KR20060110991A - Method for coding/decoding a data in communication system - Google Patents

Abstract

A method for encoding/decoding data in a communication system is provided to reduce interference on a communication channel and realize a system having a low PAR(Peak-to-Average Power Ratio). A method for encoding/decoding data in a communication system includes the steps of: extracting time and frequency information from data to be transmitted according to a request of data transmission(701,702); storing the extracted time information at a time slot information variable and the extracted frequency information at a frequency slot information variable(702); and encoding the data to the time slot corresponding to a value of the time slot information variable and a sub-channel corresponding to the frequency information variable according to a synchronization signal transmitted from a base station(704).

Description

Method for coding / decoding a data in communication system

1 is an exemplary view showing an FDM multicarrier modulation scheme and an OFDM multicarrier modulation scheme used in the present invention;

2 is an exemplary diagram illustrating spectrum and OFDM spectrum of an OFDM subchannel;

3 is an exemplary diagram for a multiple access scheme in an OFDM system to which the present invention is applied;

4 is a flowchart of an embodiment of a conventional encoding method;

5 is a flowchart of an embodiment of a conventional decoding method;

6 is a diagram illustrating an embodiment of data transmission efficiency in a conventional OFDM system.

7 is a flowchart illustrating an encoding method in an OFDM system according to the present invention;

8 is a flowchart illustrating an embodiment of a decoding method in an OFDM system according to the present invention;

9 is a diagram illustrating an embodiment of data transmission efficiency in an OFDM system to which the present invention is applied;

10 is a diagram illustrating an embodiment of a signal used for two-dimensional PPM encoding according to the present invention.

The present invention relates to a method of encoding / decoding in a communication system, and more particularly, to transmit a large amount of data with a small number of signals by encoding / decoding data bits according to a time slot and a frequency slot in which a signal is transmitted in a communication system. The present invention relates to an encoding / decoding method in a communication system.

In an embodiment of the present invention, an orthogonal frequency division multiplexing (OFDM) system will be described as an example of a communication system.

OFDM is a type of multicarrier modulation, and has attracted attention as a modulation method suitable for next generation wireless data communication, terrestrial digital TV, and digital voice broadcasting because of its excellent performance in a multipath and mobile reception environment. In this case, the conventional frequency division multiplex (FDM) multicarrier modulation scheme (a) and the OFDM multicarrier modulation scheme (b) are shown in FIG. 1.

The OFDM modulation scheme separates a high speed data stream into a plurality of low speed streams and then transmits each separated low speed data stream using a plurality of subcarriers. Since the data transmission rate of each parallel-transmitted subchannel is slower than the original data transmission rate, the symbol length becomes longer, thereby reducing the intersymbol interference due to the multipath delay. At this time, the spectrum and OFDM spectrum of the OFDM sub-channel is as shown in FIG.

Inter-symbol interference can be almost completely eliminated using guard time. During the guard time, the OFDM signal is repeatedly transmitted until the guard time to remove interchannel interference.

One OFDM signal is the sum of a plurality of subchannels modulated by Phase Shift Keying (PSK) or Quadrature Amplitude Modulation (QAM). At this time, each of the sub-channels must transmit an integer number of signals for a predetermined time (T), the number of signals sent for a predetermined time (T) must be exactly one difference between the adjacent sub-channels. This property is called orthogonality between subcarriers.

Comparing the multi-carrier scheme with a single carrier scheme having a constant transmission bandwidth and bit rate, when transmitting data is distributed over N carriers, the duration of one transmission symbol is approximately N times that of the single carrier scheme. As described above, when the duration of one transmission symbol is significantly longer than that of the single carrier, a guard interval may be added on the time axis to minimize distortion due to multipath delay.

In addition, since data is distributed and transmitted throughout the transmission band, even if an interference signal exists in a specific frequency band, the influence is limited to some data bits, and the interleaving and error correction codes can be used to effectively improve characteristics. have.

Inter-symbol interference due to the multipath channel can be overcome by using the OFDM scheme. However, when the attenuation of a particular subchannel is severe, the reception signal-to-noise ratio (SNR) is low, which increases the error probability of data transmitted on the subchannel. . In order to prevent such performance degradation, the OFDM scheme overcomes the fading phenomenon of multipath channels by using forward error correction codes together.

As error correction codes, block codes such as Reed-Solomon and convolutional codes are mainly used, and two trellis codes that improve bandwidth efficiency are used. A concatenated code, a turbo code, an LDPC code, etc. used by combining two different codes are used.

In addition, interleaving is used together to prevent the degradation of error correction performance due to burst error, and the type and size of interleaving are used for the error correction code and the frequency and time fading of the channel. The decision is made by considering all delays due to interleaving.

Meanwhile, when the OFDM transmission method is used for a communication system such as cellular mobile communication, a wireless ATM, or a wireless LAN (LAN) for a plurality of users, a multiple access method for a plurality of users is similar to a single carrier transmission method. This is necessary.

3 is an exemplary view of a multiple access scheme in an OFDM system to which the present invention is applied.

As shown in FIG. 3, a multiple access scheme in an OFDM system to which the present invention is applied includes a time division multiple access (TDMA), a frequency division multiple access (FDMA), and a code division multiple access (CDMA) scheme. Multiple access is used in conjunction with OFDM.

First, in OFDM / TDMA (A), the entire band is composed of N subchannels, and each user uses all N subchannels during the allotted time.

In addition, OFDM / FDMA (B) uses some subchannels among all subchannels without being limited in time, and the allocation of subchannels may be dynamically changed according to a user's request.

In addition, OFDM / CDMA (C) each user uses a unique spreading code every time and subchannel, where MC-CDMA, multicarrier DS-CDM according to the spreading method It may be classified into DS (CDMA) and MT-CDMA (MT-CDMA).

Meanwhile, a conventional encoding method will be described with reference to FIG. 4.

First, a data transmission request is received (401).

Thereafter, time information is extracted from the data to be transmitted and stored in the time slot information variable, and the synchronization signal from the base station is waited for (402).

Thereafter, it is checked whether the timeslot information variable is 0 (403).

As a result of the check 403, if the time slot information variable is 0, the signal is modulated and transmitted (404). The process then proceeds to "401".

On the other hand, if the time slot information variable is not 0, the time slot information variable value is decreased by 1 whenever a time corresponding to one time slot length elapses after the synchronization signal or the last signal transmission (405). ). The process then proceeds to step "403".

Meanwhile, a conventional decoding method will be described with reference to FIG. 5.

First, it waits for reception of a synchronization signal from a transmitting side (501).

Thereafter, the time slot information variable is reset to 0, and a signal from the transmitting side is waited (502).

Thereafter, it is checked whether a signal is received from the transmitting side (503).

As a result of the check 503, if a signal is not received, the time slot information variable is increased by 1 whenever a time corresponding to one time slot length elapses after receiving a synchronization signal or a signal. The process then proceeds to step 503.

On the other hand, when the check result 503 receives the signal, the time slot information variable value is stored in the time slot information variable for the received signal and combined with the demodulated signal to restore the original data (505). The process then proceeds to step 503.

6 is a diagram illustrating an embodiment of data transmission efficiency in a conventional OFDM system.

As shown in FIG. 6, the conventional OFDM system transmits data in units of frames consisting of one or more time slots and subchannels, and each user controls data in an allocated subchannel because the multiple access is controlled by the FDMA scheme. You can send continuously.

Here, a case where the signal uses a basic binary signal coding scheme (BPSK) having only a value of "0" or "1" will be described as an example. The value of data transmitted for one time frame on subchannel 1 is "1000001". to be. If it is assumed that the scheduling for multi-user control between users is perfect, a 7-bit signal may be transmitted using 7 signals for each subchannel during one time frame corresponding to 7 time slots. Therefore, a total of 28 bits can be transmitted using four subchannels and seven time slots.

In the conventional OFDM system, the encoding method encodes data so that one data can be transmitted as one signal, as shown in FIG. 6, thereby reducing data transmission efficiency.

The present invention has been proposed to solve the above problems, and in encoding a communication system for transmitting a large amount of data with a small number of signals by encoding data bits according to a time slot and a frequency slot in which a signal is transmitted in a communication system. Its purpose is to provide a decryption method.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a method of encoding a communication system, the method comprising: extracting time information and frequency information from data to be transmitted in response to a request for data transmission; Storing the extracted time information in a time slot information variable and storing the extracted frequency information in a frequency slot information variable; And encoding the data into a subchannel corresponding to the frequency information variable in a time slot corresponding to the value of the time slot information variable in accordance with a synchronization signal from a base station.

Meanwhile, another method of the present invention provides a decoding method in a communication system, comprising: a reset step of resetting a time slot information variable to zero upon receiving a synchronization signal; And restoring the original data by combining the demodulated signal by storing the timeslot information variable value in the timeslot information variable for the received signal and storing the corresponding subchannel number as a frequency information variable upon receiving the signal. It is characterized by.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

7 is a flowchart illustrating an encoding method in an OFDM system according to the present invention.

First, a data transmission request is received (701).

Thereafter, time information and frequency information are extracted from the data to be transmitted, the time information is stored in the time slot information variable, and the frequency information is stored in the frequency slot information variable, and then waited for a synchronization signal from the base station (702).

Thereafter, it is checked whether the timeslot information variable is 0 (703).

As a result of the check 703, if the time slot information variable is 0, the signal is modulated and transmitted to the subchannel corresponding to the frequency information (704). The process proceeds to step "701".

On the other hand, if the time slot information variable is not 0, the time slot information variable value is decreased by 1 whenever a time corresponding to one time slot length elapses after the synchronization signal or the last signal transmission (705). ). The process then proceeds to step "703".

8 is a flowchart illustrating a decoding method in an OFDM system according to the present invention.

First, the receiver waits for reception of a synchronization signal (801).

Thereafter, the time slot information variable is reset to 0 and waits for a signal from the transmitting side (802).

Thereafter, it is checked whether a signal is received from the transmitting side (803).

As a result of the check 803, if the signal is not received, the time slot information variable is increased by 1 whenever a time corresponding to one time slot length elapses after the synchronization signal or data signal is received. And proceeds to step "803".

On the other hand, when the check result 803, the signal is received, the time slot information variable value is stored in the time slot information variable for the received signal, and the corresponding subchannel number is stored as the frequency information variable and combined with the demodulated signal to the original data. Restore 805. And proceeds to step "803".

9 is a diagram illustrating an embodiment of data transmission efficiency in an orthogonal frequency division multiplexing system to which the present invention is applied.

As shown in FIG. 9, the orthogonal frequency division multiplexing system to which the present invention is applied transmits data in units of frames consisting of one or more time slots and subchannels, and each user is assigned a control because multiple accesses are controlled by CDMA. The received orthogonal code can be used to continuously transmit data to all subchannels.

Here, a case where the signal uses the basic binary signal coding scheme (BPSK) having only a value of "0" or "1" will be described as an example. The value of data transmitted for one time frame to subchannel 1 is "10000". The value of the data transmitted for one time frame in sub channel 2 is “01101”. In the OFDM / FDMA system, the same subchannel cannot be used by the same user at the same time. However, in the OFDM / CDMA system capable of two-dimensional PMM encoding, data is spread by an orthogonal code designated for each user. Therefore, the number of orthogonal code length users can simultaneously transmit data using the same subchannel without collision. In addition, the value of each signal (data) is determined by the phase of the corresponding signal in the case of using the BPSK, the time slot information from which the signal is started, and the sub channel number where the signal is transmitted.

Therefore, assuming that the scheduling for multi-user control between users is perfect, a 5-bit signal can be transmitted using four signals for each subchannel during one time frame corresponding to seven time slots. have. Therefore, when using the 2D PPM encoding method, 80 bits of data can be transmitted using four orthogonal codes having four subchannels, seven time slots, and a length of four.

As a result, in the conventional method, 28 signals have to be transmitted for transmission of 28 bits, but when two-dimensional PPM encoding is applied, 64 signals may be transmitted for transmission of 80 bits, thereby transmitting the same amount of information. In the following case, since only fewer signals are used than the conventional OFDM system, mutual interference in the system can be reduced.

In the exemplary embodiment of the present invention, the basic two-dimensional PPM coding is applied as an example for brief description. However, if a different time frame reference is used for each channel and user, data transmission of 5.375 bits can be performed without additional overhead. In this case, 86-bit data can be transmitted during one time frame.

10 is a diagram illustrating an embodiment of a signal used for two-dimensional PPM encoding according to the present invention.

As shown in FIG. 10, a signal used for two-dimensional PPM encoding according to the present invention includes a guard time for preventing inter-symbol interference (ISI), and the signal includes inter-channel interference (ICI). It is extended repeatedly to the previous Guard Time to prevent). In this case, if PPM code length is P, spread orthogonal code length is L, time frame length is N, and the number of subchannels used for communication is S, then N = P + L-1.

은 하기의 [수학식 1]과 같다.Meanwhile, in the conventional OFDM system, the amount of data that can be sent in one time frame using a BPSK signal is indicated.

Is shown in Equation 1 below.

는 하기의 [수학식 2]와 같다. On the other hand, it indicates the amount of data that can be transmitted by the 2D PPM coding method.

Is as shown in Equation 2 below.

라 하면 기존의 OFDM 시스템의 경우에 BPSK신호를 이용하는 경우 초당 데이터 전송률을 나타내는

은 하기의 [수학식 3]과 같다.Therefore, the chip rate or OFDM symbol rate of an orthogonal spreading code

In case of the conventional OFDM system, the BPSK signal indicates the data rate per second.

Is shown in Equation 3 below.

는 하기의 [수학식 4]와 같다.In this case, it represents the data rate by the two-dimensional PPM coding method

Is as shown in Equation 4 below.

On the other hand, assuming that complete data scheduling is possible, the result of comparing the transmission rate per subchannel when the number of subchannels and the OFDM symbol rate is fixed is shown in Table 1 below.

As shown in Table 1, as the length of the spreading code increases, the data rate increases, and as the number of time frames for PPM coding per frame increases, the data rate decreases.

Thereafter, the encoded data is separated into time information, frequency information, and actual data to be transmitted and transmitted to a subchannel corresponding to frequency information according to a synchronization signal from a base station. At this time, the time information is stored in the time slot information variable and the frequency information should be stored in the frequency information variable.

In addition, the device receiving the encoded data stores the time slot information variable value at the time of receiving the data as a time slot information variable for the received signal, and stores the corresponding subchannel number as a frequency information variable and demodulates the signal. Combine with to restore the original data.

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

As described above, the present invention has an effect of transmitting a large amount of data with a small number of signals by encoding data bits according to time slots and frequency slots in which signals are transmitted in a communication system.

In addition, the present invention enables a system having a low peak-to-average power ratio (PAR) by encoding data bits according to time slots and frequency slots in which signals are transmitted in a communication system, and also interference on a communication channel. Has the effect of lowering.

Claims (4)

In the coding method in a communication system, An information extraction step of extracting time information and frequency information from data to be transmitted in response to a request for data transmission; Storing the extracted time information in a time slot information variable and storing the extracted frequency information in a frequency slot information variable; And An encoding step of encoding the data into a subchannel corresponding to the frequency information variable in a time slot corresponding to a value of the time slot information variable in accordance with a synchronization signal from a base station Encoding method in a communication system comprising a. The method of claim 1, The communication system, A coding method in a communication system characterized by using a multiple access control scheme of a code division multiple access (CDMA) scheme. In the decoding method in a communication system, A reset step of resetting the time slot information variable to zero upon receiving the synchronization signal; And Restoring the original data by combining the demodulated signal by storing the timeslot information variable value in the timeslot information variable for the received signal and storing the corresponding subchannel number as a frequency information variable as the signal is received. Decryption method in a communication system comprising a. The method of claim 3, wherein The communication system, A decoding method in a communication system characterized by using a multiple access control scheme of a code division multiple access (CDMA) scheme.

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