RMS Delay Spread Research Articles

Low‐altitude UAV air‐ground propagation channel measurement and analysis in a suburban environment at 3.9 GHz

Unmanned aerial vehicles (UAVs) have been applied to various promising applications because of their features of high-mobility, portability, rapid deployment, and modest power consumption. Small UAVs fly at low altitudes and typically short distances from the ground controller. It is of interest and value to model the propagation channel between low-altitude UAVs and ground stations. This article presents results of channel measurements at 3.9 GHz carried out in a suburban environment with a small-size UAV flying at low altitudes, up to 40 m. The authors also present comparative results from ray-tracing simulations. Height-dependent models for path loss, root mean square (RMS) delay spread, and the number of multipath components are provided. The results illustrate that although multipath effects exist at low altitudes in this environment, the two-ray path loss model works reasonably well in describing the channel behaviour. Initial ray tracing simulations show reasonable agreement with measurements. In addition, RMS delay spread results indicate that distant scatterers have an appreciable effect on the UAV air-ground (AG) propagation channels, which can be different from some terrestrial channels. Authors' results should be of use in the modelling of low-altitude AG propagation channels and in the performance analysis of UAV-enabled AG communication systems.

Stochastic Multipath Model for the In-Room Radio Channel Based on Room Electromagnetics

We propose a stochastic multipath model for the received signal for the case where the transmitter and receiver, both with directive antennas, are situated in the same rectangular room. This scenario is known to produce channel impulse responses with a gradual specular-to-diffused transition in delay. Mirror source theory predicts the arrival rate to be quadratic in delay, inversely proportional to room volume and proportional to the product of the antenna beam coverage fractions. We approximate the mirror source positions by a homogeneous spatial Poisson point process and their gain as complex random variables with the same second moment. The multipath delays in the resulting model form an inhomogeneous Poisson point process which enables derivation of the characteristic functional, power/kurtosis delay spectra, and the distribution of order statistics of the arrival delays in closed form. We find that the proposed model matches the mirror source model well in terms of power delay spectrum, kurtosis delay spectrum, order statistics, and prediction of mean delay and rms delay spread. The constant rate model, assumed in e.g. the Saleh-Valenzuela model, is unable to reproduce the same effects.

Experimental Analysis of Ultra-Wideband Body-to-Body Communication Channel Characterization in an Indoor Environment

This paper presents an experimental and analytical investigation of ultra-wideband (3-8 GHz) body-to-body (B-to-B) channel characterization. The channel parameters obtained are compared with off-body (off-B) and no-body (no-B) links. Measurements have been carried out considering different body positions and orientation of the Tx-Rx pair. The type of channel link and position of the wearable antenna lead to significant changes in the radio link channel. Path loss (PL) computed shows the increase in magnitude for non line of sight (NLOS) in comparison to line of sight (LOS), though the variation over a distance of 5 m is more significant for LOS (10 dB) than NLOS links (4-5 dB). For total NLOS links, B-to-B channels have slightly higher PL and delay spread parameters in comparison to off-B channel. The B-to-B LOS channels have least PL (44-56 dB), rms delay spread (0.5-4 ns), and multipath components (3-20) which can be attributed to the directional radiation pattern due to the presence of the human body for both Tx and Rx nodes. For back-to-back antenna orientation of the B-to-B channel, maximum signal strength degradation and multipath are observed. It can be concluded that for certain links, the B-to-B channel shows a significant change in channel behavior in comparison to off-B/no-B scenario.

Comparative Study of Indoor Propagation Model Below and Above 6 GHz for 5G Wireless Networks

It has been widely speculated that the performance of the next generation based wireless network should meet a transmission speed on the order of 1000 times more than the current cellular communication systems. The frequency bands above 6 GHz have received significant attention lately as a prospective band for next generation 5G systems. The propagation characteristics for 5G networks need to be fully understood for the 5G system design. This paper presents the channel propagation characteristics for a 5G system in line of sight (LOS) and non-LOS (NLOS) scenarios. The diffraction loss (DL) and frequency drop (FD) are investigated based on collected measurement data. Indoor measurement results obtained using a high-resolution channel sounder equipped with directional horn antennas at 3.5 GHz and 28 GHz as a comparative study of the two bands below and above 6 GHz. The parameters for path loss using different path loss models of single and multi-frequencies have been estimated. The excess delay, root mean square (RMS) delay spread and the power delay profile of received paths are analyzed. The results of the path loss models show that the path loss exponent (PLE) in this indoor environment is less than the free space path loss exponent for LOS scenario at both frequencies. Moreover, the PLE is not frequency dependent. The 3GPP path loss models for single and multi-frequency in LOS scenarios have good performance in terms of PLE that is as reliable as the physically-based models. Based on the proposed models, the diffraction loss at 28 GHz is approximately twice the diffraction loss at 3.5 GHz. The findings of the power delay profile and RMS delay spread indicate that these parameters are comparable for frequency bands below and above 6 GHz.

A 3D Non-Stationary Wideband GBSM for Low-Altitude UAV-to-Ground V2V MIMO Channels

Due to the high-mobility of unmanned aerial vehicles (UAVs), actual UAV channel measurements show that low-altitude air-to-ground (A2G) channels in UAV communications illustrate non-stationary properties. This fact motivates us to develop a non-stationary channel model for UAV-to-ground links. In this paper, we propose a three-dimensional (3D) wideband non-stationary A2G vehicle-to-vehicle (V2V) geometry-based stochastic channel model (GBSM). In the proposed model, both UAVs and ground terminals can be moving, which makes the model more general. In order to mimic the non-stationary channel characteristics, parameters like the number of clusters, power, time delays, angels of departure (AoDs), and angles of arrival (AoAs) are all time-variant. The proposed model combining a line-of-sight (LoS) component, a ground reflection component, a cylinder model, and multiple confocal truncated ellipsoid models has the ability to investigate the impact of UAV heights and transceivers' movements on channel characteristics in diverse environments. Statistical properties like temporal autocorrelation function (ACF), spatial cross-correlation function (CCF), Doppler power spectral density (PSD), and stationary interval of A2G channels are derived and analyzed in detail. In addition, derived root mean square delay spread (RMS-DS), temporal ACF and spatial CCF are validated against channel measurement results. Furthermore, by adjusting channel parameters, the proposed GBSM is sufficiently generic and adaptable to model various UAV-to-ground communication scenarios.

Vehicle-to-Vehicle Propagation Channel Performance for Overtaking Cases Based on Measurements

Overtaking case is a common traffic situation, but it is likely to pose a threat to traffic safety. To ensure reliable communication, it is necessary to study the characteristics of wireless channel under overtaking cases. In this paper, we focus on Vehicle-to-Vehicle (V2V) radio channel characteristics based on measurements at 5.9GHz. Through research and analysis, we can present empirical results of propagation channels in four scenarios. Our main concern is the difference in channel characteristics between overtaking and non-overtaking case. We propose a method to divide overtaking cases and non-overtaking cases points based on small-scale fading distribution, and results show that the dividing point is about 11 meters between the measured vehicles. Judging by Akaike Information Criterion(AIC), Weibull distribution is best under overtaking cases, while it follows Ricean distribution under non-overtaking. Then, we prove that the result of the AIC decision is valid by the Kolmogorov-Smirnov test. Therefore, we further compare Weibull $\beta $ -factor and Ricean K-factor under two cases. The values of root-mean-square (RMS) delay spreads and average fade duration under overtaking cases are higher than those under non-overtaking, but RMS Doppler spreads and the level crossing rate are smaller than those under non-overtaking. The cross-correlation between RMS delay spread and Ricean K-factor is also calculated. The correlation value in OT case is higher than that in NOT case. The value of the correlation in the case of overtaking is higher than the case of non-overtaking. By comparing the above methods, it is proved that the dividing point between overtaking cases and non-overtaking cases is effective.

Position-Specific Statistics of 60 GHz Vehicular Channels During Overtaking

The time-variant vehicle-to-vehicle radio propagation channel in the frequency band from 59.75 to 60.25 GHz has been measured in an urban street in the city center of Vienna, Austria. We have measured a set of 30 vehicle-to-vehicle channel realizations to capture the effect of an overtaking vehicle. Our experiment was designed for characterizing the large-scale fading and the small-scale fading depending on the overtaking vehicle’s position. We demonstrate that large overtaking vehicles boost the mean receive power by up to 10 dB. The analysis of the small-scale fading reveals that the two-wave with diffuse power (TWDP) fading model is adequate. By means of the model selection, we demonstrate the regions where the TWDP model is more favorable than the customarily used the Rician fading model. Furthermore, we analyze the time selectivity of our vehicular channel. To precisely define the Doppler and delay resolutions, a multitaper spectral estimator with discrete prolate spheroidal windows is used. The delay and Doppler profiles are inferred from the estimated local scattering function. Spatial filtering by the transmitting horn antenna decreases the delay and Doppler spread values. We observe that the RMS Doppler spread is below one-tenth of the maximum Doppler shift 2f v/c. For example, at 60 GHz, a relative speed of 30 km/h yields a maximum Doppler shift of approximately 3300 Hz. The maximum RMS Doppler spread of all observed vehicles is 450 Hz; the largest observed RMS delay spread is 4 ns.

28-GHz Channel Characterization for a Short Tunnel

This letter investigates the channel propagation characterization in a short tunnel through a time-domain channel measurement at 28-GHz frequency band. The statistic parameters of the channel, such as root-mean-square delay spread (RMS-DS), K-factor, and shadowing are studied, and the results reveal that the parameters align better to the normal distribution. RMS-DS is positively correlated with the shadowing but negatively correlated with the K-factor. We also deduced that the K-factor is negatively correlated with the shadowing. From the angular measurements, it is inferred that the signal propagation in the tunnel is around 0° and 180° directions, and the maximum number of reflections at 30 and 75 m are 6 and 8, respectively. Furthermore, it is found that the angular spread pursues a decreasing function of transmitter-receiver distance.

Novel Device Reproduce In-Vehicle Wireless Multipath Radio Channels

This paper describes and evaluates a new test facility able to generate different wireless multipath radiocommunication channels. It is used to recreate various electromagnetic (EM) environments, such as those inside vehicles. This test facility, in the form of a moderate volume metallic chamber, contains apertures, left opened or obstructed as required, and a variable quantity of salt water. Both are used to adjust the EM losses and to control smoothly and accurately the delay spread of the communication channel inside the test facility. A frequency range between 2 and 3 GHz is studied. As a first step, the root-mean-square (rms) delay spread is measured inside a vehicle for several locations of the receiving antenna and for different scenarios including different line-of-sight and non-line-of-sight paths. Then, the test facility is introduced, dimensioned, and evaluated, trying to reproduce the rms delay spread of each previous in-vehicle radiocommunication configuration. A comparison between the measurement data performed both in the vehicle and in the configured test facility is presented. This comparison shows a good agreement between these two sets of measurements. It demonstrates that different static wireless in-vehicle multipath channels, corresponding to various transmitting and receiving antenna configurations, can be reproduced inside the proposed prototype test facility.

Sum Rate Maximization With Shortened Cyclic Prefix in a MIMO-OFDM System

This correspondence paper addresses linear precoding design for sum rate maximization in low-latency orthogonal frequency-division multiplexing systems. In order to mitigate the overhead of cyclic prefix (CP) originating from shortened symbol duration for low-latency communications, 5G wireless systems need to adopt short CP lengths. As channel delay spread must be less than the CP length, we first derive the effective root-mean-square (RMS) delay spread and the achievable rate using the zero-forcing assumption. We construct a sum rate optimization problem for each user subject to delay spread constraints and then convert the problem into a solvable convex problem along with a semi-definite relaxation technique. The precoding matrix is finally obtained by solving optimization problems for all users. Numerical results reveal that the proposed scheme attains superior performance to the conventional sum rate optimization, as well as small RMS delay spread.

A 2-D Non-Stationary GBSM for Vehicular Visible Light Communication Channels

In this paper, a new non-stationary regular-shaped geometry-based stochastic model (RS-GBSM) is proposed for vehicular visible light communications (VVLC) channels. The proposed model utilizes a combined two-ring model and a confocal ellipse model, in which the received optical power is constructed as a sum of single-bounced (SB) and double-bounced (DB) components, in addition to the line-of-sight (LoS) component. Using the proposed RS-GBSM, the channel impulse response is generated and utilized to investigate VVLC channel characteristics, such as channel gain and root-mean-square (RMS) delay spread. The received optical power is computed considering the distance between the optical transmitter (Tx) and the optical receiver (Rx). Moreover, the impact of the Rx height on the received power is considered for the LoS scenario. The results show that the LoS power highly depends on the distance, Rx height, and the optical source pattern. For the SB components, it is confirmed that the channel gain in dB and the RMS delay spread follow Gaussian distributions. Finally, the results indicate that the detected optical power from the DB components is low enough to be overlooked.

Parallel Channel Sounder for MIMO Channel Measurements

In order to address the challenges in MIMO channel measurement and modeling for 5G communication scenarios, a CDM-based parallel channel sounder is developed and evaluated in this article. Compared to traditional TDM-based channel sounders, our parallel channel sounder supports eight-by-eight (8 x 8) MIMO communications, 200 MHz RF bandwidth, 5 ns multipath time resolution, 36 dB dynamic range, and 2 kHz maximum Doppler shift at a speed of 350 km/h. To achieve these performance targets, a series of sophisticated technical solutions are proposed and analyzed to realize 32 ps synchronization accuracy, 51.36 Gb/s parallel data streaming, and high-precision calibration across multiple channels. Key functions and performance metrics are evaluated and verified in a microwave chamber. Real measurement results in a complex campus environment show that our CDM-based parallel channel sounder can capture more detailed channel characteristics, and therefore offer accurate PDPs and RMS delay spreads at both LoS and NLoS positions under MIMO communication scenarios.

Modeling of Path Arrival Rate for In-Room Radio Channels With Directive Antennas

We analyze the path arrival rate for an inroom radio channel with directive antennas. The impulse response of this channel exhibits a transition from early separate components followed by a diffuse reverberation tail. Under the assumption that the transmitter's (or receiver's) position and orientation are picked uniformly at random we derive an exact expression of the mean arrival rate for a rectangular room predicted by the mirror source theory. The rate is quadratic in delay, inversely proportional to the room volume, and proportional to the product of beam coverage fractions of the transmitter and receiver antennas. Making use of the exact formula, we characterize the onset of the diffuse tail by defining a "mixing time" as the point in time where the arrival rate exceeds one component per transmit pulse duration. We also give an approximation for the power-delay spectrum. It turns out that the power-delay spectrum is unaffected by the antenna directivity. However, Monte Carlo simulations show that antenna directivity does indeed play an important role for the distribution of instantaneous mean delay and rms delay spread

Impact of Body Mass Index on Ultrawideband MIMO BAN Channels—Measurements and Statistical Model

Wireless body area networks (BANs) have many important applications such as wearable communication devices and Internet of Things. Wireless propagation in on-body channels has been measured and modeled in the past. However, a crucial element that is usually ignored is the impact of the body size of the user—a 50-kg person obviously creates a different on-body channel than a 150-kg person. The status-quo “one-size-fits-all” approach to channel characterization in BAN is thus incomplete. In this paper, we provide a detailed description of a propagation measurement campaign that employs a self-developed $4 \times 4$ ultrawideband multiple-input-multiple-output array channel sounding system to perform BAN channel sounding both in an anechoic chamber and indoor laboratory environments. A total of 60 human subjects were investigated in our work. These human subjects had widely varying body mass index (BMI) values, which were grouped into three different categories, i.e., 20 per BMI category. Various propagation properties such as path gain, frequency-decay factor, shadowing gain, rms delay spread, amplitude fading, and spatial correlation are extracted for each on-body channel under consideration. A comparison of statistics among the BMI categories reveals considerable differences, emphasizing the fact that the aforementioned propagation properties are BMI dependent. Parameters such as path gain showed a monotonic decrease across the BMI categories with values ranging from 1–2 to almost 13 dB in some channels. This paper proposes a propagation channel model for the BMI-dependent parameters and validates that it can reproduce the measured channel capacities.

Wireless Channel Measurements and Modeling of LTE Broadband System for High‐Speed Railway Scenarios

In high-speed scenarios, channel model is of vital importance in Long term evolution (LTE) systems. By extensive measurements on Beijing-Tianjinrailway, this paper proposes a distance-dependent channel model. Both large-scale and small-scale channel characteristics are presented in detail. The large-scale path loss is modeled under the hierarchical network structure. Small-scale channel characteristics that include channel impulse response, power delay profile and Doppler spectrum are deduced and analyzed. In particular, a new stage-wise K-factor model is proposed. Combined with the cumulative distribution function of Root-mean squared (RMS) delay spread and the number of paths, they clearly illustrate the distancedependent variances of the channel. Finally, the integrated distance-dependent channel models are proposed to give a comprehensive description of broadband LTE channel in high-speed railway scenario.

Improvement of Channel Models Performance With Parameters Values From Measurements: A Test Case for Suburban and Rural Environments at 450 MHz

In this letter, we derive three new combined parameter sets focused on the LTE band 31 of 450 MHz, which include items from existing well-established channel models and from published measurement campaigns. These sets are used in a geometrically based stochastic channel model, and the simulation results are compared with those obtained by using their own sets of model parameters as well as with other measurements for the same frequency, for neighboring frequencies, and more extended frequency ranges. After the parameterization of the channel model and the setup of the network layout, which includes the base station, the mobile station multiple-input–multiple-output antennas, and the mobile station's track, the time or spatially varying channel coefficients and delays at the receiver's side were extracted. These values allow the computation of some crucial propagation parameters, like RMS delay spread, Ricean K-factor, and shadow fading. The presented results prove that better values for the above parameters are taken, which are in closer agreement with values from measurements campaigns.

Propagation Path Loss Modeling and Outdoor Coverage Measurements Review in Millimeter Wave Bands for 5G Cellular Communications

The global bandwidth inadequacy facing wireless carriers has motivated the exploration of the underutilized millimeter wave (mm-wave) frequency spectrum for future broadband cellular communication networks, and mmWave band is one of the promising candidates due to wide spectrum. This paper presents propagation path loss and outdoor coverage and link budget measurements for frequencies above 6 GHz (mm-wave bands) using directional horn antennas at the transmitter and omnidirectional antennas at the receiver. This work presents measurements showing the propagation time delay spread and path loss as a function of separation distance for different frequencies and antenna pointing angles for many types of real-world environments. The data presented here show that at 28 GHz, 38 GHz and 60 GHz, unobstructed Line of Site (LOS) channels obey free space propagation path loss while non-LOS (NLOS) channels have large multipath delay spreads and can utilize many different pointing angles to provide propagation links. At 60 GHz, there is more path loss and smaller delay spreads. Power delay profiles PDPs were measured at every individual pointing angle for each TX and RX location, and integrating each of the PDPs to obtain received power as a function of pointing angle. The result shows that the mean RMS delay spread varies between 7.2 ns and 74.4 ns for 60 GHz and 28 GHz respectively in NLOS scenario.

Outdoor Wideband Channel Measurements and Modeling in the 3–18 GHz Band

Fifth generation cellular systems will operate in a wide range of frequencies, covering both the traditional cellular bands, and mm-wave frequency bands, either selecting a specific band or operating in multiple bands simultaneously. For the design of such systems, a detailed understanding of the frequency dependence of the propagation channel is essential. While many channel measurements exist in either microwave bands ( 20 GHz), the results are not easily comparable, and furthermore the transition between these bands is not well studied. This paper aims to bridge the gap by providing the results from a channel measurement campaign conducted in urban macro and micro-cellular environments, over the continuous frequency band of 3–18 GHz. We characterize the pathloss, shadow fading, root-mean-square (RMS) delay spreads, Ricean factor and coherence bandwidth in urban macro-cellular and urban micro-cellular environments. Measurements were taken in both line-of-sight (LOS) and non-line-of-sight (NLOS) environments. The pathloss exponents and the RMS delay spreads increase with the base station height in NLOS environment; but not much dependency is observed in the LOS environment. By dividing the wideband channel transfer function into subbands of 1 GHz each, we study the frequency dependence of pathloss, shadow fading, Ricean factor, delay spread, and coherence bandwidth in the 3–18 GHz band. The pathloss exponents vary significantly with frequency, but not-monotonically. The shadow fading and the Ricean factor increase with frequency. The RMS delay spreads decrease with frequency in the LOS environments, but they do not change significantly in the NLOS environments. The coherence bandwidth values do not change significantly with frequency in either environment.

Hough-Transform-Based Cluster Identification and Modeling for V2V Channels Based on Measurements

In this paper, a recently conducted measurement campaign for vehicle-to-vehicle (V2V) propagation channel characterization is introduced. Two vehicles carrying a transmitter and a receiver, respectively, have been driven along an eight-lane road with heavy traffic. The measurement was conducted with 100 MHz signal bandwidth at a carrier frequency of 5.9 GHz. Channels are observed consisting of two kinds of channel components, i.e., time-evolving clusters and clutter paths. A novel approach based on Hough transform is proposed to identify the clusters. Based on the cluster identification results, channel characteristics in composite, intracluster, and time-variant levels are analyzed. The parameters investigated include the composite root-mean-square (RMS) delay spreads and power decay versus delay behaviors of clusters and clutter paths, cluster RMS delay spread, cluster RMS Doppler frequency spread, correlations of cluster parameters, and coherence time of parameters of interest. The statistics constitute an empirical stochastic clustered-delay-line channel model focusing on the wideband characteristics observed in the realistic time-variant V2V propagation scenario.

Indoor wideband directional millimeter wave channel measurements and analysis at 26 GHz, 32 GHz, and 39 GHz

AbstractThis paper presents details of the wideband directional propagation measurements of millimeter‐wave (mmWave) channels in the 26 GHz, 32 GHz, and 39 GHz frequency bands in an indoor typical office environment. More than 14 400 power delay profiles (PDPs) were measured across the 26 GHz band and over 9000 power delay profiles have been recorded for the 32 GHz and 39 GHz bands at each measurement point. A mmWave wideband channel sounder has been used, where signal analyzer and vector signal generator were employed. Measurements have been conducted for both co and cross‐antenna polarization. The setup provided 2 GHz bandwidth and the mechanically steerable directional horn antenna with 8 degrees beamwidth provides 8 degrees of directional resolution over the azimuth for 32 GHz and 39 GHz, whereas 26 GHz measurement setup provides the angular resolution of 5 degrees. Measurements provide path loss, delay, and spatial spread of the channel. Large‐scale fading characteristics, RMS delay spread, RMS angular spread, and angular and delay dispersion are presented for 3 mmWave bands for the line‐of‐sight scenario.