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Author

F.F. Digham

Other affiliations: Mitsubishi, Mitsubishi Electric
Bio: F.F. Digham is an academic researcher from University of Minnesota. The author has contributed to research in topics: Fading & Bit error rate. The author has an hindex of 11, co-authored 43 publications receiving 3833 citations. Previous affiliations of F.F. Digham include Mitsubishi & Mitsubishi Electric.

Papers
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Journal ArticleDOI
TL;DR: This letter addresses the problem of energy detection of an unknown signal over a multipath channel with the no-diversity case, and presents some alternative closed-form expressions for the probability of detection to those recently reported in the literature.
Abstract: This letter addresses the problem of energy detection of an unknown signal over a multipath channel. It starts with the no-diversity case, and presents some alternative closed-form expressions for the probability of detection to those recently reported in the literature. Detection capability is boosted by implementing both square-law combining and square-law selection diversity schemes

2,610 citations

Proceedings ArticleDOI
11 May 2003
TL;DR: It is shown that there is not much improvement in the probabilities of detection when either the probability of false alarm (P/sub f/) exceeds 0/1 or the average signal-to-noise ratio (SNR) exceeds 20 dB.
Abstract: This paper presents another look at the problem of energy detection of unknown signals over different fading channels. We start with the no diversity case and present some alternative closed-form expressions for the probability of detection (P/sub d/) to those recently reported in [V.I. Kostylev, May 2002]. We then investigate the system performance when different diversity schemes are employed. It is shown that there is not much improvement in the probability of detection when either the probability of false alarm (P/sub f/) exceeds 0/1 or the average signal-to-noise ratio (SNR) exceeds 20 dB. In addition, receiver operating characteristic (ROC) curves comparing the performance of equal-gain combining (EGC), selection combining (SC), and switch and stay combining (SSC) are presented. As an example, EGC introduces a gain of two orders of magnitude from the probability of miss perspective compared to the no diversity case while both SC and SSC introduce a gain of about one order of magnitude.

766 citations

Proceedings ArticleDOI
15 Apr 2008
TL;DR: A near-optimal yet simple algorithm with linear complexity targeting capacity maximization of a cognitive radio network while jointly optimizing power and channel allocation among users (cognitive radios) while respecting total power constraints per individual users is devised.
Abstract: Spectrum scarcity is the major challenge facing all parties working in the telecommunications industry. As recently shown, the main problem of spectrum unavailability is due to spectrum inefficient utilization rather than spectrum scarcity. Inspired by this argument, a paradigm shift in spectrum management is achieved by the aid of smart radios called cognitive radios that can opportunistically access the available spectrum. In this context, we address the problems of power control and channel assignment jointly. Namely, given a set of available channels which is determined dynamically, we devise a near-optimal yet simple algorithm with linear complexity targeting capacity maximization of a cognitive radio network while jointly optimizing power and channel allocation among users (cognitive radios) while respecting total power constraints per individual users. In an extended version, we also consider a conservative design where signal-to-interference-plus-noise ratio (SINR) constraints at the primary users have are imposed. Simulated experiments illustrate the near optimal performance of the devised algorithm compared to the exhaustive search approach. Moreover, the limits of the system capacity are quantified given both ideal (no SINR constraints) and conservative (with SINR constraints) designs.

123 citations

Proceedings ArticleDOI
01 Jan 2003
Abstract: This paper investigates a variable-rate variable-power hybrid non-coherent M-FSK M-QAM system. The goal is to combine the spectral efficiency merit of M-QAM with the power efficiency advantage of M-FSK and as such extend the region of availability even at very low channel gain values. A basic system is first designed to maximize the average spectral efficiency while meeting average power and target bit error rate constraints. In addition, a peak power constraint is imposed in a more general system. The optimization procedure leads to optimum rate and power loading functions which are compared for the different modes of operation.

98 citations

Journal ArticleDOI
TL;DR: Along with optimal bit and power loading schemes, quantizer designs and reduced complexity alternatives with low feedback overhead are developed to obtain a suite of Q-CSIT-based OFDM transceivers with desirable complexity versus power-consumption tradeoffs.
Abstract: Emerging applications involving low-cost wireless sensor networks motivate well optimization of orthogonal frequency-division multiplexing (OFDM) in the power-limited regime. To this end, the present paper develops loading algorithms to minimize transmit-power under rate and error probability constraints, using three types of channel state information at the transmitter (CSIT): deterministic (per channel realization) for slow fading links, statistical (channel mean) for fast fading links, and quantized (Q), whereby a limited number of bits are fed back from the transmitter to the receiver. Along with optimal bit and power loading schemes, quantizer designs and reduced complexity alternatives with low feedback overhead are developed to obtain a suite of Q-CSIT-based OFDM transceivers with desirable complexity versus power-consumption tradeoffs. Numerical examples corroborate the analytical claims and reveal that significant power savings result even with a few bits of Q-CSIT

58 citations


Cited by
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Journal ArticleDOI
TL;DR: The novel functionalities and current research challenges of the xG networks are explained in detail, and a brief overview of the cognitive radio technology is provided and the xg network architecture is introduced.

6,608 citations

Journal ArticleDOI
TL;DR: In this paper, a survey of spectrum sensing methodologies for cognitive radio is presented and the cooperative sensing concept and its various forms are explained.
Abstract: The spectrum sensing problem has gained new aspects with cognitive radio and opportunistic spectrum access concepts. It is one of the most challenging issues in cognitive radio systems. In this paper, a survey of spectrum sensing methodologies for cognitive radio is presented. Various aspects of spectrum sensing problem are studied from a cognitive radio perspective and multi-dimensional spectrum sensing concept is introduced. Challenges associated with spectrum sensing are given and enabling spectrum sensing methods are reviewed. The paper explains the cooperative sensing concept and its various forms. External sensing algorithms and other alternative sensing methods are discussed. Furthermore, statistical modeling of network traffic and utilization of these models for prediction of primary user behavior is studied. Finally, sensing features of some current wireless standards are given.

4,812 citations

Journal ArticleDOI
TL;DR: This letter addresses the problem of energy detection of an unknown signal over a multipath channel with the no-diversity case, and presents some alternative closed-form expressions for the probability of detection to those recently reported in the literature.
Abstract: This letter addresses the problem of energy detection of an unknown signal over a multipath channel. It starts with the no-diversity case, and presents some alternative closed-form expressions for the probability of detection to those recently reported in the literature. Detection capability is boosted by implementing both square-law combining and square-law selection diversity schemes

2,610 citations

Proceedings ArticleDOI
05 Dec 2005
TL;DR: This paper studies spectrum-sharing between a primary licensee and a group of secondary users and suggests that collaboration may improve sensing performance significantly.
Abstract: Traditionally, frequency spectrum is licensed to users by government agencies in a fixed manner where licensee has exclusive right to access the allocated band. This policy has been de jure practice to protect systems from mutual interference for many years. However, with increasing demand for the spectrum and scarcity of vacant bands, a spectrum policy reform seems inevitable. Meanwhile, recent measurements suggest the possibility of sharing spectrum among different parties subject to interference-protection constraints. In this paper we study spectrum-sharing between a primary licensee and a group of secondary users. In order to enable access to unused licensed spectrum, a secondary user has to monitor licensed bands and opportunistically transmit whenever no primary signal is detected. However, detection is compromised when a user experiences shadowing or fading effects. In such cases, user cannot distinguish between an unused band and a deep fade. Collaborative spectrum sensing is proposed and studied in this paper as a means to combat such effects. Our analysis and simulation results suggest that collaboration may improve sensing performance significantly

1,939 citations

Journal ArticleDOI
TL;DR: The state-of-the-art survey of cooperative sensing is provided to address the issues of cooperation method, cooperative gain, and cooperation overhead.

1,800 citations