On the spatial degrees of freedom benefits of reverse TDD in multicell MIMO networks

Abstract

In this paper we study the degrees of freedom (DoF) achieved by interference alignment (IA) for cellular networks in reverse time division duplex (R-TDD) mode, a new configuration associated to heterogeneous networks. We derive a necessary feasibility condition for interference alignment in the multi-cell R-TDD scenario, which is then specialized to the particular case of symmetric demands and antenna distribution. We show that, for those symmetric networks for which the properness condition holds with equality, R-TDD does not improve the DoF performance of conventional synchronous TDD systems. Nevertheless, our simulation results indicate that, in more asymmetric scenarios, significant DoF benefits can be achieved by applying the R-TDD approach.

Experimental evaluation of flexible duplexing in multi-tier MIMO networks

“…Authors in [4] analyze the degrees of freedom (DoF) benefits of flexible duplexing in 2-cell networks by combining reversed UL/DL with interference alignment. The DoF study is extended for multi-cell networks in [5], where the impact of network asymmetry on the potential multiplexing gain is discussed. First results showing the rate improvements provided by flexible duplexing can be found in [2].…”

“…Also, the aforementioned work takes into account traffic asymmetries for a better characterization of 5G mobile communications. Such asymmetries are included as well in [9], where following the same line as in [4,5], flexible duplexing is combined with IA for optimal downlink rate. In addition, the hierarchical switching (HS) scheme, which checks only a subset of possible uplink/downlink configurations, is proposed in order to reduce the computational cost of UL/DL selection.…”

Power Minimization in Multi-tier Networks with Flexible Duplexing

“…Several studies on the benefits of flexible duplexing have been recently carried out, relying on different figures of merit. Most of the existing works assume that a fixed UL/DL combination is given, and present an analysis in terms of multiplexing gain [4][5][6], or in terms of throughput [7][8][9][10][11]. A frame structure for interference mitigation can be found in [12], and flexible duplexing is further proposed as a candidate for evaluation in real deployments in [13].…”

Flexible Duplexing for Maximum Downlink Rate in Multi-Tier MIMO Networks

“…The feasibility of alignment for flexible duplexing 2-cell networks is analyzed in [10], [11], and authors in [10] establish that the existence of degrees-of-freedom (DoF) benefits due to the implementation of flexible duplexing depends on the network topology. Further DoF evaluation of 2-cell flexible duplexing HetNets is included in [12], whereas these studies are extended to a multi-cell network model in [13]. Additionally, a discussion on the applicability of interference alignment in flexible duplexing experimental deployments can be found in [14].…”