Search

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

Development of a low bit-rate voice over IP application is described. A speech coding algorithm is constructed and implemented on a digital signal processor (DSP). The algorithm is based on a sub-band mixed excitation LPC vocoder structure and operates at a rate of 2000 bits per second. Implementation is done on two TMS320C6701 floating point DSP’s each connected to a PC. On the PC, a graphical user interface (GUI) controls the data flow over the IP network. The application runs in full duplex and supports poor to fair sound quality depending on the used recording equipment., Qc 20120220

Development of a low bit-rate voice over IP application is described. A speech coding algorithm is constructed and implemented on a digital signal processor (DSP). The algorithm is based on a sub-band mixed excitation LPC vocoder structure and operates at a rate of 2000 bits per second. Implementation is done on two TMS320C6701 floating point DSP’s each connected to a PC. On the PC, a graphical user interface (GUI) controls the data flow over the IP network. The application runs in full duplex and supports poor to fair sound quality depending on the used recording equipment., Qc 20120220

Development of a low bit-rate voice over IP application is described. A speech coding algorithm is constructed and implemented on a digital signal processor (DSP). The algorithm is based on a sub-band mixed excitation LPC vocoder structure and operates at a rate of 2000 bits per second. Implementation is done on two TMS320C6701 floating point DSP’s each connected to a PC. On the PC, a graphical user interface (GUI) controls the data flow over the IP network. The application runs in full duplex and supports poor to fair sound quality depending on the used recording equipment., Qc 20120220

Development of a low bit-rate voice over IP application is described. A speech coding algorithm is constructed and implemented on a digital signal processor (DSP). The algorithm is based on a sub-band mixed excitation LPC vocoder structure and operates at a rate of 2000 bits per second. Implementation is done on two TMS320C6701 floating point DSP’s each connected to a PC. On the PC, a graphical user interface (GUI) controls the data flow over the IP network. The application runs in full duplex and supports poor to fair sound quality depending on the used recording equipment., Qc 20120220

Development of a low bit-rate voice over IP application is described. A speech coding algorithm is constructed and implemented on a digital signal processor (DSP). The algorithm is based on a sub-band mixed excitation LPC vocoder structure and operates at a rate of 2000 bits per second. Implementation is done on two TMS320C6701 floating point DSP’s each connected to a PC. On the PC, a graphical user interface (GUI) controls the data flow over the IP network. The application runs in full duplex and supports poor to fair sound quality depending on the used recording equipment., Qc 20120220

The paper presents a new method for the correction of non-linearity errors in ADCs. The method has been designed to allow self calibration in systems where an internal signal can be generated, such as base stations for mobile communications. The method has been implemented and tested in simulation on the behavioral model of a commercial ADCs, and on a hardware setup composed by a data acquisition board and a distorting circuit., QC 20120918

By imposing additional constraints in the downlink beamforming optimization. more general Quality of Service (QoS) measures than the average Signal to Interference and Noise Ratio (SINR) alone, can be introduced. Herein a rapidly converging algorithm solving the downlink beamforming problem with additional indefinite quadratic constraints on the beamforming vector is presented. The proposed algorithm is significantly faster than the previously proposed solution, which involves semidefinite programming. Also, the algorithm is easy to implement, since it only involves eigenvalue problems., QC 20110627

The deployment of vehicle airbags for maximum protection requires information about the occupant's position, movement, weight, size etc. Specifically it is desirable to discriminate between adults, children, front- or rear faced child seats, objects put on the seat or simply empty seats. 2D images lack depth information about the object and are very sensitive to illumination conditions. Herein, occupant position classification techniques are developed based on low resolution 3D image sequences. The proposed methods are of low complexity and high reliability allowing real time implementation and meeting the rigorous requirements for passenger safety systems. Features are extracted from the 3D image sequences and a Sequential Forward Search (SFS) feature subset selection algorithm is employed to reduce the size of the feature set. Two classification techniques are evaluated, the B ayes quadratic classifier and the polynomial classifier. We present the classification results based on a large set of measurements from the low resolution 3D image sequences. The full scale tests have been conducted on a wide rance of realistic situations (adults/children/child seats etc.) which may occur in a vehicle., QC 20110627

Data-aided multi-user burst frequency synchronization under interference limited conditions is analyzed. It is assumed that a unique-word based synchronization mechanism is used to achieve synchronization. In a first approach this unique-word is assumed to be located at the beginning of the burst structure. The interference represents frequency-adjacent bursts that are coarsely time synchronous. This corresponds to a typical multi frequency (MF) TDMA system with co-channel interference (CCI) limited minimal frequency separation. A novel approach is analyzed to reduce the interference impact of the carrier offset estimation, applying interference cancellation iteratively to increase the estimation accuracy. We demonstrate improved frequency synchronization with this novel approach of iterative burst synchronization., QC 230110627

QC 20111108

A method for joint estimation of the coupling matrix, element factor, and phase center of an array from calibration data is proposed. Our simulation results for an 8 element array show that optimal compensation for an adaptive antenna is only achieved if all parameters are properly estimated., QC 20120816

Characterization and testing of analog-to-digital converters (ADCs) are interesting in many different aspects. Histogram test is a common method to characterize the linearity features of an ADC. Two commonly used stimuli signals are sine waves and Gaussian noise. This paper will present a metrological comparison between Gaussian and sine wave histogram tests for wideband applications; that is evaluate the performance in characterization of the ADC and the usability of post-correction. A post-correction procedure involves characterization of the ADC non-linearity and then utilization of this information by processing the ADC output samples to remove the distortion. The results indicates that even though the Gaussian histogram test seems to give reasonable accuracy to measure non-linearities it is not thereby a suitable model for post-correction. A single-tone sine wave histogram will most likely be a better solution. Best result is to train the look-up table with several single-tone sine waves in the frequency band., QC 20120313

In this paper, single carrier frequency domain equalization with space time transmit diversity was implemented and evaluated in real-time using a DSP-based wireless MIMO test-bed. The implemented schemes supported a large set of modulations, from BPSK up to QAM64. Zero padding is introduced to mitigate inter-block interference. Robust time and frequency synchronization together with channel estimation based on Kalman filtering is used to address the adverse intersymbol interference and the severe carrier frequency offset due to hardware impairments., QC 20111107

A compact MIMO array suited for a PDA application at 1766 and 2450 MHz is presented. We chose a configuration which both maximizes the distance between the elements, and provides full polarization diversity. The performance of the array at 1766 MHz has been presented in terms of S-parameters, efficiency, calculated covariance and capacity. We conclude that the major difference between the proposed array and an ideal monopole reference array lies in the slightly lower radiation efficiency., QC 20120918

In a typical array processing scenario, noise acting on the array can not be assumed spatially white. It is in many cases necessary to use quiet periods, when only noise is received, to estimate the noise covariance. If estimation of the signal parameters, such as directions of arrivals (DOAs), and noise covariance is performed jointly, performance can be improved. This is especially true when stationarity considerations limit the amount of available, valid noise-only data. This is shown in an earlier work, together with the introduction of an optimal weighting for Weighted Subspace Fitting (WSF), when based on whitened data. An asymptotically valid approximative maximum likelihood method (AML) for the DOA estimation problem is derived in this paper. The resulting criterion can be concentrated with respect to the signal parameters. In numerical experiments, AMI, shows very promising small-sample performance compared to earlier methods. The associated criterion function is well suited for numerical optimization and allows for the development of a novel, MODE-like, non-iterative estimation procedure if the array belongs to the important class of uniform linear arrays. This non-iterative resulting procedure retains the asymptotic properties of maximum likelihood, and numerical simulations indicate superior threshold performance when compared to an optimally weighted WSF formulation of MODE. For the detection problem, no method has been presented that takes the unknown noise covariance into account Here, a well known detection scheme for WSF is extended to work in this scenario as well. The derivations of this scheme further stress the importance of correctly weighting WSF when the noise covariance is unknown. It is also shown that the minimum value of the criterion function associated with AMI, can be used for the detection purpose. Numerical experiments indicate promising performance for the AML-detection scheme., QC 20110628

In opportunistic SDMA, the base station forms several random beams simultaneously and relies on fast but limited feedback for scheduling users on the beams. In this paper, opportunistic SDMA is applied to an OFDMA downlink by having independent beamformers run in parallel on different frequency bands (SD-OFDMA). A method for improving the performance of completely random beamforming is proposed and evaluated. It exploits the temporal channel correlation and the partial channel state information available at the transmitter to keep "successful" beams over longer periods of time than the default block duration. Extensive simulation results show a significant improvement in cell throughput compared to a completely random scheme. The results also show that in order to gain more from the multiple simultaneous beams than what is lost in additional interference, the system load must be high., QC 20110509

In this paper, we consider the unclaimed sub-carriers that no user feeds back in an opportunistic OFDMA system with a per sub-carrier power constraint. Unclaimed sub-carriers appear in OFDMA systems with reduced feedback, where the users concentrate the feedback on the sub-carriers with good channel quality. Here we propose and evaluate two ways to use these sub-carriers to improve the system performance. One approach is to transmit pilots symbols on the unclaimed sub-carriers. A second approach is to schedule users based on their feedback about adjacent sub-carriers. Simulation results show that for low to moderate channel rms delay spread, it is more advantageous to transmit data on unclaimed sub-carriers, even at a low rate, than to use them for additional pilot symbols. For high delay spreads however, transmitting pilots on the unclaimed sub-carriers gives higher system throughput., QC 20110701

In this paper, the MIMO framework within WINNER for fourth generation radio systems is further developed and assessed for various deployment scenarios. The emphasis is on radio network system aspects of multi-antenna techniques where preferred configurations for three basic deployment scenarios are given. In the wide area scenario which aims to provide ubiquitous coverage for rural, suburban and urban areas, the scheme selection depends on the user density of spatially separated users. It ranges from grid of fixed beams (GoB) (TDMA based) in case of few users to SDMA with a fixed linear precoding codebook, and finally to adaptive beams with SDMA for highly dense system. In the metropolitan area scenario which is targeting system deployments in large urban environments, multi-user (MU) MIMO precoding performs very well for slow moving users. For higher velocities, per antenna rate control (PARC) or adaptive linear dispersion codes (LDCs) are better choices. In the local area scenario which is characterized by isolated sites, the combination of SDMA and spatial multiplexing achieved by MU-MIMO precoding provides high spectral efficiency., QC 20110712

Spatial division multiple access (SDMA) systems efficiently take advantage of the spatial dimensions of the channel to increase the performance of the system. A major difficulty, common to all SDMA systems, is the requirement of channel knowledge at the transmitter to enable transmission of multiple streams without catastrophic interference. Herein we show that, in wide area scenarios, statistical channel information combined with the Euclidean norm of the channel realization, fed back from the users, provide sufficient information for SDMA systems to efficiently allocate users in time and space. A joint beamforming and scheduling algorithm is proposed for the downlink, which extends the proportional fair scheduling criterion to an SDMA setting, resulting in a weighted sum rate maximization., QC 20110628

The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the largest norm to the transmitter and derive the conditional second and fourth order channel moments in order to design the downlink beamforming weights. Similar approaches have previously been presented for multi-user multiple-input single-output (MISO) systems. Herein, these techniques are generalized to MIMO systems, by either antenna selection or receive beamforming at the receiver. Two eigenbeamforming strategies are proposed and shown to outperform opportunistic beamforming, based on similar feedback information., © 2007 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 20110704

The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the largest norm to the transmitter and derive the conditional second and fourth order channel moments in order to design the downlink beamforming weights. Similar approaches have previously been presented for multi-user multiple-input single-output (MISO) systems. Herein, these techniques are generalized to MIMO systems, by either antenna selection or receive beamforming at the receiver. Two eigenbeamforming strategies are proposed and shown to outperform opportunistic beamforming, based on similar feedback information., © 2007 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 20110704

The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the largest norm to the transmitter and derive the conditional second and fourth order channel moments in order to design the downlink beamforming weights. Similar approaches have previously been presented for multi-user multiple-input single-output (MISO) systems. Herein, these techniques are generalized to MIMO systems, by either antenna selection or receive beamforming at the receiver. Two eigenbeamforming strategies are proposed and shown to outperform opportunistic beamforming, based on similar feedback information., © 2007 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 20110704

The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the largest norm to the transmitter and derive the conditional second and fourth order channel moments in order to design the downlink beamforming weights. Similar approaches have previously been presented for multi-user multiple-input single-output (MISO) systems. Herein, these techniques are generalized to MIMO systems, by either antenna selection or receive beamforming at the receiver. Two eigenbeamforming strategies are proposed and shown to outperform opportunistic beamforming, based on similar feedback information., © 2007 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 20110704

The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the largest norm to the transmitter and derive the conditional second and fourth order channel moments in order to design the downlink beamforming weights. Similar approaches have previously been presented for multi-user multiple-input single-output (MISO) systems. Herein, these techniques are generalized to MIMO systems, by either antenna selection or receive beamforming at the receiver. Two eigenbeamforming strategies are proposed and shown to outperform opportunistic beamforming, based on similar feedback information., © 2007 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 20110704

In this paper the software and hardware structure of a virtual instrument measurement system is discussed. The focus is on flexibility, modularity, generality and hardware independence. A software architecture that meets these requirements is proposed and discussed in some detail. The proposed software architecture has a layered structure that makes it suitable for implementation of versatile measurement systems. The measurement functionality is encapsulated in its own, hardware independent layer and communicates with its environment, e.g. physical hardware, through intermediary software components. Finally a measurement system for characterization of power amplifiers that is designed following the proposed software architecture, with software driven measurements, is implemented., QC 20100824

A decrease in life cycle cost is a key issue for testing of mobile communication systems. The rapid development and edge technology requires high performance instruments and state of the art measurement technology. It is desired to use virtual/synthetic instruments and put the measurement technology in software independent of hardware, i.e. software driven measurements. Increased flexibility and modularization, both in hardware and software, are requirements to support the cost decrease. The hardware basis is signal generation and signal analysis. In this paper state of the art signal generation and signal analysis capabilities are demonstrated in a modular and flexible architecture. A direct IF synthesis is used to generate 1 WideBand Code-Division Multiple Access (WCDMA) carrier with more than 72 dB Adjacent Carrier Leakage Ratio (ACLR) 2 carrier with more than 68 dBc ACLR over a total bandwidth of 100 MHz. The signal analysis capabilities, ACLR performance, for a WCDMA carrier is better than -70 dBc and for a continuous wave better than -85 dBc over a bandwidth of 42.5 MHz. The critical down converter in the set up doesn't degrade the performance., QC 20141105

The Cramer-Rao bound (CRB) is a lower bound on the error variance of any estimator. For a Gaussian scenario, the CRB is derived for a seven parameter dual channel sine wave model; a model with relevance in applications like impedance measurements and the estimation of particle size and velocity by laser anemometry. Three different parameterizations are considered: the common quadrature/in-phase and amplitude-phase models, as well as a relative amplitude-phase model. The CRB indicates the achievable error variance of an unbiased estimator as a function of the signal-to-noise ratio, number of samples, and noise power. An non-optimal non-linear least squares fit of the signal model to the collected data is employed. The problem at hand is separable and can be solved by a one dimensional search followed by a linear least-squares fit of the remaining parameters. The performance of the method is investigated by aid of a simulation study, and the outcome is compared with the corresponding CRB. For high signal-to-noise ratios, the performance of the proposed method is close to optimal with an error variance close to the predictions made by the CRB., QC 20110701

The type and quality of the channel state information at the transmitter of a fading multiple-input multiple-output system greatly affects the ergodic capacity of the wireless link. In order to compare and unify the different proposals of transmit strategies for different scenarios, recently classes of MIMO channels are introduced that share a common optimal transmit strategy. In this work, we derive the ergodic capacity achieving transmit strategy for the class of unitary invariant norm feedback which complements statistical channel information at the transmitter. The impact of the short-term feedback quality is illustrated by the beamforming optimality range. The higher the feedback norm is the more likely is single stream beamforming to be optimal., QC 20110628

The fixed-complexity sphere decoder (FSD) has been previously proposed for multiple input-multiple output (MIMO) detection to overcome the two main drawbacks of the original sphere decoder (SD), namely its variable complexity and sequential structure. As such, the FSD is highly suitable for hardware implementation and has shown remarkable performance through simulations. Herein, we explore the theoretical aspects of the algorithm and prove that the FSD achieves the same diversity order as the maximum likelihood detector (MLD). Further, we show that the coding loss can be made negligible in the high signal to noise ratio (SNR) regime with a significantly lower complexity than that of the MLD., QC 20110628

Herein, the design of linear dispersion codes for block based multiple-input multiple-output communication systems is investigated. The receiver as well as the transmitter are assumed to have perfect knowledge of the channel, and the receiver is assumed to employ maximum likelihood detection. We propose to use linear precoding and lattice invariant operations to transform the channel matrix into a lattice with large coding gain. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere packing properties. Lattice invariant transformations are then used to minimize the power consumption. An algorithm for this power minimization is presented along with a lower bound on the optimization. Numerical results indicate that there is a potential gain of several dB by using the method compared to channel inversion with adaptive bit loading., QC 20110628

The problem of optimal power allocation for a single user in an OFDMA system is considered for uplink, under the assumption that the total power is divided equally to a selected subset of subcarriers. This scenario suggests reduced feedback information for power control from base station to the user since only the information over modulation on each subcarrier is necessary. Assuming knowledge of the instantaneous users' channel gains, the rate optimization problem reduces to a subcarrier allocation problem, discribed by a discrete function with the set of possible allocated subcarriers as domain and the set of achievable sum rates as range. A continuous equivalent of the function is used to derive properties that also hold in the discrete case. The function is in general not concave and concavity holds only for high CNR regions - over a specified bound. In all cases however it is proved that the maximum is unique and a simple and efficient algorithm is proposed for subcarrier allocation which always provides the optimal solution concerning the subcarriers to be loaded. The cost in achievable capacity from the use of equal-power compared to actual waterfilling is calculated, which is shown to be small while the gain in frequency resources and feedback reduction is important., QC 20141111

A novel method is proposed for estimation of the mutual coupling matrix of an antenna array. The method extends previous work by incorporating an unknown phase center and the element factor (antenna radiation pattern) in the model, and treating these as nuisance parameters during the estimation of coupling. To facilitate this, a parametrization of the element factor based on a truncated Fourier series is proposed. The Cramer-Rao bound (CRB) for the estimation problem is derived and used to analyze how the required amount of measurement data increases when introducing a more and more flexible model for the element factor. Finally, the performance of the proposed estimator is illustrated using data from measurements on an 8-element antenna array., QC 20110628

The problem of Adjacent Satellite Interference (ACI) within the Direct-To-Home (DTH) satellite broadcast reception scenario is considered. The use of small DTH front-end reception systems results inevitably in a higher interference level from adjacent satellites using the same frequency band. The growth in satellite communication and the trend to small dishes increases the ACI problem. The general problem of interference limited DTH reception has been studied in recent work, see [2]. This paper extends the work of [21 by considering additionally an MMSE based method based on the proposal by Beidas and Gamal, see [3]. The interference channel model and the iterative interference cancellation algorithm are introduced and applied to the DTH digital broadcast case. Simulations of the interesting scenarios are conducted and discussed. It is shown, that the algorithm works well over large ranges of the considered scenarios of frequency offset and signal power levels., QC 20110701

In recent analyses of multiuser MIMO systems and their capacity achieving transmit strategies, Gaussian codebooks; are usually used. For the case in which the input signals are constrained to belong to a finite constellation, we study and explain two effects, namely Multiuser Gaussianity (MuG) and constellation randomization (CoRa). MuG means that the more users transmit simultaneously, the higher is the similarity of the received density to the optimal Gaussian one. Hence, the instantaneous mutual information is increased by MuG. This leads to a tradeoff between multiuser diversity and MuG. On the other hand, CoRa is done by linear precoding by random unitary matrices. Based on the observations from MuG, we explain why the outage capacity is increased by CoRa. The effects are illustrated by various numerical simulations., QC 20141028

QC 20141118

Static occupant classification is an important requirement in designing so-called smart airbags. Systems for this purpose can be either based on pressure sensors or vision sensors. Vision-based systems are advantageous over pressure-sensor-based systems as they can provide additional functionalities like dynamic occupant-position analysis or child-seat orientation detection. The focus of this paper is to evaluate and analyze static occupant classification using a low-resolution range sensor, which is based on the time-of-flight principle. This range sensor is advantageous, since it provides directly a dense range image that is independent of the ambient illumination conditions and object textures. Herein, the realization of an occupant-classification system, using a novel low-resolution range image sensor, is described, methods for extracting robust features from the range images are investigated, and different classification methods are evaluated for classifying occupants. Bayes quadratic classifier, Gaussian mixture-model classifier, and polynomial classifier are compared to a clustering-based linear-regression classifier using a polynomial kernel. The latter one shows improved results compared to the first-three classification methods. Full-scale tests have been conducted on a wide range of realistic situations with different adults and child seats in various postures and positions. The results prove the feasibility of low-resolution range images for the current application., QC 20100525

Orthogonal frequency-division multiple access (OFDMA) is an attractive technique for exploiting multiuser diversity in the downlink of a cellular system. This paper addresses three problems in multiuser diversity for OFDMA systems. First, we propose a way to significantly reduce the amount of channel state information (CSI) feedback without sacrificing performance too much, by selective and adaptive feedback. Second, we propose a way to increase the cell throughput and fairness by appying an opportunistic beamforming scheme to orthogonal frequency-division multiplexing. This beamforming scheme increases the frequency fading rate, which increases the multiuser diversity effect. Thirdly, we deal with the issue of fairness and quality-of-service (QoS) in opportunistic systems by proposing a modified proportional fair (PF) scheduler for OFDMA. Key features in the scheduler are that it incorporates QoS classes into the PF scheduler and that it has a tunable fairness level. Extensive simulation results are presented to evaluate. the performance of the proposed schemes. The opportunistic beamforming scheme performed well in comparison with several other schemes. The modified PF scheduler was able to give users different QoS, based on their requirements, while still exploiting multiuser diversity., Correction in: IEEE Transactions On Communications, 2007, vol. 55, issue. 6, page. 1266, doi: 10.1109/TCOMM.2007.900972

In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with long-term statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second order moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization., © 2008 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 20110701

In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with long-term statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second order moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization., © 2008 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 20110701

In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with long-term statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second order moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization., © 2008 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 20110701

In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with long-term statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second order moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization., © 2008 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 20110701

In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with long-term statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second order moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization., © 2008 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 20110701

We consider the communication of digital signals over a multiple-input multiple-output wireless channel, using a linear precoder at the transmitter and a non-linear decision feedback equalizer at the receiver. This receiver structure can exploit the signal constellation properties by using successive quantization and interference cancellation. Recently, optimal precoder designs have been found for a wide range of performance measures assuming that perfect channel-state information (CSI) is available. Herein, we propose a design taking CSI uncertainty into account by utilizing the first and second order statistics of the channel. The resulting precoder exhibits improved performance compared to similar methods based on long-term statistics., QC 20110701

The estimation of signal covariance matrices is a crucial part of many signal processing algorithms. In some applications, the structure of the problem suggests that the underlying, true covariance matrix is the Kronecker product of two valid covariance matrices. Examples of such problems are channel modeling for multiple-input multiple-output (MIMO) communications and signal modeling of EEG data. In applications, it may also be that the Kronecker factors in turn can be assumed to possess additional, linear structure. The maximum-likelihood (ML) method for the associated estimation problem has been proposed previously. It is asymptotically efficient but has the drawback of requiring an iterative search for the maximum of the likelihood function. Two methods that are fast and noniterative are proposed in this paper. Both methods are shown to be asymptotically efficient. The first method is a noniterative variant of a well-known alternating maximization technique for the likelihood function. It performs on par with ML in simulations but has the drawback of not allowing for extra structure in addition to the Kronecker structure. The second method is based on covariance matching principles and does not suffer from this drawback. However, while the large sample performance is the same, it performs somewhat worse than the first estimator in small samples. In addition, the Cramer-Rao lower bound for the problem is derived in a compact form. The problem of estimating the Kronecker factors and the problem of detecting if the Kronecker structure is a good model for the covariance matrix of a set of samples are related. Therefore, the problem of detecting the dimensions of the Kronecker factors based on the minimum values of the criterion functions corresponding to the two proposed estimation methods is also treated in this work., QC 20100525 QC 20111104

In this paper, we consider the detection of binary (antipodal) signals transmitted in a spatially multiplexed fashion over a fading multiple-input-multiple-output (MIMO) channel and where the detection is done by means of semidefinite relaxation (SDR). The SDR detector is an attractive alternative to maximum-likelihood (NIL) detection since the complexity is polynomial rather than exponential. Assuming that the channel matrix is drawn with independent identically distributed (i.i.d.) real-valued Gaussian entries, we study the receiver diversity and prove that the SDR detector achieves the maximum possible diversity. Thus, the error probability of the receiver tends to zero at the same rate as the optimal NIL receiver in the high signal-to-noise ratio (SNR) limit. This significantly strengthens previous performance guarantees available for the semidefinite relaxation detector. Additionally, it proves that full diversity detection is also possible in certain scenarios when using a noncombinatorial receiver structure., QC 20100525

We consider the interaction of several transmit-receive pairs coexisting in the same area and communicating using the same portion of the spectrum. Using a game theoretic framework, each pair is regarded as a player whose payoff function is the individual link rate and power is allocated using the iterative water-filling algorithm. We find properties of the resulting Nash equilibria and derive conditions for when various operating points are achievable. The analysis presented herein extends previous work by characterizing the set of stable solutions for a multi-user system. Also, we show how the game can be modified to obtain better operating points in terms of sum rate compared to the iterative water-filling algorithm. The increase in performance corresponding to one such modification is evaluated and compared to the iterative water-filling algorithm by numerical simulations., QC 20110408

Designing, optimizing and producing modern power amplifiers (PA) requires new and fast RF (radio frequency) measurement techniques capable of characterizing its real behavior. PAs are a truly multidimensional device where many desired performance parameters are contradictory to each other. This is especially true for the generation of modern communication PAs that require high efficiency, high linearity as well as high bandwidth. This paper presents a software-defined measurement setup for fast and cost efficient multidimensional measurements based on highly accurate standard instruments and a PC. The test bed as well as the graphical user interface is presented along with a demonstration of its functionality. During tuning of tank networks, drain quiescent current, and bias conditions, 3-dimensional graphs can be selected for the most appropriate axes of trade-off parameters to display a true behavior of the PA under test subjected to real-world or close to real-world signals. The measurement system offers the possibility to monitor envelope-tracking dynamic power consumption up to 100 MHz plus the possibility to use high crest factors., © 2009 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 20100930, KKS

Designing, optimizing and producing modern power amplifiers (PA) requires new and fast RF (radio frequency) measurement techniques capable of characterizing its real behavior. PAs are a truly multidimensional device where many desired performance parameters are contradictory to each other. This is especially true for the generation of modern communication PAs that require high efficiency, high linearity as well as high bandwidth. This paper presents a software-defined measurement setup for fast and cost efficient multidimensional measurements based on highly accurate standard instruments and a PC. The test bed as well as the graphical user interface is presented along with a demonstration of its functionality. During tuning of tank networks, drain quiescent current, and bias conditions, 3-dimensional graphs can be selected for the most appropriate axes of trade-off parameters to display a true behavior of the PA under test subjected to real-world or close to real-world signals. The measurement system offers the possibility to monitor envelope-tracking dynamic power consumption up to 100 MHz plus the possibility to use high crest factors., © 2009 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 20100930, KKS

Designing, optimizing and producing modern power amplifiers (PA) requires new and fast RF (radio frequency) measurement techniques capable of characterizing its real behavior. PAs are a truly multidimensional device where many desired performance parameters are contradictory to each other. This is especially true for the generation of modern communication PAs that require high efficiency, high linearity as well as high bandwidth. This paper presents a software-defined measurement setup for fast and cost efficient multidimensional measurements based on highly accurate standard instruments and a PC. The test bed as well as the graphical user interface is presented along with a demonstration of its functionality. During tuning of tank networks, drain quiescent current, and bias conditions, 3-dimensional graphs can be selected for the most appropriate axes of trade-off parameters to display a true behavior of the PA under test subjected to real-world or close to real-world signals. The measurement system offers the possibility to monitor envelope-tracking dynamic power consumption up to 100 MHz plus the possibility to use high crest factors., © 2009 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 20100930, KKS