Tropospheric communication is known as the tropospheric method of transmitting information through radio waves over significant distances - up to 500 kilometers or more, depending on the landscape and climatic factors. This method of signal propagation uses the tropospheric scattering phenomenon, where radio waves at UHF and microwave frequencies randomly propagate as they pass through the upper layers of the troposphere.
How it works
The propagation of radio waves in the troposphere occurs in a narrow beam passing directly above the horizon in the direction of the receiving station. When signals pass through the troposphere, part of the energy is dissipated back to Earth, allowing the operator to receive the signal.
As a rule, waves in the microwave frequency range move along straight lines and therefore are limited by the area within which the receiver can “see” the transmitting antenna. Usually the communication distance is limited by the visual horizon - it is approximately 48-64 km. Tropospheric radio communication allows the use of trans-horizon microwave communication.
Development
The system was developed in the 1950s and was actively used for long-distance communications mainly by military structures, until communication satellites replaced it in the 70s. However, tropospheric communication is still used today as an alternative to satellites in remote regions.
Pioneers in this direction were specialists from the USA, Britain and the USSR. Scientists have found that since the troposphere is turbulent and has a high moisture content, tropospheric scattering radio signals are refracted and, therefore, the receiving antenna collects only a small part of the radio resources. Practically, it was found that the transmission frequencies in the region of 2 GHz are best suited for tropospheric scattering systems, since at this frequency the wavelength of the signal interacts well with moist, turbulent parts of the upper atmosphere, improving the signal-to-noise ratio.
Development
Today, the transmission of signals over long distances has been entrusted to satellites. Radio relay communication is used at distances of up to 40-50 km. Tropospheric communications have taken an intermediate position. Typical distances between stations are 50-250 km, although much greater distances can be achieved depending on the climate, terrain and the required data rate.
For example, in the chain of stations between Okinawa (Japan) and Hawaii (USA), stretching across the Pacific Ocean, the average distance is 1000 miles, and in some sections exceeds 1300 miles. The Soviet communications line Sever had a record total length of 13,200 km. In some areas, the gap between the receiver and the transmitter was 450 km.
Technology
When using long-distance satellites, existing tropospheric line systems are used at shorter distances than previous systems of the 50-70s. This allowed at times to reduce the size of antennas and amplifiers, to reduce power consumption. At the same time, throughput has increased significantly.
Typical antenna sizes range from 1.2 to 12 meters, and typical power amplifiers range from 10 W to 2 kW. Thanks to the introduction of modern technologies, the data transfer rate can exceed 20 Mbit / s, which is quite enough to ensure the transmission of speech, information, and the functioning of automatic systems in the military and communication sphere.
This type of radio communication is a fairly safe way of disseminating information. Interception of signals is extremely difficult, which makes the technology very attractive for the military.
Specifications
Previously, the tropospheric communication lines used by the military were “narrowly targeted”. Only information channels with a narrow bandwidth were involved: as a rule, up to 32 analog channels with a bandwidth of 4 kHz. Modern military systems are “broadband” because they work with 4-16 Mbps digital channels.
Civilian tropospheric communications systems, such as the British Telecom (BT) North Sea oil relay network, required better channels of communication. Before the introduction of satellite technology, high-frequency radio signals from 3 to 30 MHz were used. BT systems were able to transmit and receive 156 analogue data and telephony channels to North Sea oil production platforms using frequency division multiplexing (FDMX) to combine the channels.
Parameters
Due to the nature of turbulence in the troposphere, to ensure 99.98% reliability, signalmen used four-way signal propagation paths. Systems with four spatial and polarization spacings required two separate antennas (spaced a few meters apart) and two differently polarized emitting devices: one with vertical polarization and the other with horizontal polarization. This ensured that at least one signal channel would be open at any given time.
Signals from four different directions were recombined at the receiver, where the phase corrector removed the phase differences of each signal. They were caused by the different path lengths of each signal from the transmitter to the receiver. After phase correction, four signals can be combined additively.
Use abroad
The tropospheric scattering phenomenon was used to create both civilian and military communication channels in a number of areas of the world where it was impossible (inexpedient) to use radio relay communication. Among the largest facilities:
- ACE High (user - NATO Europe). It functioned from 1956 to 1980.
- British Telecom (Britain). Communication Center in Mormond Hill, Shetland Islands.
- Communication lines "Peat House - Berlin" and "Klenze - Berlin" (Germany). Acted in the era of the Cold War.
- Portugal Telecom (Portugal).
- CNT (Canadian Telecommunications Company).
- Line "Cuba - Florida". It operates between the cities of Guanabo and Florida City.
- AT&T Corporation (USA). Centers in Chatham, Buckingham, Charlottesville, Leesburg, Hagerstown.
- Texas Towers (USA). Air defense radar system consisting of 5 towers.
- Mid Canada Line. A line of five radar stations stretching across the middle of Canada from the Atlantic to the Pacific Ocean.
- Pinetree Line. A series of fourteen stations providing communications for the eastern maritime radar stations of the United States and Canada.
- "White Alice" (USA). A military and civilian communications network of 80 stations that covered most of Alaska. In the late 80s, she stopped working.
- Line "Bahrain - United Arab Emirates". The system linking Al Manama (Bahrain) and Dubai (United Arab Emirates).
- Japanese Troposcatter Networks. Two networks connecting the Japanese islands from north to south.
USSR / Russia
Given the size of the Soviet Union, tropospheric communication was actively used mainly to maintain communication channels in the North, Siberia, the Far East, and also between allied countries. It:
- Line "India - USSR". Acted between the points of Srinagar (Kashmir) and Dangara (Tajikistan).
- LEOPARD. The Warsaw Pact has been spreading from Rostock (GDR) through Czechoslovakia, Hungary, Poland, the BSSR, the Ukrainian SSR, Romania and Bulgaria.
- Communication system "North". One of the largest overseas communication lines in the world, extending from the Kola Peninsula to Chukotka. It consists of 46 TRSS, mainly located along the Arctic Ocean, the Ural Mountains, the Yenisei and Lena, Barents and Okhotsk Seas.
Tactical vehicles
In addition to permanent tropospheric communication systems, a number of countries produced tactical mobile stations:
- Soviet / Russian vehicles of the MNIRTI series (Brig, Echelon, Athlete, Albatross, Cormorant), NIRTI (Baguette), Radio Communication NPP.
- China: CETC Series.
- NATO: Troposcatter AN / TRC, AN / GRC communications systems.
Today
Today, the US Army uses the tactical tropospheric scattering systems developed by Raytheon for long-term communications. They come in two configurations: heavy tropo and more modern - light tropo. These systems provide four multiplexed group channels and encryption of the external line on 16- or 32-m local analog telephone numbers.
In Russia, work is also underway to improve this type of communication. For example, NPP Radiocommunication has already developed the fifth generation of vehicles: Sosnik – 4PM and R423-AMK. For example, the mobile container station P423-AMK operates at frequencies of 4.4-5 GHz with a stated communication range of up to 230 km.
Modern stations have the ability to combine tropospheric and satellite communications. Calculations show that at the current rate of cheaper electronics, reducing the linear dimensions of stations, introducing the latest developments, the TS is more profitable in operation than building up a satellite constellation. In the event of a nuclear conflict, this is the only form of communication that will work.