KR100882879B1 - An apparatus for symbol's synchronization of ofdm rf system and the method thereof - Google Patents

Abstract

An apparatus and a method for synchronizing a symbol of an OFDM wireless communication system are provided to facilitate synchronization acquisition of the symbol by obtaining a correlation coefficient with the preamble of the receiver by simplifying the data of the preamble of the transmitter used in the correlation coefficient calculation. A data converter(21) converts the preamble received from a transmitter into digital data of N(1<=N) bit of M (1<=M) and outputs the 2 bit digital data of m according to the N bit digital data by selecting the N bit digital data of m (1<=m<=M). The m buffers(22) receives and stores the 2 bit digital data. The m multiplexer(23) is arranged to correspond to the m buffers and multiplies an output value of the m buffers by the preamble data value of the receiver corresponding to the output value of the buffers. An adder(24) calculates the correlation coefficient by adding up the output of the m multiplexers. A synchronization unit(25) performs the synchronization of the symbol by confirming the correlation coefficient above a predetermined critical value.

Description

Symbol synchronization apparatus and method of PFDM wireless communication system {AN APPARATUS FOR SYMBOL'S SYNCHRONIZATION OF OFDM RF SYSTEM AND THE METHOD THEREOF}

The present invention relates to an apparatus and method for symbol synchronization in an orthogonal frequency division multiplexing (OFDM) wireless communication system. Particularly, only part of a transmitter and receiver preamble is used to calculate a correlation coefficient for symbol synchronization. In addition, the present invention relates to a symbol synchronization apparatus and method of an OFDM wireless communication system in which the transmitter preamble is simplified to simplify the number of bits.

In order to implement a wireless broadband multimedia system capable of high-speed reliability and high-capacity services, an OFDM transmission method that can transmit signals at high data rates in a time-division multiple access wireless channel of a millimeter wave band ranging from several GHz to several tens of GHz is widely used. I am getting it.

Orthogonal Frequency Division Multiplexing (OFDM) divides the data to be transmitted by inverse fast Fourier transform and divides the used bandwidth into a plurality of subcarriers (subcarriers). A frequency multiplexing scheme that converts original data into a frequency multiplexing scheme, in which a specific orthogonal condition is applied between subcarrier frequencies, so that each subcarrier can be separated at the receiving device in spite of overlapping spectrum. .

In general, an OFDM transmission system loads information on a subcarrier using an Inverse Fast Fourier Transform (IFFT). At this time, in order to reduce the influence of the multipath, an OFDM symbol having a guard interval inserted before the effective symbol interval is transmitted. The OFDM reception system removes the guard interval from the received OFDM symbol and recovers the original signal by performing demodulation using a fast Fourier transform (FFT).

Accordingly, in an OFDM reception system, frequency synchronization, OFDM symbol synchronization, and frame synchronization are essential, and thus communication quality varies.

OFDM data is transmitted and received in units of frames including a plurality of symbols, one symbol consisting of a plurality of data.

The first symbol of each frame is called a preamble. The preamble is used for initial synchronization, that is, in radio, to secure a time for a transmitter / receiver to perform an operation required for data transmission, and to search for a cell through base station identification.

In order to recover useful data in the receiving system, it is very important to set the start timing of the data symbol in the OFDM signal of the frame-based periodic structure. The start timing of such a frame is called frame synchronization. The symbol synchronization timing for fast Fourier transform of the period is generated.

An OFDM reception system performs OFDM symbol synchronization by various methods, and the obtained OFDM symbol synchronization is updated every OFDM symbol time or every several symbol times. Once a sync is acquired, it is continuously updated until it is completely out of sync and continues to track the changing sync.

1 is a block diagram illustrating a symbol synchronization circuit of an OFDM wireless communication system according to the prior art. As shown in FIG. 1, the symbol synchronization circuit includes a plurality of buffers 11 corresponding to OFDM symbol lengths, a multiplier 12 having the same quantity as the buffer 11 to multiply the buffer output data and the preamble signal, A summer 13 and a synchronizer 14 for summing the output of the multiplier 12 in symbol units.

The data input to the buffer is N-bit digital data obtained by converting a preamble (that is, a preamble of a transmitter) among the received baseband analog OFDM signals (Analog To Digital Converter). In this case, N is the number of bits of data obtained by digitally converting the analog transmitter preamble to a constant of 1 or more and depends on the characteristics of the analog-to-digital converter that digitally converts the transmitter preamble.

The buffers 11_1 to 11_M are provided with the number of data (M) per symbol to receive and store N-bit digital data, and transfer the previously stored N-bit digital data to the next buffer 11 in series. That is, the output of the i th buffer 11_i is input to the i + 1 th buffer 11_i + 1, where i is a constant of 1 or more and M or less, and is a sequential number of preamble data, and the maximum value of i + 1 is M.

In addition, one buffer 11 has at least an N-bit parallel input, a parallel output and a storage.

The multiplier 12 is provided as many as the number (12_1 ~ 12_M) of the buffer, the i-th multiplier 12_i multiplies the output of the i-th buffer (11_i) and the i-th data of the transmitter preamble.

The summer 13 adds the M multipliers 12 outputs to calculate a correlation coefficient Y. While delaying the transmitter preamble by one N-bit digital data unit, a correlation coefficient is continuously calculated.

The synchronizer 14 finds the maximum value of the calculated correlation coefficient value and synchronizes the symbols.

Here, the receiver preamble is a value previously known by the receiver, and the preamble of the transmitter is a value detected by a method such as power detection in an OFDM received signal transmitted in units of frames.

The symbol synchronization circuit of the conventional OFDM wireless communication system has to compute all the data of the preamble in order to detect the synchronization.

When the data transmission rate is low and the preamble length is short, it takes a long time to input data and output the calculation result, so it is possible to operate with a small number of multipliers and multipliers by sharing a small number of adders and multipliers in time. Higher data rates or longer preamble lengths lead to enormous hardware sizes.

In other words, high speed modems require real-time calculations, which makes it difficult to share adders and multipliers in time, and the longer the preamble, the more the buffers and multipliers require.

Literature Information of the Prior Art

[Document 1] Application Number: 020040022507

The present invention provides a symbol synchronization apparatus of an OFDM wireless communication system that obtains symbol synchronization by easily obtaining the correlation coefficient with a receiver preamble by simplifying the total quantity, the number of bits, and the output data of a multiplier in the transmitter preamble. And to provide a method.

In order to achieve the above object, a symbol synchronization device of an OFDM wireless communication system according to the present invention converts a preamble received from a transmitter into M (1≤M) N (1≤N) bits of digital data, wherein m A data converter for selecting (1 ≦ m ≦ M) N-bit digital data and outputting m 2-bit digital data according to the value of the N-bit digital data, and m buffers for receiving and storing the 2-bit digital data And m multiplexers arranged corresponding to each of the m buffers and multiplying the output values from the m buffers with the corresponding values of the receiver preamble data, and outputting the m multiplexer outputs to obtain a correlation coefficient. And a synchronizer which performs synchronization of symbols by checking an adder for calculating and checking whether the correlation coefficient is greater than or equal to a predetermined threshold. have.

The data converter preferably outputs 1 when the N-bit digital data is greater than 0, -1 when it is less than 0, and 0 when 0.

In addition, the data converter selects m data from M data, selects all or part of the data continuously, or extracts data at predetermined intervals when m data is selected from the M data.

In this case, the m buffers have at least two bits of parallel input and storage, the m buffers are connected in series so that the first buffer receives the output of the data converter, and the second to mth buffers are each 1. The characteristic is that the output of the first buffer to the m-1th buffer is input.

The multiplexer disposed corresponding to each of the m buffers receives i-th data of m receiver preambles corresponding to i (1 ≦ i ≦ m), which is a sequential number of the buffers, and receives the i-th data of the 2-bit digital data. The maximum value of the i-th data, 0, and a negative value of the maximum value are output according to the size.

Here, N is determined according to the performance of the analog-to-digital converter for digitally converting the received transmitter preamble, wherein the operation of the buffer, the multiplexer, the adder and the synchronizer is the time that the data converter outputs the 2-bit digital data. It is preferably executed in synchronization with.

According to another aspect of the invention (a) converting a preamble received from a transmitter into M (1≤M) N (1≤N) bits of digital data, and (b) m (1≤) among the M selecting m≤M) N-bit digital data and outputting m 2-bit digital data one by one according to the value of the N-bit digital data; and (c) when the output occurs, the 2-bit digital data in a buffer. (B) multiplying the stored 2-bit digital data to the next serially buffered buffer; and (d) multiplying the stored 2-bit digital data by m receiver preamble data values corresponding thereto. (E) summing up the manipulated m preamble data values to calculate a correlation coefficient, (f) checking whether the correlation coefficient is greater than or equal to a predetermined threshold value, and (g) the correlation The value of the coefficient If the threshold value or more is that characterized by comprising the step of determining that a successful acquisition of symbol synchronization.

Meanwhile, after step (f), it is necessary to repeat step (a) to step (e) at predetermined time intervals to continue symbol synchronization tracking. In the step (f), if the correlation coefficient is equal to or less than a predetermined threshold value, it is determined that the synchronization acquisition of the symbol fails.

In this case, step (b) outputs 1 when the N-bit digital data is greater than 0, -1 when the N-bit digital data is less than 0, and 0 when 0, wherein N is an analog for converting the transmitter preamble into N-bit digital data. It depends on the performance of the digital converter.

In addition, in step (b), when selecting m pieces of data from the M pieces of data, all or part of them may be continuously selected, or data may be extracted and selected at predetermined intervals.

Step (d) includes selecting data in the receiver preamble corresponding to the m two-bit digital data, and, if the value is 1 for the m two-bit digital data, the corresponding data in the receiver preamble. If the maximum value of -1, the negative value of the maximum value, and 0 if 0 is output.

The symbol synchronization apparatus and method of the OFDM wireless communication system according to the present invention can easily obtain the symbol synchronization by obtaining the correlation coefficient with the receiver preamble by simplifying the data of the transmitter preamble used for the correlation coefficient calculation.

In the present invention, the hardware size and the number of logic used are small, with little performance difference from the existing algorithm, so the design is simple, the power consumption efficiency is high, and the debugging is easy.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments are provided to those skilled in the art to fully understand the present invention, can be modified in various forms, the scope of the present invention is limited to the embodiments described below no.

2 is a block diagram illustrating a symbol synchronization circuit of an OFDM wireless communication system according to an embodiment of the present invention. As shown in FIG. 2, the preamble received from the transmitter is converted into M (1≤M) N (1≤N) bit digital data, and m (1≤m≤M) N bit digital data is A data converter 21 for selecting and outputting m two-bit digital data according to the value of the N-bit digital data, m buffers 22 for receiving and storing the two-bit digital data, and the m buffers ( 22) m multiplexers 23 arranged correspondingly to each of the m multiplexers 23 for manipulating and outputting corresponding receiver preamble data according to output values from the m buffers 22, and the m multiplexers 23; An adder 24 for summing outputs to calculate a correlation coefficient, and a synchronizer 25 for synchronizing symbols by checking whether the correlation coefficient is greater than or equal to a predetermined threshold value.
Here, the predetermined threshold value is a value obtained by multiplying an autocorrelation coefficient of the preamble by a suitable scale vector of less than one. That is, it will be apparent to those skilled in the art that the predetermined threshold means a correlation coefficient value such that each communication system can acquire the synchronization of the symbol.

Here, N is determined according to the capability of the analog to digital converter to digitally convert the received transmitter preamble.

The data converter 21 receives N-bit digital data and outputs 2-bit digital data. That is, the data converter 21 outputs 1 when the N-bit digital data is larger than 0, -1 when it is smaller than 0, and 0 when 0.

Further, when selecting m pieces of data from the M pieces of data, all or part of them are continuously selected, or data is extracted and selected at regular intervals.

3 shows a block algorithm of the data converter 21 according to an embodiment of the present invention. As shown in FIG. 3, the data converter 21 uses N-bit digital data (data of -V or more and V or less), that is, a value obtained by dividing the input data by L (1≤L), -1, 0, Output data of 1.

Here, L is normally 1/10 of the maximum value V of the input data, and the value may vary depending on the system.

2 again, the description of the symbol synchronization circuit is continued.

The buffer 22 includes m parallel inputs and storages of at least two bits, and the input / output values of the individual buffers 22 are values converted by the data converter 21 so that any one of -1, 0, 1 is provided. Is the value of.

In addition, the m buffers 22 are connected in series so that when the data converter 21 outputs 2-bit digital data, the buffer 22 stores the output value and stores the 2-bit digital data previously stored. To pass on.

That is, at the time when the data converter 21 outputs 2-bit digital data, the output of the j-th (1 ≦ j ≦ m) buffer 22_j is j + 1 (where the maximum value of j + 1 is m). It is delivered to the 1st buffer 22_j + 1.

The multiplexer 23 is disposed corresponding to each of the m buffers 22 and receives the i-th data of the m receiver preambles corresponding to i (1 ≦ i ≦ m), which is a sequential number of the buffers 22, and receives two bits. The maximum value Ci of the i-th data, 0, and a negative value (-Ci) of the maximum value are output according to the size of the digital data.

Since the output of the i-th buffer 22_i is any one of -1, 0, 1, the output of the i-th multiplexer 23_i is the i-th data used for synchronization acquisition between the output of the i-th buffer 22_i and the transmitter preamble data. Equal to the product of the values.

Summer 24 calculates the correlation coefficient Y by summing the outputs of the m multiplexers 23.

The synchronizer 25 checks whether the value of the correlation coefficient is greater than or equal to a predetermined threshold value and performs symbol synchronization. If the value of the correlation coefficient is less than or equal to a predetermined threshold, symbol synchronization acquisition fails. If symbol synchronization acquisition fails, the transmitter preamble is delayed in data units, that is, the data converter 21 receives one N-bit digital data. Outputs 2-bit digital data to the buffer 22, and the buffer 22 continuously connects previously stored 2-bit digital data to the next buffer 22 to continuously acquire symbol synchronization.

Even if the symbol synchronization is successfully acquired, synchronization tracking is continued at predetermined time intervals, thereby minimizing errors in the received data.

4 is a flowchart illustrating an operation procedure of a symbol synchronization circuit of an OFDM wireless communication system according to an embodiment of the present invention. A description with reference to FIG. 4 is as follows.

First, the preamble received from the transmitter is converted into digital data of M (1≤M) N (1≤N) bits (S401).

Here, N is determined according to the capability of the analog to digital converter to digitally convert the analog preamble received from the transmitter.

Subsequently, m (1 ≦ m ≦ M) N bit digital data are selected from M pieces, and m two bit digital data are output one by one according to the value of the N bit digital data (S402).

Here, the 2-bit digital data is 1 when the N-bit digital data is larger than 0, -1 when it is smaller than 0, and 0 when 0.

In addition, when m pieces of data are selected from M pieces of data, all or part of them may be selected continuously or data may be extracted and selected at regular intervals.

When the output occurs, the 2-bit digital data is received and stored, and the stored 2-bit digital data is serially connected and then transferred to the buffer (S403).

According to the size of the 2-bit digital data stored in the buffer 22, m receiver preamble data values corresponding thereto are manipulated and output (S404).

In detail, data in the receiver preamble corresponding to m two-bit digital data are selected, and m two-bit digital data is any one of -1, 0, and 1, so if the value is 1, A maximum value of data in the receiver preamble, -1, a negative value of the maximum value, and 0, a zero value is output.

Next, the correlation coefficient is calculated by calculating the sum of the m manipulated output values (S405).

Then, it is checked whether the value of the correlation coefficient is greater than or equal to the predetermined threshold value, and if it is greater than or equal to the predetermined threshold value (S406), the synchronization of the symbol is obtained (S407).

On the other hand, if the value of the correlation coefficient is less than or equal to a predetermined threshold (S406), the synchronization acquisition of the symbol fails (S409).

Subsequently, the symbol synchronization is acquired by repeatedly performing the operation (S406) in the operation (S402), and the symbol synchronization is updated every OFDM symbol time or several symbol times even if the symbol synchronization is obtained. Once obtained, the synchronization is continuously updated until the synchronization is completely lost, and the changing synchronization is continuously tracked (S408).

The configuration of the present invention has been described above through the preferred embodiments and the accompanying drawings. However, these are only examples and are not used to limit the scope of the present invention. Those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this, and the true scope of protection of the present invention should be determined by the technical spirit of the appended claims. .

1 is a block diagram showing a symbol synchronization circuit of an OFDM wireless communication system according to the prior art.

2 is a block diagram illustrating a symbol synchronization circuit of an OFDM wireless communication system in accordance with the present invention.

3 is a block algorithm of a data converter according to the present invention;

4 is a flowchart illustrating an operation procedure of a symbol synchronization circuit in an OFDM wireless communication system according to an embodiment of the present invention.

<Description of main parts of drawing>

21: Data converter 22: Buffer (22_1 to 22_m)

23: multiplexer (23_1 to 23_m) 24: summer

Claims (16)

 The preamble received from the transmitter is converted into M (1≤M) N (1≤N) bits of digital data, and m (1≤m≤M) N-bit digital data are selected from the N-bit digital data. A data converter that outputs m two-bit digital data according to M buffers for receiving and storing the 2-bit digital data; M multiplexers disposed corresponding to each of the m buffers and multiplying an output value from the m buffers by a value of a corresponding receiver preamble data; An adder configured to add the m multiplexer outputs to calculate a correlation coefficient; A synchronization unit for synchronizing symbols by checking whether the correlation coefficient is greater than or equal to a predetermined threshold value Symbol synchronization apparatus of the OFDM wireless communication system comprising a. The method of claim 1, wherein the data converter, And 1 if the N-bit digital data is greater than 0, -1 if less than 0, and 0 if 0. The method of claim 1, wherein the data converter, The symbol synchronization apparatus of the OFDM wireless communication system, characterized in that when selecting the m data from the M data, all or part of the selection in succession. The method of claim 1, wherein the data converter, When selecting m pieces of data from the M data, symbol synchronization apparatus of the OFDM wireless communication system, characterized in that for extracting the data at a predetermined interval. The method of claim 1, wherein the m buffers include at least two bits of parallel input and storage, The m buffers are connected in series so that the first buffer receives the output of the data converter, and the second through mth buffers receive the outputs of the first through m-1th buffers, respectively. Symbol synchronizer in communication system. The method of claim 1, The multiplexer disposed corresponding to each of the m buffers receives i-th data of m receiver preambles corresponding to i (1 ≦ i ≦ m), which is a sequential number of the buffers, And a maximum value of the i-th data, a zero value, and a negative value of the maximum value according to the size of the 2-bit digital data. The method of claim 1, N is determined according to the performance of the analog-to-digital converter for digitally converting the received transmitter preamble. The method of claim 1, And the buffer, the multiplexer, the adder, and the synchronizer are performed in synchronization with the time when the data converter outputs the 2-bit digital data. (a) converting the preamble received from the transmitter into M (1≤M) N (1≤N) bits of digital data; (b) selecting m (1≤m≤M) N-bit digital data from the M pieces and outputting m 2-bit digital data one by one according to the value of the N-bit digital data; (c) receiving and storing the 2-bit digital data in a buffer when the output occurs, and transferring the 2-bit digital data stored in series to the next buffer; (d) multiplying and outputting the stored 2-bit digital data values and m receiver preamble data values corresponding thereto; (e) calculating a correlation coefficient by summing the manipulated m preamble data values; (f) confirming whether the correlation coefficient is greater than or equal to a predetermined threshold value; (g) determining that symbol acquisition is successful when the value of the correlation coefficient is greater than or equal to a threshold value; Symbol synchronization method of the OFDM wireless communication system comprising a. The method of claim 9, wherein after step (f) A symbol synchronization method of an OFDM wireless communication system, characterized by continuing symbol synchronization tracking by repeating steps (a) to (e) at predetermined time intervals. The method of claim 9, wherein in step (f), And if the correlation coefficient is equal to or less than a predetermined threshold value, determine that symbol acquisition fails. The method of claim 9, and (b) outputting 1 when the N bit digital data is greater than 0, -1 when less than 0, and 0 when 0 is zero. The method of claim 9 or 12, N is determined according to the performance of the analog-to-digital converter for converting the transmitter preamble into N-bit digital data. The method of claim 9, wherein in step (b), When selecting m data from the M data, all or part of the symbol synchronization method of the OFDM wireless communication system, characterized in that the selection. The method of claim 9, wherein in step (b), When selecting m data from the M data, the symbol synchronization method of the OFDM wireless communication system, characterized in that for extracting the data at a predetermined interval. The method of claim 9, wherein step (d), Selecting data in a receiver preamble corresponding to the m two-bit digital data, respectively; And outputting a maximum value of the data in the receiver preamble corresponding to a value of 1 for the m two-bit digital data, a negative value of the maximum value for a value corresponding to -1, and a zero value for 0 for the two 2-bit digital data. A symbol synchronization method of an OFDM wireless communication system.

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