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This paper describes the implementation of a Doppler spectrum measurement platform for narrowband frequency-dispersive vehicle-to-vehicle (V2V) channels. The platform is based on a continuous-wave (CW) channel sounding approach widely used for path-loss and large-scale fading measurements, but whose effectiveness to measure the Doppler spectrum of...
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... Scenario #1: Road sections that pass through mountain cutouts. In these sections, tall and long rock walls carved through the mountain are found on both sides of the road. Some of the walls are long enough to flank both vehicles at the same time, as illustrated in Fig. 9(a), whereas others are shorter and border only one vehicle at a time, as shown in Fig. 9(b). The rock walls have a slight inclination, and produce strong multipath around the transmitter and/or the receiver. Multipath stemming from double scattering or double reflections is possible in this scenario, as discussed in the following ...
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... #1: Road sections that pass through mountain cutouts. In these sections, tall and long rock walls carved through the mountain are found on both sides of the road. Some of the walls are long enough to flank both vehicles at the same time, as illustrated in Fig. 9(a), whereas others are shorter and border only one vehicle at a time, as shown in Fig. 9(b). The rock walls have a slight inclination, and produce strong multipath around the transmitter and/or the receiver. Multipath stemming from double scattering or double reflections is possible in this scenario, as discussed in the following subsection. Some of these road sections also pass under bridges, e.g., see Fig. 10. These ...
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... sections with sharp curves bordered by steep mountain walls. These curved sections are interesting since the walls can hinder a prompt visual detection of oncoming vehicles, as in the scenario shown in Fig. 11(b). Furthermore, such sharp curves can obstruct the LOS path between communicating vehicles. This latter situation is illustrated in Fig. 9(b), where the receiver is about to lose LOS contact with the transmitter as both vehicles take a long curve stretch that passes through a mountain cutout. During the experiments, we observed LOS blockages also in straight sections of the road. These blockages were caused by vehicles of large dimensions that found themselves momentarily ...
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... 18 presents three pictures of this event captured by the transmitter's video camera at the time instants at which: the reflection from the oncoming truck was detected (Fig. 18(a)), the truck and the receiver were side by side (Fig. 18(b)), and the truck was driving away and the reflected signal was about to disappear (Fig. 18(c)). Figure 19 shows the corresponding Doppler spectra of these three time instants. We can observe from Figs. 17 and 19 that the reflection of the oncoming truck produces a tall spectral spike that commutes from an initial positive frequency of around 250 Hz to a negative frequency of −250 Hz. ...
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Vehicular communication based visible light presents an excellent solution to ensure road safety and transportation efficiency in critical environments like tunnels, underground garages, or covered parking lots where traditionally RF solutions cannot provide an efficient communication. In this paper, we propose a new multipath channel model for V2V...
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... For our measurement experiments, we employed a CW channel-sounding platform as the one described in [29] to mimic the transmission and reception of an unmodulated pilot signal. The platform comprises a transmitting station with an RF signal generator that transmits a CW probe signal using a half-wave dipole antenna at a central frequency of 2.5 GHz. ...
... One of the alternatives is to measure the impact that a different configuration has on the hardware of our platform. Our detection system operates as a narrow-band channel-sounding platform with low spectral resolution [29]. We have considered that reconfigurable systems such as software-defined radios (SDR) can help our system adapt to the conditions of different real-world scenarios, such as rural roads. ...
This paper presents the idea of an automatic head-on-collision warning system based on a decentralized radio sensing (RS) approach. In this framework, a vehicle in receiving mode employs a continuous waveform (CW) transmitted by a second vehicle as a probe signal to detect oncoming vehicles and warn the driver of a potential head-on collision. Such a CW can easily be incorporated as a pilot signal within the data frame of current multicarrier vehicular communication systems. Detection of oncoming vehicles is performed by a machine learning (ML) module that analyzes the features of the Doppler signature imprinted on the CW probe signal by a rapidly approaching vehicle. This decentralized CW RS approach was assessed experimentally using data collected by a series of field trials conducted in three different two-lane vehicular scenarios: a high-speed highway, a rural road, and an urban road. Detection performance was evaluated for three different ML algorithms: a support vector machine radial basis function kernel,
K
-nearest neighbors, and Boosted Trees. The obtained results demonstrate the feasibility of the envisioned head-on-collision warning system based on the fusion of ML and decentralized CW RS.
... These factors cause the systems based on orthogonal frequency division multiplexing (OFDM) to suffer from a severe problem known as intercarrier interference (ICI) [5][6][7]. In V2V communication systems, the ICI is accentuated by the high Doppler spread frequencies caused by the high mobility in the vehicular links [5,[8][9][10][11]. ICI severely degrades the overall performance of OFDM-V2V systems, making channel estimation, data detection, and error correction tasks extremely challenging. ...
This paper examines the performance of orthogonal frequency division multiplexing (OFDM) systems for vehicle-to-vehicle (V2V) communication channels. More specifically, a doubly selective channel under high intercarrier interference (ICI) is considered. Current solutions involve complex detection and/or reduced spectral efficiency receivers. This paper proposes the use of virtual carriers (VC) in an OFDM system with a low-complexity maximal ratio combining (MRC) detector to improve the bit error rate (BER) performance. The results show that VC provides diversity in received data, resulting in a ≥5 dB gain compared to previous OFDM systems with conventional linear/nonlinear detectors used as a reference. The detector presented in this paper has linear complexity, making it a suitable solution for real-time V2V communication systems.
... In V2V scenarios with high mobility and multipath propagation, two significant factors come into play: the Doppler effect caused by high mobility and the delay spread caused by multipath propagation. When both phenomena impact the received signal, it leads to the so-called dual selective channel (DSC) [8,9]. ...
... Substituting the channel for its BEM in (9) and considering only Tx-Rx coupling yields the expression: ...
Vehicle-to-vehicle (V2V) communication networks are based on vehicles that wirelessly exchange data, traffic congestion, and safety warnings between them. The design of new V2V systems requires increasingly energetically and spectrally efficient systems. Conventional multiple-input–multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems have been used successfully for the last decade. However, MIMO-OFDM systems need to be improved to face future communication networks in high-mobility environments. This article proposes an efficient index modulation (IM)-based MIMO-OFDM system for V2V channels. The proposed transmission system is evaluated in high Doppler-spread channels. The results demonstrate that the proposed scheme reduces the required computational complexity in data detection and exhibits gains of up to 3 dB in bit error rate (BER) performance when compared to the conventional MIMO-OFDM system under the same conditions and parameters, along with achieving superior spectral efficiency. The results show the viability of implementing the proposed system in practical applications for high-transmission-rate V2V channels.
... V2V channel sounding campaigns in various scenarios (urban, suburban, parking garage, highway, intersections) were primarily restricted to frequencies below 6 GHz [4]- [8]. In [9] the authors performed a measurement campaign using directional antennas both at the transmitter and the receiver, and fixed them at a low elevation position on the car bumpers for V2V communications at 38 GHz and 60 GHz frequency bands. ...
Fifth generation new radio (5G NR) is now offering sidelink capability, which allows direct vehicle-to-vehicle (V2V) communication. Millimeter wave (mmWave) enables low-latency mission-critical V2V communications, such as forward crash warning, between two vehicles crossing on a road without dividers. In this article, we present a measurement-based path loss (PL) model for V2V links operating at 59.6 GHz mmWave when two vehicles approach from opposite sides and cross each other. Our model outperforms other existing PL models and can reliably model both approaching and departing vehicle scenarios.
... The statistics of the envelope distributions were not analyzed, nor those of the IMDS and IDS. In addition, this paper complements the work of [32], where the Doppler shift statistics of V2V channels at 760 and 2,500 MHz in a mountainous highway are investigated empirically. ...
... The value of N fft is equal to the length of the discrete Fourier transform employed to estimate the Doppler spectrum. To establish a correspondence between the results of the small-scale envelope distribution and those of the instantaneous Doppler shift, we define N fft = 2 log 2 K Q , (32) where K Q is given by (30). The number of blocks in the partition of g m is therefore obtained as ...
... The effects of Doppler dispersion due to multipath propagation by reflections off the rock walls surrounding the roads in SLP can therefore be regarded as mild. In fact, a com-parison with the results presented in [32] for the IDS statistics at 760 MHz and 2,500 MHz in the scenarios SLP3 and SLP4, shows that increasing the carrier frequency diminishes the effectiveness of multipath propagation by reflections off rocky surfaces, as is to be expected. On the other hand, the mean and standard deviation of D ν obtained for the Utah location show a larger signal dispersion due to multipath propagation, which can be explained by the dense vegetation present at both sides of the roads in the Utah State Route 92. ...
Abstract: Land transportation of people and goods often relies on strategic routes that pass through mountains. Despite the importance of these routes, the characteristics of the vehicular radio communication channel in such environments have received little attention. To close the gap, this paper presents the results of a measurement campaign at 5.9 GHz in mountainous roads. Data collected during the measurement campaign were used to quantify the envelope distribution and Doppler spectrum of small-scale vehicle-to-vehicle (V2V) communication channels. The measurements were taken in three different locations, two in San Luis Potosí (SLP), México, and one near Provo, Utah, USA. The locations in SLP are shrubland areas, whereas that in Utah is a coniferous forest. The diverse mountainous environments observed during the experiments were classified into five reference propagation scenarios. For each reference scenario the empirical channel envelope distribution was computed and compared with previously-published theoretical models based on the Rice, Nakagami, Weibull, and Gamma distributions. The Rice model provided the best fitting in 72.3% of the analyzed cases, whereas the Nakagami, Weibull and Gamma distributions were the best option in the remaining 11.3%, 14.9% and 1.3%, respectively. Likewise, the empirical distributions of the instantaneous mean Doppler shift (IMDS) and instantaneous Doppler spread (IDS) were computed. The results show that the IMDS follows the Generalized Extreme Value and Logistic distributions, whereas the Birnbaum-Saunders, Exponential, Burr and Nakagami distributions are proper models for the IDS. Our analysis also shows that the line-of-sight (LOS) path is the dominant factor for V2V communication in mountainous terrain, especially in roads surrounded by rocky structures with sparse vegetation. However, the contribution of non-LOS paths is not negligible, and it appears capable of supporting short intervals of communication. The results presented here can be used as guidelines for the analytical modeling and computer simulation of small-scale V2V channels in mountainous environments.
... However, these signals are subject to frequency dispersions caused by the Doppler effect. Such frequency dispersions are known as Doppler signatures and have been widely used for sensing purposes [8][9][10]. The Doppler signatures produced by the interaction of the CW probe signal with a moving person can be analyzed to characterize falling events. ...
Falling events are a global health concern with short- and long-term physical and psychological implications, especially for the elderly population. This work aims to monitor human activity in an indoor environment and recognize falling events without requiring users to carry a device or sensor on their bodies. A sensing platform based on the transmission of a continuous wave (CW) radio-frequency (RF) probe signal was developed using general-purpose equipment. The CW probe signal is similar to the pilot subcarriers transmitted by commercial off-the-shelf WiFi devices. As a result, our methodology can easily be integrated into a joint radio sensing and communication scheme. The sensing process is carried out by analyzing the changes in phase, amplitude, and frequency that the probe signal suffers when it is reflected or scattered by static and moving bodies. These features are commonly extracted from the channel state information (CSI) of WiFi signals. However, CSI relies on complex data acquisition and channel estimation processes. Doppler radars have also been used to monitor human activity. While effective, a radar-based fall detection system requires dedicated hardware. In this paper, we follow an alternative method to characterize falling events on the basis of the Doppler signatures imprinted on the CW probe signal by a falling person. A multi-class deep learning framework for classification was conceived to differentiate falling events from other activities that can be performed in indoor environments. Two neural network models were implemented. The first is based on a long-short-term memory network (LSTM) and the second on a convolutional neural network (CNN). A series of experiments comprising 11 subjects were conducted to collect empirical data and test the system’s performance. Falls were detected with an accuracy of 92.1% for the LSTM case, while for the CNN, an accuracy rate of 92.1% was obtained. The results demonstrate the viability of human fall detection based on a radio sensing system such as the one described in this paper.
... One of the main critical issues to be considered when evaluating the performance of V2X communications is the characterization of their fading channels [11,12]. Unlike the traditional wireless communication systems with stationary terminals, fading channels in V2X communications are non-stationary due to the motion of vehicular terminals [11][12][13][14]. ...
... One of the main critical issues to be considered when evaluating the performance of V2X communications is the characterization of their fading channels [11,12]. Unlike the traditional wireless communication systems with stationary terminals, fading channels in V2X communications are non-stationary due to the motion of vehicular terminals [11][12][13][14]. Hence, the classical random distributions, such as Rayleigh, Rician or Nakagami-m, cannot be adopted directly in V2X communications without the proper modification needed to reflect the effects inherited by the vehicular motion. ...
A vehicular Rayleigh fading communication system in which a vehicular transmitter (VT) is communicating with a vehicular receiver (VR) only through a dedicated stationary amplify-and-forward (AF) relaying roadside unit (RSU) is proposed in this paper (i.e., V2RSU2V system). To capture the effect of VT and VR motion, system's fading channels from VT to RSU and from RSU to VR are modeled to be time-varying in accordance with the first order autoregressive model. For the sake of performance comparison, the three common AF relaying sub-schemes are adopted at the RSU relay in separate scenarios; namely, the optimal channel-state-information-and-noise-assisted variable-gain (CSIN-VG) sub-scheme, the blind fixed-gain (B-FG) sub-scheme, and the semi-blind fixed-gain (SB-FG) sub-scheme. Under these AF relaying sub-schemes, closed-form expressions for outage probabilities are derived. The derived expressions are given in terms of variant vehicular system and channel parameters and can be directly considered for the special scenario of stationary VT and VR. Numerical and simulation results are reported to validate the analytical work and to reveal new insightful guidelines into vehicular systems outage performance. For example, results reveal that, for low average signal-to-noise-ratio (SNR) per symbol values, the SB-FG sub-scheme is superior in terms of outage performance for all vehicular scenarios and all threshold SNR values. As well, at high per-symbol average SNR values, results illustrate that the CSIN-VG sub-scheme is superior for high threshold SNR values, while the SB-FG is superior for low threshold SNR values. The study in this paper is timely due to the rapid advancements towards autonomous vehicles and smart transportation networks.
A photonic architecture for remote multi-parameter measurement and transmission of microwave signals is proposed and demonstrated, which utilizes a dual-parallel dual-drive Mach-Zehnder modulator (DP-DDMZM) in the antenna unit and a dual-drive Mach-Zehnder modulator (DDMZM) in the processing unit. Doppler frequency shift (DFS) and angle of arrival (AOA) can be determined by analyzing the down-converted intermediate frequency signals. Introducing a reference signal in the processing unit ensures DFS measurement without directional ambiguity. The proposed architecture can also be applied for instantaneous frequency measurement based on down-conversion. Due to the use of optical single sideband modulation, long-distance transmission of radio frequency (RF) signals without dispersion-induced power fading can be achieved. Experiments for accurate and stable DFS and AOA measurement as well as long-distance RF signal transmission with dispersion-induced power fading are presented. The approach avoids the use of optical filters and polarization-related devices, facilitating wideband and stable operation, which is highly desirable. The proposed architecture is a potential solution for microwave photonic antenna remoting, offering support for both remote transmission and multi-parameter measurement.
This paper presents an experimental analysis of the depolarization effects that multipath propagation produces on radio-frequency (RF) signals. The analysis is based on the results of a measurement campaign conducted in a suburban scenario in the city of San Luis Potosí, México. Such a campaign collected empirical data of the instantaneous power and Doppler power spectrum (DPS) of an infrastructure-to-vehicle (I2V) channel at 2.45 GHz. The measured data were used to compute three different cross-polarization discriminators (XPD). One of such discriminators has been widely used in the literature to assess the power ratio between co-polarized and cross-polarized signals. The other two discriminators, which are based on the Doppler shift ratio and Doppler spread ratio, are introduced in this paper as new figures of merit to measure the impact of multipath depolarization on the frequency-dispersion characteristics of vehicular RF channels. The results demonstrate that the cross-polarized multipath components of the I2V channel response produce a Doppler frequency dispersion similar to that of the co-polarized components.
