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  • 151. He, Shiwen
    et al.
    Wang, Jiaheng
    Huang, Yongming
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES). Univ Luxembourg, Luxembourg.
    Hong, Wei
    Codebook-Based Hybrid Precoding for Millimeter Wave Multiuser Systems2017In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 65, no 20, p. 5289-5304Article in journal (Refereed)
    Abstract [en]

    In millimeter-wave (mmWave) systems, antenna architecture limitations make it difficult to apply conventional fully digital precoding techniques but call for low-cost analog radio frequency (RF) and digital baseband hybrid precoding methods. This paper investigates joint RF-baseband hybrid precoding for the downlink of multiuser multiantenna mmWave systems with a limited number of RF chains. Two performance measures, maximizing the spectral efficiency and the energy efficiency of the system, are considered. We propose a codebook-based RF precoding design and obtain the channel state information via a beam sweep procedure. Via the codebook-based design, the original system is transformed into a virtual multiuser downlink system with the RF chain constraint. Consequently, we are able to simplify the complicated hybrid precoding optimization problems to joint codeword selection and precoder design (JWSPD) problems. Then, we propose efficient methods to address the JWSPD problems and jointly optimize the RF and baseband precoders under the two performance measures. Finally, extensive numerical results are provided to validate the effectiveness of the proposed hybrid precoders.

  • 152.
    Henriksson, Christian
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Jakobsson, Andreas
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Reducing Bluetooth Interference with Diversity Techniques in IEEE 802.11b Networks2002In: Proceedings Nordic Signal Processing Symposium, 2002Conference paper (Refereed)
    Abstract [en]

    Lately different kinds of wireless networks have become more frequently used. If they occupy the same frequency band they are likely to interfere with each other. In this paper, we examine how spatial diversity can be exploited to suppress Bluetooth interference on a IEEE 802.11b network. Two dual antenna receivers, the maximum ratio combining (MRC) and the interference rejection combining (IRC) methods, have been evaluated and compared to the ordinary single antenna receiver. Simulation results show that adding spatial diversity yields a signicant reduction in biterror rate (BER) and as a consequence the throughput is increased, especially for larger fragment sizes.

  • 153.
    Huang, Yongming
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yang, Luxi
    School of Information Science and Engineering, Southeast University, Nanjing, China.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Codebook-Based Precoding For Dual-Hop Downlink With Mimo Amplify-And-Forward Relaying2009In: SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2009, p. 245-249Conference paper (Refereed)
    Abstract [en]

    This paper deals with the practical precoding design for a two-hop downlink with MIMO amplify-and-forward relaying. A novel scheme of codebook-based joint precoding at both the base station and the relay station is first presented, in which a distributed codeword selection is proposed to concurrently choose two joint precoders such that the feedback delay is considerably reduced. Then, the joint codebook design in such a joint precoding system is analyzed, revealing that independent codebook designs at the base station and relay station using the conventional Grassmannian subspace packing method is able to guarantee that the overall performance improves with either size of two codebooks. The excellent performances of the proposed scheme, in terms of both the sum rate and the BER, are finally confirmed with computational simulations.

  • 154.
    Huang, Yongming
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yang, Luxi
    School of Information Science and Engineering, Southeast University, Nanjing, China.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Limited Feedback Joint Precoding for Amplify-and-Forward Relaying2010In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 58, no 3, p. 1347-1357Article in journal (Refereed)
    Abstract [en]

    This paper deals with the practical precoding design for a dual hop downlink with multiple-input multiple-output (MIMO) amplify-and-forward relaying. First, assuming that full channel state information (CSI) of the two hop channels is available, a suboptimal dual hop joint precoding scheme, i.e., precoding at both the base station and relay station, is investigated. Based on its structure, a scheme of limited feedback joint precoding using joint codebooks is then proposed, which uses a distributed codeword selection to concurrently choose two joint precoders such that the feedback delay is considerably decreased. Finally, the joint codebook design for the limited feedback joint precoding system is analyzed, and results reveal that independent codebook designs at the base station and relay station using the conventional Grassmannian subspace packing method is able to guarantee that the overall performance of the dual hop joint precoding scheme improves with the size of each of the two codebooks. Simulation results show that the proposed dual hop joint precoding system using distributed codeword selection scheme exhibits a rate or BER performance close to the one using the optimal centralized codeword selection scheme, while having lower computational complexity and shorter feedback delay.

  • 155.
    Huang, Yongming
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yang, Luxi
    School of Information Science and Engineering, Southeast University, Nanjing, China.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Limited Feedback SDMA scheme with Dynamic Multiplexing Order2009In: SPAWC: 2009 IEEE 10TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2009, p. 211-215Conference paper (Refereed)
    Abstract [en]

    This paper proposes a new codebook-based SDMA scheme, which employs a variable number of active beams, i.e., a dynamic multiplexing order, to target a good tradeoff between the multiplexing gain and the inter-user interference. The new transmit scheme consist of a modification of the conventional feedback information and the development of a novel scheduling algorithm, where the new scheduling algorithm utilizes a merging of the channel correlation with limited feedback information, and is based on a proposed ML estimate of the possible user interferences. Simulation results demonstrate that in sparse networks the proposed SDMA scheme considerably outperforms some conventional SDMA schemes in terms of the sum throughput, with a comparable feedback overhead.

  • 156.
    Huang, Yongming
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yang, Luxi
    School of Information Science and Engineering, Southeast University, Nanjing, China.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A multiuser downlink system combining limited feedback and channel correlation information2010In: IEEE International Conference on Communications, 2010, p. 1-5Conference paper (Refereed)
    Abstract [en]

    We address the problem of combining limited feedback information with long-term channel statistical information in the design of downlink SDMA schemes. A novel combining method is developed to improve the quality of channel knowledge at the base station. More specifically, a set of novel feedback parameters is proposed and a related method is developed to estimate a representation of the multiuser channel vectors at the base station. This method utilizes the hybrid information by combining instantaneous channel feedback and long-term channel statistics, and is based on a channel phase codebook designed using the generalized Lloyd algorithm. The estimated channel knowledge at the base station can be used for joint design of multiuser precoding and opportunistic scheduling. The advantage of the proposed scheme over existing CSI quantization based SDMA schemes is further confirmed by computer simulations.

  • 157.
    Huang, Yongming
    et al.
    School of Information Science and Engineering, Southeast University, Nanjing.
    Yang, Luxi
    School of Information Science and Engineering, Southeast University, Nanjing.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Exploiting Long-Term Channel Correlation in Limited Feedback SDMA Through Channel Phase Codebook2011In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 59, no 3, p. 1217-1228Article in journal (Refereed)
    Abstract [en]

    Improving channel information quality at the base station (BS) is crucial for the optimization of frequency division duplexed (FDD) multi-antenna multiuser downlink systems with limited feedback. To this end, this paper proposes to estimate a particular representation of channel state information (CSI) at the BS through channel norm feedback and a newly developed channel phase codebook, where the long-term channel correlation is efficiently exploited to improve performance. In particular, the channel representation is decomposed into a gain-related part and a phase-related part, with each of them estimated separately. More specifically, the gain-related part is estimated from the channel norm and channel correlation matrix, while the phase-related part is determined using a channel phase codebook, constructed with the generalized Lloyd algorithm. Using the estimated channel representation, joint optimization of multiuser precoding and opportunistic scheduling is performed to obtain an SDMA transmit scheme. Computer simulation results confirm the advantage of the proposed scheme over state of the art limited feedback SDMA schemes under correlated channel environment.

  • 158.
    Huang, Yongming
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zheng, G.
    University of Luxembourg.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wong, Kai-Kit
    University College London.
    Yang, Luxi
    Southeast University, Nanjing, China.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Multicell Beamforming Design Approaching Pareto Boundary with Max-Min Fairness2012In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 11, no 8, p. 2921-2933Article in journal (Refereed)
    Abstract [en]

    This paper addresses coordinated downlink beamforming optimization in multicell time division duplex (TDD) systems where a small number of parameters are exchanged between cells but with no data sharing. With the goal to reach the point on the Pareto boundary with max-min rate fairness, we first develop a two-step centralized optimization algorithm to design the joint beamforming vectors. This algorithm can achieve a further sum-rate improvement over the max-min optimal performance, and is shown to guarantee max-min Pareto optimality for scenarios with two base stations (BSs) each serving a single user. To realize a distributed solution with limited intercell communication, we then propose an iterative algorithm by exploiting an approximate uplink-downlink duality, in which only a small number of positive scalars are shared between cells in each iteration. Simulation results show that the proposed distributed solution achieves a fairness rate performance close to the centralized algorithm while it has a better sum-rate performance, and demonstrates a better tradeoff between sum-rate and fairness than the Nash Bargaining solution especially at high signal-to-noise ratio.

  • 159.
    Huang, Yongming
    et al.
    School of Information Science and Engineering, Southeast University, Nanjing.
    Zheng, Gan
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Wong, Kai-Kit
    Yang, Luxi
    School of Information Science and Engineering, Southeast University, Nanjing, China.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Distributed Multicell Beamforming With Limited Intercell Coordination2011In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 59, no 2, p. 728-738Article in journal (Refereed)
    Abstract [en]

    This paper studies distributed optimization schemes for multicell joint beamforming and power allocation in time-division-duplex (TDD) multicell downlink systems where only limited-capacity intercell information exchange is permitted. With an aim to maximize the worst-user signal-to-interference-and-noise ratio (SINR), we devise a hierarchical iterative algorithm to optimize downlink beamforming and intercell power allocation jointly in a distributed manner. The proposed scheme is proved to converge to the global optimum. For fast convergence and to reduce the burden of intercell parameter exchange, we further propose to exploit previous iterations adaptively. Results illustrate that the proposed scheme can achieve near-optimal performance even with a few iterations, hence providing a good tradeoff between performance and backhaul consumption. The performance under quantized parameter exchange is also examined.

  • 160. Hyberg, P.
    et al.
    Jansson, Magnus
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Array interpolation and bias reduction2004In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 52, no 10, p. 2711-2720Article in journal (Refereed)
    Abstract [en]

    Interpolation (mapping) of data from a given antenna array onto the output of a virtual array of more suitable configuration is well known in array signal processing. This operation allows arrays of any geometry to be used with fast direction-of-arrival (DOA) estimators designed for linear arrays. Conditions for preserving DOA error variance under such mappings have been derived by several authors. However, in many cases, such as omnidirectional signal surveillance over multiple octaves, systematic mapping errors will dominate over noise effects and cause significant bias in the DOA estimates. To prevent mapping errors from unduly affecting the DOA estimates, this paper uses a geometrical interpretation of a Taylor series expansion of the DOA estimator criterion function to derive an alternative design of the mapping matrix. Verifying simulations show significant bias reduction in the DOA estimates compared with previous designs. The key feature of the proposed design is that it takes into account the orthogonality between the manifold mapping errors and certain gradients of the estimator criterion function. With the new design, mapping of narrowband signals between dissimilar array geometries over wide sectors and large frequency ranges becomes feasible.

  • 161. Hyberg, P
    et al.
    Jansson, Magnus
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Sector array mapping: Transformation matrix design for minimum MSE2002In: THIRTY-SIXTH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, 2002, p. 1288-1292Conference paper (Refereed)
    Abstract [en]

    This paper treats mapping (interpolation) of the output vector from an existing antenna array onto the output vector of an imaginary array when the directions of arrival (DOA) are known only to within a sector. The problem of constructing a mapping matrix, common to the sector, that minimizes DOA Mean Square Error (MSE) across the sector, is analyzed. We derive a general condition on the mapping errors that prevents them from affecting the calculated DOAs. Thereafter we propose a design, algorithm for the transformation matrix that generates mapping errors fulfilling this condition. Simulations show conspicuous. MSE improvements in relevant scenarios.

  • 162.
    Hyberg, Per
    et al.
    Swedish Defence Research Agency (FOI), SE-172 90, Stockholm, Sweden.
    Jansson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Array interpolation and DOA MSE reduction2005In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 53, no 12, p. 4464-4471Article in journal (Refereed)
    Abstract [en]

    Interpolation or mapping of data from a given real array to data from a virtual array of more suitable geometry is well known in array signal processing. This operation allows arrays of any geometry to be used with fast direction-of-arrival (DOA) estimators designed for linear arrays. In an earlier companion paper [21], a first-order condition for zero DOA bias under such mapping was derived and was also used to construct a design algorithm for the mapping matrix that minimized the DOA estimate bias. This bias-minimizing theory is now extended to minimize not only bias, but also to consider finite sample effects due to noise and reduce the DOA mean-square error (MSE). An analytical first-order expression for mapped DOA MSE is derived, and a design algorithm for the transformation matrix that minimizes this MSE is proposed. Generally, DOA MSE is not reduced by minimizing the size of the mapping errors but instead by rotating these errors and the associated noise subspace into optimal directions relative to a certain gradient of the DOA estimator criterion function. The analytical MSE expression and the design algorithm are supported by simulations that show not only conspicuous MSE,improvements in relevant scenarios, but also a more robust preprocessing for low signal-to-noise ratios (SNRs) as compared with the pure bias-minimizing design developed in the previous paper.

  • 163.
    Hyberg, Per
    et al.
    Swedish Defence Research Agency (FOI), Stockholm, Sweden.
    Jansson, Magnus
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Array Mapping: Optimal Transformation Matrix Design2002In: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2002, p. 2905-2908Conference paper (Refereed)
    Abstract [en]

    Mapping of the data output vector from an existing antenna array onto the data vector of an imaginary array of more suitable configuration is well known in array signal processing. By mapping onto an array manifold of lower dimension or uniform structure for example., processing speed can be improved. Conditions for the retaining of DOA error variance under such mapping have been formulated by several authors but the equally important systematic mapping errors, the bias, has been less treated to date. This paper uses a geometrical interpretation of a Taylor expansion of the DOA estimator cost function to derive an alternative design of the mapping matrix that almost completely removes the bias. The key feature of the proposed design is that it takes the orthogonality between the manifold mapping errors and certain gradients of the estimator cost function into account.

  • 164.
    Hyberg, Per
    et al.
    Swedish Defence Research Agency (FOI), SE-172 90, Stockholm, Sweden.
    Jansson, Magnus
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Array Mapping: Reduced Bias Transformation Matrix Design2002In: Nordic Conference on Radio Science and Communications (RVK), 2002, p. 596-600Conference paper (Other academic)
  • 165.
    Hyberg, Per
    et al.
    Swedish Defence Research Agency (FOI), SE-172 90, Stockholm, Sweden.
    Jansson, Magnus
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Sector Array Mapping: Transformation Matrix Design for Minimum MSE2003Conference paper (Refereed)
  • 166.
    Hybergand, Per
    et al.
    Swedish Defence Research Agency (FOI), Stockholm, Sweden.
    Jansson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Error Minimized Array Mapping Applied to Experimental Data2005In: Nordic Conference on Radio Science and Communications (RVK), 2005Conference paper (Other academic)
  • 167.
    Jalden, Joakim
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Skoglund, Mikael
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On the random coding exponent of multiple antenna systems using space-time block codes2004In: 2004 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, PROCEEDINGS, NEW YORK: IEEE , 2004, p. 189-189Conference paper (Refereed)
    Abstract [en]

    The random coding exponent of multiple antenna systems using space time block codes (STBC) was studied. The effects of different choices of STBC's on the overall performance of a antenna system was analyzed. A narrow band, block fading, multiple antenna channel with Nt antennas at the transmitter and Nr antennas at the receiver were considered for the analysis. The STBC symbols were transmitted across the channel using maximum likelihood, ML, sequence detection. The random coding exponent were found for the cases Nr = 1 and 2. It was concluded that by properly designing the inner STBC the length of the outer code could be reduced while maintaining some target error probability.

  • 168.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Barbero, Luis G.
    Joint Research Institute for Signal & Image Processing, University of Edinburgh, EH9 3JL Edinburgh, UK.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Thompson, John S.
    Joint Research Institute for Signal & Image Processing, University of Edinburgh, EH9 3JL Edinburgh, UK.
    Full diversity detection in MIMO systems with a fixed-complexity sphere decoder2007In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, p. 49-52Conference paper (Refereed)
    Abstract [en]

    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.

  • 169.
    Jaldén, Joakim
    et al.
    Institute of Communications and Radio-Frequency Engineering, Vienna University of Technology.
    Barbero, Luis G.
    Institute for Digital Communications, Joint Research Institute for Signal and Image Processing, The University of Edinburgh, UK.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Thompson, John S.
    Institute for Digital Communications, Joint Research Institute for Signal and Image Processing, The University of Edinburgh, UK.
    The Error Probability of the Fixed-Complexity Sphere Decoder2009In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 57, no 7, p. 2711-2720Article in journal (Refereed)
    Abstract [en]

    The fixed-complexity sphere decoder (FSD) has been previously proposed for multiple-input multiple-output (MIMO) detection in order to overcome the two main drawbacks of the sphere decoder (SD), namely its variable complexity and its sequential structure. Although the FSD has shown remarkable quasi-maximum-likelihood (ML) performance and has resulted in a highly optimized real-time implementation, no analytical study of its performance existed for an arbitrary MIMO system. Herein, the error probability of the FSD is analyzed, proving that it achieves the same diversity as the maximum-likelihood detector (MLD) independent of the constellation used. In addition, it can also asymptotically yield ML performance in the high-signal-to-noise ratio (SNR) regime. Those two results, together with its fixed complexity, make the FSD a very promising algorithm for uncoded MIMO detection.

  • 170.
    Jaldén, Joakim
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Martin, Cristoff
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Semidefinite Programming for Detection in Linear Systems – Optimality Conditions and Space-Time Decoding2003In: IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2003, Vol. 2, p. 9-12Conference paper (Refereed)
    Abstract [en]

    Optimal maximum likelihood detection of finite alphabet symbols in general requires time consuming exhaustive search methods. The computational complexity of such techniques is exponential in the size of the problem and for large problems sub-optimal algorithms are required. In this paper, to find a solution in polynomial time, a semidefinite programming approach is taken to estimate binary symbols in a general linear system. A condition under which the proposed method provides optimal solutions is derived. As an application, the proposed algorithm is used as a decoder for a linear space-time block coding system and the results are illustrated with numerical examples.

  • 171.
    Jaldén, Joakim
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    An Exponential Lower Bound on the Expected Complexity of Sphere Decoding2004In: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, 2004, p. 393-396Conference paper (Refereed)
    Abstract [en]

    The sphere decoding algorithm is an efficient algorithm used to solve the maximum likelihood detection problem in several digital communication systems. The sphere decoding algorithm has previously been claimed to have polynomial expected complexity. While it is true that the algorithm has an expected complexity comparable to that of other polynomial time algorithms for problems of moderate size it is a misconception that the expected number of operations asymptotically grow as a polynomial function of the problem size. In order to illustrate this point we derive an exponential lower bound on the expected complexity of the sphere decoder.

  • 172.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Channel dependent termination of the semidefinite relaxation detector2006In: 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing, NEW YORK, NY: IEEE , 2006, p. 185-188Conference paper (Refereed)
    Abstract [en]

    We study the problem of semidefinite relaxation (SDR) for detection of symbols transmitted over a general MIMO channel. In the SDR detector the maximum likelihood detection problem is relaxed into a semidefinite program (SDP) which is solved numerically using an interior-point path-following algorithm. Herein, we provide a criteria which, based on the channel matrix realization, determine the accuracy required by the SDP solver to give a good bit error rate performance of the overall SDR detector. This also reduce the complexity of the SDR detector as it limits the number of interior iterations required in the SDP solver. The performance is demonstrated through simulations.

  • 173.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Detection Based on Relaxation in MIMO Systems2008In: Handbook on Advancements in Smart Antenna Technologies for Wireless Networks / [ed] Chen Sun, Jun Cheng, and Takashi Ohira, Premier Reference Source , 2008, 1, p. 308-327Chapter in book (Other academic)
  • 174.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    High diversity detection using semidefinite relaxation2006In: 2006 Fortieth Asilomar Conference on Signals, Systems and Computers, 2006, p. 2082-2086Conference paper (Refereed)
    Abstract [en]

    Receiver diversity is an important measure of a receivers robustness towards fading in wireless communications. For the detection of binary symbols transmitted over a general MIMO channel, the semidefinite relaxation (SDR) detector is a computationally attractive alternative to exact ML detection. In the SDR detector, the hard combinatorial optimization problem arising in the ML detector is relaxed into a simple convex optimization problem followed by component wise threshold decisions. In this work, we argue that the SDR detector win provide an increase in diversity over simpler decoder structures such as the ZF and NMSE detectors. Specifically, for the case of uncoded V-BLAST transmission over a MIMO channel with real valued i.i.d. Gaussian channel coefficients we present an analytic result stating that the SDR detector achieves the maximum possible receiver diversity.

  • 175.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the complexity of sphere decoding in digital communications2005In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, ISSN 1053-587X, Vol. 53, no 4, p. 1474-1484Article in journal (Refereed)
    Abstract [en]

    Sphere decoding has been suggested by a number of authors as an efficient algorithm to solve various detection problems in digital communications. In some cases, the algorithm is referred to as an algorithm of polynomial complexity without clearly specifying what assumptions are made about the problem structure. Another claim is that although worst-case complexity is exponential, the expected complexity of the algorithm is polynomial. Herein, we study the expected complexity where the problem size is defined to be the number of symbols jointly detected, and our main result is that the expected complexity is exponential for fixed signal-to-noise ratio (SNR), contrary to previous claims. The sphere radius, which is a parameter of the algorithm, must be chosen to ensure a nonvanishing probability of solving the detection problem. This causes the exponential complexity since the squared radius must grow linearly with problem size. The rate of linear increase is, however, dependent on the noise variance, and thus, the rate of the exponential function is strongly dependent on the SNR. Therefore sphere decoding can be efficient for some SNR and problems of moderate size, even though the number of operations required by the algorithm strictly speaking always grows as an exponential function of the problem size.

  • 176.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    On the limits of sphere decoding2005In: 2005 IEEE International Symposium on Information Theory (ISIT), Vols 1 and 2, NEW YORK: IEEE , 2005, p. 1691-1695Conference paper (Refereed)
    Abstract [en]

    The sphere decoder has emerged as one of the most promising techniques for maximum likelihood detection of symbols transmitted over a general MIMO channel. Although efficient for problems of moderate size it is known that the original sphere decoder is of exponential (expected) complexity which limits its usage for large scale problems. However, at this stage, many alterations and improvements over the original algorithm have appeared in the literature. Herein we study a generic sphere decoder for the i.i.d. Rayleigh fading MIMO channel. The detection ordering and search radius (parameters of the algorithm) are allowed to be arbitrary functions of the decoder input, the only restriction being that the search radius is chosen such that the detection problem is solved. It is shown that the set of problem instances solvable by the sphere decoder in less than exponential time will tend to zero with increasing problem size. This extends previous results by providing a statement which is stronger than exponential expected complexity while relaxing the assumptions regarding the specific decoder implementation.

  • 177.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the maximal diversity order of spatial multiplexing with transmit antenna selection2007In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 53, no 11, p. 4273-4276Article in journal (Refereed)
    Abstract [en]

    Zhang et al. recently derived upper and lower bounds on the achievable diversity of an N-R X N-T, i.i.d. Rayleigh fading multiple antenna system using transmit antenna selection, spatial multiplexing and a linear receiver structure. For the case of L = 2 transmitting (out of N-T available) antennas the bounds are tight and therefore specify the maximal diversity order. For the general case with L

  • 178.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Parallel implementation of a soft output sphere decoder2005In: 2005 39th Asilomar Conference on Signals, Systems and Computers, NEW YORK: IEEE , 2005, p. 581-585Conference paper (Refereed)
    Abstract [en]

    Transmission at rates close to capacity over fading multiple antenna channels can be achieved by concatenating inner space-time block codes and powerful outer codes such as turbo or LDPC codes. However, in such systems, computation of the required soft information, or log-likelihood ratios (LLR), for the bits transmitted over the channel is rather complex and some form of approximations are typically used. Herein, we show how the complexity of computing the max-log approximation of the LLR can be reduced by computing all LLR values simultaneously using a parallel sphere decoder implementation.

  • 179.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The diversity order of the semidefinite relaxation detector2008In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 54, no 4, p. 1406-1422Article in journal (Refereed)
    Abstract [en]

    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.

  • 180.
    Jaldén, Joakim
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ma, Wing-Kin
    Dept. Electrical & Electronic Engineering, University of Melbourne Parkville, Vic., Australia.
    Reducing the average complexity of ML detection using semidefinite relaxation2005In: 2005 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESSING, 2005, p. 1021-1024Conference paper (Refereed)
    Abstract [en]

    Maximum likelihood (ML) detection of symbols transmitted over a MIMO channel is generally a difficult problem due to its NP-hard nature. However, not every instance of the detection problem is equally hard. Thus, the average complexity of an ML detector may be significantly smaller than its worst-case counterpart. This is typically true in the high SNR regime where the received signals are closer to the noise free transmitted signals. Herein, a method which may be used to lower the average complexity of any ML detector is proposed. The method is based on the ability to verify if a symbol estimate is ML, using an optimality condition provided by the near-ML semidefinite relaxation technique. The average complexity reduction advantage of the proposed method is confirmed by numerical results.

  • 181.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bergman, Svante
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Werner, Karl
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cross layer implementation of a multi-user MIMO test-bed2010Conference paper (Refereed)
    Abstract [en]

    This paper describes an implementation of a realtime multi-user multiple-input multiple-output (MU-MIMO) communication system, with cross-layer channel-aware scheduling. The system is implemented using software reconfigurable nodes that may be configured as either user terminals, or as base stations, communicating in the GSM 1800 uplink band. Three different commonly used scheduling algorithms (based on channel state information fed back by the receiver nodes) are studied and compared experimentally for three different signal to noise ratios in an indoor non line of sight environment. It is shown that channel-aware scheduling increases not only the system throughput, but also the fairness. Further, using the possibility of changing antenna polarization through software controlled switches, the multiuser gains may be increased even further, both in total throughput as well as fairness.

  • 182.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Directional dependence of large scale parameters in wireless channel models2008Conference paper (Refereed)
    Abstract [en]

    In this paper the autocorrelation properties of shadow fading and angle spread at both the base station (BS) and at the mobile station (MS) are analyzed using urban macro cellular measurement data. The shadow fading parameter is shown to have a longer decorrelation distance than the angle spread at both the BS and at the MS. Furthermore, we observe variations in the shadow fading that depend on the direction of the MS movement due to street canyons. The same dependence is not observed in the angle spreads. These results indicate that the origin of the angle spread is local to the transmitter and receiver, while the shadow fading depends on the intermediate environment.

  • 183.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Modelling angle spread autocorrelations and the impact on multi-user diversity gains2010In: IEEE Wireless Communications and Networking Conference, 2010, Vol. WCNC, p. 1-6Conference paper (Refereed)
    Abstract [en]

    One way of modelling the wireless channel is in a statistical manner, based on a few parameters describing the characteristics of the environment. In most current wireless channel models, these key parameters are assumed independent between separate links, i.e. on the channels modelling the propagation between one base station and several mobile stations, or one mobile station and several base stations. In practice, dependencies between these wireless channels is expected and as a consequence, system performance evaluations based on models with independent links may be inaccurate. Herein, we consider simulations of a system that depend on the spatial nature of the channel. In particular, we study a system with multi-user scheduling using a single carrier. We investigate the impact of angle spread correlations on multi-user diversity gains using opportunistic scheduling. To facilitate this, a novel method of modelling the angle spread correlations for multi-user system simulations is developed. It is shown that in systems with multiple user scheduling, modelling the angle spread autocorrelation is necessary to obtain reliable system performance results, especially as the number of simultaneous scheduled users increases.

  • 184.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Garcia, Laura
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Inter-and Intrasite Correlation of Large Scale Parameters from Macro Cellular Measurements at 1800MHz2007In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2007Article in journal (Refereed)
    Abstract [en]

    Herein, the inter- and intra-site correlation propertiesof shadow fading and power-weighted angular spreadat both the mobile station and the base station are studiedutilizing narrow band multi-site MIMO measurements in the1800MHz band. The influence of the distance between two basestations on the correlation is studied in an urban environment.Measurements have been conducted for two different situations,widely separated as well as closely positioned base stations. Novelresults regarding the correlation of the power-weighted anglespread between base station sites with different separations arepresented. Furthermore, the measurements and analysis presentedherein confirm the autocorrelation and cross-correlationproperties of the shadow fading and the angle spread that havebeen observed in previous studies.

  • 185.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hong, Aihua
    Institute for Information Technology Technische Universit¨at Ilmenau PSF 100 565, D-98684 Ilmenau, Germany.
    Thomae, Reiner
    Institute for Information Technology Technische Universit¨at Ilmenau PSF 100 565, D-98684 Ilmenau, Germany.
    Correlation properties of large scale fading based on indoor measurements2007In: 2007 IEEE WIRELESS COMMUNICATIONS & NETWORKING CONFERENCE, VOLS 1-9, NEW YORK: IEEE , 2007, p. 1894-1899Conference paper (Refereed)
    Abstract [en]

    Statistical channel models are attractive for their simplicity but sometimes lack in precision. In order to improve modelling accuracy, statistical model parameters, which are dependent on the environment, are extended to include spatial and temporal correlation. In outdoor scenarios these parameters are assumed constant over '' large '' areas of several wavelengths hence the name large scale parameters. This paper studies the large scale fading (LSF) and the applicability of bringing this previously used outdoor variable to the indoor case. The impacts of the model of the LSF on the outdoor system-performance have been studied and several relevant models have been proposed for outdoor cases. We present the intra-site autocorrelation as well as the inter-site cross correlation of the LSF for an indoor channel. The results are based on two separate measurement campaigns conducted at KTH, Stockholm and TUI, Ilmenau, using a single mobile station (MS) and multiple base stations (BSs) to investigate such models. We observe that the areas under which the LSF could be assumed constant are, in indoor scenarios, so small that it can be assumed independent from one local area to another. Furthermore, we find results that point towards the existence of inter-site correlation in some specific scenarios.

  • 186.
    Jansson, Magnus
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Göransson, Bo
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    A Subspace Method for Direction of Arrival Estimation of Uncorrelated Emitter Signals1999In: IEEE Transactions on Signal Processing, ISSN 1053-587X, Vol. 47, no 4, p. 945-956Article in journal (Refereed)
    Abstract [en]

    A novel eigenstructure-based method for direction estimation is presented. The method assumes that the emitter signals are uncorrelated. Ideas from subspace and covariance matching methods are combined to yield a noniterative estimation algorithm when a uniform linear array is employed. The large sample performance of the estimator is analyzed. It is shown that the asymptotic variance of the direction estimates coincides with the relevant Cramer-Rao lower bound (CRB). A compact expression for the CRB is derived for the ease when it is known that the signals are uncorrelated, and it is lower than the CRB that is usually used in the array processing literature (assuming no particular structure for the signal covariance matrix). The difference between the two CRBs can be large in difficult scenarios. This implies that in such scenarios, the proposed methods has significantly better performance than existing subspace methods such as, for example, WSF, MUSIC, and ESPRIT. Numerical examples are provided to illustrate the obtained results.

  • 187.
    Jansson, Magnus
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Göransson, Bo
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Analysis of a Subspace-based Spatial Frequency Estimator1997In: Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP-97), 1997, p. 4001-4004Conference paper (Refereed)
    Abstract [en]

    In a previous paper we presented a novel method for spatial and temporal frequency estimation assuming that the sources are uncorrelated. The current paper analyzes this method in the case of spatial frequency estimation. In particular an optimal weighting matrix is derived and it is shown that the asymptotic variance of the frequency estimates coincides with the relevant Cramer-Rao lower bound. This means that the estimator is in large samples an efficient subspace-based spatial frequency estimator. The proposed method thus utilizes the a priori knowledge about the signal correlation as opposed to previously known subspace estimators. Moreover, when a uniform linear array is employed, it is possible to implement the estimator in a non-iterative fashion.

  • 188.
    Jansson, Magnus
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Covariance Preprocessing in Weighted Subspace Fitting1995In: IEEE/IEE workshop on signal processing methods in multipath environments, 1995, p. 23-32Conference paper (Refereed)
  • 189.
    Jansson, Magnus
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Structured Covariance Matrix Estimation: A Parametric Approach2000In: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2000, p. 3172-3175Conference paper (Refereed)
    Abstract [en]

    The problem of estimating a positive semi-definite Toeplitz covariance matrix consisting of a low rank matrix plus a scaled identity from noisy data arises in many applications. We propose a computationally attractive (noniterative) covariance matrix estimator with certain optimality properties. For example, under suitable assumptions the proposed estimator achieves the Cramer-Rao lower bound on the covariance matrix parameters. The resulting covariance matrix estimate is also guaranteed to possess all of the structural properties of the true covariance matrix. Previous approaches to this problem have either resulted in computationally unattractive iterative solutions or have provided estimates that only satisfy some of the structural relations

  • 190.
    Jansson, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Viberg, Mats
    Department of Electrical Engineering, Linkoping University, Linkoping, Sweden..
    Swindlehurst, Andrew Lee
    Brigham Young University, Utah ,US.
    Optimal Subspace Techniques for DOA Estimation in the Presence of Noise and Model Errors2006In: Space-Time Wireless Systems: From Array Processing to MIMO Communications / [ed] Bölcskei, H.; Gesbert, D.; Papadias, C.; Veen, A. J. van der, Cambridge University Press , 2006Chapter in book (Other academic)
  • 191.
    Jansson, Magnus
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Swindlehurst, Andrew Lee
    Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT 84602 USA.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Robust Weighted Subspace Fitting in the Presence of Array Model Errors1998In: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 1998, p. 1961-1964Conference paper (Refereed)
    Abstract [en]

    Model error sensitivity is an issue common to all high resolution direction of arrival estimators. Much attention has been directed to the design of algorithms for minimum variance estimation taking only finite sample errors into account. Approaches to reduce the sensitivity due to array calibration errors have also appeared in the literature. Herein, a weighted subspace fitting method for a wide class of array perturbation models is derived. This method provides minimum variance estimates under the assumption that the prior distribution of the perturbation model is known. Interestingly enough, the method reduces to the WSF (MODE) estimator if no model errors are present. On the other hand, when model errors dominate, the proposed method turns out to be equivalent to the “model-errors-only subspace fitting method”. Unlike previous techniques for model errors, the estimator can be implemented using a two-step procedure if the nominal array is uniform and linear, and it is also consistent even if the signals are fully correlated.

  • 192.
    Jansson, Magnus
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Swindlehurst, Andrew Lee
    Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT 84602 USA.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Weighted subspace fitting for general array error models1998In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 46, no 9, p. 2484-2498Article in journal (Refereed)
    Abstract [en]

    Model error sensitivity is an issue common to all high-resolution direction-of-arrival estimators. Much attention has been directed to the design of algorithms for minimum variance estimation taking only finite sample errors into account. Approaches to reduce the sensitivity due to army calibration errors have also appeared in the literature. Herein, one such approach is adopted that assumes that the errors due to finite samples and model errors are of comparable size. A weighted subspace fitting method for very general array perturbation models is derived. This method provides minimum variance estimates under the assumption that the prior distribution of the perturbation model is known. Interestingly, the method reduces to the WSF (MODE) estimator if no model errors are present, Vice versa, assuming that model errors dominate, the method specializes to the corresponding "model-errors-only subspace fitting method." Unlike previous techniques for model errors, the estimator can be implemented using a two-step procedure if the nominal array is uniform and linear, and it is also consistent even if the signals are fully correlated. The paper also contains a large sample analysis of one of the alternative methods, namely, MAPprox, It is shown that MAPprox also provides minimum variance estimates under reasonable assumptions.

  • 193.
    Jansson, Magnus
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wirfält, Petter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Werner, Karl
    Ericsson Research, Ericsson AB, Kista, Sweden.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ml estimation of covariance matrices with kronecker and persymmetric structure2009In: 2009 IEEE 13TH DIGITAL SIGNAL PROCESSING WORKSHOP & 5TH IEEE PROCESSING EDUCATION WORKSHOP, VOLS 1 AND 2, PROCEEDINGS, NEW YORK: IEEE , 2009, p. 298-301Conference paper (Refereed)
    Abstract [en]

    Estimation of covariance matrices is often an integral part in many signal processing algorithms. In some applications, the covariance matrices can be assumed to have certain structure. Imposing this structure in the estimation typically leads to improved accuracy and robustness (e.g., to small sample effects). In MIMO communications or in signal modelling of EEG data the full covariance matrix can sometimes be modelled as the Kronecker product of two smaller covariance matrices. These smaller matrices may also be structured, e.g., being Toeplitz or at least persymmetric. In this paper we discuss a recently proposed closed form maximum likelihood (ML) based method for the estimation of the Kronecker factor matrices. We also extend the previously presented method to be able to impose the persymmetric constraint into the estimator. Numerical examples show that the mean square errors of the new estimator attains the Cramer-Rao bound even for very small sample sizes.

  • 194.
    Jarmyr, Simon
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jorswieck, Eduard A.
    Dresden University of Technology (TUD), Germany.
    Statistical Precoding With Decision Feedback Equalization Over a Correlated MIMO Channel2010In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 58, no 12, p. 6298-6311Article in journal (Refereed)
    Abstract [en]

    The decision feedback (DF) transceiver, combining linear precoding and DF equalization, can establish point-to-point communication over a wireless multiple-input multiple-output channel. Matching the DF-transceiver design parameters to the channel characteristics can improve system performance, but requires channel knowledge. We consider the fast-fading channel scenario, with a receiver capable of tracking the channel-state variations accurately, while the transmitter only has long-term, channel-distribution information. The receiver design problem given channel-state information is well studied in the literature. We focus on transmitter optimization, which amounts to designing a statistical precoder to assist the channel-tailored DF equalizer. We develop a design framework that encompasses a wide range of performance metrics. Common cost functions for precoder optimization are analyzed, thereby identifying a structure of typical cost functions. Transmitter design is approached for typical cost functions in general, and we derive a precoder design formulation as a convex optimization problem. Two important subclasses of cost functions are considered in more detail. First, we explore a symmetry of DF transceivers with a uniform subchannel rate allocation, and derive a simplified convex optimization problem, which can be efficiently solved even as system dimensions grow. Second, we explore the tractability of a certain class of mean square error based cost functions, and solve the transmitter design problem with a simple algorithm that identifies the convex hull of a set of points in R-2. The behavior of DF transceivers with optimal precoders is investigated by numerical means.

  • 195.
    Jorswieck, Eduard A.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Hammarwall, David
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ergodic capacity achieving transmit strategy in MIMO systems with statistical and short-term norm CSI2007In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, p. 393-396Conference paper (Refereed)
    Abstract [en]

    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.

  • 196.
    Jorswieck, Eduard A.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sezgin, Aydin
    Information Systems Laboratory, Computer Forum, Department of Electrical Engineering, School of Engineering, Stanford University, USA.
    Paulraj, Arogyasvsami
    Information Systems Laboratory, Computer Forum, Department of Electrical Engineering, School of Engineering, Stanford University, USA.
    Guaranteed performance region in fading orthogonal space-time coded broadcast channels2008In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499Article in journal (Refereed)
    Abstract [en]

    Recently, the capacity region of the MIMO broadcast channel (BC) was completely characterized and duality between MIMO multiple access channel (MAC) and MIMO BC with perfect channel state information (CSI) at transmitter and receiver was established. In this work, we propose a MIMO BC approach in which only information about the channel norm is available at the base and hence no joint beamforming and dirty paper precoding (DPC) can be applied. However, a certain set of individual performances in terms of MSE or zero-outage rates can be guaranteed at any time by applying an orthogonal space-time block code (OSTBC). The guaranteed MSE region without superposition coding is characterized in closed form and the impact of diversity, fading statistics, and number of transmit antennas and receive antennas is analyzed. Finally, six CSI and precoding scenarios with different levels of CSI and precoding are compared numerically in terms of their guaranteed MSE region. Depending on the long-term SNR, superposition coding as well as successive interference cancellation (SIC) with norm feedback performs better than linear precoding with perfect CSI.

  • 197.
    Jorswieck, Eduard A.
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sezgin, Aydin
    Information Systems Laboratory, Stanford University, USA.
    Paulraj, Arogyaswami
    Information Systems Laboratory, Stanford University, USA.
    Guaranteed performance region in fading orthogonal space-time coded broadcast channels2007In: 2007 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY PROCEEDINGS, NEW YORK: IEEE , 2007, p. 96-100Conference paper (Refereed)
    Abstract [en]

    Recently, the capacity region of the MIMO broadcast channel (BC) was completely characterized and duality between MIMO multiple access channel (MAC) and MIMO BC with perfect channel state information (CSI) at transmitter and receiver was established. In this work, we propose a MIMO BC approach in which only information about the channel norm is available at the base and hence no dirty paper precoding (DPC) can be applied. However, a certain set of individual performances in terms of MSE or zero-outage rates can be guaranteed at any time by applying an orthogonal space time block code (OSTBC). The guaranteed MSE region without superposition coding is characterized in closed form and the impact of diversity, fading statistics, and number of transmit antennas is analyzed. The guaranteed MSE region with superposition coding is also studied. Finally, the guaranteed sum MSE is briefly discussed.

  • 198.
    Jorswieck, Eduard A.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sezgin, Aydin
    Information Systems Laboratory, Stanford University, USA.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Paulraj, Arogyasvsami
    Information Systems Laboratory, Stanford University, USA.
    Feedback reduction in uplink MIMO OFDM systems by chunk optimization2008In: EURASIP Journal on Advances in Signal Processing, ISSN 1687-6172, E-ISSN 1687-6180Article in journal (Refereed)
    Abstract [en]

    The performance of multiuser MIMO systems can be significantly increased by channel-aware scheduling and signal processing at the transmitters based on channel state information. In the multiple antenna uplink multicarrier scenario, the base station decides centrally on the optimal signal processing and spectral power allocation as well as scheduling. An interesting challenge is the reduction of the overhead in order to inform the mobiles about their transmit strategies. In this work, we propose to reduce the feedback by chunk processing and quantization. We maximize the weighted sum rate of a MIMO OFDM MAC under individual power constraints and chunk size constraints. An efficient iterative algorithm is developed and convergence is proved. The feedback overhead as a function of the chunk size is considered in the rate computation and the optimal chunk size is determined by numerical simulations for various channel models. Finally, the issues of finite modulation and coding schemes as well as quantization of the precoding matrices are addressed.

  • 199.
    Jorswieck, Eduard A.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Svedman, Patrick
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Performance of TDMA and SDMA based Opportunistic Beamforming2008In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, no 11, p. 4058-4063Article in journal (Refereed)
    Abstract [en]

    In this work, we analyze opportunistic beamforming with finite number of single-antenna users under the constraint that the feedback overhead from the mobiles to the base is constant. First, we characterize the impact of the fading variances of the users and the spatial correlation on the sum rate of TDMA based opportunistic beamforming using majorization theory. Further, we describe quantitatively the high-SNR behavior in terms of throughput slope and power offset. Next, the impact of the fading variances of the users on an upper bound of the sum rate for space division multiple access (SDMA) based opportunistic beamforming is derived which is tight for high SNR. We propose to adapt the number of active beams to the SNR and the number of active users in a cell and illustrate the corresponding optimization problem by simulations.

  • 200.
    Jorswieck, Eduard Axel
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    On the interplay between scheduling, user distribution, CSI, and performance measures in cellular downlink2006In: European Signal Processing Conference, 2006Conference paper (Refereed)
    Abstract [en]

    The cross-layer design of future communication systems jointly optimizes multiple network layers with the goal of boosting the system wide performance. This trend brings together the physical and the medium access layers. For the joint optimization of these two lowest layers, it is necessary to understand and relate their terms and concepts. In this paper, we study the interplay between four terms, namely channel state information from link-level, scheduling and user distribution from system level, and different performance measures from both levels. The envisaged scenario is the cellular downlink transmission. The average sum rate describes the long-term performance from a system perspective. The optimal scheduling policy as well as the impact of the user distribution can be clearly characterized as a function of the channel state information (CSI). In contrast, the short-term system performance which is described by the outage sum rate, shows a varying behavior in terms of the optimal scheduling policy and as a function of the user distribution. The analysis is performed by employing Majorization theory for comparing different user distributions. Three different CSI scenarios, namely the uninformed base, the perfectly informed base, and the base with covariance knowledge are studied. Finally, the extension to two less well known performance measures, the maximum throughput and the delay-limited sum rate is addressed.

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