A fine-grained adaptive OFDM modulation and demodulation system and method

Abstract

The application discloses a fine-grained adaptive OFDM modulation and demodulation system, which comprises a transmitting end and a receiving end, the transmitting end comprises a first serial-parallel conversion module, a fine-grained adaptive modulation module, a Hermite symmetry module, an IFFT module and a first parallel-serial conversion module, wherein the fine-grained adaptive modulation module can perform fine-grained adaptive modulation on data according to a channel estimation result fed back by the receiving end; and the receiving end comprises a second serial-parallel conversion module, an FFT module, a channel estimation module, a frequency domain equalization module, a fine-grained adaptive demodulation module and a second parallel-serial conversion module. The application can effectively solve the influence of low-pass frequency response of an actual system and realize maximization of system transmission rate.

Description

Technical Field

[0001] This invention belongs to the field of wireless optical communication, specifically relating to a fine-grained adaptive OFDM modulation and demodulation system and method. Background Technology

[0002] 6G networks promise to provide ultra-high capacity, ultra-low latency communication covering space, air, land, and underwater environments. With the increasing demands of underwater activities such as marine exploration, marine environmental monitoring, and marine safety, underwater wireless communication (UWC) has attracted significant attention from academia and industry. In recent years, visible light communication (VLC), one of the key enabling technologies for 6G, has been widely applied and researched in underwater environments. Compared with traditional UWC technologies such as underwater acoustic communication and underwater radio frequency communication, underwater VLC (UVLC) has inherent advantages such as large bandwidth, low propagation latency, high security, small size, low power consumption, and low cost. Therefore, UVLC is often considered an effective complementary technology to traditional underwater acoustic communication, enabling the establishment of efficient communication links in underwater environments. Recently, UVLC systems based on light-emitting diodes (LEDs) have received widespread attention. However, the limited modulation bandwidth of practical UVLC systems restricts the transmission rate. High-spectral-efficiency modulation techniques, such as high-order modulation orthogonal frequency division multiplexing (OFDM), can be considered to improve the available data rate of the system.

[0003] OFDM has multi-carrier characteristics, and the modulation order allocated to each subcarrier can be the same or different. Adaptive techniques dynamically allocate different modulation schemes to different subcarriers based on the system's channel gain information, thereby maximizing the system's transmission rate under a given total transmit power. Traditional OFDM adaptive bit loading technology allocates a corresponding number of bits to each subcarrier at the same time. Specifically, based on known channel information and under the premise of meeting the target bit error rate, it assigns the optimal modulation order to each subcarrier to obtain the maximum spectral efficiency of the system, enabling the system to transmit more bits and achieving the best balance between spectral efficiency and bit error rate. Since the channel of a real UVLC system has low-pass characteristics, the channel states experienced by subcarriers at different positions are different. Transmit power and information bits can be flexibly allocated to each subcarrier according to the actual channel state. This allows for the allocation of higher-order modulation schemes to low-frequency subcarriers to load more bits, and lower-order modulation schemes to high-frequency subcarriers to adapt to channel characteristics. All subcarriers transmit their corresponding bit information independently without being affected by interference from adjacent carriers. However, the number of bits allocated to each subcarrier by traditional OFDM adaptive bit loading technology is an integer, which limits the realization of the system's transmission rate. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a fine-grained adaptive OFDM modulation and demodulation system and method.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A fine-grained adaptive OFDM modulation and demodulation system includes a transmitter and a receiver, characterized in that...

[0007] The transmitter includes a first serial-to-parallel conversion module, a fine-grained adaptive modulation module, a Hermitian symmetry module, an IFFT module, and a first parallel-to-serial conversion module.

[0008] The fine-grained adaptive modulation module includes an integer-level modulation unit and a fractional-level modulation unit. It receives the channel estimation result fed back from the receiver and performs fine-grained adaptive modulation on the data based on the channel estimation result.

[0009] Integer-level modulation units are used for integer-level granularity modulation, which are implemented by OFDM using different constellation methods;

[0010] The fractional-level modulation unit is used to perform fractional-level granular modulation. It includes a DF-DMIM modulator, which uses a dual-frame-based dual-mode index modulation method to perform modulation, that is, to perform dual-mode index modulation on all subcarriers in adjacent time slots to generate OFDM modulated signals.

[0011] The receiver includes a second serial-to-parallel conversion module, an FFT module, a channel estimation module, a frequency domain equalization module, a fine-grained adaptive demodulation module, and a second parallel-to-serial conversion module.

[0012] The fine-grained adaptive demodulation module includes an LLR detector and a DF-DMIM demodulator corresponding to the DF-DMIM modulator.

[0013] Furthermore, the DF-DMIM modulator includes a time slot index selector, a constellation mapper A, a constellation mapper B, and a DF-DMIM mapper, wherein,

[0014] The slot index selector is used to encode all subcarriers in two adjacent slot indices;

[0015] Constellation mapper A is used to perform constellation mapping on the data of active time slots in adjacent time slots using constellation diagram A, generating M. A -QAM signal, M A Indicates the order of constellation A;

[0016] Constellation mapper B is used to perform constellation mapping on data from inactive time slots in adjacent time slots using constellation diagram B, generating M. B -QAM signal, M B Indicates the order of constellation B;

[0017] The DF-DMIM mapper is used to generate DF-DMIM modulated signals based on the results of slot index coding and constellation mapping.

[0018] Among them, constellation chart A and constellation chart B are different constellation charts.

[0019] Furthermore, the DF-DMIM demodulator includes an LLR detector, a time slot index selector, a constellation demapper A, and a constellation demapper B, wherein,

[0020] The time slot index selector is used to decode the encoded time slot index of the received signal;

[0021] Constellation demapper A is used to map the M corresponding to the decoded active slot index. A - Demapping of QAM signals;

[0022] Constellation demapper B is used to process the M corresponding to the decoded inactive time slot index. B -QAM signals are demapped.

[0023] Furthermore, M A and M B They can be the same or different.

[0024] The present invention also provides a fine-grained adaptive OFDM modulation and demodulation method, which includes:

[0025] At the sending end,

[0026] The input data is converted from serial to parallel to generate the first serial data.

[0027] Based on the channel estimation results fed back from the receiver, fine-grained adaptive modulation is performed on the first serial data. The fine-grained modulation includes integer-level and fractional-level granularity. For integer-level granularity, different constellation methods are used in OFDM. For fractional-level granularity, the dual-frame dual-mode indexed modulation (DF-DMIM) method is used for modulation, i.e., dual-mode indexed modulation is performed on all subcarriers in adjacent time slots, including...

[0028] Encode all subcarriers in two adjacent time slot indices;

[0029] For data from active time slots in adjacent time slots, constellation mapping is performed using constellation diagram A to generate M. A -QAM signal, M A This indicates the order of constellation A.

[0030] For data from inactive time slots in adjacent time slots, constellation mapping is performed using constellation diagram B to generate M. B -QAM signal, M B This indicates the order of constellation chart B, where constellation chart A and constellation chart B are different constellation charts.

[0031] DF-DMIM modulated signals are generated based on the results of slot index coding and constellation mapping;

[0032] At the receiving end,

[0033] Fine-grained adaptive demodulation is performed on the received data, specifically including:

[0034] Decode the encoded time slot index of the received signal;

[0035] The M corresponding to the active slot index obtained by decoding A - Demapping of QAM signals;

[0036] The M corresponding to the inactive time slot index obtained from decoding B -QAM signals are demapped.

[0037] Furthermore, after fine-grained adaptive modulation, the process also includes Hermitian symmetry, IFFT, parallel-to-serial conversion, digital-to-analog conversion, and adding DC bias to the DF-DMIM modulated signal to generate the transmission signal.

[0038] Furthermore, before performing fine-grained adaptive demodulation, the received transmitted signal needs to undergo analog-to-digital conversion, DC bias removal, serial-to-parallel conversion, FFT, channel estimation, frequency domain equalization, and other operations. After that, fine-grained adaptive demodulation is performed, and parallel-to-serial conversion is performed to generate the output signal.

[0039] The beneficial effects of this invention are:

[0040] On the one hand, this invention extends the number of transmitted bits to a fractional granularity, maximizing the system transmission rate by combining fractional and integer granularity. On the other hand, since a real system with fractional granularity, when considering signal transmission on two adjacent subcarriers, is affected by low-pass frequency response, mainly due to the different power attenuation of adjacent subcarriers, this invention addresses this problem by considering the bit allocation of all subcarriers in adjacent time slots, achieving fractional granularity loading, effectively solving the impact of low-pass frequency response in the actual system, and maximizing the system transmission rate.

[0041] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0043] Figure 1 This is a schematic diagram of a fine-grained adaptive OFDM modulation and demodulation system according to an embodiment of this application;

[0044] Figure 2 This is a schematic diagram of a 0.5 bit / s / Hz granularity implementation based on BPSK OFDM;

[0045] Figure 3 This is a schematic diagram of DF-DMIM modulation and demodulation. Detailed Implementation

[0046] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the preferred embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0047] Figure 1 This is a schematic diagram of a fine-grained adaptive OFDM modulation and demodulation system, such as... Figure 1 As shown, the system includes a transmitter and a receiver.

[0048] The transmitter includes a first serial-to-parallel conversion module, a fine-grained adaptive modulation module, a Hermitian symmetry module, an IFFT module, a first parallel-to-serial conversion module, and a digital-to-analog conversion module. Input data is first converted from serial to parallel (i.e., S / P) by the first serial-to-parallel conversion module to achieve parallel data transmission.

[0049] The fine-grained adaptive modulation module can receive the channel estimation results (such as channel gain, SNR estimation, etc.) fed back from the receiver and perform fine-grained adaptive modulation on the parallel data after serial-to-parallel conversion based on the channel estimation results.

[0050] The fine-grained adaptive modulation module includes an integer-level modulation unit and a fractional-level modulation unit.

[0051] Integer-level modulation units are used for integer-level granularity modulation, which are implemented by OFDM using different constellation methods.

[0052] The fractional-level modulation unit is used for fractional-level granular modulation and includes a DF-DMIM modulator.

[0053] The DF-DMIM modulator uses a dual-frame-based dual-mode index modulation method for modulation, that is, dual-mode index modulation is performed on all subcarriers in adjacent time slots to generate DF-DMIM modulated signals.

[0054] Figure 3 This is a schematic diagram of DF-DMIM, a dual-frame dual-mode indexed modulation. (Example) Figure 3 As shown, the DF-DMIM modulator includes a time slot index selector, constellation mapper A, constellation mapper B, and a DF-DMIM mapper, wherein,

[0055] The slot index selector is used to encode all subcarriers in two adjacent slot indices;

[0056] Constellation mapper A is used to perform constellation mapping on the data of active time slots in adjacent time slots using constellation diagram A, generating M. A -QAM signal, M A Indicates the order of constellation A;

[0057] Constellation mapper B is used to perform constellation mapping on data from inactive time slots in adjacent time slots using constellation diagram B, generating M. B -QAM signal, M B Indicates the order of constellation B;

[0058] The DF-DMIM mapper is used to generate DF-DMIM modulated signals based on the results of slot index coding and constellation mapping.

[0059] Constellation chart A and constellation chart B are different constellation charts; their constellation order M is different. A and MB They can be the same or different, as long as the two constellation charts are distinguishable.

[0060] Combination Figure 3 (a) It can be seen that in the process of DF-DMIM modulation, S / P is first performed to obtain parallel data, and then the obtained signal is passed through the time slot index selector, constellation mapper A and constellation mapper B to complete dual-mode index modulation. After DF-DMIM mapping, the DF-DMIM modulated signal can be obtained.

[0061] In other words, during DF-DMIM modulation, all subcarriers can be encoded at two adjacent time slot indices; then, for the data in the active time slots of adjacent time slots, constellation mapping is performed using constellation diagram A to generate M. A -QAM signals, for data in inactive time slots in adjacent time slots, use constellation diagram B to perform constellation mapping to generate M B -QAM signal, and then generate DF-DMIM modulated signal based on the results of time slot index coding and constellation mapping.

[0062] In some embodiments, to generate a real signal, a Hermitian symmetry (HS) operation is applied before performing an inverse Fast Fourier Transform (IFFT), and a parallel-to-serial (P / S) conversion is performed after the IFFT to obtain a serial signal. The resulting serial signal is then converted to an analog signal via a digital-to-analog (D / A) converter, and a DC bias is further added to ensure the non-negativity of the analog signal. Finally, the resulting analog, real-valued, and non-negative signals are used to modulate an LED, enabling signal transmission in an underwater environment.

[0063] A schematic diagram of the 0.5 bit / s / Hz granularity implementation based on BPSK OFDM is shown below. Figure 2 As shown. Among them, in Figure 2 In the middle, SC1, SC2, SC3, ... SC N This represents all subcarriers, where N is the number of subcarriers in a single frame. i j represents the BPSK constellation symbol.

[0064] like Figure 2 As shown, information transmission occurs between adjacent time points, occupying the entire system bandwidth; that is, information is transmitted on all subcarriers of OFDM. Furthermore, only one time a signal is transmitted on the same subcarrier, while at another time no signal is transmitted on that subcarrier, thus enabling the system to achieve a spectral efficiency of 0.5 bit / s / Hz. Table 1 is an illustrative DF-DMIM mapping table.

[0065] Table 1 DF-DMIM Mapping Table

[0066]

[0067] DF-DMIM considers index modulation of all subcarriers in adjacent time slots, with the active time slots transmitting constellation A symbols and the remaining time slots transmitting constellation B symbols to achieve a two-frame index modulation process. In Table 1, The zodiac symbol corresponding to constellation A. The zodiac symbol corresponding to constellation B.

[0068] The fractional granularity of dual-frame dual-mode index modulation is 0.5+nbit / s / Hz (n=1,2,…). By performing dual-mode index modulation on all subcarriers in adjacent time slots, the activated time slots transmit constellation A symbols, and the remaining time slots transmit constellation B symbols. Different spectral efficiencies are obtained by changing the constellation order of the two distinguishable constellations. In the DF-DMIM modulation process, index modulation is performed on the parallel data after S / P. Specifically, dual-mode index modulation is performed in adjacent time slots. Each two time slots contain p bits. The p bits mainly have three functions: (1) to convert p bits into p bits. I Bits are fed into the time slot index selector, which allows selection of one time slot from adjacent time slots to transmit M. A -QAM constellation signal, silent time slot transmission M B -QAM constellation signal index information, M A and M B The order of constellation A and constellation B are respectively; (2)p A Bits enter constellation mapper A to generate M A -QAM constellation signal; (3) p B Bits are fed into constellation mapper B to generate M. B -QAM constellation signal, and satisfies p = p I +p A +p B Then, by performing DF-DMIM mapping on the obtained index bits and constellation bits, the DF-DMIM modulated signal can be generated.

[0069] Back Figure 1 The receiver includes a second serial-to-parallel conversion module, an FFT module, a channel estimation module, a frequency domain equalization module, a fine-grained adaptive demodulation module, and a second parallel-to-serial conversion module.

[0070] At the receiving end, after propagation through the water channel, the optical signal is first received by a photodetector (PD) to achieve photoelectric conversion. Then, the converted analog signal is converted into a digital signal by an analog-to-digital converter (A / D) and the DC bias is removed. Finally, the generated digital signal is demodulated to obtain the final output signal.

[0071] The fine-grained adaptive demodulation module includes an LLR detector and a DF-DMIM demodulator corresponding to the DF-DMIM modulator.

[0072] Figure 3 (b) is a schematic diagram of DF-DMIM demodulation. As shown in the figure, the DF-DMIM demodulator includes an LLR detector, a time slot index selector, a constellation demapper A, and a constellation demapper B.

[0073] The time slot index selector is used to decode the encoded time slot index of the received signal.

[0074] Constellation demapper A is used to map the M corresponding to the decoded active slot index. A -QAM signals are demapped.

[0075] Constellation demapper B is used to process the M corresponding to the decoded inactive time slot index. B -QAM signals are demapped.

[0076] Therefore, in the DF-DMIM demodulation process, the received signal is detected by an LLR detector. Then, the obtained index bit information, the constellation signal corresponding to constellation A, and the constellation signal corresponding to constellation B are respectively processed by a time slot index selector, constellation demapping unit A, and constellation demapping unit B to decode the encoded time slot index of the received signal. Furthermore, the M corresponding to the decoded active time slot index can be... A -QAM signal demapping and M corresponding to the decoded inactive time slot index B The -QAM signal is demapped. After passing through the P / S gate, the DF-DMIM demodulation process can be achieved.

[0077] The fine-grained adaptive OFDM modulation technique proposed in this invention can achieve fractional-level and integer-level bit loading for each subcarrier, thereby maximizing the system transmission rate. When achieving fractional-level granularity, all subcarriers are transmitted in adjacent time slots, which can also mitigate the impact of low-pass frequency response characteristics on band-limited UVLC systems.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A fine-grained adaptive OFDM modulation and demodulation system, comprising a transmitter and a receiver, characterized in that, The transmitter includes a first serial-to-parallel conversion module, a fine-grained adaptive modulation module, a Hermitian symmetry module, an IFFT module, and a first parallel-to-serial conversion module. The fine-grained adaptive modulation module includes an integer-level modulation unit and a fractional-level modulation unit. It receives the channel estimation result fed back from the receiver and performs fine-grained adaptive modulation on the data based on the channel estimation result. Integer-level modulation units are used for integer-level granularity modulation, which are implemented by OFDM using different constellation methods; The fractional-level modulation unit is used to perform fractional-level granular modulation. It includes a DF-DMIM modulator, which uses a dual-frame-based dual-mode index modulation method to perform modulation, that is, to perform dual-mode index modulation on all subcarriers in adjacent time slots to generate OFDM modulated signals. The receiver includes a second serial-to-parallel conversion module, an FFT module, a channel estimation module, a frequency domain equalization module, a fine-grained adaptive demodulation module, and a second parallel-to-serial conversion module. The fine-grained adaptive demodulation module includes an LLR detector and a DF-DMIM demodulator corresponding to the DF-DMIM modulator; The DF-DMIM modulator includes a time slot index selector, constellation mapper A, constellation mapper B, and a DF-DMIM mapper, wherein... The slot index selector is used to encode all subcarriers in two adjacent slot indices; Constellation mapper A is used to perform constellation mapping on the data of active time slots in adjacent time slots using constellation diagram A, generating M. A -QAM signal, M A Indicates the order of constellation A; Constellation mapper B is used to perform constellation mapping on data from inactive time slots in adjacent time slots using constellation diagram B, generating M. B -QAM signal, M B Indicates the order of constellation B; The DF-DMIM mapper is used to generate DF-DMIM mapped signals based on the results of slot index coding and constellation mapping. Among them, constellation chart A and constellation chart B are different constellation charts.

2. The fine-grained adaptive OFDM modulation and demodulation system according to claim 1, characterized in that, The DF-DMIM demodulator includes an LLR detector, a time slot index selector, constellation demapper A, and constellation demapper B, among which... The time slot index selector is used to decode the encoded time slot index of the received signal; Constellation demapper A is used to map the M corresponding to the decoded active slot index. A - Demapping of QAM signals; Constellation demapper B is used to process the M corresponding to the decoded inactive time slot index. B -QAM signals are demapped.

3. The fine-grained adaptive OFDM modulation and demodulation system according to claim 2, characterized in that, M A and M B same.

4. The fine-grained adaptive OFDM modulation and demodulation system according to claim 2, characterized in that, M A and M B different.

5. A fine-grained adaptive OFDM modulation and demodulation method, characterized in that, include: At the sending end, The input data is converted from serial to parallel to generate the first serial data. Based on the channel estimation results fed back from the receiver, fine-grained adaptive modulation is performed on the first serial data. The fine-grained modulation includes integer-level and fractional-level granularity. For integer-level granularity, different constellation methods are used in OFDM. For fractional-level granularity, the dual-frame dual-mode indexed modulation (DF-DMIM) method is used for modulation, i.e., dual-mode indexed modulation is performed on all subcarriers in adjacent time slots, including... Encode all subcarriers in two adjacent time slot indices; For data from active time slots in adjacent time slots, constellation mapping is performed using constellation diagram A to generate M. A -QAM signal, M A This indicates the order of constellation A. For data from inactive time slots in adjacent time slots, constellation mapping is performed using constellation diagram B to generate M. B -QAM signal, M B This indicates the order of constellation chart B, where constellation chart A and constellation chart B are different constellation charts. DF-DMIM modulated signals are generated based on the results of slot index coding and constellation mapping; At the receiving end, Fine-grained adaptive demodulation is performed on the received data, specifically including: Decode the encoded time slot index of the received signal; The M corresponding to the active slot index obtained by decoding A - Demapping of QAM signals; M corresponding to the inactive time slot index obtained from decoding B -QAM signals are demapped.

6. The fine-grained adaptive OFDM modulation and demodulation method according to claim 5, characterized in that, M A and M B same.

7. The fine-grained adaptive OFDM modulation and demodulation method according to claim 5, characterized in that, M A and M B different.

8. The fine-grained adaptive OFDM modulation and demodulation method according to claim 5, characterized in that, After fine-grained adaptive modulation, the process also includes Hermitian symmetry, IFFT, parallel-to-serial conversion, digital-to-analog conversion, and adding DC bias to the DF-DMIM modulated signal to generate the transmission signal.

9. A fine-grained adaptive OFDM modulation and demodulation method according to claim 8, characterized in that, Before fine-grained adaptive demodulation, the received transmitted signal needs to undergo analog-to-digital conversion, DC bias removal, serial-to-parallel conversion, FFT, channel estimation, and frequency domain equalization. After that, fine-grained adaptive demodulation is performed, followed by parallel-to-serial conversion to generate the output signal.

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