John AnkcornNetworks and Mobile

Systems GroupMIT LCS

Software Technologies for Wireless Communication and

Multimedia

January 2001 John Ankcorn Slide 2

Better communication (not just better networks)

Different applications have different requirementsBandwidth, latency, error rate, security

In a wireless network channel conditionsVary significantly over timeHard to predict

Customize network on-the-flyApplication-specific and condition-specific

Design for the actual caseNot the worst (or even average) case

Integrate applications and communicationsAdapt to user needs and conditions

January 2001 John Ankcorn Slide 3

Digital Communication

Only the channel is out of our control

SourceSource

Encoder

Channel

Encoder

SinkSource

Decoder

Channel

Decoder

ChannelOne-many

Many-one

One-one

One-one

Many-one

January 2001 John Ankcorn Slide 4

An Adaptive Wireless Network Interface

Physical

Data link

LinkFraming

bytes

bits

bits

symbols

Discrete signal

Discrete signal

Continuous signal

Continuous signal

Channel Coding

Line Coding

Modulation

Multiple Access

A/D Conversion

Freq. Conv.

OSI Layers Virtual Radio Layers

January 2001 John Ankcorn Slide 5

pages = (BlockSize/4096) +1; if((guppi_open("guppi0",pages)) < 0 ) exit(0); guppi_start_rec(); for ( i=0 ; i< NumBlocks ; i++){

pdata = (char *)guppi_rec_buf(); for ( j=0 ; j< IntsPerBlock ; j++){

RealTap_ptr=RealTap; ImagTap_ptr=ImagTap; OutputDataReal = 0.0; OutputDataImag = 0.0; a=cos(TwoPi * CenterFreq / (float)SampleFreqIn * index); b=sin(TwoPi * CenterFreq / (float)SampleFreqIn * index); index += DecFactor; for ( k=0; k< FilterLength ; k++, pdata++){ OutputDataReal += ((float)*pdata * RealTap[k]); OutputDataImag += ((float)*pdata * ImagTap[k]); ...

From Physical Radios to Virtual Radios

Edison’s RadioEdison’s Radio SpectrumWare RadioSpectrumWare Radio

January 2001 John Ankcorn Slide 6

Ideal Software Radio

Processor

and

Memory

A/D

D/A

RF PowerAmp

WidebandAntenna Wideband

ADC

January 2001 John Ankcorn Slide 7

A Short Demonstration

January 2001 John Ankcorn Slide 8

PC

Linux

WidebandIF

(33MSPS)

PSpectra Environment

AMPS TVPatchPanel

SpectrumWare Virtual Radio

MultibandFrontend

A/D,D/AGuPPI

January 2001 John Ankcorn Slide 9

Modulation: 8-PSK with high SNR

January 2001 John Ankcorn Slide 10

Modulation: 8-PSK with low SNR

January 2001 John Ankcorn Slide 11

Modulation: QPSK with low SNR

January 2001 John Ankcorn Slide 12

Footprint Processing Model

Start of footprint for ak

ak

Detection: Compute an estimate for

symbol ak from samples

Synchronization: Determine which samples

have information about ak

January 2001 John Ankcorn Slide 13

Fundamental sample relationships

Filter

Duration of Input

Time duration of input ability to resolve frequencies

Number of samples used reduce effect of noise

January 2001 John Ankcorn Slide 14

To decide whether transmitted bit was “1” or “0”

1) Compute filter output

2) Apply Threshold Test

Symbol detection: matched filter

N

kkknn coeffinout

1

0

10 20 30N =

Sum > decide “1”

Sum < - decide “0”

January 2001 John Ankcorn Slide 15

Adaptive symbol detection

Terms in sum

0

10 20 30N =

Receiver uses:

Quality of channel

Desired error rate

To control:

Accuracy

Power consumption

Bit rate (with protocol)

2

Threshol

d

0

10 20 30N =

Software optimization

Sort samples!

2

-10

-10

10

10

January 2001 John Ankcorn Slide 16

How many terms to compute?

CalibrateFor n = 1..N

Plot bit-error rate vs. To achieve a given BER

Pick n,

n = 3

n = 4

n = 10

BER

10-7

10-5

10-3

10-1

Test after n stepsIf |sum| < , test again after N steps

n1 2 3 4 5 6 7 8 9 10

10

20

30

Av

Average number of steps Lowest after 6th step

January 2001 John Ankcorn Slide 17

Research Directions: Low power communications

SensorsBattery operated Simple function

ProbeAnalog-to-digital conversionTransmitter

Low data rate

GatewayConnect devices to wired LANAdd timestamp to data

January 2001 John Ankcorn Slide 18

Low power communications: Application

First application: Hospital Operating Rooms

Gateway

Display

Firewall To Hospital

Network

Operating Room

Sensor

Local Area Network

January 2001 John Ankcorn Slide 19

Current Research Directions: Universal Availability

Multimedia data communications

Dynamic resource allocation by applicationEnergySpectrum

Explore uses of communication between layersAdapt protocol based on transmission channelAdapt transmission to needs of protocol

Flexible physical networksSome access everywhereDownload physical layer processingLocal communication standards

January 2001 John Ankcorn Slide 20

Summary

Flexible processing yields:Better communications availabilityBetter resource utilizationApplication-optimized communications performance

January 2001 John Ankcorn Slide 21

More Information

Project home page:

http://nms.lcs.mit.edu/spectrumware

Contact:

John Ankcorn jca@lcs.mit.edu