A PRACH format determination method based on LTE PRACH time domain frame structure

Abstract

The present invention relates to a PRACH format determination method based on an LTE PRACH time domain frame structure. The present invention proposes a PRACH format and Zadoff‑Chu (ZC) index number parameter synchronization method using a time-frequency signal structure for an LTE PRACH signal. The method uses the cyclic prefix structure of a PRACH signal frame and the cyclic prefix and preamble sequence lengths under different PRACH formats in the time domain to perform multiple rounds of binary classification on the format of the PRACH signal frame. In the frequency domain, the constant amplitude characteristic of the ZC sequence is used for verification. The method can accurately determine the format of the LTE PRACH signal frame, and since it does not need to decode the system information module parameters from the upper layer, it has lower implementation complexity and processing delay.

Description

Technical Field

[0001] The present invention relates to a determination method, in particular to a PRACH format determination method based on an LTE PRACH time domain frame structure, and belongs to the technical field of wireless communications. Background Art

[0002] The existing LTE PRACH signal synchronization method is mainly based on decoding the upper layer system parameters from the physical layer, generating a priori preamble sequences locally, and further performing cross-correlation operations and format determination on the unknown format received signal. The existing method increases the synchronization process delay and reduces the actual availability because it needs to decode the upper layer system information module. Therefore, a new solution is urgently needed to solve the above technical problems. Summary of the invention

[0003] The present invention is aimed at the problems existing in the prior art and provides a PRACH format determination method based on the LTE PRACH time domain frame structure. The technical problem to be solved by the technical solution is to avoid decoding the upper layer system information module and to avoid using local prior parameters to implement PRACH frame format determination in the process of format determination of the LTE PRACH signal. The present invention uses the frame structure characteristics of the LTE PRACH signal frame to design a format determination method without any other prior information, thereby reducing the implementation complexity and processing delay.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows: a PRACH format determination method based on the LTE PRACH time domain frame structure, a PRACH format determination method based on the LTE PRACH time domain frame structure, characterized in that the method comprises the following steps:

[0005] Step 1: Sample the LTE PRACH signal and process it synchronously;

[0006] Step 2: Carrier frequency offset estimation and correction;

[0007] Step 3: Determine whether the PRACH sample is format 2 / format 3, or format 0 / format 1 / format 4, based on whether there are two repeated 800 microsecond preamble sequences in the sampled signal;

[0008] Step 4: Determine whether the PRACH sample is format 2 / format 3 or format 0 / format 1 / format 4, based on whether there are two repeated 800 microsecond preamble sequences in the sampled signal;

[0009] Step 5: For the two major categories in step 4, calculate the correlation value between the cyclic prefix and its repeated part, and further determine the specific format of the PRACH sampling according to the length of the preamble sequence;

[0010] Step 6: The LTE PRACH frame obtained according to the above steps is further transformed into the frequency domain and the format determination result is verified according to the banner characteristic of the ZC sequence.

[0011] Among them, step 1 is as follows: Based on the cyclic prefix structure of the PRACH signal frame, the following formula can be used to achieve symbol synchronization in time:

[0012]

[0013] Where r(n) is the sampled PRACH signal, N CP is the sample length of the cyclic prefix, N SEQ is the sample length of the preamble sequence part in the PRACH frame, and N PRACH is the total sample length of the PRACH frame. The s value obtained according to formula (1) is the first sample point of the actual valid data. The method of implementing symbol synchronization according to the above steps utilizes the cyclic prefix structure of the PRACH sampling time domain frame. It does not need to use the locally known PRACH sequence to correlate with the PRACH sampling sequence for synchronization, and gets rid of the limitation of the prior information requirement.

[0014] Among them, step 2: is as follows:

[0015] Still using the cyclic prefix structure of the PRACH signal frame, the phase deviation of the signal sampling is estimated as

[0016]

[0017] Where k = 1L L and L is the number of repeated PRACH frames. Then, the carrier frequency offset can be calculated as

[0018]

[0019] where f s As the sampling rate, the signal sampling carrier frequency offset compensation can be

[0020]

[0021] The above steps can effectively estimate the frequency offset caused by the transmitter-receiver local oscillator error contained in the PRACH sampling signal and compensate for it, thereby effectively avoiding the adverse effect of the frequency deviation component in the PRACH sampling signal on the subsequent PRACH format determination processing.

[0022] Among them, step 3 is as follows: After the above steps, the PRACH signal frame has the following format: Figure 1There are five possibilities shown. Among them, format 2 and format 3 have two repeated preamble sequence parts, while format 1 and format 3 have the same cyclic prefix length, both of which are 684.3 microseconds. In terms of length, format 0 occupies one subframe, that is, 1 millisecond in length, format 1 and format 2 have the same length, both of which are 2 milliseconds, format 3 occupies 3 milliseconds in length, and format 4 is only valid in LTE TDD mode, and its length is less than one subframe. Utilizing the above characteristics of the LTE PRACH frame structure, the present invention uses a binary method to determine the format to which the unknown PRACH signal frame belongs;

[0023] First, starting from the first sampling point, calculate whether the current 800 microseconds data is strongly correlated with the next 800 microseconds data, and determine whether there are two repeated 800 microseconds length preamble sequences in the unknown format PRACH signal frame, so as to determine whether the current PRACH signal belongs to format 2 / 3 or format 0 / 1 / 4;

[0024] Then, for the above two cases, starting from the first sampling point, calculate whether the current 684 microseconds of data are strongly correlated with the next 684 microseconds of data, and determine whether the current PRACH signal frame belongs to format 3 or format 1;

[0025] Secondly, since the cyclic prefix lengths of format 0 and format 2 are 103.1 microseconds and 203.1 microseconds respectively, it is possible to calculate whether the current 103.1 microsecond data is strongly correlated with the next 103.1 microsecond data, and whether the current 203.1 microsecond data is strongly correlated with the next 203.1 microsecond data to determine whether the current PRACH signal frame belongs to format 0 or format 2;

[0026] Again, for the LTE TDD mode, it is possible to determine whether the unknown PRACH signal frame belongs to format 4 by calculating whether the current 14.58 microseconds data is strongly correlated with the next 14.58 microseconds data.

[0027] Finally, the format result obtained by the above method is verified by using the frequency domain ZC sequence. Fourier transform processing is performed on the PRACH signal frame r(n) (n=1...L, L is)

[0028] R(ω)=W L [FFT(r(n))] (5)

[0029] Where W L [g] represents a window of length L. Then R(ω) in formula (5) represents the frequency domain ZC sequence. The PRACH frame format determination result proposed in the present invention is verified by judging whether its amplitude |R(ω)| is constant. If the value of |R(ω)| is constant, it means that the frequency domain ZC sequence is extracted accurately, thereby indirectly indicating that the format determination of r(n) is correct.

[0030] Compared with the prior art, the present invention has the following advantages: the technical solution can quickly determine the format of the LTE PRACH signal frame according to the above method, and does not need to rely on the communication parameters of the upper layer of the communication protocol, avoiding decoding the system information module of the media access layer to obtain the local PRACH sequence format information, thereby simplifying the complexity of LTE PRACH signal format determination and reducing processing delay. Simulation experimental results show that even under low signal-to-noise ratio conditions, the accuracy of this method remains above 98%, and under conditions where the signal-to-noise ratio is higher than 0 decibels, the format determination accuracy of this method reaches 100%. This shows that the present method can effectively realize accurate determination of the PRACH signal frame format at the physical layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the LTE PRACH signal frame format;

[0032] Figure 2 Schematic diagram of the performance of the binary method for determining the PRACH signal frame format; DETAILED DESCRIPTION

[0033] In order to deepen the understanding of the present invention, the present embodiment is described in detail below with reference to the accompanying drawings.

[0034] Example 1: See Figure 1 The present invention proposes a PRACH format synchronization method using a time-frequency signal structure for LTE PRACH signals, and the specific technical steps are as follows.

[0035] 1. Sample the LTE PRACH signal and perform synchronization and frequency offset preprocessing according to the following steps.

[0036] (1) Synchronization

[0037] Based on the cyclic prefix structure of the PRACH signal frame, the following formula can be used to achieve symbol synchronization in time:

[0038]

[0039] Where r(n) is the sampled PRACH signal, N CP is the sample length of the cyclic prefix, N SEQ is the sample length of the preamble sequence part in the PRACH frame, and N PRACH is the total sample length of the PRACH frame. The s value obtained according to formula (1) is the first sample point of the actual valid data.

[0040] (2) Carrier frequency offset estimation and correction

[0041] Still using the cyclic prefix structure of the PRACH signal frame, the phase deviation of the signal sampling is estimated as

[0042]

[0043] Where k = 1L L and L is the number of repeated PRACH frames. Then, the carrier frequency offset can be calculated as

[0044]

[0045] where f s is the sampling rate. The signal sampling carrier frequency offset compensation can be

[0046]

[0047] (3) PRACH format determination

[0048] The PRACH signal frame processed by the above steps has the following format: Figure 1 There are five possibilities shown. Among them, format 2 and format 3 have two repeated preamble sequence parts, while format 1 and format 3 have the same cyclic prefix length, both of which are 684.3 microseconds. In terms of length, format 0 occupies one subframe, that is, 1 millisecond in length, format 1 and format 2 have the same length, both of which are 2 milliseconds, format 3 occupies 3 milliseconds in length, and format 4 is only valid in LTE TDD mode, and its length is less than one subframe. Utilizing the above characteristics of the LTE PRACH frame structure, the present invention designs a binary method to determine the format to which the unknown PRACH signal frame belongs.

[0049] First, starting from the first sampling point, calculate whether the current 800 microseconds data is strongly correlated with the next 800 microseconds data, and determine whether there are two repeated 800 microseconds length preamble sequences in the unknown format PRACH signal frame, so as to determine whether the current PRACH signal belongs to format 2 / 3 or format 0 / 1 / 4;

[0050] Then, for the above two cases, starting from the first sampling point, calculate whether the current 684 microseconds of data are strongly correlated with the next 684 microseconds of data, and determine whether the current PRACH signal frame belongs to format 3 or format 1;

[0051] Secondly, since the cyclic prefix lengths of format 0 and format 2 are 103.1 microseconds and 203.1 microseconds respectively, it is possible to calculate whether the current 103.1 microsecond data is strongly correlated with the next 103.1 microsecond data, and whether the current 203.1 microsecond data is strongly correlated with the next 203.1 microsecond data to determine whether the current PRACH signal frame belongs to format 0 or format 2;

[0052] Again, for the LTE TDD mode, it is possible to determine whether the unknown PRACH signal frame belongs to format 4 by calculating whether the current 14.58 microseconds data is strongly correlated with the next 14.58 microseconds data.

[0053] Finally, the format result determined by the above method is verified by using the frequency domain ZC sequence. Fourier transform processing is performed on the PRACH signal frame r(n) (n=1...L, L is).

[0054] R(ω)=W L [FFT(r(n))] (5)

[0055] Where W L [g] represents a window of length L. Then R(ω) in equation (5) represents the frequency domain ZC sequence. The PRACH frame format determination result proposed in the present invention is verified by judging whether its amplitude |R(ω)| is constant. If the value of |R(ω)| is constant, it means that the frequency domain ZC sequence is extracted accurately, which indirectly indicates that the format determination of r(n) is correct.

[0056] like Figure 2 The figure shows the performance of the LTE PRACH format binary determination method proposed in the present invention. For LTE FDD format, formats 0 to 3 can be determined with a very low error rate. Especially in the area where the signal-to-noise ratio is greater than 0, the error rate of the method proposed in the present invention in determining the LTE PRACH format is 0.

[0057] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A PRACH format determination method based on LTE PRACH time domain frame structure, characterized in that: The method comprises the following steps: Step 1: Sample the LTE PRACH signal and process it synchronously; Step 2: Carrier frequency offset estimation and correction; Step 3: Determine whether the PRACH sample is format 2 / format 3 or format 0 / format 1 / format 4, based on whether there are two repeated 800 microsecond preamble sequences in the sampled signal; Step 4: For the two major categories in step 4, calculate the correlation value between the cyclic prefix and its repeated part, and further determine the specific format of the PRACH sampling according to the length of the preamble sequence; Step 5: The LTE PRACH frame obtained according to the above steps is further transformed into the frequency domain and the format determination result is verified according to the banner characteristic of the ZC sequence; Step 1 is as follows: Based on the cyclic prefix structure of the PRACH signal frame, the following formula is used to achieve symbol synchronization in time: Where r(n) is the sampled PRACH signal, N CP is the sample length of the cyclic prefix, N SEQ is the sample length of the preamble sequence part in the PRACH frame, and N PRACH is the total sample length of the PRACH frame. The s value obtained according to formula (1) is the first sample point of the actual valid data. Step 2: The details are as follows: Still using the cyclic prefix structure of the PRACH signal frame, first estimate the phase deviation of the signal sampling as Where k = 1...L, and L is the number of repeated PRACH frames, then the carrier frequency offset can be calculated as where f s As the sampling rate, the signal sampling carrier frequency offset compensation can be Step 3 is as follows: using a binary search method to determine the format of the unknown PRACH signal frame; First, starting from the first sampling point, calculate whether the current 800 microseconds data is strongly correlated with the next 800 microseconds data, and determine whether there are two repeated 800 microseconds length preamble sequences in the unknown format PRACH signal frame, so as to determine whether the current PRACH signal belongs to format 2 / 3 or format 0 / 1 / 4; Then, for the above two cases, starting from the first sampling point, calculate whether the current 684 microseconds of data are strongly correlated with the next 684 microseconds of data, and determine whether the current PRACH signal frame belongs to format 3 or format 1; Secondly, since the cyclic prefix lengths of format 0 and format 2 are 103.1 microseconds and 203.1 microseconds respectively, it is possible to calculate whether the current 103.1 microsecond data is strongly correlated with the next 103.1 microsecond data, and whether the current 203.1 microsecond data is strongly correlated with the next 203.1 microsecond data to determine whether the current PRACH signal frame belongs to format 0 or format 2; Again, for LTE TDD mode, it is possible to determine whether the unknown PRACH signal frame belongs to format 4 by calculating whether the current 14.58 microseconds data is strongly correlated with the next 14.58 microseconds data; Finally, the format result obtained by the above method is verified using the frequency domain ZC sequence. For the PRACH signal frame r(n), n=1…L, L is the Fourier transform processing. R(ω)=W L [FFT(r(n))](5) Where W L [g] represents a window of length L, then R(ω) in equation (5) represents the frequency domain ZC sequence. The PRACH frame format determination result is verified by judging whether its amplitude |R(ω)| is constant. If the value of |R(ω)| is constant, it means that the frequency domain ZC sequence is extracted accurately, which indirectly indicates that the format determination of r(n) is correct.

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