Spatial Interference Alignment Relying on Limited Precoding Matrix Feedback Indices

Abstract

Spatial Interference alignment(IA) is a promising scheme to efficiently mitigate interference and to enhance the capacity of a wireless communication network. In this paper, the sufficient conditions of spatial interference alignment operating under a realistic limited feedback are provided for a K-user MIMO interference channel. The transmit precoder's matrix index is fed back to the corresponding transmitter through an error-free non-interfered link. We investigate the number of feedback bits required for achieving the maximum theoretical multiplexing gain for the spatial interference alignment schemes considered and demonstrate the feasibility of spatial interference alignment under the limited feedback constraint investigated. It is shown that in order to maintain the same spatial multiplexing gain as that of the idealized scheme relying on perfect channel state information, the number of feedback bits per receiver scales as N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ≥ d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> (M - d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> ) log <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SNR, where M and di denote the number of transmit (receive) antennas and the number of data steams for user i. Finally, the analytical results are verified by simulations for realistic practical interference alignment schemes relying on limited precoding matrix feedback indices.