Performance improvement of long distance MIMO links using cross polarized antennas

Abstract

The hype with respect to MIMO systems is due to the theoretical analysis which have been reported, stating that such systems may increase the channel capacity by a factor equivalent to the smallest value between Nt and Nr, where Nt and Nr are the number of transmit and receive antennas respectively. Moreover, an improvement in the range may be observed if the number of antennas is increased at both the transmitter and the receiver, without demanding more transmit power. However, point-to-point long distance MIMO links are limited by the “keyhole” effect which results in a degenerate channel. The use of polarization diversity or artificial scatterers was proposed to eliminate the “keyhole” effect. In this analysis the effect of polarization diversity on the throughput of an IEEE 802.11n Draft 2.0 MIMO system for point-to-point long distance links is reported. IEEE 802.11n is an amendment to the IEEE 802.11 family of standards employing MIMO technology at the PHY layer besides improving the MAC layer to reduce the overhead incurred from acknowledgements and taking advantage of frame aggregation. The outcomes prove the hypothesis that a 2x2 MIMO system consisting of cross polarization at both ends of the communication link will mitigate the “keyhole” effect. Moreover, it also highlights the efficiency of IEEE 802.11n draft 2.0 via comparison of SISO systems utilizing IEEE 802.11g and IEEE 802.11n. Another point which resulted from the measurement campaign adopted was the improvement with respect to throughput that one can achieve by using 40 MHz channel spacing.