Upload
others
View
11
Download
1
Embed Size (px)
Citation preview
1
Cognitive Radio opportunities
and RF Receiver Challenges.
Yann Le Guillou
Séminaire SCEE, Supélec, 19 Mars 2014
Overview
2
� Evolution Trends of Spectrum Usage
� TV White Spaces
o Interest
oUsage example
oHardware Radio Challenges
� Cognitive Radio and ADCs challenges and directions
� Receiver challenges
� Some Solution Directions
oRF filtering Interference
o Interference Cancellation
oDigital assistance of dirty RF
� Conclusion
Séminaire SCEE, Supélec, 19 Mars 2014
2008
� Trend: Increasing growth of mobile traffic
� More than 4 billion mobile phone users today and growing at a startling rate
� “7 trillion wireless device serving 7 billion people in 2017” – Wireless World
Research Forum
� Mobile Internet traffic handled by mobile operators grow from 7 billion
megabytes worlwilde [in 2008] into 63 billion megabytes in 2013 (CAGR 54%)”
- Informa
2008
1924
Gap Between Wireless Traffic Supply and Demand Widens
3Séminaire SCEE, Supélec, 19 Mars 2014
Spectrum Scarce?
Spectrum not well managed in time domain and in geographical area
[Swisscom]
TV Bands
Séminaire SCEE, Supélec, 19 Mars 2014 4
Unlicensed secondary re-use of TV broadcast spectrum
[Swisscom]
Séminaire SCEE, Supélec, 19 Mars 2014 5
Overview
Séminaire SCEE, Supélec, 19 Mars 2014 6
� Evolution Trends of Spectrum Usage
� TV White Spaces
o Interest
oUsage example
oHardware Radio Challenges
� Cognitive Radio and ADCs challenges and directions
� Receiver challenges
� Some Solution Directions
oRF filtering Interference
o Interference Cancellation
oDigital assistance of dirty RF
� Conclusion
Why the interest in TV White Space?
�Switch-off of Analog TV
oThe release underutilized and valuable spectrum in UHF bands that can be used for next generation wireless network and low-cost communications
�UHF Signal properties
oMore spectrum available!
oGood propagation ability (long range for low power)
oGood building penetration (e.g. public safety applications)
Séminaire SCEE, Supélec, 19 Mars 2014 7
� Frequency: 470-698MHz
� Channels: 6-8MHz
� Incumbent protection (WSDB)
� Power Levels and control of secondary users
8© 2013
General Agreement at high level
Séminaire SCEE, Supélec, 19 Mars 2014
… but Roadblocks are still there
� harmonization across regulatory regimes are difficult
� Industry is still waiting…
Application Example – Rural Broadband
9© 2013
Outstanding propagation characteristic in the VHF/UHF
reduce build-out costs and open era to Rural Broadband
& Smart Agriculture Séminaire SCEE, Supélec, 19 Mars 2014
Example - Offload 3G/4G Traffic
� “Super-WiFi” in TV White Spaces: similar coverage as mobile broadband
� with just a 20% deployment density and 10-50 times faster than 3G
[Maziar Nekovee, BT]
5.8GHz 2.4GHz ~0.8GHz
� 1 km² area in Central London,
� 5 000 homes
� 100 mW (WiFi), 20 mW (TVWS)
Feasibility study Central London
Séminaire SCEE, Supélec, 19 Mars 2014 10
� PHY Receiver Challenge
o Wide dynamic range (especially in ADC)
o Highly sensitive
o Interference Management
o Spectrum Sensing over wide frequency range
� PHY Transmitter Challenge (=SDR + extreme frequency agility)
o Spectral Emission
o Low Power
11
TVWS Radio Hardware Challenges
© 2013
� Both PHY
o Frequency Agility: Operation Frequency range from ~ 10’ MHz to several GHz
o Bandwidth Agility
o Flexibility/upgradability: Standard agnostic transceiver able to Rx/Txcurrent and future standards
o Low cost
o Low PowerSéminaire SCEE, Supélec, 19 Mars 2014
Overview
12
� Evolution Trends of Spectrum Usage
� TV White Spaces
o Interest
oUsage example
oHardware Radio Challenges
� Cognitive Radio and ADCs challenges and directions
� Receiver challenges
� Some Solution Directions
oRF filtering Interference
o Interference Cancellation
oDigital assistance of dirty RF
� Conclusion
Séminaire SCEE, Supélec, 19 Mars 2014
ADC Bandwidth versus SNDR
Far from feasible …
[Murmann- ADC Performance Survey 1997-2014]
http://www.stanford.edu/~murmann/adcsurvey.html
Cognitive Radio
(6GHz and 100dB)
TV WS
(900MHz and 100dB)
Séminaire SCEE, Supélec, 19 Mars 2014 13
Jitter=1psRMS
Jitter=100fsRMS
Jitter=10fsRMS
Jitter=1fsRMS
Energy/fs versus SNDR
Today, FOM=1pJ/conv-step for high speed high SNDR
10fJ/conv-step
100fJ/conv-step
1pJ/conv-step
Séminaire SCEE, Supélec, 19 Mars 2014 14
Required ADC Power (w/o clocking system)
Suppose:o 1pJ/conversiono Signal -100dBm … 0dBm ↔17 bits
� Cognitive Radio50MHz-6GHZ↔ fsample~12GHz
P=Econv.fsample.2#bits=10-12.12.109.217≈1.5kW
� TVWS Radio700MHz-900MHZ↔ fsample~1.8GHz
P=Econv.fsample.2#bits=10-12.1,8.109.217≈235W
RF-ADC most flexible « software-defined » receiver far from
being Green today
….but also ~225x(1.8GS/s for 8MHz channel) to 1000x(10GS/s for ~10MHz channel)
overkill
Séminaire SCEE, Supélec, 19 Mars 2014 15
Required clock power
Suppose
o100dB SNDR ↔ Clock Jitter, σt ~1fsRMS (see slide 16)
o State of the art FOMPLL~-230dB
where
Then PPLL~ 10 kW !!
Séminaire SCEE, Supélec, 19 Mars 2014 16
Not achievable today neither tolerable for low
power.
Today 20mW dissipation is tolerable, resulting in
~0,7psRMS clock jitter
Down-conversion / filtering required
This radio is still very flexible with software
f-shift (Mixer) ADC
Band Filter
LNAAnti-aliasing
Filter
DFE
Down-conversionFiltering
IMEC-Renesas- 11b- 410MSPs
– TI SAR ADC - ~1psRMS jitter
Séminaire SCEE, Supélec, 19 Mars 2014 17
TI-SAR ADC� 2x time-interleaved pipeline SAR ADC
in 28nm CMOS
� 11-bit, 0-410MSPs, 2.1mW
� 6.5fJ/conv-step
� Power consumption scale linearly withsampling
� SNDR=55dB@205MHz
� On-chip calibration engine for gain and offset errors
Time Skew issue
[Verbruggen, VLSI, 2013]
Séminaire SCEE, Supélec, 19 Mars 2014 18
� To push TI-ADC SNDR above 11-bits need to calibrate frequency dependant spurs
due to time-skew and bandwidth mismatches.
� Digital calibration is required to get the right accuracy
Pushing TI- ADC SFDR
Frequency dependant analytic expression
SFDR=~60dB~120dB
[Paquelet, Kamdem De Teyou, Le Guillou, IEEE NEWCAS, 2013]
Séminaire SCEE, Supélec, 19 Mars 2014 19
Estimation accuracy needed to reach the desired
SFDR of 90 dB in 99.9% of cases with a 4TI-ADCs, an
input signal x(t) =1.5 sin(2πfot), fo = 146.29MHz and
fs = 320MHz.
Gain Offset Time-Skew Bandwidth
Accuracy
[ppm]20 120 7 540
Overview
20
� Evolution Trends of Spectrum Usage
� TV White Spaces
o Interest
oUsage example
oHardware Radio Challenges
� Cognitive Radio and ADCs challenges and directions
� Receiver challenges
� Some Solution Directions
oRF filtering Interference
o Interference Cancellation
oDigital assistance of dirty RF
� Conclusion
Séminaire SCEE, Supélec, 19 Mars 2014
A - Interference from CR to Primary networks ( CR Transmitter)
B - Interference from Primary networks to CR networks (CR Receiver)
C - Interference from CR to CR ( CR Transmitter and Receiver)
Interference Management Challenge� TVWS Radio are envisioned to be capable of sensing and
reasoning about the operating radio environments and thereby
autonomously adjusting their transceiver parameters to exploit
the underutilized radio resources in a dynamic fashion
� Cognitive Radio operates in interference-intensive environments.
� Minimum interference is therefore essential to the coexistence of Primary and TVWS Radio (Secondary System)
21Séminaire SCEE, Supélec, 19 Mars 2014
� On top classical Rx noise due to Receiver RF Front End Impairment (Phase noise,
linearity, Noise etc.)
� Tx noise due to Tx leakage
� IntPrimary due to Primary Network Interferers
� CRNetworks due to all CR networks
22
Additional RF impairment for TVWS device
SIGNAL
Thermal NoisePhase Noise
ImageHarmonicsIsolation
XmodIP2IP3
SNR
Rx
NOISE
Tx leakage
CR networksIntPrimary
ADC
LNA LO
90°
ADC
DSP
PA LO
90°
ADC
ADC
Duplexer
Séminaire SCEE, Supélec, 19 Mars 2014
Linearity requirements challengesAssumption: 2 tones at Pin [dBm]
IM level equal to Noisefloor N=-100dBm
Challenge: high linearity broadband receivers
Required IIP3 [dBm] Required IIP2 [dBm]
Séminaire SCEE, Supélec, 19 Mars 2014 23
Overview
24
� Evolution Trends of Spectrum Usage
� TV White Spaces
o Interest
oUsage example
oHardware Radio Challenges
� Cognitive Radio and ADCs challenges and directions
� Receiver challenges
� Some Solution Directions
oRF filtering Interference
o Interference Cancellation
oDigital assistance of dirty RF
� Conclusion
Séminaire SCEE, Supélec, 19 Mars 2014
Tunable RF filtering challenges
� Frequency selection by coil L &
capacitor C
� Tuned mechanically by variable
plate-capacitor C
Center frequency:
� On-chip CMOS filters:
o limited Q inductors =fc/bandwidth<15 (lossy, bulky, not flexible)
o Limited fc tuning-range ~30%
o Active inductors (noisy, non-linear)
� Alternative Idea
o Do not use inductor
o Switch & capacitors are very linear
o Switch & capacitors scale with CMOS
Séminaire SCEE, Supélec, 19 Mars 2014 25
N-path filter concept
� N signal paths switched series R-C
ϕ1
VBB1≠0
VBB1=0
[Franks, ISSCC1960]
Ghaffari, RFIC2010/JSSC2011]
[Mirzaei,VLSI10/TCAS2011]
[Darvishi, ISSCC2013]
VRF , fRF= fLO
VRF , fRF= 1.5fLO
� In-band (fRF≈fLO): High ZRF
� Out of band: low ZRF (Short circuit)
RC>>TON
TLO
TON=TLO/N
ϕ1
ϕ2
ϕN
VRF
C
R ϕ1VBB1
C
ϕ2VBB2
C
ϕNVBBN
Séminaire SCEE, Supélec, 19 Mars 2014 26
N-path filter properties
CMOS:
Switches & capacitors
TLO
TON=TLO/N
ϕ1
ϕ2
ϕN
fLO 0
Frequency filtering
@ RF
Frequency filtering
@ baseband
High-Q RF filter
Linear
Widely tunableC
ϕ1VBB1
C
ϕ2VBB2
C
ϕNVBBN
Resistive (R)
Séminaire SCEE, Supélec, 19 Mars 2014 27
[Darvishi, van der Zee, Nauta, ISSCC 2013]
65nm CMOS
Séminaire SCEE, Supélec, 19 Mars 2014
Filtering properties: flexibly tunable6th order 8-path
28
Frequency Hopping according to the free IM spot….
Take a look in the past …
Interference Cancellation Techniques …
25-Year Old Hollywood Star
invents frequency hopping
10th June 1940
Hedy Lamarr
29Séminaire SCEE, Supélec, 19 Mars 2014
Exploit the spectrum Sensing and use the Free IM Spots
�Select the IM3-free spotsSéminaire SCEE, Supélec, 19 Mars 2014 30
IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 44, NO. 6, JUNE 2009
…and in the future
Bio Inspired RF Silicon Cochlea 100MHz-10GHz
31© 2013 Séminaire SCEE, Supélec, 19 Mars 2014
• Today’s mobile device (Tablet PC etc.) have more processing
capabilities than the original supercomputers !
• Capitalize on it to bring the required flexibility and assist
dirty RF© 2013
Capitalize on trend in the embedded digital
core processor
Séminaire SCEE, Supélec, 19 Mars 2014 32
33© 2013
Some digitally assist analog and RF impairment
directions …
• Linearity (IP2, IP3) enhancement techniques
• Noise reduction by cross-correlation techniques (as in Spectrum Analyser)
• I and Q magnitude and phase imbalance
• TI-ADC impairments
• Clock spur cancellation …
Séminaire SCEE, Supélec, 19 Mars 2014 33
Example - clock spur cancellation
� Clock spur reduced by 40dB
Séminaire SCEE, Supélec, 19 Mars 2014 34
Overview
35
� Evolution Trends of Spectrum Usage
� TV White Spaces
o Interest
oUsage example
oHardware Radio Challenges
� Cognitive Radio and ADCs challenges and directions
� Receiver challenges
� Some Solution Directions
oRF filtering Interference
o Interference Cancellation
oDigital assistance of dirty RF
� Conclusion
Séminaire SCEE, Supélec, 19 Mars 2014
Conclusion
� Cognitive Radio receiver challenges are
interdisciplinary in nature (RF, analog, digital signal
processing, …)
� Capitalize on CMOS technology and DSP but think out
of the box
o Make optimum use of Switches and Cap in CMOS
technologies to built RF functions
o Make optimum use of technology speed and high speed
clock possibility
o Digitally assist dirty RF & Analog to boost the performances
36Séminaire SCEE, Supélec, 19 Mars 2014