KR20010017851A - Method of initial access synchronization in return link using DS/CDMA in satellite communications system - Google Patents

Abstract

PURPOSE: A method for establishing the initial access synchronization of a satellite communication system using a DS/CDMA system in a return link is provided to increase the data transmission efficiency and reliability of packets by extracting the deviation information of a carrier wave frequency and a timing using an initial access time slot before real signal information and traffic data are transmitted and by compensating it in a terminal office. CONSTITUTION: A terminal office receives reference timing information periodically sent from a central office through an MPEG-2 transport stream(201,202) and generates a transmitting timing dependent on a return link channel structure(203). The terminal office sends an initial access CDMA burst at an initial access time slot(204). The terminal office drives a timer and transits to a standby state to receive a response message from the central office(205). A receiving part in the central office acquires PN code synchronization using a preamble of the initial access CDMA burst and extracts a frequency error(207). The receiving part calculates a timing deviation value and a frequency deviation value(208) and transfers them to a management part with demodulated data. The management part reconfigures them into an IP packet to transfer them to the terminal office(209) and transfers the IP packet to a transmitting part. The transmitting part multiplexes the IP packet into an MPEG-2 transport stream and sends it to the terminal office(210). Receiving the response message before the timer operation ends, the terminal office releases the timer and executes the next operation(211).

Description

Method of initial access synchronization in return link using DS / CDMA in satellite communications system}

The present invention relates to a direct sequential code division multiple access (hereinafter referred to as DS / CDMA) satellite communication system. In particular, the carrier frequency and timing deviation information using an initial access time slot before actual signal information and traffic data are transmitted. The PN synchronization can be obtained with short length preambles in real signal information and traffic bursts by extracting and correcting them to the terminal station. In the return link that can improve the data transmission efficiency of packets and increase their transmission reliability. The present invention relates to a method for establishing initial access synchronization in a satellite communication system using a DS / CDMA scheme.

In the asymmetric multimedia satellite communication system, which consists of a forming network between a central station and a plurality of terminal stations and uses a DS / CDMA transmission method for the return link from the terminal station to the central station, carrier frequency transitions occurring on the return link and the wide area of the terminal station The timing shift of the signal received to the central station due to the industrial accidents causes the loss of actual signal information data and traffic data, or it takes a lot of time to acquire the PN synchronization of the DS / CDMA signal. Thus, the preamble length of the bursts must be long, which in turn reduces the transmission efficiency of the burst packets.

Terrestrial cellular CDMA system using the conventional DS / CDMA scheme continuously transmits the CDMA signal to be transmitted in the reverse channel until the terminal receives a response signal from the base station. In addition, in the quasi-synchronous DS / CDMA satellite communication system proposed to use the bidirectional DS / CDMA scheme, the terminal station receives the master signal transmitted from the central station and the echo signal sent from its own terminal station, and thus the frequency and timing deviation information on the satellite link. Extract and compensate.

Applying these methods to satellite communication systems can increase the complexity of the system configuration and overuse system and satellite transponder power. In addition, the application to the satellite communication system that uses a different transmission scheme in the forward link and the return link, and must intermittently transmit a finite length burst signal on the return link is unsuitable.

Therefore, the present invention extracts the deviation information of the carrier frequency and timing by using the initial access time slot before actual signal information and traffic data is transmitted, and corrects it by providing it to the terminal station, thereby shortening the actual signal information and traffic burst. It is an object of the present invention to provide a method for improving data transmission efficiency and increasing transmission reliability of packets by enabling PN synchronization to be obtained with a length of preamble.

The present invention for solving the above-described problem, after starting or resetting the terminal station PC, receiving the reference timing information periodically transmitted from the central station through the MPEG-2 transport stream at the terminal station, and receiving at the terminal station; Extracting one reference timing information to generate a transmission timing, and then transmitting an initial access CDMA burst to an initial access time slot of an access channel, wherein the terminal station that has sent the initial access CDMA burst drives a timer and Transitioning to a standby state for receiving a response message, acquiring PN code synchronization at the central station receiving unit receiving the initial access CDMA burst, extracting a frequency error, and calculating a timing deviation amount and a frequency deviation amount at the central station receiving unit; Compute and pass along the demodulated data to the central station control station And reconstructing them into IP packets by the central station manager receiving the timing deviation amount, frequency deviation amount, and demodulated data, and forwarding them to a central station transmitter. Multiplexing the two transport streams and sending them to the terminal station; if the terminal station receives the response message before the timer operation is terminated, the terminal station performs the next operation required with the release of the timer. And upon retrying the next initial access frame.

1 is a block diagram of an asymmetric multimedia satellite communication system to which the present invention is applied.

2 is a flowchart for explaining a method for establishing initial access synchronization according to the present invention;

3 is a channel structure diagram of a return link according to the present invention;

4 is an initial access burst structure diagram in accordance with the present invention.

5 is a functional diagram of a central station receiving unit according to the present invention;

6 is a functional configuration diagram of a central station transmitter according to the present invention.

7 is a functional configuration diagram of a terminal station set-top box according to the present invention.

<Explanation of symbols for main parts of drawing>

101: terminal station 102: terminal station PC

103: set top box 104: central station

105: central station transmitter 106: central station receiver

107: central station management 108: satellite

According to the present invention, a time slot for transmitting a burst is specified by designating a specific initial access frame between periodically set reference timings in order to achieve a network synchronization. The transmitting and receiving central station extracts the carrier frequency and timing deviation information generated on the satellite transmission path between the terminal stations through the demodulation process, and transmits the information to the terminal station through the forward link to compensate. As a result, PN code synchronization can be obtained quickly and reliably even in a short preamble of a burst generated on the return link, thereby increasing the transmission efficiency of the burst packet.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1 is a configuration diagram of an asymmetric multimedia satellite communication system to which the present invention is applied, and includes one central station 104 and a plurality of terminal stations 101.

The central station transmitter 105 existing in the central station 104 multiplexes the reference synchronization timing information generated by the network synchronizer timing generator (not shown) of the central station and the extracted frequency / timing deviation information. The terminal station 101 transmits an initial access CDMA burst in accordance with the generated transmission slot timing, receives, stores and compensates for the extracted deviation information. The central station receiver 106 extracts frequency and timing deviation information of the CDMA bursts received in the initial access mode of operation. The central station management station 107 is responsible for overseeing system operations such as system management and resource allocation.

2 is a flowchart illustrating a procedure for establishing initial access synchronization according to the present invention.

After starting or resetting the terminal station PC, the terminal station receives 202 the reference timing information which is periodically transmitted 201 through the MPEG-2 transport stream from the central station and 202 extracts the reference timing information according to the return link channel structure described in FIG. The transmission timing is generated (203). The terminal station sends (204) an initial access CDMA burst having the configuration described in FIG. 4 to an initial access time slot 303 of the access channel. The terminal station drives the timer and transitions to the standby state for receiving a response message from the central station (205). The central station receiver acquires PN code synchronization using the preamble 401 of the received initial access CDMA burst 206 and extracts a frequency error (207). The central station receiving unit calculates a frequency deviation amount on the return link transmission path between the central station and the corresponding terminal station from the timing deviation amount and the extracted frequency error using the obtained PN code synchronization acquisition time point and the reference timing start time point (208). Together with the central station management department. The central station manager reconstructs them into IP packets for transmission to the terminal station (209) and forwards them to the central station transmitter. The central station transmitter multiplexes the data into an MPEG-2 transport stream and transmits it (210). If the terminal station receives the response message before the timer operation ends, the terminal station performs the next operation required with the timer release. If the timer operation is terminated before receiving the response message, the terminal station retries the next initial access frame (212).

3 is a channel structure diagram of a return link according to the present invention.

The return link is largely divided into an access channel and a traffic channel. The access channel is a channel for transmitting a signal information message for requesting a traffic channel allocation for transmitting actual traffic information and a signal information message for extracting transmission timing and frequency deviation information between the corresponding terminal station and the central station at an initial connection. . The traffic channel is a channel for transmitting a traffic information message generated at the request of the terminal station user, which is allocated to each terminal station user based on the request allocation method and released after use. The channel of the return link consists of several time slots, which form a plurality of frames 301, 302 based on the reference timing 306. Each frame includes a number of time slots 304, 305, of which M time slots 304 at the beginning of the frame are used as access channels and the next N time slots 305 are used as traffic channels. Any frame 301 (application example: frame 0) within the reference timing period is an interval used for establishing initial access synchronization, and includes an initial access time slot 303 and a guard time 307 or a traffic time slot 305. It is composed together. Guard time 307 ensures that the initial access CDMA burst does not overlap the previous / post time slots, taking into account the delay in satellite transmission paths that may occur due to the wider nature of the terminal station distribution.

4 is a structure of an initial access CDMA burst according to the present invention, which includes a preamp 401, a unique word 402, a control field 403, a data length field 404, data 405, an encoder checksum 406. And tail bits 407.

5 is a functional configuration diagram of the central station receiving unit according to the present invention, and comprises a set top box 501 for receiving a central station network synchronizer, a CDMA burst processing unit 502, and a receiving data processing unit 503. FIG. The central station network synchronizer set-top box 501 receives a MPEG-2 transport stream transmitted from the central station transmitter, extracts reference timing, and provides the CDMA burst processing unit. The CDMA burst processing unit 502 performs the function of receiving and demodulating initial access CDMA bursts sent from terminal stations on the return link. The PN code synchronization is obtained during the preamble time of the received burst, and the frequency error is extracted using the data despread from this point. After performing this function, a series of demodulation procedures are followed to demodulate the data. The CDMA burst processing unit 502 delivers the frequency error extracted along with the demodulated data and timing error information between the reference timing and the PN code synchronization acquisition time to the reception data processing unit 503. The receiving data processing unit 503 configures this as an IP packet and delivers it to the central station management unit. The central station manager reconstructs the received IP packet into the deviation information IP packet for the corresponding terminal station and delivers the received IP packet to the central station transmitter.

6 is a functional configuration diagram of a central station transmitter according to the present invention, which includes a network synchronizer information generating unit 601, an MPEG-2 transport stream generating unit 602, an MPEG-2 transport stream remultiplexing unit 603, and modulation. It consists of units 604.

The network synchronizer information generating unit 601 is composed of a reference clock generator, a counter and a bit register so that the counter on the reference clock counts the reference clock indefinitely and periodically from the MPEG-2 transport stream generation unit 602. The counter value at that time is output by the network synchronizer information latch signal. The MPEG-2 transport stream generation unit 602 receives the network synchronizer information and the frequency / timing deviation information from the network synchronizer information generation unit 601 and the central station management unit, respectively, and configures the MPEG-2 transport stream packet. The MPEG-2 transport stream thus constructed is broadcasted to all terminal stations via satellite via the MPEG-2 transport stream remultiplexing unit 603 and the modulation unit 604.

7 is a functional configuration diagram of a terminal station set-top box that performs a function of receiving an MPEG-2 transport stream of a TDM forward link and transmitting a CDMA packet on a return link. The terminal station TDM receiving unit 701 transmits timing. And a generation unit 702 and a DS / CDMA burst transmitter 703.

The terminal station TDM receiver 701 receives, demodulates and demultiplexes MPEG-2 transport streams continuously transmitted from the central station. Demultiplexed packets are separated by the program identifier. The traffic information packet is transmitted to the terminal station PC, the network synchronizer packet to the transmission slot timing generator 702, and the signal information packet for the frequency / timing deviation information is transmitted to the DS / CDMA burst transmitter 703, respectively. The transmission slot timing generator 702 receives the network synchronizer packet, generates a reference timing and a transmission slot timing used in the terminal station, and provides the same to the DS / CDMA burst transmitter 703. The DS / CDMA burst transmitter 703 corrects the transmission carrier frequency by using the carrier frequency deviation and reference carrier frequency information, and generates an initial access burst, an access burst, and a traffic burst input from the terminal station PC 102 to generate a transmission slot timing. On the basis of the transmission slot timing input from the unit 702, transmission is performed in accordance with the corrected time slot using the timing deviation information.

The terminal station 101 is operated in an initial access mode, an access mode and a traffic mode, depending on the time of operation. The initial access mode is an initial state immediately after the terminal station PC 102 is powered on or reset and booted, and refers to a state before the user receives or requests an actual service. At this time, the terminal station 101 is initialized with the initially set frequency / timing deviation and operating parameters, and the service is started with the frequency and timing deviation between the central station 104 and the corresponding terminal station 101 generated in the state of interruption of service. The initial access CDMA burst is sent to the central station 104 through the series of processes mentioned in connection with FIG. According to the initial access synchronization establishment procedure of FIG. 2, the terminal station 101 which has received the frequency / timing deviation stores this information. The access mode and the traffic mode are operation modes which are subsequently transitioned sequentially and are transmitted in corresponding time slots according to the frequency and timing at which the signal information and traffic CDMA bursts generated by the service start are corrected. In these modes of operation, functions for frequency and timing deviation extraction are continuously performed. When the value of these information changes, the terminal station 101 replaces the changed new deviation information with the existing value and corrects the deviation.

The present invention described above is capable of various substitutions, modifications, and changes within the scope without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, the foregoing embodiments and the accompanying drawings. It is not limited to this.

As described above, the present invention relates to the frequency and timing deviations existing between the satellite link between each terminal station and the central station in asymmetric multimedia satellite communication system using DS / CDMA scheme for the return link. By configuring slots, frequency and timing deviations can be extracted and corrected before service is started, ensuring fast and reliable PN code synchronization for subsequent burst packets and shorter preamble lengths for signal and traffic bursts. This has the effect of increasing the transmission efficiency of burst packets.

Claims (3)

Receiving, by the terminal station, reference timing information periodically transmitted from the central station through the MPEG-2 transport stream after the terminal station PC is started or reset; Extracting the reference timing information received by the terminal station to generate a transmission timing and transmitting an initial access CDMA burst in an initial access time slot of an access channel; The terminal station sending the initial access CDMA burst starts a timer and transitions to a standby state for receiving a response message from the central station; Acquiring PN code synchronization and extracting a frequency error in a central station receiving unit that receives the initial access CDMA burst; Calculating, by the central station receiving unit, a timing deviation amount and a frequency deviation amount, together with the demodulated data, to the central station management station; Receiving, by the central station manager, the timing deviation, frequency deviation, and demodulated data, reconstructing them into IP packets and forwarding them to a central station transmitter; Transmitting the IP packet to the terminal station by multiplexing the IP packet into an MPEG-2 transport stream by a central station transmitting unit receiving the IP packet; If the terminal station receives the response message before the timer operation ends, the terminal station performs the next operation required together with timer release and deviation compensation, and retrying in the next initial access frame when the timer operation ends before receiving the response message. A method of establishing initial access synchronization in a satellite communication system using a DS / CDMA scheme for a return link, characterized in that the 2. The method of claim 1, wherein the transmission timing comprises one initial access time slot and a guard time. 2. The initial access synchronization of a satellite communication system using a DS / CDMA scheme for a return link according to claim 1, wherein the transmission timing comprises one initial access time slot, guard time, and one or more traffic time slots. How to establish.