Iridium Communications
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 derives its name from the chemical element known as Iridium; the size of the satellite constellation projected in the early stages of planning was 77 – which is equivalent to the atomic number for Iridium.
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 and went into Chapter 11 bankruptcy on August 13, 1999. The first Iridium call was made by then-Vice President of the United States Al Gore. Motorola provided the technology and major financial backing.
Its financial failure was largely due to insufficient demand for the service, coupled with a massive initial capital cost running into the billions of dollars (the handsets could not operate until the entire constellation was in place). 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 also prohibitive for many users, despite the continuous worldwide coverage of the Iridium service. In addition, 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 website and a "run-around" from the company's representatives. After Iridium filed bankruptcy it cited "difficulty gaining subscribers".[1]
The initial commercial failure of Iridium has 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 proposed schemes were never constructed.
At one stage there was a threat that the Iridium satellites would have to be de-orbited;[2] however they remained on orbit and operational. 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.[3]
Present status
Iridium Satellite LLC claims to have 203,000 subscribers as of June 30, 2007, an 11% increase from the total by the end of the first quarter 2007. Revenue for the second quarter of 2007 was $66.7 million with EBITDA of $20.2 million. Revenue in 2006 was $212.4 million and EBITDA was $53.9 million.
The system is being used extensively by the U.S. Department of Defense for its communication purposes through the DoD gateway in Hawaii. 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 to communications with remote science camps, especially the Amundsen-Scott South Pole Station. As of December 2006, an array of 12 Iridium modems was put online providing 24/7 data services to the station for the first time. Total bandwidth is 28.8 kbit/s, making real time e-mail conversations finally possible.[4]
Iridium and other satellite phones may be identifiable to the listener because of the particular "clipping" effect of the data compression and the latency (experienced as a noticeable lag or time delay) due to the electronic equipment used and the distances the signal must travel. Iridium operates at 2200 to 3800 baud, which requires very aggressive voice compression and decompression algorithms. The voice codec used is called Advanced Multi-Band Excitation. Iridium claims data rates up to 10 kilobits per second for their "direct internet" service. Phones can be connected to computers using a RS-232 connection, as can the 9522A, which is just a transceiver module. These can be used for data-logging applications in remote areas. This is a common practical use for Iridium's services, and the new tsunami warning system uses Iridium satellites to communicate with their base. The remote device must be programmed to call the base at specified intervals, or it can be set to accept calls in order for it to offload its collected data. Despite the bandwidth limitations, transparent TCP/IP is supported. Latency is around 1500 milliseconds.
The former Iridium provided phones from two vendors, Kyocera and Motorola. Neither still manufacture these handsets. Kyocera phone models SS-66K and SD-66K are no longer in production but still available in the second-hand and surplus market. The Motorola phone 9500 is a design from the first commercial phase of Iridium, whereas the current 9505A model is the most current version of the handset and the 9522A is the most current version of the OEM L-Band Transceiver module designed for integration into specific applications. The 9505A phone is functionally identical to the 9505 but is no longer manufactured by Motorola and contains a slightly different set of components.
Services
Calls to Iridium phones are notoriously expensive, ranging from $3 to $14 per 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.
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. Regardless of the price, each pre-paid card or monthly plan comes with a number of minutes. These minutes are the "basic rate" to landlines. For a 500-min annual plan the cost of the "basic rates" fluctuates around $1.50/min. depending on a 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 and 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: 5–13.50×
- Data calls: 1.00×
Prepaid service
Prepaid SIM cards are available from a variety of different outlets and sometimes appear on 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 $45. It is also possible to refill such an account without purchasing a new SIM card.
The most common card is the 500 minute one, which remains valid for one year and can usually be bought for $600–750, while the 75 minute card can cost up to $200 and the 5,000 minute card costs around $4,000.
Post-paid service
There is a basic "Emergency" plan for around $30 to $40 a month that offers no minutes at all with calls charged at around $1.39 per minute, and also numerous plans with included minutes. For the more expensive plans (around $250 per month) the price per minute is slightly below $1 per minute.
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 will 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).
Paging service
The one-way paging service is still operational despite the pagers no longer being in production for many years now. Messages will be delivered to pre-selected "MDA's" that are the size of an average country and three of these MDA's may be selected or updated automatically if the paging service is bound to an Iridium phone. This service costs around $70 per month with a limited number of messages allowed or $140 for an unlimited number of inbound messages.
Technical details
The constellation
The Iridium system requires 66 active satellites in orbit to complete its constellation, with spare satellites in orbit to fill 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 neighbouring satellites via 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. Because satellites use an over-the-pole orbital constellation design there is 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; Iridium only supports intersatellite links between satellites orbiting in the same direction.
The cellular lookdown antenna has 48 spot beams arranged as 16 beams in three sectors. The four intersatellite cross links on each satellite operate at 10 Mbit/s. The cross links were originally envisioned to be optical, and future satellites may be equipped with optical links. Such cross-links are unique in the satellite telephone industry as other providers such as Globalstar depend on local base stations and do not relay data between satellites. Iridium's use of cross-links means that calls between satellite phones are cheaper, as many such calls never get passed through a ground-based repeater station.
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.
The satellites
The satellites each contain seven Motorola/Freescale PowerPC 603E processors running at roughly 200 MHz. 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 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[5] and weighs about 700kg.[6]
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, however Iridium exclusively controls 7.775MHz of this and shares a further 0.95MHz. In 1999 Iridium agreed to timeshare a portion of spectrum allowing radio astronomers to observe hydroxyl emissions but the amount of shared spectrum was recently reduced from 2.625MHz.[7][8]
The type of modulation used is QPSK[9] and each timeslot is 8.28ms long and sits in a 90ms frame. Within each FDMA channel there are four TDMA channels in each direction. The TDMA frame starts off with a 20.32ms 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. Small guard periods are used in between timeslots. Channels are spaced at 41.666KHz and each channel occupies a bandwidth of 31.5KHz - this allows space for doppler shifts[10]
Earth base-stations
Iridium routes phone calls through space. There are four earth stations and the space-based backhaul routes 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.
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.
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 does not have roaming agreements with terrestrial/cellular operators, except for Telstra in Australia which allows postpay GSM subscribers to use their SIM card. However, both incoming and outgoing calls are charged to this account and the call rate is around $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.
Patents
The main patents on the Iridium system are in the area of mass production of satellites. Iridium made a key hire of the engineer who set up the automated factory for Apple's Macintosh, and he created the technology necessary to mass-produce satellites in weeks (instead of months or years) on a gimbal, at a record low cost of only $5 million per satellite ($40M including launch costs, 1998 dollars).[citation needed]
In popular culture
- An Iridium satellite phone handset appears briefly in the 2006 James Bond film Casino Royale. It is used by one of the villains in a scene set in Uganda. It is also used frequently throughout another 2006 movie Miami Vice.
- A Iridium satellite phone was used in the movie "Sahara".
Quotes
- "Iridium will succeed because every time we estimated the growth of cellular phones, we were LOW by a factor of four"—Bary Bertiger of Motorola, system inventor.
See also
Notes
- ^ David Rohde (February 24, 1999). "So how do you order satellite service?". CNN. Retrieved 2007-08-20.
{{cite web}}: Check date values in:|date=(help) - ^ "Flaming end for satellites". BBC. March 18 2000. Retrieved 2007-08-20.
{{cite news}}: Check date values in:|date=(help) - ^ David Vernon (February 20 2007). "A Heavenly Sign - The Iridium satellite story". Retrieved 2007-08-20.
{{cite web}}: Check date values in:|date=(help) - ^ http://www.computerworld.com/action/article.do?command=printArticleBasic&articleId=9049898
- ^ "All About Satellite Phone Service". The Travel Insider. Retrieved 2007-08-20.
- ^ http://www.iridium.ru/engindex.htm
- ^ http://www.esf.org/media-centre/press-releases/ext-single-news/article/radio-astronomers-agree-to-6-year-frequency-time-share-with-iridium-llc-210.html
- ^ http://iridium.mediaroom.com/index.php?s=press_releases&item=848
- ^ http://www.decodesystems.com/iridium.html
- ^ http://www.icao.int/anb/panels/acp/wg/m/iridium_swg/ird-08/ird-swg08-ip05%20-%20ams(r)s%20manual%20part%20ii%20v4.0.pdf