|IRIDIUM SATELLITE TIME AND LOCATION|
Iridium launched the Satellite Time and Location (STL) service in May 2016,
with primary technology partner Satelles (a division of iKare Corporation).
STL uses the narrowband paging channels of Iridium, a one-way transmission from the satellite with a high gain system. The STL signal is different from the wide band, lower gain two-way channel of the Iridium phone.
The STL signal is 1,000 times stronger than GPS because it originates from the Iridium constellation of 66 satellites orbiting in a low earth orbit. It is also encrypted for high security, which greatly enhances resilient positioning, navigation and timing (PNT).
The Iridium Constellation consists of 66 Low Earth Orbiting (LEO) satellites, primarily used for global communications. The satellites transmit in the L-Band at carrier frequencies in the range of 1616-1626.5 MHz, using Quadrature Phase Shift Keying (QPSK) with a symbol rate of 25,000 symbols per second. Transmission is frame based, with frame length of 90 ms.
Iridium satellites travel at speeds of about 7500 m/s, resulting in variations of up to +/- 40 kHz from the nominal carrier frequency due to Doppler effects. Compared to GNSS signals, Iridium signals have much higher raw signal power (300 ~ 2400x) as seen by a receiver on Earth.
Two main technical innovations are applied to the existing Iridium QPSK transmission scheme in order to facilitate precision measurements. First, the QPSK data at the beginning of a STL burst is manipulated to form a continuous wave (CW) marker, which can be used for burst detection and coarse measurement. Second, the remaining QPSK data in the burst is organized into pseudo-random sequences, reducing the effective information data rate while providing a mechanism for precise measurement via correlation with locally generated sequences. The processing gain associated with the sequence correlation operation also enhances the capability of the STL signal to penetrate buildings and other occlusions.
STL bursts are transmitted once every 1.4 seconds on average. If coarse time is known, such as in the case of a receiver with a network connection, then precise time can be calculated by processing a single burst. Assuming the receiver can process a burst in < 0.6 seconds, precise time and frequency can typically be acquired using STL in under 2 seconds. The precise time and frequency information derived from a single STL burst can be used to assist weak-signal GNSS acquisitions. Since the STL signal is more robust than GNSS, precise assistance is provided to acquire GNSS signals as weak as -160 dBm, assuming that the STL and GNSS signals are attenuated similarly by path occlusions.
In October 2008, the FCC granted Iridium exclusive access to
1617.775 to 1618.725 MHz and shared access to 1618.725 to 1626.5 MHz,
based on a sharing plan set out in November 2007.
Iridium uses a Frequency Division Multiple Access/Time Division
Multiple Access (FDMA/TDMA) scheme for communication with the
satellites using differentially-encoded QPSK modulation at 2400 bits per second.
The subscriber links are in L-band between 1616 and 1626.5 MHz.
Feederlinks are in Ka band, with downlinks between 19.4 and 19.6 GHz and uplinks between 29.1 and 29.3 GHz.
Intersatellite links are between 23.18 and 23.38 GHz at 25 Mbps.
Ka band uplinks and cross-links are packetized TDMA, transmitted via QPSK with 1/2 rate convolutional forward error correction.
Each satellite provides 48 individual spot beams with a frequency re-use pattern. This provides a total of 1628 cells, with each cell covering about 30 mile footprint. Each cell has 174 full-duplex voice channels (there are 283,272 channels worldwide).
Frequency access is 41.667 kHz
The uplink and downlink traffic channels use identical burst structures.
All data is transmitted at 50 kbps, so a 8.28 ms frame transfers 414 bits.
A 2400 bps traffic channel uses one Uplink and one Downlink per frame
From the FCC Order and Authorization (DA 96-1789). [MSC is Motorola Satellite Communications, Inc.]
Enhanced ringing and paging services. MSC requests explicit authorization for the IRIDIUM System to provide enhanced ringing and paging services, in addition to the kinds of MSS service that it originally proposed to provide. The enhancement would enable users to receive ringing and paging messages during heavier atmospheric fading conditions and in buildings where attenuation is greater, according to MSC. One-way "ring alert" channels at 1626.270833 MHz would be used to alert subscribers with special receive-only mobile earth terminals to the presence of incoming paging calls. Paging messages would be transmitted to the receive-only terminals at 1626.437500, 1626.395833, 1626.145833, or 1626.104167 MHz. Their duration would not exceed 20.32 milliseconds. The transmit power for the ring alert channel would be somewhat higher than the power used for a voice/data channel, so as to enable the mobile earth terminals to receive ring alerts even when their antennas are stowed, but spurious- emission performance would be better than that of the two-way channels on the system when fully loaded. MSC therefore contends that the addition of these services would not increase interference levels or complicate satellite-system coordination. No one else filed comments on this proposal.
Short Burst Data (SBD)
At the output of the BCH decoding process, there are ten, 20-bit words (one header word, eight data words and one CRC word) that make up one SBD PDU being fed to the CRC-16 decoding process.
The pertinent emission designator for the mobile satellite phone is 41K7Q7W.
Bandwidth is primarily determined by a 96 tap FIR filter used to filter I and Q channel modulating signals and is consistent with a necessary bandwidth specification of 41.667 kHz. Converting this result yields 41K7.
a. First Symbol - Type of Modulation of the main carrier.
b. Second Symbol - nature of signal(s) modulating the main carrier.
This corresponds to symbol 7, derived from two channels "containing quantized or digital information" modulated in-phase and quadrature modulated.
c. Third Symbol - Type of information to be transmitted.
This corresponds to W, defined as "combinations of above" which would be the combination of the symbol D, "Data transmission, telemetry, telecommand", and symbol E, "Telephony (including sound broadcasting)". The resulting complete emission designator is then 41K7Q7W.
|IRIDIUM 9501 PAGER|
FCC ID: E969898
Dimensions: 77w x 72.3h x 22.5d mm (3.03w x 2.85h x .88d in)
Motorola Part Numbers
The frequency range of the equipment is in the band of 1616 MHz to 1626 MHz.
Band is channelized. Center frequency determined by:
A 12-frequency access band is reserved for the simplex (ring alert and messaging) channels. These channels are located in a globally allocated 500 kHz band between 1626.0 MHz and 1626.5 MHz. These frequency accesses are only used for downlink signals and they are the only L-band frequencies that may be transmitted during the simplex time-slot.
Frequency Stability: +/- 0.00015 % (1.5 ppm)
This equipment uses Automatic Frequency Control (AFC) to lock within +/- 600 Hz of the received frequency from the Space Vehicle (SV). The mobile performs all frequency pre-correction for Doppler shifts, up to +/- 37.5 kHz. The system is designed to be tolerant of these frequency offsets.
Radio Frequency Output Power ranges from 0.1 to 0.6 Watts. The mobile maximum output power is achieved under closed loop control with the SV network. The mobile power will respond to commands from the SV network to change power levels as defined in the specifications.
RF Power Output: Variable range from 0.1 to 0.6 Watts (by control of satellite network via closed loop power control). The transmitter duty cycle allows for bursted transmission every 8.28 ms out of 90 ms, or 9.2%, at a rate of 50 kbps, or 25 k symbols/sec.
Modulation is DEQPSK (Differentially Encoded Quadrature Phase Shift Keying).
|ACCESS AND PRIORITY|
Each satellite beam broadcasts which Acquisition Classes are allowed
to acquire satellite resource on that beam. Only SDUs with the
proper Acquisition Class (AC) are allowed to start the acquisition
process. Acquisition Class ranges from 0-15. Default non-safety Iridium
terminals use an Acquisition Class in the range of 0-9.
Acquisition Class is mainly used for satellite load shedding. In a satellite beam with heavy traffic load, certain Acquisition Classes (e.g., AC0-9) will be shut down to prohibit further traffic load on the satellite.
0-9: Regular Subscribers
The Acquisition Class affects how calls initially gain access to the satellite constellation.
The Iridium Satellite Network allows for four levels of priority. Each satellite has priority queuing for both channel assignment of new calls and handoff order of in-progress calls. High priority calls, taking precedence, are queued before low priority calls.
Currently both the Acquisition Class and Priority Class are encoded on a SIM card; hence the Acquisition Class and Priority Class are associated with a SIM card and an SDU that uses that SIM card.
Iridium devices that are capable of completing circuit-switched calls use a
Subscriber Identity Module (SIM), a type of
|IRIDIUM-Specific SIM Files|
Besides the standard SIM files for a GSM (Global System for Mobiles) network, Iridium SIMs also contain
an additional Directory File (DF) called DFIRIDIUM with an identifier of 5F30.
[MF/DF] RFU: 00 00 Free Memory: 00 00 File ID: 5F 30 (DF-IRIDIUM) File Type: 02 (Directory File) RFU: 00 00 00 00 00 Length Following: 0D File characteristics: 13 Clock stop: Allowed, no preferred level Required speed: 13/4 CHV: Enabled Child DFs: 00 Child EFs: 07 CHVs, Unblock CHVs, etc: 04 RFU: 00 CHV1 Status: 83 (Initialized, 3 remaining) Unblock CHV1 Status: 8A (Initialized, 10 remaining) CHV2 Status: 83 (Initialized, 3 remaining) Unblock CHV2 Status: 8A (Initialized, 10 remaining) RFU: 00
This DF contains seven Elementary Files. I do not have documentation for these files:
4F20 (16 bytes): FF 15 FC AF 05 2C 0A 4C FE 44 EB DC 1B 00 08 31 4F21 Record 1 (14 bytes): FF FF FF FF FF FF FF FF FF FF FF FF FF FF 4F23 (3 bytes): 13 F0 10 4F24 Record 1 (4 bytes): 11 F2 FF 08 4F24 Record 2 (4 bytes): 19 F1 FF 08 4F24 Record 3 (4 bytes): FF FF FF FF 4F24 Record 4 (4 bytes): FF FF FF FF 4F25 (1 byte): 05 4F26 (1 byte): 05 4F27 (1 byte): 05
The Iridium authentication process is adapted without change directly from the GSM specifications.
The GSM encryption algorithm A3 is executed on SIM card to generate Signed Result (SRES) response based on the following inputs:
The Iridium SIM supports the standard GSM authentication algorithm (known as A3) and the ciphering key generating algorithm (known as A8). They are combined in a single SIM instruction called "RUN GSM ALGORITHM".
To SIM (21): A0 88 00 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 (The "RUN GSM ALGORITHM" and 16 bytes representing RAND)
It is interesting to note that the last ten bits of Kc are always zero, reducing the effective keyspace from 64 to 54 bits. Terrestrial GSM has long been limited, as summarized in a document (Tdoc SMG P-99-011) from an ETSI/TC/SMG meeting in Italy in 1998:
The GSM encryption uses in principle a 64 bit key. However at introduction of GSM it was decided to limit the effective key size to 54 bits. This should have been realised by the SIM and the Authentication Centre (AuC) both forcing 10 specific bits of the encryption key to zero.
The original Motorola 9500 handset supports a test mode using a special test SIM card.
There is some overlap between the test commands used on Motorola GSM cellular telephones.
I would be interested in receiving a list of all the available test mode commands, and/or the entire service manual for an Iridium phone.
With the special SIM card in place, press and hold the [#] key for more than three seconds.
27 is a transmit test.
xxx = channel number
Transmit random data (z = 1) on channel 001 at maximum power (00): 27001001#
Transmit a tone (z = 0) on channel 240 at minimum power (08): 27240080#
Stop transmitting: 27#
One command that is different is the Static Traffic Channel command ( #29xxyyzabc# ).
|9602 AT COMMANDS|
The 9602 is a Short Burst Data (SBD) module that provides packetized data connectivity.
It communicates with an external device via a serial connection
and uses "AT" commands.
Default serial communication parameters: 9600 baud, no parity, 8 data bits, 1 stop bit.