate renegotiate if relevant alt b force a new burst alt e display current BER statistics alt w write EQ coef and EC coef for current observation direction to log file x alt up arrow increase noise power by 1 dB alt down arrow decrease noise power by dB up arrow advance demod symbol timing by 1 quanta own arrow retard demod symbol timing by 1 quanta right arrow advance demod LO phase left arrow retard demod LO phase page up increase vertical scale page down decrease vertical scale
13. is would be simulated as VSIM vdtmf 01 5 Both tones in this case row and column are offset by 1 5 of their respective frequencies So for digit zero the nominal row col frequencies of 9410 1336 0 Hz would be offset to 942 4 1338 0 Hz 1 1 34 h freg and H ratio Options The h option specifies the frequency of an added sinusoidal interferer summed into the channel and is entered as a floating point number in Hz The H option specified the signal to hum added in the channel model and is entered as a floating point number in dB The default hum amount is infinity or no hum For example v 29 with a 60 Hz signal to hum ratio of 0 dB would be entered as VSIM v29 h60 HO osamples dat The output file samples dat will contain v 29 modulated samples with a strong 60 Hz component 1 1 35 S Option The S option suppresses the text screen printing at the end of a simulation run 1 1 36 P Option The p option sets the XY plot persistence similar to the persist knob on an oscilloscope and is entered in samples The default persistence is of the XY buf length For example v 27 with a shorter persistence in XY plot mode would be entered as VSIM v29 c P200 1 1 37 EC plot taps Option The EC plot taps option enables plotting of the echo canceller coefficient vector EC coeff during echo canceller training if relevant The near end segment of EC _coef is plotted in yellow and the fa
14. le and all of the interpolator decimator filter coefficients The type parameter selections are 1 C format 2 Texas Instruments C3x 32 bit words 3 Texas Instruments C54x 16 bit words 4 Lucent DSP16xx 16 bit words 5 Analog Devices 21xx 24 bit words 6 Analog Devices 2106x 32 bit words For example to product a file of coefficients for the rcoscoef h filter include file for C the user would enter VSIM C1 1 1 33 O freq Option The O option specifies a frequency offset and is entered as a floating point number in Hz or as a percentage if Yo is immediately appended The default frequency offset is 0 Hz It is used to set the tone frequency for vtone simulations and to set the amount of carrier frequency offset in all modems For example generation of a 1 kHz tone would be entered as VSIM vtone O1000 osamples dat The output file samples dat will contain samples of a IkHz sinusoid As a second example v 29 with a carrier frequency offset of 7 Hz would be entered as VSIM v29 07 If the percent operator 1s used then GenDet dual tone generators will calculate the frequency of the tone offset by the specified percentage of the tone fundamental This 1s primarily used in the digit generators for DTMF and MFC where frequency tolerance performance specifications are given in percent For example in ITU T Recommendation Q 24 Annex A the frequency tolerance for AT amp T is given as 1 5 for operation Th
15. loating point number in Hz and the J option sets the phase jitter amplitude and is entered as a floating point number in degrees As an example v 29 with 10 degrees of sinusoidal phase jitter at 60 Hz would be entered as VSIM v29 360 J10 1 1 20 s offset Option The s option specifies the transmitter symbol clock offset frequency and 1s entered as a floating point number in Hz For example v 29 with 1 0 Hz of symbol clock offset would be entered as VSIM v29 s 1 0 1 1 21 BER filename Option The BER option enables the Bit Error Rate measurement mode In this mode the file output of the demodulated data to x is suspended and filename is opened for BER output If BER is entered with no filename then the default file ber dat 1s opened The modem specified by the v option is initiated and the SNR 1s set to that specified by the n option VSIM then executes the modem with all ones as the data pattern transmitted and it counts the number of bit errors and block errors When the number of bits specified by the L option default 1e7 bits are received or the number of bit errors specified by the E option default 1e7 are counted then the BER and BLER are computed the Tx and Rx burst counters are incremented the SNR 1s incremented by 1 0 and a new burst is initiated This lets the user set an initial minimum SNR level for a BER curve and then let the simulation sweep through the SNR range
16. m mode gt Tx gt mode M mode gt Rx gt mode n ratio gt Signal to Noise Ratio dB default 100 dB t power gt CALL Tx power dBm0 default 16 dBm0 T ratio gt answer call Tx power ratio dB default 0 dB twist ratio gt high low tone Tx power ratio dB default 0 dB r rate gt data rate 1200 through 14400 bits sec default 9600 c filename gt plot constellation or file i type gt gain distortion impairment default 0 O none 1 AT amp T spec 2 PSTN typical 3 CONUS MV 4 CONUS PV didir gt direction a answer c call default a p gt enable pause between modem calls w gt enables wattmeter l delay gt Rx Tx path delay 8kHz samples default 0 gllevel gt gain hit level dB Glfrequency gt sinusoidal gain mod jJ freq gt phase jitter freq Hz J level gt jitter level degrees s offset gt Tx symbol clock offset default 0 BER filename gt measure BER write results to file default ber dat ACQ gt enable acquisition measurement mode L length gt BER burst length bits default 1e7 Ellength gt BER errors per SNR level bits default 1e7 YA delay gt ANS Tx gt system delay 8kHz samples default 0 NA delay gt ANS near end path delay 8kHz samples default 0 NC delay gt CALL near end path delay 8kHz samples default 0 F delay gt Rx Tx far end path delay 8kHz samples default 0 ERLnearAlgain gt
17. neral run time continuous dump in a file called simply x and a time tagged log of all transmitter and receiver state ID s for both CALL and Answer sides in a file called states dat VSIM can optionally accept input for a specified sample file 8 kHz samples one per line ASCII HEX format so that users can digitize live line signals feed them to VSIM which implements exactly the same algorithms as the DSP ports and readily observe the modem s behavior off line The VSIM channel model provides a complete and accurate method for Bit Error Rate BER and Acquisition ACO testing under a variety of impairments in an automated fashion In BER and ACQ modes the SNR is automatically swept and the BER BLER Block Error Rate and acquisition statistics are logged to ber dat 1 1 VSIM Command Line Options The general form for execution of the VSIM simulator under MS DOS is VSIM option option option Where the options are v modem gt modem type default is v29 Op 7 ATTE 21y 22 23 235 265 264 26B 26P Zi 2118P 29 29TEP 52 228154 34 58111035 Dell Osh belli02F2 bell202 noise tone CED ECSD DTMF R1 R2F R2B CAS CID CNG dialtone ringback busy reorder f filename gt file input o filename gt output IF to file default rxif dat D filename gt data file input ASCII hex one symbol per line NUM samples gt num_samples frame size 8kHz samples default 20
18. put because the transmitter s signals have been overwritten by the file samples 1 1 3 o filename Option The o option allows the user to dump the samples produced by both the CALL and Answer transmitter s at the point where they are applied to the CALL receiver if CALL direction is selected or to the Answer receiver if the Answer direction 1s selected The file format is 4 characters ASCII HEX samples one per line and samples at 8 kHz 1 1 4 D filename Option The D option allows the user to modulate data from a text file that is formatted as one hex ASCII symbol per line For example to modulate symbols using v 29 at 9 600 bits sec 4 bits symbol from a file called data dat you would run VSIM v29 r9600 Ddata dat Where the data dat file might contain hex ASCII symbols 0 l e f 1 1 5 NUM samples The NUM option sets the frame size num_ samples This is the number of 8kHz samples created in one call to the TX function and the minimum number of samples processed by one call to the RX function The RX function will return a zero value without processing samples if at least num_ samples samples are not available The default frame size 1s 20 samples 1 1 6 m mode M mode Options The m and M mode options modify Tx gt mode and Rx gt mode respectively These correspond to the mode definitions presented later in this manual and are automatically invoked using the v options abov
19. r end segment is plotted in green For example v32 with the 11 gain distortion impairment enabled and 10 dB of far end echo at 10 msec would be entered as VSIM v32 F80 ERLfarA 10 EC plot taps 1 1 38 V Option The V option causes VSIM to open the transmitter test vector file txvector dat and the receiver test vector file rxvector dat and write test vectors to them during the run A variety of internal components relevant to the modulator are captured on a per symbol basis and for the demodulator every half symbol For example capturing v 29 test vectors would be enabled as VSIM v29 V 1 1 39 IQ Option The IQ option causes VSIM to open the file q dat and write the I and Q symbol components from currently selected direction of the demodulator to the file The file format is 4 character ASCII HEX samples one per line X or I sample first then Y or O sample The file format is consistent with the c filename option and dat can be viewed using e ciq dat option For example v 29 I Q symbol capture would be entered as VSIM v29 IQ 1 1 40 nographics Option The nographics option suppresses the VGA graphics mode switch in VSIM so that a text only simulation can be run This option 1s useful when the user wants to run multiple simulations simultaneously or in the background while performing other tasks For example a v 29 BER test would be entered as VSIM v29 BER n10 no
20. specifying a value of 1000 or higher using the E option The default number of errors is le7 bit errors For example a v 29 BER test starting at SNR 10 dB with le4 errors per burst would be entered as VSIM v29 BER n10 Ele4 1 1 25 YA delay and YC delay Option The Y option specifies the transmit system delay Tx gt system delay for CALL and ANSWER modems and is entered in samples at 8 kHz This is the amount in samples between the time a sample of the transmitted signal 1s produced at the output of your system s DAC to the time that signal is sampled by your ADC It is used by the echo canceller modems v26 v32 to align the peaks in the EC coef buffer and optimizes the span of the cancellers The default delay is zero samples Also see the discussion under TX CONTROL BLOCK Member Descriptions For example v32 with a Tx gt system delay of 40 would be entered as VSIM v32 Y A40 1 1 26 NA delay and NC delay Option The N option specifies the near path delay for CALL and ANSWER modems and is entered in samples at 8 kHz The near path delay is the delay from transmitter s sample output to the near end echo return attenuator 1 e the 4 to 2 wire conversion hybrid and back into the corresponding receiver The default near path distance is 0 samples so that there is no delay The user would include block sample delays if any in transferring samples from Tx sample to the actual D A conversion device It
21. until no bit errors are detected BER and BLER waterfall curves can be plotted from the results logged in filename or ber dat For example generating a BER curve to ber dat for v 29 starting at SNR 10 dB would be entered as VSIM v29 BER n10 1 1 22 ACQ Option The ACQ option causes VSIM to successively burst the modem specified by the v option for the number of bits specified by the L option without altering any of the impairments selected initially The burst spacing is randomized The number of bursts transmitted and the number of bursts received is logged in ber dat For example an acquisition test for v 29 at 16 dB SNR and CONUS Mid Voice with bursts of 10 000 bits would be entered as VSIM v29 n16 13 ACQ Lle4 1 1 23 L length Option The L option specifies the number of bits per burst in a BER or ACO mode simulation and is entered as a floating point number in bits The default length if L is not specified is le7 bits For example a v 29 ACQ test for 1 thousand bits per burst would be entered as VSIM v29 ACQ Lie 1 1 24 E length Option The E option specifies the number of errors allowed per burst in a BER mode simulation and is entered as a floating point number in bit errors When the BER measurement function has counted E bit errors then the statistics are logged the SNR is incremented and a new burst is initiated Valid burst statistics can be more quickly obtained by
22. value for the CALL side near end Echo Return Loss gain block and 1s entered as a floating point number in dB The default value for the ERLnearC gain block is 0 dB unity gain so that VSIM normally runs with 100 of a channel s transmitted signal reflected back into its receiver A good analog hybrid design will typically provide 20 dB or more of attenuation of the near end echo For example v 32 with a near end echo return loss of 20 dB would be entered as VSIM v32 ERLnearC 20 dc EC plot taps In this example the user can clearly see the reduced echo return by the reduction in the main tap height plotted using the EC plot taps option 1 1 31 ERLfarC gain Option The ERLfarC option sets the gain value for the Caller side far end Echo Return Loss gain block and 1s entered as a floating point number in dB The default value for the ERLfarC gain block is infinity dB so that VSIM normally runs with no far end echo For example v 32 with a far end echo return loss of 10 dB at 10 msec would be entered as VSIM v32 ERLfarA 10 F80 dc EC plot taps In this example the user can clearly see the far end echo canceller tap grow in the far end green component of EC coefT 1 1 32 C type Option The C option causes VSIM to write various coefficients to the file coef dat in the format specified by the type parameter These coefficients include the sine look up table the DFT filter coefficient look up tab
23. y running VSIM IO to produce the file ig dat which logs the demodulator s I Q base band pair Then this file can be displayed by VSIM cig dat 1 1 13 i type Option The option selects the gain distortion impairment applied to both CALL and Answer transmitters in the channel model The type options are e Type 0 none or flat line e Type 1 AT amp T specification is a typical band pass codec filter response for telephony channels AT amp T spec l l _ La IW UI I I gp asuodsay apnpubeyy 1500 2000 2500 3000 3500 4000 1000 Frequency Hertz 100 saalbap aseyy 2000 2500 2000 3500 4000 Hertz 1500 1000 Frequency AT amp T spec 0 7 cl EA ao O O asu Aga dno l l l l l l L l l l l l l l l l l l l l l l l l l T l l l l l 0 1 1500 2000 2500 3000 3500 4000 Hertz 1000 500 Frequency PSTN Typical which is a heuristic average of measured PSTN lines Type 2 measured PSTN Ap asuodsay apnyubepy 2000 2500 3000 3500 4000 1500 1000 Frequency Hertz 200 ls a is a e il i I I I I I I L I I I I I I E I I I I I I I I I I I I r I I I I I I LI al 100 saa bap asey 4 200 2000 2500 3000 3500 4000 Hertz 1500 1000 Frequency measured PSTN 0 4 E EE I I I I I I 1 I I I I I I I I I I I I
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