Location of Radio Sources

Many services in future mobile radio systems like E-911, location sensitive billing, cellular system design, resource management, fleet management and intelligent transportation systems need information on the location of the mobile terminals. Consequently, an important requirement for the physical layer of future mobile radio systems is the ability to deliver precise location information. State of the art solutions based on the measurement of channel attenuation or access delay cannot fulfil the stringent performance requirements of future applications especially in typical mobile radio scenarios with multipath propagation. Even satellite navigation systems like GPS do not fulfil the requirements as they do not work inside of buildings. The Research Group for Radio Communications investigates novel database based location techniques. Furthermore, hybrid location techniques, which combine several of the mentioned techniques, are taken into consideration.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Multi-Static and Synthetic Aperture Radar System

In co-operation with research institutes such as DLR and FGAN problems of multi-static radar systems for the location of objects moving on the ground and of high resolution SAR radar systems are considered.


Source:www.eit.uni-kl.de/baier/Research/research.htm

System Modeling and Simulation by ML-Designer

For the design and optimization of radio communications systems modeling and simulation tools are required. As such a tool the Research Group for Radio Communications adapted ML-Designer. For the system concept JOINT mentioned above a complete simulation chain was implemented on ML-Designer and utilized for extensive system simulations. Important functional modules which had to be established in this work concern JD, JT and JCE. The generated JOINT simulation chain can serve as a reference model for the demonstration of the features and performance of ML-Designer.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Interference and Co-Existence in Mobile Radio Scenarios

mobile radio communications, often several cellular networks of different operators have to co-exist in the same geographic area. Although the networks of the operators nominally use different frequency bands, interference can occur due to intermodulation, blocking and oscillator noise. The impact of such interferences heavily depends on the system parameters and the scenario, in which the networks are deployed. The interference is most severe, when base stations of two different operators are dislocated. Then, a mobile station MSB far from its serving base station BSB using very high transmit power can be very close to a base station BSA of the other operator A, thus creating very high interference. Similar co-existence situations can occur between different systems which are adjacent in frequency, such as the UMTS TDD and FDD modes in Europe. The main objectives of the research project are to categorize the different interference types, choose suitable measures to evaluate the interactions between the networks, identify critical constellations and parameters, and develop methods to combat interference between different networks for critical cases.



Source:www.eit.uni-kl.de/baier/Research/research.htm

Channel Estimation

Although 3rd generation mobile radio systems have not yet become widely operational, research concerning beyond 3G mobile radio systems has already started around the globe. At the Research Group for Radio Communications the system architecture with the acronym JOINT (Joint Detection and Transmission Integrated Network) is developed. JOINT is a contribution to the project “Joint Research Beyond 3G” (JRB3G) sponsored by the SIEMENS Company, Germany, in which German and Chinese universities are involved. JOINT is a service area (SA) based concept. Each service area consists of access points (APs) receiving/transmitting radio signals from/to the mobile terminals (MTs) active in the SA. Each SA is equipped with a central unit (CU), which is responsible for signal processing. Joint Detection (JD) is applied for uplink data detection and Joint Transmission (JT) is used for downlink data transmission. Both techniques rely on the knowledge of the mobile radio channel, which is gained by the technique termed Joint Channel Estimation (JCE). JCE is a pilot-aided channel estimation technique. The active MTs transmit known symbols - termed pilots – to the APs, and based on these symbols and on the corresponding received signals, estimates of all radio channels between each MT and AP are obtained at the CU. Exploiting the potential and evaluating the performance of JCE in JOINT is the task of this work.


Source:www.eit.uni-kl.de/baier/Research/research.htm

MIMO Systems

In MIMO (Multiple-Input-Multiple-Output) systems, multiple antenna elements are placed at both the access point (AP) and the mobile terminals (MTs). Therefore, a spatial dimension is introduced at both the AP and MTs, which gives large potential to increase the system capacity. Basically, MIMO systems can be classified in single-user MIMO systems, where the AP communicates with only a single MT, and multi-user MIMO systems, where AP communicates simultaneously with several MTs.

The focus of this project is to

study the basic properties of single-user MIMO systems, e.g. the distribution of eigenvalues of the MIMO channel,
study the basic properties of multi-user MIMO systems, e.g. the cross-correlation between eigenmodes of MIMO channels between AP and MTs, and
develop novel base band signal processing techniques for multi-user MIMO systems, especially for downlink communication.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Beyond 3G Mobile Radio Systems (JOINT)

At the Research Group for Radio Communications a system concept termed JOINT (Joint Transmission and Detection Integrated Network) for beyond 3G mobile radio systems is being developed. JOINT applies adaptive antenna techniques as well as the joint transmission (JT) and joint detection (JD) techniques. The main goals are to increase capacity compared to 3G cellular systems and WLAN systems as for instance IEEE 802.11, and to keep the complexity of the mobile terminals at a low level. In the following, important characteristics of JOINT are listed:

The entire area intended for mobile radio services is subdivided into service areas (SA). The SAs can be adjacent to each other or isolated. One SA can represent a building, a floor of a building or even a part of an inner city. Thus, a SA corresponds to a number of cells of a common pico- or micro-cellular system. Since the above mentioned JD and JT techniques can eliminate the interference within a SA, the advantage of cancelling intercell interference is obtained by the introduction of the SA instead of cells.
Within each SA numerous mobile terminals (MT) can be active.
On the fixed network side multiple access points (APs) per SA, which are connected to a central unit (CU), will be used. The central unit is connected to the core network.
Each AP and each MT applies an antenna consisting of a single antenna element or an array of antenna elements.
The communication of a MT with the CU occurs over several APs simultaneously.
The MTs are kept simple, and the necessary processing efforts are concentrated in the CU.
Multicarrier transmission using orthogonal carriers will be applied. The option of combining the multicarrier transmission with the multiple access schemes TDMA, FDMA and CDMA is given.
TDD is the duplexing scheme in favor.
In the uplink JD is used. This means that the received signals at the antennas of the APs are jointly processed in the CU. The goal is to eliminate multiple access interference (MAI) originating inside the SAs.
In the downlink JT is used. The antennas of the APs transmit signals, which are structured in such a way that each MTs of a SA obtains the corresponding signal practically free from any MAI by applying a simple receiver structure.
For channel estimation the scheme joint channel estimation (JCE) is proposed.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Transmit Array Processing for CDMA Downlinks

It is expected that in the near future the demand for high data rates will dramatically increase especially in the downlink of mobile radio systems. This expectation is currently being reflected by the lively high speed downlink packet access (HSDPA) standardization efforts within 3GPP. CDMA mobile radio standards, e.g., the UTRA-FDD mode, are prepared for such requirements by means of orthogonal variable spreading factor (OVSF) codes allowing the coexistence of high and low data rate users. To achieve high data rates, low spreading factors have to be utilized, which goes along with a massive impact of interference and noise degrading the system performance. On the part of the transmitting base stations, high downlink data
rates may be enabled by utilizing adaptive multi-element transmit antennas. For the efficient operation of such antennas information about the downlink radio channels is required at the base stations. The 3G partial standard WCDMA designed for the Frequency Division Duplexing (FDD) radio frequency bands suffers from the inherent disadvantage that, due to the frequency gap between uplink and downlink, the results of the uplink channel estimation cannot be directly used as the channel information required for adjusting the multi-element transmit antennas. In the FDD case, two general basic approaches to obtain knowledge about the spatial properties of the downlink channels exist, namely either exploiting the spatial properties of the uplink channels, or feedback downlink channel information from the mobile stations to the supplying base stations. The first approach is based on the assumption that the directional properties and the attenuations of the respective radio propagation paths of the uplink channels and the corresponding downlink channels are equal. If this assumption holds, methods for an at least sub-optimum adjustment of the downlink transmit antenna weights based on uplink channel estimates exist, which do not rely on complex DOA estimation techniques. The comparison of the performances achievable by uplink channel estimation based techniques with those achievable if actual downlink channel information is available shows the superiority of techniques which directly exploit information about the spatial downlink channels. The only way to obtain information about the spatial downlink channels at the base station is via feedback from the mobile stations which leads to the development of efficient feedback schemes.

If among the mobile stations served by the same base station high and low data rate links have to coexist, mobile station specific minimum signal to noise and interference (SINR) constraints have to be fulfilled. Thus, transmit array processing and power control techniques should explicitly operate to support these demands. It is not possible to optimize transmit array processing and the adjustment of transmit powers in seperate steps. Iterative methods may be exploited to fulfill the mobile station specific SINR constraints and at the same time to keep the total transmit power as low as possible in order to reduce intercell interference.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Joint Processing of received Signals in CDMA Mobile Radio Systems with Infinite and Quasi Infinite Data Transmission

Mobile radio systems are interference limited. Therefore, in future mobile radio systems a significant performance enhancement can only be achieved by utilizing techniques which reduce the degrading impact of interference. A highly attractive class of such techniques are techniques for joint received signal processing. To date the systematic design and analysis of such techniques for CDMA mobile radio systems with infinite or quasi-infinite data transmission is not yet well understood, even though such systems are to be a particularly interesting class of future mobile radio systems, see for instance the third generation mobile radio systems currently put into operation. This project contributes to the systematization of the design and optimization of techniques for joint received signal processing in such mobile radio systems. It is shown that the task of joint received signal processing can logically be split into the five subtasks block establishment, data assignment, interblock signal processing, intrablock signal processing and combining + decision. Besides to the exact definition of these five subtasks, the main focus of the project is the development of attractive proposals for suboptimal and, according to certain criteria, optimal solutions of these subtasks.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Interference Reduction in CDMA Mobile Radio Systems

One of the most important performance limiting factors in CDMA mobile radio systems is the multiple access interference. Consequently, some of the proposals for third generation mobile radio systems as for instance the Chinese TD-SCDMA already incorporate simple joint detection techniques like linear zero forcing estimation. However, these linear joint detection techniques are rather complex and can only be applied in systems with low numbers of simultaneously active users, i.e., CDMA systems with an additional TDMA component. Furthermore, the performance of linear joint detection especially in scenarios with high system loads, i.e., numbers of users close to the spreading factor, is unsatisfactory. At the Research Group for Radio Communications advanced joint detection techniques which combine low complexity and superior performance are developed. These advanced joint detection techniques rely on the turbo principle. The FEC code typically used in mobile radio systems and the CDMA spreading are considered as a serially concatenated code. A low complexity high performance decoder for such serially concatenated codes consists of two decoders alternately decoding the two codes and exchanging extrinsic information between the two decoders. A generalized detector architecture, which includes turbo detectors as well as conventional joint detectors like the zero forcing estimator or parallel interference cancellation is designed. By using sliding window techniques the above mentioned advanced joint detection techniques can also be applied in CDMA systems without a TDMA component, e.g. W-CDMA.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Air Interface Design by Transmitter Orientation and Receiver Orientation

transmission schemes are transmitter oriented, which means that the transmitter algorithms are a priori given, whereas the algorithms to be used at the receivers have to be a posteriori adapted under consideration of channel state information. In contrast to trans­mitter orientation, in receiver oriented systems the receiver algorithms are a priori given, and the transmitter algorithms, again under consideration of channel state information, have to be a posteriori adapted correspondingly. Recently, receiver oriented schemes have been proposed as promising approaches for mobile radio downlinks which utilize the duplexing scheme TDD. In such applications the rationale receiver orientation may offer the following advantages:

The a priori determined receiver algorithms can be chosen with a view to arrive at particularly simple receiver structures. In this way, as compared to transmitter oriented systems, complexity can be transferred from the MTs to the AP.

Channel information is only required at the AP. Therefore, no downlink transmission resources have to be sacrificed for training signals, and no channel estimators are required at the MTs.

The project has the focus to illuminate the basic commonalities and differences between the two rationales transmitter orientation and receiver orientation. Based on the gained results proposals for future air interfaces should be developed.


Source:www.eit.uni-kl.de/baier/Research/research.htm

Hypertext Semantics

How does the medium of hypertext, including both its forms and the practices, artifacts, and technologies which comprise it, dispose towards principles of organization and sequencing of information and meaning, in the medium itself as object-text, and in the traversal practices of the user, as meaning-text? What are the currently typical organizations of meaning and their interpretations by users? What are alternative strategies for meaning-development, both in authoring and in using hypertexts? How do existing and potential meaning organizations differ from those of more linear text media? How do the principles of intertextuality and co-text contextualization translate in the hypertext medium? What are the analogues of multivariate structural organization and co-variate textual-cohesive organization? How are text units constructed so as to facilitate construal of semantic ties between linked units?


Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Ecosocial Dynamics of Self-organizing System-Networks

How do the dynamics of ecosystems including human semiotic artifacts and practices differ systematically in their dynamic potential from simpler ecosystems lacking (or with only much simpler) semiotic bases for couplings among system-constitutive processes? How does the role of semiotic artifacts and semiotic-material practices in such systems break the separability of scales typical of dynamical systems without semiotic mediation? What are the general consequences of interpenetration and overlapping (i.e. dynamical interdependence) of processes at very different temporal and spatial scales for the analysis of human meaning systems, specific events, and the time-development and evolution of ecosocial systems and system-types?




Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Semiotics of Action

How are the actions that are conventional and meaningful in various typical activity contexts organized as a semiotic resource system? How do they make typological meaning by paradigmatic contrast? by syntagmatic catenation? How do they make topological meaning by their pacing, intensity, and other dimensions of gradable degree of performance? What principles are shared by the linguistic, depictional, gestural, and actional semiotic resources systems and their typical deployment practices and products?


Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Presentational, Orientational, and Organizational Meaning

How do ideational, world-representational (Presentational); social-interactional, attitudinal (Orientational); and cohesive, structural (Organizational) meaning dimensions of signs-in-use integrate with and mutual contextualize one another? How does this occur (ideally) within a single semiotic resources system (e.g. language, gesture, depiction) and (actually) among multiple co-deployed semiotic systems? What are the genre conventions in different situated-use activities for such relations?


Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Mathematics as a Semiotic Resource System

How is the relationship of mathematics to natural language most usefully characterized? How, historically, did mathematical registers of natural languages and mathematical symbolisms evolve and diverge from spoken and written verbal texts? What were the original functional specializations of mathematical registers and symbolic expressions? how were they integrated in use with verbal reasoning and exposition and with visual-graphical representations? What are the range of typical relations among these resources today, and what additional possibilities remain to be tried? What kinds of meanings are made better with mathematical registers and symbolic systems than with standard verbal language or graphical representations alone? What kinds of meanings and meaning dynamics are characteristic of the integrated combination of mathematics, verbal language, and graphical representations?


Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Typological and Topological Meaning

How are various systems of semiotic resources (e.g. language, depiction, gesture) specialized for the construction of category-contrastive, or typological, meanings vs. continuous-variation, or topological meanings? How does each system provide resources for each broad type of meaning? How are the typological and topological resources integrated in the (idealized) use of a single system, and in the (actual) use of multiple, integrated semiotic resource systems? How historically have meanings of each of these broad types influenced meanings of the other kind, and how have semiotic resource systems more specialized toward one been typically integrated with those more specialized toward the other? How are topological meanings typically coded by signs and signifying actions? what alternatives are available to the contrastive valeur-principle for typological semiosis?


Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Multimedia Semiotics

How do verbal, visual, auditory, and tactile-interactional semiotic resources combine and integrate in multimedia productions, systems, and events? How are these resource system co-evolved to integrate with one another? What are the historical traditions in various cultures by which they are conventionally linked or integrated? What kinds of differences in meaning-making typically occur for resources of each type in the context of co-deployment of resources of the other modalities? What possible cross-multiplications of meaning-potential among these systems have not yet been realized by existing or historical systems in various cultures? How can those which have been realized be usefully hybridized for various contemporary projects and agendas?


Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Computer-mediated Communication, Learning, and Education

Which combinations of the various modes of CMC are optimally supportive of learning for various kinds of people and various kinds of skills and knowledges (i.e. culturally recognized meaning-making practices and meaningful actions)? What are the relative learning and educational affordances of synchronous vs. asynchronous communication? of presentational vs. interactional modes? of densely interlinked hypertext vs. more linearly connected text? of nonverbal media in various forms of integration with verbal text? of static vs. animated images? of abstract vs. photorealistic images? of 2-dimensional vs. 3-dimensional forms? of fixed vs. mobile user apparent-viewpoint? of tactile force-feedback and full-presence virtual environments vs. passive-interactive and framed-view systems/experiences? What are the optimum combinations for various types of learners and mentors of face-to-face interaction, computer-mediated communication, and human-artifact-environment interaction without computational mediation? of passive-readable text, interactive text, peer communication, mentor communication, dyadic, and group social interaction?





Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm

Human-Computer Interaction: Interfaces and Ideologies

Functional interfaces between users and computational systems present specific affordances for human-meaningful, i.e. semiotic interactions between user and system. Various semiotic resources, from verbal signs to visual patterns to meaning-laden actions by users and responses by the system (including apparent initiations by the system), are designed to mediate between human cultural systems and meaningful behavior patterns on the one hand and the underlying computational programs and hardware on the other. Such interfaces are a genre of multimedia, polysemiotic texts, not unlike films or videogames. As such, they embody the ideological dispositions of their creators, who, historically, have been far less culturally diverse than the human population as a whole. How do widely used interfaces today, their metaphors and cultural assumptions, reflect specifically masculinist, middle-class, eurocultural attitudes and assumptions? How do, or would, interfaces designed from other cultural, gender/sexuality, and class positions differ, and with what effects on the potential of computational systems to aid the full range of human projects and agendas?



Source:academic.brooklyn.cuny.edu/education/jlemke/phd-tops.htm