The potential of time reversal in multiple antenna systems Persefoni Kyritsi, George Papanicolaou (Stanford University) Hung Tuan Nguyen, Jørgen Bach Andersen,

The potential of time reversal in multiple antenna

systems

Persefoni Kyritsi, George Papanicolaou (Stanford University) Hung Tuan Nguyen, Jørgen Bach Andersen, Gert Frølund

Pedersen, and Patrick Eggers (Aalborg University)

• TR can achieve delay spread reduction and spatial focusing.– Delay spread* study: TR for fixed wireless applications

(FWA)– Spatial focusing study: TR in a multi-user context

• Discussion– Normalizations and objectives– What kinds of measurements do we need?

*Delay spread:

dhh

dhh

hhh

2

2

22

22 1

,1

MISO TR to a single user

tg jNT

tg j1

tg j2

User j

TX1

TX2

TXN

T

sj

• TR with antenna weighting:

• Weight selection algorithms

mm

TRpurem

hA

2

1

Pure TR Equal powerOptimal weighting

m

EPm hMA

11

opt

optoptm

mA

a

a )(

tsRAtr

tsththAtsthAthtr

thAtg

j

N

khhkjj

j

N

kkjkjkj

N

kjkjkjkjj

kjkjkj

TX

kjkj

TXTX

1

1

*

1

*

*

FWA: Measurement equipment

• Carrier frequency: 5 GHz

• Transmitted power: PT = 100mW

• 3dB bandwidth = 25MHz • 8 element uniform linear arrays (ULA) • Spacing: s = /2• Vertical polarization • Vertical (V) or Horizontal (H) orientation

FWA: Measument locations

LOCATION A

LOCATION B

LOCATION C

1.2km

2.6km

2km

29 floors (5, 19, 28)

Balconies SW & NE 28 floors (19, 29)

7 floors (roof)

Classification of MISO situations

Clear to cluttered Cluttered to clear

Delay spread reduction: heq/h

Spatial focusing in MISO TR to multiple users

• Each receiving antenna represents one of the Nr users

Interference calculation

• Signal on target user

• Interference from other users

• The SIR

tsRAtr

tsththAtsthAthtr

j

N

khhkjj

j

N

kkjkjkj

N

kjkjkjkjj

TX

kjkj

TXTX

1

1

*

1

*

r TX

klkj

N

jlll

N

khhklj tsRAtI

,1 1

2

2

max

max

tI

trSIR

j

j

j

Reminder: The near-far problem

BS

U1

U2

100

1

110

11S

100110

1010S

1,10

2

2

2

2*21

*122

2

2

1

2*21

*111

21

IR

txthtxththty

IR

txthtxththty

tthtth

Power control scenarios

• The scaling factors normalize so that the total transmitted power is kept constant

• Additional constraints– No power control across users

– Simple power control across users

||||

1*

measuredkjkj thA

rN

j

M

kmeasuredkj

rkj

th

MNconstA

1 1

2*

Multi-user operation– Nu=2 – Antennas of 2 different terminals at locations

along the route separated by distance d

Measurement route

BS

d d

Measurements• fc=2.14GHz,

• BW > 7MHz• 2 measurement routes of

l=1km• Transmitter

– 8 TX antennas

– htx=20m (Balcony on 5th floor)

• Receiver

_ On a trolley pulled by a van– Velocity 20-40km/hr– 4 RX antennas: A1, A2, B1,

B2 at the four corners

Results for NR=2, multi-user

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

18

20

Distance in meters

SIR

in d

B

A1A2B1B2

Mean

Min

Route 1

0 50 100 150 200 250 3000

2

4

6

8

10

12

14

16

18

20

Distance in meters

SIR

in d

BA1A2B1B2

Route 2

Mean

Min

0 50 100 150 200 250 300-25

-20

-15

-10

-5

0

5

10

15

20

Distance in meters

SIR

in d

B A1A2B1B2Mean

Min

Route 1

0 50 100 150 200 250 300-25

-20

-15

-10

-5

0

5

10

15

20

Distance in meters

SIR

in d

B A1A2B1B2

Mean

Min

Route 2

With

out

pow

er

cont

rol

With

pow

er

cont

rol

Conclusions

• Spatial focusing achieved to different users with the mean SIR of up to 18dB for 8 transmitting antennas and 2 users.

• Multi-stream operation to a single user is not always possible