Random access preamble detection method for aeronautical communication

Abstract

The invention provides a random access preamble detection method for aeronautical communication, and provides a scheme based on shift partial combination auxiliary peak detection and double-end correlation auxiliary round-trip delay estimation. The scheme mainly comprises the following steps: constructing a communication system model, dividing received signals, combining shift related windows to construct a super-window, detecting a signal peak value in the super-window, calculating a total round-trip delay estimated value according to a signal peak point, and completing random access preamble detection. On one hand, based on a short preamble format, a peak detection algorithm assisted by shift part merging is designed, and the algorithm can provide better detection performance and higher spectrum efficiency, and can support large coverage and resist a high Doppler effect at the same time; on the other hand, the invention further designs a round-trip time delay estimation method, cross-correlation operation is executed at the two ends of the leading rough position detected by the shift part merging method, and therefore more robust round-trip time delay estimation is achieved.

Description

Technical Field

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

[0002] With the rapid development of air transportation, aeronautical communication has become a promising wireless technology to meet the rapidly growing demand for airborne data services. Similar to the ground network, aerial user equipment (AUE) uses a random access process 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 the Zadoff-Chu (ZC) sequence to support scenarios with different coverage requirements and AUE mobility. Among them, the long preamble format supports a maximum cell radius of 57km by utilizing a small subcarrier spacing, but is susceptible to large Doppler shift; the short preamble format using a larger subcarrier spacing can solve the problem of large Doppler shift, but due to the use of a shortened cyclic prefix (CP), it only supports a cell radius of 9km. In aviation communication scenarios, the speed of AUE may be higher than 1080km / h. In addition, aviation communication networks need to support high-mobility AUE and provide a coverage range of about 100 to 400km. However, such a large propagation delay requires the use of long CP compensation, which reduces spectrum efficiency.

[0003] In order to alleviate the above problems, scholars have proposed a variety of joint peak detection (JPD) techniques 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 “Rootpair 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] In order to overcome the defect that the above-mentioned prior art uses longer preamble and random access duration to process 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 communication, and proposes a scheme based on shifted partial combination (SPC) assisted peak detection and dual-end correlation (DEC) assisted RTD estimation, which is denoted as SPC and DEC assisted preamble detection (SPC and DEC assisted Preamble Detection, SPC-DEC-PD) scheme. The scheme is based on a short preamble format, can provide better detection performance and higher spectrum efficiency, can support large coverage and resist high Doppler effect, and can also achieve more robust RTD estimation.

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

[0006] A random access preamble detection method for aviation communication comprises the following steps:

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

[0008] S2: obtaining a received signal of the base station, dividing the PRACH resource block into a plurality of shift correlation windows, obtaining a received signal of each shift correlation window and performing signal preprocessing;

[0009] S3: merging K consecutive shift correlation windows to construct a super window, and detecting the signal peak point and its corresponding peak value in 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 in the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and step S5 is executed; otherwise, the random access preamble does not exist, and step S2 is executed again to obtain a new received signal;

[0011] S5: Calculate an estimated value of the fractional round trip delay according to the signal peak point in 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 in 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 in 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 a plurality of airborne user equipments, the number of transmitting antennas of each airborne user equipment is 1, and the number of receiving antennas of the base station is M;

[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 starts a random access process;

[0017] A PRACH resource block occupies L subcarriers in the frequency domain and has a duration of T in the time domain. b ; The subcarrier spacing of the aviation communication system is Δf, and the duration of an OFDM symbol is The length of the fast Fourier transform and the length of an OFDM symbol used in the aviation communication system are both N, and 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 sequence that satisfies x from a predefined set of preamble sequences. H x=L conditional leading sequence x∈C L×1 , a random access preamble is generated using the selected preamble sequence x and sent to the base station in the PRACH resource block, wherein C represents a complex set; the random access preamble adopts a preamble structure without a cyclic prefix, and is composed of K repeated OFDM symbols of length N, and the total length of the random access preamble is N p =KN.

[0019] Preferably, the generating a random access preamble by using the selected preamble sequence x comprises:

[0020] The airborne user equipment calculates the frequency domain sequence X=[X[0],…,X[L-1]] by L-point discrete Fourier transform T ∈C L×1 , expressed as X = F L x, where F L ∈C L×L represents the discrete Fourier transform matrix, whose elements are Where l1, l2 = 0, ..., L-1;

[0021] Map the frequency domain sequence X to the subcarriers of the PRACH resource block and use N-point inverse fast Fourier transform to generate OFDM symbols s = [s[0], ..., s[N-1]] T ∈C N×1 , expressed as:

[0022]

[0023] Among them, G is an intermediate variable, satisfying M is the subcarrier mapping matrix, satisfying M=[0 L×ξ ,I L ,0 L×(N-ξ-L) ] T ∈R N×L , R represents the real number domain; ξ is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable G also satisfies G HG=NI L ;

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

[0025]

[0026] The generated random access preamble It is composed of K repeated s cascades, expressed as:

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

[0028]

[0029] Where a[n] is the binarization coefficient. If n∈{0,…,N p -1}, then a[n]=1, otherwise a[n]=0; <·> N Represents a modulo-N operation.

[0030] Preferably, in the aviation communication system, the random access preamble The hypotheses that do not exist and exist in the received signal of the base station are denoted as H0 and H1 respectively;

[0031] Under the assumption H0, the received signal y of the mth antenna in the PRACH resource block is m [n] is:

[0032] H0:y m [n] = w m [n]

[0033] Among them, w n [n] represents additive white Gaussian noise with power spectral density N0; m = 0,…,M-1; n = 0,…,N b -1;

[0034] Under assumption H1, the received signal y of the mth antenna in the PRACH resource block is m [n] is:

[0035]

[0036] Among them, z m [n] is the combined effect of non-line-of-sight signal and noise, satisfying ρ is the transmit power, is the path loss coefficient, h m [n] and h′ m [n] are line-of-sight and non-line-of-sight channel coefficients, respectively, satisfying E[|h m [n]|2 ]+E[|h′ m [n]| 2 ]=1; ε is the round-trip delay of the line-of-sight channel; ε′ is the delay of the non-line-of-sight channel relative to the line-of-sight channel.

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

[0038] Set the length to N b The PRACH resource block is divided into shift correlation windows, each shift correlation window has a length of N;

[0039] The vector formed by the signal in each shift correlation window is recorded as: m,q =[y m [qN],…,y m [qN+N-1]] T ∈C N×1 , where m = 0, ..., M-1; q = 0, ..., Q-1;

[0040] Under the assumption H0, the received signal of each of the shifted correlation windows only contains additive white Gaussian noise;

[0041] Under the assumption H1, the received signal of each shifted correlation window is expressed as:

[0042]

[0043] in,

[0044] The round-trip delay ε of the line-of-sight channel is expressed as ε=αN+β, where β=<ε> N , α and β represent the integer and fractional parts of the round-trip delay ε relative to the OFDM symbol length N, respectively.

[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 correlate the frequency domain signal with the phase-shifted frequency domain sequence X to obtain the preprocessed signal in each shift correlation window, which is expressed as:

[0047]

[0048] Among them, G H =M H F N, represents the N-point fast Fourier transform and subcarrier demapping operation; V is the preset number of phases;

[0049] By detecting the signal c m,q The peak value of [v] is used for preamble detection.

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

[0051]

[0052] Wherein, Λ[u,v] is the signal in the super window; u represents the sequence number of the first shift correlation window in each super window, satisfying u=0,…,QK;

[0053] Detect the signal peak point within the super window and its corresponding peak value It is expressed as:

[0054]

[0055] In step S4, the peak value Compared with the preset threshold value λ, if If assumption H1 holds, the random access preamble exists, and step S5 is executed; otherwise, if assumption H0 holds, the random access preamble does not exist, and 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 It is 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 r m,1 and the second intercepted signal r m,2 , expressed as:

[0058]

[0059] Among them, the first intercepted signal r m,1 and the second intercepted signal r m,2 Satisfy r m,1 ∈C N×1 and r m,2 ∈C N×1 .

[0060] Preferably, in step S6, the first intercepted signal r m,1 and the second intercepted signal r m,2 Cross-correlate with OFDM symbols respectively to construct the first discriminant factor γ1 and the second discriminant factor γ2, which are expressed as:

[0061]

[0062] Combine the signal peak points within the super window Calculates an estimate of the round-trip delay for integers It is expressed as:

[0063]

[0064] The overall round-trip delay estimate It is expressed as:

[0065] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0066] The invention provides a random access preamble detection method for aviation communication, and proposes a scheme based on shifted partial combination (SPC) assisted peak detection and dual-end correlation (DEC) assisted RTD estimation, which is recorded as SPC and DEC assisted preamble detection (SPC and DEC assisted Preamble Detection, SPC-DEC-PD) scheme; the steps of the scheme include: building a communication system model, dividing received signals, combining shifted correlation windows to build a super window, detecting a signal peak in the super window, calculating an overall round trip delay estimation value according to a signal peak point, and completing random access preamble detection;

[0067] On the one hand, the present invention designs an SPC-assisted peak detection algorithm based on the short preamble format. Different from the traditional algorithm that combines the cross-correlation results of all correlation windows, SPC combines the cross-correlation results in a super window composed of partial shifting correlation windows (SCW) until all candidate SCWs are traversed; therefore, the algorithm can provide better detection performance and higher spectrum efficiency, while supporting large coverage and resisting high Doppler effect;

[0068] On the other hand, compared with a 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 a more robust RTD estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a flow chart of a random access preamble detection method for aviation communications provided in Example 1.

[0070] Figure 2 This is an example diagram of receiving signal division in two different situations provided in Example 2.

[0071] Figure 3 This is a comparison chart of the false detection rate performance provided in Example 2.

[0072] Figure 4 This is a performance comparison chart of random access success rate provided in Example 2. DETAILED DESCRIPTION

[0073] The drawings are for illustrative purposes only and should not be construed as limiting the present patent;

[0074] In order to better illustrate the present embodiment, some parts in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product;

[0075] It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0076] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0077] Example 1

[0078] like Figure 1 As shown, this embodiment provides a random access preamble detection method for aviation communication, including the following steps:

[0079] S1: Establishing an aviation communication system based on orthogonal frequency division multiplexing, in which an airborne user equipment sends a signal to a base station through a PRACH resource block;

[0080] S2: obtaining a received signal of the base station, dividing the PRACH resource block into a plurality of shift correlation windows, obtaining a received signal of each shift correlation window and performing signal preprocessing;

[0081] S3: merging K consecutive shift correlation windows to construct a super window, and detecting the signal peak point and its corresponding peak value in the super window; wherein K is the number of OFDM symbols included in the preset random access preamble;

[0082] S4: Determine whether the signal peak value in the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and step S5 is executed; otherwise, the random access preamble does not exist, and step S2 is executed again to obtain a new received signal;

[0083] S5: Calculate an estimated value of the fractional round trip delay according to the signal peak point in the super window;

[0084] intercepting the received signal of the base station according to the signal peak point and the estimated value of the fractional round-trip delay in the super window to obtain a first intercepted signal and a second intercepted signal;

[0085] 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 in the super window;

[0086] 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.

[0087] In the specific implementation process, an aviation communication system based on orthogonal frequency division multiplexing is first established. In the aviation communication system, the airborne user equipment sends signals to the base station through the PRACH resource block;

[0088] 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 the signal preprocessing is performed;

[0089] Then, K consecutive shifted correlation windows are merged to construct a super window, and the signal peak point and its corresponding peak value in the super window are detected; wherein K is the number of OFDM symbols included in the preset random access preamble;

[0090] Then, it is determined whether the signal peak value in 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;

[0091] When the random access preamble exists, the estimated value of the fractional round trip delay is calculated according to the signal peak point in the super window;

[0092] intercepting a received signal of the base station according to a signal peak point in the super window and an estimated value of a fractional round trip delay to obtain a first intercepted signal and a second intercepted signal;

[0093] 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 a signal peak point within the super window;

[0094] Obtaining an overall round trip delay estimate value according to an estimate value of a fractional round trip delay and an estimate value of an integer round trip delay, and completing random access preamble detection;

[0095] 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.

[0096] Example 2

[0097] This embodiment provides a random access preamble detection method for aviation communication, including the following steps:

[0098] S1: Establishing an aviation communication system based on orthogonal frequency division multiplexing, in which an airborne user equipment sends a signal to a base station through a PRACH resource block;

[0099] S2: obtaining a received signal of the base station, dividing the PRACH resource block into a plurality of shift correlation windows, obtaining a received signal of each shift correlation window and performing signal preprocessing;

[0100] S3: merging K consecutive shift correlation windows to construct a super window, and detecting the signal peak point and its corresponding peak value in the super window; wherein K is the number of OFDM symbols included in the preset random access preamble;

[0101] S4: Determine whether the signal peak value in the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and step S5 is executed; otherwise, the random access preamble does not exist, and step S2 is executed again to obtain a new received signal;

[0102] S5: Calculate an estimated value of the fractional round trip delay according to the signal peak point in the super window;

[0103] intercepting the received signal of the base station according to the signal peak point and the estimated value of the fractional round-trip delay in the super window to obtain a first intercepted signal and a second intercepted signal;

[0104] 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 in the super window;

[0105] Obtaining an overall round trip delay estimate value according to 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;

[0106] In the step S1, the aviation communication system based on orthogonal frequency division multiplexing includes a base station and a plurality of airborne user equipments, each airborne user equipment has 1 transmitting antenna, and the base station has M receiving antennas;

[0107] 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 starts a random access process;

[0108] A PRACH resource block occupies L subcarriers in the frequency domain and has a duration of T in the time domain. b ; The subcarrier spacing of the aviation communication system is Δf, and the duration of an OFDM symbol is The length of the fast Fourier transform and the length of an OFDM symbol used in the aviation communication system are both N, and the sampling interval is The length of a PRACH resource block is

[0109] In the random access process, each air user equipment randomly selects a sequence that satisfies x from a predefined set of preamble sequences. H x=L conditional leading sequence x∈C L×1 , a random access preamble is generated using the selected preamble sequence x and sent to the base station in the PRACH resource block, wherein C represents a complex set; the random access preamble adopts a preamble structure without a cyclic prefix, and is composed of K repeated OFDM symbols of length N, and the total length of the random access preamble is N p =KN;

[0110] The generating a random access preamble by using the selected preamble sequence x includes:

[0111] The airborne user equipment calculates the frequency domain sequence X=[X[0],…,X[L-1]] by L-point discrete Fourier transform T ∈C L×1 , expressed as X = F L x, where F L ∈C L×L represents the discrete Fourier transform matrix, whose elements are Where l1, l2 = 0, ..., L-1;

[0112] Map the frequency domain sequence X to the subcarriers of the PRACH resource block and use N-point inverse fast Fourier transform to generate OFDM symbols s = [s[0], ..., s[N-1]] T ∈C N×1 , expressed as:

[0113]

[0114] Among them, G is an intermediate variable, satisfying M is the subcarrier mapping matrix, satisfying M=[0 L×ξ ,I L ,0 L×(N-ξ-L) ]T ∈R N×L , R represents the real number domain; ξ is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable G also satisfies G H G=NI L ;

[0115] Each element in the OFDM symbol s is represented as:

[0116]

[0117] The generated random access preamble It is composed of K repeated s cascades, expressed as:

[0118] The random access preamble Each element in is represented as:

[0119]

[0120] Where a[n] is the binarization coefficient. If n∈{0,…,N p -1}, then a[n]=1, otherwise a[n]=0; <·> N Represents modulo N operation;

[0121] In the aviation communication system, the assumptions that the random access preamble s does not exist and exists in the received signal of the base station are denoted as H0 and H1 respectively;

[0122] Under the assumption H0, the received signal y of the mth antenna in the PRACH resource block is m [n] is:

[0123] H0:y m [n] = w m [n]

[0124] Among them, w n [n] represents additive white Gaussian noise with power spectral density N0; m = 0,…,M-1; n = 0,…,N b -1;

[0125] Under assumption H1, the received signal y of the mth antenna in the PRACH resource block is m [n] is:

[0126]

[0127] Among them, z m [n] is the combined effect of non-line-of-sight signal and noise, satisfying ρ is the transmit power, is the path loss coefficient, h m[n] and h′ m [n] are line-of-sight and non-line-of-sight channel coefficients, respectively, satisfying E[|h m [n]| 2 ]+E[|h′ m [n]| 2 ] = 1; ε is the round trip delay of the line-of-sight channel; ε′ is the delay of the non-line-of-sight channel relative to the line-of-sight channel;

[0128] In the step S2, obtaining the received signal of each shifted correlation window includes:

[0129] Set the length to N b The PRACH resource block is divided into shift correlation windows, each shift correlation window has a length of N;

[0130] The vector formed by the signal in each shift correlation window is recorded as: m,q =[y m [qN],…,y m [qN+N-1]] T ∈C N×1 , where m = 0, ..., M-1; q = 0, ..., Q-1;

[0131] Under the assumption H0, the received signal of each of the shifted correlation windows only contains additive white Gaussian noise;

[0132] Under the assumption H1, the received signal of each shifted correlation window is expressed as:

[0133]

[0134] in,

[0135] The round-trip delay ε of the line-of-sight channel is expressed as ε=αN+β, where β=<ε> N , α and β represent the integer and fractional parts of the round-trip delay ε relative to the OFDM symbol length N, respectively;

[0136] In step S2, signal preprocessing includes:

[0137] Perform fast Fourier transform and subcarrier demapping operations on the signal in each shift correlation window to extract the frequency domain signal, and correlate the frequency domain signal with the phase-shifted frequency domain sequence X to obtain the preprocessed signal in each shift correlation window, which is expressed as:

[0138]

[0139] Among them, G H =MH F N , represents the N-point fast Fourier transform and subcarrier demapping operation; V is the preset number of phases;

[0140] By detecting the signal c m,q The peak value of [v] is used for leading detection;

[0141] In step S3, K consecutive shifted correlation windows are merged to construct a super window, which is expressed as:

[0142]

[0143] Wherein, Λ[u,v] is the signal in the super window; u represents the sequence number of the first shift correlation window in each super window, satisfying u=0,…,QK;

[0144] Detect the signal peak point within the super window and its corresponding peak value It is expressed as:

[0145]

[0146] In step S4, the peak value Compared with the preset threshold value λ, if If assumption H1 holds, the random access preamble exists, and step S5 is executed; otherwise, if assumption H0 holds, the random access preamble does not exist, and step S2 is executed again to obtain a new received signal;

[0147] In step S5, according to the signal peak point in the super window Calculate an estimate of fractional round trip delay It is expressed as:

[0148] 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 r m,1 and the second intercepted signal r m,2 , expressed as:

[0149]

[0150] Among them, the first intercepted signal r m,1 and the second intercepted signal r m,2 Satisfy r m,1 ∈C N×1 and r m,2 ∈C N×1 ;

[0151] In step S6, the first intercepted signal r m,1 and the second intercepted signal r m,2 Cross-correlate with OFDM symbols respectively to construct the first discriminant factor γ1 and the second discriminant factor γ2, which are expressed as:

[0152]

[0153] Combine the signal peak points within the super window Calculates an estimate of the round-trip delay for integers It is expressed as:

[0154]

[0155] The overall round-trip delay estimate It is expressed as:

[0156] In the specific implementation process, firstly, an aviation communication system based on orthogonal frequency division multiplexing is established;

[0157] In this embodiment, an aviation communication system based on orthogonal frequency division multiplexing (OFDM) includes a base station (BS) and a plurality of air user equipments (AUEs), each air user equipment has 1 transmitting antenna, and the base station has M receiving antennas.

[0158] 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 block and starts the random access process.

[0159] A PRACH resource block occupies L subcarriers in the frequency domain and has a duration of T in the time domain. b ; The subcarrier spacing of the aviation communication system is Δf, so the duration of an OFDM symbol is The Fast Fourier Transform (FFT) used in aviation communication systems has a length of N and a sampling interval of 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

[0160] In the random access process, each air user equipment randomly selects a sequence that satisfies x from the predefined preamble sequence set. Hx=L conditional leading sequence x∈C L×1 , a random access preamble is generated using the selected preamble sequence x and sent to the base station in the PRACH resource block, where C represents a complex set; the random access preamble adopts a preamble structure without a cyclic prefix (CP), which is composed of K repeated OFDM symbols of length N, and the total length of the random access preamble is N p =KN;

[0161] Generating a random access preamble using the selected preamble sequence x includes:

[0162] The airborne user equipment calculates the frequency domain sequence X=[X[0],…,X[L-1]] through L-point discrete Fourier transform (DFT) T ∈C L×1 , expressed as X = F L x, where F L ∈C L×L represents the discrete Fourier transform matrix, whose elements are Where l1, l2 = 0, ..., L-1;

[0163] Map the frequency domain sequence X to the subcarriers of the PRACH resource block and use N-point Inverse Fast Fourier Transform (IFFT) to generate OFDM symbols s = [s[0], ..., s[N-1]] T ∈C N×1 , expressed as:

[0164]

[0165] Among them, G is an intermediate variable, satisfying M is the subcarrier mapping matrix, satisfying M=[0 L×ξ ,I L ,0 L×(N-ξ-L) ] T ∈R N×L , R represents the real number domain; ξ is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable G also satisfies G H G=NI L ; is a normalization coefficient such that s H s = N;

[0166] Formula (1) can also be expressed as:

[0167]

[0168] Generated random access preamble It is composed of K repeated s cascades, expressed as:

[0169]

[0170] According to formula (2), formula (3) can be expressed as:

[0171]

[0172] Where a[n] is the binarization coefficient. If n∈{0,…,N p -1}, then a[n]=1, otherwise a[n]=0; <·> N represents a modulo N operation; note that although the random access preamble The length is N p , formula (4) still holds s[n]=0 is defined to facilitate the representation of received signals;

[0173] In aviation communication systems, random access preambles The hypotheses that do not exist and exist in the received signal of the base station are denoted as H0 and H1 respectively;

[0174] Under the assumption H0, the received signal y of the mth antenna in the PRACH resource block is m [n] is:

[0175] H0:y m [n] = w m [n] (5)

[0176] Among them, w n [n] represents additive white Gaussian noise with power spectral density N0; m = 0,,M-1; n = 0,…,N b -1;

[0177] Under the assumption H1, the received signal is the superposition of the Line-of-Sight (LOS) component and the Non-Line-of-Sight (NLOS) component. The received signal y of the mth antenna in the PRACH resource block is m [n] is:

[0178]

[0179] Among them, z m [n] is the combined effect of non-line-of-sight signal and noise, satisfying ρ is the transmit power, is the path loss coefficient, h m [n] and h′ m [n] are line-of-sight and non-line-of-sight channel coefficients, respectively, satisfying E[|hm [n]| 2 ]+E[|h′ m [n]| 2 ] = 1; ε is the round trip delay of the line-of-sight channel; ε′ is the delay of the non-line-of-sight channel relative to the line-of-sight channel; in the aviation communication scenario, the power of the NLOS signal is much smaller than that of the LOS signal, so the impact of the NLOS signal on the random access performance can be ignored;

[0180] Based on the above aviation communication system model, the goal of preamble detection is to use the received signal y m [n], determine which assumption H0 or H1 is valid, and estimate the round-trip delay ε when H1 is valid, denoted as

[0181] Then obtain the received signal of the base station, divide the PRACH resource block into several shift correlation windows, and obtain the received signal of each shift correlation window.

[0182] In cells with larger radius, the range of RTD variation will also be larger. In order to expand the coverage, a common method is to use long CP to compensate RTD. However, this method reduces the spectrum efficiency. Another problem that needs to be solved is the channel coefficient h caused by the Doppler effect. m [n] time-varying characteristics; 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;

[0183] 1) Receive signal division:

[0184] Set the length to N b The PRACH resource block is divided into A window of length N, such as Figure 2 As shown, K=4 is used as an example; for simplicity, the length of the PRACH resource block N b Set to an integer multiple of the OFDM symbol length N;

[0185] The motivation for partitioning the PRACH resource blocks is that since the channel varies less in windows of shorter duration, the problem of fast time-varying channels can be solved by short preamble formats; 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 long CPs;

[0186] The vector composed of the signal of each window is recorded as y m,q =[y m [qN],…,y m [qN+N-1]] T ∈C N×1(m=0,…,M-1;q=0,…,Q-1); according to Figure 2 The round-trip delay ε can be expressed as ε = αN + β, where and β=<ε> N They represent the integer and fractional parts of the round-trip delay ε relative to the OFDM symbol length N, respectively;

[0187] According to equation (5), under assumption H0, the received signal of each window contains only noise;

[0188] Under the assumption H1, according to equations (4) and (6), we can get:

[0189]

[0190] Where n = 0, ..., N-1;

[0191] In addition, according to formula (2), we can get:

[0192]

[0193] Among them, for any φ, D(φ)=diag{1,e -j2πφ ,…,e -j2π(L-1)φ}∈C L×L , [·] n Represents the nth element of a vector;

[0194] Therefore, under assumption H1, the received signal of each window is:

[0195]

[0196] in:

[0197]

[0198] 2) SPC-assisted peak detection:

[0199] Similar to the traditional PRACH receiver, the SPC algorithm performs FFT and subcarrier demapping operations on each window to extract the frequency domain signal. The frequency domain signal is then correlated with the phase-shifted local sequence X. These operations can be expressed as:

[0200]

[0201] Among them, G H =M H F N represents the N-point FFT and subcarrier demapping operation, V is the number of phases; according to formula (11), we can derive If V is set to be no less than L and a power of 2, equation (11) can be efficiently calculated by IFFT;

[0202] When the subcarrier spacing Δf is sufficiently large, the channel can be considered to remain unchanged in one OFDM symbol period, then the channel matrix H of equation (10) is m,q It can be approximated as H m,q ≈H m,q I N ; Then, substitute equation (9) into equation (11) to obtain:

[0203]

[0204] Since β=〈ε〉 N , using the periodicity of D(·) we can get If the qth window, for example Figure 2 q∈{2,3,4} in contains a cyclic shift version of an OFDM symbol, then A q (ε)=I N ; This is because A q The nth diagonal element of (ε) indicates whether the nth sample of the qth window has sampled the leading edge; in this case, the following part of equation (12) can be simplified to:

[0205]

[0206] If (13) satisfies Then c shown in formula (12) m,q [v] will have a peak value; this means that m,q [v] peak detection leader;

[0207] However, the BS does not know which windows contain complete OFDM symbols, so it cannot detect the peak directly. A direct solution is to merge the correlation results of all windows, but this method also merges windows containing only noise, which reduces the detection performance. To overcome this shortcoming, this method proposes to merge the correlation results in a super window composed of K consecutive SCWs, which can be expressed as:

[0208]

[0209] Where u = 0, ..., QK represents the sequence number of the first window in each super window, and v = 0, ..., V-1; the next step is to find the peak value of Λ[u, v]:

[0210]

[0211] Then the peak value and a predefined threshold Compare; if , then it is assumed that If established, otherwise the assumption Established; 3) DEC-assisted RTD estimation: If we assume If holds, then the estimated value of the fractional round-trip delay is ; The remaining problem is to estimate the integer part of the round-trip delay ; 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. The windows are numbered 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:

[0216] However, the calculation results of the TBD algorithm may be unreliable, especially in the The first window and the The window contains a leading edge of close length, i.e. 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 RTDα;

[0217] Specifically, two parts of the received signal are intercepted r m,1 ∈C N×1 and r m,2 ∈C N×1 , respectively and Given; r m,1 and r m,2 Cross-correlating with the time domain OFDM symbol shown in equation (1) yields:

[0218]

[0219] Then the estimated value of the integer round-trip delay α is:

[0220]

[0221] Finally, the RTD is estimated as

[0222] Note that Equation (17) uses two fractionally shifted windows {r m,1 ,r m,2}, one of the windows contains the complete OFDM symbol, and the other window contains only noise; this makes the decision method based on {γ1,γ2} in equation (18) more accurate than the decision method based only on {γ1,γ2} in equation (16). The decision method of is more robust to noise; specifically, when the The first window and the The window contains a leading edge of close length, and equation (15) may be Output or in Output This makes formula (16) get the wrong result; therefore, formula (18) will be more reliable than formula (16);

[0223] Based on the above discussion, the SPC-DEC-PD algorithm involved in this method is summarized in Algorithm 1:

[0224]

[0225] In order to more fully illustrate the beneficial effects of this method, the effectiveness and advancement of this method are further explained in combination 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 obtained by replacing the DEC module in the SPC-DEC-PD scheme proposed by this method with the RTD estimation module based on TBD will also be used for comparison.

[0226] Table 1 Simulation parameters

[0227]

[0228]

[0229] 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 2.55μs, it is considered a false detection. The false detection rate performance of different algorithms is Figure 3 Given in, where E p / N0 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 SPC-DEC-PD algorithm proposed in this method has a signal-to-noise ratio gain of 2 to 4 dB compared with the existing algorithm; in addition, it can be observed that SPC-DEC-PD eliminates the false detection rate flattening caused by the limited estimation accuracy of the TBD module in SPC-TBD-PD;

[0230] 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 2.55μs, 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 Where P represents the number of preamble sequences, and U represents 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 by this method is better than the existing algorithm and is close to the theoretical upper limit, especially when the BS has more antennas;

[0231] Based on the short preamble format, this method designs an SPC-assisted peak detection algorithm. Unlike the traditional algorithm that merges the cross-correlation results of all correlation windows, SPC merges the cross-correlation results in a super window composed of partially shifted correlation windows (SCW) 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 position of the preamble detected by the SPC method, thereby achieving more robust RTD estimation.

[0232] The same or similar reference numerals correspond to the same or similar components;

[0233] The terms used in the drawings to describe positional relationships are only used for illustrative purposes and should not be construed as limiting this patent;

[0234] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A random access preamble detection method for aviation communication, 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 sends a signal to a base station through a PRACH resource block; S2: obtaining a received signal of the base station, dividing the PRACH resource block into a plurality of shift correlation windows, obtaining a received signal of each shift correlation window and performing signal preprocessing; S3: merging K consecutive shift correlation windows to construct a super window, and detecting the signal peak point and its corresponding peak value in 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 in the super window is greater than or equal to a preset threshold value. If so, the random access preamble exists, and step S5 is executed; otherwise, the random access preamble does not exist, and step S2 is executed again to obtain a new received signal; S5: Calculate an estimated value of the fractional round trip delay according to the signal peak point in 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 in 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 in 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. A 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 a plurality of airborne user equipments, each airborne user equipment has 1 transmitting antenna, and the base station has M receiving antennas; 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 starts a random access process; A PRACH resource block occupies L subcarriers in the frequency domain and has a duration of T in the time domain. b ; The subcarrier spacing of the aviation communication system is Δf, and the duration of an OFDM symbol is The length of the fast Fourier transform and the length of an OFDM symbol used in the aviation communication system are both N, and the sampling interval is The length of a PRACH resource block is In the random access process, each air user equipment randomly selects a sequence that satisfies x from a predefined set of preamble sequences. H x=L conditional leading sequence x∈C L×1 , a random access preamble is generated using the selected preamble sequence x and sent to the base station in the PRACH resource block, wherein C represents a complex set; the random access preamble adopts a preamble structure without a cyclic prefix, and is composed of K repeated OFDM symbols of length N, and the total length of the random access preamble is N p =KN.

3. The random access preamble detection method for aviation communication according to claim 2, characterized in that: The generating a random access preamble by using the selected preamble sequence x includes: The airborne user equipment calculates the frequency domain sequence X=[X[0],…,X[L-1]] by L-point discrete Fourier transform T ∈C L ×1 , expressed as X = F L x, where F L ∈C L×L represents the discrete Fourier transform matrix, whose elements are Where l1, l2 = 0, ..., L-1; Map the frequency domain sequence X to the subcarriers of the PRACH resource block and use N-point inverse fast Fourier transform to generate OFDM symbols s = [s[0], ..., s[N-1]] T ∈C N×1 , expressed as: Among them, G is an intermediate variable, satisfying M is the subcarrier mapping matrix, satisfying M=[0 L×ξ ,I L ,0 L×(N-ξ-L) ] T ∈R N×L , R represents the real number domain; ξ is a positive integer used to indicate the starting position of the subcarrier in the PRACH resource block; the intermediate variable G also satisfies G H G=NI L ; Each element in the OFDM symbol s is represented as: The generated random access preamble It is composed of K repeated s cascades, expressed as: The random access preamble Each element in is represented as: Where a[n] is the binarization coefficient. If n∈{0,…,N p -1}, then a[n]=1, otherwise a[n]=0; <·> N Represents a modulo-N operation.

4. The random access preamble detection method for aviation communication according to claim 3, characterized in that: In the aviation communication system, the assumptions that the random access preamble s does not exist and exists in the received signal of the base station are denoted as H0 and H1 respectively; Under the assumption H0, the received signal y of the mth antenna in the PRACH resource block is m [n] is: <h2 style=";text-align:left;direction:ltr">H0:y<h2 style=";text-align:left;direction:ltr"> m <h2 style=";text-align:left;direction:ltr"> [n]=w<h2 style=";text-align:left;direction:ltr"> m <h2 style=";text-align:left;direction:ltr"> [n] Among them, w n [n] represents additive white Gaussian noise with power spectral density N0; m = 0,…,M-1; n = 0,…,N b -1; Under assumption H1, the received signal y of the mth antenna in the PRACH resource block is m [n] is: Among them, z m [n] is the combined effect of non-line-of-sight signal and noise, satisfying ρ is the transmit power, is the path loss coefficient, h m [n] and h′ m [n] are line-of-sight and non-line-of-sight channel coefficients, respectively, satisfying E[|h m [n]| 2 ]+E[|h′ m [n]| 2 ]=1; ε is the round-trip delay of the line-of-sight channel; ε′ 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 the step S2, obtaining the received signal of each shifted correlation window includes: Set the length to N b The PRACH resource block is divided into shift correlation windows, each shift correlation window has a length of N; The vector formed by the signal in each shift correlation window is recorded as: m,q =[y m [qN],…,y m [qN+N-1]] T ∈C N×1 , where m = 0, ..., M-1; q = 0, ..., Q-1; Under the assumption H0, the received signal of each of the shifted correlation windows only contains additive white Gaussian noise; Under the assumption H1, the received signal of each shifted correlation window is expressed as: in, The round-trip delay ε of the line-of-sight channel is expressed as ε=αN+β, where β=<ε> N , α and β represent the integer and fractional parts of the round-trip delay ε relative to the OFDM symbol length N, respectively.

6. A 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 correlate the frequency domain signal with the phase-shifted frequency domain sequence X to obtain the preprocessed signal in each shift correlation window, which is expressed as: Among them, G H =M H F N , represents the N-point fast Fourier transform and subcarrier demapping operation; V is the preset number of phases; By detecting the signal c m,q The peak value of [v] 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: Wherein, Λ[u,v] is the signal in the super window; u represents the sequence number of the first shift correlation window in each super window, satisfying u=0,…,QK; Detect the signal peak point within the super window and its corresponding peak value It is expressed as: In step S4, the peak value Compared with the preset threshold value λ, if If assumption H1 holds, the random access preamble exists, and step S5 is executed; otherwise, if assumption H0 holds, 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 communication 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 It is 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 r m,1 and the second intercepted signal r m,2 , expressed as: Among them, the first intercepted signal r m,1 and the second intercepted signal r m,2 Satisfy r m,1 ∈C N×1 and r m,2 ∈C N×1 .

10. The random access preamble detection method for aviation communication according to claim 9, characterized in that: In step S6, the first intercepted signal r m,1 and the second intercepted signal r m,2 Cross-correlate with OFDM symbols respectively to construct the first discriminant factor γ1 and the second discriminant factor γ2, which are expressed as: Combine the signal peak points within the super window Calculates an estimate of the round-trip delay for integers It is expressed as: The overall round-trip delay estimate It is expressed as:

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