Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/001—Modulated-carrier systems using chaotic signals

Definitions

• the present invention concerns the field of information and communication technology (ICT), and in particular concerns a wireless communication method which uses chaotic signals.
• ICT information and communication technology
• Wireless communication ranging from satellite communication, acoustic communication, mobile phone to wireless Wi-Fi, has become one of the most important methods for communicating information.
• the wireless communication channel can introduce interference, noise and distortion in the signal transmitting the information, for example from damping, phase shift, multipath propagation, and Doppler frequency shift.
• Damping refers to the phenomenon in which the amplitude of the signal decreases as a function of the distance to the transmitter.
• Phase shift refers to the filter effect due to the limited bandwidth of the channel.
• Multipath propagation refers to the signal traveling by different routes and arriving at the receiver end with different time delays.
• Doppler frequency shift refers to the phenomenon of signal frequency variation with relative movement between the transmitter and receiver. How to recover the information from the received signal remains the main challenge in wireless communication systems.
• Chaotic signals have a relationship to initial conditions, are broadband and are easy to generate, which make them suitable for communication applications. Chaotic communication can be divided into four groups: chaos shift key, chaotic masking, chaotic modulation, and chaotic symbolic message bearing method. Most previous work has dealt with an ideal channel situation.
• a wireless communication method wherein data to be transmitted is in binary format, the method comprising :- converting the data to be transmitted into a bipolar binary sequence;
• a method of wireless transmitting wherein data to be transmitted is in binary format, the method comprising :- converting the data to be transmitted into a bipolar binary sequence;
• the wireless communication method can cope with the effect of multipath propagation in the wireless communication channel, and can communicate with broadband chaotic signals.
• the chaotic signal keeps its positive Lyapunov exponents unchanged after being transmitted through the wireless communication channel
• the return map of the received signal keeps the same structure as that of the transmitted signal.
• the return map of the transmitted signal has constant derivative, then the return map of the received signal will also have the same constant derivative.
• the rules to decode are therefore equal to the encoding rules.
• Figure 1 shows a plot of a binary sequence to be transmitted
• Figure 2 shows a plot of the bipolar binary information series to be transmitted
• Figure 3 shows the chaotic attractor of the chaotic signal used in an illustrative embodiment
• Figure 4 shows a time series of the transmitted signal at the transmitter end
• Figure 5 shows the return map of the transmitted signal constructed using measurements from the time Poincare point
• Figure 6 shows the return map of the received signal constructed using measurements from the time Poincare point
• Figure 7 shows the transmitted information (top panel) and received information (bottom panel) using the illustrative method
• Figure 8 shows the bit error rate versus noise amplitude of an experiment conducted using the illustrated method.
• the present invention is based on generating a chaotic signal, to be transmitted over a wireless communication channel, by using a chaotic nonlinear system that has an attractor with a special return map.
• a chaotic nonlinear system that has an attractor with a special return map.
• Equation (1) is a hybrid system because it combines the continuous state x with the discrete switched signal s.
• the information or data to be sent over the wireless communication channel is transmitted over the channel as a chaotic signal.
• c [c(l),c(2), - -,c(N)] .
• ASCII code binary sequence
• the bipolar binary sequence C is then used in equation (1) to encode the information into the transmitted signal.
• a new sequence is produced with M compensating randomly chosen Is or -Is at the end of C s , forming a new set
• the compensating code allows one to calculate the last bits of the message by deriving proper initial conditions.
• N c is N ⁇
• B c is the bit length of the floating number used by a computer in the calculation of equation (1)
• E is the error bound of the decoder
• /) is the positive Lyapunov exponent of Eq. (1).
• the compensating code aims to save energy in the transmision side, to prevent the generation of incorrect signals due to internal noise fluctuations and due to sensitivity to initial conditions, and finally to enable the creation of apparatus on the transmission side that has no need of special hardware to deal with unlimited floating numbers. Given the set of values s, that encodes the information to be transmitted, the larger the number of values (or symbols to be transmitted), the larger will be the floating number representing the initial condition in Eq. (4).
• the present invention aims to create an initial condition with a finite resolution from which a signal generated by Eq. (4) encodes Ni bits.
• N c Ni/2 cycles (each cycle has a period of T s )
• This initial condition is used to create the signal (using Eq. (1)) to retransmit the next N c bits of the message.
• the compensating coding needs to be considered, providing the required extra bits at the end of the original message to be transmitted, so that an initial condition that will generate the signal (encoding the last bits of the original message) can be calculated by Eq. (4).
• the compensated bipolar binary sequence C' is then converted into an impulse control series x by calculating
• the signal to be transmitted that will contain the information is then calculated.
• the parameter ⁇ and the time-transformation coefficient ⁇ are chosen.
• the largest Lyapunov exponent of the system will be ln2 (for ⁇ - ⁇ ) meaning that more bits per time unit can be sent.
• the time -transformation coefficient ⁇ in order for the chaotic signal not to have its dimension altered by the filtering action of the wireless channel, the following needs to be satisfied:
• x(999At) we replace ⁇ (999 ⁇ ) with x e (l)
• s 9 sgn(x e (l))
• x (l999At) we replace x(1999At) with x e (2)
• s 19 sgn (x e (2)) , then go on calculating using equation (2), effectively, a numerical integration.
• N3 « N2 . x RS (/) is the time Poincare-point of the received signal.
• ⁇ ( ⁇ ) represents the transmitted signal xj (t) after being filtered by the second part of equation (6).
• x R is the received signal after being transmitted through the wireless communication channel
• x is the transmitted signal
• L is the number of multipaths
• ⁇ . is the time delay corresponding to y ' th of the L paths
• e ⁇ ' is the signal damping
• Figures 5 and 6 illustrate the respective return map of the transmitted signal and the received signal. It will be noted that the slopes of the two maps are the same meaning that the positive Lyapunov exponents of the received signal equals the positive Lyapunov exponents of the transmitted signal.
• figure 7 illustrates, for the example described above, the received (decoded) binary information and the lower part illustrates the transmitted binary information. Comparing the two subplots, it is clear that the decoded information is the same as the transmitted information.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Dc Digital Transmission (AREA)
• Compression, Expansion, Code Conversion, And Decoders (AREA)

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• 2014
  • 2014-05-14 CN CN201410203969.9A patent/CN104065470B/zh not_active Expired - Fee Related
• 2015
  • 2015-05-13 WO PCT/GB2015/051411 patent/WO2015173568A1/en active Application Filing
  • 2015-05-13 GB GB1620295.4A patent/GB2540714A/en not_active Withdrawn

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