KR20080037304A - Method and apparatus of orthogonal frequency division multiple access using group coding - Google Patents

Abstract

A method and an apparatus of executing an OFDM(Orthogonal Frequency Division Multiple) access using group coding are provided to enhance whole system performance by coding channels using long codes. A signal transmitting device using an OFDM access includes coders(210,220), interleavers(212,222), modulators(214,216,224,226), and an inverse fast Fourier transformer(230). The coders add codes used for encoding respective data of mobile stations and code data of grouped mobile station using a code having an added length according to the addition result. The interleavers execute interleaving on the coded data according to interleaving patterns. The modulators modulate interleaved signals. The modulated signals transformed by the inverse fast Fourier transformer is transmitted to the mobile stations through an inverse fast Fourier transform access.

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 diagram schematically illustrating 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 receiver 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 grouping 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 system uses the multiplexing scheme, each 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. In the OFDMA scheme, sub-carriers are allocated according to data rates of respective mobile stations.

1 is a diagram schematically illustrating a structure of a transmitting end using a conventional OFDMA scheme.

Referring to FIG. 1, the transmitting end has data to transmit to multiple users. The type of data may be the same or different for each user. Respective user data are input to the respective 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. Each of the interleavers 112, 122, 132, and 142 interleaves data encoded according to a preset interleaving pattern, and outputs the interleaved data to the modulators 114, 124, 134, and 144. Each of the modulators 114, 124, 134, and 144 modulates the interleaved data by using a preset modulation scheme, and then inverse fast Fourier transform (IFFT). ) 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.

Secondly, 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, when the multiplexing method is used, overall system performance may be degraded 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 first method of the present invention for achieving the above object is a signal transmission method using orthogonal frequency division multiple access, the base station to form a group of at least two or more mobile stations, the base station is each of the mobile stations Summing the codes used to encode the data, and encoding the data of the mobile stations formed into groups using codes having the summed length, and the base station performs interleaving according to a predetermined interleaving pattern for the encoded data. And a process of modulating the interleaved signal by the base station, and a process of transmitting the inverse fast Fourier transform of the modulated signal to the mobile stations by the base station.

A second method of the present invention for achieving the above object is a signal receiving method using orthogonal frequency division multiple access, the mobile station receives a signal containing a group identifier, and the received signal by fast Fourier transform in advance Converting into a unit signal having a set size, the mobile station demodulating a fast Fourier transformed unit signal by a predetermined demodulation method, and collecting, by the mobile station, only a unit signal corresponding to the group identifier; The mobile station includes deinterleaving the collected unit signals, and the mobile station performs decoding using a code having a length corresponding to the deinterleaved signal.

A first apparatus of the present invention for achieving the above object is a signal transmission apparatus using orthogonal frequency division multiple access, wherein at least two or more mobile stations are formed in groups, and codes used for data encoding of each of the mobile stations. And a coder for encoding the data of the mobile stations formed as a group using a code having a summed length, an interleaver for interleaving according to a predetermined interleaving pattern for the encoded data, and a modulator for modulating the interleaved signal. And an inverse fast Fourier transformer for inversely fast Fourier transforming the modulated signal and transmitting it to the mobile stations.

A second apparatus of the present invention for achieving the above object is a signal receiving apparatus using an orthogonal frequency division multiple access, receiving a signal including a group identifier, fast Fourier transform the received signal to a predetermined size A fast Fourier transformer for converting a unit signal having a signal, a demodulator for demodulating the fast Fourier transformed unit signal in a predetermined demodulation scheme, a group identifier for identifying the group identifier, and unit signals corresponding to the group identifier A deinterleaver for deinterleaving and a decoder for decoding using a code having a length corresponding to the deinterleaved signal.

Hereinafter, exemplary 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 will be described, and other background art will be omitted so as not to distract from 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. In this case, the length of the code is equal to the sum of the lengths of codes originally to be used by each of the mobile stations before being formed into groups.

2 is a diagram schematically illustrating 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. In FIG. 2, for example, 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.

Therefore, the first encoder 210 encodes the input data by applying a preset code and outputs the encoded data to the interleaver 212. In addition, the second encoder 220 also performs encoding by applying a predetermined code to the input data and outputs the encoded data to the 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 the encoded data according to an interleaving pattern and outputs the interleavers 212 and 222 to the modulators 214, 216, 224, and 226. Here, the signals output from the interleavers 212 and 222 are redistributed into modulators corresponding to respective users.

The redistribution method allocates the data in order of the user corresponding to the required data rate for each user service type. This redistributed data is mixed with 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 diagram schematically illustrating 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 term "a single code block" means a code block used for collecting and decoding 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 scheme 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 is a graph illustrating a gain result when 1/2 coding rate, QPSK modulation, and the same resource are allocated 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 the 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, when group decoding is performed, FER degradation occurs, and thus 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. The grouping described below in FIG. 5 may be preferably applied to a user-selective fading channel, and may also exhibit good performance when applied to an AWGN channel.

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

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 the mobile stations in the group, some of the mobile stations must be regrouped in another group.

Therefore, in step 510, the base station re-allocates the MCS level of the corresponding mobile station 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 may be set to zero.

6 is a diagram illustrating a grouping matrix for obtaining mutual gains according to an 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. In FIG. 9, the base station may reselect the MCS level, the mobile station group, and the mobile station chunk to satisfy the target QoS in order to obtain mutual gain (ie, BER performance gain and data rate gain). .

7 is a diagram illustrating 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 are output. do. 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 a 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 groups for mobile stations that have failed to satisfy requirements by performing orthogonal frequency division multiple access (OFDMA) scheduling.

In the detailed description of the present invention, specific embodiments have been described, but various modifications are possible 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 defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

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 a code 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)

In the signal transmission method using orthogonal frequency division multiple access, The base station forms at least two or more mobile stations in groups; The base station summing codes used for data encoding of each of the mobile stations, group coding the data of the mobile stations formed into groups using codes having the added length; The base station performing interleaving according to a preset interleaving pattern on the encoded data; The base station modulates the interleaved signal, And transmitting the modulated signal by inverse fast Fourier transform to the mobile stations. The method of claim 1, wherein the forming of the group Allocating a predetermined initial modulation and coding scheme (MCS) level to the mobile stations; Obtaining channel state information of each of the mobile stations; Determining whether the service quality of each mobile station can be satisfied by considering the obtained channel state information; Determining whether the service quality can be satisfied by forming a group if the service quality cannot be satisfied; And if the quality of service can be satisfied, forming the mobile stations into a group and generating a group identifier. The method of claim 2, And if there is a mobile station that cannot satisfy the quality of service among the mobile stations, configuring the mobile station in another group capable of satisfying the quality of service of the mobile station. In the signal transmission apparatus using orthogonal frequency division multiple access, An encoder for forming at least two mobile stations into a group, summing codes used for data encoding of each of the mobile stations, and group-encoding data of the mobile stations formed into groups using codes having a summed length; An interleaver for interleaving according to an interleaving pattern preset for the encoded data; A modulator for modulating the interleaved signal, And an inverse fast Fourier transformer for inversely fast Fourier transforming and transmitting the modulated signal to mobile stations. In the signal receiving method using orthogonal frequency division multiple access, Receiving, by the mobile station, a signal including the group identifier, converting the received signal into a unit signal having a predetermined size by performing fast Fourier transform; The mobile station demodulating the fast Fourier transformed unit signal in a predetermined demodulation scheme; The mobile station collecting only a unit signal corresponding to the group identifier; The mobile station deinterleaving the collected unit signals; And the mobile station performs group decoding using a code having a length corresponding to a deinterleaved signal. In the signal receiving apparatus using orthogonal frequency division multiple access, A fast Fourier transformer for receiving a signal including a group identifier, converting the received signal into a fast Fourier transform, and converting the received signal into a unit signal having a predetermined size; A demodulator for demodulating the fast Fourier transformed unit signal in a predetermined demodulation scheme; A group identifier for identifying the group identifier; A deinterleaver for collecting and deinterleaving unit signals corresponding to the group identifiers; And a decoder for performing group decoding using a code having a length corresponding to the deinterleaved signal.

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