Intelligence in the Skies
With the ability to provide signal gain, double-hop elimination, IP multiplexing and mesh networking without a teleport, what impact can on-board processing have on satellite communications? On-board processing has the potential to bring video on-demand, capacity growth and convergence of ground and space networks, thus promising to revolutionize satellite as we know it.
But what exactly is on-board processing, and what are the characteristics of the payloads equipped with this technology? “Satellite architectures can be put into three categories: conventional bent-pipe radiofrequency systems, on-board processed bent-pipe systems and on-board digital processed systems,” says Jeff Snyder, group vice president, SkyTerra Communications Inc., a mobile satellite services operator that relies on ancillary terrestrial component (ATC) technology. “The first type is used in fixed service and direct broadcast satellites, the second type in systems such as SkyTerra satellites, while the last type is typical of systems such as the Iridium constellation.”
The differences between these systems are significant. On-board processed bent-pipe systems typically perform frequency channelization of signals by digitally processing them at baseband or near baseband. The resulting channelized signals can then be conditioned and processed prior to up-conversion for retransmission. However, the signals are not demodulated to their digital content. “The advantage of on-board processed bent-pipe systems over conventional bent-pipe systems is that relatively narrowband channels can be processed and the resulting channels can be switched between a large number of beams,” says Snyder. In other words, this architecture allows for the optimization of the satellite’s spectrum assignments, directing satellite resources where they are needed. This results in frequency reuse in narrowband communications networks.
On-board digital processed systems, on the other hand, take the capacity optimization process a step further. They process signals by demodulating and decoding the received waveforms to the digital packet or bit level. “This allows the system to have extremely flexible signal and information routing,” says Snyder. Depending on the capabilities of the on-board digital payload, the resulting individual data streams can even be decoded and recoded to match the channel characteristics of the intended downlink beam. These systems allow capacity reassignment in real-time at the packet level in response to the traffic loading. Furthermore, depending on the complexity of the digital payload, services such as packet replication and directed multicasting can also be implemented. That is to say that on-board digital processing transforms satellite payloads into “routers in the sky,” but that is not all — crucially, such systems also enable inter-satellite links, thus reducing the need for gateways in a global satellite network.
A Networked Future
Within industry circles, there is a heated debate about the advantages presented by on-board processing and how this could affect satellite communications. Expectations are high, as many argue that this technology has the potential to increase capacity many times over, change the way some existing services are provided as well as make new ones possible.
In today’s satellite communications business, services are provided on specific beams on specific satellites. Each geostationary satellite is isolated from other spacecraft, while the end user must provision each service separately. In the future, however, satellites empowered by on-board processing could be linked together to create a network. “This network would be intelligent and only require knowledge of some key parameters to successfully route the signals to the final destination in the most efficient manner, with complete transparency to the user,” says Mohammad Marashi, Intelsat’s vice president of product strategy and development.
In essence, onboard processing would support services similar to those supported today in the terrestrial sector and, as commentators often put it, allow the satellite industry to truly join the Internet. If such a scenario might appear to be faraway in the future, it is worth bearing in mind that trials are already being carried out today. The Internet Routing in Space (IRIS), an on-board processor developed by Cisco Systems and launched in November on an Intelsat satellite, is undergoing testing.
What impact is on-board processing likely to have on the satellite industry? Many applications, after all, only need bent-pipe delivery of bandwidth, as this is still the most efficient way to support services such as broadcast television, for example. Yet, technology is naturally evolving, and trends in large service provider networks seem to indicate that an increasing level of content is being personalized and delivered in unicast or multicast modes rather than broadcast. All this points to an increasingly prominent role to be played by on-board processing in the future. “As more and more of our services and content are delivered on two-way IP connections, there will be much more need for on board processing and routing in satellites,” says Greg Pelton, general manager of Cisco IRIS.
But one thing is for sure: Even assuming an immediate boom in the adoption of this technology, in the short-to-medium term, bent-pipe and on-board processing will have to necessarily coexist. As a hybrid payload featuring the two technologies, the Intelsat 14 payload developed for IRIS is a good example of how satellites could look like in the near future. “The IRIS payload on Intelsat 14 today coexists with other bent-pipe transponders. Only three of the transponders on Intelsat 14 are connected to the space router. We will see hybrid deployments like this for many years until the volumes of space routers go up and technology costs come down,” says Pelton.
On a more general level, however, the hanging question is to see what types of services on-board processing technology will be able to support.
Military and More
Any enquiry into possible future applications supported by on-board processing should start from understanding the characteristics of this technology and the advantages it provides. “One of the most significant advantages is the ability to provide mesh connectivity, which offers lower latency as data is transferred. Onboard processing also provides higher bandwidth efficiencies and cross-strapping between various beams utilizing different frequencies,” says Marashi.
Given these features, it is evident that some of the most dynamic applications supported by on-board processing center around mobile communications. “These services have been built over the years to operate in different frequency bands, and there is a significant need for mesh connectivity using small terminals. Onboard processing enables isolated networks to be connected together as if they are all operating over one large network,” says Marashi.
This is, in broad terms, the focus of Cisco’s IRIS program, which aims to provide the ability to integrate terrestrial and space communications nodes through a common network layer protocol enabling users to communicate seamlessly. In particular, having an IP network node in space would avoid the latency and costs associated with a double-hop to the teleport, thereby dramatically increasing the efficiency, flexibility and data throughput of satellite links and communication networks. It can be argued that IP-based routing in space is a path to achieve multi-protocol interoperability while enhancing operational performance.
On-board digital processing also is excellent for national security satellite networks where access denial and cryptographic security might be a concern. In fact, the military, a sophisticated communications customer that buys and deploys secure commercial networking technology, represents a major target customer for this technology. “On-board signal processing is best applied for critical command and control communications where assured connectivity and protection are key performance requirements,” says Joe Vanderpoorten, technical director of the Milsatcom Advanced Concept Group, Space and Missile Systems Center, U.S. Air Force Space Command.
While the military likely will remain a primary user of on-board processing, there is nothing to stop such technology from being used for civilian applications as well. After all, voice, video and data communications with high security and efficient operations are key requirements for a number of civilian applications as well. Once again, Cisco’s IRIS is a case in point.
Pelton believes technology changes here will help defense and government customers. “Today satellite is an important part of government networks but is not well integrated into the Everything over IP (EoIP) communications vision. Defense forces need to operate on a global scale, in locations and situations where terrestrial infrastructure may be absent or compromised. This means that satellite services are critical to being able to achieve the mission. The challenges going forward are how to seamlessly integrate satellite into the rest of the global IP network and how to deploy new capabilities in a timely and cost effective manner. This is where there is opportunity for greater collaboration between government and commercial industry,” he says.
Pelton expects traditional models will change when defense customers analyze their communications needs. “The traditional model of acquiring dedicated technology for government use and paying the entire costs of developing that technology is not working any longer. The government has shown a real desire to partner with industry and industry is responding. There will always be government specific requirements but it make sense for the government to just pay for those capabilities and leverage commercial industry for the bulk of their requirements. This is a win-win for everyone involved,” he adds. However, the technology will have benefits beyond defense customers. “IRIS is designed to support both military and civilian applications. It is 100 percent commercially developed and the requirements were driven by commercial needs. The civilian applications are exactly the same as the military applications, they just have different use cases,” says Pelton. Examples of civilian applications include connecting oil drilling platforms with oil company operations, providing emergency services during a natural disaster or a fiber cut, extending the enterprise data center to branch offices, satellite newsgathering, video feeds from sporting events, and more.
How far away are large-scale deployments of on-board processing? Much of it will depend on the assessment studies being conducted today. For the military, on-board processing capabilities supporting mission protection are key discriminators to assure scarce satellite communication resources are available to troops on the ground. The U.S. Department of Defense is still evaluating this technology but “has yet to determine if commercial-like IP routing will support future military requirements. That subject will be a focus of pending “Joint Space Layer” requirements assessments,” says Vanderpoorten.
A thorough technical assessment of the technology is at the core of such assessment process. Other considerations might have to do with costs, though. “Fully processed systems with combined signal processing and routing in stressed military requirements can cost significantly more than bent-pipe systems. They also impose significant cost on terminals and related platform infrastructures,” says Vanderpoorten. “The commercial industry is working on alternatives that focus on message-routing services that could be cheaper if enterprise factors like security and network interoperability standards are resolved, and can be certified within” the Defense Department, he says.
The issue of costs, however, is not so easily defined. “In order to look at the cost one must consider the total cost of ownership from the user’s perspective. It is not correct to compare megahertz to megahertz,” says Marashi. “One should take into consideration the capabilities and efficiencies received using onboard processing against what one would get with bent-pipe alone.”
In addition, the overall cost of a system, including space segment as well as Earth terminals, should be taken into consideration. The SkyTerra system is a case in point. “Typically, on-board processed satellites will be somewhat more expensive than conventional bent-pipe delivery satellite systems, as their on-board complexity is significantly increased,” says Snyder. Each of the SkyTerra satellites process approximately 2,500 2.5 megahertz (MHz) channels (1,500 return link and 1,000 channels in the forward link) resulting in about 5 GHz of capacity versus conventional C-band and Ku-band hybrid satellites that may have 72 to 90 36 MHz wide channels for approximately 2.0 gigahertz of capacity (1 gigahertz GHz C-band 1 GHz Ku-band). The added number of channels, the on-board processor and a large reflector drive the costs to be about one-third more than a conventional hybrid. The SkyTerra system supports up to 30 MHz of spectrum in each direction on the user-links while supporting up to 500 user spot beams.
However, the system bandwidth efficiency and the high-link performance produced by the formation of small spot beams via the large reflector enable the use of handsets and devices that directly connect with the satellite using conventional cellular-like devices with conventional cellular device performance — e.g., battery and transmitter power. “Thus, the additional cost on the satellite side is fully justified by the resulting reduced cost of the user equipment,” says Snyder.
The other issue normally raised in the context of feasibility of on-board processing is that of aging technology. Traditionally, signal processing in space has been performed by Application Specific Integrated Circuits (ASIC) which are hardwired and not reconfigurable. A challenge with putting processing on board a commercial communication satellite is that they are normally designed for a lifetime of 10 to 15 years, while protocols and applications can change dramatically over the course of just a few years. In order to overcome this challenge, there is only one possible solution: the processor needs to be reconfigurable.
This is what SEAKR Engineering did when it developed the Application Independent Processor (AIP) for the IRIS platform. The AIP processors were specifically designed to allow for complete on-orbit reconfiguration and support of multiple simultaneous images. “This means that you can upload new applications, operating systems or waveforms without removing the original golden images,” says Paul Murray, SEAKR’s director of IP and Reconfigurable Processors.
Cisco’s Pelton echoes this view. “Technology has reached a point where all of IRIS function is provided by software on orbit,” he says. “This means that satellites can be upgraded over time with new capabilities and are future-proof.”
Only time will tell whether on-board processing turns out to be truly future-proof. Alongside enthusiasm among pundits, this technology is raising some questions relating to a number of key financial and technological issues. “The technical advantages of on-board processing are undeniable,” says Dave Bettinger, iDirect’s CTO and senior vice president of engineering. “However, there are issues that need to be addressed before on-board processing is rolled out on a large scale. In particular, the cost and complexity of such systems are going to be very challenging on the satellite side.”
The issue of scarcity of applications supported by on-board processing, aside from mobile satellite services, is another factor that is often mentioned. Besides, while it is true that the military is interested in the technology, this still has to translate into actual programs being rolled out. “In my experience, the request from operators is for satellites to be flexible, simple, reliable and cheap,” says Bettinger.
While all agree that the simple bent-pipe architecture will remain a mainstay in the satellite industry, some remain more optimistic about the future of on-board processing. “I think on-board processing will significantly change point-to-point applications for the satellite industry, particularly for mobile applications,” says Snyder.
What view will prevail in the future: optimism or healthy realism? The future has yet to be written.