JP2001211139A - Bidirectional transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the communication rate of a spread spectrum communication system. SOLUTION: For a system start-up, a center device and a terminal device are both provided with a spread code storage part 18 stored with the same spread code. The terminal device sends an SS modulated signal with the spread code on the basis of a clock Ckd sent out of the center device. The center device performs SS demodulation with the same spread code and a phase synchronism detection part 16 detects the degree of phase matching. With a phase shift instruction, control data Dpc are sent to the terminal device. The terminal device generates a spread code with the phase control data and sends an SS modulated wave out again. Consequently, nearly complete SS demodulation is carried to on the center device side by repeating the mentioned processes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional transmission system using a spread spectrum communication system. In particular, the present invention relates to a transmission system that eliminates synchronization acquisition of a spreading code and improves data transmission throughput.

[0002]

2. Description of the Related Art Conventionally, as an example of a bidirectional transmission system, there is a broadband transmission system such as a CATV system provided with an uplink channel and a downlink channel by frequency multiplexing. The upstream channel uses a low group frequency band (several tens of MHz), and the downstream channel uses a high group frequency band (several hundred MHz). In this frequency multiplexing system, noise degradation is small in a high frequency band and large in a low frequency band. For this reason, in a low group frequency band, adoption of a spread spectrum communication system has been proposed as disclosed in Japanese Patent No. 2727297.

Conventionally, a synchronization method using a sliding correlator has been adopted as a reception method of the spread spectrum communication system (hereinafter, SS system). The synchronization pull-in by the sliding correlator is performed as follows. FIG. 5A shows a modulation unit of the direct spreading SS system.
First, the carrier Wc is multiplied by the data signal d (t). The PSK modulated wave obtained here is further multiplied by a spreading code of p (t) to generate an SS modulated wave. This SS modulated wave is transmitted to a transmission path (not shown).

Next, FIG. 5B shows a demodulation unit. In the demodulation unit, the data signal d (t) is demodulated by an operation reverse to that of the modulation unit. However, complete demodulation requires a synchronized state in which the patterns and phases of the spreading codes on the modulation side and the demodulation side are almost the same.

FIG. 6 shows an ideal state of the direct diffusion SS system. The ideal transmission is that the same spreading code is used for modulation and demodulation. In reality, it is impossible to share the same spreading code generator, so that the phase of the spreading code generator on the receiving side is sequentially shifted to synchronize with the transmitting side. The case where the amplitude of the demodulation-side PSK wave becomes maximum is set as a synchronization condition, and reception is performed at that phase. This method is a synchronization method using a sliding correlator. In such a system, reception of the spread spectrum communication system is performed.

[0006]

However, the synchronization method based on the sliding correlation has a simple circuit configuration and can be expected to operate stably, but has a drawback that much time is required until synchronization is established. In particular, the longer the period of the spreading code becomes, the more the tendency becomes. Also, in burst communication, a time for establishing synchronization is required for each packet, which causes a problem that an effective transmission speed is reduced.

[0007] In data communication using, for example, a CATV system, each terminal device sends out data using an idle time of a transmission path. Therefore, when a large number of transmission requests are generated, idle time is detected from each terminal one after another, and data is transmitted. In this case, if synchronization is achieved using a sliding correlator for each packet, a great deal of time is required until synchronization is achieved. Therefore, there is a problem that the idle time of the transmission path cannot be used effectively.

As another method for shortening the period until the synchronization is established, there is a matched filter method using a matched filter or the like. However, there is a disadvantage that the circuit scale becomes large (complicated) and the cost increases with an increase in the code length of the spread code.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a spread spectrum communication system in which phase is taken into consideration from a terminal device side in a spread spectrum communication system performed between a center device and a fixed terminal device. The purpose of the present invention is to transmit a modulated wave and eliminate the synchronization acquisition time in both devices to improve the net communication speed.

[0010]

Means for solving the above problem are as follows. In a two-way transmission system having a transmission band based on a spread spectrum communication system, a transmission is performed from a transmission side on a reception side when the system is initialized. Demodulating incoming spread spectrum modulated signal (spectrum despreading)
Then, the phase information that can be demodulated is transmitted to the transmitting side, and the transmitting side generates a spread code with a phase based on the phase information and performs spread spectrum modulation (spread spectrum) to generate the phase information. Is a bidirectional transmission system characterized in that the phase of a spread code is optimized, and after initialization, the transmitting side generates a spread code with the optimized phase and performs spread spectrum modulation. .

The bidirectional transmission system is not limited to a bidirectional communication system as long as bidirectional communication is possible. The upstream line and the downstream line may be different from each other like an optical fiber transmission line, or may be a single line such as a frequency multiplexed broadband transmission line. As a broadband transmission line for frequency multiplexing, a CATV transmission line capable of bidirectional transmission by dividing into a high group band and a low group band can be used. Instead of dividing into two, the multi-channel may be formed by simple frequency multiplexing to enable two-way communication.

[0012] As a method of dividing a high group band and a low group band into two, a head end for converting a frequency from a high group to a low group and from a low group to a high group is provided at one end of the transmission line, and the transmission line is provided with There is a method that enables two-way communication between connected devices. Further, in this method, a center device is connected to the transmission line, and a predetermined video signal or data is transmitted from the center device to the transmission line, and two-way communication is performed between the terminal devices connected to the transmission line. A system that enables the terminal device and the two-way communication between the terminal device and the center device is conceivable.

Further, in view of the system configuration, a center device may be provided at the position where the head end is located, in addition to the head end or instead of the head end. When a center device is provided instead of the head end, communication between terminal devices is performed via the center device. As described above, various methods can be considered, but the present invention is not limited to these methods. However, in a CATV transmission line where a video signal is transmitted from a center device, when the terminal device is used for data transmission between a terminal device and the center device, for Internet communication with a center device interposed, etc., an upstream ingress noise is generated. This is particularly effective because it becomes stronger.

Further, the communication using the spread spectrum method is sufficient if it is used in some bands of the system, and need not be used in all channels. In particular,
The use of the spread spectrum method for data transmission of the low group uplink channel has the advantage of being resistant to ingress noise as described above.

The transmitting side and the receiving side are devices connected to the transmission path, which are devices that transmit data by the spread spectrum method and devices that receive the data. For example, the transmitting side is a terminal device, and the receiving side is a center device. However, the system may be such that one of the terminal devices is on the receiving side and the other terminal device is on the transmitting side. The spreading code used at the time of initialization may be the same as or different from the spreading code used after initialization. That is, if there are a plurality of transmitting sides, a spreading code for exclusive use at the time of initialization can share the spreading code for initialization. If they are different, it is sufficient to use the spreading code of each transmitting side assigned during normal operation.

According to a second aspect of the present invention, a clock signal is generated on the receiving side, the clock signal is transmitted to the transmitting side, and the receiving side generates a spread code in synchronization with the clock signal. Is characterized in that a spread code is generated in synchronization with a phase based on the clock signal and the optimized phase.

According to the third aspect of the present invention, the receiving side has a spreading code storage unit storing a predetermined spreading code, and a phase synchronization detection for detecting the phase of the spread spectrum modulated signal transmitted from the transmitting side. The transmitting side includes a spreading code storage unit that stores the same spreading code as a predetermined spreading code.At the time of initialization, the transmitting side causes the transmitting side to transmit a spread spectrum modulated signal with the predetermined spreading code. It is characterized in that spread spectrum demodulation is performed with the same spread code, a phase is obtained by a phase synchronization detection unit, and an optimized phase is notified to the transmission side.

According to the fourth aspect of the present invention, the transmitting side:
A phase storage unit for storing each optimized phase is provided. After initialization, a spread code is generated using the optimized phase stored in the phase storage unit, and a spread spectrum modulation signal is transmitted. .

According to a fifth aspect of the present invention, the transmitting side is a terminal device connected to the transmission line, and the receiving side is a center device connected to the transmission line.

[0020]

According to the first aspect of the present invention, in the spread spectrum communication system, the transmitting side generates a spreading code on the transmitting side in accordance with the phase of the spread code generation at the time of spread spectrum demodulation on the receiving side. Transmits spread spectrum modulated signals. This eliminates the need for the receiving side to match the phase with the spread spectrum modulated signal transmitted from each transmitting side during spread spectrum demodulation.
That is, the spread spectrum modulated signal from each transmitting side can be demodulated immediately. Phase adjustment time on the receiving side,
That is, since the waiting time on the transmission side is omitted, the net transmission time is shortened. Therefore, a bidirectional transmission system with high transmission efficiency is obtained.

According to another aspect of the present invention, the receiving side generates a spread code on the basis of a clock of the receiving side. Further, the transmitting side generates a spreading code on the transmitting side at an optimized phase based on the clock signal transmitted from the receiving side. The spreading code on the receiving side and the spreading code on the transmitting side are generated based on the same clock. Therefore, both spreading codes can be reliably synchronized.

According to another aspect of the present invention, the receiving side includes a spreading code storing section storing a predetermined spreading code and a phase synchronization detecting section detecting the phase of the spread spectrum modulated signal transmitted from the transmitting side. Each transmitting side is provided with a spreading code storage unit that stores the same spreading code as a predetermined spreading code on the receiving side.

Then, at the time of system initialization, the transmitting side first transmits a spread spectrum modulated signal using the predetermined spreading code. The receiving side performs spread spectrum demodulation with the same spreading code. At this time, for complete demodulation, it is necessary that the spreading code on the transmitting side and the spreading code on the receiving side match and their phases match (phase synchronization). However, the phases do not generally match due to delay due to propagation.

The phase synchronization detecting section detects the degree of coincidence from, for example, the amplitude value of the spread spectrum demodulated signal or its change, and notifies the transmitting side of the optimized phase. As a result, a unique phase is set for each transmission side, that is, for the phase (occurrence time) of the spread code on the transmission side. On the receiving side, the spreading code on the transmitting side matches the spreading code on the receiving side and the phase also matches, so that complete demodulation is performed. As a result, highly accurate communication is guaranteed.

According to another aspect of the invention, at the time of system initialization, each transmitting side stores the optimized phase in the phase storage unit. After the initialization, the transmitting side generates a predetermined spread code using the optimized phase stored in the phase storage unit and transmits the spread spectrum modulated signal to the receiving side. That is, it is not necessary to perform phase adjustment with the receiving side each time, and data can be immediately transmitted to the receiving side by the spread spectrum communication method. Therefore, spread spectrum communication with an increased transmission speed becomes possible.

According to another aspect of the invention, the transmitting side is a terminal device and the receiving side is a center device. Therefore, CATV
It is possible to use the spread spectrum method of this method for the uplink channel in the transmission path, and it is possible to improve the data transmission efficiency and the noise resistance.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following examples. (Embodiment) FIG. 1 shows a bidirectional broadband transmission system using a spread spectrum communication system as an example of a bidirectional transmission system. The figure is a schematic configuration diagram. The bidirectional broadband transmission system according to the present embodiment includes a center device (reception side) 10, a plurality of terminal devices (transmission side) 20, and a transmission line 30 connecting them. Here, a CATV system using an optical fiber and a coaxial cable for the transmission line 30 is assumed as the system. In this system, it is assumed that a high group downstream signal from the center apparatus 10 is constantly transmitted, and a low group upstream signal from each terminal apparatus 20 to the center apparatus 10 is transmitted sharing the same band in a time division manner. Here, it is assumed that the spread spectrum communication method is not applied to the high group downlink channel from the center device 10 but is applied only to the low group uplink channel from the terminal device 20.

FIG. 2 shows a center device 10 according to the present embodiment.
The figure is a system block diagram. The center device 10 of the present embodiment includes a demultiplexer 11 for separating a low-group up signal and a high-group down signal, and a despreader 12 for performing spread-spectrum demodulation (spread spectrum despreading) of a spread-spectrum modulated low-group signal. , A spreading code generator 13 for generating a spreading code used for SS demodulation, and a PS demodulated by a despreader 12.
A digital demodulation unit 17 for further demodulating the K modulation signal into a clock signal CK _u and a data signal _Du , a synchronization detection unit 16 for detecting the synchronization state (phase) of the input SS modulated wave, the communication control unit 15 for processing the control data such as control data D _pc, using the digital modulation unit 14 and startup of the system, and sends modulates the control data and the data signals D _d with the clock CK _d as a downlink signal S _d Spreading code storage unit 18 storing the spreading code to be
Consists of

FIG. 3 shows a system block diagram of the terminal device 20. The terminal device 20 of the present embodiment includes a demultiplexer 21 for separating a high-group downlink signal and a low-group uplink signal, and a digital signal for demodulating a clock signal CK _d , a data signal D _d , and phase control data D _pc from the downlink signal S _d. Demodulator 23, data signal D _d
Determining an address match from then, the communication control unit 24 for taking the phase control data D _pc if they match, based on the phase control data D _pc and the clock signal CK _d (adjusts the phase) to generate a spreading code digital modulation unit 26 to generate a PSK-modulated signal spreading code generator 25, and when the data transmitted from the terminal side by modulating the clock signal CK _u and the data signal D _u, the PSK modulation signal from the diffusion code generator 25 A spreader 22 for further modulating (spread spectrum) with the output spreading code to generate an SS modulated signal;
The spread code storage unit 28 stores a spread code used only when the system is started.

The purpose of the present embodiment is to receive data transmitted from the terminal device 20 by the spread spectrum communication method in a short time. For this purpose, it is necessary to match the phase of the spread code received by the center device 10 (ie, the phase of the received SS modulated signal) with the phase of the spread code generated by the spread code generator 13. The phase is adjusted because the transmission distance of the transmission path 30 and the propagation delay (phase shift) by a relay device (not shown) are present.

Conventionally, the signal obtained by the spread code synchronization detecting section 16 in the center device 10 is fed back to the spread code generator 13 to adjust the phase of the spread code on the center device 10 side, and the phase synchronization is performed while taking time. Was taking. The present embodiment is characterized in that the SS modulation signal having the same phase is transmitted from the terminal device 20 in advance, so that the phase adjustment time on the center device 10 side is eliminated and the net reception speed is increased. For this purpose, the terminal device 20 is set in advance by the following procedure.
It is necessary to store the optimized phase on the side.

FIG. 2, FIG. 3 and FIG.
This will be described with reference to the flowchart shown in FIG. FIG.
FIG. 4A shows the operation of the center device 10 side, and FIG.
That is on the terminal device 20 side. The broken line in the figure indicates transmission.
To taste. First, the operation of the center device 10 will be described. S
At step S100, an operation for specifying the target terminal device 20 is performed.
Dress and phase control data D_pcDown signal S_dSent as
I believe. Downlink signal S from center device 10_dIs a branching wave
The signal is separated by the demodulator 21 and enters the digital demodulation unit 23 (see FIG.
3). Then, the received data D
_d, Clock CK_d, Address data, and phase control data
Data D_pcAre separated.

The terminal device 20 waits for polling from the center device 10 in step S200. If the addresses match, the process proceeds to step S210. In step S210, the communication control unit 24 receives the phase control data _Dpc . The phase control data D _pc is data for instructing the generation phase of the spreading code generator 25. When the system is started, the spread code generator 25 reads the test spread code from the spread code storage unit 28 and generates the spread code by adjusting the phase with the phase control data _Dpc . For example, startup of the system generates a test spreading code in phase 0 ° of the clock CK _d as a reference. The PSK modulated wave including the generated spread code and the test data from the digital modulator 26 is further SS-modulated by the spreader 22. This SS-modulated uplink signal for test S _u is transmitted to the center device 10 and received in step S110. After the system is started, a predetermined spreading code is generated at a predetermined phase assigned to each terminal device 20 as described later.

In step S110, an uplink signal S _u including the test data is received. This step S11
The process of receiving 0 is as follows. The uplink signal S _u from the terminal device 20 enters the despreader 12 via the demultiplexer 11. In the despreader 12, SS demodulation is performed by the test spreading code from the spreading code generator 13, and the original PSK The modulated signal is restored. Thereafter, PSK modulated signals are further demodulated by the digital demodulation unit 17 is separated into reception data D _u and the clock signal CK _u.

However, for complete demodulation, the terminal 2
It is necessary that the phase of the spreading code on the 0 side and the phase of the spreading code on the center apparatus 10 side are synchronized (matched). Step S1
In 20, it is sent from the despreader 12 calculates a matching degree of the spreading code phase from the PSK-modulated signal and the data signal D _u, determining a match-mismatch phase. The degree of phase matching is calculated based on the level of the PSK modulated signal restored by despreading. The determination is also made by comparing the data signal _Du with the test data.

If the degree of coincidence is equal to or less than the predetermined value, step S1
Move to 30. In step S130, the phase synchronization detection unit 16 calculates the amount of phase adjustment generated by the terminal device 20 from the degree of coincidence, and sends the phase control data _Dpc to the communication control unit 15 as a phase shift command. Then, the communication control unit 15 and the digital modulation unit 14 modulate the phase control data _Dpc again and transmit it to the terminal device 20 as the downlink signal _Sd data. Moreover, the degree of coincidence if more than a predetermined value, the process proceeds to step S140, similarly transmits the phase matching as a downlink signal S _d to the terminal device 20.

This downlink signal S _d is received as downlink data in step S 220 on the terminal device 20 side. If it is determined in step S240 that the phases do not match, the process proceeds to step S230, and the phase control data _Dpc is instructed to the spreading code generator 25. And step S21
The phase shifts to 0, a test spread code is generated based on the phase difference of the phase control data _Dpc , and the SS modulated wave signal is updated and transmitted to the center device 10. That is, step S is performed until the phases of the center device 10 and the terminal device 20 match.
Steps S110 and S12 sequentially from 210
0, step S130, step S220, step S
Step 240, step S230, and step S210 are repeated in a closed loop. The phases match during a plurality of repetitions.

If the phases match, the process shifts from step S120 to step S140, and the phase matching data is transmitted from the center device 10 to the terminal device 20. Then, the terminal device 20 receives the phase coincidence data in step S220,
This is determined in step S240, and the process ends. As a result, the center device 10 performs almost complete SS demodulation.

At the end, the final phase shift amount is stored in the phase storage unit 24a in the communication control unit 24 (step S230). This is the terminal device 20
Is the amount of phase shift unique to. After the start of the system, a spreading code is generated using the phase shift amount stored in the phase storage unit 24a. In other words, the terminal device 20 always sets the S-phase matching S to the center device 10.
An S-modulated signal is transmitted. As in the conventional case, since the time for phase matching is eliminated, data communication can be immediately performed by the spread spectrum communication method.

In this case, the clock C in the center device is used.
K _d is used for the clock of the spread code generator 25 in the terminal device 20. That is, the phase shift (spread code generation time) is determined based on the same clock CK _{d as} that of the center device 10. Then, in the center device 10,
The spread code generator 13 using the clock CK _d
Demodulated. Since the phase adjustment is performed using the same clock CK _d , once the phases of the spreading code generators 13 and 25 are matched at the time of starting the stem, the state is maintained thereafter. Therefore, the center device 10 can accurately and reliably receive the data transmitted from the terminal device 20 by the SS method.

Further, according to this method, normal digital modulation (QPSK modulation, PSK modulation) is performed without performing processing for synchronizing spread codes on the center apparatus 10 side, that is, without being aware of the spread spectrum communication method. Can be treated as After the system is started, the loss of the synchronization pull-in time, which is a problem in the spread spectrum demodulation, is omitted on both the center device 10 and the terminal device 20 side. As a result, the net communication speed can be improved. This means that data from many terminal devices 20 is efficiently processed. Thus, for example, CAT
Applying this method to the V system results in a high-speed bidirectional data communication system.

(Modifications) Although one embodiment of the present invention has been described, various other modifications are conceivable. In the above embodiment, a unified code is used as the spread code at the time of initialization, but a different spread code may be used for each terminal device.
For example, even when the spreading code differs for each terminal device during normal operation, an initialization procedure for phase adjustment may be executed using the spreading code during operation.

In the above embodiment, the direct spread modulation (DS) system described above was used as the spread spectrum modulation system, but other systems such as frequency hopping modulation (FH) are used.
System, a pulsed frequency modulation (pulsed FM) system, a chirp modulation system, or the like.

In the above embodiment, a transmission line such as a CATV is assumed, but a fixed spatial transmission line of a base station such as a broadcast wave including other terrestrial broadcasts and satellite broadcasts, microwaves, and optical space transmission is assumed. You can also.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a bidirectional data transmission system according to an embodiment of the present invention.

FIG. 2 is a system block diagram of a center device according to the embodiment of the present invention.

FIG. 3 is a system block diagram of a terminal device according to the embodiment of the present invention.

FIG. 4 is a flowchart showing operations of the center device and the terminal device according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining a modulator (a) and a demodulator (b) of the conventional spread spectrum communication system.

FIG. 6 is an explanatory diagram illustrating modulation and demodulation of an ideal spread spectrum communication system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Center apparatus 11 Demultiplexer 12 Despreader 13 Spread code generator 14 Digital modulation part 15 Communication control part 16 Phase synchronization detection part 17 Digital demodulation part 18 Spread code storage part 20 Terminal equipment 21 Demultiplexer 22 Spreader 23 Digital Demodulation unit 24 Communication control unit 25 Spread code generator 26 Digital modulation unit 28 Spread code storage unit 30 Transmission path

Claims (5)

[Claims] In a two-way transmission system having a transmission band based on a spread spectrum communication system, at the time of system initialization, a reception side demodulates a spread spectrum modulation signal transmitted from a transmission side, and a phase at which demodulation is possible. By transmitting information to the transmitting side, the transmitting side generates a spreading code with a phase based on the phase information and performs spread spectrum modulation, thereby optimizing the phase of the spreading code generated on the transmitting side, A bidirectional transmission system characterized in that after the initialization, the transmitting side generates a spread code with the optimized phase and performs spread spectrum modulation. 2. A clock signal is generated on the receiving side.
The clock signal is transmitted to the transmitting side, the receiving side generates a spread code in synchronization with the clock signal, and the transmitting side spreads the code in synchronization with a phase based on the clock signal and the optimized phase. The bidirectional transmission system according to claim 1, wherein the code is generated. 3. The receiving side comprises: a spreading code storing section storing a predetermined spreading code; and a phase synchronization detecting section detecting a phase of a spread spectrum modulated signal transmitted from the transmitting side. Comprises the spreading code storage unit that stores the same spreading code as the predetermined spreading code, and at the time of the initialization, causes the transmitting side to transmit a spread spectrum modulated signal with the predetermined spreading code, and the receiving side 3. The two-way transmission system according to claim 1, wherein the phase spread detection is performed by the phase synchronization detection unit, and the optimized phase is notified to the transmitting side by performing spread spectrum demodulation with the same spread code. . 4. The transmission side includes a phase storage unit for storing each of the optimized phases, and after the initialization, generates the spread code using the optimized phase stored in the phase storage unit. The two-way transmission system according to claim 3, wherein the spread spectrum modulation signal is transmitted. 5. The transmission device according to claim 1, wherein the transmission side is a terminal device connected to a transmission line, and the reception side is a center device connected to the transmission line. 2. The bidirectional transmission system according to claim 1.