MF-TDMA or (Dynamic) SCPC: Not an Easy Choice!

Tuesday 25 March 2014
MF-TDMA or (Dynamic) SCPC: Not an Easy Choice!
Mobile connectivity with tablets and smart phones in emerging countries creates ample opportunities for mobile network operators using satellite as a economically viable solution to limit ARPU numbers.


by Dave Suffys, Sales Support Manager at Newtec

According to Mobile World, in most European countries the mobile (smart)phone penetration is over 100%. This means that the likes of Apple, Sony and Samsung have limited potential to further expand their market reach any further within this geographical area. A potentially growing market for them are the emerging countries which they do not target with smartphones we pay 700$ for but rather with affordable (as low as 50$) smartphones offering basic capabilities to go online and get connected.

Where 5 years ago there were some efforts to provide the emerging countries with affordable laptops (for example the “One Laptop Per Child” initiative by Nicholas Negroponte) we now see that these countries frog-leaped over this and went straight for mobile connectivity with tablets and smart phones.

Come into play the mobile network operators. They too see an almost saturated market penetration with 100% coverage in most developed countries. Hence their need for expansion towards the emerging countries. To quote O3B “there are still the other 3 billion people that have a need to get connected”.

But reaching out to those people means rolling out more terrestrial networks which is a tricky economical exercise with average revenue per user (ARPU) numbers that are far below what is seen on existing networks. And this is where satellite comes into play!

Which Return Technology Do You Use? MF-TDMA or Dynamic SCPC?

But it is not an easy choice… which technology do you use? Do you use typical MF-TDMA technology because of the low rate and bursty nature of the traffic? Do you take advantage of the fact that some platforms can switch from MF-TDMA to SCPC when traffic demands increase and evolve toward a more steady-state?

Sure that would be an excellent idea, given the fact that typical satellite routers are an affordable kit where the majority of the cost resides in the hub. But on the downside, MF-TDMA has limited transmission efficiency and once the investment in the hub infrastructure and terminals is made, the cost of the satellite bandwidth remains the major recurring cost driver.

Technically, MF-TDMA requires a serious overhead (20%) because of guard times between bursts. On top of that there is the serious overhead of encapsulation and thirdly, given a large enough population of mobiles to service, the traffic isn’t that burstable anymore.

Comes to the rescue another type of return technology, SCPC, but dynamic, because these networks tend to evolve and grow from small pico-cells to larger aggregated continuous traffic sites. Interesting technology, short block codes for minimal delay and jitter, while it is possible to change the transmit parameters such as symbol rate and frequency. You only need to simply stop the carrier and bring it up again with the new parameters, but you need to plan ahead. In order to avoid defragmentation of the satellite capacity, a change in a carrier requires adjusting other carriers.

Dynamic SCPC? YES, but not too often please because a change has some serious impact on the network and reshuffling services, and of course creates traffic interruptions.

So there you have it. On the one hand MF-TDMA, which is able to handle bursty traffic and is overbookable but with limited transmission efficiency and on the other hand dynamic SCPC but with a serious impact on traffic when changes are needed.

Wouldn’t you want a system that behaves like MF-TDMA but with SCPC efficiency? Comes into play Newtec’s Dialog system with Mx-DMA and High Resolution Coding (HRC).

Wait a minute… Mx-DMA, what’s that?

Mx-DMA for Techies

Let’s start with a definition:

Mx-DMA = Cross dimensional multiple access technology

It cross-correlates and assigns in real-time:  return frequency plan, symbol rate,  modulation, coding and power  based on return traffic demand, QoS management and channel conditions simultaneously for all terminals in the network.  With each carrier assigned to just 1 terminal,  highest return SCPC like efficiencies are achieved  while maintaining the flexibility of MF-TDMA.

A couple of things are worth noticing:

  • cross-correlation:  there is a Newtec scheduler that looks at the whole of the return carrier population that determines the best means of transmitting  each carrier
  • real-time: meaning that there is a kind of carrier planning that is assigned over the return carriers which is continuously adjusting itself in real time
  • based on return traffic demand: simply by having a demand for more traffic in the return channel, a terminal which requests more traffic, will automatically be assigned more space capacity
  • QoS management: by having QoS in the return channels individually, but also over the complete return channel pool, one can effectively take advantage of statistical multiplexing and effectively overbook the return channels
  • channels conditions: ACM is nothing new, even for return channels. But when applying Newtec’s FlexACM to certain return carriers that require it (by giving them more space capacity to maintain their SLA) in combination with statistical multiplexing, one can truly do ACM and at the same time stick to the SLA without the need for extra buffer capacity
  • each carrier is assigned to just 1 terminal: meaning that each terminal gets its own dedicated SCPC return channel. Hence the SCPC efficiency so no need for guard times between “bursts”. There are no bursts, the carrier is always there. It simply continuously adjusts all transmit parameters (like symbol rate and frequency).
Business Case with Mx-DMA

Ok, wait a minute, enough of the techno-talk. So in essence what I get is a MF-TDMA system but with SCPC efficiency that will seriously drive down my recurring satellite cost? Yes, you do!

So back to reality. I want to roll-out a network for backhauling the exponentially increasing mobile data traffic in low ARPU generating emerging countries. So I need a solution that offers anything between the very small cell with bursty traffic up to the more continuous traffic kind of larger cell and all this with the highest spectral efficiency (read what I pay for the satellite capacity)?

Say hello to Newtec Dialog, a platform that can offers just that. Newtec credo has been “Shaping the Future of Satellite Communications” for quite some time and that is exactly what we are bringing here to you.

A single platform that allows the roll-out of a network with very low cost remote terminals, ranging from anywhere from the highly overbookable MF-TDMA type of remote to the more continuous kind of traffic typically served by SCPC modems.

So don’t worry anymore, there is no need to select a:

  • pure MF-TDMA system to take advantage of being able to handle bursty traffic but with its lack of efficiency
  • pure SCPC system to take advantage of the higher efficiency and dedicated capacity (read simple SCPC modems)
  • dynamic SCPC system that brings up and tears down carriers depending on the need
  • system that switches between MF-TDMA and SCPC when the need arises with a few mouse clicks and a down time

All of this belongs now to the past, instead, you can create a network with a mix of terminals that require a few kbits of bursty and steady state continuous traffic all with the highest spectral efficiency possible.

And even though I say it myself, what you need is simply a Flexible, Scalable and Efficient platform like our very own Newtec Dialog system.