The global satellite constellation IRIDIUM took another step forward on November 8th with the launch of five additional satellites from Vandenberg Air Force Base in California. As of this writing 39 space vehicles are in orbit, although Motorola Satellite Communications reports that one of the previously launched satellites experienced an attitude control problem and is not expected to be included in the operational constellation. Since each of the six orbital planes envisioned by IRIDIUM planners will contain a spare, this loss should not delay commercial service rollout scheduled for the third quarter of 1998.

The IRIDIUM satellite telephone network will operate using a slightly modified Global System for Mobiles (GSM) standard, incorporating their 1600 MHz transceiver into a multiband GSM handset. Customers will use the handset over 900, 1800, and 1900 MHz GSM terrestrial networks, switching to the IRIDIUM satellites when no such local system is available. Subscribers will contract with their local GSM carrier to automatically roam on the IRIDIUM system, which is expected to cost in the range of $3 per minute.

Globalstar, another satellite-based voice service provider, announced their first launch is now scheduled for February of 1998, eight weeks later than previously expected. The postponement is apparently to allow additional time for testing and rehearsals of the ground equipment that will provide tracking, telemetry, and control (TT&C) for the 56 low earth orbit (LEO) satellites.

LITTLE LEOs

While IRIDIUM and other voice service Big LEO satellite systems gather headlines, they may soon be sharing the spotlight with their less expensive counterparts. Termed Non-Voice Non-Geosynchronous (NVNG) systems by the Federal Communications Commission, these Little LEOs utilize constellations of smaller, less costly satellites to provide low speed, low volume digital wireless links. Using small, inexpensive user terminals, little LEOs are poised to provide such services as vehicle tracking, two-way data messaging and electronic mail, routine and emergency position location, remote environmental monitoring, and security warnings.

A Report and Order released by the FCC in October specifies a number of operational rules and frequencies for five Little LEO systems, all of whom will transmit and receive on VHF and UHF frequencies. Of the five, Orbcomm and VITA are already licensed and operating, Orbcomm with two satellites in orbit and VITA with one launched last September. Three newer entrants, LEO One, Final Analysis, and E-Sat, are preparing for construction and launch.

All five will share the same slice of spectrum, 148 MHz to 150 MHz for the uplink (Earth to space) as well as 137 MHz to 138 MHz and 400 MHz to 401 MHz for the downlink (space to Earth). This band of frequencies is already fairly crowded, with National Oceanic and Atmospheric Administration (NOAA) and Department of Defense (DoD) weather satellites transmitting in the 137 MHz and 400 MHz bands, respectively. Russian and French satellites also use this part of the spectrum, adding to complexity of frequency coordination.

Because geosynchronous satellites orbit 22,000 miles above the earth and make one rotation every 24 hours they appear to be stationary in the sky, "hanging" above a particular spot. Low earth orbiting satellites operate much closer to the earth, at altitudes from a few hundred to several thousand miles and complete an orbit many times each day. Because these satellites are moving so quickly, spectrum allocations must also take into account an effect called Doppler, which is the apparent change of transmitted frequency due to the motion of the satellite. A stationary receiver listening to a satellite moving overhead will experience a change in frequency, higher as the satellite approaches and lower as the satellite moves away. Doppler for a single beam from a Little LEO is expected to be on the order of 5 to 10 kHz, requiring a shift up or down in receiver tuning depending on the location of the receiver and the motion of the satellite.

A comprehensive plan proposed by the participants and ordered by the FCC distributes the available spectrum among each Little LEO and requires each operator to avoid interfering with the transmissions of government satellites. Accurate orbital locations and movement information ("ephemeris" data) will be collected and processed to predict their coverage areas ("footprints" in satellite parlance) up to week in advance, and where overlaps occur the Little LEO satellite must change operating frequencies or not transmit at all. In addition, to insure a failure will not create havoc, each satellite must have a fail-safe mechanism by which it will cease transmitting if a "reset" signal is not received from the ground every 72 hours.

SYSTEM	SATELLITES (Planned)	MODULATION METHOD	EXPECTED COST ($ millions)
E-Sat	6	CDMA	50
Final Analysis	26	FDMA/TDMA	250
LEO One	48	FDMA/TDMA	250
Orbcomm	28	FDMA/TDMA	350
VITA	2	FDMA/TDMA	10

Table 1: Little Low Earth Orbit (LEO) systems.

NEW FCC COMMISSIONERS

There's been a changing of the guard at the Federal Communications Commission. Four of the five Commissioners are new as of November, when William Kennard, Harold Furchtgott-Roth, Michael Powell, and Gloria Tristani were confirmed by the Senate. Susan Ness is the only Commissioner staying on. The new Chairman, Mr. Kennard, had previously served as FCC General Counsel, and worked as a communications lawyer before coming to the FCC in 1993. He is seen as less confrontational and more of a consensus-builder than his often-controversial predecessor Reed Hundt. The other Commissioners come from other parts of the government with varied backgrounds in economics and law.

LOCAL MULTIPOINT DISTRIBUTION SERVICE

The largest spectrum auction in the history of the FCC is scheduled for December 1997, where 986 licenses covering 1.3 GHz of spectrum will be sold to the highest bidder for use under the moniker Local Multipoint Distribution Service (LMDS). Two blocks of spectrum in each of the nation’s 493 Basic Trading Areas (BTAs) will be auctioned, with a 150 MHz block available to all bidders and a 1150 MHz block available to all except in-region cable television and local telephone companies. Because of radio signal characteristics at these frequencies, the services offered by licensees will be fixed rather than mobile, and are expected to include interactive video, high speed Internet access, and two-way voice telephony. LMDS pioneer CellularVision has been running a one-way video service for several years, transmitting more than 40 cable-quality analog channels to customers in the Brighton Beach, New York area, but future services will most likely be interactive and fully digital. Internet access, for instance, is expected to be a marketing winner with transfer speeds approaching 1.5 gigabits per second, orders of magnitude faster than ordinary dial-up modems. Thousands of voice channels can fit in the LMDS blocks, providing an alternative to the local telephone company.

LMDS transmitters are generally line of sight, with a typical range of 4 to 6 miles. Development of low-cost equipment that operates in the 28 to 30 GHz band will take some time, leading most analysts to believe that initial license winners will focus on business customers, supplying wireless voice and Internet access to corporate locations that can afford relatively high-cost transceivers. As performance improves and hardware costs drop, LMDS should gradually reach residential consumers.

Because the wireless signals bypass the local infrastructure of cable television and telephone companies, the FCC expects LMDS to eventually become a competitor to these local monopolies, driving down prices and increasing the variety and quality of services.

A Block	27.5 to 28.35 GHz 29.1 to 29.25 GHz 31.075 to 31.225 GHz	1150 MHz
B Block	31.0 to 31.075 GHz 31.225 to 31.3 GHz	150 MHz

Table 2: Local Multipoint Distribution Service license blocks

PENTIUM BUGS

Another interesting bug has been discovered that affects the operation of certain Intel Pentium microprocessors. Several years ago it was reported that early generation Pentium chips suffered from a double precision division problem in the floating point arithmetic unit, where serious errors, although unlikely, could occur. More recently the Pentium Pro was shown to occasionally fail to correctly report a float-to-integer conversion overflow, again creating the possibility of incorrect answers. Other "deviations from published specifications," as Intel refers to such bugs, are usually listed in an errata for each microprocessor.

This latest bug, nicknamed the "Pentium F0 Bug," causes Intel Pentium and Pentium MMX microprocessors to "hang," or stop functioning until reset, when executing the instruction F00FC7C8, regardless of the operating system. This bug does not appear in compatible chips manufactured by Advanced Micro Devices (AMD) or Cyrix. It also does not appear to affect Pentium II or Pentium Pro microprocessors, and does not affect earlier generations of processors such as the 80486.

Microprocessor operations are controlled by microcode, a special form of software that directs the internal operation of the chip. With modern chips growing in complexity and sophistication, testing the microcode is extremely difficult. Microcode with hard-to-detect faults, perhaps triggered by specific but unusual code sequences, may remain undetected for long periods of time but leave computer systems vulnerable to unexpected results, or worse.

This particular instruction should only occur in programs deliberately created to exploit the bug, and will not exist in commercial software such as spreadsheets and word processors. Many Internet service providers use Pentium-based equipment, and any service that allows a user to run their own programs would be vulnerable to the following program, regardless of the operating system or other software on the computer:

/* C language program to demonstrate Pentium F0 bug */

char bug_code[4] = { 0xF0, 0x0F, 0xC7, 0xC8 };

main()
{
void (*f)() = (void (*)()) bug_code;
f();
}

Intel processors are in more than 80% of the world's personal computers, and Intel ships almost 100 million chips each year. Last July Intel revealed that the microcode in Pentium Pro and Pentium II chips can be upgraded, presumably to correct such defects. Although not available to end users, such microcode patches offer the possibility of repairing flaws and limitations without the need to replace any hardware.

As more receivers and radio equipment are controlled by microprocessors of various types, how many unexpected "features" will surface and how will they affect the operation of the device?

That's all for this month. Comments, questions, and Pentium horror stories can be sent to dan@decode.com. More information is also available at the PCS Front Line web site, http://www.grove.net/~dan. Until next month, happy monitoring!