Hybrid blind interference alignment in homogeneous cellular networks with limited coherence time

Abstract

The work presented in this paper is inspired by the user grouping approach of topological blind interference alignment (top-BIA), which is a semi-blind IA scheme and the fact that the partially connected networks can be advantageous in terms of degree of freedom (DoF) and sum rate. The hybrid-BIA scheme proposed in the paper uses top-BIA to group users that are randomly distributed in a dense small-cell network and aims to reduce the supersymbol length and overcome the DoF loss of the state-of-the-art hierarchical BIA (h-BIA) technique. The proposed scheme is very suitable for channels where coherence time is limited and also could attain a good DoF over a small number of symbol extensions.Both the sum-DoF and the network throughput for hybrid-BIA is greater than that of h-BIA. By varying the number of user groups, the paper shows that h-BIA constitutes a special case of hybrid-BIA. Finally, the paper demonstrates the effect of changing the number of transmit antennas and number of small cells on the sum-DoF gain of hybrid-BIA over that of h-BIA. KEYWORDSblind interference alignment, hierarchical BIA, hybrid-BIA, reconfigurable antenna, topological BIA Int J Commun Syst. 2019;32:e3836.wileyonlinelibrary.com/journal/dac the DoF of the network would collapse, and hence, the transmissions would become unreliable. 10 An interference alignment method that did not require CSIT for the broadcast channel (BC) was first proposed in Tiango et al 2 and then was elaborated upon in Jafar. 3 This new technique referred to as the standard blind interference alignment (s-BIA) assumes a K-user M × 1 MISO BC ([K, M] configuration) in which the BS is equipped with M transmit antennas and each receiver is equipped with a single reconfigurable antenna capable of switching between M preset modes. With no knowledge about CSIT, s-BIA can still align all intracell interference with only a mild assumption on the channel coherence structure and has been shown to achieve KM∕(K + M − 1) DoF. In addition, Lu et al 11,12 have used s-BIA under the K-user M × 1 MISO interference channel (IC) where users were assumed to have different number of preset modes. The s-BIA technique requires that the channel remains unchanged throughout the duration of the transmission. Therefore, coherence time or bandwidth is important when determining whether BIA can be used. 13 This motivates the search for BIA schemes that can provide short supersymbol lengths that will correspond to realistic coherence times. The performance of s-BIA in cellular and clustered systems was first analyzed in Wang et al. 14 It was shown that although s-BIA can totally cancel the intracell interference, the rates of users located at the cell edges will deteriorate due to the intercell interference coming from the neighboring cells. However, in Wang et al, 14,15 it is mentioned that if the BIA codes of the neighboring cells are synchronized (sync-BIA), then the effect of intercell interference can considerably be reduced.Under cellular networks, coordinated BIA scheme (c-BIA) 16 that ...

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