References of "Bengtsson, Mats"
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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 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 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 detailFeedback design in multiuser MIMO systems using quantization splitting and hybrid instantaneous/statistical channel information
Björnson, Emil; Hammarwall, David; Zakhour, Randa et al

in Proceedings ICT Mobile and Wireless Communications Summit (2008)

In the design of next generation multiuser communication systems, multiple antenna transmission is an essential part providing spatial multiplexing gain and allowing efficient use of resources. A major ... [more ▼]

In the design of next generation multiuser communication systems, multiple antenna transmission is an essential part providing spatial multiplexing gain 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. To this effect we propose two independent approaches for an efficient representation of the channel in multiuser MIMO systems. In the first approach, channel quantization is considered where the total number of feedback bits is limited. A resource allocation scheme is proposed where the available rate is split between the scheduling phase, where all users feed back a coarse CSI quantization, and the precoding phase where the selected receivers refine their CSI. The optimum splitting of the available feedback rate provides a large increase in performance and even simple heuristic splitting gives a noticeable advantage. In the second approach, we exploit a combination of instantaneous and statistical channel information. For spatially correlated Rayleigh and Ricean channels, it is shown that the CSI to large extent can be represented by the channel norm when the long-term channel statistics are known. Within a minimum mean square error (MMSE) estimation framework, feedback of a few bits of the quantized channel norm is sufficient to perform efficient resource allocation and achieve performance close to that of full CSI. [less ▲]

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See detailSystem Evaluation of Optimal Downlink Beamforming in Wireless Communication
Stridh, Rickard; Bengtsson, Mats; Ottersten, Björn UL

in Vehicular Technology Conference, 2001. VTC 2001 Fall. IEEE VTS 54th (2001)

We investigate the use of joint optimal downlink beamforming, power control and access point allocation, in a multicell SDMA system. Smart antennas are used at the access points and single antennas are ... [more ▼]

We investigate the use of joint optimal downlink beamforming, power control and access point allocation, in a multicell SDMA system. Smart antennas are used at the access points and single antennas are used at the terminals. The possibility to send messages to multiple terminals on the same frequency in the same time slot is exploited. An algorithm for removing users from a congested system, in order to avoid outage is proposed and evaluated Results show that the proposed algorithm gives substantial increase of the system performance compared to random removal of users. [less ▲]

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