Experimental evaluation of relative calibration in a MISO-TDD system
Abstract
We study the transmit time reversal beamforming in a 8x1 MISO communication system at 2.68GHz. We consider the downlink time reversal transmission where a BS communicates with one user. A prototype composed by 8 antennas and designed by Orange labs acts as the BS while the user has a single antenna. The reciprocity property is destroyed by the non-symmetric characteristics of the RF electronic circuitry. We use relative calibration which is based exclusively on signal processing techniques to solve this issue. Utilizing a controlled test setup based on OpenAirInterface, the ExpressMIMO2 SDR boards, as well as a servo controlled rail, we show the feasibility of a relative calibration method through beamforming SNR measurements. We also evaluate the performance of an antenna selection scheme at the transmit side as a low-cost low-complexity alternative to capture many of the advantages of multi-antenna systems. The measurements show that the relative calibration method is performing almost optimal and that the complexity can be significantly reduced by using antenna selection.
Keywords
signal processing techniques
servo controlled rail
relative calibration method
reciprocity property
non-symmetric characteristics
multi-antenna systems
Antenna measurements
transmit time reversal beamforming
OpenAirInterface
MISO communication system
Calibration
Array signal processing
downlink time reversal transmission
frequency 2.68 GHz
ExpressMIMO2 SDR boards
Antennas
UHF antennas
time division multiplexing
MIMO communication
OFDM
RF electronic circuitry
Radio frequency
antenna selection scheme
beamforming SNR measurements
controlled test setup
Signal to noise ratio