Digi Comms SA1 Flashcards
The need for ___ and ____ transmission of information is essential and important
fast; reliable
Alphabets/Symbols are ____ in analog and ____ in digital systems
uncountably infinite; discrete
Signals are ____ in analog and ____ in digital (hint: characteristic)
Continuous; Discrete
Fidelity is measured in ____ in analog systems while it is measured in ____ in digital systems
SNR;BER
T or F: Digital Systems in general are resistant to noise
True
T or F: The source output in a digital communication system is an analog signal
False. It can also be a digital signal
____efficiently converts an analog signal into a sequence of binary bits
Source Encoder
Another term for data compression
lossy
Another term for data compaction
lossless
This element removes redundant information from the message signal, and is responsible for the efficient use of the channel
Source Encoder
3 parts of the source encoder
sampling, quantization, and source coding
____ converts an analog signal into a corresponding sequence of samples usually spaced uniformly in time`
sampling
the output of sampling is ____ in amplitude and ___ in time
continuous; discrete
process of transforming the sample amplitude into a discrete amplitude is called
quantization
the output produced in quantization is ____ in amplitude and ___ in time
discrete; discrete
what are the two types of quantization?
midtread and midrise
T or F: Efficient use of channel means removing redundancy in the signal
True
Element in the digital communication system which uses redundancy in a controlled manner
Channel Encoder
T or F: Redundancy can be used at the receiver to overcome the effects of noise and interference
True
Channel Encoder increases reliability and improves the ____ of the received signal`
fidelity
The resulting sequence of symbols from the channel encoder is called
channel codeword
This serves as the interface to the communication channel
digital modulator
Digital Communication element whose primary purpose is to map the binary information sequence into signal waveforms
Digital Modulator
each symbol in the channel codeword is represented by an ____ symbol
analog
type of digital modulation technique used for data transmission in which instead of one bit, two or more bits are transmitted at a time
M-ary modulation
The ______ ________ is the physical medium used to send the signal from the transmitter to the receiver
communication channel
Communication channels can either be ____ (wired communications) or _____ (wireless communications)
guided; unguided
Effect in communication channel described as a decrease in power as the inverse of square distance; measured in dB
Attenuation
Effect in communication channel described as an additive in nature that falls within the passband of the signal
Noise
Noise is typically modeled using what mathematical model?
White Gaussian Noise (WGN)
Effect in communication channel where the channel has a smaller bandwidth compared to the signal bandwidth
Filtering
Form of distortion of a signal in which one symbol interferes with the subsequent symbols
Intersymbol Interference (ISI)
____ is the variations of the channel strength over time and over frequency
Fading
Large-scale fading is due to path loss of a signal as a function of distance and ____ by large objects such as buildings and hills
Shadowing
small-scale fading is due to the interference of the _____ signal paths between transmitter and receiver
multiple
These channels cause signal fading
Time-varying channels
______ processes the channel-corrupted transmitted waveform and translates the waveforms into a sequence of numbers
Digital Demodulator
T or F: The channel encoder attempts to reconstruct the original information sequence
False, channel decoder dapat
The channel decoder performs what two processes?
error-detection and error-correction
Another term for when the source decoder attempts to reconstruct the original signal from the source
decompression
T or F: The output of the source decoder is an accurate copy of the original source output
False, it is only an approximation
The difference of original and reconstructed signals is a measure of ____
distortion
Common Communication Channels
Wireline channel
Fiber-optic channel
Wireless electromagnetic channels
Underwater acoustic channels
Storage channels
Mathematical models are used in the design of the _____ and _____ at the transmitter and ____ and ____ at the receiver
channel encoder; modulator; demodulator; channel decoder
Simplest mathematical model for a communication channel
Additive noise Channel
Thermal noise is statistically characterized as a _____ noise process
Gaussian
Mathematical model that ensures transmitted signals do not exceed specified bandwidth limitations and thus do not interfere with one another
LTI Filter Channel with Additive Noise
Mathematical model used for physical channels that exhibit time-variant multipath propagation
LTV Filter Channel with Additive Noise
Average power of the transmitted signal
Transmit Power
width of the passband channel
Channel bandwidth
2 types of power-limited channels
wireless channels and satellite channels
2 examples of bandwitdh-limited channels
Telephone and Television channels
Give an example off the challenges in designing communication channels
Limited Spectrum, Power consumption, Interference, Seamless access, system on chip design
Good communication system should have:
____ signal power
____ bandwidth
____ data rate
____ distortion
____ cost
small
small
large
low
low
It is a measure of how efficiently a limited frequency spectrum is utilized
Bandwidth Efficiency
Unit of measurement used in energy efficiency
bits/joule
Defined as the ratio of transmitted data to consumed energy
Energy efficiency
T or F: Power efficiency is more important than spectral efficiency in cellular transmission because sending data with more power can interfere with adjacent cells
True
____ means the digital systems can withstand the effects of channel noise and signal distortion
Ruggedness
Digital Systems permit the use of ____ which can eliminate degrading effects of channel noise and signal distortion
regenerative repeaters
T or F: Digital Systems are more efficient in terms of tradeoff between bandwidth and SNR
True
