KR100605269B1 - Apparatus and method for transmitting the data on the remote terminal in the satellite spread multiple access system - Google Patents

Abstract

The present invention relates to a bidirectional satellite communication system in which forward link data transmitted from a central station to a satellite terminal uses a time division multiple access scheme, and reverse link data transmitted from the satellite terminal to the central station uses a code division multiple access scheme. In particular, the apparatus for transmitting data to be transmitted through the reverse link in the satellite terminal, comprising: a phase locked loop control signal generator for generating an intermediate frequency control signal from a frequency offset compensation value received from the central station; A local oscillator for generating a compensated intermediate frequency signal by controlling a phase locked loop circuit according to an intermediate frequency control signal output from the phase locked loop control signal generator; And a multiplier for multiplying data to be transmitted with an intermediate frequency signal output from the local oscillator.

Two-way satellite communication, central station, satellite terminal, frequency offset, local oscillator

Description

APPARATUS AND METHOD FOR TRANSMITTING THE DATA ON THE REMOTE TERMINAL IN THE SATELLITE SPREAD MULTIPLE ACCESS SYSTEM}

1 is a view showing the overall configuration of a two-way satellite system to which the present invention is applied.

2 is a diagram showing a detailed structure of a central station in a bidirectional satellite system to which the present invention is applied.

3 is a diagram illustrating a detailed structure of a satellite terminal in a bidirectional satellite system to which the present invention is applied.

4 is a signal flow diagram of a receiver in a central station of a bidirectional satellite system to which the present invention is applied;

5 is a diagram illustrating a detailed structure of a transmitting device in a satellite terminal of a bidirectional satellite system according to an embodiment of the present invention.

6 is a flowchart illustrating a procedure for compensating for and transmitting a frequency offset in a satellite terminal of a bidirectional satellite system according to an embodiment of the present invention.

7 is a flowchart illustrating a procedure for transmitting a spread code offset in a satellite terminal of a bidirectional satellite system according to an embodiment of the present invention.

8 is a diagram illustrating a method for selecting a spreading code offset during retransmission in a satellite terminal of a bidirectional satellite system according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: communication satellite 200: central station (base station)

210: central station antenna 220: wireless processing unit

230: central station transmitter (DVB-S) 231: modulator

232: multiplexer 233: IP encapsulation

240: central station receiving unit (W-CDMA)

241: medium frequency interface card assembly

242: Multi-rate channel card assembly

243: digital unit control card assembly

244: Alarm Control Processor Card Assembly

245 hub control processor card assembly

246: clock supply

250: Ethernet network 300: satellite terminal

310: baseband processor 320: terminal transmitter (W-CDMA)

330: Terminal receiver (DVB-S) 501: First multiplier

502, spreading code generator 503: QPSK modulator

504: second multiplier 505: third multiplier

506: adder 507: automatic gain control unit

508: phase rotation part 509: local oscillation part

510: PLL control signal generator

The present invention relates to a two-way satellite system, and more particularly, to an apparatus and method for transmitting data in a satellite terminal of a two-way satellite system.

In general, the satellite broadcasting system is unidirectional, so that it is possible to provide satellite broadcasting to a user, but a method of receiving a desired data or request from the user is not implemented.

In addition, the two-way satellite broadcasting service currently in service is not strictly referred to as a two-way communication using a satellite because the user's request is not transmitted using the satellite but the ground network.

On the other hand, in recent years, a two-way system using satellites has been developed, but the two-way satellite system, which has been developed and used in the past, uses the same communication method in which all communication methods are connected from the central station to the user and the user to the central station.

For example, both the forward link and the reverse link use Time Division Multiple Access (hereinafter referred to as 'TDMA') or Frequency Division Multiple Access (hereinafter referred to as 'FDMA'). Use the method.

Accordingly, since the user terminal is a terminal corresponding to one communication method, there is bound to be a limitation of the communication service that can be provided. That is, the data transmitted from the central station to the users are broadcast data that transmits the same large amount of data to multiple users in real time, whereas the data transmitted by each user is relatively small data transmitted when needed and It is used irregularly. Therefore, in implementing a two-way system via satellite, when the same communication method is applied to both the user in the central station and the communication method connected from the user to the central station, it is difficult to provide an effective service, and therefore, many service constraints follow.

On the other hand, if the conventional system to receive a communication service by accepting a different communication method has a disadvantage that must have a plurality of terminals having a different communication method.

Therefore, in order to solve various problems that occur when performing communication using the above-described conventional satellite, the present applicant has a bidirectional satellite for transmitting and receiving data in a different communication method between a central station and a user in Korean Patent Application No. 2003-70510 (2003.10.10). A communication system is proposed.

Hereinafter, the proposed bidirectional satellite communication system will be briefly described.

In the satellite bidirectional communication system, a forward link (ie, a channel transmitted from a central station to a user terminal) and a reverse link or return link (ie, a channel transmitted from a user terminal to a central station) are different from each other. I adopt the method. For example, the forward link uses a DVB-S (Digital Video Broadcasting via Satellite) method using a TDMA method, and the reverse link uses a code division multiple access (CDMA) method. Wideband CDMA (hereinafter, referred to as W-CDMA) is used.

1 is a view showing the overall configuration of a two-way communication system using a satellite.

Referring to FIG. 1, a central station (CS) 200 transmits broadcast data received from a predetermined broadcast information provider (eg, an Internet service provider (ISP) 110) through a communication satellite (Satellite) 100. It transmits to the subscriber terminal (or satellite terminal) (Remote Terminal) 300. Information such as the broadcast data may be provided through the Internet 120, a content delivery network (CDN) 130, an application service 140, and the like.

In this case, the central station 200 transmits broadcast information and the like to the plurality of subscriber stations 300 in a DVB-S format through a forward link, and each subscriber station 300 transmits to the central station 200 through a reverse link. Data is transmitted by the W-CDMA method.

Accordingly, the central station 200 manages each user who uses the service (that is, subscriber terminals 300), processes data transmitted in a W-CDMA manner from various users, and converts the data desired by the user into the DVB. It converts to the -S format and transmits to the user through the satellite 100.

In addition, each subscriber station 300 receives and processes the DVB-S multimedia data transmitted from the central station 200 through the satellite 100, and requests W- to the satellite 100 upon request of necessary data. CDMA transmission data is transmitted.

On the other hand, the two-way satellite communication system as described above may cause various problems in its implementation.

For example, when the CDMA scheme is applied to the satellite reverse link, the capacity of the subscriber stations 300 can be increased and data security can be enhanced. However, CDMA data is transmitted through a satellite, thereby providing a general CDMA scheme. In addition to the problem of time delay that does not occur in the system, there is also a problem of frequency shifting. Accordingly, there is a need for an effective implementation method for solving the above problems caused when applying the CDMA scheme to a system for bidirectional satellite communication.

An object of the present invention relates to an apparatus and method for transmitting data in a satellite terminal of a two-way satellite system.

The present invention also relates to an apparatus and method for transmitting data modulated by a code division multiple access scheme in a satellite terminal of a bidirectional satellite system.

The present invention also relates to an apparatus and method for transmitting data modulated by a code division multiple access scheme by compensating for a time delay value in a satellite terminal of a bidirectional satellite system.

The present invention also relates to an apparatus and method for transmitting data modulated by a code division multiple access scheme by compensating a frequency shifted value in a satellite terminal of a bidirectional satellite system.

The apparatus of the present invention for achieving the above object; A satellite communication system includes a predetermined communication satellite, a central station transmitting predetermined broadcast information to a plurality of subscribers through the communication satellite, and a plurality of satellite terminals receiving information transmitted from the central station through the communication satellite. And the forward link data transmitted from the central station to the satellite terminal uses a time division multiple access scheme, and the reverse link data transmitted from the satellite terminal to the central station uses a code division multiple access scheme in a bidirectional satellite communication system. An apparatus for transmitting data to be transmitted through the reverse link in the satellite terminal, comprising: a phase locked loop control signal generator for generating an intermediate frequency control signal from a frequency offset compensation value received from the central station; A local oscillator for generating a compensated intermediate frequency signal by controlling a phase locked loop circuit according to an intermediate frequency control signal output from the phase locked loop control signal generator; And a multiplier for multiplying data to be transmitted with an intermediate frequency signal output from the local oscillator.

Meanwhile, the apparatus extracts a frequency offset compensation value from data including the frequency offset compensation value received from the central station, generates a control signal corresponding to the frequency offset compensation value, and converts the generated control signal into the phase synchronization. And a controller for transmitting to the loop control signal generator.

The apparatus may further include: a spreading code generator for generating a predetermined spreading code based on a predetermined spreading code offset initial value; And a multiplier for multiplying the data to be transmitted by the satellite terminal with a spreading code output from the spreading code generator to spread the data.

The apparatus may further include a QPSK modulator for modulating data to be transmitted by the satellite terminal according to a QPSK scheme.

The spreading code generator outputs the spreading code by reflecting a spreading code offset compensation value received from the central station.

The first method of the present invention for achieving the above object; A satellite communication system includes a predetermined communication satellite, a central station transmitting predetermined broadcast information to a plurality of subscribers through the communication satellite, and a plurality of satellite terminals receiving information transmitted from the central station through the communication satellite. And the forward link data transmitted from the central station to the satellite terminal uses a time division multiple access scheme, and the reverse link data transmitted from the satellite terminal to the central station uses a code division multiple access scheme in a bidirectional satellite communication system. A method for transmitting data to be transmitted through the reverse link in the satellite terminal, the method comprising: generating a phase locked loop control signal from a frequency offset compensation value received from the central station; Generating a compensated intermediate frequency signal by controlling a phase locked loop circuit according to the generated intermediate frequency control signal; And frequency modulating multiplying the data to be transmitted with the generated intermediate frequency signal.

The generating of the phase locked loop control signal may include: extracting a frequency offset compensation value from data including the frequency offset compensation value received from the central station; Generating a control signal corresponding to the frequency offset compensation value; And transmitting the generated control signal to the phase locked loop control signal generator.

In addition, the central station extracts the position value of the satellite terminal through the data received from the satellite terminal and feeds back to the satellite terminal to compensate for the time delay of the received data.

The second method of the present invention for achieving the above object; A satellite communication system includes a predetermined communication satellite, a central station transmitting predetermined broadcast information to a plurality of subscribers through the communication satellite, and a plurality of satellite terminals receiving information transmitted from the central station through the communication satellite. And the forward link data transmitted from the central station to the satellite terminal uses a time division multiple access scheme, and the reverse link data transmitted from the satellite terminal to the central station uses a code division multiple access scheme in a bidirectional satellite communication system. A method for transmitting data to be transmitted through the reverse link in the satellite terminal, the method comprising: spreading data to be transmitted by using an initial value of a spreading code offset and transmitting the data to the central station; And setting a spreading code offset from the initial value of the spreading code offset to a value changed from the initial value of the spreading code offset when there is no response from the central station, and spreading and retransmitting data by the set spreading code offset. It features.

The method of changing the spreading code offset value may be set to be far from the initial value of the spreading code offset every time retransmission is repeated, and the range of changing the spreading code offset value is 0.5ms.

On the other hand, when receiving a response signal from the central station within a predetermined time, comparing the received spreading code offset value and the spreading code offset value of the satellite terminal to determine whether it is valid; And resetting a spreading code offset according to the received spreading code offset value if valid as a result of the determination.

In addition, the reverse link data is characterized by using a wideband code division multiple access (W-CDMA) scheme.

Hereinafter, a detailed description of a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description, detailed descriptions of well-known functions or configurations will be omitted when it is determined that the detailed descriptions of the known functions or configurations may unnecessarily obscure the subject matter of the present invention.

The present invention is a bidirectional satellite communication system in which the forward link and the reverse link are different from each other, particularly in a bidirectional satellite communication system in which the reverse link is applied by Code Division Multiple Access (hereinafter, referred to as 'CDMA'). An apparatus and method for transmitting data to be transmitted from a satellite terminal through a reverse link are provided.

In this case, since the data transmitted by the CDMA method through the reverse link is transmitted over a very long distance, a serious time delay phenomenon (generally about 300 ms) occurs unlike the CDMA method applied to a general mobile communication system. In addition, shifting of a carrier frequency occurs. Therefore, functions for compensating and transmitting the time delay and frequency shifting phenomena in the transmitting device of the satellite terminal should be implemented.

Before describing the present invention, first, a bidirectional satellite communication system to which the present invention is applied, and configurations of a central station and a satellite terminal in the bidirectional satellite communication system will be described.

The bi-directional satellite communication system to which the present invention is applied is a DVB-enabled device that enables internet, e-mail, satellite broadcasting, video conferencing, video transmission and reception, and other high-speed multimedia services using an artificial satellite. S satellite broadcasting technology (hereinafter referred to as 'DVB-S') and broadband code division multiple access (hereinafter referred to as 'W-CDMA') is a satellite bidirectional communication system through integration.

More specifically, in case of a two-way communication using a satellite between a remote terminal (RT) receiving a service and a central station (CS) providing a service, a forward link and a reverse link are used. It consists of a link (Reverse link or Return link), and adopts DVB-S and W-CDMA, respectively, different communication methods to realize integration of satellite broadcasting technology (DVB-S) and W-CDMA wireless communication technology. . In addition, the W-CDMA reverse link enables W-CDMA circuit switching and packet switching communication.

Meanwhile, two-way satellite communication methods using code division multiple access schemes in the reverse link, respectively, to which the present invention is applied, are called satellite spread multiple access (SSMA) schemes. It will be called. In addition, a base station apparatus that transmits broadcast data to a plurality of users through a forward link in the SSMA system will be referred to as a 'central station' (CS), and in the SSMA system, broadcast data is transmitted from the central station (CS). A subscriber station apparatus that receives and transmits data to the central station CS through a reverse link will be referred to as a "remote terminal" (RT).

Hereinafter, detailed configurations of the central station CS and the satellite terminal RT constituting the SSMA communication system will be described with reference to FIGS. 2 and 3.

2 is a diagram illustrating a detailed structure of a central station in a bidirectional satellite system to which the present invention is applied.

Referring to FIG. 2, the central station 200 of the bidirectional satellite system includes a satellite antenna 210, a radio frequency (RF) processor 220, a transmitter 230, and a receiver 240. That is, the central station 200 modulates and transmits the transmission unit 230 in the same manner as the DVB-S, and demodulates the reception unit 240 in the same manner as the W-CDMA.

In more detail, the transmitter 230 modulates data to be transmitted to each satellite terminal 300 by a satellite broadcast transmission method such as DVB-S, and then modulates the modulated data to the radio processor 220. In the transmission (Tx) radio (RF) processing unit 221 and transmits the radio through the antenna 210. The transmitter 230 includes an Internet Protocol (IP) encapsulator 233, a multiplexer 232, a modulator 231, and the like. The IP encapsulation unit 233 performs a function of adding an IP header by receiving broadcast data received from a network such as Ethernet 250. The multiplexer 232 receives a plurality of data from the IP encapsulation unit 233 and multiplexes the data. In addition, the modulator 231 receives the multiplexed data from the multiplexer 232 and encodes the data by a method such as Forward Error Correction (FEC) / Digital Video Broadcasting (DVB) / Quadrature Phase Shift Keying (QPSK). Modulates the role.

That is, an IP encapsulation is received through a multimedia stream server (not shown) that generates a multimedia stream for a user or data received from an external network or multimedia stream data generated by the multimedia stream server through an internal communication interface Ethernet 250. The unit 233 converts the IP data into a format for IP communication and converts the IP data converted by the IP encapsulation unit 233 into a data such as MPEG-2 DVB-S (Digital Video Broadcasting-Satellite) scheme by the modulation unit 231. Will be modulated by

The broadcast data supplied to the transmitter 230 may be provided through an application server 251 or a database server 252, or may be provided with a gateway 254 and a router 256. It may be provided from an external content provider in connection with the Internet 257.

In addition, the central station 200 manages its state and the like through a network management system (hereinafter, referred to as 'NMS') 253 connected to the Ethernet 250.

Meanwhile, the receiver 240 of the central station 200 receives and demodulates W-CDMA format data received from the satellite terminals 100. That is, signals transmitted by the satellite terminals 100 are received through the satellite antenna 210, and radio signals processed by the Rx radio processor 222 of the RF processor 220. After that, the demodulation is performed at the receiver 240.

The receiving unit 240 is composed of a plurality of channel cards to enable processing of signals received from a plurality of subscribers subscribed to the system. In addition, each channel card provides a digital unit for demodulating directly received data (hereinafter, referred to as a 'DU') and a hub control processor for supplying a clock to the DU and managing the receiver 240. Control Processor Unit (hereinafter referred to as "HCPU").

The DU is an intermediate frequency interface card assembly (IF interface card assembly) for converting an intermediate frequency (hereinafter, referred to as IF) signal received from the RF processor 220 into a digital signal corresponding thereto. 241), and a multi-rate channel card assembly (hereinafter referred to as 'MCCA') for QPSK demodulation of the digital IF signal converted in the intermediate frequency interface card assembly 241. The digital unit control for transmitting the data output from the 242 and the MCCA 242 through the Ethernet 250 in synchronization with a clock supplied from a hub system clock (hereinafter, referred to as “HBSC”) 246. It consists of a digital unit control card assembly (hereinafter referred to as "DCCA") (243).

In addition, the HCPU is a clock supply unit (HBSC) 246 for generating and supplying a required clock (Clock) in the unit (Unit) in the central unit 200 based on the clock synchronized to the GPS receiver, the alarm in the central station 200 ( An alarm control processor card assembly (hereinafter referred to as 'ACPA') 244 which collects signals and reads state information of each unit, and is connected to the ACPA 244 and the HBSC 246. Hub control processor card assembly (hereinafter referred to as 'HCPA') that operates and manages the reverse link as a whole and controls each unit to perform call setup and release, abnormal state management, and maintenance functions. 245).

That is, the received radio processor 222 wirelessly processes the data received and outputs an L-band (eg, a 950 to 1450 MHz band) signal, and the L-band signal is an intermediate frequency signal by the IFCA 241. (For example, a 70 MHz band), and a digital signal by an A / D converter.

The digital signal output from the IFCA 241 is input to the MCCA 242, and demodulated to the DCCA 243 by demodulating the input digital signal, that is, reverse channel data. Meanwhile, the DCCA 243 controls the entire DU and transfers the clock received from the HBSC 246 to each unit. In addition, the demodulated data is received from the MCCA 242, and the received demodulated data is output by a clock inputted from the HBSC 246.

Meanwhile, the central station 200 manages user information on the RTs 300 and the like through a satellite subscriber management system (hereinafter referred to as 'RSMS') 256 connected to the Ethernet 250. do.

3 is a diagram illustrating a detailed structure of a satellite terminal (RT) 300 in a bidirectional satellite system to which the present invention is applied.

Referring to FIG. 3, the satellite terminal 300 of the bidirectional satellite system includes a baseband processor 310, a transmitter 320, a receiver 330, and the like. That is, in the satellite terminal 300, the transmitter 320 modulates and transmits the signal in the same manner as the W-CDMA, and the receiver 330 demodulates the signal in the same manner as the DVB-S.

The baseband processor 310 may provide a memory area for operating a terminal and a space for a buffer used to process data, and a memory 313 for providing a storage space of an operating system for operating a terminal. 313 is connected to the control unit for controlling the operation of receiving and processing data transmitted to the forward link through the satellite, and converts the data required by the user to the transmission data to control the operation of transmitting to the satellite via the reverse link 314 ), A data processing unit 311 which is connected to the control unit 314 to demodulate MPEG-2 data on DVB-S transmitted through a forward link, and forms information such as a state of a terminal as a 7-segment. The display unit 312 and the base band processor 310 output to the external interface unit 315 for communicating with an external network, etc. is configured.

On the other hand, the baseband processor 310 is connected to the control unit 314 through the external interface unit 315 is connected to the serial communication unit 318, the control unit 314 to provide a serial communication interface of up to 1Mbps And an analog audio / video interface unit 319 providing an analog video / audio interface for satellite broadcasting and an Ethernet 317 providing a 10 base-T Ethernet interface.

The receiving unit 330, when receiving the DVB-S method of the forward link, the DVB-S demodulation and QPSK demodulation function to perform the function of the receiving tuner 333, the signal transmitted from the receiving tuner 333 digital data The analog / digital conversion and data error correction unit (ADC &FEC; 332) and the analog / digital conversion and data error correction unit 332 for converting the digital data into the digital data and correcting the converted digital data are performed. The demultiplexer 331 may be demultiplexed and temporarily stored in the memory 313.

In addition, the transmitter 320 may include a clock generator 321 that provides a clock for W-CDMA modulation and a clock required for data transmission, and transmits W data according to a clock supplied from the clock generator 321. A W-CDMA modulator 322 modulated with CDMA scheme data (i.e., multiplied by a predetermined spreading code (e.g., PN code) and QPSK modulated), W-modulated by the W-CDMA modulator 322; It modulates CDMA data into an analog signal, and consists of a transmit tuner 323 for performing L-band direct conversion and automatic gain control.

In the bidirectional satellite communication system applied to the present invention configured as described above, the forward link and the data transmitted from the terminal 300 receive data transmitted from the central station 200 to the terminal 300 via the satellite 100. It operates as a reverse link transmitted to the central station 200 via the &lt; RTI ID = 0.0 &gt;

First, the operation of the forward link is as follows.

When the user requests a multimedia service after connecting to the central station 200 through the satellite 100, the user can access the network through a network address transfer (NAT) (not shown) under the control of a web server (not shown). The website is linked.

Thereafter, the stream data generated by the multimedia stream server (not shown) or the like for data provided to the user on the website or the multimedia service is transferred to the IP encapsulation unit 233 through the Ethernet 250.

The IP encapsulation unit 233 receives the multimedia stream data generated by the multimedia stream server or the like received from an external network through Ethernet 250, an internal communication interface, and converts the multimedia stream data into a format for IP (Internet Protocol) communication. The signal is transmitted to the modulator 231 through the multiplexer 232.

The modulator 231 modulates the IP data converted by the IP encapsulator 233 into MPEG-2 DVB-S data and transmits the data to the satellite 100 through the RF processor 220.

The forward link signal thus transmitted is transmitted to the satellite terminal 300 via the satellite 100, and the satellite terminal 300 receives and processes it.

That is, the control unit 314 in the satellite terminal 300 is responsible for the overall control of the receiver 330 when the DVB-S data of the forward link is received through the satellite 100, and the reception tuner in the receiver 330. In operation 333, the DVB-S demodulation and QPSK demodulation functions are performed and transmitted to the analog / digital conversion and error correction unit 332.

The analog / digital conversion and error correction unit 332 in the receiver 330 converts a signal transmitted from the reception tuner 333 into digital data and corrects an error of the converted data. 331).

The demultiplexer 331 in the receiver 330 demultiplexes the data stream transmitted from the analog / digital conversion and error correction unit 332 and demultiplexes the data from the data processor 311 for processing. Temporarily store the data stream.

The controller 314 controls the demultiplexer 331 to transmit data to the data processor 311 at a point in time where the user desires data, and the data processor 311 demodulates the received MPEG-2 data. .

Through the above-described processes, data of the forward link is received and processed. Next, the operation of the reverse link for transmitting data from the terminal 300 to the central station 200 through the satellite 100 is as follows.

First, when the terminal 300 wants to request necessary data through the satellite 100, the transmitter 320 generates and transmits corresponding transmission data under the control of the controller 314.

In more detail, the clock generator 321 in the transmitter 320 generates a clock for W-CDMA modulation and a clock required for data transmission to the CDMA modulator 322 and the transmit tuner 323. Each will be provided. For example, the clock generator 321 generates a 32.768 MHz clock and a 10 MHz system clock for data modulation, and supplies the same to each block.

Next, the W-CDMA modulator 322 modulates the transmission data into W-CDMA scheme data according to a clock supplied from the clock generator 321 (ie, multiplies a predetermined spreading code and performs QPSK modulation). ), The transmit tuner 323 converts the W-CDMA QPSK modulated digital data modulated by the W-CDMA modulator 322 into a corresponding analog signal, and L-band direct conversion. And auto gain control to transmit the data to the satellite 100 through the satellite transmitter.

As described above, the backward signal transmitted to the satellite 100 is transmitted to the central station 200 through the satellite 100.

Meanwhile, the IFCA 241 of the central station 200 converts the intermediate frequency (IF) signal received from the RF portion into a digital signal corresponding thereto and transmits the converted digital signal to the MCCA 242.

The multi-rate channel card assembly 242 QPSK demodulates the digital IF signal converted in the IFCA 241 and delivers the QPSK demodulated signal to the DCCA 243.

Meanwhile, the HBSC 246 generates a clock required by the central station unit based on the clock synchronized with the GPS receiver and supplies the clock to each block. The ACPA 244 collects the alarm signals in the central station. The state information of the unit is read and transmitted to the HCPA 245.

The HCPA 245 is connected to the ACPA 244 and the HBSC 246, operates and manages the reverse link as a whole, and controls each unit to perform call setup and release, abnormal state management, and maintenance functions. do.

In addition, the DCCA 243 transmits the data output from the MCCA 2428 to the transmitter through the Ethernet 250 in synchronization with the clock supplied from the HBSC 246 under the control of the HCPA 245.

In the above, detailed structures of the central station 200 and the satellite terminal 300 in the bidirectional satellite system have been described in detail with reference to FIGS. 2 and 3. Hereinafter, with reference to FIG. 4, the signal flow between the respective components constituting the receiver 240 of the central station 200 will be described.

4 is a diagram illustrating a signal flow of a receiver in a central station of a bidirectional satellite system according to an embodiment of the present invention.

Referring to FIG. 4, the IFCA 241 is an L-band signal from a low noise block down converter (hereinafter referred to as 'LNB') of the satellite antenna 210 of the central station 200. Down conversion to an intermediate frequency (IF) band (eg, 70 MHz), and extracts In phase / Quadrature (I / Q) data. In addition, the IFCA 241 performs the operation according to the system clock provided by the HBSC 244.

The MCCA 242 performs a function of demodulating the I / Q data received from the IFCA 241 and performs the operation according to the system clock provided by the HBSC 244 like the IFCA 241.

The DCCA 243 receives demodulated digital data from the MCCAs 242 and transmits the demodulated digital data to the Ethernet. On the other hand, the function of the DCCA (243) can be implemented to be performed in the MCCA (242), each MCCA 242 can be implemented to transmit data directly to the Ethernet (Ethernet). In addition, although only one MCCA 242 is shown in FIG. 4, several MCCAs 242 may be actually mounted in the system according to the number of subscribers.

The HBSC 244 generates system clocks (eg, 10 MHz, 32.768 MHz) that are synchronized with the Global Positioning System (hereinafter, referred to as 'GPS'). The generated clocks are supplied to the IFCA 241, the MCCA 242, and the like.

The ACPA 246 aggregates and manages alarms generated in an operation state of each unit and transmits the result to the HCPA 245. At this time, the HCPA 245 monitors the state of each unit in the system, and controls the units with reference to the information received from the ACPA 246.

Meanwhile, in the bidirectional satellite communication system using the reverse link as described above, the CDMA data transmitted through the reverse link is transmitted over a satellite over a long distance, and thus CDMA applied to a general mobile communication system. Unlike the scheme, a serious time delay phenomenon (generally about 300 ms) and shifting of a carrier frequency occur. Accordingly, the present invention implements the above-described transmission apparatus of the satellite terminal 300, in particular, the modulator 322 and the transmission tuner 323 so that the time delay and frequency shift phenomenon are compensated for.

Hereinafter, an apparatus and method for modulating and transmitting in consideration of time delay and carrier frequency shift in a transmitting apparatus (particularly, W-CDMA modulator 322 and transmitting tuner 323) of the satellite terminal 300 according to the present invention. Explain.

5 is a diagram illustrating a detailed structure of a transmitting device in the satellite terminal 300 of the bidirectional satellite system according to an embodiment of the present invention.

Referring to FIG. 5, the transmitting apparatus of the satellite terminal 300 according to the embodiment of the present invention spreads the data to be transmitted and QPSK modulates the W-CDMA modulator 322 and the modulated data to a predetermined L. And a transmit tuner 323 which converts the band signal.

The W-CDMA modulator 322 is a spreading code generator 502 for generating a predetermined spreading code (for example, a PN code) according to a control signal, and multiplies the data to be transmitted by the spreading code. The first multiplier 501 and the QPSK modulator 503 modulate the quadrature phase shift keying (QPSK).

That is, when a signal to be transmitted is input to the W-CDMA modulator 322, a signal spread by being multiplied by a spread signal output from a predetermined spread code generator 502 is output. At this time, according to the present invention, the offset value of the spreading code output from the spreading code generator 502 is changed by a predetermined control signal. In addition, the spreading code offset value is set according to a response signal from the central station 200 that receives the data, and details thereof will be described later.

That is, the signal transmitted by spreading by the predetermined spreading code in the satellite terminal 300 is transmitted through the satellite, so that the receiving central station 200 receives a signal having a severe time delay. Therefore, since the spreading code offset value for the signal transmitted from the satellite terminal 300 on the transmission side is changed according to the time delay of the transmission data, it is difficult to accurately demodulate it in the central station 200. Therefore, in the present invention, the demodulation code offset value for the signal transmitted from the satellite terminal 200 is changed and retransmitted according to whether the central station 200 receives data normally, thereby enabling accurate demodulation in the central station 200. . That is, the control signal input to the spreading code generator 502 is changed according to the response signal received from the central station 200.

On the other hand, the signal spread as described above is QPSK modulated by the QPSK modulator 503, is output as an I channel signal and a Q channel signal, and is input to the transmission tuner 323.

The transmission tuner 323 generates an intermediate frequency control signal (ie, a PLL circuit control signal) for controlling a phase lock loop (hereinafter, referred to as a 'PLL') according to a predetermined control signal (Control Signal). A phase locked loop control signal generator (hereinafter referred to as a &quot; PLL control signal generator &quot;) 510 and an intermediate frequency control signal (i.e., a PLL circuit control signal) output from the PLL control signal generator 510. The local oscillator 509 for outputting a predetermined L-band signal, the phase rotator 508 for rotating the output signal of the local oscillator 509 by 90 degrees, and the local oscillator 509 and the phase rotator 508 An adder 506 that adds the output signals of the second multiplier 504 and the third multiplier 505, the second multiplier 504, and the third multiplier 505 to multiply an output signal with the I and Q channel signals, respectively. ), The automatic gain control of the output signal of the adder 506 and output Auto Gain Control (hereinafter referred to as "AGC") is composed of a part 507.

The control signal input to the PLL control signal generator 510 is calculated by a frequency offset correction signal received from the central station 200 as a signal for controlling the frequency offset of the carrier frequency signal output from the local oscillator 509. Is a signal. Detailed description of the control signal will be described later.

That is, the frequency offset value of the L-band carrier frequency signal output from the local oscillator 509 is transmitted because the signal to be transmitted is transmitted through a long path through a satellite, thereby causing a distortion of the frequency offset value. Accordingly, it is difficult for the central station 200 to accurately demodulate the signal transmitted by the satellite terminal 300.

Therefore, in the present invention, by measuring the exact frequency offset value for the carrier frequency from the signal received by the central station 200, the feedback value for the frequency offset to the satellite terminal 300 (feedback), The satellite terminal 300 compensates the shift of the frequency offset as described above by determining the frequency offset value of the output signal of the local oscillator 509 based on the frequency offset change value of the carrier frequency received from the central station 200. can do.

Hereinafter, a procedure of performing time delay compensation and frequency shift compensation on data to be transmitted through the respective functional blocks shown in FIG. 5 will be described in detail with reference to FIGS. 6 to 8. First, the frequency shift compensation procedure will be described with reference to FIG. 6.

6 is a flowchart illustrating a procedure for compensating for a frequency offset of data to be transmitted by a satellite terminal of a bidirectional satellite system according to an embodiment of the present invention.

Referring to FIG. 6, first, the satellite terminal 300 transmits data to the central station 200 by the initial frequency offset value. The central station 200 calculates a difference value from the initial frequency offset value transmitted by the central station 200 from the data received from the satellite terminal 300. Then, the central station 200 feeds back the frequency offset compensation value of the data to be transmitted by the satellite terminal 300 to the satellite terminal 300 from the difference value of the frequency offset.

The satellite terminal 300 receives data including the frequency offset compensation value from the central station 200 (step S601), and reflects the received frequency offset compensation value to data to be transmitted later. Will be sent.

In more detail, the satellite terminal 300 receiving the data including the frequency offset compensation value from the central station 200 extracts the frequency offset compensation value from the received data in step S602. ) Then, the control signal according to the extracted frequency offset compensation value is generated (step S603). The control signal is a signal for controlling a frequency offset value with respect to an output signal of the local oscillator 506 as predetermined address data.

On the other hand, the control signal output from the control unit 314 is input to the intermediate frequency control signal generator (ie, PLL control signal generator) 510 of the transmission tuner 323, the PLL control signal generator ( In operation 604, the intermediate frequency control signal (that is, the PLL control signal), which is a control signal for the intermediate frequency output from the corresponding local oscillator, is generated according to the control signal received from the controller 314. Here, the PLL control signal generator 510 may be embodied as a field programmable gate array (FPGA).

The intermediate frequency control signal (ie, PLL control signal) output from the PLL control signal generator 510 is input to a local oscillator 509, and the local oscillator 509 receives the input intermediate frequency control signal (ie By adjusting the input voltage value of the phase lock loop circuit according to the PLL control signal (step S605), the final compensated intermediate frequency signal is output (step S606).

Meanwhile, the frequency offset compensation value received by the satellite terminal 300 from the center station 200 is a value calculated from a signal transmitted from the satellite terminal 300, and the center station 200 is assigned to each satellite terminal 300. This allows the signals received from the system to demodulate to the same frequency offset value. That is, even if each satellite terminal 300 transmits data by the same carrier frequency, the central station 200 performs a frequency shift through a long path as described above. Receive differently shifted frequency signals.

Accordingly, the central station 200 is transmitted by transmitting the compensation value of the frequency offset distorted by the frequency shift between the satellite terminals 300 to the satellite terminals 300 and reflecting the data when the satellite terminals 300 transmit the data. In order to enable normal demodulation

Hereinafter, a procedure of compensating for and transmitting a time delay by the W-CDMA modulator 322 of the satellite terminal implemented according to the present invention will be described in detail with reference to FIGS. 7 and 8.

As described above, the W-CDMA modulator 322 whose primary function is data modulation of a signal to be transmitted by the satellite terminal 300 in the satellite bidirectional system to which the present invention is applied, has spread multiple access to communication using satellite. A software algorithm is added to compensate for the time delay that may occur due to the Spread Multiple Access.

That is, the signal transmitted from the satellite terminal 300 to the central station 200 via the satellite 100 must go much further than the distance that the conventional terrestrial wave passes. Therefore, this time delay is bound to occur. This time delay is also the most important problem in general satellite communication. Therefore, for reliable satellite communication, the central station 200 according to the present invention compensates for the time delay by the following procedure for mutual communication with the satellite terminal 300.

Particularly, in the CDMA scheme, since spreading codes (eg, PN (Pseudo Noise) codes) on the transmitting and receiving side must match, demodulation, the present invention using the code division multiple access scheme in the reverse link is a transmission side according to a time delay. The spreading codes at the satellite terminal 300 and the central station 200 at the receiving end may not match so that demodulation may not be performed properly.

On the other hand, the spreading code used in the conventional mobile communication system is used to distinguish the base station, each base station has a unique PN offset value, each terminal confirms this to perform normal data communication between the base stations. However, the spreading code applied to the present invention is not intended to distinguish the base stations, and since the spreading data is reached over a considerable distance through the satellite, a time delay problem is not considered in a general mobile communication system. Accordingly, there is a problem that accurate demodulation cannot be performed in the central station 200 according to the mismatch of the spreading codes according to the time delay. Accordingly, the central station 200 should be implemented to compensate for the time delay in order to solve the spreading code mismatch problem caused by the time delay.

7 is a flowchart illustrating a procedure for compensating and transmitting a time delay offset for data to be transmitted by a satellite terminal of a bidirectional satellite system according to an embodiment of the present invention.

Referring to FIG. 7, first, the satellite terminal 300 transmits data by an initial spreading code offset value that does not take time delay of the satellite terminal 300 in step S701. Then, the satellite terminal 300 waits for a response from the central station 200 for a predetermined reference time set in consideration of the time delay caused by transmission through the satellite and the information processing delay time of the central station 200 (S702). step).

At this time, the central station 200 receives and demodulates the data transmitted by the satellite terminal 300 by the initial spreading code offset value, and the difference of the spreading code offset of the data transmitted by the initial spreading code offset value is If the signal cannot be demodulated normally (eg, outside the window range of 1 ms), the response signal cannot be transmitted to the satellite terminal 300.

In this case, the satellite terminal 300 does not receive a response signal from the central station 200 within the predetermined reference time (step S703), and the satellite terminal 300 has the spreading code offset It is determined that there is a difference, and the spreading code offset is changed from an initial value (step S704). In this case, since the changed spreading code offset value has a high probability of being around the initial value, the changed spreading code offset value is implemented to be far from the initial value. A detailed method for setting the changed value will be described later with reference to FIG. 8.

Then, the satellite terminal 300 retransmits the data by the changed spreading code offset value (step S705).

The satellite terminal 300 waits for a response signal again for the set time, and if the response signal is not received again, sets the spreading code offset value to a value further away from the initial value to transmit data. do.

If the satellite terminal 300 receives the response signal from the central station 200 that the data is normally transmitted by the changed spreading code offset value, the satellite terminal 300 receives the spreading code offset value and the spreading code offset that the satellite terminal has. The values are compared (step S706), and it is determined whether the values are valid (step S707).

As a result of the determination, if it is determined that the received value is a valid value, the spreading code offset is checked and set again according to the correction value for the received spreading code offset (S708), and the data according to the set spreading code offset value. Will be sent.

Meanwhile, a method of setting a retransmission value from the initial value of the spread code offset in order to correct the spread code offset value described above with reference to FIG. 7 will be described.

8 is a diagram illustrating a method of selecting a spreading code offset during retransmission in a satellite terminal of a bidirectional satellite system according to an embodiment of the present invention.

Referring to FIG. 8, when the satellite terminal 300 transmits initial data as described above with reference to FIG. 7 (801), the satellite terminal 300 transmits the initial value of the spreading code offset. Then, if there is no response from the central station 200 for a predetermined time, it is determined that the spreading code offset value is not correct, and the spreading code offset value is changed and retransmitted.

As described above, even if the spreading code offset value is distorted, since the probability of becoming the peripheral value of the preset initial value is high, the value to be retransmitted to be set away from the peripheral value of the initial value is set.

For example, when there is no response signal from the central station 200 and the secondary transmission 802 is to be performed, the changed spreading code offset value used in the secondary transmission can be transmitted by setting it to the next value 0.5 ms from the initial value. .

In addition, when there is no response to the secondary transmission due to the changed spreading code offset value as described above, the third spreading may be performed by setting the spreading code offset value to a value 0.5 ms before the initial value.

Similarly, if there is no response to the third transmission, the spreading code offset value is set to 1.0 ms from the initial value and then transmitted.

By the same method, the spreading code offset can be confirmed quickly by changing the spreading code offset value away from the initial value and retransmitting.

By performing as described above, the central station 200 can perform fast demodulation by setting a search window value within 1 ms. That is, as described above, the spreading code offset value is changed and retransmitted with a difference value of 0.5 ms, and the central station 200 receiving the changed data of the spreading code offset value performs a search process within 1 ms. When the changed spreading code offset value enters into the search window, the search process is completed, and a more accurate spreading code offset value is fed back to the corresponding satellite terminal 300 to quickly and accurately use the spreading code in the satellite communication system. The spreading code offset value may be determined.

Accordingly, more reliable satellite communication between the satellite terminal 300 and the central station 200 can be implemented.

On the other hand, in the embodiment of the present invention has been described with respect to specific embodiments, various modifications are possible without departing from the scope of the invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the appended claims, but also by those equivalent to the claims.

According to the present invention, by applying the CDMA scheme to the reverse link of the two-way satellite communication system, there is an advantage that the capacity of subscriber stations can be increased and data security can be enhanced. In addition, according to the present invention it is possible to implement an effective two-way satellite communication by solving the problem of time delay and frequency shifting caused by transmitting the CDMA data through the satellite.

Claims (15)

A satellite communication system includes a predetermined communication satellite, a central station transmitting predetermined broadcast information to a plurality of subscribers through the communication satellite, and a plurality of satellite terminals receiving information transmitted from the central station through the communication satellite. And the forward link data transmitted from the central station to the satellite terminal uses a time division multiple access scheme, and the reverse link data transmitted from the satellite terminal to the central station uses a code division multiple access scheme in a bidirectional satellite communication system. In the apparatus for transmitting the data to be transmitted through the reverse link in the satellite terminal, A phase locked loop control signal generator for generating an intermediate frequency control signal from the frequency offset compensation value received from the central station; A local oscillator for generating a compensated intermediate frequency signal by controlling a phase locked loop circuit according to an intermediate frequency control signal output from the phase locked loop control signal generator; A multiplier for multiplying the data to be transmitted with an intermediate frequency signal output from the local oscillator; And Extracting the frequency offset compensation value from the data including the frequency offset compensation value received from the central station, generating a control signal corresponding to the frequency offset compensation value, and converting the generated control signal to the phase locked loop control signal generator. And a controller for transmitting the data transmission apparatus of the satellite terminal in the bidirectional satellite system. delete The method of claim 1, The device, A spreading code generator for generating a predetermined spreading code based on a predetermined spreading code offset initial value; And And a multiplier for spreading the data by multiplying the data to be transmitted by the satellite terminal with a spreading code output from the spreading code generator. The method of claim 1, The device, And a QPSK modulator for modulating the data to be transmitted by the satellite terminal according to a QPSK scheme. The method of claim 3, And the spreading code generator outputs the spreading code by reflecting a spreading code offset compensation value received from the central station. The method of claim 1, And the reverse link data is a wideband code division multiple access (W-CDMA) scheme. A satellite communication system includes a predetermined communication satellite, a central station transmitting predetermined broadcast information to a plurality of subscribers through the communication satellite, and a plurality of satellite terminals receiving information transmitted from the central station through the communication satellite. And the forward link data transmitted from the central station to the satellite terminal uses a time division multiple access scheme, and the reverse link data transmitted from the satellite terminal to the central station uses a code division multiple access scheme in a bidirectional satellite communication system. In the method for transmitting data to be transmitted through the reverse link in the satellite terminal, Extracting a frequency offset compensation value from data including the frequency offset compensation value received from the central station; Generating a control signal corresponding to the frequency offset compensation value; Transmitting the generated control signal to the phase locked loop control signal generator; Generating a compensated intermediate frequency signal by controlling a phase locked loop circuit according to the generated intermediate frequency control signal; And And a frequency modulating multiplying the data to be transmitted with the generated intermediate frequency signal. delete The method of claim 7, wherein The central station compensates for the time delay of the received data by extracting the position value of the satellite terminal through the data received from the satellite terminal to feed back to the satellite terminal. The method of claim 7, wherein And the reverse link data is a wideband code division multiple access (W-CDMA) scheme. A satellite communication system includes a predetermined communication satellite, a central station transmitting predetermined broadcast information to a plurality of subscribers through the communication satellite, and a plurality of satellite terminals receiving information transmitted from the central station through the communication satellite. And the forward link data transmitted from the central station to the satellite terminal uses a time division multiple access scheme, and the reverse link data transmitted from the satellite terminal to the central station uses a code division multiple access scheme in a bidirectional satellite communication system. In the method for transmitting data to be transmitted through the reverse link in the satellite terminal, Spreading the data to be transmitted by using an initial value of a spreading code offset and transmitting the spread data to the central station; And If there is no response from the central station for a preset time, the spreading code offset is set to a value changed from the initial value of the spreading code offset, the spreading data is spread by the set spreading code offset, and retransmitted. When receiving a response signal from the central station, it is determined whether the received spreading code offset value and the spreading code offset value of the satellite terminal are valid, and if the result is valid, the received spreading code offset value is determined. Resetting the spreading code offset according to the data transmission method of the satellite terminal in the bidirectional satellite system. The method of claim 11, The method of changing the spreading code offset value is And retransmitting the satellite terminal away from the initial value of the spreading code offset each time the retransmission is repeated. The method of claim 11, And a change range of the spread code offset value is 0.5 ms. delete The method of claim 11, And the reverse link data is a wideband code division multiple access (W-CDMA) scheme.

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