Lecture #1 - Mobile Communication Systems Flashcards
Millimeter-wave frequency rage is used in 4G, 5G, or both?
The millimeter-wave frequency is used in 5G.
This is because ‘mm’ waves are shorter, meaning that it travels at a faster frequency.
A line-of-sight link between a transmitter and receiver suffers from which loss or losses?
FSPL, Atmospheric Loss
Why do we use a higher order modulation e.g. 64 QAM in 4G/5G?
Better spectral efficiency
The maximum rate of information transmitted over a communication channel is limited by which factors?
Bandwidth, SNR
Name the potential use cases of 5G technology
- Broadband access in dense areas; in a stadium or smart office
- Broadband access anywhere; min. data rate guaranteed everywhere, 50+ Mbps
- Higher user mobility; mobile services in vehicles, trains and aircrafts.
- IOT; wearables and smart cities
- Extreme real-time communication
- Lifeline communication
Name the frequency band of LTE
Between 410 MHz and 5.9 GHz
Name the frequency band of 5G
The 5G NR spectrum is divided into two frequency range:
- sub-6GHz frequency bands, 410 MHz to 7.125 GHz
- Millimeter-wave (mm-Wave) range including frequency
bands from 24.25 GHz to 52.6 GHz
What happens if the 5G NR band overlaps with the 4G LTE?
The same band number is used.
Explain who the International Telecommunication Union is and what they do
Who:
- Global spectrum management (the spectrum is limited, rapid growth in services and its users)
What:
- Ensure rational, equitable, efficient and economical use of the spectrum by all radiocommunication services.
- Carry out studies and approve recommendations and radiocommunication matters.
What are the advantages of common standards for frequency management
- Interoperability between devices of different vendors
- Global usage of customer devices
Explain who the 3GPP and what they develop/maintain the following standards for?
3GPP is a consortium of 7 national telecommunication standard organizations
that develop protocols for mobile telecommunications
They develop and maintain:
- 2G
- 2.5G
- 3G
- 4G
- 5G
Explain the concept of ‘Listen-before-talk’.
- Used to manage and control access to the shared radio frequency spectrum.
- Avoid collisions and interference between multiple devices trying to transmit data simultaneously.
In a wireless network, multiple devices, such as smartphones or Wi-Fi access points, communicate with each other using radio waves. These devices operate within a limited frequency spectrum, and it is crucial to avoid conflicts when multiple devices want to transmit data simultaneously.
The LBT mechanism ensures that a device intending to transmit data first listens to the radio channel before initiating the transmission. By listening to the channel, the device can determine whether it is occupied by ongoing transmissions from other devices or if it is clear for transmission.
Explain the difference between LTE-LAA and LTE-U?
LAA mandates a ‘listen-before-talk’ capability, which is a requirement for unlicensed operation in Europe and Japan.
Explain the concept of carrier aggregation
A technique used to increase the data rate per user, whereby multiple frequency blocks (component carriers) are assigned to the same user.
The maximum possible data rate per user is increased the more frequency blocks are assigned to a user.
Describe the three cases of carrier aggregation
- Intra-band contiguous; the same component carriers are adjacent and in the same frequency band
- Inra-band continguous; the component carriers are not adjacent, but in the same frequency band
- Inter-band carrier aggregation; the component carriers are in different frequency band. Highest complexity case from an RF point of view.
How many carrier aggregations are in LTE-A and 5G
LTE-A; 5 CA
LITE-A PRO & 5G;32 CA
Why use mm-waves for wireless communications?
- Significantly higher bandwidth, hence higher capacity for base station-to-device and backhaul links
- Rapid and less-expensive deployment of wireless backhauls compared to fibre.
What’s the challenge/loss to using mm-waves for wireless communication.
Three types of losses:
- Free space path loss (FSPL): increases
with frequency (𝑓) & distance (𝑑) - Atmospheric loss (AL): due to water
vapour, oxygen, rain & other forms of
precipitation e.g. fog, snow. - Other losses (OL): cable loss, “wet
antenna attenuation” etc.
Give the equation for the receiver signal power, taking into account the different losses.
𝑃Rx = 𝑃Tx + 𝐺Tx + 𝐺Rx − FSPL − AL − OL
Explain the concept of Free Space Path Loss and its equation
Free space path loss refers to the loss of signal power that occurs as an electromagnetic wave propagates through free space without any obstacles or obstructions.
It gives a rough estimate of the signal attenuation in free space and is commonly used as a starting point a wireless system design and determining the coverage area of a transmitter.
FSPL = (4πdf/c)^2
Give the equation for atmospheric loss and name the factor which causes the most atmospheric loss
AL = 𝐴r + 𝐴v + 𝐴o + 𝐴p
𝐴r - attenuation caused by rain, 𝐴v- water vapour
attenuation, 𝐴o- attenuation due to dry air, 𝐴p- attenuation due
to precipitation other than rain e.g. fog, all values in dB
Rain causes the highest amount of signal loss compared to other atmospheric factors
What’s the difference between a 77GHZ and 240GHZ wireless link
77GHz is used for longer communication, whereas, 240GHZ is still used within LOS but larger lengths (in km)
What happens to the spectral efficiency when you increase the SNR?
You decrease the spectral efficiency; the amount of information that can be reliably transmitted per unit of bandwidth or spectral resources.
Explain small-cell technology and its characteristicsovcvgffgg
