Results 1  10
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24
A geometrybased stochastic MIMO model for vehicletovehicle communications
 IEEE Transactions on Wireless Communications
, 2008
"... Abstract—Vehicletovehicle (VTV) wireless communications have many envisioned applications in traffic safety and congestion avoidance, but the development of suitable communications systems and standards requires accurate models for the VTV propagation channel. In this paper, we present a new wideb ..."
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Cited by 41 (17 self)
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Abstract—Vehicletovehicle (VTV) wireless communications have many envisioned applications in traffic safety and congestion avoidance, but the development of suitable communications systems and standards requires accurate models for the VTV propagation channel. In this paper, we present a new wideband multipleinputmultipleoutput (MIMO) model for VTV channels based on extensive MIMO channel measurements performed at 5.2 GHz in highway and rural environments in Lund, Sweden. The measured channel characteristics, in particular the nonstationarity of the channel statistics, motivate the use of a geometrybased stochastic channel model (GSCM) instead of the classical tappeddelay line model. We introduce generalizations of the generic GSCM approach and techniques for parameterizing it from measurements and find it suitable to distinguish between diffuse and discrete scattering contributions. The timevariant contribution from discrete scatterers is tracked over time and delay using a high resolution algorithm, and our observations motivate their power being modeled as a combination of a (deterministic) distance decay and a slowly varying stochastic process. The paper gives a full parameterization of the channel model and supplies an implementation recipe for simulations. The model is verified by comparison of MIMO antenna correlations derived from the channel model to those obtained directly from the measurements. Index Terms—Channel measurements, MIMO, vehicular, nonstationary, Doppler, geometrical model, statistical model.
Characterization of VehicletoVehicle Radio Channels from Measurements at 5.2 GHz
 WIRELESS PERS COMMUN
, 2008
"... The development of efficient vehicletovehicle (V2V) communications systems requires an understanding of the underlying propagation channels. In this paper, we present results on pathloss, powerdelay profiles (PDPs), and delayDoppler spectra from a high speed measurement campaign on a highway in ..."
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Cited by 16 (4 self)
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The development of efficient vehicletovehicle (V2V) communications systems requires an understanding of the underlying propagation channels. In this paper, we present results on pathloss, powerdelay profiles (PDPs), and delayDoppler spectra from a high speed measurement campaign on a highway in Lund, Sweden. Measurements were performed at a This work is an extended version of the conference paper [1].
Iterative TimeVariant Channel Estimation for 802.11p Using Generalized Discrete Prolate Spheroidal Sequences
 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY
, 2012
"... This paper deals with channelestimation for orthogonal frequency division multiplexing (OFDM) in timevariant wireless propagation channels. We particularly consider the challenges of the IEEE 802.11p standard, the worldwide dominant system for vehicular communications. For historic reasons, 802.1 ..."
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Cited by 10 (7 self)
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This paper deals with channelestimation for orthogonal frequency division multiplexing (OFDM) in timevariant wireless propagation channels. We particularly consider the challenges of the IEEE 802.11p standard, the worldwide dominant system for vehicular communications. For historic reasons, 802.11p uses a pilot pattern that is identical to the one used in 802.11a, which was initially designed for the estimation of indoor channels with no or little time variations. Therefore, this pilot pattern violates the sampling theorem for channels with both, large delay spread and large Doppler spread, as often occurs in vehicular communications. To remedy this problem, we design a robust iterative channel estimator based on a twodimensional subspace spanned by generalized discrete prolate spheroidal sequences. Due to the tight subspace design the iterative receiver is able to converge to the same bit error rate as a receiver with perfect channel knowledge. Furthermore, we propose a backward compatible modification of the 802.11p pilot pattern such that the number of iterations sufficient for convergence can be reduced by a factor of two to three, strongly reducing implementation complexity.
Adaptive ReducedRank Estimation of NonStationary TimeVariant Channels Using Subspace Selection
 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, TO BE PUBLISHED
, 2012
"... In this work we focus on adaptive timevariant channel estimation for vehicletovehicle (V2V) communications in intelligent transportation systems using the IEEE 802.11p physical layer. The IEEE 802.11p pilot pattern is identical to the one in the wellknown IEEE 802.11a/g (WiFi) standard, which wa ..."
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Cited by 9 (6 self)
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In this work we focus on adaptive timevariant channel estimation for vehicletovehicle (V2V) communications in intelligent transportation systems using the IEEE 802.11p physical layer. The IEEE 802.11p pilot pattern is identical to the one in the wellknown IEEE 802.11a/g (WiFi) standard, which was initially designed for indoor environments with little or no mobility. However, in a V2V driveby situation the channel impulse response changes rapidly due to the high relative velocity between transmitter and receiver as well as changes in the scattering environment. Hence, for such V2V channels, advanced decision directed channel estimation methods are needed to reach a frame error rate (FER) smaller than 10 −1. Even more importantly, the channels are nonstationary, which implies that the Doppler power spectral density (DSD) and the powerdelay profile (PDP) change on a timescale comparable to the frame
Analysis of local quasistationarity regions in an urban macrocell scenario
 in Proc. 71st IEEE Vehicular Technology Conference (VTC 2010Spring
, 2010
"... Abstract—A common simplification in the treatment of random linear channels is the widesense stationary and uncorrelated scattering (WSSUS) assumption. For wireless channels, this assumption is, however, only fulfilled in an approximative sense inside local timefrequency regions. Since algorithms ..."
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Cited by 8 (5 self)
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Abstract—A common simplification in the treatment of random linear channels is the widesense stationary and uncorrelated scattering (WSSUS) assumption. For wireless channels, this assumption is, however, only fulfilled in an approximative sense inside local timefrequency regions. Since algorithms in wireless digital communications often rely on knowledge of second order statistics of the channel, it is important to know the size of local quasistationarity regions. Thus, we determine quasistationarity regions in distance for an urban macrocell scenario. We observe that, based on the chosen measure and in our specific scenario, the timefrequency properties are dominant compared to the spatial properties in defining the size of quasistationarity regions. Furthermore, we find that in some cases the quasistationarity regions strongly depend on the mobile terminal orientation. I.
Parametrization of the Local Scattering Function Estimator for VehiculartoVehicular Channels
"... Abstract—Non widesense stationary (WSS) uncorrelatedscatterering (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 mult ..."
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Cited by 6 (6 self)
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Abstract—Non widesense stationary (WSS) uncorrelatedscatterering (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 multitaperbased 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 on the MMSE under different lengths of the stationarity regions and signaltonoise ratio values. The analysis is performed considering three different scenarios representing different scattering properties. We show that there is an optimal combination of estimator parameters for different lengths of stationarity region and signaltonoise ratio values which provides a minimum MMSE. I.
InTunnel Vehicular Radio Channel Characterization
"... Abstract—The radio wave propagation mechanisms when communicating inside a tunnel are different than the well understood in ”openair ” conditions. Characterization of these environments is crucial in order to deploy reliable vehicular communication systems operating under these conditions. In this ..."
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Cited by 5 (5 self)
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Abstract—The radio wave propagation mechanisms when communicating inside a tunnel are different than the well understood in ”openair ” conditions. Characterization of these environments is crucial in order to deploy reliable vehicular communication systems operating under these conditions. In this paper we evaluate vehicletovehicle intunnel radio channel measurements. We estimate the timevarying root mean square (rms) delay and Doppler spreads, as well as the excess delay, maximum Doppler dispersion. We also characterize the stationarity time, where we consider the statistical properties of the process to be constant. We evaluate these parameters for a whole measurement set consisting of 7 measurement runs. They all were taken for the intunnel scenario under several conditions, i.e., different distance between vehicles, constant or increasing speed, with and without cars driving beside. Firs, we present the detailed results for a
Characterization of NonStationary Channels Using Mismatched Wiener Filtering
"... Abstract—A common simplification in the statistical treatment of linear timevarying (LTV) wireless channels is the approximation of the channel as a stationary random process inside certain timefrequency regions. We develop a methodology for the determination of local quasistationarity (LQS) regi ..."
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Cited by 4 (2 self)
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Abstract—A common simplification in the statistical treatment of linear timevarying (LTV) wireless channels is the approximation of the channel as a stationary random process inside certain timefrequency regions. We develop a methodology for the determination of local quasistationarity (LQS) regions, i.e., local regions in which a channel can be treated as stationary. Contrary to previous results relying on, to some extent, heuristic measures and thresholds, we consider a finitelength Wiener filter as realistic channel estimator and relate the size of LQS regions in time to the degradation of the mean square error (MSE) of the estimate due to outdated and thus mismatched channel statistics. We show that for certain power spectral densities (PSDs) of the channel a simplified but approximate evaluation of the matched MSE based on the assumption of an infinite filtering length yields a lower bound on the actual matched MSE. Moreover, for such PSDs, the actual MSE degradation is upperbounded and the size of the actual LQS regions is lowerbounded by the approximate evaluation. Using channel measurements, we compare the evolution of the LQS regions based on the actual and the approximate MSE; they show strong similarities. I.
SPATIAL DIVERSITY AND SPATIAL CORRELATION EVALUATION OF MEASURED VEHICLETOVEHICLE RADIO CHANNELS AT 5.2 GHZ
"... In this contribution, we estimate the spatial diversity order and spatial correlations from channel sounder measurements of doublyselective vehicletovehicle MIMO radio channels in the 5.2 GHz band. Ivrlac and Nossek [1] have defined a diversity measure for MIMO Rayleigh fading channels which is b ..."
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Cited by 4 (1 self)
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In this contribution, we estimate the spatial diversity order and spatial correlations from channel sounder measurements of doublyselective vehicletovehicle MIMO radio channels in the 5.2 GHz band. Ivrlac and Nossek [1] have defined a diversity measure for MIMO Rayleigh fading channels which is based on the spatial correlations of the channel. Subsequently, Nabar et al. [2] have shown the existence of an SNRdependent critical rate for Ricean fading MIMO channels below which reliable transmission with zero outage is achievable. Here, we evaluate and discuss the temporal evolution of the spatial diversity order of doublyselective vehicletovehicle MIMO radio channels from realworld measurements by extending [1] and [2] to timevariant channels. Index Terms — MIMO channel measurements, V2V channel measurements, spatial correlation, spatial diversity. 1.
LowComplexity GeometryBased Modeling of Diffuse Scattering
"... Abstract—Modelling diffuse components in geometrybased radio channel models is computationally very complex. It usually requires to add a large number of complex exponentials, which is very time consuming. To overcome this complexity constraint, we propose to use the simulation method from Kaltenbe ..."
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Cited by 2 (2 self)
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Abstract—Modelling diffuse components in geometrybased radio channel models is computationally very complex. It usually requires to add a large number of complex exponentials, which is very time consuming. To overcome this complexity constraint, we propose to use the simulation method from Kaltenberger et al. [1]. With this approach, the simulation time becomes independent of the number of multipath components in the channel. We demonstrate the lowcomplexity approach by modelling the diffuse components of the vehicular radio channel. Our new implementation reduces simulation time by a factor of 30. I.