References of "Ottersten, Björn 50002797"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailRobust Collaborative-Relay Beamforming
Zheng, Gan UL; Wong, Kai-Kit; Paulraj, Arogyaswami et al

in IEEE Transactions on Signal Processing (2009), 57(8), 3130-3143

Relay communications is a promising technique to extend the range of wireless communications by forwarding the message from the sender to the intended destination. While fixed or variable-power relays ... [more ▼]

Relay communications is a promising technique to extend the range of wireless communications by forwarding the message from the sender to the intended destination. While fixed or variable-power relays have been previously investigated, this paper addresses the collaborative use of variable-phase variable-power amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of the CSI error vector from the relays to the destination. Our main contribution is that we prove, under a condition on the quality of the estimated CSI, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-procedure and rank relaxation techniques. In addition, a distributed algorithm is developed by examining the structure of the optimal CRBF solution. Results demonstrate a significant gain of CRBF over non-robust approaches. [less ▲]

Detailed reference viewed: 125 (1 UL)
Full Text
Peer Reviewed
See detailThe Error Probability of the Fixed-Complexity Sphere Decoder
Jalden, Joakim; Barbero, Luis G.; Ottersten, Björn UL et al

in IEEE Transactions on Signal Processing (2009), 57(7), 2711-2720

Download Citation Email Print Request Permissions Save to Project The fixed-complexity sphere decoder (FSD) has been previously proposed for multiple-input multiple-output (MIMO) detection in order to ... [more ▼]

Download Citation Email Print Request Permissions Save to Project 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. [less ▲]

Detailed reference viewed: 118 (0 UL)
Full Text
Peer Reviewed
See detailCollaborative-Relay Beamforming with Perfect CSI: Optimum and Distributed Implementation
Zheng, Gan UL; Wong, Kai-Kit; Paulraj, Arogyaswami et al

in IEEE Signal Processing Letters (2009), 16(4), 257260

This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI ... [more ▼]

This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI) in a flat-fading channel. In particular, we optimize the relay weights jointly to maximize the received signal-to-noise ratio (SNR) at the destination terminal with both individual and total power constraints at the relays. We show that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system. Another main contribution of this letter is a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis. [less ▲]

Detailed reference viewed: 120 (0 UL)
Full Text
Peer Reviewed
See detailReduced feedback SDMA based on subspace packings
Svedman, Patrick; Jorswieck, Eduard A.; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2009), 8(3), 13291339

Herein, we treat Space Division Multiple Access (SDMA) based on partial channel state information and limited feedback. We propose a novel framework utilizing subspace packings, where beamforming ... [more ▼]

Herein, we treat Space Division Multiple Access (SDMA) based on partial channel state information and limited feedback. We propose a novel framework utilizing subspace packings, where beamforming, feedback, and scheduling are integrated. Advantages of the proposed framework are that the fed back supportable rates are based on the post-scheduling SINR and that the feedback implicitly contains information about the spatial compatibility of the users. The feasibility region of packings of different dimensions is indicated by the allocation outage probability which is derived. Grassmannian subspace packings, DFT-based packings, and non-orthogonal Grassmannian packings are formulated and studied as candidates. Numerical simulations show better performance for the proposed scheme compared to conventional channel quantization at the receiver with zero-forcing transmission in i.i.d. Rayleigh fading. Finally, we propose and evaluate a beam-graph method to further reduce the feedback load, that can be used in the context of tracking quantized beamformers. [less ▲]

Detailed reference viewed: 136 (0 UL)
Full Text
Peer Reviewed
See detailOn the Impact of Spatial Correlation and Precoder Design on the Performance of MIMO Systems with Space-Time Coding
Björnson, Emil; Ottersten, Björn UL; Jorswieck, Eduard

in Acoustics, Speech and Signal Processing, 2009. ICASSP 2009. IEEE International Conference on (2009)

The symbol error performance of spatially correlated multi-antenna systems is analyzed herein. When the transmitter only has statistical channel information, the use of space-time block codes still ... [more ▼]

The symbol error performance of spatially correlated multi-antenna systems is analyzed herein. When the transmitter only has statistical channel information, the use of space-time block codes still permits spatial multiplexing and mitigation of fading. The statistical information can be used for precoding to optimize some quality measure. Herein, we analyze the performance in terms of the symbol error rate (SER). It is shown analytically that spatial correlation at the receiver decreases the performance both without precoding and with an SER minimizing precoder. Without precoding, correlation should also be avoided at the transmitter side, but with an SER minimizing precoder the performance is actually improved by increasing spatial correlation at the transmitter. The structure of the optimized precoder is analyzed and the asymptotic properties at high and low SNRs are characterized and illustrated numerically. [less ▲]

Detailed reference viewed: 113 (0 UL)
Full Text
Peer Reviewed
See detailTraining-Based Bayesian MIMO Channel and Channel Norm Estimation
Björnson, Emil; Ottersten, Björn UL

in Acoustics, Speech and Signal Processing, 2009. ICASSP 2009. IEEE International Conference on (2009)

Training-based estimation of channel state information in multi-antenna systems is analyzed herein. Closed-form expressions for the general Bayesian minimum mean square error (MMSE) estimators of the ... [more ▼]

Training-based estimation of channel state information in multi-antenna systems is analyzed herein. Closed-form expressions for the general Bayesian minimum mean square error (MMSE) estimators of the channel matrix and the squared channel norm are derived in a Rayleigh fading environment with known statistics at the receiver side. When the second-order channel statistics are available also at the transmitter, this information can be exploited in the training sequence design to improve the performance. Herein, mean square error (MSE) minimizing training sequences are considered. The structure of the general solution is developed, with explicit expressions at high and low SNRs and in the special case of uncorrelated receive antennas. The optimal length of the training sequence is equal or smaller than the number of transmit antennas. [less ▲]

Detailed reference viewed: 114 (0 UL)
Full Text
Peer Reviewed
See detailOn the Principles of Multicell Precoding with Centralized and Distributed Cooperation Björnson, Emi Ottersten, Björn
Björnson, Emil; Ottersten, Björn UL

in Wireless Communications & Signal Processing, 2009. WCSP 2009. International Conference on (2009)

Cooperative precoding is an attractive way of improving the performance in multicell downlink scenarios. By serving each terminal through multiple surrounding base stations, inter-cell interference can be ... [more ▼]

Cooperative precoding is an attractive way of improving the performance in multicell downlink scenarios. By serving each terminal through multiple surrounding base stations, inter-cell interference can be coordinated and higher spectral efficiency achieved, especially for terminals at cell edges. The optimal performance of multicell precoding is well-known as it can be treated as a single cell with distributed antennas. However, the requirements on backhaul signaling and computational power scales rapidly in large and dense networks, which often makes such fully centralized approaches impractical. In this paper, we review and generalize some recent work on multicell precoding with both centralized and distributed cooperation. We propose practical precoding strategies under Rician channel conditions, and illustrate how the major gain of multicell precoding originates from having good base station synchronization and not from making centralized precoding decisions. [less ▲]

Detailed reference viewed: 110 (0 UL)
Full Text
Peer Reviewed
See detailSpectrum Allocation for Decentralized Transmission Strategies: Properties of Nash Equilibria
von Wrycza, Peter; Shankar, Bhavani UL; Bengtsson, Mats et al

in EURASIP Journal on Advances in Signal Processing (2009)

Detailed reference viewed: 132 (1 UL)
Full Text
Peer Reviewed
See detailDetection Based on Relaxation in MIMO Systems
Jalden, Joakim; Ottersten, Björn UL

in Handbook on Advancements in Smart Antenna Technologies for Wireless Networks (2009)

Detailed reference viewed: 104 (1 UL)
Full Text
Peer Reviewed
See detailOn the Asymptotic Optimality of Opportunistic Norm-based User Selection with Hard SINR Constraint
Zhang, Xi; Jorswieck, Eduard A.; Ottersten, Björn UL et al

in EURASIP Journal on Advances in Signal Processing (2009)

Detailed reference viewed: 124 (1 UL)
Full Text
Peer Reviewed
See detailA Limited Feedback SDMA scheme with Dynamic Multiplexing
Huang, Yongming; Yang, Luxi; Bengtsson, Mats et al

in Signal Processing Advances in Wireless Communications, 2009. SPAWC '09. IEEE 10th Workshop on (2009)

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 ... [more ▼]

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. [less ▲]

Detailed reference viewed: 82 (0 UL)
Full Text
Peer Reviewed
See detailA Game Theoretic Approach to Multi-User Spectrum Allocation
von Wrycza, Peter; Shankar, Bhavani UL; Bengtsson, Mats et al

in A Game Theoretic Approach to Multi-User Spectrum Allocation (2009)

Detailed reference viewed: 133 (0 UL)
Full Text
Peer Reviewed
See detailDistributed Multicell and Multiantenna Precoding: Characterization and Performance Evaluation
Björnson, Emil; Zakhour, Randa; Gesbert, David et al

in Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE (2009)

This paper considers downlink multiantenna communication with base stations that perform cooperative precoding in a distributed fashion. Most previous work in the area has assumed that transmitters have ... [more ▼]

This paper considers downlink multiantenna communication with base stations that perform cooperative precoding in a distributed fashion. Most previous work in the area has assumed that transmitters have common knowledge of both data symbols of all users and full or partial channel state information (CSI). Herein, we assume that each base station only has local CSI, either instantaneous or statistical. For the case of instantaneous CSI, a parametrization of the beamforming vectors used to achieve the outer boundary of the achievable rate region is obtained for two multi-antenna transmitters and two single-antenna receivers. Distributed generalizations of classical beamforming approaches that satisfy this parametrization are provided, and it is shown how the distributed precoding design can be improved using the so-called virtual SINR framework. Conceptually analog results for both the parametrization and the beamforming design are derived in the case of local statistical CSI. Heuristics on the distributed power allocation are provided in both cases, and the performance is illustrated numerically. [less ▲]

Detailed reference viewed: 134 (0 UL)
Full Text
Peer Reviewed
See detailA codebook-based precoding for dual-hop downlink with MIMO amplify-and-forward relaying
Huang, Yongming; Yang, Luxi; Bengtsson, Mats et al

in Signal Processing Advances in Wireless Communications, 2009. SPAWC '09. IEEE 10th Workshop on (2009)

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 ... [more ▼]

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. [less ▲]

Detailed reference viewed: 107 (0 UL)
Full Text
Peer Reviewed
See detailRobust and Distributed Beamforming
Gan, Zheng; Kai-Kit, Wong; Arogyaswami, Paulraj et al

in Wireless Communications & Signal Processing, 2009. WCSP 2009. International Conference on (2009)

This paper studies the use of amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst ... [more ▼]

This paper studies the use of amplify-and-forward (AF) relays for robust beamforming, with the aid of imperfect channel state information (CSI) at the sender. In particular, the maximization of the worst-case signal-to-noise ratio (SNR) at the destination terminal is studied under a bounded spherical region for the norm of CSI error vector. We show that under a condition on the estimated CSI quality, the robust-optimal collaborative-relay beamforming (CRBF) can be obtained by S-Procedure and rank relaxation techniques. In addition, a distributed algorithm is proposed by examining the structure of the optimal CRBF. [less ▲]

Detailed reference viewed: 144 (0 UL)
Full Text
Peer Reviewed
See detailConvergence of the Iterative Water-Filling Algorithm in Multiple User Spectrum Sharing Scenarios
Shankar, Bhavani UL; von Wrycza, Peter; Bengtsson, Mats et al

in Communication Technologies Workshop (Swe-CTW), 2011 IEEE Swedish (2009)

Spectrum sharing between multiple independent, coexisting transmit-receive pairs (TRPs, also termed as users) is formulated as a non-cooperative game with the TRPs as players, their individual link rates ... [more ▼]

Spectrum sharing between multiple independent, coexisting transmit-receive pairs (TRPs, also termed as users) is formulated as a non-cooperative game with the TRPs as players, their individual link rates as payoffs and the iterative water-filling algorithm (IWFA) as the strategy for each TRP. The dynamics of this distributed algorithm are studied for sequential and simultaneous update mechanisms to determine the nature of convergence. Global convergence to unique Nash Equilibrium (NE) is considered and sufficient conditions tighter than those in the literature are derived. Necessary conditions are also derived to complement the sufficient conditions. The necessary conditions serve as tools for characterizing the structure of NE and also highlight the sensitivity of convergence to update orders in sequential IWFA. [less ▲]

Detailed reference viewed: 166 (0 UL)
Full Text
Peer Reviewed
See detailAcquiring Partial CSI for Spatially Selective Transmission by Instantaneous Channel Norm Feedback
Hammarwall, David; Bengtsson, Mats; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2008), 56(3), 11881204

In the design of next-generation multiuser communication systems, multiple-antenna transmission is an essential part providing additional spatial degrees of freedom and allowing efficient use of resources ... [more ▼]

In the design of next-generation multiuser communication systems, multiple-antenna transmission is an essential part providing additional spatial degrees of freedom and allowing efficient use of resources. A major limiting factor in the resource allocation is the amount of channel state information (CSI) available at the transmitter, particularly in multiuser systems where the feedback from each user terminal must be limited. Herein, we show that the Euclidean norm of the instantaneous channel, when combined with long-term channel statistics provides sufficient information for the transmitter to efficiently utilize multiuser diversity in time, frequency, and space. We consider the downlink of a communication system where the base station has multiple transmit antennas whereas each user terminal has a single receive antenna. The CSI provided by channel statistics and feedback of the norm of the instantaneous channel vector is studied in depth for correlated Rayleigh and Ricean fading channels, within a minimum mean-square error (MMSE) estimation framework. An asymptotic analysis (high instantaneous SNR) is presented which shows that channel realizations with large channel norm provide additional spatial CSI at the transmitter. This makes the proposed scheme ideal for multiuser diversity transmission schemes, where resources are only allocated to users experiencing favorable channel conditions. [less ▲]

Detailed reference viewed: 143 (0 UL)
Peer Reviewed
See detailStatistical Analysis and Optimal Design for Efficient Mobile Satellite Broadcast With Diversity
Martin, Cristoff; Geurtz, Alexander; Ottersten, Björn UL

in IEEE Transactions on Vehicular Technology (2008), 57(2), 9861000

Detailed reference viewed: 4 (0 UL)
Peer Reviewed
See detailDirectional Dependence of Large Scale Parameters in Wireless Channel Models
Jalden, Niklas; Zetterberg, Per; Ottersten, Björn UL

in IEEE Wireless Communications (2008)

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 ... [more ▼]

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. 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. [less ▲]

Detailed reference viewed: 109 (1 UL)
Peer Reviewed
See detailUtilizing the Spatial Information Provided by Channel Norm Feedback in SDMA Systems
Hammarwall, David; Bengtsson, Mats; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2008), 56(7), 32783293

Detailed reference viewed: 4 (0 UL)