A kind of dual mode satellite call method based on orthogonal frequency division multiplexingTechnical field
The present invention relates to satellite-based fields of communication technology, and in particular to a kind of bimodulus based on orthogonal frequency division multiplexing is defendedStar call method.
Background technology
The imagination of satellite communication is that British A Se C Clarkes propose earliest, in October, 1945 he《Radio generationBoundary》One delivered on magazine is entitled《Extraterrestrial relay station》Article in, it is proposed that in stationary orbit place 3 satellitesTo realize the imagination of global communication.
Since first satellite goes up to the air, no matter at home or at abroad, satellite communication system is communicating always neckIrreplaceable important function is played in domain, either marine navigation and communication at sea or disaster occurs and answersAnxious communication, when the area of not communication overlay or GCF ground communication facility are by destroying, people remain to ensure to believe by satelliteBreath transmits.Exactly because satellite communication has vast potential for future development and great strategic importance, so either applicationOr all to satellite communication, more stringent requirements are proposed for technological layer.
Since satellite communication grows up on the basis of space technology and terrestrial microwave trunking traffic technology, by bigThe relaying of satellite outside gas-bearing formation realizes telecommunication.The radio wave of its load information will get through the earth's atmosphere, process it is very long away fromPropagated between earth station and satellite, therefore it is affected by various factors, propagation problem influence whether signal quality andSystem performance.In addition, the fast offset at receiving terminal relative transmission end, can make centre frequency movement, originally transmitted signal attribute hairIt is raw to change, to be brought a negative impact to wireless signal transmission.
Invention content
The technical problem to be solved by the present invention is to：It is proposed a kind of dual mode satellite call method based on orthogonal frequency division multiplexing.
The technical solution that the present invention proposes to solve above-mentioned technical problem is：A kind of bimodulus based on orthogonal frequency division multiplexing is defendedStar call method, this method are based on local cellular communication unit, satellite communication unit, pattern switching control unit, dial/answerOperation interface and voice pickup/broadcast unit, including following characteristics step：
A, to be found to be target, by local cellular communication unit search for cellular communications network in any base station signal and detect andIts signal strength such as detects that base station signal and its intensity meet call demand and execute step b, such as can't detect base station signal and holdRow step c；
B, the local cellular communication unit establishes cellular communication with the base station under the control of the pattern switching control unitLink realizes that voice is logical by the operation interface that dials/answer, voice pickup/broadcast unit and the cellular communication linkWords；
C, the satellite communication unit is established with low rail telecommunication satellite based on just under the control of the pattern switching control unitThe satellite communication link for handing over frequency-division multiplex multi-carrier modulating/demodulating pattern, is picked up by dial/answer operation interface, the soundTake/broadcast unit and the satellite communication link realize voice communication.
Further, the satellite communication link in the step c includes the modulation of transmitting terminal；
Transmitting terminal is in modulation：I, to by the original signal by the bracket operation interface and/or the acquisition of voice pickup unitBinarization processing is carried out, obtained binary data is subjected to serial to parallel conversion, serial data is converted to N number of parallel dataAnd distribute to N number of different subchannels；
Ii, N number of plural subsymbol Xk is mapped to by the parallel data in the roads N are encoded；
Iii, Fast Fourier Transform is carried out to the output signal of coding mapping, N number of plural number subsymbol Xk in frequency domain is transformed into2N real number sample value Xk in time domain adds a cyclic prefix before calculated transformation sample value, one cyclic extensions of formationOrthogonal frequency division multiplexing information code word；
Iv, the orthogonal frequency division multiplexing information code word is carried out and goes here and there variation, and pass through D/A conversions and low pass filtered in a serial fashionBaseband signal is exported after wave；
V, by the baseband signal after up-conversion output OFDM signal.
Further, from t=tsThe orthogonal frequency division multiplexing information code word from moment is indicated by following formula：
In formula：
T is the width of orthogonal frequency division multiplexing information code word；
For the carrier frequency of O subcarrier；
To distribute to the data symbol of every sub-channels.
Further, the satellite communication link in the step c includes the demodulation of receiving terminal；
Receiving terminal is integrated in demodulation after being multiplied respectively with the superposed signal received by the separated subcarrier of its self-generating, pointEach circuit-switched data is separated out, then serial data output is obtained through parallel serial conversion, the receiving terminal is carried in i-th son of the docking collection of letters numberWave number by being integrated in time span T, obtains initial data according to being restoreddiCalculation process be：
。
The beneficial effects of the invention are as follows：
Dual mode satellite call method based on orthogonal frequency division multiplexing in the present invention, by when there is call request, being first detectedAnd the existing cellular communications networks signal of tradition is connected, and it is conversed by conventional cellular communication if it can establish connection, it canWith the communication effect for providing better quality and lower call rate.If being located at " no signal " region, satellite telephony is used insteadPattern ensures that timely call requires.
In addition, the present invention has also made improvement to the signal circulation way of conventional satellite communication, using orthogonal frequency division multiplexingMulti-carrier modulation/demodulation techniques can improve the interference and decaying that signal is subject in the air, and be conducive to utmostly land productivityWith limited communication frequency domain.
Specific implementation mode
The dual mode satellite call method based on orthogonal frequency division multiplexing in the present invention, this method are based on local cellular communication unitMember, satellite communication unit, pattern switching control unit, dial/answer operation interface and voice pickup/broadcast unit, including withLower step：
A, to be found to be target, by local cellular communication unit search for cellular communications network in any base station signal and detect andIts signal strength such as detects that base station signal and its intensity meet call demand and execute step b, such as can't detect base station signal and holdRow step c；
B, local cellular communication unit establishes cellular communication link with the base station under the control of pattern switching control unit, passes throughDial/answer operation interface, voice pickup/broadcast unit and cellular communication link realizes voice communication；
C, satellite communication unit is established with low rail telecommunication satellite and is based on orthogonal frequency division multiplexing under the control of pattern switching control unitWith the satellite communication link of multi-carrier modulation/demodulation modes, by dial/answer operation interface, voice pickup/broadcast unit andSatellite communication link realizes voice communication.
Voice communication in step c includes the modulation of transmitting terminal；
Transmitting terminal is in modulation：I, to being carried out by the original signal by bracket operation interface and/or the acquisition of voice pickup unitBinarization is handled, and obtained binary data is carried out serial to parallel conversion, and serial data is converted to N number of parallel data and is dividedThe N number of different subchannels of dispensing；
Ii, N number of plural subsymbol Xk is mapped to by the parallel data in the roads N are encoded；
Iii, Fast Fourier Transform is carried out to the output signal of coding mapping, N number of plural number subsymbol Xk in frequency domain is transformed into2N real number sample value Xk in time domain adds a cyclic prefix before calculated transformation sample value, one cyclic extensions of formationOrthogonal frequency division multiplexing information code word；
Iv, orthogonal frequency division multiplexing information code word is carried out and goes here and there variation, and in a serial fashion after D/A conversions and low-pass filteringExport baseband signal；
V, by baseband signal after up-conversion output OFDM signal.
From t=tsOrthogonal frequency division multiplexing information code word from moment is indicated by following formula：
In formula：
T is the width of orthogonal frequency division multiplexing information code word；
For the carrier frequency of O subcarrier；
To distribute to the data symbol of every sub-channels.
In step c, receiving terminal in demodulation, by the separated subcarrier of its self-generating respectively with the superposed signal that receivesIt is integrated after multiplication, isolates each circuit-switched data, then serial data output is obtained through parallel serial conversion；
Receiving terminal is restored in i-th subcarrier data of the docking collection of letters number, by being integrated in time span T, is obtainedTo initial datadiCalculation process be：
。
The present invention's is not limited to the above embodiment, and the technical solution of above-mentioned each embodiment of the invention can be handed over each otherFork combination form new technical solution, in addition it is all using equivalent replacement formed technical solution, all fall within the present invention claims guarantorIt protects in range.