KR100592495B1 - Code Division Procession Cable Modem using Synchronizer - Google Patents

Abstract

The present invention relates to a cable modem of a multiple access method using a synchronization circuit. An input unit for inputting a signal through a cable, a demodulator for demodulating the input signal, and an initial value of a PN generator is extracted from the demodulated signal. An initialization unit for generating an initial value, a PN code generation unit for generating a PN code based on the generated initial value, a synchronization signal detection unit for detecting a synchronization signal, and the PN code generation unit if the synchronization signal is detected; And an actuating portion for actuating.

Code Division, Cable Modem, Synchronization, PN Code, Walsh Code

Description

Multi-access cable modem using synchronization circuit {Code Division Procession Cable Modem using Synchronizer}

1 is a block diagram of a conventional cable modem system.

2 is a general block diagram of a demodulation stage that multiplies PN codes in a code division multiple access scheme.

3 is a block diagram illustrating the concept of a code division multiple access method.

4 is a block diagram in which a PN block for code division is added to an existing cable modem system.

FIG. 5 is a detailed circuit diagram of the block diagram of FIG. 4.

6 is a schematic block diagram of a multiple access type cable modem including a synchronization signal detector according to an embodiment of the present invention.

7 is a block diagram schematically illustrating a receiver according to an embodiment of the present invention.

{Description of Major Symbols in Drawings}

101: MPEG frame portion 102: FEC encoder

103: QAM modulator 104: channel

105: QAM demodulator 106: FEC decoder

107: MPEG frame unit 401: PN code generation unit

501: latch 502: second multiplexer

503: control unit 504: band pass filter

505: first multiplexer 506: demodulator

507: adder 508: first multiplier

510: PN code generator 520: demodulator

530: initialization unit 701: second multiplier

702: Walsh code generator 703: first comparator

704: adder 705: first delay

706: second comparator 707: second delay

708: OR gate 710: Sync signal detector

720: operating part

The present invention relates to a multiple access type cable modem using a synchronization circuit, and more particularly, to improve the efficiency of the code division method using the synchronization circuit.

Existing cable modems have a limited frequency and time that can be used as a time division multiple access (TDMA) / frequency division multiple access (FDMA) method. Therefore, as the number of users increases, it is necessary to use a predetermined frequency and time by dividing, so that the speed may not be prevented from slowing down.

1 is a block diagram of a conventional cable modem system.

Referring to FIG. 1, an existing cable modem is configured to frame 101 MPEG frames, transmit them through an encoder 102 and a modulator 103, and the receiver detects the signals in reverse. However, the above configuration is used by dividing the time or frequency, so that the speed decreases as subscribers increase. Thus, code division multiple access (CDMA) is needed.

FIG. 2 is a general block diagram of a demodulation stage that multiplies PN codes in a code division multiple access scheme, and FIG. 3 is a block diagram illustrating a concept of a code division multiple access scheme.

The above embodiment generally illustrates a process of restoring an incoming signal multiplied by a PN code.

In FIG. 3, it is assumed that there are only two users in order to explain the concept of code division.

Referring to FIG. 3, first, at a transmitter, M ₁ and M ₂ are signals to be transmitted, and S ₁ and S ₂ are signals obtained by modulating the M ₁ and M ₂ . Multiply each S ₁ and S ₂ by a different PN code and send them together. The receiver then multiplies each received PN code by the received signal, leaving only its own signal and other signals like noise, and passing it through the bandpass filter leaves only its own signal.

For example, if you have a PN code of 1110100 and you want to send data of 1010101 (conceptually, 0 is replaced by -1).

At the sending end

PN codes 1, 1, 1, -1, 1, -1, -1 and

If you multiply data 1, -1, 1, -1, 1, -1, 1

PN x data 1, -1, 1, 1, 1, 1, -1

If the data received at the receiver is multiplied by its PN code

PN x DATA 1, -1, 1, 1, 1, 1, -1

PN code 1, 1, 1, -1, 1, -1, -1

Data 1, -1, 1, -1, 1, -1, 1 (= 1 0 1 0 1 0 1)

In this way, he restores his original data.

4 is a block diagram in which a PN block for code division is added to an existing cable modem system, and FIG. 5 is a detailed circuit diagram of the block diagram of FIG.

In the above embodiment, the cable modem further includes a PN code generator and a PN code detector in the configuration of FIG. 1.

Referring to FIGS. 4 and 5, when the transmitter multiplies the data signal by the PN code and transmits the signal, the receiver receives the signal and multiplies the PN code to extract the corresponding data. That is, by multiplying each signal by a different PN code, it is possible to transmit different signals at the same time.

However, in FIG. 5, it is unclear at which point in time, the receiver should multiply the PN code. If the desired data and the PN code are out of sync, all data is recovered only by noise through despreading.

An object of the present invention is to add a code division function to the existing cable modem to be able to transmit multiple signals at the same frequency at the same time to compensate for the disadvantage that the speed decreases as more subscribers.

Another object of the present invention is to provide a circuit that includes a synchronization block so that data can be recovered normally by synchronizing the PN code with the data.

In order to achieve the above object, a multiple access type cable modem using a synchronization circuit of the present invention includes an input unit for inputting a signal through a cable, a demodulator for demodulating the input signal, and an initial part of the PN generator in the demodulated signal. An initialization unit for extracting a value to generate an initial value, a PN code generation unit for generating a PN code based on the generated initial value, a synchronization signal detection unit for detecting a synchronization signal, and when the synchronization signal is detected, And an operation unit for operating the PN code generation unit.

In the present invention, the initialization unit includes a control unit and a plurality of second multiplexers, the control unit extracts the initial value of the PN generation unit sent from the CMTS according to the address of each cable modem from the demodulated signal, and according to the extracted value It is preferable to perform an operation of adjusting the value of the multiplexer and selecting an input of the first multiplexer according to whether a synchronization signal is detected.

In the method of the present invention, the control unit selects an input of the first multiplexer such that only a data signal input through the cable is input before a synchronization signal is detected, and only a value obtained by multiplying the data signal by the PN code when the synchronization signal is detected. It is preferable to input after passing through this bandpass filter.

In the present invention, it is preferable that the PN code generation unit is configured such that a plurality of 1-bit delay units are connected in series, and the output of the first delay unit and the output of the last delay unit are added to the final delay unit by an adder.

In the present invention, the synchronization signal detection unit is a second multiplier to multiply the input data signal by the Walsh code, and the output of the second multiplier to determine the output of 1 if the value 1 is input, and if the other value is inputted A comparator, an adder for counting the number of outputs 1 using a first delay unit, and a value of 1 for comparing the counted number of 1s with a Walsh code length and outputting a value of 0 otherwise. It is preferable to include two comparators.

In the present invention, the switch unit includes an OR gate and a second delay unit, and the OR gate preferably inputs a value fed back from the output value of the second comparator and its value to the second delay unit.

In the present invention, a demodulator includes a first multiplier for multiplying the output data and a PN code, a first multiplexer for receiving a signal selected from the input data signal, or a signal multiplied with the input data signal and the PN code, and the first multiplexer. It is preferable to include a demodulator for demodulating the output signal of one multiplexer.

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

6 is a schematic block diagram of a multiple access type cable modem including a synchronization signal detector according to an embodiment of the present invention.

In the above embodiment, the multi-mode cable modem includes an MPEG frame unit 101, an FEC encoder 102, a QAM modulator 103, a PN code generator 401, a sync signal synthesizer 601, and a sync signal detector. 710, a PN code detector 510, a QAM demodulator 105, an FEC decoder 106, and an MPEG frame unit 107.

This embodiment outlines the downstream processing of a cable modem.

Referring to FIG. 6, the cable modem includes a transmitter and a receiver. The transmitter controls the signal transmitted from the user's computer or the terminal to the CMTS, and the receiver controls the signal transmitted from the CMTS to the user's computer or the terminal.

The transmitter includes an MPEG frame unit 101, an FEC encoder 102, a QAM modulator 103, a PN code generator 401, and a synchronization signal synthesizer 601.

The processing for downstream modulation performed by the transmitter is a frame error processing of the MPEG-2 data stream input in the packet unit from the MPEG frame unit 101, and then a forward error correction algorithm in the FEC (Forward Error Correction) encoder 102 By performing the operation to obtain reliable data by the channel 70. Subsequently, the FEC codeword output from the FEC encoder 102 is QAM modulated by the QAM modulator 103 and then multiplies the signal generated by the generator 401 with a PN code for code division. The signal multiplied by the PN code has a Walsh code attached to the start of the signal while passing through the synchronization signal synthesizing unit 601.

The completed signal is transmitted to the receiver using an RF signal through a cable channel.

The receiver includes a synchronization signal detector 710, a PN code detector 510, a QAM demodulator 105, an FEC decoder 106, and an MPEG frame unit 107.

First, the synchronization signal detector detects a Walsh code included in the received signal. When the Walsh code is detected, the PN code generator starts to generate the PN code initial value and starts multiplying from the received signal except for the Walsh code.

Subsequently, the QAM demodulation unit 100, the FEC decoder 110, and the MPEG frame unit 120 are performed in a reverse process to the modulation.

At this time, the MPEG framing process provides a parity check pattern for packet synchronization between the transmitting and receiving sides, and the QAM modulation process supports 64QAM mode and 256QAM mode. In addition, the FEC encoding process uses a concatenated coding technique, and an inner coder uses a TCM codeword that generates a coded modulation code so that an error that is not corrected by an internal decoder is corrected by the external decoder. Typically, the error rate should be near zero.

Detailed operation of the receiver will be described with reference to FIG. 7.

7 is a block diagram schematically illustrating a receiver according to an embodiment of the present invention.

In the above embodiment, the receiver includes an input unit, a synchronization signal detector 710, an operation unit 720, an initialization unit 530, a PN code generator 510, and a demodulator 520.

The embodiment illustrates a method of multiplying a PN code after detecting a synchronization signal from an input signal.

Referring to Figure 7, the signal recovery process will be described.

First, the receiver of the cable modem receives a signal and multiplies the signal with the Walsh code 702. The receiver of the first comparator 703 checks whether the output a of the second multiplier 701 is 1 or not. If the output aout is 1 and not 1, aout is 0. Since the Walsh code 702 is multiplied by its own code, it is all 1, and when it is multiplied by another code, 1 and 0 are evenly distributed, so if the transmitter sends the Walsh code immediately before the signal multiplied by the data and the PN code, At the output of the first comparator 703, one comes out continuously.

For example, if the length of the Walsh code 702 is 4, the output of the second comparator 706 is 1 when the counter is implemented by using the adder 704 and the first delay unit 705. If 1 comes out before 4 consecutive runs, the first delay unit 705 is reset so that the value of the counter is counted again from 0 and the counter becomes 4 only when 4 consecutive 1s come out. You can find the sync signal made by code.

If the bout becomes 1 when the synchronization signal is found, the enable signal, which is the output of the OR gate 708, becomes 1 and the signal is connected to the latch enable signal to operate the PN code generator 510.

The circuit implemented by the OR gate 708 and the second delay unit 707 is configured such that when bout becomes 1, enable is continuously 1, so that the PN code generator 510 continues to operate even if other data enters after the synchronization signal. Do it.

When the operation unit 720 operates the PN code generation unit 510, a signal previously input directly to the demodulation unit 520 is multiplied by the PN code to be input to the band pass filter 504 and then demodulated.

Hereinafter, the operation principle of the PN code generator will be described.

In the above embodiment, a simple PN code generation unit 510 is used for a simple description, but it is also possible to use a PN code generation unit 510 having a long period in accordance with the purpose of the invention.

First, the three latches 501a to 501c and the binary adder 507 are PN generation circuits, and multiply the signals into the input signals and pass the band pass filter 504 to recover their signals.

In the present invention, when the signal is first received, the input signal is directly demodulated by selecting 0 of the selection signal of the first multiplexer 505 to demodulate the input like a conventional cable modem without first multiplying the PN code.

From the demodulated signal, extract the initial value of the PN code generator sent from the CMTS according to the Mac address of each cable modem, and determine the selection signals of the three second multiplexers 503a to 503c on the left side according to each initial value. Determine the initial value. The initial value is connected to VCC and GND to have a value of 1 or 0, respectively.

When the PN code is generated by the PN code generation unit 51, the first multiplexer 505 selects the selection signal as 1, passes the input signal and the product multiplied by the PN code, and passes the band pass filter 504 to the demodulator 506. Enter it.

The control unit generates a selection signal of the first multiplexer 505 according to the initial value of the PN code generator 5100 of each cable modem sent from the CMTS.

When each cable modem needs to receive different data, if it is a conventional case, it uses different frequencies or spends time sequentially. As the number of subscribers increases, the transmission speed of data becomes slow because the fixed frequency and time are limited.

However, if the code division function is inserted, decoding can be performed according to each code even when data is sent at the same frequency and time, so that the speed can be prevented from slowing down even if there are many subscribers.

As described above, according to the present invention, it is possible to simultaneously transmit data to several cable modems, thereby preventing the speed from slowing down even if there are many subscribers.

  In addition, by inserting the synchronization signal detection circuit, the PN code can be synchronized with the data received, thereby enabling accurate recovery of the signal.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and modified within the scope of the present invention without departing from the spirit and scope of the present invention described in the claims below. It will be appreciated that it can be changed.

Claims (7)

An input unit for inputting a signal through a cable, a demodulator for demodulating the input signal, an initializer for generating an initial value by extracting an initial value of the PN generator from the demodulated signal, and a PN based on the generated initial value And a PN code generation unit for generating a code, a synchronization signal detection unit for detecting a synchronization signal, and an operation unit for operating the PN code generation unit when the synchronization signal is detected. The apparatus of claim 1, wherein the initialization unit comprises a control unit and a plurality of second multiplexers. The control unit extracts an initial value of the PN generation unit sent from the CMTS according to the address of each cable modem from the demodulated signal, and extracts an initial value from the demodulated signal. Accordingly, the multi-access type cable modem using a synchronization circuit, which adjusts a value of a second multiplexer and selects an input of the first multiplexer according to whether a synchronization signal is detected. The method of claim 1, wherein the control unit selects an input of the first multiplexer such that only a data signal input through the cable is input before a synchronization signal is detected, and the data signal and the PN code are detected when the synchronization signal is detected. The multi-mode cable modem using a synchronization circuit, characterized in that only the value multiplied to be input after passing through the bandpass filter. The method of claim 1, wherein the PN code generating unit is configured such that a plurality of 1-bit delay units are connected in series, and an output of the first delay unit and an output of the last delay unit are added to the final delay unit and provided to the last delay unit. Cable modem using code division multiple access method. The method of claim 1, wherein the synchronization signal detector determines the output of the second multiplier and the second multiplier to multiply the input data signal by the Walsh code, and outputs 1 when a value of 1 is input and 0 when another value is input. A first comparator for outputting, an adder for counting the number of outputs 1 using a first delayer, a value of 1 if the number of counters and the Walsh code are equal to each other are compared, and a value of 0 otherwise. Cable modem using a code division multiple access method comprising a second comparator to output. 6. The switch unit of claim 5, wherein the switch unit includes an OR gate and a second delay unit, and the OR gate has a value fed back from the output value of the second comparator and its value to the second delay unit as its input. Cable modem using code division multiple access method. The apparatus of claim 1, wherein the demodulator comprises: a first multiplier for multiplying the output data with a PN code, a first signal for selecting one of the input data signal or a signal multiplied with the input data signal and the PN code is input; And a demodulator for demodulating the output signal of the first multiplexer and the multiplexer.

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