Feedback Cancellation for T-DMB Repeaters Based on Frequency-Domain Channel Estimation

This paper presents a novel feedback canceller for a terrestrial digital multimedia broadcasting (T-DMB) on-channel repeater (OCR). There is a crucial requirement for an OCR that the isolation between the transmitter and the receiver antennas should be sufficiently secured to prevent unwanted oscillation. The required isolation, however, may not be satisfied by some physical or technical limitations. In order to overcome these obstacles, undesired feedback signals have been usually reduced by feedback cancellation techniques based on pilot-aided frequency-domain channel estimation (FDCE). In case of the T-DMB system, however, there are no pilot symbols except for the phase reference symbols (PRSs), which are transmitted only once every 76 OFDM symbols. Consequently, the convergence speed and the tracking capability of the FDCE-type feedback cancellers may not meet the required robustness in coping with dynamic feedback channels. To improve the immunity to time-varying channels, we increase the usable number of updates in our feedback canceller, where the PRS is divided into several sub-PRSs during the PRS period and pseudo pilots are generated by decision-directed estimation in the data-symbol duration. Simulation results show that the proposed methods do improve the convergence speed and the tracking capability of the conventional method in both static and dynamic feedback channels.