@phdthesis {544,
	title = {Analysis and Experimental Evaluation of Flexible Duplexing for Multi-Tier MIMO Networks},
	year = {2019},
	month = {April},
	school = {University of Cantabria},
	author = {Fanjul, Jacobo}
}
@article {500,
	title = {Interference Alignment Testbeds},
	journal = {IEEE Communications Magazine},
	volume = {55},
	year = {2017},
	month = {October},
	pages = {120-126},
	author = {Yenk, Cenk and Fanjul, Jacobo and Garc{\'\i}a-Naya, J. A. and Moghadam, Nima and Farhadi, Hamed}
}
@article {482,
	title = {Homotopy Continuation for Spatial Interference Alignment in Arbitrary MIMO X Networks},
	journal = {IEEE Transactions on Signal Processing},
	volume = {65},
	year = {2017},
	month = {April},
	pages = {1752-1764},
	issn = {1053-587X},
	doi = {10.1109/TSP.2016.2637310},
	author = {Fanjul, Jacobo and Gonz{\'a}lez, {\'O}scar and Santamar{\'\i}a, Ignacio and Beltr{\'a}n, Carlos}
}
@article {593,
	title = {Experimental evaluation of flexible duplexing in multi-tier MIMO networks},
	journal = {EURASIP Journal onWireless Communications and Networking},
	year = {2020},
	month = {September},
	author = {Fanjul, Jacobo and Fern{\'a}ndez, Renzo D. and Ib{\'a}{\~n}ez, Jes{\'u}s and Garc{\'\i}a-Naya, J. A. and Santamar{\'\i}a, Ignacio}
}
@conference {463,
	title = {Statistical Analysis of Single-Beam Interference Alignment Schemes},
	booktitle = {IEEE Workshop on Signal Processing Advances on Wireless Communications (SPAWC)},
	year = {2016},
	month = {July},
	address = {Edimburgh, UK},
	abstract = {In this work, we derive analytical approximate expressions for the user rates achievable by interference alignment (IA) algorithms in single-beam multiple-input multiple-output (MIMO) networks for a fixed channel realization. Unlike previous works that perform a large-system analysis in which the number of users, antennas, or streams is required to tend to infinity, in this paper we only require that the number of different IA solutions (precoders and decoders) for the given scenario is sufficiently high, which typically happens even for moderate-size feasible networks. Based on the assumption that the IA beamformers for a given channel realization are random vectors isotropically distributed on the complex unit sphere, we characterize the user rates by averaging over the (possible finite) set of IA solutions. Some simulation results show the accuracy of the proposed rate expressions.},
	author = {Santamar{\'\i}a, Ignacio and Fanjul, Jacobo}
}
@conference {476,
	title = {On the Spatial Degrees of Freedom Benefits of Reverse TDD in Multicell MIMO Networks},
	booktitle = {24th European Signal Processing Conference (EUSIPCO 2016)},
	year = {2016},
	month = {September},
	pages = {1363-1367},
	address = {Budapest, Hungary},
	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},
	author = {Fanjul, Jacobo and Santamar{\'\i}a, Ignacio}
}
@conference {503,
	title = { A quaternion-based approach to interference alignment with Alamouti coding},
	booktitle = {IEEE International Symposium on Signal Processing and Information Technology (ISSPIT)},
	year = {2017},
	month = {December},
	publisher = {IEEE},
	organization = {IEEE},
	address = {Bilbao, Spain},
	abstract = {Based on the representation of Alamouti space-time codewords as quaternions, this paper proposes a scheme that combines interference alignment (IA) with Alamouti signals. The proposed formulation allows for a separation of the space-time block coding (to gain spatial diversity) and the IA precoding (to reduce or ideally suppress interference). Although this separation is not necessarily optimal, the splitting of alignment precoding and Alamouti encoding is particularly convenient because it enables the independent optimization of the IA solution using quaternionic versions of standard alternating optimization techniques such as the maximum signal-to-interference-plus-noise algorithm. Some numerical simulations are included to compare the performance of the proposed quaternion IA+Alamouti algorithm with standard IA algorithms in the complex domain as well as with interference cancellation schemes at the receiver side.},
	author = {Fanjul, Jacobo and Santamar{\'\i}a, Ignacio and Loucera, Carlos}
}
@conference {540,
	title = {Power Minimization in Multi-tier Networks with Flexible Duplexing},
	booktitle = {IEEE Int. Conference on Acoustics, Speech, and Signal Processing (ICASSP)},
	year = {2019},
	month = {May},
	address = {Brighton, UK},
	abstract = {In this paper we present an algorithm to minimize transmit power in multiple-input multiple-output (MIMO) heterogeneous
networks (HetNets) with flexible duplexing, a promising strategy that allows the coexistence of uplink and downlink cells within the same time and frequency resource block. First, the proposed algorithm minimizes transmit power for a given uplink/downlink (UL/DL) combination, and afterwards, the optimal solution out of the explored UL/DL combinations is selected. To reduce
the computational cost of exploring all the UL/DL settings, we propose a hierarchical switching (HS) approach
that considers a reduced subset of transmit directions. By means of Monte Carlo simulations, we show that the proposed
technique provides significant power savings with respect to a conventional time-division duplex (TDD) scheme.},
	author = {Fanjul, Jacobo and Santamar{\'\i}a, Ignacio}
}
@conference {399,
	title = {Homotopy Continuation for Vector Space Interference Alignment in MIMO X Networks},
	booktitle = {2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)},
	year = {2014},
	month = {May},
	pages = {6232--6236},
	author = {Gonz{\'a}lez, {\'O}scar and Fanjul, Jacobo and Santamar{\'\i}a, Ignacio}
}
@conference {536,
	title = {Flexible Duplexing for Maximum Downlink Rate in Multi-tier MIMO Networks},
	booktitle = {26th Telecommunications Forum TELFOR 2018},
	year = {2018},
	month = {November},
	address = {Belgrade, Serbia},
	abstract = {In this paper, we propose an algorithm to maximize downlink rate performance in the context of multiple-input multiple-output (MIMO) Heterogeneous Networks (HetNets). Specifically, we evaluate the benefits of flexible duplexing, a promising strategy that consists in combining uplink and downlink cells within the same channel use. In order to handle intercell interference, we rely on the interference alignment (IA) technique, taking into account the impact of the channel estimation errors on the inter-cell interference leakage. Determining the best uplink/downlink configuration is a combinatorial problem, and therefore we consider several approaches to reduce the computational demands of the problem. First, we use a statistical characterization for the average rates achieved by IA in order to avoid the calculation of alignment solutions for all possible settings in the network. Additionally, we propose two hierarchical switching (HS) strategies so that only a subset among the total number of combinations is explored. As a performance baseline, we include in the comparison the conventional time division duplex (TDD) approach and the well-known minimum mean square error (MMSE) decoder. The obtained results show that downlink rates achieved by implementing flexible duplexing
and applying inter-cell IA significantly outperform conventional TDD transmissions. Finally, the proposed hierarchical schemes are shown to obtain almost the same rates as exhaustive search with much lower computational cost.},
	author = {Fanjul, Jacobo and Santamar{\'\i}a, Ignacio}
}
@conference {496,
	title = {Experimental Evaluation of Non-Coherent MIMO Grassmannian Signaling Schemes},
	booktitle = {16th International Conference on Ad Hoc Networks and Wireless (AdHoc-Now 2017)},
	year = {2017},
	month = {September},
	address = {Messina, Italy},
	abstract = {In this paper, we present an over-the-air (OTA) performance
analysis of Grassmannian signaling strategies in an orthogonal frequencydivision
multiplexing (OFDM) single-user multiple-input multiple-output
(SU-MIMO) scenario. Specically, we compare the Grassmannian signaling
technique to the dierential Alamouti scheme and a novel space-time
non-coherent scheme recently proposed in the context of 5G. As a performance
benchmark we include in the comparison the coherent Alamouti
scheme. We study the practical impairments associated to frequency
synchronization mismatches (frequency osets), as well as the eects of
time-varying channels for dierent spectral eciencies. The experimental
results show that non-coherent techniques are more robust to the
aforementioned impairments than the coherent Alamouti approach, while
Grassmannian methods are close to the dierential Alamouti scheme with
2 transmit antennas.},
	keywords = {Grassmannian signaling, MIMO testbed, Non-coherent communications, OFDM, Over-the-air (OTA) experiments},
	author = {Fanjul, Jacobo and Santamar{\'\i}a, Ignacio and Ib{\'a}{\~n}ez, Jes{\'u}s and Loucera, Carlos}
}
@conference {445,
	title = {An Experimental Evaluation of Broadband Spatial IA for Uncoordinated MIMO-OFDM Systems},
	booktitle = {IEEE International Conference on Digital Signal Processing (DSP)},
	year = {2015},
	month = {July},
	pages = {570--574},
	address = {Singapore},
	author = {Fanjul, Jacobo and Lameiro, Christian and Santamar{\'\i}a, Ignacio and Garc{\'\i}a-Naya, J. A. and Castedo, Luis}
}
