JP6008103B2 - Short message communication terminal - Google Patents

Description

  The present invention relates to a satellite communication access system suitable for bidirectional communication.

  Conventionally, a satellite communication access method in which a plurality of terminal devices access a base station using CDMA (Code Division Multiple Access) via a non-geostationary satellite such as a quasi-zenith satellite is well known. . Further, a technique using an orthogonal code as a spreading code sequence for performing CDMA is also well known.

  For example, Non-Patent Document 1 describes an orthogonal Gold code sequence as a spreading code sequence for code division multiple access (CDMA), and the generated orthogonal Gold code sequences are orthogonal to each other with a shift of 0. It is described that.

  Japanese Patent Laid-Open No. 2002-57613 (Patent Document 1) discloses a conventional satellite communication access system. According to the satellite communication access method disclosed in Japanese Patent Laid-Open No. 2002-57613, each terminal generates a reference synchronization signal having a fixed period by GPS, and randomly selects a timing for transmitting data in the period. This is a technique for preventing simultaneous data communication from a plurality of terminals.

  Furthermore, in the conventional satellite communication access method disclosed in Japanese Patent Application Laid-Open No. 2004-289717 (Patent Document 2), the base station notifies predetermined delay time information to each terminal device, and then each terminal device The transmission data is spread with the same spreading code, and the spread transmission data whose delay time is individually adjusted based on the delay time information is arranged and transmitted in a prescribed slot.

  Japanese Patent Laid-Open No. 2006-253799 (Patent Document 3) describes a non-stationary satellite when performing bidirectional satellite communication between a master station and a slave station via a non-stationary satellite such as a quasi-zenith satellite. A technique is disclosed in which a Doppler frequency shift of a carrier wave generated by movement is compensated based on orbit information of a non-geostationary satellite and position information of a slave station.

  Non-Patent Document 2 discloses a basic study on a two-way communication system using a quasi-zenith satellite, and uses a quasi-zenith satellite or a GPS (Global Positioning System) satellite to send an extremely short message such as safety information to a satellite ( There is a statement that it is assumed to be transmitted via the Quasi-Zenith Satellite). Further, it is also disclosed that a carrier wave frequency deviation is compensated using a GPS signal and a propagation delay difference is compensated using a GPS signal.

JP 2002-57613 A JP 2004-289717 A JP 2006-253799 A

Hiromasa Hana, “Series Constructed Based on M Series and Its Application to Communication” The Institute of Electronics, Information and Communication Engineers Fundamental / Boundary Society, Fundamentals Review, Vol. 3 No. 1, July 2009, p. 32-42 Taku Kameda, Kenji Suematsu, Fumihiro Yamagata, Hiroshi Oguma, Nao Takagi, Kazuo Tsubouchi "Fundamental study of wireless access method for location and short message bidirectional communication system using quasi-zenith satellite" IEICE Technical Report May 2012 35-40

  Non-Patent Document 1 describes that orthogonal Gold code sequences as spreading code sequences for code division multiple access (CDMA) are orthogonal to each other with a shift of 0. Therefore, when a plurality of terminal devices access a base station using code division multiple access (CDMA) using orthogonal codes via a non-stationary satellite such as a quasi-zenith satellite, they are transmitted from each terminal device on the non-stationary satellite. In order to make the orthogonal codes orthogonal, it is necessary to synchronize the orthogonal codes of the CDMA signals transmitted from the terminal devices on the non-geostationary satellite.

  However, the conventional Non-Patent Document 1 and Patent Documents 1 to 3 have a problem that means for synchronizing orthogonal codes transmitted from each terminal device on a non-geostationary satellite is not described. Further, the conventional non-patent document 2 has a problem that it does not mention a specific means for synchronizing orthogonal codes transmitted from each terminal device on a non-geostationary satellite.

The present invention has been made to solve the above-described problems, and is transmitted from each terminal apparatus on a non-stationary satellite when a plurality of terminal apparatuses access a base station using CDMA based on orthogonal codes. orthogonal codes of CDMA signals and to obtain a tio over preparative message communication terminal synchronized.

A short message communication terminal according to the invention of claim 1 is one of a plurality of short message communication terminals accessing a satellite, and receives a forward link signal relayed to the satellite and transmitted from a base station And an orthogonal code generator for generating orthogonal codes, an information acquisition unit for acquiring a predetermined time accuracy from the outside, and a one-chip length longer than the predetermined time accuracy based on the time information acquired by the information acquisition unit A chip clock consisting of: a transmission timing generator using the chip clock as a reference for the generation timing of the orthogonal code by the orthogonal code generator; and a short message according to the forward link signal received by the receiver. A transmission signal generation unit that generates a transmission signal including the transmission signal generation unit, and an orthogonal code generated by the orthogonal code generation unit. A CDMA spreading unit that spreads the generated transmission signal to generate a CDMA signal; and a delay process that corrects a delay caused by a distance between the short message communication terminal and the satellite when the CDMA signal is transmitted to the satellite Unit, a carrier generation unit that generates a carrier wave, a modulation unit that modulates the CDMA signal after correction by the delay processing unit, using the carrier wave generated by the carrier generation unit, and the modulation unit modulated by the modulation unit A transmitter that transmits a CDMA signal as a return link signal to the satellite, and synchronizes the generation timing of the orthogonal code by the orthogonal code generator between the plurality of short message communication terminals based on the time information. .

The short message communication terminal according to the invention of claim 2 has a Doppler frequency calculation unit that calculates a frequency shift due to a Doppler frequency shift of the CDMA signal from a change in relative distance to the satellite, and the carrier wave generation unit includes: wherein is the Doppler frequency calculation portion frequency shift due to the Doppler frequency shift calculated as described in claim 1 is intended to compensate at the frequency of the carrier wave.

In the short message communication terminal according to the invention of claim 3, the delay processing unit derives a distance to the satellite from the position information and calculates a delay time, and the delay time calculation unit calculates from the delay time is according to claim 1 or 2 comprising a delay correction unit for correcting the transmission signal.

According to a fourth aspect of the present invention, there is provided the short message communication terminal, wherein the transmission signal generator receives the CDMA signal modulated by the modulator at a slot timing based on a chip clock generated by the transmission timing generator. by transmitting to the satellite, those described for the slot timing in any one of claims 1, 2, 3 is to synchronize among said plurality of short message communication terminal.

In the short message communication terminal according to the invention of claim 5, the transmission signal generating unit generates a chip clock having a length of one chip longer than a predetermined time accuracy based on the time information acquired by the information acquisition unit. The slot timing is synchronized among the plurality of short message communication terminals by transmitting the CDMA signal modulated by the modulation unit to the satellite at slot timing based on the chip clock. It is a thing of any one of claim | item 1 , 2 and 3 .

As described above , according to the inventions according to claims 1 to 5 , in CDMA using orthogonal codes, it is possible to provide a satellite communication access method with low interference due to cross-correlation between codes, so that transmission is performed from each terminal apparatus to the base station. Suitable for a short message communication system that can increase the return link communication capacity because the quality of the CDMA signal can be improved and interference due to cross-correlation between codes can be reduced even when multiple communication terminals access simultaneously. A short message communication terminal can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic (flowchart which shows the chip clock generation method and orthogonal code generation method which concern on Embodiment 1 of this invention) which shows the outline of the communication system which concerns on Embodiment 1 of this invention. It is a functional block diagram of the communication terminal which concerns on Embodiment 1 of this invention (schematic diagram which shows the outline of the communication system which concerns on Embodiment 1 of this invention). 2 is a functional block diagram of a base station according to Embodiment 1 of the present invention and a schematic diagram showing an outline of a communication system according to Embodiment 1. FIG. It is a flowchart which shows the process of the communication terminal (communication system) which concerns on Embodiment 1 of this invention. It is a functional block diagram of the orthogonal code generation part of the communication terminal which concerns on Embodiment 1 of this invention. It is the figure which considered the phase difference in the communication terminal which concerns on Embodiment 1 of this invention. It is a wave form diagram which shows the waveform of each part in the communication terminal which concerns on Embodiment 1 of this invention. It is a wave form diagram which shows that the orthogonal code start timing between the communication terminals which concerns on Embodiment 1 of this invention is synchronizing. It is a figure which shows the distance of the communication terminal which concerns on Embodiment 1 of this invention, and a quasi-zenith satellite. It is a figure which shows the distance of the communication terminal which concerns on Embodiment 1 of this invention, and a non-geostationary satellite. It is a flowchart which shows the process of the satellite orbit information in the communication terminal which concerns on Embodiment 1 of this invention. It is a flowchart which shows the calculation process of delay time difference (tau) in the communication terminal which concerns on Embodiment 1 of this invention. It is the schematic which shows derivation | leading-out of the Doppler frequency shift in the communication terminal which concerns on Embodiment 1 of this invention. It is a functional block diagram which shows the frequency subtractor and frequency multiplier in the communication terminal which concerns on Embodiment 1 of this invention. It is a flowchart which shows the compensation process of the Doppler frequency shift in the communication terminal which concerns on Embodiment 1 of this invention. It is a functional block diagram of the communication terminal which concerns on Embodiment 2 of this invention. It is the schematic (flowchart which shows the chip clock generation method which concerns on Embodiment 2 of this invention) which shows the outline of the communication system which concerns on Embodiment 2 of this invention. It is a wave form diagram which shows that the orthogonal code start timing between the communication terminals which concerns on Embodiment 2 of this invention is synchronizing. It is a figure which shows the parameter table (table) for the data burst transmission of the communication terminal which concerns on Embodiment 2 of this invention. It is a flowchart which shows the process of the time slot start timing in the communication terminal which concerns on Embodiment 2 of this invention. It is a flowchart which shows the process of the communication terminal (communication system) which concerns on Embodiment 2 of this invention. It is a wave form diagram which shows that the time slot start timing between the communication terminals which concerns on Embodiment 2 of this invention is synchronizing. It is a flowchart which shows the process of the time slot start timing (process of a CDMA de-spreading part) in the base station of the communication system which concerns on Embodiment 2 of this invention. It is a functional block diagram of the communication terminal which concerns on Embodiment 3 of this invention (schematic diagram which shows the outline of the communication system which concerns on Embodiment 1 of this invention). It is a functional block diagram which shows the frequency subtractor and frequency multiplier in the communication terminal which concerns on Embodiment 3 of this invention. It is a flowchart which shows the process of the movement speed calculation part in the communication terminal which concerns on Embodiment 3 of this invention. It is a flowchart which shows the compensation process of the Doppler frequency shift in the communication terminal which concerns on Embodiment 3 of this invention. It is the schematic which shows the outline of the communication system which concerns on Embodiment 4 of this invention. It is a functional block diagram of the communication terminal which concerns on Embodiment 4 of this invention. It is a functional block diagram of the communication terminal which concerns on Embodiment 4 of this invention. It is a functional block diagram of the communication terminal which concerns on Embodiment 4 of this invention. It is a functional block diagram of the communication terminal which concerns on Embodiment 4 of this invention.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to FIGS. In the drawings, the same reference numerals denote the same or corresponding parts, and detailed descriptions thereof are omitted. First, the overall system, communication terminal, and base station according to Embodiment 1 of the present invention will be described with reference to FIGS. In the first embodiment, a plurality of communication terminals perform random access by a so-called pure ALOHA system in which burst data spread by CDMA (Code Division Multiple Access) is randomly transmitted to a satellite.

  1A is a configuration diagram showing a configuration of a communication system (short message communication system) according to the first embodiment, and FIG. 1B is used for a chip clock generation method and an orthogonal code generation method according to the first embodiment. Functional block diagram of a chip clock generator (transmission timing generator, information acquisition unit) and orthogonal code generator, FIG. 1 (c) is a flowchart of chip clock generation (generation), and FIG. 1 (d) is chip clock generation (generation) ) And a flowchart of orthogonal code generation (generation), and FIG. 1E is a flowchart of chip clock generation (generation) (S001 omitted). 2A is a functional block diagram of the communication terminal according to the first embodiment, FIG. 2B is a schematic diagram of the communication system according to the first embodiment, and FIG. 3 is a function of the base station according to the first embodiment. It is a block diagram.

  In FIG. 1A, the base station 2 transmits data to the communication terminals 1-1 to 1-3 via the forward link communication line 8 via the non-stationary satellite 3 represented by the quasi-zenith satellite. (The three communication terminals are exemplarily shown, and the number of communication terminals is not limited to this. Therefore, in this application, the communication terminal 1 may be referred to as a communication terminal 1-n. n is a positive integer). The data includes individual communication data or control data for each communication terminal, but may include control data common to each communication terminal. The communication terminals 1-1 to 1-3 individually transmit communication data or control data to the base station 2 via the non-stationary satellite 3 via the return link communication line 9. The base station 2 is connected to a service center 6 and a satellite tracking control center 7 via a terrestrial network 5. The service center 6 transmits and receives messages to and from the communication terminals 1-1 to 1-3 via the base station 2 to provide services.

  Using a quasi-zenith satellite or a GPS (Global Positioning System) satellite, an extremely short message (short message, short message, location / short message, hereinafter referred to as a short message) such as safety information can be transmitted to a satellite (quasi-zenith satellite). ) Is described in Non-Patent Document 2 “Overview”. Therefore, as an example of the service using the short message, a rescue message, an emergency message, a rescue signal, etc. including location information transmitted from the user terminal (mobile terminal) of the disaster victim at the time of a disaster, etc. are used as a return link. A signal (transmission signal) is transmitted to the service center via a satellite line, and at the service center, a reply message can be transmitted to the user terminal via the satellite line in response to the received short message. In the invention according to the present application, the quasi-zenith satellite may have a GPS satellite function.

  The invention according to the present application relates to these services. The invention according to the embodiment of the present application includes a communication system (short message communication system), a communication terminal (short message communication terminal), a communication method (short message communication method), a chip clock generation method, and an orthogonal code generation method. Yes.

  The satellite tracking control center 7 transmits satellite orbit information of the non-stationary satellite 3 to the base station 2. For example, the communication terminals 1-1 to 1-3 receive the GPS signal 10 including the position information and time information (time information) from the GPS satellite 4 in order to include the position information of the own terminal in the rescue message. (Note that the GPS satellite 4 may include a quasi-zenith satellite having a GPS positioning function).

  An example of a non-geostationary satellite communication system (the communication system according to Embodiment 1) as shown in FIG. 1A is a quasi-zenith satellite system. As an example of this quasi-zenith satellite system, three satellites go around the earth in one day through a predetermined orbit, and at least one of the three satellites is located near the sky (zenith) in Japan. There is a type of satellite system. Further, if the satellite is switched every 8 hours, an elevation angle of 60 degrees or more is always secured, and the user can always be provided with a good mobile communication service with less interruption of the communication line by a building or the like.

  Next, the structure of the communication terminal 1 used for the communication system provided with the base station 2 which communicates with the some communication terminal 1 is demonstrated using FIG. The communication terminal 1 generates a chip clock based on time information acquired by an orthogonal code generation unit 22 that generates an orthogonal code, and an information acquisition unit 310 that acquires time information from the outside, and generates the chip clock as an orthogonal code generation unit. A transmission timing generator 23 as a reference for the generation timing of the orthogonal code by 22, and a CDMA spreading unit 21 that generates a CDMA signal by spreading the transmission signal to be transmitted to the base station 2 by the orthogonal code generated by the orthogonal code generator 22. Have. Therefore, the some communication terminal 1 can synchronize the production | generation timing of the orthogonal code by the orthogonal code generation part 22 between the some communication terminals 1-n from time information.

  Specifically, in the communication terminal 1, the signal of the forward link communication line 8 from the base station 2 is received by the satellite communication antenna 11 of the communication terminal 1 (FIG. 2 (b)), as shown in FIG. 2 (a). Then, after being received by the satellite communication antenna 11 of the communication terminal 1 and separated from the transmission signal by the duplexer 12, the wireless reception unit 13 performs low noise amplification or the like, and then the QPSK demodulation unit 14 performs QPSK (Quadrature Phase Shift). (Keying) modulated wave is demodulated. The received data after QPSK demodulation is subjected to error correction decoding by the error correction decoding unit 15 and becomes original information data. Here, the information data of the forward link line is transmitted by TDM (Time Division Multiplex), and communication data or control data addressed to each communication terminal 1 is time-division multiplexed. The TDM separation unit 16 separates the reception data addressed to the terminal itself and outputs it to the reception data output terminal 34, and also separates the orbit information of the satellite, which is a part of the control data, to obtain the orbit information reception unit 17 (first It outputs to the information acquisition part 17 (information acquisition part 17).

  On the other hand, the GPS signal 10 from the GPS satellite 4 is received by the GPS receiver 31 via the GPS antenna 30, and is subjected to signal processing by the GPS signal processing unit 32, whereby a GPS time signal and GPS position data are obtained. The second information acquisition unit 310 (information acquisition unit 310) includes a GPS antenna 30, a GPS receiver 31, and a GPS signal processing unit 32.

  Next, the transmission side of the communication terminal 1 will be described. The transmission data input to the data input terminal 18 (transmission data (short message) input terminal) is converted into a predetermined burst format by adding a synchronization bit, a control bit, etc. to the transmission data in the data generation unit 19, The error correction coding unit 20 performs error correction coding, and the CDMA spreading unit 21 adds modulo 2 to the orthogonal code sequence generated by the orthogonal code generation unit 22 and spreads it for CDMA. The transmission signal generation unit 180 includes a data input terminal 18, a data generation unit, an error correction coding unit 20, and a CDMA spreading unit 21.

  The transmission timing generation unit 23 generates a clock signal and a timing signal to each unit synchronized with the GPS time signal from the GPS signal processing unit 32. Specifically, the chip clock generator (transmission timing generator 23, information acquisition unit 310) and orthogonal code generator shown in FIG. 1B, and the first embodiment shown in FIGS. 1C, 1D, and 1E. The chip clock generation method (and the orthogonal code generation method) according to FIG.

  S002 in FIG. 1C (S represents a step) generates a chip clock consisting of one chip longer than a predetermined time accuracy (clock generation step). Prior to S002, S001 (acquisition step) for acquiring time information having a predetermined time accuracy may be performed. In S003 (determination step), the chip clock start timing in S002 (clock generation step) is determined from the time information (which may be acquired from the GPS satellite 4 in S001). Note that S001 may acquire time information from the GPS satellite 4. A detailed description of a chip clock composed of one chip longer than a predetermined time accuracy will be described later.

  S004 (orthogonal code generation step) shown in FIG. 1 (d) generates an orthogonal code based on the chip clock start timing generated by this chip clock generation method. In other words, FIG. 1C shows up to the determination of the timing of starting the chip clock, and FIG. 1D shows up to the generation of the orthogonal code based on the timing of starting the chip clock. Further, in the chip clock generation method, as long as time information having a predetermined time accuracy can be acquired in advance, S001 may be omitted as shown in FIG.

  The CDMA spread data output from the CDMA spreading unit 21 is subjected to a delay correction unit 24 to correct a delay time difference due to a distance difference between the communication terminals 1 to the satellite, and then a carrier wave is generated by the BPSK modulation unit 25 (modulation unit 25). BPSK modulation using the output of the unit 26 as a carrier wave, power amplification and the like by the radio transmission unit 27, and from the satellite communication antenna 11 via the duplexer 12, as a transmission burst signal of the return link communication line 9, a non-stationary satellite 3 (FIG. 2B).

  The delay time calculation unit 29 calculates the delay time difference due to the distance difference between the communication terminals 1 to the satellite 3 using the GPS position data output from the GPS signal processing unit 32. The delay processing unit 240 includes a delay correction unit 24 and a delay time calculation unit 29. The Doppler frequency calculation unit 28 is generated when the non-stationary satellite 3 moves with respect to the communication terminal 1 using the satellite orbit information from the orbit information receiving unit 17 and the GPS position data from the GPS signal processing unit 32. Calculate the Doppler frequency shift corresponding to the RF carrier frequency.

  In other words, it can be said that the Doppler frequency calculation unit 28 calculates the frequency shift due to the Doppler frequency shift of the CDMA signal from the change in the relative distance between the satellite 3 and the communication terminal 1. Note that the case where the communication terminal 1 moves will be described in the third embodiment. That is, in the communication system, communication terminal, and communication method according to Embodiment 1, the Doppler frequency calculation unit 28 can be said to calculate the Doppler frequency shift from the moving speed of the satellite 3. On the other hand, in the communication system, communication terminal, and communication method according to the third embodiment, the Doppler frequency calculation unit 28 calculates the Doppler frequency shift from the moving speed of the communication terminal 1, or the Doppler frequency calculation unit 28 It can be said that the Doppler frequency shift is calculated from the moving speed of the communication terminal 1 and the moving speed of the satellite 3.

  The Doppler frequency processing unit 250 includes a BPSK modulation unit 25, a carrier wave generation unit 26, and a Doppler frequency calculation unit 28. The ON / OFF of the carrier wave from the carrier wave generating unit 26 is matched with the CDMA signal transmitted from the CDMA spreading unit 21 in accordance with the chip clock generated by the transmission timing generating unit 23. The carrier ON / OFF itself may be performed by either the BPSK modulator 25 or the carrier generator 26, or a switch may be provided between the BPSK modulator 25 and the carrier generator 26.

  Next, the configuration of the base station 2 will be described with reference to FIG. In FIG. 3, data to be transmitted to each communication terminal 1 transmitted from the service center 6 to the base station 2 via the ground network 5 is received by the ground interface unit 41 of the base station 2. On the other hand, data (mainly satellite orbit information) transmitted from the satellite tracking control center 7 to the base station 2 via the ground network 5 is received by the ground interface unit 41 of the base station 2.

  The data generation unit 42 of the base station 2 receives data to be transmitted for each communication terminal 1 from the ground interface unit 41, generates transmission data for each communication terminal 1, and in the TDM multiplexing unit 43, from the control information transmission unit Along with the control data to be transmitted (satellite orbit information, etc.), it is TDM multiplexed. The TDM multiplexed data is subjected to error correction coding by the error correction coding unit 45, then QPSK modulated by the QPSK modulation unit 46, frequency-converted to an RF frequency by the wireless transmission unit 47, and then amplified by high power. Then, it is transmitted as a forward link communication line signal from the satellite communication antenna 49 to the non-stationary satellite 3 via the duplexer 48.

  Next, the receiving side of the base station 2 will be described. The signals transmitted from the plurality of communication terminals 1 are received by the satellite communication antenna 49 via the non-geostationary satellite 3 (relay), are amplified by the radio receiver 50 via the duplexer 48, and then are amplified by IF. The frequency is converted into a frequency signal. The CDMA despreading unit 51 captures the chip clock and the orthogonal code start timing from the received CDMA signal, and performs CDMA despreading.

  The signal despread in the CDMA despreading unit 51 of the base station 2 is BPSK demodulated in the BPSK demodulating unit 52 and then error-corrected and decoded in the error correcting and decoding unit 53, and the data processing unit 54 sends it to the service center 6. Data to be output is formed and transmitted to the ground interface unit 41. The ground interface unit 41 transmits data to the service center 6 via the ground network 5.

  A communication method according to the first embodiment (note that the satellite communication access method according to the first embodiment relates to a communication method between a plurality of communication terminals and a base station) will be described. In the communication method according to Embodiment 1, the plurality of communication terminals 1 synchronize the generation timing of the orthogonal code by the orthogonal code generation unit 24 between the plurality of communication terminals 1-n from the time information.

  The configuration includes an acquisition step in which the information acquisition unit 310 of the communication terminal 1 acquires time information having a predetermined time accuracy from the GPS satellite 4, and a one-chip length in which the transmission timing generation unit 23 of the communication terminal 1 is longer than the predetermined time accuracy. S104 comprising: a clock generation step for generating a chip clock comprising: a determination step for determining the chip clock start timing of the clock generation step from the time information acquired by the transmission timing generation unit 23 of the communication terminal 1 in the acquisition step; The orthogonal code generation unit 22 generates an orthogonal code based on the chip clock start timing of the clock generation step determined in the determination step (S105 in FIG. 4), and the CDMA of the communication terminal 1 The spreader 21 uses the orthogonal code generated in the orthogonal code generation step to generate a base station It is obtained by a CDMA signal generating step (S108 in FIG. 4) which spreads the transmission signal to be transmitted to generate a CDMA signal to.

  Details will be described with reference to FIG. FIG. 4 is a flowchart showing the operation of the communication terminal according to the satellite communication access system of the first embodiment. In FIG. 4, when the communication terminal is turned on, the GPS signal 10 from the GPS satellite 4 is received in S101, and then in S102, it is determined whether or not to transmit data. For example, it is determined whether the user has selected data transmission by operating the communication terminal 1 (mobile terminal). If it is determined in S102 that data is to be transmitted, the reception system of the communication terminal 1 is activated in S103, and the forward link signal from the base station 2 is received. Note that the forward link signal may always be received regardless of whether or not data is transmitted. In this case, S103 is a step before S102.

  Next, in S104, the transmission timing generation unit 23 generates a transmission timing signal synchronized with the GPS time signal generated by the GPS signal processing unit 32. Here, the transmission timing signal is a chip clock for generating an orthogonal code, an orthogonal code start timing, an error correction coding clock, a data clock, or the like. In S105, the orthogonal code generation unit 22 randomly selects one orthogonal code from among a plurality of orthogonal codes, and selects the orthogonal code selected in the previous period based on the chip clock synchronized with the GPS time signal and the orthogonal code start timing. generate. As a result, the chip clock and the orthogonal code start timing of the orthogonal code of the CDMA signal transmitted from the plurality of communication terminals to the satellite can be synchronized between the plurality of communication terminals, and the distance from each communication terminal to the satellite can be increased. If they are the same, the orthogonal code chip clock and the orthogonal code start timing of the CDMA signal transmitted from each terminal on the satellite transponder are synchronized.

  However, in general, communication terminals that perform satellite communication are spread over a wide area (for example, all over Japan). Therefore, the distance to the satellite differs depending on the geographical position where each communication terminal exists, and therefore, the CDMA of each communication terminal. The delay time between the signal transmission time and the satellite transponder arrival time also differs depending on the position of each communication terminal. Therefore, in S106, the delay time calculation unit 29 uses the position data measured by the GPS signal processing unit 32 to calculate the distance from the position of the terminal to the satellite and the reference ground position stored in advance in a memory or the like. A difference from the distance to the satellite is obtained, a delay time difference corresponding to the distance difference is calculated, and the delay correction unit 24 compensates for the delay time difference. Here, the GPS position data specifically refers to latitude data, longitude data, and altitude data.

  Next, when there is a difference in the carrier frequency of the CDMA signal transmitted from each communication terminal, the orthogonality of the orthogonal code is lost as will be described later, so in step S107, the Doppler frequency calculation unit 28 determines the Doppler frequency deviation due to satellite movement. Is calculated according to the position of the communication terminal 1 and compensated by the carrier wave generator 26. In S108, the transmission data is spread by the orthogonal code generated in the orthogonal code generator 22 by the chip clock synchronized with the GPS time signal and the orthogonal code start timing, and transmitted to the satellite as a CDMA signal.

  FIG. 5 shows details of the orthogonal code generator 22 shown in FIG. When code division multiple access (CDMA) is performed, a sequence satisfying that the number of code sequences that can be generated is large and the cross-correlation value between the generated code sequences is small is desired. One example of satisfying such a condition is an orthogonal gold code. FIG. 5 illustrates, for example, an orthogonal gold code generation circuit described in Non-Patent Document 1. However, the orthogonal code is not limited to the orthogonal gold code, but may be a code obtained by spreading a Walsh code (Walsh Code) often used in a mobile phone system with a PN code.

  In FIG. 5, the M sequence (cycle: N−1) generated by the M sequence generator 61 and the M sequence (cycle: N−1) generated by the M sequence generator 62 are a preferred pair, and a modulo 2 adder 63 is provided. Output gold code sequence (period; N-1). Here, N is the number of chips, and the 0 inserter 64 in FIG. 5 adds 0 to the end of the Gold code sequence generated every period N−1. As a result, the output of the 0 inserter 64 is , An orthogonal Gold code sequence of period N. Further, since the number of orthogonal gold code sequences that can be generated from a given preferred pair is the same as the sequence length, N number of orthogonal gold code sequences can be generated.

  The sequences generated in this way are mutually shifted by 0, that is, mutually orthogonal with a phase difference of 0, and the cross-correlation value can be suppressed to 0. Therefore, when performing code division multiple access (CDMA) using orthogonal codes in satellite communication, in order to orthogonalize CDMA signals spread by orthogonal codes transmitted from each communication terminal 1 on the satellite transponder, It is necessary to control and synchronize the transmission timing of each terminal so that the phase difference between the orthogonal codes transmitted from the terminal 1 is as small as possible within one chip on the satellite transponder.

  For this purpose, a method of controlling the transmission timing of each terminal from the base station as in the method disclosed in Patent Document 2 can be considered. However, when the number of terminals to be accessed increases, the base station and each terminal communicate with each other. The number of control bits becomes enormous, the processing amount of the base station increases, the frequency utilization efficiency deteriorates, control delays occur, and congestion occurs. Therefore, in the invention according to Embodiment 1, in order to synchronize the transmission timing of each communication terminal 1, the chip according to Embodiment 1 described with reference to FIGS. 1 (b), (c), (d), and (e). A clock generation method (and an orthogonal code generation method) is used. The communication terminal (communication system) according to Embodiment 1 will be described assuming that the GPS time signal output from the GPS signal processing unit 32 is used.

  Next, it is examined how much the phase difference within one chip between orthogonal codes should be suppressed. As shown in FIG. 6, it is assumed that a CDMA signal is accessed by two orthogonal codes of a desired signal and an interference signal, and the length of one chip of the orthogonal codes of both signals is Tc, and between the orthogonal codes of both signals Let ΔTc be the phase difference within one chip. However, ΔTc is the range of the following mathematical formula 1.

  Assuming that the period of the orthogonal code is N chips, when the autocorrelation value for one period of the orthogonal code of the desired signal is considered as the signal component (Signal) of the desired signal, the following mathematical formula 2 is obtained.

  Next, consider the cross-correlation value between the desired signal orthogonal code and the interference signal orthogonal code. As shown in FIG. 6, the cross-correlation between these two orthogonal code sequences is divided into two parts. That is, the cross-correlation value of the overlapping part, such as the part other than the shaded part in FIG. .

  On the other hand, the hatched portion is a phase difference portion within one chip, and this portion is correlated with the adjacent code chip, so that the cross-correlation value is random and can be considered as a noise component with respect to the desired signal component. The amount (Noise) of the noise component is expressed by the following mathematical formula 3.

  Therefore, the signal-to-noise ratio of the desired signal is expressed by the mathematical formula 4.

  In Equation 4, 20 * logN / √N can be considered as an S / N ratio due to cross-correlation interference between spreading codes in CDMA that does not use a general orthogonal code.

  20 * logTc / √ (Tc / ΔTc) uses a technique in which an orthogonal code is used for CDMA and the orthogonal code of the CDMA signal of the present invention is synchronized on the satellite with a phase difference within one chip. It can be considered as a degree of improvement of the S / N ratio, and a figure of merit. For example, when ΔTc / Tc = 1/10 chip, the improvement is 10 dB.

  In Equation 4, when the period N = 1024 and ΔTc / Tc = 1/10 chip, Equation 4 is obtained from Equation 4, and the signal-to-noise ratio of the desired signal is 40 dB.

  In the case of ΔTc / Tc = 1/10 chip, assuming that the number of terminals accessing at the same time is 150, and the desired signal receives the interference amount due to the same cross-correlation from all other signals, the signal-to-noise ratio is Since 10 × log (149) ≈22 dB, the signal-to-noise ratio of the desired signal is about 18 dB, which is sufficiently higher than the signal-to-noise ratio (several dB) normally required for satellite communications. .

  For example, if ΔTc / Tc = 1/100 chip, the signal-to-noise ratio of the desired signal is 50 dB as described above. In the case of ΔTc / Tc = 1/100 chip, even if there is the number of simultaneous access terminals equal to the number 1024 of orthogonal code sequences in the period 1024, the signal-to-noise ratio is degraded by about 30 dB, and the desired signal The signal-to-noise ratio is about 20 dB. However, the above corresponds to a case where all other interference signals are shifted by 1/10 chip or 1/100 chip with respect to one desired signal, and the desired signal receives interference from all other interference signals. It is the worst case, and in fact, a better signal-to-noise ratio can be obtained. Therefore, as described above, a chip clock having a length of one chip longer than a predetermined time accuracy (time accuracy) may be used.

  Next, a specific system parameter is assumed and examined. In general, the information rate of the return link in satellite communication is limited by the transmission power of the terminal. For example, even when considering the size of a mobile phone as a terminal, message communication with an information rate of about 50 bps is possible. it is conceivable that. Considering an error correction code with a coding rate of 1/2, when spreading with an orthogonal code having a code sequence length of 1024 chips, the chip rate of the orthogonal code is 50 × 2 × 1024 = 102.4 kcps, and the length of one chip is This is about 10 μsec. Since the time accuracy of the GPS time signal can be 0.1 μsec to 1 μsec, ΔTc / Tc of each terminal transmission signal can be synchronized within 1/100 chip to 1/10 chip.

  From the above, the communication system (communication terminal, communication method) according to Embodiment 1 is particularly effective for CDMA using low-speed chip rate orthogonal codes. That is, it is effective for CDMA using orthogonal codes having a chip rate such that the duration of one chip is sufficiently longer than the GPS time accuracy. In other words, this can be said to be one chip longer than a predetermined time accuracy (time accuracy).

  As an application example to which CDMA by such low-speed chip rate orthogonal code can be applied, for example, a rescue message service by a short message by a quasi-zenith satellite as described above can be considered. The reason is that the minimum information necessary for the rescue message is the ID and position information of the distress (the communication terminal 1 holder), so the number of information bits is small, and therefore the information rate of the message may be lowered. This is because the chip rate of orthogonal codes can be reduced.

  Also, in the event of a large-scale disaster, rescue messages are sent almost simultaneously from a large number of victims. Therefore, in order to secure as much line capacity as possible, it is necessary to reduce the cross-correlation interference between codes by CDMA as much as possible. Therefore, a technique for synchronizing the orthogonal codes of the respective communication terminals 1 according to the present invention within one chip is effective. Specifically, in the communication terminal (communication system) according to Embodiment 1, the second information acquisition unit 310 acquires time information having a predetermined time accuracy, and the transmission timing generation unit 23 has a predetermined time accuracy. A chip clock consisting of a longer one chip is generated.

  FIG. 7 shows a waveform example of each part of the transmission circuit in the block diagram of the communication terminal 1 of FIG. 2, and shows how these waveforms are synchronized with the GPS time signal (second signal, 1 PPS). In FIG. 7, the GPS time signal is the output waveform of the GPS signal processing unit 32, the orthogonal code and the chip clock are the output waveform of the orthogonal code generation unit 22, the error correction encoded data is the output waveform of the error correction encoding unit 20, The data after spreading indicates the output waveform of the CDMA spreading unit 21. In FIG. 7, one period (N chips) of orthogonal code C1 (t) and data D1 (t) after error correction coding are synchronized and modulo 2 is added to obtain data after CDMA spreading.

  FIG. 8 shows the outputs of the orthogonal code generator 22 in FIG. 2 of the communication terminal 1-1 and the communication terminal 1-2, and the orthogonal code A and the communication terminal 1-2 respectively transmitted by the communication terminal 1-1 and the communication terminal 1-2. The state that the orthogonal code start timing of the orthogonal code B is synchronized with the GPS time signal at the chip clock level is shown. However, in FIG. 8, it is assumed that there is no phase difference between orthogonal codes due to the time accuracy of the GPS time signal. The circuits are configured such that the delay times of the transmission circuits after the CDMA spreading unit 21 in both communication terminals 1 are equal, and the positions of both communication terminals 1 are close to each other and the distance from both communication terminals 1 to the satellite transponder. When there is no difference, the timing relationship between the orthogonal code A and the orthogonal code B shown in FIG. 7 is maintained on the satellite transponder, and the cross-correlation value between the orthogonal codes A and B is zero.

  Next, details of the processing of S106 in FIG. 4 will be described below. FIG. 9 shows the relationship between the ground position of the terminal and the distance to the quasi-zenith satellite. In FIG. 9, for simplification of calculation, it is assumed that the quasi-zenith satellite S (satellite 3) is located at akm just above the reference ground position A point. The terminal position B is dkm away from the point A, the distance from the quasi-zenith satellite S is bkm, the radius of the earth is rkm, and the points A and B viewed from the earth center O are Assuming that the angle formed is θrad, the following mathematical formula 6 is established from the cosine theorem.

  Here, since the earth radius r is sufficiently larger than the distance between the points A and B, the following mathematical formula 7 is established. Therefore, the mathematical formula of Formula 6 becomes the mathematical formula of Formula 8.

  Therefore, when a = 39,000 km and r = 6400 km, for example, when d = 30 km, when the speed of light is c = 300,000 km / second, the delay time difference τ is τ = (b−a) / c = 0. In the case of .27 μsec and d = 200 km, τ = (ba) /c=12.1 μsec.

  Using the above system parameters, the chip rate of orthogonal code is about 100 kcps, so the duration of one chip is about 10 μsec. Suppose that a terminal located at point A and a terminal located at point B in FIG. 9 simultaneously transmit CDMA signals based on orthogonal codes toward the satellite. The difference in delay time to the satellite between the two terminals is 2.7 / 100 chips from the above result when d = 30 km, which is very small and can be ignored. However, when d = 200 km, the difference is 1.21 chips. Thus, the delay time difference to the satellite becomes larger than one chip, and orthogonality between orthogonal codes cannot be ensured on the satellite transponder. Therefore, the terminal needs to compensate for the delay time difference to the satellite according to the position of the terminal. The processing contents will be described below using the communication terminal (communication terminal) 1 according to the first embodiment.

  As shown in FIG. 10, it is assumed that the non-geostationary satellite S is constantly moving on the satellite orbit with respect to the ground surface, and the latest orbit can be predicted by the latest satellite orbit information downloaded from the base station. Suppose that Here, the satellite orbit information is a parameter that represents the orbit of the artificial satellite.For example, as the orbital element of the artificial satellite, the original period, the average motion, the eccentricity, the orbit inclination angle, the ascending intersection red longitude, There is an angle, an average near point angle.

  First, as shown in FIG. 11, the orbit information receiving unit 17 (first information acquiring unit 17) of the communication terminal 1 receives the latest satellite orbit information from the base station 2 (S201), and then in a memory (not shown). The satellite orbit information is constantly updated (S202). As shown in FIG. 12, the delay time calculation unit 29 of the communication terminal 1 reads the satellite orbit information in the memory in S301. Here, the orbit information of the satellite uses the latest orbit information downloaded from the base station to each terminal through the forward link line, but the default orbit information stored in the memory in advance may be used. .

  For simplification of calculation, using the fact that the quasi-zenith satellite is always near the zenith, instead of the orbit information of the satellite, as shown in FIG. 9, the position of the satellite is approximately the reference ground position. It may be calculated that it exists at a fixed altitude above the zenith direction. In this case, the delay time difference from the reference ground position and the own terminal position to the satellite can be calculated using the above mathematical formula (8). Furthermore, when the non-stationary satellite 3 is a quasi-zenith satellite and the quasi-zenith satellite has a GPS satellite function, the satellite orbit information may be acquired from a GPS signal transmitted by the quasi-zenith satellite. In this case, it can be said that the first information acquisition unit 17 (orbit information reception unit 17) has the function of the second information acquisition unit 310. Specifically, since the GPS antenna 30 and the GPS receiver 31 constituting the second information acquisition unit 310 correspond to the satellite communication antenna 11 and the wireless reception unit 13, respectively, the orbit information reception unit 17 receives the GPS signal. It can be said that it has the function of the processing unit 32.

  Next, in S302, the delay time calculation unit 29 inputs the GPS position data (latitude, longitude, altitude) of the own terminal (communication terminal 1) from the GPS signal processing unit 32. In S303, the distance b from the own terminal (communication terminal 1) to the satellite 3 is calculated from the satellite orbit information and the GPS position data. Next, in S304, the delay time calculation unit 29 reads the reference ground position data stored in the memory. In S305, the distance a from the reference ground position to the satellite 3 is calculated from the satellite orbit information and the reference ground position data.

  Further, in S306, the delay time calculation unit 29 calculates the distance difference b−a and divides by the speed of light c to calculate the delay time difference τ. In S307, the delay time difference τ is set in the delay correction unit 24. To do. Here, when the distance b between the position of the terminal (communication terminal 1) and the satellite 3 is shorter than the distance a between the reference position and the satellite 3, the sign of τ is negative (that is, the signal is an absolute value τ). Minutes later than the GPS time signal).

  Conversely, if the distance from the terminal (communication terminal 1) to the satellite 3 is longer than the distance from the reference ground position to the satellite 3, the sign of τ is positive (that is, the signal is the absolute value τ minutes GPS time). It is advanced from the signal). However, since the orbit information of the satellite 3, the distance a from the reference ground position to the satellite 3, and the distance b from the own terminal (communication terminal 1) to the satellite are all functions of time, the delay time difference τ is also a function of time. Therefore, it is necessary to predict τ at the time when the communication terminal transmits the CDMA signal to the satellite and set it in the delay correction unit 24.

  In the above description, the case where the delay time difference τ is positive (that is, the signal is advanced from the GPS time signal by the absolute value τ) is considered, but in this case, the control becomes complicated. Therefore, if the reference ground position is always a ground position where the distance difference ba is 0 or negative, and the sign of τ is always negative (that is, the signal is always delayed from the GPS time signal by the absolute value τ), the delay There is an effect that the control for setting the time is simplified.

  In the above description, the distance a from the reference terminal position and the satellite 3 and the distance b from the own terminal (communication terminal 1) to the satellite 3 are calculated, and the distance difference ba is calculated. The distance a to the satellite 3 may be a default fixed value. Thereby, the calculation can be simplified.

  Furthermore, in the above, the distance b between the terminal (communication terminal 1) and the satellite 3 is calculated using the orbit information of the satellite 3 and the GPS position data of the terminal (communication terminal 1). When the geostationary satellite is a quasi-zenith satellite and the quasi-zenith satellite has a GPS satellite function, when calculating the GPS position data of the terminal from the GPS signal transmitted by the quasi-zenith satellite, the own terminal and the satellite Therefore, this value may be used as the distance b between the terminal and the satellite. Thereby, the calculation can be simplified.

  As described above, each communication terminal 1 adjusts the delay time with respect to the GPS time signal of the CDMA signal transmitted from the terminal itself, thereby synchronizing the orthogonal codes of the CDMA signals transmitted from the communication terminals on the satellite transponder. Therefore, the communication terminal 1 generates a transmission timing that synchronizes the transmission timing of the transmission signal to be transmitted to the satellite 3 between the plurality of communication terminals 1-n. When the transmission signal generated by the generation unit 23, the transmission signal generation unit 180 that generates the transmission signal, and the transmission signal generated by the transmission signal generation unit 180 is transmitted to the satellite 3 at the transmission timing, it is generated due to the distance between the communication terminal 1 and the satellite 3. The plurality of communication terminals 1-n each compensate for the delay of the transmission signal depending on the distance from each satellite 3. It can be said that is intended to.

Next, details of the processing of S107 in FIG. 4 will be described below. First, it will be described that when there is a deviation in the carrier frequency of the CDMA signal transmitted by each communication terminal 1, the cross-correlation between orthogonal codes is adversely affected. Now, a modulated wave BPSK-modulated with the orthogonal code C ₁ (t) transmitted by the communication terminal 1-1 is represented by the following mathematical formula 9.

Similarly, a modulated wave in which the orthogonal code C ₂ (t) transmitted by another communication terminal 1-2 is BPSK-modulated is expressed by the following equation (10).

Here, A and B are carrier wave amplitudes, f ₁ and f ₂ are carrier wave frequencies, and θ ₁ and θ ₂ are carrier wave phases. However, for simplification, it was assumed that there was no data modulation. On the satellite transponder, the above two signals are added together to obtain the following equation (11).

  In the CDMA despreading / demodulation on the base station receiving side, when demodulating the signal from the communication terminal 1-1, the following equation 12 is multiplied by the equation 11 to obtain a correlation.

The result of the correlation is expressed by the following equation (13).

Here, T is the time for correlation, and is an integral multiple of the period of the orthogonal code. For simplification of explanation, A = B = 1 and the harmonic component is ignored because it is filtered. The first term of Equation 13 is the desired signal, and the second term is the intersymbol interference component. The second term of Equation (13) is 0 when f ₁ = f ₂ , that is, when there is no frequency deviation between both carriers, C ₁ (t) and C ₂ (t) are orthogonal codes, and thus 0. . However, if f ₁ ≠ f ₂ , the second term of Equation 13 is not 0 and an interference component due to cross-correlation remains. Therefore, it is necessary to reduce the carrier frequency deviation of the CDMA signal transmitted by each communication terminal 1 and to reduce the cross-correlation between orthogonal codes.

  In general, in satellite communication, a terminal receives a forward signal in which the local frequency deviation of the satellite transponder is compensated on the base station side from the base station, and uses the received carrier frequency of the forward signal as a reference to return link of its own terminal. By generating the carrier frequency of the signal, the carrier frequency deviation of the return link signal transmitted by the terminal is reduced.

  In the case of a non-stationary satellite, the non-stationary satellite moves relative to the base station, thereby causing a Doppler frequency shift in the carrier wave of the forward link signal, and this frequency shift is common to each terminal. The Doppler frequency shift of the forward link signal carrier due to the relative movement of the satellite to the base station can also be compensated on the base station side. The carrier frequency compensation of the forward link signal on the base station side can be achieved by returning the pilot signal to the satellite on the base station side, and details of the method are described in Patent Document 3.

  However, the Doppler frequency shift of the forward link signal due to the relative movement of the non-stationary satellite relative to the terminal and the Doppler frequency shift of the return link signal due to the relative movement of the non-stationary satellite relative to the terminal Since the magnitudes of the Doppler frequency shifts are different if the geographical positions of the base stations are different from each other, the base station cannot compensate.

  Therefore, in the first embodiment, in order to reduce the carrier frequency deviation of the CDMA signal transmitted from each communication terminal 1 and to reduce the cross-correlation between orthogonal codes, each communication terminal 1 side has the communication terminal 1. A method of transmitting a return link signal having a small carrier frequency deviation between each communication terminal 1 by compensating for a carrier Doppler frequency shift between the non-stationary satellite and the terminal due to the movement of the non-stationary satellite based on the geographical position of Used. In the first embodiment, each communication terminal 1 is not moving or is moving slowly even if it is moving, and the Doppler frequency shift of the carrier with respect to the non-stationary satellite due to the movement of the communication terminal 1 is ignored. It is supposed to be possible.

FIG. 13 shows the Doppler frequency shift of the carrier frequency of the communication terminal 1. Now, it is assumed that the communication terminal 1-n exists at the geographical position Pn. Here, it is assumed that the communication terminal 1-n is stationary on the ground surface and the moving speed of the terminal VT _n = 0.

  Now, assume that the carrier frequency of the received forward link signal of the communication terminal 1-n is Frn and the speed of light is C. Further, the center frequency of the forward link signal carrier frequency received by the communication terminal 1-n is assumed to be Fro. However, as described above, the local frequency deviation of the satellite and the Doppler frequency deviation due to the relative movement of the non-stationary satellite to the base station are compensated on the base station transmission side. Is not included. From FIG. 13, the Doppler frequency shift ΔFro1 corresponding to the received carrier wave in the terminal direction due to satellite movement is expressed by the following equation (14).

However, ΔFro1 is positive when the satellite 3 and the communication terminal 1 approach each other.
Therefore, the carrier frequency Frn of the received forward link signal of the communication terminal 1-n is expressed by the following equation (15).

  The communication terminal 1-n first obtains the relative moving speed VSn at which the non-stationary satellite moves with respect to the communication terminal 1 based on the satellite orbit information and the GPS position data of the terminal, and then corresponds to the received carrier center frequency from the above equation. A Doppler frequency shift ΔFro1 is obtained by calculation. Next, as illustrated in FIG. 14, in the frequency subtracter 71, the communication terminal 1-n generates Fro according to the following equation 16 using the carrier frequency Frn of the received forward link signal as a reference.

  That is, the Doppler frequency shift ΔFro1 corresponding to the received carrier center frequency is compensated. If the ratio of the carrier center frequency Fro of the received forward link signal to the carrier center frequency Fto of the transmission return link signal is Rrt, the frequency multiplier 72 can generate Fto by the following equation (17).

  Here, Rrt is a preset value. Next, from FIG. 13, a Doppler frequency shift ΔFto1 corresponding to the transmission carrier center frequency is obtained by calculation (Formula 18). However, ΔFto1 is positive when the satellite 3 and the communication terminal 1 approach each other.

Further, in the frequency subtractor 73, the following equation 19 is used.

  By obtaining Ftn, the Doppler frequency shift ΔFto1 corresponding to the transmission carrier center frequency can be compensated. That is, when the communication terminal 1-n transmits a return link signal having a carrier frequency of Ftn given by the above equation, when the return link signal is received by the satellite transponder, Therefore, the carrier frequency Ftn ′ of the return link signal received from the communication terminal 1-n on the satellite transponder is expressed by the following equation (20).

  Therefore, the carrier frequency deviation between the return link CDMA signals transmitted by each communication terminal 1 on the satellite transponder becomes almost zero, and the deterioration due to the orthogonal carrier frequency deviation between the orthogonal codes transmitted by each communication terminal 1 is reduced. Can do.

  FIG. 15 shows a Doppler frequency shift compensation flowchart of the carrier frequency in the communication terminal 1-n, and these processes are mainly performed in the carrier generation unit 26 and the Doppler frequency calculation unit 28 of FIG. First, in S401, the Doppler frequency calculation unit 28 reads the satellite orbit information in the memory, and in S402, inputs the GPS position data of the own terminal (communication terminal 1) from the GPS signal processing unit 32. Further, in step S403, the Doppler frequency calculation unit 28 calculates the speed VSn of the non-stationary satellite in the direction of its own terminal (communication terminal 1) from the satellite orbit information and the GPS position data. In step S404, the Doppler frequency calculation unit 28 uses the VSn. Then, a Doppler frequency shift ΔFro1 corresponding to the carrier center frequency Fro of the forward link signal is calculated.

  Next, in S405, the carrier generation unit 26 generates the carrier center frequency Fro of the forward link signal from Fro = Frn−ΔFro1 from the carrier frequency Frn of the received forward link signal input from the QPSK demodulation unit 14. Further, in step S406, the carrier generation unit 26 generates the carrier center frequency Fto of the transmission return link signal by Fto = Fro × Rrt. Next, in S407, the Doppler frequency calculation unit 28 calculates the carrier center frequency ΔFto1 of the return link signal using the speed VSn of the non-geostationary satellite in the direction of its own terminal. Finally, in S408, the carrier wave generator 26 compensates for the Doppler frequency shift corresponding to the transmission carrier center frequency Fto of the return link from Ftn = Fto−ΔFto1.

  Here, when the operations of the communication system and the communication terminal according to Embodiment 1 are summarized, an orthogonal code generation unit 22 in which the communication terminal 1 generates an orthogonal code, a second information acquisition unit 310 that acquires time information from the outside, and , Generating a chip clock based on the time information acquired by the information acquisition unit 310, and using the chip clock as a reference for the generation timing of the orthogonal code by the orthogonal code generation unit 22, and an orthogonal code generation unit The basic configuration is such that the transmission signal to be transmitted to the satellite 3 is spread by the orthogonal code generated by the line 22 and the CDMA spreading unit 21 generates a CDMA signal.

  Further, the delay processing unit 240 of the communication terminal 1 derives the distance to the satellite 3 from the position information of the communication terminal 1, calculates the delay time (delay time calculation unit 29), and transmits the transmission signal from the calculated delay time. Correction (delay correction unit 24) may be performed. Further, the Doppler frequency processing unit 250 of the communication terminal 1 may correct the frequency shift due to the Doppler frequency shift of the transmission signal from the change in the relative distance between the satellite 3 and the communication terminal 1.

  Here, the short message communication system (short message method) and the short message communication terminal according to the first embodiment will be described. First, the short message communication system according to Embodiment 1 receives a forward link signal transmitted by a base station 2 that transmits a forward link signal, and transmits a transmission signal including the short message to the base station 2 as a return link signal. A plurality of short message communication terminals 1-n and a satellite 3 that relays communication between the base station 2 and the plurality of short message communication terminals 1-n. Is used to synchronize the generation timing of orthogonal codes between the plurality of short message communication terminals 1-n.

  Specifically, the short message communication terminal 1 uses the orthogonal code generation unit 22 that generates orthogonal codes, the information acquisition unit 310 that acquires predetermined time accuracy from the outside, and the time information acquired by the information acquisition unit 310 as a reference. A chip clock having a length of one chip longer than a predetermined time accuracy is generated, and a transmission signal is generated with a transmission timing generator 23 using the chip clock as a reference for the generation timing of the orthogonal code by the orthogonal code generator 22. Transmitting signal generator 180, CDMA spreading section 21 that generates a CDMA signal by spreading the transmission signal generated by transmission signal generator 180 using the orthogonal code generated by orthogonal code generator 22, and CDMA signal to satellite 3. A delay processing unit 240 for correcting a delay caused by the distance between the short message communication terminal 1 and the satellite 3 when transmitting, and a carrier wave The carrier generation unit 26 to be generated, the modulation unit 25 that modulates the CDMA signal corrected by the delay processing unit 240 using the carrier generated by the carrier generation unit 26, and the CDMA signal modulated by the modulation unit 25 to the satellite 3 And a transmitting unit 27 for transmitting to.

  The short message communication terminal 1 also includes a Doppler frequency calculation unit 28 that calculates a frequency shift due to a Doppler frequency shift of the CDMA signal from a change in the relative distance between the satellite 3 and the short message communication terminal 1. 26 compensates the frequency shift due to the Doppler frequency shift calculated by the Doppler frequency calculation unit 28 with the frequency of the carrier wave. Furthermore, the delay processing unit 240 of the short message communication terminal 1 derives the distance to the satellite 3 from the position information of the short message communication terminal 1, and the delay time calculation unit 29 for calculating the delay time and the delay time calculation unit 29 include The delay correction unit 24 corrects the transmission signal from the calculated delay time.

  In the event of a disaster, the user terminal (mobile terminal 1) that has received the forward link signal transmitted from the base station 2 sends a rescue message, emergency message, rescue signal, etc. including location information to the return link signal (transmission). As a signal), whether to transmit to the service center 6 via the base station 2 using a satellite line may be determined on the user terminal (mobile terminal 1) side, or a forward link signal is received. In this case, a return link signal (transmission signal) may be forcibly transmitted.

Embodiment 2. FIG.
A second embodiment of the present invention will be described with reference to FIGS. The description will focus on the parts different from the first embodiment, and the description of the parts common to the first embodiment may be omitted. In the drawings, the same reference numerals denote the same or corresponding parts, and detailed descriptions thereof are omitted. In Embodiment 1, the start timing of the orthogonal code is synchronized with the GPS time signal at the chip clock level, and each communication terminal 1 randomly transmits the CDMA signal on the burst toward the non-stationary satellite (3). However, in the second embodiment, the communication terminal further transmits the data on the burst subjected to CDMA spreading to the satellite in a slot on the time axis, thereby enabling satellite communication access by the so-called slotted ALOHA system. To improve throughput. At this time, the communication terminal 1 not only synchronizes the start timing of the orthogonal code with the GPS time signal at the chip clock level, but also synchronizes the slot timing with the GPS time signal, thereby synchronizing the slots between the terminals. To make it easier.

  That is, the communication signal (short message communication system), the communication terminal (short message communication terminal), and the communication method (short message communication method) according to the second embodiment are generated by the transmission signal generation unit 180 and the transmission timing generation unit 23. The CDMA signal modulated by the modulation unit 25 is transmitted to the satellite 3 at the slot timing with the chip clock as a reference, or the transmission signal generation unit 180 uses the time information acquired by the information acquisition unit 310 as a reference, A chip clock having a length of one chip longer than a predetermined time accuracy is generated, and a CDMA signal modulated by the modulation unit 25 is transmitted to the satellite 3 at a slot timing with the chip clock as a reference. The message communication terminal 1-n sets the slot timing to a plurality of short messages. It is intended to synchronize between sage communication terminal 1-n.

  The structure of the communication terminal 1 which concerns on Embodiment 2 is shown to Fig.16 (a) (b). The configuration of the entire system has a configuration corresponding to FIG. 1 and FIG. 2 described in the first embodiment. In addition to the configuration and operation of the portion particularly described in the second embodiment, the configuration of the embodiment is as follows. 1 has a configuration and operation corresponding to the configuration and operation of the portion described in FIG. The communication terminal 1 described in FIG. 16A and FIG. 16B is that the Doppler frequency calculation unit 28 is omitted from the communication terminal 1 described in FIG. That is, when compensation for frequency deviation is not necessary, the configuration shown in FIG.

  The configuration of base station 2 according to Embodiment 2 is shown in FIG. The configuration of the entire system has a configuration corresponding to FIG. 1 and FIG. 2 described in the first embodiment. In addition to the configuration and operation of the portion particularly described in the second embodiment, the configuration of the embodiment is as follows. 1 has a configuration and operation corresponding to the configuration and operation of the portion described in FIG. Specifically, FIG. 17A is a configuration diagram showing a configuration of a communication system (short message communication system) according to the second embodiment, and FIG. 17B is a chip clock used for the chip clock generation method according to the second embodiment. 1 is a functional block diagram of a generation unit (reception timing generation unit, information acquisition unit), FIG. 1C is a flowchart of chip clock generation (generation), and FIG. 1D is a flowchart of chip clock generation (generation) (S001 omitted). It is.

  The configuration of base station 2 according to Embodiment 2 shown in FIG. The following configuration is added to the base station 2 according to the second embodiment with respect to the configuration of the base station 2 according to the first embodiment shown in FIG. In FIG. 17A, the base station 2 receives the GPS signal 10 from the GPS satellite 4 by the GPS antenna 30 and the GPS receiver 31 in the same manner as the communication terminal 1. The GPS signal processing unit 32 processes the received GPS signal 10 and outputs a GPS time signal to the reception timing generation unit 55.

  The reception timing generation unit 55 uses the satellite orbit information from the ground interface unit 41, the base station position from the input terminal 56, and the reference ground position, and uses the GPS time signal from the GPS signal processing unit 32 as a reference, and the reference ground position The chip clock, the orthogonal code start timing, and the slot timing delayed by the delay time from the non-stationary satellite to the base station reception are generated. The CDMA despreading unit 51 predicts the temporal position of the signal transmitted from the communication terminal 1 based on the chip clock, the orthogonal code start timing, and the slot timing, and performs CDMA despreading.

  As described above, the reception timing generation unit 23 generates a clock signal and a timing signal to each unit synchronized with the GPS time signal from the GPS signal processing unit 32. Specifically, the chip clock generation unit (reception timing generation unit 55, information acquisition unit 310) shown in FIG. 1B and the chip clock generation method according to the first embodiment shown in FIGS. It explains using.

  In FIG. 17C, S002 (S represents a step) is to generate a chip clock consisting of one chip longer than a predetermined time accuracy (clock generation step). Prior to S002, S001 (acquisition step) for acquiring time information having a predetermined time accuracy may be performed. In S003 (determination step), the chip clock start timing in S002 (clock generation step) is determined from the time information (which may be acquired from the GPS satellite 4 in S001).

  Then, instead of starting the chip clock at the timing determined in S003, a predetermined delay time is added to finally determine the chip clock start timing in S005. This is a point in which the timing determination step is different from that described in the first embodiment. The reason is that, as described above, the transmission signal (return link signal) from the communication terminal (terminal) is delayed by the delay time from the reference ground position to the reception of the base station via the non-geostationary satellite, This is because it is necessary to generate orthogonal code start timing and slot timing.

  That is, the predetermined delay time means a delay time from reception of a transmission signal (return link signal) from a communication terminal (terminal) to reception of a base station via a non-stationary satellite from a reference ground position. Note that S001 may acquire time information from the GPS satellite 4. The detailed description of the chip clock consisting of one chip longer than the predetermined time accuracy is as described in the first embodiment. Note that in the chip clock generation method, S001 may be omitted as shown in FIG. 1D as long as time information having a predetermined time accuracy can be acquired in advance.

  Next, a communication method according to the second embodiment (note that the satellite communication access method of the second embodiment relates to a communication method between a plurality of communication terminals and a base station) will be described. In the communication method according to Embodiment 2, the plurality of communication terminals 1 synchronize the generation timing and slot timing of the orthogonal code by the orthogonal code generation unit 24 between the plurality of communication terminals 1-n from the time information. .

  In FIG. 18, the communication terminal 1-1, the communication terminal 1-2, and the communication terminal 1-3 respectively transmit a burst signal spread by CDMA according to the chip clock, the orthogonal code start timing, and the slot timing synchronized with the GPS time. Randomly transmit to the slot. That is, by transmitting the chip clock, orthogonal code start timing, and slot timing generated by the transmission timing generation unit 23 to the data generation unit 19, the error correction encoding unit 20, and the CDMA spreading unit 21, respectively, the CDMA spread burst signal is transmitted. , Send randomly in time slots.

  Thereby, random access by the slotted ALOHA system in which the phase between orthogonal codes of the CDMA signal transmitted by each communication terminal 1 is controlled to be a phase difference within one chip is realized. The table (example of transmission parameters of communication terminal 1 (short message terminal 1)) shown in FIG. 19 illustrates parameters for data burst transmission of typical communication terminal 1 of the second embodiment.

  In the example of the transmission parameter in the table shown in FIG. 19, the synchronization of the slot with the GPS time signal is performed as follows, for example. A slot is generated every 2.5 seconds with reference to 00 seconds per minute of the GPS time signal. Therefore, 24 slots can be generated in one minute. Similarly, when the start time of the orthogonal code is based on 00 seconds per minute, an orthogonal code of 250 cycles can be generated in one slot.

  FIG. 20 is a diagram showing an operation flow of the transmission timing generation unit 23 of FIG. 16 (FIG. 17) in the second embodiment. 20, S501 to S503 are the same operations corresponding to S101, S104, and S105 shown in FIG. 4 in the first embodiment, respectively, but in the second embodiment, in S504, the operation is synchronized with the GPS time signal. Generate time slot start timing. Thereby, the transmission slot timing of each communication terminal 1 can be easily synchronized between the communication terminals 1. In FIG. 20, the explanation of the steps corresponding to S102 and S103 in FIG. 4 and the steps after S106 is omitted with priority given to the understanding of the features of the second embodiment. I will explain.

  FIG. 21 is an operation flow of the communication terminal, and steps denoted by the same numbers as those in FIG. 4 have the same functions as those in the first embodiment. In S601, a slot timing signal synchronized with the GPS time signal is generated, and in S602, one of the transmission slots is randomly selected. As a method of selecting at random, there is, for example, a method of randomly generating a waiting time until a slot to be actually transmitted. In S603, the data is spread by the orthogonal code selected in S105, and transmitted as a CDMA burst signal toward the satellite in the transmission slot.

  FIG. 21 shows a method of randomly selecting one of the transmission slots and one of the orthogonal codes to perform random access. However, one of a plurality of FDMA frequency channels is selected at random. Then, random access may be performed using the selected transmission slot, orthogonal code, and frequency channel. This operation is performed by the transmission signal generator 180. As a result, the collision of random access bursts does not occur unless the transmission slot, orthogonal code, and frequency channel all match, so the collision probability of random access bursts can be further reduced. There is an effect that the throughput can be increased.

  Next, the receiving side of the base station 2 according to Embodiment 2 will be described. As shown in FIG. 22, the chip clock synchronized with the GPS time of the CDMA signal transmitted from the communication terminals 1-1 to 1-3, the orthogonal code start timing (not shown), and the transmission slot timing are , A round trip delay time D to the non-geostationary satellite is received. As shown in the first embodiment, the delay time difference due to the difference in the position of each communication terminal 1 in the return link is compensated for in each terminal transmission. Therefore, on the base station 2 side, the satellite round-trip time from the reference ground position The delay time D seconds can be estimated by calculating.

  For example, when a quasi-zenith satellite is used as a non-geostationary satellite, if the quasi-zenith satellite is located at 36,000 km directly above the reference ground position, and the base station is at the same geographical position as the reference ground position, the delay Time D is calculated to be 0.24 seconds. When the delay due to the satellite transponder or the delay due to the base station reception system cannot be ignored, the delay time can be measured in advance and added to the delay time D for calculation.

  Therefore, the base station 2 also receives a GPS signal from the GPS satellite 4 to generate a GPS time signal, and if the chip clock, the orthogonal code start timing and the slot timing generated in synchronization therewith are delayed by D seconds, The chip clock, orthogonal code start timing, and slot timing of the CDMA signal received from each communication terminal 1 can be easily estimated on the base station receiving side, and the orthogonal code, chip clock, and burst signal are captured by the CDMA despreading unit 51. And has the effect of speeding up synchronization. Needless to say, delaying the chip clock, the orthogonal code start timing, and the slot timing by D seconds corresponds to the predetermined delay time described above.

  FIG. 23 is a diagram illustrating an operation flow of the reception timing generation unit 55 of the base station 2 illustrated in FIG. 17. First, a GPS time signal is input from the GPS reception processing unit 32 in S701. Next, in S702, a chip clock, an orthogonal code start timing, and a slot timing synchronized with the GPS time signal are generated. Next, in S703, a delay time from the reference ground position to reception of the base station via the non-stationary satellite is calculated using the satellite orbit information, the reference ground position, and the base station position. Here, the satellite orbit information is input from the ground interface unit 41 in FIG. 3, and the reference ground position and the base station position are input from the input terminal 53. The reference ground position and the base station position may be stored in advance in a memory (not shown).

  In S704, the chip clock, orthogonal code start timing, and slot timing are delayed by the delay time, and these timing signals are output to the CDMA despreading unit 51 in S705. In the CDMA despreading unit 51, in order to despread the CDMA burst signal from each communication terminal 1, it is necessary to estimate the chip clock, the orthogonal code start timing, and the burst timing from the received signal. By using the clock, orthogonal code start timing, and slot timing, the processing required for the above estimation can be reduced, and therefore the time required for estimation can be shortened, so that the acquisition and synchronization of the orthogonal code, chip clock, and burst signal can be accelerated. There is.

  As described above, in the second embodiment, the communication terminal 1 transmits the data on the CDMA spread burst to the satellite at random in the slot on the time axis, so that the so-called slotted ALOHA system is used. Through satellite communication access, throughput can be improved. Furthermore, if one of a plurality of frequency channels subjected to FDMA is randomly selected and random access is performed using the selected transmission slot, orthogonal code, and frequency channel, the random access throughput can be further increased.

  Further, the communication terminal 1 not only synchronizes the start timing of the orthogonal code with the GPS time signal at the chip clock level, but also synchronizes the slot timing with the GPS time signal, so that the slots can be easily synchronized between the terminals. Can be taken. Furthermore, on the base station receiving side, the chip clock, the orthogonal code start timing, and the slot timing are delayed by a delay time (predetermined delay time) from the reference ground position to the reception of the base station via the non-geostationary satellite. This has the effect of speeding up the capture and synchronization of the clock and burst signals.

Embodiment 3 FIG.
A third embodiment of the present invention will be described with reference to FIGS. A description will be given mainly of parts different from the first and second embodiments, and description of parts common to the first and second embodiments may be omitted. FIG. 24A is a functional block diagram of the communication terminal according to the third embodiment, and FIG. 24B is a schematic diagram of the communication system according to the third embodiment. In the drawings, the same reference numerals denote the same or corresponding parts, and detailed descriptions thereof are omitted. In the first embodiment, the Doppler frequency shift due to the velocity VSn in the position direction of the communication terminal 1-n of the moving speed of the non-stationary satellite in FIG. 13 is compensated. In the third embodiment, the communication terminal in FIG. It also compensates for the Doppler frequency shift due to the velocity VTns in the non-geostationary satellite direction with 1-n moving velocity.

  That is, in the communication system (short message communication system) and the communication terminal (short message communication terminal) according to Embodiment 3, the Doppler frequency calculation unit 28 calculates the Doppler frequency shift from the moving speed of the communication terminal 1. Alternatively, the Doppler frequency calculation unit 28 calculates the Doppler frequency shift from the moving speed of the communication terminal 1 and the moving speed of the satellite 3.

  Specifically, the communication terminal 1 has a moving speed detector 33 that detects a moving speed, and the Doppler frequency calculator 28 calculates a Doppler frequency shift from the moving speed detected by the moving speed detector 33. is there. Note that the communication terminal 1 has an orbit information receiving unit 17 (moving speed acquiring unit 17) that acquires the moving speed of the satellite 3 from the outside, as in the first and second embodiments, and the Doppler frequency calculating unit 28 includes: The Doppler frequency shift may be calculated from the movement speed acquired by the movement speed acquisition unit 17.

  The configuration of the communication terminal 1 according to Embodiment 3 is shown in FIG. The configuration of the entire system and the base station 2 corresponds to FIGS. 1 to 3 described in the first embodiment, and corresponds to FIGS. 16 and 17 described in the second embodiment. In addition to the configuration and operation of the portion particularly described in the third embodiment, the configuration and operation corresponding to the configuration and operation of the portion described in the first and second embodiments are provided.

  A configuration of the communication terminal 1 according to Embodiment 2 shown in FIG. The following configuration is added to the configuration of the communication terminal 1 according to the third embodiment with respect to the configuration of the communication terminal 1 according to the first embodiment shown in FIG.

  The movement speed calculation unit 33 calculates the movement speed and movement direction of the communication terminal 1 based on the GPS position data output from the GPS signal processing unit 32 and outputs the calculated movement speed and direction to the Doppler frequency calculation unit 28. The Doppler frequency calculation unit 28 uses the satellite orbit information from the orbit information reception unit 17, the GPS position data from the GPS signal processing unit 32, the terminal movement speed data from the movement speed calculation unit 33, and the terminal movement direction data. The Doppler frequency shift corresponding to the RF carrier frequency generated by the movement of the geostationary satellite and the communication terminal is calculated.

FIG. 25 shows a Doppler frequency shift compensation block diagram of the carrier frequency in the communication terminal according to the third embodiment. 25 differs from the first embodiment in FIG. 14 in that ΔFro1 and ΔFto1 in FIG. 14 are ΔFro1 + ΔFro2 in FIG.
This is a point that is replaced by ΔFto1 + ΔFto2. Here, as described in the first embodiment, ΔFro1 represents a Doppler frequency shift equivalent to Fro due to relative movement of the non-stationary satellite with respect to the terminal, and ΔFto1 represents Fto due to relative movement with respect to the terminal of the non-stationary satellite. It represents a substantial Doppler frequency shift. ΔFto2 and ΔFto2 are characteristic of the third embodiment, and the Doppler frequency shift corresponding to Fro due to the relative movement of the terminal with respect to the non-stationary satellite and the Doppler frequency equivalent to Fto due to the relative movement of the non-stationary satellite with respect to the terminal, respectively. Represents a shift. However, ΔFto2 and ΔFto2 are positive when the satellite 3 and the communication terminal 1 are close to each other. Referring to FIG. 13, the following mathematical formula 21 holds.

  Here, C is the speed of light, and VTns is the terminal moving speed in the direction of the non-stationary satellite position. Therefore, similarly to Embodiment 1 in FIG. 14, in Embodiment 3, the Doppler frequency deviation of the transmission carrier frequency of communication terminal 1-n can be compensated based on FIG. However, in order to compensate the Doppler frequency deviation based on FIG. 25, it is necessary to know the moving speed and moving direction of the communication terminal 1-n.

  FIG. 26 shows a functional flow for obtaining the moving speed and moving direction of the communication terminal 1 using the GPS position data in the moving speed calculation unit 33 in FIG. First, in S801, GPS position data and its acquisition time are periodically input from the GPS signal processing unit 32. In S802, they are stored in the memory as position history data. In S803, the current moving speed and moving direction of the communication terminal 1 are estimated from the position history data read from the memory. In S804, the current moving speed and moving direction of the communication terminal 1 are stored in the memory as the current moving speed and moving direction.

  In FIG. 26, the moving speed calculation unit 33 uses the GPS position data to determine the moving speed and moving direction of the communication terminal 1, but a gyro sensor or acceleration sensor equipped in the communication terminal (mobile terminal). Alternatively, the moving speed and moving direction of the terminal may be obtained using a geomagnetic sensor. In this case, since the gyro sensor, the acceleration sensor, and the geomagnetic sensor serve as the movement speed detection unit 33, the movement speed detection unit 33 and the GPS signal processing unit 32 (information acquisition unit 310 (second information acquisition unit 310)) are connected. There is no need to do.

  FIG. 27 is a flow chart of carrier wave frequency Doppler frequency shift compensation in communication terminal 1 according to Embodiment 3. In FIG. 27, in S901, the Doppler frequency calculation unit 28 reads out the current movement speed and movement direction of its own terminal (communication terminal 1) from the memory of the movement speed calculation unit 33. Next, in step S902, the Doppler frequency calculation unit 28 determines whether the own terminal is moving from the current moving speed of the own terminal (communication terminal 1).

  If not, compensation for Doppler frequency shift is performed according to FIG. If it is determined that it is moving, satellite orbit information is read from the orbit information receiving unit 17 in S903. In S904, GPS position data is input from the GPS signal processing unit 32. Next, in step S905, the Doppler frequency calculation unit 28 calculates the speed VSn of the satellite in the direction of its own terminal from the satellite orbit information and GPS position data, and the satellite orbit information, GPS position data, and the current moving speed of the communication terminal. Then, the moving speed VTns in the satellite direction of the communication terminal is calculated from the moving direction.

  Further, in step S906, the Doppler calculation unit 28 calculates Doppler frequency shifts ΔFro1 and ΔFro2 corresponding to the carrier center frequency Fro of the forward link signal using the VSn and VTns and outputs them to the carrier generation unit 26. Furthermore, in step S907, the Doppler frequency calculation unit 28 calculates Doppler frequency shifts ΔFto1 and ΔFto2 corresponding to the carrier center frequency Fto of the return link signal using the VSn and VTns, and outputs them to the carrier generation unit 26.

  First, the carrier generation unit 26 generates Fro by Fro = Frn− (ΔFro1 + ΔFro2) from the carrier frequency Frn of the received forward link signal in S908. Further, in step S909, the carrier generation unit 26 generates the carrier center frequency Fto of the transmission return link signal by Fto = Fro × Rrt. Finally, in S910, the carrier wave generator 26 compensates for the Doppler frequency shift of the transmission carrier frequency Fto by Ftn = Fto− (ΔFto1 + ΔFto2).

  As described above, in Embodiment 3, the communication terminal 1 includes the orthogonal code generation unit 22 that generates orthogonal codes, the information acquisition unit 310 that acquires time information from the outside, and the time information acquired by the information acquisition unit 310. A reference clock is generated, a transmission timing generation unit 23 using the chip clock as a reference for the generation timing of the orthogonal code by the orthogonal code generation unit 22, and the satellite 3 by the orthogonal code generated by the orthogonal code generation unit 22 A CDMA spreading unit 21 that spreads a transmission signal to be transmitted to generate a CDMA signal, and a delay processing unit 240 that corrects a delay caused by the distance between the communication terminal 1 and the satellite 3 when transmitting the CDMA signal to the satellite 3. And the carrier wave generation unit 26 that generates the carrier wave, and the carrier wave generated by the carrier wave generation unit 26, the CDMA signal corrected by the delay processing unit 240 A modulator 25 for modulating, it can be said that the change in the relative distance between the satellite 3 and the communication terminal 1 and a Doppler frequency calculating unit for calculating a frequency shift due to the Doppler frequency shift of the CDMA signal.

  Therefore, the carrier wave generation unit 26 can compensate the frequency shift due to the Doppler frequency shift calculated by the Doppler frequency calculation unit 28 with the frequency of the carrier wave. That is, even when the communication terminal 1 moves on the ground, the Doppler frequency deviation of the carrier frequency of the return link signal transmitted by the communication terminal 1 is compensated according to the moving speed and moving direction. The carrier frequency deviation between the return link CDMA signals transmitted from the terminal 1 is almost zero, and the deterioration due to the orthogonal carrier frequency deviation between the orthogonal codes transmitted from each communication terminal 1 can be suppressed to almost zero. be able to.

Embodiment 4 FIG.
A fourth embodiment of the present invention will be described with reference to FIGS. The description will focus on the parts different from the first to third embodiments, and the description of the parts common to the first to third embodiments may be omitted. FIG. 28A is a schematic diagram showing an outline of a communication system according to the fourth embodiment (no reception from the GPS satellite 4), and FIG. 28B is a schematic diagram showing an outline of the communication system according to the fourth embodiment. (No reception from GPS satellite 4). In the drawings, the same reference numerals denote the same or corresponding parts, and detailed descriptions thereof are omitted.

  In Embodiments 1 and 2, assuming that each communication terminal 1 is not moving or moving slowly even if it is moving, each communication terminal 1 is moving in Embodiment 3. I was assuming a case. In the fourth embodiment, it is assumed that each communication terminal 1 is fixed or hardly moves, or each communication terminal 1 moves within a predetermined range. That is, in the fourth embodiment, when the communication terminals 1 are intensively arranged such that the delay time difference due to the distance difference between the communication terminals 1 to the satellite 3 does not occur, or the satellites 3 between the communication terminals 1 This case is assumed to move within a range in which a delay time difference due to a difference in distance does not occur (corresponding to the above-mentioned “predetermined range”). This means that it is not necessary to form the delay processing unit 240 in the communication terminal 1.

  As shown in FIG. 28, the communication system (short message communication system), the communication terminal (short message communication terminal), and the communication method (short message communication method) according to the fourth embodiment are applied to the fourth embodiment. The case where the communication terminal which concerns on is installed in each house in small villages, such as a mountainous area, is considered. FIG. 28A shows a case where the operation is performed without reception from the GPS satellite 4. FIG. 28B shows a case where reception from the GPS satellite 4 is performed. In the case of FIG. 28A, the operation of the communication terminal 1 shown in FIG. 29 and the communication terminal 1 shown in FIG. 32 can be considered. In the case of FIG. 28B, the operation of the communication terminal 1 shown in FIG. 30 and the communication terminal 1 shown in FIG. 31 can be considered. Of course, each of the plurality of communication terminals 1 shown in FIGS. 28A and 28B may move within a range in which a delay time difference due to a distance difference between the communication terminals 1 to the satellite 3 does not occur.

  First, the communication terminal 1 described in FIG. 29 includes an orthogonal code generation unit 22 that generates orthogonal codes, an information acquisition unit 310 that acquires time information, and a chip clock based on the time information acquired by the information acquisition unit 310. The transmission timing generator 23 using the chip clock as a reference for the generation timing of the orthogonal code by the orthogonal code generator 22 and the transmission signal to be transmitted to the satellite 3 by the orthogonal code generated by the orthogonal code generator 22 are spread. CDMA spreading section 21 for generating a CDMA signal, carrier generation section 26 for generating a carrier, modulation section 25 for modulating a CDMA signal using the carrier generated by carrier generation section 26, satellite 3 and communication terminal And a Doppler frequency calculation unit 28 for calculating a frequency shift due to a Doppler frequency shift of the CDMA signal from a change in relative distance from 1.

  The carrier wave generator 26 compensates the frequency shift due to the Doppler frequency shift calculated by the Doppler frequency calculator 28 with the frequency of the carrier wave. Here, the Doppler frequency calculation unit 28 receives the position data of the communication terminal 1 held by the communication terminal 1 itself as an alternative to the GPS position data. Of course, the Doppler frequency calculation unit 28 itself may hold the position data of the communication terminal 1. The information acquisition unit 310 acquires or holds time information having a predetermined time accuracy, and the transmission timing generation unit 23 generates a chip clock having a length of one chip longer than the predetermined time accuracy.

  In the communication terminal 1 illustrated in FIG. 30, the Doppler frequency calculation unit 28 calculates the Doppler frequency shift from the moving speed of the satellite 3. The communication terminal 1 illustrated in FIG. 30 has a configuration in which the delay processing unit 240 in the communication terminal 1 illustrated in FIG. Further, in the communication terminal 1 shown in FIG. 31, the Doppler frequency calculation unit 28 calculates the Doppler frequency shift from the moving speed of the satellite 3 and the moving speed of the communication terminal 1. The communication terminal 1 illustrated in FIG. 31 has a configuration in which the delay processing unit 240 in the communication terminal 1 illustrated in FIG.

  The communication terminal 1 described in FIG. 32 includes a moving speed calculation unit 33 such as a gyro sensor, an acceleration sensor, or a geomagnetic sensor provided in the communication terminal (mobile terminal) in the terminal device of the communication terminal 1 described in FIG. It has been added. Therefore, the communication terminal 1 described in FIG. 32 can compensate for the frequency shift due to the Doppler frequency shift of the method as described in the third embodiment.

  In the first to fourth embodiments, a chip clock generation method and an orthogonal code generation method necessary for the satellite communication access method and the satellite communication access method can be obtained. Specifically, when a plurality of terminal devices access a base station using CDMA with an orthogonal code via a non-stationary satellite such as a quasi-zenith satellite, the orthogonality of the CDMA signal transmitted from each terminal device on the non-stationary satellite A communication system (short message communication system) and communication including a clock generation method and an orthogonal code generation method suitable for a satellite communication access system in which codes are synchronized with a phase difference of less than one chip and interference by cross-correlation between orthogonal codes is small A terminal (short message communication terminal) and a communication method (short message communication method) can be obtained.

  A communication system (short message communication system), a communication terminal (short message communication terminal), and a communication method (short message communication method) including the clock generation method and the orthogonal code generation method according to the first to fourth embodiments are as follows. Needless to say, the configuration, status, and content of the short message can be interchanged between the forms. Needless to say, the short messages according to the first to fourth embodiments may be used not only in an emergency, but also when providing information on the Internet. Communication terminals according to Embodiments 1 to 4 may be mobile or fixed. Moreover, you may comprise the communication terminal which concerns on Embodiment 1-4 by adding hardware and software to terminal devices, such as a mobile telephone, a communication apparatus, and a disaster prevention radio | wireless.

1 .... Communication terminal (short message communication terminal) 2 .... Base station 3 .... Satellite (non-geostationary satellite) 4 .... GPS satellite 5 .... terrestrial network 6 .... service center 7 .... satellite Tracking control center, 8 ·· Forward link line, 9 ·· Return link line, 10 ·· GPS signal, 11 · Satellite communication antenna (terminal side satellite communication antenna), 12 ·· Duplexer (terminal), 13 · -Wireless receiver (terminal side receiver), 14 ... QPSK demodulator, 15 ... Error correction decoder, 16 ... TDM demultiplexer, 17 ... Trajectory information receiver (information acquisition unit (first information acquisition unit) ), Moving speed acquisition unit), 18... Data input terminal (transmission data (short message) input terminal), 180... Transmission signal generation unit, 19.. Data generation unit, 20.・CDMA spreading unit, 22 .... orthogonal code generation unit, 23 ... transmission timing generation unit, 240 ... delay processing unit, 24 ... delay correction unit, 250 ... Doppler frequency processing unit, 25 ... BPSK modulation unit, 26 ..Carrier generation unit 27..Radio reception unit (terminal side reception unit) 28..Doppler frequency calculation unit 29..Delay time calculation unit 30..GPS antenna 310..Information acquisition unit (No. 2 information acquisition unit), 31 ... GPS receiver, 32 ... GPS signal processing unit, 33 ... Movement speed calculation unit, 34 ... Received data output terminal, 41 ... Ground interface unit, 42 ... Data generation unit 43..TDM multiplexing unit 44..Control information transmission unit 45..Error correction coding unit 46..QPSK modulation unit 47..Radio transmission unit (base station side transmission unit) 48 .. Duplexer (base ), 49 .. Satellite communication antenna (base station side satellite communication antenna), 50.. Wireless receiver (base station side receiver), 51.. CDMA despreading unit, 52. Error correction decoding section 54 Data processing section 55 Reception timing generator 56 Base station position and reference ground position 61 M sequence generator 62 62 M sequence generator 63 Modulo 2 adder, 64 ... 0 feeder, 71 ... Frequency subtractor, 72 ... Frequency multiplier, 73 ... Frequency subtractor.

Claims (5)

One of a plurality of short message communication terminals accessing a satellite, a receiving unit that receives a forward link signal relayed to the satellite and transmitted from a base station, an orthogonal code generation unit that generates an orthogonal code, An information acquisition unit for acquiring a predetermined time accuracy from the outside, and generating a chip clock having a length of one chip longer than the predetermined time accuracy based on the time information acquired by the information acquisition unit. A transmission timing generator as a reference for generation timing of an orthogonal code by the orthogonal code generator; a transmission signal generator that generates a transmission signal including a short message according to the forward link signal received by the receiver; A CDMA signal is generated by spreading the transmission signal generated by the transmission signal generation unit using the orthogonal code generated by the orthogonal code generation unit. A CDMA spreading unit, a delay processing unit for correcting a delay caused by a distance between the short message communication terminal and the satellite when transmitting the CDMA signal to the satellite, a carrier generating unit for generating a carrier, A modulation unit that modulates the CDMA signal corrected by the delay processing unit using the carrier wave generated by the carrier wave generation unit, and a transmission that transmits the CDMA signal modulated by the modulation unit to the satellite as a return link signal A short message communication terminal that synchronizes the generation timing of the orthogonal code by the orthogonal code generation unit among the plurality of short message communication terminals from the time information. A Doppler frequency calculation unit that calculates a frequency shift due to a Doppler frequency shift of the CDMA signal from a change in relative distance to the satellite, and the carrier generation unit is based on the Doppler frequency shift calculated by the Doppler frequency calculation unit. 2. The short message communication terminal according to claim 1, wherein a frequency shift is compensated by a carrier frequency. The delay processing unit derives a distance to the satellite from position information and calculates a delay time, and a delay correction unit that corrects the transmission signal from the delay time calculated by the delay time calculation unit The short message communication terminal according to claim 1 or 2, comprising: The transmission signal generation unit transmits the CDMA signal modulated by the modulation unit to the satellite at the slot timing with the chip clock generated by the transmission timing generation unit as a reference, so that the plurality of slot timings are transmitted. 4. The short message communication terminal according to claim 1, wherein the short message communication terminal is synchronized with each other. The transmission signal generation unit generates a chip clock having a length of one chip longer than a predetermined time accuracy based on the time information acquired by the information acquisition unit, and at a slot timing based on the chip clock, 4. The slot timing is synchronized among the plurality of short message communication terminals by transmitting the CDMA signal modulated by a modulation unit to the satellite. Short message communication terminal.

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