Jump to content

Iridium Communications

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Hydrargyrum (talk | contribs) at 09:38, 12 February 2009 (→‎Handoff: grammar, punctuation). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Iridium Satellite LLC
Company typeLimited liability company
IndustrySatellite Telecommunication
Founded2001
Headquarters
Bethesda, Maryland
,
United States
Area served
Worldwide
Key people
Matt Desch (CEO), Dan Colussy, Liz DeCastro
ProductsSatellite communications equipment
ServicesSatellite voice and data services
Websitehttp://iridium.com

The Iridium satellite constellation is a system of 66 active communication satellites with spares in orbit and on the ground. It allows worldwide voice and data communications using handheld satellite phones. The Iridium network is unique in that it covers the whole earth, including poles, oceans and airways.

The company, based in Bethesda, Maryland, derives its name from the chemical element iridium. The number of satellites projected in the early stages of planning was 77, the atomic number of iridium, evoking the metaphor of 77 electrons orbiting the nucleus.

The satellites are frequently visible in the night sky as satellite flares, a phenomenon typically observed as short-lived bright flashes of light.

History

Iridium communications service was launched on November 1, 1998. The first Iridium call was made by then-Vice President of the United States Al Gore.[1] Motorola provided the technology and major financial backing.

The founding company went into Chapter 11 bankruptcy nine months later, on August 13, 1999. The handsets could not operate as promoted until the entire constellation of satellites were in place, causing a massive initial capital cost running into the billions of dollars. The increased coverage of terrestrial cellular networks, e.g., GSM, and the rise of roaming agreements between cellular providers proved to be fierce competition. The cost of service was prohibitive for many users, and the bulkiness and expense of the handheld devices when compared to terrestrial cellular mobile phones discouraged adoption among potential users.

Mismanagement has also been cited as a major factor in the original program's failure. In 1999, CNN writer David Rohde detailed how he applied for Iridium service and was sent information kits, but was never contacted by a sales representative. He encountered programming problems on Iridium's Web site, and a "run-around" from the company's representatives. After Iridium filed bankruptcy, it cited "difficulty gaining subscribers".[2]

The initial commercial failure of Iridium had a dampening effect on other proposed commercial satellite constellation projects, including Teledesic. Other schemes (Orbcomm, ICO Global Communications, and Globalstar) followed Iridium into bankruptcy protection, while a number of other proposed schemes were never constructed.

At one stage there was a threat that the Iridium satellites would have to be de-orbited; however, they remained in orbit and operational.[3][4] Their service was restarted in 2001 by the newly founded Iridium Satellite LLC, which was owned by a group of private investors. Although the satellites and other assets and technology behind Iridium were estimated to have cost on the order of US$6 billion, the investors bought the firm for about US$25 million.[5]

On February 10, 2009, Iridium 33 collided with a defunct Russian satellite, Template:Kosmos.[6] A pair of massive debris clouds was created and the magnitude of the situation, it is thought, will not to be fully known for several weeks.[7]

Present status

Iridium Satellite LLC claims to have 285,000 subscribers as of early August 2008 (compared to 203,000 in July 2007). Revenue for the second quarter of 2008 was US$81.7 million with EBITDA of US$25.8 million.[8].

The system is being used extensively by the U.S. Department of Defense through the DoD gateway in Hawaii.[9] The DoD pays $36 million a year for unlimited access for up to 20,000 users.[10] The commercial gateway in Tempe, Arizona, provides voice, data, and paging services for commercial customers on a global basis. Typical customers include maritime, aviation, government, the petroleum industry, scientists, and frequent world travelers.

Iridium satellites are now an essential component of communications with remote science camps, especially the Amundsen-Scott South Pole Station. As of December 2006, an array of twelve Iridium modems was put online, providing continuous data services to the station for the first time. Total bandwidth is 28.8 kbit/s.[11]

Future development

Iridium is currently engaged in studies to build and launch a second generation of satellites, consisting of 66 satellites and six spares. These satellites will incorporate features such as data transmission which were not emphasized in the original design. The current plan is to begin launching new satellites in 2014.[12]

Subscriber equipment

Handsets

The former Iridium provided phones from two vendors, Kyocera and Motorola. The Motorola 9500 phone is a design from the first commercial phase of Iridium, whereas the current 9555 model is the most current version of the handset and was released in October 2008.[13] Until the release of the 9555 the 9505A was the sole handset sold by the company — a functionally identical clone of the Motorola 9505 with some slightly different components.[14]

Kyocera phone models SS-66K and SD-66K are no longer in production but still available in the second-hand and surplus market. The SD-66K phone was a small 900 MHz GSM phone that fitted in a cradle (KI-G100) that included a large antenna and facilitated connection to the Iridium network. [15] The SS-66K was a self contained phone, but featured a rather unusual ball antenna.

All handsets can receive SMS, but only the 9505, 9505A, 9555 and those based on the 9522 can send them.

Pagers

Two pagers were made for the Iridium network — the Motorola 9501 and Kyocera SP-66K.[16] These are one-way devices that could receive messages delivered in the form of SMS.

Other satellite phones

Several other Iridium-based telephones exist, such as payphones, bag phones, car phones and equipment intended for installation on ships and aircraft. A handset made by NAL research combined with a 9522 transceiver is used for some of these products. The DPL handset provides a user interface nearly identical to that of the 9505 series phones.[17]

Standalone transceiver units

Iridium 9522A

These can be used for data-logging applications in remote areas, now a common practical use for Iridium's services. Some types of buoys, such as those used for the tsunami warning system, use Iridium satellites to communicate with their base. The remote device is programmed to call or send SBD messages to the base at specified intervals, or it can be set to accept calls in order for it to offload its collected data. Most of these units can be connected to a handset and used as a fixed telephone.

The following transceivers have been released over the years:

  • Iridium 9522B — The most recent transceiver released in late 2008, is smaller than the 9522A and has similar features.
  • Iridium 9522A — Based on the 9522, some variants have built in GPS and autonomous reporting functions. Supports SBD.
  • Motorola 9522 — Last Motorola transceiver, supports outgoing SMS but no SBD.
  • Motorola 9520 — Original transceiver module, does not support outgoing SMS or SBD. Designed for use in vehicles with accompanying handset[18]
  • Iridium 9601 — Supports only SBD, several tracking devices and other products have been built around this modem. It is the only mass-produced Iridium transceiver that does not use a SIM card, instead it only uses its IMEI number for identification.

SIM card

Removable Subscriber Identity Modules (SIMs) are used in Iridium phones, much like those used for GSM. Prepaid SIM cards are usually green while post-paid cards are red.

Services

Calls to Iridium phones from landlines and mobile phones, etc. are notoriously expensive, costing several dollars a minute. It is possible to call with charges reversed by first dialing a number in Arizona; the call is charged to the receiver at the standard rate for satellite to landline calls, but the caller only pays for the call to Arizona.[19]

Since Iridium will not sell prepaid cards or even its subscription call service directly, it is hard to obtain the exact price of making a call. There are numerous distributors that will activate Iridium phones and sell pre-paid vouchers and SIM cards.

Voice and data calls

The Iridium system deals with "minutes", which are subdivided into several much smaller "units". These minutes are the "basic rate" to landlines and ordinary mobile phones around the world. For a 500 minute annual plan the cost of the "basic rates" fluctuates around US$1.25 per minute, depending on the distributor. There are also regional plans that offer slightly cheaper rates than the normal, but these minutes can only be used in a specified geographic location (such as Africa, North America, Canada or Alaska).

  • Calls to landlines worldwide: 1.00× basic rate
  • Calls to other Iridium phones or voice mail: 0.50×
  • Sending SMS messages: 0.33×
  • Calls to other satellite phones: 5.00–13.50×
  • Data calls: 1.00×

Iridium and other satellite phones may be identifiable to the listener by the "clipping" effect of the data compression and the latency (time delay) due to the electronic equipment used and the distances the signal must travel. The voice codec used is called Advanced Multi-Band Excitation.

Iridium operates at only 2.2 to 3.8 kbit/s, which requires very aggressive voice compression and decompression algorithms.[20] Latency for data connections is around 1800 ms round-trip, using small packets.[21]

Despite the bandwidth limitations, transparent TCP/IP is supported. Iridium claims data rates up to 10 kilobits per second for their "direct Internet" service which utilizes proprietary compression software. Phones can be connected to computers using an RS-232 connection, as can the 9522A transceiver module.

Prepaid service

Prepaid SIM cards are available from a variety of different outlets and sometimes appear on auction sites such as eBay. Their values range from 50 to 5,000 minutes; the 50 minute cards have no validity and the 75 minute vouchers are valid for only a month, but the 5,000 minute cards stay valid for two years. Since Iridium charges quite a bit for merely accessing their network without making calls it is possible to extend the validity of such an account by a month for around US$45. It is also possible to refill such an account without purchasing a new SIM card.

The 500 minute card is the most common one, which remains valid for one year and can usually be bought for US$600 to $750, while the 75 minute card can cost up to US$175 and the 5,000 minute card costs around US$4,000.

Post-paid service

There is a basic "Emergency" plan for around US$30 to US$40 per month that offers no minutes at all with calls charged at around US$1.39 per minute, and also numerous plans with included minutes. For the more expensive plans (around US$250 per month) the per-minute price dips slightly below US$1.

Phone numbers

Iridium controls the virtual country codes +8816 and +8817, part of the 881 range designated by the ITU for the Global Mobile Satellite System. Each subscriber is given an 8-digit number prefixed by one of these country codes. However many regional telephone service operators such as Meteor have no interconnect agreement with Iridium or other satellite networks and users on these networks need to call reversed charge to a U.S.-based number.

Since spring 2007, postpaid Iridium subscribers have an option to associate their Iridium numbers with a direct U.S.-based number (the so-called +1 Access service).[19]

Paging service

The one-way paging service is still operational, despite the pagers no longer being in production for many years now. Messages are delivered to pre-selected "MDAs" which cover a certain geographic area. Three of these MDAs may be selected on a web-based portal or updated automatically if the paging service is bound to an Iridium phone. Each country has its own MDA based on its country code, some of the larger countries are divided into several MDAs while separate MDAs exist for sections of ocean and common aeronautic routes. This service costs around US$70 per month with a limited number of messages allowed or US$140 for an unlimited number of inbound messages.

Pagers are assigned with telephone numbers in area code 480 and can also be contacted using email, SMS and the web-based interface used to send messages to Iridium phones.[22]

Short burst data

Special modems such as the 9522A and Quake Q9612 can be used for sending and receiving short data bursts, less than 2 kilobytes at a time. This service is often used for asset tracking and remote monitoring. Messages are converted to be delivered in email format or over HTTP to a preconfigured address; the mobile unit does not include a destination address when sending a SBD message. A crude positioning report is also included in each message sent.[23] SBD messages take from 6 to 22 seconds to send or receive.[21]

Technical details

The constellation

An Iridium satellite

The Iridium system requires 66 active satellites in orbit to complete its constellation, with spare satellites in-orbit to serve in case of failure. Satellites are in low Earth orbit at a height of approximately 485 miles (780 km) and inclination of 86.4°. Satellites communicate with neighboring satellites via Ka band intersatellite links. Each satellite can have four intersatellite links: two to neighbors fore and aft in the same orbital plane, and two to satellites in neighboring planes to either side. The satellites orbit from pole to pole with an orbit of roughly 100 minutes. This design means that there is excellent satellite visibility and service coverage at the North and South poles, where there are few customers. The over-the-pole orbital design produces a "seam" where satellites in counter-rotating planes next to one another are travelling in opposite directions. Cross-seam intersatellite-link handoffs would have to happen very rapidly and cope with large Doppler shifts; therefore, Iridium supports intersatellite links only between satellites orbiting in the same direction.

Next-generation constellation

The existing constellation of 66 satellites is expected to remain operational until at least 2014, with many satellites expected to remain in service until the 2020s. Iridium is planning a new generation of satellites with improved bandwidth to be operational by 2016. This system will be backward compatible with the current system. In August 2008, Iridium selected two companies — Lockheed Martin and Thales Alenia Space — to participate in the final phase of the procurement of the next generation satellite constellation, with the winner to be announced in mid-2009.

In-orbit spares

Spare satellites are usually held in a 667 kilometres (410 mi) storage orbit.[24] These will be boosted to the correct altitude and put into service in case of a satellite failure. Many satellites have failed over the years, the most recent being Iridium 28, which failed in July 2008.[25] Currently there appear to be seven spares in orbit, along with several partially failed satellites that are not in active service.[26] Five non-functional satellites have also reentered the Earth's atmosphere.[26]

Collision with Russian satellite

Main article: 2009 satellite collision
See also: Iridium 33 and Kosmos-2251

At 16:55 GMT on February 10, 2009 Iridium 33 collided with a defunct Russian communications satellite.[6] Iridium plans to move one of its on-orbit spares into the network to replace the destroyed satellite within 30 days of the collision.[27] This is the first collision of satellites of this scale. [28]

The satellites

The satellites each contain seven Motorola/Freescale PowerPC 603E processors running at roughly 200 MHz.[29] Processors are connected by a custom backplane network. One processor is dedicated to each cross-link antenna ("HVARC"), and two processors ("SVARC"s) are dedicated to satellite control, one being a spare. Late in the project an extra processor ("SAC") was added to perform resource management and phone call processing.

The cellular lookdown antenna has 48 spot beams arranged as 16 beams in three sectors.[30] The four inter-satellite cross links on each satellite operate at 10 Mbit/s. The inventors of the system had previously worked on a government study in the late 1980s that showed that microwave cross links were simpler and had fewer risks than optical crosslinks. Although optical links could have supported a much greater bandwidth and a more aggressive growth path, microwave crosslinks were favored because the bandwidth was more than sufficient for the desired system. Nevertheless, a parallel optical crosslink option was carried through a critical design review, and ended when the microwave crosslinks were shown to support the size, weight and power requirements allocated within the individual satellite's budget. In recent press releases, Iridium Satellite LLC has stated that their second generation satellites would also use microwave, not optical, inter-satellite communications links. Such cross-links are unique in the satellite telephone industry, as other providers do not relay data between satellites.

The original design envisioned a completely static 1960s "dumb satellite" with a set of control messages and time-triggers for an entire orbit that would be uploaded as the satellite passed over the poles. It was found that this design did not have enough bandwidth in the space-based backhaul to upload each satellite quickly and reliably over the poles. Therefore, the design was scrapped in favor of a design that performed dynamic control of routing and channel selection late in the project, resulting in a one year delay in system delivery.

Each satellite can support up to 1100 concurrent phone calls and weighs about 700 kg.[31][32] The vast majority of patents filed by Motorola during the Iridium project concern ways to manufacture and launch satellites affordably. The satellites were designed to mount sideways on a gimbal for easy access during manufacture (most satellites up until that time had been assembled vertically.) Motorola hired the chief manufacturing engineer from Apple Computer, who had set up the first Macintosh manufacturing line, to help design and automate satellite production.

Air interface

Communication between satellites and handsets is done using a TDMA and FDMA based system using L-band spectrum between 1616 and 1626.5 MHz.[30] Iridium exclusively controls 7.775 MHz of this and shares a further 0.95 MHz. In 1999 Iridium agreed to timeshare a portion of spectrum, allowing radio astronomers to observe hydroxyl emissions; the amount of shared spectrum was recently reduced from 2.625 MHz.[33][34]

The type of modulation used is normally DE-QPSK, although DE-BPSK is used on the uplink (mobile to satellite) for acquisition and synchronization.[35] Each time slot is 8.28 ms long and sits in a 90 ms frame. Within each FDMA channel there are four TDMA time slots in each direction.[36] The TDMA frame starts off with a 20.32 ms period used for simplex messaging to devices such as pagers and to alert Iridium phones of an incoming call, followed by the four upstream slots and four downstream slots. This technique is known as time division multiplexing. Small guard periods are used between time slots. Regardless of the modulation method being used, communication between mobile units and satellites is performed at 25 kilobaud.

Channels are spaced at 41.666 kHz and each channel occupies a bandwidth of 31.5 kHz; this allows space for Doppler shifts.[30]

Handoff

The Iridium system uses three different handoff types. As a satellite travels over the horizon, calls are handed to adjacent spot-beams; this occurs approximately every fifty seconds. A satellite only stays in view for seven minutes at the equator.[37] When the satellite disappears from view, an attempt is made to hand the call to another satellite. If no other satellite is in view, the connection is dropped. This may occur when the signal from either satellite is blocked by an obstacle. When successful, the inter-satellite handoff may be noticeable by a quarter-second interruption.[36]

The satellites are also able to transfer mobile units to different channels and time slots within the same spot beam.

Earth base-stations

A Motorola 9500 phone

Iridium routes phone calls through space. There are four earth stations, and the space-based backhaul will route phone call packets through space to one of the downlinks ("feeder links"). Station-to-station calls can be routed directly through space with no downlink. As satellites leave the area of an Earth base station, the routing tables change and frames are forwarded to the next satellite just coming into view of the Earth base station. Communication between satellites and earth stations is at 20 and 30 GHz.[38]

Gateways are located in

In previous years there were eleven gateways in service, many of which have since been closed.[40] Gateways have also been built in Pune, India; Beijing, China; Moscow, Russia; Nagano, Japan; Seoul, South Korea; Taipei, Taiwan; Jiddah, Saudia Arabia; and Rio de Janeiro, Brazil.

Other technical information

Like other satellite networks, Iridium terminals need open line-of-sight to open sky in order to function. For instance, units will not work consistently indoors, or under forest cover. Iridium does have a very powerful paging channel that can ring the phone indoors, but the customer may have to walk outdoors to take the call.

There is a Web/e-mail to SMS gateway which enables messages to be sent from the Internet or an e-mail account to Iridium handsets for free. There is also a voice mail service.

Iridium generally does not have roaming agreements with terrestrial/cellular operators. Telstra in Australia allows postpay GSM subscribers to use their SIM card. However, global roaming has to be activated and both incoming and outgoing calls are charged to this account, and the call rate is around US$4 per minute; the incoming calls are via the GSM phone number of the account, with country code, etc., prefixed. In order to use the network, it is necessary to have not only appropriate equipment, such as a handset or the optional cellular cassette for the Motorola 9505 phone, but also a pay-as-you-go or contract Iridium SIM card.

Tracking transceiver units

Without an extra GNSS receiver tracking is difficult, but not impossible, as the position of a mobile unit can be determined using a Doppler shift calculation from the satellite. These readings however can be inaccurate with errors in the tens of kilometers.[23] Even without using Doppler shifts, a rough indication of a unit's position can be found by checking the location of the spot-beam being used.

The position readings can be extracted from some transceiver units and the 9505A handset using the -MSGEO AT command. It returns values as the number of kilometers from the prime meridian and the equator with a resolution of 4 km.[41] In the past, Iridium has used this method of tracking to block service to U.S. embargoed countries, such as North Korea, and other unpopular regions, such as Northern Sri Lanka. It is also used to stop geographically bounded plans from being used outside the designated area.

Patents, manufacturing, and launch campaign

The main patents on the Iridium system, U.S. Patents 5,410,728 and 5,604,920, are in the field of satellite communications, and the manufacturer generated several hundred patents protecting the technology in the system. Satellite manufacturing initiatives were also instrumental in the technical success of the system. Motorola made a key hire of the engineer who set up the automated factory for Apple's Macintosh. He created the technology necessary to mass-produce satellites on a gimbal, taking weeks instead of months or years and at a record low construction cost of only US$5 million per satellite. At its peak during the launch campaign in 1997 and 1998, Motorola produced a new satellite every 4.3 days, with the throughput time of a single satellite being 21 days.

Motorola used launch vehicles from three companies from three different countries — the Delta II from McDonnell-Douglas; the Proton K from Krunichev Industries in Russia; and the Long March IIC from China Great Wall Manufacturing Company. The original constellation of 66 satellites, plus six spares, was launched in 12 months and 12 days, between May 5, 1997, and May 17, 1998, with an astounding success rate of 15 out of 15 successful launches and all 72 satellites put into the intended orbits. In one 13-day period (late-March to early-April 1998) they successfully put 14 satellites into orbit.

Product placement

See also

References

  1. ^ Iridium Satellite Phones — The Amazing Worldwide Service
  2. ^ David Rohde (February 24, 1999). "So how do you order satellite service?". CNN. Retrieved 2007-08-20.
  3. ^ "Flaming end for satellites". BBC. March 18, 2000. Retrieved 2007-08-20.
  4. ^ Iridium, Bankrupt, Is Planning a Fiery Ending for Its 88 Satellites
  5. ^ David Vernon (February 20, 2007). "A Heavenly Sign - The Iridium satellite story". Retrieved 2007-08-20.
  6. ^ a b Harwood, Bill (2009-02-11). "U.S. And Russian Satellites Collide". Retrieved 2009-02-11.
  7. ^ "2 orbiting satellites collide 500 miles up". AP DIGITAL. February 12, 2009. Retrieved 2009-02-12.
  8. ^ "Iridium Announces Q2 2008 Results".
  9. ^ DISA establishes portal for telecom satellite system
  10. ^ CNet news — Iridium sets up shop in Iraq
  11. ^ Robert L. Mitchell (December 10, 2007). "The Big Chill: Ch-Ch-Chatting with the IT manager at the South Pole". Computer World. Retrieved 2007-02-14.
  12. ^ Max Jarman (February 1, 2009). "Iridium Satellite Phones Second Life". The Arizona Republic.
  13. ^ [http://www.ubergizmo.com/15/archives/2008/10/iridium_launches_9555_satellite_phone.html Iridium Launches 9555 Satellite Phone]
  14. ^ Iridium Smithsonian - Satellite Phones from Globalcom
  15. ^ PCW - Kyocera SD-66K
  16. ^ Motorola Iridium Kyocera satellite telephone
  17. ^ DPL handset user guide
  18. ^ Iridium 9520.
  19. ^ a b Iridium 1+ Dialing
  20. ^ Iridium Bandwidth
  21. ^ a b Measuring latency in Iridium satellite
  22. ^ iridium 9501, iridium pager
  23. ^ a b Iridium SMS and SBD
  24. ^ Iridium satellites
  25. ^ Iridium 28 replacement by Iridium 95
  26. ^ a b Iridium Constellation
  27. ^ Iannotta, Becky (2009-02-11). "U.S. Satellite Destroyed in Space Collision". Space.com. Retrieved 2009-02-11.
  28. ^ http://www.nytimes.com/2009/02/12/science/space/12satellite.html?ref=space
  29. ^ How the Iridium Network Works
  30. ^ a b c "Manual for ICAO Aeronautical Mobile Satellite (ROUTE) Service Part 2-IRIDIUM; DRAFT v4.0" (PDF). ICAO. 21 March 2007. Retrieved 2007-02-14.
  31. ^ "All About Satellite Phone Service". The Travel Insider. Retrieved 2007-08-20.
  32. ^ IRIDIUM (Information Only)
  33. ^ "Radio astronomers agree to 6-year frequency "time share" with Iridium LLC" (Press release). European Science Foundation. 31 May 1999. Retrieved 2007-02-14.
  34. ^ "FCC Grants Iridium Exclusive Access to Additional Domestic and Global Spectrum for Mobile Satellite Services" (Press release). Iridium Satellite LLC MediaRoom. Retrieved 2007-02-14.
  35. ^ Dan Veeneman. "Iridium". Decode Systems. Retrieved 2007-02-14.
  36. ^ a b Iridium From Concept to Reality
  37. ^ Iridium Modem configuration
  38. ^ Work projects
  39. ^ DISA establishes portal for telecom satellite system
  40. ^ Iridium gateway closures
  41. ^ ISU Command Set - p57
Retrieved from "https://en.wikipedia.org/w/index.php?title=Iridium_Communications&oldid=270189903"