WO2022036766A1 - 移动无线光通信系统的容量优化方法、通信方法及系统 - Google Patents

移动无线光通信系统的容量优化方法、通信方法及系统 Download PDF

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WO2022036766A1
WO2022036766A1 PCT/CN2020/113662 CN2020113662W WO2022036766A1 WO 2022036766 A1 WO2022036766 A1 WO 2022036766A1 CN 2020113662 W CN2020113662 W CN 2020113662W WO 2022036766 A1 WO2022036766 A1 WO 2022036766A1
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modulation
format
bit error
receiver
error rate
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French (fr)
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由骁迪
沈纲祥
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Suzhou University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
    • H04L1/0005—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes applied to payload information
    • 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
    • H04B10/5161—Combination of different modulation schemes
    • 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
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
    • H04B10/0795—Performance monitoring; Measurement of transmission parameters
    • H04B10/07953—Monitoring or measuring OSNR, BER or Q
    • 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
    • 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
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0015—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the adaptation strategy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
    • H04L1/203—Details of error rate determination, e.g. BER, FER or WER
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/02—Arrangements for optimising operational condition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
    • H04W64/003—Locating users or terminals or network equipment for network management purposes, e.g. mobility management locating network equipment

Definitions

  • the present invention relates to the technical field of optical communication, in particular to a capacity optimization method, communication method and system of a mobile wireless optical communication system.
  • the current solution is to use traditional adaptive modulation technology, which estimates the channel by sending a training sequence, the receiving end feeds back the real-time channel state information obtained by channel estimation to the transmitting end, and the transmitting end adjusts the modulation format and modulation according to the channel state.
  • the parameters such as order are adaptively selected and optimized.
  • the disadvantages of traditional adaptive modulation techniques are as follows: For a single-carrier system, the correspondence between the spectral efficiency that can be achieved by a single modulation format and the farthest transmission distance it supports remains discrete.
  • the processing complexity of OFDM is higher, and the peak-to-average ratio of the signal is higher, which will cause the degradation of the system performance.
  • the technical problem to be solved by the present invention is to provide a capacity optimization method, communication method and system for a mobile wireless optical communication system, which can effectively adapt to the actual state of the mobile wireless optical channel, and perform a signal transmission scheme according to the mobile state information of the terminal.
  • Self-adaptive adjustment and optimization so that the spectral efficiency of the system and the mobile transmission capacity are dynamically optimized, ensuring reliable transmission quality of the link, and meeting the specific needs of different types of services.
  • the present invention provides a capacity optimization method for a mobile wireless optical communication system, comprising the following steps:
  • S5. Determine the number of symbols of the first modulation format and the second modulation format in each data frame, so that the average mixed bit error rate of the first modulation format and the second modulation format is less than a preset bit error rate threshold, wherein the first The modulation format and the number of symbols of the second modulation format maximize the transmission capacity of the corresponding wireless optical communication system;
  • the step S3 further includes, descending ordering the obtained sets of bit error rate values, and obtaining the sorted sets of bit error rate values;
  • bit error rate values corresponding to the first modulation format and the second modulation format are adjacent values in the sorted sets of bit error rate values.
  • the S6 includes:
  • the S1 specifically includes:
  • the impulse response of the mobile channel is obtained:
  • the transmitter coordinate T i is (x ti , y ti , z ti ), i represents the ith LED light source, the receiver coordinate R is (x r , y r , z r ), and the receiver azimuth O is ( ⁇ , ⁇ ), ⁇ is the azimuth angle of the receiver, ⁇ is the polar angle of the receiver; N LED is the number of LED light sources; for the i-th LED light source, wi is the weighting coefficient of the light source’s emission power, ⁇ i, los and ⁇ i,nlos are the signal propagation delays of the line-of-sight and non-line-of-sight links, respectively, H i,los (0) is the normalized DC gain of the line-of-sight link, and A i,nlos is the non-line-of-sight link The normalized channel gain of the channel.
  • the S2 specifically includes:
  • P r,sig is the power of the received signal
  • P r,isi is the intersymbol interference
  • N is composed of the shot noise variance ⁇ 2 shot and the thermal noise variance ⁇ 2 thermal
  • ⁇ is the photoelectric conversion efficiency of the photodetector
  • t 0 is the pulse start time after integration
  • R s is the pulse rate
  • P t is the average transmit power of each light source
  • m is the modulation index of the transmit signal
  • s(t) is the normalized rectangular pulse, represents the convolution operation
  • the shot noise is further expressed as:
  • k is the Boltzmann constant
  • T k is the absolute temperature
  • ⁇ is the fixed capacitance
  • A is the photodetector area
  • g m is the transconductance of the FET
  • ⁇ is the channel noise factor of the FET
  • the S3 specifically includes the following steps:
  • the calculated bit error rate of the wireless optical communication system is:
  • L-PAM and L-PPM with different modulation orders are used as candidate modulation formats
  • PAM is pulse amplitude modulation
  • PPM is pulse position modulation
  • L is the signal modulation order
  • the S4 specifically includes:
  • the set bit error rate threshold is BER T ;
  • the S5 includes the following steps:
  • the average mixed bit error rate of the time-domain mixed modulation data frame is:
  • D represents the proportion of the above-mentioned format k, the range of D is 0 ⁇ D ⁇ 1, SE k and SE k+1 represent the spectral efficiency of modulation format k and modulation format k+1 respectively;
  • floor() represents rounding down
  • ceil() represents rounding up
  • N total is the total number of symbols in each time-domain mixed modulation data frame.
  • the invention discloses a communication method for a mobile wireless optical communication system, which is based on the above-mentioned capacity optimization method optimization of the mobile wireless optical communication system, and is characterized in that it includes the following steps:
  • the invention discloses a mobile wireless optical communication system, comprising a transmitter and a receiver, an optimization module is arranged on the transmitter or the receiver, and the optimization module runs the capacity optimization method of the mobile wireless optical communication system;
  • the optimization module calculates and obtains the optimization parameter information of the time-domain mixed modulation frame, and the optimized parameter information of the time-domain mixed modulation frame is transmitted from the receiver to the transmitter, and the transmitter Construct a time-domain hybrid modulation frame according to the received optimized parameter information of the time-domain hybrid modulation frame, and perform data transmission;
  • the receiver sends the position information of the receiver and the azimuth information of the receiver to the transmitter, and the optimization module calculates and obtains the optimization parameter information of the time-domain hybrid modulation frame, and the transmitter
  • the time-domain hybrid modulation frame is constructed according to the received optimized parameter information of the time-domain hybrid modulation frame
  • the transmitter sends the time-domain hybrid modulation frame and its optimized parameter information to the receiver
  • the receiver according to the received time-domain hybrid modulation frame
  • the optimized parameter information of the mixed modulation frame demodulates the time domain mixed modulation frame.
  • the present invention is based on single-carrier modulation, has a simple structure and high real-time processing flexibility, and can effectively avoid the inherent defects of the OFDM technology.
  • the present invention is suitable for a mobile wireless optical communication system.
  • the mobile wireless optical channel state can be estimated efficiently and the transmission overhead of the uplink feedback link can be effectively reduced.
  • the present invention can dynamically optimize the spectral efficiency and transmission capacity of the system according to the movement state information perceived by the terminal, so as to efficiently adapt to the time-varying TNR in the wireless optical channel, and realize the spectral efficiency and transmission capacity in the terminal movement process. Dynamic optimization of transmission capacity.
  • the present invention can realize the continuous change of the system transmission capacity in the process of changing the position and orientation of the receiver, which is beneficial to the smooth handover of the carried services and the continuous and smooth transition of the transmission rate.
  • the present invention can meet the bit error rate thresholds specified by different services, thereby ensuring reliable mobile transmission quality of the wireless optical communication link.
  • the present invention can effectively adapt to the actual state of the mobile wireless optical channel, and can adjust and optimize the signal transmission scheme adaptively according to the mobile state information of the terminal.
  • Fig. 1 is the principle diagram of the present invention
  • Fig. 2 is the flow chart of the capacity optimization method of the mobile wireless optical communication system of the present invention.
  • Fig. 3 is a wireless optical communication system model
  • Fig. 4 is the transmission capacity comparison diagram of different positions on the diagonal
  • Fig. 5 is the modulation format adopted by the proposed optimization scheme at different positions on the diagonal and the corresponding D opt ;
  • Fig. 6 is a bit error rate comparison diagram at different positions on the diagonal
  • FIG. 7 is a comparison diagram of the transmission capacity of two modulation modes in the receiving plane, wherein (a) adopts the traditional adaptive modulation method; (b) adopts the optimization method of the present invention;
  • FIG. 8 is a schematic diagram of a complementary accumulation function of a data transmission capacity improvement range
  • FIG. 1 it is a schematic diagram of the present invention.
  • the terminal moves or changes its orientation (ie, the orientation of the receiver's field of view)
  • both the optical power and the signal-to-noise ratio received by the receiver will fluctuate.
  • the signal-to-noise ratio received by the receiver will fluctuate.
  • the terminal when the terminal is located in a bright area and the signal-to-noise ratio is large, two modulation formats with high spectral efficiency are mixed (the modulation format 1 with higher spectral efficiency accounts for D1%) to form frame structure 1, In order to obtain higher spectral efficiency; and when the terminal moves to a darker area, the signal-to-noise ratio is low, then the two modulation formats with lower spectral efficiency are mixed (the modulation format 2 with higher spectral efficiency accounts for For D2%), frame structure 2 is formed to ensure the quality of link transmission and meet the requirements of receiver sensitivity.
  • the system can effectively improve the performance of the system.
  • FEC forward error correction
  • the present invention discloses a capacity optimization method for a mobile wireless optical communication system.
  • the input of the method is the movement state of the terminal, including information such as the position and orientation of the receiver.
  • the constraint condition of the method is the bit error rate.
  • Threshold value and pulse rate supported by the device, the output of this scheme is the system configuration parameters such as the optimized modulation format, modulation order, mixing ratio, and mixed frame structure, which can finally realize the dynamic improvement of the mobile transmission capacity in the system.
  • the capacity optimization method of the mobile wireless optical communication system of the present invention comprises the following steps:
  • Step 1 Obtain the position information of the transmitter, the position information of the receiver and the azimuth information of the receiver, and establish a mobile channel impulse response model, which specifically includes:
  • the channel state of wireless optical communication mainly depends on the geometrical relationship between the transmitter and the receiver. Therefore, the mobile state information of the terminal is considered, including transmitter coordinates, receiver coordinates, and receiver orientation.
  • the transmitter coordinate T i is (x ti , y ti , z ti )
  • i represents the ith LED light source
  • the receiver coordinate R is (x r , y r , z r )
  • the receiver azimuth O is ( ⁇ , ⁇ ), where ⁇ is the azimuth angle that the receiver is facing, and ⁇ is the polar angle that the receiver is facing, as shown in Figure 3 below.
  • the impulse response of the mobile channel can be obtained as follows:
  • N LED is the number of LED light sources; for the i-th LED light source, wi is the weighting coefficient of the emitted power of the light source, and ⁇ i,los and ⁇ i,nlos are the signal propagation times of the line-of-sight and non-line-of-sight links, respectively where H i,los (0) is the normalized DC gain of the line-of-sight link, and A i,nlos is the normalized channel gain of the non-line-of-sight link.
  • Step 2 Calculate the TNR output by the receiver based on the mobile channel impulse response model, which specifically includes:
  • Equation (1) At the receiving end, we can calculate the TNR SNR output by the photodetector and express it in the form of the receiver moving state:
  • P r,sig is the power of the received signal
  • P r,isi is the intersymbol interference
  • N is composed of the shot noise variance ⁇ 2 shot and the thermal noise variance ⁇ 2 thermal
  • ⁇ is the photoelectric conversion efficiency of the photodetector
  • t 0 is the pulse start time after integration
  • R s is the pulse rate
  • P t is the average transmit power of each light source
  • m is the modulation index of the transmit signal
  • s(t) is the normalized rectangular pulse, represents the convolution operation
  • the shot noise is further expressed as:
  • k is the Boltzmann constant
  • T k is the absolute temperature
  • ⁇ is the fixed capacitance
  • A is the photodetector area
  • g m is the transconductance of the FET
  • ⁇ is the channel noise factor of the FET
  • Step 3 Calculate the bit error rate values of the wireless optical communication system under different candidate modulation formats according to the TNR output by the receiver, obtain multiple sets of bit error rate values, and then decrease the obtained multiple sets of bit error rate values. Sorting to obtain the sorted sets of bit error rate values, which specifically includes the following steps:
  • bit error rate (BER) of the wireless optical communication system can be expressed as:
  • L-PAM and L-PPM with different modulation orders are used as candidate modulation formats
  • PAM is pulse amplitude modulation
  • PPM is pulse position modulation
  • L is the signal modulation order
  • Step 4 Select a first modulation format and a second modulation format from different candidate modulation formats, wherein the bit error rate value corresponding to the first modulation format is greater than the preset bit error threshold, and the second modulation format corresponds to The bit error rate value is less than the preset bit error rate threshold, wherein the bit error rate values corresponding to the first modulation format and the second modulation format are adjacent values in the sorted sets of bit error rate values, Specifically include the following steps:
  • the set bit error rate threshold is BER T ;
  • Step 5 Determine the number of symbols of the first modulation format and the second modulation format in each data frame, so that the average mixed bit error rate of the first modulation format and the second modulation format is less than the preset bit error rate threshold, wherein the The number of symbols in the first modulation format and the second modulation format maximizes the transmission capacity of the corresponding wireless optical communication system, which specifically includes the following steps:
  • the average mixed bit error rate of the time-domain mixed modulation data frame is:
  • D represents the proportion of the above-mentioned format k, the range of D is 0 ⁇ D ⁇ 1, SE k and SE k+1 represent the spectral efficiency of modulation format k and modulation format k+1 respectively;
  • floor() represents rounding down
  • ceil() represents rounding up
  • N total is the total number of symbols in each time-domain mixed modulation data frame.
  • the reliable transmission quality of the system can be ensured, that is, the bit error rate does not exceed BER T .
  • Step 6 Construct a time-domain hybrid modulation frame according to the number of symbols in the first modulation format and the second modulation format, and modulate data through the time-domain hybrid modulation frame and perform data transmission.
  • the invention also discloses a communication method for a mobile wireless optical communication system, which is optimized based on the above-mentioned capacity optimization method of the mobile wireless optical communication system, including the following steps:
  • Step 1 Acquire different time-domain mixed modulation frames according to preset bit error rate thresholds and different pulse rate levels of different service types
  • Step 2 Store the time-domain mixed modulation frames corresponding to different preset bit error rate thresholds and pulse rate levels in the database;
  • Step 3 Obtain the current preset bit error rate threshold and pulse rate level, call the corresponding time-domain mixed modulation frame in the database, and perform wireless optical communication.
  • modulation format k, modulation format k+1 and D opt are all related to the movement state of the terminal, the relationship between these parameters and the movement state of the receiver can be recorded by using a table look-up method.
  • the terminal is in the mobile state of (T, R, O) for the first time, we will establish the table index corresponding to (T, R, O) and initialize the system parameters.
  • We paginate the table according to different business types and different pulse rate levels. In the table on each page, we assume that the bit error rate threshold of the service is BER T , and the pulse rate supported by the system is R s , then we take the same BER T and R s as the constraints of the table on this page.
  • R b (T, R, O) D opt (T, R, O) ⁇ SE k (T, R, O) ⁇ R s + [1-D opt (T, R, O)] ⁇ SE k+ 1 (T,R,O) R s (7)
  • R b will be used as an important basis to judge whether the service to be carried can maintain stable and reliable data transmission.
  • the parameters of the time-domain hybrid modulation scheme can be adaptively adjusted and optimized according to the movement state of the terminal.
  • negotiation between the transmitter and the receiver is required. What we use is a feedback mechanism from the receiver to the transmitter. Divided into the following two ways:
  • the optimal calculation of parameters is completed by the receiver, and the optimal time-domain hybrid modulation format and frame structure information to be used are fed back to the transmitter.
  • the receiver obtains its own coordinate information R through indoor wireless optical positioning.
  • the receiver uses its own angle sensor to obtain its azimuth angle information O (that is, the orientation), and then uses the fixed transmitter coordinates Information T, directly at the receiving end through the above steps 1 to 6 to optimize the parameters to obtain the optimal time-domain hybrid modulation format and frame structure information to be used in the (T, R, O) moving state, and then pass the uplink
  • the link preferably WiFi
  • Mode 2 feedback (R, O) to the transmitter, and the optimization calculation of parameters is completed by the transmitter.
  • the receiver obtains its own coordinate information R through indoor wireless optical positioning, and at the same time, the receiver uses its own angle sensor to obtain its azimuth angle information O (that is, the orientation) , the receiver feeds back (R, O) these two kinds of information to the transmitter through the uplink (preferably WiFi).
  • the transmitter uses its own coordinate information T, and then combines the received (R, O) to optimize the parameters through the aforementioned steps 1 to 6, and obtain the optimal need to be used in the (T, R, O) moving state.
  • the time-domain hybrid modulation format, as well as the frame structure information are communicated to the receiver through the downlink in a fixed modulation format before sending a new time-domain hybrid modulation signal.
  • the present invention discloses a mobile wireless optical communication system, including a transmitter and a receiver, and an optimization module is arranged on the transmitter or receiver, and the optimization module runs the above The capacity optimization method of the mobile wireless optical communication system; when the receiver is provided with an optimization module, the optimization module calculates and obtains the optimization parameter information of the time-domain hybrid modulation frame, and the optimization parameter information of the time-domain hybrid modulation frame is determined by The receiver transmits to the transmitter, and the transmitter constructs the time-domain hybrid modulation frame according to the received optimized parameter information of the time-domain hybrid modulation frame, and performs data transmission;
  • the receiver sends the position information of the receiver and the azimuth information of the receiver to the transmitter, and the optimization module calculates and obtains the optimization parameter information of the time-domain hybrid modulation frame, and the transmitter
  • the time-domain hybrid modulation frame is constructed according to the received optimized parameter information of the time-domain hybrid modulation frame
  • the transmitter sends the time-domain hybrid modulation frame and its optimized parameter information to the receiver
  • the receiver according to the received time-domain hybrid modulation frame
  • the optimized parameter information of the mixed modulation frame demodulates the time domain mixed modulation frame.
  • the transmitted mixed signal format and ratio D opt remain unchanged. Only when the position or orientation of the terminal changes, it is necessary to re-select and optimize the transmission signal according to the new movement state information.
  • the optimal time-domain hybrid modulation format and frame structure information to be used in each moving state are stored in a table.
  • the optimal time-domain hybrid modulation parameters at each moment can be obtained by periodically looking up the table, so as to maximize the transmission capacity of the periodic movement.
  • this embodiment In order to evaluate the proposed capacity optimization method for a mobile wireless optical communication system, this embodiment considers a specific indoor space scene with a size of 8m ⁇ 8m ⁇ 3m (length ⁇ width ⁇ height). The light source is deployed on the ceiling, the mobile terminal is located on the receiving plane, and the height of the receiving plane is 0.85m. As shown in Figure 3. In FIG. 3 , this embodiment also defines the azimuth angle ⁇ and the polar angle ⁇ used in this patent to indicate the orientation of the receiver.
  • this embodiment will consider an LED transmitter light source, which is installed at the coordinates (4, 4, 3) and illuminates downward, and its emitted light power is 18W. At the same time, this The embodiment assumes that the receiver is facing upward, and the received signal components mainly come from the line-of-sight link;
  • this embodiment will consider a total of four LED light sources installed at coordinates (3, 3, 3), (3, 5, 3), (5, 3, 3), (5, 5, 3), the transmitted optical power of each LED light source is 4.5W.
  • the received signal component includes both the line-of-sight link component and the non-line-of-sight link component. road component.
  • Figure 5 shows the two hybrid modulation formats required by the proposed optimization scheme at different positions on the diagonal, and the corresponding D opt , it can be seen that , the diagonal range is divided into 9 regions, each with its own time-domain hybrid modulation format.
  • the most corner position uses the combination of PPM8+PPM4
  • the most middle position uses the combination of PAM8+PAM16
  • the mixed modulation formats used in other positions are listed in the figure.
  • the blue curve is the optimal ratio D opt of the format with the larger spectral efficiency among the two hybrid modulation formats used at each position. It can be seen that due to the continuous change of the receiver position, D opt also Continuous optimization and adjustment are required to achieve optimal spectral efficiency.
  • Figure 6 compares the system bit error rate performance at different positions of the diagonal.
  • the low bit error rate means a waste of spectrum resources to a certain extent, because it does not need to be very low, as long as it is not higher than BER T )
  • this embodiment compares the system transmission capacity in the receiving plane before and after the proposed optimization scheme is adopted. It can be seen that adopting the proposed optimization method can effectively improve the system capacity at various positions of the whole receiving plane, for example, when the receiver is located at (4, 4, 0.85), the maximum data rate can be increased from 150Mbps (only PAM8 is adopted) to 197Mbps (using mixed PAM8+PAM16).
  • Fig. 8 shows the transmission capacity improvement that can be obtained by adopting the proposed optimization method in the receiving plane.
  • the complementary cumulative distribution function (CCDF) of the data rate improvement magnitude is given after statistics. According to the statistical results, when R s is 100MHz, a total of 19.8% indoor areas in the entire receiving plane can obtain a capacity improvement of more than 20%.
  • Fig. 9 compares the situation where the azimuth and polar angles of the receiver's orientation change within a certain range at the position of coordinates (4, 4, 0.85), the solid line in the figure The maximum data rates achievable in each orientation are given. It can be seen that when the receiver is tilted, the proposed optimization method can still effectively improve the system capacity of mobile wireless optical communication.

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Abstract

本发明公开了一种移动无线光通信系统的容量优化方法、通信方法及系统，包括以下步骤：建立移动信道冲激响应模型；计算接收机输出的电信噪比；根据接收机输出的电信噪比，计算不同的候选调制格式下无线光通信系统的误比特率值；从不同的候选调制格式中选取第一调制格式和第二调制格式；确定每个数据帧中第一调制格式和第二调制格式的码元数量；根据第一调制格式和第二调制格式的码元数量构造时域混合调制帧，通过时域混合调制帧调制数据并进行数据传输。其能够有效地适应移动无线光信道的实际状态，根据终端的移动状态信息对信号传输方案进行自适应的调整与优化，从而使系统的频谱效率以及移动传输容量均达到动态最优，保证链路的传输质量可靠。

Description

移动无线光通信系统的容量优化方法、通信方法及系统 技术领域
本发明涉及光通信技术领域，具体涉及一种移动无线光通信系统的容量优化方法、通信方法及系统。
背景技术
随着移动互联网、物联网、虚拟现实等技术的不断发展，人们对室内无线光通信技术开展了大量的研究。然而，这些研究主要集中于终端静止的点对点传输场景。近年来，在多样化的无线光通信应用中，用户或业务对终端移动性的需求不断增加。例如，家庭用户希望在室内不同位置可以通过灯光上网，且拥有良好的用户体验；在工业场景中，安装在移动机械臂、生产线上的传感器和中继节点在利用灯光互联时，需要拥有优质的服务质量。然而，无线光通信接收机的移动会导致无线光通信信道发生时变，这给实现高速无线光通信带来了挑战。由于室内光照强度空间分布并非均匀，用户终端即使只在单个小区内进行移动或改变方位，接收光信号的电信噪比性能也会发生较大的波动，若采用传统的针对静态传输场景的固定调制格式，系统的频谱效率和传输容量都难以维持动态最优，难以为移动用户提供高速且连续不间断的数据传输服务。
目前的解决方式是采用传统的自适应调制技术，其通过发送训练序列对信道进行估计，接收端将信道估计所得到的实时信道状态信息反馈至发射端，发射端根据信道状态对调制格式、调制阶数等参数进行自适应的选择与优化。传统的自适应调制技术的缺点如下：对于单载波系统，采用单一调制格式可达到的频谱效率和其所支持的最远传输距离之间的对应关系仍保持离散。例如，当移动终端的位置介于两种调制格式(如PAM2和PAM4)所支持的最远传输距离 之间时，为了保证链路传输质量，只能选择较低阶的调制格式(即PAM2)，故无法实现最优的频谱效率。虽然采用多载波OFDM技术可以进一步提升频谱效率，但是为了对OFDM信号进行自适应调制，通常需要将完整的(例如各个频点的)信道状态信息进行反馈，因此当终端移动时，信道的不断变化将导致大量的反馈开销，降低上行传输效率，在上行传输资源受限的情况下难以维持可靠的系统传输性能。同时，相较于单载波调制方式，OFDM的处理复杂度更高，且信号的峰均比更高，这都会引起系统性能的下降。
发明内容
本发明要解决的技术问题是提供一种移动无线光通信系统的容量优化方法、通信方法及系统，其能够有效地适应移动无线光信道的实际状态，根据终端的移动状态信息对信号传输方案进行自适应的调整与优化，从而使系统的频谱效率以及移动传输容量均达到动态最优，保证链路的传输质量可靠，满足不同种类业务的具体需求。
为了解决上述技术问题，本发明提供了一种移动无线光通信系统的容量优化方法，包括以下步骤：
S1、获取发射机位置信息、接收机的位置信息和接收机的方位信息，建立移动信道冲激响应模型；
S2、基于所述移动信道冲激响应模型计算接收机输出的电信噪比；
S3、根据接收机输出的电信噪比，计算不同的候选调制格式下无线光通信系统的误比特率值，获得多组误比特率值；
S4、从不同的候选调制格式中选取第一调制格式和第二调制格式，其中，所述第一调制格式对应的误比特率值大于预设的误比特阈值，所述第二调制格式对应的误比特率值小于预设误比特率阈值；
S5、确定每个数据帧中第一调制格式和第二调制格式的码元数量，使得第一调制格式和第二调制格式的平均混合误比特率小于预设误比特率阈值，其中，第一调制格式和第二调制格式的码元数量使得对应的无线光通信系统的传输容量最大；
S6、根据所述第一调制格式和第二调制格式的码元数量构造时域混合调制帧，通过所述时域混合调制帧调制数据并进行数据传输。
作为优选的，所述S3还包括，对获得的多组误比特率值递减排序，获得排序后的多组误比特率值；
所述S4中，所述第一调制格式和第二调制格式对应的误比特率值为所述排序后的多组误比特率值中相邻的数值。
作为优选的，所述S6包括：
比较第一调制格式的码元数量N k和第二调制格式的码元数量N k+1大小，
若N k≥N k+1，则令I＝floor(N k/N k+1)，且在构造时域混合调制数据帧结构的过程中，每传输I个第一调制格式符号，就传输1个第二调制格式符号，两种调制格式的符号交替传输，直至码元全部发送完毕，则一帧发送完毕，
若N k<N k+1，则令I＝ceil(N k+1/N k)，则在构造时域混合调制数据帧结构的过程中，每传输I个第二调制格式符号，就必须传输1个第一调制格式符号，两种调制格式的符号交替传输，直至码元全部发送完毕，则一帧发送完毕。
作为优选的，所述S1具体包括：
根据T、R、O终端移动状态，获得移动信道冲激响应：
Figure PCTCN2020113662-appb-000001
其中，发射机坐标T i为(x ti,y ti,z ti)，i表示第i个LED光源，接收机坐标R 为(x r,y r,z r)，接收机方位O为(α,β)，α为接收机朝向的方位角，β为接收机朝向的极角；N LED是LED光源的数量；对于第i个LED光源，w i是光源发射功率的加权系数，τ i,los和τ i,nlos分别为视距和非视距链路的信号传播时延，H i,los(0)为视距链路的归一化直流增益，A i,nlos为非视距链路的归一化信道增益。
作为优选的，所述S2具体包括：
Figure PCTCN2020113662-appb-000002
其中，P r,sig为接收信号的功率，P r,isi代表码间干扰，N由散粒噪声方差σ 2 shot和热噪声方差σ 2 thermal组成，γ为光电探测器的光电转换效率，t 0为积分后的脉冲起始时间，R s为脉冲速率，P t为每个光源的平均发射功率，m为发射信号的调制指数，s(t)为归一化矩形脉冲，
Figure PCTCN2020113662-appb-000003
代表卷积运算；
其中，散粒噪声进一步表示为：
Figure PCTCN2020113662-appb-000004
其中，q是电子电荷数，I bg是背景电流，I 2是噪声带宽因子；
热噪声表示为：
Figure PCTCN2020113662-appb-000005
其中，k是玻尔兹曼常数，T k是绝对温度，μ是固定电容，A是光电检测器面积，g m是场效应晶体管的跨导，Г是FET的信道噪声因子，G是开环电压增益，I 3＝0.0868。
作为优选的，所述S3具体包括以下步骤：
计算得到无线光通信系统的误比特率为：
Figure PCTCN2020113662-appb-000006
此处，采用不同调制阶数的L-PAM和L-PPM作为候选的调制格式，PAM为脉冲幅值调制，PPM为脉冲位置调制，L为信号调制阶数；
计算得到每种不同的候选的调制格式所对应的误比特率，并将所有的误比特率值从高到低排列，得到BER 1(T,R,O)、BER 2(T,R,O)、……、BER K(T,R,O)，它们所对应的调制格式可分别表示为格式1、格式2、……、格式K。
作为优选的，所述S4具体包括：
当终端的移动状态为(T,R,O)时，设定误比特率阈值为BER T；
当满足BER k(T,R,O)≥BER T>BER k+1(T,R,O)时，选择格式k以及格式k+1来构造时域混合调制数据帧，其中，1≤k<k+1≤K，格式k记为第一调制格式，格式k+1记为第二调制格式。
作为优选的，所述S5包括以下步骤：
S51、所述时域混合调制数据帧的平均混合误比特率为：
Figure PCTCN2020113662-appb-000007
其中，D表示上述格式k的所占比重，D的范围为0≤D≤1，SE k和SE k+1分别表示调制格式k和调制格式k+1的频谱效率；
S52、获得D的最优值，记为D opt，使无线光通信系统的动态传输容量最大，具体包括：将从D＝1开始，增量为ΔD<0，通过逐渐减小D，一旦当D的值无法满足平均混合误比特率小于预设误比特率阈值BER T时，则将当前D的值减去ΔD，并将相减后的结果作为在(T,R,O)移动状态下的D opt；
S53、对于调制格式k，每一帧中所需的码元数量为N k＝floor(N total×D opt)， 对于调制格式k+1，每一帧中所需的码元数量为N k+1＝ceil(N total×(1-D opt))，
其中，floor()表示向下取整，ceil()表示向上取整，N total为每一个时域混合调制数据帧中的码元总数。
本发明公开了一种移动无线光通信系统的通信方法，基于上述的移动无线光通信系统的容量优化方法优化，其特征在于，包括以下步骤：
针对不同的业务类型的预设误比特率阈值和不同的脉冲速率级别，获取不同的时域混合调制帧；
将不同预设误比特率阈值和脉冲速率级别对应的时域混合调制帧存储至数据库；
获取当前的预设误比特率阈值和脉冲速率级别，调用数据库中对应的时域混合调制帧并进行无线光通信。
本发明公开了一种移动无线光通信系统，包括发射机和接收机，所述发射机或接收机上设置有优化模块，所述优化模块运行上述的移动无线光通信系统的容量优化方法；
当所述接收机上设置有优化模块时，所述优化模块计算获得时域混合调制帧的优化参数信息，所述时域混合调制帧的优化参数信息由接收机传输至发射机，所述发射极根据接收的时域混合调制帧的优化参数信息构造时域混合调制帧，进行数据传输；
当所述发射机上设置有优化模块时，接收机将接收机的位置信息和接收机的方位信息发送至发射机，所述优化模块计算获得时域混合调制帧的优化参数信息，所述发射机根据接收的时域混合调制帧的优化参数信息构造时域混合调制帧，所述发射机将时域混合调制帧及其优化参数信息发送至接收机，所述接收机根据所接收到的时域混合调制帧的优化参数信息对时域混合调制帧进行解 调。
本发明的有益效果：
1、本发明基于单载波调制，结构简单、实时处理灵活性高，可以有效避免OFDM技术的固有缺陷。
2、本发明适用于移动无线光通信系统，通过从接收端向发射端反馈简单的终端移动状态信息，便可对移动无线光信道状态进行高效的估计，并有效降低上行反馈链路的传输开销。
3、本发明可以根据终端所感知的移动状态信息对系统的频谱效率和传输容量进行动态优化，从而能够高效地适应无线光信道中电信噪比的时变性，实现终端移动过程中频谱效率和传输容量的动态最优。
4、本发明可在接收机改变位置、方位的过程中实现系统传输容量的连续变化，有利于所承载业务的平稳切换以及传输速率的连续、顺利的过渡。
5、本发明可以满足不同业务所规定的误比特率门限，从而保证无线光通信链路的移动传输质量可靠。
6、本发明可以有效地适应移动无线光信道的实际状态，根据终端的移动状态信息对信号传输方案进行自适应的调整与优化。
附图说明
图1为本发明的原理图；
图2为本发明的移动无线光通信系统的容量优化方法的流程图；
图3为无线光通信系统模型；
图4为在对角线上不同位置的传输容量对比图；
图5为在对角线上不同位置下所提出的优化方案采用的调制格式以及所对应的D opt；
图6为在对角线上不同位置的误比特率对比图；
图7为两种调制方式在接收平面内的传输容量对比图，其中，(a)采用传统的自适应调制方法；(b)采用本发明的优化方法；
图8为数据传输容量提升幅度的互补累计函数示意图；
图9为接收机倾斜情况下的传输容量对比图，其中，(a)α＝0°；(b)α＝45°。
具体实施方式
下面结合附图和具体实施例对本发明作进一步说明，以使本领域的技术人员可以更好地理解本发明并能予以实施，但所举实施例不作为对本发明的限定。
参照图1所示，为本发明的原理图。在室内无线光通信系统中，当终端移动或改变方位(即接收机视场角的朝向)时，接收机接收到的光功率和信噪比均会发生波动。对于传统的单载波调制，为了适应信噪比的变化，需要选择一种最有效的调制格式。然而，对于移动无线光通信系统，采用离散调制格式很难达到最佳的频谱效率。例如，当一个终端位于两种调制格式(例如PAM2和PAM4)所支持的最远传输距离之间时，只能采用较低阶的调制格式(即PAM2)来确保可靠的链路质量。这显然无法实现最佳的频谱效率。为了改善频谱效率，我们提出一种可感知接收机移动状态的时域混合调制方案，如图1所示。通过时分复用的方式，我们将两种不同的调制格式交替传输，可以根据移动信道的时变情况自适应地调整平均的频谱效率。例如，当终端位于明亮的区域时，信噪比较大，则将两种具有高谱效率的调制格式混合(其中谱效率较高的调制格式1占比为D1％)，形成帧结构1，以获得更高的频谱效率；而当终端移动到较暗的区域时，信噪比较低，则将两种具有较低频谱效率的调制格式混合(其中谱效率较高的调制格式2占比为D2％)，形成帧结构2，以保证链路传输质量，满足接收机灵敏度的需求。只要确保每一个帧中的平均误比特率(BER)刚好低于所采用前向纠错(FEC)所规定的误比特率阈值(如BERT＝4.6×10 -3)，便 可以有效提升系统的移动传输容量。
参照图2所示，本发明公开了一种移动无线光通信系统的容量优化方法，该方法的输入是终端移动状态，包括接收机的位置、朝向等信息，该方法的制约条件为误比特率门限值和器件所支持的脉冲速率，该方案的输出是优化后的调制格式、调制阶数、混合比例以及混合帧结构等系统配置参数，最终可实现系统中移动传输容量的动态提升。
本发明的移动无线光通信系统的容量优化方法包括以下步骤：
步骤一、获取发射机位置信息、接收机的位置信息和接收机的方位信息，建立移动信道冲激响应模型，具体包括：
无线光通信的信道状态主要取决于发射机和接收机之间的几何位置关系。因此，考虑终端的移动状态信息，包括发射机坐标、接收机坐标和接收机方位。其中，发射机坐标为T i为(x ti,y ti,z ti)，i表示第i个LED光源，接收机坐标R为(x r,y r,z r)，接收机方位O为(α,β)，其中，α为接收机朝向的方位角，β为接收机朝向的极角，如后面图3所示。根据T、R、O这些终端移动状态，可以得到移动信道冲激响应，如下所示：
Figure PCTCN2020113662-appb-000008
其中，N LED是LED光源的数量；对于第i个LED光源，w i是光源发射功率的加权系数，τ i,los和τ i,nlos分别是视距和非视距链路的信号传播时延，H i,los(0)是视距链路的归一化直流增益，A i,nlos是非视距链路的归一化信道增益。
步骤二、基于所述移动信道冲激响应模型计算接收机输出的电信噪比，具体包括：
基于公式(1)，在接收端，我们可以计算光电检测器输出的电信噪比SNR， 并将其表示成接收机移动状态的形式：
Figure PCTCN2020113662-appb-000009
其中，P r,sig为接收信号的功率，P r,isi代表码间干扰，N由散粒噪声方差σ 2 shot和热噪声方差σ 2 thermal组成，γ为光电探测器的光电转换效率，t 0为积分后的脉冲起始时间，R s为脉冲速率，P t为每个光源的平均发射功率，m为发射信号的调制指数，s(t)为归一化矩形脉冲，
Figure PCTCN2020113662-appb-000010
代表卷积运算；
其中，散粒噪声进一步表示为：
Figure PCTCN2020113662-appb-000011
其中，q是电子电荷数，I bg是背景电流，I 2是噪声带宽因子；
热噪声表示为：
Figure PCTCN2020113662-appb-000012
其中，k是玻尔兹曼常数，T k是绝对温度，μ是固定电容，A是光电检测器面积，g m是场效应晶体管的跨导，Г是FET的信道噪声因子，G是开环电压增益，I 3＝0.0868。
步骤三、根据接收机输出的电信噪比，计算不同的候选调制格式下无线光通信系统的误比特率值，获得多组误比特率值，之后，对获得的多组误比特率值递减排序，获得排序后的多组误比特率值，具体包括以下步骤：
根据式(2)中的SNR，则无线光通信系统的误比特率(BER)可以表示为：
Figure PCTCN2020113662-appb-000013
此处，采用不同调制阶数的L-PAM和L-PPM作为候选的调制格式，PAM为脉冲幅值调制，PPM为脉冲位置调制，L为信号调制阶数；
通过式(5)，计算得到每种不同的候选的调制格式所对应的误比特率，并将所有的误比特率值从高到低排列，得到BER 1(T,R,O)、BER 2(T,R,O)、……、BER K(T,R,O)，它们所对应的调制格式可分别表示为格式1、格式2、……、格式K。
步骤四、从不同的候选调制格式中选取第一调制格式和第二调制格式，其中，所述第一调制格式对应的误比特率值大于预设的误比特阈值，所述第二调制格式对应的误比特率值小于预设误比特率阈值，其中，所述第一调制格式和第二调制格式对应的误比特率值为所述排序后的多组误比特率值中相邻的数值，具体包括以下步骤：
当终端的移动状态为(T,R,O)时，对于某种特定的业务，设定的误比特率阈值为BER T；
当满足BER k(T,R,O)≥BER T>BER k+1(T,R,O)时，选择格式k以及格式k+1来构造时域混合调制数据帧，其中，1≤k<k+1≤K，格式k记为第一调制格式，格式k+1记为第二调制格式。
步骤五、确定每个数据帧中第一调制格式和第二调制格式的码元数量，使得第一调制格式和第二调制格式的平均混合误比特率小于预设误比特率阈值，其中，第一调制格式和第二调制格式的码元数量使得对应的无线光通信系统的传输容量最大，具体包括以下步骤：
S51、所述时域混合调制数据帧的平均混合误比特率为：
Figure PCTCN2020113662-appb-000014
其中，D表示上述格式k的所占比重，D的范围为0≤D≤1，SE k和SE k+1分别表示调制格式k和调制格式k+1的频谱效率；
S52、根据(6)中的约束条件，我们需要找到D的最优值，即D opt，使系统的动态传输容量最大。因此，我们通过穷举法来搜索得到D opt，在穷举的过程中，为降低计算量，将从D＝1开始，增量为ΔD<0，通过逐渐减小D，一旦当D的值无法满足平均混合误比特率小于预设误比特率阈值为BER T时，则将当前D的值减去ΔD，并将相减后的结果作为在(T,R,O)移动状态下的D opt；
S53、对于调制格式k，每一帧中所需的码元数量为N k＝floor(N total×D opt)，对于调制格式k+1，每一帧中所需的码元数量为N k+1＝ceil(N total×(1-D opt))，
其中，floor()表示向下取整，ceil()表示向上取整，N total为每一个时域混合调制数据帧中的码元总数。
通过上述取整函数的正确使用，可以确保系统传输质量可靠，即误比特率不超过BER T。
步骤六、根据所述第一调制格式和第二调制格式的码元数量构造时域混合调制帧，通过所述时域混合调制帧调制数据并进行数据传输。
比较第一调制格式的码元数量N k和第二调制格式的码元数量N k+1大小，
若N k≥N k+1，则令I＝floor(N k/N k+1)，且在构造时域混合调制数据帧结构的过程中，每传输I个第一调制格式符号，就传输1个第二调制格式符号，两种调制格式的符号交替传输，直至码元全部发送完毕，则一帧发送完毕，
若N k<N k+1，则令I＝ceil(N k+1/N k)，则在构造时域混合调制数据帧结构的过程中，每传输I个第二调制格式符号，就必须传输1个第一调制格式符号，两种调制格式的符号交替传输，直至码元全部发送完毕，则一帧发送完毕。
本发明还公开了一种移动无线光通信系统的通信方法，基于上述的移动无线光通信系统的容量优化方法优化，包括以下步骤：
步骤一、针对不同的业务类型的预设误比特率阈值和不同的脉冲速率级别， 获取不同的时域混合调制帧；
步骤二、将不同预设误比特率阈值和脉冲速率级别对应的时域混合调制帧存储至数据库；
步骤三、获取当前的预设误比特率阈值和脉冲速率级别，调用数据库中对应的时域混合调制帧并进行无线光通信。
具体的，由于调制格式k、调制格式k+1以及D opt均与终端移动状态有关，因此，可以通过查表法来记录这些参数与接收机移动状态之间的关系。当终端首次位于(T,R,O)的移动状态时，我们将建立(T,R,O)所对应的表格索引，并对系统参数进行初始化。我们将根据不同的业务类型和不同的脉冲速率级别对表格进行分页。在每一页表格中，我们假设业务的误比特率门限为BER T，系统所支持的脉冲速率为R s，则我们将相同的BER T和R s作为这一页表格的制约条件。由于发射机的坐标T通常为固定的，因此，我们通过查阅终端在室内的实时坐标R和朝向O，来获得如下信息：调制格式k、调制格式k+1、交替传输所遵照的帧结构(即包含N k、N k+1、I的相关信息)。最终，所提出的方案可以在(T,R,O)的终端移动状态下获得最优的传输容量R b如下：
R b(T,R,O)＝D opt(T,R,O)·SE k(T,R,O)·R s+[1-D opt(T,R,O)]·SE k+1(T,R,O)·R s   (7)
而R b将作为重要依据，用来判断待承载业务是否能够维持稳定、可靠的数据传输。
从以上步骤可以看出，本发明中，时域混合调制方案的参数可以根据终端的移动状态进行自适应的调整和优化，为了传输此类信号，需要发射端与接收端之间进行协商。我们所采用的是从接收端到发射端的反馈机制。分为以下两种方式进行：
方式1，参数的优化计算由接收机来完成，并向发射机反馈所需采用的最优时域混合调制格式，以及帧结构信息。在该方式中，接收机通过室内无线光定位获得其自身的坐标信息R，同时，接收机利用其自带的角度传感器，获得 其方位角信息O(即朝向)，然后利用固定的发射机坐标信息T，直接在接收端通过前述步骤一到步骤六进行参数优化，得到在(T,R,O)移动状态下所需采用的最优时域混合调制格式，以及帧结构信息，然后通过上行链路(优选WiFi)反馈至发射端，进行自适应的通信协商。
方式2，向发射机反馈(R,O)，参数的优化计算由发射机来完成。在该方式中，为了进一步降低终端的复杂度，接收机通过室内无线光定位获得其自身的坐标信息R，同时，接收机利用其自带的角度传感器，获得其方位角信息O(即朝向)，接收机将(R,O)这两种信息然后通过上行链路(优选WiFi)反馈至发射端。发射端利用自身的坐标信息T，再结合所接收到的(R,O)，通过前述步骤一到步骤六进行参数优化，得到在(T,R,O)移动状态下所需采用的最优时域混合调制格式，以及帧结构信息，并通过下行链路以固定的调制格式在发送新的时域混合调制信号之前告知接收机。
基于上述发射端与接收端的两种通信协商方式，本发明公开了一种移动无线光通信系统，包括发射机和接收机，所述发射机或接收机上设置有优化模块，所述优化模块运行上述的移动无线光通信系统的容量优化方法；当所述接收机上设置有优化模块时，所述优化模块计算获得时域混合调制帧的优化参数信息，所述时域混合调制帧的优化参数信息由接收机传输至发射机，所述发射极根据接收的时域混合调制帧的优化参数信息构造时域混合调制帧，进行数据传输；
当所述发射机上设置有优化模块时，接收机将接收机的位置信息和接收机的方位信息发送至发射机，所述优化模块计算获得时域混合调制帧的优化参数信息，所述发射机根据接收的时域混合调制帧的优化参数信息构造时域混合调制帧，所述发射机将时域混合调制帧及其优化参数信息发送至接收机，所述接收机根据所接收到的时域混合调制帧的优化参数信息对时域混合调制帧进行解调。
另外，在上面所提出的方法中，若终端位置和朝向均保持不变，则所传输的混合信号格式和比例D opt保持不变。只有当终端的位置或朝向任何一种发生 变化时，才需要根据新的移动状态信息重新进行传输信号的选择与优化。
对于终端移动模式固定的情形，即接收机周期性地重复同一种移动轨迹或转动方向，此时，根据终端移动模式(如初始位置、速度、方向等)对各个时刻的位置坐标与方位角进行预测，然后根据步骤一至步骤六，将各个移动状态下所需采用的最优时域混合调制格式，以及帧结构信息存入表格中。当接收机进行周期性移动时，通过周期性地查阅表格，可以得到各个时刻的最优时域混合调制参数，实现周期性移动传输容量的最大化。
为了评估所提出的用于移动无线光通信系统的容量优化方法，本实施例考虑一个具体的室内空间场景，其尺寸为8m×8m×3m(长×宽×高)。光源部署于天花板上，移动终端位于接收平面上，接收平面的高度为0.85m。如图3所示。在图3中，本实施例还定义了本专利中用来表示接收机朝向的方位角α和极角β。
在下面的图中，从图4到图8，本实施例将考虑一个LED发射机光源，安装于坐标(4，4，3)处，向下照射，其发射光功率为18W，同时，本实施例假设接收器朝向朝上，接收到信号分量主要来自于视距链路；
而对于图9，本实施例将考虑总共有四个LED光源，分别安装于坐标(3，3，3)、(3，5，3)、(5，3，3)、(5，5，3)处，每个LED光源的发射光功率为4.5W，同时，考虑接收器倾斜的情况，即接收机朝向发生变化，接收到信号分量既包括视距链路分量，也包括非视距链路分量。
以图3所示的接收平面中的虚线对角线上各位置为例，进行分析。在图4中，在采用所提出优化方案前后，将对角线上不同位置的传输容量进行对比，这里考虑了不同的脉冲速率R s，并将业务误比特率门限值BER T设置为4.6×10 -3，也就是说，当误比特率不高于4.6×10 -3，则认为在FEC前向纠错码的帮助下可实现无差错传输。如图4所示，对于传统的单载波方案，由于采用了离散调制格式，当终端从中心位置移动到角落位置时，系统容量将急剧下降。然而，在采用所提出的容量优化方案后，容量曲线呈现连续性的变化。因此，所提出的方法助于有效补偿传统离散调制格式引起的数据速率降低，尤其是在调制格式 进行改变的位置附近。
基于图4，当R s为50MHz时，图5给出了在对角线上不同位置下，采用所提出的优化方案所需的两种混合调制格式，以及所对应的D opt，可以看出，对角线范围被划分为9个区域，每个区域都有各自采用的时域混合调制格式。例如，最角落位置是采用PPM8+PPM4的组合，而最中间位置是采用PAM8+PAM16的组合，其他位置所采用的混合调制格式均列于图中。蓝色的曲线是在各个位置下，所采用的两种混合调制格式中频谱效率较大的那一种格式的最优占比D opt，可以看出由于接收机位置的不断变化，D opt也需要不断进行优化与调整，从而实现最优的频谱效率。
基于图5，图6比较了对角线不同位置下的系统误比特率性能。为了获得更高的信噪比，所提出的优化方案的系统误比特率始终紧贴BER T＝4.6×10 -3，但又不超过该值，因此可以在确保获得可靠移动传输质量的同时，尽可能多地提升系统的传输效率。(解释：在采用FEC后，误比特率很低从一定程度上意味着频谱资源的浪费，因为其实并不需要非常低，只要不高于BER T即可)
当R s为50MHz时，在图7中，本实施例比较了采用所提出的优化方案前后，在接收平面内的系统传输容量。可以看出，采用所提出的优化方法可以在整个接收平面的各个位置有效提高系统容量，例如，当接收机位于(4，4，0.85)时，最大数据速率可从150Mbps(仅采用PAM8)增加到197Mbps(采用混合的PAM8+PAM16)。
对于不同的R s，图8展示了在接收平面内采用所提出的优化方法可获得的传输容量提升，本实施例经过统计，给出了数据速率提升幅度的互补累积分布函数(CCDF)。根据统计结果，当R s为100MHz时，在整个接收平面内总共有19.8％的室内区域可获得20％以上的容量提升幅度。
考虑到移动终端向着不同的朝向转动，图9比较了在坐标为(4，4，0.85)的位置处，接收机朝向的方位角和极角在一定范围内变化的情况，图中的实线给出了在各个朝向下可获得的最大数据速率。可以看出，当接收机倾斜时，采用所提出的优化方法仍然可以使移动无线光通信的系统容量得到有效改善。
以上所述实施例仅是为充分说明本发明而所举的较佳的实施例，本发明的保护范围不限于此。本技术领域的技术人员在本发明基础上所作的等同替代或变换，均在本发明的保护范围之内。本发明的保护范围以权利要求书为准。

Claims (10)

  1. 一种移动无线光通信系统的容量优化方法，其特征在于，包括以下步骤：
    S1、获取发射机位置信息、接收机的位置信息和接收机的方位信息，建立移动信道冲激响应模型；
    S2、基于所述移动信道冲激响应模型计算接收机输出的电信噪比；
    S3、根据接收机输出的电信噪比，计算不同的候选调制格式下无线光通信系统的误比特率值，获得多组误比特率值；
    S4、从不同的候选调制格式中选取第一调制格式和第二调制格式，其中，所述第一调制格式对应的误比特率值大于预设的误比特阈值，所述第二调制格式对应的误比特率值小于预设误比特率阈值；
    S5、确定每个数据帧中第一调制格式和第二调制格式的码元数量，使得第一调制格式和第二调制格式的平均混合误比特率小于预设误比特率阈值，其中，第一调制格式和第二调制格式的码元数量使得对应的无线光通信系统的传输容量最大；
    S6、根据所述第一调制格式和第二调制格式的码元数量构造时域混合调制帧，通过所述时域混合调制帧调制数据并进行数据传输。
  2. 如权利要求1所述的移动无线光通信系统的容量优化方法，其特征在于，所述S3还包括，对获得的多组误比特率值递减排序，获得排序后的多组误比特率值；
    所述S4中，所述第一调制格式和第二调制格式对应的误比特率值为所述排序后的多组误比特率值中相邻的数值。
  3. 如权利要求1所述的移动无线光通信系统的容量优化方法，其特征在于， 所述S6包括：
    比较第一调制格式的码元数量N k和第二调制格式的码元数量N k+1大小，
    若N k≥N k+1，则令I＝floor(N k/N k+1)，且在构造时域混合调制数据帧结构的过程中，每传输I个第一调制格式符号，就传输1个第二调制格式符号，两种调制格式的符号交替传输，直至码元全部发送完毕，则一帧发送完毕，
    若N k<N k+1，则令I＝ceil(N k+1/N k)，则在构造时域混合调制数据帧结构的过程中，每传输I个第二调制格式符号，就必须传输1个第一调制格式符号，两种调制格式的符号交替传输，直至码元全部发送完毕，则一帧发送完毕。
  4. 如权利要求1所述的移动无线光通信系统的容量优化方法，其特征在于，所述S1具体包括：
    根据T、R、O终端移动状态，获得移动信道冲激响应：
    Figure PCTCN2020113662-appb-100001
    其中，发射机坐标T i为(x ti,y ti,z ti)，i表示第i个LED光源，接收机坐标R为(x r,y r,z r)，接收机方位O为(α,β)，α为接收机朝向的方位角，β为接收机朝向的极角；N LED是LED光源的数量；对于第i个LED光源，w i是光源发射功率的加权系数，τ i,los和τ i,nlos分别为视距和非视距链路的信号传播时延，H i,los(0)为视距链路的归一化直流增益，A i,nlos为非视距链路的归一化信道增益。
  5. 如权利要求4所述的移动无线光通信系统的容量优化方法，其特征在于，所述S2具体包括：
    Figure PCTCN2020113662-appb-100002
    其中，P r,sig为接收信号的功率，P r,isi代表码间干扰，N由散粒噪声方差σ 2 shot 和热噪声方差σ 2 thermal组成，γ为光电探测器的光电转换效率，t 0为积分后的脉冲起始时间，R s为脉冲速率，P t为每个光源的平均发射功率，m为发射信号的调制指数，s(t)为归一化矩形脉冲，
    Figure PCTCN2020113662-appb-100003
    代表卷积运算；
    其中，散粒噪声进一步表示为：
    Figure PCTCN2020113662-appb-100004
    其中，q是电子电荷数，I bg是背景电流，I 2是噪声带宽因子；
    热噪声表示为：
    Figure PCTCN2020113662-appb-100005
    其中，k是玻尔兹曼常数，T k是绝对温度，μ是固定电容，A是光电检测器面积，g m是场效应晶体管的跨导，Г是FET的信道噪声因子，G是开环电压增益，I 3＝0.0868。
  6. 如权利要求5所述的移动无线光通信系统的容量优化方法，其特征在于，所述S3具体包括以下步骤：
    计算得到无线光通信系统的误比特率为：
    Figure PCTCN2020113662-appb-100006
    此处，采用不同调制阶数的L-PAM和L-PPM作为候选的调制格式，PAM为脉冲幅值调制，PPM为脉冲位置调制，L为信号调制阶数；
    计算得到每种不同的候选的调制格式所对应的误比特率，并将所有的误比特率值从高到低排列，得到BER 1(T,R,O)、BER 2(T,R,O)、……、BER K(T,R,O)，它们所对应的调制格式可分别表示为格式1、格式2、……、格式K。
  7. 如权利要求6所述的移动无线光通信系统的容量优化方法，其特征在于， 所述S4具体包括：
    当终端的移动状态为(T,R,O)时，设定误比特率阈值为BER T；
    当满足BER k(T,R,O)≥BER T>BER k+1(T,R,O)时，选择格式k以及格式k+1来构造时域混合调制数据帧，其中，1≤k<k+1≤K，格式k记为第一调制格式，格式k+1记为第二调制格式。
  8. 如权利要求6所述的移动无线光通信系统的容量优化方法，其特征在于，所述S5包括以下步骤：
    S51、所述时域混合调制数据帧的平均混合误比特率为：
    Figure PCTCN2020113662-appb-100007
    其中，D表示上述格式k的所占比重，D的范围为0≤D≤1，SE k和SE k+1分别表示调制格式k和调制格式k+1的频谱效率；
    S52、获得D的最优值，记为D opt，使无线光通信系统的动态传输容量最大，具体包括：将从D＝1开始，增量为ΔD<0，通过逐渐减小D，一旦当D的值无法满足平均混合误比特率小于预设误比特率阈值BER T时，则将当前D的值减去ΔD，并将相减后的结果作为在(T,R,O)移动状态下的D opt；
    S53、对于调制格式k，每一帧中所需的码元数量为N k＝floor(N total×D opt)，对于调制格式k+1，每一帧中所需的码元数量为N k+1＝ceil(N total×(1-D opt))，
    其中，floor()表示向下取整，ceil()表示向上取整，N total为每一个时域混合调制数据帧中的码元总数。
  9. 一种移动无线光通信系统的通信方法，基于权利要求1-8任一项所述的移动无线光通信系统的容量优化方法优化，其特征在于，包括以下步骤：
    针对不同的业务类型的预设误比特率阈值和不同的脉冲速率级别，获取不同的时域混合调制帧；
    将不同预设误比特率阈值和脉冲速率级别对应的时域混合调制帧存储至数据库；
    获取当前的预设误比特率阈值和脉冲速率级别，调用数据库中对应的时域混合调制帧并进行无线光通信。
  10. 一种移动无线光通信系统，其特征在于，包括发射机和接收机，所述发射机或接收机上设置有优化模块，所述优化模块运行权利要求1-8任一项所述的移动无线光通信系统的容量优化方法；
    当所述接收机上设置有优化模块时，所述优化模块计算获得时域混合调制帧的优化参数信息，所述时域混合调制帧的优化参数信息由接收机传输至发射机，所述发射极根据接收的时域混合调制帧的优化参数信息构造时域混合调制帧，进行数据传输；
    当所述发射机上设置有优化模块时，接收机将接收机的位置信息和接收机的方位信息发送至发射机，所述优化模块计算获得时域混合调制帧的优化参数信息，所述发射机根据接收的时域混合调制帧的优化参数信息构造时域混合调制帧，所述发射机将时域混合调制帧及其优化参数信息发送至接收机，所述接收机根据所接收到的时域混合调制帧的优化参数信息对时域混合调制帧进行解调。
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