This contribution provides experimental evidence for the two-wave with diffuse power (TWDP) fading model. We have conducted two indoor millimetre wave measurement campaigns with directive horn antennas at both link ends. One horn antenna is mounted in a corner of our laboratory, while the other is steerable and scans azimuth and elevation. Our first measurement campaign is based on scalar network analysis with 7 GHz of bandwidth. Our second measurement campaign obtains magnitude and phase information, additionally sampled directionally at several positions in space. This second measurement campaign is limited to 2 GHz bandwidth. We apply Akaike's information criterion to decide whether Rician fading sufficiently explains the data or the generalized TWDP fading model is necessary. Our results indicate that the TWDP fading hypothesis is favoured over Rician fading in situations where the steerable antenna is pointing towards reflecting objects or is slightly misaligned at line-of-sight. We demonstrate TWDP fading in several different domains, namely, frequency, space, and time.
TWDP fading has already successfully been applied to describe @math ,GHz near body shadowing @cite_11 . Furthermore, as quoted above, TWDP must be considered for arrays, as they act as spatial filters @cite_43 @cite_78 . While theoretical work on TWDP fading is already advanced @cite_32 @cite_51 @cite_79 @cite_36 @cite_13 @cite_52 @cite_83 , experimental evidence, especially at millimetre waves, is still limited. For enclosed structures, such as aircraft cabins and buses, the applicability of the TWDP model is demonstrated by Frolik @cite_38 @cite_21 @cite_34 @cite_9 @cite_53 . A deterministic two ray behaviour in ray tracing data of mmWave train-to-infrastructure communications is shown in @cite_85 . A further extension of the TWDP -fading model, the so called fluctuating two-ray fading model, was also successfully applied to fit mmWave measurement data @cite_13 .
@cite_13 @cite_38 @cite_78 @cite_36 @cite_9 @cite_21 @cite_53 @cite_32 @cite_52 @cite_85 @cite_43 @cite_79 @cite_83 @cite_34 @cite_51 @cite_11
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Recent work presented empirical data for which the small-scale fading statistics were more severe than Rayleigh; a phenomena deemed hyper-Rayleigh fading. This paper considers whether commonly utilized small-scale propagation models can be appropriately adapted to represent this class of fading. The work argues that the most meaningful model for the hyper- Rayleigh regime is based on a physical wave model (as opposed to stochastic); in particular, the TWDP model, where Deltaap1, holds the greatest promise. The crux of the argument is that the stochastic models significantly over-predict the amount of constructive interference in comparison to what is physically realizable. This paper presents outdoor wideband small-scale spatial fading and autocorrelation measurements and results in the 73 GHz millimeter-wave (mmWave) band conducted in downtown Brooklyn, New York. Both directional and omnidirectional receiver (RX) antennas are studied. Two pairs of transmitter (TX) and RX locations were tested with one line-of-sight (LOS) and one non-line-of-sight (NLOS) environment, where a linear track was employed at each RX to move the antenna in half-wavelength increments. Measured data reveal that the small-scale spatial fading of the received signal voltage amplitude are generally Ricean-distributed for both omnidirectional and directional RX antenna patterns under both LOS and NLOS conditions in most cases, except for the log-normal distribution for the omnidirectional RX antenna pattern in the NLOS environment. Sinusoidal exponential and typical exponential functions are found to model small-scale spatial autocorrelation of the received signal voltage amplitude in LOS and NLOS environments in most cases, respectively. Furthermore, different decorrelation distances were observed for different RX track orientations, i.e., for different directions of motion relative to the TX. Results herein are valuable for characterizing small-scale spatial fading and autocorrelation properties in multiple-input multiple-output (MIMO) systems for fifth-generation (5G) mmWave frequencies. This work is motivated by the problem of characterizing small-scale radio propagation environments for wireless sensor networks. If sensors are statically deployed near the ground or within structures, temporal fading may not exist but the channel may nevertheless experience severe frequency-selective behavior. The work presents real-world, frequency-selective fading data measured for in-vehicle wireless sensor applications. This fading data often exhibit statistics more severe than predicted by the Rayleigh fading model; a scenario referred herein as to as being hyper-Rayleigh. A two-ray, small-scale model is proposed as a new worst-case for this application space. A two-ray, small-scale fading model was recently proposed as a worst-case fading scenario for certain wireless sensor applications. Empirical data motivated this development for fading was found to be more severe than predicted by Rayleigh fading statistics, a behavior referred to as hyper-Rayleigh fading. Based on the two-ray model, we study the benefits of M-branch diversity in the context of signal-to-noise ratio (SNR) and bit-error rate (BER) performance metrics. While these results are well-known for Rayleigh fading, this work is the first analysis of diversity for the hyper-Rayleigh regime.