Submarine Cable Communication

PART A (Research Paper)

SUBMARINE CABLE COMMUNICATIONS 1. INTRODUCTION Submarine cables are cables for underwater (undersea) uses and communications. They are usually laid on the ocean floor to provide international links. The important of submarine cable in modern communication systems cannot be over emphasised. This is because data and voice transfer via these cables is cheaper and quicker when compare to satellite counterpart. According to Carter et al [2], Installation and operation of submarine cables is one of the oldest and the most important uses of the sea. As supported by [1], submarine fibre optic cable system is also preferable to satellite systems for intercontinental communication in terms of economic and technological considerations. Over 95% of international communications are routed via submarine fibre-optic cables. More than 500,000 of modern submarine cables connect continents, islands and countries around the world.

2. HISTORY OF SUBMARINE CABLE The first submarine cable was laid across the Atlantic Ocean in 1858, about 140 years ago, but was not strong enough and only lasted for a few weeks [1]. 1866 mark the beginning of first successful undersea cable communication system and it connected North America to Europe. The next development took about 90 years when the first Trans-Atlantic Telephone (TAT-1) cable (based on coaxial cables with amplifiers) was developed in 1956. It was used to connect Newfoundland and Scotland using 48 telephone circuits. The cables increase at an annual rate of about 20% to 4200 telephone circuit until 1983. However, the motives to use fibre optic technology in development of submarine cables started in mid-1970s [2]. In 1979, as scientists continued to improve and refine fibre-optic technology, fibreoptic cable was tried out in Loch Fyne and it was found that the cable possess the mechanical strength and transmission characteristics required for effective functionality. The first international installation of the fibre-optic cable system was across Belgium and United Kingdom in 1986. The use of these fibre optic cables for

trans-Atlantic communication systems commenced in 1988 and was discovered that they performed better than satellites in terms of speed, volume and economics of data and voice. In 1988, the 8th transatlantic telecommunications cable (TAT-8) was constructed by a consortium of companies led by AT&T, British Telecom and France Telecom and was used to link France, USA and United Kingdom [4]. This mark a revolution in internet growth as cables carried large volumes and high speed of secured voice and data traffic while the internet made that data and information accessible and usable in various forms.

3. STRUCTURES OF SUBMARINE CABLES Ever since the beginning of submarine cables communication, the shape and structure of the cable have gone through modifications to meet its functional requirements. Therefore the cables are designed to protect them from being affected by temperature changes, pressure, ocean waves, ocean current and other natural conditions including human activities such as fishing and shipping.

Figure 1: Submarine telegraph calbles of early 1900s [2] From early 1900s, the submarine telegraph cables consist of inner copper conductor, insulating tree resin and one or more outer layers of iron wire (see figure 1). The

copper conductor transmits messages while the iron wire strenghten and protect the cable.

Figure 2: Cable of the coaxial telephonic era, around 1933 – 1978 [2] Submarine cables of coaxial telephonic era, between 1933 and 1978, are shown in figure 2. They are also called analogue cables. Each consists of core steel wire for strength, an inner conducting copper shield enclosed in polyethylene dielectric and an outer conductor for more strength [3]. To be able to withstand shallow water they were coated externally with black polyethylene and armoured with wire for protection. Figure 3 shows the submarine cables of fibre-optic era, which begins in late 1970s. They consist of inner cores with supporting pairs of optical-fibres surrounded by wire layers to provide strength, copper conductors and a case of polyethylene dielectric. Each fibre-optic cable consists of repeaters, which are power by the copper conductors, for signal regeneration or amplifiers that processes the light signal. Also, they are wire-armoured externally after been coated with black polyethylene to be able to withstand shallow water. Cable construction varies with seabed conditions and manufacturers. They may have more armour layers for energetic water zones

and no armour in stable, ocean sites. The cross section of modern fibre-optic cable is shown in figure 4.

Figure 3: Fibre-optic submarine cables for shallow to deep water (left to right) [2]

Figure 4: Cross section of modern fibre optic submarine cabe [3]

4. SUBMARINE CABLE REQUIREMENTS AND CONSIDERATIONS The requirements of submarine cables depend on their applications. It depends on whether they are being use for electric power transmission or for telecommunication purposes, deep-ocean, seabed or shallow water. However, what is important is to produce a highly reliable cable for the purpose in question. The design could involve the use of one or more multiplexed transmission, single channel with high fibre count, repeatered amplification or power distribution [7]. However, companies operating in the submarine industries typically work to the standards and the management systems set by the International Organization under ISO 9000 and ISO 9001. The international cable Protection Committee (ICPC) also publishes recommendations on key issues such as cable routing, protection and recovery although their observance is not mandatory. These recommendations are designed to improved cable quality and are often referred to by 3rd party [8]. According to Gary [7], the following are the key considerations when selecting or specifying a submarine cable. 

Expected life time of the cable (about 25 years)

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Pressure and temperature range of the type of sea water to use the cable

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Penetration of the sea water

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Cable hydrogen content

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Cable recovery for repair, replacement or removal

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Operating voltage and current

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Nominal transient tensile strength (NTTS)

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Fibre types (attenuation and chromatic dispersion)

5. LAYING, INSTALLATION AND MAINTENANCE OF SUBMARINE CABLES Firstly, the route of the cable is selected after which the potential impact on the environment is critically examined to ensure that the design, laying and installation are carried out to meet environmental conditions. Then a full survey of route is carried out to minimise environmental impacts and maximise cable safety. Cable route survey relies on acoustic-based sounding, sonar and seismic systems and it focuses on seabed surface. Where burial is concerned, the survey is taken deep into few meters of sediment below the seabed [9]. After survey, the cable is laid with purposely built ships on or under the seabed as guided by the route survey. Laying involving deep water is done with remotely operated vehicles while shallow water laying may be aided by divers. During installation, care is taken to protect cables from human activities. Therefore cables are buried into the seabed at water depths down to c.1,500 m. In water depths greater than c.1,500 m or areas where burial is not practicable (e.g. rock or highly mobile sound) the shallow-water cables are placed on the seabed. After installation, regular cable maintenance, monitoring and recovery are necessary at regular or required intervals for best cable performance. While maintenance includes repairs, monitoring is carried out using ocean observatories. Observation sites are linked via subsea cables that will allow data transfer to shore in real time. As a result of cable failure, damage, aging, congestion and redundancy, cable recovery is usually carried out for repairs, replacement or removal [10].

6. EXISTING AND NEW PRODUCTIONS Ever since the beginning of submarine cable communications, researchers and engineers have been working hard to improve the cables to meet the specifications required for advanced communication systems. Figure 5 below compares the old and modern submarine communication cables.

Figure 5: Comparing early telegraph cable and modern submarine cable [8] Submarine cables between 1866 and 1956 were classified as old cable systems [8, 12]. The cost of 7 word telegraph/telegram messages reduced from £20 in 1866 to 80pence for 20 word message. Later in 1956, 36 telegraph calls can be made once on TAT-1 submarine cables and hence call cost was further reduced to US$12 for 3 minutes call. Modern production of submarine cables begins in 1988 when fibre-optic technology was introduced to the production of submarine cable to produce TAT-8 cable. It is the first trans-Atlantic fibre-optic cable. This cable can be used to make up to 40,000 phone calls at a time, about 10 times that of the last copper cable. With improvement in technology ever since 1988, today each fibre pair within a submarine cable can carry digitised information of about 150,000 simultaneous call. However, submarine cable design and operations are constantly evolving and greater capacity and reliability is expected in the nearest future.

7. APPLICATIONS OF SUBMARINE CABLES The two major applications of submarine cables are in telecommunications and in electric power industries. In telecommunications, submarine fibre optic cables are used to carry telecommunication signals across oceans and seas to link different places together across the globe. Almost 100% of transoceanic internet traffic is sent via fibre-optic submarine cables. In power industry, submarine power cables are used to carry electric power below oceans and seas [5]. They carry up to 1000 MVA AC and 10 – 1100 MW DC over long distances. Moreover, disused submarine telephone cables are used to measure ocean current. These cables are used to measure the Florida Current by measuring voltage across the cable and hence determine the flow of water [6]. Florida Current is a strong oceanic current flowing northward along the eastern coast of Florida between Miami and the island of Grand Bahama. Also, old and new submarine cables are used as a major resource and real time global network to monitor climate variables such as water temperature, salinity and pressure on the ocean floor [11]. This will help in predicting natural disasters such as Tsunami and hence warnings can be issued. 8. CONCLUSION Ever since the first submarine cable has been produced in the telegraph era, it has undergone several changes in structures and sizes to meet desired functional requirement. Cable construction varies with manufacturers, seabed conditions and application (whether being used for power transmission or telecommunications). However, submarine cable manufacturers and operators must follow the standards set by the International Organizations for Standards under the ISO 9000 and ISO 9001 schemes. Submarine cable communications has greatly revolutionized and transformed international telecommunication systems. They can transport about 100 times bigger traffic than satellites. Modern fibre-optic submarine cable networks are now providing

internet traffic (data, voice and video) of over almost unlimited bytes across seas, oceans and land. Applications of submarine cables are also found in electrical power industries, ocean current measurement and climate variables monitoring. Although a remarkable growth and development has been recorded in the submarine cable industries, more research into the industry is recommended for greater capacity and reliability of future systems.

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[9] National Research Council, 2003. Ocean Noise and Marine Mammals. National Academy Press, Washington, DC. http://www.nap.edu/openbook.php?isbn=03090 85365 [10] N. Kojima, Y. Miyajima, Y. Murakami, T. Yabuta, O. Kawata, K. Yamashita and N. Yoshizawa. Studies on designing of submarine optical fiber cable. Microwave Theory and Techniques, IEEE Transactions on 30(4), pp. 579-586. 1982. [11] ITU, 2010. Using Submarine Communication Networks to Monitor the Climate. ITU-T Technology Watch Report. Internet: http://www.itu.int/dms_pub/itut/oth/23/01/T23010000110003PDFE.pdf Accessed 23 March 2012. [12] M. Schwartz and J. Hayes. A history of transatlantic cables. Communications Magazine, IEEE 46(9), pp. 42-48. 2008.