CN110557203B - OFDM-based underwater current field communication method - Google Patents
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- 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
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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
- H04L27/2626—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
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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
- H04L27/2697—Multicarrier modulation systems in combination with other modulation techniques
Abstract
The invention discloses an OFDM-based underwater current field communication method, which comprises the following steps: the method comprises the following steps: calculating a magnetic vector position by a Maxwell equation set, and obtaining three components of the electric field strength by combining an electric dipole radiation theory, thereby calculating the potential difference of the receiving electrode and verifying the feasibility of current field communication; step two: the serial information transmitted by the current field is modulated onto N paths of mutually orthogonal subcarriers through serial-to-parallel conversion, a time domain signal is synthesized according to the inverse Fourier transform theory, the signal is sent out through a power amplifier, and a receiving end obtains information carried by each path of subcarriers according to the inverse Fourier transform. The invention realizes the combination of the underwater current field theory and the OFDM technology, makes the underwater short-distance electromagnetic wave high-speed communication possible, and lays a solid foundation for the underwater long-distance communication.
Description
Technical Field
The invention relates to an OFDM-based underwater current field communication method, and belongs to the field of underwater wireless communication.
Background
Since the 21 st century, people are paying more attention to research, development and application of underwater resources, and especially in the process of building and maintaining underwater facilities such as underwater pipelines, submarine optical cables, wave-preventing dams, wharves and the like, and in the process of underwater salvage and underwater lifesaving, divers are usually required to dive underwater for operation, so that the importance of an underwater communication system is increasingly highlighted. However, the conductivity of water is high, high-frequency electromagnetic waves are seriously attenuated in water, a very long antenna needs to be erected for low-frequency communication, the engineering quantity is large, the operation is complex, and the underwater working device is not suitable for the requirements of general underwater operation. The urgent need for underwater wireless high-speed communication arises from underwater electromagnetic communication systems based on current field theory, and is a near-distance underwater communication form with a relatively promising development prospect. Because the underwater electromagnetic noise is low, the underwater wireless communication with shorter distance can be completely realized by using the underwater current field communication principle, on the other hand, because the underwater geographic environment is usually complex, and the underwater acoustic communication belongs to mechanical wave propagation, when the propagation medium changes, such as the change of the underwater temperature, the change of the density, obstacles and the like, the reflection and the refraction of the sound wave propagation can be caused, the communication failure can be caused by the generated multipath effect and blind area, and the communication is difficult especially in the area with obvious underwater medium layering. These problems do not exist with the use of an electric field communication. The wireless communication can be achieved by using the current field communication without erecting a huge antenna, and the wireless communication is simple, convenient and flexible. Current field communication also has the advantage over underwater communication that speech is intelligible and has no reverberation. Even if there are circumstances such as marine alga, submerged reef, the electric current field still can realize penetrating communication, and the communication effect is influenced by the relative position between the diver for a short time. Because the conductivity of the seawater is high, the underwater current field communication frequency is low, the displacement current can be ignored, and the conduction current is mainly used in the seawater. Through analysis of the underwater current field mathematical model, the communication distance of the current field is much shorter than that of underwater acoustic communication, and the underwater current field mathematical model is suitable for short-distance high-speed communication.
The current field communication frequency is low, and in order to improve the transmission rate and the spectrum utilization rate as much as possible, an OFDM modulation and demodulation method is adopted. Compared with the traditional multi-carrier, the OFDM system divides a frequency band into a plurality of mutually overlapped sub-bands, the sub-carriers are mutually orthogonal, a guard band is not needed among the sub-carriers, and the frequency spectrum resources are utilized to the maximum extent. The high-speed data stream is converted into the low-speed data stream through serial-to-parallel conversion, so that the duration of data symbols on each sub-channel is relatively increased, the ISI caused by wireless channel time dispersion is effectively reduced, the complexity of equalization in a receiver is reduced, and even an equalization technology is not required. The wireless channel is easily affected by multipath interference, so that the signal generates serious frequency selective fading, a plurality of subcarriers adopted by the OFDM system cannot simultaneously suffer from the frequency selective fading, and the subchannels with higher signal-to-noise ratio are fully utilized by the methods of dynamic bit allocation and dynamic subchannel allocation, so that the fading is reduced to the maximum extent, and the system performance is improved. In addition, narrowband interference can only affect a small fraction of the subcarriers and thus can be resisted to some extent. Due to its various advantages, OFDM is widely used in various communication systems.
Disclosure of Invention
The invention provides an OFDM-based underwater current field communication method, and aims to solve the problem of underwater radio high-speed communication.
The invention realizes the underwater current field communication method based on OFDM by the following technical scheme, and the underwater current field communication method comprises the following steps:
the method comprises the following steps: calculating a magnetic vector position by a Maxwell equation set, and obtaining three components of the electric field strength by combining an electric dipole radiation theory, thereby calculating the potential difference of the receiving electrode and verifying the feasibility of current field communication;
step two: researching the basic principle of the OFDM system;
step three: the serial information transmitted by the current field is modulated onto N paths of mutually orthogonal subcarriers through serial-to-parallel conversion, a time domain signal is synthesized according to the inverse Fourier transform theory, the signal is sent out through a power amplifier, and a receiving end obtains information carried by each path of subcarriers according to the inverse Fourier transform.
Further, in the first step, specifically,
a current field communication theoretical model is provided:
when the underwater current field communication is adopted under the condition of deep water and short distance, the transmitted communication signal can be regarded as direct transmission, reflected waves and side waves are not needed to be considered, and the radiation field can be approximately regarded as a current field radiated by an electric dipole in seawater.
According to maxwell's system of equations:
because of the fact that
According to vector identity
Order to
Substituting into formula (1) b to obtain
Namely, it is
According to vector identity
To obtain
Wherein A is vector magnetic potential, and the unit is Tesla meter or Weibull/meter;
referred to as scalar potential, in volts.
In a time-varying magnetic field, the magnetic vector A and the scalar bit
The wave equation satisfied in the uniform coal quality is a constitutive relation equation of linear, uniform and isotropic coal quality
B＝μH，D＝εE，J＝σE (6)
Bringing the formulas (2) and (5) into the formulas (1) d and (1) a to obtain
And
after finishing has
Selecting
Bringing formula (11) into formulae (8) and (10) to obtain
The magnetic vector A can be decomposed into three rectangular coordinate components, the solution of which has the form:
the electromagnetic field of the electric basic vibrator is obtained by indirect method, namely, the magnetic vector A (r) of the electric basic vibrator is obtained by formula (14) and then substituted into the formula
Thus, magnetic induction B (r) is determined, finally, the magnetic induction B (r) is substituted into Maxwell' S first equation to obtain electric field intensity E (r), the length of the short wire is dl, the cross-sectional area is Delta S, and for the electric dipole, the volume dV is dl.Delta S, so that the electric field intensity E (r) is obtained by:
the magnetic vector position generated by the electric basic oscillator at the field point P can be obtained from equation (14):
the magnetic vector A (r) represented by the formula (17) is subjected to coordinate transformation to obtain a spherical coordinate system
A＝erAr+eθAθ+eφAφ＝erAzcosθ-eθAzsinθ (18)
The magnetic field generated by the electric basic oscillator at the field point P is obtained by substituting the above formula into formula (15):
thereby can be solved
Substituting equation (20) into Maxwell's equation in passive region, and in seawater, σ > ω ε,
three components of the available electric field strength:
e and H are perpendicular to each other, E being in the plane of the dipole (meridian plane) and H being in a plane parallel to the equatorial plane; the magnetic field strength having only one component HφAnd the electric field intensity has two divisions ErAnd EθWhichever component decreases with increasing distance r, only their components decrease faster with r and slower with r, and furthermore, in the near and far regions of the source point, the dominant components are different,
for the near field, when kr < 1,
i.e. the region where the distance r between the field point P and the source point is much smaller than the wavelength lambda is called the near zone,
therefore, in the formulae (20) and (22), it is effective
To a higher power, and retaining the higher power
Where p-Qdl is the complex amplitude of the electric dipole moment, since the current carrying stub has been considered as an oscillating electric dipole, the relationship between the charge and current at its upper and lower ends is I-jwQ,
from the above results, it can be seen that in the near region, the complex amplitude of the electric field of the electric elementary vibrator (time-varying electric dipole) is the same as the electric field expression of the electrostatic dipole of the static field.
When the receiving electrode coincides with the transmitting electrode axis and the distance is R, when θ is 90 °, the field strength at the receiving electrode is:
a spacing of d2The potential difference between the receiving electrodes of (2) can be expressed as:
wherein
From the above analysis, it can be seen that the voltage of the received signal is related to the transmit current, the transceiver electrode spacing and the communication distance.
Further, in step one, in particular, in terms of the OFDM communication principle, it is assumed that the symbol length is T, the number of subcarriers is N, and the sequence { d }0,d1,...dK-1At the transmitting end, the bits to be transmitted are firstly mapped by the symbols, and K bits to be transmitted are mapped to obtain a complex sequence { X ] with the length of N according to different mapping schemes0,X1,...XN-1In which XN＝an+jbnThen modulating the complex sequence to N sub-carriers in turn, the real part and imaginary part respectively corresponding to cosine and sine sub-carriers, if fiAt the frequency of the ith subcarrier, there are
The sub-carriers are mutually orthogonal, the sending waveform of the last sending end is the superposition of the modulated sub-carriers, the rectangular function rect (T) is 1, | T | is less than or equal to T/2, and T | -T is TsThe first OFDM symbol from the beginning can be represented as:
at the receiving end, since the sub-carriers of the OFDM symbol are orthogonal to each other, the received waveform can be passed through a matched filter and then respectively used at a frequency fiIs integrated over time T to obtain a complex sequence { X }0,X1,...XN-1And obtaining a sending bit through demapping.
The main advantages of the invention are: the receiving voltage influence parameters are derived through Maxwell equations, the electromotive force amplitude between the receiving electrodes is obtained to be in direct proportion to the transmitting electrode current and the electrode spacing, and the amplitude of the receiving signals is obviously reduced along with the increase of frequency, the conductivity of water and the communication distance. The establishment of the current field mathematical model provides powerful theoretical support for underwater electromagnetic communication, and the communication distance can be improved to the maximum extent by analyzing corresponding parameters. The OFDM technology is utilized to utilize originally scarce frequency band resources to the maximum extent, and the frequency band utilization rate is improved. In the OFDM technology, all paths of subcarriers are orthogonal to each other, frequency spectrums are overlapped with each other, a guard interval does not exist, the frequency band utilization rate is high, and the OFDM frequency band transmission method is very suitable for transmission in an underwater sound channel with a very limited communication frequency band. The modulation of the sub-carrier in the OFDM is flexible, the dynamic allocation can be realized, meanwhile, the OFDM is also easily combined with the multiple access technology, and the networked underwater electromagnetic communication transmission is realized. The combination of the underwater current field theory and the OFDM technology enables underwater short-distance electromagnetic wave high-speed communication to be possible, and lays a solid foundation for underwater long-distance communication.
Drawings
FIG. 1 is a schematic diagram of electric dipole radiation in water;
FIG. 2 is a basic schematic diagram of an OFDM system;
fig. 3 is a flowchart of a method of the underwater current field communication method based on OFDM according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying 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.
Referring to fig. 3, the underwater current field communication method based on OFDM includes the following steps:
the method comprises the following steps: calculating a magnetic vector position by a Maxwell equation set, and obtaining three components of the electric field strength by combining an electric dipole radiation theory, thereby calculating the potential difference of the receiving electrode and verifying the feasibility of current field communication;
step two: the serial information transmitted by the current field is modulated onto N paths of mutually orthogonal subcarriers through serial-to-parallel conversion, a time domain signal is synthesized according to the inverse Fourier transform theory, the signal is sent out through a power amplifier, and a receiving end obtains information carried by each path of subcarriers according to the inverse Fourier transform.
In the preferred embodiment of this section, step one, specifically,
a current field communication theoretical model is provided:
when the underwater current field communication is adopted under the condition of deep water and short distance, the transmitted communication signal can be regarded as direct transmission, reflected waves and side waves are not needed to be considered, and the radiation field can be approximately regarded as a current field radiated by an electric dipole in seawater.
According to maxwell's system of equations:
it is known from electromagnetic field theory that the divergence of the helicity is constant at 0. The entire current field communication is similar to a static field, and the vector bit function a can be introduced like a static field.
Because of the fact that
According to vector identity
Can make
Substituting into formula (1) b to obtain
Namely, it is
According to vector identity
Can obtain
Wherein A is vector magnetic potential, and the unit is T.m (Tesla.m) or Wb/(Weber/m);
referred to as scalar potential, in units of V (volts).
In a time-varying magnetic field, the magnetic vector A and the scalar bit
The wave equation satisfied in the uniform coal quality is a constitutive relation equation of linear, uniform and isotropic coal quality
B＝μH，D＝εE，J＝σE (6)
Bringing the formulas (2) and (5) into the formulas (1) d and (1) a to obtain
And
after finishing has
Thus, two equations (8) and (10) are obtained, which are expressed as bit functions, but both equations contain A and
are simultaneous equations. If appropriate
Can be further simplified to equations that each contain only one bitfunction. Select for this purpose
Equation (11) is referred to as the Lorentz condition or Lorentz specification. It can be demonstrated that the lorentz condition conforms to the current continuity equation. It is taken into the formulas (8) and (10) to obtain
The magnetic vector A can be decomposed into three rectangular coordinate components, the solution of which has the form:
the electromagnetic field of the electric basic vibrator is obtained by indirect method, namely, the magnetic vector A (r) of the electric basic vibrator is obtained by formula (14) and then substituted into the formula
Thereby determining the magnetic induction B (r), and finally substituting the magnetic induction B (r) into the Maxwell first equation to obtain the electric field intensity E (r). The schematic diagram of electric dipole radiation in seawater is shown in fig. 1. The length of the short wire is dl, the cross-sectional area is Delta S, and for the electric dipole, the volume dV is dl.Delta S, so that the following are provided:
the magnetic vector position generated by the electric basic oscillator at the field point P can be obtained from equation (14):
the magnetic vector A (r) represented by the formula (17) is subjected to coordinate transformation to obtain a spherical coordinate system
A＝erAr+eθAθ+eφAφ＝erAzcosθ-eθAzsinθ (18)
The magnetic field generated by the electric basic oscillator at the field point P is obtained by substituting the above formula into formula (15):
thereby can be solved
Substituting equation (20) into Maxwell's equation in passive region, and in seawater, σ > ω ε,
three components of the available electric field strength:
e and H are perpendicular to each other, E being in the plane of the dipole (meridian plane), andh is in a plane parallel to the equatorial plane; the magnetic field strength having only one component HφAnd the electric field intensity has two divisions ErAnd EθWhichever component decreases with increasing distance r, only their components decrease faster with r and slower with r, and furthermore, in the near and far regions of the source point, the dominant components are different,
for the near field, when kr < 1,
i.e. the region where the distance r between the field point P and the source point is much smaller than the wavelength lambda is called the near zone,
therefore, in the formulae (20) and (22), it is effective
To a higher power, and retaining the higher power
Where p-Qdl is the complex amplitude of the electric dipole moment, since the current carrying stub has been considered as an oscillating electric dipole, the relationship between the charge and current at its upper and lower ends is I-jwQ,
from the above results, it can be seen that in the near region, the complex amplitude of the electric field of the electric elementary vibrator (time-varying electric dipole) is the same as the electric field expression of the electrostatic dipole of the static field.
When the receiving electrode coincides with the transmitting electrode axis and the distance is R, when θ is 90 °, the field strength at the receiving electrode is:
a spacing of d2Receiving electricity ofThe potential difference between the poles can be expressed as:
wherein
From the above analysis, it can be seen that the voltage of the received signal is related to the transmit current, the transceiver electrode spacing and the communication distance.
In this preferred embodiment, specifically, similar to other multicarrier modulation techniques, the basic idea of OFDM is to divide the transmission channel into several subchannels in the frequency domain, and each subchannel uses subcarriers for modulation transmission, but subcarriers in different subchannels of OFDM are mutually orthogonal.
And the output waveform of the transmission data after OFDM is the superposition of the transmission data and the waveform modulated by each path of subcarrier.
The basic principle block diagram of OFDM is shown in fig. 2, where the basic transmission unit of the OFDM system is an OFDM symbol, the symbol length is T, the number of subcarriers is N, and the sequence { d }0,d1,...dK-1At the transmitting end, the bits to be transmitted are firstly mapped by the symbols, and K bits to be transmitted are mapped to obtain a complex sequence { X ] with the length of N according to different mapping schemes0,X1,...XN-1In which XN＝an+jbnThen modulating the complex sequence to N sub-carriers in turn, the real part and imaginary part respectively corresponding to cosine and sine sub-carriers, if fiAt the frequency of the ith subcarrier, there are
The sub-carriers are mutually orthogonal, the sending waveform of the last sending end is the superposition of the modulated sub-carriers, the rectangular function rect (T) is 1, | T | is less than or equal to T/2, and T | -T is TsThe first OFDM symbol from the beginning can be represented as:
at the receiving end, since the sub-carriers of the OFDM symbol are orthogonal to each other, the received waveform can be passed through a matched filter and then respectively used at a frequency fiIs integrated over time T to obtain a complex sequence { X }0,X1,...XN-1And obtaining a sending bit through demapping.
Specifically, the working principle of the underwater current field communication based on the OFDM is as follows: underwater electric field communication is realized by using an electric field as an information carrier. The transmitting antenna used in the system is two pairs of electrodes. At a transmitting end, a transmission signal is firstly subjected to symbol mapping, information to be transmitted is mapped onto a complex sequence with the length of N according to different mapping schemes, the complex sequence is sequentially modulated onto N subcarriers, the subcarriers are mutually orthogonal, and finally a transmitting waveform at the transmitting end is superposition of the modulated subcarriers. The signal power is amplified and then the transmitting electrodes are driven, and as the seawater is a good conductor, current can pass through a loop formed by the two transmitting electrodes and the seawater. The current forms an electric field around, the electric field induces electromotive force at two ends of a receiving electrode, the received signal is subjected to Fourier transform to obtain a complex sequence on each orthogonal subcarrier, and then the transmitted information is obtained through demapping. The underwater current field communication principle is shown in figure 3.
Claims (2)
1. The OFDM-based underwater current field communication method is characterized by comprising the following steps of:
the method comprises the following steps: establishing an underwater mathematical model, namely calculating a magnetic vector position by a Maxwell equation set, and obtaining three components of electric field intensity by combining an electric dipole radiation theory, thereby calculating the potential difference of a receiving electrode and verifying the feasibility of current field communication;
step two: the basic principle research of the OFDM system comprises the steps that information is firstly converted in a serial/parallel mode in the OFDM system, a sending end decomposes an input signal into N paths of sub-signals and then respectively transmits the sub-signals, and the output of the N paths of sub-signals is superposed at a receiving end to obtain a final output signal;
step three: serial information transmitted by a current field is modulated onto N paths of mutually orthogonal subcarriers through serial-to-parallel conversion, time domain signals are synthesized according to the inverse Fourier transform theory, the signals are sent out through a power amplifier, a receiving end obtains information carried by each path of subcarriers according to the inverse Fourier transform,
in the first step, specifically,
a current field communication theoretical model is provided:
when the underwater current field communication is adopted under the condition of deep water and short distance, the transmitted communication signal can be regarded as directly transmitted without considering reflected wave and side wave, the radiation field can be approximately regarded as the current field radiated by an electric dipole in the seawater,
according to maxwell's system of equations:
because ·
B＝▽×A (2)
Substituting into formula (1) b to obtain
Namely, it is
According to vector identity
To obtain
Wherein A is vector magnetic potential, and the unit is Tesla meter or Weibull/meter;
referred to as a scalar potential, in volts,
in a time-varying magnetic field, the magnetic vector A and the scalar bit
The wave equation satisfied in the homogeneous medium, the constitutive relation equation of the linear, homogeneous and isotropic medium is
B＝μH，D＝εE，J＝σE (6)
Bringing the formulas (2) and (5) into the formulas (1) d and (1) a to obtain
And
after finishing has
Selecting
Bringing formula (11) into formulae (8) and (10) to obtain
The magnetic vector A can be decomposed into three rectangular coordinate components, the solution of which has the form:
the electromagnetic field of the electric basic vibrator is obtained by indirect method, namely, the magnetic vector A (r) of the electric basic vibrator is obtained by formula (14) and then substituted into the formula
B＝▽×A (15)
Thus, magnetic induction B (r) is determined, finally, the magnetic induction B (r) is substituted into Maxwell' S first equation to obtain electric field intensity E (r), the length of the short wire is dl, the cross-sectional area is Delta S, and for the electric dipole, the volume dV is dl.Delta S, so that the electric field intensity E (r) is obtained by:
the magnetic vector position generated by the electric basic oscillator at the field point P can be obtained from equation (14):
the magnetic vector A (r) represented by the formula (17) is subjected to coordinate transformation to obtain a spherical coordinate system
A＝erAr+eθAθ+eφAφ＝erAzcosθ-eθAzsinθ (18)
The magnetic field generated by the electric basic oscillator at the field point P is obtained by substituting the above formula into formula (15):
thereby can be solved
Substituting equation (20) into Maxwell's equation in passive region, and in seawater, σ > ω ε,
▽×H＝jwεE (21)
three components of the available electric field strength:
e and H are perpendicular to each other, E is in the plane of the dipole, and H is in the plane parallel to the equatorial plane; the magnetic field strength having only one component HφAnd the electric field intensity has two divisions ErAnd EθWhichever component decreases with increasing distance r, only their components decrease faster with r and slower with r, and furthermore, in the near and far regions of the source point, the dominant components are different,
for the near field, when kr < 1,
i.e. the region where the distance r between the field point P and the source point is much smaller than the wavelength lambda is called the near zone,
therefore, in the formulae (20) and (22), it is effective
To a higher power, and retaining the higher power
Where p-Qdl is the complex amplitude of the electric dipole moment, since the current carrying stub has been considered as an oscillating electric dipole, the relationship between the charge and current at its upper and lower ends is I-jwQ,
from the above results, it can be seen that, in the near region, the complex amplitude of the electric field of the electric basic vibrator is the same as the electric field expression of the electrostatic dipole of the static field,
when the receiving electrode coincides with the transmitting electrode axis and the distance is R, when θ is 90 °, the field strength at the receiving electrode is:
a spacing of d2The potential difference between the receiving electrodes of (2) can be expressed as:
wherein
From the above analysis, the voltage of the received signal is related to the transmission current, the transmitting-receiving electrode spacing and the communication distance.
2. The method according to claim 1, wherein in step two, specifically, OFDM communicationIn principle, assume a symbol length of T, a number of subcarriers of N, and a sequence { d }0,d1,...dK-1At the transmitting end, the bits to be transmitted are firstly mapped by the symbols, and K bits to be transmitted are mapped to obtain a complex sequence { X ] with the length of N according to different mapping schemes0,X1,...XN-1In which XN＝an+jbnThen modulating the complex sequence to N sub-carriers in turn, the real part and imaginary part respectively corresponding to cosine and sine sub-carriers, if fiAt the frequency of the ith subcarrier, there are
The sub-carriers are mutually orthogonal, the sending waveform of the last sending end is the superposition of the modulated sub-carriers, the rectangular function rect (T) is 1, | T | is less than or equal to T/2, and T | -T is TsThe first OFDM symbol from the beginning can be represented as:
at the receiving end, since the sub-carriers of the OFDM symbol are orthogonal to each other, the received waveform can be passed through a matched filter and then respectively used at a frequency fiIs integrated over time T to obtain a complex sequence { X }0,X1,...XN-1And obtaining a sending bit through demapping.
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| CN101064570A (en) * | 2007-04-18 | 2007-10-31 | 白坤生 | Electric signal transmission method and its apparatus |
| CN105164944A (en) * | 2013-03-15 | 2015-12-16 | 费尔菲尔德工业公司 | High-bandwidth underwater data communication system |
| AU2016219679B1 (en) * | 2016-08-26 | 2018-02-08 | King Abdullah University Of Science And Technology | Systems and methods for underwater illumination, survey, and wireless optical communications |
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