In this work, we consider a two-tiered network, where a tier of cognitive small base stations is deployed inside the coverage area of a preexisting macro-cell. The cross-tier interference caused by a complete bandwidth sharing is managed by introducing a new orthogonal precoder based mechanism, implemented by the small base stations. This technique, called multi-user Vandermonde-subspace division multiplexing (MU-VFDM), allows to cancel the interference generated by several cognitive small base stations towards legacy macro cell receivers, without any cooperation between the two tiers. The achievable sum rate of the small-cell network, satisfying the interference cancelation requirement, is evaluated for perfect/imperfect channel state information at the transmitter (CSIT). Simulation results for MU-VFDM show a comparable performance to that of state-of-the-art dirty paper coding technique, for the case of a dense cellular layout. Finally, we propose a comparison between MU-VFDM and a standard spectrum partitioning strategy, and show promising gains in terms of achievable rate for the two-tiered network w.r.t. the traditional bandwidth management approach.