Certus
Iridium Satellite Time and Location
Deorbiting
New Frequencies
Collision
Signals
Hardware
SIM
Test Mode
References
9602 AT Commands

IRIDIUM Corporate webpage.

Iridium History and News.

The new Certus waveform will allow for more efficient channels and newantenna types that will increase bandwidth for handheld man-packableradios from 9.6 kilobytes per second to 88 kps. Large terminals, whichare more likely to be used on vessels and land stations in the Arcticwill range from 32 kps to 128 kps.

Iridium Certus terminals are being built by Cobham, L3 Communications,Rockwell-Collins, and Thales USA.

New satellites orbit at 780 km with an 86.4° inclination and can support 1,100 simultaneousequivalent user channels (peak).

STL uses the narrowband paging channels of Iridium, a one-way transmissionfrom the satellite with a high gain system. The STL signal is differentfrom the wide band, lower gain two-way channel of the Iridium phone.

The STL signal is 1,000 times stronger than GPSbecause it originates from the Iridium constellation of 66 satellitesorbiting 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 satellitestransmit in the L-Band at carrier frequencies in the range of 1616-1626.5MHz, using Quadrature Phase Shift Keying (QPSK) with a symbol rate of25,000 symbols per second. Transmission is frame based, with framelength of 90 ms.

Iridium satellites travel at speeds of about 7500 m/s,resulting in variations of up to +/- 40 kHz from the nominal carrierfrequency due to Doppler effects. Compared to GNSS signals, Iridiumsignals have much higher raw signal power (300 ~ 2400x) as seen by areceiver on Earth.

Two main technical innovations are applied to the existing Iridium QPSKtransmission scheme in order to facilitate precision measurements.First, the QPSK data at the beginning of a STL burst is manipulatedto form a continuous wave (CW) marker, which can be used for burstdetection and coarse measurement. Second, the remaining QPSK data in theburst is organized into pseudo-random sequences, reducing the effectiveinformation data rate while providing a mechanism for precise measurementvia correlation with locally generated sequences. The processing gainassociated with the sequence correlation operation also enhances thecapability of the STL signal to penetrate buildings and other occlusions.

STL bursts are transmitted once every 1.4 seconds on average. If coarsetime is known, such as in the case of a receiver with a networkconnection, then precise time can be calculated by processing a singleburst. Assuming the receiver can process a burst in < 0.6 seconds,precise time and frequency can typically be acquired using STL in under2 seconds. The precise time and frequency information derived from asingle STL burst can be used to assist weak-signal GNSS acquisitions.Since the STL signal is more robust than GNSS, precise assistance isprovided to acquire GNSS signals as weak as -160 dBm, assuming that theSTL and GNSS signals are attenuated similarly by path occlusions.

A SpaceX Falcon 9 rocket launched from Vandenburg Air Force Base liftedthe second set of ten Iridium NEXT satellites on June 25, 2017.

A SpaceX Falcon 9 rocket launched from Vandenburg Air Force Base liftedthe third set of ten Iridium NEXT satellites in October 9, 2017.

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 GHzand 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-usepattern. This provides a total of 1628 cells, with each cell coveringabout 30 mile footprint. Each cell has 174 full-duplex voice channels(there are 283,272 channels worldwide).

Voice
The Iridium SDU incorporates a 2.4 kbps Advanced Multi-Band Excitation(AMBE) vocoder developed by Digital Voice System Inc. (DVSI). Thisvocoder is tailored to the Iridium communication channel.

Channels
An Iridium channel is a specific FDMA frequency and TDMA timeslot.
Duplex Frequencies

Frequency access is 41.667 kHz
Occupied bandwidth is 31.5 kHz
Eight frequency accesses in a sub-band of 333.333 kHz
30 sub-bands total (240 frequency accesses)
currently sub-bands 8 - 30 in use

Simplex Frequencies

• Simplex
  • Ring Alert (downlink only)
    Broadcast every 48 frames in each beam
    User sees Ring burst every 4.32 sec in each beam
    Length is between 7 and 20.32 ms
  • Broadcast (downlink only)
    Frequency, timing, and other system information
    Acquisition acknowledgment
    Channel assignments
  • Acquisition (uplink only)
    Slotted aloha random access
    Uses DE-BPSK
  • Message (downlink only)
• Duplex
  • Synchronization
    prior to traffic channel operation
    same frequency and slot as traffic channel
    uplink uses DE-BPSK
  • Traffic
    Voice and Data
    Data uses 24-bit Frame Check Sequence

TDMA Frame
90 ms (2250 symbols = 4500 bits)
25 ksps

Data Bursts

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

• Simplex Time Slot
  • Ring Alert
  • Messaging
• Uplink Time Slot
  • Acquisition
  • Synchronization
  • Traffic
• Downlink Time Slot
  • Broadcast
  • Synchronization
  • Traffic

Paging

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 theIRIDIUM System to provide enhanced ringing and paging services, in addition to the kinds ofMSS service that it originally proposed to provide. The enhancement would enable users toreceive ringing and paging messages during heavier atmospheric fading conditions and inbuildings where attenuation is greater, according to MSC. One-way 'ring alert' channels at1626.270833 MHz would be used to alert subscribers with special receive-only mobile earthterminals to the presence of incoming paging calls. Paging messages would be transmitted to thereceive-only terminals at 1626.437500, 1626.395833, 1626.145833, or 1626.104167 MHz. Theirduration would not exceed 20.32 milliseconds. The transmit power for the ring alert channelwould be somewhat higher than the power used for a voice/data channel, so as to enable themobile 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 whenfully loaded. MSC therefore contends that the addition of these services would not increaseinterference levels or complicate satellite-system coordination. No one else filed comments onthis proposal.

Acquisition

1. Turn on receiver
2. Acquire Ring Alert Channel
3. Determine Broadcast Channel frequency and time
4. Acquire Broadcast Channel for current beam
5. Listen to Broadcast Acquisition Information message
6. If acqusition is permitted, continue
7. Select random Acquisition Channel
8. Determine Doppler to correct uplink burst timing
9. Transmit Acquisition Request message
10. Listen for acknowledgment on Broadcast Channel
11. If no answer, try again on random Acquisition Channel after random delay (slotted Aloha)
12. Receive Channel Assignment message
13. Move to Synchronization Channel
14. Transmit Synchronization Check message
15. Receive Synchronization Report message
16. If Sync Status = Repeat Burst, adjust freq and timing and transmit Sync Check message
17. If Sync Status = OK, send Sync Check message
18. Receive Synchronization Report message or Traffic Switch message

Ring Alert

The Iridium Ring Alert broadcast channel operates at 1626.270 MHz and isan unencrypted downlink-only channel used to send messages to individualsubscriber units. These messages contain the satellite identifier,beam identifier, the latitude and longitude of the satellite location atground level (derived from a proprietary algorithm), satellite altitude.

Each beam transmits a Ring Alert message every 4.32 seconds. Since eachsatellite has 48 beams, a subscriber unit will receive a generic RingAlert message every 90 milliseconds (4,320 ms /48 beams).

Short Burst Data (SBD)

• Data transfer rate: 125 bytes per second
• Maximum Mobile-Originated: 1960 = 70 byte header segment + up to 14 segments of 135 bytes
• Maximum Mobile-Terminated: 1890 = Up to 14 segments of 135 bytes
• Service start announced in June 2003

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 oneSBD PDU being fed to the CRC-16 decoding process.

Bandwidth is primarily determined by a 96 tap FIR filter used to filter I and Qchannel modulating signals and is consistent with a necessary bandwidthspecification of 41.667 kHz.Converting this result yields 41K7.

a. First Symbol - Type of Modulation of the main carrier.
The main carrier is pulsed in a TDMA format, utilizing Differentially Encoded Quadrature Phase-Shift Keying (DEQPSK) techniques. This corresponds to symbol Q, associated with the carrier being 'angle modulated during the period of the pulse'.

b. Second Symbol - nature of signal(s) modulating the main carrier.
In-phase (I) and Quadrature (Q) modulating signals representing sampled, quantized voice or other audio information or data, modulates the main carrier.

This corresponds to symbol 7, derived from two channels 'containingquantized or digital information' modulated in-phase and quadraturemodulated.

c. Third Symbol - Type of information to be transmitted.
The information transmitted is a combination of data transmission (command data) and telephony (sample quantized voice or other audio signals).

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.

Dimensions: 77w x 72.3h x 22.5d mm (3.03w x 2.85h x .88d in)
Weight: 118 grams (4.16 oz)
Battery Life: 30 days
Operating Temperature: -10°C to +50°CC (14°CF to 122°CF)
Operating Frequencies:
Primary: 1626.437500 MHz
Secondary: 1626.395833 MHz
Tertiary: 1626.145833 MHz
Quaternary: 1626.104167 MHz
Power Supply: one 1.5v AA-size alkaline battery
Alert Tone Frequency/Duration: 3200 Hz standard alert with 9 user selectable alerts
Alert Tone Loudness: 80dB typical at 12'

Motorola Part Numbers

Band is channelized. Center frequency determined by:
1616 + 0.020833(2n - 1) MHz where (n = 1, ..., 240)

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 between1626.0 MHz and 1626.5 MHz. These frequency accesses are only used for downlinksignals and they are the only L-band frequencies that may be transmitted during thesimplex time-slot.

Frequency Stability: +/- 0.00015 % (1.5 ppm)

This equipment uses Automatic FrequencyControl (AFC) to lock within +/- 600 Hz of the received frequency from theSpace Vehicle (SV). The mobile performs all frequency pre-correction forDoppler shifts, up to +/- 37.5 kHz. The system is designed to be tolerant of these frequencyoffsets.

Radio Frequency Output Power ranges from 0.1 to 0.6 Watts. The mobilemaximum output power is achieved under closed loop control with the SVnetwork. The mobile power will respond to commands from the SV networkto change power levels as defined in the specifications.

RF Power Output: Variable range from 0.1 to 0.6 Watts (by control of satellitenetwork via closed loop power control). The transmitter duty cycle allows forbursted transmission every 8.28 ms out of 90 ms, or 9.2%, at a rate of 50kbps, or 25 k symbols/sec.

Modulation is DEQPSK (Differentially Encoded Quadrature Phase Shift Keying).

Acquisition Class is mainly used for satellite load shedding. In asatellite beam with heavy traffic load, certain Acquisition Classes(e.g., AC0-9) will be shut down to prohibit further traffic load on thesatellite.

0-9: Regular Subscribers
10: Emergency Calls
11: Fire, Police, Rescue Agencies
12-13: Reserved
14: Aeronautical Safety Service
15: Iridium Use

The Acquisition Class affects how calls initially gain access to thesatellite constellation.

The Iridium Satellite Network allows for four levels of priority. Eachsatellite has priority queuing for both channel assignment of new callsand handoff order of in-progress calls. High priority calls, takingprecedence, are queued before low priority calls.

Currently both the Acquisition Class and Priority Class are encoded on aSIM card; hence the Acquisition Class and Priority Class are associatedwith a SIM card and an SDU that uses that SIM card.

This DF contains seven Elementary Files. I do not have documentationfor these files:

The GSM encryption algorithm A3 is executed on SIM card to generate Signed Result (SRES) response based on the following inputs:

• Secret Ki parameter stored in SIM card
• RAND parameter supplied by network

The Iridium SIM supports the standardGSM authentication algorithm (known as A3) and theciphering key generating algorithm (known as A8). They are combined in a single SIMinstruction called 'RUN GSM ALGORITHM'.

Example:

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)
From SIM (2): 9F 0C (Instruction was successful, 12 bytes of response are available)
To SIM (5): A0 C0 00 00 0C (The 'GET RESPONSE' instruction)
From SIM (14): 00 91 AD C7 49 58 94 27 2C 02 90 00 90 00 (12 bytes of response plus two additional bytes)

• The first four bytes (00 91 AD C7) comprise the signed response (SRES)
• The next eight bytes (49 58 94 27 2C 02 90 00) are the cipher key (Kc)
• The last two bytes (90 00) indicate successful execution of the command.

It is interesting to note that the last ten bits of Kc are always zero, reducing the effective keyspacefrom 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 limitthe 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.

I would be interested in receiving a list of all the available test mode commands, and/or the entireservice 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
yy = power step
z = modulation

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# ).

• Application of Iridium Telecommunications to Oceanographic and Polar Research, 2004
• Manual on the Aeronautical Mobile Satellite (Route) Service, ICAO Document 9925, 2010
• 3rd Generation Partnership Project; Technical Specification Group Services and system Aspects; Security related network functions (Release 11), 3GPP TS 43.020, 2011

Default serial communication parameters: 9600 baud, no parity, 8 data bits, 1 stop bit.
DTR and RTS lines are raised. CTS and DSR will be asserted in response.