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
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.
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.
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.
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.