KR101368105B1 - Apparatus and method for transmitting ack/nack signal in orthogonal frequency division multiplexing access system - Google Patents

Abstract

The present invention relates to a method of transmitting acknowledgment (ACK) / NACK (Nacknowledgement) information, which is a response signal for uplink data transmission, in a mobile communication system through a physical downlink control channel in downlink based on orthogonal frequency division multiple access. The present invention generates control information to be transmitted to a mobile terminal, determines whether the generated control information is ACK / NACK information, and if the generated control information is not the ACK / NACK information, the control information transmission. Check the control channel format indicator (CCFI) indicating the number of OFDM symbols used, and transmit the generated control information through OFDM symbols corresponding to the value indicated by the CCFI, and the determination result If the generated control information is the ACK / NACK information, the A is determined using the maximum number of OFDM symbols available for the control information transmission. Send CK / NACK information.

OFDM (A), ACK / NACK, CCFI, CDM, repetition, control information

Description

ACC / NAC signal transmission apparatus and method in orthogonal frequency division multiple access system {APPARATUS AND METHOD FOR TRANSMITTING ACK / NACK SIGNAL IN ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING ACCESS SYSTEM}

1 is a diagram illustrating a configuration of a subframe used in a mobile communication system of a general orthogonal frequency division multiple access method;

2 is a diagram illustrating a method of determining an area of a resource for transmitting ACK / NACK information according to the prior art;

3 is a diagram illustrating a method of determining an area of a resource for transmitting ACK / NACK information according to an embodiment of the present invention;

4 is a diagram illustrating a method of determining an area of a resource for transmitting ACK / NACK information according to an embodiment of the present invention;

5 is a diagram illustrating resource mapping in a frequency band in which ACK / NACK information is transmitted according to an embodiment of the present invention;

6 is a control flowchart illustrating a process of transmitting ACK / NACK information according to an embodiment of the present invention;

7 is a control flowchart illustrating a process of receiving ACK / NACK information according to an embodiment of the present invention;

8 is a block diagram illustrating a structure of a transmitter for transmitting ACK / NACK information according to an embodiment of the present invention;

9 is a block diagram illustrating a receiver structure for receiving ACK / NACK information according to a preferred embodiment of the present invention.

The present invention relates to a mobile communication system, and in particular, a response to uplink data transmission through a downlink control channel of a mobile communication system based on an Orthogonal Frequency Division Multiple Access (hereinafter, referred to as "OFDMA") scheme. The present invention relates to an ACK / NACK signal transmission apparatus and method for signaling acknowledgment (ACK) / NACK (Nacknowledgement) information indicating to achieve a required low bit error rate.

In recent mobile communication systems, orthogonal frequency division multiple access (OFDM), or a similar method, is useful for high-speed data transmission in a wireless channel. Frequency division multiple access (hereinafter referred to as "SC-FDMA") is being actively studied.

Currently, the 3rd Generation Partnership Project (3GPP), an asynchronous cellular mobile communication standard organization, is studying a long-term LTE (Long Term Evolution) system based on the multiple access method. Recently, the mobile communication system has been actively studied for the OFDM method which is useful for high-speed data transmission in wired and wireless channels. The OFDM method is a method for transmitting data using a multi-carrier, a plurality of sub-carriers having mutually orthogonality by converting a series of symbols input in parallel to each other, That is, it is a kind of multi-carrier modulation (MCM) scheme that modulates and transmits a plurality of sub-carrier channels.

The OFDM scheme is widely used in digital transmission technologies such as digital audio broadcasting, digital video broadcasting, wireless local area network, and wireless asynchronous transfer mode. Is being applied. In particular, the OFDM scheme uses a frequency spectrum superimposed so that frequency use is efficient, strong in frequency selective fading, strong in multipath fading, and inter-symbol interference using a guard interval. It is possible to reduce the influence and to simply design the equalizer structure in hardware. In addition, the OFDM method has an advantage of being resistant to impulsive noise, and thus can be actively used in a communication system structure.

1 is a diagram illustrating a configuration of a subframe used in a mobile communication system of a general orthogonal frequency division multiple access method. The radio resource can be represented as a two-dimensional array of time and frequency domains as shown in FIG. 1. In FIG. 1, since the horizontal axis represents the time domain and the vertical axis represents the frequency domain, one resource may be represented by one rectangular figure consisting of time and frequency. That is, one square in the frequency domain represents one subcarrier and one square in the time domain represents one OFDM symbol. In addition, for example, seven OFDM symbols are gathered to form one slot, and two slots are gathered to form one subframe. The subframe is a basic transmission unit of a downlink channel transmitted from a base station to a mobile terminal in an OFDMA mobile communication system.

On the other hand, in FIG. 1, for example, in the time domain, 7 OFDM symbols (one slot) are configured, and in the frequency domain, one component unit consisting of 12 subcarriers is referred to as a resource block (RB). Is called). An RB is a resource allocation unit for a physical resource allocated by the base station to the mobile terminal for transmitting information to the mobile terminal, that is, a physical resource block (hereinafter referred to as a "PRB").

Physical Downlink Control Channel (PDCCH) shown in FIG. 1 is a physical downlink control channel transmitted from a base station to a mobile station, and resource allocation information for downlink transmission from the base station to the mobile station; The mobile station transmits scheduling information (down-link / up-link grant) including resource allocation information for uplink transmission from the mobile station to the base station. In addition, an ACK / NACK response signal or the like for data transmitted in uplink may be transmitted through a resource region through which the PDCCH is transmitted.

The PDCCH is transmitted in a subframe unit shown in FIG. 1 and may be transmitted through first or less OFDM symbols (eg, n = 3) in each subframe. If each slot is composed of seven symbols as shown in Figure 1, it is possible to transmit the PDCCH using the first three or less OFDM symbols in the first slot, for example. That is, up to three OFDM symbols initially located in each subframe are used for PDCCH transmission. OFDM symbols other than the symbols used to transmit the PDCCH in one subframe are used for data transmission.

The amount of downlink control information transmitted through the PDCCH may vary for each subframe according to the amount of control information to be transmitted (determined according to the number of mobile terminals present in a cell and the channel state of the mobile terminal). Therefore, in order to successfully demodulate the transmitted control channel at the receiving end, information indicating the amount of resources required to transmit the information of the PDCCH is required separately for each subframe. As such, information indicating the amount of resources used for PDCCH transmission through the corresponding subframe for each subframe is referred to as a control channel format indicator (CCFI). The CCFI information is necessary for the mobile station to know the size of the control channel transmitted by the base station, and 2 bits are used because it should be able to represent 0 to 3 OFDM symbols according to the amount of resources used. do. In addition, as described above, for successful demodulation of the control channel, since the amount of resources used to transmit the control channel must be known first, CCFI information is transmitted through the first OFDM symbol.

A scheduling grant including allocation information and transmission time interval (TTI) information for radio resources to be used for data transmission in downlink and uplink is a basic unit constituting the PDCCH. A control channel element (hereinafter referred to as "CCE") consisting of two subcarriers is transmitted. For example, in the PDCCH transmission region defined by CCFI, one, two, four, or eight (channel conditions are very bad and low coding rates depending on the channel state of the mobile station are very good). One PDCCH is configured using CCEs, and the number of PDCCHs or CCEs transmitted at the same time may vary in units of subframes according to the total number of mobile terminals and channel conditions as described above.

ACK / NACK (Acknowledgement / Nacknowledgement) information transmitted using a radio resource region in which the PDCCH is transmitted indicates a response signal for data transmitted in uplink, and generally, reliability and data yield of data transmission in a packet-based mobile communication system Control information transmitted from a system to which HARQ (Hybrid ARQ) technology is used to increase throughput. Since HARQ is a combination of ARQ (Automatic Repeat Request) technology and Forward Error Correction (FEC), the receiving end decodes the received data through a predetermined FEC reverse process and then decodes the cyclic redundancy check (CRC) on the decoded data. The test is used to determine whether there is an error, and if there is no error, feedback the ACK to the transmitter so that the transmitter transmits the next packet of data, and if the CRC test determines that there is an error in the received data, The NACK is fed back to the transmitter to retransmit the previously transmitted packet.

FIG. 2 is a diagram illustrating a method of determining an area of a resource for transmitting ACK / NACK information according to the prior art. FIG. This is how the area is determined. In FIG. 2, it is assumed that two transmitters are used in a transmitter. When the first one OFDM symbol is a radio resource region in which a PDCCH is transmitted based on CCFI information, information that can be transmitted in the resource region is shown.

Referring to FIG. 2, first, reference symbols (hereinafter referred to as "RS") represented by T1 and T2 are used, and a resource factor (hereinafter referred to as "RE") denoted by T1 is the first antenna. The reference symbol used is denoted by, and the RE denoted by T2 represents the RS used for the second antenna. If four antennas are used, the RSs for the third and fourth antennas are transmitted through the second OFDM symbol of each slot, and the positions of the REs where the first and second RSs are located in the frequency domain, respectively Is the same as Here, RS is used to estimate the quality of the downlink channel, to estimate the channel of the downlink so as to perform coherent demodulation, or to search for a cell in an asynchronous system. RS has a one-to-one correspondence for each antenna. In addition, orthogonality among a plurality of RSs used by different transmission antennas may be maintained by using each subcarrier with different RSs.

As shown in FIG. 2, CCFI, CCE, and ACK / NACK information is transmitted in addition to the RSs in the first OFDM symbol. Since CCFI is transmitted through the first symbol regardless of the resource size to which the PDCCH (ie, CCEs) are transmitted, it can be seen that CCFI is always present in the first symbol. Since the CCFI is essential information for successful demodulation of control information in the receiver, the CCFI may be transmitted by applying a transmit diversity (“TD”) technique. Spatial-Frequency Block Coding (hereinafter referred to as " SFBC ") in which the coding is performed in the frequency domain, and two remaining REs except for RS are available resources for transmitting control information. Since the antenna is used, CCFI information is transmitted using two neighboring REs as one unit among the available REs as shown in FIG. 2.

Meanwhile, in the resource region indicating that the CCE is transmitted, a scheduling grant including resource allocation information and a transmission interval for downlink and uplink scheduling is transmitted. The number of PDCCHs transmitted simultaneously varies for each subframe according to the number of mobile terminals or channel conditions, and the number of CCEs constituting one PDCCH may also vary.

Finally, ACK / NACK information may be transmitted through the remaining resources except for the REs used to transmit RS, CCFI, and CCE in the resource region in which the PDCCH is transmitted. Since the transmission of the ACK / NACK information aims at high reliability, a code division multiplexing (hereinafter referred to as "CDM") scheme may be applied to achieve this. CDM technology mitigates interference by randomizing the interference between ACK / NACK channels of different users, for example, when using a Walsh sequence with a Spreading Factor (hereinafter referred to as "SF") of 4, FIG. As shown in FIG. 4, ACK / NACK information is transmitted using four consecutive REs among the available REs. That is, one ACK / NACK symbol is spread by a Walsh sequence having a length of 4, and up to four users can transmit an ACK / NACK channel using the same resource (four REs). In addition, repetition transmission is possible to obtain diversity gain in the frequency domain. Frequency diversity helps to improve the received signal-to-noise ratio (hereinafter referred to as " SNR ") of these mobile terminals, especially when considering mobile terminals located at cell boundaries and in very bad channel conditions. 2 shows the results of performing four iterations over the entire system band. Several values are possible for the number of repetitions. However, since the results show that the performance gain saturates when four repetitions are performed, the situation is assumed for four repetitions.

As shown in FIG. 2, in the conventional ACK / NACK channel transmission, an area of a resource for transmitting the ACK / NACK channel is determined according to the value of CCFI. That is, as shown in FIG. 2, when the number of OFDM symbols indicated by CCFI is 1, an ACK / NACK channel is transmitted through the first symbol. When the symbol is 2, the symbols are spread over the first and second symbols. In the case of 3, the ACK / NACK channel is transmitted over the first three symbols. In this case, when the transmission of the ACK / NACK channel depends on the value of CCFI, in particular, when control information is transmitted only for the first one OFDM symbol, the first symbol includes RS, CCFI, CCE, and ACK / NACK information. Is loaded and resources are limited, so the total number of ACK / NACK channels to be transmitted is not guaranteed.

In addition, since the ACK / NACK information has to be used separately for other resources and time-frequency domains for the radio resources, and for the power, the ACK / NACK information has a low bit error rate (typically 10 ^) due to the limited total power. -4 aims to be difficult to achieve.

Accordingly, the present invention provides an apparatus and method for transmitting an ACK / NACK signal capable of supporting as many ACK / NACK channel number as possible in an orthogonal frequency division multiple access system.

In addition, the present invention allocates a separate time-frequency resource region for ACK / NACK channel transmission, and repeatedly transmits the ACK / NACK information over a plurality of OFDM symbols to reduce the low bit error rate at the receiving end with a limited total power An apparatus and method for transmitting an ACK / NACK signal that can be achieved are provided.

According to an embodiment of the present invention, there is provided a method of generating control information to be transmitted to a mobile terminal, determining whether the generated control information is ACK / NACK information, and as a result of the determination, the generated control information is the ACK. If not / NACK information, check the control channel format indicator (CCFI) indicating the number of orthogonal frequency division multiplexing (OFDM) symbols used for transmission of control information, and generates through the OFDM symbols corresponding to the value indicated by the CCFI Transmitting the received control information; and if the generated control information is the ACK / NACK information, transmitting the ACK / NACK information using the maximum number of OFDM symbols available for transmitting the control information. Include.
A method according to another embodiment of the present invention is a method for a mobile station to receive control information in an orthogonal frequency division multiple access communication system, the method comprising receiving control information from a base station, and wherein the received control information is ACK / NACK Determining whether the information is information; and if the received control information is the ACK / NACK information, combining the ACK / NACK information by the number of times the ACK / NACK information is repeatedly transmitted by the base station; And demodulating and decoding the combined ACK / NACK information.
An apparatus according to an embodiment of the present invention is a base station apparatus for transmitting control information in an orthogonal frequency division multiple access communication system, generating control information to be transmitted to a mobile terminal, and whether the generated control information is ACK / NACK information. A control channel format indicator indicating a number of orthogonal frequency division multiplexing (OFDM) symbols used for transmission of control information, if the generated control information is not the ACK / NACK information. CCFI) and transmits the generated control information through OFDM symbols corresponding to the value indicated by the CCFI, and if the generated control information is the ACK / NACK information, the control information is transmitted. And a transmitter for transmitting the ACK / NACK information using the maximum number of OFDM symbols available.
An apparatus according to another embodiment of the present invention is a mobile terminal apparatus for receiving control information in an orthogonal frequency division multiple access communication system, comprising: a receiving unit for receiving control information from a base station, and the received control information includes ACK / NACK information. And a control unit for determining whether the control unit determines whether the received control information is the ACK / NACK information, and combines the ACK / NACK information by the number of times the ACK / NACK information is repeatedly transmitted by the base station. And a demodulation and decoding unit for demodulating and decoding the combined ACK / NACK information.

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Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, specific details appear in the following description, which is provided to help a more general understanding of the present invention, and it is obvious to those skilled in the art that the present invention may be practiced without these specific details. something to do. In the following description of the present invention, detailed descriptions of related well-known functions or configurations will be omitted when it is determined that the detailed descriptions may unnecessarily obscure the subject matter of the present invention. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intentions or customs of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification.

3 illustrates a method of transmitting ACK / NACK information through a downlink control channel of an OFDM or OFDMA based mobile communication system according to an embodiment of the present invention. 3 is a diagram illustrating a method for determining a region of a resource for transmitting ACK / NACK information according to an exemplary embodiment of the present invention, and a method for determining an area of a resource for transmitting ACK / NACK information irrespective of CCFI information. Indicates. As shown in FIG. 3, when the number of OFDM symbols indicated by CCFI is 1, CCFI and CCEs except for ACK / NACK information are transmitted through the first symbol, and control information is transmitted in the case of ACK / NACK information. It is transmitted over OFDM symbols corresponding to the maximum number of OFDM symbols. In this case, it is assumed that the maximum number of OFDM symbols that can transmit control information is three.

In this case, when the subframe received by the mobile terminal is a broadcasting signal instead of the unicast signal as described above, the maximum number of OFDM symbols for transmitting control information may be two. In this case, the ACK / NACK information is transmitted, for example, ACK / NACK repetitive transmission is performed over two symbols.

Assuming four repeated transmissions for the ACK / NACK channel, as shown in FIG. 3, the first ACK / NACK transmission is transmitted through the first OFDM symbol, and the second ACK / NACK transmission is transmitted using the second symbol. The third and fourth ACK / NACK transmission is performed through the third OFDM symbol. At this time, the larger the value of the index indicating the position of the OFDM symbol, the same or more times ACK / NACK repeated transmission is to be made. That is, if the indexes from the first OFDM symbol to the third symbol are indexed as index 1, index 2, and index 3, then index 3 rather than at the symbol of index 1 and index 3 rather than at the symbol of index 2 The ACK / NACK repeated transmission is performed a lot in the symbol of. As an example, in FIG. 3, one ACK / NACK transmission is performed in the OFDM symbol of index 1, one ACK / NACK transmission is performed in the symbol of index 2, and two ACK / NACK transmissions are repeated in the symbol of index 3. . That is, in the example of FIG. 3, the repetitive transmission pattern of ACK / NACK may be expressed as [1 1 2]. Since two transmit antennas are assumed, RS, CCFI, CCE, and ACK / NACK information exist in the first OFDM symbol, but only ACK / NACK information may be carried in the second symbol. Here, if there is data to be transmitted, the data is loaded on the REs other than the REs carrying the ACK / NACK information.

FIG. 4 is a diagram illustrating a method of determining an area of a resource for transmitting ACK / NACK information according to an embodiment of the present invention. In contrast to FIG. 3, in which the number of antennas is 2, FIG. If the number is 4 and two OFDM symbols are used for transmitting control information by CCFI, this indicates transmission on an ACK / NACK channel. Since the number of transmit antennas is 4, RS is transmitted not only at the symbol at index 1, but also at the symbol at index 2, and since two symbols are used by CCFI, CCEs are the first two OFDM symbols (symbols having index 1 and index 2). ) Is transmitted over As shown in FIG. 4, the ACK / NACK channel is repeatedly transmitted through one transmission in the symbol of index 1, one in the symbol of index 2, and two transmissions in the symbol of index 3 for four repeated transmissions. At this time, CCFI, CCE, and ACK / NACK information exists in addition to RS in symbol 1, but only RS and CCE exist in symbol 2, and RS does not carry any control information in symbol 3 of index 2. Only / NACK information is transmitted. Therefore, a symbol having a high index may be relatively less affected by other channels or information, resulting in a power margin. That is, in the OFDM symbol of index 3, it is possible to obtain an advantage that more power can be used for the ACK / NACK channel.

As described above, the method for transmitting an ACK / NACK signal according to the present invention repeatedly transmits an ACK / NACK channel using a maximum number of symbols that can be transmitted with control information irrespective of the number of symbols indicated by CCFI. More OFDM symbols with indexes of values allow a greater number of ACK / NACK repetitive transmissions. As a result, the capacity of the supportable ACK / NACK channel not only increases, but also reduces the number of cases in which it is transmitted over three OFDM symbols in the time domain to share power by different information in each symbol. Since the amount of energy carried in the ACK / NACK is up to three times higher than that of only one symbol, the low bit error rate required by the ACK / NACK channel can be easily achieved.

When the ACK / NACK channel is repeatedly transmitted through three OFDM symbols according to an embodiment of the present invention, the repetitive transmission pattern represented by the number of transmissions of the ACK / NACK in each OFDM symbol is determined according to the total number of repetitive transmissions. ] Can be set. As shown in Table 1, the largest number of repetitive transmissions are performed through the OFDM symbol of the highest index, and in some cases, if there is no RS and other control information for the OFDM symbol of index 2, The same number of repetitive transmissions may be performed on the symbol and index 3 symbol. Accordingly, ACK / NACK transmission may or may not be present in the symbol of index 1 based on a series of criteria for determining the repetitive transmission pattern. In addition, in the case of receiving a subframe for broadcasting, the ACK / NACK repeating transmission pattern may be determined based on the same criterion as described above. For example, [1 3] or [2 2] may be used.

1st OFDM symbol 2nd OFDM symbol 3rd OFDM symbol Repeat 8 times 2 2 4 One 3 5 4 repetitions 0 One 3 One One 2 Repeat 3 times 0 One 2 Repeat 2 times 0 0 2 0 One One

In this case, when the criterion that the largest number of repetitive transmissions are performed through the OFDM symbol of the highest index is applied, the repetitive transmission pattern shown in [Table 1] is just one example, and various other patterns may exist. Self-explanatory That is, the repeating transmission pattern for the ACK / NACK channel may be set in advance in a pre-defined form between the base station and the mobile terminal, or may be set in the mobile terminal at the base station through L1 / L2 signaling or higher layer (L3) signaling. In this case, the pattern shape may be changed for each subframe or at a predetermined period.

Meanwhile, the position in the frequency domain where the ACK / NACK channel is repeatedly transmitted to obtain the frequency diversity gain is randomly hopped over the entire system band by using a cell-specific frequency hopping sequence, and has a different hopping pattern for each cell. It is possible to prevent the collision of inter-cell ACK / NACK channel. Alternatively, the location of a specific frequency region within each zone may be determined by zone-based mapping or hopping.

FIG. 5 is a diagram illustrating resource mapping in a frequency band in which ACK / NACK information is transmitted according to an embodiment of the present invention, showing repeated transmission of ACK / NACK using a zone-based hopping scheme. For example, if the ACK / NACK channel is hopped in units of RB, zone-based hopping must first create a zone, which is a unit in the frequency domain in which hopping is performed. Since the number of zones to be generated is set equal to the value of a repetition factor indicating the number of repetitive transmissions of ACK / NACK, when the repetition factor is 4 as shown in FIG. 5, the entire frequency band (for example, 25 RBs corresponding to 5 MHz are divided into four hopping zones of approximately equal size. Then, the position in the frequency domain where ACK / NACK is transmitted in each zone is determined by intra-zone ordering with the size of each zone (the total number of RBs constituting the zone or the total number of groups divided by SF by zone). permutation) function. At this time, by using the cell-specific information together with the symbol index and / or (sub) frame index as the input of the order transform function, it is possible to perform cell-specific hopping in each zone over time. Instead of considering the entire system band, hopping by zone unit can basically guarantee the interval between each repeatedly transmitted ACK / NACK channel, thereby helping to obtain diversity gain.

6 is a control flowchart of a transmitter for transmitting ACK / NACK information according to a preferred embodiment of the present invention. Referring to FIG. 6, an operation of a transmitter for transmitting ACK / NACK information according to the present invention will be described. First, in step 601, a base station generates control information such as CCFI, CCE, and ACK / NACK to be transmitted to a mobile terminal. In step 603, the generated control information is determined whether or not the ACK / NACK information. If the generated control information is ACK / NACK information, the process proceeds to step 605 and sets the maximum number of OFDM symbols that can support CCFI, for example, 3, in step 605. In step 607, the number of repetitive transmissions in each of the three OFDM symbols is determined according to the number of repetitive ACK / NACK transmissions. For example, assuming four repetitions as shown in Figs. 3 to 5, ACK / NACK transmission is performed once each in OFDM symbols of index 1 and index 2, and two ACK / signals in symbol 3 of index 3. NACK transmission is performed, and the ACK / NACK repeating transmission pattern is [1 1 2].

After determining each parameter or function value in step 607, the process proceeds to step 609 to perform encoding and modulation on the ACK / NACK bit string. In this case, rate matching and interleaving may be additionally performed as necessary. The ACK / NACK symbol string subjected to the encoding and modulation process in step 609 is repeated N times in step 611 to increase the probability of successful demodulation at the receiving end. The ACK / NACK symbol string repeated N times in step 611 is mapped to actual subcarriers to be used for transmission in the frequency domain in step 613. In step 619, after the multiplexing with other control channels, the conventional OFDM is performed. It will go through the transmission process.

On the other hand, if it is determined as control information other than ACK / NACK information in step 603, the transmission is performed using the number of OFDM symbols indicated by CCFI in step 615, and in step 617, as in the ACK / NACK channel. After encoding and modulation, rate matching and interleaving are additionally performed, and multiplexing and OFDM transmission are performed in step 619.

7 is a control flowchart illustrating a process of receiving ACK / NACK information at a receiving end according to an exemplary embodiment of the present invention. As shown in FIG. 7, after the normal OFDM reception process in step 701, the ACK / NACK channel is separated from other control channels through demultiplexing in step 703. At this time, demultiplexing is performed in consideration of the number of ACK / NACK transmitted OFDM symbols and the ACK / NACK repeated transmission pattern used in the transmitter. In step 703, the ACK / NACK channel separated through demultiplexing is determined in step 705. As a result, in case of the ACK / NACK channel, step 707 proceeds to step 707. combining) to increase the received energy as compared with the case of not performing repeated transmission. Subsequently, in step 709, the ACK / NACK symbol string despread according to the SF used by the transmitter is demodulated and decoded and recovered into an ACK / NACK bit string. At this time, the deinterleaving and rate de-matching process may be performed in the next step after the combining step of step 707 as in the transmitter. On the other hand, as a result of the determination in step 705, control information other than the ACK / NACK information is separated through demultiplexing in step 711 and then restored to the control information bit string through normal demodulation and decoding. In this case, the deinterleaving and rate de-matching processes may be additionally performed.

8 is a block diagram illustrating a structure of a transmitter for transmitting ACK / NACK information according to an embodiment of the present invention. As shown in FIG. 8, the controller 810 first determines the number of OFDM symbols to which ACK / NACK is transmitted, the number of repetitions of the ACK / NACK channel, the ACK / NACK repetitive transmission pattern, and the frequency domain to which the ACK / NACK is transmitted. Determining parameter or function values are generated and provided to configuration devices that perform each process in a series of processes where the ACK / NACK bit string is later passed. Referring to FIG. 8, a structure of a transmitter according to the present invention will be described in detail. The generated ACK / NACK bit string is converted into an ACK / NACK symbol string through an encoding and modulation process by an encoding and modulator 820. In this case, rate matching and interleaving may be additionally performed.

For example, if the number of data channels supported for the system band of 10 MHz in the uplink is 50, the maximum number of ACK / NACK bits to be supported in the downlink is 50 bits, and the tail of 8 bits When channel coding is performed using a convolutional code having a code rate of 1/3, the total number of bits is (50 + 8) * 3, and a total of 174 bits are generated. If QPSK is used as the modulation technique, 87 ACK / NACK modulation symbols are generated and input to the spreader 830. In the spreader 830, the ACK / NACK symbol string is spread using an orthogonal sequence according to the SF value input from the controller 810. For example, if the Walsh sequence with SF 4 is used, each ACK / NACK symbol is spread. Each time a Walsh sequence of length 4 is multiplied. Therefore, when using the Walsh sequence with SF of 4, the number of modulation symbols that can be transmitted by one RB consisting of 12 subcarriers is 8 when the number of RSs available in the RB is 8 and 2 A modulation symbol of (= 8/4) may be transmitted. On the other hand, when RS is not present in the RB, since all 12 subcarriers are available, three (= 12/4) ACK / NACK modulation symbols are transmitted.

In the iterator 840, the 87 spread ACK / NACK modulation symbols are repeated according to the number of repetitions N provided from the controller 810. Subsequently, the subcarrier mapper 850 maps the repeated ACK / NACK modulation symbols in RB units to subcarriers of the corresponding frequency band using information on a frequency domain for transmitting the ACK / NACK input from the controller 810. Let's do it. The multiplexer 860 multiplexes the ACK / NACK information and other control information according to the number of OFDM symbols transmitted from the controller 810 and the ACK / NACK repetitive transmission pattern. That is, if the ACK / NACK repetitive transmission pattern of [1 1 2] is used, whether there are ACK / NACK transmissions for each symbol and how many transmissions exist over three OFDM symbols on which ACK / NACKs are transmitted. In this case, ACK / NACK information is transmitted through a frequency band determined by subcarrier mapping, and multiplexed so that other control information and data information are transmitted in the remaining time (ie, OFDM symbols) and frequency domain. Subsequent processes are transmitted through a process of a conventional mobile communication system based on OFDM such as IFFT 870, bottle / serial converter 880, Cyclic Prefix (CP) inserter, and multiple antenna transmission.

9 is a block diagram illustrating a receiver structure for receiving ACK / NACK information according to a preferred embodiment of the present invention. As shown in FIG. 9, the structure of the receiver according to the present invention is constructed in the reverse order of the transmitter structure shown in FIG. Referring to FIG. 9, a CP remover 920, a serial / parallel converter 930, an FFT 940, or the like, a process of a conventional mobile communication system based on OFDM, such as a singular or plural receiving antennas and an FFT, is first described. Receive the signal via.

Subsequently, the demultiplexer 950 separates the ACK / NACK channel, the other control channel, the data channel, etc. by the number of OFDM symbols and the ACK / NACK repetitive transmission pattern transmitted from the ACK / NACK provided from the controller 910. The subcarrier demapper 960 extracts the ACK / NACK information from the actual frequency band in which the ACK / NACK is transmitted using the information on the frequency domain in which the ACK / NACK received from the controller 910 is transmitted. Then, the combiner 970 combines the number of repetitions by the information on the number of repetitions of the ACK / NACK provided by the controller 910. The energy-enhanced ACK / NACK symbols through combining are despread using the same length Walsh sequence used by the transmitter in despreader 980, and then recovered to the ACK / NACK bitstream via demodulator and decoder 990. . In this case, the demodulator and decoder 990 may use a QPSK demodulator and a convolutional decoder.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the 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 varies the amount of resources used for transmission according to whether control information transmitted from the base station to the mobile terminal is ACK / NACK, and in the case of ACK / NACK information, the higher the index value of the symbol, the ACK. By using the ACK / NACK repetitive transmission pattern which allocates a large number of repetitive transmissions of / NACK, it is possible to increase the demodulation success rate for the ACK / NACK at the receiving end of the mobile terminal by utilizing a limited total power amount for each symbol.

In addition, the present invention can increase the number of channels of ACK / NACK that can be supported by ensuring the amount of resources to be transmitted ACK / NACK.

Claims (10)

A method for transmitting control information from a base station in an orthogonal frequency division multiple access communication system, Generating control information to be transmitted to the mobile terminal and determining whether the generated control information is ACK (Acknowledgement) / NACK (Nacknowledgement) information; If the generated control information is not the ACK / NACK information, the control channel format indicator (CCFI) indicating the number of orthogonal frequency division multiplex (OFDM) symbols used for transmission of control information is checked and the CCFI is indicated. Transmitting the generated control information through OFDM symbols corresponding to a value; And if the generated control information is the ACK / NACK information, transmitting the ACK / NACK information using the maximum number of OFDM symbols available for transmitting the control information. The method of claim 1, The process of transmitting the ACK / NACK information, Determining a repetitive transmission pattern of the ACK / NACK information; And transmitting the ACK / NACK information repeatedly in a corresponding OFDM symbol according to the determined repetitive transmission pattern. 3. The method of claim 2, A method for transmitting control information of a base station, characterized in that the largest number of repetitive transmissions are performed in the OFDM symbol of the highest index. In the orthogonal frequency division multiple access communication system, the mobile terminal receives control information, Receiving control information from a base station, Determining whether the received control information is ACK (Acknowledgement) / NACK (Nacknowledgement) information; Combining the ACK / NACK information with the number of times the ACK / NACK information is repeatedly transmitted by the base station if the received control information is the ACK / NACK information; Demodulating and decoding the combined ACK / NACK information; The ACK / NACK information is transmitted by the base station using the maximum OFDM symbols available for transmission of the control information. A base station apparatus for transmitting control information in an orthogonal frequency division multiple access communication system, A control unit for generating control information to be transmitted to a mobile terminal and determining whether the generated control information is ACK (Acknowledgement) / NACK (Nacknowledgement) information; If the generated control information is not the ACK / NACK information, the control channel format indicator (CCFI) indicating the number of orthogonal frequency division multiplex (OFDM) symbols used for transmission of control information is determined and the CCFI is determined. The generated control information is transmitted through OFDM symbols corresponding to a value indicated by. If the generated control information is the ACK / NACK information, the maximum number of OFDM symbols available for transmitting the control information is determined. A base station apparatus comprising a transmitter for transmitting the ACK / NACK information by using the. The method of claim 5, If the generated control information is the ACK / NACK information, the controller determines a repetitive transmission pattern of the ACK / NACK information, and the transmitter determines the ACK / NACK information in the corresponding OFDM symbol according to the repetitive transmission pattern determined by the controller. Base station apparatus characterized in that for repeatedly transmitting. The method according to claim 6, And the transmitter performs a plurality of repetitive transmissions in the OFDM symbol of the highest index. A mobile terminal apparatus for receiving control information in an orthogonal frequency division multiple access communication system, A receiving unit for receiving control information from the base station, A controller for determining whether the received control information is ACK (Acknowledgement) / NACK (Nacknowledgement) information; A combining unit for combining the ACK / NACK information by the number of times the base station repeatedly transmits the ACK / NACK information when the received control information is the ACK / NACK information; A demodulation and decoding unit for demodulating and decoding the combined ACK / NACK information, The ACK / NACK information is transmitted by the base station using the maximum OFDM symbols available for transmission of the control information. 5. The method of claim 4, If the received control information is not the ACK / NACK information, the control information is an OFDM symbol corresponding to a value indicated by a control channel format indicator (CCFI) indicating the number of orthogonal frequency division multiplex (OFDM) symbols. Method for receiving control information of a mobile terminal, characterized in that transmitted using the. 9. The method of claim 8, If the received control information is not the ACK / NACK information, the control information corresponds to a value indicated by a control channel format indicator (CCFI) indicating the number of orthogonal frequency division multiplex (OFDM) symbols. Mobile terminal device characterized in that the transmission using the OFDM symbols.

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