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Application Scenarios Licensed network Secondary markets Third party access in licensed networks Unlicensed network Cellular, PCS band Improved spectrum efficiency Improved capacity Public safety band Voluntary agreements between licensees and third party Limited QoS TV bands (400-800 MHz) Non-voluntary third party access Licensee sets a protection threshold Automatic frequency coordination Interoperability Co-existence ISM, UNII, Ad-hoc
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Cognitive Radio Functions D/A PA LNA A/D IFFT FFT ADAPTIVE LOADING INTERFERENCE MEAS/CANCEL MAE/ POWER CTRL CHANNEL SEL/EST TIME, FREQ, SPACE SEL LEARN ENVIRONMENT QoS vs. RATE FEEDBACK TO CRs Sensing Radio Wideband Antenna, PA and LNA High speed A/D & D/A, moderate resolution Simultaneous Tx & Rx Scalable for MIMO Physical Layer OFDM transmission Spectrum monitoring Dynamic frequency selection, modulation, power control Analog impairments compensation MAC Layer Optimize transmission parameters Adapt rates through feedback Negotiate or opportunistically use resources RF/Analog Front-end Digital Baseband MAC Layer
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Sensing Radio A/D converter: High resolution Speed depends on the application Low power ~ 100mWs RF front-end: Wideband antenna and filters Linear in large dynamic range Good sensitivity Interference temperature: Protection threshold for licensees FCC: 2400-2483.5 MHz band is empty if: Need to determine length of measurements 0 0.5 1 1.5 2 2.5 x 10 9 -90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -40 Frequency (Hz) Signal Strength (dB) TV bands Cell PCS Spectrum usage in (0, 2.5) GHz Measurement taken at BWRC
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Cognitive Radio Baseband Processing IFFT FFT ADAPTIVE LOADING INTERFERENCE MEAS/CANCEL MAE/ POWER CTRL CHANNEL SEL/EST TIME, FREQ, SPACE SEL LEARN ENVIRONMENT QoS vs. RATE FEEDBACK TO CRs MCMA processing OFDM System Agile, efficient FFT Spatial processing: Exploits clustered model Scalable with # of antennas PHY MAC PHY – adaptive, parametrizable MAC – intelligent, optimization algo’s PHY+MAC can be implemented on: Software Defined Radios Reconfigurable Radios
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From WiFi to Cognitive Radios Functionality WiFi Cognitive Radio Multiple channels for agility 27 fixed 20MHz channels Variable # and BW Sensing collisions/interference WiFi interference only Any interference Simultaneous spectrum sensing and transmission Not possible Necessary Modulation scheme, rate Fixed per packet Adaptive bit loading Packet length, preamble Fixed More flexible Power level Fixed per packet Adaptive control Interference mitigation WiFi interference only Any interference Spatial processing Some (802.11n) Lots… QoS, rate, latency Limited Sophisticated