A method for measuring distance using a wireless communication signal cycle structure

Abstract

This invention discloses a method for measuring distance using the cyclic structure of wireless communication signals. Addressing the issue of decreased ranging accuracy caused by the two-way multipath delay of OFDM signals exceeding the length of the single cyclic prefix (CP) after user reflection, this invention utilizes the CP cyclic structure of OFDM symbols, dividing the twice-CP length into two segments for cyclic correlation calculation. Common-mode interference is suppressed by taking the modulus ratio of the two correlation values, sharpening the symbol's initial peak value, and accurately locating the initial sampling position of the reflected symbol. The position is then converted into signal propagation time, and the distance between the base station and the communication user is calculated using the speed of light. This invention requires no dedicated sensing signal, does not alter the existing communication system or transmitter structure, and only adds software calculations at the receiver, with no additional hardware overhead. It is compatible with all six ISAC sensing modes, achieving high-precision and high-interference-resistance ranging while ensuring normal communication, and is suitable for 5G / 6G integrated communication and sensing systems.

Description

Technical Field

[0001] This invention relates to the field of signal processing in mobile communication systems, and specifically to a communication sensing integration (ISAC) ranging method based on an orthogonal frequency division multiplexing (OFDM) signal cyclic structure. Background Technology

[0002] Unlike fifth-generation mobile communication systems (5G), sixth-generation mobile communication systems (6G) will support six typical scenarios: immersive communication, ultra-large-scale connectivity, ultra-reliable low-latency communication, convergence of artificial intelligence and communication, convergence of sensing and communication (ISAC), and ubiquitous connectivity. From the current standardization process, 6G still uses multi-carrier modulation technology based on orthogonal frequency division multiplexing (OFDM) for its air interface, and uses polar codes and low-density parity-check codes (LDPC) as channel coding schemes.

[0003] By sensing parameters such as distance, speed, and radar cross section (RCS) of targets through wireless communication signals, ISAC can detect and track targets such as unmanned aerial vehicles (UAVs), vehicles, pedestrians, automated guided vehicles (AVGs), and ships; monitor infrastructure collapse and health; reconstruct the environment; and create digital twins. Currently, there are six main sensing schemes: 1) Single-base station mode, where the base station both transmits sensing signals and receives reflected signals from the target; 2) Dual-base station mode, where base station A transmits sensing signals and base station B receives reflected signals; 3) Base station-user mode, where the base station transmits sensing signals and user equipment (UE) receives reflected signals; 4) User-base station mode, where the UE transmits sensing signals and the base station receives reflected signals. Modes 5) and 6) are similar to modes 1) and 2), except that the base station is replaced by the UE.

[0004] In ISAC, when the sensing target is a communication user, communication must be maintained during the sensing process. In this case, a dedicated sensing signal cannot be used; instead, OFDM data symbols sent to the communication user must be used as the sensing signal. However, after the transmitted OFDM signal reaches the sensing target and returns, the delay spread of the multipath channel becomes greater than the length of the cyclic prefix (CP), which disrupts the orthogonality of the subcarriers and affects the sensing effect. Summary of the Invention

[0005] Purpose of the invention: In view of the above-mentioned prior art, this invention proposes a method for measuring distance using the cyclic structure of wireless communication signals, which solves the problem that in the prior art, the time delay spread of OFDM communication signals after being reflected by the user exceeds the single CP length, resulting in enhanced inter-symbol interference, decreased timing synchronization accuracy, and increased ranging error.

[0006] Technical solution: A method for measuring distance using the loop structure of wireless communication signals, comprising:

[0007] 1) The system settings include the number of subcarriers N, the cyclic prefix CP length G, and the number of observed symbols M for OFDM symbols;

[0008] 2) The base station sends OFDM signals to the communication users;

[0009] 3) After receiving the signal, the communication user removes the CP, performs a discrete Fourier transform to obtain the frequency domain signal, and then obtains the transmitted data information through processing including demodulation and decoding.

[0010] 4) The base station receives the transmitted signals reflected back from the communication users and obtains a continuous time-domain sampling sequence. , The sampling point number;

[0011] 5) Each base station calculates the first CP correlation value. And the second CP related value and according to and Calculate decision measure ;

[0012] 6) The base station searches within a consecutive (N+G) sampling point range. The maximum value determines the starting position of the OFDM symbol. ;

[0013] 7) The base station obtains the signal round-trip time based on the reception time and transmission time corresponding to the symbol's starting position, and calculates the distance to the communication user by combining the speed of light.

[0014] Furthermore, the first CP-related value in step 5). The calculation formula is:

[0015]

[0016] The second CP-related value The calculation formula is:

[0017] ;

[0018] in, express . conjugate.

[0019] Furthermore, in step 5), the decision measure... The calculation formula is:

[0020] ;

[0021] in, The operator indicates taking the modulus of a complex number.

[0022] Furthermore, in step 5), the decision measure... The calculation formula is:

[0023]

[0024] in, The operator indicates taking the modulus of a complex number.

[0025] Furthermore, in step 7), the base station determines the sampling period. Receive time Then, based on the receiving time... and sending time Calculate the round-trip time of the signal. The distance between the base station and the communication user is calculated based on this. , It is the speed of light.

[0026] Working Principle: This invention is based on the cyclic replication characteristic of OFDM symbols (CPs). Utilizing the channel law that the two-way propagation delay is less than twice the CP length, it suppresses inter-symbol interference through segmented correlation, achieving precise timing ranging. Specifically, the total length of the OFDM symbol is (N+G), and the CP is replicated from the G points at the tail of the symbol, exhibiting cyclic self-similarity. The single-way multipath delay is less than G, and the two-way multipath delay is less than 2G. The first CP interval has strong interference, while the second CP interval has weak interference. Cyclic correlation is performed on the two CP segments respectively, using the correlation modulus ratio to cancel common-mode interference, forming a sharp peak at the symbol's starting point. The peak is used to locate the symbol's starting position, the sampling position is converted into the reception time, and combined with the transmission time to obtain the propagation delay, ultimately calculating the distance.

[0027] Beneficial effects: 1. The ranging method of the present invention does not require a dedicated sensing signal and can complete ranging during normal communication, and is compatible with all six ISAC sensing modes.

[0028] 2. This method does not change the existing communication protocol, frame structure, or sending process; the receiving end does not require additional devices, only additional calculations.

[0029] 3. This method suppresses two-way multipath and inter-symbol interference through piecewise correlation and ratio calculation, resulting in high timing accuracy.

[0030] 4. This method only adds time-domain correlation calculations at the base station receiver, without requiring complex channel estimation and frequency-domain equalization, and the hardware modification is zero.

[0031] 5. This method is applicable to various scenarios such as single base station, dual base station, and base station-user reflection, and can be used for low-cost integrated 6G sensing deployment. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the principle of the single-base station sensing mode of the present invention.

[0033] Figure 2 This is a diagram of the multipath delay extension structure in this invention. Detailed Implementation

[0034] The invention will now be further explained with reference to the accompanying drawings.

[0035] A method for measuring the distance to a communication user using the cyclic structure of OFDM signals, the implementation steps of which are as follows:

[0036] Step 1: The system sets the number of subcarriers N, CP length G, and number of observed symbols M for OFDM symbols. In this embodiment, N=1024, G=72, M=8, and the total symbol length (N+G)=1096.

[0037] Step 2: The base station sends OFDM signals to the communication users. The signals use a conventional CP structure, and the transmission time is recorded as follows: .

[0038] Step 3: After receiving the signal, the communication user removes the CP, performs Discrete Fourier Transform (FFT), demodulation, channel decoding, and descrambling to restore the communication data without adding any additional sensing processing.

[0039] Step 4: The base station receives the transmitted signal reflected back from the communication user and obtains a continuous time-domain sampling sequence. , This is the sampling point number.

[0040] Step 5: The base station calculates the first CP correlation value. :

[0041] ;

[0042] The base station calculates the second CP correlation value. :

[0043] ;

[0044] Then calculate the decision measure. ;

[0045] in, express The conjugate; The operator indicates taking the modulus of a complex number.

[0046] Step 6: The base station is in Internal search maximum position That is, the starting position of the discrimination symbol.

[0047] Step 7: The base station operates according to the sampling period. Receive time .

[0048] Step 8: The base station determines the reception time. and sending time Calculate the round-trip time of the signal. The distance between the base station and the communication user is calculated based on this. , It is the speed of light.

[0049] The principle is explained as follows: Consider an OFDM system with N subcarriers and a cyclic prefix (CP) length of G samples. Taking a single base station mode as an example, the base station sends OFDM communication signals to the user and uses the reflected signals to measure the distance to the user, such as... Figure 1 As shown. After receiving the communication signal from the base station, the user removes the CP (Concurrent Path) and performs a Discrete Fourier Transform (FFT) to obtain the frequency domain signal. Then, through demodulation and decoding, the downlink data is obtained. Since the maximum multipath delay between the base station and the user is usually less than the CP length, the user can use traditional methods to receive the communication signal without any modifications, such as... Figure 1 As shown.

[0050] In practical communication systems, since the CP (Content Carrier) is merely a copy of the symbol tail and does not carry any useful information, its length is usually set to be only greater than the maximum multipath delay of a one-way multipath channel. Extending the CP length will lead to a significant loss of spectral efficiency. Therefore, the communication signal reflected back to the base station from the user has traveled twice the distance, and the maximum multipath delay will usually exceed the CP length, causing the subcarrier orthogonality to be destroyed and affecting the accuracy of the sensing process, such as... Figure 1 As shown.

[0051] Because the length of the CP (Cumulative Path) is greater than the maximum multipath delay for a single trip, the maximum delay spread for a round trip is typically less than twice the CP length. Meanwhile, within the CP length of the m-th symbol, the interference introduced by the multipath channel in the (m-1)-th symbol is very significant, only disappearing within the second CP length, such as... Figure 2 As shown, since the CP is a copy of its symbol tail, the CP of the m-th symbol still has the same signal components as its tail, except for the interference introduced by the (m-1)-th symbol, although the energy of the identical part is lower. Furthermore, since the multipath delay is greater than the CP length, the second CP of the m-th symbol still has the same signal components as the CP of the (m+1)-th symbol, and with higher energy. Therefore, the starting position of the symbol can be estimated using related methods.

[0052] If the number of observed symbols is M, the correlation value within the first CP is calculated as follows:

[0053] ;

[0054] The correlation values ​​within the second CP are obtained as follows:

[0055] ;

[0056] Because the interference within the first CP length is higher than that within the second CP length, meaning the first CP interval is severely affected by multipath interference from the previous symbol, The signal-to-interference ratio is relatively low, and the inter-symbol interference in the second CP interval is significantly reduced. It contains relatively strong effective cycle-related energy, therefore the ratios are as follows:

[0057] ;

[0058] Ratio calculations can suppress common-mode interference such as noise and channel fading, resulting in a significant peak at the symbol start point and achieving high-precision timing.

[0059] It is important to note that the starting point of the discriminant needs to be calculated from at least (N+G) points, and the position of the maximum value needs to be found among them, that is:

[0060] ;

[0061] Base station according to sampling period Get the receiving time Due to the time of sending symbols It is known that the round-trip time can be obtained by subtracting the two. Finally passed with the speed of light Multiplying these gives the distance to the communication user.

[0062] It should be noted that the result of addition can also be used as a criterion for judgment, that is: .

[0063] This method does not affect normal communication throughout the process, and distance measurement is achieved solely through software algorithms, making it suitable for large-scale integrated sensing system deployments.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for measuring distance using a loop structure of wireless communication signals, characterized in that, include: 1) The system settings include the number of subcarriers N, the cyclic prefix CP length G, and the number of observed symbols M for OFDM symbols; 2) The base station sends OFDM signals to the communication users; 3) After receiving the signal, the communication user removes the CP, performs a discrete Fourier transform to obtain the frequency domain signal, and then obtains the transmitted data information through processing including demodulation and decoding. 4) The base station receives the transmitted signals reflected back from the communication users and obtains a continuous time-domain sampling sequence. , The sampling point number; 5) Each base station calculates the first CP correlation value. And the second CP related value and according to and Calculate decision measure ; 6) The base station searches within a consecutive (N+G) sampling point range. The maximum value determines the starting position of the OFDM symbol. ; 7) The base station obtains the signal round-trip time based on the reception time and transmission time corresponding to the symbol's starting position, and calculates the distance to the communication user by combining the speed of light.

2. The method according to claim 1, characterized in that, The first CP-related value in step 5) The calculation formula is: The second CP-related value The calculation formula is: ； in, express . conjugate.

3. The method according to claim 1, characterized in that, Decision measure in step 5) The calculation formula is: ； in, The operator indicates taking the modulus of a complex number.

4. The method according to claim 1, characterized in that, Decision measure in step 5) The calculation formula is: in, The operator indicates taking the modulus of a complex number.

5. The method according to claim 1, characterized in that, In step 7), the base station determines the sampling period. Receive time ; Then based on the receiving time and sending time Calculate the round-trip time of the signal. The distance between the base station and the communication user is calculated based on this. , It is the speed of light.

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