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jared nationals > 64 QAM > Flashcards

64 QAM Flashcards

1
Q

DOCSIS

A

Data Over Cable Services Interface Specification

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2
Q

HFC

A

Hybrid Fiber Coaxial

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3
Q

The first DOCSIS specification, version 1.0 was issued in

A

March 1997

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4
Q

DOCSIS 2 was released in

A

January 2002

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5
Q

CMTS

A

Cable Modem Termination System

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6
Q

Created the ability for the CMTS to talk to the cable modem in the customer’s home

A

DOCSIS 1.0

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7
Q

Provided the control and enhanced security lacking in DOCSIS 1.0

A

DOCSIS 1.1

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8
Q

Supports higher upstream speed by allowing for additional profiles

A

DOCSIS 2.0

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9
Q

Triples the maximum upstream capacity when compared to DOCSIS 1.1

A

DOCSIS 2.0

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10
Q

Enables transmission across 6.4 MHz channel and increases upstream throughput to 30.72Mbps by using 64 or 128 QAM

A

DOCSIS 2.0

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11
Q

FEC

A

Forward Error Correction

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12
Q

Features “Channel bonding” which enables multiple downstream and upstream channels to be used together at the same time by a single subscriber

A

DOCSIS 3.0

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13
Q

DOCSIS 3.0 feature that supports IPv6 standards and expands the number of available IP addresses from existing 8 and 16 bit strings to as much as 32 and 128 bit strings

A

Channel Bonding

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14
Q

Similar to voice and visual systems and use signals that vary over time in Amplitude and/or Frequency

A

Analog transport systems

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15
Q

Transmitted at a fixed frequency and are comprised of a string of on and off states usually referred to as ones and zeros

A

Digital communications

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16
Q

Signal to be transmitted must be mathematically manipulated and converted into a string of On/Off states

A

Digital communications

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17
Q

These distortions are actually caused by the electronics and equipment used to complete the modulation

A

Non-Linear distortions

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18
Q

These errors occur during analog to digital conversion

A

digitizing errors

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19
Q

The basic analog to digital conversion process

A

sampling, quantization, and encoding

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20
Q

Occurs when the amplitude of the signal is determined at fixed points in time

A

sampling

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21
Q

The maximum frequency of the analog signal determines this

A

sampling rate

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22
Q

must be at least two times the frequency that is being digitized

A

sampling rate

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23
Q

The process of recording each sample as a number corresponding to the amplitude of the signal at that time

A

Quantizing

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24
Q

These determine how well the analog signal is represented, digitally.

A

Sampling and Quantizing

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25
Q

The process of measuring an analog signal at specific intervals so that a digitized signal can be created to represent the original analog waveform

A

sampling

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26
Q

A principle that engineers follow in the digitization of analog signals

A

The Nyquist Theorem

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27
Q

ADC

A

Analog to Digital Conversion

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28
Q

States that the minimum sampling frequency must be at least twice the highest frequency of the signal to be digitized, also known as the sampling theorem

A

The Nyquist Theorem

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29
Q

In signal processing and related disciplines, this refers to an effect that causes different signals to become indistinguishable

A

aliasing

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30
Q

a 6 MHz baseband signal requires a sampling frequency of this

A

12MHz

31
Q

is a phenomenon that causes frequencies higher than the nyquist frequency to be mapped to a frequency below the nyquist frequency

A

Digital Aliasing

32
Q

Steps to calculate the total data rate

A

Determine minimum sampling rate, Determine bit resolution, Multiply bit resolution and sampling rate.

33
Q

QAM

A

Quadrature Amplitude Modulation

34
Q

A digital modulation scheme by which digital cable channels are encoded so they can be transmitted via cable

A

Quadrature Amplitude Modulation (QAM)

35
Q

Allows digital information to be transmitted on an analog system by using two carriers of the same frequency that are shifted to operate 90 degrees out of phase with each other.

A

Quadrature Amplitude Modulation (QAM)

36
Q

This carrier is the reference carrier

A

I or In-Phase

37
Q

This carrier is shifted 90 degrees

A

Q or Quadrature

38
Q

QPSK

A

Quadrature Phase Shift Keying

39
Q

Simplest form of QAM and is sometimes referred to as 4 QAM

A

QPSK

40
Q

Works by transmitting two “carriers” of the same frequency such that they are at a 90 degrees phase relative to one another

A

QPSK

41
Q

Similar to QPSK except that each axis is allowed to have more than two levels

A

Quadrature Amplitude Modulation or QAM

42
Q

What Modulation is twice as efficient as QPSK

A

16 QAM

43
Q

QPSK (4 QAM) supports this transmission speed

A

2 bits/symbol

44
Q

16 QAM supports this transmission speed

A

4 bits/symbol

45
Q

64 QAM supports this transmission speed

A

6 bits/symbol

46
Q

is a combination of QPSK and ASK

A

QAM

47
Q

In QAM this axis is represented by “I” or In Phase

A

X axis or horizontal axis

48
Q

In QAM this axis is represented by “Q” or Quadrature

A

Y axis or vertical axis

49
Q

uses the same two phase states of the I and Q channels, but increases the number of amplitude changes to four.

A

64 QAM

50
Q

has 6 bits per symbol and contains 16 symbols per quadrant.

A

64 QAM

51
Q

provides 8 bits per symbol and contains 64 symbols in each quadrant.

A

256 QAM

52
Q

Modulation format data rate at 5MHz: QPSK

A

10Mb/s

53
Q

Modulation format data rate at 5MHz: 16 QAM

A

20Mb/s

54
Q

Modulation format data rate at 5MHz: 64 QAM

A

30Mb/s

55
Q

Modulation format data rate at 5MHz: 256 QAM

A

40Mb/s

56
Q

Constellation Diagram: While the picture will be perfect, any other degradation will bring total failure: In this situation, a fuzzy circular pattern will occupy most of the cell

A

Poor Carrier to Noise Ratio

57
Q

Constellation Diagram: Caused by coherent noise, this situation results in circular patterns in each cell

A

Ingress, Composite Triple Beat(CTB) Composite Second Order(CSO), or spurs

58
Q

Constellation Diagram: Caused by residual FM, is normally a headend problem

A

Phase Shift

59
Q

Constellation Diagram: Caused by IF and RF amplifiers and filters, up/down converters of IF equalizers.

A

Gain Compression

60
Q

Constellation Diagram: Caused by problems with baseband amplifiers, filters, or the digital modulator and normally a headend problem.

A

IQ imbalance

61
Q

Constellation Diagram: Caused by an imbalance in the modulators mixer or undesirable DC voltage in the transmission system

A

Carrier Leakage

62
Q

BER

A

Bit Error Rate

63
Q

Measurement of the bits received incorrectly.

A

Bit Error Rate or BER

64
Q

Calculated by dividing the number of received errors by the number of transmitted bits

A

Bit Error Rate or BER

65
Q

MER

A

Modulation Error Rate

66
Q

Measurement of the average deviation from the center of the symbol region.

A

Modulation Error Rate or MER

67
Q

Ratio of the average symbol deviation to the average symbol magnitude expressed in dB

A

Modulation Error Rate or MER

68
Q

Both of these indicate the ratio between the data signal and the noise or whatever it is that is interfering with the signal

A

MER and SNR

69
Q

Only measure CONSTANT, non-intermittent, non impulsive interfering sources such as fixed off-air ingress, distortion beats, hum modulation, etc

A

MER and SNR

70
Q

SNR

A

Signal to Noise Ratio

71
Q

As the modulation rate increases, the symbol regions decrease and are what the area of the prior region

A

1/4th the area

72
Q

NPR

A

Noise Power Ratio

73
Q

These must increase by 6dB for each increase in modulation rate if the same BER is to be maintained

A

NPR, CNR, SNR

74
Q

Best method to isolate noise

A

Divide and conquer

jared nationals (14 decks)

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