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Next Generation Networks > NM-1.03 > Flashcards

NM-1.03 Flashcards

1
Q

What is latency

A

The time that passes from a user sending a piece of data quest (e.g filge download or loading a webpage), to the time when the user gets a response.

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2
Q

Explain spectral flexibility

A
  1. Ability of a system or device to operate across a range of frequencies or wavelengths within the electromagnetic spectrum.
  2. Capacity of comm. systems to adapt to difference frequency bands or channels.

.. operation in a wide range of spectrum and in different-sized bands

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3
Q

Describe the protocal layers

A
  1. Physical Layer
    - Handles communication impairments
    - Responsible for modulation, frequency selection, signal detection
    - Encryption
  2. Medium Access Control
    - Responsible for mediating access to wireless medium
  3. Radio link control
    - Handover between different networks
  4. Packet data convergence protocol
    - Reliable end-to-end tx
    - Flow and congestion
    - Error recovery
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4
Q

Explain the concept of scheduling

A

A scheduler is a system component in charge of allocating over time the radio resources needed to transmit to the wireless users

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5
Q

How does OFDMA work?

A

Orthogonal Frequency Division Multiple Access:

  • OFDMA divides the available frequency spectrum into multiple smaller subcarriers.
  • Subcarriers are orthogonal to each other -> don’t interfere with each other.
  • Each carrier is capable of carrying data independently.
  • Key feature of OFDMA is its ability to dynamically allocate subcarriers to different users based on their data rate requirements and channel conditions.
  • OFDMA can adapt the modulation and coding schemes for each subcarrier based on the channel conditions.
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6
Q

Explain Multi-Antenna Techniques

A
  1. Transmit diversity
  2. Beam-forming
  3. Spatial multiplexing
  4. Multi-user MIMO
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7
Q

Explain some goals of LTE Advanced

A

Peak data rates: DL - 1 Gbps; UL - 500 Mbps

Spectrum efficiency: 3 times greater than LTE

Cell edge user throughput: twice that of LTE

Average user throughput: 3 times that of LTE

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8
Q

What is mobile broadband?

A

When you use the internet at home.

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9
Q

What is the issue of carrier aggregation evolution?

A

wavelength = c/f; if we have a lower wl, then we must have to have large antennas and can travel further.

A higher wl can cause smaller antennas; add more antennas -> MIMO. But higher wl can’t travel as far.

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10
Q

What benefits do we get from LTE

A
  1. Connect the IOT
  2. New ways to connect and interact -> vehicle communication
  3. Latency-ctritical control
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10
Q

For which of the following devices the battery lifetime is not a metric of major interest?

  1. Wireless sensors
  2. Mobile phones
  3. Cellular base stations
A

Base stations as it’s connected to the grid

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11
Q

What is round robin?

A

Schedules users cyclically i.e. schedules users independently of their channel conditions.

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12
Q

Give the equation for the Proportional Fair schedule and what happens to r_n

A

n_max = argmax{d(t)/rn(t)}

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13
Q

Explain the max C/I

A

Max throughput;

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14
Q

How can latency be measured?

A

The latency can be measured by the time it takes for an IP packet to travel from the terminal through the network to the Internet server, and back

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15
Q

What are the LTE features

A
  1. OFDM/OFDMA
  2. All-IP architecture; simplified network management
  3. Spectrum flexibility
16
Q

Why does the broadcast channel use QPSK?

A

It uses QPSK as since it only transmits two bits per time, it’s a lot less error-prone than modulation schemes using more.

17
Q

Where is the scheduler located?

A

The scheduler is in the eNodeB

18
Q

Explain the PHY layer in detail

A
  1. OFDMA with cyclic prefix in downlink
  2. SC-FDMA with cyclic prefix in uplink
  3. 10 ms radio frames, containing 20 slots of 0.5ms duration
  4. Maximum information block size: 6144 bits
  5. CRC-24 for error detection
19
Q

In scheduling, slots consist of either 6 or 7 OFDM symbols. What are longer cyclic prefixes are used for?

A

Longer cyclic prefixes are used to address longer multipath fading channel length.

20
Q

In OFDM what does the number of available subcarrier change depend on?

A

Number of available subcarriers changes depending on transmission bandwidth

21
Q

For which is the following devices is the battery lifetime not a metric of major interest?

  • Wireless sensors
  • Mobile phones
  • Cellular base stations
A

Base stations; connected by cable

22
Q

Which of these access
techniques is the one adopted in
4th generation cellular systems
(LTE/LTE-A)?

  • TDMA
  • OFDMA
  • CDMA
A

OFDMA

TDMA -> 2G
CDMA -> 3G

Next Generation Networks (25 decks)

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