Whispers & Screams
And Other Things

Spread Spectrum Modulation Techniques

As an ex military satellite communications engineer I certainly remember working with spread spectrum modulation and also frequency hopping technology in the 1980's. Wireless Local Area Networking technology today exploits a technology which was thitherto mostly hidden inside this shadowy domain of military communications and radar. This technology comprises a collection of ideas which are termed Spread Spectrum Techniques (SST). Spread Spectrum techniques have some powerful properties which make them an excellent candidate for networking applications. To better understand why, we will take a closer look at this fascinating area, and its implications for networking.

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Isn't Satellite Communication Old School Now

Space travel has and continues to fascinate us. As humans it will always be our intrinsic instinct to explore and discover whatever lies over the next horizon. Such was the motivation for the space race which ultimately provided the world with satellite communications amongst many other things. When we look back at the grainy pictures from that febrile time in history however what we see is a world which looks very different to that of today. Indeed most of the sci-fi of the 1960's was set around about now. As people of their future looking back it all seems rather quaint to us but the benefits we have enjoyed from satellite communications have been many and varied. Since the launch of Telstar, satellite communications has enabled us to beam the finger of mass communications to every corner of the planet

The above notwithstanding, our world today is criss-crossed by undersea cables between every continent and across every sea. Satellite communication (or SATCOM as we will refer to it moving forward) would seem to no longer be necessary... or is it? Lets take a look at the benefits it brought to us at its genesis.

Satcom is the ultimate mobile technology. It provides us with the possibility for cable free communications across the whole footprint of a beam. For some types of spacecraft such a footprint can cover many hundreds of thousands of square miles from only one beam. A single spacecraft can support many beams. That we can utilise this technology anywhere within the beam is such an enormous asset that it completely revolutionises our activity in the remotest areas of the planet. It is now possible to call your mum from a rowing boat in the middle of the atlantic ocean on mothers day, or indeed on any day. Such is the ease of use that is possible using technology no more byzantine than a satellite phone. 

Satellite comms is also relatively cheap although the person who owns the satellite phone may ask you to keep it brief whilst calling your mum. Mobile terminals are however cheap and cheerful when examined in the context of global communication methods. They can also be quite easily adapted to support voice, video or data or indeed all three at once. It is being used extensively as a medium through which to deliver broadband internet services to difficult to reach areas within developed countries not to mention those with a less ubiquitous infrastructure. The frequencies used for satcom are selected specifically because of their ability to resist absorption enabling them to cover the enormous distances required. On top of this it is impossible to ignore the enormous usage of satellite for broadcast media such as television broadcasting where the system is set up primarily for one way communication. In summary then satellite communications has and continues to deliver enormous benefits and has a number of key unique selling points.

 

The premise of this post however does not seek to confirm the obsolescence of Satcom but rather to examine its place in the ever changing telecommunications landscape. In today's world of wireless communications, high definition television and global access to the Internet, many people are unclear about the inherent advantages of satellite communications but they persist and are many. 

 

Cost Effective - The cost of satellite capacity doesn't increase with the number of users/receive sites, or with the distance between communication points. Whether crossing continents or staying local, satellite connection cost is distance insensitive. 

Global Availability - Communications satellites cover all land masses and there is growing capacity to serve maritime and even aeronautical markets. Customers in rural and remote regions around the world who cannot obtain high speed Internet access from a terrestrial provider are increasingly relying on satellite communications.

Superior Reliability - Satellite communications can operate independently from terrestrial infrastructure. When terrestrial outages occur from man-made and natural events, satellite connections remain operational.

Superior Performance - Satellite is unmatched for broadcast applications like television. For two-way IP networks, the speed, uniformity and end-to-end control of today's advanced satellite solutions are resulting in greater use of satellite by corporations, governments and consumers.

Immediacy and Scalability - Additional receive sites, or nodes on a network, can readily be added, sometimes within hours. All it takes is ground-based equipment. Satellite has proven its value as a provider of "instant infrastructure" for commercial, government and emergency relief communications.

Versatility and More - Satellites effectively support on a global basis all forms of communications ranging from simple point-of-sale validation to bandwidth intensive multimedia applications. Satellite solutions are highly flexible and can operate independently or as part of a larger network.

 

As we move froward and the need for ubiquitous communications becomes ever more embedded into the fabric of our lives, satellite communication will move into a golden age. Techniques and mechanisms with which to leverage the spacecraft as a communications platform are continually evolving and it is this swathe of new and exciting use cases that will take the communications satellite into the rest of the 21st century and beyond. 

Ingenious new techniques such as that envisioned by companies like Leosat and OneWeb demonstrate that the traditional paradigm of teleport-satellite-teleport communications is no longer de rigeur. As new business models seek to create optical meshed networks in the sky, new uses continue to emerge. Such networks will ultimately become the fastest communication links for distances over 10,000 miles because light travels faster through a vacuum than it does through glass. For applications which need to shave every possible fraction of a second from network delays (and there are many) these new networks will surpass the existing terrestrial networks no matter how few routed hops are required. The high speed world of financial algo trading, where microseconds cost millions will quickly move to these types of networks once they reach production.

As we move slowly away from the turn of the 21st century some may have expected that satellite communication may have been headed for its swansong given the ubiquity and reach of terrestrial networks. I'd appreciate your thoughts in the comments section below as to what the future may hold for satellite communication or indeed perhaps more broadly for spacecraft communication. I think its fair to say that reports of its demise have been greatly exaggerated.

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Prestwick Airport ready for takeoff as the UK spaceport.

prestwickThe Civil Aviation Authority has shortlisted Campbeltown, Prestwick and Stornoway airports to host the UK’s first spaceport, after narrowing down the field of possible locations to five in a consultation. Prestwick Airport, currently owned by The Scottish Government, and a strategically positioned airport on the Clyde Estuary coast in Ayrshire welcomed todays announcement from Westminster along with South Ayrshire Council which establishes the framework around which the selection of the first UK spaceport will be made.

One of the key drivers of the push is the well established notion that the country needs to have a fully operational Spaceport by 2018 in order to further vitalise the blooming UK space industry. The new location will become a centre of operations for the launch of new high tech instrumentation and satellite based technology and vehicles. Furthermore it may well become a major technological hub for all UK companies involved in the space industry providing launch and maintenance facilitiues for such companies as Virgin Galactic and Spacex.

Iain Cochrane, Chief Executive of Glasgow Prestwick Airport, said: "Prestwick Airport has been a pioneer of the UK aerospace industry and aviation since its foundation in 1935. I believe Prestwick offers the perfect conditions for space launches and our extensive developed concrete airfield and 3km runway provide the facilities needed for all types of re-usable spacecraft in development.

Screenshot_7"We have an experienced high-tech aerospace workforce and a substantial aviation and high-tech engineering industrial footprint. Our Scottish Enterprise incentive zone supports the growth of the space industry. Our universities in Glasgow and Ayr are at the forefront of space and aerospace engineering research and teaching. While we have safe over-water flight paths, we also have over 4m people within a 2 hour drive giving us access to the widest range of specialists and expertise. This combination of features is unique amongst the sites being considered and positions Prestwick as the leading candidate to become the UK's first Spaceport."

Andrew Miller, Chairman of Glasgow Prestwick Airport, said: "Winning the Spaceport for Scotland and Prestwick will create a platform for revenue growth and industrial development for the next thirty years and more. It is a truly strategic development that will underpin jobs and growth regionally and nationally. Prestwick is the only site that can release this potential. It will drive transformational change both at the airport and local level and also in Scotland and the UK as a whole."

Prestwick Spaceport Director Stuart McIntyre said: "We have been working hard to structure our programme since the consultation programme closed last October. We have a detailed understanding of what is required and have already begun our bid preparations.

"We have secured strong support from our stakeholders in the region as well as internationally. We are determined to offer the global space industry a highly capable facility that will exploit Scotland's perfect location for polar orbit launches and space programme research and development. Prestwick will sit at the heart of an end-to-end space industrial capability allowing commercial space application developers to realise their designs, launch them to orbit and distribute their service to their global customers."

Councillor Bill McIntosh, Leader of South Ayrshire Council and Chair of the Glasgow Prestwick Airport and Aerospace Stakeholder Group, applauded Prestwick's bid: "Glasgow Prestwick Airport has extensive developed facilities and the ideal infrastructure and resources to deliver a first-class spaceport for the UK. This includes a significant amount of land for aerospace and spaceport industries. With direct motorway access, we are less than half an hour from Glasgow and easily accessible from all parts of the UK – you really couldn't ask for anywhere better to fulfil this important role. Aerospace is a major part of our lives in Ayrshire and we look forward to making the Glasgow Prestwick spaceport a reality and welcoming the space industry to this wonderful part of the world."

The UK Government selection programme is expected to run until October 2015 with Prestwick one of the possible locations being considered alongside Newquay in Cornwall, Llanbedr in Wales and a number of alternative Scottish sites.
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Enhancing Oil,Gas and Power Operations - SCADA via Rustyice Satellite Solutions

Oil and gas operations are located in unforgiving environments, from the blistering cold of the arctic to the scorching heat of the deserts and the storming conditions out on the open sea. To sustain secure operating conditions in these remote areas, reliable communication is as vital to the end-user as the umbilical cord is to an unborn child.

 

Supervisory Control And Data Acquisition

Supervisory control and data acquisition (SCADA) is a unique aspect of oil, gas and power distribution operations in that it does not entail communication between people, but between machines, also known as machine–machine (M2M).

SCADA describes a computer based system that manages mission critical process applications on the ‘factory floor’. These applications are frequently critical for health, safety and the environment.

The term telemetry is often used in combination with SCADA. Telemetry describes the process of collating data and performing remotely controlled actions via a suitable transmission media. In the context of this article, the telemetry media is a satellite communications solution.

SCADA in Oil, Gas and Power Distribution Operations

SCADA is not limited to a particular aspect of these types of operations. In the Oil and Gas industry, SCADA applications can be found in upstream areas such as well monitoring, downstream in areas such as pipeline operations, in trade by managing the fiscal metering/custody transfer operations and logistics in applications such as inventory management of tank storage facilities. SCADA systems in the Power Distribution industry use RTUs and PLCs to perform the majority of on-site control. The RTU or PLC acquires the site data, which includes meter readings, pressure, voltage, or other equipment status, then performs local control and transfers the data to the central SCADA system. However, when comparing and specifying a solution for challenging SCADA environments, RTU and PLC-based systems are not equal.

PLC Systems are Sub-Optimal for Complex SCADA Systems

Originally designed to replace relay logic, PLCs acquire analog and/or digital data through input modules, and execute a program loop while scanning the inputs and taking actions based on these inputs. PLCs perform well in sequential logic control applications with high discrete I/O data counts, but suffer from overly specialized design, which results in limited CPU performance, inadequate communication flexibility, and lack of easy scalability when it comes to adding future requirements other than I/O.
With the rapid expansion of remote site monitoring and control, three critical industry business trends have recently come into focus:

• System performance and intelligence – Process automation improves efficiency, plant safety, and reduces labor costs. However, complex processes like AGA gas flow calculations and high-resolution event capture in electric utility applications require very high performance and system-level intelligence. The reality is that even high-performance PLCs cannot meet all these expectations.

• Communication flexibility – Redundant communication links between remote systems and the central SCADA application form the basis of a reliable, secure, and safe enterprise. Power routing automation in electric applications, water distribution, warning systems, and oil and gas processes all require unique communication mediums including slow dial-up phone lines, medium speed RF, and broadband wired/wireless IP.

• Configurability and reduced costs – Although process monitoring and control are well defined and understood within many industries, the quest for flexibility and reduced Total Cost of Ownership (TCO) remains challenging. In the past, proprietary PLC units customized with third party components filled the niche, but suffered from lack of configurability and higher maintenance costs than fully integrated units. Today, businesses look for complete modular off-the shelf systems that yield high configurability with a significant improvement in TCO.

At the technical level, several requirements currently influence the SCADA specification process:
• Local intelligence and processing – High processing throughput, 64 bit CPUs with expanded memory for user applications and logging with support for highly complex control routines.

• High-speed communication ports – Monitoring large numbers of events requires systems that support multiple RS232/485 connections running at 230/460 kb/s and multiple Ethernet ports with 10/100 Mb/s capability.

• High-density, fast, and highly accurate I/O modules Hardware that implements 12.5 kHz input counters with 16-bit analog inputs and 14-bit analog outputs for improved accuracy.

• Broadband wireless and wired IP communications. Recent innovations in IP devices demands reliable connectivity to local IEDs (Intelligent Electronic Devices) as well as emerging communication network standards.

• Strict adherence to open standard industry protocols including Modbus, DNP3, and DF-1 on serial and TCP/IP ports

• Robust protocols for support of mixed communication environments.

• Protection of critical infrastructure – Enhanced security such as password-protected programming, over the air encryption, authentication, and IP firewall capability.

Selecting a Satellite Communication Solution – Factors to Consider

Security

When selecting a satellite communications solution, there are numerous factors that must be considered. Enterprise applications like e-mail, Internet access, telephony, videoconferencing, etc. frequently tie into public communications infrastructure. Due to security and reliability considerations it is considered best practice to isolate mission critical SCADA communications infrastructure from public networks.

The Rustyice solution is a dedicated satellite communications network solution tailored for the SCADA applications environment. By virtue of system design, our solution offers greater security against hacker attacks and virus infestation which mainly target computers that are connected to the Internet and are running office applications.

Reliability

Due to the critical nature of most SCADA operations, a reliable communication solution is of utmost importance. The satellite communications industry is mature with a proven track record. Satellite transponder availability is typically in the 99.99 percentile range, a number far superior to that of terrestrial networks. To build on this strength, our solution utilises a miniature satellite hub that is deployed at the end-users SCADA control centre. Data to/from the remote terminal units (RTUs) are piped directly into the SCADA system. There is no vulnerable terrestrial back-haul from a communication service providers facility, which can cause the entire network to crash if cut during public works, i.e. digging.

To increase the reliability of the hub, it is frequently deployed in a redundant/load sharing configuration. This ensures that the hub is available more than 100% of the time, making it far from the weakest link in the communication chain.

Types of Connectivity

Contrary to enterprise-related communications which take place randomly, SCADA communication is quite predictable. It is a continuous process, where the SCADA application polls the RTUs at regular intervals. The outgoing poll request is a short datagram (packet) containing as few as 10 bytes. The returned data from the RTUs are also in a datagram format with the message size being from 10 bytes to 250 bytes. One could easily assume that a satellite solution based upon dial-up connectivity such as Inmarsat, Iridium or Globalstar would be ideal for this application environment. Since SCADA is not just data collection, but also entails control (which at times can be of an emergency nature), you simply cannot wait for the system to encounter a busy connection. What is needed is a system that provides an ‘always on’ type of connection, commonly referred to as leased line connectivity.

A Rustyice solution supports both circuit switched (leased line and multi drop) and packet switched (TCP/IP and X.25) applications concurrently.

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An Introduction to layer 4 handling of RT traffic on satellite networks.

slideSatellite telecommunications is, by its very nature, prone to long propagation delays and higher error rates which can impair the performance of the TCP protocol and most specifically the use of TCP to transport real time applications. At Apogee Internet, the use of satellite broadband services to enable the use of such services is a core component of the services delivered. As such therefore, it is important to understand these effects and how they impact the efficiency of the TCP exchange and the consequent streaming video delivery.

In this regard, we have examined the field using a framework of techniques which can serve to maximise the usability of these channels and in some cases to simply ensure they are usable in the first place. There are various implementations of TCP that can be used which enhance protocol performance by means of adjusting the role of acknowledgements or delaying them.

Most existing solutions do not live up to the requirements of today’s real time applications which at best results in inefficient utilisation of bandwidth and in extreme cases can affect the transponder in use quite dramatically.

Satellite systems have evolved through the delivery of television services to the point where nowadays, they have an integrated part to play in any national broadband IP delivery strategy. With their ubiquitous reach and ability to broadcast, todays core communications satellites enable the delivery of time sensitive information over macrogeographical areas. These systems however do have their drawbacks such as bandwidth asymmetry. Also, due to the inherent propagation delays involved in transmission across such vast distances, these networks always have a high Bandwidth Delay Product (BDP) and can certainly be described as Elephant Networks (LFN’s).

These long transmission distances also result in low power channels which in turn bring about high relative Bit Error Rates which are always higher than terrestrial networks.

The mainstream layer 4 protocols in use today are not best placed to make efficient use of these conditions. TCP for example, built on the principles of Slow Start, Congestion Management and Additive Increase Multiplicative Decrease was designed for far more error free networks such as hard wired networks demonstrates that it is manifestly unsuitable for use in heterogeneous network environments such as satellite links.

TCP has three major shortfalls in these circumstances.

1                     Ineffective Bandwidth Utilisation

2                     Chatty Congestion Prevention Mechanisms

3                     Wasteful Windowing

In future posts, we shall go on to examine the implications of this shortcoming in the layer 4 mechanisms as well as ways to mitigate the undesirable effects.

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