New Opportunities in Wireless Communications

1. New Opportunities in Wireless Communications Ali M Niknejad Robert W Brodersen Understanding and Increasing Mesh Capacity MSR Mesh Networking Summit Berkeley Wireless Research Center

2. Presentation Outline • 60 GHz CMOS Radio Research • Cognitive Radio at BWRC • Overview of COGUR Project

3. 60 GHz CMOS Radios Chinh Doan, Sohrab Emami, David Sobel Mounir Bohsali, Sayf Alalusi

4. Lots of Bandwidth!!! 7 GHz of unlicensed bandwidth in the U.S. and Japan Same amount of bandwidth is available in the 3-10 UWB band, but the allowed transmit power level is 104 times higher ! Why is operation at 60 GHz interesting? 57 dBm 40 dBm

5. Applications of 60 GHz WLAN

6. 60 GHz Challenges • High path loss at 60 GHz (relative to 5 GHz) • Antenna array results in better performance at higher frequency because more antennas can be integrated in fixed area • Silicon substrate is lossy – high Q passive elements difficult to realize? • No, the Q factor is even better at high frequencies with T-lines, MIM caps, and loop inductors (Q > 20) • CMOS device performance at mm-wave frequencies • CMOS building blocks at 60 GHz • Design methodology for CMOS mm-wave • Low power baseband architecture for Gbps communication

7. 60 GHz CMOS Wireless LAN System 10-100 m • A fully-integrated low-cost Gb/s data communication using 60 GHz band. • Employ emerging standard CMOS technology for the radio building blocks. Exploit electronically steer-able antenna array for improved gain and resilience to multi-path.

8. Advantages of Antenna Array • Antenna array is dynamic and can point in any direction to maximized the received signal • Enhanced receiver/transmitter antenna gain (reduced PA power, LNA gain) • Improved diversity • Reduced multi-path fading • Null interfering signals • Capacity enhancement through spatial coding • Spatial power combining means • Less power per PA (~10 mW) • Simpler PA architecture • Automatic power control

9. Multi-Stage Conversion • 9 GHz VCO is locked to reference. Power consumption of frequency dividers is greatly reduced. • A frequency tripler generates a 27 GHz LO. • Gain comes from RF at 60 GHz, at IF of 33 GHz, and through a passband VGA at 6 GHz (easier than a broadband DC solution).

10. 130-nm CMOS Maximum Gain VGS = 0.65 V VDS = 1.2 V IDS = 30 mA W/L = 100x1u/0.13u

11. CPW Microstrip Co-planar (CPW) and Microstrip T-Lines • Microstrip shields EM fields from substrate • CPW can realize higher Q inductors needed for tuning out device capacitance • Use CPW

12. 11.5-dB Gain @ 60 GHz First Ever 60 GHz CMOS Amplifier! • Gain > 11 dB ; Return loss > 15 dB • Design methodology is incredibly accurate! Reference: “Millimeter-Wave CMOS Design”, to appear in JSSC Chinh H. Doan, Sohrab Emami, Ali M. Niknejad, and Robert W. Brodersen

13. Modeling of 60-GHz CMOS Mixer • Conversion-loss is better than 2 dB for PLO=0 dBm • IF=2GHz • 6 GHz of bandwidth

14. To IFRX LNA From IFTX PA SLO(f) Vout LORX LOTX Vin f fc System Design Considerations • 60 GHz CMOS PA will have limited P1dB point • Tx power constraint while targeting 1Gbps • Must use low PAR signal for efficient PA utilization • 60 GHz CMOS VCOs have poor phase noise • -85dBc/Hz @ 1MHz offset typical (ISSCC 2004) • Modulation must be insensitive to phase noise

15. Modulation Scheme Comparison Beamforming to combat multipath. Simple modulation (MSK) for feasible CMOS RF circuits.

16. VGA RF Analog Digital The Hybrid-Analog Architecture • Condition the signal prior to quantization • Phase and timing recovery, equalization in analog domain • Greatly simplifies requirements on the ADC/VGA circuitry • Synchronization estimators in the digital domain • Can still use robust digital algorithms for synchronization Proposed Baseband Architecture Clk Clock Rec BB’I Timing, DFE Carrier Phase, Estimators BBI IF Complex DFE ejq BB’Q BBQ LOIF

17. 60 GHz Conclusions • At 130 nm, mainstream digital CMOS is able to exploit the unlicensed 60-GHz band • Accurate device modeling is possible by extending RF frequency methodologies • A transmission-line-based circuit strategy provides predictable and repeatable low-loss impedance matching and filtering • Analog equalization with digital domain estimation and calibration will enable low-power Gb/s baseband

18. Cognitive* Radios Danijela Cabric * Adapting behavior based on external factors

19. Window of Opportunity • Existing spectrum policy forces spectrum to behave like a fragmented disk • Bandwidth is expensive and good frequencies are taken • Unlicensed bands – biggest innovations in spectrum efficiency • Recent measurements by the FCC in the US show 70% of the allocated spectrum is not utilized • Time scale of the spectrum occupancy varies from msecs to hours Frequency (Hz) Time (min)

20. Spectrum Sharing • Existing techniques for spectrum sharing: • Unlicensed bands (WiFi 802.11 a/b/g) • Underlay licensed bands (UWB) • Opportunistic sharing • Recycling (exploit the SINR margin of legacy systems) • Spatial Multiplexing and Beamforming • Drawbacks of existing techniques: • No knowledge or sense of spectrum availability • Limited adaptability to spectral environment • Fixed parameters: BW, Fc, packet lengths, synchronization, coding, protocols, … • New radio design philosophy: all parameters are adaptive • Cognitive Radio Technology

21. What is a Cognitive Radio? • Cognitive radio requirements • co-exists with legacy wireless systems • uses their spectrum resources • does not interfere with them • Cognitive radio properties • RF technology that "listens" to huge swaths of spectrum • Knowledge of primary users’ spectrum usage as a function of location and time • Rules of sharing the available resources (time, frequency, space) • Embedded intelligence to determine optimal transmission (bandwidth, latency, QoS) based on primary users’ behavior

22. Application Scenarios Third party access in licensed networks Licensed network Cellular, PCS band Improved spectrum efficiency Improved capacity TV bands (400-800 MHz) Non-voluntary third party access Licensee sets a protection threshold Unlicensed network Secondary markets ISM, UNII, Ad-hoc Public safety band Voluntary agreements between licensees and third party Limited QoS Automatic frequency coordination Interoperability Co-existence

23. FCC Announcement • Released on Dec 30th 2003, (ET Docket No. 03-108) Facilitating Opportunities for Flexible, Efficient, and Reliable Spectrum Use Employing Cognitive Radio Technologies “We recognize the importance of new cognitive radio technologies, which are likely to become more prevalent over the next few years and which hold tremendous promise in helping to facilitate more effective and efficient access to spectrum” “We seek to ensure that our rules and policies do not inadvertently hinder development and deployment of such technologies, but instead enable a full realization of their potential benefits.”

24. 90 120 60 150 30 180 0 210 330 240 300 270 Channel and Interference Model • Measurement of the spectrum usage in frequency, time, and space • Wideband channel • Common with UWB • Spatial channel model • Clustering approach • Interference correlation • Derive statistical traffic model of primary users • Power level • Bandwidth • Time of usage • Inactive periods Angular domain Frequency (Hz) Time (min)

25. IFFT FFT D/A LEARN ENVIRONMENT TIME, FREQ, SPACE SEL FEEDBACK TO CRs ADAPTIVE LOADING QoS vs. RATE MAE/ POWER CTRL INTERFERENCE MEAS/CANCEL PA CHANNEL SEL/EST Cognitive Radio Functions • 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 LNA A/D RF/Analog Front-end Digital Baseband MAC Layer

26. Cell -40 -45 PCS TV bands -50 -55 Signal Strength (dB) -60 -65 -70 -75 -80 -85 -90 Frequency (Hz) 0 0.5 1 1.5 2 2.5 9 x 10 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 Spectrum usage in (0, 2.5) GHz Measurement taken at BWRC

27. IFFT FFT LEARN ENVIRONMENT TIME, FREQ, SPACE SEL FEEDBACK TO CRs ADAPTIVE LOADING QoS vs. RATE MAE/ POWER CTRL INTERFERENCE MEAS/CANCEL CHANNEL SEL/EST Cognitive Radio Baseband Processing PHY MAC • MCMA processing • OFDM System • Agile, efficient FFT • Spatial processing: • Exploits clustered model • Scalable with # of antennas • PHY – adaptive, parametrizable • MAC – intelligent, optimization algo’s • PHY+MAC can be implemented on: • Software Defined Radios • Reconfigurable Radios

28. From WiFi to Cognitive Radios

29. CR1 CR2 CR3 Test Scenario at 2.4 GHz, Indoor • Unlicensed band 80 MHz bandwidth • OFDM system (like 802.11a/g) • Multiple antennas for interference avoidance and range extension • Centralized approach through AP Microwave oven AP 802.11 b/g Bluetooth Dynamic Frequency Selection Cordless phone

30. Testbed for Wireless Experimentation • BWRC infrastructure: • BEE Processing Units (4) • 2.4 GHz RF Front-ends (32) • Scalable multiple antenna transmission system

31. Research Agenda • Derive system specification from measurements • Analog front-end specification and design • Develop and implement algorithms for: • Sensing environment • Dynamic frequency selection and adaptive modulation • Transmit power control and spatial processing • Interference cancellation in spatial domain • Spectrum rental strategies • Test algorithms in realistic wireless scenarios • Design an architecture for a Cognitive Radio

32. COGURCognizant Universal Radio Axel Berny Gang Liu Zhiming Deng Nuntachai Poobuapheun

33. COGUR Design Goals • An agile dynamic radio cognizant of its environment • Universal operation ensures multi-standard and future standard compatibility • Cognitive behavior allows spectrum re-use, underlay, and overlay • Dynamic operation allows low power (only need linearity and low-phase noise VCO in a near-far situation) • Multi-mode PA can work in “linear” mode for OFDM and high PAR modulation schemes. Efficiency is maintained while varying output power

34. Dynamic Operation: Near-Far Problem • High power consumption due to simultaneous requirement of high linearity in RF front-end and low noise operation • The conflicting requirements occur since the linearity of the RF front-end is exercised by a strong interferer while trying to detect a weak signal • The worst case scenario is a rare event. Don’t be pessimistic! • A dynamic transceiver can schedule gain/power of the front-end for optimal performance

35. COGUR Transceiver • Broadband dynamic LNA/mixer • Wide tuning agile frequency synthesizer • Dual-mode broadband PA with integrated power combining and control • Linear VGA or attenuator • High-speed background calibrated ADC/DAC

36. Acknowledgements • BWRC Member Companies • DARPA TEAM Project • STMicroelectronics and IBM for wafer processing and design support • Agilent Technologies (measurement support) • National Semiconductor • Qualcomm • Analog Devices