Interference Suppression Method between Primary Broadcasting and Secondary Systems Using Load Modulation

Takuma ITO  Naoki HONMA  Keisuke TERASAKI  Kentaro NISHIMORI  Yoshitaka TSUNEKAWA  

IEICE TRANSACTIONS on Communications   Vol.E98-B   No.5   pp.861-869
Publication Date: 2015/05/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E98.B.861
Type of Manuscript: PAPER
Category: Antennas and Propagation
load modulation,  frequency sharing,  interference control,  channel capacity,  

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Controlling interference from the secondary system (SS) to the receiver of the primary system (PS) is an important issue when the SS uses the same frequency band as the television broadcast system. The reason includes that the SS is unaware of the interference imposed on the primary receiver (PS-Rx), which does not have a transmitter. In this paper, we propose an interference control method between PS-Rx and SS, where a load modulation scheme is introduced to the PS-Rx. In this method, the signal from the PS transmitting station is scattered by switching its load impedance. The SS observes the scattered channel and calculates the interference suppression weights for transmitting, and controls interference by transmit beamforming. A simulation shows that the Signal-to-Interference Ratio (SIR) with interference control is improved by up to 41.5dB compared to that without interference control at short distances; the results confirm that the proposed method is effective in controlling interference between PS-Rx and SS. Furthermore, we evaluate the Signal-to-Noise Ratio (SNR) and channel capacity at SS.