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VSAT technology and installation >> LinkStar Forum: VSAT hubs and terminals >> BER and RSCorrectedErrorCount

Message started by EDWIN on Aug 21st, 2007 at 5:25pm

Title: BER and RSCorrectedErrorCount
Post by EDWIN on Aug 21st, 2007 at 5:25pm
At a region where most of the BER values is 0 and RSCorrectedErrorCount is also 0, having a site on the same satellite and the BER is 0.00002909231 while the RSCorrectedErrorCount is 0. Can this amounts to slow browsing at the site? All efforts have been made to bring the BER value to 0 but still not working. RSCorrectedErrorCount and RSUcorrectedErrorCount what they for?

Title: Re: BER and RSCorrectedErrorCount
Post by Forum Admin on Aug 21st, 2007 at 10:21pm
The receive QPSK bit error rate is an indication of the raw bit error rate based on the effort being needed to correct errors based on the main FEC system.  If the raw bit error rate is 0.01 then 1 bit in every hundred is probably wrong.  The FEC system will correct most of them but a few, particularly when several come close together will not be corrected and there will be bursts of errors in your corrected receive data stream.  If the raw bit error rate is 0.001 then hardly any errors will appear in your corrected receive data stream.  If the BER is 0.0001 or less then the number of error bits in your corrected receive data stream might be 1 per day - vitually none.  With a raw BER of 0.00002909231 your performance is so good that I would be suprised if you had any errors in several days, unless it rains heavily !

Read the raw BER very many times during the beam pointing and peaking up process.

The RSCorrectedErrorCount and RSUcorrectedErrorCount refer to additional FEC processing called Reed Soloman, this is an outer code and is designed to correct any residual errors from the basic FEC coding system.  The counts may briefly increment from zero shortly after power up but should not increase much from day to day.

Best regards, Eric.

27 Jan 2008:  I have amended this posting in bold to clarify that we are only talking about the receive process.  The data that comes out of the LinkStar modem into the ethernet cable towards your PC or router is derived from the corrected receive data stream.

Title: Re: BER and RSCorrectedErrorCount
Post by cylent on Jan 27th, 2008 at 8:58pm
Heres whats weird for me.

My QPSKBER   fluctuates between 0.00004848719 and 0.0006 and sometimes every so lightly hits 0.0001 but then goes back to the 0.0004 - 6, 7 and so on.

my corrected error count on the other hand doesnt like to stick at 0.

for example i just rebooted the modem and its reading 0.00004 but theres an error count of 3.

you said this may have to do with the OUTPUT ? does that mean the TX power?

I believe BW is doing auto power settings ?
what about the values in pconf?

pls advise.

Title: Re: BER and RSCorrectedErrorCount
Post by Maxim Usatov on Jan 27th, 2008 at 9:12pm
Cylent, your Tx circuit has no impact on the QPSKBER as it is basically the error measurement on your Rx. If it abnormally fluctuates, you shall look into your Rx circuit - antenna alignment, feed, cables and connectors. Terrestrial interference can also cause sporadic or periodic drops of QPSKBER - usually in C-Band and very rare in Ku. Additionally, local weather conditions at the teleport area also impacts on your QPSKBER. A rain or snow over the transmitting dish at the teleport can fade the signal and thus your QPSKBER increases.

Title: Re: BER and RSCorrectedErrorCount
Post by Forum Admin on Jan 27th, 2008 at 10:07pm
Thanks for the clarification, my use of the word output was misleading.  I was referring to the receive data following its FEC processing.

When the uncorrected BER is very low, like 0.0001 to 0.00001, it is normal for the displayed value to change from measurement to measurement.

You say

"my corrected error count on the other hand doesnt like to stick at 0.

for example i just rebooted the modem and its reading 0.00004 but theres an error count of 3."

The corrected error count is cumulative; it increments if an error gets through the FEC process.   This will typically occur during a heavy rain storm, when you may see the number increase from say 27433 to 43564.   It also quite often increments from its starting value of zero, during a fraction of a second at the moment of carrier lock after a reboot.    So an initial non zero value (like 3) is nothing to worry about at all.   If you are interested write down the number once per hour, day, week or month and see how much it goes up, if at all.   Long periods of no increase is normal during clear sky conditions.  A burst of interference, from say a car ignition, might increment the number.  Remember that your receive bit rate is probably about 30 Mbit/s so  a burst of many tens, hundreds or thousands of errors might be generated from an interruption of less a than a second.

Your system is working perfectly with a BER of 0.0001 to 0.00001    There are no errors at all in the corrected receive data stream so there is no effect at all on your browsing etc.

Best regards, Eric.

Title: Re: BER and RSCorrectedErrorCount
Post by cylent on Jan 27th, 2008 at 10:12pm
Thank you.

You guys really cleared things up for me.

I was literally worrying myself like crazy.

Whats odd is the cables are the same ones i used in the past for my starcom system. the connectors are new. the buc is new. the lnb is the not new but its from the same system when i used it before.
the dish is new.
I have tightened ever bolt and screw as good as i can get it.
yet the BER value cannot sit still ... it likes to jump between 0.00004 to 0.0001.  and as i mentioned the error rate increases at a very slow slow rate. for example: all night the modem is on with NO ONE doing any traffic i wake up to find 800 or so CorrectedErrors.

Now I am having a new issue.

My TimeSynced Value refuses to sit still. Even though the modem is locked whenever I do tcmp i notice it keeps increasing with every refresh.

This is very strange and I dont know why it keeps increasing.

Frankly i am getting very sick of these non-stop issues.

pls advise.

   RSCorrectedErrorCount        10    RSUncorrectedErrorCount       0
   QPSKBER           0.00006788207    I2CErrorCount                 0
   LostSyncCount                 0    TimeSynced                  674
   MaxTimeSynced               674    Synced                        1
   TimeUnSynced                  0    NCODeviation                -12
   CarrDeviation      -0.003019264    VCOLocked                     0
   CodeRate                    5/6    CarrierPhase             LOCKED
   RSVit                    LOCKED    UCActive             NOT ACTIVE
   Rs                     27.50000    Fs                           85
   frequency                  1616    UCLoaded                      1
   RxPower               -36.14841    RSFrameLength                 0

5 minutes later:

   RSCorrectedErrorCount        13    RSUncorrectedErrorCount       0
   QPSKBER           0.00005333591    I2CErrorCount                 0
   LostSyncCount                 0    TimeSynced                 1223
   MaxTimeSynced              1223    Synced                        1
   TimeUnSynced                  0    NCODeviation                 -4
   CarrDeviation      -0.002914877    VCOLocked                     0
   CodeRate                    5/6    CarrierPhase             LOCKED
   RSVit                    LOCKED    UCActive             NOT ACTIVE
   Rs                     27.50000    Fs                           85
   frequency                  1616    UCLoaded                      1
   RxPower               -36.14841    RSFrameLength                 0

BER 0.00005333591

notice the TimeSynced value. and error count. and signal is of course fluctuating.

Title: Re: BER and RSCorrectedErrorCount
Post by Eric Johnston on Jan 28th, 2008 at 11:08am
First, the varying uncorrected bit error rate.

Errors are caused by noise, which is randomly varying all of the time, so variations from one BER measurement to the next are quite normal.   Transmissions from the satellite are analogue radio symbols with 4 different phase angles and the added noise is analogue also.  In the demodulator in your modem an effort made to decide what two binary bits each received symbol is supposed to represent.   Each symbol had four possible values when it was created.  If the noise added is low then the meaning at the demodulator is clear.  If the noise added is high then the meaning may be uncertain or wrong.

The purpose of the FEC system is to analyse the stream of demodulated bit pairs and based on which are certain and which are doubtful correct all the errors if possible.  In this process the bit rate is reduced by 5/6, which is the FEC code rate.

Your receive transmission data rate is 54 Mbit/s and with an estimated uncorrected bit error rate of 0.0001 to 0.00001 the number of bit errors per second ranges from 54000 to 5400 per sec.  Each second you will get a different count, with wide variations.  This is all quite normal and nothing to worry about.

I must emphasise that ALL of these errors are being corrected and the bit rate reduced to 45 Mbit/s (information rate after FEC), so there is nothing for you to worry about.

Regarding the TimeSynced.

The fact that it increases is nothing to feel sick or worry about.   If you have a digital clock on your PC or on the wall that will also show an increase each time you look at it.  It is a similar, like a clock counting the time since it was last switched on.   Don't worry.   If you have a service outage due to blockage of the beam the TimeSynced will restart once the service is restored.   The MaxTimeSynced will represent the longest time ever recorded between service outages.

Best regards, Eric.

Title: Re: BER and RSCorrectedErrorCount
Post by cylent on Jan 28th, 2008 at 2:48pm

You really are a Godsend!
I've been on this S1 platform for well over a year now. I've even tried the iDirect system and to be honest I think iDirect are cheapskates.
Viasat at least puts in a fan for their modems.

I've once again gone up to the antenna and did some very minor antenna az. tuning as well as polarization tuning.

I've managed to get it down to 0.00006 or so. again. it never stabilizes and I've decided its quitting time and to leave it alone.

Now. I currently use a product called RouterOS by for my routing and inet sharing.
I've heard of a product called udgateway that promises sat internet acceleration.

I am a Redhat certified Systems engineer by trade so i can dish out a router for you in no time.
I just want to know whats so special about this udgateway and whether whats it doing is doable free.

Do you know of an alternate solution to this udgateway product?
if not, where does one purchase one?

at this time i am not ready to purchase a new modem although BW and everyone else is doing their best pitching the HX system to me. I simply wont bow down to hughes because their level 1 quota is simply too little.

with that said; i await your feedback.

Title: Re: BER and RSCorrectedErrorCount
Post by cylent on Jan 30th, 2008 at 9:10am

Title: Re: BER and RSCorrectedErrorCount
Post by Forum Admin on Jan 30th, 2008 at 9:18am
I know nothing about mikrotic or udgateway.

You need a hub or switch to physically allow more ethernet cables to be connected using up the existing IP LAN address range (as per the LAN IP/gateway-IP/subnet mask in your modem).  

If you want more devices you need to ask the service provider for a larger IP address range or to expand into your own private IP address space using your own router. Cisco routers work fine for me - but configuration needs a lot of learning.

Best regards, Eric.  

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