CN112751613B - Adjustable light self-adaptive bias O-OFDM transmission method based on PWM - Google Patents

Adjustable light self-adaptive bias O-OFDM transmission method based on PWM Download PDF

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CN112751613B
CN112751613B CN202011631304.XA CN202011631304A CN112751613B CN 112751613 B CN112751613 B CN 112751613B CN 202011631304 A CN202011631304 A CN 202011631304A CN 112751613 B CN112751613 B CN 112751613B
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ofdm
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CN112751613A (en
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李宝龙
陆波
丁文杰
薛晓妹
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Ictehi Technology Development Jiangsu Co ltd
Nanjing University of Information Science and Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114—Indoor or close-range type systems
    • H04B10/116—Visible light communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/524—Pulse modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2649—Demodulators

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Abstract

The invention discloses a PWM-based dimmable adaptive offset O-OFDM transmission method, wherein a sending end comprises the following steps: loading the symbol Q to be transmitted to the odd number subcarrier and the 2(2i +1) th subcarrier of the OFDM system, setting the value of the rest subcarriers to be zero, and generating a frequency domain signal Xk(ii) a For frequency domain signal XkPerforming inverse Fourier transform to generate time domain signal xm(ii) a Generating an adaptive bias signal b from a PWM signalmAnd adaptively bias signal bmCalculating the adaptive bias signal b for a periodic sequence with a period of M/4m(ii) a Biasing b adaptivelymAnd time domain signal xmAdding the signals to obtain a dimmable adaptive offset O-OFDM signal ymThen the adjustable light self-adaptive bias O-OFDM signal ymAnd D/A conversion is carried out, and the conversion result and the PWM signal are superposed and then transmitted to the LED of the transmitting end to drive the LED to emit light.

Description

Adjustable light self-adaptive bias O-OFDM transmission method based on PWM
Technical Field
The invention relates to the field of wireless optical communication, in particular to a PWM-based dimmable adaptive offset O-OFDM method.
Background
The visible light communication is a wireless optical communication technology based on a Light Emitting Diode (LED), and high-speed data transmission is realized by using light rays emitted by the LED as a transmission medium, so that the wireless optical communication technology has the advantages of no need of spectrum license, no electromagnetic interference, environmental friendliness, low realization cost and the like. With the rapid development of information technology and the increasing shortage of radio frequency spectrum resources, visible light communication becomes a wireless communication technology with great development potential.
Dimming control can realize the brightness adjustment of the LED, meet the lighting requirements of different users and scenes, and is considered as an important function of the visible light communication system. In order to realize dual functions of dimming control and high-speed communication, an optical orthogonal frequency division multiplexing (O-OFDM) technology compatible with dimming control is widely used in the field of visible light communication. These dimmable O-OFDM techniques can be divided into analog and digital dimming techniques, depending on the dimming technique employed. One typical analog dimming is direct current biased optical OFDM (DCO-OFDM), where different dimming levels are achieved by varying the direct current bias. Analog dimming, however, results in a change in the wavelength of the light, resulting in significant chromaticity variation.
Digital dimming can linearly adjust dimming level by duty ratio, reducing the probability of occurrence of chromaticity variation, and thus is favored in the industrial field. At present, the polarity reversal O-OFDM (RPO-OFDM) based on Pulse Width Modulation (PWM) is a popular digital dimmable O-OFDM scheme, but because the RPO-OFDM method adopts asymmetrically tailored optical OFDM (ACO-OFDM), only odd subcarriers are utilized to transmit information, resulting in lower spectral efficiency. To improve spectral efficiency, some digital dimming schemes employ superposition O-OFDM, such as hybrid ACO-OFDM (HACO-OFDM), hierarchical ACO-OFDM (LACO-OFDM), and so on. In these digital dimming schemes based on the superposition O-OFDM, the transmitting end needs to rely on multiple IFFT modules to produce different signal components, and meanwhile, the receiving end needs to use an iterative receiver to sequentially detect multiple signal components. Therefore, compared with the traditional scheme, the digital dimming method based on the superposition O-OFDM obviously improves the complexity of the transceiver and introduces higher processing time delay of the receiver. More importantly, in the existing digital dimming scheme, the detection of the signal depends heavily on information such as dimming degree, and the receiver needs to detect the PWM signal first to successfully complete the subsequent information detection, which further increases the difficulty in implementing the scheme in practical application.
Disclosure of Invention
Aiming at the problems, the invention provides a PWM-based adjustable light self-adaptive offset O-OFDM transmission method.
In order to realize the purpose of the invention, the invention provides a PWM-based dimmable adaptive offset O-OFDM transmission method, and a transmitting end comprises the following steps:
s1, loading the symbol Q to be transmitted to the odd number sub-carrier and the 2(2i +1) th sub-carrier of the OFDM system, setting the value of the rest sub-carriers of the OFDM system to 0, and generating the frequency domain signal XkAssuming that the OFDM system has M subcarriers,
Figure BDA0002880114080000021
Xkdenotes the kth subcarrier, k 0, 1.., M-1, of the frequency domain signal X.
s2, for the frequency domain signal XkPerforming inverse Fourier transform to generate time domain signal xmWherein M is 0, 1mRepresenting the mth subcarrier of the time domain signal x.
s3, generating PWM signal based on preset dimming degree, and generating one-period self-adaptive bias signal b according to the PWM signalrThe adaptive bias signal b is appliedrRepeating four cycles to obtain an adaptive bias signal bmWherein r is 0, 1mThe mth signal representing the adaptive bias signal b.
s4, calculating the adaptive bias signal bmAnd time domain signal xmAdding the signals to obtain a dimmable adaptive offset O-OFDM signal ymThen the adjustable light self-adaptive bias O-OFDM signal ymD/A conversion is carried out, the conversion result and the PWM signal are superposed and then are transmitted to the LED of the transmitting end to drive the LED to emit light, wherein ymThe mth signal representing the dimmable adaptive offset O-OFDM signal y.
Further, in step s3, the adaptive bias signal brThe calculation formula of (a) is as follows:
Figure BDA0002880114080000022
further, by setting both the cycle time and the pulse time width of the PWM signal in step s3 to be integral multiples of the number M of subcarriers of the OFDM system and changing the pulse time width of the PWM signal, different dimming levels can be realized.
Further, the adjustable optical adaptive offset O-OFDM signal y in step s4mThe calculation formula of (a) is as follows:
ym＝xm+bm。
further, the receiving end adopts a standard OFDM receiver.
Compared with the prior art, the invention has the following beneficial effects:
the method is based on the PWM dimming technology favored by the industry, and can realize the linear adjustment of the dimming degree and effectively reduce the probability of the occurrence of the chromaticity change compared with the analog dimming scheme.
In the invention, the signal detection at the receiving end does not depend on the information such as the dimming degree, and in contrast, the traditional digital dimmable O-OFDM scheme adopted at the receiving end is influenced by the dimming control, and the additional PWM signal detection operation is required to be introduced, thereby increasing the difficulty of the system.
Compared with the existing popular ACO-OFDM-based digital dimmable scheme, the invention can realize higher spectral efficiency. Meanwhile, the sending end of the invention scheme only needs one IFFT module, and the receiving end can adopt standard O-OFDM to finish detection, therefore, the invention scheme and ACO-OFDM have the same hardware realization complexity. In addition, for the adoption of the superimposed O-OFDM, a plurality of IFFT modules are needed at a sending end, and an iterative receiver is needed at a receiving end to sequentially detect signals, so that the complexity and the processing time delay of the scheme of the invention are obviously lower than those of a digital dimming scheme adopting the superimposed O-OFDM.
Drawings
Fig. 1 is a block diagram of a transmitting end of a PWM-based tunable adaptive offset O-OFDM transmission method according to an embodiment;
FIG. 2 is a block diagram of a receiving end of the PWM-based tunable adaptive offset O-OFDM transmission method according to an embodiment;
FIG. 3 is a diagram illustrating the relationship between the PWM duty cycle and the dimming level achieved for different scale factors β according to an embodiment;
FIG. 4 illustrates an embodiment with a bit error rate target of 2 × 10-3The relationship between the achievable spectral efficiency and the degree of modulation is shown schematically.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.
The invention provides a PWM-based dimmable adaptive offset O-OFDM transmission method, wherein a sending end comprises the following steps:
s1, loading the symbol Q to be transmitted to the odd number sub-carrier and the 2(2i +1) th sub-carrier of the OFDM system, setting the value of the rest sub-carriers of the OFDM system to 0, and generating the frequency domain signal XkAssuming that the OFDM system has M subcarriers,
Figure BDA0002880114080000041
Xkdenotes the kth subcarrier of the frequency domain signal X, k being 0, 1kThe calculation formula is as follows:
Figure BDA0002880114080000042
l subcarriers are calculated as conjugates.
s2, for the frequency domain signal XkPerforming inverse Fourier transform to generate time domain signal xmWherein M is 0, 1mRepresenting the mth subcarrier of the time domain signal x.
s3, generating PWM signal based on preset dimming degree, and generating one-period self-adaptive bias signal b according to the PWM signalrThe adaptive bias signal b is appliedrRepeating four cycles to obtain an adaptive bias signal bmWherein r is 0, 1mThe mth signal representing the adaptive bias signal b.
s4, calculating the adaptive bias signal bmAnd time domain signal xmAdding the signals to obtain a dimmable adaptive offset O-OFDM signal ymThen the adjustable light self-adaptive bias O-OFDM signal ymD/A conversion is carried out, the conversion result and the PWM signal are superposed and then are transmitted to the LED of the transmitting end to drive the LED to emit light, wherein ymThe mth signal representing the dimmable adaptive offset O-OFDM signal y.
In one embodiment, in step s3, the adaptive bias signal brThe calculation formula of (a) is as follows:
Figure BDA0002880114080000043
in one embodiment, both the period time and the pulse time width of the PWM signal in step s3 are set to be integer multiples of the number M of subcarriers of the OFDM system, so as to ensure that the PWM signal does not interfere with information transmission of the dimmable adaptive offset OFDM, and different dimming levels can be realized by changing the pulse time width of the PWM signal.
In one embodiment, the tunable optical adaptive offset O-OFDM signal y in step s4mThe calculation formula of (a) is as follows:
ym＝xm+bm。
in one embodiment, the receiving end employs a standard OFDM receiver.
Fig. 1 is a block diagram of a structure of a PWM-based tunable adaptive offset O-OFDM method. It can be seen from the figure that the scheme of the invention only needs one IFFT module to complete modulation at the transmitting end, and a standard OFDM receiver can be used at the receiving end, without being affected by the dimming control and without detecting the PWM signal. Fig. 2 is a block diagram of a receiving end of the PWM-based tunable adaptive offset O-OFDM transmission method according to an embodiment.
Fig. 3 is a schematic diagram showing the relationship between the PWM duty ratio and the dimming degree achieved under different scale factors β according to the present invention. Scale factor β ═ I (I)H-IL) σ, for evaluating clipping distortion of the scheme, wherein σ2Is the energy of O-OFDM. As can be seen from the figure, the two are linear relationships, indicating that by varying the duty cycle, a linear adjustment of the dimming level can be achieved.
As shown in FIG. 4, the error rate target for the inventive scheme is 2 × 10-3In this case, a plot of spectral efficiency versus dimming can be achieved, where the noise is set to-5 dBm. It can be observed from the figure that the inventive solution achieves a higher achievable rate at intermediate dimming levels than at lower or higher dimming levels. Furthermore, the inventive scheme has better performance in terms of spectral efficiency than the RPO-OFDM scheme and the hybrid LACO-OFDM (HLACO-OFDM) employing L ═ 2 layers.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
It should be noted that the terms "first \ second \ third" referred to in the embodiments of the present application merely distinguish similar objects, and do not represent a specific ordering for the objects, and it should be understood that "first \ second \ third" may exchange a specific order or sequence when allowed. It should be understood that "first \ second \ third" distinct objects may be interchanged under appropriate circumstances such that the embodiments of the application described herein may be implemented in an order other than those illustrated or described herein.
The terms "comprising" and "having" and any variations thereof in the embodiments of the present application are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product, or device that comprises a list of steps or modules is not limited to the listed steps or modules but may alternatively include other steps or modules not listed or inherent to such process, method, product, or device.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (3)

1. The adjustable light self-adaptive bias O-OFDM transmission method based on PWM is characterized in that a sending end comprises the following steps:
s1, loading the symbol Q to be transmitted to the odd number sub-carrier and the 2(2i +1) th sub-carrier of the OFDM system, setting the value of the rest sub-carriers of the OFDM system to 0, and generating the frequency domain signal XkAssuming that the OFDM system has M subcarriers,
Figure FDA0003305484350000013
Xkdenotes the kth subcarrier, k 0, 1, of the frequency domain signal X..，M-1；
s2, for the frequency domain signal XkPerforming inverse Fourier transform to generate time domain signal xmWherein M is 0, 1mRepresents the mth subcarrier of the time domain signal x;
s3, generating PWM signal based on preset dimming degree, and generating one-period self-adaptive bias signal b according to the PWM signalrThe adaptive bias signal b is appliedrRepeating four cycles to obtain an adaptive bias signal bmWherein r is 0, 1mAn mth signal representing the adaptive bias signal b; the adaptive bias signal brThe calculation formula of (a) is as follows:
Figure FDA0003305484350000012
setting the cycle time and the pulse time width of the PWM signal as integral multiples of the number M of the subcarriers of the OFDM system, and changing the pulse time width of the PWM signal to realize different dimming degrees;
s4, calculating the adaptive bias signal bmAnd time domain signal xmAdding the signals to obtain a dimmable adaptive offset O-OFDM signal ymThen the adjustable light self-adaptive bias O-OFDM signal ymD/A conversion is carried out, the conversion result and the PWM signal are superposed and then are transmitted to the LED of the transmitting end to drive the LED to emit light, wherein ymThe mth signal representing the dimmable adaptive offset O-OFDM signal y.
2. The PWM-based dimmable adaptive offset O-OFDM transmission method according to claim 1, wherein the dimmable adaptive offset O-OFDM signal y in step s4mThe calculation formula of (a) is as follows:
ym＝xm+bm。
3. the PWM-based dimmable adaptive offset O-OFDM transmission method according to claim 1, wherein a standard OFDM receiver is adopted by a receiving end.
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