a mimo architecture for sar application

Company General Use

A MIMO architecture for SaR application

08/10/2019 Lerici, MSAW 2019

Francesco Prodi, Luigi Pierno , Melissa Pullo,

Alfonso Farina* ,Roberto Lalli, Alessandro Manuale *Consultant

© Leonardo - Società per azioni 2

Company General Use

- Reference MIMO architecture with orthogonal waveforms

- TDM (Time Domain Multiplexing) architecture

-. Signal Processing techniques

- based on slow time sampling

- based on TX sequence staggering

- Simulation results

- Conclusions

the Ranger Project


Company General Use

target

ULA TX

1 2 Mt

2rM

TX domain

RX

do

main

1 2

1

2

1

2

Ns

Mt

Mr

1 Mr 2

ULA RX TX

RX

REFERENCE MIMO ARCHITECTURE

Mt [5,20] # TX antennas

Mr[5,20]: # RX antennas

Nr[4,32]: # cycles

T[200,1000] msec


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input domain output domain processing

goal

fast time range range resolution

RX location azimuth azimuth

resolution TX location

time Doppler clutter

cancellation

processing domains

range-Azimuth-doppler independend domains only with

Orthogonal Waveforms

FFT-s

3D hologram reconstructed by 3 1D FFT-s


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Time Domain Multiplexing vs. Orthogonal Wafeforms

TX domain azimuth

time Doppler leakage

If TDM

- leakage between TX domain and time

- incomplete 2D domain support

TX domain

tim

e

T*Mt=

1*20 msec

TX domain

tim

e

T=1 msec

TDM Ortho WFs

- partial orthogonality of signals

- complete 2D support


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RX-TX hologram

TX

RX

1 2 20

1

2

2

0

i

j

point target with azimutJ and radial speed vr

virtual array

J

vr )]))(sin(

)sin((2exp[ jTfi

Ms d

r

ij JJ

j

i=0,Mr-1; j=0,Mt - 1

leakage between

Doppler and azimuth

time

leakage between TX and time


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breaking leakage by slow-time processing

slow-time processing

sampling at Mt*T=20 msec

rather than at T=1 msec

TX

domain

tim

e

jTfMj dtj J 2),mod()sin(2

kdk jTfj J 2)sin(2 0

jk=j0 + (k-1)*Mt , k=1,2... sub-sampling

depending on doppler, not on J !


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slow time processing flow


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doppler processing

TX(j) 1 2 20

1

2

32

RX(i)

slo

w tim

e (

k)

FFT-s along columns of 3D holo(i,j,k)

for each i, j:


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doppler equalization

equalization of doppler effect

TX(j) 1 2 20

1

2

32

RX(i)

dopple

r filter

(k)

for each k,i:

)2exp(td

ijkijkMN

jkhp j j=1,Mt

td MN

k2 is the phase variation between two adjacent Tx-s

relative do the k-th doppler filter


Company General Use

MIMO beamforming with no RMC

TX

RX

1 2 20

1

2

20

for each range bin and doppler cell

Mt*Mr virtual array joining together columns of the 2D holo

2D hologram

Let h(p), p=1,2… Mt*Mr be the complex samples on the virtual array.

H=fft (h) is the azimuth compressed vector

Big FFT


Company General Use

Range Migration Compensation (RMC)

RX domain azimuth

TX domain

target

TXi

RXj

range delay DTOT depends on:

a) i, j

b) pointing angle

c) target radial speed v

DTOT ≈D(i,j, ) + Dv

D(i,j) depends to a good approximation, on J

has to be estimated from target motion

(negligible for low speed targets)

Dv

J

D(i,j, J) = R(i,j,J ) - R(i,j,J)

J

J


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TX

RX

1 2 20

1

2

20

3D complex hologram corresponding to a TX cycle interval (20 msec)

Range Migration Compensation (RMC) (2)

for each , i , j , each range column of complex data is shifted by: J

Int (D(i,j) / rb )

computationally heavy

J

rb=range bin


Company General Use

MIMO beamforming with RMC

a) for each RX beam pointing J, RMC is performed

on the 3D hologram

b) for each range bin MIMO processing is performed

on the 2D (RX,TX) hologram as 1D ‘big FFT’

c) only narrow (0.15°) beams contained

in the selected RX beams are retained

Jbr = /Lr=5.7° Jb t= /Lt=0.15°

beam resolutions at boresight for full configuration

RX beam

TX beam

J

for each range bin and doppler cell


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breaking leakage by TX staggering law (1)

1 2 3 1 3 2 1 2 3

TX permuation law changed from cycle to cycle

Tx antennas are activated with a pseudo-random law

1 2 3 20

1-st cycle 2-nd cycle 16-th cycle

1 2 3 20 1 2 3 20


Company General Use

jTfMj dtj J 2),mod()sin(2

sequential law

jTfMjperm dtj J 2)),(mod()sin(2

pseudo random law

linear in j not linear in j

breaking leakage by TX staggering law (2)

point target with azimutJ and radial speed vr

try de-leakage


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TX staggering law processing flow


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joining holograms

Ntot=Mt*Nr h(i,j) i=1,2…Mr j=1,2…Ntot

time

RX

TX azimuth and doppler infos are merged in the time domain


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matched filtering (1)

s(j)=h(i,j)

for any i-th receiver

Ntot

j td

mfM

kjpermj

N

ljjjsklf

1

)))(

2(exp)2(exp)(),(ˆ

matching

linear Doppler phase matching

staggered TX phase

Doppler filter

index

TX beam index

dynamic range of limitate by (Nd) ),(ˆ klfmf

Mt=20, Nr=32, NTOT= Mt*Nr=640


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dynamic

TX lobe

RX lobe weak target

strong target

TX array

azimut

strong target masks

weak target


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azimuth (deg)


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azimuth and radial speed are ambiguous !


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improving dynamic by

CLEAN TECHNIQUE

peak removal is critical

and computationally heavy


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comparison of two algorythms

slow PRT TX stagger

sampling T/Mt still acceptable for

low speed targets

T

dynamic good not good (typically <25 dB)

computation charge good

heavy with

CLEAN technique

better, now

actually not good Improvable with

spectral techniques


Company General Use

simulation parameters

range R0=12 Km

Jb < 0.2°

dv=12.5 m/sec

requirements

Mt=Mr=20

Jb=1/(Mr Mt)=2.5*10-3 rad (0.15°)

T=200 msec

Nr=32

T0<128 msec

MIMO parameters

gdB=10*log(Mr*Mt*Nr) = 41 dB ha=10 m or 50 m

Vertical Polarization

antenna parameters

target reflectivity

4 Small boats modelled by:

4 point reflectors SW0

reflectivity=0 dB m2 for all targets

vr=[2, 0.1, 3, 5] m/sec

azimuth [-60.2 -10.2 4.3 40.7].°

waveform

Chirp:

BW=100 MHz

T=100 msec


Company General Use

- compound clutter with an amplitude Gamma distribution /1/ this is a refinement of GIT (Georgia Institute of Technology)

Clutter Reflectivity model

Sea State=3 is assumed

- gaussian Spectrum r(t)=exp[-2( sf t)

2] exp(j2 hf t)

sf =2sv/ sea clutter standard deviation

hf : mean clutter frequency

/1/ S. Watts, K. Wards, R. Tough: Modelling the shape parameter of sea clutter, 2009

International Radar Conference: Surveillance for a Safer World, 12-16 Oct. 2009,

Bordeaux

Sea Clutter model


Company General Use

instrumental range and radial velocity ambiguity

Ti t

T

T = Ti +

t

pulse width

instrumental

range

PRT

WF t

(ms)

Ti

(ms)

T

(ms)

dv

(m/sec)

Short Range 100 100

(15 Km)

200 12.5

Long Range 300 400

(60 Km)

700 3.5


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azimuth (deg)

radia

l speed (

m/s

ec)

-90° 90° 0°

range-doppler map

ha=10 m


Company General Use

90° -90° 0° azimuth (deg)

radia

l speed (

m/s

ec)

range-doppler map

ha=50 m


Company General Use

CONCLUSIONS (1)

The MIMO architecture shows key advantages for the detection of

rubber boats with small size and reduced RCS (0 dB m2) in sea

Clutter, mainly due to:

1) narrow range resolution cell due to large instantaneous BW

2) narrow beam-width due to the distributed Tx antenna

3) long time on target (up to more than 100 msec) increasing sub-

clutter visibility of small boats

slow time processing


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CONCLUSIONS (2)

fast time processing

de-leakage azimuth and doppler domains through

- TX staggering (with CLEAN)

- 2D spectral techniques (MMSE)

not good results, at present

follow on: investigate on 2D spectral techniques


Company General Use

This work is a part of the RANGER project. RANGER has

received funding from the European Union’s Horizon 2020

research and innovation program under grant agreement no

700478. The authors would like to thank all partners within

RANGER for their cooperation and valuable contribution.

a mimo architecture for sar application

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