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Message started by Eric Johnston on May 5th, 2008 at 12:06pm

Title: ACM and DLA added to LinkStar S2
Post by Eric Johnston on May 5th, 2008 at 12:06pm
ViaSat adds Adaptive Coding & Modulation (ACM) and Dynamic Link Adaptation (DLA) to DVB-S2 LinkStar

ViaSat has started shipping LinkStarŪ modems equipped with Adaptive Coding and Modulation (ACM) and Dynamic Link Adaptation (DLA).

ACM reduces satellite bandwidth requirements by up to 63% for the outlink (hub to remotes) traffic, or alternatively, gives more bit rate for the same satellite power and bandwidth capacity.

DLA can reduce required bandwidth by up to 18% for the return link traffic

Two other features worth noting are:
SSL (Secure Sockets Layer) security for Virtual Private Networks (VPNs).
VNO (Virtual Network Operator) possibility providing many virtual networks from a single shared hub each with traffic performance reporting tools.

For more information read the ViaSat press release.

Title: Re: ACM and DLA added to LinkStar S2
Post by abbas89 on Mar 28th, 2010 at 7:34am
Helloe Mr.Eric

We have recently installed Linkstar S2A Hub with ACM Could you please send me some presentation over ACM that how it works.

My email id is leoboy89@gmail.com

Title: Re: ACM and DLA added to LinkStar S2
Post by Eric Johnston on Mar 28th, 2010 at 12:46pm
DVB-S2 Adaptive Coding and Modulation (APC)

A DVB-S2 outlink carrier comprises a series of symbols. The symbols come blocks of symbols, each block having symbols of the same modulation/FEC.  The coding and FEC for each block of symbols may differ, according to the intended receive site location in the downlink beam contours, size of receive dish, local rain fade etc. If the remote site tells the hub that it is suffering from rain fade (temporary low receive quality at the remote site) then hub can then temporarily put the outlink traffic intended for that site into a block of symbols with say QPSK modulation and 4/5 rate FEC, instead of the clear sky 8PSK 8/9 FEC.

DVB-S2 LDPC
QPSK @ 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10
8PSK @ 3/5, 2/3, 3/4, 5/6, 8/9, 9/10
16APSK @ 2/3, 3/4, 4/5, 5/6, 8/9, 9/10

The above only describes my understanding of the general principle of APC.  How it is implemented in your specific case will depend on how you configure the hub and the actual options available in the LinkStar hub software.

Conventional satellite systems might use QPSK 4/5 all of the time and have a large link margin to avoid outage in light rain. Total bit rate is limited by the QPSK 4/5 set up. The receive quality at the remote site is excessively good in clear sky conditions.

When you use APC, in clear sky conditions the modulation/coding will be perhaps 8PSK 8/9, resulting in increased information bit rate.  In rain conditions it might drop to QPSK 4/5 (as for conventional service).

I suggest you download and save this document:
http://www.etsi.org/deliver/etsi_en/302300_302399/302307/01.02.01_60/en_302307v010201p.pdf

Best regards, Eric.

Title: Re: ACM and DLA added to LinkStar S2
Post by abbas89 on Mar 29th, 2010 at 7:13am
Thanks for your instant reply Eric.

Take Care

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