Title :
Performance of multiple-receive multiple-transmit beamforming in WLAN-type systems under power or EIRP constraints with delayed channel estimates
Author :
Zetterberg, P. ; Bengtsson, M. ; McNamara, D. ; Karlsson, P. ; Beach, M.A.
Author_Institution :
Signal Process., R. Inst. of Technol., Stockholm, Sweden
fDate :
6/24/1905 12:00:00 AM
Abstract :
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.
Keywords :
Doppler effect; MIMO systems; adaptive antenna arrays; array signal processing; delays; directive antennas; land mobile radio; radio links; receiving antennas; transmitting antennas; wireless LAN; Doppler frequency; EIRP constraints; MIMO system; WLAN-type systems; access points; beamforming vectors; channel estimation; delayed channel estimates; directional transmitter antennas; downlink beamforming; equivalent isotropic radiated power; measured channels; mobile radio; multiple-receive multiple-transmit beamforming; ping-pong; receive antennas; simulated channels; sounding; stationary conditions; time division duplex; transmit power constraints; Antenna measurements; Array signal processing; Degradation; Delay estimation; Downlink; Mobile antennas; Performance gain; Receiving antennas; Transmitters; Transmitting antennas;
Conference_Titel :
Vehicular Technology Conference, 2002. VTC Spring 2002. IEEE 55th
Print_ISBN :
0-7803-7484-3
DOI :
10.1109/VTC.2002.1002954