Digital Cross-Polar Interference Canceller

Abstract

Dual-polarized data transmission promises to double the system capacity by transmitting independent signals simultaneously on both polarizations in the same channel. However, the polarization orthogonality of the propagation field can not always be perfectly preserved in various environments. Also the antenna and waveguide networks may not be able to achieve absolute polarization isolation. Therefore cross-polarization interference becomes a severe source of performance degradation in dual-polar systems. This paper presents an all-digital design of the cross-polarization interference canceller (XPIC or CPIC). This canceller is designed to remove the cross-polar interference so that comparable performance to single-polar system can be achieved for each polarization. Specifically, this digital design aims for • Mitigating the cross-polarization interference caused primarily by antenna orientation. (Delay between the signals from both polarizations is considered insignificant.) • Can operate with time varying cross-polar interference varying at rates of 2-3 Hz and beyond. • Initial isolation can be as low as 10 dB. • Is well suited to an all digital modem where clocking from the A/D is independent of symbol timing recovery clocks.