Network operator using dynamic coding techniques projects savings over US$1 million in three years

By Viasat

Budget calculations for a small hub-spoke satellite network in West Africa showed US$ 1.1 million in bandwidth savings over three years through implementation of Adaptive Coding and Modulation (ACM) and ViaSat Dynamic Link Adaptation (DLA) technologies. Imagine the savings in large, enterprise or national networks. Or the ability to add more network locations where bandwidth is scarce.

Adaptive Coding and Modulation for DVB-S2
In addition to the 30% savings promised by the data broadcast standard called DVB-S2, advanced satellite networking systems are implementing the ACM mode of operation, in which the hub dynamically changes the values of modulation and forward error correction (FEC) of network data traffic in response to changing link conditions.

During clear sky conditions, transmissions from the hub to remote sites use a highly bandwidth efficient modulation and coding point at all sites. When heavy rain fades occur at one or more locations, the modulation and coding automatically changes to a more robust rate for traffic only to the faded sites.

The diagram that follows presents the satellite bandwidth reduction provided by the ACM feature as compared to a DVB-S2 downstream carrier without ACM for various combinations of rain intensity (millimeters per hour) and Ku-band satellite performance.

As a reminder, these bandwidth savings from ACM are in addition to the 30%-40% bandwidth savings already provided by DVB-S2 technology compared to the previous standard, DVB-S.

Additional Performance and Reliability with DLA
ACM is an industry standard that more than one satellite communication system vendor is offering, but there are additional techniques that enable performance above and beyond the standard.

Bandwidth Savings with DLA – Dynamic Link Adaptation
The new LinkStar® S2A system uses a ViaSat-patented technology called DLA (Dynamic Link Adaptation) to provide operators with additional improvements in the overall satellite link strength in rain or other heavy weather fade conditions.

If the rain fade gets severe enough, the remote terminal site is automatically switched to a satellite carrier signal optimized for maximum mitigation of fade conditions. In this way the LinkStar DLA feature provides the maximum data speed possible in the least amount of satellite bandwidth for the majority of the time.

Here’s an example calculated from different combinations of data rates and coding techniques:

• Without DLA assume the traffic and satellite characteristics of a network require 20 carriers requiring 16.0 MHz of satellite bandwidth.
• With DLA this same aggregate rate of 16.7 Mbps can be contained within 16 carriers, which results in bandwidth of only 13.2 MHz, a bandwidth savings of 18%.

Better Performance for Remote Workers Using Satellite Satellite networks include inherent delay (latency) in network traffic and packet-based networks (such as Internet Protocol) also tend to produce additional slowing of network and software application performance with a lot of back and forth “chattiness”. But using wireless WAN data acceleration products can enable high-speed service performance on these types of networks

AcceleNet™, a product of ViaSat subsidiary ICT, reduces the “chattiness” to accelerate applications, dramatically reducing the time it takes to browse the Web, download e-mail and attachments, and transfer corporate files – all while maintaining data integrity. AcceleNet enables broadband-like performance on low rate and high latency networks through a combination of advanced data compression and accelerating the performance of standard business software.

Bandwidth Savings Case Study
The network in Western Africa, referenced at the beginning of this article, is using satellite capacity on NSS-7 that offers broad coverage in the EMEA region. This example shows the typical benefits of adding ACM and DLA to your network. (Savings may vary.)

The following conditions applied to the network:

• NSS-7 satellite
• Network hub-to-remote over-the-air link rate of 20 Mbps and remote-to-hub over-the-air link rate of 10 Mbps
• ITU rain rate of 80 millimeters per hour for Nigeria
• Network availability objective of 99.7% with balanced transponder power and bandwidth
• 1.2-meter antennas with 2.5 watt transmit power at each remote

Detailed satellite link calculations show that a 20 Mbps DVB-S2 hub-to remote carrier without ACM requires 18.6 MHz to support the required link objective. Conversely, a 20 Mbps DVB-S2 downstream carrier with ACM can use more efficient modulation and coding which requires only 12.5 MHz, yielding a tremendous 33% bandwidth savings (6.1 MHz).

On the remote terminal side 10 Mbps of aggregate over-the-air link rate using a traditional return link scheme without DLA technology, results in a requirement of 9.6 MHz of satellite bandwidth. A network using DLA needs only nine upstream traffic carriers, plus one more to assign for rain fade, for a total bandwidth of only 8.0 MHz. The bandwidth savings is 1.6 MHz or 17%.

In monetary terms, the combined bandwidth savings from ACM and DLA technologies in this case study is 7.7 MHz. Assuming a transponder cost of US$ 4000 per MHz per month, results in the cost savings of US$ 1.1 million over a 3-year service period.

The technologies also save capital expenditures up front. By enabling consistent performance throughout the network, regardless of satellite power variations based on the location of network sites within a satellite footprint, operators save on antenna costs. For this example, locations in Nigeria, Cameroon, and Niger were all able to use smaller, 1.2 meter antennas despite weaker satellite power in some locations.

Save Costs and Expand Transponder Capacity
In heavy weather environments on Ku-band satellites, the ViaSat LinkStar S2A system with Adaptive Coding and Modulation (ACM) technology can provide an additional satellite bandwidth savings of up to 46% compared to non-ACM networks. And ViaSat-exclusive DLA technology typically adds another 18% in satellite bandwidth efficiency on top of that. Using these technologies operators and service providers can lower their network overhead costs or free bandwidth to reach more network customers.