KR20060115200A - Method for link adaptation in a communication system using multi-carrier - Google Patents

Abstract

A link adaptation method in a communication system using a multi-carrier is provided to minimize complexity by using one adaptive modulation, a code method set, and a puncturing pattern. A link adaptation method in a communication system using a multi-carrier includes the steps of: determining a basic AMC(Adaptive Modulation and Coding) set and a data size(701); generating encoded information by encoding with a mother code rate(703); determining a segment type(705); setting the number of HARQ(Hybrid Automatic Retransmission Request) maximum retransmission as 1(707); generating a code rate required for a retransmission through puncturing(709); and transmitting data to a terminal(719).

Description

METHOD FOR LINK ADAPTATION IN A COMMUNICATION SYSTEM USING MULTI-CARRIER}

1 is a diagram schematically illustrating segment allocation in a communication system using an OFDMA scheme according to an embodiment of the present invention.

2 is a diagram schematically illustrating segment types supported by a communication system using an OFDMA scheme according to an embodiment of the present invention.

3 is a diagram schematically illustrating a segment structure supported by a communication system using an OFDMA scheme when the number of transmit antennas is 4 or more according to an embodiment of the present invention.

4 schematically illustrates a frame structure of a communication system using an OFDMA scheme according to an embodiment of the present invention.

5 schematically illustrates link adaptation of an NRB segment type in a communication system using an OFDMA scheme according to an embodiment of the present invention.

FIG. 6 schematically illustrates link adaptation of an RT segment type in a communication system using an OFDMA scheme according to an embodiment of the present invention.

7 schematically illustrates a link adaptation process of a base station in a communication system using an OFDMA scheme according to an embodiment of the present invention.

The present invention relates to a communication system using a multi-carrier, and more particularly, to a link adaptation method according to a characteristic of data transmitted from a base station to a terminal.

The present invention relates to a communication system using a multi-carrier, and more particularly, to a data transmission and reception apparatus and a method for operating a segment by applying a differential signal combination scheme according to the priority of data.

The next generation communication system, the 4th generation (4G: 4G) communication system has a variety of quality of service (QoS: QoS) with a transmission rate of about 100Mbps We want to provide services to our users.

Accordingly, 4th generation communication systems are actively researching orthogonal frequency division multiplexing (OFDM) as a useful method for high-speed data transmission in wired and wireless channels. The OFDM method, which is one of methods for transmitting data using a plurality of sub-carriers, that is, a plurality of sub-carriers having mutually orthogonality, is performed by converting serially input symbol strings in parallel. Multi Carrier Modulation (MCM) is a type of multi-carrier modulation that modulates and transmits sub-carrier channels.

The OFDM scheme is similar to the conventional Frequency Division Multiplexing (FDM) scheme, but most of all, an optimal transmission efficiency can be obtained in high-speed data transmission by maintaining orthogonality among a plurality of subcarriers. In addition, since the frequency usage efficiency is good and the characteristics are strong against multi-path fading, an optimum transmission efficiency can be obtained in high-speed data transmission. In addition, it is strong in frequency selective fading and multipath fading, and it is possible to reduce the influence of Inter Symbol Interference (ISI) by using the guard interval, and to simply design the equalizer structure in hardware. It is possible, and has the advantage of being resistant to impulsive noise, and is being actively used in the communication system structure.

In general, the OFDM scheme has good spectral efficiency because the spectra between sub-carrier channels overlap each other while maintaining mutual orthogonality. In the OFDM scheme, modulation is implemented by an Inverse Fast Fourier Transform (IFFT), and demodulation is called a Fast Fourier Transform (FFT). Is implemented by In the multiple access scheme based on the OFDM scheme, an orthogonal frequency division multiple access (OFDMA) for allocating some subcarriers of all subcarriers to a specific terminal is used. There is a way. The OFDMA scheme does not require a spreading sequence for spreading, and can dynamically change a set of subcarriers allocated to a specific terminal according to fading characteristics of a wireless transmission path.

As described above, the fourth-generation communication system consequently has a spectral efficiency to provide a software aspect and the best quality of service (QoS) to develop more diverse contents. In order to develop a high wireless access method,) is being developed to consider the hardware aspect at the same time.

In addition, the hardware aspects considered in the fourth generation mobile communication system are as follows.

In general, the factors that hinder high-speed, high-quality data services in mobile communication are largely due to the channel environment. In the wireless communication, the channel environment includes a Doppler due to power change, shadowing, movement of the terminal, and frequent speed change in addition to white additive Gaussian noise (AWGN). Doppler), interference with other terminals and multipath signals are frequently changed. A method of adaptively coping with a link situation by using an appropriate transmission scheme in such a channel environment is called link adaptation.

Conventionally, a mobile communication system based on a circuit scheme and a code division multiple access (hereinafter referred to as "CDMA") scheme employs a power control scheme for adapting the link. However, gradually entering the fourth generation mobile communication system based on high-speed, high-quality packet data service, the rate control scheme is more suitable in terms of efficiency than the conventional power control scheme for link adaptation. Accordingly, the adaptive modulation and coding (AMC) scheme and hybrid automatic retransmission request (HARQ) schemes (HARQ) are adopted as methods adopted for such rate control. It will be called ').

The AMC method is a method of changing a modulation scheme and a coding scheme according to the state of a channel. To this end, a transmitter to which the AMC scheme is applied has a characteristic of periodically feedbacking each channel state information from each receiver. However, in the AMC scheme, when the channel state information measurement is delayed or an error occurs in the channel state estimation due to the above characteristics, performance is degraded.

Therefore, it is not easy to secure the Signal to Interference and Noise Ratio (hereinafter referred to as 'SINR'), so that the channel condition estimation accuracy does not reach a certain level. As a result, when the AMC scheme is applied in an environment in which channel conditions are difficult to predict, such as a channel environment that is severely changed and a channel environment due to high speed movement, the performance of the AMC scheme is greatly reduced.

In addition, the HARQ scheme is an automatic retransmission request (hereinafter referred to as ARQ) scheme previously performed in a data link layer and an error correction performed in a physical layer (FEC). The technique is combined. Therefore, compared to the conventional ARQ scheme, the retransmission process involves a change in modulation rate and channel code rate corresponding to the physical layer.

There are two types of HARQ schemes: Chase Combining (CC) and Incremental Redundancy (IR). do.

In the CC scheme, the transmitting side uses the same format for initial transmission and retransmission. If m symbols are transmitted in one coded block in the first transmission, the same m symbols are transmitted in retransmission. Here, the coding block represents user data transmitted for one transmission time interval (TTI: hereinafter referred to as "TTI"). That is, the same coding rate is applied to the initial transmission and retransmission. The receiving side soft combines the first transmitted coding block and the retransmitted coding block, performs a cyclic redundancy check (CRC) operation using the combined coded block, and checks whether an error occurs.

On the other hand, in the IR scheme, the transmitting side uses different formats for initial transmission and retransmission. If n bits of user data are generated with m symbols through channel coding, the transmitter transmits only some of the m symbols in the first transmission, and sequentially redundancy in retransmission. ). In other words, the coding rates of initial transmission and retransmission are different. The receiving side attaches retransmissions to the rear part of the initially transmitted coding block, constructs a coding block having a high coding rate, and then executes error correction. In the IR scheme, the first transmission and each retransmission are distinguished by a version number. The version number of the first transmission is named 1, the version number of the next retransmission is 2, and the version number of the next retransmission is 3, and the receiving side correctly combines the first transmitted coding block and the retransmitted coding block using the version information. can do. Therefore, the IR scheme improves decoding reliability by lowering the code rate due to retransmission.

Therefore, the IR method generally has better performance than the CC method by actively changing the code rate, but when the code rate is low, there is a problem that the performance gain obtained by the IR is not relatively large, and a channel for supporting a low code rate The complexity of the coder also increased.

A comparison of the characteristics of the AMC scheme and the HARQ scheme is shown in Table 1 below.

As a result, the AMC scheme has the advantage of having a smaller transmission delay than the HARQ scheme, and is applied to a channel environment in which terminals with low mobility exist and an environment in which channel estimation is easy such as a cell center. However, the AMC method has a problem in that its performance decreases when measurement of channel state information is delayed or an error occurs in the channel state estimation.

In addition, the HARQ scheme has characteristics that are robust to channel changes, and it is easy to control transmission rates. Accordingly, the HARQ scheme is applied to a channel environment in which terminals with high mobility exist and an environment in which accurate channel estimation is difficult, such as a cell boundary, that is, a cell edge. However, the HARQ scheme has a problem in that its performance decreases when retransmission is delayed and a channel coder that can variably adjust a transmission rate is required.

Therefore, in the 4G mobile communication system that provides high-speed and high-quality packet data service, if the initial transmission rate is accurately estimated, the AMC scheme that performs link adaptation using the transmission rate suitable for the channel situation and the transmission rate appropriate for the channel situation are adaptively applied. There has been a need for link adaptation using a combination of the two techniques of the HARQ scheme, which can complement the incorrectly estimated initial rate by visiting.

Accordingly, an object of the present invention is to propose a link adaptation method through a rate control in a communication system using a multi-carrier.

Another object of the present invention is to propose a link adaptation method using a combination of an adaptive modulation and coding scheme and a complex retransmission scheme in a communication system using a multicarrier.

The present invention for achieving the above object; In a link adaptation method in a communication system using a multi-carrier having a plurality of terminals and a base station providing a service to the terminal, the entire frequency band of the communication system is divided into a plurality of subcarrier frequency bands, Generate a plurality of segments having a set number of sub-frequency bands and a frequency domain and a time domain occupied by a preset set number of time periods, and divide the segments into a plurality of segment types for data transmission; Determining a size of the data to be transmitted to the terminal, an adaptive modulation and encoding set, encoding the data to be transmitted to each segment at a predetermined code rate, setting the number of retransmissions according to each segment type, and retransmitting the encoded data to the retransmission. Generate the required code rate to the terminal It characterized in that it comprises the step of transmitting.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

The present invention applies a differential segment structure and uses a multi-carrier communication system, that is, communication using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme. The system will be described with an example.

The present invention uses a combination of the AMC scheme and the HARQ scheme for link adaptation in a system using the differential segment structure. To this end, the AMC scheme is applied to each segment type using a predetermined modulation scheme, coding rate, and AMC set, and the maximum number of retransmissions of the HARQ scheme is applied to predetermined values according to the characteristics of each segment type.

Prior to describing the present invention, the differential segment system, along with a discussion of a new multiple access scheme capable of guaranteeing priority of data while providing excellent spectrum efficiency for high-speed and high-quality packet data service, It is one of the systems that emerged. Accordingly, the differential segment system divides segments divided into frequency domain and time domain into respective segment types according to channel conditions, types of data, and the like, and differentiates transmission strategies. Next, a communication system having the structure of the differential segment will be described with reference to FIG. 1 below.

1 is a diagram schematically illustrating segment allocation in a communication system using an OFDMA scheme according to an embodiment of the present invention.

Referring to FIG. 1, the horizontal axis represents the time domain and the vertical axis represents the frequency domain. The communication system using the OFDMA scheme, that is, the OFDMA communication system divides the total bandwidth into a plurality of sub-carrier frequency bands.

개의 변조된 OFDM 심벌들을 송신할 수 있게 된다. 이에 상기 세그먼트는 하나의 패킷을 전송하는 단위가 된다. As shown in FIG. 1, the segment occupies Nt OFDM symbol intervals preset in the time domain and occupies Nf subcarrier frequency bands preset in the frequency domain. ) '. Thus, one segment

Two modulated OFDM symbols can be transmitted. Accordingly, the segment becomes a unit for transmitting one packet.

The number Nt of OFDM symbol intervals and the number Nf of subcarrier frequency bands constituting the segment may be variably set according to a system situation of the OFDMA communication system. As a result, the OFDMA communication system has a plurality of segments in a predetermined time period.

In FIG. 1, segment allocation of a communication system using an OFDM scheme according to an embodiment of the present invention has been described. Next, segment types supported by a communication system using the OFDM scheme will be described with reference to FIG. Let's do it.

2 is a diagram schematically illustrating segment types supported by a communication system using an OFDMA scheme according to an embodiment of the present invention.

Referring to FIG. 2, a differential segment structure is implemented by differentiating the applied signal processing scheme according to priority. Here, the priority is generated according to a delay tolerance condition, that is, according to a QoS level condition, and according to a distance from BS condition, that is, considering channel quality. Here, the QoS level condition is a condition for distinguishing whether a real time (RT) service or a non real time (NRT) service is used, and the channel quality condition is a cell center area or a cell boundary. (cell boundary) A condition that distinguishes whether it is a region. Thus, the cell center and the cell boundary do not simply depend on the absolute distance from the base station, and the channel information such as the average CINR, the correlation between the antennas, and the moving speed are applied in a complex manner.

According to the priority, the segment type is divided into four types, that is, four types of the first type (type I) to the fourth type (type IV). Here, the four segment types are NRC (Non Realtime Center, hereinafter referred to as 'NRC') segment type, and the second type is RC in consideration of the delay tolerance and the distance from the base station. (Realtime Center, hereinafter referred to as 'RC') Segment type, the third type is NRB (Non Realtime Boundary, hereinafter referred to as 'NRB') Segment type, the fourth type is RB (Realtime Boundary, hereinafter 'RB') It is divided into segment types.

Next, a segment structure according to the differential segment type will be described with reference to FIG. 3.

3 is a diagram schematically illustrating a segment structure supported by a communication system using an OFDMA scheme when the number of transmit antennas is 4 or more according to an embodiment of the present invention.

Referring to FIG. 3, a segment type is shown according to a differential segment structure. And each segment type having a different type is shown as an example and in FIG. The vertical axis represents frequency and the horizontal axis represents time.

According to each segment type, the RC segment type, the RB segment type, the NRC segment type, and the NRB segment type are shown in FIG. 3, which corresponds to a downlink.

The non-real time (hereinafter referred to as NRT) segment type, that is, the NRC segment type and the NRB segment type have sizes of Nt = 64 and Nf = 8. Here, Nt means 64 OFDM symbol transmission intervals on a time axis, and Nf has 8 subcarriers. However, the real-time (RealTime, referred to as 'RT') segment type has a size of Nt = 8, where Nf of the RB segment type is 64, Nf of the RC segment type is 32 and 16.

Here, the NRC segment type and the RC segment type are channels that are located at the cell center, that is, assigned to users having a good channel environment. Therefore, a large spectral efficiency can be obtained through a parallel transmission technique using spatial multiplexing.

Since the NRC segment type uses opportunistic scheduling, different users are allocated to each spatial channel in order to maximize multi-user diversity. However, in the case of the RC segment type, all spatial channels are allocated to one user for stable transmission, thereby maximizing spatial diversity. In addition, in the case of the RC segment type, two or four spatial channels exist on the spatial axis, depending on the number of channels multiplexed on the spatial axis. Since the spatial channels are all assigned to one user, the shape of a segment changes according to the number of spatial channels in order to have the same number of symbols per segment type.

Accordingly, when the double-space time diversity (Double-STTD) technique, which is one of multiple antenna transmission schemes, is applied to the base station, two spatial layers are generated. And, as shown in the RC-2 segment shown in FIG. 3, the value of Nf = 32. In addition, when the V-Blast (Vertical-Bell Laboratory Layered Space-Time) scheme, which is one of the multi-antenna transmission schemes, is applied, four spatial layers, that is, four spatial channels are generated. And Nf = 16 as in the RC-4 segment shown in FIG. 3.

The segments according to the differential segment structure of FIG. 3 may actually have different sizes and shapes, which have a two-dimensional map structure of a frequency domain and a time domain. In addition, since the distribution of traffic corresponding to each of the segment types and traffic, ie, user data, may be changed according to the situation of the OFDMA communication system, the resource map according to the differential segment structure. The structure of the is not limited to the shape and size as shown in FIG. 3 and can be changed to other forms of course. However, the form of the resource map structure should be changed to a form for maximizing the transmission efficiency of the OFDMA communication system. In addition, it is possible to design different resource map structures to minimize inter-cell interference (ICI) between neighbor cells.

In FIG. 3, the segment structure supported by the communication system using the OFDMA method has been described. Next, the frame structure of the communication system using the OFDMA method will be described with reference to FIG. 4.

4 is a diagram schematically illustrating a frame structure of a communication system using an OFDMA scheme according to an embodiment of the present invention.

Referring to FIG. 4, the frame includes a preamble 401, a broadcast channel 403, a traffic channel 305, a dedicated control channel 407, It consists of a pilot channel 409.

Herein, the frame shows a structure of a frame applied to downlink. Looking at the structure, the preamble 401 is located at the beginning of the frame, and performs a function for synchronization and cell search. The broadcast channel 403 includes cell information and paging information. In addition, the dedicated control channel 407 is a traffic control channel (hereinafter referred to as TCCH) that informs downlink and uplink scheduling results, and signaling for supporting opportunistic transmission. signaling). The pilot channel 309 is used to perform fine synchronization and coherent demodulation and to estimate channel state for rate adaptation. The pilot channel 409 is used for synchronization with the mobile station. In addition, the traffic channel 405 is divided into a channel for transmitting user data, that is, the segment type (RC, RB, NRC, NRB).

In addition, the structure of the traffic channel transmitted according to the type of each segment in the frame structure is shown as an example. Referring to this, resource maps of frames for the NRC segment and the NRB segment are divided, but the NRT segment performs feedback on the instantaneous channel state based on an opportunistic scheduling scheme. Therefore, since the instantaneous channel state is received, it is necessary to distinguish between an NRC segment and an NRB segment region. The RT segment, that is, the RC segment and the RB segment, is transmitted without distinguishing a region. This is because there is no feedback information due to opportunistic scheduling.

4 illustrates a structure of a frame according to segments in a communication system using an OFDMA scheme. Next, a method of controlling a transmission rate according to each differential segment structure of the OFDMA mobile communication system will be described.

First, a basic AMC set is used to apply the present invention, and the basic AMC set means a set consisting of initial transmission rates determined by the AMC scheme. That is, during initial transmission, data is transmitted at one of the basic AMC sets according to the AMC result. When there is a reception error, additional redundant data is transmitted through retransmission through HARQ. Table 2 below shows the basic AMC set in the differential segment system according to an embodiment of the present invention.

The base station selects selected user data, that is, data to be transmitted to each terminal through a predetermined scheduling scheme. Since the size of data to be sent to each segment varies depending on which AMC set is selected, the AMC set is selected and the size of the data to be sent to the segment is automatically determined. Here, selecting the AMC set means which modulation scheme and coding rate are selected from the basic AMC set. That is, the AMC set number is determined. Then, the channel state determines the size of data to be transmitted in one segment and the modulation scheme and coding rate of the basic AMC set.

According to the data size, an amount of information bits are transmitted down to each segment, and the mother code rate is encoded through a coder of 1/5, and the information bit size, that is, AMC set Therefore, each retransmission will be punctured or repeated with varying code rates.

Accordingly, the basic AMC set is composed of AMC sets having various code rates. Each AMC set is divided into a predetermined modulation scheme, a code rate, and a size (size of data to be transmitted in one segment). The basic AMC set includes six AMC sets as an example in Table 2.

In the present invention, all of the segment types use the same pattern. In addition, the complexity of the system is reduced, and the size of the basic AMC set is a transmission of an integer number of medium access control-layer protocol data units (hereinafter referred to as MPDUs). To do this, set it to be an integer multiple of the smallest AMC set size.

In the following, a combination of the AMC scheme and the HARQ scheme is applied to each segment, and the basic AMC set is used. The application strategy for each segment will be described. The link adaptation is performed by dividing into three segments of NRB segment, NRC segment, and RB / RC segment.

1. NRC segment type

Since the NRC segment is a segment for non-real-time data transmission, it is not sensitive to transmission delay. Therefore, the link adaptation of the NRC segment type is advantageous to maximize the multi-user gain, and the segment adaptation for the terminals having a good channel environment is performed to maximize the spatial multiplexing gain.

Therefore, each spatial channel is assigned to different terminals in order to maximize multi-user gain. To this end, each terminal feeds back a transmission rate that can be transmitted through each beam to a base station, and each base station determines a user to be serviced at each moment using the information about the transmission rate returned from each terminal. And in order to use the opportunistic transmission, the estimation of the channel state must be accurate. However, since the NRC segment type is located at the cell center, that is, a segment type provided to terminals having good channel state, the NRC segment type has a feature of low inter-cell interference or change. Therefore, it is possible to make accurate channel estimation by measuring accurate SINR. By using the channel estimate through the channel estimation, the link application using the AMC scheme is applied.

In the case of the NRC segment type, a transmission scheme using multiple beams is used based on opportunistic transmission. To this end, the signal provided to each terminal in the base station is generated to minimize interference to different terminals. However, if the delay of the channel feedback is increased, the interference between the multiple beams is increased and the reception performance may be greatly reduced. Therefore, when the HARQ scheme is applied, the transmission delay problem due to retransmission occurs because the segment type is configured to be long in the time domain. Therefore, the NRC segment type depends on the correct AMC, and the HARQ scheme applies the maximum number of transmissions to one time for the interference problem between channels due to transmission delay. As a result, the HARQ scheme is not applied to the NRC segment type. That is, the HARQ scheme is not applied because the link adaptation is performed correctly through the AMC.

On the other hand, when an error occurs during link transmission, it is possible to cope with a transmission error through asynchronous retransmission in units of MPDU in the medium access control layer, and the link adaptation scheme of the NRC segment type Is shown in Table 3 below as an example.

In the NRC segment type, link adaptation was performed by using a basic AMC set and limiting the maximum number of transmissions of HARQ to one time. Next, a link adaptation method of the NRB segment type will be described.

2. NRB segment type

The link adaptation of the NRB segment type solves the problem of reducing the transmission power corresponding to the beam and the interference between multiple beams due to spatial multiplexing and improving the reception performance by using a single beam rather than obtaining a spatial multiplexing gain.

Therefore, for the opportunity transmission, each terminal returns a transmission rate that can be transmitted from the base station through the beam to the base station, and like the NRC segment type, the base station uses the information received from each terminal to service the user at every moment. Decide

However, unlike the NRC segment type, the NRB segment type has a poor channel environment because it is a segment type provided to terminals located at a cell edge. Therefore, it has relatively low SINR and low accuracy of channel estimation. Furthermore, since the variation range of the interference signal from the adjacent cell is large, it is difficult to predict the instantaneous SINR. Therefore, since it is difficult to perform accurate link adaptation using the AMC scheme, it is not easy to perform accurate link adaptation using only the AMC scheme.

In addition, the NRC segment type reduces the multi-user gain when the user's moving speed is increased or the channel feedback delay is increased by performing the opportunity transmission like the NRB segment type. However, the NRB segment performs the opportunity transmission but uses a single beam, so unlike the NRC segment, there is no interference problem between beams due to channel delay.

Therefore, the NRB segment type can be supported in a relatively high Doppler frequency environment compared to the NRC segment type. That is, when a terminal having a high moving speed cannot provide a service to each terminal in the NRC segment type due to an interference problem between beams, it is possible to receive a service through the NRB segment.

As a result, in the NRB segment type, the link adaptation using only the AMC scheme like the NRC segment type does not guarantee the performance of a predetermined criterion. Therefore, the HARQ scheme is used to compensate for data transmission errors due to the incorrect AMC scheme. The closer the terminal is to the edge of the cell, the greater the inaccuracy of the AMC due to channel SINR. Therefore, the number of HARQ retransmissions is set larger for an AMC set used at a lower SINR. And the link adaptation scheme of the NRB segment type is shown in Table 4 below as an example.

As shown in Table 4, in the case of the first AMC set having the lowest transmission rate in the NRB segment type, the number of retransmissions of the HARQ scheme is set to be possible up to eight times. On the other hand, since the sixth AMC set having the highest data rate experiences a good channel environment, the number of retransmissions of the HARQ is limited to two because the influence of the inaccuracy of the AMC scheme is small. Of course, even if the channel environment is good, setting the number of retransmissions through HARQ without limiting it to 2 does not affect the system performance. However, the transmitter, that is, the base station, must store redundant data necessary for the buffer for HARQ transmission. Therefore, the number of retransmissions is reduced in consideration of the buffer size of the system.

In addition, in order to support a lower code rate according to the increase in the number of HARQ retransmissions, when the transmission rate is higher than the mother code rate, that is, the code rate is punctured by the IR method, and when the transmission rate is less than the mother code rate, the CC is used. Perforate the form. In addition, it is possible to retransmit once every two segments in consideration of the delay in the reception and transmission / reception processes of the feedback response of the ACK / NACK in the retransmission process according to the application of the HARQ scheme. That is, the retransmission interval is two segments, and the transmission of the second AMC set of Table 4 will be described below with reference to FIG. 5.

FIG. 5 schematically illustrates link adaptation of an NRB segment type in a communication system using an OFDMA scheme according to an embodiment of the present invention.

Referring to FIG. 5, a HARQ scheme retransmission process corresponding to the second AMC set of the NRB segment type is schematically illustrated. The NRB segment type is illustrated as an example, and the NRB segment interval and retransmission interval are 1.63 ms, for example. And data with a mother code rate of 1/5 is shown. In addition, the base station receives an ACK / NACK from the receiving end, i.e., the terminal, at every transmission, and after receiving the ACK, subsequent retransmissions are canceled, and when the NACK is returned, additional redundant data is transmitted. It is also possible to transmit data for another terminal during the time between retransmissions.

In the HARQ scheme, the IR scheme that actively converts the code rate has better performance than the CC scheme, but when the code rate is very low, the channel coder becomes complicated, and when the code rate is low, the performance gain of the IR scheme is not large. Has Therefore, after generating codes with the appropriate mother code rate, various code rates are generated through puncturing and repetition. Therefore, where the code rate is high, the IR method is applied to obtain a coding gain, and where the code rate is low, that is, where the code rate is lower than the mother code rate, the CC method is applied to improve reception performance. Therefore, if the HARQ scheme is added to the AMC scheme, even if the initial transmission fails, the reception performance is improved by combining with the data received during retransmission, thereby compensating for performance degradation due to an incorrect transmission rate during initial transmission.

Therefore, when the code rate (3/4, 3/8, 3/12) higher than the mother code rate (1/5) is used, the IR method is used and the code rate (3/16) lower than the mother code rate is used. Is transmitted using the CC method. When a code rate higher than the mother code rate is required, the information bits encoded at the mother code rate are punctured, and when a code rate lower than the mother code rate is required, the code is generated through repetition. Therefore, the CC scheme is shown in the fourth transmitted segment. Next, a link adaptation method of the RC / RB segment type will be described.

3. RT (RC / RB) segment type

The link adaptation of the real-time segment type RT segment type has a strict demand due to transmission delay since the data to be transmitted is real-time data. Therefore, an opportunistic transmission scheme that allows transmission delay is not suitable, and a link level diversity scheme for stable transmission is applied.

The link level diversity scheme has a small amplitude of channel change over time due to the application of the frequency hopping and spatial diversity techniques, and thus, an AMC scheme based on an average SINR, that is, a slow AMC scheme and an instantaneous SINR. The difference between the AMC scheme, that is, the fast AMC scheme, is not large. Therefore, for the AMC scheme, users do not feedback the instantaneous channel environment from time to time, but only intermittently feedback the SINR averaged for a long time.

Therefore, the transmitter, that is, the base station applies the AMC scheme based on this information. However, if there are few diversity resources in the channel (small multi-path delay spread and large antenna-to-antenna correlation), it is difficult to obtain sufficient link diversity despite the link level diversity scheme. Due to the difference in SINR, the accuracy of the AMC scheme is reduced. For this purpose, the HARQ scheme should be applied to overcome the error of link adaptation due to inaccurate AMC. However, since the RT data is sensitive to transmission delay, the maximum number of transmissions of HARQ should be determined in consideration of channel delay. And the link adaptation scheme of the RT (RC / RB) segment type is shown in Table 6 below as an example.

And transmitting the second AMC set of Table 5 with reference to Figure 6 will be described below.

FIG. 6 schematically illustrates link adaptation of an RT segment type in a communication system using an OFDMA scheme according to an embodiment of the present invention.

Referring to FIG. 6, a HARQ scheme retransmission process corresponding to a second AMC set according to the RT (RC / RB) segment type is schematically illustrated. In addition, the RT segment type is designed to be short in the time domain in order to minimize the HARQ loop delay, and one segment occupies 0.204 ms as an example. The time interval between retransmission packets considering the ACK / NACK of the HARQ scheme is 0.612 ms. Therefore, when the maximum number of retransmissions is 4, the time interval is about 2.45 ms. And data with a mother code rate of 1/5 is shown.

In addition, the base station receives an ACK / NACK from the receiving end, i.e., the terminal, at every transmission, and after receiving the ACK, subsequent retransmissions are canceled and additional redundant data is transmitted when the NACK is returned. It is also possible to transmit data for another terminal during the time between retransmissions. In addition, data transmission according to the RT segment type is performed at intervals of four segment intervals. Like the NRB segment type, in the RT segment type, where the code rate is high, the IR gain is applied to obtain a coding gain, where the code rate is low, that is, the code rate is lower than the mother code rate. Improve performance Therefore, when the code rate (3/4, 3/8, 3/12) higher than the mother code rate (1/5) is used, the IR method is used and the code rate (3/16) lower than the mother code rate is used. Is transmitted using the CC method. When a code rate higher than the mother code rate is required, the information bits encoded at the mother code rate are punctured, and when a code rate lower than the mother code rate is required, the code is generated through repetition. Therefore, the IR method was used until the third transmission, and the CC method was applied to the fourth transmitted segment having a code rate lower than the mother code rate.

Next, an operation process of a base station for link adaptation in a mobile communication system using the OFDM scheme will be described with reference to FIG. 7.

7 is a diagram illustrating a link adaptation process of a base station in a communication system using an OFDMA scheme according to an embodiment of the present invention.

Referring to FIG. 7, in step 701, the base station determines the size of a basic AMC set and data, and proceeds to step 703. Here, the basic AMC set is determined using feedback information of terminals. In step 703, the base station performs encoding at a predetermined mother code rate to generate encoded information, and proceeds to step 705. In step 705, the base station determines each segment type, and when the determination result is the NRC segment type, the base station proceeds to step 707. In the case of the NRB segment type as a result of the determination, the process proceeds to step 711 and, in the case of the RT segment type, that is, the RC segment type or the RB segment type, proceeds to step 715. Since the number of code rates required for each segment type is different, the segment type is first determined before generating the code rates through puncturing and repetition. For example, a code rate of 3/4 is required for the NRC segment type for the second AMC set in the basic AMC set, but a code rate of 3/4, 3/8, 3/12, 3/16 for the RT segment type is required. Since both are required, determine the segment type.

In step 707, the base station sets the maximum number of HARQ retransmissions for each AMC set to 1 and proceeds to step 709. Thus, setting the maximum number of retransmissions to 1 has the same meaning as not applying the HARQ scheme. In step 709, the base station generates a code rate necessary for retransmission of the NRC segment through the puncturing, and proceeds to step 719.

In step 711, the base station sets a maximum number of HARQ retransmissions in the AMC set having a low data rate and proceeds to step 713. In step 713, the base station generates a code rate for retransmission of the NRB segment through puncturing and repetition, and proceeds to step 719.

In step 715, the base station sets a predetermined number of HARQ maximum retransmissions and proceeds to step 717. In step 717, the base station generates a code rate necessary for retransmission of the RT segment through puncturing and repetition, and proceeds to step 719.

Finally, in step 719, the basic AMC set is applied to each segment type, the number of retransmissions is set for each segment type, the necessary code rate is generated through puncturing and repetition, and data is transmitted.

In summary, the amount of data to be transmitted in one segment type is determined according to the channel state, and accordingly, the AMC set is also automatically determined. Subsequently, data to be transmitted in one segment is encoded at a mother code rate, and the encoded information is punctured and repeated at a code rate required for HARQ retransmission according to each AMC set.

As a result, link adaptation is performed by transmitting data by applying the AMC technique and the HARQ technique using the basic AMC set. In this case, when the data is transmitted, the NRB segment type and the RT segment type use an IR method among HARQ methods when the code rate according to the application of the AMC method is equal to or greater than the mother code rate. In addition, when the code rate according to the application of the AMC scheme is less than the mother code rate, the CC scheme is used among the HARQ scheme.

Thus, Table 6 shows a summary of a differential segment system using a combination of the AMC scheme and the HARQ scheme for each segment type.

In the present invention, the basic AMC set is applied according to each segment type and the maximum number of HARQ retransmissions has been described, but the modulation scheme, code rate, AMC size, and maximum number of HARQ retransmissions of the basic AMC set are provided for convenience of explanation and understanding. As described above, the elements are variously applicable according to the system situation or characteristics, and are not limited to the set values applied to the basic AMC set. In addition, the present invention has been described as an example of a differential segment system in a mobile communication system using an orthogonal frequency division multiple access scheme. However, as described above, the present invention is also applied to other systems for differentiating a transmission strategy according to channel environment or traffic type. As in the present invention, it is possible to apply a method for link adaptation using the AMC technique and the HARQ scheme.

Meanwhile, 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 the equivalents of the claims.

As described above, the present invention has proposed a link adaptation method using a rate control in a mobile communication system using an orthogonal frequency division multiple access scheme, and employs a link adaptation by using an adaptive modulation and coding scheme and a complex retransmission scheme in combination. Has the advantage. In addition, the present invention has the advantage of minimizing complexity by using one adaptive modulation and coding scheme set and using a puncturing pattern. In addition, by using the AMC scheme applied to all segment types, link adaptation is effectively performed by controlling the maximum number of HARQ retransmissions for each segment.

Claims (11)

In the link adaptation method in a communication system using a multi-carrier having a plurality of terminals and a base station for providing a service to the terminal, Divides the entire frequency band of the communication system into a plurality of subcarrier frequency bands and has a frequency domain and a time domain occupied by a preset set number of sub-frequency bands and a preset set number of time periods Create segments of the, segment the segments into multiple segment types for data transmission, Determining a size of the data to be transmitted to the terminal, an adaptive modulation and encoding set, and encoding data to be transmitted to each segment at a predetermined code rate; And setting the number of retransmissions according to each segment type, and generating the encoded data at a predetermined code rate necessary for retransmission and transmitting the encoded data to the terminal. The method of claim 1, The adaptive modulation and coding set comprises information on a modulation scheme, a code rate, and data size. The method of claim 2, The size of the data is the size of the data to be transmitted in one segment, the method characterized in that it is set to be an integer multiple of the size of the data to be transmitted in the segment of the smallest unit. The method of claim 1, If the segment type is non-real-time data and corresponds to a segment type provided to a cell-centric terminal, the maximum number of retransmissions of the complex retransmission scheme is set to one. The method of claim 1, If the segment type is non-real-time data and corresponds to a segment type provided to a terminal at a cell boundary, the maximum retransmission count of the complex retransmission scheme is set to a predetermined value according to the data transmission rate. . The method of claim 1, And when the segment type corresponds to a segment type that is real time data, setting the maximum number of retransmissions of the complex retransmission scheme to a predetermined value. The method of claim 1, And if a code rate generated at the time of retransmission of the data is a code rate equal to or greater than a preset code rate, a method of increasing redundancy is applied. The method of claim 1, And if the code rate generated when the data is retransmitted is a code rate less than a preset code rate, the chase combining method is applied. The method of claim 1, And if the segment type corresponds to a segment type of non-real-time data, determining a terminal to be serviced by receiving transmission rate information from the terminal. The method of claim 1, The method of link adaptation by performing a complex retransmission scheme has a predetermined retransmission interval. The method of claim 1, The method according to claim 1, wherein the predetermined code rate is generated through puncturing or repetition.

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