CA2995500C  A differential chaos shift keying (dcsk) based on hybrid chaotic system  Google Patents
A differential chaos shift keying (dcsk) based on hybrid chaotic systemInfo
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 CA2995500C CA2995500C CA2995500A CA2995500A CA2995500C CA 2995500 C CA2995500 C CA 2995500C CA 2995500 A CA2995500 A CA 2995500A CA 2995500 A CA2995500 A CA 2995500A CA 2995500 C CA2995500 C CA 2995500C
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 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04B—TRANSMISSION
 H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00  H04B13/00; Details of transmission systems not characterised by the medium used for transmission
 H04B1/69—Spread spectrum techniques

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04B—TRANSMISSION
 H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00  H04B11/00
 H04B13/02—Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy

 H—ELECTRICITY
 H04—ELECTRIC COMMUNICATION TECHNIQUE
 H04B—TRANSMISSION
 H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00  H04B13/00; Details of transmission systems not characterised by the medium used for transmission
 H04B1/69—Spread spectrum techniques
 H04B1/707—Spread spectrum techniques using direct sequence modulation
 H04B1/7097—Interferencerelated aspects
Abstract
Description
A DIFFERENTIAL CHAOS SHIFT KEYING (DCSK) BASED ON HYBRID
CHAOTIC SYSTEM
TECHNICAL FIELD
The invention belongs to the field of spread spectrum communication technology, and relates to a differential chaos shill keying (DCSK) communication method based on a hybrid system.
BACKGROUND ART
With the problems such as resource shortage, environment pollution monitoring, national security, defense, and so on, being serious the development and exploration of marine resources becomes the focus of scientific and technological research. As electromagnetic waves cannot propagate over long distances in the water, underwater acoustic communication is only feasible technique for the long distance communication in the water.
However, the reliability of acoustic communications is susceptible to acoustic channel constraints, such as multipath propagation, amplitude damping, timevarying parameters, and ambient noise. It is significant to find reliable methods for the underwater acoustic communication.
SUMMARY
The purpose of the present invention is to provide a DCSK communication method based on a hybrid system to improve the reliability of the underwater acoustic communication as compared to the existing methods.
The proposed invention provides a DCSK communication method based on a hybrid system, it includes the following steps:
Step 1: Set up parameters of a communication system Assume that bit transmission rate is Rb bits/s, and corresponding bit duration is Tb, at the same time, a base frequency of the hybrid system is f, symbol rate in chaotic signal is R, bits/s, which corresponds symbol duration, Te=1/Rd=1/f, and spreading gain in this case is defined as L=R,IRb=(11T,)1 (11Tb)=TbiTc;
Step 2: Prepare binary information to be transmitted Set binary infoiniationBn={4,b2õbn} , where b, represent +1 or 1, i=1, n represent the ith binary information to be transmitted and n is the number of the binary information;
Step 3: Generate of the chaotic signal ui(t) The hybrid system given by:
(t)2flit1 (t)+ (co' +132)(u1 (t)¨s)= 0 is used to generate the chaotic signal ui(t), and discrete state s is defined by guard condition, and the discrete state s is set as sgn(ui(t)), if and only if ü (t) =0;
otherwise, s keeps unaltered, where sgn() is defined as:
+1, ul 0 sgn =
¨1, ui < 0 co=27tf, /3=j1n2 are parameters, f is the base frequency of the chaotic signal and a switching period of the discrete state s is denoted as T, =271 I co =11 f ;
Step 4: Modulate transmitted signal For the ith binary information to be transmitted, the transmitted signal, u3(t), composing of ui(t) in first half slot and u2(t) in second half slot, in the first time slot (i1)Tb<t<(i1)Tb+Tb/2, reference signal piece, ui(t), generated by the hybrid system is sent;
the same reference piece is multiplied by an information bit to be transmitted, i.e., +1 or 1, to form the signal piece, which is sent in the second time slot (i1)Tb+T1,12<t<iTb;
Step 5: Match filter for received signal
2 The received signal, v(t), is firstly fed into the match filter to filter ambient noise and decrease effect of interference, and the match filter is given by:
{(t)+ 2/3(t) + (co2 + 132 )g (t) ¨ 77(0 = 0 , where 4t) is a filter output and '1(0 is an intermediate state;
Step 6: Recover the received information bits The filter output signal, 4t), for the ith binary information, (11)Tb<t<Tb, is divided into two equal time slots , given by 1,(t)=(t+(i1)Tb) '21(t) 4t+(i1)Tb+Tb12), Ot< TbI2, and a correlation output is given by:
r Tb /2 Zi (t)=¨ j i (r) i (t ¨ r)dr , and the binary information bit could be detected by i), = sgn(Z, (Tb /2)).
The advantages of the present disclosure are as follows:
1) The proposed disclosure does not need the chaotic synchronization, channel estimation, and complicated equalization technology, which are necessary for the conventional wireless communication methods. Different from other enhanced versions of DCSK
that demands extra hardware or more complicated algorithm, the proposed method recovers the received information bits at the low cost by using the simple algorithm, thus facilitating the realtime applications.
2) A chaotic match filter corresponding to the hybrid system is used to relieve the effect of interference and to improve signal to noise (SNR) ratio of the received signal. By this way, the proposed communication scheme has a good performance in underwater acoustic channel, in the sense of low Bit Error Rate (BER).
3) The base frequency of the hybrid system can be conveniently adjusted by changing the system parameter in order to adapt to the available communication channel bandwidth.
4) The present invention has a good performance to resist narrowband interference, especially in the case of the interference frequency is larger than the base frequency of the hybrid system.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is the block diagram of the proposed DCSK invention;
Fig. 2 is the binary information to be transmitted, `11' during [0, 11s, and `1' during [1,2[s;
Fig. 3 is the continuous state variable and the discrete variable in the hybrid system;
Fig. 4 is the transmitted signal for information bits [1,1];
Fig. 5 is the received signal after being transmitted through the communication channel and the transmitted one;
Fig. 6 is the filter out signal after the match filter;
Fig. 7 is the correlation output of the first information bit;
Fig. 8 is the correlation output of the second information bit;
Fig. 9 is the bit error rate (BER) performance over an additive white Gaussian noise (AWGN) channel and comparison with the conventional DCSK;
Fig. 10 is the BER performance over an underwater acoustic channel and comparison with the conventional DCSK;
Fig. 11 is the BER performance under the different interference amplitudes;
Fig. 12 is the BER performance under the different interference frequencies.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Certain exemplary embodiments of the present invention will be described in greater detail with reference to the accompanying drawings.
Refer to Fig. 1, the bit duration is divided into two equal time slots, in the first time slot, the reference signal piece, ul, generated by the hybrid system is sent; the same reference signal piece is multiplied by the information bit bi, i.e., one bit in the binary information sequence Bn={b1,b2,...,b,}, to be transmitted to form the signal piece, u2, which is sent in the second time slot; The transmitted signal, u3=[221, 222], composing of u1 in first half time slot and 122 in second half time slot is sent over the communication channel; The received signal, v, is firstly fed into the match filter to filter the noise and decrease the effect of interference. The filter output signal for the ith bit information, 4t)(i1)Tb<t<iTb, is divided into two equal time slots as done at the transmitter, i.e., and 61, then two time slots are used for correlation operation, the correlation output is sampled at the specified instant, the sign function of the sampled value is used to recover the received information bits.
Based on the above principle, the invention includes the following steps:
Step 1: Set up parameters of a communication system Assume that bit transmission rate is Rb bits/s, and corresponding bit duration is Tb (the duration for transmitting one bit), at the same time, a base frequency of the hybrid system is f, symbol rate in chaotic signal is Rc. bits/s, which corresponds symbol duration, 71=1/Rc=1/f, and spreading gain in this case is defined as L=RcIRb=(1171)1 (11Tb)=TbITc;
Set the base frequency f=8Hz in exemplary embodiment, bit duration Tb=ls, this means that the spreading gain L=8;
Step 2: Prepare binary information to be transmitted Set binary information Bn = , b2, .. bõ1, where b, represent +1 or 1, i=1, n represent the ith binary information to be transmitted and n is the number of the binary information;
Assume the bits to be transmitted is B2=1+1,11 as shown in Fig. 2, where the bit duration Tb=ls in the exemplary embodiment;
Step 3: Generate of the chaotic signal ut(i) The hybrid system given by:
(t)2Piti(t)+(co2 +p2 )(,11 (t)¨ s)= 0 (1) is used to generate the chaotic signal ui(t), and discrete state s is defined by guard condition, and the discrete state s is set as sgn(ui(t)), if and only if U1(t) = 0;
otherwise, s keeps unaltered, where sgn() is defined as:
+1 u 0 sgn (u, ) = (2) ,13 U1 < 0 co=27rf, fl=fin2 are parameters, f is the base frequency of the chaotic signal and a switching period of the discrete state s is denoted as T, = 2irl co =1 I f ;
As shown in Fig. 3, the chaotic signal generated by system (1) with f=8Hz and the discrete symbol, s, are shown in the solid line and dotted line, respectively, we can see that eight discrete symbols are generated in one second.
Step 4: Modulate transmitted signal For the ith binary information to be transmitted, the transmitted signal, u3(t), composing of ui(t) in first half slot and u2(t) in second half slot, in the first time slot (i1)Tb<K(i1)Tb+Tb/2, reference signal piece, ui(t), generated by the hybrid system is sent;
the same reference piece is multiplied by an information bit to be transmitted, i.e., +1 or 1, to form the signal piece, which is sent in the second time slot (i1)Th+Th/2<t<iTb;
In the exemplary embodiment, the first time slot, [0,0.5]s, for the first bit, the reference signal piece ui(t), corresponding to ui(t) during [0,0.5]s, is sent, and the same piece signal multiplied by first information bit, i.e., "1", is sent in the second time slot [0.5,1]s. For the second information bit, "A", in the first time slot, i.e., [1, 1.5]s, the signal piece of ui(t) during [0.5, 1 ]s is sent as the reference signal, and the same piece of reference signal multiplied by the second information bit, i.e., "4", is sent duration [1.5,2]s, as shown in Fig. 4.
Step 5: Match filter for received signal The received signal, v(t), is firstly fed into the match filter to filter ambient noise and decrease effect of interference, and the match filter is given by:
{ (t)+ 2 fie(t)+ (co' + p2.)((t) To), 0 7j(t)= v(t + Tc) ¨ v(t) , (3) where ".(t) is a filter output and )7(0 is an intermediate state;
After the transmitted signal, u3, passes through the wireless communication channel (affected from multipath propagation, amplitude damping, timevarying characteristics, and ambient noise) with SNR=10dB, the received signal, v(t), is shown in Fig. 5, where the transmitted signal and the received signal (amplified 40 times for easy comparison) are shown in dotted line and solid line, respectively. The received signal, v(i), is fed into the match filter, and the output of the match filter, (t), is shown in Fig. 6. It can be seen that the filter relieves the effect of interference and ambient noises significantly.
Step 6: Recover the received information bits The filter output signal, (t), for the ith binary information, (i1)Tb<t<iTb, is divided into two equal time slots , given by 6 i(t)=(t+(i1) Tb) &(0= 4t+(i1)Tb+Tb12), 05J< Th/2, and a correlation output is given by:
,Tb/2 4 (i), j , (r)2,(t¨r)cir , (4) and the binary information bit could be detected by b, = sgn (Z, (Tb / 2)) , i.e., if Zr(Tb/2)>0, E., = +1; otherwise, if Z1(Tb/2)<O, 6, = ¨1.
In the exemplary embodiment, the filter out signal 40 of the first bit t=[0,1]s is divided into two equal time slots, i.e., 4i (0= (t), t=[0,0.5]s and 21 (0= (t+Tb/2)=
(t+0.5), t=[0,0.5]s. The filter out signal 40 of the second bit t=[1,2]s is divided into .12 (0= (t+Tb), 1=[0,0.5]s and 2 (0= (1 1.5Tb), t=[0,0.5]s.
The two binary information bit could be decoded by Eq. (4), and the result are 151 = sgn (Z1 (0.5)) and ic = sgn (Z2 (0.5)) . Z1(0.5) and Z2(0.5) are shown in Figs.7 and 8 with a star mark.
Embodiments 1) Ability to resist to noise The proposed invention has a better ability to resist to noise than the conventional DCSK due to the usage of the chaotic signal generated by the hybrid system and the corresponding match filter. The BER versus SNR for the proposed method and the conventional DCSK using Logistic map over an additive Gaussian white noise (AWGN) channel are shown in Fig. 9. The base frequency of the hybrid systemf=50kHz and spreading gain L=50. From Fig. 9, we know that the proposed invention is more robust to the noise compared with the conventional DCSK methods, due to the usage of the match filter corresponding to the chaotic signal at the receiver end.
2) BER perfounance in underwater acoustic channel The characteristics of the underwater acoustic channel require that the communication system resists more serious multipath propagation, ambient noise, and interference as compared to the airbased counterpart. The BER versus SNR for the proposed method and the conventional DCSK in the underwater acoustic channel are given in Fig. 10 for comparison, where the base frequency f=50kHz and spreading gain L=50. In Fig. 10, we learn that the conventional DCSK has higher BER even though the SNR is high, while the proposed invention gets lower BER.
3) The ability to resist to narrowband interference Since the broad band characteristic of the chaotic signal, it is able to resist narrowband interference. We consider the fixed amplitude and frequency of a sinusoidal interference. Here the chaotic signal base frequency is f=50kHz. Figure 11 shows the BER
performance versus SNR under the different interference amplitude A51õ. We find that the BER
increases with the increasing interference amplitude.
Figure 12 shows the BER versus SNR using different interface frequency, where interference signal amplitude 24,,,=1. we obtain that i) with the decreasing of the interference frequency F, BER increases; ii) the BER is not changed significantly when the interference frequency is larger than the base frequency of the chaotic signal.
In conclusion, the proposed invention used the continuous state of the hybrid chaotic system as the modulated signal, at the same time, the spread gain is determined by the discrete symbols; The base frequency of the hybrid system can be conveniently adjusted by changing the system parameter in order to adapt to available channel bandwidth. At the receiver end, a special match filter corresponding to the hybrid chaotic system is used to relieve the effect of interference and to improve SNR of the received signal.
Claims (2)
Step 1: Set up parameters of a communication system Assume that bit transmission rate is R b bits/s, and corresponding bit duration is T b, at the same time, a base frequency of the hybrid system is .function., symbol rate in chaotic signal is R c bits/s, which corresponds symbol duration, T c=1/R c=1/.function., and spreading gain in this case is defined as L=R c/R b=(1/T c)/(1/T b)=T b/T c;
Step 2: Prepare binary information to be transmitted Set binary information B n ={b1,b2,......,b n}, where b i represent +1 or 1, i=1, 2,..., n represent the ith binary information to be transmitted and n is the number of the binary information;
Step 3: Generate of the chaotic signal u1(t) The hybrid system given by:
~1(t)2).beta.u1 (t)+ (.omega.2 + .beta.2 )(u1 (t)¨ s) = 0 is used to generate the chaotic signal u1(t), and discrete state s is defined by guard condition, and the discrete state s is set as sgn(u1(t), if and only if ù1(t)=0;
otherwise, s keeps unaltered, where sgn(.) is defined as:
.omega.=2.pi..function., .beta.=.function.ln2 are parameters, .function. is the base frequency of the chaotic signal and a switching period of the discrete state s is denoted as T c = 2.pi. / .omega.
=1/.function. ;
Step 4: Modulate transmitted signal For the ith binary information to be transmitted, the transmitted signal, u3(t), composing of u1(t) in first half slot and u2(t) in second half slot, in the first time slot (i1)Tb<=t<(i1)T b+T b/2, reference signal piece, u1(t), generated by the hybrid system is sent;
the same reference piece is multiplied by an information bit b i to be transmitted, to form the signal piece, which is sent in the second time slot (i1)T b+T b/2<=t<iT
b;
Step 5: Match filter for received signal The received signal, v(t), is firstly fed into the match filter to filter ambient noise and decrease effect of interference, and the match filter is given by:
where .xi.(t) is a filter output and .eta.(t) is an intermediate state;
Step 6: Recover the received information bits The filter output signal, .xi.(t), for the ith binary information, (i1)Tb<=t<iT b, is divided into two equal time slots , given by .xi1.i(t)=.xi.(t+(i1)T b) .xi.2i(t)= .xi.(t+(i1)T b+T b/2),0<=t < T b/2, and a correlation output is given by:
, and the binary information bit could be detected by ~i = sgn (Z i (T b /2)) .
If Z i(T b/2)>0, ~i = +1; otherwise, if Z i(Tb/2)<=0, ~i = ¨1 .
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CN106209712B (en) *  20160622  20190416  厦门大学  Difference chaotic shift keying modulation demodulating equipment based on the modulation of code subscript 
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CN108449297B (en) *  20180208  20200925  西安理工大学  Phase separation differential chaos keying communication method based on hybrid system 
WO2020113462A1 (en) *  20181205  20200611  北京控制与电子技术研究所  Chaotic sequencebased 5g multicarrier spread spectrum underwater acoustic communication method 
CN110278041B (en) *  20190617  20201110  广东工业大学  Differential chaos keying modulation and demodulation method, device and system and readable storage medium 
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