Precoding for MIMO Channels in Cognitive Radio Networks With CSI Uncertainties and for Compound Capacity
Inaccurate knowledge of channel state information
(CSI) limits the performance offered by MIMO communications.
The design of a MIMO precoder should take the CSI uncertainty
into consideration to mitigate its effects. This paper proposes
a method to design the precoder for a secondary user in an
underlay cognitive radio framework that maximizes its transmission
performance, where the direct link to its receiver and
the interference link to a primary user have CSI uncertainties.
We model the CSI uncertainties through the Schatten norm
that encompasses most commonly used norm measures such
as the spectral and Frobenious norms. The proposed method
solves iteratively a minimax problem by deriving the optimal
solution for the worst case interference CSI uncertainty, applying
the alternate-iterate technique for the worst case direct link
CSI deviation, and developing a feasible direction projected
subgradient technique for the precoder. Simpler solutions for the
precoder are also derived under some specific norm measure
of CSI uncertainty and certain requirement of transmission
power. Simulations corroborate the expected performance of the
proposed design.
KeyWords
Cognitive radio, compound capacity, minimax,
MIMO, Schatten norm, alternate iterate, Lagrange dual, leakage
rate.
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