A random access preamble detection method for aviation communications

Abstract

The present invention provides a random access preamble detection method for aviation communications, and proposes a scheme based on shifted partial merging-assisted peak detection and dual-end correlation-assisted round-trip delay estimation. The steps of the scheme mainly include: constructing a communication system model, dividing the received signal, merging shifted correlation windows to construct a super window, detecting the signal peak within the super window, calculating the overall round-trip delay estimate based on the signal peak point, and completing the random access preamble detection. On the one hand, the present invention designs a shifted partial merging-assisted peak detection algorithm based on the short preamble format, and the algorithm can provide better detection performance and higher spectrum efficiency, while supporting large coverage and resisting high Doppler effects. On the other hand, the present invention also designs a round-trip delay estimation method, which performs a cross-correlation operation at both ends of the coarse preamble position detected by the shifted partial merging method, thereby achieving more robust round-trip delay estimation.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation communications, and more particularly to a random access preamble detection method for aviation communications. Background Art

[0002] With the rapid development of air transportation, aeronautical communications have become a promising wireless technology to meet the rapidly growing demand for inflight data services. Similar to terrestrial networks, aerial user equipment (AUE) uses a random access procedure for initial access. More specifically, the AUE sends a preamble to the base station (BS) to obtain uplink time synchronization. The 5G New Radio (NR) standard specifies several random access preamble formats based on Zadoff-Chu (ZC) sequences to support scenarios with varying coverage requirements and AUE mobility. The long preamble format utilizes a small subcarrier spacing to support a maximum cell radius of 57 km but is susceptible to large doppler shift. The short preamble format, which utilizes a larger subcarrier spacing, mitigates large doppler shift but, due to the use of a shortened cyclic prefix (CP), only supports a cell radius of 9 km. In aviation communications scenarios, AUEs can reach speeds exceeding 1080 km / h. Furthermore, aviation communication networks must not only support highly mobile AUEs but also provide coverage of approximately 100 to 400 km. However, such long propagation delays require the use of long CPs to compensate, resulting in reduced spectrum efficiency.

[0003] To alleviate the above problems, scholars have proposed a variety of joint-peak detection (JPD) technologies based on long preamble formats, such as paired ZC sequence aided JPD (PZC-JPD) in “Improved preamble detection and round-trip delay estimation for random access in high-mobility airborne communication systems”, concatenated two-root ZC sequence aided JPD (C2RZC-JPD) in “Root pair selection for two-root random access preamble”, and concatenated conjugate ZC sequence aided JPD (CCZC-JPD) in “Random access preamble design for 3GPP non-terrestrial networks”. Although these JPD-based solutions can overcome the Doppler effect in high-mobility scenarios and ensure large cell coverage, they consume more time resources due to the use of longer preamble and random access duration to handle the large round trip delay (RTD) of AUE. Summary of the Invention

[0004] To overcome the drawback of the prior art in using longer preamble and random access durations to handle the large round-trip delay of AUE, resulting in large consumption of time resources, the present invention provides a random access preamble detection method for aviation communications. A scheme based on shifted partial combination (SPC)-assisted peak detection and dual-end correlation (DEC)-assisted RTD estimation, denoted as SPC and DEC assisted preamble detection (SPC-DEC-PD) scheme, is proposed. This scheme, based on a short preamble format, can provide better detection performance and higher spectrum efficiency, while supporting large coverage and resisting high Doppler effects. Furthermore, it can achieve more robust RTD estimation.

[0005] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0006] A random access preamble detection method for aviation communications, comprising the following steps:

[0007] S1: Establishing an aviation communication system based on orthogonal frequency division multiplexing, in which an airborne user equipment transmits a signal to a base station via a PRACH resource block;

[0008] S2: Obtain a received signal from the base station, divide the PRACH resource block into a plurality of shift correlation windows, obtain a received signal from each shift correlation window, and perform signal preprocessing;

[0009] S3: Merge K consecutive shifted correlation windows to construct a super window, and detect the signal peak point and its corresponding peak value within the super window; wherein K is the number of OFDM symbols included in the preset random access preamble;

[0010] S4: Determine whether the signal peak value within the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and execute step S5; otherwise, the random access preamble does not exist, and re-execute step S2 to re-acquire a new received signal;

[0011] S5: Calculating an estimated value of the fractional round trip delay according to the signal peak point within the super window;

[0012] intercepting the received signal of the base station according to the signal peak point and the estimated value of the fractional round-trip delay within the super window to obtain a first intercepted signal and a second intercepted signal;

[0013] S6: constructing a first discriminant factor and a second discriminant factor according to the first intercepted signal and the second intercepted signal, and calculating an estimated value of the integer round-trip delay in combination with the signal peak point within the super window;

[0014] An overall round-trip delay estimate is obtained according to the estimated value of the fractional round-trip delay and the estimated value of the integer round-trip delay, and random access preamble detection is completed.

[0015] Preferably, in step S1, the aviation communication system based on orthogonal frequency division multiplexing includes a base station and several airborne user equipments, each airborne user equipment has one transmitting antenna, and the base station has several receiving antennas. ;

[0016] The time-frequency resources in the aviation communication system are allocated into a plurality of PRACH resource blocks, and the airborne user equipment sends a signal to the base station through the PRACH resource blocks and initiates a random access process;

[0017] A PRACH resource block occupies subcarriers, with a duration in the time domain of ; The subcarrier spacing of the aviation communication system is , the duration of an OFDM symbol is The length of the fast Fourier transform used in the aviation communication system and the length of an OFDM symbol are both , the sampling interval is , the length of a PRACH resource block is ;

[0018] In the random access process, each air user equipment randomly selects a preamble sequence from a predefined set of preamble sequences that satisfies Leading sequence of conditions , using the selected leading sequence Generate a random access preamble and send it to the base station in a PRACH resource block, where: Represents a complex set; the random access preamble adopts a preamble structure without a cyclic prefix, The length of the repetition is OFDM symbols, the total length of the random access preamble is .

[0019] Preferably, the use of the selected leader sequence Generate a random access preamble, including:

[0020] The airborne user equipment passes Point discrete Fourier transform calculation frequency domain sequence , expressed as ,in represents the discrete Fourier transform matrix, whose elements are ,in ;

[0021] The frequency domain sequence Mapped to the subcarriers of the PRACH resource block and used Point-wise inverse fast Fourier transform to generate OFDM symbols , expressed as:

[0022]

[0023] in, is an intermediate variable, satisfying ; is the subcarrier mapping matrix, satisfying , represents the field of real numbers; is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable Also satisfied ;

[0024] The OFDM symbol Each element in is represented as:

[0025]

[0026] The generated random access preamble Depend on Repeated Cascaded, expressed as: ;

[0027] The random access preamble Each element in is represented as:

[0028]

[0029] in, is the binarization coefficient, if ,but ,otherwise ; Representation model operate.

[0030] Preferably, in the aviation communication system, the random access preamble The assumptions that the BS does not exist and exists in the received signal are respectively denoted as and ;

[0031] In the assumption In the PRACH resource block, Received signal from antenna for:

[0032]

[0033] in, The power spectral density is Additive Gaussian white noise; ; ;

[0034] In the assumption In the PRACH resource block, Received signal from antenna for:

[0035]

[0036] in, The combined effect of non-line-of-sight signals and noise satisfies ; is the transmit power, is the path loss coefficient, and They are line-of-sight and non-line-of-sight channel coefficients, satisfying ; is the round-trip delay of the line-of-sight channel; It is the delay of the non-line-of-sight channel relative to the line-of-sight channel.

[0037] Preferably, in step S2, obtaining the received signal of each shifted correlation window includes:

[0038] The length is The PRACH resource block is divided into shift correlation windows, each of which has a length of ;

[0039] The vector formed by the signal in each shift correlation window is recorded as: ,in ; ;

[0040] In the assumption Under the above conditions, the received signal of each shifted correlation window contains only additive white Gaussian noise;

[0041] In the assumption The received signal of each shifted correlation window is expressed as:

[0042]

[0043] in, ;

[0044] The round-trip delay of the line-of-sight channel Expressed as ,in , , and Represents the round-trip delay Relative to OFDM symbol length The integer and fractional parts of .

[0045] Preferably, in step S2, the signal preprocessing includes:

[0046] Perform fast Fourier transform and subcarrier demapping operations on the signal in each shift correlation window to extract the frequency domain signal, and compare the frequency domain signal with the phase-shifted frequency domain sequence. Correlation is performed to obtain the preprocessed signal within each shift correlation window, which is expressed as:

[0047]

[0048] in, ,express Point fast Fourier transform and subcarrier demapping operations; is the preset number of phases;

[0049] By detecting the signal The peak value is used for preamble detection.

[0050] Preferably, in step S3, K consecutive shift correlation windows are merged to construct a super window, which is expressed as:

[0051]

[0052] in, is the signal within the super window; Indicates the sequence number of the first shift-related window in each super window, satisfying ;

[0053] Detect the signal peak point within the super window and its corresponding peak size , expressed as:

[0054]

[0055] In step S4, the peak value and preset thresholds Compare, if , then assume If the random access preamble exists, execute step S5; otherwise, assume that If the random access preamble does not exist, step S2 is executed again to obtain a new received signal.

[0056] Preferably, in step S5, according to the signal peak point in the super window Calculate an estimate of fractional round-trip delay , expressed as: .

[0057] Preferably, in step S5, according to the signal peak point in the super window and an estimate of the fractional round-trip delay Intercept the received signal of the base station to obtain a first intercepted signal and the second intercept signal , expressed as:

[0058]

[0059]

[0060] Among them, the first intercepted signal and the second intercept signal Satisfy respectively and .

[0061] Preferably, in step S6, the first intercepted signal and the second intercept signal Cross-correlate with OFDM symbols respectively to construct the first discriminant factor and the second discriminant factor , expressed as:

[0062]

[0063] Combine the signal peak points within the super window Calculates an estimate of the integer round-trip delay , expressed as:

[0064]

[0065] The overall round-trip delay estimate Expressed as: .

[0066] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0067] The present invention provides a random access preamble detection method for aviation communications. A scheme based on shifted partial combination (SPC)-assisted peak detection and dual-end correlation (DEC)-assisted RTD estimation is proposed, which is denoted as an SPC and DEC-assisted preamble detection (SPC-DEC-PD) scheme. The scheme includes the following steps: constructing a communication system model, dividing a received signal, combining shifted correlation windows to construct a super-window, detecting a signal peak within the super-window, and calculating an overall round-trip delay estimate based on the signal peak point to complete random access preamble detection.

[0068] On the one hand, the present invention designs an SPC-assisted peak detection algorithm based on the short preamble format. Unlike traditional algorithms that combine the cross-correlation results of all correlation windows, SPC combines the cross-correlation results in a super-window composed of partially shifted correlation windows (SCWs) until all candidate SCWs are traversed. Therefore, the algorithm can provide better detection performance and higher spectral efficiency, while supporting large coverage and resisting high Doppler effects.

[0069] On the other hand, compared with the simple threshold-based RTD estimation method, the present invention designs an RTD estimation method that performs a cross-correlation operation at both ends of the leading coarse position detected by the SPC method, thereby achieving more robust RTD estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 This is a flow chart of a random access preamble detection method for aviation communications provided in Example 1.

[0071] Figure 2 This is an example diagram of receiving signal division in two different situations provided in Example 2.

[0072] Figure 3 This is a comparison chart of the false detection rate performance provided in Example 2.

[0073] Figure 4 This is a performance comparison chart of random access success rate provided in Example 2. DETAILED DESCRIPTION

[0074] The accompanying drawings are for illustrative purposes only and are not to be construed as limiting this patent;

[0075] In order to better illustrate this embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size;

[0076] It is understandable to those skilled in the art that some well-known structures and descriptions thereof may be omitted in the drawings.

[0077] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0078] Example 1

[0079] like Figure 1 As shown, this embodiment provides a random access preamble detection method for aviation communications, including the following steps:

[0080] S1: Establishing an aviation communication system based on orthogonal frequency division multiplexing, in which an airborne user equipment transmits a signal to a base station via a PRACH resource block;

[0081] S2: Obtain a received signal from the base station, divide the PRACH resource block into a plurality of shift correlation windows, obtain a received signal from each shift correlation window, and perform signal preprocessing;

[0082] S3: Merge K consecutive shifted correlation windows to construct a super window, and detect the signal peak point and its corresponding peak value within the super window; wherein K is the number of OFDM symbols included in the preset random access preamble;

[0083] S4: Determine whether the signal peak value within the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and execute step S5; otherwise, the random access preamble does not exist, and re-execute step S2 to re-acquire a new received signal;

[0084] S5: Calculating an estimated value of the fractional round trip delay according to the signal peak point within the super window;

[0085] intercepting the received signal of the base station according to the signal peak point and the estimated value of the fractional round-trip delay within the super window to obtain a first intercepted signal and a second intercepted signal;

[0086] S6: constructing a first discriminant factor and a second discriminant factor according to the first intercepted signal and the second intercepted signal, and calculating an estimated value of the integer round-trip delay in combination with the signal peak point within the super window;

[0087] An overall round-trip delay estimate is obtained according to the estimated value of the fractional round-trip delay and the estimated value of the integer round-trip delay, and random access preamble detection is completed.

[0088] In the specific implementation process, an aviation communication system based on orthogonal frequency division multiplexing is first established. In the aviation communication system, the user equipment in the air sends signals to the base station through the PRACH resource block;

[0089] Then, the received signal of the base station is obtained, the PRACH resource block is divided into several shift correlation windows, the received signal of each shift correlation window is obtained and signal preprocessing is performed;

[0090] Then, K consecutive shifted correlation windows are merged to construct a super window, and the signal peak point and its corresponding peak value within the super window are detected; where K is the number of OFDM symbols included in the preset random access preamble;

[0091] Then, it is determined whether the signal peak value within the super window is greater than or equal to the preset threshold value. If so, the random access preamble exists; otherwise, the random access preamble does not exist and a new received signal is acquired again.

[0092] When the random access preamble exists, the estimated value of the fractional round trip delay is calculated based on the signal peak point within the super window;

[0093] intercepting a received signal of the base station according to a signal peak point within the super window and an estimated value of the fractional round-trip delay to obtain a first intercepted signal and a second intercepted signal;

[0094] Constructing a first discriminant factor and a second discriminant factor based on the first intercepted signal and the second intercepted signal, and calculating an estimated value of the integer round-trip delay in combination with a signal peak point within the super window;

[0095] Obtaining an overall round-trip delay estimate based on the fractional round-trip delay estimate and the integer round-trip delay estimate, and completing random access preamble detection;

[0096] This method can provide better detection performance and higher spectrum efficiency, while supporting large coverage and resisting high Doppler effect, and can also achieve more robust RTD estimation.

[0097] Example 2

[0098] This embodiment provides a random access preamble detection method for aviation communications, including the following steps:

[0099] S1: Establishing an aviation communication system based on orthogonal frequency division multiplexing, in which an airborne user equipment transmits a signal to a base station via a PRACH resource block;

[0100] S2: Obtain a received signal from the base station, divide the PRACH resource block into a plurality of shift correlation windows, obtain a received signal from each shift correlation window, and perform signal preprocessing;

[0101] S3: Merge K consecutive shifted correlation windows to construct a super window, and detect the signal peak point and its corresponding peak value within the super window; wherein K is the number of OFDM symbols included in the preset random access preamble;

[0102] S4: Determine whether the signal peak value within the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and execute step S5; otherwise, the random access preamble does not exist, and re-execute step S2 to re-acquire a new received signal;

[0103] S5: Calculating an estimated value of the fractional round trip delay according to the signal peak point within the super window;

[0104] intercepting the received signal of the base station according to the signal peak point and the estimated value of the fractional round-trip delay within the super window to obtain a first intercepted signal and a second intercepted signal;

[0105] S6: constructing a first discriminant factor and a second discriminant factor according to the first intercepted signal and the second intercepted signal, and calculating an estimated value of the integer round-trip delay in combination with the signal peak point within the super window;

[0106] Obtaining an overall round-trip delay estimate based on the estimated value of the fractional round-trip delay and the estimated value of the integer round-trip delay, and completing random access preamble detection;

[0107] In step S1, the aviation communication system based on orthogonal frequency division multiplexing includes a base station and several airborne user equipments, each of which has one transmitting antenna and the base station has one receiving antenna. ;

[0108] The time-frequency resources in the aviation communication system are allocated into a plurality of PRACH resource blocks, and the airborne user equipment sends a signal to the base station through the PRACH resource blocks and initiates a random access process;

[0109] A PRACH resource block occupies subcarriers, with a duration in the time domain of ; The subcarrier spacing of the aviation communication system is , the duration of an OFDM symbol is The length of the fast Fourier transform used in the aviation communication system and the length of an OFDM symbol are both , the sampling interval is , the length of a PRACH resource block is ;

[0110] In the random access process, each air user equipment randomly selects a preamble sequence from a predefined set of preamble sequences that satisfies Leading sequence of conditions , using the selected leading sequence Generate a random access preamble and send it to the base station in a PRACH resource block, where: Represents a complex set; the random access preamble adopts a preamble structure without a cyclic prefix, The length of the repetition is OFDM symbols, the total length of the random access preamble is ;

[0111] The use of the selected leader sequence Generate a random access preamble, including:

[0112] The airborne user equipment passes Point discrete Fourier transform calculation frequency domain sequence , expressed as ,in represents the discrete Fourier transform matrix, whose elements are ,in ;

[0113] The frequency domain sequence Mapped to the subcarriers of the PRACH resource block and used Point-wise inverse fast Fourier transform to generate OFDM symbols , expressed as:

[0114]

[0115] in, is an intermediate variable, satisfying ; is the subcarrier mapping matrix, satisfying , represents the field of real numbers; is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable Also satisfied ;

[0116] The OFDM symbol Each element in is represented as:

[0117]

[0118] The generated random access preamble Depend on Repeated Cascaded, expressed as: ;

[0119] The random access preamble Each element in is represented as:

[0120]

[0121] in, is the binarization coefficient, if ,but ,otherwise ; Representation model operate;

[0122] In the aeronautical communication system, the random access preamble The assumptions that the BS does not exist and exists in the received signal are respectively denoted as and ;

[0123] In the assumption In the PRACH resource block, Received signal from antenna for:

[0124]

[0125] in, The power spectral density is Additive Gaussian white noise; ; ;

[0126] In the assumption In the PRACH resource block, Received signal from antenna for:

[0127]

[0128] in, The combined effect of non-line-of-sight signals and noise satisfies ; is the transmit power, is the path loss coefficient, and They are line-of-sight and non-line-of-sight channel coefficients, satisfying ; is the round-trip delay of the line-of-sight channel; It is the delay of the non-line-of-sight channel relative to the line-of-sight channel;

[0129] In step S2, obtaining the received signal of each shifted correlation window includes:

[0130] The length is The PRACH resource block is divided into shift correlation windows, each of which has a length of ;

[0131] The vector formed by the signal in each shift correlation window is recorded as: ,in ; ;

[0132] In the assumption Under the above conditions, the received signal of each shifted correlation window contains only additive white Gaussian noise;

[0133] In the assumption The received signal of each shifted correlation window is expressed as:

[0134]

[0135] in, ;

[0136] The round-trip delay of the line-of-sight channel Expressed as ,in , , and Represents the round-trip delay Relative to OFDM symbol length The integer and fractional parts of ;

[0137] In step S2, signal preprocessing includes:

[0138] Perform fast Fourier transform and subcarrier demapping operations on the signal in each shift correlation window to extract the frequency domain signal, and compare the frequency domain signal with the phase-shifted frequency domain sequence. Correlation is performed to obtain the preprocessed signal within each shift correlation window, which is expressed as:

[0139]

[0140] in, ,express Point fast Fourier transform and subcarrier demapping operations; is the preset number of phases;

[0141] By detecting the signal The peak value of the leading edge detection is performed;

[0142] In step S3, K consecutive shifted correlation windows are merged to construct a super window, which is expressed as:

[0143]

[0144] in, is the signal within the super window; Indicates the sequence number of the first shift-related window in each super window, satisfying ;

[0145] Detect the signal peak point within the super window and its corresponding peak size , expressed as:

[0146]

[0147] In step S4, the peak value and preset thresholds Compare, if , then assume If the random access preamble exists, execute step S5; otherwise, assume that If the random access preamble does not exist, step S2 is executed again to obtain a new received signal.

[0148] In step S5, according to the signal peak point in the super window Calculate an estimate of fractional round-trip delay , expressed as: ;

[0149] In step S5, according to the signal peak point in the super window and an estimate of the fractional round-trip delay Intercept the received signal of the base station to obtain a first intercepted signal and the second intercept signal , expressed as:

[0150]

[0151]

[0152] Among them, the first intercepted signal and the second intercept signal Satisfy respectively and ;

[0153] In step S6, the first intercepted signal and the second intercept signal Cross-correlate with OFDM symbols respectively to construct the first discriminant factor and the second discriminant factor , expressed as:

[0154]

[0155] Combine the signal peak points within the super window Calculates an estimate of the integer round-trip delay , expressed as:

[0156]

[0157] The overall round-trip delay estimate Expressed as: .

[0158] During the specific implementation process, an aviation communication system based on orthogonal frequency division multiplexing will be established first;

[0159] In this embodiment, the aviation communication system based on Orthogonal Frequency-Division Multiplexing (OFDM) includes a base station (BS) and several airborne user equipments (AUEs). The number of transmitting antennas of each airborne user equipment is 1, and the number of receiving antennas of the base station is ;

[0160] The time and frequency resources in the aviation communication system are allocated into several PRACH (Physical Random Access Channel) resource blocks. The airborne user equipment sends a signal to the base station through the PRACH resource blocks and initiates the random access process.

[0161] A PRACH resource block occupies subcarriers, with a duration in the time domain of ; The subcarrier spacing of the aviation communication system is , so the duration of an OFDM symbol is ; The Fast Fourier Transform (FFT) length used in aviation communication systems is , the sampling interval is If length is used to describe the number of sampling points occupied by a physical signal or physical resource in the time domain, the length of an OFDM symbol is , the length of a PRACH resource block is ;

[0162] In the random access process, each air user equipment randomly selects a preamble sequence that satisfies Leading sequence of conditions , using the selected leading sequence Generate a random access preamble and send it to the base station in a PRACH resource block, where: Indicates a complex set; the random access preamble adopts a preamble structure without a cyclic prefix (CP), consisting of The length of the repetition is OFDM symbols, the total length of the random access preamble is ;

[0163] Using the selected leader sequence Generate a random access preamble, including:

[0164] Air user equipment through Point Discrete Fourier Transform (DFT) calculation frequency domain sequence , expressed as ,in represents the discrete Fourier transform matrix, whose elements are ,in ;

[0165] The frequency domain sequence Mapped to the subcarriers of the PRACH resource block and used Point Inverse Fast Fourier Transform (IFFT) generates OFDM symbols , expressed as:

[0166]

[0167] in, is an intermediate variable, satisfying ; is the subcarrier mapping matrix, satisfying , represents the field of real numbers; is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable Also satisfied ; is a normalization coefficient such that ;

[0168] Formula (1) can also be expressed as:

[0169]

[0170] Generated random access preamble Depend on Repeated Cascaded, expressed as:

[0171]

[0172] According to formula (2), formula (3) can be expressed as:

[0173]

[0174] in, is the binarization coefficient, if ,but ,otherwise ; Representation model operation; note that although the random access preamble The length is , formula (4) is still When defined ,The purpose is to facilitate the representation of received signals;

[0175] In aviation communication systems, random access preambles The assumptions that the BS does not exist and exists in the received signal are respectively denoted as and ;

[0176] In the assumption In the PRACH resource block, Received signal from antenna for:

[0177]

[0178] in, The power spectral density is Additive Gaussian white noise; ; ;

[0179] In the assumption In this case, the received signal is the superposition of the Line-of-Sight (LOS) component and the Non-Line-of-Sight (NLOS) component. Received signal from antenna for:

[0180]

[0181] in, The combined effect of non-line-of-sight signals and noise satisfies ; is the transmit power, is the path loss coefficient, and They are line-of-sight and non-line-of-sight channel coefficients, satisfying ; is the round-trip delay of the line-of-sight channel; The delay of the non-line-of-sight channel relative to the line-of-sight channel. In aviation communication scenarios, the power of the NLOS signal is much smaller than that of the LOS signal, so the impact of the NLOS signal on random access performance can be ignored.

[0182] Based on the above aviation communication system model, the goal of preamble detection is to use the received signal ,judge and Which assumption holds true and Estimated round-trip delay at establishment , recorded as ;

[0183] Then obtain the received signal of the base station, divide the PRACH resource block into several shift-related windows, and obtain the received signal of each shift-related window.

[0184] In cells with larger radius, the range of RTD variation will also be larger. To expand coverage, a common method is to use a long CP to compensate for RTD. However, this method reduces spectrum efficiency. Another problem that needs to be solved is the channel coefficient caused by the Doppler effect. To solve these problems, this method designs a SPC-DEC-PD scheme based on the short preamble format, which will be described in detail below.

[0185] 1) Received signal division:

[0186] The length is The PRACH resource block is divided into The length is Window, such as Figure 2 As shown, For example, for simplicity, the length of the PRACH resource block is Set to OFDM symbol length an integer multiple of ;

[0187] The motivation for dividing the PRACH resource blocks is that since the channel varies less in a window of shorter duration, the problem of fast time-varying channels can be solved by using a short preamble format; in this case, although the RTD may be much larger than the duration of the short preamble, the preamble can still be detected by joint processing of multiple windows. Therefore, large RTD uncertainties can be handled without using a long CP.

[0188] The vector composed of the signal of each window is recorded as ( ; );according to Figure 2 The division method, round-trip delay It can be expressed as ,in and Represents the round-trip delay Relative to OFDM symbol length The integer and fractional parts of ;

[0189] According to formula (5), under the assumption Under this condition, the received signal in each window contains only noise;

[0190] In the assumption Then, according to formula (4) and formula (6), we can get:

[0191]

[0192] in, ;

[0193] In addition, according to formula (2), we can get:

[0194]

[0195] Among them, for any , , Represents the vector elements;

[0196] Therefore, under the assumption The received signal of each window is:

[0197]

[0198] in:

[0199]

[0200] 2) SPC-assisted peak detection:

[0201] Similar to a traditional PRACH receiver, the SPC algorithm performs FFT and subcarrier demapping operations on each window to extract the frequency domain signal; then, the frequency domain signal is combined with the phase-shifted local sequence. Related; these operations can be expressed as:

[0202]

[0203] in, express Point FFT and subcarrier demapping operations, is the number of phases; according to formula (11), we can deduce ; If set Not less than And it is a power of 2, Equation (11) can be efficiently calculated by IFFT;

[0204] When the subcarrier spacing When it is large enough, the channel can be considered to remain unchanged in one OFDM symbol period, then the channel matrix of formula (10) Can be approximated as ; Then, substitute formula (9) into formula (11) to obtain:

[0205]

[0206] because ,use The periodicity can be obtained If windows, such as Figure 2 in , contains a cyclically shifted version of an OFDM symbol, then This is because No. The diagonal elements represent the The first window whether the sample has sampled the leading edge; in this case, the following part of Equation (12) can be simplified as:

[0207]

[0208] If (13) satisfies , then the formula (12) A peak will appear; this means that Peak detection preamble;

[0209] However, the BS does not know which windows contain complete OFDM symbols and therefore cannot directly detect peaks. A straightforward solution is to merge the correlation results of all windows, but this approach also merges windows containing only noise, thus degrading detection performance. To overcome this shortcoming, this method proposes merging the correlation results in a superwindow consisting of K consecutive SCWs, which can be expressed as:

[0210]

[0211] in Indicates the sequence number of the first window in each super window, ; The next step is to find Peak value:

[0212]

[0213] Then the peak size and a predefined threshold Compare; if , then the assumption is If established, otherwise the assumption Established;

[0214] 3) DEC-assisted RTD estimation:

[0215] If we assume If holds, the estimated value of the fractional round trip delay is ; The remaining problem is to estimate the integer part of the round trip delay ;

[0216] According to the definitions of Equations (14) and (15), the goal of SPC-assisted peak detection is to find the continuous peaks containing the most leading energy. windows, whose serial numbers are recorded as ;from Figure 2 (a) It can be observed that if , the SPC algorithm has a greater probability of obtaining , because the The window containing the leading character is longer than the The window is longer; on the contrary, Figure 2 (b) It can be observed that if , the SPC algorithm has a greater probability of obtaining ; Therefore, the estimated value based on the fractional RTD , a direct estimate The method is based on the threshold decision (Threshold-Based Decision, TBD) method:

[0217]

[0218] However, the calculation results of the TBD algorithm may be unreliable, especially in the Window and The window contains a leading edge of approximately the length at the worst In the case of or In order to eliminate this ambiguity as much as possible, this method proposes the DEC algorithm to estimate the integer RTD ;

[0219] Specifically, two parts of the received signal are intercepted and , respectively and give; give and Cross-correlating with the time-domain OFDM symbol shown in equation (1) yields:

[0220]

[0221] The integer round trip delay The estimated value of is:

[0222]

[0223] Finally, the RTD is estimated as ;

[0224] Note that Equation (17) utilizes two fractionally shifted windows , where one window contains the complete OFDM symbol and the other window contains only noise; this makes the equation (18) based on The judgment method is better than that based only on The decision method is more robust to noise; specifically, when the Window and The window contains a leading edge of close length, and Equation (15) may be Time output , or Time output , which makes Equation (16) get the wrong result; therefore, Equation (18) will be more reliable than Equation (16);

[0225] Based on the above discussion, the SPC-DEC-PD algorithm involved in this method is summarized in Algorithm 1:

[0226]

[0227] To more fully illustrate the beneficial effects of this method, the effectiveness and advancement of this method are further illustrated below in conjunction with specific simulation analysis and results. The simulation parameters are given in Table 1, which includes the parameters of the PZC-JPD algorithm, C2RZC-JPD algorithm, and CCZC-JPD algorithm for comparison. In addition, the SPC-TBD-PD scheme proposed in this method is obtained by replacing the DEC module with the TBD-based RTD estimation module, and the resulting SPC-TBD-PD scheme will also be used for comparison.

[0228] Table 1 Simulation parameters

[0229]

[0230] According to the test method of 3GPP specification, the false detection rate of each algorithm is evaluated in the single-user access configuration. If the BS fails to detect the random access preamble sent by the AUE, or the RTD estimation error exceeds 2.55 μs, it is considered a false detection. The false detection rate performance of different algorithms is compared in Figure 3 Given in represents the preamble signal-to-noise ratio, Represents the leading energy; Figure 3 It can be seen that at a typical false detection rate of 10 −2 Under the requirement of , the proposed SPC-DEC-PD algorithm has a signal-to-noise ratio gain of 2~4 dB compared with the existing algorithms. In addition, it can be observed that SPC-DEC-PD eliminates the false detection rate plateau caused by the limited estimation accuracy of the TBD module in SPC-TBD-PD.

[0231] Next, the random access success rate under the multi-user access configuration is evaluated. The successful access of an AUE should meet three conditions: the preamble is detected, the RTD estimation error does not exceed 2.55 μs, and no other AUE sends the same preamble. Under the assumption that the preamble detection is accurate, the upper bound of the random access success rate is ,in Indicates the number of leading sequences, Indicates the number of AUEs; the random access success rate performance of different algorithms is Figure 4 It can be seen that the random access success rate performance of the SPC-DEC-PD algorithm proposed in this method is better than the existing algorithm and is close to the theoretical upper bound, especially when the BS has more antennas;

[0232] Based on the short preamble format, this method designs an SPC-assisted peak detection algorithm. Unlike traditional algorithms that merge the cross-correlation results of all correlation windows, SPC merges the cross-correlation results in a super-window composed of partially shifted correlation windows (SCWs) until all candidate SCWs are traversed. Therefore, the algorithm can provide better detection performance and higher spectral efficiency, while supporting large coverage and resisting high Doppler effects. In addition, compared with the simple threshold-based RTD estimation method, this method designs an RTD estimation method that performs cross-correlation operations at both ends of the coarse preamble position detected by the SPC method, thereby achieving more robust RTD estimation.

[0233] The same or similar reference numerals correspond to the same or similar components;

[0234] The terms used in the drawings to describe positional relationships are for illustrative purposes only and should not be construed as limiting this patent;

[0235] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A random access preamble detection method for aviation communications, characterized in that: The following steps are involved: S1: Establishing an aviation communication system based on orthogonal frequency division multiplexing, in which an airborne user equipment transmits a signal to a base station via a PRACH resource block; S2: Obtain a received signal from the base station, divide the PRACH resource block into a plurality of shift correlation windows, obtain a received signal from each shift correlation window, and perform signal preprocessing; S3: Merge K consecutive shifted correlation windows to construct a super window, and detect the signal peak point and its corresponding peak value within the super window; wherein K is the number of OFDM symbols included in the preset random access preamble; S4: Determine whether the signal peak value within the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and execute step S5; otherwise, the random access preamble does not exist, and re-execute step S2 to re-acquire a new received signal; S5: Calculating an estimated value of the fractional round trip delay according to the signal peak point within the super window; intercepting the received signal of the base station according to the signal peak point and the estimated value of the fractional round-trip delay within the super window to obtain a first intercepted signal and a second intercepted signal; S6: constructing a first discriminant factor and a second discriminant factor according to the first intercepted signal and the second intercepted signal, and calculating an estimated value of the integer round-trip delay in combination with the signal peak point within the super window; An overall round-trip delay estimate is obtained according to the estimated value of the fractional round-trip delay and the estimated value of the integer round-trip delay, and random access preamble detection is completed.

2. The random access preamble detection method for aviation communication according to claim 1, characterized in that: In step S1, the aviation communication system based on orthogonal frequency division multiplexing includes a base station and several airborne user equipments, each of which has one transmitting antenna and the base station has one receiving antenna. ; The time-frequency resources in the aviation communication system are allocated into a plurality of PRACH resource blocks, and the airborne user equipment sends a signal to the base station through the PRACH resource blocks and initiates a random access process; A PRACH resource block occupies subcarriers, with a duration in the time domain of ; The subcarrier spacing of the aviation communication system is , the duration of an OFDM symbol is The length of the fast Fourier transform used in the aviation communication system and the length of an OFDM symbol are both , the sampling interval is , the length of a PRACH resource block is ; In the random access process, each air user equipment randomly selects a preamble sequence from a predefined set of preamble sequences that satisfies Leading sequence of conditions , using the selected leading sequence Generate a random access preamble and send it to the base station in a PRACH resource block, where: Represents a complex set; the random access preamble adopts a preamble structure without a cyclic prefix, The length of the repetition is OFDM symbols, the total length of the random access preamble is .

3. The random access preamble detection method for aviation communication according to claim 2, characterized in that: The use of the selected leader sequence Generate a random access preamble, including: The airborne user equipment passes Point discrete Fourier transform calculation frequency domain sequence , expressed as ,in represents the discrete Fourier transform matrix, whose elements are ,in ; The frequency domain sequence Mapped to the subcarriers of the PRACH resource block and used Point-wise inverse fast Fourier transform to generate OFDM symbols , expressed as: in, is an intermediate variable, satisfying ; is the subcarrier mapping matrix, satisfying , represents the field of real numbers; is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable Also satisfied ; The OFDM symbol Each element in is represented as: The generated random access preamble Depend on Repeated Cascaded, expressed as: ; The random access preamble Each element in is represented as: in, is the binarization coefficient, if ,but ,otherwise ; Representation model operate.

4. The random access preamble detection method for aviation communication according to claim 3, characterized in that: In the aeronautical communication system, the random access preamble The assumptions that the BS does not exist and exists in the received signal are respectively denoted as and ; In the assumption In the PRACH resource block, Received signal from antenna for: in, The power spectral density is Additive Gaussian white noise; ; ; In the assumption In the PRACH resource block, Received signal from antenna for: in, The combined effect of non-line-of-sight signals and noise satisfies ; is the transmit power, is the path loss coefficient, and They are line-of-sight and non-line-of-sight channel coefficients, satisfying ; is the round-trip delay of the line-of-sight channel; It is the delay of the non-line-of-sight channel relative to the line-of-sight channel.

5. The random access preamble detection method for aviation communication according to claim 4, characterized in that: In step S2, obtaining the received signal of each shifted correlation window includes: The length is The PRACH resource block is divided into shift correlation windows, each of which has a length of ; The vector formed by the signal in each shift correlation window is recorded as: ,in ; ; In the assumption Under the above conditions, the received signal of each shifted correlation window contains only additive white Gaussian noise; In the assumption The received signal of each shifted correlation window is expressed as: in, ; The round-trip delay of the line-of-sight channel Expressed as ,in , , and Represents the round-trip delay Relative to OFDM symbol length The integer and fractional parts of .

6. The random access preamble detection method for aviation communication according to claim 5, characterized in that: In step S2, signal preprocessing includes: Perform fast Fourier transform and subcarrier demapping operations on the signal in each shift correlation window to extract the frequency domain signal, and compare the frequency domain signal with the phase-shifted frequency domain sequence. Correlation is performed to obtain the preprocessed signal within each shift correlation window, which is expressed as: in, ,express Point fast Fourier transform and subcarrier demapping operations; is the preset number of phases; By detecting the signal The peak value is used for preamble detection.

7. The random access preamble detection method for aviation communication according to claim 6, characterized in that: In step S3, K consecutive shifted correlation windows are merged to construct a super window, which is expressed as: in, is the signal within the super window; Indicates the sequence number of the first shift-related window in each super window, satisfying ; Detect the signal peak point within the super window and its corresponding peak size , expressed as: In step S4, the peak value and preset thresholds Compare, if , then assume If the random access preamble exists, execute step S5; otherwise, assume that If the random access preamble does not exist, step S2 is executed again to obtain a new received signal.

8. The random access preamble detection method for aviation communications according to claim 7, characterized in that: In step S5, according to the signal peak point in the super window Calculate an estimate of fractional round-trip delay , expressed as: .

9. The random access preamble detection method for aviation communication according to claim 8, characterized in that: In step S5, according to the signal peak point in the super window and an estimate of the fractional round-trip delay Intercept the received signal of the base station to obtain a first intercepted signal and the second intercept signal , expressed as: Among them, the first intercepted signal and the second intercept signal Satisfy respectively and .

10. The random access preamble detection method for aviation communication according to claim 9, characterized in that: In step S6, the first intercepted signal and the second intercept signal Cross-correlate with OFDM symbols respectively to construct the first discriminant factor and the second discriminant factor , expressed as: Combine the signal peak points within the super window Calculates an estimate of the integer round-trip delay , expressed as: The overall round-trip delay estimate Expressed as: .

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