Claims:

1. A method of chaotic modulation based encryption and spreading for physical layer data of an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system, the method comprising:
receiving, by a chaotic modulator (201,401), a plurality of modulated symbols from a modulation mapper (102,302), said plurality of modulated symbols corresponding to a plurality of symbols of a data channel;
determining an initial seed value and an attractor for chaotic modulation;
generating, by a chaotic generator (502) in the chaotic modulator (201), a plurality of chaotic symbols based on the initial seed value and the attractor;
combining, by a combiner (504) in the chaotic modulator (201), M modulated symbols with L chaotic symbols for generating M*L chaotic modulated symbols, wherein L is a spreading factor for the chaotic modulator (201);
buffering, by a buffer (506), the M*L chaotic modulated symbols continuously; and
providing, by the buffer (506), the buffered M*L chaotic modulated symbols to a layer mapper (103) or a transform precoder (303).

2. The method as claimed in claim 1, wherein the modulated symbols are N Quadrature Amplitude Modulated (N-QAM) symbols.

3. The method as claimed in claim 1, wherein a start of buffering is controlled by an offset value k.

4. The method as claimed in claim 3, wherein the initial seed value, the offset value k, and the spreading factor L are transmitted in a control channel corresponding to the data channel.

5. The method as claimed in claim 1, wherein the attractor is a chaotic attractor that generates one or more continuous chaotic signals.

6. The method as claimed in claim 5, wherein the chaotic attractor is based on one or more differential equations initialized by the initial seed value.

7. A chaotic modulator (201,401) in an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system, the chaotic modulator (201,401) comprising:
a chaotic generator (502) configured to:
receive a plurality of modulated symbols from a modulation mapper (102,302),
determine an initial seed value and an attractor for chaotic modulation, and
generate a plurality of chaotic symbols based on the initial seed value using the attractor;
a combiner (504) configured to combine M modulated symbols with L chaotic symbols to generate M*L chaotic modulated symbols, wherein L is a spreading factor for the chaotic modulator (201); and
a buffer (503) configured to:
store the M*L chaotic modulated symbols, and
provide the M*L chaotic modulated symbols to a layer mapper (103) or a transform precoder (303).

8. A method of chaotic demodulation based decryption and de-spreading for physical layer data of an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system, the method comprising:
receiving, by a chaotic demodulator (202,402), a control channel and a data channel;
decoding, by the chaotic demodulator (202,402), the control channel to obtain an initial seed value, an offset value k, and a spreading factor L;
generating, by a chaotic generator (602), a plurality of chaotic symbols based on the initial seed value and a predefined attractor;
buffering, by a buffer (603), L chaotic symbols continuously starting from offset value k;
receiving, by the chaotic demodulator (202,402), a plurality of chaotic modulated symbols;
buffering, by a buffer (605), L*M chaotic modulated symbols continuously; and
separating, by a separator (604), M modulated symbols from the L*M chaotic modulated symbols based on the L chaotic symbols.

9. The method as claimed in claim 8, wherein the modulated symbols are N Quadrature Amplitude Modulated (N-QAM) symbols.

10. The method as claimed in claim 8, wherein a start of buffering is controlled by the offset value k.

11. The method as claimed in claim 8, wherein the initial seed value, the offset value k, and the spreading factor L is transmitted in the control channel corresponding to the data channel.

12. The method as claimed in claim 8, wherein the attractor is a chaotic attractor that generates one or more continuous chaotic signals.

13. The method as claimed in claim 12, wherein the chaotic attractor is based on one or more differential equations initialized by the initial seed value.

14. A chaotic demodulator (202,402) in an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system, the chaotic demodulator (202,402) comprising:
a chaotic generator (602) configured to:
receive an initial seed value, and
generate a plurality of chaotic symbols based on the initial seed value using a pre-defined attractor;
a buffer (603) configured to store L chaotic symbols continuously, from the offset k and onwards;
a buffer (605) configured to:
receive a plurality of chaotic modulated symbols, and
store L*M chaotic modulated symbols continuously; and
a separator (604) configured to separate M modulated symbols from the L*M chaotic modulated symbols based on the L chaotic symbols.
, Description:FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[SEE SECTION 10, RULE 13]

CHAOTIC MODULATION AND DEMODULATION IN OFDMA OR SC-FDMA SYSTEMS

BHARAT ELECTRONICS LIMITED
WITH ADDRESS:
OUTER RING ROAD, NAGAVARA, BANGALORE 560045, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF INVENTION
[0001] The present invention relates generally to wireless communication and particularly to chaotic modulation and demodulation.

BACKGROUND
[0002] Current wireless communications are protocol-based systems and have well defined standards. In these systems, user data and network information data are carried on a physical layer data channel. The network information data can be decoded to perform network layer attacks. Therefore, encrypting the data shared channel is essential to avoid network attacks.
[0003] US 7076065 B2 titled “Chaotic Privacy System and Method” describes system and method of protecting privacy in analog information signal transmission. This technique combines information signal with an analog random signal generated by a chaotic circuit. A received signal is synchronized using a receiving chaotic circuit. The received signal is demodulated using a synchronized replica of the analog random signal. However, the technique does not provide encryption of digital data.
[0004] US 8645678 B2 titled “Chaotic Cryptography for OFDM based Communication Systems” discloses a symmetric key based chaotic cryptography technique utilized for OFDM based wired/wireless communication system. The secret key is required at the receiver, without which the data cannot be recovered. The system security is proportional to (LxN)! where N is the number of OFDM subcarriers and L is the number of OFDM symbols. However, the technique cannot perform synchronization, channel estimation, and equalization without the secret key.
[0005] Therefore, there is a need for an efficient chaotic modulation and demodulation that protects digital data and offers easy synchronization.

SUMMARY
[0006] This summary is provided to introduce concepts related to a method of chaotic modulation based encryption and spreading for physical layer data of an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system; a chaotic modulator in an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system; a method of chaotic demodulation based decryption and de-spreading for physical layer data of an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system; and a chaotic demodulator in an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system. This summary is neither intended to identify essential features of the present invention nor is it intended for use in determining or limiting the scope of the present invention.
[0007] In an embodiment of the present invention, a method of chaotic modulation based encryption and spreading for physical layer data of an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system is provided. The method includes receiving a plurality of modulated symbols from a modulation mapper by a chaotic modulator. The plurality of modulated symbols correspond to a plurality of symbols of a data channel. The method includes determining an initial seed value and an attractor for chaotic modulation. The method includes generating a plurality of chaotic symbols based on the initial seed value and the attractor by a chaotic generator in the chaotic modulator. The method includes combining M modulated symbols with L chaotic symbols for generating M*L chaotic modulated symbols by a combiner in the chaotic modulator. L is a spreading factor for the chaotic modulator. The method includes buffering the M*L chaotic modulated symbols continuously by a buffer. The method includes providing the buffered M*L chaotic modulated symbols to a layer mapper or a transform precoder by the buffer.
[0008] In an embodiment of the present invention, a modulator in an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system is provided. The chaotic modulator includes a chaotic generator, a combiner, and a buffer. The chaotic generator receives a plurality of modulated symbols from a modulation mapper. The chaotic generator determines an initial seed value and an attractor for chaotic modulation. The chaotic generator generates a plurality of chaotic symbols based on the initial seed value using the attractor. The combiner combines M modulated symbols with L chaotic symbols to generate M*L chaotic modulated symbols. L is a spreading factor for the chaotic modulator. The buffer stores the M*L chaotic modulated symbols. The buffer provide the M*L chaotic modulated symbols to a layer mapper or a transform precoder.
[0009] In an embodiment, the modulated symbols are N Quadrature Amplitude Modulated (N-QAM) symbols.
[0010] In an embodiment, a start of buffering is controlled by an offset value k.
[0011] In an embodiment, the initial seed value, the offset value k, and the spreading factor L are transmitted in a control channel corresponding to the data channel.
[0012] In an embodiment, the attractor is a chaotic attractor that generates one or more continuous chaotic signals.
[0013] In an embodiment, the chaotic attractor is based on one or more differential equations initialized by the initial seed value.
[0014] In an embodiment of the present invention, a method of chaotic demodulation based decryption and de-spreading for physical layer data of an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system is provided. The method includes receiving a control channel and a data channel by a chaotic demodulator. The method includes decoding the control channel to obtain an initial seed value, an offset value k, and a spreading factor L by the chaotic demodulator. The method includes generating a plurality of chaotic symbols based on the initial seed value and a predefined attractor by a chaotic generator. The method includes buffering L chaotic symbols continuously starting from offset value k by a buffer. The method includes receiving a plurality of chaotic modulated symbols by the chaotic demodulator. The method includes buffering L*M chaotic modulated symbols continuously by a buffer. The method includes separating M modulated symbols from the L*M chaotic modulated symbols based on the L chaotic symbols by a separator.
[0015] In an embodiment of the present invention, a chaotic demodulator in an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system is provided. The chaotic demodulator includes a chaotic generator, a buffer, another buffer, and a separator. The chaotic generator receives an initial seed value. The chaotic generator generate a plurality of chaotic symbols based on the initial seed value using a pre-defined attractor. The buffer stores L chaotic symbols continuously, from the offset k and onwards. The buffer receives a plurality of chaotic modulated symbols. The buffer stores L*M chaotic modulated symbols continuously. The separator separates M modulated symbols from the L*M chaotic modulated symbols based on the L chaotic symbols.
[0016] In an embodiment, the modulated symbols are N Quadrature Amplitude Modulated (N-QAM) symbols.
[0017] In an embodiment, a start of buffering is controlled by the offset value k.
[0018] In an embodiment, the initial seed value, the offset value k, and the spreading factor L is transmitted in the control channel corresponding to the data channel.
[0019] In an embodiment, the attractor is a chaotic attractor that generates one or more continuous chaotic signals.
[0020] In an embodiment, the chaotic attractor is based on one or more differential equations initialized by the initial seed value.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0021] The detailed description is described with reference to the accompanying figures.
[0022] Figure 1a illustrates a schematic block diagram of a conventional OFDMA based physical transmit chain.
[0023] Figure 1b illustrates a schematic block diagram of a conventional OFDMA based physical receive chain.
[0024] Figure 2a illustrates a schematic block diagram of a chaotic modulation system in OFDMA based physical transmit chain in accordance with an embodiment of the present invention.
[0025] Figure 2b illustrates a schematic block diagram of a chaotic demodulation system in OFDMA based physical receive chain in accordance with an embodiment of the present invention.
[0026] Figure 3a illustrates a schematic block diagram of a conventional SC-FDMA based physical transmit chain.
[0027] Figure 3b illustrates a schematic block diagram of a conventional SC-FDMA based physical receive chain.
[0028] Figure 4a illustrates a schematic block diagram of a chaotic modulation system in SC-FDMA based physical transmit chain in accordance with an embodiment of the present invention.
[0029] Figure 4b illustrates a schematic block diagram of a chaotic demodulation system in SC-FDMA based physical receive chain in accordance with an embodiment of the present invention.
[0030] Figure 5 illustrates a schematic block diagram of a chaotic modulator for spreading and encrypting physical layer data in accordance with an embodiment of the present invention.
[0031] Figure 6 illustrates a schematic block diagram of a chaotic demodulator for de-spreading and decrypting physical layer data in accordance with an embodiment of the present invention.
[0032] Figure 7a illustrates an example of chaotic signal using Lorenz attractor in accordance with an embodiment of the present invention.
[0033] Figure 7b illustrates an example of chaotic signal selection for buffering to perform chaotic modulation in accordance with an embodiment of the present invention.
[0034] Figure 8 illustrates a flowchart of a chaotic modulation method in accordance with an embodiment of the present invention.
[0035] Figure 9 illustrates a flowchart of a chaotic demodulation method in accordance with an embodiment of the present invention.
[0036] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative methods embodying the principles of the present invention. Similarly, it will be appreciated that any flow charts, flow diagrams, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION
[0037] The various embodiments of the present invention provide a method of chaotic modulation based encryption and spreading for physical layer data of an Orthogonal Frequency Division Multiple Access (OFDMA) or a Single Carrier - Frequency Division Multiple Access (SC-FDMA) system, a chaotic modulator in an OFDMA or SC-FDMA system, a method of chaotic demodulation based decryption and de-spreading for physical layer data of OFDMA or SC-FDMA system, and a chaotic demodulator in an OFDMA or SC-FDMA system.
[0038] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details.
[0039] One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.
[0040] However, the systems and methods are not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the presently invention and are meant to avoid obscuring of the presently invention.
[0041] It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0042] The present invention relates to a method of spreading and encrypting OFDMA/SCFDMA based physical layer data using chaotic signal. Chaotic signal are continuous random signal generated using chaotic attractor. The chaotic signal depends on the attractor used and the initial value with which the attractor has been initiated.
[0043] The physical layer of wireless technologies are vulnerable to eavesdropping leading to network layer attack. The network configuration information is carried in the data shared channel which is mapped to physical data channel at the physical layer. Encrypting physical data channel will lead to secrecy of data shared channel carrying network information and user data. The present invention provides chaotic signal to spread and encrypt the physical data channel of OFDMA/SC-FDMA based physical layer. The chaotic signal is combined with the digital modulated data prior to OFDMA/ SC-FDMA modulation. The same chaotic signal is generated locally at the receiver to perform chaotic demodulation post equalization. The parameters to generate the chaotic signal at the receiver are transmitted as part of the control channel associated with the data channel.
[0044] Referring now to Figure 1a, a schematic block diagram of a conventional OFDMA based physical transmit chain (100a) is shown. The conventional OFDMA based physical transmit chain (100a) includes a scrambling unit (101), a modulation mapper (102), a layer mapper (103), a precoding unit (104), a resource element mapper (105), and an OFDMA signal generation unit (106).
[0045] A codeword is the data from shared channel carrying user data or the system information. The codeword is scrambled by the scrambling unit (101) using a pseudo random sequence and later is provided to the modulation mapper (102) wherein, the scrambled data undergoes N-QAM modulation, where ‘N’ is an integer and depicts the modulation order. The digital modulated data is layer mapped and precoded by the layer mapper (103) and the precoding unit (104) in case of MIMO application. A number of layers in layer mapping and a precoding matrix size depends on the MIMO size of the system. The precoding weights are decided as per the channel condition between the transmitter and the receiver. The precoded data is resource element mapped at by the resource element mapper (105) along with other reference signal and control channel. A size of resource element mapped data per layer is PxQ, where P is the number of subcarriers and Q is the number of OFDMA symbols. The resource element mapped data is later OFDM modulated by the OFDMA signal generation unit (106) and mapped to antenna ports for transmission after analog conversion and RF up conversion.
[0046] Referring now to Figure 1b, a schematic block diagram of a conventional OFDMA based physical receive chain (100b) is shown. The conventional OFDMA based physical receive chain (100b) includes an OFDMA demodulation unit (107), a resource element demapper (108), an inverse precoding unit (109), a layer demapper (110), a modulation demapper (111), and a de-scrambling unit (112).
[0047] Antenna ports receive the data for the configured frequency and is digital converted using ADC for configured bandwidth. The received data undergoes OFDM demodulation by the OFDMA demodulation unit (107) prior to which synchronization is done. The OFDM demodulated data is resource element demapped by the resource element demapper (108) to segregate the reference signal, control channel and the data channel. The reference signals are used to perform channel estimation and then based on the estimates; the control and data channel is equalized. The equalized data from each layer is inverse precoded by the inverse precoding unit (109) and layer demapped by the layer demapper (110). Each layer of the layer demapped data is passed through individual modulation demapper per layer by the modulation demapper (111). The order of modulation demapper and the number of bits to be demodulated is derived from the control channel of the associated data channel. The digital demodulated data is descrambled with the same pseudo random sequence as that of the transmitter by the descrambling unit (112) to get the codeword carrying user data and system information data.
[0048] Referring now to Figure 2a, a schematic block diagram of a chaotic modulation system (200a) in OFDMA based transmit chain is shown in accordance with an embodiment of the present invention. The chaotic modulator (201) in the OFDMA based transmitter encrypts and spreads the physical layer data. The chaotic modulator (201) receives the digital modulated data from the modulation mapper (102), combines the digital modulated data with chaotic signal and provides chaotic modulated data to the layer mapper (103).
[0049] Referring now to Figure 2b, a schematic block diagram of a chaotic demodulation system (200b) in OFDMA based receive chain is shown in accordance with an embodiment of the present invention. The chaotic demodulator (202) in the OFDMA based receiver decrypts and de-spreads the physical layer data. The layer demapper (110) provides the layer demapped data to the chaotic demodulator (202), where the chaotic signal is separated from the received data. The chaotic demodulated data is provided to the modulation demapper (111) for digital demodulation.
[0050] Referring now to Figure 3a, a schematic block diagram of a conventional SC-FDMA based physical transmit chain (300a) is shown. The conventional SC-FDMA based physical transmit chain (300a) includes a scrambling unit (301), a modulation mapper (302), a transform precoder (303), a resource element mapper (304), and an SC-FDMA signal generator (305).
[0051] A codeword is scrambled by the scrambling unit (301) with a pseudo random sequence. The scrambled data is digitally modulated over N-QAM modulation at the modulation mapper (302). The modulated data is precoded, resource element mapped and SC-FDMA modulated by the transform precoder (303), the resource element mapper (304), and the SC-FDMA signal generator (305) respectively.
[0052] Referring now to Figure 3b, a schematic block diagram of a conventional SC-FDMA based physical receive chain (300b) is shown. The conventional SC-FDMA based physical receive chain (300b) includes an SC-FDMA demodulation unit (306), a resource element demapper (307), an inverse transform precoder (308), a modulation demapper (309), and a de-scrambling unit (310).
[0053] The received data from ADC is SC-FDMA demodulated by the SC-FDMA demodulation unit (306) prior to which frame synchronization is done. The SC-FDMA demodulated data is resource element mapped by the resource element demapper (307) to segregate the reference signal, control channel and the data channel. The reference signal is used to perform channel estimation and the channel estimates are applied by the equalizer to equalize the control and data channel. The equalized data is inverse precoded by the inverse transform precoder (308) and provided to the modulation demapper (309) for performing digital demodulation.
[0054] The demodulated data is descrambled by the de-scrambling unit (310) using the same pseudo random sequence as that of the transmitter.
[0055] Referring now to Figure 4a, a schematic block diagram of a chaotic modulation system (400a) in SC-FDMA based transmit chain is shown in accordance with an embodiment of the present invention. The Figure 4a illustrates the position of the chaotic modulator (401) in the SC-FDMA based transmitter for encrypting and spreading the physical layer data. The chaotic modulator (401) takes the digital modulated data from the modulation mapper (302), combines it with chaotic signal and provides chaotic modulated data to the transform precoder (303).
[0056] Referring now to Figure 4b, a schematic block diagram of a chaotic demodulation system (400b) is shown in accordance with an embodiment of the present invention. Figure 4b shows the position of the chaotic demodulator (402) in the SC-FDMA based receiver for decrypting and de-spreading the physical layer data. The inverse transform precoder (308) provides the inverse precoded data to the chaotic demodulator (402), where the chaotic signal is separated from the received data. The chaotic demodulated data is provided to the modulation demapper (309) for digital demodulation.
[0057] Referring now to Figure 5, a schematic block diagram of a chaotic modulator (201,401) is shown in accordance with an embodiment of the present invention. The chaotic modulator (201,401) includes an initial seed unit (501), a chaotic generator (502), a buffer (503), a combiner (504), and a buffer (505).
[0058] The chaotic generator (502) is a chaotic attractor used for generating chaotic signal. The chaotic attractor uses set of differential equations which are initialized by the initial seed provided by the initial seed unit (501). The chaotic signal is selected and buffered by the buffer (503) for L samples, where L is the spreading factor. The start of buffering is controlled by an offset value ‘k’. The first L samples of the chaotic signal are combined by the combiner (504) with one N-QAM modulated data and are buffered at 505. The buffering by the buffer (503) is a continuous process until the M samples of modulation mapper are combined and the buffer (505) has M*L chaotic modulated samples. These chaotic modulated symbols are layer mapped, precoded and OFDM modulated. Additionally, the initial seed, spreading factor ‘L’ and the offset value ‘k’ is transmitted in the control channel associated with the data channel. These values vary for individual data channel making the system robust.
[0059] Referring now to Figure 6, a schematic block diagram of a chaotic demodulator (202,402) is shown in accordance with an embodiment of the present invention. The chaotic demodulator (202,402) includes an initial seed unit (601), a chaotic generator (602), a buffer (603), a separator (604), and a buffer (605).
[0060] After equalization, the receiver decodes the control channel to find initial seed, spreading factor ‘L’ and the offset value ‘k’. The chaotic attractor in the chaotic generator (602) is same as that of the transmitter. The decoded initial seed by the initial seed unit (601) is used to initialize the attractor. The same initial value and attractor at both transmitter and receiver enable the generation of same chaotic signal. The generated chaotic signal is buffered by the buffer (603) from the offset ‘k’ for ‘L’ samples, where k and L are decoded as part of the control channel. Additionally, post equalization the complete data channel M*L samples are buffered by the buffer (605). The separator (604) de-spreads and decrypts the chaotic signal M times using continuous L buffered samples of the buffer (603), where each time the L samples vary as the chaotic signal is time varying. As the locally generated chaotic signal is same as that of the transmitter the physical data can be decoded.
[0061] In an embodiment, the chaotic modulator (201,401) and the chaotic demodulator (202,402) are hardware. Examples of hardware include, but are not limited to, an electronic circuit, a processor and/or a programmable logic device (PLD). An example of a processor is a general purpose processor, a microprocessor, a microcontroller unit such as a microcontroller, a digital signal processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) and an Application Specific Instruction-Set Processor (ASIP).
[0062] In an embodiment, the chaotic modulator (201,401) and the chaotic demodulator (202,402) are hardware modules configured to perform one or more logic functions. The logic functions can be hardwired or fixed programmed in a one-time programmable hardware module (unchangeable). The logic functions can be programmed in a programmable hardware module (changeable) (for e.g. by firmware).
[0063] Referring now to Figure 7a, an example of chaotic signal generated using Lorenz attractor is shown in accordance with an embodiment of the present invention. The Lorenz attractor generates 3 continuous chaotic signals x (t), y (t) and z (t) as shown at 701, 702 and 703 respectively. The chaotic attractor needs initial value to kick start the chaotic signal generation and the signal generation is governed by a set of differential equation. All the three signals shown in the figure are continuous, time varying and non periodic in nature. The Figure 7a depicts the random nature of chaotic signal.
[0064] Referring now to Figure 7b, an example of chaotic signal selection is shown in accordance with an embodiment of the present invention. The Figure 7b shows selecting and buffering chaotic signal for chaotic modulation by the chaotic modulator (201,401). The chaotic signal is generated using a set of differential equation initialized by an initial value. This simulated figure shows the sensitivity of the chaotic attractor on the initial value 704 for the chaotic signal generation. If chaotic signal y (t) 702 is selected, then 705 depicts the offset (k) from onwards which the chaotic signal is buffered at the buffer (503) and the buffer (603) for chaotic modulation.
[0065] Referring now to Figure 8, a flowchart of a chaotic modulation method is shown in accordance with an embodiment of the present invention. The flowchart indicates the method of chaotic modulation based encryption and spreading for the physical layer data of the OFDMA or the SC-FDMA system.
[0066] At step 802, the chaotic modulator (201,401) receives the modulated symbols from the modulation mapper (102,302). The modulated symbols correspond to a plurality of symbols of the data channel.
[0067] At step 804, the chaotic modulator (201,401) determines an initial seed value and an attractor for chaotic modulation.
[0068] At step 806, the chaotic generator (502) generates the chaotic symbols based on the initial seed value and the attractor.
[0069] At step 808, the combiner (504) combines M modulated symbols with L chaotic symbols for generating the M*L chaotic modulated symbols. L is the spreading factor for the chaotic modulator (201).
[0070] At step 810, the buffer (506) buffers the M*L chaotic modulated symbols continuously. The buffer (506) provides the buffered M*L chaotic modulated symbols to the layer mapper (103) or the transform precoder (303).
[0071] Referring now to Figure 9, a flowchart of a chaotic demodulation method is shown in accordance with an embodiment of the present invention. The flowchart indicates the method of chaotic demodulation based decryption and de-spreading for the physical layer data of the OFDMA or the SC-FDMA system.
[0072] At step 902, the chaotic demodulator (202,402) receives the control channel and the data channel.
[0073] At step 904, the chaotic demodulator (202,402) decodes the control channel to obtain the initial seed value, the offset value k, and the spreading factor L.
[0074] At step 906, the chaotic generator (602) generates the chaotic symbols based on the initial seed value and a predefined attractor.
[0075] At step 908, the buffer (603) buffers L chaotic symbols continuously.
[0076] At step 910, the chaotic demodulator (202,402) receives the chaotic modulated symbols.
[0077] At step 912, the buffer (605) buffers L*M chaotic symbols continuously.
[0078] At step 914, the separator (604) separates the M modulated symbols from the L*M chaotic modulated symbols based on the L chaotic symbols.
[0079] Advantageously, the present invention provides spreading and encrypting digital modulated data channel using chaotic modulation prior to OFDM modulation. The parameters for generating keys are exchanged via control information. The OFDM signal properties are not altered.
[0080] The present invention provides spreading and encryption of digital modulated data using chaotic signal. The present invention also utilizes the chaotic signal for encryption which is implemented before OFDM modulation making the receiver less complicated. The receiver of the present invention can perform synchronization, channel, estimation and equalization without the requirement of key.
[0081] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.