Altruistic Transmit Beamforming for Cross-layer Interference Mitigation in Heterogeneous Networks

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Sähkötekniikan korkeakoulu | Master's thesis
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[10] + 86 s.
The emergence of heterogeneous networks, with low-power nodes operating under the umbrella of high-power macro cells, simplifies planning procedures for operators, but introduces the problem of cross-layer interference between the overlapping cells. An effective technique for combating interference is transmit beam-forming (TBF), a transmitter-side technique which utilizes partial knowledge of the channel and presence of multiple antennas at the transmitter to enhance the signal reception quality at a receiver. When applied to the base station associated with the receiver, TBF boosts the desired signal. On the other hand, when applied to the interfering base station, TBF reduces the effect of the interference signal. The former technique is commonly referred to as egoistic TBF, while the latter is known as altruistic TBF. In this thesis, we provide theoretical evaluation of the performance gains that altruistic TBF is able to offer to a heavily interfered user in a heterogeneous setting, when channel state information is conveyed from the receiver to the transmitter through a limited feedback channel. We show that the application of altruistic TBF to specifically defined clusters of interferers is able to drastically improve performance for the victim user. Furthermore, we prove the exact upper bound for the performance of the victim user, when only phase feedback is used for altruistic TBF and the source of interference is a single dominant interferer. Finally, we investigate and propose new techniques that can be applied to multi-antenna heterogeneous network scenarios for interference mitigation purposes.
Hämäläinen, Jyri
Thesis advisor
Dowhuszko, Alexis
heterogeneous networks, femtocells, interference mitigation, MIMO, closed-loop methods, transmit beamforming, cross-layer interference
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