From Sub-6 GHz to Millimeter-Wave: Dynamic Indoor Measurements, Channel Characteristics and Performance Evaluation

Future wireless communication systems will extend the employed frequency bands from sub-6 GHz to millimeter wave (mmWave) bands to achieve higher data rates. To investigate different propagation characteristics between sub-6 GHz and mmWave bands in indoor environments, it is essential to conduct multi-band channel measurements. In this work, we perform dynamic channel measurements using a measurement setup that enables comparing sub-6 GHz and mmWave bands in a fair manner. Measurements are conducted in an indoor environment at center frequencies of 2.55 GHz and 25.5 GHz at transmitter velocities of 50 km/h and 100 km/h. Based on the acquired measurement data, we conduct a comparative analysis of the multi-band propagation characteristics. Specifically, we compare the channels in terms of root-mean-square (RMS) delay spread, Rician K-factor, RMS Doppler spread and RMS angular spread. Additionally, we evaluate the system performance at both frequency bands in terms of achievable spectral efficiency derived from the measured channels. Our results show that differences in delay-domain parameters (RMS delay spread and Rician K-factor) and angular-domain (RMS angular spread) are relatively minor and are unlikely to significantly impact system design. However, the RMS Doppler spread increases proportionally with carrier frequency and transmitter velocity, causing channel state information (CSI) at mmWave frequencies to become outdated much more rapidly. This imposes a substantial performance limitation for mmWave systems in dynamic scenarios.