Combined transmit beamforming and channel-aware scheduling for interference mitigation in femtocells

Abstract

The introduction of femtocells in mobile networks gives rise to new co-layer and crosslayer interference scenarios. To mitigate interference, several approaches have been proposed in the literature including, e.g., transmit beamforming (TBF), power control, and fractional frequency reuse. In this article, we present an interference mitigation approach that relies on a low-rate control channel between the victim terminal and the interfering femto access point (FAP). The proposed method combines both, practical TBF schemes and simple one-bit channel-aware scheduling algorithms. We show that the proposed method can be effectively used not only to mitigate interference among FAPs, but also to balance user rates in adjacent cells with small signaling overhead.

Performance of Transmit Beamforming Codebooks with Separate Amplitude and Phase Quantization

“…In [8], the relative channel phase information of the different Tx antennas is uniformly quantized (with respect to a reference antenna) and the order information of channel gains are informed separately. Nevertheless, when CCI minimization becomes the design criterion of a TBF codebook, the use of additional bits for the quantization of channel amplitudes is expected to provide notable performance improvements [9]. Among other advantages, the use of separate quantization schemes for both channel amplitudes and phases allows to adapt the structure of the TBF codebook on-the-fly, based on the feedback overhead that each user can generate.…”

Performance of transmit beamforming for interference mitigation with random codebooks

“…The selection of a the best beamforming vector is done in the receiver to optimize a given objective function. In what follows, two different approaches are analyzed: egoistic TBF and altruistic TBF [7].…”

“…Based on this simplified interference mitigation approach, the performance of altruistic TBF has been characterized analytically in [5] for a dominant co-layer interfering source, and in [6] for multiple dominant cross-layer interfering sources. In [7], the performance of a scheme that combines altruistic TBF with channel-aware scheduling is studied for the single interfering source case. Nevertheless, in all these papers, the codebook designs to implement altruistic TBF are generalized versions of practical UTRA-based transmit-diversity methods (originally designed for scenarios with 2 transmit antennas), which cannot be easily extended when a larger number of transmit antennas is used for interference mitigation purposes.…”