Smartwaves International

Antenna Based SDMASchemes for Wireless

Communications

Dr. J. R. Sanford

Smart Waves International3385 Scott Boulevard

Santa Clara, CA 95054

Tel. (415) 412 8694

swaves@pacbell.net

2

Assumptions

• Wireless communication, that is not line of sight,has a limited usable spectrum due to propagationissues (0-3GHz)

• There is no limit to the amount of data we willwish to send

• Therefore, this spectrum must be used asefficiently as possible– All degrees of freedom must be used optimally

3

Outline

• Environment

• Goal

• Space Diversity Combining

• Multiple Beam Arrays

• Digital Beam Forming

• Frequency Scanned Systems

• Holographic Beam Forming

• Conclusions

Overview

New

}}

4

Angular Spread

• Angular spread is a function of base stationlocation, distance and environment

5

Angular Spread

• Suburban base station directed toward atown

3dB

Ang

ular

Spr

ead

(deg

)

Position (km)

0

10

20

1 105

6

Angular Spread

• Signal Loss over

Los

s Fa

ctor

3dB Angular Spread (deg)

1

500

1000

1 2010

1

r2

BernRapperswil

7

Link Directivity

• Signal Loss over

Los

s (d

B)

Average/Peak (dB)

0

15

30

-25 -15-20

1

r2

BernRapperswil

8

Interference Rejection

• Resolution is directly related to interferencerejection

Res

olut

ion

Angular Spread

0

15m

30m

0 2010

9

Smart Antenna Systems

• Main Goals:– Increase Capacity

– Increase Range

– Eliminate Down Time

• Additional Advantages– Emergency Tracking

– Jamming Suppression

10

Degrees of Freedom

time

spac

e

GSM

frequency

CDMA

• GSM, AMS, CDMA all reside in two dimensions

• Space is four dimensional (x,y,z, polarization)

• Code is a subset of the time-frequency space

op timal

6 Dimensional SpaceKnowns:Propagation environmentHardware performanceComponent costRegulations

11

Optimization

ASP Algorithm

Antenna

Channel Model

Polarization

Power AmplifierFiltering

DSPModulation

Best System A/D Converter

Rx and Tx Bands

LNA

Site Planning

Demodulator

12

Present Standard Trends

• UMTS plans services and features

• Wide Band CDMA is the leading futurestandard– TD-CDMA as a subset for smart antennas

• Data over Voice

• Down link limits performance– why not allocate more bandwidth to the down

link

13

Common Space Diversity CombiningTechniques

Antenna

LNA

DownConverter

Antenna

LNA

DownConverter

Logic

Switch

Antenna

LNA

DownConverter

Antenna

LNA

DownConverter

Estimate Weightand Phase

Switch

A

Σ

Antenna

LNA

DownConverter

Antenna

LNA

DownConverter

Estimate Phase

Switch

Σ

Selection Combining Equal Gain CombiningMaximum Ratio Combining

14

Space Diversity

• Configuration can be considered 2 element array

• Optimized when antennas are maximally spaced

– more than 2 wavelengths

– decorrelated noise

• Maximum ratio is preferred in basic combiners

• A dual polarized antenna may be used instead oftwo antennas

– polarization diversity

15

Butler Matrix Fed Array

l

(n-1)l

l

Port n1 3 4 5 6 7

Transceiverband 2

Butler Matrix

Phase Front

Element Element Element Element Element Element Element Element

(n-1)l

• Combined at RF

• Elements are within awavelength

16

f2

f6f7 f3f5 f4

f1f8

Beam Distribution

Cell Boundary

17

Butler Matrix Fed Array

• Utilization– Sectorize a cell into n-cells with increased link energy

• 3dB gain increase

– Combined beams eliminate gaps• 6dB gain increase

– Cross channel interference is reduced• 10dB improvement

– Frequency hopping dramatically improves worst casefading

• Application– Low density sites with large cells

18

RF Phased Array

Calibration Network

LNAPA

3 3

Calibration Network

LNAPA

3 3

19

RF Scanning Array

• All channels are directed together

• Best for broad band TDMA packeted information

20

Digital Beam Forming Array

Calibration Network

A/D D/A

Transceiver

Computer

DSP

DSP

Elements

• Combined at IF

• Elements arewithin awavelength

21

SDMA Concept

Channel 1

• Gain

• Interference suppresion

• Fade compensation

22

Digital Beam Forming Array

• Total independent channels

• Channel bandwidth limited– DSP speed relates to bandwidth

– Wide band CDMA?

• Allows distributed power– One low power amp per element

• Very good interference rejection– channels(elements-1) “nulls”

23

Frequency Scanned Array

Transceiver

f2

24

Frequency Scanned System

• Employs frequency tracking mobiles– Radio chooses the optimal channel band

• Improves range– High gain frequency scanned antennas are easily

constructed

• Adaptive nulling through frequency channelselection– Each direction corresponds to a frequency

• Best used in wide band systems

25

Frequency Scanned

Sign

al (

dB)

f

Tra

nsm

issi

on (

dB)

f

Cancellation Signals

Channel 1 Radio 1 Reception

Cha

nnel

3

Cha

nnel

1

Cha

nnel

2

Channel 1

26

Holographic Communications Concept

27

Holographic

• VLBI applied to wireless communications

• Local signal maxima are formed on transmit

• Fades are uncorrelated at the base stations

• Offers the maximum capacity and range increaseof any conceivable system

• Allows tracking, and jamming suppression (GPSlike)

28

Holographic7.7dB,-7.6dB

2.6dB-29.6dB

62.6dB, -

13.0dB,-22.6dB

19.8dB,-12.6dB

3.4dB-17.8dB

• Channel link improvement

• Adaptive nulling (WSF)

Single Omni

Array Element

Measurement CH1

Measurement CH2

29

Optimized Hardware Control

ASP Algorithm

Channel Model

Power Amplifier

DSP

Modulation

GA Channel Optimization A/D Converter

Rx and Tx Bands

LNA

Demodulator

• Create the best link through optimized hardwarecontrol

Power Control

30

Conclusions

• We will use SDMA schemes as they become costeffective

• SDMA implementation becomes more costeffective as new DSPs become available

• SDMA will be necessary to improve capacity

• TDMA (ATM) combines nicely with SDMA

• Holographic techniques provide the greatestpotential