Day 1: Signal Design Flashcards
What is the process of converting analog signals to digital signals?
Sampling
Why do we convert digital to analog before transmitting?
It proprogates through space better
Identify
The method of putting information onto a carrier signal by changing one or more properties of the wave in a pre-determined pattern to represent data
Modulation
When we modulate, what are we changing?
Frequency, amplitude, and/or phase
Identify
A method of encoding digital information (bits) onto an analog carrier wave for transmission over media that does not support direct digital transmission
Digital Modulation
Most common is shift-keying
Identify
Presents digital data as variations in the amplitude of a carrier wave
Shift Keying
Amplitude Shift Keying
It is also relatively inexpensive.
Identify
Shifts the output frequency between predetermined waves
Shift Keying
Frequency Shift Keying
Changes the phase of a carrier wave
Phase Shift Keying
BPSK and QPSK most common mod scheme due to better efficiency; idea for video
Identify
- Stands for In-phase and Quadrature
- It represents two 90 degrees perpendicular components to each other
Constellation Diagrams
I/Q
Identify
Graphical representation showing possible symbol locations in I/Q space
Constellation Diagrams
Constellation Plots
What do constellation diagrams represent?
Amplitude (I) and phase (Q) of a signal
Identify
Uses 2 phase shifts 180 degrees apart
Modulation Scheme
BPSK
Identify
Less sensitive to phase noise than other types
Modulation Scheme
BPSK
Identify
Used when lower data rates are required or more robustness is required
Modulation Scheme
BPSK
Identify
2 bits per symbol
Modulation Scheme
QPSK
Identify
More susceptible to nosie than BPSK and QPSK
Modulation Scheme
8PSK
Identify
Less BW required than BPSK and QPSK
Modulation Scheme
Identify
Often used for digital video
Modulation Scheme
QAM
Identify
Combination of modulating amplitude and phase
Modulation Scheme
QAM
Expressed as a percentage (%) deviation of Rx’d symbol vs Reference Point
Error Vector Magnitude
Identify
Expressed as a percentage (%), deviation of Rx’d symbol from desired phase angle
Phase Shift Error (PSE)
Identify
The range of frequencies where the majority of the signal’s power resides
Occupied Bandwidth
The bandwidth actually used for transmitting data
Effective Bandwidth
Always narrower than occupied BW due to guard intervals and other factors (ex. roll off factor)
How is effective bandwidth is closely related to symbol rate?
The faster symbols are transmitted (higher symbol rate), the more bandwidth is needed
Identify
Intentional periods (time) where signals do not transmit to prevent interfering with themselves
Guard Intervals
Identify
Unoccupied spaces between signals to prevent interfering with one another
Guard Bands
Identify
The difference in frequency between the effective and occupied bandwidth
Roll-off factor
Identify
Speed at which raw data is transmitted
Data rate
Identify
Overall speed of all bits being transmitted, including raw data and any additional bits like error correction
Total Bit Rate
Rate at which symbols (which can represent multiple bits) are transmitted (changes)
Symbol Rate
Identify
Adds “gain” to the signal (computational/coding)
Forward Error Correction (FEC)
Identify
Added in the MODEM (prior to Tx)
Forward Error Correction (FEC)
Identify
The ability to detect the presence of errors caused by noise or other impairments during transmission between the transmitter to the receiver
FEC
Error detection
Identify
The additional ability to reconstruct the original, error-free data
FEC
Error correction
Identify
Non-data bit added to data bit stream that enables receiver to detect errors or to detect and correct errors
FEC
Parity bit
Identify
The actual information (1s, 0s) you are attempting to send
FEC
Data bits
Identify
The entire series of “ones” or “zeros” (data and parity)
FEC
Bit stream
Identify
A radio technology allowing one-way communication from a transmitter to a receiver
Communication Protocols
Simplex
Identify
Operation mode of a radio communication system in which each end can transmit and receive, but not simultaneously
Communication Protocols
Half-duplex RF systems
Ex. walkie-talkie, wireless keyboard, mouse
Identify
Radio system in which each end can transmit and receive simultaneously
Communication Protocols
Full-duplex RFsystem
Identify
Combining multiple signals into ONE signal (Analog or Digital)
Multiplexing
Identify
The separation of combined signals
De-multiplexing
What are the methods of multiplexing?
- Frequency Division MUX (FDM)
- Time Division MUX (TDM)
- Code Division MUX (CDM)
Identify
The process of two or more signals physically taking turns on a channel (frequency)
This enables efficient use of the available bandwidth
Time Division Multiplexing (TDM)
Identify
Assigns non-overlapping frequency ranges to different signals or to each “user” of a medium
Frequency Division MUX (FDM)
A data signal is sent over a range of frequencies in an assigned frequency spectrum using a pseudo-random spreading code
Code Division MUX (CDM)
Ex. cellular network
Multiple access differs from multiplexing because it occurs ____________ transmission.
After
What are the types of multiple access?
- Frequency Division Multiple Access (FDMA)
- Time Division Multiple Access (TDMA)
- Code Division Multiple Access (CDMA)
Identify
Users share the satellite simultaneously, but each user transmit at a single frequency
Frequency Division Multiple Access (FDMA)
List
Frequency Division Multiple Access (FDMA) Advantages
- Simplicity
- Proven and reliable
List
Frequency Division Multiple Access (FDMA) Disadvantages
- Needs more BW as you add users
- In-flexible, not easy to reconfigure
Identify
Users share a single RF channel without interference by allocating different time slots to each user
Time Division Multiple Access (TDMA)
Time Division Multiple Access (TDMA) Advantage
Efficient use of BW (user gets full BW during their time slot)
Time Division Multiple Access (TDMA) Disadvantages
- Needs to account for Tx delay for differing Earth Stations
- Large Earth Segment investment (transmit equip/controllers)
- Need for very precise time standards
- Limited time slots
Tx technique that employs a scheme that codes every digital packet it sends with a unique key to allow users to be multiplexed over the same frequency channel
Code Division Multiple Access (CDMA)
List
Code Division Multiple Access (CDMA) Advantages
- More resistant to jamming and interference than FDMA and TDMA
- Resistant to interception
Code Division Multiple Access (CDMA) Disadvantage
Equipment cost is much higher, along with the larger BW that is required
