Asynchronous interference suppression in broadband cyclic-prefix communications

This paper explores asynchronous interference suppression in cyclic prefix communication systems such as orthogonal frequency division multiplexing (OFDM). An asynchronous interferer is defined as a signal whose cyclic prefix does not line up in time with the desired signal´s cyclic prefix. First, this paper presents an analysis of frequency-domain approaches to show that traditional circular-convolution based approaches cannot perfectly suppress the asynchronous interferer unless the number of receive elements is greater than the number of spatially distinct multipath rays. Second, this paper exploits the cyclic redundancy to design semi-blind space-time weights that are very effective at combating both synchronous and asynchronous interference. Simulation results demonstrate that frequency-domain weights have difficulty in suppressing asynchronous interference and also show the effectiveness of the proposed semi-blind suppression technique.