SatSig topic:

HX and Telstar 11 triumph

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Jun 18^th, 2009 at 10:45am

Bentley Walker are very proud to report that their clients using the latest HX NOC on Telstar 11 are receiving the highest quality modulation possible on 1 meg uploading carriers from the satellite and in recent tests in West Africa the HX50 stayed locked in the heaviest of rain storms while C Band systems costing nearly 4 times more were unlocking; could this be the death knell for C Band in Africa ?

For more details of this high powered DVB-S2 service and how to apply to be a BW reseller contact Sales@BentleyWalker.com

Jun 18^th, 2009 at 12:47pm

Doubtful.

What that statement lacks is the likelihood of that "highest quality modulation" NOT being possible due to the HX Adaptive Coding and Modulation reverting back to QPSK/BPSK when attenuated by weather. Therefore, seriously degrading throughput. Partial truths are dangerous.

As for the Ku staying up, and Cband going down when under weather. That statement is suspect and frankly - highly unlikely. I would have to see both budgets (and possibly with my own eyes) before I would believe it. I have seen Cband links stay up in the "heaviest of downpours" with Ku shots (QPSK/BPSK long and short block FEC) right next to them dropping link at the first sign of clouds and rain.

C-Band is nothing short of impressive under weather.

Jun 18^th, 2009 at 1:32pm

This is too generalizing and hysteric. I am sorry, but I have to step in.

It looks like you're telling that customers have to prefer higher order modulation links as they deliver better quality. That's nonsense. The 'modulation' does not have 'quality'. It can be of a lower or a higher order. Customers do not bother whether you use 8PSK, QPSK, 16QAM or BPSK to deliver their IP bandwidth. It's up to the satellite ISP which modulation to use to satisfy the link budget requirements. While higher order modulation schemes allow the satellite ISP to squeeze more IP bits per Hz this may result in a less expensive service for the end customer. That's the only reason for the satellite ISP to prefer, say, 8PSK instead of lower order QPSK. It has no impact on the quality of service at all if you consider equivalent link budgets.

For the C-Band, I agree with Mike here. What C-Band link this was compared to? We run lots of C-Band in Africa and nobody has ever complained on any weather outages so far. C-Band uses lower frequency that is less susceptible to rain. That's physics. Ku-Band uses higher frequency and it has to be supported by the ACM to stay alive in tropical climate. Running Ku-Band in tropical climate has actually been pathetic until ACM was introduced recently. However, ACM is not a complete panacea. If the ACM Ku link on Anthony's Hughes system is designed to, say, run at 8PSK 7/8 during normal weather conditions and had to drop to, say, BPSK 1/2 to live through the rain, the remotes wil have around 4 times IP throughput decrease. The link is up, at a much slower rate. It's still better than non-ACM Ku links which would go down immediately.

IMHO, this makes such Ku/ACM/tropical climate combination to work for small DTH/SOHO customers only. (I wonder if the whole T-11N Ku Africa coverage thing has been designed with this Ku/ACM technology and DTH customers in mind.) The Ku equipment is small, service is cheaper, however expect performance to drop during the rain. If you run a dedicated WISP backbone over that you end up with very unhappy customer base during rains. At the other hand, C-Band can be designed to provide full IP throughput during the rain and without any neccessity to use ACM.

Jun 18^th, 2009 at 4:54pm

We are using a 1.2 mtrs dish with standard 2 watt Radio head and on a 1 meg return carrer we get maximum values 4/5 fec and 8/9 psk on the downstream . significantly Hughes with its adapative in route coding as well as adaptive out route coding is staying locked when C Band systems using larger dishes are loosing lock , customers dont need loads of technical waffle they can see with their own eyes our system remaining locked and passing traffic .....our agents/resellers are happy to testify if you want !

Jun 18^th, 2009 at 5:00pm

Sorry wanted to add that if we moved up to 1.8 mtrs dish with 4 watt BUC and our new HX 200 which has higher processing power the values would be much higher , we are comparing 2.4 C Band set ups costing far more than our Ku Band , I really think that Hughes adaptive inroute coding makes a significant difference , the downside of C Band apart from the cost is its vulnerabilty to interference at the low frequency and in Angola and DRC they are replacing their C band links with Ku as they have had so much trouble with Wi Fi links and other devise spoiling and interferring with the service ..........

Jun 18^th, 2009 at 5:11pm

"4/5 fec and 8/9 psk"? Technical waffle? No more words.

Jun 18^th, 2009 at 5:18pm

Mike

Our minimum system setting is QPSK 4/5 , therefore even with rain fade our Hub would still be operating at the most common commercial FEC modulation and throughput.

We do indeed have the ability to configure the system by the outroute and inroute to floor QPSK 1/4 and I agree with you were we to do this the IP throughput would be reduced however this is not the case as the signal on T11 is so strong we can run with good values .

I have 2 customers who observed the HX 50 on 1,2dish staying locked while their C Band systems unlocked , if you like I will ask them to provide screenshots of their modulation and inroute rate at time of hevy weather .

its seems that really this type of platform will provide a cost effective alternative to C Band in the T11 coverage zones =))))

Jul 1^st, 2009 at 9:18am

Maxim and Mike this is what clients are saying ...

Dear Anthony,
Hope this finds you well.
I would like to take this opportunity to thank you all at BW for your continues support and commitment and for providing us with the best cost effective solutions.
After performing tests on the new HX platform on T11, we are happy to inform you that the results are excellent and the reliability is also excellent.
We have tried the system in heavy rainy conditions and we never faced any disconnections. The modem locks back in 20 seconds after any power failure, and browsing is as smooth and fast as any normal DSL line.
We have only had the system installed for testing for 6 days, and already have sold and installed several systems.
Well done, keep it going !

Once again, thank you.
Best regards,
Nasser Matar

GM. Telecommunication
Powertech Inc.
91 Randall Street
T: +2316788111

Hi,

Words can hardly express ones inner thoughts… but I must congratulate you as well as the technical support team with this new system you have put and implemented in place...

I have installed the system at a diplomatic site, I was shocked as well as highly impressed with the results…. The Ambassador, The Secretary, and his Commercial Attaché, all congratulated me and expressed their sincere gratitude with what we have provided….. This new system is simply like DSL over the sky (Fast and stable)…... Currently its our winter season….. and the system did not even blink….

Well done….

Kind Regards

Hussein

**********************************************************
K E T R A C O
32 Malamah Thomas Street
Freetown
Sierra-Leone

Tel: 232-22-223014, 232-22-227532
Fax: 232-22-229458

Jul 1^st, 2009 at 12:24pm

Andrew,

Point of clarity - I was never stating that the T11/HX system was flawed or sub-par. I was merely discounting your statement about Ku holding up over C in heavy rain storms. Also pointing out the fact that throughput WILL be affected by ACM. Nothing more.

Honestly, I am glad to hear you guys are doing well with it and reports from the field are positive.

M

Jul 21^st, 2009 at 7:04pm

A Ku service on T11N may very well hold up under Adaptive Code Modulation, but in reality the throughput would grind to a halt on your typically over-contended hub service. Its not just about having a lock light.

C Band is and will always remain the preferred choice for tropical climates, hence the difference in price (particularly over Africa).

While the receiver may have maintained its "Lock", (aided by the demod steping down a few gears), what was the actual affect on packet loss and it's actual usability during this storm?

What was status of the return carrier?

On a bird as strong as T11N is in clear sky, QPSK 4/5 does not impress me.

Jul 21^st, 2009 at 8:56pm

My opinon is that to obtain 1 Mbit/s for the up return path from the remote site back to the hub using 1.2m dish and 2 watt BUC with 4/5 FEC is rather good going. Many systems would need to drop to 1/2 FEC to make such a high bit rate possible with 1.2m dish and such low power. So I have the opposite impression to the above message.

Regarding the arguments of C band versus Ku band. C band suffers less from rain fades. This may be compensated for by more powerful/more sensitive satellite and by using larger dish size and adaptive coding and uplink power control.

What should be avoided is dual-polarisation linear polarisation C band operation in the tropics. The ionosphere rotates the polarisation and you get severe cross pol interference on both uplink and downlink. You must use circular polarisation (RHCP and LHCP) at C band (and lower frequencies) for satcomms in the tropics.

C band satellite operation is becoming increasingly affected by radio interference from terrestrial wireless systems in Africa. The WiMAX terrestrial wireless systems operate on partially overlapping and adjacent frequencies.

Each operator has their own idea of contention ratio in shared VSAT networks. If some want to sell cheap service and high contention while others sell higher price service and low contention that is their business. Very high contention leads to very low bit rates and customers buying such cheap service need to be forewarned that that is all they will get. At the other extreme, some operators sell dedicated service with no contention where you have a steady, continuous, guaranteed bit rate 24/7.

In a shared system, when a good FAP policy is applied, everyone gets their fair share, depending on what tariff they pay.

Best regards, Eric.