Outline • Motivation Cognitive Radio Communications • What are Cognitive Radios? • How are they “cognitive”? for Dynamic Spectrum Access • Agile Transmission • Kansas University Agile Radio (KUAR) Yao Zheng • Conclusion 1 2 Presentation Overview Current Spectrum Allocation • Motivation • What are Cognitive Radios? • How are they “cognitive”? • Agile Transmission • Kansas University Agile Radio (KUAR) • Conclusion FCC frequency allocations for US radio spectrum 3 4 Increasing Demand Increasing Demand • Rapid growth in the wireless communications sector, requiring 200 Million more spectral bandwidth Subscribers! o Increasing number of users o 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 o Number of licensed transmissions are increasing within a finite allocated bandwidth o Unlicensed users constrained to a few overloaded bands Source: CTIA 5 6
Increasing Demand Apparent Scarcity • Measurement studies have shown that in both the time and frequency domains that spectrum is underutilized 1.4 Trillion Minutes! Spectrum Holes Spectrum measurement across the 900 kHz –1 GHz band (Lawrence, KS, USA) Source:CTIA 7 8 Potential Solution But not in my spectrum! • Incumbent license holders are very concerned about co- • Dynamic Spectrum Access (DSA) existing transmissions from unlicensed users o Large-scale investments in developing communication infrastructure around spectrum Fill with secondary • Maintain quality-of-service to its paying customers users o Unlicensed users providing competing services (e.g., VoIP) but without the large-scale investment o Transmissions are a time-varying phenomena … a signal not interfering at one point in time may do so at another Spectrum measurement across the 900 kHz –1 GHz band (Lawrence, KS, USA) 9 10 Example Presentation Overview • Motivation • What are Cognitive Radios? • How are they “cognitive”? • Agile Transmission • Kansas University Agile Radio (KUAR) • Conclusion • Conclusion : Wireless equipment designed for DSA communications must be rapidly reconfigurable and spectrum-aware 11 12
Software-Defined Radios 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 o Baseband radio functions can be entirely implemented in digital logic and software Radio functions performed in the software domain 13 14 What is a Cognitive Radio? What is a Cognitive Radio? • An intelligent wireless communications system • Based on SDR technology “ Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e., outside world), and uses the o Reconfigurable methodology of understanding-by-building to learn from the environment o Agile Functionality and adapt its internal states to statistical variations in the incoming RF stimuli by making corresponding changes in certain operating parameters • Aware of its environment (e.g., transmit-power, carrier-frequency, and modulation strategy) in real- time, with two primary objectives in mind: o RF spectrum occupancy • highly reliable communications whenever and wherever needed; o Network traffic • efficient utilization of the radio spectrum.” o Transmission quality • Learns from its environment and adapts to new scenarios S. Haykin, “Cognitive Radio: Brain-Empowered Wireless based on previous experiences Communications”, IEEE J-SAC, Feb. 2005. 15 16 Presentation Overview Cognition Framework • Distinction between reconfigurability and adaptability • Motivation • Reconfigurability • What are Cognitive Radios? o Involves choosing radio building blocks • How are they “cognitive”? o Choice of blocks lasts for relatively long period of time o Requires “flashing” of programmable logic • Agile Transmission • Adaptability • Kansas University Agile Radio (KUAR) o Fine-tunes radio operating parameters o Parameter choices last for a short period of time • Conclusion o Does not require “flashing” of programmable logic 17 18
Cognition Framework Reconfigurability • Given several desired radio requirements, determine best-possible choices for radio components Basic schematic of the cognition component of a cognitive radio 19 20 AI-Based Adaptation Adaptation in Cognitive Radios • Genetic Algorithms (GA) o Biologically-inspired technique used typically for problems with large parameter spaces o Execution time becomes larger as number of operational and environmental parameters grows o Does not require much memory to run; requires long execution time • Expert Systems o Decisions determined offline and stored in radio memory o Decision making time is very fast o Interesting trade-off exists between rule base size and the efficiency of decision Cognitive adaptation module possessing several knobs and dials 21 22 Example: GA Convergence Example: GA Solution Converges to an overall fitness score of 0.8 Subcarrier channel attenuation, throughput, and transmit power levels GA Convergence for a cognitive radio operating in emergency mode T. R. Newman et al ., “Cognitive Engine Implementation for T. R. Newman et al ., “Cognitive Engine Implementation for Wireless Multicarrier Transceivers”, To appear in the Wiley Wireless Multicarrier Transceivers”, To appear in the Wiley Wireless Communications and Mobile Computing Journal, 2007. Wireless Communications and Mobile Computing Journal, 2007. 23 24
Transmission Approaches for DSA Presentation Overview • Transmission in licensed spectrum classified into • Motivation three categories • What are Cognitive Radios? o Cooperative Approach • How are they “cognitive”? • Primary and secondary users coordinate with each other regarding spectrum usage • Agile Transmission o Underlay Approach • Kansas University Agile Radio (KUAR) • Secondary signals transmitted at very low power spectral density; undetected by primary users • Conclusion • e.g., ultra wideband (UWB) o Overlay Systems • Secondary signals fill in the spectrum unoccupied by primary users 25 26 NC-OFDM Transmission FFT-Pruning for NC-OFDM • Based on conventional orthogonal frequency division multiplexing (OFDM) • Uses spectrum sensing measurements to “turn off” potentially interfering subcarriers 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. 27 28 Presentation Overview Example: FFT Execution Time • Motivation • What are Cognitive Radios? • How are they “cognitive”? • Agile Transmission • Kansas University Agile Radio (KUAR) • Conclusion 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. 29 30
KUAR KUAR Schematic • Programmable, agile radio platform for networking (and other) research Enabled by support from NSF and DARPA • • Flexible foundation for experimental research o Agile platform for research at physical, link, MAC layers o Capability to sense and act across layers o Enables building new network architectures • Evolving into a cognitive radio platform o Provide sufficient computing resources for cognition experiments Front view of a KUAR unit 31 32 KUAR RF and Digital Boards KUAR Software/Firmware • RF Board • PC runs Linux 2.6 kernel o Frequency Range: 5.25 – 5.85 GHz (includes UNII and ISM bands) • Software measures radio power usage o SW controls Tx Power, Rx Front-end attenuation and IF gain o 30 MHz Baseband Bandwidth • Radio Net scripts automate multi-radio • Digital Board experiments o PC employing industry standard COMeXpress form-factor • KUAR Radio Systems • Pentium-M @ 1.4GHz, 1 GB SDRAM, 6GB CF+ Disk o BPSK with phase and timing recovery o FPGA: Xilinx Virtex II Pro P30 • FPGA External Memory: 4 Mb SRAM o Multi-carrier demo o Dual ADC (14 bits parallel, 105 MSPS) • KUAR VHDL components: o Dual DAC (16-bits parallel, 160/400 MSPS) o Energy Detector, Digital Sampler, Absolute Value, Clocks, Sin Generators, Control Processor, Bus Utilities, Delay, Register controls, etc… 33 34 KUAR System Diagram KUAR Transmit Performance System diagram of a KUAR unit (Version 3.0) #16 36 35 36
Recommend
More recommend
