CN114389717A - Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM) - Google Patents

Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM) Download PDF

Info

Publication number
CN114389717A
CN114389717A CN202111633054.8A CN202111633054A CN114389717A CN 114389717 A CN114389717 A CN 114389717A CN 202111633054 A CN202111633054 A CN 202111633054A CN 114389717 A CN114389717 A CN 114389717A
Authority
CN
China
Prior art keywords
user
frequency
carriers
estimation
sequence
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
CN202111633054.8A
Other languages
Chinese (zh)
Other versions
CN114389717B (en
Inventor
徐立军
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Beijing Institute of Technology BIT
Original Assignee
Beijing Institute of Technology BIT
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Beijing Institute of Technology BIT filed Critical Beijing Institute of Technology BIT
Priority to CN202111633054.8A priority Critical patent/CN114389717B/en
Publication of CN114389717A publication Critical patent/CN114389717A/en
Application granted granted Critical
Publication of CN114389717B publication Critical patent/CN114389717B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00
    • H04B13/02—Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0008—Modulated-carrier systems arrangements for allowing a transmitter or receiver to use more than one type of modulation
    • 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
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • 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
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/2628—Inverse Fourier transform modulators, e.g. inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Landscapes

  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • Discrete Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Power Engineering (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

The invention discloses an asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM), wherein the method comprises the following steps: combining OFDM modulation with frequency division multiple access, distributing frequency domain subcarriers, and taking a narrow-band reduced sequence as a synchronous sequence to be related to a local sequence through a correlation value calculation formula; performing Doppler estimation on the plurality of narrow-band ascending sequences, and respectively calculating the offset of the correlation between the plurality of narrow-band ascending sequences and the local sequence so as to perform signal synchronization and Doppler estimation; allocating sub-carriers to different users, allocating the sub-carriers of each user, and taking idle waves in the sub-carriers as frequency spectrum guard bands; and performing channel estimation by adopting a frequency domain estimation algorithm of pilot frequency interpolation, and performing channel equalization by utilizing the interpolation to obtain a channel estimation result. The invention can simultaneously support the high-speed communication of a plurality of mobile nodes, well meets the requirement of underwater multi-user information transmission, and has the advantages of simple algorithm, low calculation amount and strong application value.

Description

Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM)
Technical Field
The invention relates to the technical field of wireless information transmission, in particular to an asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM).
Background
The underwater acoustic communication is a main technical means of wireless information transmission in the ocean, has the advantages of simple equipment layout, strong flexibility, high safety factor, low cost and the like compared with wired communication, and plays a wide role in the aspects of submarine environment observation, ocean engineering construction, submersible and aircraft operation, military field and the like. However, the underwater acoustic channel has the characteristics of low-pass characteristic, large propagation delay, large multi-path delay spread, obvious doppler shift effect, time-varying channel, high environmental noise, easy distortion and fluctuation of signals and the like, so compared with wireless electromagnetic communication, the underwater acoustic communication has the disadvantages of serious bandwidth limitation, low communication rate, more noise interference, large transmission delay, special anti-doppler shift and anti-time-varying processing requirements and the like, and the difficulty in designing the underwater acoustic communication system is greatly increased.
Early underwater acoustic communication mainly used a point-to-point communication mode, and only supported mutual communication between two users. However, in recent years, with more and more frequent human ocean activities, various underwater manned submersible vehicles, underwater unmanned autonomous submersible vehicles, submerged buoys, buoys and other ocean equipment are increasingly applied, the data volume and the number of nodes of underwater information transmission are continuously increased, the traditional communication mode cannot realize information interaction among a plurality of equipment, and the cooperative action and advantages are played, so that the practical application requirements are difficult to meet. Therefore, multi-user underwater acoustic communication is produced and rapidly becomes a hot point of research.
Multi-user communication generally uses three methods, Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA), to allocate and share channels. Time division multiple access is the simplest and most common multiple access mode, a plurality of users are divided from a time domain by allocating time slots in advance or establishing an upper layer networking protocol, and only one user is ensured to transmit in each time period, and the time division multiple access is still point-to-point communication in principle. Because the underwater acoustic communication has the characteristics of prolonged transmission time, high equipment synchronization difficulty, strong node mobility and the like, in practical application, each node is difficult to transmit information according to a fixed time slot, and only can realize channel application and distribution through a networking protocol, and the defects of the need of carrying out handshake for many times, complex protocol and possibility of signal collision are caused. The carrier frequency band is divided by the frequency division multiple access, each user occupies different sub-channels to transmit information in parallel, the principle and the realization are very simple, the interference and the collision among the users do not exist, the clock synchronization and the repeated handshake are not needed, the transmission is realized when the users want to send the information, the application is very convenient, but the transmission efficiency is very low, the bandwidth waste is serious, the bandwidth of the underwater acoustic communication is limited, and the frequency band is difficult to be divided for many times. The CDMA allocates different spread spectrum codes to each user, a plurality of users transmit information at the same frequency, the users are distinguished according to the difference of the spread spectrum codes, and the number of the users only depends on the number of the spread spectrum codes. In the case of many users, cdma has a great advantage over time and frequency division multiplexing, and thus is widely used in wireless communication. However, in underwater acoustic communication, the transmission performance of the code division multiple access is seriously affected by channel multipath, time-varying doppler and near-far effect, the capture and tracking of the spread spectrum code are difficult, the algorithm is complex and has poor stability, and the single-user rate after the spread spectrum is very low, so that when the number of nodes in a communication area is not large, the code division multiple access mode is rarely selected to realize multi-user communication. When the three multiple access modes are applied in an underwater acoustic channel environment, certain problems and defects exist, and the transmission requirement of multi-user underwater acoustic communication is difficult to meet.
The underwater acoustic channel has the characteristics of serious bandwidth limitation, prolonged propagation time, large transmission attenuation, serious Doppler frequency offset, large multipath delay spread and the like, brings great challenges to the design and implementation of a multi-user underwater acoustic communication algorithm, and the existing multi-access mode is difficult to be directly well applied in a complex underwater acoustic channel environment.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, the invention aims to provide an asynchronous multi-user underwater acoustic communication method based on Orthogonal Frequency Division Multiplexing (OFDM), which directly avoids mutual interference of multiple users during asynchronous communication from a design level, does not need to introduce a complex interference elimination algorithm, can simultaneously support high-speed communication of multiple mobile nodes, has transmission performance almost the same as that of single-node OFDM communication, well meets the requirement of underwater multi-user information transmission, and has the advantages of simple algorithm, low calculation amount and strong application value.
Another objective of the present invention is to provide an asynchronous multi-user underwater acoustic communication device based on orthogonal frequency division multiplexing OFDM.
In order to achieve the above object, in one aspect, the present invention provides an asynchronous multi-user underwater acoustic communication method based on orthogonal frequency division multiplexing OFDM, including:
combining OFDM modulation and frequency division multiple access, and distributing frequency domain subcarriers to enable multi-user communication; based on multi-user communication, the narrow-band reduced sequence is used as a synchronous sequence to be related to a local sequence through a correlation value calculation formula; performing Doppler estimation on the plurality of narrow-band ascending sequences, and calculating the offset by correlating the plurality of narrow-band ascending sequences with the local sequence respectively so as to perform signal synchronization and Doppler estimation; based on signal synchronization and Doppler estimation, allocating subcarriers to different users, allocating subcarriers of each user, and taking idle waves in the subcarriers as a frequency spectrum guard band; and based on the frequency spectrum guard band, performing channel estimation by adopting a frequency domain estimation algorithm of pilot frequency interpolation, obtaining a channel estimation result by utilizing interpolation, and performing channel equalization based on the channel estimation result.
In addition, the asynchronous multi-user underwater acoustic communication method based on orthogonal frequency division multiplexing OFDM according to the above embodiment of the present invention may further have the following additional technical features:
further, in one embodiment of the present invention, the correlation value calculation formula is:
Figure BDA0003441623500000021
wherein, X is a local sequence, Y is a receiving sequence, and gamma is a correlation value.
Further, in an embodiment of the present invention, the estimation formula for performing doppler estimation on a plurality of narrow-band chirp-up sequences is as follows:
Figure BDA0003441623500000031
Figure BDA0003441623500000032
wherein y (t) is a received sequence, xpre(t)、xpost(t) is a local sequence which is,
Figure BDA0003441623500000033
and
Figure BDA0003441623500000034
respectively, the arrival times of the front and rear HFM sequences, calculating the actual received data frame length:
Figure BDA0003441623500000035
according to TtpAnd
Figure BDA0003441623500000036
the relationship, the estimated doppler is:
Figure BDA0003441623500000037
further, in an embodiment of the present invention, the allocating the subcarriers to different users and allocating the subcarriers of each user includes: distributing the sub-carriers to different users according to the number of the users, and distributing the sub-carriers of each user according to the functions of the sub-carriers; the sub-carriers are divided into null carriers, pilot carriers and data.
Further, in an embodiment of the present invention, the performing channel estimation by using a frequency domain estimation algorithm using pilot frequency interpolation obtains a channel estimation result by using interpolation, including: and calculating the frequency response of the pilot frequency position according to the known pilot frequency sequence and the actually received pilot frequency data by adopting a frequency domain estimation algorithm of pilot frequency interpolation, and obtaining the frequency response estimation result of the data subcarrier position by utilizing interpolation.
Further, in an embodiment of the present invention, the obtaining a frequency response estimation result of a data subcarrier position by using interpolation includes:
the vector expression of the input-output relationship without considering the mutual interference among the carriers is as follows:
Y＝XH+η
the frequency response of the channel is estimated by adopting a least square method as follows:
Figure BDA0003441623500000038
further, in an embodiment of the present invention, the obtaining a frequency response estimation result of a data subcarrier position by using interpolation further includes: and recovering the frequency response estimation results of the rest positions by an interpolation mode, wherein the interpolation mode expression is as follows:
Hi＝Pa+(Pb-Pa)×(i-1)/length
wherein, PaFor the frequency domain impulse response of the previous pilot position, PbAnd i is the distance between a data point and a pilot frequency point, and length is the distance between the pilot frequency positions a and b.
Further, in an embodiment of the present invention, the performing equalization based on the channel estimation result includes: and performing channel equalization by using an MMSE algorithm based on the channel estimation result, wherein the expression is as follows:
Figure BDA0003441623500000041
wherein the content of the first and second substances,
Figure BDA0003441623500000042
in order to be the power of the signal,
Figure BDA0003441623500000043
is the noise power.
The asynchronous multi-user underwater acoustic communication method based on the orthogonal frequency division multiplexing OFDM of the embodiment of the invention is based on the OFDM modulation technology, realizes multi-user underwater acoustic communication by adopting a frequency domain subcarrier multiplexing mode, fully reduces mutual interference among multiple users by adding a frequency spectrum guard band, eliminates the clock synchronization requirement of a system among the multiple users, and realizes flexible and convenient multi-user asynchronous communication. According to the number of users and the algorithm requirement, the sub-carriers are distributed, the pilot frequency and the null carrier are inserted, and frequency domain channel estimation and equalization are performed, so that the multi-path resisting effect is good, the calculated amount is small, and the real-time performance is strong. The method researches a synchronization and Doppler estimation algorithm in a multi-user asynchronous communication system, selects a narrow-band chirp sequence as a synchronization sequence, can accurately realize signal synchronization and Doppler estimation under the condition of multi-user overlapping, and can also effectively avoid the interference to signal waveforms of other users.
In order to achieve the above object, another aspect of the present invention provides an asynchronous multi-user underwater acoustic communication device based on orthogonal frequency division multiplexing OFDM, including:
the first distribution module is used for combining OFDM modulation and frequency division multiple access and distributing subcarriers of a frequency domain so as to realize multi-user communication;
the calculation estimation module is used for taking the narrow-band reduced sequence as a synchronous sequence to be related to the local sequence through a correlation value calculation formula based on multi-user communication; performing Doppler estimation on the plurality of narrow-band ascending sequences, and calculating the offset by correlating the plurality of narrow-band ascending sequences with the local sequence respectively so as to perform signal synchronization and Doppler estimation;
the second allocation module is used for allocating subcarriers to different users based on signal synchronization and Doppler estimation, allocating subcarriers of each user and taking idle waves in the subcarriers as a frequency spectrum guard band;
and the channel equalization module is used for performing channel estimation by adopting a frequency domain estimation algorithm of pilot frequency interpolation based on the frequency spectrum guard band, obtaining a channel estimation result by interpolation, and performing channel equalization based on the channel estimation result.
The asynchronous multi-user underwater acoustic communication device based on the orthogonal frequency division multiplexing OFDM of the embodiment of the invention is based on the OFDM modulation technology, realizes multi-user underwater acoustic communication by adopting a frequency domain subcarrier multiplexing mode, fully reduces mutual interference among multiple users by adding a frequency spectrum guard band, eliminates the clock synchronization requirement of a system among the multiple users, and realizes flexible and convenient multi-user asynchronous communication. According to the number of users and the algorithm requirement, the sub-carriers are distributed, the pilot frequency and the null carrier are inserted, and frequency domain channel estimation and equalization are performed, so that the multi-path resisting effect is good, the calculated amount is small, and the real-time performance is strong. The method researches a synchronization and Doppler estimation algorithm in a multi-user asynchronous communication system, selects a narrow-band chirp sequence as a synchronization sequence, can accurately realize signal synchronization and Doppler estimation under the condition of multi-user overlapping, and can also effectively avoid the interference to signal waveforms of other users.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a flowchart of an asynchronous multi-user underwater acoustic communication method based on orthogonal frequency division multiplexing OFDM according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a frequency spectrum of an OFDM signal according to an embodiment of the present invention;
FIG. 3 is a process flow diagram of an OFMD system in accordance with an embodiment of the present invention;
FIG. 4 is a schematic diagram illustrating a subband-based subcarrier allocation scheme according to an embodiment of the present invention;
FIG. 5 is a flow chart of a multi-user OFDM modulation system according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating the autocorrelation characteristics of an 8192-point narrowband chirp sequence with a bandwidth of 1kHz at a Doppler of 0m/s and a Doppler of 5m/s according to an embodiment of the present invention;
fig. 7 is a schematic diagram of synchronization sequence cross-correlation characteristics of neighboring users according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of a signal frame format design according to an embodiment of the present invention;
fig. 9 is a diagram illustrating subcarrier allocation results according to an embodiment of the present invention;
FIG. 10 is a waveform diagram of 5 users according to an embodiment of the present invention;
fig. 11 is a spectrum diagram of 5 users according to an embodiment of the present invention;
FIG. 12 is a diagram illustrating the result of multi-user synchronous transmission according to an embodiment of the present invention;
FIG. 13 is a diagram illustrating the result of multi-user asynchronous transmission according to an embodiment of the present invention;
FIG. 14 is a diagram illustrating the results of multi-user asynchronous and Doppler transmissions according to an embodiment of the present invention;
FIG. 15 is a schematic diagram of a demodulation error rate curve of a system with white Gaussian noise channel according to an embodiment of the present invention;
fig. 16 is a schematic structural diagram of an asynchronous multi-user underwater acoustic communication device based on orthogonal frequency division multiplexing OFDM according to an embodiment of the present invention.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
In order to make the technical solutions of the present invention better understood, 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, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The following describes an asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM) according to an embodiment of the present invention with reference to the accompanying drawings.
It can be known that OFDM (Orthogonal frequency-division multiplexing) is an emerging multi-carrier modulation technique, and is different from a conventional frequency-division multiplexing method in that subcarriers are overlapped with each other, and mutual interference between different carriers is eliminated through waveform orthogonality, so as to achieve higher spectrum utilization rate and transmission rate, where fig. 2 is a spectrum diagram of an OFDM signal.
The baseband signal waveform of the OFDM modulation is:
Figure BDA0003441623500000061
where K is the number of subcarriers and T is the signal period, which is actually an expression of the inverse fourier transform. Therefore, in practical application, OFDM modulation and demodulation can be realized by IFFT and FFT, and the amount of computation is significantly reduced.
The processing flow chart of the OFMD system is shown in fig. 3, so that the OFDM system has high frequency spectrum utilization rate, strong multipath resistance and simple and effective frequency domain equalization, and is very suitable for near-distance underwater acoustic communication.
Fig. 1 is a flowchart of an asynchronous multi-user underwater acoustic communication method based on orthogonal frequency division multiplexing OFDM according to an embodiment of the present invention.
As shown in fig. 1, the asynchronous multi-user underwater acoustic communication method based on orthogonal frequency division multiplexing OFDM includes:
and S1, combining the OFDM modulation with frequency division multiple access, and allocating the subcarriers of the frequency domain to enable multi-user communication.
Specifically, the invention combines OFDM modulation and FDMA multiple access, and realizes multi-user underwater acoustic communication by distributing a plurality of subcarriers of a frequency domain to different users for use.
As an implementation manner, a subband type subcarrier allocation manner is adopted, and a schematic diagram is shown in fig. 4:
when a single user sends a signal, the signal is equivalent to point-to-point communication, only the subcarrier corresponding to the user transmits information, and the rest subcarriers are zero; when multiple users transmit signals simultaneously, there can be collisions and overlap of waveforms. The receiving end needs to receive the waveforms from multiple users at the same time and distinguish them. At this time, the process flow diagram is as shown in FIG. 5,
the waveform sent by each user reaches a receiving end after passing through different channels, if the sent signals are completely synchronous at the receiving end, the waveforms are still orthogonal, mutual interference among users does not exist, but the method is very difficult to realize under the condition of underwater acoustic communication, particularly mobile nodes; if the transmitted signals are not synchronized and overlap to different degrees, mutual interference among multiple users occurs. By inserting null carriers between users as frequency guard bands, mutual interference between users when overlapping is reduced as much as possible.
S2, based on multi-user communication, using the narrow-band reduced sequence as the synchronous sequence to be related to the local sequence through the related value calculation formula; and performing Doppler estimation on the plurality of narrowband ascending sequences, and calculating the offset by correlating the plurality of narrowband ascending sequences with the local sequence respectively so as to perform signal synchronization and Doppler estimation.
It is understood that in a multi-user asynchronous communication system, the signal detection and synchronization, and the doppler estimation and compensation algorithms are also different from those of a single user. The synchronization sequence of each user needs to have good auto-correlation and cross-correlation characteristics, and also needs to avoid interference of the synchronization sequence to signal waveforms of other users, and ensure that each user can still be accurately synchronized when a plurality of synchronization sequences are overlapped, and respective doppler is estimated. In view of the above, a narrowband chirp sequence is selected as a synchronization sequence whose frequency band coincides with the subcarrier band of each user.
As shown in fig. 6, where the self-correlation characteristics of 8192 narrow-band chirp sequences with a bandwidth of 1kHz at doppler of 0m/s and 5m/s, respectively, can be seen, the sequence has good self-correlation characteristics and is affected by doppler very little.
As shown in fig. 7, it can be seen that mutual interference is very low due to different frequency bands for the synchronization sequence cross-correlation characteristics of adjacent users. The sequence has the same frequency band as the signal waveform of other users, and does not interfere with each other.
Further, a narrow-band chirp sequence is selected as a synchronization sequence, and the signal frame format is designed as shown in fig. 8:
the previous chip-down sequence in fig. 8 is a synchronization sequence, and the signal detection and synchronization are realized by correlating with the local sequence. The correlation value calculation formula is as follows:
Figure BDA0003441623500000071
in the formula, X is a local sequence, Y is a receiving sequence, gamma is a correlation value, when the correlation value exceeds a threshold, a signal is considered to be detected, and a position with the maximum correlation value in a section of area is selected as a synchronous position.
The ascending chirp sequences before and after in fig. 8 are doppler-estimated, and the two sequences are correlated with the local sequence, respectively, and the offset is calculated to obtain the stretch compression coefficient, that is, doppler. The estimation method comprises the following steps:
Figure BDA0003441623500000072
Figure BDA0003441623500000073
wherein y (t) is a received sequence, xpre(t)、xpost(t) is a local sequence which is,
Figure BDA0003441623500000074
and
Figure BDA0003441623500000075
the HFM sequence arrival times before and after, respectively, whereby the actual received data frame length can be calculated:
Figure BDA0003441623500000076
by TtpIndicating the length of the transmitted data frame, ideally
Figure BDA0003441623500000077
However, the waveform is actually affected by doppler, and the waveforms are not equal to each other due to stretching change. According toTtpAnd
Figure BDA0003441623500000078
the relationship, doppler can be estimated as follows:
Figure BDA0003441623500000079
according to the synchronization and Doppler estimation algorithm, the received sequence is respectively correlated with the local sequence of each user, so that the detection, synchronization and Doppler estimation of the waveform of each user can be realized simultaneously, and the signal waveform of each user is obtained.
And S3, allocating subcarriers to different users based on signal synchronization and Doppler estimation, allocating the subcarriers of each user, and taking idle waves in the subcarriers as frequency spectrum guard bands.
It can be understood that the Subcarriers of the OFDM system are divided into three classes, i.e., Null carriers (Null Subcarriers), Pilot carriers (Pilot Subcarriers) and Data carriers (Data Subcarriers), according to roles. The idle wave at the edge is used as a frequency spectrum guard band, and the idle wave in the middle is used for estimating Doppler and noise energy; the pilot may be used for channel estimation; the data segment is used to transmit information. In the OFDM multi-purpose communication system, it is necessary to allocate subcarriers to different users according to the number of users, and then allocate subcarriers to each user according to the difference in function.
As an implementation manner, an OFDM multi-user communication system with a working frequency band of 9-15 kHz, a subcarrier number of 1024 and a user number of 5 is taken as an example. First, considering the spectrum guard band among users, under the non-orthogonal condition, each user will cause interference to the adjacent 2-3 sub-carriers. Considering the frequency shift caused by doppler, the maximum doppler shift at 15kHz is about 100Hz, i.e. a maximum shift of 17 subcarriers, calculated with a maximum relative velocity between users of 10 m/s. So that about 20 null carriers are required between each user as a guard band. In addition, data, pilot, and null allocation needs to be performed at the subcarrier position of each user, and the allocation principle is approximately 4 pilot intervals and 16 null intervals. From the above analysis, the final assignment results are shown in FIG. 9:
first, 12 idler waves are inserted as spectrum guard bands on both sides of 1024 sub-carriers, so that 1000 sub-carriers remain. The 1000 sub-carriers are divided equally into 5 users, and each user is divided into 200 sub-carriers. 11 null carriers are inserted into the left side of each user, 12 null carriers are inserted into the right side of each user, one pilot frequency is inserted into each 4 of the remaining 177 sub-carriers, one null carrier is inserted into each 16 sub-carriers, and data is placed in the rest positions. Based on this, the number of data subcarriers in each user is 121, the number of pilots is 45, the number of intermediate position null carriers is 11, and 23 null carriers exist between each user as guard intervals.
And S4, based on the frequency spectrum guard band, performing channel estimation by adopting a frequency domain estimation algorithm of pilot frequency interpolation, obtaining a channel estimation result by interpolation, and performing channel equalization based on the channel estimation result.
Specifically, the channel estimation adopts a frequency domain estimation algorithm of pilot frequency interpolation, calculates the frequency response of the pilot frequency position according to the known pilot frequency sequence and the actually received pilot frequency data, and then obtains the frequency response estimation result of the data subcarrier position by utilizing the interpolation.
It will be appreciated that this algorithm is computationally inexpensive and simple to apply. In principle, the final frequency domain response result is directly calculated without considering specific time domain parameters such as channel multipath, Doppler and the like, and the method has high stability in a complex channel environment. When mutual interference between carriers is not considered, the input-output relationship is as follows:
y[m]＝h[m]*x[m]+η[m]
written as a vector expression of
Y＝XH+η
Estimating the frequency domain response of a channel using least squares
Figure BDA0003441623500000091
The pilot frequency is uniformly distributed, the frequency response results of other positions can be recovered through interpolation, the interpolation mode is linear interpolation, and the expression is
Hi＝Pa+(Pb-Pa)×(i-1)/length
Wherein, PaFor the frequency domain impulse response of the previous pilot position, PbAnd i is the distance between a data point and a pilot frequency point, and length is the distance between the pilot frequency positions a and b.
After obtaining the channel estimation result, equalizing by using MMSE algorithm, wherein the expression is
Figure BDA0003441623500000092
Wherein the content of the first and second substances,
Figure BDA0003441623500000093
the signal power, which is determined by the mapping method,
Figure BDA0003441623500000094
the noise power is calculated by a carrier wave.
The technical effects of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
As an example, Matlab is used to simulate the multi-user underwater acoustic communication system, and the system parameter settings are shown in table 1:
TABLE 1
Sampling rate fs 96kHz Center frequency fc 12kHz
System bandwidth B 6kHz Number of subcarriers 1024
Length of synchronization sequence 8192 point Guard interval 50ms
Peak-to-average ratio (PAPR) suppression threshold 2/3*max|x(t)| Window function Lifting cosine window (beta is 0.25)
Maximum number of users 5 Single user rate 730bps (QPSK, uncoded)
Fig. 10 is a time domain waveform diagram of 5 users, and fig. 11 is a frequency spectrum diagram of 5 users. It can be seen from the frequency spectrum that each user occupies different frequency bands, and there is no mutual interference.
Further, the mutual interference situation among users of the asynchronous multi-user underwater acoustic communication system under different situations is simulated. Fig. 12, 13 and 14 are a waveform diagram and a constellation diagram of a signal transmitted by multiple users simultaneously in an ideal environment without noise and multipath, the waveform diagram is a time domain waveform overlapped by 5 users at a receiving end, the constellation diagram is a result of combining the 5 users, and different colors represent different users. FIG. 12 shows the transmission results when the users are completely synchronized, FIG. 13 shows the transmission results when the users are asynchronous, and the delay of each user relative to the previous user is Tbl/5，TblRepresenting an OFThe length of the DM symbol, fig. 14 shows the transmission result of asynchronous transmission and different doppler, and the moving speeds of 5 users relative to the receiving end are-4 m/s, -3m/s, and 0m/s, respectively. It can be seen from the constellation diagram that the spectrum guard band can effectively eliminate the mutual interference between users caused by the overlapping of waveforms and doppler frequency shift.
Further, the transmission performance of the asynchronous multi-user underwater sound communication system under different conditions is simulated. Each time producing 5 [0, T ]bl]Random number of 5 [ -5,5 ] as user delay]The random number between the two is used as the relative speed of the user and the receiving end, and the bit error rate is calculated through multiple times of simulation. Fig. 15 is a demodulation error rate curve of a system under a white gaussian noise channel, where a black curve is an ideal case where users are synchronized and do not have doppler, a red curve is a result where random delay and doppler exist between users and synchronization and doppler compensation are performed with a standard value, and a blue curve is a result where random delay and doppler exist between users and synchronization and doppler estimation and compensation are performed with a narrow-band chirp as a synchronization sequence. The performance of the red curve and the black curve is consistent, which shows that the system well eliminates the mutual interference between users caused by asynchronization and Doppler, the performance of the blue curve is reduced by about 3dB compared with the ideal situation because of the synchronization and Doppler estimation errors, and the narrow-band chirp sequence has better application performance.
Simulation results show that the invention can well eliminate mutual interference among multiple users and support stable communication of multiple mobile nodes in a complex underwater acoustic channel environment.
According to the asynchronous multi-user underwater acoustic communication method based on the orthogonal frequency division multiplexing OFDM, the multi-user underwater acoustic communication is realized by adopting a frequency domain subcarrier multiplexing mode, the mutual interference among multiple users is fully reduced by adding a frequency spectrum guard band, the clock synchronization requirement of a system among the multiple users is eliminated, and the flexible and convenient multi-user asynchronous communication is realized. According to the number of users and the algorithm requirement, the sub-carriers are distributed, the pilot frequency and the null carrier are inserted, and frequency domain channel estimation and equalization are performed, so that the multi-path resisting effect is good, the calculated amount is small, and the real-time performance is strong. The method researches a synchronization and Doppler estimation algorithm in a multi-user asynchronous communication system, selects a narrow-band chirp sequence as a synchronization sequence, can accurately realize signal synchronization and Doppler estimation under the condition of multi-user overlapping, and can also effectively avoid the interference to signal waveforms of other users. The method has the advantages that mutual interference of multiple users in asynchronous communication is directly avoided from the design level, a complex interference elimination algorithm is not required to be introduced, high-speed communication of multiple mobile nodes can be supported simultaneously, the transmission performance is almost the same as that of single-node OFDM communication, the underwater multi-user information transmission requirement is well met, the algorithm is simple, the calculated amount is low, and the method has a strong application value.
In order to implement the above embodiments, as shown in fig. 16, the present embodiment further provides an asynchronous multi-user underwater acoustic communication device 10 based on orthogonal frequency division multiplexing OFDM, where the device 10 includes: a first allocation module 100, a calculation estimation module 200, a second allocation module 300 and a channel equalization module 400.
A first allocation module 100, configured to combine OFDM modulation with frequency division multiple access, and allocate subcarriers in a frequency domain, so as to enable multi-user communication;
a calculation estimation module 200, configured to use the narrowband reduced sequence as a synchronization sequence to be correlated with a local sequence through a correlation value calculation formula based on multi-user communication; performing Doppler estimation on the plurality of narrow-band ascending sequences, and calculating the offset by correlating the plurality of narrow-band ascending sequences with the local sequence respectively so as to perform signal synchronization and Doppler estimation;
a second allocating module 300, configured to allocate subcarriers to different users based on signal synchronization and doppler estimation, allocate subcarriers of each user, and use idle carriers in the subcarriers as a spectrum guard band;
the channel equalization module 400 is configured to perform channel estimation by using a frequency domain estimation algorithm of pilot frequency interpolation based on the spectrum guard band, obtain a channel estimation result by using interpolation, and perform channel equalization based on the channel estimation result.
Further, the second allocating module 300 is further configured to:
allocating the sub-carriers to different users according to the number of the users, and allocating the sub-carriers of each user according to the functions of the sub-carriers; the sub-carriers are divided into null carriers, pilot carriers and data.
According to the asynchronous multi-user underwater acoustic communication device based on the orthogonal frequency division multiplexing OFDM, the multi-user underwater acoustic communication is realized by adopting a frequency domain subcarrier multiplexing mode, the mutual interference among multiple users is fully reduced by adding a frequency spectrum guard band, the clock synchronization requirement of a system among the multiple users is eliminated, and the flexible and convenient multi-user asynchronous communication is realized. According to the number of users and the algorithm requirement, the sub-carriers are distributed, the pilot frequency and the null carrier are inserted, and frequency domain channel estimation and equalization are performed, so that the multi-path resisting effect is good, the calculated amount is small, and the real-time performance is strong. The method researches a synchronization and Doppler estimation algorithm in a multi-user asynchronous communication system, selects a narrow-band chirp sequence as a synchronization sequence, can accurately realize signal synchronization and Doppler estimation under the condition of multi-user overlapping, and can also effectively avoid the interference to signal waveforms of other users. The method has the advantages that mutual interference of multiple users in asynchronous communication is directly avoided from the design level, a complex interference elimination algorithm is not required to be introduced, high-speed communication of multiple mobile nodes can be supported simultaneously, the transmission performance is almost the same as that of single-node OFDM communication, the underwater multi-user information transmission requirement is well met, the algorithm is simple, the calculated amount is low, and the method has a strong application value.
It should be noted that the foregoing explanation on the embodiment of the asynchronous multi-user underwater acoustic communication method based on orthogonal frequency division multiplexing OFDM is also applicable to the asynchronous multi-user underwater acoustic communication device based on orthogonal frequency division multiplexing OFDM of this embodiment, and details are not repeated here.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (10)

1. An asynchronous multi-user underwater acoustic communication method based on Orthogonal Frequency Division Multiplexing (OFDM) is characterized by comprising the following steps of:
combining OFDM modulation and frequency division multiple access, and distributing frequency domain subcarriers to enable multi-user communication;
based on the multi-user communication, the narrow-band reduced sequence is used as a synchronous sequence to be related to a local sequence through a correlation value calculation formula; performing Doppler estimation on a plurality of narrow-band ascending sequences, and calculating the offset by correlating the narrow-band ascending sequences with the local sequence respectively so as to perform signal synchronization and Doppler estimation;
based on the signal synchronization and Doppler estimation, allocating the subcarriers to different users, allocating the subcarriers of each user, and taking idle waves in the subcarriers as a spectrum guard band;
and based on the frequency spectrum guard band, performing channel estimation by adopting a frequency domain estimation algorithm of pilot frequency interpolation, obtaining a channel estimation result by utilizing interpolation, and performing channel equalization based on the channel estimation result.
2. The method of claim 1, wherein the correlation value is calculated by the formula:
Figure FDA0003441623490000011
wherein, X is a local sequence, Y is a receiving sequence, and gamma is a correlation value.
3. The method of claim 1, wherein the estimating the doppler estimates for the plurality of narrowband chirp-rising sequences is according to the following equation:
Figure FDA0003441623490000012
Figure FDA0003441623490000013
wherein y (t) is a received sequence, xptr(t)、xpost(t) is a local sequence which is,
Figure FDA0003441623490000014
and
Figure FDA0003441623490000015
respectively, the arrival times of the front and rear HFM sequences, calculating the actual received data frame length:
Figure FDA0003441623490000016
according to TtpAnd
Figure FDA0003441623490000017
the relationship, the estimated doppler is:
Figure FDA0003441623490000018
4. the method of claim 1, wherein the allocating the subcarriers to different users and allocating the subcarriers of each user comprises:
distributing the sub-carriers to different users according to the number of the users, and distributing the sub-carriers of each user according to the functions of the sub-carriers; the sub-carriers are divided into null carriers, pilot carriers and data.
5. The method of claim 1, wherein the channel estimation using the frequency domain estimation algorithm with pilot frequency interpolation uses interpolation to obtain a channel estimation result, comprising:
and calculating the frequency response of the pilot frequency position according to the known pilot frequency sequence and the actually received pilot frequency data by adopting a frequency domain estimation algorithm of pilot frequency interpolation, and obtaining the frequency response estimation result of the data subcarrier position by utilizing interpolation.
6. The method of claim 5, wherein the obtaining the frequency response estimate of the data subcarrier locations using interpolation comprises:
the vector expression of the input-output relationship without considering the mutual interference among the carriers is as follows:
Y＝XH+η
the frequency response of the channel is estimated by adopting a least square method as follows:
Figure FDA0003441623490000021
7. the method of claim 6, wherein the obtaining the frequency response estimate for the data subcarrier location using interpolation further comprises: and recovering the frequency response estimation results of the rest positions by an interpolation mode, wherein the interpolation mode expression is as follows:
Hi＝Pa+(Pb-Pa)×(i-1)/length
wherein, PaFor the frequency domain impulse response of the previous pilot position, PbAnd i is the distance between a data point and a pilot frequency point, and length is the distance between the pilot frequency positions a and b.
8. The method of claim 1, wherein the equalizing based on the channel estimation result comprises: and performing channel equalization by using an MMSE algorithm based on the channel estimation result, wherein the expression is as follows:
Figure FDA0003441623490000022
wherein the content of the first and second substances,
Figure FDA0003441623490000023
in order to be the power of the signal,
Figure FDA0003441623490000024
is the noise power.
9. An asynchronous multi-user underwater acoustic communication device based on Orthogonal Frequency Division Multiplexing (OFDM), comprising:
the first distribution module is used for combining OFDM modulation and frequency division multiple access and distributing subcarriers of a frequency domain so as to realize multi-user communication;
the calculation estimation module is used for taking the narrow-band reduced sequence as a synchronous sequence to be related to a local sequence through a correlation value calculation formula based on the multi-user communication; performing Doppler estimation on a plurality of narrow-band ascending sequences, and calculating the offset by correlating the narrow-band ascending sequences with the local sequence respectively so as to perform signal synchronization and Doppler estimation;
a second allocating module, configured to allocate the subcarriers to different users based on the signal synchronization and doppler estimation, allocate subcarriers of each user, and use idle carriers in the subcarriers as a spectrum guard band;
and the channel equalization module is used for performing channel estimation by adopting a frequency domain estimation algorithm of pilot frequency interpolation based on the frequency spectrum guard band, obtaining a channel estimation result by interpolation, and performing channel equalization based on the channel estimation result.
10. The apparatus of claim 9, wherein the second allocating module is further configured to:
distributing the sub-carriers to different users according to the number of the users, and distributing the sub-carriers of each user according to the functions of the sub-carriers; the sub-carriers are divided into null carriers, pilot carriers and data.
CN202111633054.8A 2021-12-29 2021-12-29 Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM) Active CN114389717B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202111633054.8A CN114389717B (en) 2021-12-29 2021-12-29 Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202111633054.8A CN114389717B (en) 2021-12-29 2021-12-29 Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM)

Publications (2)

Publication Number Publication Date
CN114389717A true CN114389717A (en) 2022-04-22
CN114389717B CN114389717B (en) 2022-11-15

Family

ID=81200541

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202111633054.8A Active CN114389717B (en) 2021-12-29 2021-12-29 Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM)

Country Status (1)

Country Link
CN (1) CN114389717B (en)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008157609A2 (en) * 2007-06-18 2008-12-24 University Of Connecticut Apparatus, systems and methods for enhanced multi-carrier based underwater acoustic communications
CN102868659A (en) * 2012-08-31 2013-01-09 中国船舶重工集团公司第七一五研究所 Symbol synchronization and Doppler compensation method for mobile orthogonal frequency division multiplexing (OFDM) underwater sound communication signal
CN105490978A (en) * 2015-10-30 2016-04-13 哈尔滨工程大学 Asynchronous multi-user access method for underwater acoustic OFDM
CN107426120A (en) * 2017-07-24 2017-12-01 哈尔滨工程大学 A kind of underwater sound OFDM MFSK channel equalization methods based on least mean-square error
CN107911133A (en) * 2017-11-17 2018-04-13 厦门大学 The Doppler factor estimation and compensation method of a kind of mobile underwater sound communication
CN110830403A (en) * 2019-10-12 2020-02-21 天津大学 Method for improving underwater sound sparse orthogonal frequency division multiplexing multi-carrier modulation performance
CN111131098A (en) * 2019-12-31 2020-05-08 哈尔滨哈船海洋信息技术有限公司 Doppler factor estimation method based on autocorrelation output peak interpolation of underwater sound OFDM signal

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008157609A2 (en) * 2007-06-18 2008-12-24 University Of Connecticut Apparatus, systems and methods for enhanced multi-carrier based underwater acoustic communications
CN102868659A (en) * 2012-08-31 2013-01-09 中国船舶重工集团公司第七一五研究所 Symbol synchronization and Doppler compensation method for mobile orthogonal frequency division multiplexing (OFDM) underwater sound communication signal
CN105490978A (en) * 2015-10-30 2016-04-13 哈尔滨工程大学 Asynchronous multi-user access method for underwater acoustic OFDM
CN107426120A (en) * 2017-07-24 2017-12-01 哈尔滨工程大学 A kind of underwater sound OFDM MFSK channel equalization methods based on least mean-square error
CN107911133A (en) * 2017-11-17 2018-04-13 厦门大学 The Doppler factor estimation and compensation method of a kind of mobile underwater sound communication
CN110830403A (en) * 2019-10-12 2020-02-21 天津大学 Method for improving underwater sound sparse orthogonal frequency division multiplexing multi-carrier modulation performance
CN111131098A (en) * 2019-12-31 2020-05-08 哈尔滨哈船海洋信息技术有限公司 Doppler factor estimation method based on autocorrelation output peak interpolation of underwater sound OFDM signal

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
徐立军等: "基于Gold序列调制Chirp信号的多用户水声信号识别方法", 《2017年西安-上海声学学会第五届声学学术交流会议论文集》 *

Also Published As

Publication number Publication date
CN114389717B (en) 2022-11-15

Similar Documents

Publication Publication Date Title
CN101433038B (en) The distribution of uplink reference signals
Ebihara et al. Underwater acoustic communication with an orthogonal signal division multiplexing scheme in doubly spread channels
CN101771657B (en) Multicarrier underwater acoustic communication method
CN103051578B (en) With the iteration error propagation judgement OFDM channel estimation method that ICI eliminates
CN110868369A (en) Uplink channel estimation method and device based on 5G NR system
WO2020069530A1 (en) Method and apparatus for high data rate long range acoustic and rf communication using chirp waveform modulation
CN104253680A (en) Synchronous signal sending method and synchronous signal sending device for FBMC (filter bank multicarrier) system
CN101414986A (en) Channel estimation method and apparatus
Zhou et al. OFDMA initial ranging for IEEE 802.16 e based on time-domain and frequency-domain approaches
WO2010015101A1 (en) A radio channel model for ici cancellation in multi-carrier systems
CN107454031B (en) OFDM-MFSK underwater acoustic communication technology based on packet signal-to-noise ratio confidence
CN104333527A (en) COFDM (Coded Orthogonal Frequency Division Multiplexing) modulating and demodulating method used for airplane
CN114389717B (en) Asynchronous multi-user underwater acoustic communication method and device based on Orthogonal Frequency Division Multiplexing (OFDM)
CN107592277B (en) MIMO-OFDM (multiple input multiple output-orthogonal frequency division multiplexing) fast time-varying channel estimation method
CN102113285A (en) A simplified equalizationscheme for distributed resource allocation in multi-carrier systems
CN112134822A (en) Method for improving marine inductive coupling anchor chain multi-user transmission performance based on OFDM + FDMA technology
Zhang et al. Simulation and analysis of OFDM system based on simulink
Cheon Frequency offset estimation for high speed users in E-UTRA uplink
CN102104433A (en) Symbol detection method and equipment
Wang et al. Low-complexity carrier frequency offset estimation algorithm in TD-LTE
KR20050074884A (en) Apparatus and method for estimating noise and interference in communication system and apparatus and method for estimating cinr
Asim et al. Cell search techniques for underwater acoustic cellular systems
Qi et al. Orthogonal Signal Division Multiple Access for Multiuser Underwater Acoustic Networks
KR101513518B1 (en) A method for channel estimation in a wireless communication system and an apparatus thereof
Yang et al. Windowed OFDM for mixed‐numerology 5G and beyond systems

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant