Alexander M. Wyglinski

Cognitive radio communications and networks : principles and practice

Cognitive Radio Communications and Networks gives comprehensive and balanced coverage of the principles of cognitive radio communications, cognitive networks, and details of their implementation, including the latest developments in the standards and spectrum policy. Case studies, end-of-chapter questions, and descriptions of various platforms and test beds, together with sample code, give hands-on knowledge of how cognitive radio systems can be implemented in practice. Extensive treatment is given to several standards, including IEEE 802.22 for TV White Spaces and IEEE SCC41. Written by leading people in the field, both at universities and major industrial research laboratories, this tutorial text gives communications engineers, R&D engineers, researchers, undergraduate and post graduate students a complete reference on the application of wireless communications and network theory for the design and implementation of cognitive radio systems and networks

Bit loading with BER-constraint for multicarrier systems

We present discrete adaptive bit loading algorithms for multicarrier systems with uniform (nonadaptive) power allocation operating in a frequency selective fading environment. The algorithms try to maximize the overall throughput of the system while guaranteeing that the mean bit error rate (BER) remains below a prescribed threshold. We also study the impact of imperfect subcarrier signal-to-noise ratio information on throughput performance. Results show that the proposed algorithms have approximately the same throughput and mean BER as the optimal allocation while having a significantly lower computational complexity relative to other algorithms with near-optimal allocations. Moreover, when compared with algorithms that employ approximations to water filling, the computational complexity is comparable while the overall throughput is closer to the optimum.

KUAR: A Flexible Software-Defined Radio Development Platform

In this paper, we present the details of a portable, powerful, and flexible software-defined radio development platform called the Kansas University Agile Radio (KUAR). The primary purpose of the KUAR is to enable advanced research in the areas of wireless radio networks, dynamic spectrum access, and cognitive radios. The KUAR hardware implementation and software architecture are discussed in detail. Radio configurations and applications are presented. Future research made possible by this flexible platform is also discussed.

Sidelobe Suppression for OFDM-Based Cognitive Radios Using Constellation Expansion

In this paper, we present a novel algorithm for reducing sidelobe interference power levels in OFDM-based cognitive radios. Existing techniques for sidelobe suppression can be computationally intensive when determining the complex-valued amplitude levels for the cancellation subcarriers. Exploiting the fact that different sequences have different sidelobe power levels, the proposed algorithm employs a constellation expansion-based iterative approach in order to suppress the sidelobe power levels. An important advantage of the proposed technique is that, no side information needs to be transmitted. Simulation results show that the proposed algorithm can be employed in a wide range of operating conditions at the cost of a slight increase in the bit error rate and the peak-to-average power ratio characteristics.

A framework for statistical wireless spectrum occupancy modeling

In this paper, we propose a novel spectrum occupancy model designed to generate accurate temporal and frequency behavior of various wireless transmissions. Our proposed work builds upon existing concepts in open literature in order to develop a more accurate time-varying spectrum occupancy model. This model can be employed by wireless researchers for evaluating new wireless communication and networking algorithms and techniques designed to perform dynamic spectrum access (DSA). Using statistical characteristics extracted from actual radio frequency measurements, first- and second-order parameters are employed in a statistical spectrum occupancy model based on a combination of several different probability density functions (PDFs) defining various features of a specific spectrum band with several concurrent transmissions. To assess the accuracy of the model, the output characteristics of the proposed spectrum occupancy model are compared with realtime radio frequency measurements in the television and paging bands.

Parametric Adaptive Spectrum Sensing Framework for Dynamic Spectrum Access Networks

The opportunistic usage of the spectrum must be done without causing any interference to the licensed spectrum users. Conventional non-adaptive wideband spectrum sensing approaches could potentially be inefficient since they generally employ the same scanning resolution, even though the spectrum might contain different types of signals, individually requiring scans with different resolutions. In this paper, we present a novel spectrum sensing framework that adapts its parameters across the spectrum of interest according to the characteristics of its occupancy. We also propose a dynamic scheduling algorithm for spectrum sensing which allocates different time resolutions to different portions of the spectrum. We demonstrate that the proposed algorithm improves the efficiency of spectrum sensing over a non-adaptive approach.

A Spectrum Surveying Framework for Dynamic Spectrum Access Networks

Dynamic spectrum access networks and wireless spectrum policy reforms heavily rely on accurate spectrum utilization statistics, which are obtained via spectrum surveys. In this paper, we propose a generic spectrum-surveying framework that introduces both standardization and automation to this process, as well as enables a distributed approach to spectrum surveying. The proposed framework outlines procedures for the collection, analysis, and modeling of spectrum measurements. Furthermore, we propose two techniques for processing spectrum data without the need for a priori knowledge. In addition, these techniques overcome the challenges associated with spectrum data processing, such as a large dynamic range of signals and the variation of the signal-to-noise ratio across the spectrum. Finally, we present mathematical tools for the analysis and extraction of important spectrum occupancy parameters. The proposed processing techniques have been validated using empirical spectrum measurements collected from the FM, television (TV), cellular, and paging bands. Results show that the primary signals in the FM band can be classified with a miss-detection rate of about 2% at the cost of 50% false-alarm rate, while nearly 100% reliability in classification can be achieved with the other bands. However, the classification accuracy depends on the duration and the range of frequencies over which data are collected, as well as the RF characteristics of the spectrum measurement receiver.

Effects of Bit Allocation on Non-Contiguous Multicarrier-Based Cognitive Radio Transceivers

In this paper, we evaluate a cognitive radio transceiver employing both non-contiguous multicarrier modulation (NC-MCM) and adaptive bit allocation. Although NC-MCM and bit allocation have potential benefits with respect to enabling dynamic spectrum access (DSA) and increasing throughput, they also require the transmission of overhead information between the transmitter and the receiver. To reduce this overhead information, operating parameters can be assigned to a block of subcarriers, at the cost of some throughput. The trade-offs between subcarrier block size and two different bit allocation approaches for several DSA scenarios are assessed in this work. The results show that as percentage of available spectrum decreases, the throughput loss of systems employing larger subcarrier block sizes rapidly increases. Nevertheless, larger block sizes also yield greater reductions in transmission overhead.

Characterization of vacant UHF TV channels for vehicular dynamic spectrum access

In this paper, we present quantitative and qualitative results obtained as a result of a TV spectrum measurement campaign. We used these measurements to characterize vacant TV channels a along major interstate highway (I-90) in the state of Massachusetts, USA. By characterizing the availability of vacant TV channels in the 470–806 MHz frequency range, we show the trends in the availability of vacant channels from a vehicular dynamic spectrum access perspective. We also describe the design constraints imposed on a point-to-multipoint communications based architecture in such a setting. Specifically, we described a general geo-location database approach to create a spectral map of available channels in a given geographical area. We presented the results obtained by applying such a technique in the state of MA over several locations on I-90. Furthermore, we presented a discussion on the implications of the non-contiguous channel availability in the TV spectrum on the design of a cognitive radio transceiver from the perspective of vehicular communications. In our future work, we will be presenting a comparative study of the channel availability in the above mentioned geographical area before and after the switch-over carried out on June 12, 2009.

Quantitative Comparison of Agile Modulation Techniques for Cognitive Radio Transceivers

In this paper, we present a quantitative comparison of two agile modulation techniques employed by cognitive radio transceivers operating in a dynamic spectrum access (DSA) network. One of the modulation technique is non-contiguous orthogonal frequency division multiplexing (NC-OFDM), which is designed to avoid interference with the transmissions of incumbent users by deactivating subcarriers within their vicinity. The other modulation technique under study is a variant of multicarrier code division multiple access (MC-CDMA). Although several studies comparing conventional OFDM and MC-CDMA has been conducted in literature to justify robust error performance of MCCDMA, a quantitative performance evaluation of these schemes has not been performed when employed in a DSA network. Due to deactivated subcarriers in DSA networks, in this paper we showed their performance can be significantly different from the conventional setup. Analytical expressions for the error probability of an NC-OFDM transceiver have been derived and compared with computer simulation results. The results show that the error robustness of NC-OFDM is relatively constant regardless of the number of deactivated subcarriers, unlike MC-CDMA transmissions, whose error performance degrades with an increase in deactivated subcarriers.