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Iridium
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Iridium is a mobile-satellite service (MSS) system that was first licensed by the FCC in 1995, and began commercial service in 1998.
Iridium utilizes an FDMA/TDMA Time Division Duplex (TDD) access technology, so that the same frequency band is used for both the user uplink and downlink transmissions, on a time-shared basis. It shares a portion of its spectrum (1617.775-1618.725 MHz) with Globalstar, which has mobile uplinks to its own MSS system in the 1610-1618.725 MHz band.
Each Iridium user uplink/downlink channel has a bandwidth of 31.5 kHz and is separated in frequency by 41.67 kHz to allow for Doppler shift. A single Iridium TDMA frame is 90 ms long, which begins with 22.48 ms guard time, followed by four user uplink and four user donwlink time slots (8.28 ms burst time each, separated by small guard times).
A good discussion of the Iridium system architecture, constellation design, and multi-access scheme can be found in chapter 2 of the thesis by Abdul Jabbar (link below).
In February 2013, Iridium was granted authority by the FCC to provide aeronautical mobile-satellite (route) service (AMS(R)S) in the 1618.725-1626.5 MHz portion of its spectrum, limited to oceanic, polar, and remote regions. According to the FCC, "for purposes of this authorization, we consider oceanic regions to be those beyond 12 nautical miles from the baselines of the coastal states." Authorization for remote areas of other territories is contingent upon completing the agreement-seeking process under 5.367 of the ITU Radio Regulations.
At the end of 2012, Iridium reported approximately 368,000 subscribers. The company plans to launch a new generation of satellites, Iridium Next, beginning in 2015.
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Frequency Bands |
| Band | Use | Service | Table |
| 1617.775 - 1626.5 MHz | Iridium (user terminal uplinks and downlinks) | Mobile-satellite | N |
| 1618.725 - 1626.5 MHz | Iridium AMS(R)S | ARMR | N |
| 19.1 - 19.6 GHz | Iridium satellite gateway downlinks | Fixed-satellite | N |
| 22.55 - 23.55 GHz | Iridium inter-satellite links | Inter-satellite | N |
| 29.1 - 29.3 GHz | Iridium gateway uplinks | Fixed-satellite | N |
External Links:
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ViaSat-1 Ka-band Satellite
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ViaSat uses this spectrum for its Ka-band direct-to-consumer broadband Internet service, under the trade name "exede." The ViaSat-1 satellite was launched from Baikonur on October 19th, 2011, and entered commercial service on January 16th, 2012.
The satellite downlinks and uplinks use both right- and left-hand circular polarizations from a geostationary orbit at 115.1 deg west longitude.
ViaSat-1 has 72 user beams, of which 63 serve the U.S. Nine beams serve Canada.
User terminals utilize a dish of 0.695 m (about 27") maximum diameter, and will uplink using carriers between 625 kHz and 10 MHz wide using max EIRP between 47.2-50.3 dBW. The antennas have transmit gain of about 44 dBi, and receive gain of about 40 dBi. ViaSat is authorized for up to 250,000 such terminals in the continental U.S., operating under the callsign E120026.
The satellite downlink bandwidth is between 52-416 MHz.
As of March 2013, ViaSat claimed 512,000 customers. They have also announced plans for the ViaSat-2 satellite, to be launched in mid-2016, which will have 2.5 times the capacity of ViaSat-1, and will have a single beam that covers the continental U.S., Mexico, most of Canada, portions of Central America and the Caribbean, and the North Atlantic over to the western edge of Europe.
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Frequency Bands |
| Band | Use | Service | Table |
| 18.3 - 18.8 GHz | ViaSat-1 downlink | Fixed-satellite | N |
| 18.8 - 19.3 GHz | ViaSat-1 downlink | Fixed-satellite | N |
| 19.7 - 20.2 GHz | ViaSat-1 downlink | Fixed-satellite | N |
| 28.1 - 28.6 GHz | ViaSat-1 uplink | Fixed-satellite | N |
| 28.6 - 29.1 GHz | ViaSat-1 uplink | Fixed-satellite | N |
| 29.5 - 30 GHz | ViaSat-1 uplink | Fixed-satellite | N |
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NASA Tracking and Data Relay Satellite System (TDRSS)
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According to NASA:
The Tracking and Data Relay Satellites (TDRS) comprise the communication satellite component of the Tracking and Data Relay Satellite System (TDRSS). TDRSS is a communication signal relay system which provides tracking and data aquisition services between low-earth orbiting spacecraft and control and/or data processing facilities. The system is capable of transmitting to and receiving data from spacecraft over at least 85% of the spacecraft's orbit.
The TDRSS space segment consists of six on-orbit Tracking and Data Relay Satellites located in geosynchronous orbit. Three TDRSs are available for operational support at any given time. The operational spacecraft are located at 41°, 174° and 275° West longitude. The other TDRSs in the constellation provide ready backup in the event of a failure to an operational spacecraft and, in some specialized cases, resources for target of opportunity activities.
The TDRSS ground segment is located near Las Cruces, New Mexico, known as the White Sands Complex. Forward data is uplinked from the ground segment to the TDRS and from the TDRS to the spacecraft. Return data is downlinked from the spacecraft via the TDRS to the ground segment and then on to the designated data collection location.
The Tracking and Data Relay Satellite (TDRS) Project is providing follow-on and replacement spacecraft necessary to maintain and expand the Space Network. The contract to build three additional TDRS spacecraft, known as TDRS K, L, and M, was awarded to Boeing Space Systems in December 2007. TDRS K launched January 30, 2013, and TDRS L launched January 23, 2014. TDRS M's launch readiness date is scheduled for 2015. The contract also has options for one additional spacecraft, TDRS N. In addition to building the TDRS K, L, and M spacecraft, the contract also includes the modifications to the White Sands Complex (WSC) ground system required to support these new spacecraft.
The TDRS Project, established in 1973, is responsible for the development, launch, and on-orbit test and calibration of TDRS spacecraft. There have been four procurements of TDRS spacecraft, which include the Basic Program (TDRS F1-F6), the Replacement Program (TDRS F7), the TDRS H,I,J Program, and the TDRS K,L,M Program. TDRS Flight 7 was a replacement for Flight 2, which was lost aboard Challenger in 1986. The first seven spacecraft (TDRS F1-F7) are referred to as the First Generation, the H,I,J series are called the Second Generation, and the K,L,M series are known as the Third Generation. TDRS F1-7 spacecraft were built by TRW (now Northrop Grumman) in Redondo Beach, CA. The TDRS F8-10 (H,I,J) spacecraft were built by Hughes (now Boeing) in El Segundo, CA.
The NASA Space Network consists of the on-orbit telecommunications TDRS satellites, placed in geosynchronous orbit, and the associated TDRS ground stations, located in White Sands, New Mexico and Guam. The TDRS constellation is capable of providing nearly continuous high bandwidth (S, Ku, and Ka band) telecommunications services for expandable launch vehicles and user spacecraft in low Earth orbit. Examples include: the Hubble Space Telescope, the Earth Observig Fleet and the International Space Station. The TDRS System is a basic agency capability and a critical national resource.
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Paired Frequency Bands |
| Paired Bands | Use | Service | Table |
| 2025.8 - 2117.9 MHz | S-band Single Access (TDRS transmit) | Space Operation | F |
| 2200 - 2300 MHz | S-band Single Access (TDRS receive) | Space Research (space-to-Earth) | F |
| 2103.4 - 2109.4 MHz | S-band Multiple Access (TDRS transmit) | Space Operation | F |
| 2285 - 2290 MHz | S-band Multiple Access (TDRS receive) | Space Operation (space-to-Earth) | F |
| 13.4 - 14.05 GHz | TDRS downlink | Space Research | F |
| 14.6 - 15.25 GHz | TDRS uplink | Space Research (Earth-to-space) | F |
| 13.75 - 13.8 GHz | Ku-band Single Access (TDRS transmit) | Space Operation | F |
| 14.891 - 15.116 GHz | Ku-band Single Access (TDRS receive) | Space Research (space-to-Earth) | F |
Frequencies |
| Frequency | Bandwidth | Use | Service | Table |
| 2036 MHz | - | TDRS command uplink | Space Operation | F |
| 2211 MHz | - | TDRS telemetry downlink | Space Operation | F |
| 13.731 GHz | - | TDRS telemetry downlink | Space Operation | F |
| 14.785 GHz | - | TDRS command uplink | Space Operation | F |
| 15.15 GHz | - | TDRS reference frequency signal uplink | Space Operation | F |
Frequency Bands |
| Band | Use | Service | Table |
| 25.25 - 27.5 GHz | Ka-band Single Access (TDRS receive) | Space Research | F |
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Other 3 billion (03b) Networks
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O3b is a planned satellite system that will help provide broadband service to the world's "other 3 billion" people, generally in the equatorial region, that do not otherwise have good access.
O3b consists of 12 satellites in equatorial medium Earth orbit (MEO) at 8,062 km altitude. The satellites will be able to provide optimal service to +/-45 deg latitude, with limited service to +/-45-62 deg. Therefore, O3b will be able to provide services outside the equatorial regions, including in developed countries, although its main target area is developing countries. MEO was chosen to reduce the latency (round trip travel time) of the data connection, compared to the much larger distance/travel time to geostationary orbit and back.
The satellites will provide broadband service to "Tier 1" customers such as Internet Service Providers (ISPs), and "Tier 2" customers including cellular backhaul and VSAT network services. Because the satellites are not in geostationary orbits, customers will have to use tracking antennas to communicate with the satellites.
Each satellite provides service using ten 216 MHz channels.
O3b will operate in the fixed-satellite service, although FSS allocations do not exist throughout the anticipated frequency range.
O3b is based in Jersey, Channel Islands, and is therefore governed by Ofcom, the U.K. telecommunications regulatory authority. Its network operations center is in Virginia (USA), and its satellite operations center will be in Luxembourg. Multiple ground stations will operate around the globe.
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Frequency Bands |
| Band | Use | Service | Table |
| 17.8 - 18.6 GHz | O3b Networks service and gateway downlinks | Fixed-satellite | N |
| 18.8 - 19.3 GHz | O3b Networks service, gateway, and TT&C downlinks | Fixed-satellite | N |
| 27.6 - 28.4 GHz | O3b Networks service and gateway uplinks | Fixed-satellite | N |
| 28.6 - 29.1 GHz | O3b Networks service, gateway, and TT&C uplinks | Fixed-satellite | N |
External Links:
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