WHAT IS SATE LLITE COMMUNICATION?
satellite communication, in telecommunications, the use of artificial satellites to provide communication links between various points on Earth Satellite communications play a vital role in the global telecommunications system. Approximately 2,000 artificial satellites orbiting Earth relay analogue and digital signals carrying voice, video, and data to and from one or many locations worldwide.
Satellite communication has two main components: the ground segment, which consists of fixed or mobile transmission, reception, and ancillary equipment, and the space segment, which primarily is the satellite itself. A typical satellite link involves the transmission or uplinking of a signal from an Earth station to a satellite. The satellite then receives and amplifies the signal and retransmits it back to Earth, where it is received and reamplified by Earth stations and terminals. Satellite receivers on the ground include direct-to-home (DTH) satellite equipment, mobile reception equipment in aircraft, satellite telephones, and handheld devices.
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth.
How do satellites communicate?
Satellites communicate by using radio waves to send signals to the antennas on the Earth. The antennas then capture those signals and process the information coming from those signals. Information can include:
- scientific data (like the pictures the satellite took),
- the health of the satellite, and
- where the satellite is currently located in space.
Development of satellite communication
The idea of communicating through a satellite first appeared in the short story titled “The Brick Moon,” written by the American clergyman and author Edward Evaret Hale and published in The Atlantic Monthly in 1869–70. The story describes the construction and launch into Earth orbit of a satellite 200 feet (60 metres) in diameter and made of bricks. The brick moon aided mariners in navigation, as people sent Morse code signals back to Earth by jumping up and down on the satellite’s surface.
The first practical concept of satellite communication was proposed by 27-year-old Royal airforce officer Arthur C Clark in a paper titled “Extra-Terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?” published in the October 1945 issue of Wireless World. Clarke, who would later become an accomplished science fiction writer, proposed that a satellite at an altitude of 35,786 km (22,236 miles) above Earth’s surface would be moving at the same speed as Earth’s rotation. At this altitude the satellite would remain in a fixed position relative to a point on Earth. This orbit, now called a “geostationary orbit” is ideal for satellite communications, since an antenna on the ground can be pointed to a satellite 24 hours a day without having to track its position. Clarke calculated in his paper that three satellites spaced equidistantly in geostationary orbit would be able to provide radio coverage that would be almost worldwide with the sole exception of some of the polar regions.
The first artificial satellite, Sputnik 1 was launched successfully by the Soviet Union on October 4, 1957. Sputnik 1 was only 58 cm (23 inches) in diameter with four antennas sending low-frequency radio signals at regular intervals. It orbited Earth in a elliptical orbit, taking 96.2 minutes to complete one revolution. It transmitted signals for only 22 days until its battery ran out and was in orbit for only three months, but its launch sparked the beginning of the space race between the United States and the Soviet Union.
Need for Satellite Communication
We know that there are different ways to communicate and the propagation of these waves can take place in different ways. Ground wave propagation and skywave propagation are the two ways in which communication took place for a certain distance. The maximum distance covered by them is 1500 km and this was overcome by the introduction of satellite communication.
How Satellite Communications Work?
The communication satellites are similar to the space mirrors that help us in bouncing the signals such as radio, internet data, and television from one side of the earth to another. There are three stages that are involved which explain the working of satellite communications. These are:
Let’s consider an example of signals from a television. In the first stage, the signal from the television broadcast on the other side of the earth is first beamed up to the satellite from the ground station on the earth. This process is known as uplink.
The second stage involves transponders such as radio receivers, amplifiers, and transmitters. These transponders are used for boosting the incoming signal and to change their frequency so that the outgoing signals are not altered. Depending on the incoming signal sources, the transponders vary.
The final stage involves a downlink in which the data is sent to the other end of the receiver on the earth. It is important to understand that usually there is one uplink and multiple downlinks.
Satellite Communication Services
There are two categories in which the satellite communication services can be classified:
- One-way satellite communication
- Two- way satellite communication
One-way satellite communication
In one-way satellite communication, the communication usually takes place between either one or multiple earth stations through the help of a satellite.
The communication takes place between the transmitter on the first earth satellite to the receiver which is the second earth satellite. The transmission of the signal is unidirectional. Some common one-way satellite communication is:
- Position location services are provided by the radio
- Tracking is a part of space operations services
- Internet services take place with broadcasting satellites
Following is the figure which explains the one-way satellite communication:
Two-way Satellite Communication
In two-way satellite communication, the information is exchanged between any two earth stations. It can be said that there is a point to point connectivity.
The signal is transmitted from the first earth station to the second earth station such that there are two uplinks and two downlinks happening between the earth stations and the satellite.
Following is the figure of the two-way satellite communication:
Advantages of Satellite Communication
The following are the advantages of satellite communication:
- Installments of circuits are easy.
- The elasticity of these circuits is excellent.
- With the help of satellite communication, every corner of the earth can be covered.
- The user fully controls the network.
Disadvantages of Satellite Communication
The following are the disadvantages of satellite communication:
- Initial expenditure is expensive.
- There are chances of blockage of frequencies.
- Propagation and interference.
Applications of Satellite Communication
- Digital cinema
- Radio broadcasting
- Amateur radio
- Internet access
- Disaster Management
The characteristics of satellite communications such as Variable channel, Propagation Delay, and Limited Bandwidth, present challenges and opportunities for the service providers. Effective test tools are required for monitoring, analysis, troubleshooting and management satcom networks.
- wide area connectivity almost anywhere and everywhere in the footprint of the satellite beam – thus applications such as video broadcast and mobile phone are possible for large populations
- almost instantaneous network deployment, with no wired infrastructure required – thus voice, data, and video applications can be available almost immediately
- propagation delay of about 250 milliseconds (up + down) and if you consider round trip, then almost 500 milliseconds
- an RF channel that is more than 36,000 km long before amplification or repetition – this results in a free space path loss in the range of 190 to 208 dB!! (for frequencies in the 2 GHz to 15 GHz range). In the older days this was a show stopper, but now – high gain antennas, power amplifiers, ultra-low-noise receiver sensitivities and such that this is no longer a problem!
- variable channel characteristics that can be totally absent or severely degraded as during sun outages, or bursty errors during rain and snow, or during clear sky low random/gaussian errors if power/signal constrained
- limited bandwidth since the available electromagnetic spectrum must be shared among all users – one area of world politics in which engineers and scientists have actually cooperated without acrimony!
The above characteristics present challenges and opportunities.
GL provides various test solutions to monitor and test backhaul networks no matter what type of media, bandwidth, or signaling is over the network. Our products are portable, hand-held, or compact rack-based equipment and deployed successfully by customers world-wide to monitor and troubleshoot satcom networks.
Test Tools, and Requirements for Satellite Backhaul for Mobile Networks
A complete wireless network test suite by GL Communications provides reliable integrated solutions to vendors and service providers for simulation, monitoring, troubleshooting any wireless network, including, 4G, 3G, 2G and upcoming 5G. All functionalities conform to industry standards.
Test, monitor, and troubleshoot all the core network elements and traffic types within the Wireless infrastructure for deployment-readiness, functionalities, inter-operability, performance and latest mobile features. Test end-user applications, devices, and services on a simulated wireless infrastructure environment prior to deployment on a real-time network.
Satellite Delay Measurement over Ethernet/IP, T1 E1, Datacom, T3 E3, & Optical Interfaces
- Test the echo cancellers or simulate the echo cancellation across the network to ensure error-free voice communications. GL provides many tools to test and measure echo canceller performance –
- Emulate ISDN / SS7 / SIP networks in the lab, simulate delay, and error rates to measure real life performance of data applications. GL’s Signaling and Traffic Emulation tools are widely used in the industry for such simulations
- IP-based satellite mobile backhaul networks are characterized by the service level agreement (SLA). An Ethernet/IP tester used in satellite communications must support BERT, RFC 2544, and Y.1564 SLA tests at minimum. GL’s Ethernet Testers are precisely designed to handle these testing requirements –
- GL’s Datacom Analyzer/Emulator can be used to test and verify data communications equipment and circuits which are commonly encountered in military links, satellite circuits, WAN, and data modem interfaces. Voice, video, and data may be transported through Datacom (serial) interfaces such as V.35, RS-232, RS-422/449, RS-485, or special baseband coding –
Test Suite for Air Traffic Management via Satellite Communication
GL tools for Air Traffic Management (ATM) offer signaling and traffic simulation, monitoring quality of service, and critical network delay measurements. The satellite-based solution ensures reliable management during tactical& disaster situations. With customized test solutions, the ATM core network and all its underlying entities (CWP, GRS, VoIP Gateways) can be accurately tested for performance, and functionalities. Test tools simulate communication events between different ATM core network entities, precisely time these events and measure critical delay, jitter, packet loss, and voice quality. Monitoring Probes deployed across ATM network captures and sends call records, measurements results, and network performance statistics to a centralized surveillance system.
Satellite Delay Compensation Application
- Variations in delay can potentially cause gaps in the speech. The greater the time discrepancy between the audio signals, the more difficulties to understand the messages. GL’s Echo Mitigation System (EMS) Software can be deployed on the backhaul systems to eliminate the varying delay/echo resulting from different backhaul technologies used to transport audio through the system. EMS solution allows for the measurement of delay from each site of a group of radio sites as well as the application of offsetting delays to mitigate the echo impairment.
- Test platforms for T1 E1 from GL can insert independent delays for each DS0 in each direction with increments as low as 0.125ms and receive an accurate measurement in milliseconds of the round-trip circuit delay. GL provides tools that permit delay and error simulation over TDM networks to assess voice, data, and video applications.
- Network Delay Emulator application can emulate packet delays that occur over SONET/SDH carrying ATM/PoS traffic. It provides full duplex delay simulation for PoS and ATM based traffic from 1 ms to 500 ms, with incremental delays of 1 ms. Test platforms for Ethernet / Optical networks from GL can simulate real-time network impairments.
Satellite Delay, Error, Jitter Simulation
- Re-create a Satcom network environment emulating satellite delay or latency, jitter, random bit errors, restricted bandwidth, packet re-ordering, packet-duplication, and packet loss. GL’s simulation tools are simple and affordable and allows to test the various applications in a controlled lab environment prior to live deployment to optimize the performance of the applications for the end-users. GL offers host of such solutions for testing and simulation of network impairments
- Test equipment permit adding delays, errors, and other impairments over GigE Ethernet, and Optical networks. They also allow the user to accurately emulate bandwidth, latency, loss and congestion. GL offers host of such solutions for simulation and testing
- GL provides tools that permits delay and error simulation over TDM networks to assess voice, data, and video applications
Voice and Data Quality Testing of Satellite Channels
GL’s versatile test suite allow users to send and receive the simulated voice and data traffic (as seen in real-time) over satellite network and perform the QoS measurements using ITU-T standard – PEQSQ and POLQA. These capabilities are provided within a portable-single-box solution with the flexibility of connecting to and between any network, any service, and any interface
Testing Satellite WAN Links
Application performance over WAN networks can be highly sensitive to bandwidth, latency, jitter, loss, and other WAN impairments. Testing these applications on the local network generally fails to identify critical issues that impact the end user experience. Fortunately, GL provides a new generation of WAN network emulation appliances that makes it simple and affordable to test applications in the lab under real-world conditions, ensuring smooth roll-outs of new applications and helping to optimize the performance of the applications for the end-users
Testing DCME (Digital Circuit Multiplication Equipment)
- The DCME testing, analysis and verification can be performed with DCME monitoring software such as GL’s DCME analysis software. Additionally, a Facsimile subframe analysis software may be used that permits bit level analysis and verification of fax data sub-multiplexing on the DCME output bearer signal.
Centralized Network Monitoring
- GL’s Surveillance System is scalable, so that it can be used for various applications like Billing Verification, Fraud Detection, Protocol Analysis, Traffic Engineering, QoS, Call Recording etc. T1/E1/PSTN/VoIP Probes are deployed in the field to monitor various protocols, which are collected at a central site into a database. Various client applications can be developed to interrogate database records. GL offers a variety of Protocol Analysis probes over TDM, IP, and Wireless networks that capture packets/frames, perform detailed analysis of voice band streams gathering QOS statistics such as ITU G.107 E Model MOS, along with detailed packet/frame statistics, such as total packets, reordered, duplicate and missing packet counts, gap, jitter, and delay measurements. The client can access database information remotely via Web Browsers
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