KR101292888B1 - Method and apparatus of orthogonal frequency division multiple access using group coding - Google Patents

Abstract

According to the present invention, a base station forms a plurality of mobile stations into a group, adds codes used for encoding data to be transmitted to each of the plurality of mobile stations forming the group, and adds a code having a length corresponding to the sum. Encodes data to be transmitted to a plurality of mobile stations that form one group. The interleaved coded data is interleaved according to a predetermined interleaving pattern, and then modulated and inverse fast Fourier transformed to be transmitted to a plurality of mobile stations forming the one group.

Orthogonal Frequency Division Multiple Access, Group Coding, Code

Description

Orthogonal Frequency Division Multiple Access using Group Coding and Its Apparatus {METHOD AND APPARATUS OF ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS USING GROUP CODING}

1 is a view schematically showing a structure of a transmitting end using a conventional OFDMA scheme;

2 is a diagram schematically illustrating a structure of a transmitter using group coding according to an embodiment of the present invention;

3 is a diagram schematically illustrating a receiving end structure for receiving a signal to which group coding is applied according to an embodiment of the present invention;

4 is a graph showing a gain result when the 1/2 coding rate, the QPSK modulation, and the same resource are allocated to mobile stations according to an embodiment of the present invention;

5 is a flowchart illustrating a group organization process of a mobile station according to an embodiment of the present invention;

6 illustrates a grouping matrix for obtaining mutual gains according to an embodiment of the present invention;

7 is a diagram illustrating a service allocation method according to an embodiment of the present invention.

The present invention relates to a communication system, and more particularly, to an apparatus and method for Orthogonal Frequency Division Multiple Access (hereinafter referred to as 'OFDMA').

In general, a communication system considers a multiplexing scheme to effectively distribute limited frequency, time, and spatial resources to multiple mobile stations. As the multiplexing scheme is used in the communication system, the mobile station can be provided with a satisfactory quality of service (QoS).

Recently, the OFDMA method is used in the next generation mobile communication system. The OFDMA scheme allocates a sub-carrier according to the data rate of the mobile station.

1 schematically shows a structure of a transmitter using an OFDMA scheme in a conventional communication system.

Referring to FIG. 1, the transmitting end has data to transmit to multiple users. Types of the data may be the same or different for each user. Respective user data are input to the encoders 110, 120, 130 and 140. Each of the encoders 110, 120, 130, and 140 encodes the input data by applying a preset coding rate, and outputs the data to the interleavers 112, 122, 132, and 142. The interleavers 112, 122, 132, and 142 interleave the data encoded by the predetermined interleaving pattern and then output the data to the modulators 114, 124, 134, and 144. The modulators 114, 124, 134, and 144 are modulated by applying a preset modulation scheme to the interleaved data, and then inverse fast fourier transform (IFFT). Will output The IFFT unit 150 converts a signal in the frequency domain into a signal in the time domain and outputs the signal.

The multiplexing scheme including the OFDMA scheme has the following problems.

First, one user must be assigned one code, and cannot be assigned a code that is longer than the data frame or chunk size. However, according to Shannon's theory, code performance is proportional to code length. Since next generation mobile communication systems transmit signals based on packets, a limited data frame size limits the code length, which has a negative effect on system performance.

Second, resource allocation in the system is performed through adaptive modulation and coding (AMC), subchannels, power allocation, and the like. Efficient scheduling and resource allocation are required for the number of mobile stations, interference problems at the cell edge, and QoS satisfaction. However, such efficient scheduling and resource allocation is difficult to implement due to limited radio resources and code length constraints.

Third, the multiplexing scheme can degrade the overall system performance due to interference from adjacent cells.

The present invention was devised to solve the above problems, and an object of the present invention is to provide an apparatus and method for improving overall system performance by applying a multiplexing method using group coding.

A method for transmitting a signal using an orthogonal frequency division multiple access scheme in a base station of a wireless communication system for achieving the above object includes the steps of forming a plurality of mobile stations into one group, and forming the one group. Summing the lengths of the allocated codes for encoding data to be transmitted to each of the plurality of mobile stations, and group-coding the data to be transmitted to each of the plurality of mobile stations forming the one group by using codes having the length corresponding to the summation. And redistributing coded data corresponding to each of the plurality of mobile stations that form the one group by interleaving the group coded data based on a preset interleaving pattern. A plurality of movements forming each of the signals into one group And a step of modulating by a modulation scheme designated for each station, and transmitting the modulated signals to a plurality of mobile stations forming the one group by performing inverse fast Fourier transform.

In an apparatus for transmitting a signal using an orthogonal frequency division multiple access scheme in a wireless communication system for achieving the above object, the apparatus for transmitting signals to each of a plurality of mobile stations forming a group includes An encoder for performing group encoding on data to be transmitted to each of a plurality of mobile stations that form the one group using a code having a length corresponding to the summation, and the group encoding according to a preset interleaving pattern An interleaver for redistributing the coded data corresponding to each of the plurality of mobile stations forming the one group by interleaving the data, and for each of the plurality of mobile stations forming the one group of the signals redistributed by the interleaver. Modulated by the specified modulation method Group, a inverse fast Fourier transform to be transmitted by the modulation signal inverse fast Fourier transform to a plurality of mobile stations to form the single group.

A method for receiving a signal using an orthogonal frequency division multiple access scheme in a mobile station of a wireless communication system for achieving the above object, receives a signal containing a group identifier from a base station, and the received signal is a fast Fourier Converting the plurality of unit signals having a predetermined size into a plurality of unit signals; demodulating each of the plurality of unit signals by the fast Fourier transform by a different demodulation scheme for each group identifier; and for each group identifier Demodulating unit signals by different demodulation methods, and classifying and outputting the input unit signals into unit signals having the same group identifier by using the group identifier received from the base station; Split into one corresponding to each identifier Deinterleaving the decoded unit signals independently, and performing a group decoding on the independently deinterleaved signal using a code having a length assigned to each group identifier to each user to which the same group identifier is assigned. The process of outputting data about the data is included.

A mobile station for receiving a signal using an orthogonal frequency division multiple access scheme in a wireless communication system for achieving the above object is a base station for receiving a signal using an orthogonal frequency division multiple access scheme in a wireless communication system. A fast Fourier transformer for receiving a signal including a group identifier from the plurality of signals, fast Fourier transforming the received signal into a plurality of unit signals having a predetermined size, and a plurality of unit signals by the fast Fourier transform A demodulator for demodulating different demodulation schemes for each group identifier, and demodulating unit signals according to different demodulation schemes for each group identifier, and receiving a group identifier received from the base station. Using the same group identifier A group identifier for classifying and outputting unit signals having one unit, a deinterleaver independently performing deinterleaving for unit signals classified as one corresponding to each of the group identifiers, and a code having a length assigned to each group identifier And a decoder to decode the independently deinterleaved signal and output data for each of the users to which the same group identifier is assigned.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, only parts necessary for understanding the operation of the present invention are described, and other background techniques are omitted so as not to disturb the gist of the present invention.

The present invention proposes an apparatus and method for grouping at least one mobile station to form a group, and assigning a long code to the formed group to perform group coding. Here, the length of the code is equal to the sum of the lengths of the codes originally used by each of the mobile stations before being formed into groups.

2 schematically illustrates a structure of a transmitter using group coding according to an embodiment of the present invention.

Referring to FIG. 2, each of the plurality of user data is input to the encoders 210 and 220. For example, in FIG. 2, data of users 1 and 2 are grouped and input to the first encoder 210, and data of users 3 and 4 are grouped and input to the second encoder 220.

Accordingly, the first encoder 210 applies a preset code to encode the input data and outputs the encoded data to the first interleaver 212. The second encoder 220 encodes the input data by applying a preset code and outputs the encoded data to the second interleaver 222. In FIG. 2, it is assumed that encoding is performed by using a 1/2 code.

Each of the interleavers 212 and 222 interleaves data encoded according to a predetermined interleaving pattern and then outputs the modulators 214, 216, 224, and 226 that support different modulation levels. Here, the signals output from the interleavers 212 and 222 are redistributed to modulators corresponding to respective users.

In this case, the redistribution is performed by the user order in consideration of the required data rate according to each user service type. This redistributed data will also contain data from other users. Therefore, if the coding rate is changed, the modulation level should be changed automatically.

The modulated signal output from each of the modulators 214, 216, 224, and 226 is input to the IFFT unit 230. Here, the modulated signals output from the modulators 214, 216, 224, and 226 are divided by a predetermined size and input to the IFFT unit 230. The IFFT unit 230 converts the input signals into signals in the time domain in the frequency domain and outputs the converted signals.

3 is a schematic view of a receiver structure for receiving a signal to which group coding is applied according to an embodiment of the present invention.

Referring to FIG. 3, the receiving end is composed of devices corresponding to the transmitting end, and the signal is processed in the reverse order of the transmitting end. Detailed description of the structure and signal processing of the receiving end will be omitted. However, the receiver further includes a group identifier 300 for identifying a group of users by using a group identifier (GID) received from the transmitter. The group identifier 300 identifies a user using a group identifier, and then sorts demodulated data of the corresponding group users in user order to generate a single code block. Here, the single code block refers to a code block used to collect and decode chunks having the same group identifier by the receiver at signals transmitted in a predetermined size at the transmitter.

Next, the application of the group coding multiplexing method according to the present invention will be described in each of an additive white Gaussian noise (AWGN) channel and a user selective fading channel.

First, the multiplexing method according to the present invention in the AWGN channel will be described.

If the channel of any mobile station is AWGN, the received frame error rate of the mobile station has the form as shown in FIG. FIG. 4 shows an example of a gain result obtained by assigning 1/2 coding rate, QPSK modulation, and the same resource to mobile stations according to an embodiment of the present invention.

The larger the number of mobile stations included in one group, the greater the gain of any mobile station. In addition, other mobile stations in the same group also gain performance. Inclusion of more mobile stations in each group results in higher performance gains, but to some extent saturation may occur. Therefore, rather than randomly increasing the number of mobile stations per group, the threshold value should be defined in advance through complexity analysis.

Next, a multiplexing method according to the present invention in a user selective fading channel will be described.

In a user-selective fading channel, randomly determining the mobile stations to belong to a group may cause performance degradation. The reason is that the mobile station having a poor channel condition may be affected by the mobile station having a good channel condition, resulting in a poor average channel condition of the group. In this case, if group decoding is performed, FER degradation occurs. As a result, performance degradation due to grouping becomes larger than coding gain, resulting in overall performance degradation. Therefore, grouping of mobile stations is an important problem in terms of performance improvement.

5 illustrates a group organization process of a mobile station according to an embodiment of the present invention. The grouping described by FIG. 5 may be preferably applied in a user selective fading channel. In addition, it can show good performance when applied to AWGN channel.

Referring to FIG. 5, in step 502, the base station allocates a preset initial modulation and coding scheme (MCS) level to all mobile stations, and proceeds to step 504. In step 504, the base station measures the bit error rate (BER) of each mobile station using the channel state information of all the mobile stations, and proceeds to step 506.

In step 506, the base station determines whether the allocated initial MCS level can satisfy the QoS of each mobile station in consideration of the measured BER. If the QoS of all mobile stations can be satisfied, a group identifier (GID) is generated and notified to the mobile stations in step 508. However, if some mobile stations cannot satisfy the QoS of all mobile stations in the group, the some mobile stations must be regrouped in another group.

Therefore, in step 510, the base station reallocates the MCS level for some mobile stations that do not satisfy the QoS, and then performs the process again from step 504. If a specific mobile station cannot be included in the group even after repeating the above-described procedure, the mobile station is determined to be a mobile station not belonging to the group. At this time, the group identifier of the mobile station not belonging to the group may be set to zero.

6 illustrates a grouping matrix for obtaining mutual gains according to an exemplary embodiment of the present invention.

Referring to FIG. 6, the base station collects channel state information of all mobile stations and performs scheduling so that the average channel state of the group satisfies the QoS of the mobile station having the worst channel state among the mobile stations. When the mobile stations are included in the group as in the present invention, channel coding can be performed using a code having a long length, thereby generating a coding gain. FIG. 6 illustrates a scheme in which the base stations can re-select an MCS level, a mobile station group, and a mobile station chunk to satisfy target QoS in order to obtain mutual gains (that is, BER performance gain and data rate gain). It was.

7 illustrates a service allocation method according to an embodiment of the present invention.

Referring to FIG. 7, when a base station processes information of resources available in a system, that is, chunk information, channel state information, and MCS level information in the form of a look up table (LUT), BER performance and data rate information may be obtained. Is output. A service map indicating a service type assignable to each mobile station is generated using the output information. When the base station finally selects a combination that can satisfy the services required by all mobile stations belonging to one group in the generated service map, a group identifier is generated and the scheduling and resource allocation process ends.

If the service type indicated in the service map does not satisfy the requirements of the mobile station, or if a scheduling conflict occurs with another mobile station, group formation will fail. In this case, it is necessary to reorganize the group for the mobile stations that do not satisfy the requirements by performing the conventional OFDMA scheme scheduling or for the mobile stations in which the collision occurs.

In the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the scope of the appended claims, and equivalents thereof.

As described above, the present invention has the advantage of improving the overall system performance by grouping the mobile stations and channel coding the grouped mobile stations using codes having a long length. In addition, since only group identifier information is additionally required for decryption, there is an advantage of improving overall system performance while minimizing system overhead.

Claims (6)

A method for transmitting a signal using an orthogonal frequency division multiple access scheme in a base station of a wireless communication system, Forming a plurality of mobile stations into one group, Summing the lengths of the allocated codes for encoding data to be transmitted to each of the plurality of mobile stations forming the one group, and using each code having the length according to the summation, to each of the plurality of mobile stations forming the one group. Performing group coding on the data to be transmitted; Redistributing the coded data corresponding to each of the plurality of mobile stations that form the one group by interleaving the group coded data based on a preset interleaving pattern; Modulating each of the redistributed signals by a modulation scheme specified for each of a plurality of mobile stations forming the one group; And transmitting the modulated signals by inverse fast Fourier transform to a plurality of mobile stations forming the one group. The method of claim 1, wherein the forming of the group comprises: Allocating a predetermined initial modulation and coding scheme (MCS) level to mobile stations capable of communicating with the base station; Obtaining channel state information of each of the mobile stations; Determining whether the allocated MCS level satisfies the quality of service of each mobile station in consideration of the obtained channel state information; And forming at least two or more mobile stations that can satisfy the quality of service into one group, and assigning a group identifier to the formed one group. 3. The method of claim 2, Allocating a new MCS level that can satisfy the quality of service for some of the base stations that can not satisfy the quality of service, and forming a different group corresponding to the new MCS level to give a group identifier Way. An apparatus for transmitting a signal using an orthogonal frequency division multiple access scheme in a wireless communication system, The lengths of the allocated codes are encoded to encode data to be transmitted to each of the plurality of mobile stations forming one group, and transmitted to each of the plurality of mobile stations forming the one group by using the code having the length corresponding to the sum. An encoder for performing group encoding on data, An interleaver for interleaving the group coded data according to a preset interleaving pattern to redistribute coded data corresponding to each of a plurality of mobile stations forming the group; A modulator for modulating each of the signals redistributed by the interleaver according to a modulation scheme specified for each of a plurality of mobile stations forming the one group; And an inverse fast Fourier transformer for inverse fast Fourier transforming the modulated signals to a plurality of mobile stations forming the one group. A method for receiving a signal using an orthogonal frequency division multiple access scheme in a mobile station of a wireless communication system, Receiving a signal including a group identifier from a base station, converting the received signal into a plurality of unit signals having a predetermined size by performing fast Fourier transform; Demodulating each of the plurality of unit signals by the fast Fourier transform in a different demodulation scheme preset for each group identifier; And demodulating the unit signals having been demodulated by different demodulation schemes for each group identifier, and classifying and outputting the unit signals having the same group identifier as one using the group identifier received from the base station. and, Independently deinterleaving unit signals classified into one corresponding to each of the group identifiers; A method of receiving a signal comprising the step of outputting data for each of the users assigned the same group identifier by performing group decoding on the signal having been independently deinterleaved using a code having a length assigned to each group identifier. . A mobile station for receiving a signal using an orthogonal frequency division multiple access scheme in a wireless communication system, A fast Fourier transformer for receiving a signal including a group identifier from a base station, converting the received signal into a fast Fourier transform, and converting the received signal into a plurality of unit signals having a predetermined size; A demodulator for demodulating each of the plurality of unit signals by the fast Fourier transform in a different demodulation scheme preset for each group identifier; A group for inputting unit signals demodulated by different demodulation schemes for each group identifier, and classifying and outputting the unit signals having the same group identifier as one using the group identifier received from the base station Identifier, A deinterleaver independently performing deinterleaving on unit signals classified into one corresponding to each of the group identifiers; And a decoder for performing group decoding on the independently deinterleaved signal using a code having a length assigned to each group identifier, and outputting data for each of the users assigned the same group identifier.

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