#16 1 Cognitive Radio Communications for Dynamic Spectrum Access Slides based on set provided by Alexander M. Wyglinski Research Assistant Professor ITTC The University of Kansas This work was generously supported by the National Science Foundation (NSF), via grants ANI-0230786 and ANI-0335272, and both the Defense Advanced Research Projects Agency (DARPA) and the Department of the Interior National Business Center, via grant NBCHC050166 #16 2 Outline • Motivation • What are Cognitive Radios? • How are they “cognitive”? • Agile Transmission • Kansas University Agile Radio (KUAR) • Conclusion
25
Embed
Cognitive Radio Communications for Dynamic Spectrum Accessfrost/Access_Technologies_Course/... · Cognitive Radio Communications for Dynamic Spectrum Access Slides based on set provided
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
#16 1
Cognitive Radio Communications for Dynamic
Spectrum AccessSlides based on set provided by
Alexander M. WyglinskiResearch Assistant Professor
ITTCThe University of Kansas
This work was generously supported by the National Science Foundation (NSF), via grants ANI-0230786 and ANI-0335272, and both the Defense Advanced Research Projects Agency
(DARPA) and the Department of the Interior National Business Center, via grant NBCHC050166
#16 2
Outline
• Motivation• What are Cognitive Radios?• How are they “cognitive”?• Agile Transmission• Kansas University Agile Radio (KUAR)• Conclusion
#16 3
Presentation Overview
• Motivation• What are Cognitive Radios?• How are they “cognitive”?• Agile Transmission• Kansas University Agile Radio (KUAR)• Conclusion
#16 4
Current Spectrum Allocation
FCC frequency allocations for US radio spectrum
Command-and-control regulation
#16 5
Increasing Demand
• Rapid growth in the wireless communications sector, requiring more spectral bandwidth– Increasing number of users– Plethora of new wireless services being offered
• Some applications are bandwidth-intensive
• As a result of this demand, available spectrum under the legacy command-and-control regime is becoming increasingly scarce– Number of licensed transmissions are increasing within a
finite allocated bandwidth– Unlicensed users constrained to a few overloaded bands
#16 6
Increasing Demand
Source: CTIA
200 Million Subscribers!
#16 7
Increasing Demand
Source: CTIA
1.4 Trillion Minutes!
#16 8
Apparent Scarcity• Measurement studies have shown that in both the
time and frequency domains that spectrum is underutilized
Spectrum measurement across the 900 kHz –1 GHz band (Lawrence, KS, USA)
Spectrum Holes
White Space:just ambient noise
Black Space:occupied byhigh-power users
Grey Space:partially occupied
#16 9
Potential Solution
Spectrum measurement across the 900 kHz –1 GHz band (Lawrence, KS, USA)
• Dynamic Spectrum Access (DSA)
Fill with secondary
users
#16 10
But not in my spectrum!• Incumbent license holders are very concerned about co-existing
transmissions from unlicensed users– Large-scale investments in developing communication
infrastructure around spectrum• Maintain quality-of-service to its paying customers
– Unlicensed users providing competing services (e.g., VoIP) but without the large-scale investment
– Transmissions are a time-varying phenomena … a signal not interfering at one point in time may do so at another
– Consider all the adaptive mechanisms in:• HSDPA/HSUPA• EV-DO• IEEE 802.16
• Trust– Validation that cognitive radios provide real benefits– Confidence that cognitive radios will not interfere with legacy
users
#16 11
Example
• Conclusion: Wireless equipment designed for DSA communications must be rapidly reconfigurable and spectrum-aware
#16 12
Presentation Overview
• Motivation• What are Cognitive Radios?• How are they “cognitive”?• Agile Transmission• Kansas University Agile Radio (KUAR)• Conclusion
#16 13
Software-Defined Radios
• Rapid evolution of microelectronics over the past several decades
• Wireless transceivers are becoming more versatile, powerful, and portable
• These advancements have given rise to Software-Defined Radio (SDR) technology– Baseband radio functions can be entirely
implemented in digital logic and software
• SDR’s are a prerequisite for Cognitive Radio
#16 14
Software-Defined Radios
Radio functions performed in the software domain
#16 15
What is a Cognitive Radio?
“Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e., outside 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;
• An intelligent wireless communications system• Based on SDR technology
– Reconfigurable– Agile Functionality
• Aware of its environment– RF spectrum occupancy– Network traffic– Transmission quality
• Learns from its environment and adapts to new scenarios based onprevious experiences
• Access techniques are – Distributed, e.g., like in ad hoc networks.– Cooperative
• Shared resources– Interference temperature (interference at the receiver)– Spectrum holes
#16 17
Presentation Overview
• Motivation• What are Cognitive Radios?• How are they “cognitive”?• Agile Transmission• Kansas University Agile Radio (KUAR)• Conclusion
#16 18
Cognition Framework
• Distinction between reconfigurability and adaptability
• Reconfigurability– Involves choosing radio building blocks– Choice of blocks lasts for relatively long period of time– Requires “flashing” of programmable logic
• Adaptability– Fine-tunes radio operating parameters– Parameter choices last for a short period of time– Does not require “flashing” of programmable logic
#16 19
Cognition Framework
Basic schematic of the cognition component of a cognitive radio
#16 20
Reconfigurability
• Given several desired radio requirements, determine best-possible choices for radio components
#16 21
Adaptation in Cognitive Radios
Cognitive adaptation module possessing several knobs and dials
#16 22
AI-Based Adaptation
• Genetic Algorithms (GA)– Biologically-inspired technique used typically for
problems with large parameter spaces– Execution time becomes larger as number of operational
and environmental parameters grows– Does not require much memory to run; requires long
execution time• Expert Systems
– Decisions determined offline and stored in radio memory– Decision making time is very fast– Interesting trade-off exists between rule base size and
the efficiency of decision
#16 23
Example: GA Convergence
GA Convergence for a cognitive radio operating in emergency mode
T. R. Newman et al., “Cognitive Engine Implementation for Wireless Multicarrier Transceivers”, To appear in the Wiley
Wireless Communications and Mobile Computing Journal, 2007.
Converges to an overall fitness score of 0.8
#16 24
Example: GA Solution
Subcarrier channel attenuation, throughput, and transmit power levels
T. R. Newman et al., “Cognitive Engine Implementation for Wireless Multicarrier Transceivers”, To appear in the Wiley
Wireless Communications and Mobile Computing Journal, 2007.
#16 25
Presentation Overview
• Motivation• What are Cognitive Radios?• How are they “cognitive”?• Agile Transmission• Kansas University Agile Radio (KUAR)• Conclusion
#16 26
Transmission Approaches for DSA
• Transmission in licensed spectrum classified into three categories– Cooperative Approach
• Primary and secondary users coordinate with each other regarding spectrum usage
– Underlay Approach• Secondary signals transmitted at very low power
spectral density; undetected by primary users• e.g., ultra wideband (UWB)
– Overlay Systems• Secondary signals fill in the spectrum unoccupied by
primary users
#16 27
NC-OFDM Transmission• Based on conventional orthogonal frequency
division multiplexing (OFDM)• Uses spectrum sensing measurements to
“turn off” potentially interfering subcarriers
#16 28
FFT-Pruning for NC-OFDM
Pruning an FFT employed in an NC-OFDM Transceiver
R. Rajbanshi et al., “An Efficient Implementation of NC-OFDM Transceivers for Cognitive Radios”, Proc. CrownCom, June. 2006.
#16 29
Example: FFT Execution Time
Mean execution times for a 1024-point FFT
R. Rajbanshi et al., “An Efficient Implementation of NC-OFDM Transceivers for Cognitive Radios”, Proc. CrownCom, June. 2006.
#16 30
Required functions for Cognitive Radios
• Radio scene analysis– Spectral estimation,
• Finding the white spaces/spectral holes• Determining the channel conditions
– Interference temperature• Worst case RF environment in a specific band at a specific
location for the receiver to operate satisfactorily • Transmit power control• Dynamic spectrum management, what to do with
the finding white spaces/spectral holes• Possibility of emergent behavior
#16 31
Presentation Overview
• Motivation• What are Cognitive Radios?• How are they “cognitive”?• Agile Transmission• Kansas University Agile Radio (KUAR)• Conclusion
#16 32
KUAR
• Programmable, agile radio platform for networking (and other) research
• Enabled by support from NSF and DARPA
• Flexible foundation for experimental research– Agile platform for research at
physical, link, MAC layers– Capability to sense and act across
layers– Enables building new network
architectures• Evolving into a cognitive radio
platform– Provide sufficient computing
resources for cognition experiments
Front view of a KUAR unit
#16 33
KUAR Team
• Principal Investigators – Gary J. Minden, Joseph B. Evans
• Investigators– Arvin Agah, James Roberts, Alexander M. Wyglinski
• Design Engineers– Leon Searl, Dan DePardo
• Graduate Research Assistants– Rakesh Rajbanshi, Qi Chen, Tim Newman, Rory Petty,
Ted Weidling, Brett Barker, Jordan Guffey, DineshDatla, Levi Pierce, Megan Lehnherr, Brian Cordill
#16 34
KUAR Schematic
#16 35
KUAR RF and Digital Boards• RF Board
– Frequency Range: 5.25 – 5.85 GHz (includes UNII and ISM bands)
– SW controls Tx Power, Rx Front-end attenuation and IF gain
– 30 MHz Baseband Bandwidth• Digital Board
– PC employing industry standard COMeXpress form-factor
• Pentium-M @ 1.4GHz, 1 GB SDRAM, 6GB CF+ Disk– FPGA: Xilinx Virtex II Pro P30
• Much work still required before deploying reliable DSA networks– Continue work on developing communication
techniques that enable DSA
#16 42
References • S. Haykin, “Cognitive Radio: Brain-Empowered Wireless
Communications”, IEEE Journal on Selected Areas in Communications, Feb. 2005.
• William Krenik and Anuj Batra, “Cognitive Radio Techniques from Wide Area Networks”, Proceedings of the 42nd Design Automation Conference, pages 409-412, 2005.
• Upcoming May 2007 Issue of the IEEE Communications Magazine(Feature Topic on Cognitive Radios for Dynamic Spectrum Access)
• USB controller or PC software programs FPGA• Dual ADC (14 bits parallel, 105 MSPS)• Dual DAC (16-bits parallel, 160/400 MSPS)
#16 49
KUAR Software/Firmware
• PC runs Linux 2.6 kernel • FPGA firmware registers addressable as PCI registers• Software measures radio power usage• Radio Net scripts automate multi-radio experiments• KUAR Radio Systems
– BPSK with phase and timing recovery LFR-QPSK – Multi-carrier Demo
• KUAR VHDL components: – Energy Detector, Digital Sampler, Absolute Value, Clocks, Sin
Generators, Control Processor, Bus Utilities, Delay, Register controls, etc…