KR101070156B1 - Method and apparatus for estimating symbol timing of input signal in upstream cable modem - Google Patents

Abstract

The present invention relates to a method and apparatus for estimating symbol timing of an input signal in an uplink cable modem. A method and apparatus for estimating symbol timing of an input signal using coefficient values of a filter are disclosed.

Upstream Cable Modem, Demodulator, Matched Filter, Preamble, Symbol Timing

Description

METHOD AND APPARATUS FOR ESTIMATING SYMBOL TIMING OF INPUT SIGNAL IN UPSTREAM CABLE MODEM}

The present invention relates to a method and apparatus for estimating symbol timing, and relates to a technique for estimating symbol timing of a signal input using a matching filter of a preamble in an uplink cable modem.

The present invention is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunications Research and Development. Development of Multimedia Transmission Technology].

A communication system according to a cable network including a cable modem may provide subscribers with various communication services such as multimedia services such as video conferencing and web surfing.

Currently, cable modem termination systems (CMTS) and cable modems (CM) that conform to the standards such as DOCSIS 1.0, 1.1, and 2.0 are widely used to transmit data in cable networks. However, with the emergence of various types of services in which communication and broadcasting are converged, the currently used standards are limiting the capacity and efficiency of service provision. In particular, the maximum data rate that can be provided in the DOCSIS 2.0 or lower standard is limited to about 40 Mbps in the downward direction and about 30 Mbps in the upward direction. To overcome this limitation, DOCSIS 3.0 allows both the cable modem termination system and the cable modem to channel-bond data using multiple physical layers.

A method and apparatus for estimating symbol timing according to an embodiment of the present invention aims to reduce hardware implemented by using only the sign of a matched filter.

A method and apparatus for estimating symbol timing according to an embodiment of the present invention aim to estimate accurate symbol timing using a matching filter of a preamble for an input signal of an uplink cable modem oversampled compared to a symbol rate. .

Method and apparatus for estimating symbol timing according to an embodiment of the present invention aims to reduce the influence on noise by using a threshold value for estimating symbol timing.

In order to achieve the above object and solve the problems of the prior art, a method of estimating symbol timing according to an embodiment of the present invention comprises the steps of receiving an input signal containing a preamble over a cable network, and matching with the preamble Computing a coefficient value of the filter to estimate the symbol timing of the input signal.

An apparatus for estimating symbol timing according to an embodiment of the present invention includes a signal receiver for receiving an input signal including a preamble through a cable network, and calculating a coefficient value of the preamble and a matched filter, thereby calculating symbol timing of the input signal. It includes an uplink cable modem demodulator to estimate.

According to the present invention, hardware implemented by using only the sign of the matched filter can be reduced.

According to the present invention, accurate symbol timing can be estimated by using a matching filter of a preamble for an input signal of an uplink cable modem oversampled compared to a symbol rate.

According to the present invention, the influence of noise can be reduced by using a threshold value for estimating symbol timing.

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

1 is a flowchart illustrating a symbol timing estimation method according to an embodiment of the present invention.

Referring to FIG. 1, the symbol timing estimation method according to an embodiment of the present invention receives an input signal including a preamble through a cable network (S101).

The input signal is oversampled rather than a symbol rate, and may be divided into a preamble and a payload. In addition, the preamble may include a Kazak sequence repeated to a predetermined size.

The input signal will be described in detail with reference to FIG. 2.

2 is a view for explaining the format of the input signal 200 according to an embodiment of the present invention.

The format of the input signal 200 according to an embodiment of the present invention may include a preamble 210 field and a payload 220 field including at least one Kazak sequence 1 211.

The structure of an input signal (packet) received by an uplink cable modem according to an embodiment of the present invention includes a preamble 210 and a payload 220. The preamble 210 has a structure in which a constant pattern is repeated and is modulated by quadrature phase-shift keying (QPSK), and the payload 220 is a QPSK of 16 bits, quadrature amplitude modulation (16QAM), and quadrature amplitude modulation (64QAM). It can be modulated in any one of the modulation scheme.

The CAZAC (Constant Amplitude Zero Auto Correlation) sequence used in the preamble 210 field may have a complex value and have 16 symbol lengths. Since the preamble 210 repeatedly uses such a Kazak sequence, the following description will be given on behalf of Kazak Sequence 1 211.

The Kazak sequence 1 211 according to an embodiment of the present invention includes a real part and an imaginary part, and the real part may be represented by any one of 1 and -1, and may be represented by 16 sample lengths as follows.

Real part (CAZAC) = (1,1,1,1,1, -1, -1,1,1, -1,1, -1,1,1, -1, -1) x (1 / sqrt (2))

In addition, the real part may be represented by any one of 1 and -1, and may be represented by 16 sample lengths as follows.

Imaginary part (CAZAC) = (1,1,1,1,1,1, -1, -1,1, -1,1, -1,1, -1, -1,1) x (1 / sqrt (2))

According to an embodiment of the present invention, the input signal 200 may be oversampled at four times the symbol rate, in which all Kazak sequences belonging to the preamble 210 are subjected to a total of 64 (16 * 4) sample values. Will have

According to an embodiment of the present invention, since the input signal 200 input to the demodulator of the upstream cable modem is oversampled compared to the symbol rate, the preamble 210 and the uplink cable modem side of the input signal 200 are known in advance. Accurate symbol timing may be estimated using coefficient values of the matched filter.

Referring back to FIG. 1, in the symbol timing estimation method according to an embodiment of the present invention, the coefficient values of the preamble and the matched filter may be calculated (S102), and the symbol timing of the input signal may be estimated based on the calculation. There is (S103).

The coefficient value of the matched filter will be described in detail with reference to FIG. 3.

3 is a diagram for describing coefficient values of a matched filter according to an exemplary embodiment of the present invention.

The coefficient value of the matched filter corresponds to the Kazak sequence 300. Specifically, the cable modem side and the transmitting end may transmit data in a preset Kazak sequence or use it to estimate symbol timing. That is, in response to the Kazak sequence included in the input signal, the cable modem side maintains the Kazak sequence 300 which conjugated the Kazak sequence included in the input signal.

That is, the cable modem side maintains the real part 310 in which the real part of the Kazak sequence 1211 of FIG. 2 is conjugated and the imaginary part 320 in which the imaginary part of the Kazak sequence 1211 is conjugated.

In other words, in order to estimate the symbol timing of the input signal, the symbol timing estimation method according to an embodiment of the present invention performs a conjugate operation on the sign value of the Kazak sequence 1 211 to determine the Kazak sequence 300 which is the coefficient value of the matched filter. Set to). Accordingly, the symbol timing estimation method according to an embodiment of the present invention may estimate the symbol timing of the input signal based on the set coefficient value of the matched filter.

Specifically, the symbol timing estimation method according to an embodiment of the present invention adds the coefficient values of the preamble and the set matching filter to generate an addition result value, and based on the generated addition result value of the input signal. The symbol timing can be estimated.

For example, when the preamble of the input signal has a real part 1 and an imaginary part −1, and the coefficient values of the matched filter are the real part 1 and the imaginary part 1, the symbol timing estimation method may use (1-1j) of the preamble. By multiplying (1 + 1j) of the coefficient value of the matched filter, the symbol timing can be estimated. However, even when (1-1j) of the preamble and (1 + 1j) of the coefficient value of the matching filter are added, the same result as that of the multiplication operation can be obtained. Therefore, the symbol timing of the input signal can be estimated accurately without performing the multiplication operation, which requires more hardware than the addition operation.

The symbol timing estimation method according to an embodiment of the present invention performs an addition operation to generate an addition result value, and then performs a division operation and an absolute value operation.

In detail, the symbol timing estimation method according to an embodiment of the present invention generates a division result value by performing a division operation on the addition result value, generates an absolute value by calculating an absolute value of the generated division result value, and generates the generation result. The symbol timing of the input signal may be estimated by comparing whether the absolute value is greater than or equal to a threshold value.

The threshold value may be determined by the experience value, and may be preferably determined as 1.0779123505.

Therefore, by using the symbol timing estimation method according to an embodiment of the present invention, the hardware to be implemented can be reduced by estimating the symbol timing only by the addition operation using only the sign of the matched filter.

In addition, for the input signal of the upstream cable modem oversampled compared to the symbol rate, the accurate symbol timing can be estimated using the matching filter of the preamble, and the influence of noise by using the threshold value for estimating the symbol timing Can be reduced.

4 is a block diagram illustrating a symbol timing estimating apparatus 400 according to an embodiment of the present invention.

Referring to FIG. 4, the symbol timing estimating apparatus 400 includes a receiver 410 and an uplink modem demodulator 420.

First, the receiver 410 receives an input signal including a preamble and a payload through a cable network, and transmits the received signal to an uplink cable modem demodulator 420 to estimate symbol timing.

Accordingly, the uplink cable modem demodulator 420 calculates the coefficient values of the preamble and the matched filter to estimate the symbol timing of the input signal.

The uplink cable modem demodulator 420 includes a switch unit 421, a counter unit 422, a sample delay unit 423, an operation unit 424, and a comparison unit 425 to estimate the symbol timing. .

First, the switch unit 421 selectively switches the input signal. For example, the switch unit 421 selects at least one of an input signal and zero. The switch unit 421 may determine whether to select the input signal or the zero based on a predetermined multiple value of a sample value of a preset Kazak sequence. For example, the switch unit 421 may determine whether to select the input signal or the zero based on twice the sample value 64 of the Kazak sequence, and according to the selection of the switch unit 421, At least one of the signal and 0 is input from the receiver 410 to the uplink cable demodulator 420.

The counter unit 422 may process windowing of the input signal based on the selection of the switch unit.

That is, the counter unit 422 is used to process the windowing of the input signal, and when the input signal IN is smaller than 128 through the switch unit 421, 0 is input when the counter unit 422 is larger. By doing so, the symbol timing estimation apparatus 400 can estimate the symbol timing even with a small amount of power.

The sample delay unit 423 delays an input of the windowing input signal for a predetermined time, and the operation unit 424 processes an operation reflecting the coefficient of the matched filter to the delayed input signal.

The operation unit 424 according to an embodiment of the present invention uses only the sign of the Kazak sequence as the coefficient value of the matched filter, which has an effect of reducing the amount of hardware by using an adder instead of a multiplier when implementing the matched filter with hardware. have.

Specifically, the operation unit 424 adds and computes the coefficient value of the matched filter and the Kazak sequence included in the preamble, and performs the operation on the absolute value after the division operation. In addition, the comparator 425 estimates the symbol timing of the input signal by comparing the calculated value with a predetermined threshold value.

In an ideal environment where no other noise is present, the correct symbol timing is when the absolute value of the output in its correlation form is at its maximum. That is, the accurate symbol timing may be estimated by comparing the absolute value output of the absolute value type with a predetermined threshold value.

The coefficient value of the matched filter is set to any one of 1 and -1 based on the sign value of the Kazak sequence. In this case, the operation unit 424 adds and computes the coefficient value of the preamble and the set matched filter. The symbol timing of the input signal may be estimated based on the generated addition result value.

5 is a block diagram illustrating an uplink cable modem demodulator 500 according to another embodiment of the present invention.

Referring to FIG. 5, the uplink cable modem demodulator 500 includes a switch 501, a counter 502, a sample delayer 503, a multiplier 504, an adder 505, a divider 506, and an absolute value device. 507, and a comparator 508.

5 may be interpreted as a structure for estimating symbol timing using a matched filter of a preamble. Although the multiplier 504 calculates coefficient values of an input signal and a matched filter, an addition operation alone may be used to calculate the multiplier 504. The multiplier 504 is practically unnecessary because it has the same effect.

The counter 502 is used for windowing, and an input signal IN is input when it is smaller than 128 through the switch 501 and 0 when it is large. This reduces power consumption when operating in hardware.

The input values are moved to the right through each input through the sample delayer 503, and each tap is multiplied by the coefficient value of the matched filter by the multiplier 504.

A total of 64 coefficient values of the matched filter, 16 actual values exist (C0 * to C15 *), the rest is 0, as shown in FIG.

3, it can be seen that the matched filter coefficient value uses only the sign of the Kazak sequence, which can reduce the amount of hardware by using an adder instead of a multiplier when implementing the matched filter in hardware.

The output values of the multiplier 504 are all added through the adder 505 and these added values are divided by 16 through the divider 506. Since the divided values are complex numbers, the absolute value abs_mat_out is obtained through the absolute value calculator 507.

This abs_mat_out is input to the comparator 508, which compares this abs_mat_out value with the threshold MATCH_THR to make STE_ENABLE 1 after 2 samples when it is large and 0 otherwise. In theory, the exact symbol timing is when abs_mat_out is the maximum value. MATCH_THR is set to 1.0779123505 because it is based on the difference between the current value and the previous value. In this way, the noise characteristics are strong.

According to the present invention, in the demodulation of an uplink cable modem, an accurate symbol timing can be estimated using a matching filter of a preamble. In addition, the amount of hardware can be reduced by using only the preamble's sign as the coefficient value of the matched filter, and the power consumption can be reduced by windowing the input of the matched filter. The noise can be reduced by determining that the difference is large.

The method of estimating symbol timing according to the present invention can be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

1 is a flowchart illustrating a method of estimating symbol timing according to an embodiment of the present invention.

2 is a view for explaining the format of an input signal according to an embodiment of the present invention.

3 is a diagram for describing coefficient values of a matched filter according to an exemplary embodiment of the present invention.

4 is a block diagram illustrating an apparatus for estimating symbol timing according to an embodiment of the present invention.

5 is a block diagram illustrating an uplink cable modem demodulator according to an embodiment of the present invention.

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

400: symbol timing estimation device

410: receiver

420: upstream cable modem demodulator

Claims (10)

Receiving an input signal comprising a preamble comprising a CAZAC sequence repeated over a cable network; Setting a sign value of the Kazak sequence to any one of 1 and -1 as a coefficient value of a matched filter; Generating an addition result value by performing an addition operation on the coefficient values of the preamble and the set matching filter; Generating a division result value by dividing the generated addition result value by a symbol length of the Kazak sequence; Generating an absolute value by calculating an absolute value of the generated division result value; And Estimating symbol timing of the input signal by comparing whether the generated absolute value is greater than or equal to a threshold value Symbol timing estimation method comprising a. The method of claim 1, And the input signal is oversampled rather than a symbol rate. delete delete delete delete The method of claim 1, And the input signal is oversampled at four times the symbol rate and the Kazak sequence has 64 sample values based on the oversampling. A signal receiver configured to receive an input signal including a preamble including a CAZAC sequence repeated through a cable network; A switch unit for selectively switching the input signal; A counter unit for processing windowing of the input signal based on the selection of the switch unit; A sample delay unit delaying an input of the windowed signal; The sign value of the Kazak sequence is set to any one of 1 and -1 as a coefficient value of the matched filter, and an addition operation is generated by adding the coefficient values of the preamble and the set matched filter, and generating an addition result. A calculation unit configured to divide a value by a symbol length of the Kazak sequence to generate a division result value, and generate an absolute value by performing an absolute value operation on the generated division result value; And A comparison unit estimating symbol timing of the input signal by comparing whether the generated absolute value is equal to or greater than a threshold value Symbol timing estimation apparatus comprising a. delete delete

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