Smart Antenna Technology CUL/EM/030854/RP/06 Development of Smart Antenna Technology Final Report August 2006 http://www.vectorfields.co.uk A Cobham company © Copyright 2006 Smart Antenna Technology CUL/EM/030854/RP/06 Final Report (Issue 2) 2 Smart Antenna Technology CUL/EM/030854/RP/06 Final Report (Issue 2) Title Development of Smart Antenna Technology Customer Ofcom Customer ref. “Contract for the Provision of Development of Smart Antenna Technology for the Office of Communications” Contract 410000267 This document has been prepared for Ofcom under the above contract. Copyright © Copyright 2006 Reference number CUL/EM/030854/RP/06 Contact Name Dr K D Ward Vector Fields Ltd 24 Bankside Kidlington OXON, OX5 1JE Telephone: 01865 370151 Facsimile: 01865 370277 Document Control Number: CUL/EM/030854/RP/06 Date of Issue: August, 2006 Issue 2 Authorization Name Signature Position Prepared by Mr M Hook Project Manager Approved by Dr K D Ward Managing Director 3 Smart Antenna Technology CUL/EM/030854/RP/06 Final Report (Issue 2) Disclaimer This report was commissioned by Ofcom to provide an independent view on issues relevant to its duties as regulator for the UK communication industry, for example issues of future technology or efficient use of the radio spectrum in the United Kingdom. The assumptions, conclusions and recommendations expressed in this report are entirely those of the contractors and should not be attributed to Ofcom. Acknowledgements The authors would like to thank those people and companies in the wireless industry who have contributed information and advice during the course of the work presented in this report. The authors would also like to thank Ofcom for sponsoring the work and for their helpful discussions and suggestions. 4 Smart Antenna Technology CUL/EM/030854/RP/06 Final Report (Issue 2) EXECUTIVE SUMMARY Introduction Wireless systems are undoubtedly an essential part of modern society and are becoming more so as we move towards the “information society” and demand access to more information, more immediately and in more places. Concurrently, technological developments are making new applications possible, opening up new markets, and promising significant economic benefits. In all cases, spectrum is an essential basic resource which, although reusable, cannot be created to meet demand. It is, therefore, increasingly important to improve the efficiency with which use is made of the spectrum. As an example, the next generation mobile telephone system may require an order of magnitude increase in capacity. Since present day systems are close to the Shannon limit, there is relatively little to be gained by improving the modulation and coding schemes, and smart antennas have been identified as one technique that may close the predicted performance gap. A smart antenna is one that responds in some way to its electromagnetic environment in order to improve a specified performance metric; in so-doing, they can provide, for example, increased immunity to interference, or reduced signal level towards a vulnerable receiver. In general, provision of these capabilities requires the use of multi-element array antennas, with control over the excitation of each element. Smart antennas are not new in concept, yet, with a number of notable exceptions, they have not seen widespread adoption. This project, which was awarded as part of the Ofcom Spectrum Efficiency Scheme, set out to investigate smart antennas and their potential application areas, in an attempt to understand the reasons why they have not been implemented widely. Possible reasons for this may be that their forecast benefits are unobtainable, that the technology for their implementation is not mature, or that they cannot currently be implemented economically. These lead to the overall objectives of the project, namely, to assess and demonstrate the potential of smart antennas for enhancing spectrum efficiency in wireless systems. To meet these aims a work programme was developed, which drew on the skills of a number of organisations, namely, Vector Fields Limited, Quotient Associates, Plextek Limited, Loughborough University, and European Antennas Limited. 5 Smart Antenna Technology CUL/EM/030854/RP/06 Final Report (Issue 2) Work programme The activities undertaken during this project divide into four main areas: Application review The first element of the work, which is described in Section 2 of the main report, considers the types of smart antenna available and the applications that are most suitable for their adoption. In addition, it must be remembered that the use of the spectrum sits within a regulatory framework. How this may affect the use of smart antennas, and whether their amendment may assist more widespread adoption of smart antennas is preliminarily considered in advance of the other activities. Technology review Section 3 details a review of the technology available for the implementation of smart antennas, the main sub-systems of which are the radiating structure and the beam forming network. Both areas are considered to determine the options presently available and possible future developments. Technology development The technology review was expected to highlight areas where more novel, less mature techniques could benefit the performance of a smart antenna system. Provision was made within the programme to select and develop such a technique; the results of this are discussed in Section 4. Performance benefits analysis The assessment of the benefits brought by smart antennas is an essential part of the programme. From the outset, it was intended to perform a hardware demonstration of a smart antenna operating in a wireless system. An analysis of a wider area wireless system has also been performed, in this case by simulation rather than by hardware demonstration. The selected system, namely broadband wireless access (BWA), was chosen during the programme following the consideration of the most likely smart antenna applications. The details of the simulation and hardware demonstration are given in Section 5 of the main report. The results of the above activities allow us to form a view on why smart antennas have not achieved widespread adoption. This is addressed in Section 6 of the main report. The remainder of this Executive Summary describes the work performed and the findings from the above activities, and concludes with a discussion of adoption issues. 6 Smart Antenna Technology CUL/EM/030854/RP/06 Final Report (Issue 2) Summary of activities The work performed under each of the activities is summarized briefly below, and the principal findings highlighted. Applications As a precursor to considering potential applications, the various types of smart antenna were reviewed. It was found to be useful to classify them broadly as operating in “beam space” or “signal space”. The former uses knowledge of the geometry of the antenna, combined with an ability to vary the excitation of each antenna element, to steer and shape the radiation pattern (ie the beam). The latter uses knowledge of the structure of parts of the received signals, and adjusts the antenna element weights to minimize the difference between the combined signal at the output and the known (or training) sequence. Basic implementations of these require relatively little integration with the receive chain or the link protocol, and are often suitable for overlaying on the system as an appliqué layer. More sophisticated implementations combine one or other of these with processing in the time domain (ie space-time processing and detection) in order to incorporate signal components that have been temporally dispersed. While these offer improved performance, they are correspondingly more demanding on the signal processing hardware. Figure E1 shows how these techniques may be viewed in relation to their complexity, level of integration and to the characteristics of the propagation environment. “Signalspace” “Space-time “Space-time Processing” Detection” Diversity combining Space-time Single channel equalisation Simple MIMO equalisation on e.g. Advanced MIMO si sper di el ann e “Beamspace” Ch Fixed beam switching ons Wideband adaptive p Narrowband adaptive beam-forming spatial beam-forming a res Temporally spread Uplink only (HSR) signal beam-forming SFIR e antenn abl SDMA t c edi Pr Integration with protocol / receive chain Complexity & performance Figure E1: Main smart antenna methods and primary constraints for their application A distinction is made between those “smart” systems that achieve improved performance using diversity methods, for example diversity combining and MIMO, and those that adapt weighted excitations to the elements of the antenna to optimise its pattern performance. Simple diversity systems are used widely, and the incorporation of MIMO techniques is rising rapidly, albeit in advance of a formal specification. This project hence concentrated on the weight adaptation techniques, which are further from widespread adoption, but which may offer additional or complementary benefits to the diversity methods. 7 Smart Antenna Technology CUL/EM/030854/RP/06 Final Report (Issue 2) A wide range of possible wireless applications that have high economic value to the UK have been considered as candidates for the early adoption of smart antennas. These include mobile and broadcast communications, wireless local area networks (WLAN) and broadband wireless access (BWA). In some cases, smart antennas based on various techniques are already available commercially, or have