Chiehping Lai

To support the design of fifth-generation (5 G) beamforming and beamtracking algorithms, a spatially consistent channel propagation model is needed, namely a model whose geometrical properties – angle-of-departure, angle-of-arrival, and delay of its multipath components – evolve smoothly while the receiver is in motion. The 3 rd Generation Partnership Project (3GPP) has proposed two spatial consistency (SC) procedures – SC-A and SC-B – as part of its popular TR 38.901 model for 0.5 GHz to 100 GHz channels. In this paper, we perform a comparison of the two procedures with measurements to determine whether the procedures accurately fit our measurements. We use over 700 channel measurements collected with our high-resolution 28 GHz and 60 GHz directional channel sounders, across two indoor and three outdoor environments and for pedestrian and vehicular motion. We show that SC-A – a fully deterministic procedure – provides a much better approximation to the measured channel in all five environments than SC-B – a fully stochastic procedure. We also computed the correlation distance for both procedures – the distance over which they are valid – showing that SC-A's average correlation distance across all environments of 13.4 m is more than twice as long as SC-B's of 6.28 m, and that the channel is spatially consistent for significantly longer outdoors than indoors.

There is strong impetus by the Telecom Infra Project to exploit the 60 GHz unlicensed band for public WiFi in urban environments, by installing access points on light poles. Although many 60 GHz urban channel measurements have been recorded to date, they have resulted only in path loss models or RMS delay spreads. What is needed at millimeter-wave is a spatially consistent channel model for beamtracking that embodies the characteristics of these short wavelengths sparsity and rough surface scattering such as the Quasi-Deterministic model. In this letter, we fit the model to channel measurements we recorded in an urban environment. The measurements were recorded at 4 m, 6 m, and 9 m antenna heights to investigate the tradeoffs between light pole heights. The large-scale channel metrics between the model and the measurements were shown to match very well.

We reduced the parameters of the Quasi-Deterministic channel propagation model, recently adopted by the IEEE 802.11ay task group for next-generation Wi-Fi at millimeter-wave (mmWave), from measurements collected in an urban environment with our 28 GHz switched-array channel sounder. In the process-as a novel contribution-we extended the clustering of channel rays from the conventional delay and angle domains to the location domain of the receiver, over which the measurements were collected. By comparing channel realizations from the model to realizations from a leading commercial ray-tracer, we demonstrated that the model effects no detriment to accuracy while maintaining the benefit of significantly reduced complexity.

This paper describes the calibration of the Volcano ray-tracing engine against channel measurements collected in an urban environment with a state-of-the-art 28-GHz directional channel sounder. A discrete set of rays, representing planar wavefronts propagating between the transmitter and receiver, were extracted from the measurements and characterized in path gain, delay, and 3D angle-of-arrival through super-resolution techniques, with average errors of only 1.2 dB, 0.55 ns, and 2.05° respectively. The extracted rays were then tracked over space as the receiver, mounted on a mobile rover equipped with military-grade GPS, traversed 66 m while amassing a total of 488 channel acquisitions. The tracked rays were then mapped to rays predicted from ray-tracing, originating through specular reflection or diffuse scattering from ambient objects. The mapping enabled object-specific calibration, namely calibrating distinct diffuse-scattering models for buildings, vehicles, and foliage. To our knowledge, this is the first effort to calibrate ray-tracing with object-specific diffuse scattering models against rays individually mapped in the path gain, delay, angle, and space domains. Results, in terms of calibrated ray-tracing parameters, fit-error statistics, and lessons learned, are included. Our chief finding was that, while most papers on millimeter-wave ray-tracing do not even consider diffuse scattering, it accounted for 20% of the total received power, whereas diffraction accounted for less than 1%.