What is CIR?
CIR (Channel Impulse Response) is a characterisation of a wireless channel obtained by correlating the received signal against the transmitted signal during testing. It captures the time-domain behaviour of the propagation channel, revealing all multipath components — their delays, amplitudes, and phases. CIR is fundamental to understanding how radio signals propagate in a given environment and is the basis for designing equalizers, channel estimation algorithms, and selecting appropriate channel models for 5G NR system design.
How Does CIR Work?
CIR is measured by transmitting a known wideband signal (such as a pseudo-random noise sequence or a channel sounding waveform) and cross-correlating the received signal with the transmitted reference. The resulting impulse response shows discrete peaks corresponding to individual multipath components, with each peak’s position on the time axis indicating the propagation delay and its amplitude indicating the received power from that path. In 5G NR, CIR measurements are used to derive channel model parameters including delay spread, angular spread, and Doppler spread across both FR1 and FR2 frequency ranges.
Use Cases
Radio channel sounding and modelling, 5G NR system design and coverage planning, indoor propagation analysis for private 5G, receiver equalizer design, and channel model validation for 3GPP standardization.
3GPP / Standards Reference
3GPP TR 38.901 (Channel model for 0.5–100 GHz), 3GPP TR 38.900 (Channel model study for LTE/NR)
Related Terms
CE | NLOS | Beamforming | FR1 | FR2
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This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
