阅读说明：本技术 一种基于索引调制的ocdm水声通信方法 (OCDM underwater acoustic communication method based on index modulation ) 是由 何成兵 张晓洋 张阳 史文涛 戴祥飞 吴新宇 于 2020-05-15 设计创作，主要内容包括：本发明提供了一种基于索引调制的OCDM水声通信方法,将空间调制技术同OCDM相结合,在激活子载波传输相位调制信息的同时,利用静默子载波的索引位置承载信息。本发明明使得OCDM通信系统中有效子载波数减少从而降低子载波间的干扰,同时因静默子载波也承载信息,使得因子载波数减少所造成的数据速率损失得到了补偿,本发明利用激活子载波索引位置承载信息,使得通信系统相比于OCDM因有效子载波数减少而系统抗频移性能得到提升的同时,弥补了因有效子载波数的减少而造成数据速率的下降。(The invention provides an OCDM underwater acoustic communication method based on index modulation, which combines a spatial modulation technology with OCDM, and utilizes the index position of a silent subcarrier to carry information while activating the subcarrier to transmit phase modulation information. The invention makes the effective sub-carrier number in the OCDM communication system reduce to reduce the interference between the sub-carriers, and simultaneously, because the silent sub-carrier also bears the information, the data rate loss caused by the reduction of the factor carrier number is compensated.)

1. An OCDM underwater acoustic communication method based on index modulation is characterized by comprising the following steps:

the method comprises the following steps: determining that the number of single symbol subcarriers is N, the index modulation order is M1, the phase modulation order is M, and the frequency domain interval is F;

step two: at the transmitting end of the communication system, serial-parallel conversion is carried out on the serial data stream after channel coding to obtain parallel data streams, and the length of each group of data streams isA bit;

step three: modulating the parallel data obtained in the second step, log₂The (M) bit data is used for selecting the index position of the active subcarrier, namely, the part of data information is carried on the index position of the active subcarrier; another part log₂(M1) converting the bit data into phase information by phase modulation, and modulating the phase information on the active sub-carrier; meanwhile, in order to eliminate ISI to the maximum extent, a fractional order domain guard interval is introduced in the mapping process, so that each group of data is activated after all data mapping is finishedA subcarrier; respectively performing inverse Fractional Fourier Transform (IDFRT) on the parallel data streams obtained in the second step, and obtaining a group of LFM signals with the same frequency modulation slope and different center frequencies after the IDFRT;

step four: respectively adding the parallel data streams obtained in the step three into a cyclic protection prefix;

step five: parallel data streams added with the cyclic prefixes in the step four are subjected to parallel-serial conversion and then transmitted through the energy converter;

step six: the receiving end carries out serial-to-parallel conversion on serial data received by the hydrophone after passing through the underwater acoustic channel;

step seven: respectively removing cyclic prefixes from the parallel data streams obtained through serial-parallel conversion in the step six;

step eight: respectively performing Fourier transform on the parallel data streams with the cyclic prefixes removed in the seventh step to convert time domain data into frequency domain data, equalizing the received data in the frequency domain by adopting Minimum Mean Square Error (MMSE), and converting the frequency domain data into time domain signals by inverse Fourier transform;

step nine: performing fractional order Fourier transform of corresponding orders on the time domain signals obtained in the step eight to obtain fractional order domain signals, and simultaneously removing the interval of sub-carriers of the fractional order domain;

step ten: searching the index position of the activated subcarrier for the fractional order domain signal obtained in the step nine so as to reflect the data information carried by the emission index position; then, phase modulation and demodulation are carried out on the phase information carried by the activated subcarrier to obtain the data information of the other part;

step eleven: and D, performing parallel-serial conversion on the demodulated parallel data information obtained in the step ten, and outputting the parallel data information.

Technical Field

The invention relates to the field of underwater acoustic communication, in particular to an OCDM (optical code division multiplexing) underwater acoustic communication method based on index modulation.

Background

With the development of the human marine industry, the development requirements of countries in the world on underwater information transmission technology are increasing day by day. As is known, electromagnetic waves cannot be transmitted underwater in a long distance, so that the underwater acoustic communication technology is the only reliable mode for the remote wireless underwater information transmission at present. However, compared to other communication channels, the underwater acoustic channel is considered to be one of the most challenging channels in the communication field due to its severe multipath spreading, time delay spreading and doppler effect, and various fading characteristics caused thereby.

The Orthogonal Frequency Division Multiplexing (OFDM) technique has a high bandwidth utilization ratio and can effectively reduce Inter Symbol Interference (ISI) caused by the multipath effect of a channel, but OFDM also has the disadvantages of being susceptible to channel time variation and Frequency attenuation, having a high peak-to-average power ratio, being sensitive to phase difference, and the like. These disadvantages result in poor performance of OFDM modulation in frequency offset and in underwater acoustic channels where multipath is significant.

Dawn red, et al, proposed an Orthogonal Chirp Division Multiplexing (OCDM) underwater acoustic communication method (dawn red, marvelous, "a mobile underwater acoustic communication method", chinese patent publication No. CN107682297A), which uses Discrete Fractional fourier transform (DFRT) to replace the fourier transform in OFDM modulation, so as to rotate the subcarriers on the time-frequency plane, so that the subcarrier signals become a set of Orthogonal LFM signals. Namely, the OCDM changes the narrow-band subcarrier of the OFDM into the broadband signal, so that the broadband signal can have the frequency band utilization rate of the multi-carrier modulation technology and simultaneously improve the frequency attenuation resistance of the system. While information transmission still uses phase modulation to carry information on the subcarriers as OFDM modulation does. In the method, the further improvement of the system performance is not only dependent on the improvement of the performance of a receiving end equalization algorithm, but also the most direct way is to increase the subcarrier interval and reduce the interference among the subcarriers, thereby improving the system performance. However, under the condition of fixed subcarriers, increasing the subcarrier spacing means a decrease in effective subcarriers, so that the performance of the communication system is improved at the expense of the data transmission rate.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides an OCDM underwater acoustic communication method based on index modulation. In order to make up for the data rate sacrificed by improving the communication performance of the OCDM, the invention provides an index modulation-based OCDM underwater acoustic communication method, which combines a spatial modulation technology with the OCDM. And carrying information by utilizing the index position of the silent subcarrier while the active subcarrier transmits the phase modulation information. The invention reduces the effective sub-carrier number in the OCDM communication system so as to reduce the interference between sub-carriers, and simultaneously compensates the data rate loss caused by the reduction of the factor carrier number because the silent sub-carrier also carries information.

The technical scheme adopted by the invention for solving the technical problem comprises the following steps:

the method comprises the following steps: determining that the number of single symbol subcarriers is N, the index modulation order is M1, the phase modulation order is M, and the frequency domain interval is F;

step two: at the transmitting end of the communication system, serial-parallel conversion is carried out on the serial data stream after channel coding to obtain parallel data streams, and the length of each group of data streams isA bit;

step three: modulating the parallel data obtained in the second step, log₂The (M) bit data is used for selecting the index position of the active subcarrier, namely, the part of data information is carried on the index position of the active subcarrier; another part log₂The (M1) bit data is converted into phase information by phase modulationInformation, modulated on the active subcarriers; meanwhile, in order to eliminate ISI to the maximum extent, a fractional order domain guard interval is introduced in the mapping process, so that each group of data is activated after all data mapping is finishedA subcarrier; respectively performing inverse Fractional Fourier Transform (IDFRT) on the parallel data streams obtained in the second step, and obtaining a group of LFM signals with the same frequency modulation slope and different center frequencies after the IDFRT;

step four: respectively adding the parallel data streams obtained in the step three into a cyclic protection prefix;

step five: parallel data streams added with the cyclic prefixes in the step four are subjected to parallel-serial conversion and then transmitted through the energy converter;

step six: the receiving end carries out serial-to-parallel conversion on serial data received by the hydrophone after passing through the underwater acoustic channel;

step seven: respectively removing cyclic prefixes from the parallel data streams obtained through serial-parallel conversion in the step six;

step eight: respectively performing Fourier transform on the parallel data streams with the cyclic prefixes removed in the seventh step to convert time domain data into frequency domain data, equalizing the received data in the frequency domain by adopting Minimum Mean Square Error (MMSE), and converting the frequency domain data into time domain signals by inverse Fourier transform;

step nine: performing fractional order Fourier transform of corresponding orders on the time domain signals obtained in the step eight to obtain fractional order domain signals, and simultaneously removing the interval of sub-carriers of the fractional order domain;

step ten: searching the index position of the activated subcarrier for the fractional order domain signal obtained in the step nine so as to reflect the data information carried by the emission index position; then, phase modulation and demodulation are carried out on the phase information carried by the activated subcarrier to obtain the data information of the other part;

step eleven: and D, performing parallel-serial conversion on the demodulated parallel data information obtained in the step ten, and outputting the parallel data information.

The invention has the advantages that the information is carried by the index position of the activated subcarrier, so that the frequency shift resistance of the communication system is improved compared with the OCDM system due to the reduction of the effective subcarrier number, and the reduction of the data rate due to the reduction of the effective subcarrier number is compensated.

Drawings

FIG. 1 is a block diagram of an IM-OCDM underwater acoustic communication system of the present invention.

Fig. 2 is a schematic diagram of IM-OCDM subcarrier mapping according to the present invention.

Fig. 3 is a diagram of the fractional fourier transform energy focusing of the IM-OCDM subcarrier of the present invention.

FIG. 4 is a diagram of the error performance of IM-OCDM, OCDM and OFDM of the present invention.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

The technical scheme adopted by the invention for solving the technical problem comprises the following steps:

the method comprises the following steps: determining that the number of single symbol subcarriers is N, the index modulation order is M1, the phase modulation order is M, and the frequency domain interval is F;

step two: at the transmitting end of the communication system, serial-parallel conversion is carried out on the serial data stream after channel coding to obtain parallel data streams, and the length of each group of data streams isA bit;

step three: modulating the parallel data obtained in the second step, log₂The (M) bit data is used for selecting the index position of the active subcarrier, namely, the part of data information is carried on the index position of the active subcarrier; another part log₂(M1) converting the bit data into phase information by phase modulation, and modulating the phase information on the active sub-carrier; meanwhile, in order to eliminate ISI to the maximum extent, a fractional order domain guard interval is introduced in the mapping process, so that each group of data is activated after all data mapping is finishedA subcarrier; respectively performing inverse Fractional Fourier Transform (IDFRT) on the parallel data streams obtained in the second step, and obtaining a group of LFM signals with the same frequency modulation slope and different center frequencies after the IDFRT;

step four: respectively adding the parallel data streams obtained in the step three into a cyclic protection prefix;

step five: parallel data streams added with the cyclic prefixes in the step four are subjected to parallel-serial conversion and then transmitted through the energy converter;

step six: the receiving end carries out serial-to-parallel conversion on serial data received by the hydrophone after passing through the underwater acoustic channel;

step seven: respectively removing cyclic prefixes from the parallel data streams obtained through serial-parallel conversion in the step six;

step eight: respectively performing Fourier transform on the parallel data streams with the cyclic prefixes removed in the seventh step to convert time domain data into frequency domain data, equalizing the received data in the frequency domain by adopting Minimum Mean Square Error (MMSE), and converting the frequency domain data into time domain signals by inverse Fourier transform;

step nine: performing fractional order Fourier transform of corresponding orders on the time domain signals obtained in the step eight to obtain fractional order domain signals, and simultaneously removing the interval of sub-carriers of the fractional order domain;

step ten: searching the index position of the activated subcarrier for the fractional order domain signal obtained in the step nine so as to reflect the data information carried by the emission index position; then, phase modulation and demodulation are carried out on the phase information carried by the activated subcarrier to obtain the data information of the other part;

step eleven: and D, performing parallel-serial conversion on the demodulated parallel data information obtained in the step ten, and outputting the parallel data information.