Rajesh GuptaUniversity of California, Irvine

rgupta@ics.uci.edu

Mani SrivastavaUCLA

mbs@ee.ucla.edu

A

•T

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•UN

IVE

RS I

T Y • O F • C

AL

I FO

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IA•

•1868•

LET THE R E BE

LIG H T

Copyright 1997 Rajesh Gupta & Mani Srivastava

ICCAD 1997 Tutorial

Design Technology for BuildingWireless Systems

2

● 35-60% annual growth in PCS users● By 2000, one in three phones will be

mobile (42% in US)● Nordic countries: 10 mobile phones

being added for every wireline phone● Japan: number of users doubled from

10M to 21M from March to october 1996● 600M mobile phone users by 2001● $17B in PCS license auctions● 300% growth in wireless data from 1995

to 1997

Big demand for portable computers:

● 2m ($290M) in 1988 to 74M ($54B) in 1998● 20% of all computers sold are laptops

Phenomenal Growth in Wireless Voice & Data Services

3

“Anytime Anywhere Anyform” Information Systems

Fax & email on the beach

PCS & MultimediaMessaging on the road

Multimedia wireless LANs & PBXsin offices, schools, hospitals, homes

UCLA

mani

Networked sensors everywhere

Wireless Sensors

4

● Battery technology is a key hurdle - no Moore’s Law here!

Battery Rechargeable? Gravimetric Density (Wh/lb) Volumetric Density (Wh/l)

alkaline-MnO2 (typical AA) NO 65.8 347

silver oxide NO 60 500

Li/MnO2 NO 105 550

zinc air NO 140 1150

NiCd YES 23 125

Li-Polymer YES 65-90 300-415

Size & Battery Life are Critical in Wireless Devices

Year

Nom

inal

Cap

acit

y

65 70 75 80 85 90 950

10

20

30

40

NiCd

NiMH

(Wat

t-h

ours

/ lb

)

5

Where does the Battery Power go?

● Typical laptop: 30% display, 30% CPU + memory, 30% rest● Wireless devices: increasing communication & multimedia processing

Low power VLSI are a key to wireless

Laptop CellularPhone

Laptop +WirelessAdapter

PersonalWirelessTerminal

Microprocessor 1-4 W 1-4 W

Memory 1 W 1 W

Logic 2 W 2 W 0.3 W

Hard Disk 1 W 1 W

Display 2-6 W 2-6 W 0.185 W

Programmable DSP 0.5 W

RF Transceiver 2 / 4 W 0.6 / 1.8 W 0.6 / 1.8 W

Commn. Processing 2.5 W 2.5 W

Sound/Audio I/O ? ? 0.085 W

6

● Increasing integration of communication & multimedia systemcomponents due to advances in semiconductor technology & circuits

- RF CMOS circuits- MEMS structures

RF components, display

● Relentless digitization continues- high speed digital circuits & A/D converters

IF and even RF processing in digital domaindirect conversion techniques

- complex communication algorithms favor digital implementation- increasing CPU MIPS make even a “software radio” possible

A wireless-system-on-a-chip is becoming possible

Wireless Systems Design: Key Driving Forces

7

Building a Wireless System on a Chip

RF & IF Transceiver

Baseband Processing

CustomASICLogic

AlgorithmAccelerationCoprocessors

DSP Core

RAM/ROM

WirelessNetwork Protocol

ProcessorRAMROM

DRAM

Network/Host/Peripheral Interface

(Microcontroller)

ApplicationProcessor

RAM/ROMDRAM

8

Challenge to VLSI & CAD

RF & IF Transceiver

Baseband Processing

CustomASICLogic

AlgorithmAccelerationCoprocessors

DSP Core

RAM/ROM

WirelessNetwork Protocol

ProcessorRAMROM

DRAM

Network/Host/Peripheral Interface

analog circuits that minimizespecial analog process steps

maximize digital andminimize analog computation

reusable communication &

energy efficient embeddedsoftware synthesis

multimedia modules

(Microcontroller)

low cost & low powerprotocol processor cores

Computer with Radios

ApplicationProcessor

RAM/ROMDRAM

9

Present basics of wireless systems,and VLSI design issues, techniques, and tools

for building integrated wireless systems

This tutorial will NOT describe:- detailed CAD algorithms for solving system design problems- theory of radio and communication systems design- detailed architecture of any wireless communication systems

Tutorial Goals

10

● Introduction to Wireless Communication Systems- system and medium characteristics- technological evolution in the design of wireless communication systems

● Wireless Systems Design- digital communications: modulation, coding, multiple access- example designs

● VLSI Circuits for Wireless Systems- micro-architecture for wireless systems-on-a-chip- direct-conversion for digital communications using VLSI

● Design technology for Wireless Systems- design entry, validation, and analysis tools

● Pre-designed Core Blocks and IP Issues for Wireless● Future Outlook and Conclusions

Tutorial Outline

Part 1:

Introduction to Wireless Communication Systems

12

Wireless Spectrum

104 106 108 1010 1012 1014 1016 1018 1020 1022 1024Frequency in Hz

Radio

IR UV

LightX-Ray Cosmic

RaysLFMF VHF UHF

HF

46 49 824-849 869-894 902-928 1850-1990 2400-2483

Cordless(CT-1)

Cellular(AMPS, IS-136,

IS-95)

ISM PCS ISM

Frequency in MHz

5.15 - 5.35 & 5.725 - 5.825 GHz

U-NII

13

Diversity of Applications in Wireless Communications

● Multimega bits/sec throughput for robust, reliable multimedia networkingover wide range of environments.

Cellular: GSM, IS95, IS54, PDC,

Wireless Data: Mobitex, CDPD, pACT, GPS

Information

Environment

0.01

100.0

Content (Mbps)

10.0

1.0

0.1

OutdoorsIndoors

Office Building Stationary Walking Vehicular

Cordless:

WirelessLAN: IEEE 802.11

WirelessATM

Mobile Wireless Multimedia

DECT, PHS, PACS, WLL

Vid

eo te

leco

nfer

enci

ng

Inte

ract

ive

Dat

aVo

ice

Low

Dat

aR

ate

14

● Wireless- limited bandwidth, high latency- variable link quality (noise, disconnections, other users)- heterogeneous air interfaces- easier snooping necessitates encryption

● Mobility- user and terminal location dynamically changes- speed of terminal mobility impacts wireless bandwidth- easier spoofing necessitate authentication

● Portability- limited battery capacity, computing, and storage- small dimensions

Characteristics of Wireless Systems

moresignalprocessing

moreprotocol

higherenergyefficiency

processing

15

Time Varying Wireless Environment

● Available wireless resource undergoes dramatic & rapid changes- multipath reflection, doppler fading, frequency collisions

● Rapid signal fades & distortions as the receiver moves- e.g. noise-like Rayleigh Fading when multipath signals are summed

R

DS

D

No LOS!

LOS

16

Simplified View of a Digital Radio Link

SourceCoder

ChannelCoder Modulator

MultipleAccess

PowerAmplifier

carrier fc

SourceDecoder

ChannelDecoder

DemodulatorMultipleAccess

RFFilter

carrier fc

& Equalizer

antenna

antenna

Sou

rces

Des

tin

atio

ns

transmittedsymbol stream

Multiplex

Demultiplex

received (corrupted)symbol stream

SourceCoder

SourceDecoder

RADIOCHANNEL“Highly variable b/w”

“Random & Noisy”

“Limited b/w”

“Spurious disconnections”

17

● Line of Sight (LOS)- free space

● Reflection (with Transmittance and Absorption)- radio wave impinges on an object >> λ (30 cm @ 1 GHz)- surface of earth, walls, buildings, atmospheric layers- if perfect (lossless) dielectric object, then zero absorption- if perfect conductor, then 100% reflection- reflection a function of material, polarization, frequency, angle

● Diffraction- radio path obstructed by an impenetrable surface with edges- secondary waves “bend” around the obstacle (Huygen’s principle)- explains how RF energy can travel even without LOS, a.k.a “shadowing”

● Scattering (diffusion)- when medium has large number of objects < λ (30 cm @ 1 GHz)- similar principles as diffraction, energy reradiated in many directions- rough surfaces, small objects (e.g. foliage, lamp posts, street signs)

Pr PtGtGrλ2( ) 4π( )2d2L( )⁄=

Propagation of Radio Waves

18

● Assume average power (in dB) decreases proportional to log of distance

● Path-loss exponent, n, depends on propagation environment

● Problem: “Environment clutter” may differ at two locations at same d● Measurements show that at a given path loss has a normal distribution

- is a zero-mean Gaussian r.v. (in dB) with standard deviation (in dB)- says how “good” the model is

Environment nFree Space 2

Urban area cellular radio 2.7 - 3.5Shadowed urban cellular radio 3 to 5

In-building LOS 1.6 to 1.8Obstructed in building 4 to 6Obstructed in factories 2 to 3

PL d( ) PL d0( ) 10ndd0-----

log+=

d

PL d( ) PL d0( ) 10ndd0-----

log Xσ+ +=

Xσ σσ

Log-normal Shadowing Path Loss Model

19

● Maximum separation distance vs. transmitted power (with fixed BW)Given:

- cellular phone with 0.6W transmit power- unity gain antenna, 900 MHz carrier frequency- SNR must be at least 25 dB for proper reception- receiver BW is B = 30 KHz, and noise figure F = 10 dB

What will be the maximum distance?

Solution:N = -174 dBm + 10 log 30000 + 10 dB = -119 dBmFor SNR > 25 dB, we must have Pr > (-119+25) = -94 dBmPt = 0.6W = 27.78 dBmThis allows path loss PL(d) = Pt - Pr < 122 dBλ = c/f = 1/3 mAssuming d0 = 1 km, PL(d0) = 91.5 dBFor free space, n = 2, so that: 122 > 91.5 + 10*2*log(d/(1 km))or, d < 33.5 kmSimilarly, for shadowed urban with n = 4, 122 > 91.5 + 10*2*log(d/(1 km))or, d < 5.8 km

Example Link Budget Calculation

20

Small-Scale Fading

● Fading manifests itself in three ways1. time dispersion caused by different delays limits transmission rate

- replicas of signals with different delays (reflection, diffraction etc.)2. rapid changes in signal strength (up to 30-40 dB) over small ∆x

21

● Received signal a sum of contributions from different directions- random phases make the sum behave as noise (Rayleigh Fading)- “fades”: intervals of increased BER, or reduced channel capacity

Error Bursts due to Raleigh Flat Fading

In FadeGoodBER = 10-5 BER = 10-1

● Function of speed of mobile as well as other objects, e.g.,- a 50 kmph car in 900 MHz band: 1 ms long >20dB fade every 100 ms- a 2 kmph pedestrian in 900 Mhz band: 25 ms long >20dB fade every 2.5s

● Also, a function of frequency, and fade depth

● Diversity techniques help- multiple antennas, multiple frequencies

22

● “Frequency selective fading” results in inter-symbol interference

- e.g. GSM has a bit period of 3.69 µs, or a rate of 270 kbps

● Data rate can be improved by “equalization”- equalizer is a signal processing function (filter)

cancels the inter-symbol interferenceusually implemented at baseband or IF in a receiver

- must be adaptive since channel is unknown & time varyingtraining, tracking, and re-training during data transmission

● GSM example- with its equalizer, GSM can tolerate up to 15 µs of delay spread- otherwise, with 15 µs of delay spread, GSM would be limited to 7 kbps

maximum data rate without significant errors 0.1delay spread------------------------------=

Data Rate Limitation in Frequency Selective Fading

23

● Increase transmitter power- counters flat fading, but costly and greatly reduces battery life

● (Adaptive) Equalization- compensates for intersymbol interference

● Antenna or space diversity for “multipath”- usually, two (or more) receiving antennas, separated by λ/2- selection diversity vs. scanning diversity vs. combining diversity- “adaptive antenna arrays” or “smart antennas”

● Forward error correction- transmit redundant data bits - “coding gain” provides “fading margin”- not very effective in slowly varying channels or long fades

● Automatic Repeat Request (ARQ) protocols- retransmission protocol for blocks of data (e.g. packets) in error- stop-and-wait, go-back-N, selective-repeat etc.

Combating the Wireless Channel Problems

24

A Digital Radio Link

SourceCoder

ChannelCoder Modulator

MultipleAccess

PowerAmplifier

carrier fc

SourceDecoder

ChannelDecoder

DemodulatorMultipleAccess

RFFilter

carrier fc

& Equalizer

antenna

antenna

Des

tin

atio

ns

transmittedsymbol stream

Multiplex

Demultiplex

received (corrupted)symbol stream

SourceCoder

SourceDecoder

RADIOCHANNEL“Highly variable b/w”

“Random & Noisy”

“Limited b/w”

“Spurious disconnections”

25

Evolution of Mobile & RF Wireless Systems

● First Generation: Analog - Voice- analog modulation- cellular phone (AMPS) with manual roaming- cordless phones- packet radio networks

● Second Generation: Digital - Voice & Data- digital modulation- cellular & PCS phones with seamless roaming, integrated paging

(IS-54, IS-95, IS-136, GSM etc.)- digital cordless, multi-zone cordless, wireless PBXs- wireless data LANs (802.11), MANs (Metricom), WANs (CDPD, ARDIS,

RAM)

● Third Generation: Digital - Multimedia- unified digital wireless access anytime, anywhere- voice, data, images, video, music, sensor etc.

26

● Introduction to Wireless Communication Systems- system and medium characteristics- technological evolution in the design of wireless communication systems

● Wireless Systems Design- digital communications: modulation, coding, multiple access- example designs

● VLSI Circuits for Wireless Systems- micro-architecture for wireless systems-on-a-chip- direct-conversion for digital communications using VLSI

● Design technology for Wireless Systems- design entry, validation, and analysis tools

● Pre-designed Core Blocks and IP Issues for Wireless● Future Outlook and Conclusions

Tutorial Outline

Part 2-A:

Wireless Systems Design:

Basics

28

Simplified View of a Digital Radio Link

SourceCoder

ChannelCoder Modulator

MultipleAccess

PowerAmplifier

carrier fc

SourceDecoder

ChannelDecoder

DemodulatorMultipleAccess

RFFilter

carrier fc

& Equalizer

antenna

antenna

Sou

rces

Des

tin

atio

ns

transmittedsymbol stream

Multiplex

Demultiplex

received (corrupted)symbol stream

SourceCoder

SourceDecoder

RADIOCHANNEL“Highly variable b/w”

“Random & Noisy”

“Limited b/w”

“Spurious disconnections”

29

● Modulation: maps sequence of “digital symbols” (groups of n bits) tosequence of “analog symbols” (signal waveforms of length TS)

● Demodulation: maps sequence of “corrupted analog symbols” tosequence “digital symbols” - e.g. maximum likelihood decision

Digital Modulation & Demodulation - A “User’s View”

...(0110) (0111) (0000)...

n-bit digital symbol

Set S = {S1, S2,... SM} of M waveforms of length TS

MOD

S1

S2

SM

t=0 t=TS

CHANNELnoise, fading, etc.

DEMOD...(0110) (0111) (0000)...

TS-long analog symbolcorrupted

best effort output

n = floor(log2 M)

e.g. obtained by distinctively modifying the phaseand/or frequency and/or amplitude of a carrier

M=2 is “binary modulation”Otherwise, M-ary modulation

30

● Coherent or Synchronous Detection: process received signal with a localcarrier of the same frequency and phase

● Noncoherent or Envelope Detection: requires no reference wave

Coherent Non-Coherent

Phase-shift keying (PSK) FSK

Frequency-shift keying (FSK) ASK

Amplitude-shift keying (ASK) Differential PSK (DPSK)

Continuous phase modulation (CPM) CPM

Hybrids Hybrids

Commonly Used Digital Modulation Techniques

31

● Provides low bit error rates (BER) at low signal-to-noise ratios (SNR)● Occupies minimal bandwidth● Performs well in multipath fading● Performs well in time varying channels (symbol timing jitter)● Low carrier-to-cochannel interference ratio● Low out of band radiation● Low cost and easy to implement● Constant or near-constant “envelope”

- constant: only phase is modulatedmay use efficient non-linear amplifiers

- non-constant: phase and amplitude modulatedmay need inefficient linear amplifiers

No perfect modulation scheme - a matter of trade-offs!

Selecting a Modulation Schemes

32

● Power Efficiency (or, Energy Efficiency)- ratio of signal energy per bit to noise power spectral density required

required at the receiver for a certain BER (e.g. 10-5)

- measures ability to give low BER at low signal power levels- impacts battery life!

● Bandwidth Efficiency- ratio of throughput data rate to bandwidth occupied by modulated signal

- measures ability to accommodate data within a given bandwidth

● Often a trade-off between power and bandwidth efficiencies, e.g.- adding redundancy (FEC) reduces bandwidth efficiency, but reduces the received power required for a given BER- modulation schemes with higher values of decrease but increase

for a given BER

ηP

ηP Eb N0⁄=

ηB

ηB R B⁄ bps/Hz=

M B Eb

Metrics to Evaluate Modulation Schemes

33

● At 0.001% BER and a fixed transmission bandwidth:

● BPSK and QPSK has the same energy efficiency but QPSK has two timesmore bandwidth efficiency (bit rate gain factor) than BPSK.

● The drawback of using QPSK is in the poor achievable energy efficiencyin practice => use GMSK to achieve a bandwidth efficiency of 1.25 withBT = 0.3.

a. Relative to BPSK (M=2)

MPowerPenalty

Factora

Bit-RateGain

Factora

EnergyPenaltyFactora

2 1 1 1

4 2 2 1

8 4.7 3 1.56

16 10 4 2.5

32 20.7 5 4.1

64 42 6 7

Choice of a Modulation Scheme

34

● Signal set represents points in a vector space

● Vector space defined by a set of orthonormal (i.e. orthogonal andwith unit energy) basis signals

- is the dimension of the vector space

● Every can be expressed as a linear combination of basis signals

● Example: BPSK signals and

can be represented as:

S s1 t( ) s2 t( ) … sM t( ), , ,{ }=

N M≤φ j t( ) j 1 2 … N, , ,={ }

N

si t( )

s1 t( ) 2Eb Tb⁄ 2π f ct( ) 0 t Tb≤ ≤cos=

s2 t( ) 2Eb Tb⁄ 2π f ct π+( )cos=

φ1 t( ) 2 Tb⁄ 2π f ct( )cos=

s1 t( ) Ebφ1 t( )=

s2 t( ) Eb– φ1 t( )=

A Geometric View of Modulation

35

● Geometric representation of is called the Constellation Diagram,e.g. for BPSK:

● Bandwidth occupied by the modulation scheme decreases as thenumber of signal points / dimension increases

- a densely packed modulation scheme is more bandwidth efficient- however, bandwidth increases with dimension

● Probability of bit error is a function of the distance between the closestpoints in the constellation diagram

- a densely packed modulation scheme is less power efficient

S

EbEb–I

Q

N

The Constellation Space

36

● M-ary QAM

● M-ary PSK

I

Q

M=16d2 6

M 1–--------------Es=

d

I

Q

M=4d 2 Es

πM-----sin=

d

Some Examples...

37

● Ref.: Wireless Information Networks by Pahlavan & Levesque, 1995

Comparison of Several Modulation Methods

38

Simplified View of a Digital Radio Link

SourceCoder

ChannelCoder Modulator

MultipleAccess

PowerAmplifier

carrier fc

SourceDecoder

ChannelDecoder

DemodulatorMultipleAccess

RFFilter

carrier fc

& Equalizer

antenna

antenna

Sou

rces

Des

tin

atio

ns

transmittedsymbol stream

Multiplex

Demultiplex

received (corrupted)symbol stream

SourceCoder

SourceDecoder

RADIOCHANNEL“Highly variable b/w”

“Random & Noisy”

“Limited b/w”

“Spurious disconnections”

39

Multiple Access

● Fundamental problem

How to share the Time-Frequency spaceamong multiple co-located transmitters?

Time

Shared Time-Frequency Subspace

Freq

uen

cy

All

ocat

edS

pec

tru

m

40

Basestation versus Peer-to-Peer Models

Basestation Peer-to-Peer(ad hoc network - fully-connected vs. multihop)(infrastructure - centralized)

41

Approaches to Wireless Multiple Access

Sharing of Time-Frequency Space

Static (Fixed) Assignment Demand-based Assignment

Contention-based

Conflict-free

e.g. Time-division &Frequency-division

e.g. Token-passing &Polling

e.g. ALOHA, PRMACarrier-sensing

“Connection Oriented”

“Packet Oriented”

Random Access Scheduled Accesse.g. DQRUMA

Slotted-timevs. Non-slotted time

Controlled RandomAccess

42

Frequency Division Multiple Access (FDMA)

● Assign different frequency bands to individual users or circuits- frequency band (“channel”) assigned on demand to users who request service- no sharing of the frequency bands: idle if not used- usually available spectrum divided into number of “narrowband” channels

symbol time >> average delay spread, little or no equalization required- continuous transmission implies no framing or synchronization bits needed- tight RF filtering to minimize adjacent band interference- costly bandpass filters at basestation to eliminate spurious radiation- usually combined with FDD for duplexing

f2

f2’ f1

f1’

Time

Freq

uen

cy

f1

f1’

f2

f2’

43

Time Division Multiple Access (TDMA)

● Multiple users share frequency band via cyclically repeating “time slots”- “channel” == particular time slot reoccurring every frame of N slots- transmission for any user is non-continuous: buffer-and-burst

digital data & modulation needed, lower battery consumption- adaptive equalization is usually needed due to high symbol rate- larger overhead - synchronization bits for each data burst, guard bits

guard bits for variations in propagation delay and in delay spread- usually combined with either TDD or FDD for duplexing

TDMA/TDD: half the slots in a frame used for uplink, half downlinkTDMA/FDD: identical frames, with skew (why?), on two frequencies

Time

Freq

uen

cy

slot 2

slot 6 slot 1

slot 5

frame i frame i+1frame i-11 2 5 6

Sync Data Guard

44

● GSM handles time dispersion widths up to 18-20 µs... i.e. 5 bits of ISI- transmission bandwidth >> channel coherence bandwidth

● IS-54 handles time dispersion up to 40 µs... i.e. 2 symbols might interfere- less complex equalizer needed than GSM|

● Need equalization indoors at rates > 2 Mbps (DECT is only 1.152 Mbps)

GSM IS-54 DECT PHS

Bit rate 270.8 kbps 48.6 kbps 1.152 Mbps 384 kbps

Carrier spacing (b/w) 200 kHz 30 kHz 1.728 MHz 300 kHz

Time slot duration 0.577 ms 6.7 ms 0.417 ms 0.625 ms

Slots/frame 8 (or 16) 3 (or 6) 12 4

FDD or TDD? FDD FDD TDD TDD

% payload in time slot 73%adaptive equalizertraining overhead

80%adaptive equalizertraining overhead

67%system control

overhead

71%

Modulation GMSK π/4 DQPSK GMSK π/4 DQPSK

Adaptive equalizer required required none none

Some TDMA Systems

45

Hybrid FDMA/TDMA

● “Pure” TDMA with single frequency band is undesirable- require tight timing tolerances

● Most TDMA systems actually employ hybrid FDMA/TDMA- multiple carriers with multiple channels per carrier- channel == (frequency band, time slot) tuple- may do “frequency hopping” on a frame-by-frame basis to combat

multipath interference (Time Division Frequency Hopping: TDFH)increases system capacity

(f5, t1)

(f3, t4)(f1, t1)

(f2, t3)

Freq

uen

cy

frame i frame i+1frame i-1

f1f2

f3

f4

f5

f6

t1 t2 t3 t4

46

Code Division Multiple Access (CDMA)

● Multiplexing in the Code Space- multiple transmitters occupy the same frequency-time space- transmissions encoded with codes with very low cross-correlation- receiver retrieves a specific transmission with its corresponding code

● CDMA may be combined with TDMA or FDMA

c1

c3c5

c2

Frequency

Cod

e

47

Spread Spectrum Signalling

● Spread Spectrum is the most common CDMA encoding technique- originally developed for military communication systems- “spread” the signal over a much larger bandwidth than the minimum- signal appears pseudo-random with noise like properties- uniform small energy (W/Hz) over a large bandwidth hides the signal

⇒ Note: use of spread-spectrum does not imply use of CDMA● Spreading is done using a unique code● Receiver does the “despreading” by using a time-synchronized

duplicate of the spreading code● Inefficient for a single user, but multiple users can share band● Inherent interference rejection capabilities (e.g. narrowband interferers)● Resistant to multipath effects

- delayed versions appear as uncorrelated noise- can even exploit multipath signals by combining them

● Processing Gain: Gp = Bspread / Bsignal- indicates improvement in signal-to-interference ratio due to spreading

48

What is Spread Spectrum Communication?

Wide BandAnti-jam -> high capacity CDMACombats multipath -> diversityLPI -> PrivacyLPD -> low power density

PGf spread

f bit---------------------=

despread signalspread interference

fdata

Adata

Ai,received

spectral density

frequency

unspread signal

spread signal

interference

fdata

fspread

frequency

spectral density

Adata

Aspread

Ai

frequency

spectral density

TRANSMIT RECEIVESpreading Code run-ning at .f spread

49

CDMA Using Direct Sequence (DS) Spread Spectrum

● Spread the narrowband data by multiplying with a wideband pseudo-random code sequence

- bits sampled, or “chipped”, at a higher frequency (e.g. 1.228 Mcps in IS-95)- signal energy is “spread” over a wider frequency (e.g. 1.25MHz in IS-95)- code sequences have little cross-correlation (orthogonal)- code sequences have little correlation with shifted versions of self

● Received signal multiplied by synchronized replica of the code sequence● Energy of each “chip” is accumulated over a full data bit time

X

transmitted signal

PN Sequence (code)

digital data

01101011

X =

01101011

Intended receiver

10110010

X =

Other receiversNoise - can be low pass filtered

Recovered signal

Chip

50

CDMA Using Frequency Hopping Spread Spectrum

● Transmission frequency is periodically changed- available spectrum divided into bands with central frequencies as carriers- sequence of data bursts with time-varying pseudo-random carrier frequencies- time duration between hops is the hop duration or hopping period Th- bandwidth of a frequency band in the hopset is the instantaneous b/w B- bandwidth of spectrum over which hopping occurs is total hopping b/w Wss- processing gain is Wss/B

● Fast frequency hopping: more than one hop during each transmitted symbol● Slow frequency hop: one or more symbols transmitted in a hop

Freq

uen

cy

f1f2

f3

f4

f5

f6

channel #1channel #2

51

Contention-based Multiple Access

● Many transmitters access a channel with no or minimal coordination● Transmission in bursts of data● Collisions may happen: need ACK or NACK with retransmission

- delays induced- lower spectral efficiency

● Three categories: random access, scheduled access, hybrid access

Packet B Packet C

Packet A

One PacketTime (τ)

Vulnerable Period (2τ)

Time

Transmitter # 1

Transmitter # 2

52

● Ethernet uses contention-based medium access...

● Following attributes make contention-based multiple access interestingwith wireless:

- “carrier sensing” is much costlier in wireless20-30 µs

- can’t listen while transmittingtherefore cannot detect collisions

- what matters is the collision at a receiver... but the transmitter can’t sense the channel at the receiver!

- effects of spatial distribution of wireless nodeshidden terminal problemexposed terminal problemnear-far problem (capture effect)

Contention-based Multiple Access in Wireless Systems?

53

IEEE 802.11 MAC

● Support for multiple PHYs: ISM band DSSS and FHSS, IR @ 1 and 2 Mbps● Efficient medium sharing without overlap restrictions

- multiple networks in same area and channel space- Distributed Coordination Function: using CSMA /CA- based on carrier sense mechanism called Clear Channel Assessment (CCA)

● Robust against interferers (e.g. co-channel interference)- CSMA/CA+ACK for unicast frames with MAC level retransmission

● Protection against Hidden Terminal problem: Virtual Carrier Sense- via parameterized use of RTS/CTS frames with duration information

● Provision for Time Bounded Services via Point Coordination Function● Configurations: ad hoc & distribution system connecting access points● Mobile-controlled hand-offs with registration at new basestation

distribution systemad hoc network

infrastructure network

54

IEEE 802.11 MAC (contd.)

● CSMA/CA: direct access if medium free for > DIFS, else defer & back-off

source

other

DIFS

DATA

DIFS

SIFS

PIFS

defer access

DATAselect slot & decrementback-off as long as idle

contentionwindow

● CSMA/CA + ACK: receiver sends ACK immediately if CRC okay- if no ACK, retransmit frame after a random back-off

source

other

DIFS

DATA

SIFS

defer access

DATAselect slot & decrementback-off as long as idle

contentionwindow

receiver ACK

DIFS

● RTS/CTS with duration: distribute medium reservation information- also used in the defer decision

55

● Replace single high power transmitter covering the entire service areawith lots of low power transmitters (basestations) each covering afraction of the service area (cell)

- mobiles in sufficiently distant basestations may be assigned identicalchannel (frequency, time slot, & code)

- system capacity may be increased without adding more spectrum

● Major conceptual breakthrough in spectral congestion & user capacity- required relatively minor technological changes

frequency reuse & co-channel interferencechannel allocationhand-offs

Cellular Systems

Pre-Cellular Post-CellularMSC PSTN

56

Space Division Multiple Access (SDMA)

● Control radiated energy for each user in space- spot beam antennas (sectorized antennas)- different areas served by different antenna beams may use same

frequency (CDMA, TDMA) or different frequencies (FDMA)- in future, adaptive antennas

Part 2-B:

Wireless Systems Design:

Standards, Design Issues, and Examples

58

The Un-wired World

Wireless Communications

Amateur Industrial Consumer Business Military/Aero Long-Haul

Automotive Monitoring

Cordless Cellular Paging WPABX WLAN PMR/SMR Mobile Data

- IVHS- GPS

- AMR- Control

Analog Digital Analog Digital

- CT-0- CT-1- CT-300

- DECT- CT-2- PHP- USCT- ISM

- AMPS- ETACS- NMT450- NMT900- NMT-0- Comvik- JTACS

- GSM- IS-54- IS-95- IS-136- RCR-27

- POSCAG- ERMES- SSB

- DECT- CT-2- PHP- USCT- ISM

- 802.11- DECT- HIPerLAN- ISM

- ARDIS- Mobitex- Omnitracs- Cellular/CDPD

ESMR

Conv

- MIRS- TETRA

PCN/PCS

- DCS1800- PHP- LEO

- FPLMTS- UMTS- RACE

- Metricom

59

Evolution of PCS Technologies, Systems, and Services

Cellular

Paging

Cordless

Wide Area Data

WLANs

High-tier PCS

Low-tier PCS

WLANs

Satellites?Macro-cellular

Micro-cellular

Messaging

Phone point

PABX

Cordless

Micro-cells

Macro-cells

WLANs

?

?

?

?

PAST PRESENT FUTURE

GrandUnification?

60

AMPS System (First Generation Analog)

● Two 25 MHz bands: 824-849 MHz upstream, 869-894 MHz downstream● Divided into 30 MHz frequency bands - pair needed for a duplex channel● FDD+FDMA: 834 duplex channels● 7-way frequency reuse (18 dB min. signal-to-co-channel interference)● Two types of channels: control and voice channels● Network controlled handoff - MSC becomes a bottleneck● Capacity constraints - 40-50 connections per cell● No on-air privacy, fraud a major problem

MSC(MTSO)

BS

BS

BS

BS

BSBS

MS

HLR VLR AUC

OMC

PSTN

databases

SS7Proprietary

AMPS CommonAir interface

MSC(MTSO)

mobilitymanagement

61

GSM System (Second Generation Digital)

● Two 25 MHz bands: 890-915 MHz upstream, 935-960 MHz downstream● Divided into 200 KHz frequency bands - 125 in each direction● FDD+TDMA+FH: 8 slots/4.615 ms frame, 270.833333 kbps raw, 22.8 kbps/user● Frequency hopping to combat multipath problems● Two types of logical channels: traffic channels and control channels● Mobile assisted handoff - BSC reduce the load on MSC● Features: subscriber identity module and on-air privacy● Services: telephone, data or bearer, short messaging

BSC

BSC

MSC(MTSO)

BTS

BTS

BTS

BTS

BTSBTS

MS

HLR VLR AUC

OMC

PSTN

databases SS7A InterfaceAbis Interface

GSM RadioAir interface MSC

(MTSO)

62

● Packet data network overlay on AMPS - same 30 KHz channels● Data packets are sent over unused voice channels● Channel hopping ensures non-interference with voice● Raw data rate is 19.2 kbps Reed-Solomon coded - real rate much less● Broadcast downlink, Data Sense Multiple Access (DSMA) MAC on uplink● Variety of connection-less, connection-oriented, and multipoint services● Reliable and unreliable classes - handling over radio link● In particular, IP (Internet Protocol) datagram connectivity● Mobile controlled handoff, registration at basestation to reduce paging● “Home MD-IS” tunnels incoming traffic to current MD-IS

Cellular Data Packet Network (CDPD)

M-ESMD-BS

MD-BS

MD-IS IS

Data n/w(internet)

M-ES

MD-BS

MD-BS

MD-IS

F-ES

ISmobility

managementconnection-less

router

63

Designing Mobile Wireless Multimedia Systems

WIRED NODE

PSTN

modem

ethernettransceiver

• antenna• RF + A/D• digital transmitter/receiver• channel codec• source codec• network protocols

BASE STATION

WIRELESSNODE

ETHERNET

PHONE

http://www.N

http://www.N

64

Generic Mobile & Wireless System Architecture

Radio, IR

Data Link

OS & Middleware

Network

Application & Services

Modulation Schemes

Multiple Access

ReroutingImpact on TCP

Link Error Control

Channel Coding

Channel Allocation

Location Tracking

Disconnection Mgmnt.Power Management

Partitioning

QoS Management

Source Coding & DSP

RF/Optical Circuits

Context Adaptation

65

Radio Design Challenges

● High speed digital processing● High performance in Eb/N0● Low complexity● Energy efficient (mW/MSps or nJ/OP)

Algorithm Fixed Point

Digital ModemIC Architecture

RF Front-endArchitecture

Partition

66

Partition between Analog and Digital Processing

Analog RF Analog IF Baseband Digital BasebandSignal Processing

ConverterTransceiver Signal ProcessingAnalog-to-Digital

Digital IFTransceiver

Analog-to-DigitalDigital BasebandSignal Processing

Converter

Analog RF Signal Processing

IF

● Advantagesallows for adaptability with little component replacementsachieves Eb/N0 performance close to optimum (coherent BPSK)parameterizable to provide ease of redesign and upgrade

● Challengesdigital circuits operate at IF signal rate rather than baseband ratedigital implementation can be more complex to minimize loss in Eb/N0

67

● Low complexity, high speed, adaptable, and energy efficienttransceiver in a single-chip

A Direct-Sequence Spread-Spectrum Radio Modem

CARRIER

LOOP

CLOCK

LOOP

PN VGA AMPLPF

LPFA/D

BPF

LNAAGC

Spread Data

6RECOVERY RECOVERY

GENERATORTX

POWER CONTROL

FREQ CNTRL

PN

LOOPAcquisition

Decision

To SIR Est. Recv. Data

TX DataCarrier DetectCODE

SELECTPROCESS

GAIN

FREQUENCYSYNTHESIZER

Ack.: C. Chien & R. Jain, UCLA

68

● Challenge: Implement a complete coherent receiver on a single chip

● Circuit Design Issuesfinite wordlengthparameterizabilitycritical path optimizationcomplexity reduction

● System Design Issuesmaintain stability in three feedback loops.

Transceiver Chip Design Issues

69

Costas Loop Filter Optimization

0 510 15

20 2530 35

0

10

20

30

40−80

−60

−40

−20

0

20

INPUT Ec/N0= -17 dB

N1

N2

Eb/N

0 (d

B)

Coefficient as powers of two shifts:

Optimization Criteria:min max N1 N2,( )( ), Eb N0⁄ 10 0.5±≥

D

C2 2N2–=

C1 2N1–= C1

C2

N1

N2

5 10 15 20 25 30

5

10

15

20

25

30

10 dB

9 dB 0 dB

-10 dB

Ack.: C. Chien &R. Jain, UCLA

70

IF Wordlength Optimization

Out

put E

b/N

0 (d

B)

IF Input Quantization Size (Bits)0 5 10 15

0

10

20

30

40

IF Input Quantization Size (Bits)

Com

plex

ity In

crea

se (

%)

❥ Minimize IF quantization size reduce complexity and powerdissipation at required throughput.

min N( ), Eb N0⁄ 10 0.5±≥

N

DD

FS

N

N

-17 dB

-11 dB

0 dB

10 dB

4 8 12 160

100

200

300Complexity increase in receiverSample rate through the multiplier50.8 MHz sample rate requirement

0

50

100

150M

ultip

lier

Sam

ple

Rat

e (M

Hz)

Ack.: C. Chien &R. Jain, UCLA

71

PN-Acquisition: Complexity/Performance Trade-off

Clock

Generation

EnergySlope

Detection

PN-CodeGenerator

❥ 800 Gates

❥ Nc * Nif * 12 Gates + 800

Nc = #chips/bit

Nif = IF Quantization

❥ 10 000 Gates with N c =127 and Nif = 6

ReceivedPN

Timing

N-TapMatched

Filter

Energy

Detection

Clock

Generation PN-CodeGenerator

Match Filter Acquisition

Serial Acquisition

Timing

ReceivedPN

● PN acquisition: correlation between the incoming bits and the P/Nsequence of the desired transmitter

72

A Single-Chip 1.2 Micron CMOS DSSS Radio Modem

❥ Low Complexity -- 51 K Transistors

❥ High Power Efficiency -- 21.7 mJ/MSample

❥ Maximum Chip Rate -- 12.7 Mchips/sec

❥ Scalable Performance -- Data Rates andProcessing Gain: 100, 200, 400, 800 kbps at12, 15, 18, 21 dB, respectively

Performance

DIGITAL IF RECEIVER

-

+

LAT

E P

N

IF S

AM

PLIN

G C

LK

PN

TR

AC

K C

ON

TR

OL

CLOCK RECOVERY

INTEGRATEDUMP I1

INTEGRATEDUMP Q1

IFSIGNAL

DATAOUT

COSTAS LOOP

INTEGRATEDUMP I1

INTEGRATEDUMP Q1

DD

FS

LOOPFILTER

PHASEDETECTOR

INTEGRATEDUMP I2

INTEGRATEDUMP Q2

LOOPFILTER NCO

CHIPDELAY

EA

RLY

PN

50.8 MHz 12.7 MHz

50.8 MHz 12.7 MHz 406.4 MHz

100 kHz -12.7 MHz

PN-ACQUISITIONLOOP

DIFFERENTIALDECODER

(100-800) kHz

DIGITAL BASEBAND TRANSMITTER

DATAINPUT SPREAD

DATA

GOLD CODEGENERATOR

(PNGEN)

DIFFERENTIALENCODER

Ack.: C. Chien & R. Jain, UCLA

73

Integration of Radio into a System

CPU

Keyboard

Memory and MassStorage

Camera

DT FrameGrabber

Custom FrameGrabber

ProximRangeLAN2

Adaptive Direct SequenceSpread Spectrum Radio

Video CodecFPGA

RF Front-endDSSS IF modem,Packet Interface,Adaptation Interface,Analog-Digital Conversion

Single-chip DSSSModem IC

Ack.: C. Chien & R. Jain, UCLA

74

Example 1: UCLA’s Wireless Multimedia Node

Wireless

Channel

Serial Data HostInterface Interface

HostCPU

Frame

Buffer 12-bit RGB

16-bit

CompressedData Interface

Host

YUV

Interface

Control

Buffer

Video

Network Interface Chip

Video

Capture

VGA

Controller

VideoCodec

Modem

PC-1

04 B

us

PacketBuffer

75

Example 2: Bell Labs’ SWAN Wireless ATM System

FHSS RF XCVR

XCVR Interface

Host Interface

CPU

Perip

he

ral

Inte

rfac

e

FHSS RF XCVR

XCVR Interface

Bus Interface

CPU

Perip

he

ral

Inte

rfac

e

FHSS RF XCVR

XCVR Interface

Bus Interface

CPU

Perip

he

ral

Inte

rfac

e

BASESTATION

FHSS RF XCVR

XCVR Interface

Host Interface

CPUPe

riph

era

lIn

terfa

ce

FAWNFlexibleAdapter

BASESTATION MOBILE END-POINTS

Mobile

SY

ST

EM

S

/W

ForWirelessNetworking

CPU

BACKBONEATM

ADAPTERCARD

To Antenna

Connection Switching

Mobility Management

Drivers for Adapter Cards

MAC

PHY

ATM SWITCH

Notebook

Personal

ET

HE

RW

AR

E

Communicator

PersonalMultimediaTerminal

Lucent

mani

76

FAWN Reconfigurable Wireless Adapter

Dimensions 10.8 cm (W) x 1.9 cm (H)x 11.4 cm (D)

Power Consumptionof FAWN

2.0 W

Power Consumptionof radio transceiver

0.6 W (receive)1.8 W (transmit)

Firmware resources 20 MIPS, 4 MByte

Reconfigurablehardware resources

10000 Gates equivalent

PCMCIA

Dual Port RAM

PCMCIAInterface

PeripheralInterface

RF Modem

ADC

ModemController

UARTSRAM

Control PAL

ARM CPU

to hostprocessor

77

● Simple hardware- peripheral card + FAWN adapter

● Multimedia interface- audio, graphics, soft keys, bar code

● Dumb end-point for “network-hosted mobile services”

Example 3: Personal Mobile Terminal

LCD display

Bar code scannerScanner switch

Soft keys

PRESS TO SCAN↓ ↓

SC

AN

NE

R

microphone

Personal Terminal 6808

78

Example 4: Berkeley’s Infopad Project

● Infopad: low power wireless multimedia terminal- no local general purpose processing (“dumb terminal” model)- speech and pen controlled user interface- audio, video, and text/graphics streams to the terminal

● Infonet: network infrastructure for Infopads- based on cell, pad, and type servers

● Medley Gateway: transport & coding of video, audio, & graphics to Infopad● http://infopad.eecs.berkeley.edu/

79

Infopad Terminal Architecture

● References:1. http://infopad.eecs.berkeley.edu/research/terminal2. [Narayanaswamy96] Narayanaswamy et. al., “Application and

Network Support for Infopad,” in IEEE Personal Communications, April ‘96

PlesseyDownlink

Radio

ProximUplinkRadio ARM

SubsystemRX/TX

Interface

Low Power Infopad Bus

LCDIF

PENIF

AUDIOIF

VIDEOIF

250 Kbps

1 Mbps

Infopad

ucb

Color

Subsystem mW

Radios 1490

ARM 877 - 2475

Custom H/W 137 - 297

B&W LCD 550 - 3800

Color LCD 3900

Pen Digitizer 150

Codec 50

Voltage Converters 2411

Crystals 75

Test H/W 629

Total 9.9W - 15W

Color

80

Example 5: Xerox PARCTAB

● Extremely portable mobile unit- 7.8x10.5x2.4 cm3, 215 gm, 6.2x4.5 cm2 & 128x64x1 touch screen, 3 buttons- IR communication at 19.2 kbaud with CSMA MAC, PWM modulation- 12 MHz Signetics 87C524/528 CPU, 128K memory

● Basestation transceiver (on ceiling of a room nanocell)- IR with variable data rate: 9.6K, 19.2K, 38.4K; CSMA MAC- 38.4K serial link up to 30m with 10 unit daisy chain capability- performs coding/decoding, buffering, link level protocol checks- connected to LAN via serial port of nearby workstations

● Remote host based applications, proxy agents (per tab),and gateways (datagram service to tab)

● http://www.ubiq.com/parctab

Tab Basestation

81

Design Trade-offs in Wireless Nodes

● Computation-communication trade-off affects:- terminal cost- service cost

Term

ina

l Co

mp

lexi

ty

Communication Needs &

Laptops

PDAs

Terminals

Comp

utation

Storag

e Palmtops

Notebooks

Infrastructure Dependence

82

● Adaptive process gain improves throughput

● Multipath fading requires equalization

● Bit rate limited by equalizer complexity

Throughput can be improved by physical layer processing

Design Issues

83

Adaptive Process Gain Improves Throughput

−15 −10 −5 0 50

20

40

60

80

100

PG = 12 dB

PG = 15 dB

PG = 21 dB

Thr

ough

put (

kbps

)

Signal-to-Interference Ratio (dB)

Desired

Achieved

84

Top

Total Radio Power = 11.87W

Total IF Power = 6.118 W

Total RF Power = 5.75W

Transmit

Receive

Freq. Synth.

AGC

Control

Bottom

Power Reg.

RF Processing: Power Dissipation

85

IF/Baseband Processing: Power Dissipation

Analog IF

DSSS

DSSS

Packet InterfaceControl

Top Bottom

Power Regulation

Total Radio Power = 11.87W

Total IF Power = 6.12W

Total RF Power = 5.75 W

Note: Power budget figures includes power dissipation from regulation inefficiencies.

86

Multipath Fading Requires Equalization

0t

102

3

t0 t2 t1 t3

τ

• τ > Its / 10 ⇒ ISI causes degradation in BER and willrequire equalization

• τ is a function of transmit power and cluttering in theenvironment

Dense Foliage Urban Clutter

Transversalequalizer

Linearfeedbackequalizer

TransversalequalizerLinear

feedbackequalizer

Linearfeedbackequalizer

Transversalequalizer

Nointerference

31 taps in transversal equalizer

16 feedforward and 15 feedbacktaps in linear feedback equalizer

γ 1No------- fk

2

k∑=

Pro

babi

lity

of e

rror

SNR, db (10 log γ)

10-1

5

2

10-2

5

5

5

2

2

10

10-3

10-4 0 15 20 25 30 35

MobileWirelessChannel

}

87

● Improved performance using MLSE over DFE/FFE

- short training sequence O(100) vs. O(1000) bits

● But, MLSE has high complexity and processing requirements- complexity ∼ O (4 τ Rs M τRs)- e.g. M=2, τ = 3ms, Rs = 2 Mbaud = 2 Mbps

then, complexity ~ 1600 operations ~ 30k gatesprocessing ~ 1600 * 2MHz = 3.2 GOPS

MlSE simulation

Destination-feedbackequalizer

Correct bits

Detected bitsfed back

MlSEbounds

Nointerference

SNR, dB (10 log γ)

Pro

babi

lity

of e

rror

1

10-1

10-2

10-3

10-40 5 10 15 20 25

fed back

Bit Rate Limited by Equalizer Complexity

88

Physical Layer Processing to Improve Throughput

preamble header DATA

throughput = Tpreamble + Theader + Tdata

Tdata

max(throughput) ⇒ min(Tpreamble), min(Theader)

Theader is protocol dependent• TCP/IP header• ATM header• MAC/link layer header

Tpreamble is physical layer dependent• time to acquire / capture packet• settling time of LO frequency

capture-time accumulatesin multihop networks

Aggressive signalprocessing canreduce this!

89

Understanding Energy Efficiency

P = α C V2 f

“Continuous”“Event-Driven”

Latency is ImportantOnly Throughput is

Important

Reduce V

e.g., Speech CodingVideo Compression

e.g., X Display Server

(Burst throughput)

Increase h/w andalgorithmic concurrency

Make f low or 0Shutdown when

Disk I/OReduce αCEnergy efficient s/w CommunicationSystem partitioning

inactive

Efficient Circuits & Layouts

90

Voltage-Parallelism Trade-Off for Low Power

● Increased parallelism & reduced voltage can increase energy efficiency- more processors or functional units or pipelining- compiler techniques are the key

● Architectural bottlenecks:- degradation of speed-up- capacitance overhead due to increased communication

1.0 1.5 2.0 2.5 3.0Supply Voltage, V

1.0

3.0

5.0

7.0

Nor

mal

ized

Del

ay

1 2 3 4 5 6 7 8Parallelism, N

1.0

3.0

5.0

7.0 Ideal Speedup

Spe

edup

91

● Radios consume a significant fraction of node powerLucent’s WaveLAN: 23 dBm 915MHz radio network interface

transmit = 3Wreceive = 1.48Wsleep = 0.18W

GEC Plessey DE6003: 20 dBm, 2.4GHz radio transceivertransmit = 1.8Wreceive = 0.6Wsleep = 0.05W

Newton PDAactive = 1.2Wsleep = 0.164W

Magic Link PDAactive = 0.7Wsleep = 0.3W

Radios need to be actively managed for low powervia energy efficient wireless link protocols.

Energy Efficiency is not just an Architecture Issue!

92

Low Power Design for Wireless

µProc

DSPs

HDD

MAC Layer

Link Layer

Radio

Display

Protocols

Modem

Protocols

• Hardware has been addressed• Low power CMOS,• Displays,• Hard drives, etc.

• Low power protocols remain