A low-complexity visible light communication system and method based on PAM-DMT modulation

Abstract

The present invention discloses a low-complexity visible light communication system and method based on PAM-DMT modulation, which belongs to the field of wireless optical communication technology. The optical communication system includes a transmitting end and a receiving end, and the transmitting end is connected to the receiving end through a VLC optical channel. By grouping data, the real part and the imaginary part of the subcarrier resource are modulated respectively, and the modulated signal is constructed and processed using different properties, and a small number of fast Fourier inverse transforms are used, so that the complexity of the transmitting end is significantly reduced; because the receiving end can perform time domain processing on the demodulated signal according to the characteristics of different signal constructions at the transmitting end, complete the reconstruction operation, and then directly demodulate the signal, thereby avoiding the noise removal operation at the receiving end, so that the complexity of the receiving end of the system is greatly reduced; compared with the traditional visible light communication modulation method, the peak-to-average power ratio of the present invention is significantly reduced, and the system performance is significantly improved.

Description

Technical Field

[0001] The invention relates to a low-complexity visible light communication system and method based on PAM-DMT modulation, belonging to the technical field of wireless optical communication. Background Art

[0002] In visible light communication, the LED lighting devices used in daily life are combined with information transmission technology to solve the problem of tight spectrum resources in radio frequency. Moreover, this technology has the advantages of high speed, high confidentiality and abundant spectrum resources. Orthogonal frequency division multiplexing (OFDM) technology is a multi-carrier modulation technology that can resist multipath fading and inter-code interference during signal transmission. Due to its unique advantages, it is widely used in visible light communication.

[0003] Intensity modulation direct detection (IM / DD) technology has been widely used in visible light communication, so the signal transmitted in the visible light communication system must be a non-negative real signal. Among the existing technologies, the hybrid asymmetric clipped optical orthogonal frequency division multiplexing (HACO-OFDM) technology ensures the non-negativity of the transmitted signal by clipping the modulated signal. However, due to the high complexity of the receiving end of this technology and the high peak-to-average power ratio (PAPR), it is easy to produce nonlinear distortion, which limits the promotion and application of this technology.

[0004] The method to reduce the complexity of the receiving end is usually as follows: no clipping operation is performed on the transmission information at the transmitting end, and a DC bias is directly added to ensure the non-negativity of the signal. This can avoid the impact of clipping noise on signal detection. Since the added DC bias is not used to transmit useful information, this will cause power loss, resulting in low power utilization and affecting the overall performance of the system; adding an adaptive bias to the transmission information at the transmitting end can ensure the non-negativity of the transmission signal while reducing the complexity of the receiving end. However, since different signals require different adaptive biases and the adaptive bias requires specific properties, special attention should be paid when designing the adaptive bias in the visible light communication system because the system has a low fault tolerance. Summary of the invention

[0005] In order to solve the problem that the visible light communication system is highly complex and has a high peak-to-average power ratio, which makes it easy to generate nonlinear distortion, the present invention provides a low-complexity visible light communication system based on PAM-DMT modulation, the visible light communication system includes a transmitting end and a receiving end, the transmitting end and the receiving end are connected through a VLC optical channel;

[0006] The transmitting end comprises: a data distributor, a PAM-DMT modulation module, a transmitting digital-to-analog converter and an LED; wherein the data distributor, the PAM-DMT modulation module, the transmitting digital-to-analog converter and the LED are connected in sequence;

[0007] The receiving end includes: an optical-to-electrical converter, a receiving analog-to-digital converter, a PAM-DMT demodulation module, and a data combiner; wherein the optical-to-electrical converter, the receiving analog-to-digital converter, the PAM-DMT demodulation module, and the data combiner are connected in sequence.

[0008] Optionally, the PAM-DMT modulation module includes: a first PAM-DMT modulator, a second PAM-DMT modulator, and a third PAM-DMT modulator connected in parallel, and connected to the data distributor respectively;

[0009] The data distributor calculates the data D to be sent and divides the data into a first group of data D1, a second group of data D2 and a third group of data D3. The first group of data D1 first passes through the first PAM-DMT modulator to form a frequency domain signal Y1, and then performs an N / 2-point inverse fast Fourier transform to obtain a time domain signal y 1,n , and then for y 1,n Perform the signal construction process and obtain the time domain signal t 1,n The second set of data D2 is first formed into a frequency domain signal Y2 by a second PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 2,n , and then for y 2,n Perform the signal construction process and obtain the time domain signal t 2,n The third set of data D3 is firstly formed into a frequency domain signal Y3 by a third PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 3,n , and then for y 3,n Perform the signal construction process and obtain the time domain signal t 3,n ; In order to ensure the non-negativity of the transmitted signal, the three sets of time domain signals t 1,n ,t 2,n ,t 3,n The trimming operation is performed separately, and then the three groups of time domain signals after trimming are superimposed to output the mixed signal z at the transmitting end n .

[0010] Optionally, the process of the PAM-DMT modulation module modulating the data D to be sent includes:

[0011] The first group of data D1 uses the first PAM-DMT modulator to modulate the real part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y1;

[0012] The second group of data D2 uses the second PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y2;

[0013] The third group of data D3 uses the third PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y3.

[0014] Optionally, the PAM-DMT modulation module obtains three groups of time domain signals through N / 2-point inverse fast Fourier transform and signal construction, and the process of clipping includes:

[0015] The time domain signal x transmitted by modulating the real part of the odd subcarrier 1,n Satisfy the following properties:

[0016]

[0017] The time domain signal y obtained in the first PAM-DMT modulator 1,n According to the time domain signal x 1,n The constructed time domain signal t 1,n , and its specific construction process is:

[0018]

[0019] Then for t 1,n Perform the cropping operation to obtain the cropped time domain signal The specific process is:

[0020]

[0021] The time domain signal x transmitted by modulating the imaginary part of the odd subcarrier 2,n Satisfy the following properties:

[0022]

[0023] The time domain signal y obtained in the second PAM-DMT modulator 2,n According to the time domain signal x 2,n The constructed time domain signal t 2,n , and its specific construction process is:

[0024]

[0025] Then for t 2,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0026]

[0027] The time domain signal x transmitted by modulating the imaginary part of the even subcarrier 3,n Satisfy the following properties:

[0028]

[0029] The time domain signal y obtained in the third PAM-DMT modulator 3,n According to the time domain signal x 3,n The constructed time domain signal t 3,n , and its specific construction process is:

[0030]

[0031] Then for t 3,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0032]

[0033] Optionally, the mixed signal z at the transmitting end n The signal is converted by the transmitting digital-to-analog converter and transmitted to the receiving end by the LED, and converted into a mixed signal z at the receiving end by the photoelectric converter and the receiving analog-to-digital converter. n ', characterized in that the PAM-DMT demodulation module is used to modulate the mixed signal z of the receiving end n 'Perform time domain processing, firstly, the time domain signal y 1,n , time domain signal y 2,n and the time domain signal y 3,n Perform the signal reconstruction process to obtain the time domain signal y 1,n ', time domain signal y 2,n ' and the time domain signal y 3,n ', and then after N / 2-point fast Fourier transform, frequency domain signal Y1', frequency domain signal Y2' and frequency domain signal Y3' are obtained, and finally the three groups of frequency domain signals are demodulated respectively.

[0034] Optionally, the PAM-DMT demodulation module performs time domain processing on the received mixed signal to complete the time domain signal y 1,n , time domain signal y 2,n , time domain signal y3,n The signal reconstruction process includes:

[0035] Mixed signal at the receiving end n 'With the mixed signal z at the transmitter n It can be expressed as z n '=z n +w, where w represents the noise in the VLC channel;

[0036] remember

[0037]

[0038] r0=z0′,r N / 4 =z N / 4 ′,r N / 2 =z N / 2 ′,r 3N / 4 =z 3N / 4 '

[0039] Right n The process of time domain processing is:

[0040]

[0041] p1=r0-r N / 2 ,p N / 4 =r N / 4 -r 3N / 4

[0042] Then the signal is reconstructed, and the process is:

[0043]

[0044] Finally, y 1,n ' and y 2,n 'At the same time, after N / 2-point fast Fourier transform, the receiving end frequency domain signal Y1' and frequency domain signal Y2' are obtained, y 3,n 'It also undergoes N / 2-point fast Fourier transform to obtain the frequency domain signal Y3'.

[0045] The present invention also provides a visible light communication method, the method comprising the following steps:

[0046] Step 1: The data D to be sent is calculated and divided into the first group of data D1, the second group of data D2 and the third group of data D3. The first group of data D1 is firstly modulated by the first PAM-DMT modulator to form the frequency domain signal Y1, and then the N / 2-point inverse fast Fourier transform is performed to obtain the time domain signal y 1,n , and then for y 1,n Perform the signal construction process and obtain the time domain signal t 1,nThe second set of data D2 is first formed into a frequency domain signal Y2 by a second PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 2,n , and then for y 2,n Perform the signal construction process and obtain the time domain signal t 2,n The third set of data D3 is firstly formed into a frequency domain signal Y3 by a third PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 3,n , and then for y 3,n Perform the signal construction process and obtain the time domain signal t 3,n ; In order to ensure the non-negativity of the transmitted signal, the three sets of time domain signals t 1,n ,t 2,n ,t 3,n The trimming operation is performed separately, and then the three groups of time domain signals after trimming are superimposed to output the mixed signal z at the transmitting end n .

[0047] Step 2: The PAM-DMT modulation module modulates the mixed signal z at the transmitting end n A cyclic prefix is ​​added to the signal, and the signal is transmitted to the digital-to-analog converter at the transmitting end to obtain a transmitting analog signal, the transmitting analog signal drives the LED to emit light, and is converted into a transmitting light signal, and the transmitting light signal is transmitted to the receiving end through the VLC channel;

[0048] Step 3: The receiving end optical-to-electrical converter receives the optical signal transmitted by the VLC channel and converts the optical signal into an electrical signal. After the electrical signal passes through the receiving end analog-to-digital converter, a mixed signal z at the receiving end is obtained. n ', the mixed signal z at the receiving end is demodulated by the PAM-DMT module n 'Demodulate, remove the cyclic prefix, and modulate the mixed signal z at the receiving end n 'Perform time domain processing, firstly, the time domain signal y 1,n , time domain signal y 2,n and the time domain signal y 3,n Perform the signal reconstruction process to obtain the time domain signal y 1,n ', time domain signal y 2,n ' and the time domain signal y 3,n ', then after N / 2-point fast Fourier transform, frequency domain signal Y1', frequency domain signal Y2' and frequency domain signal Y3' are obtained, and finally three sets of frequency domain signals Y1', Y2' and Y3' are output;

[0049] Step 4: The frequency domain signals Y1' and Y2' of the PAM-DMT1 signal and the PAM-DMT2 signal at the receiving end are simultaneously passed through the PAM-DMT demodulator to obtain data D1' and data D2', and the frequency domain signal Y3' of the PAM-DMT3 is passed through the PAM-DMT demodulator to obtain data D3';

[0050] Step 5: The three groups of demodulated data D1', D2' and D3' are transmitted to the data combiner, and the original data D' is restored by the data combiner.

[0051] Optionally, the process of modulating the data D to be sent includes:

[0052] The first group of data D1 uses the first PAM-DMT modulator to modulate the real part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y1;

[0053] The second group of data D2 uses the second PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y2;

[0054] The third group of data D3 uses the third PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y3.

[0055] Optionally, the step 2 includes:

[0056] The time domain signal x transmitted by modulating the real part of the odd subcarrier 1,n Satisfy the following properties:

[0057]

[0058] The time domain signal y obtained in the first PAM-DMT modulator 1,n According to the time domain signal x 1,n The constructed time domain signal t 1,n , and its specific construction process is:

[0059]

[0060] Then for t 1,n Perform the cropping operation to obtain the cropped time domain signal The specific process is:

[0061]

[0062] The time domain signal x transmitted by modulating the imaginary part of the odd subcarrier 2,nSatisfy the following properties:

[0063]

[0064] The time domain signal y obtained in the second PAM-DMT modulator 2,n According to the time domain signal x 2,n The constructed time domain signal t 2,n , and its specific construction process is:

[0065]

[0066] Then for t 2,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0067]

[0068] The time domain signal x transmitted by modulating the imaginary part of the even subcarrier 3,n Satisfy the following properties:

[0069]

[0070] The time domain signal y obtained in the third PAM-DMT modulator 3,n According to the time domain signal x 3,n The constructed time domain signal t 3,n , and its specific construction process is:

[0071]

[0072] Then for t 3,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0073]

[0074] Then the three groups of time domain signals after trimming are superimposed to obtain the mixed signal of the transmitting end.

[0075] Optionally, the PAM-DMT demodulation module performs time domain processing on the received mixed signal to complete the time domain signal y 1,n , time domain signal y 2,n , time domain signal y 3,n The signal reconstruction process includes:

[0076] Mixed signal at the receiving end n 'With the mixed signal z at the transmitter n It can be expressed as zn '=z n +w, where w represents the noise in the VLC channel;

[0077] remember

[0078]

[0079] r0=z0′,r N / 4 =z N / 4 ′,r N / 2 =z N / 2 ′,r 3N / 4 =z 3N / 4 '

[0080] Right n The process of time domain processing is:

[0081]

[0082] p1=r0-r N / 2 ,p N / 4 =r N / 4 -r 3N / 4

[0083] Then the signal is reconstructed, and the process is:

[0084]

[0085] Finally, y 1,n ' and y 2,n 'At the same time, after N / 2-point fast Fourier transform, the receiving end frequency domain signal Y1' and frequency domain signal Y2' are obtained, y 3,n 'It also undergoes N / 2-point fast Fourier transform to obtain the frequency domain signal Y3'.

[0086] The beneficial effects of the present invention are:

[0087] (1) In the visible light communication system and method of the present invention, at the transmitting end, the PAM-DMT modulator only uses N / 2-point inverse fast Fourier transform in the modulation of each group of signals. Compared with the traditional transmitting end which needs to use N-point inverse fast Fourier transform in the modulation of each group of signals, the complexity of the transmitting end is significantly reduced.

[0088] (2) The method of the present invention groups data, modulates the real and imaginary parts of subcarrier resources respectively, and constructs and processes the modulated signals using different properties. In this process, a smaller number of fast Fourier inverse transforms are used, so that the complexity of the transmitting end is significantly reduced. Since the receiving end can perform time domain processing on the demodulated signal according to the characteristics of the different signals constructed at the transmitting end, complete the reconstruction operation, and then directly demodulate the signal, the noise removal operation is avoided at the receiving end, so that the complexity of the receiving end of the system is greatly reduced.

[0089] (3) Simulation results show that the method of the present invention significantly reduces the peak-to-average power ratio (PAPR) compared with traditional visible light communication modulation methods such as hybrid asymmetric clipped optical orthogonal frequency division multiplexing (HACO-OFDM), effectively improving system performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0091] Figure 1 This is a schematic diagram of a low-complexity visible light communication system based on PAM-DMT modulation of the present invention.

[0092] Figure 2 This is a comparison chart of the bit error rates of a low-complexity visible light communication system based on PAM-DMT modulation and HACO-OFDM of the present invention.

[0093] Figure 3 The PAPR complementary cumulative distribution function diagram of a low-complexity visible light communication system based on PAM-DMT modulation and HACO-OFDM of the present invention. DETAILED DESCRIPTION

[0094] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0095] Embodiment 1:

[0096] This embodiment provides a low-complexity visible light communication system based on PAM-DMT modulation, including a transmitting end and a receiving end, wherein the transmitting end and the receiving end are connected via a VLC optical channel;

[0097] The transmitting end comprises: a data distributor, a PAM-DMT modulation module, a transmitting digital-to-analog converter and an LED; wherein the data distributor, the PAM-DMT modulation module, the transmitting digital-to-analog converter and the LED are connected in sequence;

[0098] The receiving end includes: an optical-to-electrical converter, a receiving analog-to-digital converter, a PAM-DMT demodulation module, and a data combiner; wherein the optical-to-electrical converter, the receiving analog-to-digital converter, the PAM-DMT demodulation module, and the data combiner are connected in sequence.

[0099] The PAM-DMT modulation module includes: a first PAM-DMT modulator, a second PAM-DMT modulator, and a third PAM-DMT modulator connected in parallel, and connected to the data distributor respectively;

[0100] The PAM-DMT demodulation module includes: a first demodulator and a second demodulator, the first demodulator is used to demodulate the frequency domain signal Y1' and the frequency domain signal Y2', and the second demodulator is used to demodulate the frequency domain signal Y3'.

[0101] The data combiner is used to combine the data D1', the data D2' and the data D3', and corresponds to the data distributor at the transmitting end.

[0102] In the system of this embodiment, the data distributor calculates the data D to be sent and divides the data into a first group of data D1, a second group of data D2 and a third group of data D3. The first group of data D1 is formed into a frequency domain signal Y1 through a first PAM-DMT modulator, the second group of data D2 is formed into a frequency domain signal Y2 through a second PAM-DMT modulator, and the third group of data D3 is formed into a frequency domain signal Y3 through a third PAM-DMT modulator.

[0103] The modulation process includes:

[0104] The first group of data D1 uses the first PAM-DMT modulator to modulate the real part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y1;

[0105] The second group of data D2 uses the second PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y2;

[0106] The third group of data D3 uses the third PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y3.

[0107] Then, the first PAM-DMT modulator, the second PAM-DMT modulator, and the third PAM-DMT modulator perform N / 2-point inverse fast Fourier transform on the frequency domain signal Y1, the frequency domain signal Y2, and the frequency domain signal Y3, respectively. After the signal construction process, three groups of time domain signals are obtained. In order to ensure the non-negativity of the transmission signal, the three groups of time domain signals are clipped respectively, and then the three groups of time domain signals after clipping are superimposed to output the mixed signal z at the transmitting end. n .

[0108] The PAM-DMT modulation module obtains three sets of time domain signals through N / 2-point inverse fast Fourier transform and signal construction, and the process of clipping includes:

[0109] The time domain signal x transmitted by modulating the real part of the odd subcarrier 1,n Satisfy the following properties:

[0110]

[0111] The time domain signal y obtained in the first PAM-DMT modulator 1,n According to the time domain signal x 1,n The constructed time domain signal t 1,n , and its specific construction process is:

[0112]

[0113] Then for t 1,n Perform the cropping operation to obtain the cropped time domain signal The specific process is:

[0114]

[0115] The time domain signal x transmitted by modulating the imaginary part of the odd subcarrier 2,n Satisfy the following properties:

[0116]

[0117] The time domain signal y obtained in the second PAM-DMT modulator 2,n According to the time domain signal x 2,n The constructed time domain signal t 2,n , and its specific construction process is:

[0118]

[0119] Then for t 2,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0120]

[0121] The time domain signal x transmitted by modulating the imaginary part of the even subcarrier 3,n Satisfy the following properties:

[0122]

[0123] The time domain signal y obtained in the third PAM-DMT modulator 3,n According to the time domain signal x 3,n The constructed time domain signal t 3,n , and its specific construction process is:

[0124]

[0125] Then for t 3,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0126]

[0127] The mixed signal z at the transmitting end n The signal is converted by the transmitting digital-to-analog converter and transmitted to the receiving end by the LED, and converted into a mixed signal z at the receiving end by the photoelectric converter and the receiving analog-to-digital converter. n ', characterized in that the PAM-DMT demodulation module is used to modulate the mixed signal z of the receiving end n 'Perform time domain processing, firstly, the time domain signal y 1,n , time domain signal y 2,n and the time domain signal y 3,n Perform the signal reconstruction process to obtain the time domain signal y 1,n ', time domain signal y 2,n ' and the time domain signal y 3,n ', and then after N / 2-point fast Fourier transform, frequency domain signal Y1', frequency domain signal Y2' and frequency domain signal Y3' are obtained, and finally the three groups of frequency domain signals are demodulated respectively.

[0128] The PAM-DMT demodulation module performs time domain processing on the received mixed signal, and the PAM-DMT demodulation module performs time domain processing on the received mixed signal to complete the time domain signal y 1,n , time domain signal y 2,n , time domain signal y 3,n The signal reconstruction process includes:

[0129] Mixed signal at the receiving end n'With the mixed signal z at the transmitter n It can be expressed as z n '=z n +w, where w represents the noise in the VLC channel;

[0130] remember

[0131]

[0132] r0=z0′,r N / 4 =z N / 4 ′,r N / 2 =z N / 2 ′,r 3N / 4 =z 3N / 4 '

[0133] Right n The process of time domain processing is:

[0134]

[0135] p1=r0-r N / 2 ,p N / 4 =r N / 4 -r 3N / 4

[0136] Then the signal is reconstructed, and the process is:

[0137]

[0138] Finally, y 1,n ' and y 2,n 'At the same time, after N / 2-point fast Fourier transform, the receiving end frequency domain signal Y1' and frequency domain signal Y2' are obtained, y 3,n 'It also undergoes N / 2-point fast Fourier transform to obtain the frequency domain signal Y3'.

[0139] Embodiment 2:

[0140] This embodiment provides a visible light communication method, comprising the following steps:

[0141] Step 1: The data D to be sent is calculated and divided into the first group of data D1, the second group of data D2 and the third group of data D3. The first group of data D1 is firstly modulated by the first PAM-DMT modulator to form the frequency domain signal Y1, and then the N / 2-point inverse fast Fourier transform is performed to obtain the time domain signal y 1,n , and then for y 1,n Perform the signal construction process and obtain the time domain signal t 1,nThe second set of data D2 is first formed into a frequency domain signal Y2 by a second PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 2,n , and then for y 2,n Perform the signal construction process and obtain the time domain signal t 2,n The third set of data D3 is firstly formed into a frequency domain signal Y3 by a third PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 3,n , and then for y 3,n Perform the signal construction process and obtain the time domain signal t 3,n ; In order to ensure the non-negativity of the transmitted signal, the three sets of time domain signals t 1,n ,t 2,n ,t 3,n The trimming operation is performed separately, and then the three groups of time domain signals after trimming are superimposed to output the mixed signal z at the transmitting end n ;

[0142] The first group of data D1 uses the first PAM-DMT modulator to modulate the real part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y1;

[0143] The second group of data D2 uses the second PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y2;

[0144] The third group of data D3 uses the third PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y3.

[0145] The time domain signal x transmitted by modulating the real part of the odd subcarrier 1,n Satisfy the following properties:

[0146]

[0147] The time domain signal y obtained in the first PAM-DMT modulator 1,n According to the time domain signal x 1,n The constructed time domain signal t 1,n , and its specific construction process is:

[0148]

[0149] Then for t 1,n Perform the cropping operation to obtain the cropped time domain signal The specific process is:

[0150]

[0151] The time domain signal x transmitted by modulating the imaginary part of the odd subcarrier 2,n Satisfy the following properties:

[0152]

[0153] The time domain signal y obtained in the second PAM-DMT modulator 2,n According to the time domain signal x 2,n The constructed time domain signal t 2,n , and its specific construction process is:

[0154]

[0155] Then for t 2,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0156]

[0157] The time domain signal x transmitted by modulating the imaginary part of the even subcarrier 3,n Satisfy the following properties:

[0158]

[0159] The time domain signal y obtained in the third PAM-DMT modulator 3,n According to the time domain signal x 3,n The constructed time domain signal t 3,n , and its specific construction process is:

[0160]

[0161] Then for t 3,n Perform the cropping operation to obtain the cropped signal The specific process is:

[0162]

[0163] Then the three groups of time domain signals after trimming are superimposed to obtain the mixed signal of the transmitting end.

[0164] Step 2: The PAM-DMT modulation module modulates the mixed signal z at the transmitting end nA cyclic prefix is ​​added to the signal, and the signal is transmitted to the digital-to-analog converter at the transmitting end to obtain a transmitting analog signal, the transmitting analog signal drives the LED to emit light, and is converted into a transmitting light signal, and the transmitting light signal is transmitted to the receiving end through the VLC channel;

[0165] Step 3: The receiving end optical-to-electrical converter receives the optical signal transmitted by the VLC channel and converts the optical signal into an electrical signal. After the electrical signal passes through the receiving end analog-to-digital converter, a mixed signal z at the receiving end is obtained. n ', the mixed signal z at the receiving end is demodulated by the PAM-DMT module n 'Demodulate, remove the cyclic prefix, and modulate the mixed signal z at the receiving end n 'Perform time domain processing, firstly, the time domain signal y 1,n , time domain signal y 2,n and the time domain signal y 3,n Perform the signal reconstruction process to obtain the time domain signal y 1,n ', time domain signal y 2,n ' and the time domain signal y 3,n ', then after N / 2-point fast Fourier transform, frequency domain signal Y1', frequency domain signal Y2' and frequency domain signal Y3' are obtained, and finally three sets of frequency domain signals Y1', Y2' and Y3' are output;

[0166] The PAM-DMT demodulation module performs time domain processing on the received mixed signal to complete the time domain signal y 1,n , time domain signal y 2,n , time domain signal y 3,n The signal reconstruction process includes:

[0167] Mixed signal at the receiving end n 'With the mixed signal z at the transmitter n It can be expressed as z n '=z n +w, where w represents the noise in the VLC channel;

[0168] remember

[0169]

[0170] r0=z0′,r N / 4 =z N / 4 ′,r N / 2 =z N / 2 ′,r 3N / 4 =z 3N / 4 '

[0171] Right n The process of time domain processing is:

[0172]

[0173] p1=r0-r N / 2 ,p N / 4 =r N / 4 -r 3N / 4

[0174] Then the signal is reconstructed, and the process is:

[0175]

[0176] Finally, y 1,n ' and y 2,n 'At the same time, after N / 2-point fast Fourier transform, the receiving end frequency domain signal Y1' and frequency domain signal Y2' are obtained, y 3,n 'It also undergoes N / 2-point fast Fourier transform to obtain the frequency domain signal Y3'.

[0177] Step 4: The frequency domain signals Y1' and Y2' of the PAM-DMT1 signal and the PAM-DMT2 signal at the receiving end are simultaneously passed through the PAM-DMT demodulator to obtain data D1' and data D2', and the frequency domain signal Y3' of the PAM-DMT3 is passed through the PAM-DMT demodulator to obtain data D3';

[0178] Step 5: The three groups of demodulated data D1', D2' and D3' are transmitted to the data combiner, and the original data D' is restored by the data combiner.

[0179] In order to further illustrate that the present invention can achieve the beneficial effect of reducing system complexity and reducing peak-to-average power ratio (PAPR), a series of experiments were conducted. The experimental results are as follows: Figure 2 and Figure 3 show.

[0180] Figure 2 This is a comparison chart of the bit error rate between a low-complexity visible light communication system based on PAM-DMT modulation and HACO-OFDM according to the present invention. HACO-OFDM uses three simulation conditions: 16QAM-4PAM, 64QAM-8PAM, and 256QAM-16PAM. The system of the present invention uses three simulation conditions: 4PAM, 8PAM, and 16PAM. In order to make a fair comparison between the two systems, the three simulation conditions of the two are compared one by one. Figure 2 It can be seen from the curve in that the bit error rate performance of the system of the present invention and the HACO-OFDM system is almost the same under the given simulation conditions. In addition, the system of the present invention maintains the same high spectrum utilization as the HACO-OFDM system, but the complexity of the system is greatly reduced compared with the HACO-OFDM system.

[0181] Figure 3 The complementary cumulative distribution function diagram of the PAPR performance of a low-complexity visible light communication system based on PAM-DMT modulation according to the present invention and the HACO-OFDM system is shown. Under fair comparison conditions, the PAPR performance of the two different modulation systems is compared. The system of the present invention is improved by about 0.9 dB compared with the HACO-OFDM system, which indicates that the system of the present invention effectively improves the PAPR performance of the system while maintaining the same spectrum utilization and greatly reducing the complexity of the receiving end.

[0182] Some steps in the embodiments of the present invention may be implemented using software, and the corresponding software program may be stored in a readable storage medium, such as a CD or a hard disk.

[0183] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-complexity visible light communication system based on PAM-DMT modulation, characterized in that: The visible light communication system comprises a transmitting end and a receiving end, wherein the transmitting end is connected to the receiving end via a VLC optical channel; The transmitting end comprises: a data distributor, a PAM-DMT modulation module, a transmitting digital-to-analog converter and an LED; wherein the data distributor, the PAM-DMT modulation module, the transmitting digital-to-analog converter and the LED are connected in sequence; The receiving end includes: an optical-to-electrical converter, a receiving analog-to-digital converter, a PAM-DMT demodulation module, and a data combiner; wherein the optical-to-electrical converter, the receiving analog-to-digital converter, the PAM-DMT demodulation module, and the data combiner are connected in sequence; The PAM-DMT modulation module includes: a first PAM-DMT modulator, a second PAM-DMT modulator, and a third PAM-DMT modulator connected in parallel, and connected to the data distributor respectively; The data distributor calculates the data D to be sent and divides the data into a first group of data D1, a second group of data D2 and a third group of data D3. The first group of data D1 first passes through the first PAM-DMT modulator to form a frequency domain signal Y1, and then performs an N / 2-point inverse fast Fourier transform to obtain a time domain signal y 1,n , and then for y 1,n Perform the signal construction process and obtain the time domain signal t 1,n The second set of data D2 is first formed into a frequency domain signal Y2 by a second PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 2,n , and then for y 2,n Perform the signal construction process and obtain the time domain signal t 2,n The third set of data D3 is firstly formed into a frequency domain signal Y3 by a third PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 3,n , and then for y 3,n Perform the signal construction process and obtain the time domain signal t 3,n ; In order to ensure the non-negativity of the transmitted signal, the three sets of time domain signals t 1,n ,t 2,n ,t 3,n The trimming operation is performed separately, and then the three groups of time domain signals after trimming are superimposed to output the mixed signal z at the transmitting end n ; The process of the PAM-DMT modulation module modulating the data D to be sent includes: The first group of data D1 uses the first PAM-DMT modulator to modulate the real part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y1; The second group of data D2 uses the second PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y2; The third group of data D3 uses the third PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y3; The PAM-DMT modulation module obtains three groups of time domain signals through N / 2-point inverse fast Fourier transform and signal construction, and the process of clipping includes: The time domain signal x transmitted by modulating the real part of the odd subcarrier 1,n Satisfy the following properties: The time domain signal y obtained in the first PAM-DMT modulator 1,n According to the time domain signal x 1,n The constructed time domain signal t 1,n , and its specific construction process is: Then for t 1,n Perform the cropping operation to obtain the cropped time domain signal The specific process is: The time domain signal x transmitted by modulating the imaginary part of the odd subcarrier 2,n Satisfy the following properties: The time domain signal y obtained in the second PAM-DMT modulator 2,n According to the time domain signal x 2,n The constructed time domain signal t 2,n , and its specific construction process is: Then for t 2,n Perform the cropping operation to obtain the cropped signal The specific process is: The time domain signal x transmitted by modulating the imaginary part of the even subcarrier 3,n Satisfy the following properties: The time domain signal y obtained in the third PAM-DMT modulator 3,n According to the time domain signal x 3,n The constructed time domain signal t 3,n , and its specific construction process is: Then for t 3,n Perform the cropping operation to obtain the cropped signal The specific process is: The mixed signal z at the transmitting end n The signal is converted by the transmitting digital-to-analog converter and transmitted to the receiving end by the LED, and converted into a mixed signal z at the receiving end by the photoelectric converter and the receiving analog-to-digital converter. n ', the PAM-DMT demodulation module is used to demodulate the mixed signal z at the receiving end n 'Perform time domain processing, firstly, the time domain signal y 1,n , time domain signal y 2,n and the time domain signal y 3,n Perform the signal reconstruction process to obtain the time domain signal y 1,n ', time domain signal y 2,n ' and the time domain signal y 3,n ', then after N / 2-point fast Fourier transform, frequency domain signal Y1', frequency domain signal Y2' and frequency domain signal Y3' are obtained, and finally the three groups of frequency domain signals are demodulated respectively; The PAM-DMT demodulation module includes: a first demodulator and a second demodulator, wherein the first demodulator is used to demodulate the frequency domain signal Y1' and the frequency domain signal Y2', and the second demodulator is used to demodulate the frequency domain signal Y3'.

2. The visible light communication system according to claim 1, characterized in that: The PAM-DMT demodulation module performs time domain processing on the received mixed signal to complete the time domain signal y 1,n , time domain signal y 2,n , time domain signal y 3,n The signal reconstruction process includes: Mixed signal at the receiving end n 'With the mixed signal z at the transmitter n It can be expressed as z n '=z n +w, where w represents the noise in the VLC channel; remember r0=z0′,r N / 4 =from N / 4 ′,r N / 2 =from N / 2 ,r 3N / 4 ′=z 3N / 4 ′ Right n The process of time domain processing is: p1=r0-r N / 2 ,p N / 4 =r N / 4 -r 3N / 4 Then the signal is reconstructed, and the process is: Finally, y 1,n ' and y 2,n 'At the same time, after N / 2-point fast Fourier transform, the receiving end frequency domain signal Y1' and frequency domain signal Y2' are obtained, y 3,n 'It also undergoes N / 2-point fast Fourier transform to obtain the frequency domain signal Y3'.

3. A visible light communication method, characterized in that: The method is applied to the visible light communication system according to any one of claims 1 or 2, comprising the following steps: Step 1: Use the data distributor to calculate the data D to be transmitted and divide the data into the first group of data D1, the second group of data D2 and the third group of data D3. The first group of data D1 first passes through the first PAM-DMT modulator to form a frequency domain signal Y1, and then performs an N / 2-point inverse fast Fourier transform to obtain a time domain signal y 1,n , and then for y 1,n Perform the signal construction process and obtain the time domain signal t 1,n The second set of data D2 is first formed into a frequency domain signal Y2 by a second PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 2,n , and then for y 2,n Perform the signal construction process and obtain the time domain signal t 2,n The third set of data D3 is firstly formed into a frequency domain signal Y3 by a third PAM-DMT modulator, and then an N / 2-point inverse fast Fourier transform is performed to obtain a time domain signal y 3,n , and then for y 3,n Perform the signal construction process and obtain the time domain signal t 3,n ; In order to ensure the non-negativity of the transmitted signal, the three sets of time domain signals t 1,n ,t 2,n ,t 3,n The trimming operation is performed separately, and then the three groups of time domain signals after trimming are superimposed to output the mixed signal z at the transmitting end n ; Step 2: The PAM-DMT modulation module modulates the mixed signal z at the transmitting end n A cyclic prefix is ​​added to the signal, and the signal is transmitted to the digital-to-analog converter at the transmitting end to obtain a transmitting analog signal, the transmitting analog signal drives the LED to emit light, and is converted into a transmitting light signal, and the transmitting light signal is transmitted to the receiving end through the VLC channel; Step 3: The receiving end optical-to-electrical converter receives the optical signal transmitted by the VLC channel and converts the optical signal into an electrical signal. After the electrical signal passes through the receiving end analog-to-digital converter, a mixed signal z at the receiving end is obtained. n ', the mixed signal z at the receiving end is demodulated by the PAM-DMT module n 'Demodulate, remove the cyclic prefix, and modulate the mixed signal z at the receiving end n 'Perform time domain processing, firstly, the time domain signal y 1,n , time domain signal y 2,n and the time domain signal y 3,n Perform the signal reconstruction process to obtain the time domain signal y 1,n ', time domain signal y 2,n ' and the time domain signal y 3,n ', then after N / 2-point fast Fourier transform, frequency domain signal Y1', frequency domain signal Y2' and frequency domain signal Y3' are obtained, and finally three sets of frequency domain signals Y1', Y2' and Y3' are output; Step 4: The frequency domain signals Y1' and Y2' at the receiving end are simultaneously passed through the first demodulator to obtain data D1' and data D2', and the frequency domain signal Y3' is passed through the second demodulator to obtain data D3'; Step 5: The demodulated three sets of data D1', D2' and D3' are transmitted to the data combiner, and the original data D' is restored through the data combiner; The process of modulating the data D to be sent includes: The first group of data D1 uses the first PAM-DMT modulator to modulate the real part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y1; The second group of data D2 uses the second PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y2; The third group of data D3 uses the third PAM-DMT modulator to modulate the imaginary part of the subcarrier, and the modulated signal is converted from serial to parallel, and then mapped and Hermitian symmetric to obtain a frequency domain signal Y3; The step one comprises: The time domain signal x transmitted by modulating the real part of the odd subcarrier 1,n Satisfy the following properties: The time domain signal y obtained in the first PAM-DMT modulator 1,n According to the time domain signal x 1,n The constructed time domain signal t 1,n , and its specific construction process is: Then for t 1,n Perform the cropping operation to obtain the cropped time domain signal The specific process is: The time domain signal x transmitted by modulating the imaginary part of the odd subcarrier 2,n Satisfy the following properties: The time domain signal y obtained in the second PAM-DMT modulator 2,n According to the time domain signal x 2,n The constructed time domain signal t 2,n , and its specific construction process is: Then for t 2,n Perform the cropping operation to obtain the cropped signal The specific process is: The time domain signal x transmitted by modulating the imaginary part of the even subcarrier 3,n Satisfy the following properties: The time domain signal y obtained in the third PAM-DMT modulator 3,n According to the time domain signal x 3,n The constructed time domain signal t 3,n , and its specific construction process is: Then for t 3,n Perform the cropping operation to obtain the cropped signal The specific process is: Then the three groups of time domain signals after trimming are superimposed to obtain the mixed signal of the transmitting end.

4. The visible light communication method according to claim 3, characterized in that: The PAM-DMT demodulation module performs time domain processing on the received mixed signal to complete the time domain signal y 1,n , time domain signal y 2,n , time domain signal y 3,n The signal reconstruction process includes: Mixed signal at the receiving end n 'With the mixed signal z at the transmitter n It can be expressed as z n '=z n +w, where w represents the noise in the VLC channel; remember r0=z0′,r N / 4 =from N / 4 ′,r N / 2 =from N / 2 ′,r 3N / 4 =from 3N / 4 ′ Right n The process of time domain processing is: p1=r0-r N / 2 ,p N / 4 =r N / 4 -r 3N / 4 Then the signal is reconstructed, and the process is: Finally, y 1,n ' and y 2,n 'At the same time, after N / 2-point fast Fourier transform, the receiving end frequency domain signal Y1' and frequency domain signal Y2' are obtained, y 3,n 'It also undergoes N / 2-point fast Fourier transform to obtain the frequency domain signal Y3'.

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