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Optimization and Fundamental Insights in Full-Duplex Cellular Networks
KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems engineering.ORCID iD: 0000-0002-4503-4242
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The next generations of cellular networks are expected to provide explosive data rate transmissions and very low latencies. To meet such demands, one of the promising wireless transmissions candidates is in-band full-duplex communications, which enable wireless devices to simultaneously transmit and receive on the same frequency channel. Full-duplex communications have the potential to double the spectral efficiency and reduce the transmission delays when compared to current half-duplex systems that either transmit or receive on the same frequency channel. Until recently, full-duplex communications have been hindered by the interference that leaks from the transmitter to its own receiver,the so-called self-interference. However, advances in digital and analog self-interference suppression techniques are making it possible to reduce the self-interference to manageable levels, and thereby make full-duplex a realistic candidate for advanced wireless systems.

Although in-band full-duplex promises to double the data rates of existing wireless technologies, its deployment in cellular networks must be gradual due to the large number of legacy devices operating in half-duplex mode. When half-duplex devices are deployed in full-duplex cellular networks, the user-to-user interference may become the performance bottleneck. In such new interference situation, the techniques such as user pairing, frequency channel assignment, power control, beamforming, and antenna splitting become even more important than before, because they are essential to mitigate both the user-to-user interference and the residual self-interference. Moreover, introduction of full- duplex in cellular networks must comply with current multi-antenna systems and, possibly, transmissions in the millimeter-wave bands. In these new scenarios, no comprehensive analysis is available to understand the trade-offs in the performance of full-duplex cellular networks.

This thesis investigates the optimization and fundamental insights in the design of spectral efficient and fair mechanisms in full-duplex cellular networks. The novel analysis proposed in this thesis suggests new solutions for maximizing full-duplex performance in the sub-6 GHz and millimeter-wave bands. The investigations are based on an optimization theory approach that includes distributed and nonconvex optimization with mixed integer-continuous variables, and novel extensions of Fast-Lipschitz optimization. The analysis sheds lights on fundamental questions such as which antenna architecture should be used and whether full-duplex in the millimeter-wave band is feasible. The results establish fundamental insights in the role of user pairing, frequency assignment, power control and beamforming; reveal the special behaviour between the self-interference and user- to-user interference; analyse the trade-offs between antenna sharing and splitting for uplink/downlink signal separation; and investigate the role of practical beamforming design in full-duplex millimeter-wave systems. This thesis may provide input to future standardization process of full-duplex communications.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2019. , p. 196
Series
TRITA-EECS-AVL ; 2019:27
Keywords [en]
full-duplex, optimization, power control, assignment, beamforming, millimeter wave, self-interference, multi-antenna
National Category
Telecommunications Information Systems
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-246499ISBN: 978-91-7873-147-3 (print)OAI: oai:DiVA.org:kth-246499DiVA, id: diva2:1297777
Public defence
2019-04-12, Kollegiesalen, Brinellvägen 8, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20190322

Available from: 2019-03-22 Created: 2019-03-21 Last updated: 2019-03-22Bibliographically approved
List of papers
1. Spectral Efficient and Fair User Pairing for Full-Duplex Communication in Cellular Networks
Open this publication in new window or tab >>Spectral Efficient and Fair User Pairing for Full-Duplex Communication in Cellular Networks
2016 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 11, p. 7578-7593Article in journal (Refereed) Published
Abstract [en]

—A promising new transmission mode in cellular networks is the three-node full-duplex mode, which involves a base station with full-duplex capability and two half-duplex user transmissions on the same frequency channel for uplink and downlink. The three-node full-duplex mode can increase spectral efficiency, especially in the low transmit power regime, without requiring full-duplex capability at user devices. However, when a large set of users is scheduled in this mode, self-interference at the base station and user-to-user interference can substantially hinder the potential gains of full-duplex communications. This paper investigates the problem of grouping users to pairs and assigning frequency channels to each pair in a spectral efficient and fair manner. Specifically, the joint problem of user uplink/downlink frequency channel pairing and power allocation is formulated as a mixed integer nonlinear problem that is solved by a novel joint fairness assignment maximization algorithm. Realistic system level simulations indicate that the spectral efficiency of the users having the lowest spectral efficiency is increased by the proposed algorithm, while a high ratio of connected users in different loads and self-interference levels is maintained.

Place, publisher, year, edition, pages
IEEE Press, 2016
Keywords
full-duplex, power control, channel assignment, spectral efficient, cellular communications
National Category
Communication Systems
Research subject
Electrical Engineering; Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-192314 (URN)10.1109/TWC.2016.2604802 (DOI)000388674700026 ()2-s2.0-84988354730 (Scopus ID)
Projects
Wireless@KTH BUSE
Funder
Lars Hierta Memorial Foundation, FO20150976Swedish National Infrastructure for Computing (SNIC)Wireless@kth, BUSE
Note

QC 20161019

Available from: 2016-09-09 Created: 2016-09-09 Last updated: 2019-03-21Bibliographically approved
2. Fast-Lipschitz Power Control and User-Frequency Assignment in Full-Duplex Cellular Networks
Open this publication in new window or tab >>Fast-Lipschitz Power Control and User-Frequency Assignment in Full-Duplex Cellular Networks
2017 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 10, p. 6672-6687Article in journal (Refereed) Published
Abstract [en]

In cellular networks, the three-node full-duplex transmission mode has the po-tential to increase spectral efficiency without requiring full-duplex capability ofusers. Consequently, three-node full-duplex in cellular networks must deal with self-interference and user-to-user interference, which can be managed by power controland user-frequency assignment techniques. This paper investigates the problem ofmaximizing the sum spectral efficiency by jointly determining the transmit powersin a distributed fashion, and assigning users to frequency channels. The problem is for-mulated as a mixed-integer nonlinear problem, which is shown to be non-deterministicpolynomial-time hard. We investigate a close-to-optimal solution approach by dividingthe joint problem into a power control problem and an assignment problem. The powercontrol problem is solved by Fast-Lipschitz optimization, while a greedy solution withguaranteed performance is developed for the assignment problem. Numerical resultsindicate that compared with the half-duplex mode, both spectral and energy efficienciesof the system are increased by the proposed algorithm. Moreover, results show that thepower control and assignment solutions have important, but opposite roles in scenarioswith low or high self-interference cancellation. When the self-interference cancellationis high, user-frequency assignment is more important than power control, while powercontrol is essential at low self-interference cancellation.

Place, publisher, year, edition, pages
IEEE Communications Society, 2017
Keywords
full-duplex, power control, assignment, cellular networks
National Category
Telecommunications
Research subject
Telecommunication
Identifiers
urn:nbn:se:kth:diva-204605 (URN)10.1109/TWC.2017.2728062 (DOI)000412591400028 ()2-s2.0-85028856446 (Scopus ID)
Funder
Lars Hierta Memorial Foundation
Note

QC 20171106

Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2019-03-21Bibliographically approved
3. Smart Antenna Assignment is Essential in Full-Duplex Communications
Open this publication in new window or tab >>Smart Antenna Assignment is Essential in Full-Duplex Communications
Show others...
2019 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857Article in journal (Refereed) Submitted
Abstract [en]

Full-duplex communications have the potential to almost double the spectralefficiency. To realize such a potentiality, the signal separation at base station’s antennasplays an essential role. This paper addresses the fundamentals of such separationby proposing a new smart antenna architecture that allows every antenna to beeither shared or separated between uplink and downlink transmissions. The benefitsof such architecture are investigated by an assignment problem to optimally assignantennas, beamforming and power to maximize the weighted sum spectral efficiency.We propose a near-to-optimal solution using block coordinate descent that divides theproblem into assignment problems, which are NP-hard, a beamforming and powerallocation problems. The optimal solutions for the beamforming and power allocationare established while near-to-optimal solutions to the assignment problems are derivedby semidefinite relaxation. Numerical results indicate that the proposed solution isclose to the optimum, and it maintains a similar performance for high and low residualself-interference powers. With respect to the usually assumed antenna separationtechnique and half-duplex transmission, the sum spectral efficiency gains increase withthe number of antennas. We conclude that our proposed smart antenna assignment forsignal separation is essential to realize the benefits of multiple antenna full-duplexcommunications.

Place, publisher, year, edition, pages
IEEE, 2019
Keywords
full-duplex, semidefinite programming, beamforming, antenna splitting, antenna assignment
National Category
Telecommunications
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-246496 (URN)
Funder
Lars Hierta Memorial Foundation, FO2017-0236
Note

QCR 20190320

Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-05-20Bibliographically approved
4. 1-bit Phase Shifters Suffice for Large-Antenna Full-Duplex mmWave Communications
Open this publication in new window or tab >>1-bit Phase Shifters Suffice for Large-Antenna Full-Duplex mmWave Communications
2019 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248Article in journal (Refereed) Submitted
Abstract [en]

Millimeter-wave using large-antenna arrays is a key technological component forthe future cellular systems, where it is expected that hybrid beamforming along withquantized phase shifters will be used due to their implementation and cost efficiency.In this paper, we investigate the efficacy of full-duplex mmWave communicationwith hybrid beamforming using low-resolution phase shifters, without any analogself-interference cancellation. We formulate the problem of joint self-interferencesuppression and downlink beamforming as a mixed-integer nonconvex joint opti-mization problem. We propose LowRes, a near-to-optimal solution using penaltydual decomposition. Numerical results indicate that LowRes using low-resolutionphase shifters perform within 3% of the optimal solution that uses infinite phaseshifter resolution. Moreover, even a single quantization bit outperforms half-duplextransmissions, respectively by 29% and 10% for both low and high residual self-interference scenarios, and for a wide range of practical antenna to radio-chain ratios.Thus, we conclude that 1-bit phase shifters suffice for full-duplex millimeter-wavecommunications, without requiring any additional new analog hardware.

Keywords
full-duplex, millimeter wave, low-resolution, phase shifter, beamforming
National Category
Telecommunications
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-246498 (URN)
Funder
Lars Hierta Memorial Foundation, FO2017-0236
Note

QCR 20190320

Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-04-12Bibliographically approved

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