فایل ورد کامل رادیو شناختگر: ارتباطات بی سیم قدرت مغزی

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تعداد صفحات این فایل: ۶۹ صفحه

پتانسیل رادیو شناختگر برای ایجاد نقطه عطف در زمینه ارتباطات بی سیم بسیار گسترده است از این روی می توان به آن یک فناوری مخرب اما محجوب گفت. در آنالیزهای نهایی مسئله کلیدی که شکل دهنده تغییرات تدریجی رادیو شناختگر در روند زمان است، به خصوص در زمینه عمرانی و نظامی، اعتماد است که دارای دو بعد می باشد(۸۱-۹۰):
• اعتماد توسط کاربران رادیو شناختگر
• اعتماد توسط همه کاربران دیگر که ممکن است درگیر رادیو شناختگر باشند.

عنوان انگلیسی:Cognitive Radio: Brain-Empowered Wireless Communications~~en~~

INTRODUCTION A. Background T HE electromagnetic radio spectrum is a natural resource, the use of which by transmitters and receivers is licensed by governments. In November 2002, the Federal Communications Commission (FCC) published a report prepared by the Spectrum-Policy Task Force, aimed at improving the way in which this precious resource is managed in the United States [1]. The task force was made up of a team of high-level, multidisciplinary professional FCC staff—economists, engineers, and attorneys—from across the commission’s bureaus and offices. Among the task force major findings and recommendations, the second finding on page 3 of the report is rather revealing in the context of spectrum utilization: Manuscript received February 1, 2004; revised June 4, 2004. The author is with Adaptive Systems Laboratory, McMaster University, Hamilton, ON L8S 4K1, Canada (e-mail: haykin@mcmaster.ca). Digital Object Identifier 10.1109/JSAC.2004.839380 “In many bands, spectrum access is a more signifi- cant problem than physical scarcity of spectrum, in large part due to legacy command-and-control regulation that limits the ability of potential spectrum users to obtain such access.” Indeed, if we were to scan portions of the radio spectrum including the revenue-rich urban areas, we would find that [2]–[۴]: ۱) some frequency bands in the spectrum are largely unoccupied most of the time; 2) some other frequency bands are only partially occupied; 3) the remaining frequency bands are heavily used. The underutilization of the electromagnetic spectrum leads us to think in terms of spectrum holes, for which we offer the following definition [2]: A spectrum hole is a band of frequencies assigned to a primary user, but, at a particular time and specific geographic location, the band is not being utilized by that user. Spectrum utilization can be improved significantly by making it possible for a secondary user (who is not being serviced) to access a spectrum hole unoccupied by the primary user at the right location and the time in question. Cognitive radio [5], [6], inclusive of software-defined radio, has been proposed as the means to promote the efficient use of the spectrum by exploiting the existence of spectrum holes. But, first and foremost, what do we mean by cognitive radio Before responding to this question, it is in order that we address the meaning of the related term “cognition.” According to the Encyclopedia of Computer Science [7], we have a three-point computational view of cognition. 1) Mental states and processes intervene between input stimuli and output responses. 2) The mental states and processes are described by algorithms. 3) The mental states and processes lend themselves to scientific investigations. Moreover, we may infer from Pfeifer and Scheier [8] that the interdisciplinary study of cognition is concerned with exploring general principles of intelligence through a synthetic methodology termed learning by understanding. Putting these ideas together and bearing in mind that cognitive radio is aimed at improved utilization of the radio spectrum, we offer the following definition for cognitive radio. Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e., outside 0733-8716/$20.00 © ۲۰۰۵ IEEE 202 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 23, NO. 2, FEBRUARY 2005 world), and uses the methodology of understanding-by-building to learn from the environment and adapt its internal states to statistical variations in the incoming RF stimuli by making corresponding changes in certain operating parameters (e.g., transmit-power, carrier-frequency, and modulation strategy) in real-time, with two primary objectives in mind: • highly reliable communications whenever and wherever needed; • efficient utilization of the radio spectrum. Six key words stand out in this definition: awareness,1 intelligence, learning, adaptivity, reliability, and efficiency. Implementation of this far-reaching combination of capabilities is indeed feasible today, thanks to the spectacular advances in digital signal processing, networking, machine learning, computer software, and computer hardware. In addition to the cognitive capabilities just mentioned, a cognitive radio is also endowed with reconfigurability.2 This latter capability is provided by a platform known as software-defined radio, upon which a cognitive radio is built. Software-defined radio (SDR) is a practical reality today, thanks to the convergence of two key technologies: digital radio, and computer software [11]–[۱۳].

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