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  • 1251.
    Zenteno, Efrain
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Sweden; Universidad Catolica San Pablo, Peru.
    Khan, Zain Ahmed
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Gävle, Sweden.
    Isaksson, M.
    Händel, Peter
    University of Gävle, Sweden.
    Using Intrinsic Integer Periodicity to Decompose the Volterra Structure in Multi-Channel RF Transmitters2016In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 26, no 4, p. 297-299, article id 7440846Article in journal (Refereed)
    Abstract [en]

    An instrumentation, measurement and post-processing technique is presented to characterize transmitters by multiple input multiple output (MIMO) Volterra series. The MIMO Volterra series is decomposed as the sum of nonlinear single-variable self-kernels and a multi-variable cross-kernel. These kernels are identified by sample averages of the outputs using inputs of different sample periodicity. This technique is used to study the HW effects in a RF MIMO transmitter composed by input and output coupling filters (cross-talk) sandwiching a non-linear amplification stage. The proposed technique has shown to be useful in identifying the dominant effects in the transmitter structure and it can be used to design behavioral models and compensation techniques.

  • 1252.
    Zenteno, Efrain
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. University of Gavle, Sweden .
    Piazza, Roberto
    University of Luxembourg, Luxembourg.
    Shankar, Bhavani
    University of Luxembourg, Luxembourg.
    Rönnow, Daniel
    University of Gävle, Sweden.
    Ottersten, Björn
    Univesity of Luxembourg, Luxembourg.
    Low Complexity Predistortion and Equalization in Nonlinear Multicarrier Satellite Communications2015In: EURASIP Journal on Advances in Signal Processing, ISSN 1687-6172, E-ISSN 1687-6180, Vol. 1, no 1, p. 1-15Article in journal (Refereed)
    Abstract [en]

    Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint amplification of multiple-carriers using a single High-Power Amplifier (HPA) is being considered. In this scenario, a carefulinvestigation of the resulting power efficiency is essential as amplification isnonlinear, and multicarrier signals exhibit enlarged peak-to-average power ratio. Thus, operating the amplifier close to saturation vastly increases signal distortion resulting in a severe degradation of performance, especially for higher order modulations. This paper proposes a reduced-complexity digital pre-distortion (DPD) scheme at the transmitter and a corresponding equalizer (EQ) at thereceiver to mitigate these nonlinear effects. Scenarios include both the forward as well as the return links. In particular, the paper exploits the MIMO Volterra representation and builds on a basis pursuit approach using a LASSO (least absolute shrinkage and selection operator) algorithm to achieve an effienct basis representation, avoiding large computational complexity, to describe the selection of pre-distorter/ equalizer model. The work further compares and contrasts the two mitigation techniques taking various system aspects into consideration. The gains, in performance and amplification efficiency, demonstrated by the use of DPD/ EQ motivate their inclusion in next generation satellite systems.

  • 1253. Zervos, T.
    et al.
    Alexandridis, A.
    Peppas, K.
    Lazarakis, F.
    Dangakis, K.
    Soras, C.
    Lindmark, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    The influence of MIMO terminal user's hand on channel capacity2006Conference paper (Refereed)
    Abstract [en]

    In this paper the impact of user's hand holding a Multiple-Input-Multiple- Output (MIMO) terminal on the system performance is investigated. A 4×4 MIMO system is considered with a Personal Digital Assistant (PDA) terminal equipped with a compact array of 4 patch elements. The radiation patterns of the antenna elements are simulated in the presence of the other elements and in the presence of a user's hand. The obtained patterns are used to evaluate the covariance matrix of the receive antenna which is incorporated in a correlation-based MIMO channel model. MIMO channel capacity is calculated to demonstrate the capacity degradation caused by the user's hand.

  • 1254.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Experimental Investigation of TDD Reciprocity-Based Zero-Forcing Transmit Precoding2011In: EURASIP J ADV SIGNAL PROCESS, ISSN 1687-6172, p. 137541-Article in journal (Refereed)
    Abstract [en]

    We describe an implementation of TDD reciprocity based zero-forcing linear precoding on a wireless testbed. A calibration technique which self-calibrates the base-station without the need for help from other nodes is described. Performance results in terms of downlink channel estimation error as well as bit error rate (BER) and signal to interference noise and distortion ratio (SINDR) are presented for a scenario with two base-stations and two mobile stations, with two antennas at the base-stations and a single antenna at the mobile-station. The results show considerable performance improvements over reference schemes (such as maximum ratio transmission). However, our analysis also reveals that the hardware impairments significantly limit the performance achieved. We further investigate how to model these impairments and attempt to predict the SINDR, such as what would be needed in a coordinated multipoint (CoMP) scenario where scheduling is performed jointly over the two cells. Although the results are obtained for a MISO scenario the general conclusions are relevant also for MIMO scenarios.

  • 1255.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    INTERFERENCE ALIGNMENT (IA) AND COORDINATED MULTI-POINT (COMP) WITH IEEE802.11AC FEEDBACK COMPRESSION: TESTBED RESULTS2014In: Proceedings of the IEEE International Conference on Acoustics, Speech and Signal Processing, ISSN 1520-6149, p. 6854791-Article in journal (Refereed)
    Abstract [en]

    We have implemented interference alignment (IA) and joint transmission coordinated multipoint (CoMP) on a wireless testbed using the feedback compression scheme of the new 802.11ac standard. The performance as a function of the frequency domain granularity is assessed. Realistic throughput gains are obtained by probing each spatial modulation stream with ten different coding and modulation schemes. The gain of IA and CoMP over TDMA MIMO is found to be 26% and 71%, respectively under stationary conditions. In our dense indoor office deployment, the frequency domain granularity of the feedback can be reduced down to every 8th subcarrier (2.5MHz), without sacrificing performance.

  • 1256.
    Zetterberg, Per
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Performance of three, six, nine and twelve sector sites in CDMA: Based on measurements2004In: IEEE International Symposium on Spread Spectrum Techniques and Applications, 2004, p. 394-399Conference paper (Refereed)
    Abstract [en]

    In this paper we investigate the performance improvement achieved by increasing the number of sectors on a W-CDMA or CDMA2000 site by increasing the number of sectors from today's typical three to six, nine or twelve. The radio propagation environment determines if the narrow beams can be created and kept separated or if they blur together, which in turn determines the sector-to-sector isolation and the soft-handoff populations. The rate of change in signal strength of the beams also determines whether the handover mechanisms are sufficiently fast to allocate the correct beam. In this paper we analyze these issues based on simultaneous measurements of two antenna panels placed on the top of a building overlooking a typical European urban environment of mostly six to eight stories high buildings. Based on these measurements and simulations we find that a nine-sector site has more than double the capacity of a conventional three-sector site.

  • 1257.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    WIreless DEvelopment LABoratory(WIDELAB) Equipment Base2013Report (Other academic)
    Abstract [en]

    This paper documents some of the hard- and soft-ware used by the signal- processing group at KTH, in it’s experimental work on wireless systems. We call these items collectively WIreless DEvelopment LABoratory (WIDELAB), and this paper aims to document the most important pieces and some of the knowledge needed to understand, operate and develop them further. To access the hard and software described contact perz@s3.kth.se

  • 1258.
    Zetterberg, Per
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Jaldén, Joakim
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Lundin, Henrik
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Samuelsson, David
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Svedman, Patrick
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zhang, Xi
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Implementation of SM and RxTxIR on a DSP-Based Wireless MIMO Test-Bed2004In: Proceedings of the European DSP Education and Research Symposium EDERS, 2004Conference paper (Refereed)
    Abstract [en]

    In this paper we describe the implementation of two smart-antenna strategies and associated signal processing algorithms on a common DSP-based wireless MIMO test-bed. The test-bed supports single cell and two-cell configurations. All nodes (MS andBS) have two antennas (either two transmit or tworeceive) and there are feedback links (via cable) from the receivers to all transmitters.These possibilities has been utilized differently in the two techniques: spatial multiplexing (SM) and joint receiver transmitter and interference rejection (RxTxIR).The SM technique targets a single-link low-mobility scenario and boosts throughput using two parallel spatially multiplexed modulation streams. The RxTxIR scheme utilizes the two-cell configuration of the testbed to demonstrate the possibility of suppressing intercell interference in transmitter as well as the receiver beamforming.

  • 1259.
    Zetterberg, Per
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Moghadam, Nima N.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    An experimental investigation of SIMO, MIMO, interference-alignment (IA) and coordinated multi-point (CoMP)2012In: 2012 19th International Conference on Systems, Signals and Image Processing, IWSSIP 2012, 2012, p. 211-216Conference paper (Refereed)
    Abstract [en]

    In this paper we present experimental implementations of interference alignment (IA) and coordinated multi-point transmission (CoMP). We provide results for a system with three base-stations and three mobile-stations all having two antennas. We further employ OFDM modulation, with high-order constellations, and measure many positions both line-of-sight and non-line-of-sight under interference limited conditions. We find the CoMP system to perform better than IA at the cost of a higher back-haul capacity requirement. During the measurements we also logged the channel estimates for offline processing. We use these channel estimates to calculate the performance under ideal conditions. The performance estimates obtained this way is substantially higher than what is actually observed in the end-to-end transmissions - in particular in the CoMP case where the theoretical performance is very high. We find the reason for this discrepancy to be the impact of dirty-RF effects such as phase-noise and non-linearities. We are able to model the dirty-RF effects to some extent. These models can be used to simulate more complex systems and still account for the dirty-RF effects (e.g., systems with tens of mobiles and base-stations). Both IA and CoMP perform better than reference implementations of single-user SIMO and MIMO in our measurements.

  • 1260. Zhang, Guowu
    et al.
    Zhang, Junwei
    Hong, Xuezhi
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Low-complexity frequency domain nonlinear compensation for OFDM based high-speed visible light communication systems with light emitting diodes2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 4, p. 3780-3794Article in journal (Refereed)
    Abstract [en]

    A novel frequency domain nonlinear compensation method, FD-NC, is proposed for orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) system. By tackling the memory nonlinear impairments from light emitting diodes (LEDs) in the frequency domain rather than in the time domain, the proposed method has much lower computational complexity than the conventional time domain Volterra nonlinear compensation method (TD-NC). Both theoretical derivation and experimental investigation of the proposed method in OFDM based VLC systems with four types of commercial LEDs are presented. The results of experiments show that the proposed low-complexity FD-NC method with a moderate truncation factor achieves a performance comparable to that of the TD-NC. The application of FD-NC method in the bit-power loading OFDM VLC system is also experimentally demonstrated. Compared with the linear equalization case, at a bit error rate (BER) of 3.8 x 10(-3) (a), the transmission distance of a 960 Mbps VLC system can be extended from 0.7 m to 1.8 m by the FD-NC, and (b) the achievable system capacity can be enhanced by 18.7%similar to 36.5% for transmission distance in the range of 0.5 m similar to 2 m with the FD-NC. The complexity analysis shows that the required number of real-valued multiplications (RNRM) of the FD-NC is independent of linear or nonlinear memory length. The reduction of RNRM achieved by the FD-NC over the TD-NC becomes more profound for a larger nonlinear memory length or a smaller truncation factor.

  • 1261. Zhang, J.
    et al.
    Guo, C.
    Liu, L.
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Hong, X.
    Demonstration of a visible light communication system based on filter bank spread OFDM/OQAM2017In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2017Conference paper (Refereed)
    Abstract [en]

    We propose and experimentally demonstrate a 2.2Gbit/s visible light communication system based on filter bank spread (FBS-) OFDM/OQAM. Both low peak-to-average power ratio and high diversity gain are achieved by FBS, which improves transmission performance. © 2017 OSA.

  • 1262. Zhang, Jianjun
    et al.
    Huang, Yongming
    Wang, Jiaheng
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. University of Luxembourg.
    Yang, Luxi
    Per-Antenna Constant Envelope Precoding and Antenna Subset Selection: A Geometric Approach2016In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 64, no 23, p. 6089-6104Article in journal (Refereed)
    Abstract [en]

    Constant envelope (CE) precoding can efficiently control the peak-to-average power ratio (PAPR) and improve the power efficiency of power amplifiers in large-scale antenna array systems. Antenna subset selection (ASS), combined with CE precoding, can further improve power efficiency by using a part of antennas to combine the desired signal. However, due to the inherent nonlinearity, the joint optimization of CE precoding and ASS is very challenging and satisfactory solutions are yet not available. In this paper, we present new methods for CE precoding and ASS optimization from a geometric perspective. First, we show the equivalence between the CE precoder design and a polygon construction problem in the complex plane, thus transforming the algebraic problem into a geometric problem. Aiming to minimize the computational complexity, we further transform the CE precoder design into a triangle construction problem, and propose a novel algorithm to achieve the optimal CE precoder with only linear complexity in the number of used antennas. Then, we investigate the joint optimization of ASS and CE precoding to minimize the total transmit power while satisfying the QoS requirement. Based on the geometric interpretation, we develop an efficient ASS algorithm, which, using only addition and comparison operations, is guaranteed to find the globally optimal solution and provides robustness to channel uncertainty. The complexity of the proposed ASS algorithm is at most quadratic in the number of antennas in the worst case. The optimality and superiority of the proposed geometric methods are demonstrated via numerical results.

  • 1263.
    Zhang, Kewei
    et al.
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Papadimitratos, Panagiotis
    KTH, School of Electrical Engineering (EES), Communication Networks.
    GNSS receiver tracking performance analysis under distance-decreasing attacks2015In: Proceedings of 2015 International Conference on Localization and GNSS, IEEE , 2015Conference paper (Refereed)
    Abstract [en]

    Numerous works have investigated the vulnerability of Global Navigation Satellite Systems (GNSS) against attacks. Upcoming systems make provisions for cryptographic civilian signal protection. However, this alone does not fully protect GNSS-based localization. In this paper, we show that attacks at the physical layer, without modification of navigation messages, can be severely effective. We analyze the influence of the, so called distance decreasing attacks, and we investigate their feasibility and we find that they can be practical and effective. Finally, we consider signal quality monitoring, but it can not readily serve as a countermeasure.

  • 1264.
    Zhang, Lu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Van Kerrebrouck, J.
    Ozolins, O.
    Lin, Rui
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Pang, Xiaodan
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Udalcovs, A.
    Spiga, S.
    Amann, M. C.
    Gan, L.
    Tang, M.
    Fu, S.
    Schatz, Richard
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Liu, D.
    Tong, W.
    Torfs, G.
    Bauwelinck, J.
    Yin, X.
    Xiao, S.
    Chen, Jiajia
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Experimental Demonstration of 503.61-Gbit/s DMT over 10-km 7-Core Fiber with 1.5μm SM-VCSEL for Optical Interconnects2018In: European Conference on Optical Communication, ECOC, Institute of Electrical and Electronics Engineers Inc. , 2018Conference paper (Refereed)
    Abstract [en]

    We experimentally demonstrate a net-rate 503.61-Gbit/s discrete multitone (DMT) transmission over 10-km 7-core fiber with 1.5μm single mode VCSEL, where low-complexity kernel-recursive-least-squares algorithm is employed for nonlinear channel equalization.

  • 1265. Zhang, X.
    et al.
    Matthaiou, M.
    Coldrey, M.
    Björnson, Emil
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. SUPELEC, France .
    Impact of residual transmit RF impairments on training-based MIMO systems2014In: 2014 IEEE International Conference on Communications, ICC 2014, 2014, p. 4741-4746Conference paper (Refereed)
    Abstract [en]

    Radio-frequency (RF) impairments, that exist intimately in wireless communications systems, can severely degrade the performance of traditional multiple-input multiple-output (MIMO) systems. Although compensation schemes can cancel out part of these RF impairments, there still remains a certain amount of impairments. These residual impairments have fundamental impact on the MIMO system performance. However, most of the previous works have neglected this factor. In this paper, a training-based MIMO system with residual transmit RF impairments (RTRI) is considered. In particular, we derive a new channel estimator for the proposed model, and find that RTRI can create an irreducible estimation error floor. Moreover, we show that, in the presence of RTRI, the optimal training sequence length can be larger than the number of transmit antennas, especially in the low and high signal-to-noise ratio (SNR) regimes. An increase in the proposed approximated achievable rate is also observed by adopting the optimal training sequence length. When the training and data symbol powers are required to be equal, we demonstrate that, at high SNRs, systems with RTRI demand more training, whereas at low SNRs, such demands are nearly the same for all practical levels of RTRI.

  • 1266. Zhang, X.
    et al.
    Nakhai, M. R.
    Zheng, G.
    Lambotharan, S.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg City L-1855, Luxembourg..
    Calibrated Learning for Online Distributed Power Allocation in Small-Cell Networks2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, p. 1-1Article in journal (Refereed)
    Abstract [en]

    This paper introduces a combined calibrated learning and bandit approach to online distributed power control in small cell networks operated under the same frequency bandwidth. Each small base station (SBS) is modelled as an intelligent agent who autonomously decides on its instantaneous transmit power level by predicting the transmitting policies of the other SBSs, namely the opponent SBSs, in the network, in real-time. The decision making process is based jointly on the past observations and the calibrated forecasts of the upcoming power allocation decisions of the opponent SBSs who inflict the dominant interferences on the agent. Furthermore, we integrate the proposed calibrated forecast process with a bandit policy to account for the wireless channel conditions unknown a priori, and develop an autonomous power allocation algorithm that is executable at individual SBSs to enhance the accuracy of the autonomous decision making. We evaluate the performance of the proposed algorithm in cases of maximizing the long-term sum-rate, the overall energy efficiency and the average minimum achievable data rate. Numerical simulation results demonstrate that the proposed design outperforms the benchmark scheme with limited amount of information exchange and rapidly approaches towards the optimal centralized solution for all case studies.

  • 1267.
    Zhang, Xi
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jorswieck, Eduard A.
    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.
    Paulraj, Arogyaswami
    Information Systems Laboratory, Stanford University, USA.
    User selection schemes in multiple antenna broadcast channels with guaranteed performance2007In: 2007 IEEE 8TH WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS, NEW YORK: IEEE , 2007, p. 1-5Conference paper (Refereed)
    Abstract [en]

    Recently, user selection algorithms in combination with linear precoding have been proposed that achieve the same scaling as the sum capacity of the MIMO BC. In this work, we study the properties of four user selection algorithms in conjunction with beamforming that guarantee certain SINR requirements under transmit power minimization. It is shown that for a large number of transmit antennas, the norm-based user selection performs close to the optimum. The results are illustrated by various numerical simulations.

  • 1268.
    Zhang, Xi
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Performance analysis of V-BLAST structure with channel estimation errors2004In: 2003 4TH IEEE WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS - SPAWC 2003, NEW YORK: IEEE , 2004, p. 487-491Conference paper (Refereed)
    Abstract [en]

    The V-BLAST structure is a promising MIMO transmission scheme that attempts to utilize the high capacity of a MIMO system while maintaining low complexity. While no channel knowledge is required at the transmitter, accurate estimates of the channel are necessary at the receiver. The performance of V-BLAST under channel estimation errors is analyzed in this paper and a very tight error floor is derived. This error floor is due to the equivalent system noise which is a combination of the channel estimation errors and the additive white Gaussian receiver noise.

  • 1269.
    Zhang, Xi
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Power Allocation and Bit Loading for Spatial Multiplexing in MIMO Systems2003In: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, 2003, p. 53-56Conference paper (Refereed)
    Abstract [en]

    The power assignment problem is important for Multiple-Input-Multiple-Output (MIMO) systems to achieve high capacity. Although this problem is solved by well-known water filling algorithms, this does not provide an optimal solution if the system is constrained to a fixed raw bit error rate threshold and to discrete modulation orders. In this work an approximate approach, called QoS based WF, is proposed to solve the power assignment problem with such constrains. It is shown to outperform quantization of the conventional water filling solution and a well known bit loading algorithm (Chow’s algorithm) used in the Digital Subscriber Lines (DSL).

  • 1270.
    Zhang, Xi
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Palomar, Daniel P.
    Dept. of Electrical Engineering, Princeton University Princeton, NJ 08544, USA.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Robust design of linear MIMO transceiver for low SNR2005In: 2005 39th Asilomar Conference on Signals, Systems and Computers, Vols 1 and 2, NEW YORK: IEEE , 2005, p. 398-402Conference paper (Refereed)
    Abstract [en]

    In practical systems, the design of linear MIMO transceivers should be robust to partial or imperfect channel state information (CSI). This paper considers the case in which only the second-order statistics of the channel is known at the transmitter while the receiver has a perfect CSI. In such a case, it is possible to optimally design robust MIMO transceivers based on a general cost function covering several well known performance criteria. In particular, two families are considered in detail: Schur-convex and Schur-concave functions. Approximations are used in the low SNR regime to obtain simple optimization problems that can be readily solved. Numerical examples show substantial gains compared to other methods.

  • 1271.
    Zhang, Xi
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Palomar, Daniel P.
    Dept. of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Robust design of linear MIMO transceivers under channel uncertainty2006In: 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing: signal processing for communication, sensor array and multichannel signal processing, 2006, p. 77-80Conference paper (Refereed)
    Abstract [en]

    This paper considers the robust design of a linear transceiver with imperfect channel state information (CSI) at the transmitter of a MIMO link. The framework embraces the design problem when CSI at the transmitter consists of the channel mean and covariance matrix or, equivalently, the channel estimate and the estimation error covariance matrix. The design of the linear MIMO transceiver is based on a general cost function covering several well known performance criteria. In particular, two families are considered in detail: Schur-convex and Schur-concave functions. Approximations are used in the low SNR and high SNR regimes separately to obtain simple optimization problems that can be readily solved. Numerical examples show gains compared to other suboptimal methods.

  • 1272.
    Zhang, Xi
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Palomar, Daniel P.
    Electrical Engineering, Princeton University, Princeton.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Statistically robust design of linear MIMO transceivers2008In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, no 8, p. 3678-3689Article in journal (Refereed)
    Abstract [en]

    The treatment of channel state information (CSI) is critical in the design of MIMO systems. Accurate CSI at the transmitter is often not possible or may require high feedback rates. Herein, we consider the robust design of linear MIMO transceivers with perfect CSI either at the transmitter or at both sides of the link. The framework considers the design problem where the imperfect CSI consists of the channel mean and covariance matrix or, equivalently, the channel estimate and the estimation error covariance matrix. The robust transceiver design is based on a general cost function of the average MSEs as well as a design with individual MSE based constraints. In particular, a lower bound of the average MSE matrix is explored for the design when only the CSI at the transmitter is imperfect. Under different CSI conditions, the proposed robust transceivers exhibit a similar structure to the transceiver designs for perfect CSI, but with a different equivalent channel and/or noise covariance matrix.

  • 1273.
    Zhang, Xi
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Svedman, Patrick
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Lundin, Henrik
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Implementation of a smart antenna multiuser algorithm on a DSP-based wireless MIMO test-bed2005In: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2005, Vol. 1, p. 126-130Conference paper (Refereed)
    Abstract [en]

    This paper describes the implementation and performance of three communication schemes on a DSP-based MIMO test-bed. A multicell scenario with two basestations and two users in the same room is evaluated. Eigenbeamforming with and without interference pre-whitening at both transmitter and receiver is compared with SISO multicell communication. Experimental results show that the gain from using interference pre-whitening is significant. The BER performance of beamforming without intercell interference suppression is only marginally better than single antenna communication. The paper also presents the implementation of synchronization, equalization, frequency offset estimation and decision directed beamforming mismatch compensation.

  • 1274.
    Zhang, Zhuo
    et al.
    South China Normal Univ, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Zhu, Yaguang
    South China Normal Univ, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Zhu, Wentao
    South China Normal Univ, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Chen, Huayang
    South China Normal Univ, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Hong, Xuezhi
    South China Normal Univ, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Chen, Jiajia
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab). South China Normal Univ, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China.;KTH Royal Inst Technol, Isafjordsgatan 22,Electrum 229, S-16440 Kista, Sweden.;Chalmers Univ Technol, Horsalsvagen 9, S-41296 Gothenburg, Sweden..
    Iterative point-wise reinforcement learning for highly accurate indoor visible light positioning2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 16, p. 22161-22172Article in journal (Refereed)
    Abstract [en]

    Iterative point-wise reinforcement learning (IPWRL) is proposed for highly accurate indoor visible light positioning (VLP). By properly updating the height information in an iterative fashion., the IPWRL not only effectively mitigates the impact of non-deterministic noise but also exhibits excellent tolerance to deterministic errors caused by the inaccurate a priori height information. The principle of the IPWRL is explained, and the performance of the IPWRL is experimentally evaluated in a received signal strength (RSS) based VLP system and compared with other positioning algorithms, including the conventional RSS algorithm, the k-nearest neighbors (KNN) algorithm and the PWRL algorithm where iterations exclude. Unlike the supervised machine learning method, e.g., the KNN, whose performance is highly dependent on the training process, the proposed IPWRL does not require training and demonstrates robust positioning performance for the entire tested area. Experimental results also show that when a large height information mismatch occurs, the IPWRL is able to first correct the height information and then offers robust positioning results with a rather low positioning error, while the positioning errors caused by the other algorithms are significantly higher.

  • 1275.
    Zhao, David Yuheng
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    HMM-based speech enhancement using explicit gain modeling2006In: 2006 IEEE International Conference on Acoustics, Speech and Signal Processing, 2006, p. 161-164Conference paper (Refereed)
    Abstract [en]

    We propose a hidden Markov model (HMM) based speech enhancement method using explicit modeling of speech and noise gains. The gains are considered to be stochastic variables in an HMM framework. The speech gain models the energy variations of speech phones, typically due to differences in pronunciation and/or different vocalizations of individual speakers. The noise gain helps to improve the tracking of the time-varying energy of non-stationary noise. The time-varying parameters of the gain models are estimated on-line using the recursive expectation maximization (EM) algorithm. The performance of the proposed enhancement system is evaluated through both objective and subjective tests. The experimental results confirm the advantage of explicit gain modeling, particularly for non-stationary noise sources.

  • 1276. Zheng, G.
    et al.
    Ho, Z.
    Jorswieck, E. A.
    Ottersten, Björn
    Univ. of Luxembourg.
    Information and energy cooperation in cognitive radio networks2014In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 62, no 9, p. 2290-2303Article in journal (Refereed)
    Abstract [en]

    Cooperation between the primary and secondary systems can improve the spectrum efficiency in cognitive radio networks. The key idea is that the secondary system helps to boost the primary system's performance by relaying, and, in return, the primary system provides more opportunities for the secondary system to access the spectrum. In contrast to most of existing works that only consider information cooperation, this paper studies joint information and energy cooperation between the two systems, i.e., the primary transmitter sends information for relaying and feeds the secondary system with energy as well. This is particularly useful when the secondary transmitter has good channel quality to the primary receiver but is energy constrained. We propose and study three schemes that enable this cooperation. First, we assume there exists an ideal backhaul between the two systems for information and energy transfer. We then consider two wireless information and energy transfer schemes from the primary transmitter to the secondary transmitter using power splitting and time splitting energy harvesting techniques, respectively. For each scheme, the optimal and zero-forcing solutions are derived. Simulation results demonstrate promising performance gain for both systems due to the additional energy cooperation. It is also revealed that the power splitting scheme can achieve larger rate region than the time splitting scheme when the efficiency of the energy transfer is sufficiently large

  • 1277. Zheng, Gan
    et al.
    Arapoglou, Pantelis-Daniel
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Physical Layer Security in Multibeam Satellite Systems2012In: IEEE Transactions on Wirelss Communications, ISSN 1536-1276, Vol. 11, p. 852-863Article in journal (Refereed)
    Abstract [en]

    Security threats introduced due to the vulnerability of the transmission medium may hinder the proliferation of Ka band multibeam satellite systems for civil and military data applications. This paper sets the analytical framework and then studies physical layer security techniques for fixed legitimate receivers dispersed throughout multiple beams, each possibly surrounded by multiple (passive) eavesdroppers. The design objective is to minimize via transmit beamforming the costly total transmit power on board the satellite, while satisfying individual intended users' secrecy rate constraints. Assuming state-of-the-art satellite channel models, when perfect channel state information (CSI) about the eavesdroppers is available at the satellite, a partial zero-forcing approach is proposed for obtaining a low-complexity sub-optimal solution. For the optimal solution, an iterative algorithm combining semi-definite programming relaxation and the gradient-based method is devised by studying the convexity of the problem. Furthermore, the use of artificial noise as an additional degree-of-freedom for protection against eavesdroppers is explored. When only partial CSI about the eavesdroppers is available, we study the problem of minimizing the eavesdroppers' received signal to interference-plus-noise ratios. Simulation results demonstrate substantial performance improvements over existing approaches.

  • 1278. Zheng, Gan
    et al.
    Chatzinotas, Symeon
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Multi-gateway cooperation in multibeam satellite systems2012In: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on, IEEE , 2012, p. 1360-1364Conference paper (Refereed)
    Abstract [en]

    Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and precoding over multiple beams has shown great throughput potential in literature. However, feeding all this data from a single gateway is not feasible based on the current frequency allocations. In this context, we investigate a range of scenarios involving beam clusters where each cluster is managed by a single gateway. More specifically, the following cases are considered for handling intercluster interference: a) conventional frequency colouring, b) joint processing within cluster, c) partial CSI sharing among clusters, d) partial CSI and data sharing among clusters. CSI sharing does not provide considerable performance gains with respect to b) but combined with data sharing offers roughly a 40% improvement over a) and a 15% over b).

  • 1279. Zheng, Gan
    et al.
    Jorswieck, Eduard
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cooperative Communications against Jamming with Half-Duplex and Full-Duplex Relaying2013In: Proceedings of IEEE 77th Vehicular Technology Conference: VTC2013-Spring, IEEE , 2013, p. 6692490-Conference paper (Refereed)
    Abstract [en]

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

  • 1280. Zheng, Gan
    et al.
    Krikidis, I.
    Li, Jiangyuan
    Petropulu, A. P.
    Ottersten, Björn
    University of Luxembourg.
    Improving Physical Layer Secrecy Using Full-Duplex Jamming Receivers2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 20, p. 4962-4974Article in journal (Refereed)
    Abstract [en]

    This paper studies secrecy rate optimization in a wireless network with a single-antenna source, a multi-antenna destination and a multi-antenna eavesdropper. This is an unfavorable scenario for secrecy performance as the system is interference-limited. In the literature, assuming that the receiver operates in half duplex (HD) mode, the aforementioned problem has been addressed via use of cooperating nodes who act as jammers to confound the eavesdropper. This paper investigates an alternative solution, which assumes the availability of a full duplex (FD) receiver. In particular, while receiving data, the receiver transmits jamming noise to degrade the eavesdropper channel. The proposed self-protection scheme eliminates the need for external helpers and provides system robustness. For the case in which global channel state information is available, we aim to design the optimal jamming covariance matrix that maximizes the secrecy rate and mitigates loop interference associated with the FD operation. We consider both fixed and optimal linear receiver design at the destination, and show that the optimal jamming covariance matrix is rank-1, and can be found via an efficient 1-D search. For the case in which only statistical information on the eavesdropper channel is available, the optimal power allocation is studied in terms of ergodic and outage secrecy rates. Simulation results verify the analysis and demonstrate substantial performance gain over conventional HD operation at the destination.

  • 1281. Zheng, Gan
    et al.
    Song, Shenghui
    Wong, Kai-Kit
    Ottersten, Björn
    University of Luxembourg.
    Cooperative Cognitive Networks: Optimal, Distributed and Low-Complexity Algorithms2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 11, p. 2778-2790Article in journal (Refereed)
    Abstract [en]

    This paper considers the cooperation between a cognitive system and a primary system where multiple cognitive base stations (CBSs) relay the primary user's (PU) signals in exchange for more opportunity to transmit their own signals. The CBSs use amplify-and-forward (AF) relaying and coordinated beamforming to relay the primary signals and transmit their own signals. The objective is to minimize the overall transmit power of the CBSs given the rate requirements of the PU and the cognitive users (CUs). We show that the relaying matrices have unity rank and perform two functions: Matched filter receive beamforming and transmit beamforming. We then develop two efficient algorithms to find the optimal solution. The first one has a linear convergence rate and is suitable for distributed implementation, while the second one enjoys superlinear convergence but requires centralized processing. Further, we derive the beamforming vectors for the linear conventional zero-forcing (CZF) and prior zero-forcing (PZF) schemes, which provide much simpler solutions. Simulation results demonstrate the improvement in terms of outage performance due to the cooperation between the primary and cognitive systems.

  • 1282.
    Zou, Zhuo
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Chen, Qing
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Uysal, Ismail
    Zheng, Lirong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Radio frequency identification enabled wireless sensing for intelligent food logistics2014In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 372, no 2017, p. 20130313-Article, review/survey (Refereed)
    Abstract [en]

    Future technologies and applications for the Internet of Things (IoT) will evolve the process of the food supply chain and create added value of business. Radio frequency identifications (RFIDs) and wireless sensor networks (WSNs) have been considered as the key technological enablers. Intelligent tags, powered by autonomous energy, are attached on objects, networked by short-range wireless links, allowing the physical parameters such as temperatures and humidities as well as the location information to seamlessly integrate with the enterprise information system over the Internet. In this paper, challenges, considerations and design examples are reviewed from system, implementation and application perspectives, particularly with focus on intelligent packaging and logistics for the fresh food tracking and monitoring service. An IoT platform with a two-layer network architecture is introduced consisting of an asymmetric tag-reader link (RFID layer) and an ad-hoc link between readers (WSN layer), which are further connected to the Internet via cellular or Wi-Fi. Then, we provide insights into the enabling technology of RFID with sensing capabilities. Passive, semi-passive and active RFID solutions are discussed. In particular, we describe ultra-wideband radio RFID which has been considered as one of the most promising techniques for ultra-low-power and low-cost wireless sensing. Finally, an example is provided in the form of an application in fresh food tracking services and corresponding field testing results.

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