E225C – Lecture 1Wireless Systems Overview

Bob BrodersenBob Brodersen

Course Outline

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.

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

First part of the semester (up to the break) will be approximately (bi)weekly homeworks that will implement each block of a wireless transceiver

A final project will be to put a complete system together and demonstrate it on BEE

Lots of new radio systems being developed now

WiFi – 10-100Mbits/sec unlicensed band» OFDM, M-ary coding

3G – .1-2 Mbits/sec wide area cellular» CDMA, GMSK

Bluetooth – .8 Mbit/sec cable replacement» Frequency hop

ZigBee – .02-.2 Kbits/sec low power, low cost» QPSK

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 2G 3G

Is this exploitation of unlicensed bands a temporary aberration or the new reality???

Unlicensed WiFi Bluetooth ZigBee UWB

FCC Chairman Powell statement

We 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:

Unregulated radio interference will lead to chaos;

Spectrum is scarce Government command and control of the scarce

spectrum resource is the only way chaos can be avoided

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

ISM

(1986)

UPCS

(1994)

802.11a

(1997)

Millimeter Wave

(1998)

UWB

(2001)

Link Control

Modulation

Total Transmit Power

Power Spect Density

Antenna Gain

Out of Band Emission

More 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

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

802.11b

802.11g

3G

UWB

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,g

3G

Infrastructure cost

$ .10

$1

$10

$100

$1000

0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz

802.11a

ZigBee

Bluetooth

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

Te

st

Te

st

Ra

da

rR

ad

ar

Mo

bil

e I

CB

NM

ob

ile

IC

BN

Ro

ad

In

fo.

Ro

ad

In

fo.

ISM

ISM

UnlicensedUnlicensedPt.-to-Pt.Pt.-to-Pt.

Sp

ace and

fixed &

mo

bile

ap

ps.

Sp

ace and

fixed &

mo

bile

ap

ps.

(Gary Baldwin)

CMOS can do it…

Year

1GHz

75 77 79 81 83 85 87 89 91 93

3u

2u

1.5u

1u0.8u 0.6u

CMOS

ft

95 97 99

0.5u0.35u

0.25u

3GHz

10GHz

30GHz

100GHz0.18u

Slope is ~1/

01

0.13u

03

Applications

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

It is now possible to use CMOS to integrate all analog and digital radio functions.

New theories of wireless signal processing. What makes an algorithm appropriate for

implementation is rapidly changing» Complex analog circuits linearly degrading» Digital computation exponentially improving

Low power consumption has become increasingly important.

Potential System Limitations

Analog impairments: digital compensation and signal processing.

Multiple access and interference: code diversity (CDMA), time diversity (TDMA), frequency diversity (OFDM), or spatial diversity (MIMO)

Multipath: frequency spreading, time-domain equalization, or frequency-domain equalization.

Integration with existing wired infra-structures. Protocol efficiency: to QoS or not to QoS?

Communication Algorithms and Their Implementation

Blast algorithms (Lucent) - antenna arrays which have demonstrated 40 b/s/Hz (1Mb/s in 25kHz)

Multi-user detection - eliminates interference from other users

OFDM - eliminates multi-path and ISI 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

DS

P

ADC

DAC

8

8

8

8

Baseb

an

d P

rocessor

ADC

I

I

Q

QDAC

Wireless Channel: Multipath Effects

Transmitter

Receiver

Dominant ReflectorMultipaths Local Scatterers

time….

time

pulse

freq

Inter-Symbol Interference (ISI)

Received data

MULTIPATH

SolutionsLower data rate

No ISI but low rate

MULTIPATH

Transmitted data

Equalization or combining Complexity, performance (TDMA or CDMA)

Code as multiple low-rate streams 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

Different data per tone Multipath just scales tones Tones remain orthogonal

even with multipath

...

20 MHz20MHz OFDM channels in 5 GHz band

Design Example: 5GHz WLAN Standard

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

Channel sampled at 20MHz» 64-sample (3.2us) per symbol» 16-sample (0.8us) cyclic prefix / guard interval» 250 Ksymbols per second

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

Data subcarrier encoding» BPSK, QPSK, 16QAM, 64QAM» 1, 2, 4, 6 bits/subcarrier

Error corrective coding» 1/2, 2/3, or 3/4 rate convolutional code» Increased robustness

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

Integrated Baseband Chip

ADC/DACViterbi

Decoder

MAC Core

Time/FreqSynch

FFTDMA

PCI

AGCFSM

A Wireless System is More Than DSP

Analog RF circuits» Amplifiers» Synthesizers» Mixers» Passive components

Analog baseband circuits» Amplifiers» Filters» A/D and D/A converters

Protocols

Transmitter Block Diagram

RF_OUT

LO IF(I)

PA

LORF(I)

LORF(Q)

LOIF(Q)

LOIF(I)

TX_I

TX_Q

5 GHz

Receiver Block Diagram

LNA

PGA

DAC

DACRF_IN

RX_I

RX_Q

Offset

PGA

off-chip

Control 5GHz

LC LPF

off-chipLC LPF

LORF LOIF (I)

LNA

PGA

DAC

DACRF_IN

RX_I

RX_Q

Offset

PGA

off-chip

Control 5GHz

LC LPF

off-chipLC LPF

LORF LOIF (I)

LOIF(Q)

CMOS Integrated Analog Chip

Bias

Digitalcontrol

TX

PA MixerVCO

RX

LNA Mixer PGA

CMOS Cost Model 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)

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).

Protocols: MAC and Network Implementation – e.g. 802.11

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

Ad-hoc mode» Ad-hoc mode allows operation without any AP

APStation

Protocol enhancements

New capabilities» Spatial multiplexing (beam-forming)» Multi-hop routing

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

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.

Dynamic switching of Gbps over multiple wireless logical channels

Wireless Multi-Hop Routing 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 areas System modeling

» Channels» Interference» Analog impairments

Wireless system algorithms» AGC» Synchronization» Modulation/Demodulation» Error correction» Protocols

Computational algorithms» FFT» Cordic» Viterbi» …

Architectures» Direct mapped» Time multiplexed» Reconfigurable» Software programmable