CN107547133B - PLC-VLC transmission method based on OFDM technology for indoor communication system - Google Patents
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Abstract
The invention relates to a PLC-VLC transmission method based on OFDM technology for an indoor communication system, which comprises the following steps: s1: demodulating and further transmitting signals damaged by the noise through a PLC channel by OFDM; s2: mapping the OFDM signal from the PLC into the VLC OFDM signal in an interleaving method; s3: the mapped signals are conditioned and transmitted in the VLC system while meeting communication and lighting requirements; s4: the receiver receives and reconstructs the signal to recover the original signal. Compared with the prior art, the PLC and the VLC in the indoor communication in the scheme of the invention adopt the OFDM technology to support high data rate transmission, firstly, after information data passes through a PLC channel, signals are damaged by noise, and are sent by the PLC after OFDM demodulation, and then, OFDM signals from the PLC are mapped into VLC OFDM signals in an interleaving method.
Description
Technical Field
The invention relates to a visible light communication technology, in particular to a PLC-VLC transmission method based on an OFDM technology for an indoor communication system.
Background
Visible Light Communication (VLC) has attracted increasing attention from researchers due to its advantages of large bandwidth, unmodulated spectrum, high data rate transmission, lack of electromagnetic interference, and high security.
In intensity modulation/direct detection (IM/DD) based VLC systems, only non-negative signals can be modulated by light intensity. Researchers have developed a large number of intensity modulations in IM/DD VLC systems, such as on-off keying (OOK), Pulse Position Modulation (PPM), and Color Shift Keying (CSK). However, these modulation schemes do not achieve high bandwidth efficiency or are susceptible to inter-symbol interference (ISI). To remedy these shortcomings, some researchers have introduced orthogonal frequency division multiplexing such as direct current offset OFDM (DCO-OFDM) and asymmetric clipped light OFDM (ACO-OFDM) into VLC systems.
Recently, white LEDs consisting of multicolored chips, i.e. red, green and blue chips (RGB-LEDs) or red, green, blue and amber chips (RGBA-LEDs), have become promising transmitters in VLC systems due to their high modulation bandwidth. Researchers have applied OFDM technology to RGB-LED based VLC systems by using color space based modulation. Furthermore, since white LEDs are composed of multicolored chips, the mixing of different colors can cause multi-color interaction, i.e. crosstalk. Considering both lighting and communication requirements, RGBA-LEDs are nowadays introduced in VLC system applications as transmitters and receivers.
However, with current technology, VLC must access a backbone network with extensive indoor coverage to ensure good communication. Since all LEDs are connected to the power line in the indoor VLC system, it is natural to use the power line as a backbone. In such an environment, the bandwidth of Power Line Communication (PLC) can reach 30MHz, so that fast and reliable communication can be supported. Currently, many documents study integrated PLC/VLC systems. Researchers first proposed an integrated PLC/VLC system and analyzed the Bit Error Rate (BER) of the binary modulation scheme, and then they further analyzed the performance of narrowband OFDM in the PLC/VLC system. Relaying and Multiple Input Multiple Output (MIMO) are potential technologies implemented in PLC/VLC systems due to their advantages. In a PLC/VLC system, an OFDM signal in a PLC is destroyed by background noise and impulse noise while passing through a PLC channel, and suffers from crosstalk caused by a multi-color signal while being transmitted in the VLC system, limiting the system performance of a high-order modulation scheme. Therefore, we present an integrated PLC/VLC system by employing OFDM technology and using RGBA-LEDs as information transmitters in VLC and analyze the error rates under the influence of different impulse noises to obtain better transmission performance.
Disclosure of Invention
The present invention is directed to overcome the above-mentioned drawbacks of the prior art and to provide a PLC-VLC transmission method based on OFDM technology for an indoor communication system.
The purpose of the invention can be realized by the following technical scheme:
a PLC-VLC transmission method based on an OFDM technique for an indoor communication system, comprising the steps of:
s1: demodulating and further transmitting signals damaged by the noise through a PLC channel by OFDM;
s2: mapping the OFDM signal from the PLC into the VLC OFDM signal in an interleaving method;
s3: the mapped signals are conditioned and transmitted in the VLC system while meeting communication and lighting requirements;
s4: the receiver receives and reconstructs the signal to recover the original signal.
The step S2 specifically includes the steps of:
s21: setting the number of subcarriers for PLC and VLC OFDM:
aN＝b(M-2)
wherein: a is the data number of the PLC, b is the data number of the VLC OFDM, N is the number of the PLC OFDM subcarriers, and M is the number of the VLC OFDM subcarriers;
s22: odd subcarriers are mapped into one VLC OFDM signal and even subcarriers are mapped into another VLC OFDM signal having Hermitian symmetry properties.
The data number of the PLC and the data number of the VLC OFDM data are both 1.
The VLC system is a white light LED VLC system composed of RGBA-LEDs,
the step S3 specifically includes the steps of:
s31: performing IFFT modulation separation on VLC OFDM signals to obtain two unipolar signals:
ximax (x,0) and xj＝-min(x,0)，
Wherein: i, j belongs to { R, G, B, A }, and represents an RGBA-LED color mark;
s32: adjusting the split unipolar signals by a post-shear bias operation;
s33: and mixing the four colors together to generate white light according to the set color mixing ratio, and transmitting the four separated and adjusted signals in a VLC channel through RGBA-LED.
The step S31 specifically includes: parallel/serial conversion and cyclic prefix addition are performed on the VLC OFDM signal, separating the bipolar discrete time domain signal into two unipolar signals.
In a VLC system, the instantaneous intensity of each color should not exceed a maximum value Imax。
The step S4 specifically includes the steps of:
s41: receiving signals of all colors, wherein the received signals of the ith color are as follows:
wherein: y isiIs the received signal of the ith color, gi,iIs the optical front-end gain, h, of the ith signaliIn order to be responsive to the optical channel,
is the transmitted signal of the ith color, gi,jIs the crosstalk between the jth color signal of the emitting end LED and the ith color signal of the receiving endjIn order to be responsive to the optical channel,
is the transmitted signal of the jth color, niIs a mean of 0 and a variance of
White additive Gaussian noise, wiIs interference;
s42: sequentially carrying out cyclic prefix removal, serial/parallel conversion and FFT demodulation operations on a received signal;
s43: performing a zero forcing equalizer to eliminate intersymbol interference in the received VLC signal, wherein for the ith signal, the output of the equalizer is:
wherein:
for the output of the equalizer, YiAnd XiIs yiAnd xiOf the frequency domain signal HiFor frequency domain channel response, WiAnd NiAre respectively wiAnd niA frequency domain representation of (a);
s44: the signals separating the two from the same data are reconstructed in the frequency domain:
s45: the reconstructed signal is demapped according to an interleaving method and then detected to restore the original information data.
Compared with the prior art, the invention has the following advantages:
1) according to the scheme, the PLC and the VLC in the indoor communication adopt the OFDM technology to support high data rate transmission, firstly, after information data pass through a PLC channel, signals are damaged by noise, the signals are transmitted by the PLC after OFDM demodulation, and then the OFDM signals from the PLC are mapped into VLC OFDM signals in an interleaving method.
2) The method meets the communication and illumination requirements, and simultaneously adopts a white light LED VLC system consisting of red, green, blue and amber LED chips (RGBA-LED) to adjust and transmit mapped signals. Using power lines as a backbone, VLC systems are interfaced to a backbone network with extensive indoor coverage. In such an environment, the bandwidth of Power Line Communication (PLC) can reach 30MHz, so that fast and reliable communication can be supported.
3) The method introduces Hermitian symmetric mapping and signal separation into OFDM in PLC and VLC systems to ensure that time domain signals are non-negative. Then, a post-clipping offset (BAC) operation is developed for OFDM while ensuring the illumination requirements. The invention considers impulse noise and OFDM modulation in PLC channel, so the method is more close to practical system and has more practical guiding significance.
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FIG. 1 is a schematic flow chart of the main steps of the method of the present invention;
FIG. 2 is a block flow diagram of the present invention;
fig. 3 is a graph of ber curves for different modulations and different snrs under additive white gaussian noise and impulse noise in indoor visible light communication according to an embodiment of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
A PLC-VLC transmission method based on OFDM technology for an indoor communication system, as shown in fig. 1 and 2, comprising the steps of:
s1: information data is firstly sent by a PLC, and is further transmitted after OFDM demodulation of signals damaged by a PLC channel and noise;
s2: modulating and transmitting signals by using an optical OFDM technology, namely mapping OFDM signals from a PLC into VLC OFDM signals by an interleaving method, and specifically comprising the following steps:
s21: for convenience of mapping, the number of subcarriers for PLC and VLC OFDM should be appropriately selected, i.e., set to:
aN＝b(M-2)
wherein: a is the data number of the PLC, b is the data number of the VLC OFDM, N is the number of the PLC OFDM subcarriers, and M is the number of the VLC OFDM subcarriers;
the number of data is the number of data to be transmitted, wherein a plurality of data can become one OFDM signal through OFDM modulation. When the OFDM modulation is used, a plurality of subcarriers are needed for modulation, wherein N subcarriers are modulated to obtain a PLC OFDM signal, and M subcarriers are modulated to obtain a VLC OFDM signal.
S22: when the data number of the PLC and the data number of the VLC OFDM are both 1, one PLC OFDM signal is mapped into two VLC OFDM signals in an interleaving method, in the interleaving mapping, odd subcarriers are mapped into one VLCOFDM signal, and even subcarriers are mapped into the other VLC OFDM signal with Hermitian symmetry property;
s3: when the communication and illumination requirements are met, the mapped signals are adjusted and transmitted in a VLC system, the VLC system is a white light LED VLC system formed by RGBA-LEDs, and the method specifically comprises the following steps:
s31: after signal mapping: performing parallel/serial conversion and Cyclic Prefix (CP) addition on the VLC OFDM signal, separating the bipolar discrete time domain signal into two unipolar signals:
ximax (x,0) and xj＝-min(x,0)，
Wherein: i, j belongs to { R, G, B, A }, and represents an RGBA-LED color mark;
in RGBA-LEDs, to ensure that the LED operates in a linear range, the instantaneous intensity of each color should not exceed a maximum value Imax。
S32: the isolated unipolar signal is adjusted by a post-clipping Bias (BAC) operation, which is followed by:
wherein λi＝Imax-βi，βiIs the offset factor.
S33: the four colors are mixed together to produce white light according to a set Color Mixing Ratio (CMR), and the four signals after separation adjustment are transmitted in a VLC channel through RGBA-LED.
S4: the receiver receives and reconstructs the signal to recover the original signal, comprising the steps of:
s41: receiving signals of all colors, wherein the received signals of the ith color are as follows:
wherein: y isiIs the received signal of the ith color, gi,iIs the optical front-end gain, h, of the ith signaliIn order to be responsive to the optical channel,
is the transmitted signal of the ith color, gi,jIs the crosstalk between the jth color signal of the emitting end LED and the ith color signal of the receiving endjIn order to be responsive to the optical channel,
is the transmitted signal of the jth color, niIs a mean of 0 and a variance of
White additive Gaussian noise, wiIs interference;
s42: sequentially carrying out cyclic prefix removal, serial/parallel conversion and FFT demodulation operations on a received signal;
s43: performing a Zero Forcing (ZF) equalizer to remove inter-symbol interference (ISI) in the received VLC signal, wherein for the ith signal, the output of the equalizer is:
wherein:
for the output of the equalizer, YiAnd XiIs yiAnd xiOf the frequency domain signal HiFor frequency domain channel response, WiAnd NiAre respectively wiAnd niA frequency domain representation of (a);
s44: the signals separating the two from the same data are reconstructed in the frequency domain:
i, j ∈ { R, G, B, a } denotes a sign of two signals separated from the data stream, and the reconstruction operation is performed in the frequency domain, equivalent to the reconstruction operation in the time domain, due to the linear characteristic of FFT;
s45: the reconstructed complex signal Y is demapped according to an interleaving method and then the signal is detected to restore the original information data.
According to the scheme of the invention, firstly, information data is sent by a PLC. The signal is modulated, then an IFFT operation is performed, and parallel/serial conversion and Cyclic Prefix (CP) addition are performed, and after passing through the PLC channel, the noise-damaged signal is OFDM-demodulated and then further transmitted. And secondly, mapping the OFDM signals from the PLC into VLC OFDM signals in an interleaving method, and adjusting and transmitting the mapped signals in a VLC system of white LEDs consisting of red, green, blue and amber LED chips (RGBA-LEDs) while meeting the communication and illumination requirements. After signal mapping, IFFT operation is performed on the VLC OFDM signal, and/or serial conversion and Cyclic Prefix (CP) addition are performed. The bipolar discrete time domain signal is then split into two unipolar signals. The separated signals are adjusted by a Bias After Clipping (BAC) operation. Again, the four colors are mixed together to produce white light according to a specific Color Mixing Ratio (CMR) for producing the four colors of illumination light, and the separately adjusted four signals are transmitted in the VLC channel via the RGBA-LED. Finally, the receiver receives and reconstructs the signal to recover the original signal.
The invention is described below in a specific case.
The inventive transmission scheme is used, where N is 1024 and CR is 10dB, K is 3, a is 0.01 and Γ is 0.1 for impulse noise in the PLC channel, and ξ is 0.06 for crosstalk in the VLC channel.
The transmission scheme of the invention is adopted, different modulation schemes are applied, and the error rate test of the system is respectively carried out under different interference ratios. The test results are shown in fig. 3, where in fig. 3 the abscissa represents the signal-to-noise ratio of the communication system, in units: dB; the ordinate represents the bit error rate.
In fig. 3, each curve represents a solid curve with crosses indicating the error rates with different snr when 4QAM modulation is used and ξ -0, a dashed curve with crosses indicating the error rates with different snr when 4QAM modulation is used and ξ -0.06, a solid curve with open circles indicating the error rates with different snr when 16QAM modulation is used and ξ -0, an open circle dashed curve indicating the error rates with different snr when 16QAM modulation is used and ξ -0.06, a solid curve with straight triangles indicating 64QAM modulation and ξ -0, an open triangle dashed curve indicating 64QAM modulation and ξ -0.06, it can be seen from fig. 3 that impulse noise severely degrades the system performance of the different modulation schemes.
Claims (3)
1. A PLC-VLC transmission method based on an OFDM technique for an indoor communication system, comprising the steps of:
s1: the signal damaged by the noise through the PLC channel is further transmitted after OFDM demodulation,
s2: the OFDM signal from the PLC is mapped into the VLC OFDM signal in an interleaving method,
s3: while meeting the communication and lighting requirements, the mapped signals are conditioned and transmitted in the VLC system,
s4: the receiver receives and reconstructs the signal to restore the original signal;
the VLC system is a white light LED VLC system composed of RGBA-LEDs,
the step S3 specifically includes the steps of:
s31: performing IFFT modulation separation on VLC OFDM signals to obtain two unipolar signals:
ximax (x,0) and xj＝-min(x,0)，
Wherein: i, j ∈ { R, G, B, A }, representing the color designation of RGBA-LED,
s32: adjusting the separated unipolar signals by a post-shear bias operation, the signals after the post-shear bias operation being:
wherein λi＝Imax-βi，βiIn order to be a factor of the offset,
s33: mixing the four colors together to generate white light according to a set color mixing ratio, and transmitting the four separated and adjusted signals in a VLC channel through RGBA-LED;
in VLC systems, the instantaneous intensity of each color is less than or equal to the maximum value Imax；
The step S31 specifically includes: performing parallel/serial conversion and cyclic prefix addition on the VLC OFDM signal, and separating the bipolar discrete time domain signal into two unipolar signals;
the step S4 specifically includes the steps of:
s41: receiving signals of all colors, wherein the received signals of the ith color are as follows:
wherein: y isiIs the received signal of the ith color, gi,iIs the optical front-end gain, h, of the ith signaliIn order to be responsive to the optical channel,
is the transmitted signal of the ith color, gi,jIs the crosstalk between the jth color signal of the emitting end LED and the ith color signal of the receiving endjIn order to be responsive to the optical channel,
is the transmitted signal of the jth color, niIs a mean of 0 and a variance of
White gaussian noiseSound, wiIn order to be a disturbance,
s42: the received signal is sequentially subjected to cyclic prefix removal, serial/parallel conversion and FFT demodulation operations,
s43: performing a zero forcing equalizer to eliminate intersymbol interference in the received VLC signal, wherein for the ith signal, the output of the equalizer is:
wherein:
for the output of the equalizer, YiAnd XiIs yiAnd xiOf the frequency domain signal HiFor frequency domain channel response, WiAnd NiAre respectively wiAnd niIs represented by the frequency domain of (a),
s44: the signals separating the two from the same data are reconstructed in the frequency domain:
s45: the reconstructed signal is demapped according to an interleaving method and then detected to restore the original information data.
2. The PLC-VLC transmission method based on OFDM technology for indoor communication system according to claim 1, wherein said step S2 specifically includes the steps of:
s21: setting the number of subcarriers for PLC and VLC OFDM:
aN＝b(M-2)
wherein: a is the data number of PLC, b is the data number of VLC OFDM, N is the number of PLC OFDM sub-carriers, and M is the number of VLCOFDM sub-carriers;
s22: odd subcarriers are mapped into one VLC OFDM signal and even subcarriers are mapped into another VLC OFDM signal having Hermitian symmetry properties.
3. The PLC-VLC transmission method based on the OFDM technique for an indoor communication system according to claim 2, wherein the number of data of the PLC and the number of data of VLC OFDM data are both 1.
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| CN103684529A (en) * | 2012-09-20 | 2014-03-26 | 中兴通讯股份有限公司 | Signal transmission method and device |
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| CN104981991A (en) * | 2013-02-14 | 2015-10-14 | 高通股份有限公司 | Methods and apparatus for efficient joint power line and visible light communication |
| CN105991499A (en) * | 2015-02-06 | 2016-10-05 | 钜泉光电科技(上海)股份有限公司 | OFDM power-frequency synchronous power carrier communication and physical layer coded modulation method |
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| CN103684529A (en) * | 2012-09-20 | 2014-03-26 | 中兴通讯股份有限公司 | Signal transmission method and device |
| CN104981991A (en) * | 2013-02-14 | 2015-10-14 | 高通股份有限公司 | Methods and apparatus for efficient joint power line and visible light communication |
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