Home >> January 2015 Edition >> The Gap—TDMA Versus SCPC... A Teledyne Paradise Datacom Focus On Technology
The Gap—TDMA Versus SCPC... A Teledyne Paradise Datacom Focus On Technology
By Tony Radford, Vice President, Sales + Marketing, Teledyne Paradise Datacom


When the company launched Q-NET earlier last year under the portraiture of ‘Solving the VSAT vs. SCPC Dilemma’, I had no idea that this release would spark such vehement debate from some of my esteemed competitors who claim ascendancy when it comes to cellular-backhaul.

Teledyne Paradise Datacom’s Q-Flex™ Satellite Modem

The intent wasn’t to step on anyone’s toes by alleging that their products were in some way inferior or that they lack relevance. After all, I’m the first to toss kudos at the begetters of burst-technology—the perfect solution for the conveyance of thin-route transactional data across hundreds or thousands of users. 

Despite the fact that manufacturers of TDMA/VSAT products have been pushing their technology into the SCPC market space by increasing throughput and enhancing link efficiency—or that some manufacturers of SCPC modems have developed platforms that allow dynamic bandwidth-assignment and ‘network-level’ monitoring and control, the absence of a true, one-size-fits-all solution suggests that the question of TDMA or SCPC is definitely alive and well. To say that the question is “wrong” or that the decision is “simple” fails to give credence to the weight of the considerations faced by service providers when adopting the best architecture for their specific needs.

Being the purveyor of perhaps the world’s most versatile SCPC satellite modem, we were merely casting light on the fact that a gap exists between the peripheries of conventional SCPC and TDMA/VSAT domains, due to the applications for which they were originally designed. By ‘gap,’ I refer to that dilating divide that lies just beyond the reach of either architecture in its traditional form—that once shaded area now being illuminated by the need to adjust bent-pipe capacity as demand for access increases and as it shifts about the network by the hour of day and day of the week. 

Networks come in a variety of flavors, varying by the number of remotes, geographic-spread, subscriber-base and offered services. Those that occupy ‘the gap’ have some common characteristics that prevent them from being fully facilitated by TDMA/VSAT or static SCPC terminals. These networks might span multiple time zones or at least have a mix of urban and rural customers whose access-points change depending on whether they’re at work, at home in the suburbs or on the road in-between. They will need to move higher volumes of traffic than TDMA can accommodate, and if the network is heavily ‘IP-centric’, they’ll probably need considerable packet-processing power and embedded optimization tools such as link acceleration, carrier-grade Ethernet and 3G/4G deep packet inspection. 

Regardless of technology, satellite-modem aficionados are cognizant of the unrivaled performance that today’s high-end SCPC modems deliver when it comes to link efficiency, throughput and raw processing power. The backplane of the SCPC modem screams versatility with its broad array of terrestrial interfaces and, in our case, the ability to combine multiple formats into a single carrier. Of course, with all of this power and sophistication, one can expect a high-end SCPC modem to cost a bit more than a typical VSAT modem. However, that additional cost can be more than offset by the savings from improved space segment utilization, thanks to higher modulation schemes, sharp roll-off filtering and carrier cancellation. For point-to-multipoint and Mesh applications, there are 8- and 16-stack multi-demodulators for the return traffic and the Q-NET network manager is a fraction of the cost of most VSAT hubs. 

The Q-NET™ Satcom Bandwidth Manager Starts Where VSAT Stops
As VSAT links must draw their resources from a shared pool, the amount of capacity that is available on a per link basis may vary greatly, depending on the number of active users. Subscribers may be underserved if their service providers set optimistic expectations of the amount of link capacity that will be available to them at any given time. An increase in the number of subscribers, combined with the proliferation of bandwidth-hungry applications, makes it even more likely that customers will feel underserved. What service providers and users really need in this situation is the best of both the VSAT and SCPC worlds. 

With the Q-NET BW Manager, bandwidth is dedicated, not shared, so the needs of medium-to-high-throughput users can be easily and reliably accommodated with greater efficiency. Unlike the case with typical VSAT products, the Q-NET BW Manager guarantees that you have the bandwidth you need—whenever you need it—without worrying about contention and inefficiency as you do with TDMA.

As an added benefit, with Q-NET comes the ability to monitor and control the entire network—including any system component that has a remote control interface. A powerful suite of graphing and scheduling tools gives operators the ability to automate and generate reports that capture network performance statistics and provide situational awareness. 

Service providers can now get “unleashed” bandwidth around the clock and stand prepared for a future of network growth without the disruption and outages that invariably result during hardware changes and upgrades. With Q-NET BW Manager, the hardship of managing a mixed TDMA and SCPC network disappears. 

The Heart of Q-NET—The Q-Flex™ Satellite Modem 
Q-Flex™, Teledyne’s flagship satellite modem, could be referred to as the heart of the Q-NET Bandwidth Manager. After all, this is the modem that manages a lot of the heavy lifting when making the most efficient use of the satellite. Far more than just a cache of high-end FPGAs and a powerful main processor, Q-Flex™ is the culmination of more than ten years of innovations and refinements. Thanks to the long list of features inherent to Q-Flex™, costs associated with the operation and maintenance of a satellite-based network can be greatly reduced. 

The Q-Flex™ modem is built upon a LINUX-based, open architecture where the vast majority of the unit’s features reside as digital code, unlike competing ASIC-based alternatives. Additional features be installed long after the modem has been placed into service and features yet to be designed can be uploaded via USB at some point in the future. The list of currently available features is extensive.

• High-order modulation schemes (up to 64 QAM) and a large selection of FECs allow the user to attain some of the highest ‘bits per hertz’ densities in the industry
• Five percent roll-off filtering allows tighter carrier spacing to the tune of 20 percent spectrum savings over standard filtering
• Embedded Paired Carrier technology from ViaSat reduces bandwidth needs on a per carrier basis by up to 50 percent
• Teledyne’s proprietary FastLink LDPC gives the user the option of optimizing each link for best Eb/No or best latency performance
• Adaptive Coding Modulation improves link integrity during rain-fade conditions
• The onboard Internet Protocol (IP) engine can pass up to 100 Mb/s WITH internal link acceleration enabled
• XStream IP™—an integrated suite of advanced IP optimization and traffic management features including TCP acceleration, header and payload compression, dynamic routing, traffic shaping and AES encryption
• Reversionary Control is a proprietary feature that prevents operators from losing communication with an unmanned remote station when changing a modem’s operational parameters. When a remote station is monitored and controlled via the satellite link, a configuration mistake can cause a link interruption. The interruption causes a loss of communications, thus prompting the need to send personnel to reestablish communications manually. Reversionary Control will force the modem into a pre-established configuration in the event communications is lost, and thereby negate the need for a costly trip
• Dual IF Interfaces—switchable L-band and 70/140MHz IF interfaces are available on every modem. 
• The Q-Flex™ modem contains a suite of powerful diagnostics tools designed to maintain not only link performance, but the health of the entire network
• Bit Error Rate Test Set (BERT)—will link with a Fireberd BERT located at the other end of the link. Communications can be established via the overhead channels so as to be transparent to actual traffic

The exceptional performance, flexibility and simplicity of the Q-NET Bandwidth Management Platform delivers real value: costs can be more easily controlled, time saved and new revenue opportunities leveraged by its reduced bandwidth requirements, increased throughput, automation features and higher network utilization. The conundrum of continual capital investment is addressed by its programmability. The familiar patterns of small gains being obviated by new technologies, and of short shelf life for evolving hardware, are mitigated by Q-NET’s long hardware life. 

The time has come to dispel old notions about TDMA-VSAT vs. SCPC and to, instead, attain the best of both worlds. Three significant challenges are overcome by the Q-NET Bandwidth Manager. 

1.    The need to make ever-greater capital investments that increase costs and reduce profits—the ability to upgrade and expand the Q-NET Bandwidth Manager eliminates the need for periodic hardware replacements as new features and technologies become available. Embedded diagnostic tools reduce the need to purchase test instruments to maintain network health, and reversionary control will reduce the number of field trips when services are accidentally interrupted during routine maintenance. 

2.    The need to create new revenue streams from existing space segment—the powerful satellite bandwidth-savings features of Q-NET will greatly reduce space segment costs that can account for as much as 30 percent of the total operating expense of a satellite-based service provider. 

3.    The need to mitigate low QoS due to network-traffic congestion and service-outages during component replacement. 

Service outages, slow services, service degradation, etc., can cause customer dissatisfaction, which can in turn lead to low customer retention. 

By combining the best features of both VSAT and SCPC technology and removing their inherent limitations, operators no longer need to make the Hobson’s choice between high-throughput and high network utilization. Q-NET Bandwidth Manager supports both, helping users to maximize profitability.

Tony Radford holds the position of Vice President of Sales and Marketing for Teledyne Microwave Solutions, which is comprised of seven Teledyne Technologies business units. Mr. Radford’s tenure in the Satellite Communications Industry spans more than 30 years and his book—Satcom Guide for the Technically Challenged—is used by companies around the world as a primer for new employees.