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IEEE Transactions on Signal Processing. 01/2011; 59:3272-3287.
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ABSTRACT: This paper aims to investigate the effects of uncertainties present in an antenna array system by employing elements of differential geometry based on the concept of the array manifold. This study is mainly focused on uncertainties on the positions of the antenna array elements, which also reflect uncertainties in the carrier frequency. Such uncertainties are inherent in the manufacturing process of antenna arrays and can greatly impact on system performance. Their effects on various performance measures such as the accuracy of channel parameter estimation and signal-to-noise ratio (SNR) at the output of a number of receivers that employ antenna arrays is studied. The results of the study are particularly applicable to array design and calibration methods.
Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
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ABSTRACT: This paper addresses the problem of joint transmitter-receiver optimization in the downlink multiple input multiple output (MIMO) DS-CDMA systems over multipath fading channels. Both the transmitter and the receivers are equipped with antenna arrays and the precoding/decoding matrices can be designed to minimize the overall mean-squared-error (MSE) of the system subject to power constraint. The study is based on the spatio-temporal array (STAR) manifold concept. The performance of the proposed algorithm is supported by numerical simulations.
Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
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ABSTRACT: The problem of joint transmitter and receiver beam- forming in the downlink DS-CDMA over multipath fading channels is considered in this paper. The proposed investigation is based on the array manifold concept and thus, the space-time properties of the channel can be fully exploited, playing a crucial role in the operation of blind channel estimation and interference suppression techniques. The beamforming weights are designed to minimise the overall mean-squared-error (MSE) of the system. An iterative solution to the optimisation problem is firstly proposed under the system framework. A closed-form solution based on channel eigendecomposition is then proposed. The convergence of the iterative method to the closed-form solution and the equivalence of the two methods are verified through numerical simulations. The performance of the proposed approach is also supported by some illustrative examples.
Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
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ABSTRACT: This paper is concerned with the investigation of a MIMO-CDMA communication system which is based on the concept of spatiotemporal array (STAR) manifold for handling multipath fading channels. Firstly a MIMO frequency selective channel is modelled as a function of both transmitter's and receiver's antenna-array manifold vectors. Then, assuming knowledge of the channel parameters of the desired user, two linear receivers are proposed. The proposed receivers are `near-far' resistant and expressed in terms of the STAR manifold vector of the desired user. The investigation is supported by computer simulation studies where the performance of the proposed receivers is compared to the performance of conventional MMSE and RAKE receivers which have been also extended in order to be expressed in terms of the STAR manifold vectors
Acoustics, Speech and Signal Processing, 2007. ICASSP 2007. IEEE International Conference on; 05/2007 · 4.63 Impact Factor
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ABSTRACT: A blind near-far resistant MIMO array receiver, incorporating the concept of orthogonal transmit diversity, is proposed for asynchronous multipath DS-CDMA systems. With the integration of the antenna-array technology, the receiver does not need any power control and requires only knowledge of the desired user's spreading code sequence
Electronics Letters 11/2006; · 0.96 Impact Factor
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ABSTRACT: Multi-carrier code division multiple access (MC-CDMA) is a modulation scheme that combines the advantages of OFDM and CDMA to provide robustness against frequency selectivity in wireless channels. Arrayed MC-CDMA systems combine MC-CDMA and antenna array technology to harness the spatial and temporal 'signatures' of received signals, thus making it possible to realize high transmission rates envisioned for next generation wireless communications. Localized scattering, which occurs for each multipath, motivates the frequency selective wireless channel to be modelled as a diffused vector channel. In this paper, space-time diffused vector channels for arrayed MC-CDMA systems are modelled and analyzed. Simulation studies show that the use of this diffused channel modelling in arrayed MC-CDMA receivers yields better bit error rate (BER) performance than receivers that ignore the presence of spatial and/or temporal diffusion.
Wireless Communication Systems, 2006. ISWCS '06. 3rd International Symposium on; 10/2006
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ABSTRACT: Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation scheme that achieves high spectral efficiency by using minimally densely spaced orthogonal subcarriers without increasing the transmitter and receiver complexities. Antenna arrays are a powerful means to exploit the spatial domain to provide an extra layer of co-channel interference cancellation and new ways of handling unwanted channel effects for more efficient utilization of spectrum and space at any time. An array-OFDM system integrates OFDM and antenna array technology to harness the spatial signatures of received signals. This provides space diversity in multipath channels, making it possible to realize high transmission rates envisioned for the next generation wireless communications. In this paper, a diversity reception algorithm is proposed for post-FFT OFDM systems employing an antenna array at the receiver. Simulation studies show that the proposed array-OFDM scheme outperforms the conventional multiple-element-OFDM receiver under various frequency-selective fading models.
Wireless Pervasive Computing, 2006 1st International Symposium on; 02/2006
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ABSTRACT: This paper is concerned with the study of linear array systems, operating in an asynchronous, multipath/multiple-access environment. In the modeling and analysis of array systems, the array manifold vector is being widely used, providing the spatial information of the signal environment. Recently, because of the inherent limitations of the array manifold to accurately model a multiple-access/multipath signal environment, the concept of the spatio-temporal array (STAR) manifold has been introduced, which extends the conventional - spatial array manifold by incorporating both temporal information and the distinct "signature" of each user/target/path. The properties of the array manifold have already been extensively studied and the aim of this paper is to examine the corresponding properties of the STAR manifold. It is shown that there is a direct relationship between these two manifolds and that the characteristics of the STAR manifold of linear arrays can be derived from those of the array manifold. Finally, this technique is generalised to handle not only the STAR manifold, but, also, a wide class of linear mappings of the array manifold
Signal Processing, 2006 8th International Conference on; 02/2006
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ABSTRACT: Arrayed wireless sensor networks are a novel type of wireless sensor networks involving a very large number of wireless nodes that are randomly distributed in a 3-dimensional space at unknown locations and are used for monitoring events of interest. When such events occur, some nodes are automatically self organized and grouped together to form wireless arrays of suitable, although random, geometries and then an ad-hoc wireless network of arrays operating in an infrastructureless environment. This paper focuses on the communication links involved in the operation of the arrayed wireless sensor network based on a multicarrier CDMA MIMO architecture
Wireless Communication Systems, 2005. 2nd International Symposium on; 10/2005
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ABSTRACT: A blind near-far resistant MIMO array receiver employing diversely polarised array is proposed for asynchronous multipath DS-CDMA systems. By means of polarisation multiplexing, the proposed MIMO system is applicable in (i) data rate, (ii) diversity, or (iii) combinatorial maximisation schemes, without exhausting the limited spreading codes available.
Electronics Letters 09/2005; · 0.96 Impact Factor
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ABSTRACT: Reception of asynchronous, multicarrier direct-sequence-code division multiple access (DS-CDMA) in time-varying, multipath radio channels with use of a receiving antenna array is investigated. Interference reducing minimum mean squared error (MMSE) receivers are discussed, and by considering the time-variation of the channel, a modified structure is derived which is efficient for channels experiencing small-scale fading. A blind implementation of this receiver is then proposed. Subspace concepts are applied to formulate a tracking, composite channel vector estimator which operates effectively in fading situations, even when high levels of interference are present. Both the modified MMSE weight matrix and diversity combining weights are generated from these channel estimates. Simulations of the proposed receiver show it to have superior performance over a standard MMSE receiver which is periodically re-evaluated to permit it to follow the channel variations due to small-scale fading. Furthermore, a hybrid MMSE receiver is proposed which applies different processing methods depending on each transmitters mobility, resulting in improved performance.
IEEE Transactions on Signal Processing 08/2005; · 2.63 Impact Factor
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ABSTRACT: In the antenna array wideband DS-CDMA systems, the propagation medium is a vector channel. Moreover the multipaths that define the channel are spatially and temporally diffused such that each multipath appears as a cluster rather than a point like signal source. Hence, channel estimation techniques that do not exploit the structure of the vector channel become inefficient. In this context, a subspace approach to estimate the diffused vector channels for multi-user wideband DS-CDMA systems is being proposed. The diffused vector channel is parameterized in terms of multipath directions and times of arrival. Then, by employing the structure of the developed diffused vector channel, a powerful blind near-far resistant channel estimation algorithm is derived. Simulation results are provided to illustrate the efficiency of the algorithm.
Wireless Communication Systems, 2004, 1st International Symposium on; 10/2004
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ABSTRACT: In this paper, a blind near-far resistant MIMO array receiver incorporated with either space-time transmit diversity (STTD) or space-time spreading (STS) schemes is proposed for time-varying multipath DS-CDMA systems, Many reported research works on MIMO, including the conventional STTD and STS schemes, often assume that the channel is flat fading and is known. However, the MIMO array receiver proposed in this study is based on a subspace-type joint space-time estimation algorithm, which does not need any power control or channel information. Furthermore, it is robust to channel estimation errors in the event of any unidentified or erroneous channel parameter. The effectiveness of the proposed approach is supported by representative examples and computer simulation studies.
Wireless Communication Systems, 2004, 1st International Symposium on; 10/2004
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ABSTRACT: A novel blind DS-CDMA array channel estimator is presented which is capable of handling severe frequency-selective channels, where the multipath delay spread can be comparable with the data symbol period. By employing the concept of the spatiotemporal array (STAR) manifold, a subspace-type estimation algorithm is proposed, in conjunction with an one-dimensional temporal smoothing procedure, to jointly estimate the spatiotemporal multipath-channel parameters associated with the desired user. Close examination of the proposed STAR channel estimator reveals that it is 'near-far' resistant and the total number of signal paths can be more than the number of antenna elements. The effectiveness of the proposed approach is supported by computer simulation results.
IEE Proceedings - Communications 09/2004; · 0.32 Impact Factor
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ABSTRACT: A blind near-far resistant MIMO array receiver is proposed for time-varying asynchronous multipath DS-CDMA systems. Unlike many other MIMO works, the proposed receiver is built on array-antenna technology which is commonly used in applications such as the well-known 'smart antenna' system. Hence, a novel space-time-Doppler estimation algorithm is devised which provides the joint angle and delay, as well as the Doppler shift frequency estimation. With the estimator integrated as the front-end, the proposed MIMO array receiver requires no knowledge of the channel and is insusceptible to near-far problems. Furthermore it is robust to channel estimation errors in the event of any unidentified or erroneous channel parameter.
Acoustics, Speech, and Signal Processing, 2004. Proceedings. (ICASSP '04). IEEE International Conference on; 06/2004 · 4.63 Impact Factor
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ABSTRACT: In this paper, the use of a crossed-dipole array is proposed in joint space-time channel estimation for asynchronous multipath direct sequence code division multiple access (DS-CDMA) systems. The polarization diversity offered by such an array, unlike linearly polarized arrays, is able to detect and estimate any arbitrary completely polarized signal path. By utilizing the polarization information inherent in the received signal to construct the polar-spatio-temporal array (polar-STAR) manifold vector, the accuracy and resolution of the polar-STAR parameters' estimation are significantly improved, and its signal detection capability is enhanced. To alleviate the need for a multidimensional search in the polarization space, a computationally efficient joint polarization-angle-delay channel parameter estimation algorithm is proposed for a "desired user" that operates in an asynchronous multiuser and multipath environment. The proposed algorithm, which can be seen as an application of MUSIC-type techniques, is based on combining a two-dimensional STAR-Subspace type technique with a set of analytical equations and is supported by representative examples and computer simulation studies.
IEEE Transactions on Antennas and Propagation 02/2004; · 2.15 Impact Factor
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ABSTRACT: The paper is concerned with asynchronous, multicarrier DS-CDMA communications using a receiver with an antenna array. An estimator is proposed to find the composite channel vector for each-intracell user; the only prerequisite being that each user's spreading sequence is available at the receiver. In the uplink, the base station typically does not have knowledge of the spreading sequences active in neighbouring cells, so that intercell interference must be blindly suppressed. Consequently, an implementation of the whitening zero-forcing receiver that reduces both intracell and intercell interference is proposed which only requires knowledge of the intracell users' spreading sequences. The effectiveness of this receiver is demonstrated by computer simulations.
Global Telecommunications Conference, 2003. GLOBECOM '03. IEEE; 01/2004
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ABSTRACT: An asynchronous, multicarrier direct-sequence code-division multiple-access (DS-CDMA) array receiver is proposed based upon blind, composite channel vector estimation. Due to the fact that the combined effect of all received paths is estimated, the total number of paths can be greater than the number of antennas in the receiver array. Furthermore, the proposed approach is not limited by multipath coherency. The receiver is classified as an interference cancelling zero-forcing receiver, and multicarrier operation in a frequency-selective channel means that its performance can exceed that of a single-carrier array DS-CDMA. The effectiveness of the proposed approach, even in the presence of strong interference, is demonstrated by computer simulation studies.
IEEE Transactions on Wireless Communications 12/2003; · 2.59 Impact Factor
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ABSTRACT: A framework is presented in this study which analyzes the importance of each sensor in an antenna array based on its location in the overall geometry. Moving away from the conventional methods of measuring sensor importance by means of application-specific criteria, a new approach, based on the array manifold and its differential geometry, is used to measure the significance of each sensor's position in an array. By considering two-dimensional manifolds (function of azimuth and elevation angles) of planar arrays of isotropic sensors, and by using previously established results on the differential geometry of such manifolds, a sensitivity analysis is performed which leads to characterization and quantification of sensor location importance in an array geometry. Based on this framework, a criterion is developed for assessing an overall geometry. This criterion may be used as a figure of merit for comparing diverse array geometries.
IEEE Transactions on Antennas and Propagation 10/2003; · 2.15 Impact Factor
