A communication method and system integrating communication and ranging based on OFDM technology

Abstract

The present invention discloses a communication method and system integrating communication and ranging based on OFDM technology. First, at the transmitting end, according to the designed original communication, ranging and indication frame signals, a communication OFDM symbol frame, a ranging OFDM symbol frame and an indication frame OFDM symbol frame are generated, and their lengths are determined by the algorithm designed by the system; then they are combined into a communication-ranging frame structure to complete the framing process, and the signal is transmitted to the receiving end through a channel; at the receiving end, the received communication-ranging frame signal is subjected to sliding sampling, and the sampled data is correlated with the local sequence to obtain multiple correlation values; the maximum correlation value is obtained to complete the synchronization process of the received signal. Therefore, the present invention adopts the above-mentioned communication method and system integrating communication and ranging based on OFDM technology, and the frame structure generated by OFDM technology is composed of an indication frame, a ranging OFDM symbol frame and a communication OFDM symbol frame, so that the integrated design of communication and ranging can be realized.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a communication method and system integrating communication and ranging based on OFDM technology. Background Art

[0002] In today's society where information technology is developing rapidly, wireless communication technology has become popular in the lives of all people. Wireless communication technology is no longer limited to voice calls, it has been fully applied to business, life, finance and work. Mobile phones, voice calls, digital television, network communications, data exchange, etc., have all been born with the platform of wireless communication technology. People only need a mobile or terminal device to enjoy the convenient services such as voice or video calls, data and exchange, images and fax brought by wireless communication technology at any place and any time.

[0003] As an efficient modulation technology, OFDM (Orthogonal Frequency Division Multiplexing) originated from multi-carrier modulation (MCM) technology and has been widely used in various communication systems since the 1990s. At present, mobile communication can be said to be one of the most widely used and fastest-growing technologies in the current communication field. OFDM modulation technology has been widely used and developed in the fields of digital television, mobile communications, etc. The core idea of ​​OFDM modulation technology is to divide the channel into several orthogonal sub-channels, convert the high-speed data signal into a parallel low-speed self-data stream, and modulate it to each sub-channel for transmission. OFDM technology uses multi-channel sub-carrier modulation technology to make the system have strong anti-narrowband interference ability, uses channel estimation and channel balancing technology to make the system have strong anti-multipath fading ability, uses mutually orthogonal sub-carriers as sub-channels, allows the spectrum of sub-channels to overlap, and has high spectrum utilization. It uses high-order modulation to make the system have a higher transmission rate. Therefore, there are many people who use OFDM technology for communication at this stage, but there are not many people who can design integrated communication and ranging systems based on OFDM technology.

[0004] Nowadays, both communication and ranging systems have transceiver systems and use signal processing methods to extract information from received signals. Therefore, with the development of technology, when the performance indicators of the system's transmitting and receiving modules can meet the system indicator requirements of communication and ranging at the same time, the communication and ranging integration design is carried out, so that the transmitter or receiver is shared to reduce the equipment of the transceiver system, and the communication function and ranging function are met through signal design and signal processing, so that the signal used to transmit information between communication devices can also be used to measure the target distance of the surrounding environment. There is no doubt that the application potential and value of this integrated communication and ranging system are quite huge. Having two functions in one system can save hardware and thus reduce production costs. Frequency band resources can also be used more effectively, because communication and ranging no longer need to occupy separate frequency bands. In order to achieve the integrated design of communication and ranging, the system adopts OFDM technology to achieve the integrated design of communication and ranging. Summary of the invention

[0005] The purpose of the present invention is to provide a communication method and system integrating communication and ranging based on OFDM technology, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides a communication method and system integrating communication and ranging based on OFDM technology, comprising the following steps:

[0007] Step 1: setting the communication original information bit, the ranging original information bit and the indication frame original information bit;

[0008] Step 2: Perform M-order QAM modulation on the communication original information, the ranging original information, and the indication frame original information;

[0009] Step 3, performing serial / parallel conversion on the modulated communication sequence, ranging sequence, and indication frame sequence;

[0010] Step 4, performing OFDM carrier modulation on the data processed in step 3 to generate valid data of a communication OFDM symbol, a valid data portion of a ranging OFDM symbol, and a valid data portion of an indication frame symbol;

[0011] Step 5: Generate a cyclic prefix by copying a segment of data at the end of the valid data part of the communication, ranging, and indication frame symbol, and place the copy at the beginning of the OFDM valid symbol. The cyclic prefix and the valid data part of the communication, ranging, and indication frame OFDM symbol together constitute the communication, ranging, and indication frame OFDM symbol.

[0012] Step 6: Perform parallel / serial conversion on the symbol sequence, the converted communication OFDM symbols form a communication OFDM symbol frame, the converted ranging OFDM symbols form a ranging OFDM symbol frame, the indication frame, the ranging OFDM symbol frame and the communication OFDM symbol frame together form a communication-ranging frame, and finally send the modulated signal to the receiving end through the channel;

[0013] Step 7: The receiving end receives the communication-ranging frame signal, and performs sliding sampling on the received communication-ranging frame signal through a sliding window;

[0014] Step 8, the data sampled by the sliding window each time are correlated with the local sequence, and the correlation value is obtained according to the correlation calculation formula. The maximum correlation value is obtained by comparing the sizes of the correlation values, and the corresponding position information is obtained according to the maximum correlation value to complete the synchronization of the received signal;

[0015] Step nine, determining the beginning and the end of the ranging OFDM symbol frame structure according to the position information of the maximum point of the correlation value, obtaining the end of the indication frame according to the beginning of the ranging OFDM symbol frame, completing the synchronization of the indication frame, obtaining the indication frame signal, obtaining the beginning of the communication OFDM symbol frame according to the end of the ranging OFDM symbol frame, completing the synchronization of the communication OFDM symbol frame, and obtaining the communication OFDM symbol frame signal;

[0016] Step ten, perform serial / parallel conversion on the obtained indication frame signal and communication OFDM symbol frame signal, remove the cyclic prefix, and perform corresponding OFDM carrier demodulation, parallel / serial conversion, and QAM demodulation to obtain indication frame information and communication information, and complete the communication process.

[0017] Preferably, in step 1, the original communication information bit a=[a 0 ,a 1 ,a 2 ,...,a l-1 ]∈{0,1}, l is an even number, the original information bit of ranging b=[b 0 ,b 1 ,b 2 ...,b m-1 ]∈{0,1}, m is an even number, indicating the original information bits of the frame s is an even number, where the size of s needs to vary according to the design of the system, and the value of s needs to be sufficient to design and generate an OFDM symbol.

[0018] Preferably, in step 2, the original communication information is modulated by M-order QAM to obtain a sequence Perform M-order QAM modulation on the original ranging information to obtain the sequence Perform M-order QAM modulation on the original information of the indication frame to obtain the sequence where i = log 2 M.

[0019] Preferably, in step 3, the communication sequence after QAM modulation is Ranging sequence and indicates the frame sequence Perform serial / parallel conversion, that is, convert serial data into Q rows of parallel data for transmission.

[0020] Preferably, in step 4, the data processed in step 3 is subjected to OFDM carrier modulation (IFFT modulation) according to an exponential power greater than the minimum 2 of the number of data subcarriers to generate valid data parts of multiple communication OFDM symbols and valid data parts of ranging OFDM symbols, as well as a valid data part indicating a frame symbol,

[0021] The IFFT modulation formula is as follows:

[0022]

[0023] X[k] is N sub-mapping symbols in the frequency domain, where k = 1, 2, ..., N, and N samples are taken in one OFDM symbol period in the time domain; after N-point IFFT transformation, the N sub-mapping symbols X[k] in the frequency domain are modulated into one time domain sub-OFDM symbol x(n) by the corresponding N subcarriers at n of the N sampling points in the time domain.

[0024] Preferably, in step 5, the OFDM symbol after adding the cyclic prefix can be expressed as:

[0025]

[0026] Among them, N g is the sampling length of the cyclic prefix, and N b =N+N g It represents the sampling length of the OFDM symbol after adding the cyclic prefix. Let Tg be the time length of the cyclic prefix, T be the time length of the valid data part of the OFDM symbol, then the time length Tb of the OFDM symbol after adding the cyclic prefix is ​​expressed as:

[0027] T b =T+T g

[0028] in Δf represents the bandwidth of the subcarrier, and T g =N g ×T s , T s is the unit sampling time, expressed as Num is the number of IFFT changes.

[0029] Preferably, in step seven, the sliding window first starts data sampling from the beginning of the received signal, and then the starting position of the sliding window slides backward according to the unit sampling point interval, and the sliding sampling process is completed G times by continuously changing the starting position of the sliding window sampling.

[0030] Preferably, in step eight, the data sampled by the sliding window each time is correlated with the local sequence, and G correlation values ​​are obtained according to the correlation calculation formula. The maximum correlation value is obtained by comparing the G correlation values, and the corresponding position information i (i=0, 1, 2, ..., G-1) is obtained according to the maximum correlation value to complete the synchronization of the received signal, and then the signal delay t is calculated according to the formula d , the distance D between the transmitting and receiving ends is obtained according to the formula, and the ranging process is completed;

[0031] Assume that the sequence after sliding sampling of the received signal is r(n+i) and the correlation operation formula between the local sequence s(n) is:

[0032]

[0033] r rs (i) is the correlation value of the correlation operation result, where N s is the total number of sampling points of the local sequence s(n), i (i=0, 1, 2, ..., G-1) is the number of sliding backwards of the starting position of the sliding window, and after the sliding window slides backward i unit sampling points, the sliding sampling obtains r(n+i),

[0034]

[0035] Where S indicates the number of sampling points of the frame;

[0036] D=t d ×c

[0037] Where c = 3 × 10 8 m / s.

[0038] Preferably, in step 10, the obtained indication frame signal and the communication OFDM symbol frame signal are subjected to serial / parallel conversion, the cyclic prefix CP is removed, and the corresponding OFDM carrier demodulation (FFT demodulation), parallel / serial conversion, and QAM demodulation are performed to obtain the indication frame information. and communication information a'=[a' 0 ,a' 1 ,a' 2 ,...,a' l-1 ], the communication process is completed, and the FFT demodulation formula is as follows:

[0039]

[0040] Therefore, the present invention adopts the above-mentioned communication method and system integrating communication and ranging based on OFDM technology, which has the following beneficial effects:

[0041] 1. The OFDM technology of the present invention adopts multi-channel subcarrier modulation technology, so that the system has a strong ability to resist narrowband interference, adopts channel estimation and channel balancing technology, so that the system has a strong ability to resist multipath fading, adopts mutually orthogonal subcarriers as subchannels, allows the spectrum of subchannels to overlap, has high spectrum utilization, and adopts high-order modulation mode, so that the system has a higher transmission rate.

[0042] 2. The frame structure generated by the OFDM technology of the present invention is composed of an indication frame, a ranging OFDM symbol frame, and a communication OFDM symbol frame, which can realize an integrated design of communication and ranging. Specifically, by correlating the local signal with the received signal, both the ranging of the system and the communication synchronization process of the system are completed, which can save pilot insertion, save frequency and bandwidth overhead, and improve the bandwidth efficiency of the system.

[0043] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a flow chart of the steps of the present invention;

[0045] Figure 2 It is a structural diagram of the main information bits of the indication frame of the present invention;

[0046] Figure 3 It is a structural diagram of the OFDM symbol of the communication, ranging and indication frame of the present invention;

[0047] Figure 4 This is a communication and ranging OFDM symbol frame structure diagram of the present invention;

[0048] Figure 5 The flowchart of the algorithm for calculating the number of OFDM symbols for communication of the present invention;

[0049] Figure 6 The flowchart of the algorithm for measuring the number of OFDM symbols of the present invention;

[0050] Figure 7 This is a communication-ranging frame structure diagram of the present invention;

[0051] Figure 8 It is a flow chart of the algorithm related to the present invention;

[0052] Fig. 9 This is a flowchart of an embodiment of the present invention; DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0054] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the usual meanings understood by persons with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. The words "include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects. The terms "set", "install" and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal connection of two elements. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0055] Example

[0056] like Figure 1 As shown, the communication method and system of the present invention that integrates communication and ranging based on OFDM technology includes the following steps:

[0057] Step 1: Set the communication original information bit, the ranging original information bit and the indication frame original information bit. Communication original information bit a = [a 0 ,a 1 ,a 2 ,...,a l-1 ]∈{0,1}, l is an even number, the original information bit of ranging b=[b 0 ,b 1 ,b 2 ...,b m-1 ]∈{0,1}, m is an even number, indicating the original information bits of the frame s is an even number, where the size of s needs to vary according to the design of the system, and the value of s needs to be sufficient to design and generate an OFDM symbol.

[0058] Indicator frame original information bits: It is composed of the first 24 bits of main information bits and padding bits, of which 0 to 4 bits are used to indicate the modulation method used by the system, including QPSK, QAM16, QAM64, etc.; 6 to 16 bits are used to indicate the subcarrier information of the system, and 6 to 8 bits indicate the starting position of the subcarrier, 9 to 12 bits indicate the number of data subcarriers selected by the system, 13 to 16 bits indicate the interval size between data subcarriers; 19 to 22 bits are used to indicate the data transmission rate. In addition to the above bit segments, some bits are reserved for later use. The structure of the main information bits of the indicator frame is as follows: Figure 2 shown.

[0059] Step 2: Perform M-order QAM modulation on the original communication information to obtain the sequence Perform M-order QAM modulation on the original ranging information to obtain the sequence Perform M-order QAM modulation on the original information of the indication frame to obtain the sequence where i = log 2 M.

[0060] There can be many digital modulation methods for each original information, such as QPSK, 16QAM, 64QAM and higher-order QAM methods. The present invention comprehensively considers the performance of noise and interference robustness and frequency band utilization, and adopts the 16QAM modulation method.

[0061] Step 3: QAM modulated communication sequence Ranging sequence and indicates the frame sequence Perform serial / parallel conversion, that is, convert serial data into Q (the number of data subcarriers) rows of parallel data for transmission.

[0062] Step 4, the data processed in step 3 is modulated by OFDM carrier (IFFT modulation) according to an exponential power greater than the minimum 2 of the number of data subcarriers, generating a valid data portion (C-DATA) of multiple communication OFDM symbols and a valid data portion (R-DATA) of the ranging OFDM symbol, as well as a valid data portion (I-DATA) of an indication frame symbol. In addition, the carrier modulation is performed in an exponential power greater than the minimum 2 of the number of data subcarriers in order to increase the sampling points while directly performing fast Fourier transform. Because when the number of sampling points is too small, the sample values ​​output by the sampling points often cannot accurately reflect the characteristics of continuous OFDM symbols, and after the sampling values ​​are restored, the high-frequency components in the signal will be interfered and inaccurate.

[0063] The IFFT modulation (IDFT) formula is as follows:

[0064]

[0065] X[k] is N sub-mapping symbols in the frequency domain, where k = 1, 2, ..., N, and N samples are taken in one OFDM symbol period in the time domain. After N-point IFFT transformation, the N sub-mapping symbols X[k] in the frequency domain are modulated into one time-domain sub-OFDM symbol x(n) by the corresponding N subcarriers at the N sampling points n in the time domain.

[0066] Step 5: Generate a cyclic prefix (CP) by copying a segment of data at the end of the effective data portion of the communication, ranging, and indication frame symbol, and place the copy at the beginning of the effective OFDM symbol to maintain the orthogonality of the subcarriers and eliminate inter-carrier interference. The cyclic prefix and the effective data portion of the communication, ranging, and indication frame OFDM symbol together constitute the communication, ranging, and indication frame OFDM symbol. The symbol structure diagram is shown in the figure below. Figure 3 shown.

[0067] The OFDM symbol after adding the cyclic prefix can be expressed as:

[0068]

[0069] Among them, N g is the sampling length of the cyclic prefix, and N b =N+N g It represents the sampling length of the OFDM symbol after adding the cyclic prefix. Let Tg be the time length of the cyclic prefix, T be the time length of the effective data part of the OFDM symbol, then the time length Tb of the OFDM symbol after adding the cyclic prefix is ​​expressed as:

[0070] T b =T+T g

[0071] in Δf represents the bandwidth of the subcarrier. g =N g ×T s , T s is the unit sampling time, expressed as Num is the number of IFFT changes.

[0072] The principle of adding cyclic prefix: One of the main advantages of OFDM technology is that it can effectively resist the multipath delay effect. In order to solve the inter-symbol interference (ISI) that may occur in the system, it is necessary to insert a guard interval (GI) of a certain length between each OFDM symbol. Usually, the length of the guard interval Tg is not less than the maximum delay spread τ of the channel. max , that is, Tg ≥ τmax . In this way, a symbol will not overlap with the valid data part of the next symbol when affected by multipath delay. In addition, in order to avoid inter-carrier interference (ICI) caused by direct zero padding, a cyclic prefix (CP) is filled in the protection interval of the OFDM symbol, that is, the time domain information of the length Tg after the OFDM symbol after IFFT transformation is copied to the header. After adding the cyclic prefix, the multipath part of the signal subcarrier only changes the arrangement order of the time domain information within the FFT time length, but because the signal maintains integrity, according to the cyclic characteristics of the Fourier transform, the multipath component does not destroy the orthogonality between subcarriers, effectively avoiding the impact of ICI.

[0073] Step 6: Perform parallel / serial conversion on the above symbol sequence. Multiple converted communication OFDM symbols form a communication OFDM symbol frame. Multiple converted ranging OFDM symbols form a ranging OFDM symbol frame. The structure of the communication and ranging OFDM symbol frames is as follows: Figure 4 As shown in FIG. 1 , the indication frame, the ranging OFDM symbol frame and the communication OFDM symbol frame together form a communication-ranging frame. Finally, the above modulated signal is sent to the receiving end through the channel.

[0074] Communication OFDM symbol frame structure: The communication OFDM symbol frame is composed of multiple communication OFDM symbols connected in series, and the number of communication OFDM symbols is determined under the constraints of the communication bit error rate parameters according to different non-ideal channel conditions (multipath effect, noise, etc.). The algorithm flow chart for determining the number of communication OFDM symbols is as follows: Figure 5 shown.

[0075] Ranging OFDM symbol frame structure: The ranging OFDM symbol frame is composed of multiple ranging OFDM symbols connected in series, and the number of ranging OFDM symbols is determined under the constraints of ranging error parameters and according to different non-ideal channel conditions (multipath effect, noise, etc.). The algorithm flow chart for determining the number of ranging OFDM symbols is as follows: Figure 6 shown.

[0076] Communication-ranging frame structure: It consists of indication frame structure, ranging OFDM symbol frame structure and communication OFDM symbol frame structure. The structure diagram of communication-ranging OFDM frame is as follows: Figure 7 shown.

[0077] Step 7: The receiving end receives the communication-ranging frame signal and performs sliding sampling on the received communication-ranging frame signal through a sliding window. First, the sliding window starts to sample data from the beginning of the received signal, and then the starting position of the sliding window slides back according to the unit sampling point interval. By continuously changing the starting position of the sliding window sampling, the G sliding sampling process is completed. In this process, the size of the sliding window remains unchanged, and the size of the sliding window is the same as the size of the local sequence (the transmitting end ranging OFDM symbol frame).

[0078] Step 8: Correlate the data sampled by the sliding window each time with the local sequence, obtain G correlation values ​​according to the correlation calculation formula, obtain the maximum correlation value by comparing the G correlation values, and obtain the corresponding position information i (i=0, 1, 2, ..., G-1) according to the maximum correlation value to complete the synchronization of the received signal, and then calculate the signal delay t according to the formula d , the distance D between the transmitter and receiver is obtained according to the formula, and the ranging process is completed.

[0079] Assume that the sequence after sliding sampling of the received signal is r(n+i) and the correlation operation formula between the local sequence s(n) is:

[0080]

[0081] r rs (i) is the correlation value of the correlation operation result. s is the total number of sampling points of the local sequence s(n), i (i=0, 1, 2, ..., G-1) is the number of sliding backwards of the starting position of the sliding window, and after the sliding window slides backward i unit sampling points, the sliding sampling obtains r(n+i),

[0082]

[0083] Where S indicates the number of sampling points in the frame.

[0084] D=t d ×c

[0085] Where c = 3 × 10 8 m / s.

[0086] Step nine, determine the beginning and end of the ranging OFDM symbol frame structure according to the position information of the maximum correlation value point. According to the beginning of the ranging OFDM symbol frame, obtain the end of the indication frame, complete the synchronization of the indication frame, and obtain the indication frame signal. According to the end of the ranging OFDM symbol frame, obtain the beginning of the communication OFDM symbol frame, complete the synchronization of the communication OFDM symbol frame, and obtain the communication OFDM symbol frame signal.

[0087] Step 10: Perform serial / parallel conversion on the obtained indication frame signal and communication OFDM symbol frame signal, remove the cyclic prefix CP, and perform corresponding OFDM carrier demodulation (FFT demodulation), parallel / serial conversion, and QAM demodulation to obtain the indication frame information. and communication information a'=[a' 0 ,a' 1 ,a' 2 ,...,a' l-1 ] to complete the communication process.

[0088] The FFT demodulation (DFT) formula is as follows:

[0089]

[0090] In this example, the transmitter and receiver use a software radio module called ADALM-PLUTO, which supports full-duplex operation, instantaneous bandwidth up to 20MHz, and supports MATLAB and Simulink development environments. The overall workflow of the system is shown in the figure below. Fig. 9 shown.

[0091] Step 1: Connect the ADALM-PLUTO software radio to the computer via a USB data cable to form the transmitter, start the MATLAB software, and design the parameters of the ADALM-PLUTO software radio. Then connect another ADALM-PLUTO software radio to another computer via a USB data cable to form the receiver, and then start the MATLAB software to design the parameters of the ADALM-PLUTO software radio. For transmitter design, use the rand() function in MATLAB to randomly generate two groups of 0 and 1 bit sequences as ranging information and communication information respectively, and design and generate the original information bit sequence of the indication frame.

[0092] Step 2: Then the generated sequence is digitally modulated using the MQAM mapping method. Taking into account the robustness to noise and interference and the frequency band utilization, this system mainly uses the 16QAM mapping method to output the mapped complex data.

[0093] Step 3: After mapping, serial complex data is obtained. According to the system design, according to the number of data subcarriers 1200, the data is converted into 1200 lines of parallel data for transmission through serial-to-parallel conversion.

[0094] Step 4: FFT modulation must satisfy the exponential power of 2 greater than the minimum number of subcarriers. The number of subcarriers in this system is 1200, so a 2048-point IFFT change is used, that is, zero is added to the following 1201 to 2048 subcarriers, which is equivalent to oversampling the system. When the number of sampling points is too small, the output sample value of the sampling point often cannot accurately reflect the characteristics of continuous OFDM symbols. After the sampling is restored, the high-frequency components of the signal are interfered and inaccurate, so a 2048-point IFFT is used to increase the sampling points while directly performing Fourier transform. At this time, the output obtains the valid data part of multiple communication OFDM symbols, the valid data part of multiple ranging OFDM symbols, and the valid data part of an indication frame symbol.

[0095] Step 5: The multipath effect generated by the multipath channel will cause symbol interference between OFDM symbols, which will destroy the orthogonality of the subcarriers in the OFDM symbol. In order to eliminate this effect, a cyclic prefix (cp) is added in the protection interval, and the length of the cyclic prefix should be greater than the maximum delay spread. The number of IFFT modulation points is 2048, and the cyclic prefix is ​​the last 144 points of the 2048 modulation points, and the 144 points of the cyclic prefix are placed at the front end of the 2048 modulation points. Therefore, cyclic prefixes are added to the valid data parts of multiple communication OFDM symbols, multiple ranging OFDM symbols, and one indication frame symbol respectively, to obtain multiple communication OFDM symbols, multiple ranging OFDM symbols, and one indication frame OFDM symbol.

[0096] The total channel bandwidth of this system is 20MHz, the subcarrier spacing is Δf=15KHz, there are 1200 subcarriers, then 1200*15KHz=18MHz, and the remaining 2MHz is the protection bandwidth. Then the length of the effective data part of an OFDM symbol is:

[0097] T OFDM =1 / Δf≈66.67μs

[0098] This system uses 2048-point IFFT, so the sampling interval of OFDM symbols is:

[0099] T s =1 / (Δf×2048)≈32.55ns

[0100] The guard interval length (cyclic prefix) is:

[0101] T g =144×T s ≈4.69μs

[0102] Step 6: After adding the guard interval, the processing of the OFDM symbol transmitter is completed. Because the signal is transmitted serially in the channel, the parallel-to-serial conversion is performed before framing, and then the modulated OFDM symbol is transmitted according to Figure 7 The designed frame structure is framed. The framed structure consists of an indication OFDM symbol frame, a ranging OFDM symbol frame, and a communication OFDM symbol frame. The generated ranging OFDM symbol frame can be stored as a local signal and called when needed to save operation time.

[0103] The algorithm flow chart for obtaining the number of ranging OFDM symbols is as follows: Figure 6 As shown, first set the system's multipath number path, SNR value snr, set the ranging error parameter to D_error_target, Monte Carlo value CNT, then the system simulation will start from a ranging OFDM symbol, according to the Monte Carlo value CNT, perform CNT simulations, average the CNT simulation errors obtained, and get the mean error D_error_final, then compare the obtained mean error D_error_final with the error parameter D_error_target, if it is less than the error parameter, output the number of ranging OFDM symbols at this time, otherwise, add one to the number of ranging OFDM symbols, and repeat the above process until the required number of ranging OFDM symbols is obtained.

[0104] The algorithm flow chart of the number of communication OFDM symbols is as follows Figure 5 As shown, first set the system's multipath number path, SNR value snr, set the bit error rate parameter to BER_target, Monte Carlo value CNT, set the initial number of data subcarriers, and then the system simulation will start from the initial number of data subcarriers. According to the Monte Carlo value CNT, CNT simulations are performed, and the CNT simulation bit error rates are averaged to obtain the mean error BER_final. Then the mean error BER_final is compared with the bit error rate parameter BER_target. If it is less than the error parameter, the number of data subcarriers at this time is output. Otherwise, the number of data subcarriers is reduced by 2, and the above process is repeated until the number of data subcarriers that meet the requirements is obtained. Then the number of communication OFDM symbols is obtained according to the system design.

[0105] Step 7: Receiver design, synchronization is a key issue in the communication system. Synchronization in digital communication mainly includes time synchronization and carrier frequency synchronization. This system completes synchronization and delay time calculation through the correlation operation of ranging OFDM symbols. While realizing the ranging function, it also completes the synchronization of communication information. The starting end of the communication OFDM symbol frame and the tail end of the indication frame are found. The communication OFDM symbol frame is converted from serial to parallel, and the cyclic prefix is ​​removed. FFT demodulation and cp removal are the inverse processes of the corresponding modules at the transmitting end. In order to enable the source data to be transmitted in the channel, the data is mapped to a constellation diagram at the transmitting end, and the data bit stream is mapped into an analog form. Therefore, when the data is recovered at the receiving end, demodulation corresponding to the mapping method of the transmitting end is required. Finally, the communication information and indication frame information are obtained.

[0106] The flowchart of the relevant algorithm is as follows Figure 8 As shown:

[0107] First, the size of the sliding window is the same as the size of the local sequence (the transmitting end ranging OFDM symbol frame), and the sliding window performs sliding sampling on the received communication-ranging frame signal. First, the sliding window starts to sample data from the beginning of the received signal, and then the starting position of the sliding window slides back according to the unit sampling point interval. By continuously changing the starting position of the sliding window sampling, the G-time sliding sampling process is completed. In this process, the size of the sliding window remains unchanged, and the data sampled by the sliding window each time is correlated with the local sequence. The data sampled by the sliding window each time is correlated with the local sequence, and the G-time correlation value is obtained according to the correlation calculation formula. The maximum correlation value is obtained by comparing the size of the G-time correlation value, and the corresponding position information i (i=0,1,2,...,G-1) is obtained according to the maximum correlation value to complete the synchronization of the received signal.

[0108] Taking 16QAM as an example, the total system bandwidth is 20MHz, the subcarrier bandwidth is 15khz, there are Nc=1200 subcarriers, and an OFDM symbol can carry up to 7200 bits of information. The highest communication rate shown is Vt=Nc×log2(16)÷(Ts×2048)=18Mbps.

[0109] The system parameters of the OFDM technology in the system are shown in the following table.

[0110] Table 1 OFDM technical solution system parameters

[0111]

[0112]

[0113] Therefore, the present invention adopts the above-mentioned communication method and system integrating communication and ranging based on OFDM technology. The frame structure generated by OFDM technology consists of an indication frame, a ranging OFDM symbol frame, and a communication OFDM symbol frame, which can realize the integrated design of communication and ranging. By correlating the local signal with the received signal, the ranging of the system is completed, and the communication synchronization process of the system is also completed, which can save pilot insertion, save frequency and bandwidth overhead, and improve the bandwidth efficiency of the system.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A communication method and system integrating communication and ranging based on OFDM technology, Features: The following steps are involved: Step 1: setting the communication original information bit, the ranging original information bit and the indication frame original information bit; Step 2: Perform M-order QAM modulation on the communication original information, the ranging original information, and the indication frame original information; Step 3, performing serial / parallel conversion on the modulated communication sequence, ranging sequence, and indication frame sequence; Step 4, performing OFDM carrier modulation on the data processed in step 3 to generate valid data C-DATA of the communication OFDM symbol, valid data part R-DATA of the ranging OFDM symbol, and valid data part I-DATA of an indication frame symbol; Step 5: Generate a cyclic prefix by copying the time domain information of length Ng at the end of the effective data part of the communication, ranging, and indication frame symbol, and place the copy at the beginning of the OFDM effective symbol. The cyclic prefix and the effective data part of the communication, ranging, and indication frame OFDM symbol together constitute the communication, ranging, and indication frame OFDM symbol. Step 6: Perform parallel / serial conversion on the symbol sequence, the converted communication OFDM symbols form a communication OFDM symbol frame, the converted ranging OFDM symbols form a ranging OFDM symbol frame, the indication frame, the ranging OFDM symbol frame and the communication OFDM symbol frame together form a communication-ranging frame, and finally send the modulated signal to the receiving end through the channel; Step 7: The receiving end receives the communication-ranging frame signal, and performs sliding sampling on the received communication-ranging frame signal through a sliding window; Step 8, the data sampled by the sliding window each time are correlated with the local sequence respectively, the local sequence refers to the OFDM symbol frame of the transmitter ranging, the correlation value is obtained according to the correlation calculation formula, the maximum correlation value is obtained by comparing the size of the correlation value, and the sliding back number i of the corresponding position information sliding window is obtained according to the maximum correlation value, i=0, 1, 2, ..., G-1, and the synchronization of the received signal is completed; Step nine, determining the beginning and the end of the ranging OFDM symbol frame structure according to the position information of the maximum point of the correlation value, obtaining the end of the indication frame according to the beginning of the ranging OFDM symbol frame, completing the synchronization of the indication frame, obtaining the indication frame signal, obtaining the beginning of the communication OFDM symbol frame according to the end of the ranging OFDM symbol frame, completing the synchronization of the communication OFDM symbol frame, and obtaining the communication OFDM symbol frame signal; Step ten, perform serial / parallel conversion on the obtained indication frame signal and communication OFDM symbol frame signal, remove the cyclic prefix, and perform OFDM carrier demodulation, parallel / serial conversion, and QAM demodulation to obtain indication frame information and communication information, and complete the communication process.

2. The communication method and system integrating communication and ranging based on OFDM technology according to claim 1, Features: In step 1, the original communication information bit a = [a 0 ,a 1 ,a 2 ,...,a l-1 ]∈{0,1}, l is an even number, the original information bit of ranging b=[b 0 ,b 1 ,b 2 ...,b m-1 ]∈{0,1}, m is an even number, indicating the original information bits of the frame s is an even number, where the size of s needs to vary according to the design of the system, and the value of s needs to be sufficient to design and generate an OFDM symbol.

3. The communication method and system integrating communication and ranging based on OFDM technology according to claim 2, Features: In step 2, the original communication information is modulated by M-order QAM to obtain the sequence Perform M-order QAM modulation on the original ranging information to obtain the sequence Perform M-order QAM modulation on the original information of the indication frame to obtain the sequence where i = log 2 M.

4. The communication method and system integrating communication and ranging based on OFDM technology according to claim 3, Features: In step 3, the communication sequence after QAM modulation Ranging sequence and indicates the frame sequence Perform serial / parallel conversion, that is, convert serial data into Q rows of parallel data for transmission.

5. The communication method and system integrating communication and ranging based on OFDM technology according to claim 4, Features: In step 4, the data processed in step 3 is modulated by OFDM carrier according to an exponential power greater than the minimum 2 of the number of data subcarriers. Here, OFDM carrier modulation is completed using an IFFT modulation method to generate valid data parts of multiple communication OFDM symbols and valid data parts of ranging OFDM symbols, as well as a valid data part of an indication frame symbol. The IFFT modulation formula is as follows: X[k] is N sub-mapping symbols in the frequency domain, where k = 1, 2, ..., N, and N samples are taken in one OFDM symbol period in the time domain; after N-point IFFT transformation, the N sub-mapping symbols X[k] in the frequency domain are modulated into one time domain sub-OFDM symbol x(n) by the corresponding N subcarriers at n of the N sampling points in the time domain.

6. The communication method and system integrating communication and ranging based on OFDM technology according to claim 5, Features: In step 5, the OFDM symbol after adding the cyclic prefix is ​​expressed as: Among them, N g is the sampling length of the cyclic prefix, and N b =N+N g It represents the sampling length of the OFDM symbol after adding the cyclic prefix. Let Tg be the time length of the cyclic prefix, T be the time length of the valid data part of the OFDM symbol, then the time length Tb of the OFDM symbol after adding the cyclic prefix is ​​expressed as: T b =T+T g in Δf represents the bandwidth of the subcarrier, and T g =N g ×T s , T s is the unit sampling time, expressed as Num is the number of IFFT changes.

7. The communication method and system integrating communication and ranging based on OFDM technology according to claim 6, Features: In step seven, the sliding window first starts to sample data from the beginning of the received signal, and then the starting position of the sliding window slides backward according to the unit sampling point interval. By continuously changing the starting position of the sliding window sampling, the G sliding sampling process is completed.

8. The communication method and system integrating communication and ranging based on OFDM technology according to claim 7, Features: In step eight, the data sampled by the sliding window each time is correlated with the local sequence, and the G-time correlation value is obtained according to the correlation calculation formula. The maximum correlation value is obtained by comparing the G-time correlation value, and the corresponding position information i (i=0, 1, 2, ..., G-1) is obtained according to the maximum correlation value to complete the synchronization of the received signal, and then the signal delay t is calculated according to the formula d , the distance D between the transmitting and receiving ends is obtained according to the formula, and the ranging process is completed; Assume that the sequence after sliding sampling of the received signal is r(n+i) and the correlation operation formula between the local sequence s(n) is: r rs (i) is the correlation value of the correlation operation result, where N s is the total number of sampling points of the local sequence s(n), i (i=0, 1, 2, ..., G-1) is the number of sliding backwards of the starting position of the sliding window, and after the sliding window slides backward i unit sampling points, the sliding sampling obtains r(n+i), Where S indicates the number of sampling points of the frame; D=t d ×c Where c = 3 × 10 8 m / s.

9. The communication method and system integrating communication and ranging based on OFDM technology according to claim 8, Features: In step 10, the obtained indication frame signal and communication OFDM symbol frame signal are converted into serial / parallel, the cyclic prefix CP is removed, and OFDM carrier demodulation, parallel / serial conversion, and QAM demodulation are performed. Here, OFDM carrier modulation is completed using the FFT demodulation method to obtain the indication frame information. and communication information a'=[a' 0 ,a 1 ',a' 2 ,...,a l ' -1 ], the communication process is completed, and the FFT demodulation formula is as follows:

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