The document discusses using OFDM signals for both radar detection and communication. It proposes a system called "RadCom" that uses coded OFDM signals to achieve high data rates for communication payloads while also providing high processing gain for radar functions like range and velocity detection. Key advantages of OFDM signals for this joint system include robust modulation for communications, the ability to do Doppler processing, and potential for digital beamforming to improve angular resolution. Simulations and measurements demonstrate the feasibility of OFDM signals to achieve both radar imaging and binary data transfer with a single transmission.

1. “RadCom”
The Intelligent Radar Signal
Communication Coding of
Pulsed Radar Systems
by Werner Wiesbeck
Forschungszentrum Karlsruhe Universität Karlsruhe (TH)
in der Helmholtz - Gemeinschaft Research University•founded 1825

2. State of the Art Coherent Pulsed Radar Modulation
State of the Art Radars are
Stupid!
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3. State of the Art Coherent Pulsed Radar Modulation
Radar type Time domain Frequency domain
A
A τp T
Pulsed-CW
t f
A
fTx
FM-Chirp
t
t
fTx A
Frequency Coded
t f
A
A
Stagger ...
t f
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4. Motivation – Basic Idea
Communication
Radar targets
RadCom
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5. Basic Idea
reflected signal
communication
RadCom Tx
signal
targets
Car equipped with
RadCom system
Interference
interferer
signal
Intelligent
Transportation
2D Radar Imaging System (ITS) Communications
by digital
Diversity, MIMO
beam-forming Driver Assistance
•range Congestion Avoidance
•traffic information
•speed Dynamic Route Planning •road condition
•azimuth PreCrash Detection •C2C communication
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6. Radar and Communication Ranges
Radar equation: Com. range:
PTx " GTx " GRx R " #2 " $ PTx " GTx " GRx C " #2
PRxRadar = PRxCom =
(4 % ) 3 " R 4 (4 $ ) 2 " R 2
4# " R 2
PRxCom = PRxRadar "
! ! $
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!

7. Coding of Radar Signals
Well known Radar coding for EW purposes:
Pulse Radar
Linear FM Chirp
FMCW
M-Sequence Example:
Multicarrier Signals
...... OFDM
Coding in communications:
Single carrier BPSK, QPSK
OFDM
CDMA
DSSS
......
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8. OFDM Signal Spectrum
-10 OFDM spectrum
sub-carrier
rel. power spectral density in dB
OFDM pulse shape:
rectangular
0 (-13dB first order
sidelobes for single
sub-carrier)
-10
N sub-carriers,
e.g. 16
-20 complex orthog.
sampling in FD
-30
-1 -0.5 0 0.5 1
normalized frequency
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9. OFDM Transmit Signal
x(t,f)
Nc-1
n=0
carrier
....
.... f
envelopes
µ=0
...
... bo
ls
.... sy
m
Nsym-1
t TOFDM
Δf
B
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10. OFDM Multi Carrier Transmit Scheme
Orthogonal(FDM) scheme as a digital multi-carrier method
cyclic prefix
pilots
guards
N
data QAM 1:N OFDM signal
symbols IFFT N:1
source modulator symbols formation
stream
Frequency Domain Time Domain
Dividing data Each sub-carrier is
Total data rates similar to
into parallel data modulated at a low
single-carrier schemes
streams symbol rate
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11. Joint Radar and Communication System Concept
communication
partner
Advantages of OFDM signals:
high data rate for payload data (no spreading required)
high processing gain
low range side lobes
possibility of Doppler processing (orthogonal to range)
Beam-forming capability
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12. OFDM System Parameters for 24 GHz ISM Band
Symbols Parameter Value
fc Carrier frequency 24 GHz
Nc Number of subcarriers 1024
f Subcarrier spacing 90.909 kHz
TOFDM Elementary OFDM symbol duration 11 µs
TG Cyclic prefix length 1.375 µs
B Total signal bandwidth 93.1 MHz
R Radar range resolution 1.61 m
Rmax Unambiguous range 1650 m
vrel,max Unambiguous velocity ± 284 m/s
Nsym Number of evaluated symbols 256
∆vrel Velocity resolution 2.22 m/s
GP Processing Gain 54.2 dB
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13. OFDM Coded Radar System Simulation
Signal: OFDM coded BPSK Targets: {X,Y}, v, RCS
Tx: G, PTx, Nsym Propagation: ray-tracing
OFDM-Tx channel
Radar
OFDM-Rx
processing
Radar image Binary data
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14. OFDM Radar Processing
x(t)
ITx (n) Tx
~ fc
! y(t)
! IRx (n) Rx
!
!
! Standard approach: New, dedicated approach:
Cross-correlation Tx-Rx Signals Complex division of symbols
IRx (n)
src (" ) = $ y(t)x(t # " ) dt Idiv (n) =
ITx (n)
, src (" ) = IFFT[ Idiv (n)]
 dependent on signal (data) completely independent
 unpredictable correlations from signal (data)
!
 high computational effort ! low computational effort
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15. OFDM-Radar Range-Doppler Processing
IFFT
.............
k=N-1
distance
.............
.
k=1
k=0
ν=0 . . . ν=M-1
Doppler
3. Step: Inverse Fourier trans-
formation in frequency direction
.............
FFT .............
frequency
frequency
n=N-1 n=N-1
. .
n=1 n=1
............. .............
n=0 n=0
µ=0 . . . µ=M-1 ν=0 . . . ν=M-1
time Doppler
2. Step: Fourier transformation in time direction
1. Step:
I ( n)
complex division I div (n) = Rx Processing gain: Nc·Nsym
of symbols I Tx (n)
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16. Range and Doppler Resolution for 3 Targets
Target Range R in m Speed v in m/s
B = 93.1 MHz
z1 33,2 10
Tsym = 12.375 µs
z2 33,2 14 Nsym = 128
z3 35 10 fc = 24 GHz
Distance R in m
Unambiguous and
independent
resolution for
distance and Doppler
for an arbitrary
number of objects
Relative velocity v in m/s
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17. “RadCom”
Verification by Measurements
by Christian Sturm and Werner Wiesbeck
Forschungszentrum Karlsruhe Universität Karlsruhe (TH)
in der Helmholtz - Gemeinschaft Research University•founded 1825

18. Measurement System Setup at 24 GHz ISM Band
A(f)
Mixer creates two sidebands Ethernet HUB
Only upper sideband is
evaluated at the receiver
frequency
cable losses
GRx = 22 dBi
≈ 3.5 dB
(( ( FSQ26
@ 24.05 GHz
GTx = 22 dBi
PTx = 22 dBm
Mixer SMR40
(( ( amp
@ 23.85 GHz
Reference
+ Trigger
OFDM
Signal SMJ 100A
@ 200 MHz
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19. Measurement on Street
Normalization to
RCS = 1 m² in 10 m distance
Radar image in dB
13.3 dBm²
8.1 dBm²
v = -14.2 km/h
Velocity ≈ 15.7 m/s = 56.7 km/h
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20. Digital Beam-forming
for
Azimuth Processing
by Christian Sturm and Werner Wiesbeck
Forschungszentrum Karlsruhe Universität Karlsruhe (TH)
in der Helmholtz - Gemeinschaft Research University•founded 1825

21. Multi-beam DBF Radar Signal Processing
Rx signal y1(t) Receive array signal vector
Rx signal y2(t)
Rx signal y3(t) # src,1 (" ) &
Rx signal y4(t) src,4 (" ) % (
KKF
KKF % src,2 (" )( !
= s (" )
KKF % src,3 (" ) ( rc
Corr % (
Sendesignal x(t)
Sendesignal x(t) $ src,4 (" )'
!
Sendesignal x(t)
Tx signal x(t)
τ !
4 3 1
2
!
d/λ d/ λ d/λ
Azimuth Processing by
Digital Beamforming
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22. Digital Beam-Forming for Multiple Targets
Coverage unprocessed: coverage Tx = coverage Rx
transmit beam ⇔multiple receive beams
DBF processed multiple receive beams
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23. Radar und Communication with Digital Beam-forming
Multiple antenna systems and coded signals for Super Resolution?
V2V communication by codes
range compression by correlation (PN-Codes, PPM, OFDM, MPSK...)
angular compression by Digital Beam-forming or by
Super-Resolution?
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24. Music Processing in OFDM Radar
G T
OFDM-Tx Channel OFDM-Rx Binary DATA
Pow N_sym
Radar
AWGN V Performance
azimuth processing
{X,Y} RCS
Image Data
time
MUSIC
.
...
s
ot
sh
p
na
.s
!
...
sc1 (n,m)
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25. Virtual Drive with Ray-Tracing DBF and Super Resolution
Ray-Tracing Kanalmodell
Radar Transmitter
Ray-tracing
(BPSK Modulation)
Radar Receiver
DBF with
Super Resolution
Range
Correlation
Azimuth
Array Processing
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26. Summary Virtual Drive
Radio detection Mobile
and ranging Communications
RadCom
one transmission
one spectrum
one code
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