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1 : MIMO Link Adaptation for WiMAX like OFDM(A) systems Work area: PHY LAYER Muhammad Imadur Rahman , Suvra Sekhar Das and Fleming B. Frederiksen Room A5-222; Telephone: +45 9635 8688; e-mail: imr@kom.aau.dk ; ssd@kom.aau.dk , fbf@kom.aau.dk Required number of students: 2 (preferably) Problem description: OFDM has been quite popular for broadband communication systems. MIMO in conjunction with OFDM promises to provide a massive improvement in system throughput. A current realization is the WiMAX standard (IEEE 802.16(a,e,d)). The project described below deals with these two advanced PHYSICAL layer technologies. MIMO diversity schemes provide higher SNR at the receiver, while MIMO multiplexing schemes provides a data rate increment. According to published research, multiplexing schemes are more robust when receive SNR is high enough, while diversity schemes perform quite satisfactorily at low SNR conditions [1,2]. This is the reason that none of the scheme can become an absolute choice for better system performance. To be exact, a user located very close to access point can exploit the multiplexing benefits, while a user at further location may benefit more by using MIMO diversity schemes. That’s why hybrid schemes, such as [3], are well studied and examined. In hybrid schemes, either MIMO diversity or MIMO multiplexing schemes are optimally chosen based on some specific selection criterion, so that optimum benefits from both type of schemes can be obtained in the system. This kind of combination is actually performed in time domain. In recent years, combining MIMO diversity and MIMO multiplexing schemes in space domain has gained a lot of interest. One such example is Joint Diversity and Multiplexing (JDM) scheme [4]. The JDM schemes are beneficial in effect that both diversity and multiplexing benefits are available at the same time. In another words, MIMO diversity schemes provide higher reliability while MIMO multiplexing gives higher throughput. In relation to this, hybrid and JDM schemes provide the flexibility to tune the system performance as per the reliability and throughput requirement. Thorough studies of different orientation of hybrid and JDM schemes in different scenarios can help prepare principles and mechanisms for optimal implementation. To summarize, the goal of this project is to determine a unified guideline for choosing optimal schemes for different scenario in WiMAX like OFDM(A) systems when different combination of diversity and multiplexing schemes are considered in regard to required system throughput and reliability. Assumptions:

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1. Both ends of the transmission links have multiple antennas. 2. Both the transmitter and the receiver can support diversity schemes. 3. Rayleigh and Ricean scenario are assumed primarily. 4. High data rate system needs to be supported; i.e. wideband low and medium mobility

system. Schemes:

1. Combination of a transmit diversity technique and a receive diversity technique from the list below [1,2]

a. Possible transmit Diversity techniques are: STBC/SFBC, transmit MRC b. Possible receive diversity technique is: MRC

2. Spatial multiplexing [1,2] a. Blind scheme such as VBLAST b. CSI assisted Spatial Multiplexing (SVD)

3. Hybrid MIMO schemes [3] (Switching between Diversity and SM) 4. Joint diversity and multiplexing scheme [4]

Analysis: 1. Achievable diversity order 2. Capacity studies 3. Finding spectral efficiency via simulations for MIMO diversity systems and comparing

the spectral efficiency with spatial multiplexing systems Expected Outcome:

1. Propose some guidelines about using diversity and multiplexing schemes in different scenario

Reference:

1. A.J. Paulraj, R. Nabar & D. Gore, Introduction to Space-Time Wireless Communications, 1st ed. Cambridge University Press, September 2003.

2. S. Barbarossa, Multiantenna Wireless Communication Systems, Artech House 2005. 3. R.W. Heath jr. and A. Paulraj, Switching Between Diversity and Multiplexing in MIMO

Systems, IEEE Transactions On Communications, Vol. 53, No. 6, pp. 962-968, June 2005.

4. M. I. Rahman, N. Marchetti, E. Carvalho, “Joint Diversity and Multiplexing Schemes for MIMO-OFDM Systems,” Aalborg University, Denmark, JADE project Deliverable, B-2005-06-3 (v1.0.0), June 2005.

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2 : Design of an Uplink Random Access Protocol for OFDMA

Work area: LINK/MAC LAYER Proposed by: Megumi Kaneko (mek@kom.aau.dk) and Petar Popovski (petarp@kom.aau.dk) Background Radio resource management for Orthogonal-Frequency-Division-Multiple-Access (OFDMA)-based 4G system is currently a key research issue in wireless communications. While a lot of studies have been made for the Downlink (DL, the link from base station (BS) to mobile station (MS)) transmissions in a 4G cellular system, there is much left for investigation regarding the multiple access schemes for the Uplink (UL, the link from MS to BS). Random access protocols such as ALOHA, CSMA, and their variations have been widely used in several standards, e.g. IEEE 802.11a WLAN [1], IEEE 802.16 [2], etc. However, more research is needed on the combination of random access protocols with OFDMA, where different users can be multiplexed on different subcarriers [3] [4]. This becomes particularly interesting when we consider the recent results [5] regarding the random access protocols which are designed in concert with the channel state information (CSI). As opposed to the DL case, in UL the BS does not have knowledge of the CSI of all users in every subcarrier, which makes it challenging to exploit full multi-user diversity. With the current state-of-the art, there is a clear need to design random access procedures that will efficiently utilize sufficient amount of CSI to reserve the resources for uplink transmissions. Project Description The project will start with a detailed survey about the state of the art in random access protocols, with emphasis on utilization of the CSI for the random access as well as the specific features of the OFDMA physical layer. The identification of the gaps in the current systems and designs should lead to a clear problem definition. In particular, the following aspects should be clarified:

• Relevant communication scenarios that should be considered • Reference protocols from literature • Suitable reservation protocol • Subcarrier/subchannel allocation algorithm performed at the BS to resolve

contention • How and how much CSI can be used • Performance metrics: throughput, fairness, QoS…

It is expected that innovative solutions will be proposed for some of the identified problems. The results should be validated by simulation and analysis. Prerequisites

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General knowledge of wireless network protocols and programming skills (Matlab, C). Remark The intellectual property items that will be proposed within the project may be subject to patenting within an ongoing industrial project. Therefore, the students will sign a suitable agreement before the start of the project. References [1] IEEE standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications; High-speed Physical Layer in the 5GHz Band, IEEE standard 802.11a, 1999 [2] IEEE standard for Local and Metropolitan Area Networks; Air Interface for Fixed Broadband Wireless Access Systems, IEEE standard 802.16, 2004 [3] J. Yun and S. Bahk, "Parallel Contention Algortihm with CSMA/CA for OFDM based High Speed Wireless LANs", in Proc. IEEE PIMRC, vol. 3, pp.2581-2585 , Sept. 2003 [4] D. Shen, V. Li, “Stabilized Multi-channel ALOHA for Wireless OFDM Networks”, in Proc. IEEE GLOBECOM, vol. 1, pp. 701-705, Nov. 2002 [5] L. Tong, V. Naware, and P. Venkitasubramaniam, “Signal processing in random access: a cross layer perspective,” IEEE Signal Processing Magazine, July 2004.

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3 : Enhanced Localization in future Wireless Communication Systems

Work area: LINK LAYER Supervisors: Simone Frattasi, WING, A5-220, sf@kom.aau.dk, João Figueiras, WING, A5-204, jf@kom.aau.dk, Petar Popovski, Hans-Peter Schwefel Background: Geolocation, or location estimation in terms of geographic coordinates of a mobile station (MS) with respect to a fixed reference point in a wireless system, has gained considerable attention over the past decade, especially since the Federal Communication Commission (FCC) passed a mandate requiring cellular providers to generate accurate location estimates for Enhanced-911 (E-911) services [1]. This has boosted the research in the field of wireless location as an important public safety feature, which can also add many other potential applications to the future cellular systems [2]: location-sensitive billing, fraud protection, person/asset tracking, fleet management, intelligent transportation systems (ITS), mobile yellow pages, and system design and management. Unlike the existing second generation (2G) and third generation (3G) networks, which achieve relatively low data rates and are mainly aimed at voice and video communications, the fourth generation (4G) is expected to provide clear advantages in terms of data rate, coverage, power consumption and spectral efficiency, thus also offering a variety of new services (from pop-up advertisements to location-based and interactive or on-demand ones – so called IP datacasting) [3]. These networks will utilize different wireless technologies, ranging from wide-range cellular to short-range ‘ad-hoc’ links. As the work on wireless location mainly concerned the previous generations, how to implement the location service in such a system it is an open area for research. Specifically, in this project we make the assumption that the aforementioned system architecture is global positioning system (GPS) free. This is a relevant assumption, because the introduction of mobile handsets with built-in GPS receivers would imply an increased cost, size, and battery consumption, a degraded location accuracy in urban and indoor environments, and a long time for a full market penetration [2]. Objective: This master project contains two possible tracks of research (which need to be selected before project start):

Sub-project 1: Cooperative localization in relay- and mobile-aided wireless communication systems.

Motivation: In order to achieve the challenging requirements on 4G networks, a potential system architecture may be identified in a wide area network (WAN) system that also supports short-range communications among the terminals [3]. The rationale for introducing short-range communications is mainly due to two arguments: (1) The need to support peer-

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to-peer (P2P) high-speed wireless links between the terminals; (2) The need to enhance the communication between a terminal and the base station by fostering cooperative communication protocols among spatially proximate devices. The communication enhancement primarily refers to a higher link reliability, a larger coverage, a lower power consumption and a higher spectral efficiency thanks to the use of exclusive cooperative stations, e.g., relay stations (RSs) deployed by operators, or short-range communications among different MSs.

Goal: Within this framework the goal of the project is to enhance the accuracy of the location estimation utilizing additional information from the short-range communication between terminals and/or relay stations. In order to achieve these goals, we propose to perform the calculation of the relative distances between MSs and RSs and between pairs of MSs. The additional information gained from the measurements between pairs of unknown-location mobiles can enhance the accuracy of the localization system [4]. As a consequence, our final target is to design the required protocols / algorithms to support the cooperative localization, and subsequently showing that the latter can outperform conventional localization schemes. The approaches may include modifications to Layer-2 protocols to enable cooperative localization.

Sub-project 2: Advanced Filtering Techniques for enhanced Localization Accuracy

The straightforward application of a localization technique (e.g. triangulation based on signal-strength measurements or time-of arrival) typically does not achieve sufficient accuracy due to variable channel conditions and measurement noise. The application of filtering techniques can dramatically improve the accuracy of such localization procedures. Several filtering techniques are known in the literature [5] which appear suitable to localization. Some of those techniques also include scenario specific assumptions, e.g. mobility models or specific radio propagation models. Goal of this sub-project is to analyze the accuracy improvement when applying different filtering techniques for a set of localization scenarios (static/mobile device, indoor/outdoor, 802.11 WLAN or Bluetooth based). The analysis will be performed in simulation models and/or experimental prototype implementations.

Benefits for students: The students will be involved in a project that will advance the state of the art in the area of localization for mobile communication. It comprises both a theoretical and implementation part that will stimulate the development of both skills in the students. In particular, while the former will form their knowledge and their reactivity in dealing with theoretical issues, the latter will develop their implementation and programming skills. The project outcomes will find directly strong interest from major industries and other players in the area of mobile communications, and the achieved results will be exploited for patents applications, conference and journal papers. Relation to project courses and required knowledge:

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This project fits well with all the basic and specialized courses of mobile radio communications, since it requires a basic knowledge of wireless communication protocols and technologies, medium access and link layer control mechanisms. Additionally, it requires some programming skills (e.g., MATLAB).

Additional references1: [1] FCC, “FCC Acts to Promote Competition and Public Safety in Enhanced Wireless 911 Services”, Washington, DC: WT

Rep. 99-27, September 15, 1999. [2] A.H. Sayed, A. Tarighat, N. Khajehnouri, “Network-Based Wireless Location: Challenges Faced in Developing

Techniques for Accurate Wireless Location Information”, Signal Processing Magazine, IEEE, vol. 22, no. 4, pp. 24-40, July, 2005.

[3] S. Frattasi, H. Fathi, F.H.P. Fitzek, M. Katz, R. Prasad, “Defining 4G Technology from the User Perspective”, accepted for publication in Network Magazine, IEEE, to appear in early 2006.

[4] S. Frattasi, M. Monti, R. Prasad, “A Cooperative Localization Scheme for 4G Wireless Communications”, in Proceedings of the Radio & Wireless Symposium (RWS), IEEE, January, 2006, San Diego (CA), USA.

[5] Dieter Fox, Jeffrey Hightower, Lin Liao, Dirk Schulz, and Gaetano Borriello, "Bayesian Filtering for Location Estimation," IEEE Pervasive Computing, vol. 2, no. 3, pp. 24-33, IEEE Computer Society Press, July-September 2003.

1 All references are directly available with the supervisors.

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4 : Power-Control and Scheduling for Multicast services in HSDPA cells Supervisors: Haibo Wang (WING, hw@kom.aau.dk, room A5-211) Hans Schwefel (WING, hps@kom.aau.dk, room A5-212) Category: link layer Background For increased down-link transmission rates up to 10Mb/s, the UMTS radio access network has been extended in Release 5 by the so-called High Speed Downlink Packet Access (HSDPA). HSDPA extends the WCDMA standards with a new shared channel transmission approach, which allows the channelization codes and transmission power in a cell to be dynamically shared among users. HSDPA also supports new features such as Fast Link Adaptation, Fast Channel-Dependent Scheduling and Fast Hybrid-ARQ. Some scenarios of real-time multimedia applications (e.g. video streaming) require the transmission of the same content to several users, even within the same cell. If these applications require high bit-rates, the utilization of multi-cast channels on the air interface is much more resource-efficient. The high transmission rates of HSDPA make it an attractive candidate access technique for such high bandwidth applications. However, the radio resource management features were originally designed for unicast services, and how to adapt them to multicast scenarios is an open issue. Objectives: Goal of this project is to propose and analyse extensions to the HSDPA access in order to

efficiently provide multicast services within a single radio cell. These extensions in particular

include an investigation of different Radio Resource Management strategies with main focus on

Power control and (channel-dependent) scheduling.

The project could include the following steps: a. To understand the CDMA/HSDPA transmission technology and the specific implementation in 3GPP UMTS/HSDPA cells. b. To survey and understand RRM techniques, in particular power control mechanisms, and packet scheduling. c. To adapt and extend current RRM techniques to real-time multicast services. d. To analyse the proposed RRM techniques in HSDPA-like scenarios using simulation models. The optimisation should be performed while using Video streaming as the suggested application, and optimisation efforts can be focused on functionalities in the Node-B. Besides power control and scheduling schemes in the multicast transmission, also different algorithms for decisions when to utilize multi-cast channels (as opposed to multiple uni-cast channels) could be investigated.

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The project is embedded in a cooperation with Ericsson-Telebit, Aarhus. References [1]. Filipe Leitão, Américo Correia, “HSDPA delivering MBMS video streaming”,

WPMC’05. [2] 3GPP TS 25.308 V5.4.0, High Speed Downlink Packet Access (HSDPA) Stage

2 – Release 5, 2002-10 [3] 3GPP TS 25.308 V5.4.0, High Speed Downlink Packet Access (HSDPA) Stage

2 – Release 6, 2004-03

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5 : Radio Resource Management and Security for Mobile Users in a Heterogeneous Environment Work area: NETWORK LAYER Proposed by/Supervisors (Albena Mihovska WING, A5- 218, albena@kom.aau.dk and SOfoklis Kyriazakos, WING sk@kom.aau.dk), Co-Supervisors: Neeli Prasad(WING), Sofoklis Kyriazakos (WING) Background Next-generation wireless networks will be a conglomeration of different networking and radio access technologies. This will allow global roaming across systems based on individual access technologies. In such a challenging scenario the specific Radio Resource Management functionalities (RRM) of each radio access network (RAN) should be coordinated not only to provide the most efficient use of available resources per access technology but also to make possible the coexistence of essentially different radio concepts. Coexistence of RANs can be ensured by implementing both a central and distributed type of RRM scheme. RRM includes mechanisms for mobility management, admission control and quality of service (QoS). As multiple types of traffic converge onto one network (frequently wireless), a tradeoff is faced between effectiveness and security. Additionally, some types of traffic [for example, voice-over-IP (VoIP)], require certain quality of service (QoS) guarantees to be effective. Objective: The objective of this proposal is to define and consequently implement into a testbed platform a successful framework for RRM to support mobile users in a heterogeneous scenario. Work will include the development of RRM algorithms for the handling of intersystem handover, admission control and QoS. End-to-end QoS support needs also to be considered, by distinguishing the inter-RAN application flows and properly handling them in network nodes. For this purpose, a scheduling mechanism must be developed that will handle the queues of inter-RAN flows so that the QoS requirements are satisfied. This scheduling mechanism should include proper user To be useful, the RRM platform should include an advanced capability for authentication and authorization of the QoS requests. Work methodology: To achieve the above objectives, work should include the following steps:

1. Develop a theoretical framework for RRM in a multiple RAN environment: define and describe appropriate algorithms for support of handover, admission control, QoS (including scheduling) and security. This will include the following steps:

• Identify the scenarios and requirements for the given problem (types of communication that will require the establishment of a session, key parameters that will characterize a user in such a session)

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• Identify the preferences and negotiations for the selection of a base station/access point by a user;

• Identify the preferences and negotiations for the redirection/or not of a user • Identify suitable signaling protocols that will allow shared information, will

be cost-effective, and will still protect the privacy of the user. 2. Define the functionalities of the entities that the proposed framework comprises. 3. Implement these entities into a testbed that will allow emulation of the proposed

RRM schemes. For this purpose, the various entities need to be described with high and low-level specifications first, and afterwards implemented in Visual C++.

Benefits for students: The project will advance the state of the art in the area of RRM and security for mobile communications. It comprises both a theoretical and implementation part that will stimulate the development of both skills in the students. It also supports work in a project group, where each involved student will be able to focus in detail on one part but eventually all will be able to put these parts together into a complete concept. The practical side of the proposed project will develop the implementation skills and will be a good way to strengthen the programming skills of the students. Further, successful project results will find directly strong interest from major industries and other players in the area of mobile communications. It will be possible to publish the achieved results as separate papers or as part of the deliverables of a large European project. Relation to project courses and required knowledge This project fits well with all basic and specialized courses of mobile radio communications. It requires basic knowledge about radio communications and radio access technologies (from GSM to UMTS and beyond), wireless networks, error control. Additionally, it requires some programming skills with C++ or Visual Basic.

Additional references: [6] A. Mihovska, S. Kyriazakos, E. Gkroustiotis, J.M. Pereira, “QoS for Heterogeneous Environments,” Proc. of WPMC’05,

September 2005, Aalborg, Denmark [7] A. Mihovska, et al., “Assessment of Radio Resource Management Schemes for Efficient Cooperation of RANs,” Proc. of

WPMC’05, September 2005, Aalborg, Denmark. [8] Sofoklis Kyriazakos and George Karetsos, “Practical Radio Resource Management in Wireless Systems”, Artech House,

April 2004, ISBN 1-58053-632-8 [9] S. Kyriazakos, E. Gkroustiotis, G. Karetsos, C. Kechagias, I. Mura, N. Papaoulakis, K. Vlahodimitropoulos, “A Real-time

Monitoring and Intelligent Decisions-making Platform for Enhanced Radio Resource Management in Wireless Cellular Systems”, Kluwer - Wireless Personal Communications 30: 77-95, 2004

[10] IST Project CAUTION, at http://www.telecom.ece.ntua.gr/CautionPlus/ [11] N. Prasad, “Adaptive Security for Heterogeneous networks,” PhD Thesis, 2004.

Note: All references are directly available with the supervisors.

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6 : Corporate Network Convergence with 3GPP IMS based networks Work area: NETWORK LAYER Supervisors: Kim L. Larsen (WING kll@kom.aau.dk room A5-207) and Hans-Peter Schwefel (WING hps@kom.aau.dk room A5-212) Motivation: Service provisioning in future heterogeneous wireless networks is envisioned to be controlled via the IP-based multimedia subsystem (IMS) domain using the Session Initiation Protocol (SIP). In future use-cases, the IMS is also supposed to inter-link different domains, in particular ‘public’ cellular networks as well as enterprise networks (corporate networks). The current technical solution to access corporate networks from a remote location via 3rd party wireless access networks (cellular, hotspot) is to establish a VPN tunnel between the user’s device and a VPN gateway in the corporate network. During the life-time of this VPN tunnel, the device has a secure connection to the corporate infrastructure and all traffic (signaling and user data) is transported via this tunnel. This approach has the advantage of high security (to the external operator it is completely hidden, what type of services are being used), but on the other hand, there are certain drawbacks, in particular limited possibilities for application specific QoS provisioning, limited support of group mobility as in the case of Personal Area Networks (that move with the user), lack of service control from the IMS domain.

Purpose of the project: Goal of this project is to develop and analyze an architecture to couple IMS networks with SIP based corporate networks. Based on that architecture, the detailed technical solution(s) for one of the following sub-aspects should subsequently be developed and analyzed:

• Inter-working of the Session Control Protocols and efficient support of device/user mobility between ‘public’ cellular access networks and corporate based WLAN networks.

• Support of group-mobility as e.g. in the case of Personal Area Networks. • Use of simultaneous connectivity through wireless access in both domains for increased

reliability/throughput. The analysis can be based on simulation models as well as on measurement experiments in an experimental implementation. For the latter, an IMS prototype implementation with different wireless access technologies (802.11 type, Bluetooth, GPRS) is available in the WING labs. References: [1] 3GPP TS 23.228: “IP Multimedia (IM) Subsystem - Stage 2”, Technical Specification, June 2001. [2] P. Kim and W. Boehm, “Support of Real-Time Applications in Future Mobile Networks: the IMS Approach”, Sixteenth Wireless Personal Multimedia Communications, October 2003. [3] J. Rosenberg, et al., “SIP: Session Initiation Protocol”, RFC 3261, June 2002. [4] 3GPP TS29.162: “Interworking between the IM CN subsystem and IP networks” [5] 3GPP TR29.962: “Signalling interworking between the 3GPP profile of the Session Initiation Protocol (SIP) and non-3GPP SIP usage”

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7 : Adaptive Security for Wireless Sensor Networks (WSNs) Proposed by: Anelia Mitseva WING, A5- 216, mitseva@kom.aau.dk and Neeli R. Prasad, WING np@kom.aau.dk), Background Low Rate Wireless Personal Area Networks (WPAN) (e.g. Bluetooth, WPAN IEEE 802.15, etc. [1 2, 3]) represent a new paradigm for reliable environment monitoring and information collection. They hold the promise of revolutionizing sensing in a wide range of application domains because of their reliability, accuracy, flexibility, cost-effectiveness, and ease of deployment. Furthermore, in future smart environments, it is likely that Low Rate WPAN (e.g. see Figure 1) will play a key role in sensing, collecting, and disseminating information about the environment. The maximum required data rate for these applications is expected to range from few bps for some sensors with high latency to several tens for some home automation and consumer electronics applications (10 Kbps is a typical value) [4, 5, 6]:

• Industrial control and monitoring; • Public safety, including sensing and location determination at disaster sites; • Automotive sensing, e.g. tire pressure monitoring; smart badges and tags; • Precision agriculture, e.g. the sensing of soil moisture, pesticide, herbicide and pH

levels; • Home automation, e.g. remote controls, consumer electronics, heating, ventilation, air

conditioning, security, lighting, windows, doors, locks; • Health monitoring, including sensors, monitors and diagnostics.

Objectives Security [7, 8, 9] has a major impact on acceptablility of a technology especially for Low Data Rate networks which will carry information like heart beat rate etc.: 1. Security implies complexity, both hardware and software. Due to this, if a high level of

security has to be achieved, it is expected that this will require high computational capabilities in the devices involved, which has direct effect on their cost.

2. Security is inherently related with a mutual exchange of signaling messages among entities. These messages need time to be generated, which involves latency, and to be transferred, which implies overhead.

3. Security has a cost in terms of energy consumption, since it always requires a certain amount of transmissions and computational time in order to perform the security functions. Again, this problem gets bigger if the devices involved have reduced battery capacity.

Work methodology: This task will investigate the security and privacy aspects of applicable usage scenarios and applications for wireless sensor network environments. This includes • Identifying key vulnerabilities of personal networks in the context of various scenarios such

as health monitoring, office, automotive or personal usage. • Investigating the current solutions for realizing secure communication

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• Identifying the optimal compromise between the capabilities of devices and networking resources on the one hand and the user’s and application’s requirements in terms of security and privacy.

• The architectural specification. The architecture work will also aim at providing novel adaptive service-aware security architecture for WSN

• Implement the security solution proposed. For this purpose, the various entities need to be described with high and low-level specifications first, and afterwards implemented in Visual C++.

Benefits for students: The project will advance the state of the art in the area of Wireless Sensor Networks and security for mobile communications. It comprises both a theoretical and implementation part that will stimulate the development of both skills in the students. It also supports work in a project group, where each involved student will be able to focus in detail on one part but eventually all will be able to put these parts together into a complete concept. The practical side of the proposed project will develop the implementation skills and will be a good way to strengthen the programming skills of the students. Further, successful project results will find directly strong interest from major industries and other players in the area of mobile communications. It will be possible to publish the achieved results as separate papers or as part of the deliverables of a large European project. Relation to project courses and required knowledge This project fits well with all basic and specialized courses of mobile radio communications. It requires basic knowledge about radio communications and radio access technologies (from GSM to UMTS and beyond), wireless networks, error control. Additionally, it requires some programming skills with C++ or Visual Basic.

Reference [1] IEEE 802.15: http://www.ieee802.org/15/pub/TG4.html [2] N.R. Prasad and H.P. Schwefel, “A state-of-the-art of WLAN and WPAN,” ECWT 2003,

Munich, Germany, Oct. 9-10, 2003. [3] http://www.c-lab.de/ubisec/ [4] Wireless sensor networks: http://www.millennial.net [5] http://www.zigbee.org/ [6] N. R. Prasad, G. Gaeta and M. Ruggieri, “Adaptive security for Low Data Rate networks,”

WPMC 2003, Yokuska, Japan, October 19-22, 2003. [7] N. R. Prasad and M. Ruggieri, “Adaptive security for Low Data Rate networks,” Special Issue on

Security, International Journal on Wireless Personal Communications, Kluwer Academic Publishers, 2004. (Accepted)

[8] A. Perrig, R. Szewczyk, J.D. Tygar, V. Wen and D. E Culler, “SPINS: Security Protocols for Sensors Networks,” Wireless Networks 8, Kluwer Academic Publishers, 2002, pp. 521 – 534.

[9] F. Akyildiz, W. Su, Y. Sankarasubramaniam and E. Cayirci, “A Survey on Sensor Networks,” IEEE Communications Magazine, vol. 40, no. 8, August 2002, pp. 102-114.

[10] PACWOMAN (Power Aware Communications for Wireless OptiMized personal Area Networks), WP6/Security for Low Data Rate Requirements and Functional Specification, home page: www.imec.be/pacwoman.

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8 : Cooperative Access for Wireless CDMA Networks Contact Person: Assoc. Prof. F.H.P. Fitzek, Room A5-206, ff@kom.aau.dk Project Description: This project tries to exploit cooperative strategies for cellular CDMA networks. In current cellular networks, communication is based on a peer to peer link between base station and terminal. In the envisioned project, the terminals form cooperative groups for sending and receiving data to or from the base station. We have shown the benefits for such approach for TDMA based systems and the project members should exploit this for CDMA technology. CDMA has some nice features such as power control and the freedom in designing the code sequences. The goal of the project is to show that cooperative reception is outperforming the state of the art communication. Skills: The students choosing this project should have some basic knowledge about communication networks and signal processing (in terms of CDMA). As the performance will be investigated using simulation tools, the students should have a profound knowledge in one simulation tool (ns or Matlab or C++).

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9 : PAPR issues in Link Adaptation for WiMAX like OFDM systems Work Area: PHYSICAL LAYER Suvra Sekhar Das, Muhammad Imadur Rahman and Fleming B. Frederiksen Room A5-222, Telephone: +45 9635 8688 e-mail: ssd@kom.aau.dk, imr@kom.aau.dk ; fbf@kom.aau.dk Required number of students: 1 (upto 2) : The amount of analysis may be accordingly modified. Problem description: OFDM has been quite popular for broadband communication systems. It has enabled high spectral efficiency systems. A current realization is the WiMAX standard, i.e. IEEE 802.16a,d,e standard. This project deals with these two advanced PHYSICAL layer technologies, namely link adapatation and PAPR issues in WiMAX like OFDM systems. Link Adaptation involves varying the bit loading (modulation level) and the power loading (power adaptation) for each sub carrier; subjected to total and peak power constraint. The strategy chooses the optimum power level and modulation order per sub-carrier, so that spectral efficiency is maximized. In the latest implementations, WiMAX is targeting optional link adaptation in OFDM. In short, link Adaptation in conjunction with OFDM promises to provide a massive improvement in system throughput. On the other hand, OFDM systems suffer from large Peak to Average Power Ratio (PAPR) problem. The power amplifier has to operate with back off, so that the peak distortion due to power amplifier does not degrade the performance. Larger the PAPR, larger is the back off needed. The larger is the back off in the power amplifier, the higher the power loss and reduction in range (coverage) [1],[3]. Although Link Adaptation in OFDM promises to improve the spectral efficiency by a large margin, it appears that they will have an impact on the PAPR of the system and thus on the range (coverage) or bit error rate degradation. In Link Adaptation, recent works have suggested that joint application of power and rate adaptation does not provide any significant gain compared either power adaptation only or rate adaptation only systems [2]. In such a situation, it can be said that power adaptation for OFDM is difficult to implement in cellular scenario, as it would increase inter cell interference, but it would enable a very simple receiver, for constant rate transmissions. On the other hand, rate adaptation would not cause higher inter cell interefence, though it would require a more complex receiver due to multi-level modulations and demodulations. It is worth noting here that these studies do not consider the effect of the rate or power adaptation on the PAPR. The study of influence of power and or rate adaptation on PAPR for OFDM is important since PAPR is already high for OFDM. If the above two link adaptation mechanisms increase the PAPR of the system, it would put heavy constraints on the power amplifier back off parameter. Either it would reduce the range coverage, or it will introduce bit error rate degradation. Therefore it is important to consider the aspects of PAPR for any improvement on OFDM

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system. It might turn out that one system is better in terms of PAPR compared to another. Now, if the spectral efficiency difference is not very high, then the link adaptation scheme with a better PAPR distribution may be selected. The goal of this project is to analyze (analytically and numerically[p1]), the effect of rate adaptation and power adaptation (one at a time and simultaneously) on PAPR in OFDM systems. This would help make wise decision on the choice of a suitable link adaptation scheme. Assumptions:

5. Discrete modulation levels such a BPSK, QPSK, QAM-16, QAM-64, QAM-256, QAM-1024, will be considered.

6. Total power constraint will be considered. Scenarios:

5. Only rate adaptation at constant transmit power 6. Only power adaptation for constant rate 7. Both power and rate adaptation.

Analysis: 4. To obtain the cumulative distribution numerically (by means of simulation), of the

PAPR in each of the above cases. 5. To study the distribution of PAPR after applying a simple PAPR reduction mechanism

(for example clipping and filtering), on OFDM systems using link adaptations mentioned earlier.

6. To develop the analytical expression of the PAPR 7. To find bit error rate degradation (by simulation) in each of the above cases, when the

threshold for the clipping (a PAPR reduction mechanism), is given, which is chosen without considering the PAPR effect of the link adaptation schemes

8. To find a suitable clipping ratio for the link adaptation mechanism for given fixed modulation levels, power limits and number of sub carriers.

Outcome: 2. Report describing the effect of rate and power control based link adaptation schemes for

OFDM based systems. Reference:

5. Ramjee Prasad, OFDM for Wireless Communication Systems. Artech House 2004. 6. Seong Taek Chung, and Andrea J. Goldsmith, Degrees of Freedom in Adaptive Modulation:

Aunified View. IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 49, NO. 9, SEPTEMBER 2001

7. Seung Hee Han et al., An Overview of Peak-to-Average Power Ratio Reduction Techniques for Multicarrier Transmission, IEEE Wireless Communications, pp. 56-65, April 2005.

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10 : Power and Rate Adaptation in Sub-Carrier and Band Hopped OFDMA for WIMAX like systems Work Area: PHYSICAL LAYER Muhammad Imadur Rahman, Suvra Sekhar Das, and Elisabeth de Carvalho Room A5-222, Telephone: +45 9635 8688 e-mail: imr@kom.aau.dk, ssd@kom.aau.dk, edc@kom.aau.dk Required number of students: 1 (preferably) Problem description: Sub-carrier and Band Hopped OFDMA (SCBH-OFDMA) is a novel hopping based OFDMA technique for cellular systems, which provide a trade-off solution between complexity and system performance [imr]. Under the same cell area, different users will experience different time and frequency selectivity characteristics depending on their distance from BS, their velocities and the wireless multi-path scenario that they observe. In SCBH-OFDMA, a flexible access technique is achieved by making use of sub-carrier and band hopping which can be adapted in different scenarios, thus creating an adaptive system in terms of heterogeneous channel scenario. The goal is to allocate the time and frequency resources efficiently among all these users simultaneously. Users are grouped together with some pre-defined channel criteria, such as coherence time and coherence bandwidth, and put into one band together. Sub-carrier hopping is performed in digital and Band hopping is done in RF domain. Sub-carriers are allocated in blocked (and/or interleaved) OFDMA fashion. Recently, WiMAX has gained huge popularity among the wireless research world, due to its promise of broadband data rate at the last mile and at higher mobility. OFDMA is a very important mode in WiMAX standard. SCBH-OFDMA can be an interesting alternative to OFDMA scheme mentioned in the standard. By using Link Adaptation (LA) techniques, it is possible to improve the system throughput in OFDMA systems by adjusting transmission parameters such as modulation scheme, code rate, power allocation etc. In SCBH-OFDMA, We assign sub-carriers based on long term CSI of the channel, so it is possible to design a long term link adaptation procedure for such a system. This can significantly improve the system performance. Recent literatures suggested that joint application of power and rate adaptation does not provide any significant gain compared either power adaptation only or rate adaptation only systems [gold]. Thus, in system design level, a trade-off between power and rate allocations need to be done, to obtain higher spectral efficiency with reasonable system implementation complexity. In this perspective, we propose to investigate the short-term power adaptation and long-term rate adaptation in SCBH-OFDMA system for WiMAX like environment. The project will require design of specific power and rate allocation techniques and implementation of such techniques in system simulator. The goal is to optimize power and/or spectral efficiency, and to

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adapt to discrete rates for different channel conditions for different users while keeping instantaneous error rate (i.e. Bit Error Rate, BER or Frame Error Rate, FER) lower than a threshold. Activities:

1. Investigate the usability of long term channel information for link adaptation in the system

2. Design link adaptation techniques for different user groups 3. Incorporate the link adaptation techniques in the system simulator developed in WING

group 4. Evaluate the adaptation techniques with original SCBH-OFDMA scheme via system

simulation. Outcome:

1. Complete framework for power and rate adaptation in SCBH-OFDMA system Reference: [imr] Muhammad Imadur Rahman et al., Sub-Carrier and Band Hopped OFDMA, JADE project delievrable, December 2005. (Available upon request from the author) [gold] Seong Taek Chung, and Andrea J. Goldsmith, Degrees of Freedom in Adaptive Modulation: A unified View, IEEE Transactions on Communications, Vol. 49, No. 9, September 2001.

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11 : Optimal spectral and spatial weighting schemes and their robustness to channel estimation errors PROJECT PROPOSER (Primary): SECONDARY PROPOSER(S): Name: Persefoni Kyritsi Name: Xin Zhou Address: AP, room A6-216 Address: AP, room A6-207 E-mail: persa@kom.aau.dk E-mail: xz@kom.aau.dk http://kom.auc.dk/~persa Background: Time reversal (TR) is a technique that has various applications in ultrasound and underwater sound. Only recently has it emerged as a promising technique in wireless communications. Its potential lays in three primary properties: temporal focusing, spatial focusing and statistical stability. Temporal focusing can be interpreted as a form of pre-equalization that simplifies the requirements on the receiver design. Spatial focusing can be interpreted as a type of broadband beam-forming that can increase the security of the communication link or increase the user density. Statistical stability indicates robustness in channel variations. It can be shown that time reversal alone with a limited number of transmitters is not optimal. Advanced spatial and spectral filtering techniques have been developed to exploit the properties of time reversal and guarantee optimal performance. Should these be used in an actual wireless system though, it is expected that channel state information will be limited or outdated. Project Description: The purpose of this project is to investigate how the performance of these weighting techniques depends on the accuracy of the channel state information (CSI). The parameters that we will investigate are the achievable error rates with imperfect CSI, and the robustness of spatial focusing. We will investigate two types of channel estimation error: noise during the channel estimation process, and continuous channel fading. They are expected to affect the temporal/ spatial focusing in different ways. The investigation of continuous channel fading can also serve as an indication of the robustness of the training requirements that these techniques pose on the system design. The evaluation will be based on simulations and/ or measurements. For the simulations, we will use the 802.11n channel model, which is already implemented in a Matlab simulator. Alternatively, we can try to approach the problem theoretically, but this requires advanced mathematical skills (random matrix theory, multiple applications of the central limit theorem would be common tools). Hopefully this project will help demonstrate the robustness of time reversal based ideas, as theoretically expected. Prerequisites: FP8-25 Propagation, Antennas and Diversity FP8-26 Inverse filtering, Deconvolution and Equalization References

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P. Kyritsi, G. Papanicolaou, P. Eggers, A. Oprea, "MISO time reversal and delay spread compression for FWA channels at 5GHz," IEEE Antennas and Wireless Propagation Letters, 2004, Vol. 3, No 6, 2004, pp. 96-99. H.T. Nguyen, J. B. Andersen and G.F.Pedersen, "The potential use of time reversal techniques in multiple element antenna systems," IEEE Communications Letters, 2004. H.T. Nguyen, I.Z. Kovacs, P.C. Eggers, “A Time Reversal Transmission Approach for Multi-user UWB Communications,” IEE Proceedings Communications, Special Issue on Ultra Wideband Systems. P. Kyritsi, G. Papanicolaou, “One-bit Time Reversal for WLAN Applications,” PIMRC’05. P. Kyritsi, C. Tsogka, and G. Papanicolaou, “Optimally Designed Time Reversal and Zero Forcing Schemes,” WPMC 2005. P. Kyritsi, P. Stoica, and G. Papanicolaou, “Time reversal and zero-forcing for WLAN applications,” WPMC 2005. Previous projects • “Time Reversal for WLAN Application”, Group 996/2004 (Jimena Llorente Martinez, Axel

Adenet, Christophe Lemasson, Xin Zhou). Fall semester 2004. • “Time reversal application in single user MIMO system”, Xin Zhou, MS Thesis, June 2005.

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12 : DVB-H Antenna in a Small Handheld Device Proposers : Gert Frølund Petersen (AP, room A6-206, gfp@kom.aau.dk) together with Siemens Mobile Phones (now BENQ Denmark ApS, Mobile Phones Development) Introduction: Digital Video Broadcasting for Handheld devices (DVB-H) is a feature that will be introduced to the consumers during 2006. With DVB-H it will be possible to watch TV with for example a mobile phone. However, since the typical size of a mobile phone is small compared to the wave length of the transmitted DVB-H signals (470 MHz to 730 MHz) and that the system has a relative bandwidth of more that 35 % makes the internal antenna design very challenging. Also, the form factor of a device is very important for the antenna design, especially for sliders and clam shell phones where the DVB-H reception in some cases should be good in both open and closed positions. In fact, if a satisfying reception is to be achieved it will be necessary to design a switchable or tuneable internal antenna for the DVB-H reception. Aim: Define and analyze possible user scenarios with a small handheld DVB-H device. Based on these definitions, establish link budgets in order to determine the requirements for the DVB-H antenna. Make design proposal for an internal switchable /tuneable DVB-H antenna which can be implemented in a handheld device. Investigate the influence on the performance and tuning-range from the form factor of this device. Content:

• Analyze the link budget for possible user scenarios and determine the requirements for the DVB-H antenna

• Make a proposal for an internal antenna design for one or more handheld devices of different form factors, with the aim of making the device as small as possible.

• Simulate and construct prototypes and if possible do live field tests to make correlation between proposed performance criteria and observed quality

Recourses & facilities Siemens Mobile Phones can support with measurement facilities, phones, testboards and other HW for testing implemented solutions. The AP group has all equipment needed as well as a channel sounder if needed, further a very efficient FDTD program package. Requriments The project fit 2 students.

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13 : Reduction of Body-Worn SAR Proposers : Gert Frølund Petersen (AP, room A6-206, gfp@kom.aau.dk) together with Siemens Mobile Phones (now BENQ Denmark ApS, Mobile Phones Development) Introduction: The main focus of Specific Absorption Ratio (SAR) reduction techniques have in the recent years mostly been on head SAR values, and several techniques for reducing the head SAR values have also been developed. However, the focus is now shifting toward the body-worn SAR since the manufactures and operators have a desire to also reduce these values. The main difference between the head SAR and body-worn SAR, is that head SAR is only measured with the face of the phone where the main Display is located Towards the Phantom (DTP), while the body-worn SAR is measured with both DTP and with the face of the phone where the Antenna is located Towards the Phantom (ATP). This is very challenging, since the known techniques from reducing the head SAR values, measured with DTP, tend to increase the SAR value when measured ATP. BENQ owns a patent where two antennas is used to reduce the head SAR values, by basically distributing the power between these two antennas and thereby transmitting half the power simultaneously on each antenna. However, this technique has only been tested and validated on head SAR values and needs to be implemented and tested for the body-worn SAR values. Some other challenges are:

• Some techniques might work for mono-block phones, but not for slider and clam-shell phones

• What decreases the body-worn SAR value for GSM 900 might increase or have no effect for GSM 1800 and GSM 1900 (UMTS ?)

Aim: Develop techniques to reduce the body—worn SAR values which can be implemented in a standard size mobile phone of a given form factors (mono-block, clam-shell and slider). The techniques described in the BENQ patent can be used as a reference. Content:

• Make a proposal for one or more techniques for reducing the body-worn SAR values on mobile phones of different form factors (mono-block, clam-shell and slider).

• Simulate the body-worn SAR values and the efficiencies of the antenna solution.

• Measure SAR and Total Radiated Power (TRP), by implementing the solutions in live phones

• Evaluate the correlation between simulated and measured results Recourses & facilities Siemens Mobile Phones can support with measurement facilities, phones, testboards and other HW for testing implemented solutions. The AP group has a large Antenna lab, as well as a very efficient FDTD program package. Requriments

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The work task is large and the project will nicely fit 2 students, further the project requires a strong theoretical background.

14 : Genetic algorithms for BER calculation in large delay spread channels PROJECT PROPOSER (Primary): Name: Persefoni Kyritsi Address: A6-216 E-mail: persa@kom.aau.dk http://kom.auc.dk/~persa Background: Imagine we have a wideband system which is described by the channel impulse response

( ) ( )∑−

=

−=1

0

L

lsl lTthth δ

Ts is the symbol time, and there are L channel taps. Without loss of generality, let us assume that lhh l ∀≥ ,22

0 , and that we are trying to perform

symbol by symbol detection without the use of equalization or advanced coding techniques (e.g. Viterbi detection). Intersymbol interference (ISI) from the previous (L-1) symbols becomes the fundamental limiting factor and we observe the phenomenon of irreducible bit error rate (BER). Commonly irreducible BER is associated with the delay spread of the channel, and is aggravated by larger delay spreads. If we are given a wideband channel and want to calculate the BER, we can:

• Approximate the ISI as additive white Gaussian noise and look at an equivalent SNR. In reality the ISI is neither white nor Gaussian and this approach tends to overestimate the BER.

• Simulate the bit transmission for very very very long trains of bits. • Calculate the exact value of the ISI for all M(L-1) possible values of the ISI (where M is

the size of the constellation), and from that the BER, and then average over the possible realizations of the ISI.

Clearly the last two solutions are very computationally intensive, and the first one is inaccurate. So what can we do? Project Description: Commonly genetic algorithms are used to find extrema within a very large set of options. With appropriate tweaking, we can use genetic algorithms to find averages over a set of options (see 1). We can use this to find the average BER as in the third approach above, keeping in mind that few combinations of previously transmitted bits can lead to low BERs. The purpose of this project is to:

• Develop the genetic algorithm for BER calculation (the code has mostly been implemented in Matlab, but needs some work).

• Study the performance in terms of accuracy and runtime for different channel parameters.

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• Specifically look at the achievable BERs for channels with and without time reversal (TR). It is expected that the symmetries in the response with TR will reduce the BER, even though the delay spread is the same.

Prerequisites: FP8-25 Propagation, Antennas and Diversity FP8-26 Inverse filtering, Deconvolution and Equalization This project is incredibly interesting but requires a strong stomach for advanced math. References

1. Pierre del Moral, Josselin Garnier, ‘Genealogical particle analysis of rare events’.

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15 : Cooperative antenna systems PROJECT PROPOSER (Primary): SECONDARY PROPOSER(S): Name: Persefoni Kyritsi Name: Patrick Eggers Address: AP, room A6-216 Address: AP, room A6-214 E-mail: persa@kom.aau.dk E-mail: pe@kom.aau.dk http://kom.auc.dk/~persa Background

Let us assume that we have an access point (AP) that provides coverage to a cell C around it. Within this cell, there are several users that can receive downlink data from the AP. Depending on the quality of the link from the AP to each user, if a user Ui is in an unfavorable channel situation, then it cannot receive data from the AP. However, it might be possible for the AP to send data to another user Uj, which can then forward them to Ui.

This concept is referred to as user cooperation and it is based on the idea that users might be

able to exchange data locally over a separate short-range communication system to enhance each other's reception quality. This way the capacity or the coverage of cellular systems can be extended. Clearly the performance of such a scheme depends on the quality of the link from the AP to the users and the link between the users. Project description: This project will be within the area of cooperative wireless systems and several possible directions are open for investigation:

• There are cooperative channel measurements available (possibly the first in the world!), and we can take more to resemble more closely a cellular scenario.

• The measurements involve multiple antenna arrays at both the AP and the user equipment. This constitutes an additional degree of freedom in the cooperative techniques (antenna selection/ beamforming).

• In broadcast transmission, each user can receive part of the information directly from the AP and the rest from the users within a cooperating group. We can explore the feasibility of this approach and its dependence on the channel properties.

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16 : The shower curtain effect in radio communications using time reversal PROJECT PROPOSER (Primary): SECONDARY PROPOSER(S): Name: Persefoni Kyritsi Name: Xin Zhou Address: AP; room A6-216 Address: AP, room A6-207 E-mail: persa@kom.aau.dk E-mail: xz@kom.aau.dk http://kom.auc.dk/~persa Background and Project Description: Time reversal (TR) is a technique that has various applications in ultrasound and underwater sound. Only recently has it emerged as a promising technique in wireless communications. Its potential lays in three primary properties: temporal focusing, spatial focusing and statistical stability. Temporal focusing can be interpreted as a form of pre-equalization that simplifies the requirements on the receiver design. Spatial focusing can be interpreted as a type of broadband beam-forming that can increase the security of the communication link or increase the user density. Statistical stability indicates robustness in channel variations. The temporal focusing properties of time reversal have been shown to depend on the scattering properties of the channel around the transmitter and the receiver. Specifically, the temporal focusing improves as the distance between the transmitter and the receiver increases if the acting transmitters are in a high clutter situation. These results are consistent with a physical phenomenon known as the shower curtain effect. This can be intuitively perceived as follows: imagine that you want to observe a light bulb (source), and you are separated from it through a shower curtain. If you are far from the shower curtain and the light bulb is close to it, seeing the light bulb is easy. If you are close to the shower curtain and the light bulb is far from it, it’s difficult to see. Recently there has also been a lot of theoretical work as well that has documented the shower effect in TR, using advanced mathematics and specific propagation regimes. The project will be structured and gradually increase in novelty. The purpose of this project is to verify the experimental results using simulations of the wireless channel, and explore the implications of the shower curtain effect on the properties of time reversal. We will use simulations based on the ring of scatterers model, and possible actual channel measurements. Material A large database of UMTS band measurements with 2x 4 dual-polarised base-station antenna panels is available. Furthermore wideband WLAN environment are also available or new measurements can performed by the group. Prerequisites: FP8-25 Propagation, Antennas and Diversity References

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P. Kyritsi, G. Papanicolaou, P. Eggers, A. Oprea, "MISO time reversal and delay spread compression for FWA channels at 5GHz," IEEE Antennas and Wireless Propagation Letters, 2004, Vol. 3, No 6, 2004, pp. 96-99. H.T. Nguyen, J. B. Andersen and G.F.Pedersen, "The potential use of time reversal techniques in multiple element antenna systems," IEEE Communications Letters, 2004. H.T. Nguyen, I.Z. Kovacs, P.C. Eggers, “A Time Reversal Transmission Approach for Multi-user UWB Communications,” IEE Proceedings Communications, Special Issue on Ultra Wideband Systems. Previous projects • “Time Reversal for WLAN Application”, Group 996/2004 (Jimena Llorente Martinez, Axel

Adenet, Christophe Lemasson, Xin Zhou). Fall semester 2004. • “Time reversal application in single user MIMO system”, Xin Zhou, MS Thesis, June 2005.

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17 : Cooperative Cross-layer Hotspot Selection with Beamforming at User Side Supervisors: Frank Fitzek (WING ff@kom.aau.dk, room A5-206), Chenguang Lu (AP cgl@kom.aau.dk, room A6-205) Motivation In data traffic dense area, it is normally covered by several overlapped hotspots with different frequency channels. Each user has to choose a hotspot to join by associating with the corresponding access point. Currently, this is implemented based on received signal strength indicator (RSSI). The user will join the hotspot which gives strongest RSSI which generally means highest transmission data rate. However, in multi-user scenario, user capacity depends not only on data rate but also on MAC delay because multiple users share the same channel. In best case without considering packet and MAC protocol overhead,

usersofNumberrateDatacapacityUser

= . High data rate does not mean high user capacity.

Furthermore, applying beamforming at user side can significantly increase data rate due to the beamforming power gain. It further increases the degree of hotspots’ overlapping. Therefore, it is very interesting to investigate smarter cross-layer hotspot selection mechanisms to optimize user capacity when beamforming is used at user side.

Figure1, Illustration of cooperative negotiation

Figure 2, Implementation structure

Cooperative negotiation between terminals is one of promising mechanisms for its simplicity and flexibility. It can be implemented at application layer, as shown in figure 2. One can convince others to handover to other hotspots when more capacity is needed. It will also benefit others, as shown in figure 1. Without cooperative negotiation, both terminals would connect to AP2, as this offers the best performance in data rate (judged individually). In this case both terminals share the capacity resulting in 27Mbit/s. From a global perspective WT1 should connect to AP1 (getting 36Mbit/s) and WT2 will achieve 54Mbit/s.

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Project Description The goal of the project is to investigate the performance of cooperation for beamforming terminals. Due to a large number of access points and the possibility of beamforming at the wireless terminal, several possible beamforming setting are possible, where as only one will give the optimal capacity in the hotspot. Within the project, the participants should exploit the inter communication among the terminals to find this optimal solution. It is an interesting approach as the radio resource management is done in a distrusted fashion. Prerequisites

• Basic knowledge on beamforming and wireless propagation • General knowledge of wireless network protocols • C programming skills are needed in experimental implementation, preferable having

Linux programming experience. Comments: Two beamforming terminals and their beamforming control software platforms are ready for experimental implementation, as shown in figure 3. It is likely that a non-disclosure agreement (NDA) needs to be signed when you accept this project because the beamforming terminal and the beamforming software are associated with a project with commercial scope.

Figure 3, Beamforming terminal

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18 : UWB interference mitigation at antenna level. Proposers : Gert F. Pedersen (AP, room A6-206, gfp@kom.aau.dk) and Yu Wang (AP, room A6-203, yw@kom.aau.dk) together with the large EU project in BAN/PAN, called “MAGNET beyond” Background For small onbody UWB devices interference can be crucial. Narrowband interference can easily be rejected by filtering at RF level but other UWB devices in the same band need to be dealt with in either a complex receiver or at the antenna level by adaptively changing the antenna radiation pattern and/or the polarization. This is caused by the fact that the UWB interference is much more problematic as it can or will have different directional and polarization state behavior wrt to delay or frequency. Project The project has two major aims 1) characterize an UWB interferer wrt direction and polarization. This can be investigated experimentally by measurement using AP labs horn antenna and pedestal with a network analyzer. Post processing of the measured frequency response should reveal the frequency domain dynamics of polarization state as well as the direction information. This knowledge is novel and could be journal paper material by it self. 2) An FDTD model of the UWB device including a model of the user can give the results in terms of the radiated fields in any direction and polarizations. This effective radiation together with the established frequency domain dynamics found under 1) can by simple Matlab calculations reveal the practical Frequency domain dynamics for interfering signal sensed by the UWB onbody device. Further, based on this response, the identification of the necessary frequency domain adaptation to achieve UWB nulling in polarization and direction can be established. Using this new technique it is possible to find the requirements for the interference mitigating antennas and optimize a single adaptive element (a smart element) or group of elements or for the small terminals possibly a group of distributed elements. Recourses & facilities The AP group has a large RF laboratory with all needed antennas, pedestal and equipment, as well as a very efficient FDTD program package. Requriments The work task is large and the project will nicely fit 2 – 3 students, further the project requires a strong theoretical background.