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