Upload
others
View
16
Download
0
Embed Size (px)
Citation preview
Berkeley Wireless Research Center
Signal Processing in Future Radio Systems
Bob BrodersenBob BrodersenDept. of EECSDept. of EECSUniv. of Calif.Univ. of Calif.
Berkeley Berkeley
http://bwrc.eecs.berkeley.edu
Berkeley Wireless Research Center
Who really does the work…
I would like to acknowledge my fellow researchers
UWBTransceiversIan O’DonnellMike ChenStanley WangFrank Wang
Cognitive Radios Danijela CabicMubaraq MishraJing YangAdam WoliszDaniel Wilcomm
60 GHzCMOSChinh DoanSohrab EmamiDavid SobelSayf AlalusiAli Niknejad
Berkeley Wireless Research Center
FCC - Unlicensed SpectraUltra WidebandUWB
ISM U-NII U-NIIU-NII
ISM
MillimeterWave Band
UPCSISM UPCS
UltraWideband
(2002)
Cognitive Radio
(2005?)
Out of Band Emission
Antenna Gain
Power Spectral Density
Total Transmit Power
Modulation
Link Control
Millimeter Wave(1998)
U-NII(1997)
UPCS(1994)
ISM(1986)
➼➼ ➼ ➼
➼➼ ➼
➼
More Sharing
➼➼
➼➼➼➼➼
➼
960
0
Frequency
1060
0
5900
0
3100
2390
2400
2484
5250
5350
5725
5825
5850
1910
1930
5150
6400
0
902
928
(MHz)
➼
Berkeley Wireless Research Center
17 GHz of New Unlicensed Bandwidth!
! The UWB bands have some use restrictions, but FCC requirements will allow a wide variety of new applications
! The 59-64 GHz band can transmit up to .5 Watt with little else constrained
! Cognitive Radio allocations in the regulatory process (400-800MHz band to start with)
! How can we use these new resources?
MmWaveBand
60 GHzComm
20 30Vehicular
UWB UWBUWB
10Comm
40 500ID
Berkeley Wireless Research Center
UWB, 60 GHz and Cognitive radios extend therange of application of radio technology
Carrier Frequency (GHz)
Pea
k D
ata
Rat
e (b
ps)
1 M
100 k
10 k
HDTV motion picture,Pt.-to-Pt. links
NTSC video;rapid file transfer
MPEG video;PC file transfer
Voice,Data
Cellular
3G
802.11b
60 GHzPt.-to-Pt.
60 GHzWLAN
Bluetooth
0.1 1 10 100
802.11a
ZigBee
UWB
UWB
CognitiveRadios
1 G
100 M
10 M
Berkeley Wireless Research Center
Lets start with UWB…
According to the FCC:
“Ultrawideband radio systems typically employ pulse modulation where extremely narrow (short) bursts of RF energy are modulated and emitted to convey information. … the emission bandwidths … often exceed one gigahertz. In some cases “impulse” transmitters are employed where the pulses do not modulate a carrier.”
-- Federal Communications Commission, ET Docket 98-153, First Report and Order, Feb. 2002
Berkeley Wireless Research Center
Two basically different signaling approaches
Sinusoidal, Narrowband
FrequencyTime
Impulse, Ultra-Wideband
FrequencyTime
Berkeley Wireless Research Center
First Major Application Area
High Speed, Inexpensive Short Range Communications (3.1-10.6 GHz)» FCC limit of -41dBm/Mhz at 10 feet severely
limits range – Power level roughly 1 mW– For short range communications this may be OK –
e.g. line of sight from 10 feet for connecting a camcorder to a set-top box, “wireless Firewire”
» Advantage is that it should be less expensive and lower power than a WLAN solution (since 802.11a > 100 Mbits/sec for short range)
Berkeley Wireless Research Center
Status of High Rate, Short Range UWB
Major standards battle in IEEE 802.15.3Two competing approaches» OFDM
– Exploits the wide bandwidth to provide higher rates with lower precision hardware (e.g. reduced A/D accuracy, linearity requirements)
– Uses a well understood technique (802.11a/g)» Impulse radios
– New approach, so somewhat unknown ultimate performance and efficiency
I’ll talk about some example new interesting signal processing possibilities using the impulse approach
Berkeley Wireless Research Center
High Rate Impulse Communications
0 2 4 6 8 10 12
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Time (nS)
Mag
nitu
de (V
)
“1” “0”Biphase signalling
! Basically pulsed rate data transmission – sort of optical fiber without the fiber…
! Key design problem, as in wireline transmission, is synchronization
Berkeley Wireless Research Center
Integrated Analog Front End
UWB attenna
BpLNA
ADC
DigitalBackend
! Mostly Digital Radio Architecture:- Wideband antenna- Wideband amplifier / matching network- RF bandpass filtering (low Q filter)- High bandwidth sample and track- High-speed and low resolution ADC- Sampling Clock generator- DSP
Berkeley Wireless Research Center
Receive match filterPN0 PN1
Nripple<= 64 ns
Trep10ns ~ 100ns
! Basic approach is to create a match filter for the above received pulse shape
! This collects all the energy associated with the waveform
Berkeley Wireless Research Center
Sampling Offset Effects! Unfortunately a small timing offset results in a very
different waveform so the match filter output is very dependent on the timing
150 160 170 180 190 200-1
0
1x 10-4 0Ts
150 160 170 180 190 200-1
0
1x 10-4 0.125Ts
150 160 170 180 190 200-1
0
1x 10-4 0.25Ts
150 160 170 180 190 200-1
0
1x 10-4 0.375Ts
150 160 170 180 190 200-1
0
1x 10-4 0.5Ts
150 160 170 180 190 200-1
0
1x 10-4 0.625Ts
150 160 170 180 190 200-1
0
1x 10-4 0.75Ts
150 160 170 180 190 200-1
0
1x 10-4 0.875Ts
Berkeley Wireless Research Center
A solution to this… (Mike Chen)
ADC
AnalyticMFHilbert
ShapeEst
Ave Det
Imag
RealPulse
in (real)
! Convert the single baseband pulse into an analytic signal (real and imaginary parts) via a Hilbert transformation.
! The analogy is the use of the I and Q channel for sinusoidal systems
Extract the hidden information and becomeinsensitive to timing!
Berkeley Wireless Research Center
Matched filter detection of the analytic impulse signal
-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035sampling offset =0Ts
-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035sampling offset =0.05Ts
-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035sampling offset =0.1Ts
-0.01 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035sampling offset =0.15Ts
0Ts 0.05Ts
0.15Ts 0.1TsReal
Imag
signal+noisenoise
0
0
Without creating the imaginary part, the signal is real and some phase shifts can’t be differentiated from the noise
Berkeley Wireless Research Center
UWB impulse signal processing
Research into the signal processing for impulse detection is just beginning – so lots of opportunities for new ideas!
Analytic impulse signal processing also achieves a timing resolution below the sampling period, what can this be used for?
Berkeley Wireless Research Center
Second Major Application Area
Low Data Rate, Short Range Communications with Locationing (< 960 MHz)» Round trip time for pulse provides range
information – multiple range estimates provides location
» Used for asset tracking – a sophisticated RFID tag that provides location
» Can be used to track people (children, firemen in buildings)
» Sensor networks
Berkeley Wireless Research Center
Location Determination Using UWB
! UWB provides» Indoor measurements» Relative location » Insensitivity to multipath» Material penetration (0-1 GHz band)
Time of flight
! Transmit short discrete pulses instead of Transmit short discrete pulses instead of modulating code onto carrier signalmodulating code onto carrier signal–– Pulses last ~1Pulses last ~1--2 ns2 ns–– Resolution of inches Resolution of inches
Berkeley Wireless Research Center
A UWB locationing transceiver chip(Ian O’Donnell)
A single chip CMOS UWB transceiver at power levels of 1 mW/Mbit for locationing and tracking applications
» Flexible design for a wide range of data rates to investigate UWB transmission characteristics
» For low rate applications, transmission at minimum possible signal level
» Develop limits of locationing accuracy
Berkeley Wireless Research Center
Chip Architecture
1 GHz bandwidth (2 Gsample/sec , 1 bit)
.
LNA AGCA/D
A/D
A/D
TransientCapture
ParallelA/D’s
....
....
Oscillator
Crystal
Correlation, detection and synchronization
PulserPLL
Detector
Din
Dout
AGCControlTiming &
ProgrammableCorrelators
ECC
Synchronization
Encoder
Berkeley Wireless Research Center
Processing to detect signals below noise levels
V[31:0]
To Analog
Data Out
• Acquisition: 128-Tap Matched Filter x 128 x 11 PN Phases• Synchronization: Early/On-Time/Late PN Phases
Berkeley Wireless Research Center
Signal processing for ranging
0 100 200 300 400 500 600 700 800 900-0.1
-0.05
0
0.05
0.1
0 100 200 300 400 500 600 700 800 900-10
-5
0
5
10
The problem is to determine the leading edge of the response
! Simple averaging…
! “Clean” algorithm (iterative best fit of time delayed waveforms)
0 10 20 30 40 50 60 70 80-0.05
0
0.05
0.1
0.15
0 10 20 30 40 50 60 70 800
0.005
0.01
0.015
Berkeley Wireless Research Center
Summary: Many new problems to solve
! Impulse signal processing (e.g. analytic processing) and timing acquisition
! Detection of signals below noise levels! Range estimation and locationing
calculations
Berkeley Wireless Research Center
Next lets look at the 60 GHz band…Mm
WaveBand
40 50 60 GHzComm
20 30Vehicular
UWB UWBUWB
10Comm
0ID
Microwave communications
Berkeley Wireless Research Center
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 » Europe CEPT “there is an urgent need to identify and
harmonize civil requirements in the frequency range 54–66GHz.”
Berkeley Wireless Research Center
Why isn’t 60 GHz in widespread use?
! Misconceptions about path loss and propagation at 60 GHz
! The technology to process signals at 60 GHz is expensive
Berkeley Wireless Research Center
Path loss of line-of-sight transmission…
" Typical path loss (Friis) formula is a function of antenna gain Gr and Gt:
" But maximum antenna gain increases with frequency for the same antenna area, A
( )22
4 rGG
PP tr
t
r
πλ=
2
4λπ AG =
Berkeley Wireless Research Center
Using the same effective area then…
22
1r
AAPP tr
t
r
λ=
" There is theoretically 22-dB gain at 60 GHz over 5 GHz with optimal antenna design
" A 16 antenna array (λ/2 pitch) at 60 GHz has 3-dB gain over a 5-GHz system with 1/10th the area
Berkeley Wireless Research Center
Why isn’t 60 GHz in widespread use?
! Misconceptions about path loss and propagation at 60 GHz
! The technology to process signals at 60 GHz is expensive
Berkeley Wireless Research Center
CMOS can do it - 130-nm CMOS has a gain of 7dB at 60 GHz
VGS = 0.65 V
VDS = 1.2 V
IDS = 30 mA
W/L = 100x1u/0.13u
Berkeley Wireless Research Center
40-GHz and 60-GHz CMOS Amplifiers
18-dB Gain@ 40 GHz
11.5-dB Gain@ 60 GHz
! Design and modeling can be incredibly accurate….! Power consumption: 36 mW (40 GHz), 54 mW (60 GHz)
Berkeley Wireless Research Center
CMOS Mixers at 60-GHz
! Conversion-loss is better than 2 dB for PLO=0 dBm
! IF=2GHz! 6 GHz of bandwidth
Berkeley Wireless Research Center
A Leap Forward for CMOS
X Where we are nowwith 130 nm
• CMOS offers two orders of magnitude cost reduction while providing higher integration and reliability
• Each new process generation moves it 20-40% higher
Berkeley Wireless Research Center
The open questions…! How best to implement a flexible, adaptive
antenna system! What is the best way to use 7 GHz of
bandwidth to implement a high datarate link?» Extremely inefficient modulation but at a very
high rate? (say 2 GHz of bandwidth for 1 Gigabit/sec) – requires analog processing
» Or use an efficient modulation, so lower bandwidth. e.g. OFDM – but needs digital processing and a fast A/D
Berkeley Wireless Research Center
Adaptive antennas by Using Multiple Antenna Beamformers
a1
b1
a0
b0
a2
b2
PA
PA
PASingle Channel
Transceiver
! Wavelength is 5mm, so in a few square inches a large antenna array can be implemented
! The signal processing challenge is how to determine the coefficients of this beamformer to maximize range while minimizing interference
Berkeley Wireless Research Center
An analog/digital hybrid 1Gb/s base-band architecture (David Sobel)
RF IF
LOIF
BBI
BBQ
BB’I
BB’Q
Clk
Timing, DFE Carrier Phase,
Estimators
VGA
Clock Rec
ComplexDFE
AnalogDigital
ejq
Proposed Baseband Architecture
! Synchronization in “hybrid-analog” architecture» ESTIMATE parameter error in digital domain» CORRECT for parameter error in analog domain
! Greatly simplifies requirements on power-hungry analog interface ckts (i.e. ADC, VGA) by using digital processing
Berkeley Wireless Research Center
Last topic – Cognitive Radios
According to the FCC:“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”
- Federal Communications Commission,
ET Docket No. 03-108, Dec 30th 2003
Berkeley Wireless Research Center
The spectrum shortage….
3 4 5 6 GHz
! All frequency bands up to 60 GHz (and beyond) have FCC allocations for multiple users
! The allocation from 3-6 GHz is typical - seems very crowded….
Berkeley Wireless Research Center
The reality…
0 1 2 3 4 5 6 GHz
The TV band
! Even though the spectra is allocated it is almost unused ! Cognitive radios would allow unlicensed users to share the
spectrum with primary users! The TV band is interesting, but higher frequencies are
even more attractive
Berkeley Wireless Research Center
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 database to determine optimal
transmission (bandwidth, latency, QoS) based on primary users’ behavior
Berkeley Wireless Research Center
Cognitive Radio Functions
D/APA
LNA A/D
IFFT
FFT
ADAPTIVELOADING
INTERFERENCEMEAS/CANCEL
MAE/POWER CTRL
CHANNELSEL/EST
TIME, FREQ,SPACE SEL
LEARN ENVIRONMENT
QoS vs.RATE
FEEDBACKTO CRs
! 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
RF/Analog Front-end Digital Baseband MAC Layer
Berkeley Wireless Research Center
Sensing Radio Function
0 0.5 1 1.5 2 2.5x 10
9
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
Frequency (Hz)Si
gnal
Str
engt
h (d
B)
TV bands
Cell
PCS
Spectrum usage in (0, 2.5) GHz
! Subdivide the spectrum into sub-channels (say 1 MHz)
! Detect primary user occupancy in each location/direction
! Continually monitor for appearance of primary user
! Provide information to MAC layer
Berkeley Wireless Research Center
From WiFi to Cognitive Radios
SophisticatedLimited QoS, rate, latency
Lots…Some (802.11n)Spatial processing
Any interferenceWiFi interference onlyInterference mitigation
Adaptive controlFixed per packetPower level
More flexibleFixedPacket length, preamble
Adaptive bit loadingFixed per packetModulation scheme, rate
NecessaryNot possibleSimultaneous spectrum sensing and transmission
Any interferenceWiFi interference onlySensing collisions/interference
Variable # and BW27 fixed 20MHz channelsMultiple channels for agility
Cognitive RadioWiFiFunctionality
Berkeley Wireless Research Center
Summary! UWB radios provide a new way to utilize the
spectrum and there is a wide variety of unique applications of this technology
However, it takes a completely new kind of radio design…
! At the present state of technology CMOS is able to exploit the unlicensed 60 GHz band
However, it will take a new design and modeling methodology…
! Cognitive radios are the ultimate solution to sharingIt will require an unprecedented level of processing to
sense, avoid interference and flexibly transmit
Berkeley Wireless Research Center
Conclusion
Lots of New Opportunities for Signal Processing in these Future Radio
Technologies!!