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TM355 > Block 1 Part 3 > Flashcards

Block 1 Part 3 Flashcards

1
Q

Noise and Interference

A
  • noise from natural sources tends to be unavoidable

- interference from unwanted transmissions sometimes avoidable

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2
Q

Electromagnetic compatibility (EMC)

A
  • mitigates causes and effects of interference
  • has standards to comply to
  • emissions - amount of power device allowed to radiate at different frequencies (when not its intended function) limited
  • immunity - device must function normally in presence of radio waves up to certain power at different frequencies
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3
Q

Two types of fading commonly distinguished

A
  • slow fading
  • fast fading
  • relates to how quickly signal changes as receiver or transmitter moves around
  • fast fading changes happen only with small change in position
  • both fading’s due to obstacles and reflections
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4
Q

log-normal fading

A
  • variation in power in slow fading can be modelled with this
  • if variation in power expressed in decibels then it falls within familiar bell curve
  • known as normal or Gaussian distribution
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5
Q

Distance of fading

A
  • fast fading cause large variations in received signal over short distances
  • slow fading takes places over distances of metres
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6
Q

Rayleigh fading

A
  • when no line of sight in fast fading this gives good approximation
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7
Q

Rician fading

A
  • when there is line of sight in fast fading Rician distribution is used
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8
Q

Doppler shift

A
  • radio receivers in vehicles can suffer from problem due directly to their speed
  • This is shifting of frequency when transmitter and receiver moving relative to each other
  • when moving towards each other received signal higher in frequency than transmitted signal
  • when moving apart it’s lower
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9
Q

Beam steering or Beamforming

A
  • technique that uses multiple transmitter antennas
    -used when communicating with single receiver
    purpose is to improve reception at target device
  • relative amplitudes and phases of signal from antennas are adjusted so when they arrive they add together constructively
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10
Q

Multiple input multiple output (MIMO)

A
  • using multiple antennas at receiver and transmitters

- increases paths available

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11
Q

Frequency diversity

A
  • provision for more than one way for signal to pass through channel in presence of fading
  • spread spectrum and OFDM provide this type
  • by spreading signal over range of frequencies, likely some signal will get through and reduce fading
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12
Q

Spatial diversity

A
  • MIMO provides this type of diversity
  • multiple paths between transmitters and receivers
  • When paths used in combination, effects of fading reduced and S/N ratio improved
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13
Q

Spatial multiplexing

A
  • MIMO can provide this too
  • more than one stream of data can be sent at one time without taking additional spectrum
  • increases overall data rate of the channel
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14
Q

Multi-user MIMO(MU-MIMO)

A
  • extends MIMO further to cover multiple users at different locations
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15
Q

Signal-to-noise ratio

A
  • signal power divided by noise power
  • higher s/n ratio, less the signal is affected by noise, and higher data rate can be obtained
  • can be expressed as decibels or simple ratio
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16
Q

Sampling theorem

A
  • puts lower limit on rate at which samples must be taken if signal is to accurately reconstructed
17
Q

Shannon limit

A
  • theoretical upper bound to data rate that can be obtained with given bandwidth and s/n ratio
18
Q

Additive white Gaussian noise (AWGN)

A
  • Shannon’s equation applies strictly to this noise
  • white noise not concentrated at any frequency, equally spread over spectrum
  • additive means different sources of noise added together
  • Gaussian relates to statistical distribution of the noise, which follows a bell curve
19
Q

Bit error rate (BER)

A
  • number of bits received in error divided by number of bits transmitted in total
20
Q

technical considerations when allocating spectrum

A
  • Line-of-sight suitable for some applications but not others
  • Using sky wave or surface wave limited to lower frequency bands
  • Not possible to accommodate wide bandwidths in low frequency bands
  • communications between ground and satellite requires window through atmosphere
  • Transmitters and receivers for highest frequencies present engineering challenges
21
Q

International telecommunications union (ITU)

A
  • radio spectrum management
  • operates at world level
  • developed global treaty Radio Regulations
  • sets out general terms on how spectrum to be used
  • updated at world radio conferences (WRCs) every few years
22
Q

Radio Regulations

A
  • frequency allocations either global or apply to one, two or three regions
  • Americas, Asia Pacific and Europe and Africa
23
Q

Ofcom

A
  • responsible at local level for spectrum
24
Q

UK frequency Allocation Table (UK FAT)

A
  • show permitted use of radio spectrum in UK
  • lists use in all sections of spectrum, start at 8.3 kHz to 275 GHz
  • primary and secondary allocations distinguished in UK FAT
25
Q

Radio regulations two classes of users

A
  • Primary users, permitted to operate provided they don’t cause interference to existing primary users
  • Secondary users, permitted as long as don’t cause interference to primary or secondary users
  • must not cause interference to new primary users
26
Q

Channels

A
  • frequency bands often organised into channels
  • occupies range of frequencies that will accommodate bandwidth of radio signal
  • usually consecutive and equally spaced
27
Q

Spectral mask or spectral envelope

A
  • specified for channel and power density must not exceed it at any frequency
28
Q

Cognitive radio

A
  • if radio device has sufficient info about other radio usage in area they could transmit on different frequencies
29
Q

How would radio device obtain info about environment

A
  • detect what transmission already taking place
  • maintain access to database of radio services
    in area
  • device might need to know
  • know about its location using GPRS
30
Q

White space

A
  • refers to any unused spectrum

TM355 (8 decks)

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