High bandwidth, portable transmission systems quicken communications.
The Australian army is taking advantage of technology that consumers recognize as a faster way to connect to the Internet. To enhance their communications capabilities in the field, the service is collaborating with industry to design equipment that meets its specialized needs. The system has broad applications across a spectrum of other fields, including transportation and energy resources.
Military communication systems must be able to handle high data flows as well as be simple to install, operate and repair. Specialized digital subscriber line technology called xDSL is enabling the Australian army to employ this capability for secure rapid deployment field communications.
xDSL technology offers advantages for tactically deployed local area network (LAN) extensions, including transmission speeds of up to 8 megabits per second at distances as far as 5 kilometers. The technology provides flexible and reliable high-speed communication over a sturdy physical infrastructure of either plain or reinforced copper cable.
Copper wire is preferred to fiber optic and wireless systems as a data infrastructure for both military and industrial field communication applications. While fiber optic transmission systems offer more bandwidth, the fiber often breaks under strain and is difficult and expensive to retrieve and repair in the field. Wireless technology poses challenges in secure communications and can only be used where radio waves can propagate. Copper addresses these problems and is also affordable. In combination with DSL technology, copper provides a viable option for high-speed data networks.
Although 60 to 80 percent of the world’s DSL markets are dominated by incumbent operators, a need remains for specialized DSL equipment tailored for military and industrial applications. A new concept of a portable DSL-based system has been designed to fulfill this need.
The P3, so named because it is portable and has three DSL channels, was developed by Defence Communications Industry, Melbourne, Australia, in collaboration with the Australian army. Incorporating basic DSL features, P3 is a transparent LAN extension device. The product offers several additional features previously unavailable in one portable, stand-alone package. Because it is predominantly a commercial product, P3 is cost-effective for both military and civilian users.
The system’s features include three flexibly assigned data channels, battery power, field telephony, videoconference and surveillance capabilities, remote sensors, data encryption, and remote instrumentation control as well as other telemetric features. No additional computer equipment is required to set up and operate the P3, which weighs less than 5 kilograms.
The P3 is the result of the incorporation of input received from the army after it worked with several functional prototypes of another system, the P4. Initial tests of the P4s immediately demonstrated how the system offered new ways that an xDSL system could operate. It could be used as a simple point-to-point transparent LAN Ethernet link or as a flexible configuration web of numerous units, including a data repeater configuration. This effectively increased the operational reach between two P4s from 5 kilometers to more than 10 kilometers. The new feature currently is not available on the market from other DSL manufacturers, company officials say.
The P4 was developed as a backup for the fiber optic-based forward deployment LAN field systems for the Australian army. The systems demonstrated that they could effectively replace fiber optic LAN rings. The fiber optic cables were damaged by heavy machinery operating in the area and replaced with steel reinforced copper cable. P4 systems were used to replicate original fiber optic links, offering transparent links over the copper.
“The Australian army uses fiber optic cable to provide a communications infrastructure for logistic support,” says Maj. Ian Thomas, RAA, Australian Department of Defence. “The fiber optic cable, kevlar-armored especially for defense [applications], is an expensive medium and breaks when caught up in the track link of tanks or severed by forklifts. These accidents, actual events during exercise phoenix, normally occur during night under blackout conditions. Although the fiber can be repaired, such repair requires returning to base and expensive facilities.”
The army traditionally uses Don-10 copper wire reinforced with strands of stainless steel to carry voice in the field. Although capable of withstanding heavy stress, this cable still gets broken, but users can repair it easily. Wire is also considerably easier than optical fiber to deploy. The P4 xDSL was employed during exercises phoenix and crocodile west to prove the ability to replace fiber optic segments with Don-10 on selected long runs, Maj. Thomas adds.
The P4 features internal batteries, which enable operation in isolated locations for up to 4 hours. The device also can be powered by standard sources such as solar panels and generators. It offers field telephony that is independent of data transmission channels, functioning as a self-contained backup field telephone. The maximum transmission bandwidth between any two P4s was automatically set depending on the line condition.
In initial field tests, 1- to 3-kilometer lengths of reinforced copper cable produced data throughput of more than 8 megabits per second in one direction and 1 megabit per second in the other. As the distance of the link increased, the effective throughput decreased, producing data rates of 4.6 megabits per second and 1 megabit per second, respectively.
Applications for the P4 also include general LAN extensions and fiber optic-based LAN backups as well as a variety of data and telemetry communications for fire brigades, police, general emergency data networks and mining communications networks. When used as a range extender with video cameras, the P4 can be employed as an effective surveillance device along railways, tunnels and gas and oil pipelines. It also can act as an effective line qualification and testing tool, offering automatic loop-back facility and displaying actual line operating parameters.
The Australian Defence Department has conducted several strategic deployments of the technology, including HMAS Cerberus, Holsworthy Barracks, Fort Queenscliff and other bases. The Royal Australian Air Force Airborne Telecommunications Unit also has deployed a number of DSL systems.
In the most recent operation, the Australian army successfully deployed eight P4 systems in East Timor during the INTERFET peacekeeping mission.
Following the P4’s initial deployment, the P3 was designed. The new system is both smaller and lighter than the P4. It offers all of the P4 features in a custom housing specifically designed to operate in a field environment. It is a stand-alone, rate-adaptive DSL system and has been significantly optimized since its first release as a result of the close collaboration between various services of the Australian Department of Defence and the company.
Alec Umansky is the general manager of Defence Communications Industry, Melbourne, Australia, an independent company that focuses on designing specialized communications products.
The Dynamics of xDSL
XDSL is a digital subscriber line transmission or modulation technique for sending data that takes advantage of the unused bandwidth or frequency spectrum in telephone copper cables. The technology is effectively asymmetric due to the signal interference arising at high data rates and also is referred to as asymmetric digital subscriber line (ADSL).
The new transmission speeds are more than 50 times faster than the speed of conventional dial-up modems, and the technique requires no new cabling. In addition, xDSL modulation frequencies are above that of voice telephony, leaving the telephone services unaffected. The same copper line is used for both high-speed data applications and standard telephony.
One advantage of ADSL technology is that it bypasses telephony switching equipment, which relieves carriers from very long duration data calls using today’s dial-up modems. Because xDSL is not a dial-up service, the connection time can be virtually instant.
The two distinctive modulation techniques are carrierless amplitude/phase (CAP) modulation and discrete multitone (DMT).
CAP is a version of quadrature amplitude modulation (QAM) in which incoming data modulates a single carrier that is then transmitted on a telephone line. The carrier itself is suppressed before transmission because it contains no information and can be reconstructed at the receiving end.
DMT is a version of multicarrier modulation in which incoming data is collected and distributed over a large number of small individual carriers, each of which uses a form of QAM. DMT creates these channels using a xDSL is a digital technique known as discrete fast Fourier transform.