| 1. |
- Abbas, Taimoor, et al.
(författare)
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Directional Analysis of Vehicle-to-Vehicle Propagation Channels
- 2011
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Ingår i: IEEE Vehicular Technology Conference.
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Konferensbidrag (refereegranskat)abstract
- This paper presents a double directional analysis of vehicle-to-vehicle channel measurements conducted in three different traffic scenarios. Using a high-resolution algorithm, we derive channel parameters like Angle-of-Arrival (AOA), Angle-of-Departure (AOD), propagation delay and Doppler shift and identify underlying propagation mechanisms by combining these estimates with maps of the measurement sites. The results show that first-order reflections from a small number of interacting objects can account for a large part of the received signal in the absence of line-of-sight (LOS). This effect is especially pronounced in the two traffic scenarios where the road is not lined with buildings. We also found that the direction spread is low (and conversely that the antenna correlation is high) in such scenarios, which suggests that beam forming rather than diversity-based methods should be used if multiple antenna elements are used. The situation is reversed, however, in the third scenario, a narrow urban intersection, where a larger number of higher-order reflections is found to result in a higher direction spread.
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| 2. |
- Abbas, Taimoor, et al.
(författare)
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Directional Analysis of Vehicle-to-Vehicle Propagation in Different Traffic Environments
- 2010
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Ingår i: [Host publication title missing].
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a double directional analysis of vehicle-to-vehicle channel measurements conducted in two different traffic environments. Using a high-resolution algorithm, we derive channel parameters like angle-of- arrival, angle-of-departure, propagation delay and Doppler’s spread and identify underlying propagation mechanisms by combining these estimates with maps of the measurement sites. The results show that single-bounce interaction with static objects is the dominating effect in the absence of line-of-sight, and that the contribution from other vehicles is small. We also find that in the absence of line-of-sight the direction spread at both sides of link is large which indicates possible diversity gain using multi-antenna arrangements.
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| 3. |
- Abbas, Taimoor, et al.
(författare)
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Measurements Based Channel Characterization for Vehicle-to-Vehicle Communications at Merging Lanes on Highway
- 2013
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Ingår i: 2013 IEEE 5th International Symposium on Wireless Vehicular Communications, WiVeC 2013 - Proceedings. - : IEEE. - 9781467363396
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Konferensbidrag (refereegranskat)abstract
- This paper presents results for vehicle-to-vehicle channel characterization based on measurements conducted for the merging lane scenarios on a highway. We present power delay profiles as well as channel gains and analyze important propagation mechanisms to see the impact of line-of-sight (LOS) and the antenna radiation pattern on the total received power. It is found that the absence of LOS and strong scattering objects, close to the point where the ramp merges with a highway, may result in poor received signal strength. The probability of dropping packets also increases where there is LOS between TX and RX but the antenna pattern is not omni-directional. A dip in the antenna pattern affects the received signal strength severely which poses a challenge for vehicle-to-vehicle communication in safety critical situations.
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| 4. |
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| 5. |
- Bernadó, Laura, et al.
(författare)
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Complexity reduction for vehicular channel estimation using the filter-divergence measure
- 2011
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Ingår i: 2010 Conference Record of the Forty Fourth Asilomar Conference on Signals, Systems and Computers. - 9781424497225 - 9781424497218
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Konferensbidrag (refereegranskat)abstract
- In vehicular communications systems the channel estimation filter suppresses the additive noise in channel estimates obtained from pilot symbols. Vehicular channels show local stationarity for a finite region in time and frequency, only. Such a process can be divided into consecutive stationarity regions, allowing to calculate a Wiener filter. We analyze the increase of the mean square error (MSE) when using a mismatched Wiener filter calculated for a past stationarity region. The MSE increase of the filter is related to a new metric, the filter divergence directly observable at the receiver side. By accepting an increase of MSE, measured by the filter-divergence, the same filter coefficients can be used for several stationarity regions, allowing computational complexity reduction in a real system.
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| 6. |
- Bernado, Laura, et al.
(författare)
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Delay and Doppler Spreads of Non-Stationary Vehicular Channels for Safety Relevant Scenarios
- 2014
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Ingår i: IEEE Transactions on Vehicular Technology. - 1939-9359. ; 63:1, s. 82-93
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedVehicular communication channels are characterized by a nonstationary time-frequency-selective fading process due to rapid changes in the environment. The nonstationary fading process can be characterized by assuming local stationarity for a region with finite extent in time and frequency. For this finite region, the wide-sense stationarity and uncorrelated scattering assumption approximately holds, and we are able to calculate a time-frequency-dependent local scattering function (LSF). In this paper, we estimate the LSF from a large set of measurements collected in the DRIVEWAY'09 measurement campaign, which focuses on scenarios for intelligent transportation systems (ITSs). We then obtain the time-frequency-varying power delay profile (PDP) and the time-frequency-varying Doppler power spectral density (DSD) from the LSF. Based on the PDP and the DSD, we analyze the time-frequency-varying root-mean-square (RMS) delay spread and the RMS Doppler spread. We show that the distribution of these channel parameters follows a bimodal Gaussian mixture distribution. High RMS delay spread values are observed in situations with rich scattering, whereas high RMS Doppler spreads are obtained in drive-by scenarios.
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| 7. |
- Bernadó, Laura, et al.
(författare)
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In-tunnel vehicular radio channel characterization
- 2011
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Ingår i: [Host publication title missing]. - 1550-2252. - 9781424483327
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Konferensbidrag (refereegranskat)abstract
- Abstract in UndeterminedInside a tunnel, electromagnetic wave propagation differs strongly from the well understood "open-air" situation. The characterization of the tunnel environment is crucial for deploying vehicular communication systems. In this paper we evaluate vehicle-to-vehicle (V2V) radio channel measurements inside a tunnel. We estimate the time-varying root mean square (rms) delay and Doppler spreads, as well as the excess delay and the maximum Doppler dispersion. The fading process in V2V communications is inherently non-stationary. Hence, we characterize the stationarity time, for which we can consider the fading process to be wide sense stationary. We show that the spreads, excess delay, and maximum Doppler dispersion are larger on average when both vehicles are inside the tunnel compared to the "open-air" situation. The temporal evolution of the stationarity time is highly influenced by the strength of time-varying multipath components and the distance between vehicles. Furthermore, we show the good fit of the rms delay and Doppler spreads to a lognormal distribution, as well as for the stationarity time. From our analysis we can conclude that the IEEE 802.11p standard will be robust towards inter-symbol and inter-carrier interference inside a tunnel.
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| 8. |
- Bernadó, Laura, et al.
(författare)
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Multi-dimensional K-factor analysis for V2V radio channels in open sub-urban street crossings
- 2010
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Ingår i: [Host publication title missing]. - 9781424480173 ; , s. 58-63
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Konferensbidrag (refereegranskat)abstract
- In this paper we analyze the small-scale fading statistics for vehicle-to-vehicle (V2V) communications in a typical open sub-urban street crossing. The two cars approach the crossing from two different streets and the channel conditions vary from non line-of sight (NLOS) to line-of-sight (LOS). The small-scale fading of the first delay bin is Ricean distributed with a time-varying K-factor. The later delay bins are mostly Rayleigh distributed. The antenna arrays used for recording the multiple-input multiple-output channels are linear and consist of 4 elements with directional radiation patterns. We investigate the K-factor variation of the first delay bin in time, frequency, and space dimensions, where the measurement has a duration of 20 s, a bandwidth of 240 MHz, and 16 individual single-input single- output channels. We observe that the large/small K-factor values are not necessarily correlated with the received power. We show that the K-factor can not be assumed to be constant in any of the considered domains, not even in the frequency domain, as it has been always done for relative bandwidths up to 10%. The narrow- band K-factor for each frequency bin corroborates the need to consider its frequency variation. The antenna radiation patterns, and the illuminated objects by them at different time instances are the cause of these variations. We conclude that a multi- dimensional varying K-factor models the large-scale statistical behaviour more accurately than a constant K-factor.
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| 9. |
- Bernadó, Laura, et al.
(författare)
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Non-WSSUS Vehicular Channel Characterization at 5.2 GHz - Spectral Divergence and Time-Variant Coherence Parameters
- 2008
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Konferensbidrag (refereegranskat)abstract
- The scattering environment in vehicle-to-vehicle communication channels at 5.2 GHz changes rapidly. Hence the wide-sense stationary (WSS) uncorrelated scattering (US) assumption for the fading process is valid for short time intervals only. We characterize the spectral divergence of the local scattering function (LSF) sequence in order to assess the non-WSSUS characteristics in different scenarios. We find that the vehicle-to-vehicle channels violate the wide-sense stationarity much stronger than the US assumption. Additionally, we use the LSF to quantify the time dependence of the channel coherence time and bandwidth. Both parameters vary strongly over time depending on the chosen scenario. Furthermore the effect of the antenna radiation pattern on the fading process is quantified, which can cause the strength of a multipath component to change by more than 40 dB in drive-by experiments.
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| 10. |
- Bernadó, Laura, et al.
(författare)
-
Parametrization of the local scattering function estimator for vehicular-to-vehicular channels
- 2009
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Ingår i: [Host publication title missing]. ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- Non wide-sense stationary (WSS) uncorrelated scatterering (US) fading processes are observed in vehicular communications. To estimate such a process under additive white Gaussian noise we use the local scattering function (LSF). In this paper we present an optimal parametrization of the multitaper-based LSF estimator. We do this by quantizing the mean square error (MSE). For that purpose we use the structure of a twodimensional Wiener filter and optimize the parameters of the estimator to obtain the minimum MSE (MMSE). We split the observed fading process in WSS regions and analyze the influence of the estimator parameters and the length of the stationarity regions on the MMSE. The analysis is performed considering three different scenarios representing different scattering properties. We show that there is an optimal combination of estimator parameters and length of stationarity region which provides a minimum MMSE.
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