Cognitive Orthogonal Precoder for Two-tiered Networks Deployment

TL;DR

This paper introduces MU-VFDM, a novel precoding scheme that enables cognitive small cells to coexist with macro-cells by effectively nulling cross-tier interference without cooperation, improving spectrum efficiency.

Contribution

The paper proposes MU-VFDM, a new orthogonal precoder for small cells that cancels cross-tier interference and enhances sum-rate performance in two-tiered networks.

Findings

MU-VFDM achieves interference cancellation comparable to dirty paper coding.

Simulation results show significant sum-rate gains over traditional spectrum separation.

MU-VFDM performs well under both perfect and imperfect channel knowledge.

Abstract

In this work, the problem of cross-tier interference in a two-tiered (macro-cell and cognitive small-cells) network, under the complete spectrum sharing paradigm, is studied. A new orthogonal precoder transmit scheme for the small base stations, called multi-user Vandermonde-subspace frequency division multiplexing (MU-VFDM), is proposed. MU-VFDM allows several cognitive small base stations to coexist with legacy macro-cell receivers, by nulling the small- to macro-cell cross-tier interference, without any cooperation between the two tiers. This cleverly designed cascaded precoder structure, not only cancels the cross-tier interference, but avoids the co-tier interference for the small-cell network. The achievable sum-rate of the small-cell network, satisfying the interference cancelation requirements, is evaluated for perfect and imperfect channel state information at the transmitter. Simulation results for the cascaded MU-VFDM precoder show a comparable performance to that of state-of-the-art dirty paper coding technique, for the case of a dense cellular layout. Finally, a comparison between MU-VFDM and a standard complete spectrum separation strategy is proposed. Promising gains in terms of achievable sum-rate are shown for the two-tiered network w.r.t. the traditional bandwidth management approach.