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30 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is an analog signal? |
It can have infinitely many levels of intensity over a period of time |
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What is a digital signal? |
It can have a limited number of defined values |
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What is a periodic signal? |
It completes a pattern (cycle) within a measurable timeframe known as a period and repeats that pattern over subsequent identical periods |
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What is a nonperiodic signal? |
It changes without exhibiting a pattern on cycle that repeats over time |
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What is transmission impairment? |
Signals travel through imperfect transmission media and the imperfection causes the signal at the beginning of the medium to be different from the signal at the end |
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What are the causes of impairment? |
1. Attenuation (loss of energy) 2. Distortion (change in the signal's form or shape) 3. Noise |
AND |
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What are the types of noise? |
a. Thermal: Random motion of electrons creates extra signal b. Induced: Due to motor and appliances which act as sender and medium as receiver c. Crosstalk: Effect of one wire on another, one as sender and other as receiver d. Impulse: Spike due to power lines/lightning/etc |
TICI |
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What is signal-to-noise ratio? |
Ratio of average signal power to noise power In decibels, 10log(10)SNR |
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What factors affect data rate? |
1. Available bandwidth 2. Level of signals used 3. Level of noise/quality of channel |
BSN |
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Nyquist Bit Rate |
Bit rate = 2 x Bandwidth x log2L L = number of signal levels used to represent data |
For noiseless channel |
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Shannon Capacity |
Theoretical highest data rate for a noisy channel Capacity = bandwidth x log2(1+SNR) |
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What is bandwidth? |
In Hertz: Range of frequencies contained in a composite signal In bps: Number of bits per second that a channel, a link ,or even a network can transmit |
In hertz and bps |
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What is throughput? |
Measure of how fast data can actually be sent through a network (actual measurement) |
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What is latency? |
Defines how long it takes for entire message to completely arrive at destination from the time first bit is sent from the source |
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Components of latency |
1. Propagation time (time for a bit to travel from source to destination) 2. Transmission time (time between first bit transmission and last bit reception) 3. Queuing time (time needed for each device to hold message before processing) 4. Processing delay |
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What is bandwidth-delay product? |
It defines the number of bits that can fill the link |
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What is Jitter? |
Problem encountered when different packets of data encounter different delays, when the application using the data is time-sensitive |
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What is line coding? |
Process of converting digital data to digital signals |
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Characteristics of line coding
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1. Signal element vs Data element: r = number of data elements carried by each signal element 2. Data rate vs Signal rate: aka bit rate vs pulse/modulation/baud rate (S = CN/r) N:data rate, C:case factor, S:No. of signal Elements 3. Bandwidth: Theoretically infinite but practically finite 4. Baseline wandering (running average of received signal power affected by long strings of 0/1) 5. DC Components (Constant voltage level creates low frequencies which cannot be passed) 6. Self-synchronization (digital signal includes timing information in data) 7. Built-in error detection 8. Immunity to noise 9. Complexity (complex scheme more costly to implement) |
ERBEDSWNC |
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Categories of line coding schemes |
Unipolar Polar Bipolar Multilevel Multitransition |
UBPMM |
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Unipolar NRZ |
1: +ve 0: 0 |
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Polar NRZ-L |
0: +ve 1: -ve |
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Polar NRZ-I |
0 next bit: No change 1 next bit: Invert |
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Polar RZ |
2 signal levels for 1 data bit 0: Low to high 1: High to low |
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Manchester scheme |
Changes phase when same bit repeats 0: + to - 1: - to + |
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Differential Manchester |
0 next bit: No change 1 next bit: Invert |
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Bipolar AMI |
0: 0 1: Invert previous 1 |
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Bipolar pseudoternary |
0: Invert previous 0 1: 0 |
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Sampling methods |
Ideal sampling (fixed sampling time) Natural sampling (sampled at intervals) Flat-top sampling (first value of interval plateaued) |
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What values do quantization and encoding involve? |
Normalized value (ratio of amplitude to height of L-zone) Quantized value (Middle value of each zone) Normalized error (Q-N) Quantization code (based on quantization level) Encoded word (final product) |
NQECW |
