Abstract
The millimeter-wave (mmWave) is expected to deliver a huge bandwidth to address the future demands for higher data rate transmissions. However, one of the major challenges in the mmWave band is the increase in signal loss as the operating frequency increases. This has attracted several research interests both from academia and the industry for indoor and outdoor mmWave operations. This paper focuses on the works that have been carried out in the study of the mmWave channel measurement in indoor environments. A survey of the measurement techniques, prominent path loss models, analysis of path loss and delay spread for mmWave in different indoor environments is presented. This covers the mmWave frequencies from 28 GHz to 100 GHz that have been considered in the last two decades. In addition, the possible future trends for the mmWave indoor propagation studies and measurements have been discussed. These include the critical indoor environment, the roles of artificial intelligence, channel characterization for indoor devices, reconfigurable intelligent surfaces, and mmWave for 6G systems. This survey can help engineers and researchers to plan, design, and optimize reliable 5G wireless indoor networks. It will also motivate the researchers and engineering communities towards finding a better outcome in the future trends of the mmWave indoor wireless network for 6G systems and beyond.
Highlights
Wireless networks in an indoor environment are omnipresent, and their importance can not be underestimated in our daily lives
It can be noted from the path loss exponent (PLE) and β values of the CI and floating intercept (FI) path loss models are similar for LOS scenarios for most of the listed studies in Tables 6 and 7, for NLOS scenarios, there is a deviation between both models in most of the indoor environments
While the path loss increases as the operating frequency increases, the path loss exponent is not frequency-dependent, but it depends on the environment type and structure
Summary
Wireless networks in an indoor environment are omnipresent, and their importance can not be underestimated in our daily lives. Deterministic channel models characterize the radio wave propagation in a certain physical environment based on assumptions of the propagation mechanisms. These models require a detailed geometry of the environment as well as electromagnetic parameters of the materials. Different measurement techniques with various experimental setups have been used to study the different aspects of the radio frequency (RF) channels They can be classified as narrowband (NB) and wideband (WB) techniques based on the relationship between the probing signal bandwidth and the channel coherent bandwidth. If the bandwidth of the signal is high, the WB measurement technique should be used to estimate the time dispersion parameters of the channel
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