KR100746554B1 - Signal transmitter and receiver - Google Patents

Abstract

The present invention relates to a signal transmission / reception apparatus.

A signal receiving apparatus for receiving an OFDM symbol including a cyclic section and a preamble from a signal transmitting apparatus of the present invention includes an analog-to-digital conversion module for receiving an OFDM symbol and converting it into a digital symbol; Extracts the cyclic section and the preamble from the digital symbols, calculates the phase and sync using the extracted preamble and the annular section, and calculates the channel for the digital symbols using the calculated sync and phase values. A time domain channel estimation module for compensating for the loss; And a discrete Fourier transform module for performing a discrete Fourier transform on the symbols received from the time domain channel estimation module.

According to the present invention, by minimizing the sampling clock error due to the minute period difference, it is possible to prevent the accumulated error difference caused by the minute time error, and to improve the SNR can be expected.

In addition, it is possible to expect the effect of minimizing the delay between symbols generated during channel compensation in the receiving device.

OFDM, sampling, symbol delay, annular interval, preamble, channel estimation

Description

Signal transmitting and receiving device {SIGNAL TRANSMITTER AND RECEIVER}

1 is a block diagram illustrating a data packet used in a conventional OFDM system.

2 is a block diagram illustrating a signal transmission apparatus of an OFDM system according to an embodiment of the present invention.

3 is a block diagram illustrating a symbol structure including a preamble and an annular section generated by a transmitter according to an embodiment of the present invention.

4 is a block diagram illustrating a receiving apparatus of an OFDM system according to an embodiment of the present invention.

5 is a block diagram illustrating in detail a time domain channel estimation module of a receiving apparatus according to an embodiment of the present invention.

6 is a diagram illustrating linear cross correlation of a time domain channel estimation module of a reception apparatus according to an embodiment of the present invention.

The present invention relates to a signal transmission and reception apparatus, and more particularly, to a signal of an orthogonal frequency-division multiplexing (OFDM) system that minimizes sampling clock errors due to minute period differences. It relates to a transmission / reception device.

The radio channel environment distorts all subcarrier phases and causes variations in subcarrier power magnitudes. In order to compensate for such a distorted signal, a system using OFDM uses many methods for compensating for a channel after a discrete Fourier transform.

As a conventional technique for compensating for such a wireless channel, ICPWC '97 (International Conference on Personal Wireless Communications) pp. An Analysis of Two Dimensional Pilot Symbol Assisted Modulation for OFDM is disclosed in 71-74 (published in 1997).

This conventional technique relates to a two-dimensional channel compensation method used in an OFDM system, and transmits a pilot satisfying a pilot insertion interval condition of a time axis and a frequency axis satisfying the conditions of Equations 1 and 2 below. By inserting into a symbol, a method for estimating a channel using interpolation in a receiving apparatus and demodulating data through the estimated channel is proposed.

Where S _t is the time base pilot insertion interval and Bd is the Doppler Spread.

Where S _f is the frequency axis pilot insertion interval and t _max is the maximum delay spread.

Such a prior art can optimize the pilot insertion interval when there is no time difference between the transmitter and the receiver (packet synchronization is completely matched), but the disadvantage of not optimizing the pilot insertion interval when the time difference occurs. have. In addition, the OFDM apparatus in which the first pilot signal is inserted is delayed for a predetermined time to obtain a channel estimate using the OFDM symbol in which the first pilot signal is inserted and the OFDM symbol in which the second pilot signal is inserted.

This delay is not suitable for systems that must report the decoding error fact of each transmitted packet after decoding.

In addition, a conventional technique for a method of compensating for a wireless channel is the "OFDM Physical Layer Specification for the 5GHz Band" disclosed in IEEE P802.11 Wireless LANs, pp. 1-27 (published in July, 1998).

This conventional technique is a technique for preventing inter-symbol delay that occurs during channel estimation. The transmitter inserts a preamble signal into subcarriers of two consecutive OFDM symbols, and transmits only the subcarrier interval specified for the other OFDM symbols. Insert a pilot signal. The receiver estimates a channel using two OFDM symbols including a preamble signal and demodulates other OFDM symbols based on the estimated channel.

This conventional technique shows the best performance when the channel change caused by the first two consecutive OFDM symbols is consistently the same until the last symbol is transmitted, but in most cases the channel change is not continuous on the actual system. Because of this, it is difficult to achieve optimal performance.

1 is a block diagram illustrating a data packet used in a conventional OFDM system.

As shown in FIG. 1, a conventionally used data packet includes an annular section 11 and a data region 12, and has a feature sensitive to a delay profile predicted in a wireless channel environment.

According to FIG. 1, when the synchronization system acquires synchronization using the annular section 11, the timing system estimates a timing error and a frequency error on the time axis to cancel the error.

However, the estimated error leaves a residual frequency offset. In addition, when a time error occurs between a transmitter and a receiver, the residual frequency offset causes a cumulative phase difference between the first subcarrier and the last subcarrier. If the cumulative phase difference is not compensated in each OFDM symbol, it becomes larger in the second and third OFDM symbols than the first OFDM symbol and eventually cannot be canceled, so that demodulation is impossible. In particular, this cumulative phase difference has a problem that can cause a loss of signal to noise ratio (SNR).

Differences in the cumulative phases generated in the conventional OFDM system will be described by Equation 3 and Equation 4 below.

The clock error of sampling due to the sampling period difference between the transmitter and the receiver is expressed by Equation 3 below.

Here, T and T 'are sampling periods of a transmitter and a receiver, respectively. The influence on the subcarriers R _{n, k} of the _nth symbol received after the Discrete Fourier Transform is expressed by Equation 4 below.

Here, T _s and T _u denote intervals of the entire OFDM symbol and data intervals that are actually applied, respectively, and w _{n, k} denotes additive white Gaussian noise (AWGN) noise.

이다.

정도의 주기 차이가 발생했을 때, 첫번째 부반송파와 마지막 부반송파간의 위상 회절 정도는 점점 차이가 벌어진다. 특히, 부반송파 개수 가 많을수록 회절의 정도는 심해진다. The term representing the degree of diffraction of the phase generated by each subcarrier

to be.

When a period difference of degree occurs, the degree of phase diffraction between the first subcarrier and the last subcarrier gradually increases. In particular, the greater the number of subcarriers, the greater the degree of diffraction.

The annular interval compensation is offset by estimating the error on the time axis to estimate the finer error than the packet acquisition. Leaves a positive residual phase. That is, the sampling clock error due to the difference between the sampling periods of the transmitter and the receiver does not cancel the frequency offset of the accumulated subcarriers due to the annular interval estimation using only the annular interval.

Accordingly, an object of the present invention is to provide a signal transmission / reception apparatus of an OFDM system that minimizes a sampling clock error due to a slight period difference.

In order to solve the above technical problem, the signal transmission apparatus according to the first aspect of the present invention,

An inverse discrete Fourier transform module configured to receive the modulated specific data and perform inverse Fourier Discrete Fourier transform to generate a first symbol; An annular interval addition module configured to add a predetermined annular interval to the first symbol to generate a second symbol; A preamble adding module configured to add a preamble set to the second symbol to generate a third symbol; And a digital-analog conversion module for converting the third symbol including the cyclic interval and the preamble into an analog symbol. Here, the preamble uses a short preamble and has a feature of being added to the front of the second symbol in consideration of a radio environment delay.

According to a second aspect of the present invention, a signal receiving apparatus for receiving an OFDM symbol including a cyclic section and a preamble from a transmitter,

An analog-digital conversion module for receiving an OFDM symbol and converting it into a digital symbol; Extracts the cyclic section and the preamble from the digital symbols, calculates the phase and sync using the extracted preamble and the annular section, and calculates the channel for the digital symbols using the calculated sync and phase values. A time domain channel estimation module for compensating for the loss; And a discrete Fourier transform module for performing a discrete Fourier transform on the symbols received from the time domain channel estimation module.

Here, the time-domain channel estimation module performs a first compensation on the digital symbol through the symbol synchronization and the first phase value obtained by using the preamble, and after performing the second phase value through the second phase value obtained by using the annular interval. 2 has the feature of performing compensation.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

In addition, the term module described herein refers to one unit for processing a specific function or operation, which may implement hardware or software or a combination of hardware and software.

Referring now to the drawings with respect to the signal transmission / reception apparatus according to an embodiment of the present invention will be described in detail.

2 is a block diagram illustrating a signal transmission apparatus of an OFDM system according to an embodiment of the present invention.

As shown in FIG. 2, the signal transmission apparatus 100 according to an exemplary embodiment of the present invention includes an encoder 120, a modulation module 130, an inverse discrete Fourier transform module (IDFT) 140, and an annular segment addition module 150. ), A preamble adding module 160 and a digital-to-analog conversion module (DAC) 170.

The encoder 120 performs encoding on the received binary source and transmits the encoded signal to the modulation module 130.

The modulation module 130 modulates the data received from the encoder 120 according to a preset modulation scheme and transmits the data to the inverse discrete Fourier transform module 140.

The inverse discrete Fourier transform module (IDFT) 140 converts the data received from the modulation module 130 to the inverse discrete Fourier transform and transmits the data to the annular segment addition module 150.

The annular segment addition module 150 transmits the generated symbol to the preamble addition module 160 by adding a preset cyclic interval to the symbol received from the inverse discrete Fourier transform module 140. In this case, the annular section is a section determined in consideration of the delay to the cell boundary region, and is a preset parameter value. In addition, the annular section includes predictable channel information so that the receiver can compensate for the sampling clock error later.

Meanwhile, the annular section is used as a variable section, and when the delay profile is small, it may be extended to the preamble region.

The preamble adding module 160 adds a preamble preset to the symbol received from the annular section adding module 150 and transmits the preamble to the digital-analog conversion module 170.

In this case, the preamble uses a short preamble and does not use a long preamble as in the case of finding a packet start point. This is because an OFDM system that intends to transmit a high capacity packet already finds a packet starting point using a long preamble, and roughly synchronizes the packet using the found packet starting point.

The digital-analog conversion module 170 converts the symbols received from the preamble adding module 160 to analog.

The signal transmission apparatus 100 according to the embodiment of the present invention secures the annular section and the preamble section at the same time so that the receiving apparatus performs symbol synchronization and phase compensation using these sections. In addition, according to an embodiment of the present invention, a fine sample generated between a transmitting device and a receiving device of terminals having an excellent channel environment, ie, having a high SNR and using a higher-order modulation scheme, by using the annular section and the preamble section variably. There is an advantage that can prevent the performance degradation due to the difference in the sampling cycle.

3 is a block diagram illustrating a symbol structure including a preamble and an annular section generated by a transmitter according to an embodiment of the present invention.

As shown in FIG. 3, the symbol 300 according to an embodiment of the present invention includes a preamble 310, an annular section 320, and a data region 330.

The preamble 310 and the annular section 320 are generated by the annular section adding module 150 and the preamble adding module 160 shown in FIG. 2 and may vary when the delay profile is small.

The receiving device receiving the data packet adjusts the primary symbol synchronization using the preamble and compensates the secondary phase synchronization using the annular interval to compensate for the sampling clock error caused by the minute period difference. .

4 is a block diagram illustrating a receiving apparatus of an OFDM system according to an embodiment of the present invention.

As shown in FIG. 4, the receiving apparatus 200 according to an embodiment of the present invention includes an analog-digital modulation module (ADC) 210, a time domain channel estimation module 220, and a discrete Fourier transform module (FFT) 230. ), A frequency domain channel estimation module 240, a demodulation module 250, and a decoder 260.

The analog-digital modulation module (ADC) 210 receives the OFDM symbol transmitted from the transmitting apparatus 100 shown in FIG. 2, converts the OFDM symbol into a digital symbol, and transmits the same to the time domain channel estimation module 220.

The time domain channel estimation module 220 extracts the preamble 310 and the annular section 320 of the symbol received from the analog-digital modulation module (ADC) 210, and extracts the extracted preamble 310 and the annular section. The sync and phase for estimating the channel are calculated using 320, and the channel is compensated using the calculated sync and phase values. The compensated symbol is then transmitted to the discrete Fourier transform module 230.

At this time, the time-domain channel estimation module 220 obtains symbol synchronization by first obtaining an index having the highest correlation using a linear cross-correlation expression as shown in Equation 5 to synchronize symbols. The symbol synchronization is then synchronized using the acquired symbol synchronization. At this time, the linear cross correlation is shown in FIG.

Here, x ₁ to x _L are preamble information, and y ₁ to y _PL are received symbol information.

In addition, the time domain channel estimation module 220 obtains a q value for phase compensation by using Equation 6 below, and performs first phase compensation on the received data using the obtained q.

In this way, after performing synchronization and phase using the preamble, the time domain channel estimation module 220 removes the preamble section and performs the second phase compensation once again using the annular section.

The discrete Fourier transform module 230 performs a discrete Fourier transform on the symbols received from the time domain channel estimation module 220 and transmits them to the frequency domain channel estimation module 240.

The frequency domain channel estimation module 240 estimates the frequency domain channel based on the data received from the discrete Fourier transform module 230 and performs compensation according to the estimation.

The demodulation module 250 demodulates data received from the frequency domain channel estimation module 240 to generate a binary source, and transmits the generated binary source to the next stage (omitted).

Such a reception device 200 according to an exemplary embodiment of the present invention compensates for synchronization and phase with respect to data received from the transmission device 100 to prevent a cumulative error difference caused by a minute time error of the transmission / reception device. There is an advantage to improve the SNR.

5 is a block diagram illustrating in detail a time domain channel estimation module of a receiving apparatus according to an embodiment of the present invention.

As shown in FIG. 5, the time-domain channel estimation module 220 according to an embodiment of the present invention includes a preamble channel estimator 221, a channel estimator 222, a channel compensator 223, and a preamble eraser. The unit 224 includes an annular section channel estimator 225 and a channel compensator 226.

The preamble channel estimator 221 detects a preamble from a symbol received from the analog-digital conversion module 210 shown in FIG. 4 and estimates a channel using the detected preamble.

The channel estimate calculator 222 calculates a channel estimate based on the channel estimate of the preamble channel estimator 221. In this case, the calculated channel estimate refers to symbol synchronization and phase values calculated by Equations 5 and 6 above.

The channel compensator 223 compensates the channel estimation value with the data received from the analog-digital conversion module 210 and transmits the channel estimate to the preamble deleter 224.

The preamble deleter 224 deletes the preamble included in the symbol received from the channel compensator and transmits the preamble to the annular interval channel estimator 225.

 The annular interval channel estimator 225 estimates the channel using the annular interval included in the symbol received from the preamble deleter 224. In this case, the annular section channel estimator 225 calculates a phase value for channel compensation using the annular section.

The channel compensator 226 compensates the channel of the symbol by using the channel estimate (calculated phase value) of the annular interval channel estimator 225 and transmits the channel of the symbol to the discrete Fourier transform module 230 shown in FIG. 4.

6 is a diagram illustrating linear cross correlation of a time domain channel estimation module of a reception apparatus according to an embodiment of the present invention.

As shown in FIG. 6, the linear cross correlation according to the embodiment of the present invention multiplies the preamble 400 and the received signal information 410 to achieve symbol synchronization.

The embodiments of the present invention described above are not only implemented through the apparatus and the method, but may also be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Implementations can be easily implemented by those skilled in the art from the description of the above-described embodiments.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

According to the above-described configuration, the signal transmission / reception apparatus minimizes the sampling clock error caused by the minute period difference generated in the transmission / reception device, thereby preventing the accumulated error difference caused by the minute time error and improving the SNR. You can expect the effect to be made.

In addition, it is possible to expect the effect of minimizing the delay between symbols generated during channel compensation in the receiving device.

Claims (10)

An inverse discrete Fourier transform module configured to receive the modulated specific data and perform inverse Fourier Discrete Fourier transform to generate a first symbol; An annular interval addition module configured to add a predetermined annular interval to the first symbol to generate a second symbol; A preamble adding module generating a third symbol by adding a preamble set to the second symbol; A digital-analog conversion module for converting the third symbol including the cyclic interval and the preamble into an analog symbol. Signal transmission device comprising a. The method of claim 1, The preamble uses a short preamble and is added to the front of the second symbol in consideration of a radio environment delay. The method of claim 1, The annular period is determined in consideration of the delay to the cell boundary region. The method according to any one of claims 1 to 3, The annular section and the preamble may have a variable section. A signal receiving apparatus for receiving an OFDM symbol including a cyclic section and a preamble from a transmitter, An analog-to-digital conversion module for receiving the OFDM symbol and converting it into a digital symbol; The cyclic interval and the preamble are extracted from the digital symbol, the phase and the synchronization are calculated using the extracted preamble and the annular interval, and the digital symbol is calculated using the calculated synchronization and the phase value. A time domain channel estimation module for compensating for the channel for the channel; And  Discrete Fourier Transform module for performing Discrete Fourier Transform on the symbols received from the time-domain channel estimation module Signal receiving device comprising a. The method of claim 5, The time domain channel estimation module, Performing a first compensation on the digital symbol using the symbol synchronization and the first phase value obtained by using the preamble, and performing the second compensation on the second phase value obtained by using the annular interval after the performing. A signal receiving device having a feature. The method of claim 6, And the symbol synchronization is an index obtained by using a linear cross correlation equation. The method of claim 5, The time domain channel estimation module, A channel estimator detecting a preamble from the digital symbol and estimating a channel using the detected preamble; A channel estimate calculator for calculating a channel estimate based on the estimated channel; A channel compensator for compensating the digital symbol using the channel estimate; A preamble deleting unit for generating a first symbol by deleting the preamble included in the compensated digital symbol; An annular interval channel estimator for calculating a phase value for channel compensation using the annular interval included in the first symbol; A channel compensator for generating a second symbol by compensating the first symbol by using the calculated phase value Signal receiving device comprising a. The method of claim 8, And the channel estimate includes symbol synchronization information and a phase value calculated using the preamble. The method of claim 5, A frequency domain channel estimation module for estimating a channel in a frequency domain based on data received from the discrete Fourier transform module and performing compensation according to the estimation; And A demodulation module for performing demodulation on data received from the frequency domain channel estimation module Signal receiving device comprising a.

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