David Hammarwall

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Beamforming schemes have been proposed to exploit the spatial characteristics of multiple-input single-output (MISO) wireless radio channels. Several algorithms are available for optimal joint beamforming and power control for the downlink. Such optimal beamforming minimizes the total transmission power, while ensuring an individual target quality of(More)
A major limiting factor in communication systems utilizing multi-antenna transmission is the amount of spatial channel information available at the transmitter. Since the channel realizations, in most cases, can only be estimated at the receiver, such information must be fed back to the transmitter. In multiuser systems the amount of feedback must be kept(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(More)
To achieve high performance, in terms of reliability and throughput, in future multiple-antenna communication systems, it is essential to fully exploit the spatial dimensions of the wireless propagation channel. In multiuser communication systems, the throughput can be significantly increased by simultaneously transmitting to several users in the same(More)
In multiuser OFDMA FDD systems with resource allocation based on the instantaneous channel quality of the users, the feedback overhead can be very large. In this paper, a method to significantly reduce this feedback is proposed. The idea is to let the users feed back the channel quality (the SNR in this paper) of only a sub-set of their strongest(More)
Spatial division multiple access (SDMA) systems efficiently take advantage of the spatial dimensions of the channel to increase the performance of the system. A major difficulty, common to all SDMA systems, is the requirement of channel knowledge at the transmitter to enable transmission of multiple streams without catastrophic interference. Herein we show(More)
In the design of narrowband multi-antenna systems, a limiting factor is the amount of channel state information (CSI) available at the transmitter. This is especially evident in multi-user systems, where the spatial user separability determines the multiplexing gain, but it is also important for transmission-rate adaptation in single-user systems. To limit(More)
In wireless high performance systems utilizing smart antenna transmission techniques, increased pilot signaling becomes problematic when more transmit antennas are added. Herein, we propose a scheme where the pilot signaling is restricted to a subset of the transmit antennas, and the total signal strength of these antennas is fed back to the transmitter.(More)
The problem of beamforming and rate estimation in a multi-user downlink multiple-input multiple-output (MIMO) system with limited feedback and statistical channel information at the transmitter is considered. In order to exploit the spatial properties of the channel, the norm of the channel to each receive antenna is computed. We propose to feed back the(More)