Iridium System Description

Iridium was founded in 1987. It is the world’s first private global wireless communication system providing voice, data, fax, and paging services. The original configuration called for 77 satellites and was named after the Iridium atom with 77 orbital electrons. However, the constellation was optimized to increase satellite coverage and reduce costs. After this, only 66 satellites were needed.

At 780 km above the ground, 66 satellites are arranged in 6 planes, with 11 satellites on each plane. Aircraft have a near-circular orbit with co-rotating 31.6 degrees apart and counter-rotating planes (1 and 6) spaced 22 degrees apart. Minimum elevation angle for a ground station is 8.2 degrees, which maximizes the satellite coverage and improves link quality compared to lower elevation angles. Lower elevations increase fading due to and adversely affect link quality. Average satellite viewing time is about 10 minutes.

Existing satellite communication systems primarily use GEO satellites at an altitude of approximately 35,800 km. GEO satellite systems allow world coverage below 70 degrees altitude with at least 3 satellites. The unidirectional propagation delay of a GEO satellite system is about 120 msec. It is not practical to use handheld terminals in GEO satellite systems unless very large and beamed satellite antennas are used.

The orbital radius of the satellites is calculated by adding the 6378 km radius of the Earth’s equator to the satellite height. This results in Rg = 42.178 km and RI = 7158 km. The speed of a LEO satellite relative to the Earth is calculated as VI = 26.804 km/s. The IRIDIUM constellation parameters result in an orbital period of 100.13 minutes.

Minimum slope; a user’s viewing angle of a particular satellite is 8.2 degrees. At a fixed position on Earth, the average viewing time of a satellite is 9 minutes, and one or two satellites can be seen at a time. IRIDIUM satellite coverage area is calculated as 15,299,900 km2, equivalent to a footprint radius of 2209 km footprint radius.

Iridium Tracking and Decoding System

Properties:

• Phone calls, SMS message, data traffic, FAX reception
• Active satellites and ray tracing
• Automatic detection of target identification features (TMSI, IMSI, IMEI, geo coordinate location)

Hardware:

• L-band fixed mast antenna AT162-73W.
• Frequency: 1616-1 625.5 MHz — Polarization: right circular — Axial ratio: 4 dB max.
• Signal processing unit
• L-band receiver (PCI card).
• Frequency: 1616-1 625.5 MHz.
• Bandwidth: 15MHZ.
• Sensitivity: 100 dB.
• IF: 70 MHz.
• DSP – clipboard.
• CPU TM32 0C6416 720MHz..
• ADMDDC4 x 16 93MHz.
• Clock generator M33005 – 93.6 MHz.
• PC: Pentium-4 3 GHz, RAM 512 Mb, HDD 120 G

File server:

• PC: Pentium-4 3 GHz, RAM 1 GB, HDD 3Tb (RAI D5);
• Monitoring unit:
• PC: Pentium-4 3GHz, RAM 1GB, HDD 120Gb;
• Monitor: 49”
• Plotter HP Design Jet 500 plus;
• Workplace unit:
• PC: Pentium-4 3 GHz, RAM 512 Mb, HDD1

Brief Description of Unit’s Performance

RF receiver unit (RRU) receives the broadcast signal in the 1616-1626.5 MHz band, filters it down to a width of 10.5 MHz, transfers it to the intermediate frequency (IF) 70 MHz and takes it to the ADC, where it is digitized with the invalid frequency, transferred to the DDC block with 80 MHz. DDC generates 50 KHz individual narrow channels, which are transferred to low frequency (LF), refracted and filtered. Thirty-two outputs from the DDC channels are each sent to the DSP for demodulation and decoding.

The results received by the PC controlling the SPU module, which are converted to recordings are transferred over the local network to the file server (FSU). The FSU runs the current coordinates of the beams, and stores and manages the phone calls and recorded signals sent to the monitoring unit (MU). It is used for further processing of the log. The number of WPUs, determined by the summary system load and the channel capacity, the recordings in the system for the desired time, then they are automatically deleted from the database.

Signal Processing Unit

Receives and records iridium signals. The main window represents a table in the program where the current status of the SPU module is displayed.

Tables contain 32 rows, each corresponding to one of the 32 DSP channels of the SPU module.

The columns of the table include:

• Device – number of DSPs of the device
• Channels – Number of DDC channels
• SV – number of satellites
• Beam – number of beams
• Sub-band – number of sub-bands
• Time slot – number of time slots
• Frequency – number of frequencies
• Handoff – amount of transitions on the channel
• Type – channel type
• Count – counter of frames in the channel
• Time – the idle time of the channel
• Gain – signal level

If the DSP carries the traffic channel, it is marked in green. If the DSP carries the auxiliary channel of the satellite, it is not marked with any color. If the DSP channel is reserved, the relevant row in the table is not filled. DSP channels are automatically programmed by software. The operator can change the emulation via the dialog.

-DSP setting group: Parameters of DSP card:

• Clock frequency (kHz) is the frequency of the external clock generator (93600 kHz).
• Number of devices is the total number of DSP cards. (2 by default )

-RRU ayar grubu: radyo alıcı cihazın parametreleridir:

• Central frequency of the receiver (MHz) is the frequency of the RRU setting (1621 MHz).
• Inversion of a spectrum is an inversion of the RRU parameter. (1: inversion available, 0: no inversion, defaults to 0)
• RRU gain level (max 4095 by default)

-DDC setting group: down converter parameters:

• Synchronous mode is the mode of setting DSP samples. (synchronous/asynchronous)
• DMA mode is the operating mode. (DMA is allowed by default)
• Synchronous mode DDC is the dating mode of DDC instances. (synchronous/asynchronous)
• FPGA file name is the name of the FPGA file./li>
• DDC gain level (0-16383) is the gain of the FPGA firmware DDC channels (16383 by default).

-Location setting group: geographic parameters:

• Distance is the maximum distance in km at which signal reception is allowed. (default: 3000)
• Latitude is the geographic latitude of the observation point. (e.g. 55.77 degrees)
• Longitude is the geographic latitude of the observation point. (e.g. 37.49 degrees)

-MAP settings group:

• IP address is the IP address of the computer where the MU module is running. (e.g. 192.168.25.33)

-Data save settings group:

• Data save path is the location where the results of the work are hosted. It can show both the local computer and the file server. (e.g. \\192.168.25.34\Iridium\)

File Server Volume

It works by itself and does not need operator intervention. The main window has the following appearance:

It is designed for collecting, storing, and processing data from the SPU module. Together with the WPU module, it provides automated visual guidance of data, management, and presentation results. It enables further processing of secondary protocols with both integrated tools and user-created tools. The parameters of the operation of the FSU are set in the dialog data.

Workplace Unit

It works together with FSU. It provides access to the database of recorded signals. It has the following interface:

The main window of the program represents a table in which the recordings of telephone conversations are put together.

Screenshot above:

1) Filter panel
2) Calling up electronic location map
3) Grouping area of recordings
4) Navigator
5) Audio player

To add records to the database, you need to execute the “Refresh” item of the menu (Menu/Job/Refresh) or turn on the “Auto Refresh” option in the data configuration dialog. Records are filtered according to the execution point of the menu (Menu/Job/Filter). It is applied according to the following areas:

1) By date and time
2) By IMEI, TMSI, IMSI, phone number values
3) By data type
4) By geographic coordinates

In order to process the session message, it is necessary to double-click the left mouse button on the current records. To remove a record, you need to click the right mouse button on the database record.

Monitoring Unit

It is designed to reflect the geographical position of calling subscribers on the electronic location map, to monitor the displacement of the beams of artificial earth satellites. Information about incoming calls and the location of the beams is first received and processed in the SPU. It is then transferred to the MU via the UDP protocol, and it reflects the current position of the observation objects on the electronic location map.

The longitude and scale of the map in kilometers/pixels are represented in the status line. On map layouts, active satellite beams and phone calls are marked with a circle. The satellite number and the beam number are written in the center. A phone call is marked with a red triangle if the call is active, and a green triangle if the call has ended. If the call has ended, it is kept on the map for the time specified by the dial time parameter of the options dialog. The recording number is written on the right of the triangle representing a call, and there is a console where the recording data of the phone calls are displayed, together with the main window of the program. These are the start and end time, recording number, channel, and geographic coordinates of the search.

The parameters of the program are determined by using the menu commands (Menu/File/Options) or via dialog options called by clicking the right mouse button in the client window area.

On the Screen Above:

Longitude is the longitude of the observation point in degrees. (-180 …+180)
Latitude is the latitude of the observation point in degrees. (-90…+90)
Km/pix is the scale of the map in kilometers/pixels. (1…32)
Grid is the grid step in degrees. (1…90)
Dials is the maximum number of calls for reflection. (1…99)
Dial Time is the duration of calls in seconds on the screen. (0…999)
Direct is the maximum number of beams for direction indication, reflection to the satellite in the beam, reflection. (0…999)