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This paper considers the precoder designs for successive zero-forcing dirty paper coding (SZF-DPC), a suboptimal transmission technique for MIMO broadcast channels (MIMO BCs). Existing precoder designs for SZF-DPC often consider a sum power constraint. In this paper, we address the precoder design for SZF-DPC with per-antenna power constraints (PAPCs), which has not been well studied. First, we formulate the precoder design as a rank-constrained optimization problem, which is generally difficult to handle. To solve this problem, we follow a relaxation approach, and prove that the optimal solution of the relaxed problem is also optimal for the original problem. Considering the relaxed problem, we propose a numerically efficient algorithm to find the optimal solution, which exhibits a fast convergence rate. Suboptimal precoder designs, with lower computational complexity, are also presented, and compared with the optimal ones in terms of achievable sum rate and computational complexity., QC 20130118

Despite the tremendous research effort spent on MIMO systems - very few papers address the impact of hardware imperfections. In this paper we analyze the distortion noise of the transmitter branches of a MIMO transmitter. In particular we analyze the cross-correlation of the distortion noises for the case that the transmitted signals are correlated. This case arises when there is just a single stream being transmitted with beamforming or in the case of multiple streams and linear precoding. We analyze the problem in two ways: using analytical derivations and using measurements on our testbed. In the analytical case we assume a transmitter impaired by a 3rd order non-linearity. For this scenario we find that the absolute correlation coefficient of the distortion noises is given by the absolute value of the correlation coefficients of the input signals to the power of three, while the phase is the same as that of the input signal. Our measurements also show good agreement between measurements and analytical results. It seems to suggest that the distortion noises can be regarded as practically independent whenever there are two or more modulation streams being transmitted (spatial multiplexing). In a single-stream scenario, the distortion noise will tend to have the same spatial distribution as the desired signal., QC 20130118

This paper presents a measurement recipe to characterize the out-of-band nonlinear behavior of RF devices when harmonic sampling is used as a digitizing technique. A major challenge to consider when using harmonic sampling is the overlapping of the aliased spectral bins of the digitized waveform. This challenge is more pronounced when using modulated excitation signals. In addition, the excitation signal used should mimic the real behavior of signals used in today's wireless systems. Hence, this paper provides the reader with a tool to select the proper excitation signal, sampling frequency and record length in order to achieve an accurate characterization of the nonlinear behavior of RF devices., QC 20111107

Multicell joint processing has been shown to efficiently suppress inter-cell interference, while providing a high capacity gain due to spatial multiplexing across distributed Base Stations (BSs). However, the complexity of the optimal joint decoder in the multicell uplink channel grows exponentially with the number of users, making it prohibitive to implement in practice. In this direction, this paper investigates the uplink capacity performance of multicell joint linear minimum mean square error (LMMSE) filtering, followed by single-user decoding. The considered cellular multiple-access channel model assumes both Rayleigh and Rician flat fading, path loss, distributed users and correlated multiple antennas at the base station side. The case of Rayleigh fading is tackled using a free probability approach, while the case of Rician fading is addressed through a deterministic equivalent calculated using non-linear programming techniques. In this context, it is shown that LMMSE can provide high spectral efficiencies in practical macrocellular scenarios., Invited Paper. QC 20120209

This paper considers the joint design of bit loading, precoding and receive filters for a multiple-input multiple-output (MIMO) digital communication system employing decision feedback (DF) detection at the receiver. Both the transmitter as well as the receiver are assumed to know the channel matrix perfectly. It is well known that, for linear MIMO transceivers, a diagonal transmission (i.e., orthogonalization of the matrix channel) is optimal for some criteria. Surprisingly, it was shown five years ago that for the family of Schur-convex functions an additional rotation of the symbols is necessary. However, if the bit loading is optimized jointly with the linear transceiver, then the rotation is unnecessary. Similarly, for DF MIMO transceivers, a rotation of the symbols is sometimes needed. The main result of this paper shows that for a DF MIMO transceiver where the bit loading is jointly optimized with the transceiver filters, the rotation of the symbols becomes unnecessary and, consequently, also the DF part of the receiver is not required., QC 20110302

Subspace based identification of model parameters requires a low rank data model. To obtain such a model it is common to collect several snapshots of the observed vector valued sequence in a larger vector. In many cases, this “window” procedure results in a new vector valued process which can be viewed as originating from a low rank data model. When studying the performance of weighted subspace based techniques this window procedure complicates both the analysis and the implementation. In this paper an attempt is made to clarify the theoretical and numerical difficulties when applying weighting in such scenarios, Invited paper NR 20140805

Future wireless networks will employ unprecedentedly high number of transmitters along-with larger bandwidth signals. Therefore, complexity efficient Power Amplifier (PA) modelling methods with the ability to quantify memory effects are required. This paper presents a low complexity method to quantify memory effects by studying the symmetry in the PA transfer functions estimated with the density estimation method. It is shown that the symmetry helps in reducing the method complexity by more than two orders of magnitude. Further, it is verified that the symmetry can be used as a non-model based metric for quantifying memory effects in PAs., QC 20160205

This paper addresses channel training and data communication over multi-input multi-input (MIMO) interference networks. We consider a pilot-assisted interference alignment scheme in which part of radio resources are allocated to channel training and the remaining resources are used for data transmission. A more accurate channel estimation can be obtained by increasing pilot transmission power. Since each transmitter has limited energy budget, this implies that less power is available for data transmission. Clearly, there is a trade off between the allocated power for channel training and the one for data communication. In order to investigate this trade off, first we compute an achievable sum-rate, and next we find the optimum power allocation to pilot transmission and data transmission. Finally, we verify these theoretical results with experimental measurements on USRP-based test-bed., QC 20160226

Radio-frequency (RF) impairments in the transceiver hardware of communication systems (e.g., phase noise (PN), high power amplifier (HPA) nonlinearities, or in-phase/quadrature-phase (I/Q) imbalance) can severely degrade the performance of traditional multiple-input multiple-output (MIMO) systems. Although calibration algorithms can partially compensate these impairments, the remaining distortion still has substantial impact. Despite this, most prior works have not analyzed this type of distortion. In this paper, we investigate the impact of residual transceiver hardware impairments on the MIMO system performance. In particular, we consider a transceiver impairment model, which has been experimentally validated, and derive analytical ergodic capacity expressions for both exact and high signal-to-noise ratios (SNRs). We demonstrate that the capacity saturates in the high-SNR regime, thereby creating a finite capacity ceiling. We also present a linear approximation for the ergodic capacity in the low-SNR regime, and show that impairments have only a second-order impact on the capacity. Furthermore, we analyze the effect of transceiver impairments on large-scale MIMO systems; interestingly, we prove that if one increases the number of antennas at one side only, the capacity behaves similar to the finite-dimensional case. On the contrary, if the number of antennas on both sides increases with a fixed ratio, the capacity ceiling vanishes; thus, impairments cause only a bounded offset in the capacity compared to the ideal transceiver hardware case., QC 20190208

This paper presents for the first time the testbed implementation of an iterative interference alignment and power control algorithm for downlink transmission in a multiple-input multiple-output (MIMO) cellular network. The network is composed of three cells where within each cell one base station (BS) communicates with one mobile station (MS). Each terminal is equipped with two antennas. All the BSs transmit at the same time and the same frequency band. Transmitter beamforming vectors and receiver filtering vectors are computed according to the interference alignment concept, and power control is performed to guarantee successful communication of each BS-MS pair at a desired fixed rate. The indoor measurements performed on an universal software radio peripheral (USRP) based test-bed, show that the power can be reduced by at least 4 dB, 90% of the time, while at the same time reducing the bit-error-rate (BER)., QC 20150227

This paper studies the impact of jamming on the design of three-node two-hop cooperative amplify-and-forward (AF) communications with both half-duplex and full-duplex relaying. For the half-duplex relaying, the jammer is smart such that it can optimally allocate jamming power between listening and forwarding phases. Given separate source and relay power constraints, we derive the optimal jamming power allocation; with a total source and relay power constraint, we model the interaction between the legitimate system and the jammer as a noncooperative game and prove the existence and uniqueness of the Nash Equilibrium (NE). It is found that due to the fact that the end performance is limited by the weaker phase, the legitimate systems tries to balance the performance of two phases while the jammer attacks the system by making the two hops imbalanced. While for the full-duplex relaying, we show that if the self-interference can be properly controlled, it can bring substantial performance gain. Simulation results verify our analysis., QC 20140203

In this paper we present a tunable PIFA which can be used in a mobile terminal. A NanoMech™ process enabled MEMS digital variable capacitor has been used as a capacitive load to the antenna. The antenna occupies a volume of just 1.3 cc and is targeted to be placed at the bottom corner of the device. With the help of tunability the antenna is able to cover from 704-960MHz in the low-band and 1710-2170MHz in the high-band, thus covering a wide range of frequency bands required for GSM/WCDMA/LTE systems. The MEMS device has an equivalent series inductance of less than 0.1nH hence the variation in the capacitance value with respect to frequency is less than 10%up to 5GHz. Further, the equivalent series resistance (ESR) of the digital variable capacitor is <0.4 across the whole frequency range of interest, hence causing very low insertion loss to the antenna. The tunable antenna is characterized by measuring it in 3D anechoic chamber. The measured total efficiency of the antenna varies from -4 to -2dB for 700MHz-960MHz and -3dB to -2dB for 1710-2170MHz., QC 20140409

In this paper, we study virtual full-duplex (FD) buffer-aided relaying to recover the multiplexing loss of half-duplex (HD) relaying in a network with multiple buffer-aided relays, each of which has multiple antennas, through opportunistic relay selection and beamforming. The main idea of virtual FD buffer-aided relaying is that a source and a relay simultaneously transmit their own information to another relay and a destination, respectively. In this network, inter-relay interference (IRI) is a crucial problem which has to be resolved like self-interference in the FD relaying. In contrast to previous work that neglected the IRI, we propose two buffer-aided relay selection and beam-forming schemes taking the IRI into consideration. Numerical results show that our proposed relay selection scheme with zero-forcing beamforming (ZFB)-based IRI cancellation approaches the average end-to-end capacity of IRI-free upper bound as the numbers of relays and antennas increase., QC 20131318, EU FP7 METIS

This paper considers a Fractional Sampling (FS) technique to enhance the Spectrum Sensing (SS) efficiency of a Cognitive Radio (CR) using a decision statistic based on asymptotic Random Matrix Theory (RMT). Firstly, the effect of noise correlation on eigenvalue based SS is studied analytically and by numerical evaluation. Secondly, new bounds for the Standard Condition Number (SCN) are proposed to enhance the SS efficiency in correlated noise scenarios. It is shown that proposed FS method can enhance SS efficiency up to certain FS rates at the expense of receiver complexity and no performance advantage is obtained if the FS rate is increased beyond this limit. As a result, a method for determining the operating point for the FS rate in terms of sensing performance and complexity is suggested., QC 20140212

Several MIMO processing algorithms have been proposed that exploit long-term channel statistics, relaying on the critical assumption that this long-term information is valid long enough. In this paper, we consider the Correlation Matrix Distance (CMD) method previously proposed for the evaluation of MIMO channel non-stationarity. We highlight a couple of problems with the CMD measure and propose two new metrics that are more appropriate for non-stationarity evaluation. The performance of the CMD method and new correlation matrix distance metrics is investigated using measured 4×4 MIMO channels. Both Line-of-Sight (LOS) and Non-LOS (NLOS) environments are considered., QC 20140604

This paper presents an impulse-radio UWB experimental platform for ranging and positioning in GNSS-challenged environments. The platform is based on the two-way time-of-arrival principle of operation, which reduces architecture complexity and relaxes the synchronization requirements with respect to time-of-arrival or time-difference-of-arrival solutions. The modular architecture of the platform is described together with the design and features of its main components, namely the 5.6-GHz RF front end and the baseband module for measurement and processing. A set of experimental results obtained using the realized platform in an indoor office environment is presented and discussed. The platform provides a maximum range of about 30 m in line-of-sight conditions with an RMSE of the order of 40 cm., QC 20131028

Successive zero-forcing dirty paper coding (SZF-DPC) is a simplified alternative to DPC for MIMO broadcast channels (MIMO BCs). In the SZF-DPC scheme, the noncausally-known interference is canceled by DPC, while the residual interference is suppressed by the ZF technique. Due to the ZF constraints, the precoders are constrained to lie in the null space of a matrix. For the sum rate maximization problem under a sum power constraint, the existing precoder designs naturally rely on the singular value decomposition (SVD). The SVD-based design is optimal but needs high computational complexity. Herein, we propose two low-complexity optimal precoder designs for SZF-DPC, all based on the QR decomposition (QRD), which requires lower complexity than SVD. The first design method is an iterative algorithm to find an orthonormal basis of the null space of a matrix that has a recursive structure. The second proposed method, which will be shown to require the lowest complexity, results from applying a single QRD to the matrix comprising all users' channel matrices. We analytically and numerically show that the two proposed precoder designs are optimal., QC 20130116

We consider the beamformer design for zero-forcing dirty paper coding (ZF-DPC), a suboptimal transmission technique for MISO broadcast channels (MISO BCs). Beamformers for ZF-DPC are designed to maximize a performance measure, subject to some power constraints and zero-interference constraints. For the sum rate maximization problem under a total power constraint, the existing beamformer designs in the literature are based on the QR decomposition (QRD), which is used to satisfy the ZF constraints. However, the optimality of the QRD-based design is still unknown. First, we prove that the QRD-based design is indeed optimal for ZF-DPC for any performance measure under a sum power constraint. For the per-antenna power constraints, the QRD-based designs become suboptimal, and we propose an optimal design, using a convex optimization framework. Low-complexity suboptimal designs are also presented., QC 20130118

Positioning services are increasingly used for applications such as navigation, advertising and social media. While outdoor navigation based on GPS and/or cellular systems works well, indoor navigation is a much tougher challenge. This paper presents a new indoor positioning method based on Wi-Fi fingerprints, i.e. RSSI measurements from multiple Wi-Fi access points. During an offline phase, fingerprints are collected at known positions in the building. This database of locations and the associated fingerprints are called the radio map. In the online mode, the current Wi-Fi fingerprint probability distributions are compared with those of the radio map. The user location is estimated by calculating a weighted average of the three offline positions that best match the online measurements. Experiments show that our technique is superior to other proposed methods and reaches a median error of 2.4m., QC 20121119

In this paper, we present a robust technique based on cost reference particle filter (CRPF) for combined channel impulse response (CIR) estimation and phase noise (PN) tracking in OFDM systems without any priori information regarding the noise in the state and measurement equation. Contrary to previous works, we hold no assumption regarding the magnitude of the PN variance and hence no approximation is made to simplify the model. The algorithm employs CRPF along with a Rao-Blackwellization technique for CIR estimation assuming static channel state over a number of OFDM symbols. Numerical results are given to demonstrate the performance of the algorithm based on mean squared error (MSE)., QC 20120423

A brain stroke is defined as a disturbance in the blood supply of the brain. This can be due to either an obstruction in the blood vessels of the brain or a rupture in the blood vessels which causes a leakage of blood in the brain. In many cases, a stroke results in the death of the patient within 24 hours. Hence, it is crucial that the neurologist has immediately contact with the patient in the first 30 minutes after the stroke. This means that a direct broadband communication link between the ambulance and the hospital is needed in order to transmit all necessary physiological parameters, such as blood pressure and glucose level as well as video images. In this paper, we present a new architecture of a wireless communication link between the ambulance and the hospital based on the concept of cognitive radios. The sender/receiver module in the ambulance will allow measuring the wideband spectrum and search for a suitable empty frequency band to send the data., QC 20120904

This paper presents a method for pedestrian motionclassification based on MEMS inertial measurement unit (IMU)mounted on the chest. The choice of mounting the IMU on thechest provides the potential application of the current study incamera-aided inertial navigation for positioning and personalassistance. In the present work, five categories of the pedestrianmotion including standing, walking, running, going upstairs,and going down the stairs are considered in the classificationprocedure. As the classification method, the continuous hiddenMarkov model (HMM) is used in which the output densityfunctions are assumed to be Gaussian mixture models (GMMs).The correct recognition rates based on the experimental resultsare about 95%., © 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.QC 20120823

In this paper, an ego-motion estimation approach is introduced that fuses visual and inertial information, using a monocular camera and an inertial measurement unit. The system maintains a set of feature points that are observed on the ground plane. Based on matched feature points between the current and previous images, a novel measurement model is introduced that imposes visual constraints on the inertial navigation system to perform 6 DoF motion estimation. Furthermore, feature points are used to impose epipolar constraints on the estimated motion between current and past images. Pose estimation is formulated implicitly in a state-space framework and is performed by a Sigma-Point Kalman filter. The presented experiments, conducted in an indoor scenario with real data, indicate the ability of the proposed method to perform accurate 6 DoF pose estimation., QC 20120618

We present a navigation system based on a monocular camera and an inertial measurement unit. The system detects visual tags and fuses the measurements on the image plane with inertial signals to perform pose estimation and localization using a Sigma-Point Kalman filter. The tags are detected by edge-based feature extraction and channel codes. During periods in which tags are not visible, epipolar constraints, arising from past views, are exploited to significantly reduce the position error growth rate. The experimental results in an office building indicate capabilities for indoor navigation., QC 20110412. Updated from manuscript to conference paper.

This paper presents the architecture of a test bed for indoor localization based on pulse Ultra-Wideband radio technology, mainly considering the localization of first responders as a target application. A modular design approach has been employed, therefore enabling comparison of different solutions and implementation of sensor fusion techniques for localization. The realized test bed provides range estimates based on the round-trip time of radio pulses, which is accurately measured by a time-to-digital converter without the need for nano-second-level clock synchronization. Furthermore, support for digital control and processing of the acquired raw data is provided by a field programmable gate array, allowing for flexibility and reconfigurability. Results of a preliminary characterization of the test bed are presented., QC 20121015

Coordinated Multipoint comprises a set of communication strategies for cellular systems which are based on cooperation/coordination between Base Stations (BSs). These strategies have been recently included in LTE standardization in order to meet the spectral efficiency requirements. In this paper, the focus is on the uplink capacity of a cellular system over a composite fading channel, which combines Ricean fading and shadowing. In order to realistically model the cellular system, path loss and distributed users are also considered. Finally, the channel model incorporates multiple antennas, as dictated by the latest wireless standards. Based on random matrix and free probability theory, closed-form expressions are derived for the channel capacity and the MMSE achievable rate. In this context, strong Line-of-Sight component is shown to degrade capacity performance, while large shadowing statistics benefit it., QC 20120629

Next generation networks are moving towards the convergence of mobile, fixed and broadcasting services in one standard platform, which requires the co-existence of satellite and terrestrial networks in the same spectrum. This framework has motivated the concept of cognitive Satellite Communication (SatComs). In this aspect, the problem of exploiting Spectrum Sensing (SS) techniques for a dual polarized fading channel is considered. In this paper, the performance of Energy Detection (ED) technique is evaluated in the context of a co-existence scenario of a satellite and a terrestrial link. Diversity combining techniques such as Equal Gain Combining (EGC) and Selection Combining (SC) are considered to enhance the SS efficiency. Furthermore, analytical expressions for probability of detection (Pd) and probability of false alarm (Pf ) are presented for these techniques in the considered fading channel and the sensing performance is studied through analytical and simulation results. Moreover, the effect of Cross Polar Discrimination (XPD) on the sensing performance is presented and it is shown that SS efficiency improves for low XPD., QC 20130118

In this paper, multiple input multiple output (MIMO) channel estimation formulated as a chance constrained problem is investigated. The chance constraint is based on the presumption that the estimated channel can be used in an application to achieve a given performance level with a prescribed probability. The aforementioned performance level is dictated by the particular application of interest. The resulting optimization problem is known to be nonconvex in most cases. To this end, convexification is attempted by employing a Chernoff inequality. As an application, we focus on the estimation of MIMO wireless channels based on a general L-optimality type of performance measure., QC 20121214

In this paper, application-oriented experiment design formulated as a chance constrained problem is investigated. The chance constraint is based on the presumption that the estimated model can be used in an application to achieve a given performance level with a prescribed probability. The aforementioned performance level is dictated by the particular application of interest. The resulting optimization problem is known to be nonconvex in most cases. To this end, convexification is attempted by employing a Chernoff relaxation. As an application, we focus on the identification of multiple input multiple output (MIMO) wireless channel models based on a general L-optimality type of performance measure., QC 20130110

In this paper we have proposed a technique for cooperative localization where localization is done in distributive fashion without using any additional broadcast by nodes. The method relies on a fixed scheduled ultra-wideband (UWB) pulse transmissions by nodes in a predetermined way. The advantages of the proposed method is simpler hardware, comparatively less pulse transmission in the system hence energy efficient and faster update rate., QC 20130121

This paper studies different uses of two cooperating relays to improve the secrecy rate of a wiretap channel. These two relays are assumed to perform only simple functions: either amplify-and-forward (AF) or jamming. Complex functions such as decode-and-forward (DF) are not considered. We study three modes of cooperation: i) cooperative jamming (CJ), ii) AF-aided beamforming and iii) mixed AF-aided beamforming and CJ, all with individual relay power constraints. While i) is known in the literature, our efforts are spent on ii) and iii). In particular, for iii), we assume that the jamming signals in two communication stages are correlated, giving rise to improved performances. We also propose a heuristic approach for selecting the appropriate cooperating mode. Simulation results illustrate the performance gain of each scheme under different channel conditions and the effectiveness of the proposed mode selection method., QC 20130128

This paper presents a research activity aimed at developing an Ultra-Wideband sensor for personnel indoor localization, based on the round trip time measurement of Ultra-Wideband pulses. An approach combining flexibility, high measurement update rate and asynchronous operation with digital processing capability has been employed in the design of the sensor. The principle of operation of the proposed sensor, the architecture of the realized in-house test bed and the experimental setup are described and discussed., QC 20120831

In this paper, we present a modular test bed for ultra wideband ranging. The test bed comprises a 6.5 GHz radio front end interfacing with a baseband pulse transceiver and round-trip-time measurement module and with a flexible digital control and processing platform. The proposed radio front end allows to reduce antenna size and interference from narrowband users, with respect to the baseband pulse transceiver. We provide experimental characterization results, therefore proving the concept for the proposed front end architecture in the context of the considered UWB test bed., QC 20130122

In this paper, a method for determining ground plane features in a sequence of images captured by a mobile camera is presented. The hardware of the mobile system consists of a monocular camera that is mounted on an inertial measurement unit (IMU). An image processing procedure is proposed, first to extract image features and match them across consecutive image frames, and second to detect the ground plane features using a two-step algorithm. In the first step, the planar homography of the ground plane is constructed using an IMU-camera motion estimation approach. The obtained homography constraints are used to detect the most likely ground features in the sequence of images. To reject the remaining outliers, as the second step, a new plane normal vector computation approach is proposed. To obtain the normal vector of the ground plane, only three pairs of corresponding features are used for a general camera transformation. The normal-based computation approach generalizes the existing methods that are developed for specific camera transformations. Experimental results on real data validate the reliability of the proposed method., QC 20121107

In this paper, an ego-motion estimation approach is introduced that fuses visual and inertial information, using a monocular camera and an inertial measurement unit. The system maintains a set of feature points that are observed on the ground plane. Based on matched feature points between the current and previous images, a novel measurement model is introduced that imposes visual constraints on the inertial navigation system to perform 6 DoF motion estimation. Furthermore, feature points are used to impose epipolar constraints on the estimated motion between current and past images. Pose estimation is formulated implicitly in a state-space framework and is performed by a Sigma-Point Kalman filter. The presented experiments, conducted in an indoor scenario with real data, indicate the ability of the proposed method to perform accurate 6 DoF pose estimation., QC 20120618

This paper presents a method for pedestrian motionclassification based on MEMS inertial measurement unit (IMU)mounted on the chest. The choice of mounting the IMU on thechest provides the potential application of the current study incamera-aided inertial navigation for positioning and personalassistance. In the present work, five categories of the pedestrianmotion including standing, walking, running, going upstairs,and going down the stairs are considered in the classificationprocedure. As the classification method, the continuous hiddenMarkov model (HMM) is used in which the output densityfunctions are assumed to be Gaussian mixture models (GMMs).The correct recognition rates based on the experimental resultsare about 95%., © 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.QC 20120823

In this paper, a method for determining ground plane features in a sequence of images captured by a mobile camera is presented. The hardware of the mobile system consists of a monocular camera that is mounted on an inertial measurement unit (IMU). An image processing procedure is proposed, first to extract image features and match them across consecutive image frames, and second to detect the ground plane features using a two-step algorithm. In the first step, the planar homography of the ground plane is constructed using an IMU-camera motion estimation approach. The obtained homography constraints are used to detect the most likely ground features in the sequence of images. To reject the remaining outliers, as the second step, a new plane normal vector computation approach is proposed. To obtain the normal vector of the ground plane, only three pairs of corresponding features are used for a general camera transformation. The normal-based computation approach generalizes the existing methods that are developed for specific camera transformations. Experimental results on real data validate the reliability of the proposed method., QC 20121107

This paper presents a method for pedestrian motionclassification based on MEMS inertial measurement unit (IMU)mounted on the chest. The choice of mounting the IMU on thechest provides the potential application of the current study incamera-aided inertial navigation for positioning and personalassistance. In the present work, five categories of the pedestrianmotion including standing, walking, running, going upstairs,and going down the stairs are considered in the classificationprocedure. As the classification method, the continuous hiddenMarkov model (HMM) is used in which the output densityfunctions are assumed to be Gaussian mixture models (GMMs).The correct recognition rates based on the experimental resultsare about 95%., © 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.QC 20120823

In this paper, an ego-motion estimation approach is introduced that fuses visual and inertial information, using a monocular camera and an inertial measurement unit. The system maintains a set of feature points that are observed on the ground plane. Based on matched feature points between the current and previous images, a novel measurement model is introduced that imposes visual constraints on the inertial navigation system to perform 6 DoF motion estimation. Furthermore, feature points are used to impose epipolar constraints on the estimated motion between current and past images. Pose estimation is formulated implicitly in a state-space framework and is performed by a Sigma-Point Kalman filter. The presented experiments, conducted in an indoor scenario with real data, indicate the ability of the proposed method to perform accurate 6 DoF pose estimation., QC 20120618

In this paper, an ego-motion estimation approach is introduced that fuses visual and inertial information, using a monocular camera and an inertial measurement unit. The system maintains a set of feature points that are observed on the ground plane. Based on matched feature points between the current and previous images, a novel measurement model is introduced that imposes visual constraints on the inertial navigation system to perform 6 DoF motion estimation. Furthermore, feature points are used to impose epipolar constraints on the estimated motion between current and past images. Pose estimation is formulated implicitly in a state-space framework and is performed by a Sigma-Point Kalman filter. The presented experiments, conducted in an indoor scenario with real data, indicate the ability of the proposed method to perform accurate 6 DoF pose estimation., QC 20120618

This paper presents a method for pedestrian motionclassification based on MEMS inertial measurement unit (IMU)mounted on the chest. The choice of mounting the IMU on thechest provides the potential application of the current study incamera-aided inertial navigation for positioning and personalassistance. In the present work, five categories of the pedestrianmotion including standing, walking, running, going upstairs,and going down the stairs are considered in the classificationprocedure. As the classification method, the continuous hiddenMarkov model (HMM) is used in which the output densityfunctions are assumed to be Gaussian mixture models (GMMs).The correct recognition rates based on the experimental resultsare about 95%., © 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.QC 20120823

In this paper, a method for determining ground plane features in a sequence of images captured by a mobile camera is presented. The hardware of the mobile system consists of a monocular camera that is mounted on an inertial measurement unit (IMU). An image processing procedure is proposed, first to extract image features and match them across consecutive image frames, and second to detect the ground plane features using a two-step algorithm. In the first step, the planar homography of the ground plane is constructed using an IMU-camera motion estimation approach. The obtained homography constraints are used to detect the most likely ground features in the sequence of images. To reject the remaining outliers, as the second step, a new plane normal vector computation approach is proposed. To obtain the normal vector of the ground plane, only three pairs of corresponding features are used for a general camera transformation. The normal-based computation approach generalizes the existing methods that are developed for specific camera transformations. Experimental results on real data validate the reliability of the proposed method., QC 20121107

In this paper, a method for determining ground plane features in a sequence of images captured by a mobile camera is presented. The hardware of the mobile system consists of a monocular camera that is mounted on an inertial measurement unit (IMU). An image processing procedure is proposed, first to extract image features and match them across consecutive image frames, and second to detect the ground plane features using a two-step algorithm. In the first step, the planar homography of the ground plane is constructed using an IMU-camera motion estimation approach. The obtained homography constraints are used to detect the most likely ground features in the sequence of images. To reject the remaining outliers, as the second step, a new plane normal vector computation approach is proposed. To obtain the normal vector of the ground plane, only three pairs of corresponding features are used for a general camera transformation. The normal-based computation approach generalizes the existing methods that are developed for specific camera transformations. Experimental results on real data validate the reliability of the proposed method., QC 20121107

In this paper, a method for determining ground plane features in a sequence of images captured by a mobile camera is presented. The hardware of the mobile system consists of a monocular camera that is mounted on an inertial measurement unit (IMU). An image processing procedure is proposed, first to extract image features and match them across consecutive image frames, and second to detect the ground plane features using a two-step algorithm. In the first step, the planar homography of the ground plane is constructed using an IMU-camera motion estimation approach. The obtained homography constraints are used to detect the most likely ground features in the sequence of images. To reject the remaining outliers, as the second step, a new plane normal vector computation approach is proposed. To obtain the normal vector of the ground plane, only three pairs of corresponding features are used for a general camera transformation. The normal-based computation approach generalizes the existing methods that are developed for specific camera transformations. Experimental results on real data validate the reliability of the proposed method., QC 20121107

This paper presents a method for pedestrian motionclassification based on MEMS inertial measurement unit (IMU)mounted on the chest. The choice of mounting the IMU on thechest provides the potential application of the current study incamera-aided inertial navigation for positioning and personalassistance. In the present work, five categories of the pedestrianmotion including standing, walking, running, going upstairs,and going down the stairs are considered in the classificationprocedure. As the classification method, the continuous hiddenMarkov model (HMM) is used in which the output densityfunctions are assumed to be Gaussian mixture models (GMMs).The correct recognition rates based on the experimental resultsare about 95%., © 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.QC 20120823

In this paper, an ego-motion estimation approach is introduced that fuses visual and inertial information, using a monocular camera and an inertial measurement unit. The system maintains a set of feature points that are observed on the ground plane. Based on matched feature points between the current and previous images, a novel measurement model is introduced that imposes visual constraints on the inertial navigation system to perform 6 DoF motion estimation. Furthermore, feature points are used to impose epipolar constraints on the estimated motion between current and past images. Pose estimation is formulated implicitly in a state-space framework and is performed by a Sigma-Point Kalman filter. The presented experiments, conducted in an indoor scenario with real data, indicate the ability of the proposed method to perform accurate 6 DoF pose estimation., QC 20120618

In this paper we evaluate the effect of applying peak-to-average power ratio (PAPR) reduction and digital pre-distortion (DPD) on radio frequency power amplifiers when an orthogonal frequency division multiplexing (OFDM) signal is used. The PAPR reduction method, presented as a convex problem, is based on reshaping the time domain signal by redistributing its energy in the frequency domain, with respect to constraints on in-band and out-of-band errors. The DPD method consists of modeling the behavior of the power amplifier using a parallel Hammerstein model, and then extracting its inverse parameters based on the indirect learning approach. The cases where PAPR and DPD are applied separately and combined, are studied and investigated. Power amplifier figures of merit are evaluated. A good performance is shown when combining both pre-processing techniques up to a certain operating point where DPD performance deteriorates. Solutions to improve the DPD performance at strong compression are suggested., QC 20120216

In this paper, a novel method for estimating the transformation between an inertial measurement unit (IMU) and a camera together with the intrinsic parameters of the camera is proposed. The method relies on images of reflected feature points in a planar mirror captured by an uncalibrated camera mounted with an IMU. It does not rely on using a fixed calibration pattern in front of the moving camera and the motion is not limited to be planar in front of the mirror. Instead, known feature points located on the camera body are tracked over the time to estimate the IMU-camera transformation and camera intrinsic parameters. A state-space model of the system is derived and then used as input to the Sigma-Point Kalman filter framework. Simulation results show accurate estimation of both IMU-camera translation and rotation parameters as well as the camera intrinsic parameters., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111220

In this paper, we study the design of optimal robust training sequences for multiple-input multiple-output (MIMO) channel estimation, based on known second order statistics of both the channel and the colored disturbance, but with an uncertainty in the channel covariance matrix. More specifically, the training sequences are designed by taking the least-favorable channel covariance component into account throughout an iterative algorithm. Numerical experiments are carried out to demonstrate the performance gained by employing the proposed design procedure and to compare it with other relevant schemes., QC 20111129

The Kronecker model is a popular structure in the design and analysis of multiple-input multiple-output (MIMO) systems. Despite being criticized for unrealistic results in some cases, it mathematically facilitates the analysis of MIMO transmission schemes. In our earlier work [1], we proposed algorithms in order to determine a MIMO channel covariance matrix which is as far as possible from the Kronecker model based on semi-definite relaxation approach. In this paper, we develop this approach for different case studies. In particular, we verify our proposed algorithms for different size of antennas. Further, as a case study for the relevance of the Kronecker assumption, numerical analysis will be carried out to evaluate the performance of optimal pilot design for Kronecker and non-Kronecker MIMO channels., QC 20111129