KR20030092704A - Guard interval inserting/drawing appatatus and method for ofdm symbol in ofdm communication system - Google Patents

Abstract

PURPOSE: An apparatus and a method for inserting/extracting a guard interval for an OFDM(Orthogonal Frequency Division Multiplexing) symbol in an OFDM communication system are provided to remove ISI(Inter Symbol Interference) and ICI(Inter Channel Interference) in a system using an OFDM technique or a DMT system. CONSTITUTION: According to the method for inserting a guard interval to generate an OFDM symbol in a digital communication system using an OFDM technique, a received effective data stream is classified into an effective data stream in a predetermined unit and then the classified effective data stream is delayed as much as the time of a fore-guard interval(31) and data to be copied to the guard interval among the effective data stream are stored. A part of the data to be copied to the guard interval in the fore-guard interval is inserted into the fore-guard interval and the delayed effective data stream is output. And after outputting the effective data stream, the other data to be copied to the fore-guard interval is inserted to a post-guard interval and thus one OFDM symbol is generated.

Description

GUARD INTERVAL INSERTING / DRAWING APPATATUS AND METHOD FOR OFDM SYMBOL IN OFDM COMMUNICATION SYSTEM}

The present invention relates to an apparatus and method for generating a symbol in a communication system, and more particularly, to an apparatus and method for generating a symbol in an orthogonal frequency division multiplexing (OFDM-OFDM) wireless communication system.

In general, a wireless communication system transmits data to be transmitted in a predetermined carrier signal. In addition, in order to load the data to be transmitted in a certain carrier signal must be subjected to a modulation process. Various modulation methods are currently used for this modulation method. Hereinafter, an orthogonal frequency division multiplexing (OFDM) method will be described.

The OMD system is a fourth generation (4G) modulation technology expected to be adopted as a digital TV standard in Europe, Japan and Australia, and was first promoted as a wireless LAN technology in the early 1990s. The OFDM technique distributes data over a large number of carriers spaced apart at regular intervals at the correct frequency. This prevents the demodulator receiving the data from referencing other frequencies that are not sent to it. That is, it provides "orthogonality" with other signals.

As a modulation method of each carrier used in the OMD system, a multi-value modulation method such as QPSK for voice broadcasting and 64QAM having excellent band utilization efficiency for terrestrial digital TV broadcasting is used. The OMD system uses different modulation schemes according to the characteristics as described above. However, in addition to each modulation scheme, data transmission is configured in units of transmission symbols in the OMD system. Each transmission symbol used in the OMD system has a valid symbol interval and a guard interval. The guard interval is a signal period for reducing the effects of multipath (ghost).

Next, the characteristics of the OSF method will be described. The system using the OSDM method multiplexes N parallel data to be transmitted on N subcarrier frequencies having orthogonality to each other. Then, the sum of each of the multiplexed data is transmitted. In this case, when N parallel data is regarded as one OMD symbol, the orthogonality of the N subcarriers in one symbol does not affect the subcarrier channels. Therefore, compared with the conventional single carrier transmission scheme, since the symbol period can be increased by the number of subchannels N while maintaining the same symbol rate, inter-symbol interference due to multipath fading can be reduced.

In addition, in case of inserting a guard interval between symbols by extending the transmitted symbol period, it is possible to reduce intersymbol interference which may be caused by delay of received symbols through multipath, and subcarrier orthogonality may be maintained. have. In addition, this also reduces the interference between channels caused by the orthogonality of the subcarriers. In particular, the receiving end receiving the OMD signal may obtain a time synchronization of a symbol using a guard interval inserted between the symbols. This will be described below. The samples copied into the guard interval of the OMD symbol and the samples within the guard interval are correlated with each other. Therefore, when a correlation value of a guard interval and a section copied from the guard interval in an arbitrary symbol is obtained, the portion having the maximum correlation value can be regarded as the start of the symbol. This characteristic eliminates the need for pilot symbols for channel estimation. Therefore, in the case of using the OMD system as described above, it is possible to increase the bandwidth efficiency and to reduce the power consumption.

For the reasons described above, Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Digital Terrestrial Television Broadcasting (DTTB), Wireless Local Area Network, Wireless communication systems are being developed in fields requiring a high speed data transmission system such as a wireless Asynchronous Transfer Mode. Of course, the technique of inserting the guard interval in these OMD systems is an essential requirement. In addition, a technology for inserting a guard interval is essential in a digital wired communication system employing a Discrete Multi-Tone (DMT) method such as an Asymmetric Digital Subscriber Line (ADSL) and a Very-high Bit Rate Digital Subscriber Line (VDSL).

Next, a process of transmitting and receiving data and a method of generating a symbol in a wireless communication system using an OMD system will be described with reference to the accompanying drawings. 1 is a block diagram of a transmitter and a receiver including a channel environment in a typical OPM system.

First, the transmitter 110 of FIG. 1 will be described. The OMD transmitter 110 includes a modulator 111, a serial / parallel converter 112, an IFFT processor 113 having N sizes, a parallel / serial converter 114, and a guard interval insertion unit 115. , The D / A converter 116. Next, the process of transmitting data in the OMD transmitter 110 having the above-described configuration will be described. Data to be transmitted is input to the modulator 111 of the transmitter 110. Data input to the modulator 111 is modulated according to a modulation scheme used in each system and input to the serial / parallel converter 112. Accordingly, the modulated serial data is N parallel data in the serial / parallel converter 112. It is converted as follows and input to the IFFT processor 113. Accordingly, the IFFT processor 113 inversely transforms the N parallel data and inputs the parallel / serial converter 114. The parallel / serial converter 114 then converts the inverse Fourier transformed data into serial data. It is converted and printed as follows. The data output from the parallel / serial converter 114 is input to the guard interval inserter 115 to insert a guard interval to insert an OMD symbol. Convert it as shown and output it. The OMD symbol output as described above is converted into an analog signal through the D / A converter 116 and transmitted through a predetermined wireless channel.

When the OMD symbol generated by the above-described process is transmitted through a wireless channel, it is transmitted through a multipath channel. The multipath channel function Assume that the output OMD symbols are output values after the calculation by the function is performed. In addition, noise generated in the channel environment In this case, a signal obtained by adding the generated noise to a value obtained by the function becomes a signal received at the receiver.

Next, the receiver 130 of FIG. 1 will be described. The receiver 130 includes an A / D converter 131, a guard interval eliminator 132, a serial / parallel converter 133, an FFT converter 134 having N sizes, and an equalizer. And a synchronization / channel estimator 136, a parallel / serial converter 137, and a demodulator 138. Next, a process of demodulating data in the receiver having the above-described configuration will be described.

The received signal is added to the A / D converter 131 by adding noise through the multipath. The A / D converter 131 receives the received analog signal Converts to digital signal and outputs it. The digital signal output from the A / D converter 131 is input to the guard interval removing unit 132. The guard section removing unit 132 removes the guard section inserted at the time of transmission from the input signal Outputs a signal such as That is, the signal from which the guard interval is removed by the guard interval remover 132 is a signal composed of valid OMD data only. The valid OMD signal is input to the serial / parallel converter 133. The serial / parallel converter 133 processes the input signals in parallel and outputs them to the FFT processor 134. The FFT processor 134 performs an FFT transform process of size N Output parallel data such as FFT transform.

After the FFT transformed parallel data is input to the equalizer 135 and channel equalized, It is output as a signal. The signal output from the equalizer 135 is input to the bottle / serial converter 137. The parallel / serial converter 137 outputs a serial signal after converting the input signal. The serially converted signal is input to the demodulator 138 and demodulated. This allows you to extract intact data. In addition, the synchronization and channel estimator 136 acquires symbol synchronization, and performs channel estimation for tap setting of the equalizer 135.

In the above-described process, the guard interval insertion method in the guard interval inserter 115 inserts a CP (or CS) longer than the impulse response of the channel between the adjacent OFDM symbols into the guard interval, thereby interfering with adjacent symbol interference. It is to remove the effects of interchannel interference. This will be described with reference to FIGS. 2A and 2B.

FIG. 2A is a schematic diagram of an ODP DM symbol inserting a guard interval in a conventional Cyclic Prefix (CP) scheme, and FIG. 2B is a schematic diagram of an OFM DM symbol inserting a guard interval in a conventional CS (Cyclic Suffix) scheme.

In FIG. 2A, in order to maintain orthogonality between subchannels, it can be seen that a guard interval consisting of N _G samples is placed in front of valid data consisting of N samples. At this time, N _G samples of the guard period 20 are made by copying the guard period size N _G samples 21 at the back of the valid data. Therefore, the size of the OMD DM symbol is the sum of N _G samples constituting CP and N samples constituting valid data. This method first uses FFT because the guard interval is delayed by the size to be inserted (N _G samples), and then the IFFT valid data (N samples) comes in serial form and the latter of the valid data is copied as CP in the delayed interval. A delay element (buffer) of N / IFFT size N or a memory or memory address generator is required and an initial delay of N _G clocks occurs.

In FIG. 2B, the ODP DM symbol is configured to solve the above problem. Let's take a look at this. A guard interval (CS) of N _G samples is placed behind the valid data consisting of N samples, and the N _G samples of the guard interval 22 have a guard interval size (N _G samples (23) at the beginning of the valid data). Is made by copying In this method, after IFFT valid data (N samples) comes in a serial form, the front portion (N _G samples) of this data is copied to a portion extended by a guard interval from the end of the valid data interval. Thus, unlike the method of implementing the guard interval with the CP, no initial delay occurs as much as the N _G clock.

However, when performing synchronization acquisition on the symbol implemented in the manner of FIGS. 2A and 2B, the symbol interval copied to the CP (or CS) and the CP (or CS) during the guard period N _G , that is, the call interval in FIG. 2A. 20 and the valid period 21 to be copied, the valid period 22 to be copied in FIG. 2B and the protection period 23 perform a correlation process to obtain the start synchronization of the symbol. In addition, in the multipath environment, if the front part or the back part of the symbol is damaged due to fading, it is impossible to obtain the symbol start synchronization. In other words, if the symbol is damaged in this manner, there is a problem that the start synchronization cannot be obtained.

Accordingly, an object of the present invention is to provide a transmitter, a receiver, a transmission method, and a reception method capable of effectively removing Inter Symbol Interference (ISI) and Inter Channel Interference (ICI) from a system using an OMD system or a DMT system. Is in.

Another object of the present invention is to provide a transmitting apparatus, a receiving apparatus, a transmitting method, and a receiving method for preventing phase shift from occurring in a system or a DMT system using an OMD system.

It is still another object of the present invention to provide a transmitting apparatus, a receiving apparatus, a transmitting method, and a receiving method capable of shortening the symbol synchronization acquisition time in a system or a DMT system using an OMD system.

The method of the present invention for achieving the above objects is a method of inserting a guard interval for generating the OMD DM symbol in the OMD system digital communication system, the received valid data string to a valid data string of a predetermined unit Delaying the divided valid data string by the time period of the potential protection period and dividing and storing the data to be copied into the protection period among the valid data strings; and among the data to be copied into the protection period in the potential protection period. Inserting some data into the potential protection section and outputting the delayed valid data string; and inserting and outputting the remaining data of the data copied into the protection section after outputting the valid data string into the rear guard section and outputting one OF. Generating a DM symbol,

Data to be copied to the guard interval;

The valid data copied in the direction of the potential protection section on the basis of the center position among the valid data is inserted into the potential protection section, and the valid data copied in the direction of the rear guard section on the basis of the center position. Insert into the rear guard zone.

An apparatus of the present invention for achieving the above objects is an insertion device of a protection interval for generating the OMD DM symbol in the OMD system digital communication system, inputting or blocking the valid data string based on the switching control signal A switch, a first buffer for sequentially storing the valid data sequence received from the switch and outputting the valid data sequence in a receiving order, a second buffer for receiving the valid data sequence sequentially and storing the valid data sequence in sequence and receiving the valid data sequence; A counter for counting each symbol of the valid data string and outputting the counted value, a multiplexer for selectively outputting the output of the first buffer or the second buffer by an output control signal, and a count value received from the counter According to the first buffer only during a predetermined copy period of the valid data string The control unit outputs a switching control signal, outputs from the first buffer to the potential protection section, and then outputs valid data sequences of a predetermined unit from the second buffer, and then outputs a trailing protection section data from the first buffer. A control unit for outputting an output control signal to the multiplexer,

Data inserted into the front and rear guard intervals;

It is set by the same amount in the potential protective interval direction and the rear protective interval direction with respect to the position of the center of the effective data string of the predetermined unit.

An apparatus according to another aspect of the present invention for achieving the above object is an insertion device of a protection interval for generating the OMD symbol in the OMD system digital communication system, the potential of the predetermined effective unit of a valid data string A delay unit for delaying and outputting the guard interval by a time period, a first selector for distinguishing data of the guard period from the valid data strings output from the delay unit by a first control signal and outputting the data separately from the valid data strings; A protection interval storage unit for receiving and storing protection interval data received from the first selection unit and sequentially outputting the protection interval data; and a second selectively outputting the protection interval storage unit and the output of the first selection unit by a control signal. A first control signal for separating data of a protection section among valid data strings to a selector and the first selector; And a control unit for outputting the second control signal for controlling to output the valid data sequence after outputting the potential protection section data to the negative side.

In addition, the data inserted into the front and rear guard intervals;

It is set by the same amount in the potential protective interval direction and the rear protective interval direction with respect to the position of the center of the effective data string of the predetermined unit. In addition, it is possible to copy a portion of the protective section to the potential protective section and use the remaining portion of the protective section as the rear protective section.

The method according to the present invention for achieving the above objects is a method of extracting a protection interval for generating a valid data sequence from the OMD die symbol in the ODP DM type digital communication system, the potential protection from the received OMD symbol Removing and outputting the symbols corresponding to the interval, outputting a predetermined valid data string from the ODP symbol from which the potential protection interval has been removed, and outputting the valid data sequence and then storing symbols corresponding to a trailing guard interval. The process of removal.

An apparatus of the present invention for achieving the above objects is an apparatus for extracting a guard interval for generating a valid data sequence from the OMD symbol in an OMD system, the counting the received OMD symbols A counter, a switch for inputting or blocking the OSDM symbol, and a control unit for blocking the switch for a period of a potential protection period and a rearward protection period of the OSDM symbol based on a count value of the counter.

1 is a block diagram of a transmitter and a receiver including a channel environment in a typical OPM system;

FIG. 2A is a diagram of an ODP DM symbol inserted with a guard interval in a conventional CP (cyclic prefix) scheme. FIG.

FIG. 2B is a diagram of an ODP DM symbol inserted with a guard interval in a conventional CS (Cyclic Suffix) scheme. FIG.

3 is a structural diagram of an OSF symbol inserted with a protection interval using a CA (Cyclic Affix) according to the present invention;

4 is an internal block diagram of a protective section inserting unit for inserting a protective section in a CA method according to the present invention;

5 is a control flowchart when inserting a protection section in a CA method according to the present invention;

6 is a block diagram illustrating a block inside the protection section insertion unit of the OMD DM according to another embodiment of the present invention;

7 is an internal block diagram of a protection section removing unit for removing a protection section from the received OMD symbol according to an embodiment of the present invention;

8 is a view illustrating a symbol structure implemented in a CP scheme or a CS scheme according to the prior art and a symbol structure implemented in a CA scheme corresponding to the present invention;

FIG. 9 is a diagram illustrating a case of inserting a guard interval into two ODP DM symbols using a CA scheme according to the present invention. FIG.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings.

In addition, in the following description, there are many specific details such as specific messages or signals, which are provided to aid the overall understanding of the present invention, and it is understood that the present invention may be practiced without these specific details. It will be self-evident to those of ordinary knowledge. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

3 is a structural diagram of an OSF symbol inserted with a guard interval using a Cyclic Affix (CA) according to the present invention.

In a preferred embodiment according to the present invention, the area to be copied to the protection interval of the valid data is set as the central portion of the valid data. This will be described with reference to the drawings. In the present invention, the protection section is provided at the front and the rear of the valid data. In the following description, the protection section located at the front of the valid data is called a "potential protection section", and the protection section at the back of the valid data is called a "backward protection interval". Therefore, the potential protective section or the rear protective section according to the present invention does not have as much as N _G as in FIGS. 2A and 2B described above, and each of the protective sections has 1/2 of N _G. That is, the sum of the potential guard period and the trailing guard period is equal to N _G , but each of the potential guard and the trailing guard period corresponds to 1/2 of the total guard period.

The protection period is copied from valid data. Therefore, in the present invention, the data of the protection section must be copied from the valid data. In the present invention, the copy section of the valid data is copied at the position of 1/2 of the chip. Referring to FIG. 3, the data 30 corresponding to N _G / 2 is copied to the potential protection section 31 in the direction of the potential protection section at the center point of the valid data. Then, the data 32 of N _G / 2 is copied from the center point in the direction of the rear guard section to the rear guard section 33. In the preferred embodiment of the present invention, an example of copying N _G / 2 data in both directions from the center position of the valid data and inserting the data into the front and rear guard sections is described. However, any portion of the valid data may be configured to copy half of the data as much as the guard interval, that is, the valid data as much as N _G , into the potential guard period, and copy the other half to the trailing guard period. It is also possible to copy a portion of the guard period N _G to the potential guard period and use the rest of the guard period as a trailing guard period. In this way, one OMD symbol is completed.

4 is an internal block diagram of a protective section insertion unit for inserting a protective section in a CA method according to the present invention. Hereinafter, with reference to Figure 4 will be described the internal block configuration of the protective section insertion unit for inserting the protective section in the CA method according to the present invention.

As shown in FIG. 1, the data output from the parallel / serial converter 114 is IFFT-processed serial data, and is valid data having a length of N shown in FIG. 3. The valid data is a counter 112. ) And the switch 113 and the second buffer. The counter 112 increases the value of the counter each time valid data is input, and outputs the counted value to the controller 112. The second buffer 115 sequentially stores input valid data.

The switch 113 is controlled on / off by the control unit 111, and the data input when the switch 113 is turned on is stored in the first buffer 114. Data stored in the first buffer 114 and data stored in the second buffer 115 are sequentially output to the multiplexer 116. The control unit 111 controls the output of the multiplexer 116 according to the value counted by the counter 112. The multiplexer 116 selectively outputs data output from the first buffer 114 and the second buffer 115 under the control of the controller 111. This will be described in more detail with reference to FIG. 5 to be described later.

5 is a control flowchart when a protection section is inserted in a CA method according to the present invention. 4 and 5 will be described in detail the control process when the protective section is inserted in the CA method according to the present invention.

The controller 111 maintains the standby state in step 200. Here, the standby state means a state waiting for valid data to be input. The controller 111 proceeds to step 202 to check whether valid data is received. The check whether the valid data is received can be confirmed by checking whether there is a value counted from the counter 112. As such, if there is a value counted from the counter 112, the process proceeds to step 204. Otherwise, the standby state of step 200 is maintained. The control unit 111 proceeds to step 204 and the received valid data Check if the first data is to be received. The control unit 111 is a test result of step 204 If it is your turn to receive the first data, proceed to step 206; Wait for the first data to be received. The control unit 111 turns on the switch 113 in step 206. Through this, data to be copied among the valid data is input to the first buffer 114. In addition, the control unit 111 controls to output the data stored in the first buffer 114 to the multiplexer 116 while turning on the switch 113, and controls the multiplexer 116 to control the first. The data output from the buffer 114 is controlled to be output as protection interval data. Meanwhile, the valid data is continuously stored in the second buffer 115 from the moment it is received.

After that, the control unit 111 proceeds to step 208. Check whether the first data is received. The controller 111 proceeds to step 208. When the first data is received, the output of the first buffer 114 is stopped, and the data stored in the second buffer 115 is sequentially controlled to be output to the multiplexer 116. In addition, the control unit 111 controls the multiplexer 116 to output data output from the second buffer 115 as valid data. The control unit 111 proceeds to step 212 while controlling to output the data of the second buffer 115 in step 210. Check whether the first data is received. The control unit 111 is a test result of step 212 If it is time to receive the first data, the process proceeds to step 214; otherwise, the process continues to step 210. In step 214, the control unit 111 turns off the switch 113 and continuously outputs data stored in the second buffer 115 to the multiplexer 116. In addition, the controller 111 controls the multiplexer 116 to continuously output data output from the second buffer 115.

The controller 111 proceeds to step 216 and checks whether the valid data has been received up to a predetermined Nth data. When the Nth data is received in step 216, the control unit 111 outputs the data stored in the first buffer to the multiplexer 116, and simultaneously controls the multiplexer 116 to control the multiplexer 116. Output the data of the first buffer. In addition, when the controller 111 proceeds to step 218, the controller 111 resets the counter 112. Through this, one OMD symbol as shown in FIG. 3 may be generated.

Then, the characteristics of the CA FM OFM symbol according to the present invention will be described through mathematical signal analysis, and compared with the characteristics of the symbol embodying the protection interval in the conventional CP and CS method, it will not only have time diversity characteristics. Rather, the symbol time synchronization acquisition time is shortened.

First, in the conventional CP and CS schemes, the l-th OSF symbol in which CPs and CSs are inserted into a guard interval and transmitted may be illustrated as Equation 1 and Equation 2 below.

Here, Equation 1 is the l-th OMD symbol of the CP scheme, and Equation 2 is the ODP DM symbol of the CS scheme. In addition, in <Equation 1> and <Equation 2> Is the l th data symbol, N is the FFT / IFFT size, and N _G is the number of samples used in the guard interval. In addition, n is a sample index in one OMD symbol, and k is an index of valid data (N samples). In addition, "~" is an OFM signal after applying CP, and "^" means an OFM signal after applying CS. The signal received through the channel includes a frequency offset due to phase jitter, a Doppler shift, and a timing offset in the sampler. Therefore, in consideration of this, when the <Equation 1> and the <Equation 2> can be expressed as shown in the following <Equation 3> and <Equation 4>.

In Equation 3 and Equation 4, ε is a normalized frequency offset. Indicates. Δ is the normalized time offset, Is the channel frequency response of the l th symbol, Denotes Additive White Gaussian Noise (AWGN).

In the CP method, since ISI and ICI are generated while passing through a channel, when damaged CP is removed from a received signal and FFT transforms N valid data that have not undergone ISI and ICI, Equation 5 and Equation 6 Is expressed as Equation 5 below is a received OPM symbol with CP removed, and Equation 6 below is an FFT transform of this symbol. In the affected area of the ISI and the ICI, the CP method was a protection interval area, but the valid data area is damaged in the CS method. However, since the data of the damaged area is copied to the CS later, the valid data is not affected by the previous symbol. In addition, Equation 7 below is an OMD symbol composed of an undamaged valid data area and a CS after the damaged valid data area is removed as much as the CS interval, and Equation 8 is obtained by FFT transforming the symbol.

Although the frequency offset is not considered for convenience in Equations 5 to 8, the process is the same in a general case in which the frequency offset exists. However, when comparing the FFT transformed symbols of Equation 6 and Equation 8, phase shift occurs, and it is shown that the following Equation 9 has a relationship.

It is known that the phase shift generated as shown in Equation 9 can be compensated only by the frequency domain equalizer used in the existing system.

Next, the l-th OMD symbol transmitted with the guard interval inserted according to the CA method of the present invention is expressed as in Equation 10 below.

"-" Represented by a bar in Equation 10 denotes an OFM signal after applying CA. The signal received by the receiver includes the frequency offset and the time offset as in the conventional schemes.

In Equation 3 and Equation 4, ε is a normalized frequency offset. Indicates. Δ is the normalized time offset, Is the channel frequency response of the l th symbol, Denotes Additive White Gaussian Noise (AWGN).

In the present invention, since ISI and ICI are generated while passing through a channel, the damaged CA is removed from the received signal, and FFT conversion of N valid data that has not undergone ISI and ICI is performed by Equation 12 and Equation 13 below. It is expressed as Equation (12) below is a received OPM symbol with CA removed, and Equation (13) below shows FFT conversion of this symbol.

Similarly, the frequency offset is not considered for the sake of convenience in Equations 12 and 13. In addition, when comparing <Equation 6> and <Equation 13>, it can be seen that the two equations are the same, and when comparing the <Equation 8> and the <Equation 13> phase shift in the CS method It can be seen that. In other words, it can be seen that it is not necessary to use the frequency domain equalizer required in the CS scheme.

FIG. 6 is a block diagram illustrating an internal portion of a guard section insertion unit of an OMD symbol according to another embodiment of the present invention. Hereinafter, an internal block configuration and operation of the guard interval insertion unit of the OSDM symbol according to the present invention will be described in detail with reference to FIG. 6.

According to another embodiment of the present invention, the guard section insertion unit includes a delay unit 201, a selector 202, a guard section storage unit 203, a selection output unit 204, and a controller 205. . Next, the operation according to the configuration will be described. The CA protection interval inserter according to the present invention receives the IFFT modulated N samples as valid data strings. The valid data string thus received must be delayed by the potential protection section 31 because a symbol must be copied and inserted into the potential protection section 31 before the valid data is inserted according to the present invention. Accordingly, the delay unit 201 delays the input valid data string by the potential protection section 31 and outputs the valid data string to the first selector 202. The first selector 202 selects predetermined areas 30 and 32 of the valid data strings to be inserted into the potential protection period 31 and the rear protection period 33 according to the present invention, and stores the protection period. Output to the unit 203, and at the same time outputs a valid data stream to the second selector (204). An area output from the first selector 202 to the protection section storage unit 203 is based on a first control signal output from the control unit 205. In addition, a preferred embodiment according to the present invention is to copy the half of N _G from the center portion of the effective data string to the potential protection interval region and insert the half of the NG into the potential protection interval, and the N _G from the center portion of the valid data string to the trailing protection interval region. Make a copy of half of it and insert it into the trailing guard zone. However, the positions to be copied and set as the front and rear guard intervals do not necessarily need to be the center. It is also possible to copy a portion of the guard period N _G to the potential guard period and use the rest of the guard period as a trailing guard period. The guard section storage unit 203 receives and stores a valid data string output from the first selector 202 to the potential and rear guard sections, and outputs it to the second selector 204. The second selector 204 selectively outputs a signal output from the first selector 202 or a signal output from the guard interval storage unit 203 based on the second control signal of the controller 205. . That is, one OMD symbol as described with reference to FIG. 3 is generated and output using the signals output from the first selector 202 and the guard interval storage 203.

7 is an internal block diagram of a protection section removing unit for removing a protection section from the received OMD symbol according to an embodiment of the present invention. Hereinafter, an internal configuration and an operation of a guard section removing unit for removing a guard section from the OSDM symbol according to the present invention will be described in detail with reference to FIG. 7.

The OMD symbol received after A / D conversion at the receiver is input to the guard interval removing unit. The OMD symbol shown in FIG. 7 is input. The OMD symbol is then input to the buffer 301 and the counter 302. The buffer 301 may be configured as a FIFO that sequentially stores and outputs received OMD symbols, or may use a latch circuit. In addition, the counter 302 counts each received OMD symbol, and outputs it to the controller 303. The control unit 303 may be configured to reset each time the count value is one OMD symbol unit or to generate a counter in units of one OMD symbol. Since the symbol must be counted after the synchronization of the received signal is obtained, the counter 302 performs a count after the synchronization is obtained. In addition, the controller 303 generates and outputs an on / off control signal of the switch 304. Therefore, the guard section is removed from the signal output from the buffer 301 according to the on / off operation of the switch 304, thereby outputting only the valid data string.

As described above, the reason for removing the guard interval is to remove the occurrence of ISI and ICI in the OFM die symbol of the CA method according to the present invention as described above. In other words, in general, when passing through a wired or wireless communication channel, the front and rear of the symbol are damaged due to the influence of the previously transmitted symbol or the symbol transmitted to be received later. As such, when damage occurs to the effective symbol, ISI and ICI can be effectively removed by removing the symbols inserted into the potential protection section 31 and the symbols inserted into the rear guard period 33 according to the present invention.

FIG. 8 is a diagram schematically illustrating a symbol structure 50 implemented by a CP method or a CS method according to the related art, and a symbol structure 51 implemented by a CA method corresponding to the present invention. Next, the synchronization acquisition according to the present invention and the synchronization acquisition according to the prior art will be described in more detail with reference to FIG. 8.

In FIG. 8, X ′ 52 may be regarded as a CP part of a CP method or a part copied to a CS of a CS method in the prior art, and a part of the X 53 copied to a CP of a CP method or a CS of a CS method. It can be seen as a portion, X 'and X is defined by the following equation (14).

Here, samples included in X 52 and X ′ 53 have correlations with each other, but samples in other sections have no correlation with each other. This correlation is described with reference to Equation 15 and Equation 16 with respect to the observation section L of FIG. 8.

here, Is a received signal, And noise Sum of N is the number of valid data samples, ε is the frequency offset, And Indicates. Equation 15 represents a correlation characteristic when an arbitrary sample k is in the X (52) section. When m = N, the correlation characteristics of X (52) and X'53 are shown, and the maximum correlation value is taken as the symbol synchronization start point. In addition, Equation 16 shows correlation characteristics when any sample k is in a region excluding X or X '. Since there is no correlation in this section, it looks like Equation 16 above.

In the structure of the present invention shown in FIG. 8, Y 54 is inserted CA, Y '55 is copied to Y 54, and Z 57 is also extended after the valid data section. As a result Z'56 is copied. Y (54) and Y '55, Z' (56) and Z (57) are defined by Equation 17 below.

Here, samples included in Y (54) and Y '55 and samples included in Z' (56) and Z (57) have a correlation with each other, but samples in other sections are correlated with each other. have no relation. Looking at the correlation with respect to the observation interval (L _Y , L _Z ) of FIG. 8 is shown in Equation 18 and Equation 19.

Here, the correlation characteristic is the same as the process of performing symbol synchronization acquisition using the conventional method. Only case was considered. In the <Equation 18> is the observation interval L _Y, the <Equation 19> exhibits a process of calculating a correlation value for the symbol synchronization acquisition in the observation interval L _Z.

Comparing Equation 15, Equation 18, and Equation 19, and referring to FIG. 8, in the present invention, the observation section is the conventional observation section L. Wow And two observation intervals (L _Y , L _Z ) occur at the same time. And, the interval for performing the correlation process at N _G (X and X ') It is reduced to (Y and Y ', Z and Z'), and two intervals (Y and Y ', Z and Z') are performed simultaneously.

Therefore, in the present invention, two observation intervals are generated in one OFM die symbol to obtain time diversity gain in a multipath fading channel. In addition, since there are two intervals for performing the correlation process, not only the time diversity gain, but also the interval for performing the correlation process is reduced, thereby reducing the time for acquiring the symbol start synchronization.

It may be used by extending it from one OSDM symbol to two OSDM symbols. This is illustrated in FIG. 9. FIG. 9 is a diagram illustrating a case of inserting a guard interval into two OSDM symbols using a CA scheme according to the present invention.

As shown in FIG. 9, the 2 OFM die symbol has a ranging process of the IEEE 802.16 BWA system for 2 symbols, and the protection period of the 2 symbols is defined in the specification (p. 182). The ranging process is a process of informing the subscriber of the access while accessing the network. That is, the process includes requesting bandwidth allocation to allocate a call and allocating the bandwidth.

As described above, the present invention has an advantage of effectively eliminating ISI and ICI by taking a portion of the valid symbols in an OMD communication system or a DMT system, dividing them in half, and dividing them in the front and rear portions of the symbol as a guard period. In addition, the phase shift that occurs in the conventional CS method does not occur, and the observation interval and the correlation process execution interval are increased to two, so that the time diversity gain can be obtained when symbol synchronization is acquired at the receiving end, thereby reducing symbol synchronization acquisition time. There is an advantage to that.

Claims (10)

A method of inserting a guard interval for generating an OMD symbol in an OMD system, Dividing the received valid data string into valid data strings in a predetermined unit, delaying the separated valid data string by the time period of the potential protection period, and dividing and storing data to be copied into the protection interval among the valid data strings; , Inserting some data of the data to be copied to the protection interval into the potential protection interval and outputting the delayed valid data string in the potential protection interval; And inserting and outputting the remaining data of the data copied into the potential protection section after the output of the valid data string into the rear pass protection section to generate one OSDM symbol. The method of claim 1, And inserting half of the data to be copied into the protection interval into the potential protection interval, and inserting the remaining data of the data copied into the protection interval into the rear guard interval. The method of claim 1, wherein the data to be copied to the protection interval, Based on the position of the center of the effective data string, the effective data corresponding to the sum of the potential protection section and the rear protection section in both directions is inserted into the potential protection section and the rear protection section. Said method. The method of claim 1, The valid data copied in the direction of the potential protection section on the basis of the center position among the valid data is inserted into the potential protection section, and the valid data copied in the direction of the rear guard section on the basis of the center position. The method characterized in that the insertion into the rear guard interval. A device for inserting a guard interval for generating an OMD symbol in an OMD system, A switch for inputting or cutting off a valid data string based on a switching control signal; A first buffer which sequentially stores the valid data sequence received from the switch and outputs the valid data sequence in order of reception; A second buffer which receives the valid data sequence and stores the valid data sequence sequentially and outputs the valid data sequence in order of reception; A counter for counting each symbol of the valid data string and outputting the counted value; A multiplexer for selectively outputting the output of the first buffer or the second buffer by an output control signal; A switching control signal for connecting to the first buffer is output only during a predetermined copy period among the valid data strings according to the count value received from the counter, and then output from the first buffer to the potential protection section. And a controller configured to output valid data sequences of a predetermined unit from a buffer, and to output an output control signal to the multiplexer to output a trailing guard interval data from the first buffer. The method of claim 5, wherein the data inserted into the front and rear guard intervals, The method as claimed in claim 1, wherein the first and second protection intervals are set in an equal amount in the potential protection interval direction and the rear protection interval direction based on the position of the center of the valid data string of the predetermined unit. A device for inserting a guard interval for generating an OMD symbol in an OMD system, A delay unit for delaying and outputting a valid data string of a predetermined unit by a time period of the potential protection period; A first selector for distinguishing data of a protection section from valid data strings output from the delay unit by a first control signal and outputting the data separately from the valid data strings; A protection interval storage unit for receiving and storing protection interval data received from the first selection unit and sequentially outputting the protection interval data; A second selector for selectively outputting an output of the protection section storage unit and the first selector by a control signal; Outputting a first control signal for classifying data of a protection interval among valid data strings to the first selector, outputting a valid data string after outputting potential protection interval data to a second selection portion, and then outputting a trailing guard interval data; And a control unit for outputting the second control signal. The method of claim 7, wherein the data inserted into the front and rear guard intervals, The method as claimed in claim 1, wherein the first and second protection intervals are set in an equal amount in the potential protection interval direction and the rear protection interval direction based on the position of the center of the valid data string of the predetermined unit. A method of extracting a guard interval for generating a valid data string from an OFM symbol in an OFM system, Removing and outputting as many symbols as potential protection intervals from the received OMD symbol; Outputting a predetermined valid data string from the OMD symbol from which the potential protection interval has been removed; And removing symbols corresponding to a trailing guard interval after outputting the valid data sequence. An apparatus for extracting a guard interval for generating a valid data sequence from an OMD die symbol in an ODP DM type digital communication system, A counter for counting the received OMD symbols; A switch for inputting or blocking the OSF symbol; And a control unit which cuts off the switch for a period of a potential protection period and a rear protection period of an OMD symbol based on a count value of the counter.