Vehicle-to-vehicle (V2V) wireless communication systems are crucial for intelligent transportation applications such as traffic load control, autonomous vehicles, and collision avoidance. Therefore, it is essential to thoroughly understand the realistic V2V channel propagation conditions to develop suitable V2V communication systems and standards. However, due to high costs, most existing V2V studies focus on characterizing the vehicular channel theoretically and comparing it with simulation data or studying the empirical V2V channel in a specific scenario. In this work, we investigate the time variability of the received signal based on experimental data collected in an extensive measurement campaign at 5.9 GHz in a large set of propagation environments: urban-high traffic density, urban-low traffic density, suburban, highway, and rural environments. The time-variability of the received signal is characterized by time and frequency. The relationship between coherence time and the terminal velocity, coherence time and transmitter-receiver separation distance, and the relationship between Doppler spread and both effective velocity and separation distance, have been investigated. Furthermore, the correlation between coherence time and separation distance and effective velocity was investigated, as well as the correlation between Doppler spread and separation distance and effective velocity. The results provide a deeper understanding of the temporal variability of the channel and how it is influenced by factors such as traffic density, unique/multiple driving directions, terminal speed, separation distance, characteristics of the propagation environment, and visibility conditions. This knowledge is crucial for developing vehicular communication systems and can be applied to design strategies that reduce temporal variability in received signals.

In this paper, we present a narrowband power spectral density (PSD) estimation technique using a 40 MHz bandwidth channel sounder based on a lightweight and portable software-defined radio (SDR) platform. This setup is intended for the characterization of communication channels in unmanned aerial vehicle (UAV). A post-processing step using a finite impulse response (FIR) digital filter is compared with laboratory setups to verify its calibration. Tests were performed with a 1 MHz signal on carriers at 850 MHz and 3.5 GHz. In addition, the challenges of transmitting, receiving, and storing samples at a rate of 40 MS/s are discussed.

Metro and railway systems are one of the most used transportation systems for people in almost all countries. Nevertheless, the access to high throughput wireless services is still very limited inside the wagons (cars). A deep analysis of the wireless channel inside wagons is needed to deploy new efficient and high throughput networks as the ones provided by fifth-generation (5G) systems. Although several works have analyzed the intra-wagon channel, some limitations are usually present: only certain user equipment-access point situations were considered, the number of studied propagation mechanisms was limited, and only some channel parameters were extracted. For these reasons, in this work the wireless channel in an intra-wagon environment is thoroughly analyzed using simulations performed with a ray-tracing tool calibrated and validated with wideband measurements. Thanks to the accurate ray-tracing tool the main replicas are identified in different typical user equipment-access point positions; the contribution of each propagation mechanism to the total power is extracted; and the angular spread in azimuth and elevation for the direction of arrival and departure are obtained. This analysis is performed in the frequency range from 25 to 40 GHz, where spectrum for several 5G bands has been already allocated.

In this paper, the maximum achievable throughput is analyzed in the intra-wagon channel when multiple-input single-output (MISO) and orthogonal frequency division multiplexing (OFDM), MISO-OFDM, techniques are used. This analysis is performed from real wideband propagation channel measurements at 28 and 37 GHz, two potential frequency bands to deploy the future fifth-generation (5G) wireless communications networks. Four different scenarios in terms of the access point (AP) and user equipment (UE) positions inside the wagon have been considered, using 4 and 8 antennas at the AP. The performance of both quasi-orthogonal space-time block code (QSTBC), combined with Hadamard matrices, and transmit beamforming techniques is studied and evaluated from simulation results. The simulation results take into account the signal-to-noise ratio (SNR) and the antenna correlation for each antenna array configuration at the AP. These results provide useful insight to better understand the intra-wagon channel properties and deploy the future 5G wireless networks in this particular scenario at mmWave frequencies, where high-data-rates are expected to support different types of digital applications.

A thorough millimeter-wave measurement campaign is carried out in an indoor environment with an aim at characterizing the short-term fading channel behavior. The measurements are conducted in a variety of scenarios, with frequencies ranging from 55 GHz to 65 GHz, in lineof-sight and non-line-of-sight conditions, and combinations of horizontal and vertical polarizations at both transmitter and receiver. A number of fading models are tested, namely Rayleigh, Rice, Nakagami-m, α-μ, κ-μ, η-μ, and α-η-κ-μ. The statistics under analysis are those characterizing the fading amplitude and the frequency selectivity. In particular, the probability density and cumulative distribution functions for the former and level crossing rate per bandwidth unit for the latter are the respective first- and second-order statistics used. To this end, from the experimental data, the parameters of the models are estimated and the corresponding theoretical curves are plotted and compared with the empirical ones. Whereas the required theoretical formulations of the first-order statistics of these models are already well known, those of the second-order statistics as well as these fitting process in such a band shown here are unprecedented in the literature.

We present a small-scale fading analysis of the vehicular-to-vehicular (V2V) propagation channel at 5.9 GHz when both the transmitter (Tx) and the receiver (Rx) vehicles are inside a tunnel and are driving in the same direction. This analysis is based on channel measurements carried out at different tunnels under real road traffic conditions. The Rice distribution has been adopted to fit the empirical cumulative distribution function (CDF). A comparison of the K factor values inside and outside the tunnels shows differences in the small-scale fading behavior, with the K values derived from the measurements being lower inside the tunnels. Since there are so far few published results for these confined environments, the results obtained can be useful for the deployment of V2V communication systems inside tunnels.

In this work, we propose a framework to obtain estimators from a variety of distributions used in composite fast fading and shadowing modeling with applications in wireless communications: the Suzuki (Rayleigh-lognormal), Nakagami-lognormal, K (Rayleigh-gamma), generalized-K (Nakagami-gamma) and α-μ (generalized gamma) distributions. These estimators are derived from the method of moments of these distributions in logarithmic units, usually known as log-moments. The goodness-of-fit of these estimators to experimental distributions has been checked from a measurement campaign carried out in an urban environment. Moreover a new method to separate fast fading and shadowing based on the Rathgeber procedure is proposed. The results conclude that the best-fitting distribution to the measurements is the Nakagami-lognormal. Also, the α-μ distribution provides an acceptable matching with the advantage of its simplicity.

In this letter, new estimators of the α-μ distribution are derived based on the skewness of the logarithmic α-μ distribution using the moments method. This distribution has been recently proposed to model the received field strength in nonlinear propagation mediums. Therefore, simple and computationally efficient estimators are required to infer the parameters of the received signal amplitude distribution in nonlinear wireless communication propagation channels. The performance of these new estimators is compared to that obtained with the estimators calculated with the moments method of the α-μ distribution by solving numerically transcendental equations. These estimators are easily evaluated with simple expressions.

In this paper, the ultra-wideband channel with orthogonal frequency division multiplexing (UWB-OFDM) is analyzed in the frequency domain. For UWB-OFDM channels with log-normal fading in the time domain, we show that the amplitude of each subcarrier can be approximated by a Nakagami-m random variable, where the fading parameter, the mean power and the correlation coefficient are expressed in terms of the following parameters: time arrival of the clusters, inter-arrival time of rays inside clusters, and power decay constants of rays and clusters.

The spectral efficiency of MIMO (multiple input multiple output) channels is limited by both the spatial correlation and the rank deficiency of the channel. Earlier studies have focused less attention on how the frequency band affects these channel properties. In this paper, the results derived from an extensive measurement campaign performed at 4 frequency bands between 2 and 12 GHz in an office scenario, show a frequency band dependence on the MIMO channel capacity. Increasing the number of antenna elements under these correlated channels, we found a frequency band dependence on the ergodic, 10% and 1% outage capacities. Taking into account the path loss effect isolation, high SNR regime, equal electric separation between array elements, and stationary conditions in the measurements, remarkable changes on the spectral efficiency were observed for different frequency bands in line-of-sight (LOS) and non-line-of-sight (NLOS) propagation conditions.

The spectral efficiency of MIMO (multiple input multiple output) channels is limited by both the spatial correlation and rank deficiency of the channel. Precedent studies have focused less attention in how the frequency band affects these channel properties. In this paper, the results derived from an extensive measurement campaign performed between 2 and 12 GHz in an office scenario, show frequency band dependence on the MIMO channel capacity. Increasing the number of antenna elements under these correlated channels for different frequencies, we found frequency band dependence on both the ergodic and the 10% outage capacities. Taking into account the isolation of the path loss, a high SNR regime, equal electric separation between array elements, and the WSS (wide sense stationary) channel condition, remarkable changes on the magnitude spatial correlation coefficients and on the MIMO system eigenvalues were observed for different frequencies in line-of-sight (LOS) and non-line-of-sight (NLOS).

In this paper an efficient scheduling mechanism for wireless local area networks (WLAN) is proposed. This innovative scheme, named hybrid HCCA-EDCA centralised scheme (HHE-CS), is based on the hybrid coordination function (HCF) protocol introduced by the IEEE 802.11e standard. The HHE-CS aims at satisfying the user quality of service (QoS) demands for real time (RT) services with variable bit rate while maximising the throughput of best effort users. This paper proves conclusively that an adequate allocation of downlink and uplink traffic between EDCA and HCCA increases system performance as compared with more traditional schemes in which all best effort traffic is exclusively delivered by a distributed mechanism like EDCA.

Abstract In this paper, a generation procedure of two correlated Nakagami‐m random variables for arbitrary fading parameters values (not necessary identical) is described. For the generation of two correlated Nakagami‐m samples, the proposed method uses the generalized Rice distribution, which appears in the conditional distribution of two correlated Nakagami‐m variables. This procedure can be applied to simulate diversity systems such as selection combiners, equal‐gain combiners, and maximal‐ratio combiners as well as multiple‐input multiple‐output (MIMO) receiver systems, in Nakagami‐m channels. Copyright © 2006 John Wiley & Sons, Ltd.

In this paper the impact of the soft handover micro diversity gain on the UMTS system performance is investigated. First, by means of link layer simulations the micro diversity gain is measured in terms of reduction of the average Eb/N0requirement. After modelling this effect, by some system level simulations we show the high influence of this usually neglected gain in the overall performance of UMTS, demonstrating that in downlink soft handover improves not only the quality of service but also the overall system capacity

This letter presents infinite series expressions for the outage probability, the probability density function, the average error probability for binary modulations, and the average signal-to-noise ratio of dual selection combiners over correlated fading with arbitrary fading parameters at each input of the combiner. The outage probability is calculated for both thermal noise and interference-limited scenarios. The results obtained for the outage probabilities specified for identical fading parameters at both branches of the combiner are contrasted with the results of other studies in the literature

The random access channel (RACH) is defined by 3rd generation partnership project (3GPP) as an uplink channel that is used for random-access transmission and short data bursts transportation from the user equipment (UE) to the network side in the absence of a dedicated traffic channel. The random-access transmission is based on a slotted Aloha approach with fast acquisition indication, carried by the acquisition indicator channel (AICH). In this paper, the RACH performance indicators such as delay and access success ratio are obtained for different traffic loads, in a single omni cell under shadowing and fast-fading conditions. We also propose an approximation for preamble signal to interference ratio (SIR) measured at base station point, in terms of mean level and standard deviation.