Wideband Wireless Communications Laboratory,
Xiamen University
Low-Rate UWB Communication Systems
Based on Chaotic Modulations
Lin Wang1, Wei Kai Xu1, Guanrong Chen2
1.Dept. of Communication Engineering,
Xiamen University, China
2.Dept. of Electronics Engineering, CityU of HK, China
27/07/2010
Contents
 Background
 System design of UWB based chaos
modulations
 Rapid timing synchronization for FM-DCSK
UWB
 User cooperation DCSK communication
system
 Ongoing work
 Conclusions
Wideband Wireless Communications Laboratory, Xiamen University
42-2
Contents
 Background
 System design of UWB based chaos
modulations
 Rapid timing synchronization for FM-DCSK
UWB
 User cooperation DCSK communication
system
 Ongoing work
 Conclusions
Wideband Wireless Communications Laboratory, Xiamen University
42-3
Background
 Basic idea of UWB
 Communications in a frequency band already occupied
(Coexistence)
 Making frequency re-use possible by limiting the PSD of
Equivalent Isotropically Radiated Power (EIRP)
 UWB radio regulation
 Federal Communications Commission (FCC, USA) determined
only the maximum emission limit and minimum bandwidth
 Method for access to UWB frequency band has not yet been fixed
 Note: UWB regulations say nothing about the type of carrier and
technique used to generate UWB carrier. So Any kind of carriers,
including chaotic signals, may be used; any kind of modulation
scheme may be used
Wideband Wireless Communications Laboratory, Xiamen University
42-4
Background
 UWB frequency band
 Frequency band allocated to handheld UWB devices: 3.1
GHz to 10.6 GHz
 Define: UWB transmitter is an intentional radiator
that, at any time instant
 fractional bandwidth BW  2( f  f ) /( f  f )  20%
 Or, UWB bandwidth  500 MHz, regardless of the
fractional bandwidth
H
L
H
L
Wideband Wireless Communications Laboratory, Xiamen University
42-5
Background


FCC limits on radiated UWB signal
 To avoid interference caused in the existing narrowband systems, not the
radiated power but the PSD of EIRP is limited
 Definition of Equivalent Isotropically Radiated Power (EIRP)= (power
supplied to the antenna) *(antenna gain)
ERIP limits in two ways:
 Peak level of the emissions contained within a 50-MHz bandwidth
centered on the frequency at which the highest radiated emission occurs
should not exceed 0 dBm EIRP
 Average radiated emissions shall not exceed -41.3 dBm EIRP when
measured using a resolution bandwidth of 1 MHz over the frequency band
of 3.1 GHz to 10.6 GHz
 Note: Low-data rate (less than 350 kbit/s) UWB systems are peak power
limited, while high-data rate ones are average power limited
Wideband Wireless Communications Laboratory, Xiamen University
42-6
Background
 Carrier types of UWB
 Impulse radio, such as Gaussian pulse
 Sine waveform, MB-OFDM, FM-UWB etc.
 Chaotic waveform
 Modulation schemes
 Pulse-Amplitude Modulation (PAM), pulse carrier
 Pulse-Polarity Modulation (PPoM), pulse carrier
 On-Off Keying modulation (OOK), arbitrary carrier
 Pulse-Position Modulation (PPM), arbitrary carrier
 Transmitted-Reference Modulation (TR), arbitrary carrier
Wideband Wireless Communications Laboratory, Xiamen University
42-7
Background
 TR Modulation: Binary information is mapped into two wavelets,
the first chips serves as a reference, the second one carries the
information
RMS delay of channel
reference
chips
guard
interval
Ts
Tg
information
chips
Where: Tg >Tch
Delay between the
reference and information bearing chips
Note: Wavelet may be either a fixed
(impulse radio) or a chaotic waveform
Tf
Modulation:
• Bit “1” : Second chips is equal to the delayed reference one
• Bit “0” : Second chips is equal to the inverted and delayed reference one
Note: FM-DCSK/DCSK is a TR modulation based on chaotic carrier.
Wideband Wireless Communications Laboratory, Xiamen University
42-8
Background
 Applications of low-rate UWB
 Sensor networks, wireless networking devices of embedded system,
smart houses, offices and mall etc.
 Categories of low-rate UWB
 Data-rate: typically around 1Mbps
 LR-WPAN: covers personal operational area, short range from 1030m
 LR-WLAN: coverage up to 100m
 IEEE Standards about low-rate UWB
 Existing: IEEE 802.15.4 Standard, used by ZigBee alliance
 Alternative UWB(2007): IEEE 802.15.4a Standard WPAN low rate
alternative PHY
Wideband Wireless Communications Laboratory, Xiamen University
42-9
Contents
 Background
 System design of UWB based chaos
modulations
 Rapid timing synchronization for FM-DCSK
UWB
 User cooperation DCSK communication
system
 Ongoing work
 Conclusions
Wideband Wireless Communications Laboratory, Xiamen University
42-10
System model of FM-DCSK UWB
UWB Chaos
Pulse Generator
FM
Modulator
reference
chips
K
Delay
T/2
Channel
guard
interval
-1
information
chips
Binary information
to be transmitted
Transmitter
Delay
Tf/2

T f 2 T
Tf 2
Ts
Threshold
Decision
 dt
Tg
Tf
estimated bit
Signal structure
Receiver
Noncoherent detect: observation signal is
z  Re

T

r (t ) r (t  T f / 2 ) d t

Where T is integration duration.
Wideband Wireless Communications Laboratory, Xiamen University
42-11
Analysis and Optimization of System Performance
(1)
In the absence of ISI, the receive signal as
Eb
r (t ) 
2
[ g ( t )  ag ( t 
Tf
)]  n ( t )
2
Suppose a data symbol a = 1 is transmitted, the output of the
detector is
Where:ζ1 is the signal energy captured
T


z  R   r (t ) r (t 
) dt 
2


in the integration, ζ2 and ζ3 are the
signal-noise cross terms, and
E
z 
g t  dt

2
ζ4 is the noise-noise cross term.
T

f
0
2
T
b
0

Eb
2


2
0
Eb
2

 1 
Eb
g t  dt 
T
T
2

0

T f 

  dt
R  g t n  t 
2  


 t n t dt  
R g
0
2
T

T
0
3 

T f 

  dt
R  n t n  t 
2  


Above three cross terms can be approximated as
independent Gaussian random variables. And
their distributions are respectively as below:
4
 2 ,  3 ~ N (0,
N 0 Eb 
T
0
2
g t  dt
)
4
Wideband Wireless Communications Laboratory, Xiamen University
42-12
 4 ~ N ( 0 , N 0 BT )
2
Analysis and Optimization of System Performance
(2)
Then the bit error rate (BER) probability can be written as
Pe  P  y  0 
 P  1   2   3   4  0 


 Q





2
g t  dt 

2
( E b  g t  dt )
T
0
4 N 0 BT  2 N 0 E b 
2
T
0
2
According to expression of BER, the optimization of integration time
Topt is equivalent to the maximization:
(Eb 
T opt  arg max
T
T
0
2
g t  dt )
4 N 0 BT  2 N 0 E b 
2
T
0
2
2
g t  dt
Note: above expression can not only prove that the existence of the optimal integration
interval Topt, but also show that the optimal value depends on Eb, N0, B and g(t).
Wideband Wireless Communications Laboratory, Xiamen University
42-13
Simulation results(1)
CM1
0
CM4
0
10
10
-1
10
-1
10
-2
10
-2
-3
10
BER
BER
10
-4
10
-3
10
10
10
Tg = 22.5ns
Tg = 47.5ns
Tg = 97.5ns
Tg =197.5ns
10
Tg = 47.5ns
-6
10
Tg = 97.5ns
Tg =197.5ns
-7
-5
10
Tg = 7.5ns
-5
Tg = 7.5ns
Tg = 22.5ns
-4
11
12
13
14
15
16
Eb/N0 [dB]
17
18
19
20
10
10
11
12
13
14
15
16
Eb/N0 [dB]
17
18
19
20
Performance of the fixed integration interval UWB-FM-DCSK system,
when the guard interval length Tg is 7.5, 22.5, 47.5, 97.5 and 197.5ns,
with the integration interval is Tf/2 and the chip duration Ts is 2.5ns
Left: CM1 Right: CM4.
Remark: 1.When semi-bit Tf/2 duration integration interval is used,
the BER performance is obviously affected by guard interval Tg. Larger Tg, lower BER.
2. On the other hand, since the integration interval is equal to Tf /2, increasing
of Tf means more noise energy captured whereas signal energy almost unchanged, so the BER
is deteriorated when Tg great than a threshold.
Wideband Wireless Communications Laboratory, Xiamen University
42-14
Simulation results(2)
CM1
0
-1
-1
10
BER
BER
10
-2
10
10dB
11dB
12dB
13dB
14dB
15dB
16dB
17dB
18dB
-3
10
-4
10
CM2
0
10
10
0
0.2
0.4
0.6
0.8
1
T [s]
1.2
1.4
1.6
-2
10
10dB
11dB
12dB
13dB
14dB
15dB
16dB
17dB
18dB
-3
10
-4
10
1.8
2
0
-7
0.2
0.4
0.6
0.8
1
T [s]
1.2
1.4
x 10
1.6
1.8
2
-7
x 10
BER as a function of the integration interval, with Eb/N0 increases from
10dB to 18dB in CM1and CM2. Tg is set as 197.5ns and Ts is 2.5ns.
Remark: the BER of the proposed system as a function of the integration
interval T (from 0 to Tf/2 with the stepping 4ns) in different Eb/N0 condition
and different channel mode. And there exists an optimum integration interval
when BER is minimized corresponding to each Eb/N0.
Wideband Wireless Communications Laboratory, Xiamen University
42-15
Simulation results(3)
0
0
10
10
-2
BER
BER
10
-2
10
-4
CM3 T = Topt
10
CM1 T = Topt
CM3 T = Tf/2
CM1 T = Tf/2
-4
10
-6
10
11
12
13
14
15
16
Eb/N0 [dB]
17
18
19
10
20
10
11
12
13
14
15
16
Eb/N0 [dB]
17
18
19
20
14
15
16
Eb/N0 [dB]
17
18
19
20
0
10
0
10
-2
10
BER
BER
10
-2
CM2 T = Topt
-4
10
CM4 T = Topt
-6
10
CM2 T = Tf/2
CM4 T = Tf/2
-4
10
10
11
12
13
14
15
16
Eb/N0 [dB]
17
18
19
20
-8
10
10
11
12
13
Performance comparison between the non-optimal integration interval scheme and the presented
optimization scheme of CM1, CM2, CM3 and CM4, Tf is set as 400ns and Ts is 2.5ns
Remark: BER performance of the presented optimization method outperforms the
scheme when the integration interval keeps a fixed value of Tf/2 about 2.2dB in
CM1, CM3 and CM4 while about 1.2dB in CM2, because of much channel delay
in CM2 than others.
Wideband Wireless Communications Laboratory, Xiamen University
42-16
Improved DCSK/FM-DCSK Scheme
 Problem of TR-UWB receiver (including DCSK/FM-DCSK)
 All digital implementation: extremely high power consumption due
to needing GHz A/D converter.
 Analog implementation RF front-end: a RF delay line is required,
which is extremely difficult to implement in CMOS. Especially,
long delay implementation, such as several decades ns.
 How to solve this problem?
 Design an alterative DCSK transceiver which eliminates the RF
delay line.
Wideband Wireless Communications Laboratory, Xiamen University
42-17
An alterative DCSK scheme: CS-DCSK(1)
 Code-shifted DCSK (CS-DCSK)

Both the reference and information bearing wavelets are sent in the same time slot.
The two wavelets are separated by Walsh codes instead of time delay. The diagram
of transmitter and receiver as follows,
W
al g
sh en
fu er
n at
ct o
io r
n
wR , N


wR , 2
wR ,1
Tc
W
al g
sh en
f er
u
n at
ct o
io r
n
wI ,1
wI , 2

sb (t ) 

k 0

sb (t )
r (t )
~
r (t )


rect (t  kTc )
A
N 1
k 0

Ts  NTc
dt
Z
bˆ
0
B
w
I , k 1
rect (t  kTc )
Receiver
Observation signal:
Transmitter
N 1
N 1
w R , k  1 c ( t  kT c )  b  w I , k  1 c ( t  kT c ),
R , k 1
k 0



b
Transmitted signal:
N 1
Tc


wI , N
Transmitted
information


Chaotic signal
generator
N 1
w

T s  N Tc
k 0
Z 

k 0
( k  1) T c
kTc
w R , k  1 r ( t ).w I , k  1 r ( t ) dt
Wideband Wireless Communications Laboratory, Xiamen University
42-18
An alterative DCSK scheme: CS-DCSK(2)
Where w R ,. and w I ,.
are Walsh code sequences, they are orthogonality.
w R ,. and w I ,.
can be any two rows which are taken from Walsh code matrix. Such as Walsh code matrix
1

1
W  
1

1
1
1
1
1
1
1
1
1
 1

1

 1

 1
w R ,.
w
I ,.
Properties of CS-DCSK:
● eliminates the delay circuit at receiver.
● the reference and information bearing wavelets are transmitted in the
same time slot using Walsh code sequences.
● the reference and information bearing wavelets are orthogonality, which can be
proven as follows,
   w
c ( t  kT )b  w
c ( t  kT )dt
T s  N Tc N  1
N 1
R , k 1
0
T s  N Tc


I , k 1
c
k 0
c
k 0
b  w R ,1 w I ,1 c ( t )  w R , 2 w I , 2 c ( t  T c )  w R , N  1 w I , N 1 c
2
2
2
t  ( N
 1)T c   dt
0
 b  w R ,1 w I ,1  w R , 2 w I , 2 
w R , N 1 w I , N 1 
Eb
2N
 b w R wI 
T
Eb
0
2N
0
Wideband Wireless Communications Laboratory, Xiamen University
42-19
BER performance analysis of CS-DCSK
According to Gaussian Approximation (GA) method,
the BER is computed as
BER 
1
2
P r  Z  0 b   1 

 erfc 

2

1


 erfc 
2


1
2
P r  Z  0 b   1


2 var  Z b   1 

E  Z b   1
2 N  E  xk 
2
1

2 2 N  var  x k   4 N 0 N  E  x k   N  N 0
2
2
2






If the Logistic map is used, we have
E  xk  
2
var  x k  
1
2
2
1
8
So, BER of CS-DCSK can be approx.

2
2
2
  2 2 N  var  x k   4 N 0 N  E  x k   N  N 0

B E R  erfc 
2
2
2
2
2
4 N  E  xk 



1

1


2
4N0 2N  N0  2
 1
 erfc 



2
 2N 
2
Eb
Eb



1





 



1
2






BER performances of the CS-DCSK over AWGN for
theoretical results (solid lines), and simulated results
Remark: The BER performance is
function of spread-spectrum factor. It
is similar to traditional DCSK modulation.
Wideband Wireless Communications Laboratory, Xiamen University
42-20
CS-DCSK performance over multipath
fading channels
Performance comparisons of CS-DCSK and DCSK over Rayleigh fading channel conditioned with
different spread factor. Left: Channel I: PDP: [0.4 0.4 0.2] Right: Channel II, PDP: [0.6 0.3 0.1]
Remark: The BER performances of the CS-DCSK have almost
same with that of DCSK except for small SF. It is illustrated that
the CS-DCSK is a competitive alterative scheme of DCSK.
Wideband Wireless Communications Laboratory, Xiamen University
42-21
Contents
 Background
 System design of UWB based chaos
modulations
 Rapid timing synchronization for FMDCSK UWB
 User cooperation DCSK communication
system
 Ongoing work
 Conclusions
Wideband Wireless Communications Laboratory, Xiamen University
42-22
Problem of present non-coherent UWB
synchronization algorithm
● Timing synchronization is a major challenge for the implementation of
non-coherent UWB receivers.
● Present non-coherent UWB timing synchronization algorithm: the operation of
correlation between two neighboring symbols and the operation of picking the
peak from a large amount of correlation values.
● Problem: Above algorithm operation is not available for the FM-DCSK UWB system
for two reasons: first, a chaotic waveform varies from symbol to symbol, even if the same
bit is transmitted repeatedly, which is the main difference between the FM-DCSK UWB and
the conventional non-coherent TR UWB; second, noise-like chaotic signals have low
values of inter-symbol correlation.
Thus, a new timing synchronization algorithm with rapidity and low
complexity is required for the FM-DCSK UWB communication system.
Wideband Wireless Communications Laboratory, Xiamen University
42-23
Rapid timing synchronization algorithm for FMDCSK UWB receiver(1)

Algorithm basic idea: takes advantage of the excellent correlation
characteristic of chaotic signals, finish timing synchronization based
on intra-symbol correlation operation.
(k+1)th bit
kth bit
T
Algorithm step:
■Step 0: Divide the interval[ˆ, ˆ  T ] into N parts
uniformly, and take the beginning point of each r t  T / 2
r t
part as the integral starting point. Thus, within one  
symbol observation interval, N integral results
are obtained:
(0)
Si
Where

ˆ  iT / N  T I

ˆ  iT / N

r ( t )  r ( t  T / 2) dt ,
T I  [T w , T / 2]
,define: I
i  0,1,
 arg m ax S i
(0)
,
N  1.
i  0,1,
TI
S0(0)
 ˆ
S1(0)
ˆ 
T
4
S 2(0)
ˆ 
T
2
N  1.
according to
ˆ  ˆ  m od
 N
 I T / N ,T .
Wideband Wireless Communications Laboratory, Xiamen University
42-24
ˆ 
3T
4
Example for Divide the interval
into 4 parts
i
Then update ˆ
S3(0)
[ˆ , ˆ  T ]
Rapid timing synchronization algorithm for FMDCSK UWB receiver(2)
After step 0, the target interval, in which  lies, can be determined in
whose length is 2T / N .
[ˆ  T / N , ˆ  T / N ]
Step q: (q>0)
Through step q-1, it is known that  lies in the interval [ˆ  T / (2 N ), ˆ  T / (2 N )] , which is
then uniformly divided into two sub-intervals, namely [ˆ  T / (2 N ), ˆ ] and [ˆ , ˆ  T / (2 N )] . The
purpose of this step is to determine in which sub-interval lies, and the determination is
based on formulas given below:
q 1
q 1
q 1
S
(q)
j

ˆ    1 

ˆ    1
j
T
j
q
2 N
T
 TI

r ( t )  r ( t  T / 2) dt ,
j  0,1
q
2 N

T

, ˆ  ,
 ˆ  q  1
2
N


 
T

 ˆ , ˆ 
,
q

1


2
N 

Update 
if
J  0
Where: J
 arg m ax S j ,
(q)
j  0,1.
j
if
T

ˆ  q ,


2 N
ˆ  
ˆ  T ,
q

2 N

J  1.
if
J  0
if
J  1.
Wideband Wireless Communications Laboratory, Xiamen University
42-25
q 1
Rapid timing synchronization algorithm for
FM-DCSK UWB receiver(3)
Algorithm stop condition:
define synchronization resolution T . ,so needing number of steps that maximum
timing error is less than or equal to the resolution
res
T
q
2 N
So,
q  log 2
Define,
T
.
N Tres

T
q prop   log 2
N Tres

Thus, If q  q
repeat step q.
prop
,
 T res .

,

the algorithm ends; otherwise update q = q + 1,and
Wideband Wireless Communications Laboratory, Xiamen University
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Numerical and simulated results(1)
Comparison between the Proposed Algorithm and the Conventional Algorithm
4
10
In the terms of proposed algorithm and
reference algorithm, the number steps
for given synchronization solution is
q prop
q ref
3
required number of steps
10
Proposed:

T
q prop   log 2
N Tres

Reference:
q ref   T / ( N f T res )  .
2
10

,

1
10
0
10
-8
10
-9
10
Tres (s)
Required number of steps vs.
-10
10
T res
(T = 200ns, N = 4).
Remark: the time complexity of the reference algorithm is O (1 / T ) , whereas
the counterpart in the new algorithm here is only O (log (1 / T )).
res
2
res
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Numerical and simulated results(2)
Timing performance under different N
90
35
80
N=2
N=4
N=8
30
Where:
earlier timing (ET): ˆ    Tres
60
average timing error (ns)
timing probability (%)
70
ET
N=2
N=4
N=8
50
40
LT
30
25
later timing (LT): ˆ    Tres
20
15
LT
accurate timing (AT):
10
ˆ  [  Tres ,   Tres ]
20
5
10
ET
AT
0
15
20
25
Eb/N0 (dB)
(a)
30
0
15
20
25
Eb/N0 (dB)
30
(b)
Comparison among (a) timing probabilities, (b) average timing errors
vs. Eb/N0 under different values of N over CM1
Remark: Since the BER performance is highly sensitive to LT but less sensitive to ET, it is clear
that the larger the probability of LT, the worse the BER performance. Here, occurrence
probabilities of ET is great than LT. Thus, the average BER performance is good.
Wideband Wireless Communications Laboratory, Xiamen University
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Contents
 Background
 System design of UWB based chaos
modulations
 Rapid timing synchronization for FM-DCSK
UWB
 User cooperation DCSK
communication system
 Ongoing work
 Conclusions
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Motivation
 There are two fundamental aspects of wireless communication that
make the problem challenging and interesting.


First is the phenomenon of fading: the time-variation of the channel
strengths due to the small-scale effect of multipath fading
Second is the phenomenon of interference: such as, inter-user inference,
inter-symbol inference (ISI) that is introduced by multipath channel.
 So, how to deal with fading and with interference is central to the
design of wireless communication systems.

Diversity – an effective method to mitigate channel fading
 As an alterative spread-spectrum technology, DCSK/FM-DCSK has
superior capability in terms of anti-interference over multipath
fading channels.

For improving performance of DCSK, space diversity is a promising
technology. Such as, multiple antenna, user cooperative diversity, etc.
Wideband Wireless Communications Laboratory, Xiamen University
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User Cooperative Diversity (Combating fading)
 Cooperative communications can provide transmit diversity for
most wireless networks.
 Since one user’s signals can be relayed by other users’ independent
fading paths to the destination, in cooperative communications,
terminals share others’ antennas to achieve transmit diversity.
 This approach achieves spatial diversity through all partners’
antennas, which enhances the ability of combating fading in
wireless communication systems. Such as WSN, WPAN and WBAN,
which are complicated applications requesting low-cost, low power
and various demands of QoS. (VMIMO)
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DCSK/FM-DCSK (Combating multi-path interference)

Frequency modulated differential chaos shift keying (DCSK/FM-DCSK) is a
joint modulation and spread spectrum technique.

The noise performance of DCSK/FM-DCSK is superior to most conventional
modulation schemes in multi-path channel environment. In particular,
frequency-modulated differential chaos shift keying (DCSK/FM-DCSK)
technique offers robustness against multi-path interference and channel
imperfections.

DCSK/FM-DCSK demonstrates itself as a promising modulation technique for
many low-cost and low-complexity wireless transmission applications, such as
wireless sensor networks (WSN) and low-data-rate wireless personal or body
area networks (WPAN, WBAN).

Thus, combination of user cooperative diversity and DCSK/FM-DCSK is an
efficient scheme to anti-fading and anti-interference (ISI).
Wideband Wireless Communications Laboratory, Xiamen University
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DCSK user cooperative system based on
Walsh codes
User 1 data
Y1 (t ) / X 1 (t )
X 1, 2 (t )
Data of U1
U1
Data of U2
Y0 (t )
Y0 (t )
H1, 2
H 2,1
U2
H 2, 0
Data of U2
H 2, 0
Base station
U2
Base station
(a) Odd period, transmit self
data
User 1
w1 , w2
User 2
w3 , w4
w3 , w4
w1 , w2
w1 , w2
w3 , w4
w3 , w4
w1 , w2
Data of U1
(a) Conventional cooperation
X 2,1 (t )
Y2 (t ) / X 2 (t )
User 2 data
Cooperation period
H1,0
U1
H1,0
Antenna of
user #
Antenna of
user #
(b) Even period, relay the
data of partner’s
Cooperation period
User 1
w1 , w2
w1 , w2
w3 , w4
w1 , w2
w1 , w2
w3 , w4
User 2
w3 , w4
w1 , w2
w3 , w4
w3 , w4
w1 , w2
w3 , w4
Model of user cooperative communication systems
Walsh codes are used as multi-access codes for two
users. At odd slot, user 1 and user 2 transmit self
Cooperation protocol of the
information to partner and destination, respectively, at
two-user DCSK-CC system
even slot, user 1 and user 2 relay partner’s information
to destination.
According to transmit self information
(b) Space-time cooperation
or not at even slot, there are two user
cooperative diversity protocol: conventional
cooperation and space-time cooperation.
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Simulated results(1) –
Comparisons between DCSK cooperative system and CDMA cooperative system
BEP performance comparisons of the DCSK cooperation system and the CDMA cooperative system
with different distance ratio d : d : d , here all distances are normalized by the distance d SD
Spread-spectrum factor is 32 (left) and 64 (right). Spread code of CDMA is Golden sequence, CDMA
system with conventional receiver, simulation environment is multipath fading channel with PDP of [0.4
0.4 0.2].
SD
SR
RD
Remark: The BEP curves indicate that the performance of the DCSK cooperative system
with a steeper slope is more sensitive to noise than the CDMA cooperative system at high
values of SNR. The DCSK cooperative system is more effective at high SNR, especially in
near-far scenarios, such as user distance ratio 1:1:0.5 and 1:0.8:0.4.
Wideband Wireless Communications Laboratory, Xiamen University
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Simulated results(2)Performance comparisons between conventional cooperation and space-time
cooperation
BEP performance of conventional cooperation protocol and space-time cooperation protocol, spread spectrum is
32 (left) and 64 (right).
Remark: Unlike the user cooperative communication systems based on traditional digital
modulations, the performance of the space-time cooperative system is not better than that
of the conventional cooperative system in the DCSK cooperative system at all times.
Wideband Wireless Communications Laboratory, Xiamen University
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Simulated results(3)
 Performances under different chaotic maps
BEP performances of DCSK cooperative system when logistic map,
cubic map and Bernoulli-shift map are used, respectively, spread-spectrum
factor is 32
Logistic map:
Cubic map:
x k 1  1  2 x k
2
x k 1  4 x k  3 x k
Bernoulli-shift map:
3
1.2 x k  1 w hen x k  0
x k 1  
1.2 x k  1 w hen x k  0
Remark: It is found that the chaotic sequences generated by the Bernoulli-shift map
produce higher BEP, while the BEPs for the system using the cubic map and the logistic
map are the same. There are similar results in conventional multiuser DCSK systems
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Properties of user cooperative DCSK
communication system
 In near-far scenarios, the performance of DCSK user cooperative
system is better than that of CDMA user cooperative system with
conventional receiver.
 The conventional cooperation is a better cooperation protocol than
the space-time cooperation in DCSK cooperative system.

 There are similar performance results with DCSK under different
chaotic maps.
 Consequently, the DCSK cooperative system can be expected
applicable to energy-constrained and low-cost wireless networks
with simple cooperation protocols
Wideband Wireless Communications Laboratory, Xiamen University
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Contents
 Background
 System design of UWB based chaos
modulations
 Rapid timing synchronization for FM-DCSK
UWB
 User cooperation DCSK communication
system
 Ongoing work
 Conclusions
Wideband Wireless Communications Laboratory, Xiamen University
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Ongoing work
 To boost the application of chaos-based UWB
communications, chaotic signal generators working directly
in the microwave frequency region is developing.
 Chaos-based communications are used in traffic (ITS)
 Network coding and cross-layer design of DCSK/FMDCSK based network.
Wideband Wireless Communications Laboratory, Xiamen University
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Conclusions
 In meddle & low-data rate systems where the low power
consumption and low price are crucial, only non-coherent receivers
can be used. DCSK/FM-DCSK is best choice in chaos modulations.
 The rapid timing synchronization algorithm based chaotic signal
property is efficient and robust in FM-DCSK UWB non-coherent
receiver.
 An alterative simplified DCSK (CS-DCSK) scheme is more
promising in low-cost application scenarios.
 There are many space to optimize multi-user communication system
based on DCSK/FM-DCSK modulation.
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References










G. Kolumbán, M. P. Kennedy, G. Kis, and Z. Jákó, “FM-DCSK: a novel method for chaotic communications,” in
Proc. IEEE ISCAS, May, 1998, vol.4, pp. 477-480.
F.C.M. Lau and C.K. Tse, Chaos-based Digital Communication Systems:Operating Principles, Analysis Methods,
and Performance Evaluation, (Springer-Verlag, Berlin), 2003.
Y. Xia, C. K. Tse, and F. C. M. Lau, “Performance of differential chaos-shift-keying digital communication systems
over a multipath fading channel with delay spread,” IEEE Trans. Circuits Syst. II, Exp. Briefs, vol. 51, pp. 680-684,
Dec. 2004.
G. Kolumbán, “UWB technology: Chaotic communications versus noncoherent impulse radio,” in Proc. ECCTD,
Sept., 2005, vol. 2, pp. II/79-II/82.
C. C. Chong and S. K. Yong, “UWB direct chaotic communication technology for low-rate WPAN applications,”
IEEE Trans. Vehicular Technology, vol. 57, pp. 1527-1536, Mar. 2008.
X. Min, W. K. Xu, L. Wang, and G. R. Chen, “Promising performance of a frequency-modulated differential chaos
shift keying ultra-wideband system under indoor environments,” IET Commun., vol. 4, pp125-134, Jan. 2010.
Shaoyan Chen, Lin Wang and Guanrong Chen “Data-Aided Timing Synchronization for FM-DCSK UWB
Communication Systems”, IEEE Trans. Industrial Electronics, vol.57, May 2010.
Jing Xu, Weikai Xu, Lin Wang and Guanrong Chen, “Design and Simulation of a Cooperative Communication
System Based on DCSK/FM-DCSK,” in Proc. IEEE ISCAS, Paris, France, May 2010
W. K. Xu, L. Wang and G. R. Chen, “Performance of DCSK Cooperative Communication Systems over Multipath
Fading Channels,” IEEE Trans. Circuits and Systems-I, be accepted.
W. K. Xu, L. Wang and G. Kolumban, “A Novel Differential Chaos Shift Keying Scheme,” International Journal
of Bifurcation and Chaos, under review in the second round.
Wideband Wireless Communications Laboratory, Xiamen University
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Thank you!
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