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New Opportunities in Wireless Communications

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Presentation on theme: "New Opportunities in Wireless Communications"— Presentation transcript:

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

4 Why is operation at 60 GHz interesting?
57 dBm 40 dBm 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 !

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
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 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 First Ever 60 GHz CMOS Amplifier!
11.5-dB Gain @ 60 GHz 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 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 1MHz offset typical (ISSCC 2004) Modulation must be insensitive to phase noise PA LOTX From IFTX Vin Vout LNA LORX To IFRX SLO(f) f fc

15 Modulation Scheme Comparison
OFDM-QPSK High-order modulation (16-QAM) Single-carrier QPSK Constant Envelope (MSK) SNRreq (BER=10-3) 7dB 12dB PARTX ~10dB ~5.5dB ~3dB 0dB PA linearity req’t High Moderate Low Sensitivity to Phase Noise High (ICI) High (Symbol Jitter) Complexity of Multipath Mitigation Techniques Moderate (FFT) (Equalizer) Beamforming to combat multipath. Simple modulation (MSK) for feasible CMOS RF circuits.

16 The Hybrid-Analog Architecture
Proposed Baseband Architecture Clk Clock Rec BB’I Timing, DFE Carrier Phase, Estimators BBI RF VGA IF ejq Complex DFE BB’Q BBQ LOIF Analog Digital 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

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 * Adapting behavior based on external factors
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 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 ( MHz) Non-voluntary third party access Licensee sets a protection threshold Secondary markets Unlicensed network Public safety band Voluntary agreements between licensees and third party Limited QoS ISM, UNII, Ad-hoc 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 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 30 210 60 240 90 270 120 300 150 330 180 Angular domain Frequency (Hz) Time (min)

25 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 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 PA D/A LNA A/D RF/Analog Front-end Digital Baseband MAC Layer

26 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: MHz band is empty if: Need to determine length of measurements Spectrum usage in (0, 2.5) GHz 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 Measurement taken at BWRC

27 Cognitive Radio Baseband Processing
PHY MAC 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 – adaptive, parametrizable MAC – intelligent, optimization algo’s PHY+MAC can be implemented on: Software Defined Radios Reconfigurable Radios

28 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 Adaptive control Interference mitigation Spatial processing Some (802.11n) Lots… QoS, rate, latency Limited Sophisticated

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

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