Performance of multiple-receive multiple-transmit beamforming in WLAN-type systems under power or EIRP constraints with delayed channel estimates

Downlink beamforming in a WLAN-type system employing access points and mobiles equipped with multiple antennas and associated receivers and transmitters are considered. The beamforming aims at maximizing the performance under constraints on transmit power or equivalent isotropic radiated power (EIRP...

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Bibliographic Details
Main Authors: Zetterberg, P., Bengtsson, M., McNamara, D., Karlsson, P., Beach, M.A.
Format: Conference Proceeding
Language:English
Subjects:
Antenna measurements
Array signal processing
Degradation
Delay estimation
Downlink
Information technology
Informationsteknik
Mobile antennas
Performance gain
Receiving antennas
Systems engineering
Systemteknik
TECHNOLOGY
TEKNIKVETENSKAP
Transmitters
Transmitting antennas
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Summary:Downlink beamforming in a WLAN-type system employing access points and mobiles equipped with multiple antennas and associated receivers and transmitters are considered. The beamforming aims at maximizing the performance under constraints on transmit power or equivalent isotropic radiated power (EIRP). Solutions for the two constraints are derived and investigated using simulated and measured channels. Our simulation and experimental results shows that performance gains of 8-10 dB when using four directional transmitter antennas and two receive antennas (as compared with a base-line one-transmit two-receive), are possible under both constraints. For simulated channels, a delay between channel estimation and use of the same channel of up to 10% of the (inverse of the) Doppler frequency only degrades performance some tenths of a dB. In our measurements, very small degradations are seen with delays of up to 130 ms. The measurements were made under relatively stationary conditions with only occasionally moving people. Two different strategies for updating the beamforming vectors: sounding and ping-pong, are also considered in the paper.
DOI:10.1109/VTC.2002.1002954