SEW progress check 2 Flashcards
decibel (dB
-used to measure signals and communication
a logarithmic unit used to measure signals and communication; express a ratio relative to a reference value on a logarithmic scale
___________turns exponential changes into linear changes
Logarithmic scaling
Linear scales
1, 2, 3, 4, etc
Logarithmic scales
1, 10, 100, etc.
_______compares the level of desired signal to the level of background noise
SNR = Psignal / Pnoise
Signal-to-Noise Ratio (SNR)-
__________ rate at which a transmitted segment of data is received with incorrect bits as compared to the original message.
*increase noise floor = data messed up so increase transmit power
Bit Error Rate (BER)
_________ common means of encoding data to determine if any errors have been introduced to the message through channel noise, interference, or other source
Error Detection
method of adding redundant information to a data stream that allows for identification and correction of errors, and thus reduces or eliminates the need for retransmission
Forward Error Correction (FEC)-
Why choose 1/2 over 7/8
-1/2 costs more bandwidth, but ensures data is able to be corrected by sending the most parity bits, most protected
-7/8 has faster data rates, but is more prone to errors
______ increases the amount of bandwidth required
(FEC) Forward error correction
common nodes in a communication network (such as satellites) must be interconnected with all types of users as flexibility as possible.
Multiple access
_____________ assigned bandwidth is divided into segments
- User operates at the same time, using different frequencies
Frequency Division Multiple Access (FDMA) -
________ allocation of specific time slots for transmission
- User operate on same frequencies, different times
Time Division Multiple Access (TDMA)
_____________ all users transmit signals simultaneously on the multiple access channel
Code Division Multiple Access (CDMA)
_____________ the process of combining signals into a composite baseband to modulate on to a single carrier
Multiplexing
Spread spectrum
a telecommunications technique that transmits a signal over a wider frequency band than the original information
-think Hedy Lamar, she created this, breaks apart signal, spreads it across frequency, Spread spectrummakes it hard to Jam.
_________digital sequence that is intended to resemble a random succession of ones and zeros
Pseudo-random-noise (PRN) spread sequence
Pseudo-random-noise (PRN) spread sequence
-resembles random succession of ones and zeros
-hides signal from adversaries
-allows multiple users to use the same frequencies simultaneously
__________carrier frequency of the transmitted wave changes at regular intervals, based on pseudorandom sequence.
Frequency Hopping Spread Spectrum (FHSS)
__________ uses PRN code sequence to directly modulate the baseband information, allowing the user to operate below the noise floor
Direct Sequence Spread Spectrum (DSSS)
__________combines multiple streams of data into one baseband signal
Multiplexer (MUX)
__________overlays baseband data onto a carrier wave resulting in the creation of the intermediate frequency (IF)
Modulator (MOD)
___________ increase the modulated waveform from the intermediate frequency IF to the transmit radio frequency (RF)
Upconverter (U/C)
_________raise the signal power to the required output level
High Power Amplifier (HPA)
___________ raises the received low-power signal with minimal addition to noise
Low Noise Amplifier (LNA)
____________converts the received RF to the IF frequency
Down Converter
____________extracts the baseband signal
Demodulator (DEMOD)
_____________ takes one single combined baseband signal and distributes it to individual output lines
Demultiplexer (DEMUX)
__________ cannot send and receive at the same time (switch)
Half Duplex
____________can send and receive simultaneously (at the same time) (Frequency domain)
Full Duplex
____________allows a single antenna to transmit and receive signals
Duplexer
_____________ the power level required for an isotropic antenna to achieve the same EIRP as the directional antenna; signal strength
Effective Isotropic Radiated Power (EIRP)
Free Space Path Loss (FSPL)- “path loss” “space loss” “spreading loss”
- Loss caused by EM energy spreading out as it travels through space
- Ratio of TX to RX power as signal travels through a vacuum
- Inverse square law
- Ensures signal useful and not a lot of errors
_________transducer, which converts electrical power into electromagnetic waves and vice versa
Antenna
_____________ represent the emission or reception of wave front at the antenna, specifying its strength
Radiation Patterns
Amplifier
increases the magnitude of signals
Attenuator
decreases the magnitude of signals
Filter
changes the frequency response of the system
Switch
changes the signal path
Mixer
combines signals
Oscillator
produces signals
Transmission Line
connects components
________ the ratio of the radiation intensity in a given direction to the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically.
Gain
_________ the receive and transmit properties of an antenna are identical
-Equality directional patterns
-Equality directivities
-Equality of effective lengths
Reciprocity
___________ radiation from a point source, radiating uniformly in all directions, with same intensity regardless of the direction of measurement
Isotropic radiation
____________ utilizes microwave frequencies to exchange voice, data, and video information by either wired or wireless methods
Terrestrial Communication
- Less interference/disruptions
- Unnoticeable delays
- Limited coverage
- Line-of-sight (LOS)
_____________ employs satellites and Earth ground stations to exchange voice, data, and video information
Satellite Communication (SATCOM)
- Some interference/disruptions
- Data transmission delays
- Global coverage
- Beyond line-of-sight (BLOS)
- Higher bandwidth and data rate
- Flexible, mobile and deployable
SATCOM Advantages
- Mobility/flexibility
- Beyond line-of-sight
- Coverage
- Cost effective
SATCOM Disadvantages
- Congestion of frequencies
- Interference
- Propagation
SATCOM Apllications
- Radio and TV broadcasting
- Internet applications
- Commercial communications
- Military communications
_______ refers to data capacity of a channel; potential of data which can be transferred in specific period of time
Bandwidth
___________ refers to measurement of data transferred in a specific time period; “effective data rate” or “payload rate”
Throughput
LEO
altitude?
Advantages & disadvantages?
500-1000 miles
- Advantages: reduced transmission delay, reduced launch cost, reduced path loss, lower power, great for mobile cellular services
- Disadvantages: short visibility from any point on earth (15-20 mins), ground stations tracking required, inter0satellite handoffs, potentially large constellations, radiation effects on solar cell and electronics lifetime (Van Allen belt), need to compensate for Doppler shift, atmospheric drag effects
MEO
altitude?
Advantages & disadvantages?
8000 miles
- Advantages: visibility for longer periods than LEO (2-8 hrs), larger coverage area than LEO, wider footprint than LEO, fewer satellites than LEO
- Disadvantages: transmission delay more than LEO, more transmitting power than LEO, exposed to space debris and atmospheric drag, weaker signal than LEO
GEO
Altitude?
Advantages & disadvantages?
altitude 22,300 miles
- Most commonly used and Best for SATCOM- lots of coverage and don’t move
- Advantages: global view (3 satellites), no ground station tracking required, no-inter satellite handoff, almost no doppler shift, 24 hours view of a particular area
- Disadvantages: poor coverage at high latitudes, heavily regulated by the ITU, high transmission latencies, weak received signal
HEO
- Used for a special applications where coverage of high latitude locations is required
________ basic strategy used to get a signal around the earth via satellite, M-hop
Bent Pipe
_________ anti-jam, survivable technique used to get a signal around the earth via satellite (satellite to satellite)
Crosslinks
__________ mobile applications, employs variety of ground equipment
L-Band
__________ lower transmission power over wide geographical area, requires larger ground equipment, better on adverse weather on the ground
C-Band
__________ mainly military applications, employs variety of ground equipment, less crowded frequency, less affected by adverse weather
X-Band
____________ higher transmission power over a small geographical area, uses smaller ground equipment, affected by snow and rain
Ku-Band
__________ higher transmission power than Ku, high bandwidth services (high speed internet, video conferencing and multimedia applications), antenna sizes 60 cm-1.2m, affected by snow and rain
Ka-Band
