Cognitive Beamforming and Power Control in Time-Varying Channels: Design and Analysis

Heejung YU

IEICE TRANSACTIONS on Communications   Vol.E96-B    No.6    pp.1616-1624
Publication Date: 2013/06/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E96.B.1616
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Terrestrial Wireless Communication/Broadcasting Technologies
cognitive radio,  cognitive beamforming,  time-varying channels,  power control,  interference management,  

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Cognitive beamforming exploiting spatial opportunity is an attractive technique for secondary users to coexist with primary users in cognitive radio environments. If perfect channel state information of the interfering link is available, interference from a secondary transmitter to a primary receiver can be perfectly pre-nulled by choosing the ideal transmit beam. In practice, however, there is channel estimation error due to noise and the time-varying channels. To minimize the residual interference due to those channel estimation errors, channel prediction based on auto regressive (AR) model is introduced in this paper. Further, to cope with extremely rapidly-varying channels, a cognitive transmit power control technique is proposed as well. By combining channel prediction and transmit power control in cognitive beamforming, the cognitive users can share the spectrum with the primary users with a limited interference level in time-varying channels.