5G Air Interface and Top Interview Questions
Part of Interview Preparation. The articles below are meant to be read in order.
5G NR Numerology: The One Parameter That Shapes the Whole Air Interface
Why 5G NR has five subcarrier spacings instead of LTE's one, what each value buys you, and how μ ripples through symbol, slot and frame timing.
5G NR Radio Frames, Slots and Mini-Slots: How Time Is Divided
The 10 ms frame, the numerology-dependent slot, the 14-symbol structure, the extended-CP exception, and why NR added mini-slots.
5G NR Resource Blocks and Bandwidth Parts: CRB, BWP, PRB and VRB Finally Untangled
Four kinds of resource block, one coordinate system: how Point A, common resource blocks, bandwidth parts, physical and virtual resource blocks fit together, and why NR needed all four.
5G NR Channel Bandwidths: From Licensed MHz to Usable Resource Blocks
The supported channel bandwidths in FR1 and FR2, the transmission bandwidth configuration tables, how guard bands work, and why NR reaches ~98% spectrum utilisation.
5G NR Frequency Raster: NR-ARFCN, the Channel Raster and the Synchronisation Raster (GSCN)
Two rulers over the spectrum: the fine channel raster that positions carriers (NR-ARFCN) and the coarse synchronisation raster that positions SSBs (GSCN) — what each is for, the formulas, and why NR separated them.
5G NR Antenna Ports and Quasi Co-Location: What the UE Is Really Being Told
Antenna ports are not antennas, and QCL is not co-location. A plain-language explanation of both concepts, the four QCL types, TCI states, and why QCL Type D is the key that unlocks mmWave.
5G NR Modulation: From π/2-BPSK to 1024QAM, and Why Each One Exists
The modulation schemes NR supports on each link, how the MCS index ties modulation to code rate, and the design reasoning behind π/2-BPSK, 256QAM and 1024QAM.
5G NR Cyclic Prefix: The Insurance Premium Every OFDM Symbol Pays
What the cyclic prefix does, how long it is at each numerology, why two symbols per half-subframe are slightly longer, and why the extended CP exists only at 60 kHz.
5G NR Waveforms: CP-OFDM and DFT-s-OFDM, and When the Uplink Should Use Which
Why NR uses CP-OFDM everywhere but keeps DFT-s-OFDM as an uplink option, what PAPR really costs, and how the network chooses per UE.
5G NR Transmitter and Receiver Chain: Following the Bits From MAC to Antenna and Back
A block-by-block walk through the NR physical-layer transmit chain and its mirror-image receiver, explaining what each stage does and why it sits where it does.