OSI 106
Keying
"Toggle" the current ON and OFF from the sending unit to the receiving unit
1/2 rate; FEC coding
1 data bit in 2 bits out
OQPSK; Symbol rate
1 symbol created for every 2 bits
QPSK; Symbol rate
1 symbol created for every 2 bits
8PSK; Symbol rate
1 symbol created for every 3 bits
BPSK; Symbol rate
1 symbol created for every bit
L Band; Microwave
1 to 2 GHz
Common forms of modulation
1. Amplitude 2. Phase 3. Frequency
D band; Microwave
110 to 170 GHz
Ku Band; Microwave
12 to 18 GHz
K Band; Microwave
18 to 26.5 GHz
2/3 rate; FEC coding
2 data bits in 3 bits out
Ka band; Microwave
26.5 to 40 GHz
3/4 rate; FEC coding
3 data bits in 4 bits out
C Band; Microwave
4 to 8 GHz
5/6 rate; FEC coding
5 data bits in 6 bits out
What is the Line of Sight (LOS) Range?
50 Miles/80 km
7/8 rate; FEC coding
7 data bits in 8 bits ou
X Band; Microwave
8 to 12 GHz
Geostationary
A Geostationary orbit allows the satellite to effectively hover over a point on the Earth Every Geostationary satellite is in a belt around the equator
Geosynchronous
A Geosynchronous orbit has a period equal to the earth's rotational period
Satellite Footprint
A Transponder can only see about 1/3 of the earth surface Satellite footprint is the signal coverage area
Magnetic North
A compass will not point true north because it only points to the magnetic north pole
Band-pass Filter
A device that allows frequencies within a certain range and attenuates (rejects) frequencies outside that range Eliminates harmonics generated by the Mixer
Electromagnetic radiation
A maseless stream of photons traveling in a wave like pattern at the speed of light
Amplitude Shift Keying
A standard switching sequence of the reference signal ON and OFF is used to denote a specific character Morse Code
Multiple Access
Ability of communications equipment to handle more than one subscriber with minimal or no degradation in signal quality Desired feature in satellite communications because of the limited power and number or channels on board vs. the number or traffic links it services
Reed-Solomon coding
Adds check symbols to data to detect and correct errors.
TDMA/DAMA Characteristics
Advantages: All stations transmit on the same frequency More users - increased satellite capability Uses less satellite bandwidth No inter-modulation effect Disadvantages: Timing becomes critical Closer monitoring and coordination of network required The need for synchronization makes the system more complex
Viterbi encoding
Algorithm to decode information in CDMA and GSM cellular networks.
Hub and Spoke (Star) Satellite Network
All signals and transmissions from a individual terminal must be routed through a central location or hub Best suited for large amount of terminals transmitting small amounts of data that are all organized at the hub
Point-to-Point Satellite Network
Allows for high bandwidth communication between two geographically distant terrestrial terminals A Point-to-Point network will avoid any line of site link connection
Mesh Satellite Network
Allows several terminals in the same network to communicate with each other via a single relay link through the satellite The "single hop" nature of this network design leads to a minimal time delay between signal transmission and reception Modulation has made Mesh networks more cost efficient
Rule of Ten; Decibel
Any power level raised by 10 dB will multiply that power level by a factor of 10X (i.e., 1 watt x 10dB = 10 watts, 1 watt x 20dB = 100 watts, etc......)
Rule of Three; Decibel
Any power level raised by 3 dB will always DOUBLE that power level.
Reflected power
Anytime there is transition from one medium to another a certain amount of power is reflected back towards the source due to impedance mismatch
Memory tracking; Antenna tracking
Automated process of keeping the antenna pointed to the satellite using date and time stamped data
Auto tracking; Antenna tracking
Automated process of keeping the antenna pointed to the satellite using readings of downlink power
B; Decibel
Bel, The original unit of sound measurement
Two components of a Satellite
Bus - The platform that supports the payload from launch through the end of its life: Altitude Control, Power System, Orbital Control, Thermal Control and the Tracking, Telemetry and Command (TT&C) Payload - The specialized equipment needed for the satellite to perform its designed function. Payload typically consists of: Antenna, Wide-band Receivers, Input and Output Multiplexers, Attenuation Devices, and Amplifiers
Mobility of a SATCOM
Can be packed up and deployed anywhere in the world; can be mounted on trucks and trailers in order to provide high bandwidth communications anywhere
Why modulate?
Certain types of signals have characteristics that allow them to travel more efficiently as they propagate to the distant end
Right-hand circular polarization
Clockwise
Look Angle
Combine the azimuth and the elevation to get your look angle
Manchester encoding
Combines clocking signal and data signal Bit represented by high/low state
IDirect Modems
Commonly used to implement a mesh network
Frequency Conversion
Conversion involves frequency mixing (Mixer Theory) 2 inputs 4 outputs: sum and difference of inputs and the two original inputs Intermodulation - When the RF waves (frequencies) interact and cause attenuation
Encoding
Converting analog-to-digital or digital-to-analog
Left-hand circular polarization
Counterclockwise
Forward Error Correction (FEC)
Creates data symbols to ensure higher rate of data recovery
d; Decibel
Deci-, Metric prefix meaning one tenth (1/10)
dB; Decibel
Decibel, 1/10th of a bel
Center Frequency
Defined as either the arithmetic or geometric mean of the lower and upper cutoff frequency This is also known as your receive frequency
DAMA
Demand Assigned Multiple Access; technique which matches user demands to available satellite resources Satellite channels are grouped (pooled) together and DAMA assigns user variable time slots that match the users information transmission (bandwidth) requirements
Azimuth
Direction indicating the direction to your objective
Function of a Mixer
Electronic component that mixes two or more input signals to produce a single (composite) output signal Block up converter/Low Noise block: A-B and A+B
Standard Method to transmitting data long distance; expensive and fragile, transmits light
Fiber
FDMA
Frequency Division Multiple Access; Simple, Reliable, Easy Lacks flexibility, uses more bandwidth, lesser throughput
GEO; Orbits
Geostationary Orbits; Perfect for comms.
GPS
Global Positioning System GPS's are receive only systems that require at least 4 or more satellites within line of sight to develop a three-dimensional position on earth 1. Longitude 2. Latitude 3. Elevation 4. Verification
Turbo coding
High-performance forward error correction code. Used to achieve reliable information transfer over bandwidth constrained communication links in the presence of data-corrupting noise.
Manual tracking; Antenna tracking
Human intervention keeping the antenna pointed at the satellite
Site Survey
Installation Area Clear Line of Sight Electromagnetic Interference (EMI) Antenna Base Foundation Grounding Power Source - Standard 110v 20 amp circuits Cable Length Limitations - Cat5 100m
Center Feed; Parabolic Dish Antenna
Least expensive and simplest configuration Decent for smaller antennas Larger antennas lead to blockage of signal
Polar Orbits/LEO
Little Earth Orbit
LEO; Orbits
Low Earth Orbit
Monopulse tracking; Antenna tracking
Measures the variance in RF from the satellite illuminating the antenna Most accurate, but very complex and expensive
MEO; Orbits
Medium Earth Orbit
Why do we need Frequency Conversion?
Modem frequencies are not conducive for effective atmospheric propagation the frequency range of 2 to 10 GHz is the "cleanest" band available (known as the microwave window)
Yagi Antenna
More expensive, provide some directivity to signal Size is determined by frequency, usually a specific fraction of the wavelength
Parabolic (Dish) Antennas
Most expensive type Provide maximum directivity; focuses RF energy
Circular; Polarization
Orientation of the E-Plane rotates in phase with the frequency. The amplitude always stays constant. magnetic vector executes a circle perpendicular to the path of propagation with a frequency equal to that of the wave.
Bi-Phase Shift Keying (BPSK)
Phase of the carrier wave is shifted at 0 and 180 degrees
Quadra-Phase Shift Keying (QPSK)
Phase of the carrier wave is shifted at 0, 90, 180, and 270 degrees
Point-to-Multipoint Satellite Network
Provides platform for implementation of video broadcasting services Transmission cost is independent from both the numbers of receivers and extent of geographical distribution
Radio Frequency Theory (RF)
RF Theory is the theory of how electromagnetic waves travel through space and time 10 KHz - 300 GHz falls under radio wave and microwave section Used to communicate data
Types of Radiation
Radio Waves * Microwaves * Infrared Radiation Visible Light Ultraviolet Radiation X-Rays Gamma Rays
True North
Runs along the lines of longitude on the earth
What is the general rule when it comes to Radiation Hazard (RadHaz)?
Standoff from the primary lobe of any satellite antenna should be at least 20 feet
Modulation
Super-imposing a signal onto a carrier wave for transmission
Magnetic Declination
The difference in direction between the true azimuth and the magnetic azimuth
Horizon
The horizon is the point in which the Earth's curvature prevents any further line of sight In terms of elevation, the horizon will always be 0 degrees
Symbol Rate
The number of symbol changes (waveform changes or signaling events) made to the transmission medium per second using a digitally modulated signal Also referred to as baud rate Each symbol represents a phase change
Frequency Translation
The process of moving a signal from one part of the frequency axis, to another part of the axis. Done in wireless communications systems to move a pass band signal to base band before demodulation.
Orbit Degradation
The result of these forces is an apparent drift of the satellite, typically in a small figure 8 pattern which over time will become larger "stationkeeping" fixes Orbit degradation with the use of thrusters
Latitude
These lines run horizontal across the Earth's surface Equator; Positive north, negative south
Longitude
These lines run vertical across the Earth's surface Prime Meridian; Positive east, negative west Zulu time
0 dBm; Decibel
This level occurs when the measured intensity equals the reference level 0 dBm does not mean nothing or no power! It means that the power level at the measurement point is equal to the established reference level of 1 mW
TDMA
Time Division Multiple Access; satellite's capability of allowing a number of users (or links) to transmit their signals using a single frequency with a designated BW by allocating specific time intervals in a predetermined sequence
How does a Satellite Communicate?
Transponder; receives, re-transmits and amplifies signals. Can be multiple on one satellite Simplex Communication; there is always a separate transmit and receive path with a unique transmit and receive frequency
True or False: Your terminal's receive (Rx) polarization must ALWAYS match the transmit (Tx) polarization of the satellite.
True
Constructive mixing
Two separate signals of the same frequency when in phase will gain power
Destructive mixing
Two separate signals of the same frequency when out of phase will lose power
Cassegrainian; Parabolic Dish Antenna
Type of parabolic that uses two parabolic surfaces Primary large concave dish Secondary small convex dish
Offset Quadra-Phase Shift Keying (OQPSK)
Variation of QPSK Phase of the carrier wave is shifted at 90 degree increments from prior state
Offset Feeds; Parabolic Dish Antenna
Very expensive Low blockage and best performance Usually used in small earth terminals (STT) Most military parabolic dish systems are offset feed
Frequency Shift Keying
When a specific frequency represents an ON state and another frequency an OFF state
Phase Shift Keying
When a specific phase of a signal represents an ON state and another phase for an OFF state
Sequential encoding
When the channel symbol is uniquely determined by the sequence of output letters from the message source up to that time
dBm; Decibel
decibels of electrical power with respect to one milliwatt
