The large bandwidth and large antenna arrays of millimeter-wave (mm-wave) systems make them an interesting technology for integrated communication and sensing, where communication hardware and waveforms are re-used for sensing applications. Existing multipath component (MPC) estimation algorithms are designed for multi-antenna systems which rely on digital beamforming, where the baseband signal of each antenna is easily accessible at the receiver. In this paper, we propose a MPC estimation algorithm tailored to typical and cost-effective mm-wave system hardware, which typically relies on analog beamforming. The proposed MPC estimation algorithm does not suffer from the presence of an antenna array sidelobes, unlike classical angular power profile estimation algorithms. The algorithm's performance is evaluated through simulations, and is validated on a 28 GHz experimental testbed. The results show that our algorithm is effectively able to identify individual MPC contributions, without suffering from the influence of antenna array sidelobes.

This paper evaluates the downlink performance of cellular networks in terms of coverage and electromagnetic field exposure (EMFE), in the framework of stochastic geometry. The model is constructed based on datasets for sub-6 GHz macro cellular networks but it is general enough to be applicable to millimeter-wave networks as well. On the one hand, performance metrics are calculated for β-Ginibre point processes which are shown to faithfully model a large number of motion-invariant networks. On the other hand, performance metrics are derived for inhomogeneous Poisson point processes with a radial intensity measure, which are shown to be a good approximation for motion-variant networks. For both cases, joint and marginal distributions of the EMFE and the coverage, and the first moments of the EMFE are provided and validated by Monte Carlo simulations using realistic sets of parameters from two sub-6 GHz macro urban cellular networks, i.e., 5G NR 2100 (Paris, France) and LTE 1800 (Brussels, Belgium) datasets. In addition, this paper includes the analysis of the impact of the network parameters and discusses the achievable trade-off between coverage and EMFE.

In this paper, the impact of interference between multiple phase-coded Frequency Modulated Continuous Wave (FMCW) Dual Function Radar Communication (DFRC) systems is analysed. For the RADAR receiver, interference occurs when another nearby DFRC system is active. For the communication receiver, RADAR echoes from the same DFRC system interfere with the receiver. The performance achieved by interference cancellation at both functions is studied in different scenarios. Finally, stochastic geometry is used to analyse in a two-way automotive scenario which signal component (RADAR or communication) is dominant, in order to evaluate whether the interference should be cancelled at the RADAR receiver based on the communication receiver output or the opposite.

In propagation analysis it is assumed that existing shadowing losses are due to obstacles through the propagation path between two transceivers. Although classically modelled as a log-normal random variable, special attention is being recently put into models where shadowing is considered as a consequence of an Underlying Spatial Loss Field (USLF) accounting for attenuation, under Radio Channel Tomography (RCT) framework. In this paper we address the task of making shadowing predictions for transceiver locations, without the need of measurements for those locations. A spatial loss field estimate is produced from measurements for a given set of transceiver locations, and used as an input to predict the shadowing at another set of transceiver locations. Moreover, new weighting functions are proposed and developed from channel parameter estimates of the propagation paths.

For reliable and efficient communications of aerial platforms, such as unmanned aerial vehicles (UAVs), the cellular network is envisioned to provide connectivity for the aerial and ground user equipment (GUE) simultaneously, which brings challenges to the existing pattern of the base station (BS) tailored for ground-level services. Thus, we focus on the coverage probability analysis to investigate the coexistence of aerial and terrestrial users, by employing realistic antenna and channel models reported in the 3rd Generation Partnership Project (3GPP). The homogeneous Poisson point process (PPP) is used to describe the BS distribution, and the BS antenna is adjustable in the down-tilted angle and the number of the antenna array. Meantime, omnidirectional antennas are used for cellular users. We first derive the approximation of coverage probability and then conduct numerous simulations to evaluate the impacts of antenna numbers, down-tilted angles, carrier frequencies, and user heights. One of the essential findings indicates that the coverage probabilities of high-altitude users become less sensitive to the down-tilted angle. Moreover, we found that the aerial user equipment (AUE) in a certain range of heights can achieve the same or better coverage probability than that of GUE, which provides an insight into the effective deployment of cellular-connected aerial communications.

We consider a relay network based on Unmanned Aerial Vehicles (UAV). Terrestrial Base Stations (TBS) and UAV Relay Nodes (RN) are modelled using two Homogeneous Poisson Point Processes (HPPP). UAVs can hover at a fixed position or move following specific displacement schemes. The Coverage Probability (CP) of a typical user equipment (UE) is derived, either when it communicates via a direct link (from the TBS to the UE) or via a relay link (from the TBS to the UE through a UAV RN). Every link can be in Line-of-Sight (LoS) or Non Line-of-Sight (NLoS), and suffers from Rician fading with distance-dependent parameters. This coverage is calculated by means of both stochastic geometry (SG) and Monte-Carlo (MC) simulations. The benefits of the use of UAV as RNs are analysed depending on their altitude, density, and mobility scheme.

Vehicle-to-vehicle (V2V) wireless communications have many envisioned applications for ensuring traffic safety and for addressing traffic congestion. However, developing suitable communication systems and standards for this purpose requires developers to have accurate models for the V2V propagation channel. Likewise, the dynamic evolution of multipath components (MPCs) in V2V channels has not been well modeled in existing models. In this paper, we propose a geometry-based stochastic channel model for a lightly built-up urban environment and then parametrize the model from measurements. The MPCs are extracted based on a high-resolution parameter estimation; they are tracked and clustered through a joint algorithm. The identified clusters are classified as line-of-sight, reflections from static scatterers, reflections from mobile scatterers, multiple-bounce reflections, and diffuse scattering. Specifically, the multiple-bounce reflections are modeled as twin clusters that follow the COST 273/COST2100 approach. The paper gives a full parameterization of the channel model and supplies a step-by-step implementation recipe. We verify the model by comparing two second-order statistics, i.e., the root-mean-square (RMS) delay spread and the angular spreads of arrival/departure derived from the channel model, to the results obtained directly from the measurements. Furthermore, we also identify several key factors that strongly impact the synthetic channel performance.

This paper investigates device-to-device (D2D) communications where two nearby users are enabled to communicate directly with each other. A network analysis under Rician fading is proposed to account for a strong line-of-sight (LOS) component typical for this technology. Semi closed-form expressions for the cellular (CC) and underlaid D2D communication outage probabilities are derived relying on stochastic geometry theory. Schemes where D2D communications reuse the uplink (UL) or the downlink (DL) CC bands are compared. The choice between them is shown to strongly depend on the base stations (BS) and user equipments (UE) transmit powers.

The main contribution of this paper consists in integrating a physically correlated shadowing model of the aggregate interference in a stochastic geometry-based approach. The considered shadowing takes place in a Manhattan urban grid and combines both penetration and corner diffraction when modeling signal transmission from base stations to users. A tractable expression for the network coverage probability is obtained thanks to the framework of stochastic geometry. Our results suggest that the diffracted mechanisms are dominant compared to building penetration. It is also shown that the second order diffracted signal have little impact on the coverage compared to the first order signals.

This paper evaluates MIMO radio channel measurements at 3.8 GHz, conducted in various urban microcellular environments in the city of Louvain-la-Neuve, Belgium. Large-scale parameters, such as shadow fading, delay and angular spreads as well as dense multipath power are extracted and compared with values provided by existing models. A joint specular-dense multipath cluster-based model is then parametrized from the experimental data, detailing cluster spread and correlation properties.

Strategies are developed to optimize the downlink performance of a massive MIMO network constrained to a fixed global transmit power and a fixed total number of transmit antennas. Two possible degrees of freedom are analysed : the distribution of the base stations and the beamforming technique. Two different shadowing environments are considered as well. The network performance is evaluated either by means of Monte Carlo simulations, or using analytical expressions derived thanks to stochastic geometry. The results suggest that the coverage probability increases with the numbers of base stations and the cluster size.

This paper presents a physical-statistical radio channel power delay profiles model for room-to-room communication systems combining the room electromagnetic theory for modeling deterministic channel components with a geometry-based stochastic channel model with time-variant statistics for modeling stochastic components. The deterministic channel component, i.e., mean power delay spectrum, is comprised of specularly reflected paths plus diffuse components due to scattering and diffraction. The specular components are modeled with a set Dirac function, whereas the diffuse components modeling approach is a room electromagnetic theory-based model. Dynamic indoor communication channels are characterized by a non-stationary time- and delay-fading process due to changes in the environment. We analyze and model the time-delay variability of channels using K-factor for small-scale variations and the t-location scale distribution parameters for large-scale variations. It turns out that these parameters cannot be assumed to be constant in time and delay. After modeling of time-delay variations of the first order statistics, we generate channel realizations with appropriate second order statistics. As the result, the presented model enables to describe the evolution of the power delay profile in the time domain.

In this paper, an experimental performance evaluation is carried out within a communication scenario that features two of the key enablers of 5G: (i) the use of post-OFDM modulations and (ii) an efficient use of the spectrum via spectrum sharing. The experimental lab set-up has been assembled so as to operate in conditions as realistic as possible via the actual realtime implementation of the involved transceivers and also via the utilization of propagation channels which have been recorded in a field measurement campaign and which are loaded in a channel emulator that also operates in real-time. The experimental results show that co-existence in a shared spectrum scenario is possible and that the performance degradation is kept at a low level as long as one of the two users is making use of spectrally agile post-OFDM modulations such as filterbank multicarrier (FBMC).

To statistically model time-variant vehicle-to-vehicle (V2V) channels, the dynamic multi-path components (MPCs) are characterized based on suburban measurements conducted at 5.3 GHz. The correlation matrix distance (CMD) is used to determine the size of local wide-sense stationary (WSS) region. Within each WSS time window, MPCs are extracted using wideband spatial spectrum of Bartlett beamformer. A MPC distance (MCD)-based tracking algorithm is used to identify the "birth" and "death" of MPCs over different WSS regions, and the lifetime of MPC is modeled with a truncated Gaussian distribution. Distributions of number of MPCs and their positions are statistically modeled. The MPC characterization considers both angular and delay domain properties as well as the dynamic evolution of MPCs over different WSS regions. The results shows insight into the dynamic behaviors of MPCs in V2V environments, and is useful for the scatterer modeling in the geometry-based stochastic channel modeling.

A ray-tracing tool, including specular reflection, diffraction and attenuation by foliage, is experimentally validated at 12 and 30 GHz in a suburban environment. The tool is then applied to double directional channel modeling at 30 GHz in a real-world urban area in downtown Brussels. Azimuth-, elevation- and delay-spread are computed and analyzed on a stochastic viewpoint. It is found that elevation spreads remain limited (below 3 degrees), while azimuth-spreads are on average similar at both sides of the link (with a mean value of 12 degrees). Delay-spreads vary significantly over the user's locations, with a mean value of 45 nanoseconds. They are positively correlated with the directional spreads at the base station. Finally, an investigation about the impact of microscopic surface roughness is conducted: it is found that it is mostly negligible at millimeter waves, unless extremely narrow beamwidth antennas are used.

Sub-band divided ray tracing (RT) has been widely used to reproduce as reliably as possible the ultra-wideband (UWB) radio wave propagation channel in realistic indoor environments. However, its accuracy is strictly limited by the available description of the environment. Moreover, its computational complexity scales with the number of selected subbands and the number of propagation paths. In the present work, our RT tool considers not only deterministic propagation paths but also diffuse scattering components. Based on a low-complexity sub-band divided RT implementation, we propose a calibration method for indoor UWB sub-band divided RT. The method estimates the optimal material parameters, including the dielectric parameters and the scattering parameters, using channel measurements and multiobjective simulated annealing (MOSA). This calibration can improve the accuracy of sub-band divided RT in terms of the power delay profile (PDP) and the root mean square (RMS) delay spread for all test locations including those not considered by the calibration. A measurement campaign is used to verify the calibration technique.

Ray tracing has been extensively used to simulate indoor channel characteristics. For an ultra-wideband system, the channel characteristics vary significantly over the entire bandwidth. To cope with this, sub-band divided RT has been proposed by dividing the frequency of interest into multiple subbands and superposing the RT results at the individual center frequency of each subband. Thus, the computational complexity is directly proportional to the number of subbands. In this paper, we propose a mathematical method to significantly reduce the computational complexity of the sub-band divided RT, making it almost independent of the number of subbands. It is important to note that, based on our approach, not only the determination of the rays reaching a give location is made only once, but also the electromagnetic calculation of the received signal is not needed to perform repeatedly. The accuracy of low-complexity subband divided RT algorithm is verified through a measurement campaign.

Ray tracing (RT) is an accurate propagation prediction tool that has been widely used to simulate channel characteristics in indoor environments. To date, the developed RT tool includes not only specular reflection, penetration through dielectric blocks and diffraction, but also diffuse scattering mechanisms. The accuracy, provided by a detailed modeling of the environment, comes at the cost of a high computational complexity, which directly scales with the number of propagation paths considered. We are interested in simulating the radio propagation conditions for a mobile terminal, communicating in a frame based communication system indoors with several fixed nodes. This communication shall be used to obtain the position of the mobile terminal in indoor scenario. Therefore, the correlated temporal and spatial evolution of the channel impulse response is of utmost concern. In this paper, we propose a method to significantly reduce the computational complexity of RT by using a projection of all propagation paths on a subspace spanned by two-dimensional discrete prolate spheroidal (DPS) sequences. With this method the computational complexity can be reduced by more than one order of magnitude for indoor scenarios. The accuracy of our low-complexity DPS subspace based RT algorithm is verified by numeric simulations.

On-body channel dynamics are primarily affected by body motions, which not only cause dynamic scattering conditions but also modify the geometry of links over time. We experimentally investigate the Doppler spectra of narrowband on-body channels at 2.45 GHz in both anechoic and indoor environments. The body dynamics resulting from the motion are shown to directly affect the Doppler spectrum. An empirical model is proposed to describe the global and/or local Doppler spreads. The fit of a 3-cylinder-based physical model accounting for the arm swinging is also evaluated.

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while still maintaining low inter-antenna correlation. In this paper, the time-variation of the polarization of the received waves is investigated. In this scenario, a theoretical formulation is proposed in order to obtain the parameters of the elliptical polarization, based on the signals received on three perpendicularly polarized antennas. A measurement campaign has been performed in an indoor-to-indoor scenario and at a frequency of 3.6 GHz. Different measurement positions are considered in a Line-Of-Sight (LOS) and a Non-Line-of-Sight (NLOS) scenario. Based on these measurements and the proposed theoretical formulation, the time-variation of the parameters describing the polarization ellipse is analyzed and a time-variant statistical model is proposed.

For a receiver that observes a mixture of desired and interfering multiple-input multiple-output (MIMO) transmissions, not all interference has the same severity: its effect is modulated by the degree of alignment between the eigenspaces of the desired and undesired channel matrices. An analytical channel model is proposed to account for this effect. Two metrics of eigenspace compatibility are studied, and a method to generate channels of a given degree of compatibility is derived. The resulting model is parameterized using radio channel measurement data, and an implementation recipe for immediate use of the model is provided.

Based on multi-node multi-antenna channel measurements in a multi-wall office environment, we estimate the degree of separation between multiple MIMO links by means of two metrics: the correlation matrix distance and the shadowing correlation. Both nomadic and mobile node scenarios are considered and compared. Empirical models are eventually derived. Our analysis reveals that the average separation between two MIMO links sharing a joint transmitter is usually lower in mobile scenarios than in nomadic scenarios, and is strongly related to the spatial correlation of the individual MIMO links. However, there appears to be no relationship between the correlation matrix distance and the shadowing correlation.

In previous work, it has been observed that the specular and the diffuse component are linked in the angular domain. The idea of adding a diffuse component to each specular cluster has been proposed to model the specular-diffuse channel. In this paper, an approach is proposed to treat the specular and the diffuse measurement data simultaneously, with a clustering algorithm that is applied jointly on the specular and the diffuse component. The output of the clustering algorithm gives clusters that are characterized by their specular and their diffuse component. Measurement results are presented based on double-directional measurements, and parameter values are extracted using the proposed methodology.

In multiple-input multiple-output (MIMO) systems, the propagation channels can be characterized by their spatial structure, described by the (complex-valued) channel correlation. Accordingly, also interference in MIMO systems is likely to occur in a spatially structured, correlated way. We discuss that structured spatial interference affects mutual information under interference, depending on the eigenspace alignment between the channel of the desired signal and the channel carrying the interference. Intuitively, worst-case interference occurs, when the channels from the intended signal and the interference show a similar spatial structure. In contrast, least hurtful interference is encountered when these channels are maximally non-aligned. In this paper, we develop an analytical channel model generating multi-user MIMO channels with a given degree of severity of interference, described by the alignment of the channels' eigenspaces. Using radio channel measurements, we parameterize our model to reflect realistic scenarios.

The radio channels between nodes of an indoor peer-to-peer network show specific fast fading characteristics. Depending on the mobility and on the scattering properties of the environment, different kinds of fading distributions can occur: Ricean fading between static nodes, but also Rayleigh or even double-Rayleigh fading between mobile nodes. We investigate fast fading in indoor peer-to-peer networks based on radio channel measurements. It turns out that the fading statistics change over time. While the predominant fading mechanism is a combination of Rayleigh and double-Rayleigh fading, Ricean fading also occasionally occurs. On top of that, indoors, the statistics of the fast fading change over time even for small-motions of the nodes, since the propagation environment is inhomogeneous. We comprehensively model these effects using a hidden Markov model, parameterized from our measurements. The model is validated, revealing a convincing fit between the model and the measurements.

We experimentally characterize nomadic peer-to peer channels in a multi-wall indoor office environment. In particular, we derived models of path-loss, shadowing and fading statistics at 3.8 GHz in fixed scenarios, and compare them with existing results. Highlights of the paper include a multi-wall path loss model, the separation between obstruction, nomadic, and dynamic shadowing, a dynamic shadowing correlation model, as well as a multi-link analysis of MIMO links.

This work models the fast fading characteristics in indoor to indoor and outdoor to indoor channels at 3.8 GHz. Starting from real world measurements, the fast fading characteristics are extracted and properly modeled, taking into account the nodes movement conditions. For static environments, the fast fading is modeled with the well known Ricean distribution. As expected the K-factor depends on the path loss. On the other hand, in mobile environments, the probability density function of the signal envelope is accurately described by the recently developed second-order scattering fading (SOSF) distribution. The SOSF distribution combines the Rayleigh, Ricean and double Rayleigh fading and any linear combinations of these. Our results show that the higher the mobility, the more severe is the fading.

Polarized MIMO systems are an efficient solution for reducing inter-antenna correlation while maintaining compact terminal size. In this paper, a time-variant statistical channel model is proposed for tri-polarized antenna systems. The model is based on a coherent and a scattered component, where each component includes inter-channel correlation and cross-polar discriminations. The temporal variations of the channel are separated in slow and fast channel variations. A measurement campaign has been performed at 3.6 GHz to parameterize the model, in both static and mobile cases. A variant of the variogram technique has been adopted for extracting the slow-varying channel parameters. Experimental results are investigated and presented. The Doppler spectrum of the fast channel variations show fundamental differences between the static case and the mobile case. Finally, it is explained how the proposed model can be generated.

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. Cross-Polar Discrimination (XPD) and Co-Polar Ratio (CPR) are two important parameters describing multi-polarized channels. In this paper, the behavior of these parameters is investigated for different observation scales. A measurement campaign has been performed in both Outdoor-to-Indoor and Indoor-to-Indoor scenarios, at a frequency of 3.5GHz. Small-scale variations of XPD and CPR are analyzed in different spatial positions. The distance-related and large-scale variations of XPD and CPR are also investigated and a model is deduced.

The polarimetric characteristics of the signal back scattered from a building wall are studied in this paper with the aid of MIMO measurements and Ray Tracing simulation. A very simple environment with a single rural building amid an open area is considered to reduce complexity and better isolate the different kinds of back-scattered contributions: specular reflection, diffractions, diffuse scattering. Narrowband and wideband metrics are utilized to evaluate scattering characteristics focusing in particular on its polarization properties.

Cross-polarized antenna systems are an attractive way to reduce equipment size while maintaining low interantenna correlation. In this paper, the polarization behaviour of indoor channels is investigated. A measurement campaign has been conducted at 3.6 GHz for a dual-polarized transmitter and a tri-polarized receiver in a non-Line-of-Sight (NLOS) scenario. The spatial and delay characteristics are extracted using a pertap beamforming algorithm. Distinct paths are isolated and the polarization of each wave is expressed in terms of its spherical components. The cross-polarization discrimination (XPD) of the wave is investigated as a function of its physical propagation parameters. The XPD of the wave is shown to be sensitive to spatial characteristics, while being insensitive to delay.

In this paper we study the impact of the overlapping between neighboring MPCs (multipath component) on the performance of channel estimation. We consider IR-UWB (impulse radio) signals, and the IEEE802.15.3a and IEEE802.15.4a UWB channel models. We show that for a pulse width (PW) sufficiently smaller than the average MPC rate of arrival (ROA) the probability to have more than three overlapping MPCs is relatively small. We derive the CRBs (Cramer Rao bound) for the joint estimation of the MPC gain and TOA (time of arrival) in the case of up to three overlapping MPCs. We compute also the average CRBs. We show that the CRBs obtained by averaging more than 80% of possible cases of the channel, are very close to the bounds obtained under the non-overlapping assumption (NOLA).

Since multi-antenna (MIMO) systems are becoming more popular thanks to their inherent potential for capacity improvement, interference from MIMO transceivers is an increasingly serious concern. Spatial multiplexing schemes are particularly vulnerable to multi-user interference. Fortunately, this interference can be mitigated, when the channel matrices show a sufficient spatial separation. In this paper, we quantify the separability of multi-user MIMO channels using actual measurements in a scenario where a single outdoor base station transmits to two indoor mobile receivers. To quantify the spatial distance between the two users, we compare the spatial correlation matrices using two simple measures: (i) matrix collinearity, and (ii) the condition number ratio. Both measures are directly linked to MIMO system performance. Our measurement-based evaluations demonstrate that the downlink channels of different users can have a significantly different spatial structure, even when the users are in the same room. This leads to the following conclusions: (i) new multi-user MIMO models are needed to describe the spatial characteristics of different users, and (ii) spatial interference can be well managed by appropriate scheduling and precoding algorithms.

In this paper, an empirical model of the indoor distributed channel is presented. In particular, the shadowing and fading statistics are extracted from experimental data at 2.45 GHz in stationary and mobile scenarios. Highlights of the paper include a separate model for static and dynamic shadowing, a model for shadowing correlation, as well as a single analytical distribution of small-scale fading for various types of indoor node mobility.

In this paper, the capacity of several outdoor-to-indoor relay schemes has been investigated using real-world measurements at 2.45 GHz. The considered scenario encompasses an outdoor base station, possibly using multiple antennas, communicating via two hops to distributed single antenna terminals located inside a building. The single-antenna relays are located along the so-called best wall. Capacity results show that in most cases, relaying techniques increase the capacity, even when constraining the global power expense of the network. Considering a combining scheme using the source-to-destination in addition to the relay link does not bring huge benefits for the measured outdoor-to-indoor channels. The best performance is obtained in a relay-and-forward scheme using multiple cooperative relays.

A cluster-based channel model is presented that includes polarization characteristics. Measurements have been carried out in an indoor environment at 3.6 GHz using a dual-polarized transmitter and a tri-polarized receiver. Individual propagation paths are extracted using the SAGE algorithm, and a cross-polar discrimination (XPD) per ray is defined. Clusters are identified in the co-elevation-azimuth-delay domain, with an automatic clustering algorithm. The cluster properties are investigated and polarization characteristics are identified on a per-cluster basis. Finally, the obtained model is simulated and extraction-independent parameters are compared with experimental parameters for validation.

This paper investigates the polarization behaviour of indoor multi-polarized MIMO channels at 3.6 GHz. Measurements have been carried out in non-line-of-sight (NLOS) and line-of-sight (LOS) using a dual-polarized transmitter and a tri-polarized receiver. The spatial and delay characteristics are extracted using a per-tap beamforming algorithm. Distinct waves are isolated and the polarization of each wave is expressed in terms of its spherical components. The evolution of the waves polarization is investigated as function of its physical propagation parameters. The polarization of the waves is shown to be sensitive to spatial characteristics, while being insensitive to delay. Direct line-of-sight rays show to have higher XPD than in the NLOS case, while the reflected rays have a similar XPD than in a NLOS case.

In this paper, we describe experimental results characterizing the frequency/space/polarization selectivity of indoor channels at 1.9 GHz. Regarding the delay-angle dispersion, a clustered geometry-based model is developed from measurement results and validated. Regarding dual-polarized channels, a simple analytical model is extracted from experimental data, accounting for the cross-correlation between the various parameters. Finally, narrowband dual-polarized and single-polarized transmissions are compared in real-world indoor channels based on performance metrics for multiplexing and diversity gains.

Cross-polarized antenna systems are used to reduce equipment size in MIMO systems while still achieving low inter-antenna correlation. One fundamental parameter of cross-polarized MIMO systems is the cross-polar discrimination (XPD). This paper proposes a model to determine the XPD as a function of channel condition and under different antenna configurations. The environment is supposed to have a truncated Laplacian Power Angular Spectrum (PAS) that is widely used in standardization bodies. Antenna XPD is shown to be sensitive to different channel conditions, as well as to different receiver orientations. Measurements were conducted at 3.5 GHz to validate the theoretical model. Good agreement is obtained between theoretical XPD and experimental results.

The goal of this paper is to investigate the impact of rain and ice depolarization on an hypothetical high altitude platform system operating in the 47-GHz band over central Belgium, and using dual-polarized antenna arrays. An electromagnetic model based on physical parameters (rain rate, ice concentration, rain and ice anisotropy and canting angles) is first described. Time series of physical parameters are then extracted from one year of data recorded during the Olympus experiment in Belgium at 20 GHz. The prediction of attenuation and depolarization based on these parameters is then validated at 12 GHz. Finally, the prediction model is applied to HAPS scenarios by a dual frequency and elevation scaling. The specificity of HAPS is accounted for by considering a range-dependent elevation angle. Performance simulations are eventually presented and illustrate that depolarization may slightly improve the performance of polarization multiplexing schemes.

This paper proposes a closed-form expression for the correlation coefficient and the cross-polarization discrimination (XPD) of a randomly oriented dual- or tri-polarized MIMO system. The environment is supposed to have a truncated Laplacian power azimuth spectrum that is widely used in standardization bodies. correlation and XPD are shown to be highly sensitive to receiver orientation, azimuth spread and environment depolarization behavior. Measurements were conducted at 3.5 GHz to validate the theoretical model. Good agreement is obtained between theoretical curves and experimental results for correlation and XPD when comparing at different receiver orientations.

Measurements of car-to-car (C2C) radio channels with 60 MHz bandwidth at 5.3 GHz have been performed in Helsinki, Finland. We focused on 30x30 multiple-input multiple- output (MIMO) measurements, conducted in four environments (urban, sub-urban, campus and highway), under quasi-realistic traffic conditions. As first results, we present in this paper the delay spread statistics for each investigated environment. The largest values of root-mean-square (RMS) delay spread, roughly 2 mus, were obtained in the urban environment. The narrowband channel fading statistics have also been derived using composite distributions, in order to assess the global fading statistics.

Using wireless sensors worn on the body for pervasive monitoring is expected to become more and more common in the next years. The achievement of this application requires solving some challenges, especially in the power saving domain. In order to develop efficient power radio communications, an interesting investigation field is the multi-sensor MIMO (MS-MIMO) ultra-wideband (UWB) network. It is realistic to assume that each sensor carries one antenna, while the central device uses an antenna array. In this paper, a new analytical channel model for the diffracted waves mechanism is proposed. It is derived from the existing IEEE 802.15.4a standard channel model and innovates with space-time considerations.

In this paper, we address the potential benefits of dual-polarized arrays in multi-antenna wireless systems. After an extensive literature overview of experimental data, we present a new and simple analytical framework to model dual-polarized Rayleigh and Ricean fading channels for arbitrary array sizes. The model relies on a limited number of physical parameters, such as the channel spatial correlations, the channel co-polar and the cross-polar ratios and the antenna cross-polar discrimination. Then, we investigate the multiplexing advantage of dual-polarized transmissions through the evaluation of the ergodic mutual information, for both TITO and MIMO systems. Finally, the performance of two space-time coding schemes (Alamouti OSTBC and uncoded spatial multiplexing) is evaluated via a detailed analysis of the pairwise error probability.

In this communication, we address the potential benefits of dual-polarized arrays in 2 times 2 MIMO systems. We start with a new and simple analytical model of dual-polarized Rayleigh and Ricean fading channels, which relies on a limited number of physical parameters, such as the spatial correlations, the co-polar gain imbalance and the cross-polar discrimination. Then, we investigate the multiplexing advantage of dual-polarized transmissions through the evaluation of the ergodic mutual information. Finally, the performance of two space-time coding schemes (Alamouti O-STBC and uncoded spatial multiplexing) is evaluated via a detailed analysis of the pairwise error probability.

This paper considers the use of nrtimes ntdual-polarized arrays for improving the mutual information of MIMO communications. We first develop an elegant model of the multi-polarized MIMO channel, which allows to account for spatial correlation and depolarization effects. The major advantage of the model lies in its analytical expression, whose parameters have a clear physical meaning. In a second part, we investigate the ergodic mutual information of multi-polarized schemes, and derive a condition upon which multi-polarized transmissions offer a higher capacity than equivalent uni-polarized schemes using the same number of antennas under the same overall array dimensions.

Space-time code (STC) designs classically rely on the assumption of independent and identically distributed (i.i.d.) Rayleigh channels. However, poor scattering conditions may have detrimental effects on the performance of STCs. In this letter, we derive code-design criteria leading to robust STCs in a large variety of slow-fading propagation conditions. No channel knowledge is assumed at the transmitter. Codes satisfying these criteria are shown to perform much better on real-world channels than codes designed only for i.i.d. channels. As examples, the robustness of various spatial multiplexing schemes, linear dispersion codes, and space-time trellis codes is discussed based on those criteria

The performance analysis and the subsequent design of space-time codes (STC) in multiantenna channels commonly assume an infinite signal-to-noise ratio (SNR). This assumption has been shown to be justified in uncorrelated Rayleigh-fading channels. By contrast, this correspondence investigates STC in all SNR regimes and in the broad class of space-time correlated Ricean fading multiple-input-multiple-output (MIMO) channels. For rank-deficient codes, it is proven analytically that the error probability is significantly affected by spatial correlations and coherent components, irrespective of the SNR range and the temporal correlation. For full-rank codes, the performance and the code design are shown to be affected by spatial correlations and/or coherent paths only at finite SNR in slow fading channels, whereas in time-varying channels, they are affected in all SNR regimes. Hence, there is no guarantee that STC designed for independent and indentically distributed (i.i.d.) Rayleigh-fading channels perform adequately in space-time correlated Rayleigh/Ricean channels. Simulation examples confirm the conclusions drawn from the analytical derivations. They further illustrate that the use of a high SNR assumption does not allow to accurately estimate the behavior of STC in practical scenarios and should, thus, be used with care.

This contribution provides a fresh look at the asymptotic (in terms of number of antennas) design of multiple-antenna wireless systems, with the goal of giving useful insights on the deployment of future MIMO systems. For the i.i.d. Gaussian and double-directional models, we provide guidelines in terms of the repartition of the antennas between the transmitter and the receiver, and study the influence of array geometry on the ergodic mutual information per antenna. Furthermore, we compare the LOS and NLOS situations, and evaluate the relative importance of the LOS component and path loss in Ricean fading, as well as in the low-rank Ricean component case.

The goal of this paper is to investigate the validity of the Kronecker model for MIMO correlated channels. First, mathematical and equivalent propagation conditions of validity are detailed. In a second part, we address several areas where the Kronecker model is not valid. We also review the one-ring model and experimental results dealing with the validation of the Kronecker model. Based on these scarce results, the preliminary conclusion is that the Kronecker model might not be valid for arrays larger than 2times2 when antenna correlations are high across both receive and transmit arrays. The paradox is that the Kronecker model has been developed and is being widely used to account for correlation. This is in strong contrast with the popular belief that the Kronecker model is valid in many indoor and outdoor cases

This paper aims at characterizing the wireless channel for nomadic diversity-based systems operating at 1.9 GHz. Using a 1 /spl times/ 2 wideband measurement chain, four indoor environments have been investigated: a corridor, a small office, an electrical engineering laboratory, and an industrial hall. The measurement equipment is constituted by an 80-MHz transmitter. At the receiver, two omnidirectional antennas are connected to a wideband channel sounder through a switch, in order to measure an estimate of the instantaneous vector channel. Special attention is given to the experimental procedure itself, so as to take into account the specificity of nomadic systems (as opposed to usual mobile systems). The measurement analysis reveals that the shadowing, Ricean K-factor and delay-spread are lognormally distributed. A path-loss model is derived, and cross-correlations between K-factor, delay-spread and shadowing are analyzed. The channel correlations at the user terminal or at the access point are also derived, and related to the individual channel characteristics.

This paper highlights the impact of channel correlations on the capacity and performance of MIMO communications, with a focus on the so-called diagonal correlations. Based on this analysis, the limitations of simplified mathematical representations, such as the Kronecker or the diagonal-decorrelation models, are pointed out. Finally, the correlation properties of popular geometry-based statistical models are studied in order to analyze whether the correlation structure of these models can be adequately represented by simplified mathematical models, as well as to quantify the errors introduced by these simplifications. With respect to channel correlations, neither the Kronecker nor the diagonal-decorrelation assumptions are good representations of the correlation structure of the investigated geometry-based statistical models. When comparing capacity and symbol error probability results, it is found that the diagonal-decorrelation model may yield significant errors on both considered metrics. The Kronecker model generally yields errors less than one order of magnitude on the symbol error rate, but relative errors on ergodic or outage capacity may be more significant.

This paper describes a multidimensional model of the fixed wireless propagation channel, which is well suited to system-level simulations. The proposed method yields realistic predictions of various channel characteristic parameters as a function of the range and antenna beamwidths, in agreement with experimentally observed results. The originality of the approach is that the power-delay profile for omnidirectional antennas at the edge of the cell is used to predict the time-varying channel over the whole cell for any antenna beamwidth. The method is based on a set of spatially distributed scatterers, which can be scaled to any range within the cell. The time-varying channel impulse response is then calculated as the combination of all scattered contributions by means of a ray approximation. The multidimensionality of the channel model is explored through predictions of signal statistics, level-crossing rate, delay-spread and angle-spread. In contrast to most existing models, the impact of range and antenna beamwidth is clearly addressed and found to be close to experimentally observed behaviors.

Spatial multiplexing is employed in MIMO communication systems to increase spectral efficiency. The performance of spatial multiplexing is highly dependent on the propagation conditions such as the richness of scattering, the presence of dominant components and the inter-element spacings. In this paper, new robust signal constellations for use in spatial multiplexing over real fading propagation channels are developed. It is shown that these new constellations are by far more robust against fading correlations and high Rice factor than the classical PSK and QAM constellations. With these new constellations, spatial multiplexing presents excellent symbol error rate performance whatever the propagation environment and the inter-element distance.

The channel capacity and the performance of MIMO systems in the presence of fading correlation and antenna coupling are investigated. Simulation results demonstrate that mutual coupling can improve the performance depending on the inter-element spacing and the richness of scattering. It is shown the bit error rate performance of spatial multiplexing is particularly influenced by the decorrelation/correlation effect caused by mutual coupling. On the other hand, the bit error rate performance of transmit diversity is mainly affected by the resulting modification of antenna gain and received power.

This paper presents a physical scattering model that predicts multiple-input multiple-output (MIMO) channel characteristics conforming well to experimental observations in macrocells. Our approach is to start with a given single-input single-output power-delay profile (defined for specific range, bandwidth and antenna parameters) and fit a scattering model that characterizes the MIMO channel. From the derived scattering model and antenna array configurations, the MIMO channel is computed using a ray-based method. Simulations of several MIMO channels are shown to exhibit experimentally observed channel correlations, antenna beamwidth effect, range dependency, and frequency selectivity.