CN112039810A

CN112039810A - Frequency domain OFDM symbol generation method and preamble symbol generation method

Info

Publication number: CN112039810A
Application number: CN202010374107.8A
Authority: CN
Inventors: 张文军; 徐洪亮; 黄戈; 邢观斌; 何大治; 管云峰
Original assignee: Shanghai National Engineering Research Center of Digital Television Co Ltd
Current assignee: Shanghai National Engineering Research Center of Digital Television Co Ltd
Priority date: 2014-04-30
Filing date: 2014-05-05
Publication date: 2020-12-04
Anticipated expiration: 2034-05-05
Also published as: CN105024963A; CN106992951A; CN112039810B; CN107046514A

Abstract

The invention discloses a method for generating a frequency domain OFDM symbol and a method for generating a preamble symbol, wherein the method for generating the frequency domain OFDM symbol comprises the following steps: respectively generating a fixed sequence and a signaling sequence on a frequency domain; filling a fixed sequence and a signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner; and filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length. The technical scheme avoids the characteristic that the generated signaling sequence has cyclic shift or cyclic shift plus phase shift in the time domain, and solves the problem of the performance reduction of frequency domain channel estimation. Further, the receiving end can still process the received signal within the range of-500 kHz to 500kHz by ensuring the carrier frequency deviation.

Description

Frequency domain OFDM symbol generation method and preamble symbol generation method

The patent application of the invention is a divisional application of Chinese patent application having an application number of 201410185112.9 and entitled "Generation method of frequency-Domain OFDM symbol and Generation method of preamble symbol" on 5 th month 5 th 2014.

Technical Field

The invention relates to the technical field of wireless broadcast communication, in particular to a method for generating frequency domain OFDM symbols and a method for generating preamble symbols in physical frames.

Background

Generally, in order for a receiving end of an OFDM system to correctly demodulate data transmitted by a transmitting end, the OFDM system must implement accurate and reliable time synchronization between the transmitting end and the receiving end. Meanwhile, since the OFDM system is very sensitive to the carrier frequency offset, the receiving end of the OFDM system needs to provide an accurate and efficient carrier frequency spectrum estimation method to accurately estimate and correct the carrier frequency offset.

At present, a method for implementing time synchronization between a transmitting end and a receiving end in an OFDM system is basically implemented based on preamble symbols. The preamble symbol is a symbol sequence known to both the transmitting end and the receiving end of the OFDM system, and serves as the start of a physical frame (named P1 symbol), and the P1 symbol appears only once in each physical frame, and marks the start of the physical frame. The P1 symbols have the following uses:

1) enabling a receiving end to quickly detect whether a signal transmitted in a channel is an expected received signal;

2) providing basic transmission parameters (such as FFT point number, frame type information and the like) so that a receiving end can perform subsequent receiving processing;

3) and detecting initial carrier frequency offset and timing error, and compensating to achieve frequency and timing synchronization.

The DVB _ T2 standard provides a P1 symbol design based on a CAB time domain structure, and the functions are well realized. However, there are still some limitations on low complexity reception algorithms. For example, in a long multipath channel with 1024, 542, or 482 symbols, a large deviation occurs in timing coarse synchronization using the CAB structure, which results in an error in estimating the carrier integer multiple frequency offset in the frequency domain.

In addition, in the process of generating the frequency domain OFDM symbol, a fixed sequence and a signaling sequence need to be generated in the frequency domain. However, the signaling sequence generated by the prior art has a relatively high peak-to-average power, and the signaling sequence is cyclically shifted in the time domain or cyclically shifted plus shifted, which may cause a failure in the multipath channel when the transmitted sequence is detected by correlating the received signal with the set of known sequences in the time domain.

Disclosure of Invention

The invention solves the problems that the signaling sequence generated by the prior art has higher peak average power and the signaling sequence is circularly shifted or circularly shifted and phase shifted on a time domain. Moreover, the DVB _ T2 standard proposes the problem that the performance of frequency domain channel estimation is reduced due to the design of P1 symbols based on the CAB time domain structure.

In order to solve the above problem, an embodiment of the present invention provides a method for generating a frequency domain OFDM symbol, including the following steps: respectively generating a fixed sequence and a signaling sequence on a frequency domain; filling a fixed sequence and a signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner; and filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.

Optionally, generating the signaling sequence in the frequency domain includes:

determining the length and the number of the signaling sequences;

determining root values in a CAZAC sequence generation formula based on the length and the number of the signaling sequences; the length of the signaling sequence is less than or equal to a root value, and the root value is more than or equal to twice of the number of the signaling sequences; the root value is preferably chosen as the length of the signaling sequence.

Selecting different q values to generate a CAZAC sequence, wherein the number of the q values is equal to the number of the signaling sequences, and the sum of any two q values is not equal to a root value; the generated CAZAC sequence needs to be subjected to cyclic shift, and the bit number of the cyclic shift is determined by a corresponding root value and a q value;

and selecting the signaling sequence from all CAZAC sequences according to the determined number of the signaling sequences.

Optionally, the length of the signaling sequence is 353, the number of the signaling sequences is 128, and the root value is 353;

the values of q are all in the following table:

1	9	10	16	18	21	28	29	32	35	49	51	53	54	55
															57	59	60	61	65	68	70	74	75	76	77	78	82	84	85
86	88	90	95	96	103	113	120	123	125	126	133	134	135	137
															138	140	141	142	145	147	148	150	151	155	156	157	161	163	165
167	170	176	178	179	181	182	184	185	187	194	200	201	204	209
															210	217	222	223	224	225	229	232	234	235	237	239	241	244	246
247	248	249	251	252	253	254	255	262	270	272	273	280	282	290
															291	306	307	308	309	311	313	314	315	317	320	326	327	330	331
333	336	338	340	342	345	347	349

the number of bits of the cyclic shift is all the values in the following table:

105	244	172	249	280	251	293	234	178	11	63	217	83	111	282
															57	85	134	190	190	99	180	38	191	22	254	186	308	178	251
277	261	44	271	265	298	328	282	155	284	303	113	315	299	166
															342	133	115	225	13	26	326	148	195	145	185	121	58	162	118
151	182	230	39	249	305	309	144	188	181	265	140	212	137	10
															298	122	281	181	267	178	187	177	352	4	353	269	38	342	288
277	88	124	120	162	204	174	294	166	157	56	334	110	183	131
															171	166	321	96	37	261	155	34	149	156	267	332	93	348	300
245	101	186	117	329	352	215	55

optionally, generating the signaling sequence in the frequency domain includes:

determining the length and the number of the signaling sequences;

determining a plurality of root values in a CAZAC sequence generation formula based on the length and the number of the signaling sequences; the length of the signaling sequence is smaller than or equal to the minimum value of the selected plurality of root values, and the sum of the selected plurality of root values is larger than or equal to twice the number of the signaling sequence;

selecting different q values to generate a CAZAC sequence aiming at each root value, wherein the number of the q values is less than or equal to 1/2 of the corresponding root value, and the sum of any two q values is not equal to the corresponding root value; the generated CAZAC sequence needs to be subjected to cyclic shift, and the bit number of the cyclic shift is determined by a corresponding root value and a q value;

and selecting the signaling sequence from each obtained CAZAC sequence according to the determined number of the signaling sequences.

Optionally, the number of q values is selected to be different for each root value, and the sum of the number of q values is equal to the number of signaling sequences.

Optionally, one root value of the plurality of root values is selected as the length of the signaling sequence.

Optionally, the selecting the signaling sequence from each CAZAC sequence obtained according to the determined length of the signaling sequence includes: and determining the signaling sequence according to the CAZAC sequence generated by the root value selected as the length of the signaling sequence.

Optionally, the root value is a prime number.

Optionally, the generation of the fixed sequence is calculated based on the generated signaling sequence.

Optionally, the fixed sequence is as follows:

wherein, ω is_nThe values of (A) are arranged in rows from left to right in sequence as shown in the following table:

optionally, the length of the fixed sequence is equal to the length of the signaling sequence, and the length is smaller than 1/2 of the predetermined length.

Optionally, the filling zero sequence subcarriers at two sides of the effective subcarrier to form a frequency domain OFDM symbol with a predetermined length respectively includes: and filling zero sequence subcarriers with equal length on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.

Optionally, the length of the zero sequence subcarrier filled on each side is greater than a critical length value, and the critical length value is determined by the system sampling rate, the symbol rate and the predetermined length.

Optionally, the predetermined length is 1024.

Optionally, the fixed sequence and the signaling sequence are constant modulus sequences.

Optionally, the average power of the fixed sequence and the signaling sequence are the same or different.

The embodiment of the invention also provides a method for generating the preamble symbol in the physical frame, which comprises the following steps: obtaining a frequency domain OFDM symbol with a preset length according to the generation method of the frequency domain OFDM symbol; performing inverse discrete Fourier transform on the frequency domain OFDM symbol with the preset length to obtain a time domain OFDM symbol; determining a cyclic prefix length; intercepting the time domain OFDM symbol with the cyclic prefix length from the time domain OFDM symbol as a cyclic prefix; generating a modulation signal based on the intercepted time domain OFDM symbol with the cyclic prefix length; generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol, and the modulation signal.

Optionally, after the generating a modulation signal based on the truncated time domain OFDM symbol with the cyclic prefix length further includes: determining a length of the modulated signal; and based on the length of the modulation signal, transmitting the signaling information by selecting different starting positions in the part of the time domain OFDM symbols for intercepting the cyclic prefix.

Optionally, the signaling information includes hook information, transmitter flag information, or other transmission parameters.

Optionally, the predetermined length is 1024, the cyclic prefix length and the length of the modulation signal are 512.

Optionally, the generating a modulation signal based on the truncated time domain OFDM symbol with the cyclic prefix length includes: setting a frequency shift sequence; and multiplying the time domain OFDM symbol with the cyclic prefix length or a part of the time domain OFDM symbol with the cyclic prefix length by the frequency shift sequence to obtain the modulation signal.

Optionally, the generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol, and the modulation signal includes: and splicing the cyclic prefix at the front part of the time domain OFDM symbol as a guard interval, and splicing the modulation signal at the rear part of the OFDM symbol as a modulation frequency offset part to generate a preamble symbol.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

according to the method for generating the frequency domain OFDM symbol provided by the embodiment of the invention, the fixed sequence and the signaling sequence are filled on the effective subcarriers in a parity interleaving mode, and through the specific frequency domain structure design, the fixed sequence can be used as the pilot frequency in the physical frame, so that a receiving end can conveniently decode and demodulate the preamble symbol in the received physical frame.

Moreover, the signaling sequence and the fixed sequence both adopt constant modulus sequences, have smaller Peak to Average Power Ratio (PAPR), and avoid the characteristic that the generated signaling sequence has cyclic shift or cyclic shift plus phase shift in the time domain, which can cause the problem of failure in the multipath channel when the transmitted sequence is detected by correlating the time domain known sequence set with the received signal.

According to the method for generating the preamble symbol in the physical frame provided by the embodiment of the invention, the cyclic prefix length is determined according to different channel environments, and the time domain OFDM symbol with the cyclic prefix length is intercepted from the time domain OFDM symbol to be used as the cyclic prefix, so that the problem of the reduction of the frequency domain channel estimation performance is solved. And generating a modulation signal based on the intercepted time domain OFDM symbol with the cyclic prefix length, so that the generated preamble symbol has good decimal frequency offset estimation performance and timing synchronization performance.

Furthermore, a part of or all data segments copied to the cyclic prefix in the time domain OFDM symbol can be taken from the modulation signal, and the signaling parameters are transmitted by selecting different starting positions.

Furthermore, the structure of the modulation signal using the time domain OFDM symbol and the time domain OFDM symbol (as a preamble symbol) ensures that a distinct peak can be obtained at the receiving end using delay correlation. In addition, in the process of generating the preamble symbol, the modulation signal of the time domain OFDM symbol is designed to avoid that the receiving end is subjected to continuous wave interference or single frequency interference, or that a multipath channel with the same length as the modulation signal occurs, or that a false detection peak occurs when the guard interval length in the received signal is the same as the length of the modulation signal.

Drawings

Fig. 1 is a flowchart illustrating a method for generating a frequency domain OFDM symbol according to an embodiment of the present invention;

fig. 2 is a flowchart illustrating a method for generating preamble symbols in a physical frame according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a CAB structure of a preamble symbol generated by the method for generating a preamble symbol in a physical frame shown in fig. 2.

Detailed Description

The inventor finds that the signaling sequence generated by the prior art has higher peak average power and the signaling sequence is cyclically shifted or cyclically shifted plus phase shifted in the time domain.

In view of the above problems, the inventors have studied and provided a method for generating a frequency domain OFDM symbol and a method for generating a preamble symbol in a physical frame. The generated signaling sequence is prevented from having the characteristic of cyclic shift or cyclic shift plus phase shift in the time domain. And the problem of the performance reduction of frequency domain channel estimation is solved, and the time domain OFDM symbol is utilized to generate a modulation signal, so that the generated preamble symbol has good decimal frequency offset estimation and timing synchronization performance. Further, the receiving end can still process the received signal within the range of-500 kHz to 500kHz by ensuring the carrier frequency deviation.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

Fig. 1 is a schematic flow chart of a specific embodiment of a method for generating a frequency domain OFDM symbol according to the present invention. Referring to fig. 1, the method for generating a frequency domain OFDM symbol includes the steps of:

step S11: respectively generating a fixed sequence and a signaling sequence on a frequency domain;

step S12: filling a fixed sequence and a signaling sequence onto effective subcarriers, wherein the fixed sequence and the signaling sequence are arranged in a parity staggered manner;

step S13: and filling zero sequence subcarriers on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.

Specifically, as described in step S11, the fixed sequence and the signaling sequence are generated in the frequency domain, respectively. The fixed sequence includes the relevant information that the receiving end can use to do carrier frequency synchronization and timing synchronization, and the signaling sequence includes each basic transmission parameter.

In this embodiment, the fixed sequence and the signaling sequence are both constant modulus sequences, and the modulus of each complex number in the fixed sequence and the signaling sequence is equal. It should be noted that the complex number includes a real number (i.e., the imaginary part of the complex number is zero). Thus, the average power of the signaling sequence and the fixed sequence is the same.

In other embodiments, the average powers of the fixed sequence and the signaling sequence may be the same or different, and may be adjusted according to the actual application requirement, and the power of the fixed sequence is selectively increased to obtain better channel estimation and offset estimation performance, or the power of the signaling sequence is selectively increased to improve the actual signal-to-noise ratio on the signaling carrier to improve the signaling decoding performance.

In this embodiment, the signaling sequence may be generated in the frequency domain in any one of the following two ways, and the two ways of generating the signaling sequence are described in detail below.

Mode 1:

1.1, determining the length and the number of signaling sequences;

1.2 determining root values in a CAZAC sequence generation formula based on the length and the number of the signaling sequences; the length of the signaling sequence is smaller than or equal to the root value, and the root value is larger than or equal to twice of the number of the signaling sequences. Preferably, the root value is chosen as the length of the signaling sequence.

For example, the sequence length L and the number of signalings are determined. For example, if N bits are to be transmitted, the number of signaling num is 2^NAnd selects the root value of exp (j pi qn (n +1)/root) in the CAZAC sequence generation formula. Wherein, the sequence length L is less than or equal to the root value, and the root value is more than or equal to 2 x num. Root values are typically prime numbers.

1.3 selecting different q values to generate a CAZAC sequence, wherein the number of the q values is equal to the number of signaling sequences, and the sum of any two q values is not equal to a root value; and the generated CAZAC sequence needs to undergo cyclic shift, and the number of bits of the cyclic shift is determined by the corresponding root value and q value.

For example, num different q's are selected₀、q₁、……、q_num-1Generating a CAZAC sequence:

s(n)＝exp(jπqn(n+1)/root),n＝0,...root-1。

the sequences after cyclic shift are:

s_k(n)＝[s(k),s(k+1),...,s(L-1),s(0),...,s(k-1)]

where k is the number of cyclically shifted bits.

In this embodiment, q is selected_i(0. ltoreq. i. ltoreq. num-1) must satisfy the following conditions: any 2 q_i、q_j(0. ltoreq. i, j. ltoreq. num-1) satisfies q_i+q_j≠root.

Under the above conditions, a sequence that makes the PAPR of the entire frequency domain OFDM symbol low is preferentially selected. And if L is equal to or greater than 2 × num, root is preferably selected to be L.

1.4 selecting the signaling sequence from all CAZAC sequences according to the determined number of the signaling sequences. Note that, if L is root, truncation is not necessary, and the obtained CAZAC sequence can be used as a signaling sequence.

For example, each of the num sequences is truncated into a continuous partial sequence or a complete sequence with a length of L as a signaling sequence.

For example, if the length L of the signaling sequence is 353 and the number num is 128, the root can be selected as the closest prime 353. The value range of q is 1-352, and the value range of cyclic shift digits of each sequence is 1-353. Among all the selectable signaling sequences, the following 128 groups are preferred, whose q values and cyclic shift bits are respectively shown in the following table:

q value table

Cyclic shift digit table

Based on the known signaling sequence, a preferred fixed sequence is calculated as follows:

mode 2:

2.1 determining the length and the number of the signaling sequences;

2.2 determining a plurality of root values in a CAZAC sequence generation formula based on the length and the number of the signaling sequences; the length of the signaling sequence is smaller than or equal to the minimum value of the selected plurality of root values, and the sum of the selected plurality of root values is larger than or equal to twice the number of the signaling sequences. Preferably, the root value is chosen as the length of the signaling sequence.

For example, the sequence length L and the number of signalings are determined. For example, if N bits are to be transmitted, the number of signaling num is 2^NAnd selecting a plurality of K roots of exp (j pi qn (n +1)/root) in the CAZAC sequence generation formula_k(K is more than or equal to 0 and less than or equal to K-1). Wherein the length L of the signaling sequence is less than or equal to all roots_kMinimum value of, and a number of roots_kIs greater than or equal to 2 x num, i.e.

Root in general_kThe values are prime numbers.

2.3 for each root value, selecting different q values to generate a CAZAC sequence, wherein the number of the q values is less than or equal to 1/2 of the corresponding root value, and the sum of any two q values is not equal to the corresponding root value; and the generated CAZAC sequence needs to undergo cyclic shift, and the number of bits of the cyclic shift is determined by the corresponding root value and q value.

For example, for each root_k(K is more than or equal to 0 and less than or equal to K-1), num is selected_kA different q₀、q₁、

Generating a CAZAC sequence exp (j π qn (n +1)/root_k),n＝0,...root_k-1. Wherein the content of the first and second substances,

and is

In this embodiment 2, for each root value, different q values are selected to generate a CAZAC sequence, and the manner in which the generated CAZAC sequence needs to undergo cyclic shift may refer to the description of the above embodiment 1, and will not be described again here.

In this embodiment, q is selected_i(0≤i≤num_k-1) the following conditions must be satisfied: any 2 q_i、q_j(0≤i,j≤num_k-1) satisfies q_i+q_j≠root_k。

Under the above conditions, a sequence that makes the PAPR of the entire frequency domain OFDM symbol low is preferentially selected. And one of the root ═ L may be preferentially selected. So that the autocorrelation value of the sequence generated by the root is zero.

And 2.4 selecting the signaling sequence from each obtained CAZAC sequence according to the determined number of the signaling sequences. It is emphasized that if a root is L, the signaling sequence is determined from the CAZAC sequence generated from the root value selected as the length of the signaling sequence.

For example, L353 and num 128, for example. Root is preferentially selected to be 353 in mode 1. Then, q is selected to be 1,2, … 128. Satisfy q_i+q_jNot equal to 353, (i is more than or equal to 0, and j is more than or equal to 128-1). Finally, each sequence is truncated to a length of 353.

For another example, L is 350 and num is 256. In mode 2, root1 is selected as 353, root2 as 359, and then for root1 as 353, a total of 128 sequences, q 1,2,3, … 128, are selected, q_i+q_jNot equal to 353. Then 128 sequences of q 100,101,102, … 227 were selected for root2 359, for a total of 256 sequences. Finally each sequence is truncated to a length of 353.

The fixed sequence and the signaling sequence are padded on the active subcarriers and are arranged in a parity staggered manner as described in step S12.

In a preferred embodiment, the length of the fixed sequence is equal to the length of the signaling sequence, and the length is less than 1/2 of the predetermined length. The predetermined length is 1024, but it can be changed according to the system requirement in practical application.

Taking the predetermined length as 1024 as an example, let the length of the fixed sequence be N (that is, the number of the effective subcarriers carrying the fixed sequence be N), and the length of the signaling sequence be M (that is, the number of the effective subcarriers carrying the signaling sequence be M), where M is equal to N in this embodiment. In other embodiments, N may also be slightly larger than M.

The fixed sequence and the signaling sequence are arranged in a parity staggered manner, namely the fixed sequence is filled to the position of even subcarrier (or odd subcarrier), correspondingly, the signaling sequence is filled to the position of odd subcarrier (or even subcarrier), thereby the distribution state of the parity staggered arrangement of the fixed sequence and the signaling sequence is presented on the effective subcarrier of the frequency domain. It should be noted that, when the lengths of the fixed sequence and the signaling sequence are not consistent (for example, M > N), the parity interleaving of the fixed sequence and the signaling sequence may be implemented by means of zero padding sequence subcarriers.

Zero sequence subcarriers are padded on both sides of the effective subcarrier to form frequency domain OFDM symbols of a predetermined length, respectively, as described in step S13.

In a preferred embodiment, this step comprises: and filling zero sequence subcarriers with equal length on two sides of the effective subcarriers respectively to form frequency domain OFDM symbols with preset length.

Following the example of a predetermined length of 1024, the length G of the zero-sequence subcarrier is 1024-M-N, and (1024-M-N)/2 zero-sequence subcarriers are padded on both sides.

Further, in order to ensure that the receiving end can still process the received signal within the carrier frequency deviation range of-500 kHz to 500kHz, the value of (1024-M-N)/2 is usually larger than the critical length value (set to TH), which is determined by the systematic symbol rate and the predetermined length. E.g. a systematic symbol rate of 1024, 7.61M, and a sampling rate of 9.14M, the predetermined length is then 1024

For example, when M is 350, G is 324, and each side is padded with 162 zero-sequence subcarriers.

Accordingly, subcarriers (i.e., frequency domain OFDM symbols) P1_ X of a predetermined length (1024) are provided₀,P1_X₁,…,P1_X₁₀₂₃Generated by filling in the following way:

wherein the content of the first and second substances,

the parity positions may be interchanged.

Fig. 2 is a flowchart illustrating a method for generating preamble symbols in a physical frame according to an embodiment of the present invention. Referring to fig. 2, the method for generating preamble symbols in a physical frame includes the following steps:

step S21: generating a frequency domain OFDM symbol with a preset length according to the generation method of the frequency domain OFDM symbol;

step S22: performing inverse discrete Fourier transform on the frequency domain OFDM symbol with the preset length to obtain a time domain OFDM symbol;

step S23: determining a cyclic prefix length;

step S24: intercepting the time domain OFDM symbol with the cyclic prefix length from the time domain OFDM symbol as a cyclic prefix;

step S25: generating a modulation signal based on the intercepted time domain OFDM symbol with the cyclic prefix length;

step S26: generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol, and the modulation signal.

In this embodiment, reference may be made to the description of the above embodiment for implementation of the step S21, and details are not repeated here.

As shown in step S22, the frequency domain OFDM symbol with the predetermined length is inverse discrete fourier transformed to obtain a time domain OFDM symbol.

The inverse discrete fourier transform described in this step is a common way of converting a frequency domain signal into a time domain signal, and is not described herein again.

P1_X_iObtaining a time domain OFDM symbol after performing inverse discrete Fourier transform:

the cyclic prefix length is determined as described in step S23.

Unlike the prior art, in the embodiment, a Cyclic Prefix (CP) needs to be added before the time domain OFDM symbol, and the wireless broadcast communication system can determine the length of the CP (set to N) according to different channel environments_cp). For example, the cyclic prefix length may be determined based on the length of the multipath against which the wireless broadcast communication system needs to contend. That is, when generating the preamble symbol, the wireless broadcast communication system can determine the multipath length that the preamble symbol needs to contend with, and thus determine the cyclic prefix.

The time domain OFDM symbol of the cyclic prefix length is truncated from the time domain OFDM symbol as a cyclic prefix as stated in step S24.

In this embodiment, the cyclic prefix length is equal to or less than the predetermined length. Taking the predetermined length as 1024 as an example, the cyclic prefix length may be 1024 or less than 1024. Preferably, the cyclic prefix length is 512, that is, in this step, the second half (length is 512) of the time domain OFDM symbol is truncated as the cyclic prefix, so as to solve the problem of performance degradation of frequency domain channel estimation.

And as indicated by step S25, generating a modulated signal based on the truncated time domain OFDM symbol with the cyclic prefix length. In practice, the length of the modulated signal cannot exceed the length of the cyclic prefix portion.

Specifically, the method comprises the following steps:

1) setting a frequency shift sequence;

2) and multiplying the time domain OFDM symbol with the cyclic prefix length or a part of the time domain OFDM symbol with the cyclic prefix length by the frequency shift sequence to obtain the modulation signal.

For example, let N_cpFor a determined cyclic prefix length, Len_BIs the length of the modulated signal. Let N_cpFor a determined cyclic prefix length, Len_BIs the length of the modulated signal. Let N_ASetting the sampling point serial number of the time domain OFDM symbol as 0,1, … N for the length of the time domain OFDM symbol_AAnd 1, setting N1 as the sampling point sequence number of the time domain OFDM symbol corresponding to the starting point selected to be copied to the modulation signal segment, and setting N2 as the sampling point sequence number of the time domain OFDM symbol corresponding to the end point selected to be copied to the modulation signal segment. Wherein the content of the first and second substances,

N2＝N1+Len_B-1

for convenience of description, the time domain OFDM symbol is divided into 2 parts, the first part is a front part which is not truncated as a cyclic prefix, and the second part is a rear part which is truncated as a cyclic prefix. If the time domain OFDM symbols are all truncated as cyclic prefixes, the first segment is 0 length, and N1 must fall within the second segment, i.e., the range of the portion of the time domain OFDM symbols selected for the modulation signal segment does not exceed the range of the portion of the time domain OFDM symbols truncated as cyclic prefixes.

As shown in fig. 3, a segment a represents a time domain OFDM symbol, a segment C represents a cyclic prefix, and a segment B represents a modulated signal. In a preferred embodiment, the length of the time domain OFDM symbol is 1024, N_cpIs 512, Len_BAlso 512, N1 is also 512.

The frequency shift sequence is

Wherein f is_SHCan be selected as the frequency domain subcarrier interval corresponding to the time domain OFDM symbol, namely 1/N_AT, where T is the sampling period, N_AIs the length of the time domain OFDM symbol. In this example, N_AIs 1024, take f_SH1/1024T. To sharpen the correlation peak, f_SHCan also be selected to be 1/(Len)_BT). When Len_B＝N_CPWhen f is present_SH＝1/N_CPAnd T. Such as Len_B＝N_CPWhen is 512, f_SH＝1/512T。

In other embodiments, m (t) may also be designed into other sequences, such as an m-sequence or some simplified window sequence.

The modulation signal of the partial time domain OFDM symbol is P1_ b (t), P1_ b (t) is obtained by multiplying the partial time domain OFDM symbol by the frequency shift sequence m (t), i.e., P1_ b (t) is:

n1 is the sampling point number of the time domain OFDM symbol selected to be copied to the start of the modulation signal segment.

A preamble symbol is generated based on the cyclic prefix, the time domain OFDM symbol and the modulation signal as described in step S26.

Specifically, the cyclic prefix is spliced at the front of the time domain OFDM symbol as a guard interval, and the modulated signal is spliced at the rear of the OFDM symbol as a modulated frequency offset sequence to generate a preamble symbol, as shown in fig. 3.

For example, the preamble symbol may be based on employing the time domain expression:

when the time domain structure of the preamble symbol is not needed for signaling transmission, only a fixed starting point is taken when generating the modulation signal. Preferably, Len is set_B＝N_cpAnd N1 ═ N_A-N_cpI.e. by

When N is present_A＝1024，N_cpWhen equal to 512, Len_B＝512，N1＝512，N2＝1023。

In other embodiments, if the predetermined length takes on another value (i.e., not 1024), then 1024 in the above equation P1(t) will be changed to the corresponding value (i.e., consistent with the predetermined length), and N will be the same as N_cpIt may also be changed to other values, preferably N_cpIs half of said predetermined length.

Further, the following steps are also included after the step S14:

1) determining a length of the modulated signal;

2) and based on the length of the modulation signal, transmitting the signaling information by selecting different starting positions in the part of the time domain OFDM symbols for intercepting the cyclic prefix.

For example, the predetermined length is 1024, N_CPIs 512, Len_BIs 256.

Wherein, N1 can be 512+ i 160 ≦ i < 16, which can represent 16 different access methods for transmitting 4-bit signaling parameters. Different transmitters may transmit their corresponding identities by taking a different N1, the same transmitter may also transmit the transmission parameters by changing N1 in time.

As another example, the predetermined length is 1024, N_CPIs 1024, Len_BFor 512, 8 different starting points are set, N1 takes 64 × i 0 ≤ i < 8, and 3-bit signaling parameters are transmitted.

As another example, the predetermined length is 1024, N_CPIs 576, Len_BFor 448, 2 different N1 are set to transmit 1-bit signaling, 448 and 576 respectively (subscript of sample point of time domain OFDM symbol starts from 0), i.e. 1-bit signaling is transmitted from 449 sample point of time domain OFDM symbol as starting position or from 577 th sample point of time domain OFDM symbol as starting position.

As another example, the predetermined length is 1024, N_CPIs 512, Len_BAlso 512, N1 is also 512, no signaling is transmitted.

In other embodiments, based on the method for generating the frequency domain OFDM symbol described above, a person skilled in the art may use other embodiments (not limited to the generation of the preamble symbol in the physical frame provided in this embodiment) to process the frequency domain OFDM symbol to generate the preamble symbol in the time domain.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.

Claims

1. A method for generating preamble symbols in a physical frame, comprising the steps of:

obtaining a frequency domain OFDM symbol with a preset length;

performing inverse discrete Fourier transform on the frequency domain OFDM symbols with the preset length to obtain time domain OFDM symbols;

determining the length of a cyclic prefix according to the channel environment;

intercepting the time domain OFDM symbol with the cyclic prefix length from a part of the rear part in the time domain OFDM symbol as a cyclic prefix;

generating a modulation signal based on the intercepted part of the time domain OFDM symbols with the cyclic prefix length and only taking a fixed starting point to multiply a set frequency shift sequence, wherein the frequency of the frequency shift sequence is selected as a frequency domain subcarrier interval corresponding to the time domain OFDM symbols, and the range of the part of the time domain OFDM symbols used for generating the modulation signal segment is smaller than the range of the intercepted part of the time domain OFDM symbols used as the cyclic prefix;

generating a preamble symbol based on the cyclic prefix, the time domain OFDM symbol and the modulation signal, wherein the generated preamble symbol comprises: the cyclic prefix spliced in front of a time domain OFDM symbol, the time domain OFDM symbol, and the modulation signal spliced in rear of the time domain OFDM symbol.

2. The method of generating preamble symbols in a physical frame according to claim 1, wherein the generating preamble symbols based on the cyclic prefix, the time domain OFDM symbols and the modulation signal comprises:

and splicing the cyclic prefix at the front part of the time domain OFDM symbol as a guard interval, and splicing the modulation signal at the rear part of the time domain OFDM symbol as a modulation frequency offset part to generate a preamble symbol.