The radio frequency spectrum is a scarce natural resource and its efficient use is of the utmost importance. The spectrum bands are usually licensed to certain services, such as mobile, fixed, broadcast, and satellite, to avoid harmful interference between different networks to affect users. Most spectrum bands are allocated to certain services but worldwide spectrum occupancy measurements show that only portions of the spectrum band are fully used. Moreover, there are large temporal and spatial variations in the spectrum occupancy. In the development of future wireless systems the spectrum utilization functionalities will play a key role due to the scarcity of unallocated spectrum. Moreover, the trend in wireless communication systems is going from fully centralized systems into the direction of self organizing systems where individual nodes can instantaneously establish ad hoc networks whose structure is changing over time. Cognitive radios, with the capabilities to sense the operating environment, learn and adapt in real time according to environment creating a form of mesh network, are seen as a promising technology. Cognitive radio is a new technology that allows spectrum to be dynamically shared between users.

Cognitive radio

We investigate the effects of multi-user diversity in a spectrum sharing system where secondary users restrictively utilize a spectrum licensed to primary users only if interference perceived at primary users is regulated below a predetermined level. This interference regulation affects the characteristics of multiuser diversity gains previously known in non-spectrum sharing systems. Our numerical and analytical results show that the multiuser diversity gain in a spectrum sharing system increases differently according to conditions given by the transmit power of secondary users, P, and a predetermined interference temperature, Q - if P is sufficiently larger than Q, the multiuser diversity gain in terms of capacity scales like log2 (W (Ns)) similarly to a previously known scaling law in the non-spectrum sharing systems, where W(middot) and Ns denote a Lambert W function and the number of secondary transmitters, respectively. However, the scaling law of multiuser diversity gain becomes log2(Ns) as P becomes sufficiently larger such that P Gt QNs.

/pdf/multi-user-diversity-in-a-spectrum-sharing-system-5gmv0oblgj.pdf

Multi-user diversity in a spectrum sharing system

Software Defined Radio (SDR) may provide flexible, upgradeable and longer lifetime radio equipment for the military and for civilian wireless communications infrastructure. SDR may also provide more flexible and possibly cheaper multi-standard-terminals for end users. It is also important as a convenient base technology for the future context-sensitive, adaptive and learning radio units referred to as cognitive radios. SDR also poses many challenges, however, some of them causing SDR to evolve slower than otherwise anticipated. Transceiver development challenges include size, weight and power issues such as the required computing capacity, but also SW architectural challenges such as waveform application portability. SDR has demanding implications for regulators, security organizations and business developers.

Software Defined Radio: Challenges and Opportunities

Opportunistic unlicensed access to the (temporarily) unused frequency bands across the licensed radio spectrum is currently being investigated as a means to mitigate the spectrum scarcity. Such opportunistic access calls for the implementation of safeguards so that the ongoing licensed operations are not interfered with. Among different candidates, sensing-based access, where the secondary (unlicensed) users transmit if they sense the primary (licensed) band to be free, is particularly appealing due to its low deployment cost and its compatibility with legacy primary systems. Incorporating spectral awareness functionality into the radio transceivers is a major step towards the realization of the cognitive radios. In this paper performance of spectrum-sensing cognitive radios is studied under channel fading. In particular, it is shown that due to the uncertainty resulting from fading, local signal processing alone may be inadequate to meet the performance requirements. To remedy this issue, cooperation among secondary users is proposed and studied in this paper. Moreover, we characterize and study a tradeoff between local processing and cooperation, which should be balanced in order to maximize the spectrum utilization. Copyright © 2007 John Wiley & Sons, Ltd.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/wcm.479

Spectrum sensing in cognitive radio networks: the cooperation-processing tradeoff

https://www.inets.rwth-aachen.de/fileadmin/templates/images/PublicationPdfs/2009/Wellens-etal_SpectrumModels_ElsevierPhyCom2009.pdf

Full length article: Empirical time and frequency domain models of spectrum use

This book gives a thorough knowledge of cognitive radio concepts, principles, standards, spectrum policy issues and product implementation details. In addition to 16 chapters covering all the basics of cognitive radio, this new edition has eight brand-new chapters covering cognitive radio in multiple antenna systems, policy language and policy engine, spectrum sensing, rendezvous techniques, spectrum consumption models, protocols for adaptation, cognitive networking, and information on the latest standards, making it an indispensable resource for the RF and wireless engineer. The new edition of this cutting edge reference, which gives a thorough knowledge of principles, implementation details, standards, policy issues in one volume, enables the RF and wireless engineer to master and apply today's cognitive radio technologies. Bruce Fette, PhD, is Chief Scientist in the Communications Networking Division of General Dynamics C4 Systems in Scottsdale, AZ. He worked with the Software Defined Radio (SDR) Forum from its inception, currently performing the role of Technical Chair, and is a panelist for the IEEE Conference on Acoustics Speech and Signal Processing Industrial Technology Track. He currently heads the General Dynamics Signal Processing Center of Excellence in the Communication Networks Division. Dr. Fette has 36 patents and has been awarded the "Distinguished Innovator Award". It features: foreword and a chapter contribution by Joe Mitola, the creator of the field; discussion of cognitive aids to the user, spectrum owner, network operator; explanation of capabilities such as time - position awareness, speech and language awareness, multi-objective radio and network optimization, and supporting database infrastructure; detailed information on product implementation to aid product developers; thorough descriptions of each cognitive radio component technology provided by leaders of their respective fields, and the latest in high performance analysis - implementation techniques; explanations of the complex architecture and terminology of the current standards activities; and discussions of market opportunities created by cognitive radio technology.

Bruce A. Fette

Papers

Cognitive Radio Technology