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
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 gt 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
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!

• Gain gt 11 dB Return loss gt 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 PLO0 dBm
• IF2GHz
• 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
• -85dBc/Hz _at_ 1MHz offset typical (ISSCC 2004)
• Modulation must be insensitive to phase noise

15
Modulation Scheme Comparison
Modulation OFDM-QPSK High-order modulation (16-QAM) Single-carrier QPSK Constant Envelope (MSK)
SNRreq (BER10-3) 7dB 12dB 7dB 7dB
PARTX 10dB 5.5dB 3dB 0dB
PA linearity reqt High High Moderate Low
Sensitivity to Phase Noise High (ICI) High (Symbol Jitter) Moderate Low
Complexity of Multipath Mitigation Techniques Moderate (FFT) High (Equalizer) High (Equalizer) High (Equalizer)
Beamforming to combat multipath. Simple
modulation (MSK) for feasible CMOS RF circuits.
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The Hybrid-Analog Architecture
Proposed Baseband Architecture
Clk
Clock Rec
BBI
Timing, DFE Carrier Phase, Estimators
BBI
IF
Complex DFE
ejq
BBQ
BBQ
LOIF

• 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
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

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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.

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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)
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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
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
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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 algos
• PHYMAC 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
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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
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Testbed for Wireless Experimentation

• BWRC infrastructure
• BEE Processing Units (4)
• 2.4 GHz RF Front-ends (32)
• Scalable multiple antenna transmission system

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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. Dont
  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