Site: Motorola Satellite Communications Group
2501 South Price Road
Phoenix, Arizona
http://www.mot.com

Date Visited: July 24, 1997

WTEC: K. Bhasin, W. Brandon, J.V. Evans, A. Mac Rae and S. Townes

Hosts:

BACKGROUND

Motorola is currently constructing one of four global satellite systems for personal communications (PCS). Known as "Iridium," this system will be owned and operated by a separate company (Iridium, Inc.) whose investors include operators of gateways (to the terrestrial network) in 11 or 12 countries. We describe this system and its status below.

Motorola had also been proposing to build a satellite system operating at Ka-band and above for wideband data communications, such as required by corporate intranets and Internet access. Known as "Celestri," this project is apparently no longer being pursued as a result of Motorola's being named as a prime contractor for Teledesic. The Celestri project is described below.

Absence of suitable C-band orbital slots has driven satellite developers to build satellites operating at Ku-band (14 GHz earth-to-satellite and 12 GHz satellite-to-earth), and most INTELSAT satellites are now built to have transponders operating in both bands. Powerful direct-to-the-home TV broadcasting satellites all operate at Ku-band. These trends have rendered it now almost impossible to secure an orbital location where a satellite at C or Ku-band can be operated without interfering with its neighbors. This has spurred interest in operating at Ka-band (roughly 29 GHz for earth-to-satellite links and 19 GHz for satellite-to-earth links).

Interest in this band has until recently been confined to experimental satellites launched by the U.S., Italy, and Japan. This is because, unlike C-band, rain greatly attenuates Ka-band signals (and to some lesser extent, Ku-band), making this a difficult band in which to provide satellite services. However, Ka-band does offer large amounts of presently unused spectrum capable of supporting a variety of high-speed data services. To exploit this availability a group of private U.S. investors proposed a Ka-band satellite system providing a global wideband distribution capability known as "The Callingsm Network" and later renamed Teledesic. This system was to employ 840 low-altitude satellites each of which could relay to its eight nearest neighbors and provide users (with sufficiently large terminals) access at rates up to 1.2 Gbps.

Despite the very ambitious nature of this proposal, the Teledesic organization was successful in lobbying at the World Administration Radio Conference for Ka-band frequency assignments. This caused the FCC to proceed with a "Notice of Inquiry" offering other applicants the opportunity to seek Ka-band spectrum (and orbital locations). In all there were 13 applications submitted (in addition to the one from Teledesic)ľall of them for geostationary satellite systems. Motorola proposed a four-satellite system serving the Americas called "Millennium."

The largest market for these wideband Ka-band systems is thought to be access to the Internet. Driven by the existence of 200 million personal computers today and an anticipated 400 million after the year 2000 (most of which will be multimedia ready), the Internet is experiencing explosive growth. By some estimates, there will be 150 million households using the Internet by the year 2000 representing a market of over $10 billion. To tap this market via Ka-band satellite terminals will require low-cost "consumer" terminals, and this in turn will require large scale manufacturing. A second market is the use of the Internet by corporations to create their own semi-private "intranets." This could grow from over half million in 1996 to more than $30 billion by the year 2000, and represents a more attractive market than the consumer market since corporations: (a) tend to be "early adopters" of new technology and (b) are likely to require a higher level of service, justifying more expensive terminals.

A key to understanding Motorola's venture into communications satellite manufacturing is its manufacturing quality aesthetic. Motorola has won the Malcolm Baldridge Award for quality and also won awards from Japan for manufacturing quality. Company engineers approached the satellite problem as a manufacturing quality problem rather than as a space problem. They were then able to view Iridium manufacturing in a familiar context. The design for the factory was begun in 1990, and it is in full operation. Factory processes employ principles of quality control. Motorola agrees that even 66 satellites is not "volume production." The prior record, about 40 satellites for GPS, compares to about 100 for operation and spares for Iridium. However, the processes being used are very different from traditional satellite construction, and are obviously influenced by experience in manufacturing volume quantities of smaller electronic systems. Only 17 days are required for the manufacture of a complete satellite. The production output rate is one/week.

It is also important to note that the satellite bus is manufactured by Lockheed Martin. Various other components are produced by other companies (e.g., three phased array antennas/satellite are produced each week by Raytheon). Motorola produces the digital communications electronics and system software, areas of its acknowledged excellence. Components such as antennas are received, unpacked and bolted in place, usually without testing at Motorola. This is a bold departure from the traditional gradual accretion of parts, each step followed by expensive testing.

THE IRIDIUM SYSTEM

System Description

Several companies (almost all of them in the United States) have announced plans to construct and operate satellite communications systems that would provide personal communications around the globe. Much of this activity was spurred by a bold plan put forth by Motorola—to create a global personal satellite communications system employing 77 (later changed to 66) satellites in LEO known as Iridium. Other proposals for LEO systems followed, causing Inmarsat (the established GEO mobile system) to consider what type of personal communications system it might launch. Guided to some extent by design studies performed by TRW, Inmarsat adopted a system employing satellites in 6-hour orbits at 10,000 km altitude (MEO). This system is now being built by an affiliate company called ICO-Global.

Loral, TRW, Constellation and Ellipsat are also building LEO and MEO systems, respectively, but have opted for lower cost simple transponder satellites (no onboard processing) using CDMA to permit multiple users to access the same transponders.

From a technical standpoint, the Iridium system proposed by Motorola, and currently being constructed by that company in conjunction with Lockheed Martin, Raytheon, COM DEV, and other contractors, is the most ambitious of the four. The system is being purchased and will be operated by a separate company (Iridium, LLC), which has secured investment from many parts of the world (over $4 billion as of October 1997). The design employs 66 satellites placed in circular, nearly polar orbits at 780 km altitude. The satellites will be deployed into six equi-spaced orbital planes, with 11 satellites equally separated around each plane. Satellites in adjacent planes are staggered in latitude with respect to each other to maximize the coverage at the equator, where a user may be required to access a satellite that is as low as 10° above the horizon.

Users employ small handsets operating in frequency-division-multiplexed/time-division-multiple-access (FDM/TDMA) fashion to access the satellite at L-band. Most handsets are expected to be dual-purpose satellite and cellular phones. In the satellite mode, four users share transmit and receive frames in channels that have a bandwidth of 31.5 kHz and are spaced 41.67 kHz apart. That is, users are synchronized so that they all transmit and all receive in the same time windows, alternately. This approach is necessary because the (three) phased-array antennas are used for both transmitting and receiving. Uplink and downlink power control is used to overcome partial shadowing.

The Iridium system employs onboard processing to demodulate each arriving TDMA burst and retransmit it to its next destination. This can be to the ground if a gateway earth station is in view or to one of the four nearest satellites: the one ahead or behind in the same orbital plane, or the nearest in either orbital plane to the east or west. These satellite crosslinks operate at 23 GHz. The links to the gateway earth stations are at 20 GHz. down, 30 GHz up.

The use of crosslinks greatly complicates the design of the system, but allows global service to be provided with a small number of gateway earth stations. In addition, the crosslink hardware proved not very complex and represents less than four percent of the total satellite cost. At present, gateway earth stations are planned for Tempe (Arizona), Rio de Janeiro, Moscow, Rome, Bombay, Bangkok, Jakarta, Taipei, Beijing, Seoul, and Nagano (Japan). Some of these (e.g., at Tempe) have already been completed and are in use for checking out the system. To properly route the traffic, each satellite must carry a set of stored routing tables from which new routing instructions are called every 2.5 minutes.

The crosslinks to the satellite ahead and behind are the easiest to implement, since those satellites remain at a fixed distance and in a fixed viewing direction. The crosslinks to the satellites in the adjacent orbital planes have constantly changing time delays and antenna pointing requirements. To mitigate this problem, a circular polar orbit (actually an inclination of 86.4°) was chosen. Even so, it is necessary to drop these crosslinks above 68° latitude, as the angular rates for the tracking antennas become too high. To avoid congestion on these links, they must be designed so that each crosslink can handle all of the service traffic from a given satellite. Linking between satellites that are in ascending and descending planes is particularly difficult and requires that packets be routed around the globe in the opposite direction. There is also a need to monitor the number of times a packet has been routed via a node and to drop any when this exceeds a certain value (15), lest the system become clogged with undeliverable traffic.

The onboard processor is being constructed using 178 very largescale integrated circuits designed specifically for the project. It includes 512 demodulators, with closed loops that (via control channels to the handheld units) cause the arriving hand-held bursts to be centered in frequency and time. The observed Doppler shift of these arriving bursts is routed to the intended destination gateway earth station to determine the user's location. Service is then provided (or denied) based on country-by-country service agreements. Each satellite is capable of handling as many as 1,100 simultaneous calls. (It was said that as many as 500 calls could be supported in a small area such as New England.)

Services to be provided include voice (probably at 2.4-kbps encoding, although 4.2 kbps is also possible), data at 2.4 kbps, and high-penetration paging which affords 11 dB more power than the regular signal. The design, however, already provides a link margin (~16 dB) that is higher than that of any of the competing systems. This is because Motorola required that the handheld unit be usable from inside a vehicle (e.g., a taxi) and this in turn was dictated by the business plan, which depends heavily on serving international business travelers.

Station keeping for Iridium satellites uses onboard propulsion in order to overcome atmospheric drag and have sufficient fuel for an 8 year life. Four telemetry, tracking and control facilities are being built to manage the satellite operations at Hawaii, Yellowknife and Iqualuit (Canada), and Eider (Iceland), and there is a separate engineering facility to diagnose problems that may arise (e.g., the failure of a crosslink). This Master Control Facility will be in Landsdowne, Virginia with a backup in Rome, Italy.

Satellite Status

Motorola had launched the first 34 of these satellites (as of October 1997) and planned to have the entire system in operation in the fourth quarter of 1998. Electrical checkout has shown that all of these but one measured extremely close to nominal values. No component failures have been observed. Currently, satellites are being built at a rate of 1 per week and launch contracts have been secured in the U.S. (Delta), Russia (Proton) and China (Long March) to place the remaining satellites in orbit.

Iridium Handset (Hand-Held subscriber Unit)

Motorola has centered the system design around the end user and has had a cellular telephone handset user terminal in mind from the outset. Communications should be possible from within houses, in foliage, and "from the rear seat of a taxi." The phone is expected to be usable within >90% of the structures in the world. To make this possible, a link margin of 16 dB has been specified.

There has been some controversy about the Iridium handset in terms of feasibility, design and cost. Motorola has changed the design, or appeared to change it, several times over a period of several years, and the estimated price has varied, as revealed by speakers at public gatherings. Some evolution of such a new device should be expected but reports on the status may have fueled the controversy.

Motorola is a world leader in sales of subscriber telephone units, with an 18 year history in cellular phones. Primary design and manufacturing responsibility is in Schaumburg, IL. This organization is fully responsible for the Iridium handset and has extensive experience in producing complex handsets at minimal cost. The Motorola Startac phone cost $3000 when first introduced and now sells for as little as $150. It is inferred that a large production is anticipated to bring the cost of the Iridium handset down, as well. Motorola representatives stated that it is the cosmetics and features that are "fiercely guarded." There is an unsettled lawsuit with Qualcomm over the Startac design. The antenna is said to be a quadrifilar helix type, and flips up for use. The sketch we were shown was not extremely clear in terms of revealing much about the communications services or man-machine interface. It is possible that some limited form of messaging will be built in together with the paging function, for example.

Around 1990-1991, Motorola selected some of the requirements for the handset. At that time, a leading world standard for cellular was GSM. Consequently, Motorola chose GSM to be a second mode for the IRIDIUM dual-mode handset. It is likely that most, if not all, IRIDIUM handsets will be dual mode; however, some may have a different cellular standard than GSM, intended for parts of the world where GSM is not used.

Voice Quality

Codex (Mansfield, MA) is said by Motorola to have unexcelled expertise in tandem operation of digital vocoders. The implication is that some proprietary coding is used to make Iridium voice more readily integrable with world digital telephone systems. The trick is in non-uniform error protection of digital speech samples. Coding rates are said to be 7/8 for bits of low "importance" and 1/3 for bits of highest importance. As an example, 2.4 kbps LPC 10 is expected to work in tandem with Iridium with excellent speech quality at both ends.

Field Trials

About 400 to 1,000 handsets were scheduled to be manufactured for "large scale" field tests in the spring of 1998. The full constellation of 66 satellites was expected to be in orbit by springtime; and the system is to be declared operational in the fourth quarter of 1998. Some senior Motorola personnel will participate in evaluations with users so the trials are in some way a portion of the "system qualification test."

Airborne Terminal

An interesting revelation is that Allied Signal was said to be working on integration of Iridium into aircraft, with a service to be available by mid 1999. Allied is "doing whatever is necessary for airplanes," which might require an external antenna, for example, although this was not stated. This airborne capability could take several forms and may not be perfectly applicable to Air Force needs; nevertheless, it suggests that the system at least is compatible with airborne use.

Software

In response to a question, Motorola hosts estimated that the software in one of the gateway earth stations was about ten million lines of code. Of this total, about nine million lines of code are said to be commercial off the shelf ("COTS"). Although the integration was apparently not complete, there was absolutely no concern about the software in the earth stations.

The waveform, multiple access, power control, and other features that would impact software or firmware relating to the handset appear to have been frozen for some time. GSM "COTS" software is used.

The approach to the software is to develop upgradable software in increments. It is probable that the field trials will be used to make some refinements. Software used on the satellites is uploadable from the ground. Full capability is not required until the system is operated in a full-up mode (using crosslinks, ground entry stations, etc.).

Motorola is certified as a level 4 software developer and anticipates level 5 certification by the end of the year (Carnegie Mellon University, Software Engineering Institute or SEI standard). There are only four or five level 5 houses in the world, and Motorola has three of these sites. This suggests confidence in software developed for Iridium.

CELESTRI

Motorola originally filed for a system to be called "Millennium" via a wholly owned subsidiary (Comm. Inc.). This was to have been a satellite system to serve the United States, Central and South America from geostationary orbits. Subsequently, Motorola filed for a new system known as "M-Star" operating above Ka-band and employing 72 satellites in low earth orbit. M-Star would employ uplinks in the 47.2-50.2 GHz band and downlinks at 37.5 to 40.5 GHz.

In yet a third filing, Motorola proposed a system to be known as Celestri, which it has now apparently decided not to pursue since becoming the prime contractor for Teledesic. Celestri would have represented a merger of the two previous systems, employing 63 Ka-band LEO satellites at 1,400 km altitude and an unspecified number of geostationary satellites. The system was designed to offer very high data rate access (from 64 kbps to 155 Mbps) and in this sense is seen as a close competitor with the Teledesic system.

The Ka-band LEO portion of the Celestri system would employ 9 satellites equally spaced around seven orbital planes inclined at 48° to the equator. This provides visibility of one satellite above 16° elevation 100% of the time at all latitudes up to 60° and of two satellites > 90% of the time up to 55° latitude. Each satellite will have 432 downlink and 260 uplink beams. This large number of beams allows for a 35-fold reuse of the assigned frequency band using a 7-cell cluster pattern. Optical intersatellite links employing mechanically steered optics will permit connection to the six nearest satellites. Each satellite will have a capacity to support up to 1.83 Gbps peak demand over a single 7-cell cluster can vary between 0.23 and 0.34 Gbps depending on the mix of terminals accessing the satellite. Uplink rates of 2.048 Mbps, 51.84 Mbps, and 155.52 Mbps are contemplated with downlinks at 16.384 Mbps, 51.84 Mbps, and 155.52 Mbps, using demand-assigned FDM/TDMA channels.

Motorola expects some users, whose needs are not delay-sensitive, to use links afforded by geostationary satellites and has recently filed for additional orbit assignments. The M-Star system, if authorized, would have available 3 GHz of bandwidth allowing for very high speed data links between, for example, Internet service providers. These satellites are likely to be added to the system last.

OBSERVATIONS

Motorola is an extremely competent company and has secured strong partners in carrying out the Iridium project. With their help all the technical obstacles in this very complex system are said to have been overcome, and it is expected that the system will go into operation on schedule. This success has bred a strong sense of self-confidence, and Motorola sees little or no need for government support in tackling any of the satellite industry's technical challenges—other than securing lower cost launch services.

The progress seen on this visit certainly removes any doubt about the commitment and status of the satellites. While less insight was obtained on the user terminal, it appears that this area is in good hands and must also be in production. This author concludes that the Iridium system will be successful.


Published: December 1998; WTEC Hyper-Librarian