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Optimizing Energy Efficiency in Wireless Links Through Reconfigurable Intelligent Surfaces and Optimal Ratios
KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS. (Communication Systems)ORCID iD: 0000-0002-8107-1710
2024 (English)Licentiate thesis, comprehensive summary (Other academic)Alternative title
Optimering av energieffektivitet i trådlösa länkar genom optimala kvoter och rekonfigurerbara intelligenta ytor (Swedish)
Abstract [en]

This thesis explores the optimization of energy efficiency (EE) in the radiolink of wireless communication systems, focusing on both the user equipment (UE) and the base station (BS). The first part of the study examines strategies to minimize the energy consumption of the UE when transmitting short data payloads, utilizing a reconfigurable intelligent surface (RIS) controlled by the BS, to improve the channel conditions. The challenge lies in balancing the increased energy consumption due to additional pilot signals needed toconfigure the RIS against the energy savings during data transmission. We propose an innovative approach where the RIS is divided into subarrays of controllable sizes to shorten the pilot length. The analytical results provide a unique energy-minimizing solution in terms of pilot length and power which depends on an interplay between the payload size and path loss conditions between the UE, BS, and RIS. In the second part, the focus shifts to the EE of a multi-antenna BS. A comprehensive power consumption model is employed, accounting for both active and passive components of the transceiver circuitry. By treating the transmit power, bandwidth, and number of antennas as optimization variables, we derive novel closed-form solutions to the optimal value of these variables and propose an algorithm for their joint optimization. This part of the study not only optimizes the variables for maximum EE but also uncovers a new relationship between radiated power and passive transceiver power consumption, offering insights into the trade-offs between using maximum power and bandwidth. Together, these studies provide an updated view of EE optimization in wireless communication systems, offering novel theoretical insights for both UE and BS configurations.

Abstract [sv]

Denna avhandling utforskar optimeringen av energieffektivitet (EE) i trådlösa kommunikationssystem, med fokus på både användarenheten (UE) och basstationen (BS). Den första delen av studien undersöker strategier för att minimera energiförbrukningen hos UEn vid överföring av korta datapaket, genom att använda en rekonfigurerbar intelligent yta (RIS) som styrs av basstationen för att förbättra radiokanalen. Utmaningen ligger i att balansera den ökade energiförbrukningen på grund av de ytterligare pilotsignalerna som krävs för att konfigurera en RIS mot energibesparingarna som sker underdataöverföringen. Vi föreslår ett tillvägagångssätt där en RIS delas upp i delarrayer av kontrollerbar storlek för att förkorta pilotlängden. De analytiska resultaten ger en unik lösning för minimering av energikonsumptionen i termer av pilotlängd och pilotenergi och beror på paketstorleken och de relativastyrkeförhållandena i radiokanalen mellan UE, BS och RIS. I den andra delen flyttas fokus till EE hos en basstation med flera antenner. En omfattande modell för effektförbrukning som tar hänsyn till både aktiva och passiva komponenter i transceivermodulen används. Genom attbehandla utsänd effekt, bandbredd och antalet antenner som optimeringsvariabler, härleder vi nya lösningar för det optimala värdet av dessa variabler och vi föreslår en algoritm för deras gemensamma optimering. Denna del av studien optimerar inte bara variablerna för maximal EE, utan avslöjar också en ny relation mellan utstrålad effekt och passiv effektförbrukning i transceivern, vilket leder till nya insikter kring avvägningarna mellan att använda maximal effekt och bandbredd. Tillsammans ger dessa studier en uppdaterad syn på energioptimering i trådlösa kommunikationssystem, och nya teoretiska insikter för både UE- och basstationskonfigurationer.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2024. , p. 45
Series
TRITA-EECS-AVL ; 2024:21
Keywords [en]
6G, Energy Efficiency, Reconfigurable Intelligent Surfaces
Keywords [sv]
6G, energieffektivitet, rekonfigurerbara intelligenta ytor
National Category
Communication Systems
Research subject
Information and Communication Technology
Identifiers
URN: urn:nbn:se:kth:diva-343404ISBN: 978-91-8040-853-0 (print)OAI: oai:DiVA.org:kth-343404DiVA, id: diva2:1837582
Presentation
2024-03-04, https://kth-se.zoom.us/j/66105309797, Amiga, Kistagången 16, Kista, 13:00 (English)
Opponent
Supervisors
Note

QC 20240215

Available from: 2024-02-15 Created: 2024-02-14 Last updated: 2024-03-07Bibliographically approved
List of papers
1. Optimizing Reconfigurable Intelligent Surfaces for Short Transmissions: How Detailed Configurations can be Afforded?
Open this publication in new window or tab >>Optimizing Reconfigurable Intelligent Surfaces for Short Transmissions: How Detailed Configurations can be Afforded?
2023 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, p. 1-1Article in journal (Refereed) Accepted
Abstract [en]

This paper examines how to minimize the energy consumption of a user equipment (UE) when transmitting short data payloads. The receiving base station (BS) controls a reconfigurable intelligent surface (RIS), which requires additional pilot signals to be configured, to improve the channel conditions. The challenge is that the pilot signals increase the energy consumption and must be balanced against energy savings during data transmission. We derive a formula for the energy consumption, including both pilot and data transmission powers and the effects of imperfect channel state information and discrete phase-shifts. To shorten the pilot length, we propose dividing the RIS into subarrays of multiple elements using the same reflection coefficient. The pilot power and subarray size are tuned to the payload length to minimize the energy consumption. Analytical results show that there exists a unique energy-minimizing solution. For small payloads and when the direct path loss between the BS and UE is weak compared to the path loss via the RIS, the solution is using subarrays with many elements and low pilot power and vice versa. The optimal percentage of energy spent on pilot signaling is in the order of 10-40%.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2023
Keywords
Reconfigurable intelligent surface, energy efficiency, phase-shift optimization, subarrays, discrete phase-shifts, 6G
National Category
Engineering and Technology
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-343367 (URN)10.1109/twc.2023.3307605 (DOI)2-s2.0-85170544830 (Scopus ID)
Funder
Swedish Foundation for Strategic Research, FFL18-0227
Note

QC 20240212

Available from: 2024-02-12 Created: 2024-02-12 Last updated: 2024-02-14Bibliographically approved
2. Fundamentals of Energy-Efficienct Wireless Links: Optimal Ratios and Scaling Behaviours
Open this publication in new window or tab >>Fundamentals of Energy-Efficienct Wireless Links: Optimal Ratios and Scaling Behaviours
2024 (English)Manuscript (preprint) (Other academic)
Abstract [en]

In this paper, we examine the energy efficiency (EE) of a base station with multiple antennas. We use a state-of-theart power consumption model, taking into account the passive and active parts of the transceiver circuitry, including the effects of radiated power, signal processing, and passive consumption. The paper treats the transmit power, bandwidth, and number ofantennas as the optimization variables. We provide novel closed form solutions for the optimal ratios of power per unit bandwidth and power per transmit antenna. We present a novel algorithm that jointly optimizes these variables to achieve maximum EE, while fulfilling constraints on the variable ranges. We also discover a new relationship between the radiated power and the passive transceiver power consumption. We provide analytical insight into whether using maximum power or bandwidth is optimal.

Keywords
Energy Efficiency, optimization, 6G, multiple antenna communications
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-343377 (URN)
Conference
Vehicular Technology Conference (VTC) 2024 Singapore
Funder
Swedish Foundation for Strategic Research, FFL18-0227
Note

QC 20240214

Available from: 2024-02-12 Created: 2024-02-12 Last updated: 2024-02-14Bibliographically approved

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Enqvist, Anders

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