Clemens Kloeck

Occupation Measurements Supporting Dynamic Spectrum Allocation for Cognitive Radio Design

Efficient use of radio spectrum is a necessity for future wireless systems. This can, for example, be accomplished by cognitive radios. An important point for designing future systems is to gain knowledge about the occupation of the frequency bands which may be used by the cognitive radio. This includes the general characterization of the traffic density at the frequency bands as well as a detailed analysis of the temporal frequency occupation. Thus, this paper describes measurements taken in the GSM network at three different scenarios. Furthermore, a detailed analysis of the measurement results is presented including statistical as well as spectral occupation analysis.

Bio-inspired algorithms for dynamic resource allocation in cognitive wireless networks

Regulation will experience enormous changes in the near future resulting in seamless connectivity by spectrum borders. A promising approach in this context is dynamic spectrum allocation which leads to a more flexible access to spectral resources by employing intelligent radio devices called cognitive radios. This paper is concerned with bio-inspired approaches that exploit distribution in multi-radio environments where many users have to share a finite resource harmoniously. Three applications of bio-inspired techniques are described. The first one deals with the detection of spectrum holes whereas the second one describes resource allocation in orthogonal frequency division multiple access based systems. The third one is concerned with distributed resource auctioning.

Multi-agent radio resource allocation

This paper presents a spatially distributed and dynamic billing, pricing and allocation mechanism for which a user terminal requires Cognitive Radio abilities. That is, the Cognitive Radio abilities will be applied to the economical environment. The radio resource goods are allocated to the users by a multi-unit sealed-bid auction. Intelligent entities like the bidding strategy have to represent operator’s and users’ behavior and to make decisions for them in order to fulfill the preferences and QoS. The main functionalities, used to execute the dynamic auction sequence and located in the MAC are described, assuming the entities possess Cognitive Radio abilities.

A Cognitive Approach to the Detection of Spectrum Holes in Wireless Networks

The experience of ubiquitous and seamless ac- cess to heterogeneous mobile communication networks is one of the core issues of todays research. This comes along with an increasing demand in bandwidth. However, bandwidth as a natural resource is limited by technical constraints and, as several measurements have shown, is currently used very in- efficiently due to a static allocation. Consequently, we have to consider spectrum allocation techniques and employ use- ful applications for the detection of vacant frequency bands. In this paper, we present a novel, swarm-behavior based ap- proach for the detection of spectrum holes in cognitive wire- less networks. It is based on the fact that several cogni- tive radios form a cognitive network. This network is then split up into several cognitive sub-networks that collaborate among each other and scan the frequency range simultane- ously. Thus, several vacant frequency bands can be found and the overall processing time can be reduced. In addition, fading effects due to multi-path propagation can be met in a more efficient way.

Bio-Inspired Algorithms for Dynamic Resource Allocation in Cognitive Wireless Networks

Regulation will experience enormous changes in the near future resulting in seamless connectivity by bluring spectrum borders. A promising approach in this context is dynamic spectrum allocation which leads to a more flexible access to spectral resources by employing intelligent radio devices called cognitive radios. This paper is concerned with bio-inspired approaches that exploit distribution in multi-radio environments where many users have to share a finite resource harmoniously. Three applications of bio-inspired techniques are described. The first one deals with the detection of spectrum holes and the second one describes resource allocation in orthogonal frequency division multiple access based systems. The third one is concerned with distributed resource auctioning.

General expression of outage probability in cooperative networks

A general expression of outage probability in a wireless relay network with an arbitrary number of relays and selection combining at the destination is derived. This formula is then adopted to independent but not identically distributed channel coefficients and lower and upper bounds are developed. We study two relay schemes: the one-relay case and the two-relay case. The latter can further be divided into a two-phase and a three-phase transmission scheme which depend on the cooperation among the relays. For all considered cases, outage probabilities in Rayleigh fading environments are derived and analysed and it is demonstrated by numerical simulations that all relay protocols achieve full order of diversity. We further elaborate the impact of relay locations on outage probability. Finally, we discuss the required signal-to-noise ratio in order to achieve a predefined outage probability. With respect to the mentioned evaluation metrics the two-phase relaying scheme achieves by far the best performance, however, with the drawback of increased receiver complexity. Copyright

Opportunistic WiMAX-GSM coexistence

In future multi-media applications dynamic access to spectral resources will play an important role. However, regulation of spectrum will only change very slowly and spectrum rights holders might not be willing to share their resources without gaining something out of it. Therefore the authors analyse the suitability of WiMAX as an overlay system on GSM where available resources will be auctioned among several competitors. The authors design a cross-layer approach to facilitate dynamic resource allocation. It is demonstrated that, with minor changes of the original WiMAX frame and a small signalling overhead which is currently unused, GSM resources can be allocated efficiently without decreasing system performance. Thus, this adapted WiMAX system used in opportunistic coexistence to GSM offers a suitable alternative to broadband service access.

Adaptive resource management platform for reconfigurable networks

Users’ expectations towards technology, in terms of quality, service availability and accessibility are ever increasing. Aligned with this, the wireless world is rapidly moving towards the next generation of systems, featuring cooperating and reconfiguring capabilities for coexisting (and upcoming) Radio Access Technologies (RATs), so that to improve connectivity and reduce costs. In this respect, conventional planning and management techniques ought to be replaced by advanced schemes that consider multidimensional characteristics, increased complexity and high speeds. To this effect, means are needed capable to support scalability and to cater for advanced service features, provided to users at high rates and cost-effectively. This article provides a scheme to optimize resource management in future systems, by describing a platform that accommodates engineering mechanisms that deal with dynamic, demand driven planning and managing of spectrum and radio resources in reconfigurable networks. To do so, it first discusses the fundamentals and the approach followed in the proposed architecture and then investigates the basic functional modules. The architecture is validated through a set of use-cases that exemplify the operational applicability and efficiency in a wide range of communication scenarios.

Cooperative Communications in Wireless Networks - A Requested Relaying Protocol

In this paper we present a requested relaying protocol that helps mitigating multipath and shadowing effects in wireless networks. In our approach it is assumed that the destined mobile station has not been able to receive information from the base station and sends a request to surrounding terminals. Those terminals able to receive the request act as relays and help to transmit information from the base station to the destination. Performance analysis with respect to probability of decoding error and outage probability have been made with the results that both can be enormously improved by exploiting diversity. Additionally, order of diversity is defined and applied to our relaying approach as well.

Multi-level spectrum auction through radio access

This paper describes the resource exchange between all important interfaces of a communication system using an auction sequence. Differences between the different mechanisms are shown and implementation concepts are presented