Tobias Renk

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.

A Cognitive Radio Receiver Supporting Wide-Band Sensing

IEEE 802.22 defines the world-wide first cognitive radio (CR) standard. In the range between 41 MHz and 910 MHz CR overlay-systems can be installed besides licensed radio services such as radio and TV broadcasting. In order to fulfill the regulative guidelines for interference limitations, adequate spectral sensing and user detection has to be supported by the CR terminals. The wide frequency range specified in IEEE 802.22 and the high dynamic range of signals in this band lead to high demands on the CR receivers front-end. Especially the performance requirements on analog-to-digital converters (ADCs) increase significantly compared to current wireless systems. Based on measurements taken in the frequency range between 41 MHz and 910 MHz requirements to CRs ADCs are figured out. Furthermore, the measurement results are analyzed regarding expectable allocation scenarios and their impacts on spectral sensing. Derived from these results and a comparison of general spectral sensing mechanisms, an approach for a CR receiver enabling wide-band sensing is presented. By combining a-priori information resulting from scenario analysis with adapted information processing in the CR terminal, the ADCs performance requirements can be reduced.

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.

Development of a Radio Enabler for Reconfiguration Management within the IEEE P1900.4 Working Group

An important emerging capability is for mobile terminals to be dynamically reconfigured. Through ongoing advances in technology such as software defined radio, reconfiguration of mobile terminals will in the near future be achievable across all layers of the protocol stack. However, along with the capability for such wide-ranging reconfiguration comes the need to manage reconfiguration procedures. This is necessary to coordinate reconfigurations, to ensure that there are no negative effects (e.g. interference to other RATs) as a result of reconfigurations, and to leverage maximal potential benefits of reconfiguration and ensuing technologies such as those involving dynamic spectrum access. The IEEE P1900.4 working group is therefore defining three building blocks for reconfiguration management: network reconfiguration management (NRM), terminal reconfiguration management (TRM), and a radio enabler to provide connectivity between the NRM and TRMs. In this paper we concentrate on aspects of the radio enabler, highlighting its relevance in heterogeneous radio access scenarios, its advantages, and some aspects of its technical realization.

Outage Capacity of Incremental Relaying at Low Signal-to-Noise Ratios

We present the � -outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the � -outage capacity. It is shown that this location is independent of the outage probability and SNR but only depends on the channel conditions represented by a path-loss factor. We compare our results to the � -outage capacity of the cut-set bound and demonstrate that the ratio between the � -outage capacity of incremental relaying and the cut-set bound lies within 1/ √ 2 and 1. Furthermore, we derive lower bounds on the � -outage capacity for the case of K relays.

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.

Smart femto-cell controller based distributed cognitive pilot channel

This paper presents an extension of the Cognitive Pilot Channel (CPC) concept to the case of a distributed version thereof (namely, DCPC), and demonstrates a potential instantiation of this concept in the design of Smart Femto-Cell Controllers (SFC-C) for handling the management of co-existing homogeneous or heterogeneous networks. Instead of covering the various networks by a single CPC, the novel idea consists in deploying the CPC transmission in a distributed way within each of the individual Smart Femto Cell (SFC) controlled Composite Networks (CNs), an example of which can be a heterogeneous home or business deployment including the collection of a Femto- Cell Base Station (FC-BS), a Wireless LAN (WLAN) Access Point (AP), a ZigBee network controller, a Bluetooth network controller, etc. A typical implementation of this concept leads to an integration of the DCPC transmitter into a SFC which consists of the FC-BS for provision of cellular access and the SFC-C for network management and DCPC provision. In this case, the SFC owner is able to manage the attached composite network by providing suitable context and policy information within the DCPC. The paper furthermore introduces intra-network and inter-network interference scenarios and explains how the DCPC concept allows the introduction of corresponding interference management mechanisms.

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.