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E225C – Lecture 1Wireless Systems Overview
Bob BrodersenBob Brodersen
Course Outline
l Goal 1: The implementation of signal processing systems in CMOS technology» A design methodology starting from a high
level description through to an implementation optimized for hardware constraints.
l Goal 2: To understand the issues involved in the design of wireless systems» Wireless systems will be used as a design
driver to understand how to make tradeoffs in signal processing implementation
Homework and Projects
l First part of the semester (up to the break) will be approximately (bi)weekly homeworks that will implement each block of a wireless transceiver
l A final project will be to put a complete system together and demonstrate it on BEE
Lots of new radio systems beingdeveloped now
l WiFi – 10-100Mbits/sec unlicensed band» OFDM, M-ary coding
l 3G – .1-2 Mbits/sec wide area cellular» CDMA, GMSK
l Bluetooth – .8 Mbit/sec cable replacement» Frequency hop
l ZigBee – .02-.2 Kbits/sec low power, low cost» QPSK
l UWB – Recently allowed by FCC » Short pulses (no carrier), bi-phase or PPM
(Actually some not so new….just a long time coming)
Digital Cellular Market(Phones Shipped)
1996 1997 1998 1999 2000
Units 48M 86M 162M 260M 435M
Analog Baseband
Digital Baseband
(DSP + MCU )
PowerManagement
Small Signal RF
PowerRF
Communication systems: Major technology driver Why so many new systems?
The availability of unlicensed spectra…Licensed l 2Gl 3G
Is this exploitation of unlicensed bands a temporary aberration or the new reality???
Unlicensedl WiFil Bluetoothl ZigBeel UWB
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FCC Chairman Powell statementWe are still living under a spectrum "management"
regime that is 90 years old. It needs a hard look, and in my opinion, a new direction.
Historically, I believe there have been four core assumptions underlying spectrum policy:
l Unregulated radio interference will lead to chaos;
l Spectrum is scarcel Government command and control of the scarce
spectrum resource is the only way chaos can be avoided
l The public interest centers on government choosing the highest and best use of the spectrum.
Powell’s statement (cont.)Today's environment has strained these assumptions to the breaking point. Modern technology has fundamentally changed the nature and extent of spectrum use. So the real question is, how do we fundamentally alter our spectrum policy to adapt to this reality? The good news is that while the proliferation of technology strains the old paradigm, it is also technology that will ultimately free spectrum from its former shackles.
Sharing
So it looks like we are moving into a new regime that will have an ever larger number of competing radio systems that will require new technological solutions.
The FCC has been following this strategy
Millimeter Wave(1998)
Out of Band Emission
Antenna Gain
Power Spect Density
Total Transmit Power
Modulation
Link Control
UWB(2001)
802.11a(1997)
UPCS(1994)
ISM(1986)
üü
ü ü ü üü ü ü üü
üüü ü
üMore Sharing
Reference: Part 15 of the FCC Rules, September 2000.
902
928
1910
1930
2390
2400
2484
5150
5250
5350
5725
5825
5850
5900
0
6400
0
U-NII
ISM UPCS UPCS
ISM U-NIIU-NII
ISM
MillimeterWave Band
Frequency(MHz)
UWB
ü
Comparison
Now for a quick description of the various technical differences between these new radio systems.
These show the range of design constraints that we will need to address
Data rate
10 kbits/sec
100 kbits/sec
1 Mbit/sec
10 Mbit/sec
100 Mbit/sec
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWBZigBee
Bluetooth
ZigBee
802.11b802.11g
3G
UWB
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Range
1 m
10 m
100 m
1 km
10 km
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWB
ZigBee BluetoothZigBee
802.11b,g
3G
UWB
Power Dissipation
1 mW
10 mW
100 mW
1 W
10 W
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWB
UWBZigBee
Bluetooth
ZigBee
802.11bg3G
Cost (projections)
$ .10
$1
$10
$100
$1000
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWB
UWBZigBee
BluetoothZigBee
802.11b,g3G
Infrastructure cost
$ .10
$1
$10
$100
$1000
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
ZigBeeBluetooth
802.11b,g
3G
UWB
UWB
ZigBee
60 GHz???
56 57 58 59 60 61 62 63 64 65 66 56 57 58 59 60 61 62 63 64 65 66
Frequency GHzFrequency GHz
JapanJapan
EuropeEurope
U.S.U.S.
Oxygen absorption bandOxygen absorption band
Pro
hib
itedP
roh
ibited
UnlicensedUnlicensed
Wireless LANWireless LAN
Wireless LANWireless LAN
Test
Test
Rad
arR
adar
Mob
ile IC
BN
Mob
ile IC
BN
Ro
ad I
nfo
.R
oad
In
fo.
ISM
ISM
UnlicensedUnlicensedPt.Pt.--toto--Pt.Pt.
Space and fixed &
mobile apps.
Space and fixed &
mobile apps.
(Gary Baldwin)
CMOS can do it…
Year
1GHz
75 77 79 81 83 85 87 89 91 93
3u
2u1.5u
1u0.8u 0.6u
CMOS
ft
95 97 99
0.5u0.35u
0.25u
3GHz
10GHz
30GHz
100GHz0.18u
Slope is ~1/λ2
01
0.13u
03
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Applications
l Of course the most critical issue is what are these various radio systems useful for and who will buy them!
Issues in System Implementation
Wireless System Design Technologies
l It is now possible to use CMOS to integrate all analog and digital radio functions.
l New theories of wireless signal processing.l What makes an algorithm appropriate for
implementation is rapidly changing» Complex analog circuits linearly degrading» Digital computation exponentially improving
l Low power consumption has become increasingly important.
Potential System Limitationsl Analog impairments: digital compensation
and signal processing.l Multiple access and interference: code
diversity (CDMA), time diversity (TDMA), frequency diversity (OFDM), or spatial diversity (MIMO)
l Multipath: frequency spreading, time-domain equalization, or frequency-domain equalization.
l Integration with existing wired infra-structures.l Protocol efficiency: to QoS or not to QoS?
Communication Algorithms and Their Implementation
l Blast algorithms (Lucent) - antenna arrays which have demonstrated 40 b/s/Hz (1Mb/s in 25kHz)
l Multi-user detection - eliminates interference from other users
l OFDM - eliminates multi-path and ISIl Digital implementation of timing and carrier
synchronization …Requires 100’s of GOP’s of processing –
how to do it at the lowest energy and smallest area???
CMOS Radio-on-a-Chip
Rx_out
Synthesizer Control5GHz
Receiver
Tx_inTransmitter
DSP
ADC
DAC
8
8
8
8
Base
ban
d P
roce
sso
r
ADC
I
I
Q
QDAC
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Wireless Channel: Multipath Effects
Transmitter
Receiver
Dominant ReflectorMultipaths Local Scatterers
time….
time
pulse
freq
Inter-Symbol Interference (ISI)
Received data
MULTIPATH
Solutionsn Lower data rate
No ISI but low rate
MULTIPATH
Transmitted data
n Equalization or combiningn Complexity, performance (TDMA or CDMA)
n Code as multiple low-rate streamsn Each stream at different frequency - OFDM
Introduction to OFDM Modulation
Frequency
X2 *
X1 *
X3 *
X4 *
+Channel response
(multipath)
time
freq
Tx Rx
Symbol
Frequency
Y2
Y1
Y3
Y4
n Different data per tonen Multipath just scales tonesn Tones remain orthogonal
even with multipath
...
20 MHz20MHz OFDM channels in 5 GHz band
Design Example: 5GHz WLAN Standard
l 802.11a and Hiperlan II have very similar OFDM PHYs:» 20 MHz channel is divided into 64 carriers» Carriers are coded with varying modulation and error
correction code.» Each carrier is ~300kHz wide, giving raw data rates from
125kb/s to 1.5Mb/s
Symbol Encoding
l Channel sampled at 20MHz» 64-sample (3.2us) per symbol» 16-sample (0.8us) cyclic prefix / guard interval» 250 Ksymbols per second
l Of 64 the subcarriers:» 12 zero subcarriers (in black) on sides and center» 48 data subcarriers (in green) per symbol» 4 pilots subcarriers (in red) per symbol for
synchronization
20 MHz
OFDM (52 of 64 sub-carriers used)
Data Encoding
l Data subcarrier encoding» BPSK, QPSK, 16QAM, 64QAM» 1, 2, 4, 6 bits/subcarrier
l Error corrective coding» 1/2, 2/3, or 3/4 rate convolutional code» Increased robustness
l Overall data rates: » 6, 9, 12, 18, 24, 36, 48, 54 Mbps» Lowest: 48 * 1 * 1/2 * 250K = 6 Mbps» Highest: 48 * 6 * 3/4 * 250K = 54 Mbps
BPSK QPSK 16QAM 64QAM
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Integrated Baseband Chip
ADC/DACViterbi
Decoder
MAC Core
Time/FreqSynch
FFTDMA
PCI
AGCFSM
A Wireless System is More Than DSP
l Analog RF circuits» Amplifiers» Synthesizers» Mixers» Passive components
l Analog baseband circuits» Amplifiers» Filters» A/D and D/A converters
l Protocols
Transmitter Block Diagram
RF_OUT
LOIF(I)
PA
LORF(I)
LORF(Q)
LOIF(Q)
LOIF(I)
TX_I
TX_Q
5GHz
Receiver Block Diagram
LNA
PGA
DACDAC
RF_IN
RX_I
RX_Q
Offset
PGA
off-chip
Control 5GHz
LC LPF
off-chipLC LPF
LORF LO IF (I)
LNA
PGA
DACDAC
RF_IN
RX_I
RX_Q
Offset
PGA
off-chip
Control 5GHz
LC LPF
off-chipLC LPF
LORF LO IF (I)
LOIF(Q)
CMOS Integrated Analog Chip
Bias
Digitalcontrol
TX
PA MixerVCO
RXLNA Mixer PGA
CMOS Cost Model
l Cost – It doesn’t matter what you do on a CMOS chip, the cost is approximately constant and then reduces over time (e.g. $.10 per mm2)
» Cost of different data rates will be the same order of magnitude from kilobits -gigabits/sec.
» Cost is weakly dependent on carrier frequency(actually might get cheaper as the frequency goes up since passives are smaller)
» Cost increases weakly as a function of range (power amp)
l Moore’s law scaling improves the digital part of wireless system capabilities at nearly the same rate as it improves microprocessors, but doesn’t help the analog part (actually makes that part more expensive).
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Protocols: MAC and Network Implementation – e.g. 802.11
l Infrastructure mode» Access Point (AP)
– Essentially a bridge between wireless cells and wired infrastructure– Provides authentication, packet forwarding
» Stations associate with a particular AP» Stations may roam with no loss of service
– Roaming mechanism provides redundancy and robustness in addition to mobility
l Ad-hoc mode» Ad-hoc mode allows operation without any AP
APStation
Protocol enhancements
l New capabilities» Spatial multiplexing (beam-forming)» Multi-hop routing
l Requires» MAC modifications
–Coordination for multi-beam operation–More centralized scheduling for
efficiency» Compatible with standardized protocols
Basestation of Today
Non-sectorized
Basestation of Today
Non-sectorized
Co-sector interference issues
Sectorized
Basestation of the Future
Multiple simultaneous packets per sector
Multi-link beam-formed, sectorized
Future of Spatial Multiplexing
l Multiple transceiver chains performing adaptive beam-forming deliver multiple independent data streams in the same channel at the same time» Use both 5.7GHz and 2.4GHz bands -> 7 channels» Three sectors, 50 antenna element per sector» Total capacity 7*3*50/2*30Mbps = 15 Gbps !» Assumes reuse factor of one, many chips etc.
l Dynamic switching of Gbps over multiple wireless logical channels
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Wireless Multi-Hop Routing
l Route communication through intermediate nodes
» Decouple capacity from coverage
» Antenna beam-forming to create spatial diversity
» Transmit power control to limit interference“Unwired”
AP’sTraditionalapproach
AP
AP
AP
Full Mesh Network
Focus of this Course
3 components of the design problem» Algorithm specification – Matlab (or C)
» Floating point, implementation independent, system simulation
» Architecture mapping» Simulink for data flow» Stateflow for control
» Hardware optimizations» Real-time emulation» FPGA/ASIC implementation
Major topic areasl System modeling
» Channels» Interference» Analog impairments
l Wireless system algorithms» AGC» Synchronization» Modulation/Demodulation» Error correction» Protocols
l Computational algorithms» FFT» Cordic» Viterbi» …
l Architectures» Direct mapped» Time multiplexed» Reconfigurable» Software programmable