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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 ▲]

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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)

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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)

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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)

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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 ▲]

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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 ▲]

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See detailExploiting Long-term Statistics in Spatially Correlated Multi-user MIMO Systems with Quantized Channel Norm Feedback
Björnson, Emil; Ottersten, Björn UL

in Proceedings IEEE International Conference on Acoustics, Speech, and Signal (ICASSP) (2008)

In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting ... [more ▼]

In wireless multiple antenna and multi-user systems, the spatial dimensions may be exploited to increase the performance by means of antenna gain, spatial diversity, and multi-user diversity. A limiting factor in such systems is the channel information required by the transmitter to control the intra-cell interference. Herein, the properties of spatially correlated channels with longterm statistical information at the transmitter and fixed-rate feedback of the quantized Euclidean channel norm are analyzed using a spectral subspace decomposition framework. A spatial division multiple access scheme is proposed with interference suppression at the receiver and joint scheduling and zero-forcing beamforming at the transmitter. Closed-form expressions for first and second moments of the feedback conditional channel statistics are derived. It is shown that only a few bits of feedback are required to achieve reliable rate estimation and weighted sum-rate maximization. [less ▲]

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See detailThe Diversity Order of the Semidefinite Relaxation Detector
Jaldén, Joakim; Ottersten, Björn UL

in IEEE Transactions on Information Theory (2008), 54(4), 14061422

Detailed reference viewed: 43 (0 UL)
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See detailReliability Estimation of a Statistical Classifier
Devarakota, Pandu Ranga Rao UL; Mirbach, Bruno; Ottersten, Björn UL

in Pattern Recognition Letters (2008), 29(3), 243253

Detailed reference viewed: 28 (1 UL)
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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 ▲]

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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: 31 (0 UL)
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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

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See detailStatistically Robust Design of Linear MIMO Transceivers
Zhang, Xi; Palomar, Daniel; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2008), 56(8), 36783689

Detailed reference viewed: 45 (0 UL)
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See detailPerformance of TDMA and SDMA based Opportunistic Beamforming
Jorswieck, Eduard; Svedman, Patrick; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2008), 7(11), 40584063

Detailed reference viewed: 37 (0 UL)
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See detailFeedback Reduction in Uplink MIMO OFDM Systems by Chunk Optimization
Jorswieck, Eduard; Sezgin, Aydin; Ottersten, Björn UL et al

in EURASIP Journal on Applied Signal Processing (2008)

Detailed reference viewed: 114 (0 UL)
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See detailGuaranteed Performance Region in Fading Orthogonal Space-Time Coded Broadcast Channels
Jorswieck, Eduard; Ottersten, Björn UL; Sezgin, Aydin et al

in EURASIP Journal on Wireless Communications and Networking (2008)

Detailed reference viewed: 122 (1 UL)