CN114114298A - Distance measurement method and system based on IM-DD - Google Patents
Distance measurement method and system based on IM-DD Download PDFInfo
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
The invention discloses a distance measurement method and a system based on IM-DD, which relate to the field of optical communication and distance measurement, and the method comprises the following steps: the two terminals to be measured adopt the second pulse to carry out frequency measurement on the local sending clock and the local receiving clock, and the second pulse arrival time of the sending clock and the receiving clock is obtained; each terminal sends the clock number according to the ranging frame, calculates the sending time of the ranging frame based on the second pulse arrival time of the sending clock, and sends the ranging frame to the opposite terminal through an IM-DD data transmission channel along with the data stream; each terminal receives the clock number according to the ranging frame, and calculates the arrival time of the ranging frame based on the second pulse arrival time of the receiving clock and the data stream transmitted by the IM-DD data transmission channel; and the two terminals calculate respective pseudo-range values according to the arrival time of the ranging frame calculated by the terminal and the sending time of the ranging frame sent by the opposite terminal, and calculate the ranging value according to the pseudo-range values calculated by the two terminals. The invention can simultaneously give consideration to the ranging precision and the system cost.
Description
Technical Field
The invention relates to the field of optical communication and ranging, in particular to a ranging method and system based on IM-DD.
Background
An intensity modulation direct detection (IM-DD, abbreviated as direct modulation direct detection) optical communication system is one of the most common ways of digital optical communication systems, and its basic structure includes an optical transmitter, a transmission medium (such as optical fiber or spatial optical communication), and an optical receiver. The optical transmitter modulates the baseband digital signal onto an optical carrier wave in an on-off keying (OOK) modulation mode by an intensity modulation method, and information is represented by the presence or absence of the optical signal in each bit time. The optical signal reaches the optical receiver after passing through a transmission medium such as an optical fiber or spatial transmission. The optical receiver carries out envelope detection on the optical signal with modulated intensity, namely, the baseband digital signal is directly recovered through the photoelectric detector. The direct alignment and detection optical communication system has significant advantages in terms of cost, reliability, and the like, and is widely adopted in the conventional high-speed long-distance optical communication system.
With the development of mobile communication technology, research on the sixth generation mobile communication technology (6G) is continuously carried out nowadays, and a 6G network will be a world of connectivity integrating terrestrial wireless communication and satellite communication, and by integrating satellite communication into 6G mobile communication, global seamless coverage is achieved. In the field of satellite communication, two selectable communication modes are wireless communication and optical communication, and in comparison, the transmission capacity of optical communication is more than several orders of magnitude larger than that of wireless communication. For the requirements such as 6G that require a large satellite communication capacity, the optical communication technical route is the first choice for the backbone communication method between satellites and the ground. Because the environment of the satellite orbit is severe, the types of components on the satellite are limited, the selection of the components is difficult, and the requirements of commercialization are urgent in the aspects of cost, service life and the like. Due to the obvious advantages of the direct alignment and light detection communication in the aspects of cost, reliability and the like, the direct alignment and light detection communication becomes a preferred technical system for an application scene which takes a low-earth orbit satellite as a main deployment mode and needs a large-capacity communication requirement.
The acquisition of the relative position information between the satellites is a precondition for ensuring the normal operation of the formation constellation, so the satellites need to finish accurate inter-satellite and inter-satellite-ground distance measurement by themselves to determine the relative state between the satellites or the inter-satellite-ground state in the formation constellation. The system combines the optical communication technology and the ranging technology, realizes the inter-satellite and inter-satellite-ground communication, and accurately measures the satellite track, has huge potential benefits and wide application prospects, but is a problem to be solved by considering the ranging precision and the system cost well.
Disclosure of Invention
In view of the defects in the prior art, a first aspect of the present invention provides a distance measurement method based on IM-DD, which can simultaneously consider both the distance measurement accuracy and the system cost.
In order to achieve the above purposes, the technical scheme adopted by the invention is as follows:
a distance measurement method based on IM-DD comprises the following steps:
the two terminals to be measured adopt the second pulse to carry out frequency measurement on the local sending clock and the local receiving clock, and the second pulse arrival time of the sending clock and the receiving clock is obtained;
each terminal sends the clock number according to the ranging frame, calculates the sending time of the ranging frame based on the second pulse arrival time of the sending clock, and sends the ranging frame to the opposite terminal through an IM-DD data transmission channel along with the data stream;
each terminal receives the clock number according to the ranging frame, and calculates the arrival time of the ranging frame based on the second pulse arrival time of the receiving clock and the data stream transmitted by the IM-DD data transmission channel;
and the two terminals calculate respective pseudo-range values according to the arrival time of the ranging frame calculated by the terminal and the sending time of the ranging frame sent by the opposite terminal, and calculate the ranging value according to the pseudo-range values calculated by the two terminals.
In some embodiments, the two terminals to be measured adopt pulse per second to perform frequency measurement on the local transmission clock and the local reception clock, and acquiring the arrival time of the pulse per second of the transmission clock and the local reception clock includes:
the multi-stage taps of the delay chain are sampled in parallel by using the transmitting clock and the receiving clock respectively, and the delay time T of each stage of the delay chain is determinedtap；
For number NTAPSThe multi-level taps of the multi-level delay chain are sampled in parallel to obtain a sampling value Dtap[0:NTAPS-1]；
Determining the position n of a logical value transitionpulse；
According to the formula: t ispps＝npulse×TtapCalculating the second pulse arrival time T of the transmission clockpps_sAnd the second pulse arrival time T of the receiving clockpps_r。
In some embodiments, a transition from 0 to 1 is found when the rising edge of the pulse of seconds is active, or a transition from 1 to 0 is found when the falling edge of the pulse of seconds is active, to determinePosition n of logic value jumppulse。
In some embodiments, the calculating, by each terminal, the ranging frame transmission time according to the number of the ranging frame transmission clocks and based on the pulse-per-second arrival time of the transmission clock includes:
according to the formula: t iss＝(nsend×Fs)/(Fs_norm)2-Tpps_sCalculating the sending time T of the ranging framesWherein n issendSending the number of clocks for the ranging frame, FsTo transmit a measurement of the clock frequency of the clock, Fs_normIs the nominal frequency value of the transmit clock.
In some embodiments, the ranging frame transmission counter is started when the pulse-per-second arrival flag of the transmission clock is valid, and the ranging frame transmission counter is stopped when the ranging frame transmission flag is valid, so as to obtain the number n of the ranging frame transmission clockssend。
In some embodiments, the calculating, by each terminal, the ranging frame arrival time according to the number of the ranging frame receiving clocks and based on the pulse-per-second arrival time of the receiving clocks and the data stream transmitted by the IM-DD data transmission channel includes:
according to the formula:
Tr＝[(nrecv+Nr/NBITS)×Fr]/(Fr_norm)2-Tpps_r≈(nrecv×Fr)/(Fr_norm)2+Nr/NBITS/Fr_norm-Tpps_r
calculating the arrival time T of the ranging framerWherein n isrecvReceiving the clock number for the ranging frame, FrTo receive a measurement of the clock frequency of a clock, Fr_normFor receiving a nominal frequency value of the clock, NrFor parallel synchronization of bit-sliding values, NBITSIs the parallel data width.
In some embodiments, the ranging frame reception counter is started when the pulse-per-second arrival flag of the reception clock is valid, and the ranging frame reception counter is stopped when the ranging frame reception flag is valid, so as to obtain the number n of the ranging frame reception clocksrecv。
In some embodiments, the two terminals each calculate a respective pseudorange value according to the time of arrival of the ranging frame calculated by the terminal and the time of transmission of the ranging frame transmitted by the other terminal, and calculate a ranging value according to the pseudorange values calculated by the two terminals, including:
the first of the two terminals is according to the formula: t isd1＝Tr1-Ts2Calculating a first pseudorange value Td1Wherein T isr1Time of arrival, T, of ranging frame calculated for first terminals2A ranging frame transmission time calculated for the second terminal;
the second of the two terminals is according to the formula: t isd2＝Tr2-Ts1Calculating a second pseudorange value Td2Wherein T isr2Time of arrival, T, of ranging frame calculated for second terminals1A ranging frame transmission time calculated for the first terminal;
according to the formula: t isdist＝(Td1+Td2) /2 calculating the distance measurement value Tdist。
In some embodiments, the ranging method further comprises:
obtaining transmission and processing delays T inside two terminalsditerm；
According to the formula: t isdist_correct＝Tdist-TditermFor distance measurement value TdistThe distance measurement correction value T is obtained by correctiondist_correct。
The second aspect of the invention provides a distance measuring system based on IM-DD, which can simultaneously take distance measuring precision and system cost into consideration.
In order to achieve the above purposes, the technical scheme adopted by the invention is as follows:
an IM-DD based ranging system comprising at least two terminals, each of the terminals being configured to:
adopting second pulse to carry out frequency measurement on a local sending clock and a local receiving clock, and obtaining the second pulse arrival time of the sending clock and the receiving clock;
calculating the sending time of the ranging frame according to the number of the ranging frame sending clocks and based on the second pulse arrival time of the sending clocks, and sending the ranging frame sending time to the opposite terminal along with the data stream;
calculating the arrival time of the ranging frame according to the number of the ranging frame receiving clocks and based on the second pulse arrival time of the receiving clocks;
calculating respective pseudo-range values according to the arrival time of the ranging frame calculated by the terminal and the transmission time of the ranging frame transmitted by the opposite terminal, and calculating the ranging value according to the pseudo-range values calculated by the two terminals.
Compared with the prior art, the invention has the advantages that:
the invention uses a high-precision second pulse arrival time measuring method, uses a data transmission channel of direct alignment and light detection communication, inserts a small amount of ranging information into normal data frame transmission, does not need to interrupt a normal communication mode, does not need network clock frequency synchronization, does not need to keep a synchronous relation with the second pulse in the sending period of the data frame, and can use a bidirectional one-way ranging method to carry out ranging. In addition, the second pulse is used for measuring the frequency of the local clock and correcting the parameters of the ranging process, so that the ranging accuracy and precision of the time scale of the direct-tuning direct-detection communication code element can be achieved only by adopting a common crystal oscillator as a local clock source and canceling using a full-network synchronous clock signal or a high-stability clock source which is usually required by high-precision ranging, the complexity of a time-frequency synchronization system, the requirements on components and the cost of the whole communication ranging system are reduced, and the problem that the ranging accuracy and the system cost are not easy to simultaneously consider in the prior art is solved.
Drawings
FIG. 1 is a flow chart of an IM-DD based ranging method according to an embodiment of the present invention;
FIG. 2 is a block diagram of a ranging system according to an embodiment of the present invention;
fig. 3 is a block diagram of a digital logic circuit of a ranging system according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all 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 application.
Referring to fig. 1, an embodiment of the present invention provides an IM-DD based ranging method, including the following steps:
s1, two terminals to be measured adopt pulse per second to carry out frequency measurement on a local sending clock and a local receiving clock, and the arrival time of the pulse per second of the sending clock and the receiving clock is obtained.
It should be noted that, in step S1, the pulse-per-second arrival time measurement method is mainly adopted, logic circuits with deterministic delay inside digital logic circuits are cascaded to form a delay chain, a clock is used to sample multiple taps of the delay chain in parallel, and the delay time T of each stage of the delay chain is determined according to the result of the timing analysis of the digital logic circuitstapFor number NTAPSThe multi-level taps of the multi-level delay chain are sampled in parallel to obtain a sampling value Dtap[0:NTAPS-1]Finding the position n of logic value jump (if the second pulse rising edge is effective, the jump from 0 to 1 is found, or the second pulse falling edge is effective, the jump from 1 to 0 is found)pulseIf jump exists, the second pulse arrival FLAG _1PPS is valid, and the second pulse arrival time is calculated to be Tpps＝npulse×TtapWherein, TppsThe second arrival time of the clock. The sending clock and the receiving clock respectively output corresponding second pulse arrival time Tpps_sAnd Tpps_rAnd second pulse arrival FLAGs FLAG _1PPS _ S and FLAG _1PPS _ R.
And S2, each terminal sends the clock number according to the ranging frame and calculates the sending time of the ranging frame based on the pulse per second arrival time of the sending clock, and the ranging frame is sent to the other terminal along with the data stream through the IM-DD data transmission channel.
In this embodiment, the transmit clock uses the pulse-per-second arrival FLAG _1PPS _ S, and outputs a clock frequency measurement valueFs. Wherein, every time when a second pulse arrival mark is effective, the last frequency counting is ended, and the counting value at the end of counting is output as a clock frequency measuring value F of a transmission clocksAt the same time, the counter is reset and counting is restarted.
Meanwhile, when the pulse per second arrival FLAG _1PPS _ S of the transmission clock is valid, the ranging frame transmission counter is started, and when the ranging frame transmission FLAG is valid, the ranging frame transmission counter is stopped, so that the number n of ranging frame transmission clocks is obtainedsend。
Then, according to the formula: t iss＝(nsend×Fs)/(Fs_norm)2-Tpps_sCalculating the sending time T of the ranging framesWherein n issendSending the number of clocks for the ranging frame, FsTo transmit a measurement of the clock frequency of the clock, Fs_normIs the nominal frequency value of the transmit clock.
And S3, each terminal receives the clock number according to the ranging frame, and calculates the arrival time of the ranging frame based on the pulse per second arrival time of the receiving clock and the data stream transmitted by the IM-DD data transmission channel.
In this embodiment, the receiving clock uses the pulse-per-second arrival FLAG _1PPS _ R, and outputs the clock frequency measurement value Fr. Wherein, every time when a second pulse arrival mark is effective, the last frequency counting is ended, and the counting value at the end of counting is output as a clock frequency measuring value F of the receiving clockrAt the same time, the counter is reset and counting is restarted.
Meanwhile, when the pulse per second arrival FLAG _1PPS _ R of the receiving clock is valid, the ranging frame receiving counter is started, and when the ranging frame receiving FLAG is valid, the ranging frame receiving counter is stopped to obtain the number n of the ranging frame receiving clocksrecv。
Recombination of parallel sync bit sliding values NrParallel data width NBITSAnd nominal frequency value F of the receiving clockr_normWherein, for the parallel data with random bit position output by the high-speed serial receiving interface, the bit sliding adjustment is needed to make it conform to the data frameThe format is defined, so the parallel synchronization bit sliding value N is considered in this embodimentr。
Then, according to the formula:
Tr＝[(nrecv+Nr/NBITS)×Fr]/(Fr_norm)2-Tpps_r≈(nrecv×Fr)/(Fr_norm)2+Nr/NBITS/Fr_norm-Tpps_r
calculating the arrival time T of the ranging framerWherein n isrecvReceiving the clock number for the ranging frame, FrTo receive a measurement of the clock frequency of a clock, Fr_normFor receiving a nominal frequency value of the clock, NrFor parallel synchronization of bit-sliding values, NBITSIs the parallel data width.
And S4, calculating respective pseudo-range values by the two terminals according to the arrival time of the ranging frame calculated by the terminal and the sending time of the ranging frame sent by the opposite terminal, and calculating the ranging values according to the pseudo-range values calculated by the two terminals.
Specifically, the first of the two terminals is according to the formula: t isd1＝Tr1-Ts2Calculating a first pseudorange value Td1Wherein T isr1Time of arrival, T, of ranging frame calculated for first terminals2A ranging frame transmission time calculated for the second terminal.
The second of the two terminals is according to the formula: t isd2＝Tr2-Ts1Calculating a second pseudorange value Td2Wherein T isr2Time of arrival, T, of ranging frame calculated for second terminals1A ranging frame transmission time calculated for the first terminal. Then according to the formula: t isdist＝(Td1+Td2) /2 calculating the distance measurement value Tdist。
In addition, the calculated ranging value includes the inherent transmission and processing delay T inside the two terminalsditermTherefore, in a preferred embodiment, in order to obtain a more accurate measurement result, according to the formula: t isdist_correct＝Tdist-TditermFor distance measurement value TdistThe distance measurement correction value T is obtained by correctiondist_correct。
Taking into account the speed c' of the light in the transmission medium, a distance value D-T for the distance measurement can be calculateddist_correct×c’。
In summary, in the present invention, a high-precision time of arrival of the pulse per second measurement method is used, a data transmission channel for direct alignment and optical detection communication is used, a very small amount of ranging information is inserted into normal data frame transmission, a normal communication mode does not need to be interrupted, network clock frequency synchronization is also not needed, a sending period of a data frame does not need to keep a synchronous relationship with the pulse per second, and a bidirectional one-way ranging method can be used for ranging. In addition, the second pulse is used for measuring the frequency of the local clock and correcting the parameters of the ranging process, so that the ranging accuracy and precision of the time scale of the direct-tuning direct-detection communication code element can be achieved only by adopting a common crystal oscillator as a local clock source and canceling using a full-network synchronous clock signal or a high-stability clock source which is usually required by high-precision ranging, the complexity of a time-frequency synchronization system, the requirements on components and the cost of the whole communication ranging system are reduced, and the problem that the ranging accuracy and the system cost are not easy to simultaneously consider in the prior art is solved.
Meanwhile, the invention also provides a distance measuring system based on IM-DD, which comprises at least two terminals, wherein the structures and the functions of the two terminals are consistent, and each terminal is used for:
adopting second pulse to carry out frequency measurement on a local sending clock and a local receiving clock, and obtaining the second pulse arrival time of the sending clock and the receiving clock; calculating the sending time of the ranging frame according to the number of the ranging frame sending clocks and based on the second pulse arrival time of the sending clocks, and sending the ranging frame sending time to the opposite terminal along with the data stream; calculating the arrival time of the ranging frame according to the number of the ranging frame receiving clocks and based on the second pulse arrival time of the receiving clocks; calculating respective pseudo-range values according to the arrival time of the ranging frame calculated by the terminal and the transmission time of the ranging frame transmitted by the opposite terminal, and calculating the ranging value according to the pseudo-range values calculated by the two terminals.
The following further introduces the terminal in this embodiment:
referring to fig. 2, the terminal 100 in the present embodiment includes: a digital logic circuit 101, a direct modulation transmitting optical module 102 and a direct detection receiving optical module 103.
The direct modulation transmitting optical module 102 converts the electrical signal into an optical signal using a direct intensity modulation method. The direct detection receiving optical module 103 converts an optical signal into an electrical signal using a direct intensity detection method.
Referring to fig. 3, which is a block diagram of a digital logic circuit inside a terminal, the digital logic circuit 101 includes: the system comprises a pulse-per-second arrival time measuring module 111, a clock frequency measuring module 112, a ranging frame transmission time calculating module 113, a data frame framing module 114, a high-speed serial transmission interface 115, a high-speed serial reception interface 116, a parallel data synchronization module 117, a data frame deframing module 118, a ranging frame arrival time calculating module 119, a pseudo-range calculating module 120 and a ranging calculating module 121.
The pulse-per-second arrival time measuring module 111 adopts a pulse-per-second arrival time measuring method, cascade logic circuits with deterministic time delay in the digital logic circuits are used to form delay chains, a clock is used to sample the multi-stage taps of the delay chains in parallel, and the delay time T of each stage of delay chain is determined according to the result of time sequence analysis of the digital logic circuitstapFor number NTAPSThe multi-level taps of the multi-level delay chain are sampled in parallel to obtain a sampling value Dtap[0:NTAPS-1]Finding the position n of logic value jump (if the second pulse rising edge is effective, the jump from 0 to 1 is found, or the second pulse falling edge is effective, the jump from 1 to 0 is found)pulseIf jump exists, the second pulse arrival FLAG _1PPS is valid, and the second pulse arrival time is calculated to be Tpps＝npulse×TtapWherein, TppsThe second arrival time of the clock. The sending clock and the receiving clock respectively output corresponding second pulse arrival time Tpps_sAnd Tpps_rAnd second pulse arrival FLAGs FLAG _1PPS _ S and FLAG _1PPS _ R.
The clock frequency measuring module 112 adopts a clock frequency measuring methodEvery time the second pulse arrival flag is valid, the last frequency counting is ended, and the count value at the end of counting is output as the clock frequency value FsOr FrAt the same time, the counter is reset and counting is restarted. The transmitting clock and the receiving clock respectively correspond to a clock frequency measuring module, respectively use corresponding second pulse arrival marks FLAG _1PPS _ S and FLAG _1PPS _ R, respectively output corresponding clock frequency measuring values FsAnd Fr。
The ranging frame transmission time calculation module 113 starts a ranging frame transmission counter when the second pulse arrival FLAG _1PPS _ S is valid, and stops the ranging frame transmission counter when the ranging frame transmission FLAG is valid by using a ranging frame transmission time calculation algorithm to obtain a ranging frame transmission clock number nsendThen according to the second pulse arrival time T based on the sending clockpps_sSending clock frequency value FsAnd nominal frequency value F of the transmission clocks_normCalculating the corrected sending time T of the ranging frames＝(nsend×Fs)/(Fs_norm)2-Tpps_s。
The data frame framing module 114 transmits the input data and the ranging frame with a time TsPseudorange value TdThe method comprises the steps of forming a parallel data frame according to a data frame format, outputting a ranging frame sending mark FLAG _ S when sending the data frame with effective ranging information, wherein the mark takes a certain fixed position or other positions with determined time delay of the data frame as a reference, and can take a frame head or a frame tail position as a reference without loss of generality.
The high-speed serial transmission interface 115 outputs a transmission clock of the parallel data as an operation clock of the transmission section, and converts the parallel data into a high-speed serial data stream to output. The high-speed serial reception interface 116 converts an input serial data stream into parallel data, and simultaneously outputs a reception clock of the parallel data as an operation clock of the reception section.
The parallel data synchronization module 117 performs bit sliding adjustment on the parallel data with random bit positions output by the high-speed serial receiving interface to make the parallel data conform to the format definition of the data frame for outputParallel data after synchronization and parallel synchronization bit sliding value Nr。
The data frame de-framing module 118 is defined according to the format of the data frame, and resolves the output data and the sending time T of the ranging frame sent by the opposite terminals2Pseudo range value T transmitted by the other side terminald2When a data frame with valid ranging information is received, a ranging frame receiving FLAG _ R is output, and the FLAG is based on a fixed position of the data frame or other positions with determined time delay, and can be based on a frame head or frame tail position without loss of generality.
The ranging frame arrival time calculation module 119 starts the ranging frame reception counter when the pulse-per-second arrival FLAG _1PPS _ R is valid, and stops the ranging frame reception counter when the ranging frame reception FLAG _ R is valid, to obtain the ranging frame reception clock number nrecvSecond pulse arrival time T based on reception clockpps_rAnd based on the measured value F of the clock frequency of the received clockrParallel sync bit sliding value NrParallel data width NBITSAnd nominal frequency value F of the receiving clockr_normAnd calculating the arrival time of the corrected ranging frame:
Tr＝[(nrecv+Nr/NBITS)×Fr]/(Fr_norm)2-Tpps_r≈(nrecv×Fr)/(Fr_norm)2+Nr/NBITS/Fr_norm-Tpps_rwherein, TrIs the ranging frame arrival time.
The pseudo-range calculation module 120 calculates a pseudo-range value according to the time of arrival of the ranging frame calculated by the terminal and the time of transmission of the ranging frame transmitted by the other terminal. The ranging calculation module 121 calculates a pseudo range value from the local terminal and a pseudo range value transmitted from the other terminal.
Specifically, the first of the two terminals is according to the formula: t isd1＝Tr1-Ts2Calculating a first pseudorange value Td1Wherein T isr1Time of arrival, T, of ranging frame calculated for first terminals2A ranging frame transmission time calculated for the second terminal.
The second of the two terminals is according to the formula: t isd2＝Tr2-Ts1Calculating a second pseudorange value Td2Wherein T isr2Time of arrival, T, of ranging frame calculated for second terminals1A ranging frame transmission time calculated for the first terminal. Then according to the formula: t isdist＝(Td1+Td2) /2 calculating the distance measurement value Tdist. And may also be based on the formula: t isskew＝(Td1-Td2) Calculating the pulse-per-second deviation value Tskew。
In addition, the calculated ranging value includes the inherent transmission and processing delay T inside the two terminalsditermTherefore, in a preferred embodiment, in order to obtain a more accurate measurement result, according to the formula: t isdist_correct＝Tdist-TditermFor distance measurement value TdistThe distance measurement correction value T is obtained by correctiondist_correct。
Taking into account the speed c' of the light in the transmission medium, a distance value D-T for the distance measurement can be calculateddist_correct×c’。
It is noted that the pseudorange calculation module 120 and the range calculation module 121 each implement one of the steps of the two-way one-way ranging method. The resolution and accuracy of the ranging values described above is the duration of one symbol of the direct detection communication.
In summary, the ranging system in the present invention uses a high-precision time-of-second pulse arrival measurement method, uses a data transmission channel for direct alignment and optical detection communication, inserts a small amount of ranging information into normal data frame transmission, does not need to interrupt a normal communication mode, does not need network clock frequency synchronization, and does not need to keep a synchronization relationship with a second pulse in a data frame transmission period, i.e., can use a bidirectional one-way ranging method to perform ranging. In addition, the second pulse is used for measuring the frequency of the local clock and correcting the parameters of the ranging process, so that the ranging accuracy and precision of the time scale of the direct-tuning direct-detection communication code element can be achieved only by adopting a common crystal oscillator as a local clock source and canceling using a full-network synchronous clock signal or a high-stability clock source which is usually required by high-precision ranging, the complexity of a time-frequency synchronization system, the requirements on components and the cost of the whole communication ranging system are reduced, and the problem that the ranging accuracy and the system cost are not easy to simultaneously consider in the prior art is solved.
It is noted that, in the present application, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A distance measurement method based on IM-DD is characterized by comprising the following steps:
the two terminals to be measured adopt the second pulse to carry out frequency measurement on the local sending clock and the local receiving clock, and the second pulse arrival time of the sending clock and the receiving clock is obtained;
each terminal sends the clock number according to the ranging frame, calculates the sending time of the ranging frame based on the second pulse arrival time of the sending clock, and sends the ranging frame to the opposite terminal through an IM-DD data transmission channel along with the data stream;
each terminal receives the clock number according to the ranging frame, and calculates the arrival time of the ranging frame based on the second pulse arrival time of the receiving clock and the data stream transmitted by the IM-DD data transmission channel;
and the two terminals calculate respective pseudo-range values according to the arrival time of the ranging frame calculated by the terminal and the sending time of the ranging frame sent by the opposite terminal, and calculate the ranging value according to the pseudo-range values calculated by the two terminals.
2. The IM-DD based ranging method of claim 1, wherein the two terminals to be ranged both use the pulse per second to perform frequency measurement on the local transmitting clock and receiving clock, and obtain the arrival time of the pulse per second of the transmitting clock and receiving clock, comprising:
the multi-stage taps of the delay chain are sampled in parallel by using the transmitting clock and the receiving clock respectively, and the delay time T of each stage of the delay chain is determinedtap；
For number NTAPSThe multi-level taps of the multi-level delay chain are sampled in parallel to obtain a sampling value Dtap[0:NTAPS-1]；
Determining the position n of a logical value transitionpulse；
According to the formula: t ispps＝npulse×TtapCalculating the second pulse arrival time T of the transmission clockpps_sAnd the second pulse arrival time T of the receiving clockpps_rWherein, TppsThe second arrival time of the clock.
3. An IM-DD based ranging method as claimed in claim 2, wherein: looking for a transition from 0 to 1 when the rising edge of the pulse per second is valid, or a transition from 1 to 0 when the falling edge of the pulse per second is valid, to determine the position n of the logic value transitionpulse。
4. The IM-DD based ranging method of claim 2, wherein the calculating of the ranging frame transmission time by the terminals according to the number of the ranging frame transmission clocks and based on the pulse-per-second arrival time of the transmission clocks comprises:
according to the formula: t iss＝(nsend×Fs)/(Fs_norm)2-Tpps_sCalculating the sending time T of the ranging framesWherein n issendSending the number of clocks for the ranging frame, FsTo transmit a measurement of the clock frequency of the clock, Fs_normIs the nominal frequency value of the transmit clock.
5. An IM-DD based ranging method as claimed in claim 4, wherein: starting a ranging frame sending counter when the pulse per second of the sending clock reaches the effective mark, and stopping the ranging frame sending counter when the ranging frame sending mark is effective so as to obtain the number n of the ranging frame sending clockssend。
6. The IM-DD based ranging method of claim 4, wherein the terminals calculate the arrival time of the ranging frame according to the number of the receiving clocks of the ranging frame and based on the arrival time of the pulse per second of the receiving clocks and the data stream transmitted through the IM-DD data transmission channel, comprising:
according to the formula:
Tr＝[(nrecv+Nr/NBITS)×Fr]/(Fr_norm)2-Tpps_r≈(nrecv×Fr)/(Fr_norm)2+Nr/NBITS/Fr_norm-Tpps_r
calculating the arrival time T of the ranging framerWherein n isrecvReceiving the clock number for the ranging frame, FrTo receive a measurement of the clock frequency of a clock, Fr_normFor receiving a nominal frequency value of the clock, NrFor parallel synchronization of bit-sliding values, NBITSIs the parallel data width.
7. The IM-DD based ranging method of claim 6, wherein the ranging frame reception counter is started when the pulse-per-second arrival flag of the reception clock is valid, and stopped when the ranging frame reception flag is valid, to obtain the number n of the ranging frame reception clocksrecv。
8. The IM-DD based ranging method of claim 6, wherein the two terminals each calculate a respective pseudorange value according to the time of arrival of the ranging frame calculated by the terminal and the time of transmission of the ranging frame transmitted by the other terminal, and calculate the ranging value according to the pseudorange values calculated by the two terminals, comprising:
the first of the two terminals is according to the formula: t isd1＝Tr1-Ts2Calculating a first pseudorange value Td1Wherein T isr1Time of arrival, T, of ranging frame calculated for first terminals2A ranging frame transmission time calculated for the second terminal;
the second of the two terminals is according to the formula: t isd2＝Tr2-Ts1Calculating a second pseudorange value Td2Wherein T isr2Time of arrival, T, of ranging frame calculated for second terminals1A ranging frame transmission time calculated for the first terminal;
according to the formula: t isdist＝(Td1+Td2) /2 calculating the distance measurement value Tdist。
9. The IM-DD based ranging method of claim 8, wherein the ranging method further comprises:
obtaining transmission and processing delays T inside two terminalsditerm；
According to the formula: t isdist_correct＝Tdist-TditermFor distance measurement value TdistThe distance measurement correction value T is obtained by correctiondist_correct。
10. An IM-DD based ranging system comprising at least two terminals, each of said terminals being configured to:
adopting second pulse to carry out frequency measurement on a local sending clock and a local receiving clock, and obtaining the second pulse arrival time of the sending clock and the receiving clock;
calculating the sending time of the ranging frame according to the number of the ranging frame sending clocks and based on the second pulse arrival time of the sending clocks, and sending the ranging frame sending time to the opposite terminal along with the data stream;
calculating the arrival time of the ranging frame according to the number of the ranging frame receiving clocks and based on the second pulse arrival time of the receiving clocks;
calculating respective pseudo-range values according to the arrival time of the ranging frame calculated by the terminal and the transmission time of the ranging frame transmitted by the opposite terminal, and calculating the ranging value according to the pseudo-range values calculated by the two terminals.
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