| 1. |
- Astély, David, et al.
(författare)
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Constrained Complexity Spatio-Temporal Interference Rejection Combining
- 1999
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Ingår i: Proceedings of SPAWC’99, Signal Processing Advances in Wireless Communications. - : IEEE. ; , s. 110-113
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Konferensbidrag (refereegranskat)abstract
- Space-time processing for co-channel interference (CCI) rejection and equalization with antenna arrays may provide large gains over space-only processing, especially in interference limited scenarios. However, taking thetemporal correlation of the noise and CCI process into account leads to sequence detection with highercomplexity as compared to space-only processing that neglects this correlation. We propose the use of the generalized Viterbi algorithm for sequence detection with lower complexity. Special cases include the M-algorithm and the delayed decision feedback sequence estimator. A relevant comparison between spatial andspatio-temporal processing with sequence detectors of the same complexity may thus be performed. Numerical examples show substantial gains for spatio-temporal processing as compared to space-only processing also in this case when the optimality of the sequence detector is traded for interference rejection.
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| 2. |
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| 3. |
- Astély, David
(författare)
-
Spatial and spatio-temporal processing with antenna arrays in wireless systems
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats some modeling and estimation problems inthe fieldof antenna array signal processing. With multipleantennas at thereceive side, the spatial dimension is added,and processing is performed in both the temporal and spatialdomain. The work is motivated by the interest in using antennaarrays, primarily at thebase stations, in wirelesscommunication systems. Among thepotential benefits areincreased range, fading diversity, interferencerejection andspatially selective transmission.The problem of estimating the non-frequency selectivechannels, referred to as spatial signatures, for a uniformlinear array withunknown receiver gain and phase responses isstudied. Sufficientconditions for identifying the spatialsignatures using a plane wavemodel with subspace based methodsare derived, and a closed formESPRIT-like estimator isproposed. Results from simulations andprocessing ofexperimental data show that the absence of receivercalibrationis not critical for uplink signal waveform estimationusing aplane wave model.The effects of angular spread caused by multipathpropagation from local scatterers on direction of arrival (DOA)estimation with theMUSIC algorithm are studied. Under theassumption of small angularspread, an approximate distributionof the DOA estimates is derived. An extension to more generalRayleigh and Ricean fading channels is included. Experimentaldata collected in suburban environments havebeen processed, andthe results agree well with the derived distribution.A generalized array manifold model for parameterized spatialsignatureestimation in environments with local scattering isproposed. Thearray manifold commonly used for plane waves isgeneralized toinclude linear combinations of the nominal arrayresponse vectors andtheir derivatives. To estimate theparameters of the model, severalsubspace based estimators areproposed.Spatio-temporal interference rejection combining fordigitalcommunication systems is considered. The use of a finiteorder linear predictor to take the temporal correlation of theco-channelinterference (CCI) into account is studied, and amaximum likelihoodsequence estimator which handles bothintersymbol interference andtemporally correlated CCI ispresented. Spatio-temporal interferencerejection may providelarge gains over space-only interferencerejection, whichneglects the temporal correlation, especially ininterferencelimited scenarios with angular spread and timedispersion. trainingsequence based estimator of the parametersfor the sequence estimatorwith spatio-temporal interferencerejection is proposed. Resultsfrom processing data collected ina suburban environment with a dualpolarized sector antenna of aGSM base station test bed are presented.
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| 4. |
- Astély, David, et al.
(författare)
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Spatial signature estimation for uniform linear arrays with unknown receiver gains and phases
- 1999
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 47:8, s. 2128-2138
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Tidskriftsartikel (refereegranskat)abstract
- The problem of spatial signature estimation using a uniform linear array (ULA) with unknown receiver gain and phase responses is studied. Sufficient conditions for identifying the spatial signatures are derived, and a closed-Form ESPRIT-like estimator is proposed, The performance of the method is investigated by means of simulations and on experimental data collected with an antenna array in a suburban environment. The results show that the absence of receiver calibration is not critical for uplink signal waveform estimation using a plane wave model.
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| 5. |
- Astély, David, et al.
(författare)
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Spatio-Temporal Interference Rejection Combining
- 2005
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Ingår i: Smart Antennas - State-of-the-Art. - : Hindawi Publishing Corporation. - 9775945097 ; , s. 5-26
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Astély, David, et al.
(författare)
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The effects of local scattering on direction of arrival estimation with MUSIC
- 1999
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 47:12, s. 3220-3234
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Tidskriftsartikel (refereegranskat)abstract
- In wireless communication scenarios, multipath propagation may cause angular spreading as seen from a base station antenna array. Environments where most energy incident on the array is from scatterers local to the mobile transmitters are considered, and the effects on direction of arrival (DOA) estimation with the MUSIC algorithm are studied. Previous work has studied rapidly time-varying channels and concluded that local scattering has a minor effect on DOA estimation in such scenarios. In this work, a channel that is time-invariant during the observation period is considered, and under the assumption of small angular spread, an approximate distribution for the DOA estimates is derived. The results show that local scattering has a significant impact on DOA estimation in the time invariant case. Numerical examples are included to illustrate the analysis and to demonstrate that the results may be used to formulate a simple estimator of angular spread. An extension to more general Rayleigh and Ricean fading channels is also included, In addition, results from processing experimental data collected in suburban environments are presented. Good agreement with the derived distributions is obtained.
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| 7. |
- Bengtsson, Mats, 1967-, et al.
(författare)
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Measurements of Spatial Characteristics and Polarization with a Dual Polarized Antenna Array
- 1999
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Ingår i: Proceedings IEEE Vehicular Technology Conference. - : IEEE. ; , s. 366-370
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Konferensbidrag (refereegranskat)abstract
- We consider antenna arrays equipped with cross-polarized antenna elements. The multipath propagation will affect both the spatial characteristics and the polarization of the received signals which will influence the performance of the system in terms of, for example, bit error rate or direction estimation. In this paper, we present results from field measurement data recorded at the 1800 MHz band, provided by Ericsson Radio Systems AB. The study is divided into two main parts. In the first part we introduce a diversity gain measure related to the BER of an MRC receiver. The polarization diversity introduced by the radio channel is studied, and compared to the spatial diversity. In the second part we use a parameterized model of the received polarized radio waves and illustrate the typical behavior of the estimated polarization parameters
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| 8. |
- Brandt, Rasmus, 1985-
(författare)
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Coordinated Precoding for Multicell MIMO Networks
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Enabling multiple base stations to utilize the spatial dimension in a coordinated manner has been shown to be a fruitful technique for improving the spectral efficiency in wireless interference networks. This thesis considers multicell systems where base stations and mobile stations are equipped with multiple antennas. The base stations coordinate their spatial precoding, but individually serve their mobile stations with data. For such coordinated precoding systems, interference alignment (IA) is a useful theoretical tool, due to its ability to serve the maximum number of interference-free data streams. Three topics related to interference alignment and coordinated precoding are studied.First, the feasibility of IA over a joint space-frequency signal space is studied. A necessary condition for space-frequency IA feasibility is derived, and the possible gain over space-only IA is analyzed. An upper bound on the degree of freedom gain is shown to increase in the number of subcarriers, but decrease in the number of antennas. Numerical studies, using synthetically generated channels and real-world channels obtained from indoors and outdoors channel measurements, are used for sum rate performance evaluation. The results show that although a degree of freedom gain is noticeable due to the space-frequency precoding, the sum rate of the system is mainly improved due to a power gain.Second, distributed channel state information (CSI) acquisition techniques are proposed, which provide estimates of the information necessary to perform distributed coordinated precoding. The methods are based on pilot-assisted channel estimation in the uplink and downlink, and correspond to different tradeoffs between feedback and signaling, backhaul use, and computational complexity. Naively applying the existing WMMSE algorithm for distributed coordinated precoding together with the estimated CSI however results in poor performance. A robustification of the algorithm is therefore proposed, relying on the well known diagonal loading technique. An inherent property of the WMMSE solutions is derived and, when enforced onto solutions with imperfect CSI, results in diagonally loaded receive filters. Numerical simulations show the effectiveness of the proposed robustification. Further, the proposed robustified and distributed WMMSE algorithm performs well compared to existing state-of-the-art robust WMMSE algorithms. In contrast to our approach, the existing methods however rely on centralized CSI acquisition.Third, coordinated precoding systems with hardware impairments are studied. Assuming that impairment compensation techniques have been applied, a model is used to describe the aggregate effect of the residual hardware impairments. An iterative resource allocation method accounting for the residual hardware impairments is derived, based on an existing resource allocation framework. Numerical simulations show that the proposed method outperforms all benchmarks. In particular, the gain over impairments-aware time-division multiple access is substantial.
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| 9. |
- Hoymann, Christian, et al.
(författare)
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LTE Release 14 Outlook
- 2016
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Ingår i: IEEE Communications Magazine. - : IEEE. - 0163-6804 .- 1558-1896. ; 54:6, s. 44-49
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Tidskriftsartikel (refereegranskat)abstract
- Todays 4G LTE systems bring unprecedented mobile broadband performance to over a billion of users across the globe. Recently, work on a 5G mobile communication system has begun, and next to a new 5G air interface, LTE will be an essential component. The evolution of LTE will therefore strive to meet 5G requirements and to address 5G use cases. In this article, we provide an overview of foreseen key technology areas and components for LTE Release 14, including latency reductions, enhancements for machine-type communication, operation in unlicensed spectrum, massive multi-antenna systems, broadcasting, positioning, and support for intelligent transportation systems.
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| 10. |
- Jöngren, George, et al.
(författare)
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Structured Spatial Interference Rejection Combining
- 2000
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Ingår i: Proceedings European Signal Processing Conference.
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Konferensbidrag (refereegranskat)abstract
- Modern communication systems are often interferencelimited. By modeling the co-channel interference asspatially colored, temporally white Gaussian noise, itis straightforward to incorporate interference rejectionin the metric of a sequence estimator. In general, estimates of both the channels and the spatial color of theco-channel interference and the noise are needed. In thiswork, a structured model for the spatial noise covariancematrix is proposed and maximum likelihood estimates ofthe parameters are derived. The choice of model orderis also addressed. Simulation results show large gains due to the use of these structured estimates compared with the conventional, unstructured, approach.
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