NM-1.03 Flashcards
What is latency
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.
Explain spectral flexibility
- Ability of a system or device to operate across a range of frequencies or wavelengths within the electromagnetic spectrum.
- Capacity of comm. systems to adapt to difference frequency bands or channels.
.. operation in a wide range of spectrum and in different-sized bands
Describe the protocal layers
- Physical Layer
- Handles communication impairments
- Responsible for modulation, frequency selection, signal detection
- Encryption - Medium Access Control
- Responsible for mediating access to wireless medium - Radio link control
- Handover between different networks - Packet data convergence protocol
- Reliable end-to-end tx
- Flow and congestion
- Error recovery
Explain the concept of scheduling
A scheduler is a system component in charge of allocating over time the radio resources needed to transmit to the wireless users
How does OFDMA work?
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.
Explain Multi-Antenna Techniques
- Transmit diversity
- Beam-forming
- Spatial multiplexing
- Multi-user MIMO
Explain some goals of LTE Advanced
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
What is mobile broadband?
When you use the internet at home.
What is the issue of carrier aggregation evolution?
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.
What benefits do we get from LTE
- Connect the IOT
- New ways to connect and interact -> vehicle communication
- Latency-ctritical control
For which of the following devices the battery lifetime is not a metric of major interest?
- Wireless sensors
- Mobile phones
- Cellular base stations
Base stations as it’s connected to the grid
What is round robin?
Schedules users cyclically i.e. schedules users independently of their channel conditions.
Give the equation for the Proportional Fair schedule and what happens to r_n
n_max = argmax{d(t)/rn(t)}
Explain the max C/I
Max throughput;
How can latency be measured?
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
