CN108156108B - Method and device for determining starting point position of OFDM symbol - Google Patents

Method and device for determining starting point position of OFDM symbol Download PDF

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CN108156108B
CN108156108B CN201711463206.8A CN201711463206A CN108156108B CN 108156108 B CN108156108 B CN 108156108B CN 201711463206 A CN201711463206 A CN 201711463206A CN 108156108 B CN108156108 B CN 108156108B
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received signal
long
preamble
preset
lead code
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CN108156108A (en
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洪龙龙
叶进
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Ruijie Networks Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation
    • H04L27/2665—Fine synchronisation, e.g. by positioning the FFT window

Abstract

The invention discloses a method and equipment for determining the position of a starting point of an OFDM symbol, which are used for improving the accuracy of positioning the starting point of the symbol and improving the network experience quality of a user. The method comprises the following steps: the receiving end determines the position of the lead code starting point in the received signal; the preamble comprises a long preamble; the receiving end performs cross-correlation operation on the received signal and K preset long preambles included in a preset long preamble set to obtain K operation results, wherein the operation results are used for representing the positions of the long preambles in the lead codes; the receiving end stores the preset long-pilot set, and K is an integer not less than 2; the receiving end determines the position of the starting point of the OFDM symbol according to the position of the starting point of the lead code and the K operation results; wherein a starting position of the OFDM symbol is the same as a starting position of the long amble.

Description

Method and device for determining starting point position of OFDM symbol
Technical Field
The present invention relates to the field of communications technologies, and in particular, to a method and an apparatus for determining a position of an origin of an Orthogonal Frequency Division Multiplexing (OFDM) symbol.
Background
At present, in an Orthogonal Frequency Division Multiple Access (OFDMA) communication system, a communication bandwidth is divided into a plurality of sub-channels, each sub-channel includes a plurality of sub-carriers, and then the sub-channels are allocated to a plurality of user equipments as resource units, so that simultaneous communication of the plurality of user equipments can be realized, and by orthogonality among the sub-carriers, high overlapping of the sub-carriers is realized, and a spectrum utilization rate is greatly improved, so that the OFDMA communication system is widely applied.
Due to the technical characteristics of OFDMA, multiple users occupy different subcarriers in the frequency domain to communicate, but transmit signals simultaneously in the time domain, and then the signals are aliased with each other in the time domain. In a communication system requiring a preamble to be transmitted, the preamble is generally used for performing frame start positioning, symbol start positioning, frequency offset estimation, and the like. The current method of synchronization includes two steps, coarse synchronization and fine synchronization. The coarse synchronization refers to obtaining a frame starting position by delaying autocorrelation operation in a received time domain signal, and the fine synchronization refers to obtaining a starting position of an OFDM symbol by performing cross-correlation operation on the received time domain signal and a pre-stored preamble at a receiving end. The starting point position of the OFDM symbol is obtained through the following cross-correlation operation formula:
Figure BDA0001530591490000011
Figure BDA0001530591490000012
wherein z ism+qTime domain expression, p, for baseband signals received at the receiving endqThe long guide code is a signal of a whole system long guide code pre-stored by a receiving end, the length of the long guide code is Q, Q is more than or equal to 0 and less than or equal to Q-1,
Figure BDA0001530591490000013
for the conjugate of the long amble prestored at the receiving end, phizp(m) represents the received signal z acquired for a samplem+qThe (m + q) th sampling point and the conjugate of the (q) th sampling point of the pre-stored long guide code perform cross correlation operation,
Figure BDA0001530591490000021
the value of m is the maximum value of the result of the cross-correlation operation. Wherein, the sampling point corresponding to the value of m is the starting point position of the long amble, that is, the starting point position of the OFDM symbol.
The frame starting point is used for defining the starting position of a wireless signal frame, and under the condition that the frame starting point is determined, the starting position of the OFDM symbol is further determined, so that the accurate definition of the OFDM symbol can be realized, and further the subsequent decoding operation can be carried out. The positioning of the start position of an OFDM symbol may have three consequences, namely ideal, early and late. As shown in fig. 1, if the starting position of the located OFDM symbol is ideal, that is, the starting position of the OFDM symbol is exactly located at the cyclic prefix (Cy) of one OFDM symbol (Cy)c Prefix, CP), then performing Fast Fourier Transform (FFT) can just remove the CP to obtain a data segment of one OFDM symbol, i.e. the ideal FFT window shown in fig. 1 just falls on data segment 1 of OFDM symbol 1. If the starting position of the positioned OFDM symbol is advanced, the CP in one OFDM symbol is the last N of the data segment in the OFDM symbolGIThe data is copied, that is, even if the starting position of the located OFDM symbol is advanced, as long as the advanced length does not exceed the length of the CP, the data included in the OFDM symbol after FFT is still complete, and the data can be analyzed by a certain means. If the position of the start point of the located OFDM symbol is delayed, data of the next OFDM symbol is introduced, which may cause Inter-Carrier Interference (ICI) and Inter-symbol Interference (ISI), so that the data included in the OFDM symbol after FFT is incomplete and cannot be normally analyzed, thereby causing a communication process to be not normally performed. Therefore, symbol synchronization and detection are directly related to a series of subsequent operations on the data message, and therefore, the positioning of the symbol start point is a very critical step in the decoding process.
However, in the OFDMA system, a plurality of users transmit signals simultaneously, and due to channel fading, transmission power, and different positions from the base station, the signals of the users have different signal strengths and different arrival times when reaching the base station. When the existing synchronization method is used for fine synchronization, the signal intensity interference of a user is easy to occur, the positioning result is usually biased to the user with a stronger signal, that is, the symbol starting point of the positioning is biased to the symbol starting point of the user with the stronger signal, so that the symbol of the user with the weaker signal is inaccurately positioned, and further, the signal of the user with the weaker signal cannot be successfully decoded, and thus, the network experience of the user with the weaker signal is not good.
Disclosure of Invention
The embodiment of the invention provides a method and equipment for determining the position of a starting point of an OFDM symbol, which are used for improving the accuracy of positioning the starting point of the symbol and improving the network experience quality of a user.
In a first aspect, a method for determining a starting position of an OFDM symbol is provided, where the method includes:
the receiving end determines the position of the lead code starting point in the received signal; the preamble comprises a long preamble;
the receiving end performs cross-correlation operation on the received signal and K preset long preambles included in a preset long preamble set to obtain K operation results, wherein the operation results are used for representing positions of the long preambles in the lead codes; the receiving end stores the preset long-pilot set, and K is an integer not less than 2;
the receiving end determines the position of the starting point of the OFDM symbol according to the position of the starting point of the lead code and the K operation results; wherein a starting position of the OFDM symbol is the same as a starting position of the long amble.
Optionally, the receiving end performs cross-correlation operation on the received signal and all preset preambles included in a preset preamble set to obtain K operation results, including:
the receiving end utilizes a formula
Figure BDA0001530591490000031
Performing cross-correlation operation to obtain K values of m; the value of m is used for representing that the starting point position of the long lead code is positioned at the m-th sampling point of the lead code;
wherein z ism+qIs a time domain representation of the m + q sampling points in the received signal,
Figure BDA0001530591490000032
q is a time domain expression of a conjugate of a Q sampling point of a kth preset long preamble in the preset long preamble set, wherein Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long preamble; phi'zpk(m) is the result of the cross-correlation of the conjugate of the mth sampling point of the received signal and the qth sampling point of the kth preset long amble, K is greater than or equal to 0 and less than or equal to K-1,
Figure BDA0001530591490000033
is such that phi'zpk(m) the value of m when the maximum value is obtained.
Optionally, the receiving end performs cross-correlation operation on the received signal and all preset preambles included in a preset preamble set to obtain K operation results, including:
the receiving end utilizes a formula
Figure BDA0001530591490000041
Performing cross-correlation operation to obtain K values of m; the value of m is used for representing that the starting point position of the long preamble is positioned at the mth sampling point of the preamble;
wherein Z isk,m+qIs a frequency domain expression of the m + q sampling points of the signal of the kth user in the received signal,
Figure BDA0001530591490000042
a frequency domain expression of the conjugate of the Q sampling point of the kth preset lead code in the preset lead code set is represented, Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long lead code; hkA frequency domain representation of the channel response for the kth user in the received signal, Nk' is a frequency domain expression of additive white gaussian noise AWGN for a kth user in the received signal; phi'zpk(m) is the result of conjugate cross-correlation operation between the m + q sampling points of the received signal and the q sampling points of the kth preset long preamble, K is more than or equal to 0 and less than or equal to K-1,
Figure BDA0001530591490000043
is such that phi'zpk(m) the value of m when the maximum value is obtained.
Optionally, the determining, by the receiving end, the position of the start point of the OFDM symbol according to the position of the start point of the preamble and the K operation results includes:
the receiving end determines the average value of the K values of the m; the position of a sampling point in the preamble corresponding to the average value is the starting position of the long preamble in the preamble;
and the receiving end determines the position of the starting point of the OFDM symbol in the received signal according to the position of the starting point of the lead code and the average value.
In a second aspect, there is provided an apparatus for determining a starting position of an OFDM symbol, the apparatus comprising:
a determining unit for determining a position of a preamble start point in the received signal; the preamble comprises a long preamble;
an operation unit, configured to perform cross-correlation operation on the received signal and K preset long preambles included in a preset long preamble set to obtain K operation results, where the operation results are used to represent positions of the long preambles in the preamble; the receiving end stores the preset long-pilot set, and K is an integer not less than 2;
the determining unit is further configured to determine a starting position of the OFDM symbol according to the position of the starting point of the preamble and the K operation results; wherein a starting position of the OFDM symbol is the same as a starting position of the long amble.
Alternatively to this, the first and second parts may,
said arithmetic unit, in particular for using a formula
Figure BDA0001530591490000051
Performing cross-correlation operation to obtain K values of m; the value of m is used for representing that the starting point position of the long preamble is positioned at the mth sampling point of the preamble;
wherein z ism+qIs a time domain representation of the m + q sampling points in the received signal,
Figure BDA0001530591490000052
q is a time domain expression of a conjugate of a Q sampling point of a kth preset long preamble in the preset long preamble set, wherein Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long preamble; phi'zpk(m) is the result of the cross-correlation of the conjugate of the mth sampling point of the received signal and the qth sampling point of the kth preset long amble, K is greater than or equal to 0 and less than or equal to K-1,
Figure BDA0001530591490000053
is such that phi'zpk(m) the value of m when the maximum value is obtained.
Alternatively to this, the first and second parts may,
said arithmetic unit, in particular for using a formula
Figure BDA0001530591490000054
Performing cross correlation operation to obtain K values of m; the value of m is used for representing that the starting point of the long lead code is positioned at the mth sampling point of the lead code;
wherein Z isk,m+qIs a frequency domain expression of the m + q sampling points of the signal of the kth user in the received signal,
Figure BDA0001530591490000055
a frequency domain expression of the conjugate of the Q sampling point of the kth preset lead code in the preset lead code set is represented, Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long lead code; hkA frequency domain representation of the channel response for the kth user in the received signal, Nk' is a frequency domain expression of additive white gaussian noise AWGN for a kth user in the received signal; phi'zpk(m) is the result of conjugate cross-correlation operation between the m + q sampling points of the received signal and the q sampling points of the kth preset long preamble, K is more than or equal to 0 and less than or equal to K-1,
Figure BDA0001530591490000056
is such that phi'zpk(m) the value of m when the maximum value is obtained.
Alternatively to this, the first and second parts may,
the determining unit is specifically configured to determine an average value of the K values of the m; the position of a sampling point in the lead code corresponding to the average value is the starting position of the long lead code in the lead code; and determining the position of the start of the OFDM symbol in the received signal according to the position of the start of the preamble and the average value.
In a third aspect, a computer arrangement is provided, the arrangement comprising at least one processor configured to implement the steps of the method for determining a position of origin of an OFDM symbol as provided in the first aspect when executing a computer program stored in a memory.
In a fourth aspect, a computer readable storage medium is provided, on which a computer program is stored, which computer program, when being executed by a processor, realizes the steps of the method for determining a position of origin of an OFDM symbol as provided in the first aspect.
In the embodiment of the present invention, after the start position of the preamble code is determined, a cross-correlation operation is performed between the received signal and a plurality of different preset long ambles stored in the receiving end, and the start position of the long amble is determined according to K operation results and the start position of the preamble code. When the position of the long guide code in the preamble code is determined, the long guide code is cross-correlated with a plurality of preset long guide codes, so that a plurality of different operation results can be obtained, and not only can the result of the starting positions of the long guide codes in the preamble code be obtained, so that the starting position of the long guide code of a user with weak signal can also be included in the plurality of determined starting positions, and finally the starting position of the long guide code determined according to the plurality of results can be more accurate, namely the positioning of the symbol starting position is more accurate, correspondingly, the decoding success rate of the signal is higher, and the network experience quality of the user is also higher.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a diagram illustrating a possible result of a starting position of an OFDM symbol in the prior art;
fig. 2 is a schematic diagram of subcarrier distribution in the communication system according to an embodiment of the present invention;
fig. 3 is a schematic flowchart of uplink communication between a user equipment and a base station according to an embodiment of the present invention;
fig. 4 is a flowchart illustrating a method for determining a starting position of an OFDM symbol according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a data generating and sending process of a user equipment according to an embodiment of the present invention;
fig. 6 is a schematic diagram illustrating a processing flow of a received signal by a base station according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a preamble according to an embodiment of the present invention;
fig. 8 and fig. 9 are schematic diagrams illustrating comparison of results of different positioning algorithms when the power difference between two ues is 0 according to an embodiment of the present invention;
fig. 10 and 11 are graphs illustrating comparison of results of different positioning algorithms when the power difference between two ues is-3 db according to an embodiment of the present invention;
fig. 12 and 13 are graphs illustrating comparison of results of different positioning algorithms when the power difference between two ues is-6 db according to an embodiment of the present invention;
fig. 14 and 15 are graphs illustrating comparison of results of different positioning algorithms when the power difference between two ues is-9 db according to an embodiment of the present invention;
fig. 16 is a schematic structural diagram of an apparatus for determining a starting point position of an OFDM symbol according to an embodiment of the present invention;
fig. 17 is a schematic structural diagram of a computer device according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.
Hereinafter, some terms in the embodiments of the present invention are explained to facilitate understanding by those skilled in the art.
User equipment, which refers to a device that provides voice and/or data connectivity to a user, may include, for example, a handheld device having wireless connection capability, or a processing device connected to a wireless modem. The user equipment may communicate with a core Network via a Radio Access Network (RAN), and exchange voice and/or data with the RAN. The User equipment may include UE, wireless Terminal equipment, Mobile Terminal equipment, Subscriber Unit (Subscriber Unit), Subscriber Station (Subscriber Station), Mobile Station (Mobile), Remote Station (Remote Station), Access Point (AP), Remote Terminal equipment (Remote Terminal), Access Terminal equipment (Access Terminal), User Terminal equipment (User Terminal), User Agent (User Agent), or User Device (User Device). For example, mobile telephones (or so-called "cellular" telephones), computers with mobile terminal equipment, portable, pocket, hand-held, computer-included, or vehicle-mounted mobile devices may be included. Examples of such devices include Personal Communication Service (PCS) phones, cordless phones, Session Initiation Protocol (SIP) phones, Wireless Local Loop (WLL) stations, Personal Digital Assistants (PDAs), and smart wearable devices.
A base station refers to a device in an access network that communicates over the air-interface, through one or more cells, with wireless terminal devices. The base station may be configured to interconvert the received air frame with an Internet Protocol (IP) packet as a router between the user equipment and the rest of the access network, which may include an IP network. The base station may also coordinate management of attributes for the air interface. For example, the base station may include an evolved Node B (eNB or e-NodeB) in a Long Term Evolution (LTE) system or an evolved LTE system (LTE-Advanced, LTE-a), or may also include a next generation Node B (gNB) in a 5G system, and embodiments of the present invention are not limited thereto.
The technical scheme provided by the embodiment of the invention is described below by combining the accompanying drawings.
The method provided by the embodiment of the present invention may be applied to a signal receiving end in a communication system, which may be an OFDMA communication system, for example, and therefore, before the method provided by the embodiment of the present invention is described in detail, the communication system of the embodiment of the present invention will be described below.
In the OFDMA communication system according to the embodiment of the present invention, the system channel bandwidth is C, the number of subcarriers in the system is N, if M consecutive subcarriers are used as the minimum Resource Unit (RU), the maximum number of users supportable by the communication system is K N/M, K users share the N subcarriers to transmit signals, and if the number of subcarriers occupied by the kth user is NkThen there is
Figure BDA0001530591490000081
Specifically, referring to fig. 2, the subcarriers occupied by each ue are consecutive, for example, the subcarriers occupied by the 1 st ue sending signals are the subcarriers numbered 0 to 5, and the subcarriers occupied by the 2 nd ue sending signals are the subcarriers numbered 6 to 15.
The subcarriers occupied by the 1 st and 2 nd user equipments each further include a data subcarrier, a pilot subcarrier, and a guard subcarrier, where the data subcarrier is used to carry data signals, the pilot subcarrier is used for frequency offset estimation and/or channel estimation, and the guard subcarrier is used to protect subcarriers of different user equipments from overlapping. It can be seen that each user communicates on the sub-carriers occupied by itself, so that data between different users are separated from each other in the frequency domain, but in the time domain, each user occupies the whole OFDM symbol time, i.e. the data received by the receiving end is the sum of the data of all users after passing through the wireless channel.
Please refer to fig. 3, which illustrates a process of uplink communication between a plurality of ues and a base station, wherein the base station is a receiving end, and the ues 1 to K are transmitting ends. The base station needs to synchronize with the user through the trigger frame, that is, before the user equipment sends the signal, the base station informs the user equipment to start sending the signal after the time indicated by the frame interval through the trigger frame. Before the user equipment sends the signal, a section of lead code is sent to facilitate the base station to carry out frame starting point positioning, frequency offset estimation, channel estimation and the like. As can be seen in fig. 3, the user equipment 1 to the user equipment K all start to transmit signals at the time indicated by the frame interval after the trigger frame of the base station is transmitted, that is, the user equipment 1 to the user equipment K transmit the preamble first and then transmit the data that actually needs to be transmitted to the base station, where the data may include a plurality of OFDM symbols. Because the positions of different user equipments relative to the base station are different and the channel fading experienced by the signal transmitted by each user equipment is also different, the time when the signal of different user equipments reaches the base station is still different in practice, so that the preambles transmitted by the user equipments are aliased and the strength of the signal of the user equipment received by the base station is different.
Referring to fig. 4, an embodiment of the present invention provides a method for determining a starting position of an OFDM symbol, where the method includes:
step 401: the receiving end determines the position of the lead code starting point in the received signal; the preamble comprises a short amble and a long amble;
step 402: the receiving end performs cross-correlation operation on the received signal and K preset long preambles included in a preset long preamble set to obtain K operation results, wherein the operation results are used for representing the positions of the long preambles in the preamble; the receiving end stores a preset long code set, and K preset long codes included in the preset long code set are different from each other, wherein K is an integer not less than 2;
step 403: the receiving end determines the starting position of the long guide code in the received signal according to the position of the starting point of the lead code and the K operation results; wherein, the starting position of the long pilot code is the same as the starting position of the OFDM symbol.
In the embodiment of the invention, the receiving end can be realized by a base station or user equipment, wherein when the receiving end is the base station, the receiving end can receive signals sent by the user equipment; alternatively, the receiving end may also be a user equipment, and the receiving end may receive a signal transmitted by the base station. The following description will take the receiving end as a base station as an example. Wherein, assuming that the signal transmitted by the user equipment can be represented by x (t), the signal transmitted by the kth user equipmentThe signal can then be represented by xk(t), the signal received by the base station may be as follows:
Figure RE-GDA0001624893200000101
wherein h isk(t) denotes a channel response of the kth user equipment, and z (t) denotes Additive White Gaussian Noise (AWGN).
In the embodiment of the present invention, in order to describe the method more directly, a simple scenario in which the communication system includes two pieces of user equipment will be described as an example. When only two pieces of user equipment are provided, each piece of user equipment occupies half of the communication bandwidth of the whole communication system, for example, when the number of subcarriers in the communication system is N, the user equipment 1 occupies subcarriers with the numbers of 0 to (N/2-1), and the user equipment 2 occupies subcarriers with the numbers of N/2 to N. The data generation and transmission flow of two user equipments within one OFDM symbol is shown in fig. 5.
Wherein, X1,0～X1,N/2-1Frequency domain data sent by the user equipment 1 through the 0 th to (N/2-1) th subcarriers, that is, the subcarriers occupied by the user equipment 1 are the 0 th to (N/2-1) th subcarriers, and the data sent by the user equipment 1 does not exist on the rest subcarriers; x2,N/2+1～X2,N-1Frequency domain data transmitted by the user equipment 2 through the (N/2+1) th to (N-1) th subcarriers, that is, the subcarriers occupied by the user equipment 2 are the (N/2+1) th to (N-1) th subcarriers, and on the rest subcarriers, the data transmitted by the user equipment 2 does not exist; the nth/2 th sub-carrier is used as a guard sub-carrier and does not carry any data.
After the user equipment generates the frequency domain data, the frequency domain data needs to be subjected to Inverse Fast Fourier Transform (IFFT) to be converted into time domain data, and the converted time domain data is continuous in the time domain, for example, the data in the time domain after the signal of the user equipment 1 is subjected to IFFT may be l1,0～l1,n-1After the frequency domain data of the user equipment 2 is subjected to IFFTThe data in the time domain may be l2,0～l2,n-1Where n is the number of sample points.
Further, after the CP is added in front of the converted time domain data, the time domain data is changed in a serial-parallel manner, that is, the transmission sequence of the time domain data is sequenced, and the time domain data is transmitted according to the sequence when being transmitted. After the user equipment performs serial-parallel conversion, the data to be transmitted can be modulated to the frequency band by the frequency modulation operation, i.e. the data and the frequency band of the user equipment 1 shown in fig. 5
Figure BDA0001530591490000111
Multiplication, and, data of the user equipment 2 and
Figure BDA0001530591490000112
multiplication of where fcThe center frequency of the band. Each data can be carried by the corresponding subcarrier through the frequency modulation operation, so as to be sent to the base station. Since in the time domain the data of two different user equipments overlap each other, it is represented in fig. 5 by adding, i.e. the finally received signal y (t) is the sum of the signals of the two user equipments.
Please refer to fig. 6, which is a flowchart illustrating a process after the base station receives the signal y (t). After receiving the signal y (t), the base station first performs sampling by an Analog-to-digital converter (ADC) to convert the Analog signal y (t) into a digital signal zmThen, the digital signal z after serial-parallel conversion is processedmAnd performing synchronization, namely positioning the frame start point and the symbol start point, so as to perform subsequent operations such as channel estimation and frequency offset estimation. The positioning of the frame starting point and the starting point position of the OFDM symbol is the basis for subsequent operations such as channel estimation and frequency offset estimation, and if the positioning of the frame starting point and the starting point position of the OFDM symbol is inaccurate, the subsequent channel estimation and frequency offset estimation cannot be accurately performed, so the positioning of the frame starting point and the starting point position of the OFDM symbol is a particularly critical step for signal decoding. The positioning of the frame start and the start position of the OFDM symbol will be specifically described below.
Referring to fig. 4, in the embodiment of the present invention, the base station samples and obtains the received signal zmThen, the position of the preamble start point in the received signal is determined, i.e. the frame start point is located.
Specifically, the frame start location is used to find the radio frame head, i.e. to find the start position of the radio frame from the received signal. When the ue transmits the signal, the ue first transmits the preamble, that is, the starting position of the radio frame is the starting position of the preamble. Fig. 7 is a schematic diagram of a preamble structure, wherein the preamble includes a Short Training Field (STF) and a Long Training Field (LTF). The short pilot code is composed of 2 OFDM symbols, the time length of each OFDM symbol is 4 microseconds (us), each OFDM symbol comprises 5 repeated waveforms, the repetition period is 0.8us, and training sequences carried in each repetition period are completely the same. The long pilot code is composed of 1 CP and 2 OFDM symbols, and the total duration is 8us, wherein the waveforms of the 2 OFDM symbols are completely the same. As can be seen from the structure diagram of the preamble, the starting position of the preamble is also the starting position of the short preamble. Since the short amble includes a plurality of repeated periodic waveforms, the position of the start point of the short amble can be obtained by a delayed autocorrelation operation. Specifically, the formula of the delayed autocorrelation operation is as follows:
Figure BDA0001530591490000121
Figure BDA0001530591490000122
wherein phiDC(m) represents the received signal z acquired for a samplemThe conjugate of the middle m-R sampling point and the L sampling point before the m-R sampling point is subjected to autocorrelation operation, m is more than or equal to L +1, R is the repetition interval length of the signal, L is the interval distance of two autocorrelation operation windows, and L is the integral multiple of R, wherein the repetition period of the short guide code is 0.8us, and then the repetition interval length of the channel is longThe degree R is the product of the repetition period and the system bandwidth. z is a radical ofm-rRepresents the m-R sampling points, R is more than or equal to 0 and less than or equal to R,
Figure BDA0001530591490000123
representing the conjugate of the L-th sample point after the m-r sample point.
Figure BDA0001530591490000124
The value of m for making the result of the above-mentioned autocorrelation operation take on the maximum value, i.e. m
Figure BDA0001530591490000125
To make phiDC(m) the value of m when the maximum value is obtained. And the sampling point corresponding to the value of m is the starting point position of the lead code, namely the frame starting point position.
For example, when L ═ R, the delayed autocorrelation calculation is performed by passing the received signal zmAnd taking the middle and front L sampling points as a first autocorrelation operation window, wherein the first autocorrelation operation window comprises sampling points 0-L-1, the second autocorrelation operation window comprises sampling points L-1 (2L-1), and the like, multiplying the sampling points at the same position in the two autocorrelation operation windows from the sampling point 2L-1, then adding, namely multiplying the sampling point 2L-1 by the sampling point L-1, multiplying the sampling point 2L-2 by the sampling point L-2, and the like, and finally adding the multiplied results.
After acquiring the frame starting position, the positioning of the starting position of the OFDM symbol needs to be performed. If the positioning of the starting position of the OFDM symbol is performed according to the prior art, the above two examples of the user equipment are also used for description, and the signal obtained by sampling the received signal by the base station may be represented as follows:
Figure BDA0001530591490000131
wherein x is1,m、x2,mSignals h of the UE 1 and the UE 2 at the m-th sampling point, respectively1、h2The channel responses of the user equipment 1 and the user equipment 2 are respectively.
For the long guide code p pre-stored in the base stationqThe following formula exists:
pq＝IFFT(Xq)＝IFFT(X1,q+X2,q)＝IFFT(X1,q)+IFFT(X2,q)
wherein, XqIs to pqExpression after FFT, X1,qAnd X2,qAre each XqLong amble sequences corresponding to user equipment 1 and user equipment 2, e.g. X1,qOnly the sub-carrier corresponding to the user equipment 1 has the long-pilot sequence, but the part of the sub-carrier corresponding to the user equipment 2 has no data, X2,qSimilarly, then there is X1,q·X 2,q0. Wherein z ism+qIt can be expressed as:
Figure BDA0001530591490000132
then
Figure BDA0001530591490000133
Wherein H1And H2Frequency domain expressions of the channel responses of the user equipment 1 and the user equipment 2 respectively, namely expressions obtained by performing FFT on the channel responses of the user equipment 1 and the user equipment 2;
Figure BDA0001530591490000134
a frequency domain expression which is the conjugate of the long amble; n is a radical of1,oAnd N2,oFrequency domain expressions for AWGN corresponding to user equipment 1 and user equipment 2, respectively.
Due to X1,mAnd X2,mRespectively occupy different sub-carriers, so X corresponding to the same sub-carrier position1,mAnd X2,mIt is not possible to have values at the same time, then there is
Figure BDA0001530591490000141
The above formula can be further expressed as:
Figure BDA0001530591490000142
Figure BDA0001530591490000143
since the locations of different ues may be different, the distances between the ues and the base station may also be different, and the signal attenuations experienced by the signals of the different ues during the transmission process are also different, it is easy for the signals of the different ues to have different arrival times and signal strengths at the base station. For example, if | H1|＜|H2I.e. the signal strength of user equipment 1 is less than the signal strength of user equipment 2, then for Φzp(m) the result is that the data of the user equipment 2 occupies a larger value, i.e. the user equipment 2 occupies a larger value for ΦzpThe influence of the result of (m) is larger, that is, the value of m finally obtained is more biased to the starting position of the OFDM symbol of the user equipment 2, so that when the difference between the starting positions of the OFDM symbols of the user equipment 1 and the user equipment 2 is relatively large, the positioning of the starting position of the OFDM symbol of the user equipment 1 is not accurate, and therefore, ICI and ISI may be possibly caused by the signal of the user equipment 1.
In the embodiment of the present invention, a preset long amble set is prestored in a base station, where the preset long amble set includes K preset long ambles, where K is an integer not less than 2, and the number of K is related to the number of user equipments capable of being accommodated by a communication system.
In the embodiment of the present invention, after the base station determines the position of the start point of the preamble in the received signal, the position of the start point of the OFDM symbol is determined. The received signal and K preset long preambles included in the preset long preamble set are subjected to cross-correlation operation to obtain K operation results, and the obtained operation results are used for representing positions of the long preambles in the preamble.
Specifically, the first calculation method is that the base station may perform autocorrelation operation by using the following formula:
Figure BDA0001530591490000151
wherein z ism+qIs a time domain expression of the m + Q sampling points in the received signal, wherein m is 0,1,2 … …, Q is more than or equal to 0 and less than or equal to Q-1, Q is the length of the preset long lead code,
Figure BDA0001530591490000152
a time domain expression of a conjugate of a q-th sampling point of a kth preset long pilot in a preset long pilot set; phi'zpk(m) is the cross-correlation operation result of the mth sampling point of the received signal and the kth preset long code, K is more than or equal to 0 and less than or equal to K-1,
Figure BDA0001530591490000153
to make the result of the cross-correlation take on the value of m when it reaches its maximum, i.e. m
Figure BDA0001530591490000154
Is such that phi'zpk(m) the value of m when the maximum value is obtained. Wherein, phi'zpk(m) represents the sliding cross-correlation between the received signal and each preset long preamble, for example, when m is 0 and Q is 0, the received signal is multiplied by the 0 th sampling point in the kth preset long preamble from the 0 th sampling point in the received signal, the next multiplication is multiplied by the 1 st sampling point in the kth preset long preamble from the 1 st sampling point, until Q is Q-1, that is, the Q-1 th sampling point is multiplied by the Q-1 th sampling point in the kth preset long preamble, and then the next multiplication time length preamble returns to the 0 th sampling point, that is, the Q th sampling point in the received signal is multiplied by the 0 th sampling point in the kth preset long preamble, and at this time, m is equal to Q, and so on.
It is to be stated here that'zpk(m) and phiDCSubscripts zp and DC in (m) are used to indicate differences, respectivelyOperation of, e.g., #DCDC in (m) indicates autocorrelation operation, Φ'zpkZp in (m) indicates a cross-correlation operation.
And performing cross-correlation operation on the received signal and the kth preset long preamble to obtain a value of m of the cross-correlation operation, wherein the value of m of the cross-correlation operation indicates that the starting point position of the OFDM symbol of the kth user equipment is located at the mth sampling point of the preamble. Then, K values of m can be obtained through K times of cross-correlation operations, and the starting positions of the OFDM symbols corresponding to K user equipments in the received signal are obtained.
In the first calculation mode, when the length of the long amble is Q, then the number of complex multiplications required for the cross-correlation operation is Q2It can be seen that when the value of Q is large, the calculation of the correlation operation is too complicated. For example, in a practical communication system, Q is typically 128, and the number of complex multiplications required for the correlation operation is 1282The calculation amount is too large. Therefore, when determining the position of the start of the OFDM symbol, a second calculation method, i.e., for the received signal z, can also be usedm+qPerforming Q-point FFT to obtain Zm+q(ii) a Performing FFT (fast Fourier transform) on K preset long guide codes pre-stored in the base station and then calculating conjugation to obtain
Figure BDA0001530591490000161
Of course, in order to reduce the amount of calculation in determining the starting position of the OFDM symbol, the preset long ambles after the step of conjugating after the K preset long ambles have been FFT-transformed may be stored in the base station in advance, that is, directly
Figure BDA0001530591490000162
Is stored in the base station. In the presence of a catalyst to obtain Zm+qAnd
Figure BDA0001530591490000163
then Z can be directly putm+qAnd
Figure BDA0001530591490000164
respectively multiplying, and performing Q/K point IFFT transformation on the multiplied results to convert the multiplied results in the frequency domain into the time domain, namely the following formula:
Figure BDA0001530591490000165
Figure BDA0001530591490000166
wherein Z isk,m+qFor a frequency domain representation of the signal of the kth user equipment in said received signal,
Figure BDA0001530591490000167
a frequency domain expression of a conjugate of a q sampling point of a kth preset lead code in the preset lead code set; hkA frequency domain representation of the channel response for the kth user equipment in the received signal, Nk' is a frequency domain expression of additive white gaussian noise AWGN of a kth user equipment in the received signal; phi'zpk(m) is a cross-correlation result of an mth sampling point of the received signal and a kth preset long amble,
Figure BDA0001530591490000168
in order to maximize the result of the cross-correlation operation, i.e. m
Figure BDA0001530591490000169
Is such that phi'zpk(m) taking the value of m when the maximum value is obtained;
in the second calculation method, the IFFT transformation is used instead of the cross-correlation operation, thereby reducing the amount of calculation. In particular, the Q-point FFT transform has a complexity of
Figure BDA00015305914900001610
The complexity of Q/K point IFFT is
Figure BDA00015305914900001611
I.e. the total complexity of the second calculation is
Figure BDA00015305914900001612
It can be seen that the complexity of the second calculation method is lower relative to the calculation amount of the first calculation method as the value of Q is larger.
In the embodiment of the present invention, K values of m, that is, the starting positions of the OFDM symbols corresponding to K user equipments, can be obtained through the first calculation method or the second calculation method.
In the embodiment of the invention, after K values of m are obtained, the average value of the K values of m is determined; the position of a sampling point in the lead code corresponding to the average value is the starting position of the long lead code in the lead code; and determining the position of the start point of the OFDM symbol in the received signal according to the position of the start point of the preamble and the average value, namely determining the position of the start point of the OFDM symbol in the received signal according to the determined frame start point and the positions of the sampling points indicated by the average value. Therefore, the finally obtained starting position of the OFDM symbol is not biased to a certain user equipment, and the technical problem that the starting position of the OFDM symbol of part of the user equipment is not accurately positioned is solved.
The start positions of the OFDM symbols are also described by taking a communication system of two user equipments as an example. When the communication system comprises only two ues, the conjugates of the two preset long ambles can be pre-stored in the base station, i.e. the conjugate of the two preset long ambles can be pre-stored in the base station
Figure BDA0001530591490000171
And
Figure BDA0001530591490000172
if the received signal is zm+qTo z is tom+qAfter Q-point FFT, Z can be obtainedm+qThen, Z ism+qAccording to the bandwidth position of the user equipment and
Figure BDA0001530591490000173
the multiplication is carried out in such a way that,and then respectively obtaining the starting positions of the OFDM symbols corresponding to the two user equipments, and then performing an averaging operation on the starting positions of the OFDM symbols corresponding to the two user equipments, thereby obtaining an average value of the starting positions of the OFDM symbols, and taking the average value as the finally determined starting positions of the OFDM symbols of the two user equipments. The formula of the above algorithm for the starting position of the OFDM symbol for the procedure of two user equipments is as follows:
Figure BDA0001530591490000174
Figure BDA0001530591490000175
Figure BDA0001530591490000176
Figure BDA0001530591490000177
Figure BDA0001530591490000178
wherein, Z1,m+qAnd Z2,m+qFrequency domain representations of the signals of the user equipment 1 and the user equipment 2 respectively in the received signal,
Figure BDA0001530591490000179
and
Figure BDA00015305914900001710
respectively representing the conjugated frequency domain expressions of the q sampling points of the 1 st and 2 nd preset lead codes in the preset lead code set; h1And H2Frequency domain expressions for the channel responses of user equipment 1 and user equipment 2, respectively, in the received signal, N1′,OAnd N2′,OFrequency domain expressions of AWGN for user equipment 1 and user equipment 2, respectively, in the received signal;
Figure BDA0001530591490000181
and
Figure BDA0001530591490000182
are respectively phi'zp1(m) and Φ'zp2(m) the value of m when the maximum value is obtained,
Figure BDA0001530591490000183
is composed of
Figure BDA0001530591490000184
And
Figure BDA0001530591490000185
average value of (a).
If the channel and the channel response adopted by the two ues are identical, it can be seen that the above formula is substantially equivalent to the starting position locating formula of the OFDM symbol in the prior art, and thus the starting position locating algorithm of the OFDM symbol is compatible with the starting position locating algorithm of the OFDM symbol in the prior art. In addition, for the case where there is only one user, the positioning algorithm of the present invention is also applicable, that is, K is 1, only one preset long amble needs to be pre-stored in the base station, that is, the algorithm is similar to the algorithm of the prior art, but the calculation amount can be reduced by the second calculation method of the embodiment of the present invention, so that the performance of the embodiment of the present invention is better than that of the prior art when K is 1.
In the embodiment of the present invention, the positioning algorithm of the OFDM symbol in the embodiment of the present invention is further verified by comparing the influence of different power differences of two users on a Packet Error Rate (PER) when a receiving end demodulates a Signal under the condition of different Signal to Noise ratios (SNRs) of the positioning algorithm of the OFDM symbol in the prior art and the positioning algorithm of the OFDM symbol in the embodiment of the present invention. The symbol bit calculation method in the prior art is referred to as a conventional algorithm below for short, and the positioning algorithm of the OFDM symbol in the embodiment of the present invention is referred to as a new algorithm below for short. The adopted communication system is verified to be an OFDMA communication system with only two user equipments, wherein the system bandwidth is set to 40MHz, the number of subcarriers is 128, each user is allocated with 64 subcarriers, the CP length is 0.8us, the time offset of the two users is 0.4us, the preamble is modulated by Binary Phase Shift Keying (BPSK), the data field is modulated by 64 Quadrature Amplitude Modulation (QAM), the length of the data segment sent by each user is 49216 bytes, and the channel is an AWGN channel.
Please refer to fig. 8 and fig. 9, which are graphs comparing the results of different positioning algorithms when the power difference between two ues is 0. When the power difference between the signals transmitted by the user equipment 1 and the user equipment 2 corresponding to the user 1 and the user 2 is 0, that is, the strength of the signals transmitted by the two user equipment is the same, the changing trend of the PER of the conventional algorithm and the new algorithm along with the SNR is basically consistent, and the difference between the PER of the signals transmitted by the two user equipment is not large. In addition, the performance of the new algorithm is slightly better than the conventional algorithm for the same SNR.
Referring to fig. 10 and 11, a comparison of the results of different positioning algorithms for a power difference of-3 db for two user equipments is shown. When the power difference between the signals transmitted by the user equipment 1 and the user equipment 2 corresponding to the user 1 and the user 2 is-3 db, that is, the signal strength transmitted by the user equipment 1 is slightly smaller than the signal strength transmitted by the user equipment 2, the conventional algorithm obviously has the problem of inaccurate positioning, and the PER of the signals of the two user equipments is always 100%, but when the SNR of the new algorithm is greater than 28db, the PER of the signals of the two user equipments is far lower than that of the conventional algorithm.
Referring to fig. 12 and 13, a comparison of the results of different positioning algorithms for a power difference of-6 db for two user equipments is shown. When the power difference between the signals sent by the user equipment 1 and the user equipment 2 corresponding to the user 1 and the user 2 is-6 db, that is, the signal strength sent by the user equipment 1 is even smaller than the signal strength sent by the user equipment 2, it can be seen that the signal of the user equipment with weaker signal strength can not decode data correctly at all, and the signal of the user equipment with weaker signal strength can also decode data correctly at this time, and it can be seen obviously that the PER of the new algorithm is obviously lower than that of the conventional algorithm.
Please refer to fig. 14 and 15, which are graphs comparing the results of different positioning algorithms when the power difference between two ues is-9 db. When the power difference between the signals sent by the user equipment 1 and the user equipment 2 corresponding to the user 1 and the user 2 is-9 db, that is, the difference between the signal strength sent by the user equipment 1 and the signal strength sent by the user equipment 2 is larger, it can be seen that the signal of the user equipment with weaker signal strength can not correctly decode the data at all, and the signal of the user equipment with weaker signal strength can also correctly decode the data at this time, and it can be seen obviously that the PER of the new algorithm is obviously lower than that of the conventional algorithm.
Therefore, it can be seen that the positioning algorithm of the OFDM symbol according to the embodiment of the present invention is significantly better than the algorithm of the prior art, and the advantage is particularly significant when the signal strength of the ue is greatly different.
In summary, in the embodiments of the present invention, after the start position of the preamble code is determined, the received signal and a plurality of different preset long preamble codes stored in the receiving end are subjected to a cross-correlation operation, and then the start position of the long preamble code is determined according to the K operation results and the start position of the preamble code. When the position of the long guide code in the preamble is determined, the long guide code is cross-correlated with a plurality of preset long guide codes, so that a plurality of different operation results can be obtained, and not only can the result of the starting positions of the long guide codes in the preamble be obtained, so that the starting position of the long guide code of a user with weak signal can also be included in the determined starting positions, and the starting position of the long guide code determined according to a plurality of results can be more accurate finally, namely the positioning of the symbol starting position is more accurate, correspondingly, the decoding success rate of the signal is higher, and the network experience quality of the user is also higher.
Referring to fig. 16, based on the same inventive concept, an embodiment of the present invention provides an apparatus 160 for determining a starting point of an OFDM symbol, including:
a determining unit 1601 for determining a position of a preamble start point in the received signal; the preamble comprises a long preamble;
an operation unit 1602, configured to perform cross-correlation operation on the received signal and K preset long preambles included in a preset long preamble set to obtain K operation results, where the operation results are used to represent positions of the long preambles; a preset long lead code set is stored in a receiving end, and K is an integer not less than 2;
a determining unit 1601, further configured to determine a starting position of the OFDM symbol according to the position of the starting point of the preamble and the K operation results; wherein, the starting position of the OFDM symbol is the same as the starting position of the long pilot code.
Alternatively to this, the first and second parts may,
an arithmetic unit 1602, specifically for using formulas
Figure BDA0001530591490000201
Performing cross-correlation operation to obtain K values of m; the value of m is used for representing that the starting point position of the long lead code is positioned at the mth sampling point of the lead code;
wherein z ism+qFor a time domain representation of the m + q sample points in the received signal,
Figure BDA0001530591490000202
the method comprises the steps that a time domain expression of conjugate of a Q sampling point of a kth preset long code in a preset long code set is obtained, Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long code; phi'zpk(m) is the result of cross-correlation operation of the conjugate of the mth sampling point of the received signal and the qth sampling point of the kth preset long-amble, K is greater than or equal to 0 and less than or equal to K-1,
Figure BDA0001530591490000203
is such that phi'zpk(m) the value of m when the maximum value is obtained.
Alternatively to this, the first and second parts may,
an arithmetic unit 1602, specifically for using formulas
Figure BDA0001530591490000211
Performing a cross-correlation operation to obtain mK values are taken; the value of m is used for representing that the starting point position of the long preamble is positioned at the mth sampling point of the preamble;
wherein Z isk,m+qIs a frequency domain expression of the m + q sampling points of the signal of the kth user in the received signal,
Figure BDA0001530591490000212
the method comprises the steps that a conjugate frequency domain expression of a Q sampling point of a kth preset lead code in a preset lead code set is obtained, Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long lead code; hkFor the frequency domain representation of the channel response of the kth user in the received signal, Nk' is a frequency domain representation of additive gaussian white noise AWGN for the kth user in the received signal; phi'zpk(m) is the result of conjugate cross-correlation operation between the m + q sampling points of the received signal and the q sampling points of the kth preset long pilot code, K is more than or equal to 0 and less than or equal to K-1,
Figure BDA0001530591490000213
is such that phi'zpk(m) the value of m when the maximum value is obtained.
Alternatively to this, the first and second parts may,
a determining unit 1601, specifically configured to determine an average value of K values of m; the position of a sampling point in the preamble corresponding to the average value is the starting point position of the long preamble in the preamble; and determining the position of the start of the OFDM symbol in the received signal according to the position of the start of the preamble and the average value.
The device may be configured to execute the method provided in the embodiment shown in fig. 4, and therefore, for functions and the like that can be realized by each functional module of the device, reference may be made to the description of the embodiment shown in fig. 4, which is not described in detail.
Referring to fig. 17, an embodiment of the present invention further provides a computer apparatus, which includes at least one processor 1701, where the at least one processor 1701 is configured to implement the steps of the method for determining a starting position of an OFDM symbol provided in the embodiment shown in fig. 4 when executing a computer program stored in a memory.
Optionally, the at least one processor 1701 may specifically include a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), one or more integrated circuits for controlling program execution, a hardware circuit developed by using a Field Programmable Gate Array (FPGA), and a baseband processor.
Optionally, at least one processor 1701 may include at least one processing core.
Optionally, the computer apparatus further includes a memory 1702, and the memory 1702 may include a Read Only Memory (ROM), a Random Access Memory (RAM), and a disk memory. The memory 1702 is used to store data required by the at least one processor 1701 at runtime. The number of the memories 1702 is one or more. The memory 1702 is shown in fig. 17, but it should be understood that the memory 1702 is not an optional functional block, and is therefore shown in fig. 17 by a dashed line.
An embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the method for determining the starting position of an OFDM symbol provided in the embodiment shown in fig. 4.
In embodiments of the present invention, it should be understood that the disclosed apparatus and methods may be implemented in other ways. For example, the above-described embodiments of the apparatus are merely illustrative, and for example, the unit or the division of the unit is only one type of division of logic functions, and there may be other ways of dividing the actual implementation, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be through some interfaces, indirect coupling or communication connection of devices or units, and may be electrical or in other forms.
The functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may be an independent physical module.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. With this understanding, all or part of the technical solutions of the embodiments of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device, such as a personal computer, a server, or a network device, or a processor (processor), to execute all or part of the steps of the methods according to the embodiments of the present invention. And the aforementioned storage medium includes: various media that can store program codes, such as a universal serial bus flash drive (usb flash drive), a removable hard disk, a ROM, a RAM, a magnetic disk, or an optical disk.
The above embodiments are only used to describe the technical solutions of the present application in detail, but the above description of the embodiments is only used to help understanding the method of the embodiments of the present invention, and should not be construed as limiting the embodiments of the present invention. Variations or substitutions that may be readily apparent to one skilled in the art are intended to be included within the scope of the embodiments of the present invention.

Claims (8)

1. A method for determining a starting point position of an OFDM symbol, comprising:
the receiving end determines the position of the lead code starting point in the received signal; the preamble comprises a long preamble;
the receiving end performs cross-correlation operation on the received signal and K preset long preambles included in a preset long preamble set to obtain K operation results, wherein the operation results are used for representing the positions of the long preambles in the lead codes; the receiving end stores the preset long-pilot set, and K is an integer not less than 2;
the receiving end determines the position of the starting point of the OFDM symbol according to the position of the starting point of the lead code and the K operation results; wherein a starting position of the OFDM symbol is the same as a starting position of the long amble;
wherein, the receiving end determines the position of the start point of the OFDM symbol according to the position of the start point of the preamble and the K operation results, including:
the receiving end determines the average value of K values of m; the position of a sampling point in the lead code corresponding to the average value is the starting position of the long lead code in the lead code; the value of m is used for representing that the starting point position of the long lead code is positioned at the m-th sampling point of the lead code;
and the receiving end determines the position of the starting point of the OFDM symbol in the received signal according to the position of the starting point of the lead code and the average value.
2. The method of claim 1, wherein the receiving end performs a cross-correlation operation on the received signal and all preset preambles included in a preset preamble set to obtain K operation results, comprising:
the receiving end utilizes a formula
Figure FDA0002684802130000011
Performing cross-correlation operation to obtain K values of m;
wherein z ism+qIs a time domain representation of the m + q sampling points in the received signal,
Figure FDA0002684802130000021
q is a time domain expression of a conjugate of a Q sampling point of a kth preset long preamble in the preset long preamble set, wherein Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long preamble; phi'zpk(m) is the result of the cross-correlation of the conjugate of the mth sampling point of the received signal and the qth sampling point of the kth preset long amble, K is greater than or equal to 0 and less than or equal to K-1,
Figure FDA0002684802130000022
is such that phi'zpk(m) the value of m when the maximum value is obtained.
3. The method of claim 1, wherein the receiving end performs a cross-correlation operation on the received signal and all preset preambles included in a preset preamble set to obtain K operation results, comprising:
the receiving end utilizes a formula
Figure FDA0002684802130000023
Performing cross-correlation operation to obtain K values of m;
wherein Z isk,m+qA frequency domain representation of the m + q samples of the kth user's signal in the received signal,
Figure FDA0002684802130000024
a frequency domain expression of the conjugate of the Q sampling point of the kth preset lead code in the preset lead code set is represented, Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long lead code; hkIs a frequency domain representation of the channel response of the kth user in the received signal, N'kA frequency domain expression of additive white gaussian noise AWGN for a kth user in the received signal; phi'zpk(m) is the result of conjugate cross-correlation operation between the m + q sampling points of the received signal and the q sampling points of the kth preset long preamble, K is more than or equal to 0 and less than or equal to K-1,
Figure FDA0002684802130000025
is such that phi'zpk(m) the value of m when the maximum value is obtained.
4. An apparatus for determining a position of a start point of an Orthogonal Frequency Division Multiplexing (OFDM) symbol, comprising:
a determining unit for determining a position of a preamble start point in the received signal; the preamble comprises a long preamble;
an operation unit, configured to perform cross-correlation operation on the received signal and K preset long preambles included in a preset long preamble set to obtain K operation results, where the operation results are used to represent positions of the long preambles in the preamble; the receiving end stores the preset long-pilot set, and K is an integer not less than 2;
the determining unit is further configured to determine a starting position of the OFDM symbol according to the position of the starting point of the preamble and the K operation results; wherein a starting position of the OFDM symbol is the same as a starting position of the long amble;
the determining unit is specifically configured to determine an average value of K values of m; the position of a sampling point in the lead code corresponding to the average value is the starting position of the long lead code in the lead code; the value of m is used for representing that the starting point position of the long lead code is positioned at the m-th sampling point of the lead code; and determining the position of the start of the OFDM symbol in the received signal according to the position of the start of the preamble and the average value.
5. The apparatus of claim 4,
said arithmetic unit, in particular for using a formula
Figure FDA0002684802130000031
Performing cross-correlation operation to obtain K values of m;
wherein z ism+qIs a time domain representation of the m + q sampling points in the received signal,
Figure FDA0002684802130000032
q is a time domain expression of a conjugate of a Q sampling point of a kth preset long preamble in the preset long preamble set, wherein Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long preamble; phi'zpk(m) is the result of the cross-correlation of the conjugate of the mth sampling point of the received signal and the qth sampling point of the kth preset long amble, K is greater than or equal to 0 and less than or equal to K-1,
Figure FDA0002684802130000033
is such that phi'zpk(m) the value of m when the maximum value is obtained.
6. The apparatus of claim 4,
said arithmetic unit, in particular for using a formula
Figure FDA0002684802130000034
Performing cross-correlation operation to obtain K values of m;
wherein Z isk,m+qA frequency domain representation of the m + q samples of the kth user's signal in the received signal,
Figure FDA0002684802130000035
a frequency domain expression of the conjugate of the Q sampling point of the kth preset lead code in the preset lead code set is represented, Q is more than or equal to 0 and less than or equal to Q-1, and Q is the length of the preset long lead code; hkIs a frequency domain representation of the channel response of the kth user in the received signal, N'kA frequency domain expression of additive white gaussian noise AWGN for a kth user in the received signal; phi'zpk(m) is the result of conjugate cross-correlation operation between the m + q sampling points of the received signal and the q sampling points of the kth preset long preamble, K is more than or equal to 0 and less than or equal to K-1,
Figure FDA0002684802130000041
is such that phi'zpk(m) the value of m when the maximum value is obtained.
7. A computer arrangement, characterized in that the arrangement comprises a processor for implementing the steps of the method according to any one of claims 1-3 when executing a computer program stored in a memory.
8. A computer-readable storage medium having stored thereon a computer program, characterized in that: the computer program realizing the steps of the method according to any one of claims 1-3 when executed by a processor.
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