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Agile Wireless Transmission Strategies Agile wireless transmission strategies Citation for published version (APA): Ho, C. K. (2009). Agile wireless transmission strategies. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR640214 DOI: 10.6100/IR640214 Document status and date: Published: 01/01/2009 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 28. Sep. 2021 Agile Wireless Transmission Strategies Chin Keong Ho H1 H2 H3 H4 H5 A1 A2 A3 A4 A5 R1 R2 R3 R4 R5 Agile Wireless Transmission Strategies Chin Keong Ho Agile Wireless Transmission Strategies PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr.ir. C.J. van Duijn, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op dinsdag 3 maart 2009 om 16.00 uur door Chin Keong Ho geboren te Singapore, Singapore Dit proefschrift is goedgekeurd door de promotor: prof.dr.ir. J.P.M.G. Linnartz Copromotor: dr.ir. F.M.J. Willems CIP-DATA LIBRARY TECHNISCHE UNIVERSITEIT EINDHOVEN Ho, Chin Keong Agile Wireless Transmission Strategies / by Chin Keong Ho. - Eindhoven : Technische Universiteit Eindhoven, 2009. - Proefschrift. – ISBN: 978-90-386-1519-6 NUR 959 Subject headings: wireless communications rate adaptation automatic repeat request OFDM modulation majorization theory\ dynamic programming\ \ \ \ Cover design by Chin Keong Ho c 2009 by Chin Keong Ho, Singapore All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic, mechanical, including photocopy, recording, or any information storage and retrieval system, without the prior written permission of the copyright owner. v vi Samenstelling van de promotiecommissie: prof.dr.ir. J.P.M.G. Linnartz, Technische Universiteit Eindhoven, promotor dr.ir. F.M.J. Willems, Technische Universiteit Eindhoven, copromotor prof.dr.ir. S.C. (Sem) Borst, Technische Universiteit Eindhoven prof.dr. Behrouz Farhang-Boroujeny, University of Utah prof.dr. R.D. van der Mei, Centrum voor Wiskunde en Informatica dr.ir. Job Oostveen, TNO Information and Communication Technology dr. Sumei Sun, Institute for Infocomm Research, A⋆STAR, Singapore Abstract vii ABSTRACT Agile Wireless Transmission Strategies Wireless communications has received much research interest in recent years. In wire- less communications, information is conveyed using a wireless channel, from a node acting as transmitter to a node acting as receiver. As there is no need to lay cables, wireless communication systems can be deployed easily. Mobile communications, i.e., wireless communications with portable communication devices, bring further conve- nience to the end users, by permitting them to establish communications on the go. The phenomenal success of wireless communications has led to a high demand, and hence scarcity of the limited wireless spectrum. Yet, bandwidth-hungry applications, such as video streaming, that require the transfer of large amounts of data, are be- coming popular. The increase in number of users also results in a dense spatial reuse, i.e., a large number of transmissions per unit area. To achieve a high throughput with limited bandwidth in a limited area, it is important to optimize the use of radio resources over time, frequency and space. This is a challenging task as the wireless channel is time-varying in nature – a small change in the environment can cause the received signals to change considerably in amplitude and phase. These signal vari- ations become worse in mobile communications, where the transmitter and receiver typically move. These variations also become worse in multi-user wireless commu- nications, where a possibly varying number of users share the same wireless channel and generate varying amounts of multi-user interference. The transmitter is, in general, not continuously aware of the instantaneous condi- tions or state of the channel. However, a limited amount of channel state information (CSI) can often be made available by explicit feedback from the receiver, or by lis- tening to the environment. Based on this CSI, transmission parameters (e.g. rate, power, frequency and time of transmission) can be chosen to optimize a measure of system performance (e.g. long-term throughput) via a suitable adaptation algorithm. The precise CSI that is used, the set of allowable transmission parameters, and the adaptation algorithm together make up a transmission strategy. To optimize the use of the radio resources, this strategy has to be designed properly. Instead of specifying rigid standards for wireless communications, it is becoming com- mon that baseline standards are specified with hooks for proprietary add-ons and enhancements. This offers the possibility for static and dynamic optimization of the transmission parameters. For example in the recent IEEE 802.11n standards, the viii Abstract choices of modulation constellation, code rate, packet aggregation, automatic repeat request (ARQ) policy, and multi-input multi-ouput (MIMO) transmission mode are left to the device makers, and the adaptation algorithms for choosing these parameters are left open for future progress and competitive advantages. In this thesis we seek to exploit these degrees of freedom as a basis for attractive transmission strategies. The insights we obtain can also be useful for designing future cognitive radios, in which communication devices are empowered to make informed decisions on how and when to transmit and receive. In wireless communications, especially in mobile communications, the attractiveness of a transmission strategy is determined largely by its agility. By an agile transmission strategy we mean a strategy that is simultaneously lean, responsive and simple: 1. Lean in feedback: It is essential that the amount of feedback from receiver to trans- mitter is small, so that the overhead is negligible compared to the improvement in throughput (in number of bits recovered per channel use). 2. Responsive in adaptation: The nodes should be able to react rapidly and ade- quately to a changing wireless environment. 3. Simple in implementation: The complexity of the adaptation algorithm should be low to enable implementation in the mobile device, where the primary considera- tions are to have a low battery drain and a small form factor. The objectives of being simultaneously lean, responsive and simple are often contra- dictory, making the design of an agile transmission strategy a challenging task. To be lean, only partial CSI can be used in the transmission strategy. To derive an optimal strategy based on this limited knowledge involves more complex operations compared to when the channel state is known exactly, as the uncertainty of the channel state has to be taken into account. As a result, the transmission strategy becomes complex and is not simple to implement. Similarly, in being lean, the transmission strategy may not be sufficiently responsive, due to the limited channel knowledge. Many communication systems have evolved towards packet-switched systems, in which information bits are aggregated into blocks called packets which are separately trans- ported from node to node. To successfully transport each packet, different funda- mental aspects of communication across the hostile wireless channel are often solved independently across a hierarchy of communication layers. In this thesis we focus on the lowest two layers: the data link layer (DLL) and the physical (PHY) layer. Information bits to be transmitted first arrive at the DLL. The logical link control (LLC) sublayer, which is the upper sublayer of the DLL, takes note of the informa- tion bits that are sent and arranges for retransmission later if necessary. The bits are then passed to the lower sublayer, the medium access control (MAC) sublayer. The MAC sublayer decides when
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