GPS Receivers

Telecommunication Networks
Satellite Radiocommunication
Tipically broadcast networks (big geographical area, TV, Radio)
Different communication systems with small or big amount of data.
Different radio frequency band, different applications. differnet areas
Land, or satelite communication with different types of antennas
Satelite Communication
Earth is covered by satelire antennas, for different applications
Satelite Communication Orbits
Van Allen Radiation Belt
Van Allen Radiation Belt
The Van Allen radiation belt is a torus of energetic
charged particles around Earth, trapped by Earth’s
magnetic field.
The inner belt consists mostly of protons while the outer
belt consists mostly of electrons.
Satellite Orbits
LEO, Low Earth Orbit: distance 200– 1200 (2000) km-re from the Earth
surface, mainly circle but some ellipse too
MEO, Medium Earth Orbit: distance 2000–35786 km from the Earth
surface, ellipse
GEO, Geostationary Orbit: distance 35786 km from the Earth surface
Orbital planes
Middle inclination
Satellite Networks (GEO)
• FSS (Fixed Satellite Service). The transponder
receives the signal from the Earth, transforms the signal
to another fr. band, amplifies it and transmits it to an
Earth Station.
• ISL (Inter Satellit Link). Connection between to
• MSS (Mobile Satellite Service). Connection between
moving endpoints through different satellites
Services: weather, communication, TV-radio broadcast,
amateur radio…
Satellite Networks (GEO)
Satellite Networks (GEO)
Satellite Networks (LEO)
Mobile satellite communication systems: IRIDIUM,
66 active satellites (on 6 orbital
6 spare
Covers the whole Earth surface
Satellites on LEO
Distance 780 km
Period 100 minutes
Satellites connected directly
on adjacent orbits
Satellite Networks (LEO)
 48 active satellites (on 8 orbital planes, 6
satellites each)
 4 spare
 Covers the part Earth surface ( eg.
Polar areas are not covered)
 Satellites on LEO
 Distance 1414 km
 Period 114.1 minutes
 Satellites are not connected
directly on adjacent orbits
Globalstar Coverage
Iridium Connection
Globalstar Connection
MEO Satellites GPS
GPS Systems
GPS Global Positioning System
The United States' Global Positioning System (GPS) consists of up to
32 MEO satellites in six different orbital planes
Operational since 1978 and globally available since 1994, GPS is currently
the world's most utilized satellite navigation system.
GLONASS, Global'naya Navigatsionnaya Sputnikovaya Sistema (GLObal
NAvigation Satellite System),
Russian, or GLONASS, was a fully functional navigation constellation in
1995. After the collapse of the Soviet Union, it fell into disrepair, leading to
gaps in coverage and only partial availability. It was recovered and fully
restored in 2011.
European Union and European Space Agency agreed in March 2002 to
introduce their own alternative to GPS. The system of 30 MEO satellites
was originally scheduled to be operational in 2010. The original year to
become operational was 2014.
Comparision GPS Systems
Theory of Positioning
GPS satellites transmit signal information to earth. GPS receivers take this
information and use triangulation to calculate the user's exact location.
Essentially, the GPS receiver compares the time a signal was transmitted by a
satellite with the time it was received. The time difference tells the GPS
receiver how far away the satellite is. Now, with distance measurements
from a few more satellites, the receiver can determine the user's position
and display it on the unit's electronic map.
Theory of Positioning
Each GPS satellite sends out a unique code. That code is a series of ones
and zeros (Figure 3). The GPS receiver in your car or phone has a copy of
each satellite’s code. When GPS signals come in, the receiver electronics
has to figure out which satellites sent them. It carefully compares the
received GPS signals with the codes for all the satellites it knows about.
Theory of Positioning
GPS Signals
C/A codes: civil
P codes: military
Firstly, the navigation signal (50 Hz) will either modulate with C/A code or P code
depending on the type of application.
The navigation signal modulated with C/A code will mix with L1 carrier producing
a L1 signal. Whereas the navigation signal modulated with P code will mix with
both the L1 and L2 carrier produce a L2 signal. These signals contain data like
satellite orbits, clock corrections and other system parameters.
P codes in the L1 band have a signal power of -163 dBW and a power of -166
dBW in the L2 band. By contrast, the broadcast power for C/A codes in the L1
band is a minimum of -160 dBW on the earth’s surface.
GPS Navigation Message
For C/A codes, the navigation message consists of 25 frames of data, and each
frame contains 1500 bits. In addition, each frame is divided into five 300-bit
subframes, each subframe contains a unique set of information. Generally,
subframes have the following data [2][7]:
Subframe 1: Clock correction, accuracy, and health information of satellite
Subframes 2-3: The precise orbital parameters used to compute the exact
location of each satellite
Subframes 4-5: Coarse satellite orbital data, clock correction, and health
GPS Navigation Data
1) TLM – Telemetry: 30 bits, sent at the beginning of each frame. •It is used for data
synchronization and satellite maintenance. They are usually constant for any one
satellite for a long period of time.
2) HOW – Handover Word: 30 bits, sent after TLM. It indicates the time at the
beginning of the next subframe. •It also contains a sub-frame ID, some flags and
parity bits.
3) Ephemeris: It is sent in each frame by each satellite. It may take the GPS receiver
up to 30 seconds to acquire Ephemeris.
4) Almanac: It is spread out over all 25 frames of the message.
For receiving the complete Almanac, the GPS receiver may need about 12.5 minutes.
GPS Receiver
GPS Receiver Chips
Price is below 1 Euro
GPS Receivers (Navigation)
GPS Receivers (Geodesy)
GPS in Camera
Related flashcards
Create Flashcards