KR20080099063A - Method of transmission of physical downlink control channel signal in mobile communication systems using orthogonal frequency division multiplexing access - Google Patents

Abstract

A method for transmitting a physical downlink control channel signal in an OFDMA mobile communication system and an apparatus therefor are provided to enable a mobile terminal to successfully demodulate the PDCCH even in an inferior channel environment. A method used when a base station transmits a physical downlink control channel signal to a terminal in an OFDMA mobile communication system comprises the following steps of: receiving channel state information about a downlink channel from the terminal to confirm the state of the downlink channel(802); separating a symbol stream into plural segments(807), in case the channel condition of a downlink channel is bad, and then mapping the separated symbols to predetermined physical resource groups according to each segment(808); mapping channel-encoded symbols to a physical resource group predetermined for one segment, in case the channel condition of a downlink channel is good(805); and multiplexing/transmitting the mapped symbols together with data to the terminal(806).

Description

METHOD OF TRANSMISSION OF PHYSICAL DOWNLINK CONTROL CHANNEL SIGNAL IN MOBILE COMMUNICATION SYSTEMS USING ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING ACCESS}

1 illustrates a radio resource of an OFDMA-based mobile communication system

2 is a diagram illustrating a frequency band to be used by two neighboring cells for inter-cell interference coordination;

3 is a diagram illustrating definition of a control channel and a mapping scheme to physical resources;

4 is a diagram illustrating a method of transmitting a control channel to two mobile terminals belonging to different cells by using a conventional technique.

5 is a diagram illustrating a method for transmitting a control channel to a mobile station by a base station according to the present invention performing segmentation;

6 illustrates a structure of a transmitter for transmitting a control channel

7 illustrates a receiver structure for receiving a control channel.

8 is a flowchart illustrating an operation of transmitting a control channel by a base station according to a channel quality state of a mobile terminal according to the present invention.

9 is a flowchart illustrating an operation of receiving a control channel by a mobile terminal according to a channel quality state of the mobile terminal according to the present invention.

The present invention relates to downlink control signaling of a mobile communication system based on Orthogonal Frequency Division Multiple Access (hereinafter, referred to as "OFDMA"), and particularly in a system supporting a function such as an inter-cell interference coordination scheme. The present invention relates to an efficient PDCCH transmission method and apparatus capable of preventing degradation of a received signal quality of a physical downlink control channel (hereinafter, referred to as a "PDCCH") of a mobile terminal in a poor channel environment.

Recently, the mobile communication system has been actively studied for the orthogonal frequency division multiple (OFDM) scheme as a useful method 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 method uses an overlapping frequency spectrum, thus making efficient use of the frequency, resisting frequency selective fading and multipath fading, and using symbol protection intervals. 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.

In the OFDMA-based mobile communication system, a radio resource may be represented by 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, the seven OFDM symbols are gathered to form one slot 101, and the two slots are gathered to form one subframe 102. In this case, the number of OFDM symbols constituting one slot and the number of slots constituting one subframe may be set differently. A 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.

In addition, 14 OFDM symbols are configured in the time domain, and one component unit consisting of 12 subcarriers in the frequency domain is referred to as a physical resource block (hereinafter referred to as a "PRB") 103. The PRB is a resource allocation unit for physical resources that the base station allocates to the mobile terminal to transmit information to the mobile terminal. In this case, the number of OFDM symbols and subcarriers constituting one PRB may be set differently.

In the OFDMA-based mobile communication system, if all cells transmit signals in the same frequency band, signal quality may be degraded due to interference between cells. In the OFDM scheme, since radio resources are represented in a two-dimensional array of time domain and frequency domain, inter-cell interference can be greatly reduced by frequency planning that allocates a frequency band to be used by each cell in the frequency domain. The above technique is called an inter-cell interference coordination (hereinafter referred to as "ICIC") technique. The ICIC scheme is performed in a coordinated / argumented manner among cells. The contents of the coordinated / arbitrated information among the cells include whether each radio resource in the time and frequency domain to be used in the downlink is used in each cell and to be allocated to these resources. It may include a method of adjusting the size of the power.

2 shows a frequency band for use by two neighboring cells as a simple example of ICIC.

Referring to FIG. 2, in cell A 201, a frequency band 202 is allocated to mobile terminals located at a cell boundary in an entire usable frequency region, and the remaining frequency band 203 is located in a region other than the cell boundary. Allow terminals to use it. On the other hand, in the cell B 211, a portion 213 of the frequency domain other than the frequency band 212 which the cell A allocates to the mobile terminals of the cell boundary is allocated to the cell boundary mobile terminals of the cell B 211, The remaining band 214 is allocated to mobile terminals located at the cell center. The biggest reason that neighboring cells may interact with each other is a transmission / reception signal between mobile stations and base stations of each cell located at a cell boundary. Therefore, when the above ICIC technique is applied, different frequency bands are used at the cell boundary of each cell so that no inter-cell interference occurs.

Meanwhile, in the OFDMA mobile communication system, the PDCCH is a physical downlink control channel transmitted from the base station to the mobile terminal, and includes scheduling information for downlink transmission from the base station to the mobile terminal and uplink transmission from the mobile terminal to the base station. A scheduling grant or an acknowledgment (ACK / NACK) response to data transmitted through the uplink is transmitted. The PDCCH may be transmitted in subframe units and may be transmitted through first or fewer OFDM symbols in each subframe. For example, when each slot is composed of seven OFDM symbols as shown in FIG. 1, the PDCCH may be transmitted using the first three or less OFDM symbols in the first slot. That is, up to three OFDM symbols initially located in each subframe are used for PDCCH transmission. OFDM symbols other than the OFDM symbols used to transmit the PDCCH in one subframe are used for data transmission.

A plurality of PDCCHs for a plurality of mobile terminals are included in a resource region (eg, the first three OFDM symbols in each subframe) that can transmit the PDCCH. In addition, if a control channel element (hereinafter referred to as "CCE") consisting of 36 subcarriers in a frequency domain is used as a basic unit for configuring one PDCCH, one PDCCH is transmitted. One or more CCEs are used for this purpose. The number of CCEs used to transmit one PDCCH is different in order to provide various coding rates according to channel conditions experienced by each MS. In other words, since a high coding rate can be applied to a mobile station in a good channel environment, a PDCCH can be transmitted using one CCE, whereas a low coding rate must be applied to a mobile station having a poor channel state. By transmitting the PDCCH configured to enable the mobile terminal to receive the PDCCH.

3 shows that a PDCCH is defined using a plurality of CCEs, and the PDCCH is mapped to a PDCCH region composed of physical resources.

The control channel candidate 300 of FIG. 3 represents a set of CCEs that can configure one PDCCH. Since the number of CCEs constituting one PDCCH may vary according to channel conditions experienced by the mobile station, for example, as one 301, two 302, or four 303 CCEs as shown in FIG. 3. The set may be the control channel candidate 300 representing one PDCCH. If a total of N CCEs 304 exist in the resource region (eg, the region where the first three OFDM symbols are located in each subframe) 320 for transmitting the PDCCH, the number of PDCCH candidates transmitted in one CCE The number is N, the number of PDCCH candidates transmitted to two CCEs is | N / 2 |, and the number of PDCCH candidates using four CCEs is | N / 4 |. Referring to N CCEs 304 entering the mapper 310 in FIG. 3, for example, two CCEs each of the first to second CCEs and the third to fourth CCEs constitute one PDCCH, and thus two different CCEs. The four CCEs of the fifth to eighth are transmitted to the mobile station and are configured to form one PDCCH and are transmitted to the mobile station having a relatively very poor channel state. In this case, in order to perform the substantial transmission from the base station to the plurality of mobile terminals, the plurality of PDCCHs configured by the one or the plurality of CCEs must be mapped to the physical resource region used by the mapper 310 to transmit the PDCCH.

4 illustrates a method of transmitting a control channel to two mobile terminals belonging to different cells according to the prior art.

As shown in FIG. 4, in order to support an ICIC function in an OFDMA-based mobile communication system, a plurality of CCEs may be gathered to form one 'group'. In FIG. 4, it is assumed that four CCEs form one group (Group 0 and Group 1). Here, the group refers to a frequency band formed of a predetermined size in the frequency domain in order to allocate different frequency bands for each cell so that interference between cells does not occur. A frequency band to be used by each cell may be arranged based on the group.

In FIG. 4, it is assumed that the total system bandwidth is composed of three groups, and a control channel is transmitted to two mobile terminals (terminal A and terminal B) belonging to different cells. It is assumed that PDCCH of mobile station A is transmitted through group 0 including 4 CCEs, and PDCCH of mobile station B is transmitted through group 1. First, the control information of each terminal is encoded by channel coding (401, 411), interleaved (403, 413) after performing rate matching (402, 412), and is independently order-transformed (404, 414) for each group. Since the permutation 404 and 414 is also a kind of interleaving, the interleaving 403 and 413 may or may not be performed in some cases. Next, each group is mapped to PRBs which are predetermined physical resources. That is, for example, since the order-transformed control information of the mobile terminal A is mapped to PRBs of a predetermined position for each permutation, the physical resource of the position indicated as 'PRB group 0' in FIG. 4 is used.

In transmitting the PDCCH, a structure of dividing the entire system band into a plurality of groups as shown in FIG. 4 may be used to transmit a control channel regardless of whether the ICIC scheme is applied. For example, in a system supporting the ICIC function, as described above, the PRBs in the location indicated by PRB group 0 are used in cell 0, and the PRBs in the location indicated by PRB group 1 are used in cell 1. On the other hand, in a system that does not use the ICIC function, the PRBs at all positions can be used in cell 0.

In an OFDMA-based mobile communication system supporting the ICIC function, when a cell wants to transmit a PDCCH to any mobile terminal belonging to the cell, only PRBs corresponding to the CCEs of the group assigned to the cell are used. . At this time, if the mobile terminal is located at the boundary of the cell, for example, and a PDCCH having a very low Signal to Interference plus Noise Ratio (SINR) is received by the mobile terminal, the mobile terminal is received through a limited amount of physical resources. The problem of not being able to demodulate the control channel is caused.

The technical problem to be achieved in the present invention is to enable the mobile terminal to successfully demodulate the received PDCCH even if the base station transmits a control channel to the mobile terminal in a poor channel environment in an OFDMA-based mobile communication system that can support the ICIC function It is to provide a PDCCH transmission method and apparatus.

According to an embodiment of the present invention, in a method for transmitting a physical downlink control channel signal to a terminal by a base station in a mobile communication system using an orthogonal frequency multiple access method,

Receiving channel state information on the downlink channel from the terminal and confirming the channel state of the downlink channel, and when the channel state of the downlink channel is not good, the channel-coded symbol sequence into a plurality of segments Separating and mapping the symbols separated into the plurality of segments to predetermined physical resource groups for each segment; and in the case where the channel state of the downlink channel is good, the channel coded symbols are previously mapped to one segment. The method includes mapping to a predetermined physical resource group, and transmitting the multiplexed symbols with data to the terminal.

Further, according to an embodiment of the present invention, in a method of receiving a physical downlink control channel signal from a base station by a terminal in a mobile communication system of an orthogonal frequency multiple access method, receiving a physical downlink control channel signal from the base station, the reception Determining whether a signal is a segmented and transmitted signal, and extracting a symbol string transmitted through a physical resource group corresponding to each segment for each segment when the received signal is a segmented and transmitted signal, Constructing the symbol strings into a single symbol string, extracting symbols by performing demapping from a physical resource group when the received signal is a signal received by a single segment, and extracting the single symbol string or the And demodulating the symbols into control information by channel decoding.

Further, according to an embodiment of the present invention, in a transmission apparatus for transmitting a physical downlink control channel signal to a terminal in a mobile communication system of an orthogonal frequency multiple access method, decoding channel state information on the downlink channel received from the terminal A channel decoder configured to selectively separate the coded symbol strings of the downlink control channel into one or more segments according to the channel state of the downlink channel, and each of the separated symbol strings is predetermined for each segment. And a mapping unit for mapping each physical resource block, and a multiplexing unit for multiplexing the mapped symbol string with data and transmitting the same to the terminal.

Also, according to an embodiment of the present invention, in a mobile communication system of an orthogonal frequency multiple access method, a terminal receiving apparatus for receiving a physical downlink control channel signal from a base station, receiving and demultiplexing a physical downlink control channel signal from a base station A demapping unit for extracting a symbol string transmitted from the demultiplexer, a physical resource group corresponding to at least one segment constituting the demultiplexed signal, from the demultiplexed signal, and the extracted symbol string And a channel symbol decoding unit for demodulating channel control information by performing channel decoding on the single symbol string.

In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

5 shows a PDCCH transmission scheme according to an embodiment of the present invention.

Referring to FIG. 5, control information of UE A belonging to a cell is channel encoded 501 through a series of processes, interleaved 503 after rate matching 502, and independently permutation for each group. 504, 514 is performed. Since the permutation 504 and 514 is also a kind of interleaving, interleaving 503 after rate matching 502 may or may not be performed. The coded symbol string is divided into a plurality of segments. Each segment corresponds to one group in a conventional PDCCH transmission, and is composed of, for example, four CCEs. After independent permutation 504,514 corresponding to the group to be transmitted per segment is performed, output symbols are mapped to a predetermined physical resource for that group for each segment. That is, if the coded symbol string is divided into two segments, for example, two segments are subjected to independent permutation corresponding to a group to be transmitted for each segment, and the first segment to be permutated corresponds to the segment in advance. It maps to the specified PBRs and uses the physical resources at the location indicated by PBR group 0. Similarly, the second permutated segment uses PRBs at the location of PRB group 1, which is a predetermined location for that segment.

In addition, in FIG. 5, when the channel state is good and the coded symbol string is not divided into a plurality of segments, only physical resources of a location indicated by a predetermined PBR group (PBR group 0 or PBR group 1 or PBR group 2) are shown. Will be used.

In the conventional PDCCH transmission technique, after control information to be transmitted to any terminal is channel coded, it is transmitted using physical resources corresponding to the CCEs through CCEs in any one group allocated to the corresponding cell. This means that the mobile terminals belonging to each cell are performed the same regardless of the location of the mobile terminals, that is, regardless of the channel state of each mobile terminal. Therefore, in transmitting the PDCCH, a limited amount of physical resources are used.

On the other hand, in the PDCCH transmission scheme according to an embodiment of the present invention, as shown in FIG. 5, after channel coding control information to be transmitted to a mobile terminal, the PDCCH transmission scheme is divided into a plurality of segments, and each segment is transmitted through a different group of PRBs. In order to do this, a structure that performs permutation and mapping to physical resources for each group is used. According to an embodiment of the present invention, if the channel state of a mobile station to receive a PDCCH is good, if the channel-coded symbol string is transmitted within four CCE sizes corresponding to one segment, permutation is performed in a corresponding method. And mapped to PRBs, which are corresponding physical resources. However, if the mobile terminal is placed in a very poor channel environment due to location of a cell boundary, etc., a plurality of segments may be transmitted so that a channel coded symbol sequence at a lower code rate is transmitted using PRBs corresponding to a plurality of groups. It is divided and mapped to physical resources corresponding to each permutation after performing independent permutation corresponding to a group to be transmitted for each segment. That is, when the channel environment is poor, all resources of the entire system frequency band can be used without considering the frequency band used by the neighbor cell. As described above, according to the present invention, since a PRB is transmitted using a larger number of PRBs than one conventional segment or group, successful PDCCH reception at the MS can be guaranteed.

In other words, if a mobile terminal having a bad channel state continuously fails to receive a control channel in a mobile communication system to which ICIC is applied, communication with the corresponding terminal may not be possible. As in the embodiment, it may be more important to ensure successful PDCCH demodulation of the mobile station by increasing the amount of physical resources used through the segmentation process.

6 shows a transmitter structure according to an embodiment of the present invention.

Referring to FIG. 6, the control information to be transmitted to an arbitrary mobile terminal is output by the channel coding unit 601 through a series of channel encoding processes and is output as a symbol string. The symbol sequence output from the channel coding unit 601 undergoes rate matching and interleaving in the rate matching unit 602 and the interleaver 603, and is divided into a plurality of segments in the segmentation unit 604. In the permutation unit 605, an order-conversion is performed for each segment. Since the segment is basically a basic unit (PRB group of FIG. 5) representing a predetermined period of resources allocated to each cell (here, frequency), performing permutation for each segment, that is, permutation according to cell-specific characteristics Means to do. In addition, the purpose of permutation is to obtain frequency diversity or interference diversity by distributing information to be transmitted in all frequency bands (or all OFDM symbols). The output symbols, which are order-converted for each segment, are mapped to a predetermined physical resource for each segment in the mapping unit 606, and then multiplexed together with the data information generated through the data information generation unit 608 to transmit the wireless transmission unit 607. Is sent to. In FIG. 6, the interleaver 603 may be omitted.

7 shows a receiver structure according to an embodiment of the present invention.

Referring to FIG. 7, a mobile terminal demultiplexes a received signal by the demultiplexer 701 to configure a control channel, and then the demapper 702 extracts a signal mapped to a physical resource corresponding to each segment. To do this, it goes through a demapping step. In addition, the inverse permutation unit 703 performs inverse permutation corresponding to each segment, and the single symbol string forming unit 704 combines each segment to form a single symbol string. The deinterleaver 705, the rate de-matching unit 706, and the channel decoder 707 demodulate control information through a series of channel decoding processes for a single symbol string.

8 is a flowchart illustrating an operation at a transmitting end according to an embodiment of the present invention.

Referring to FIG. 8, an arbitrary cell transmits channel state information (Channel Quality Indication, hereinafter referred to as "CQI") for a downlink channel from a mobile station in order to know the channel state of the downlink channel in step 801. Receive the channel. The cell receiving the CQI channel checks the downlink channel state to the corresponding mobile terminal in step 802, and if it is determined that the channel state is not good, the cell performs segmentation on the channel-encoded symbol sequence in step 803. . Each symbol string divided into a plurality of segments is independently order-converted for each segment in operation 804, mapped to predetermined physical resource PRBs for each segment in operation 805, and then input to the multiplexing and wireless transmitter in operation 806. In this case, since the PRBs corresponding to each segment are used when the channel state is not good, the amount of physical resources used to transmit the PDCCH is less than that of performing no segmentation (that is, using a single segment). Multiplied by the number of segments.

On the other hand, when the channel state of the mobile terminal is good, since no segmentation is performed, the symbol sequence encoded in step 807 passes through an order-conversion having a size of a single segment, and is predefined in the segment in step 808. Mapped physical resources.

In the process of determining whether the channel state is good, for example, it may be determined that the value indicating the channel state is greater than or equal to a predetermined value, and that it is not good if the value indicating the channel state is less than the predetermined value.

9 is a flowchart illustrating operations at a receiving end according to an embodiment of the present invention.

Referring to FIG. 9, when a mobile terminal receives a PDCCH in step 901, it is determined in step 902 whether the received PDCCH is a signal transmitted by performing segmentation. The determination of segmentation may be performed using a CQI channel value transmitted by the mobile terminal to the base station by a predetermined rule between the base station and the mobile terminal, or may be informed to the mobile terminal through separate signaling. Alternatively, the UE may find out through blind detedtion. As a result of the determination, in the case of the segmented reception signal, in step 903, de-mapping from independent PRBs is performed for each segment to extract a symbol string transmitted to PRBs corresponding to each segment. Then, in step 904, the symbol strings for each segment are configured into a single symbol string, and in step 905, the channel decoding is performed through a series of processes.

On the other hand, if the PDCCH is received by a single segment, it is subjected to demapping from physical resources and reverse order-transformation of a single segment size in steps 907 and 908, and channel decoded and demodulated into control information in step 906.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

In the present invention operating as described above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

According to the present invention, in the OFDMA-based mobile communication system supporting the ICIC function, when the PDCCH is to be transmitted through the downlink channel, the amount of physical resources used to transmit the PDCCH is adjusted according to the channel state experienced by the mobile station. In this way, the mobile station in the poor channel environment can successfully demodulate the PDCCH.

Claims (4)

In a method for transmitting a physical downlink control channel signal to a terminal by a base station in a mobile communication system of an orthogonal frequency multiple access method, Receiving channel state information on a downlink channel from a terminal and checking a channel state of the downlink channel; When the channel state of the downlink channel is not good, separating the channel-coded symbol string into a plurality of segments, and mapping the symbols divided into the plurality of segments into predetermined physical resource groups for each segment; When the channel state of the downlink channel is good, mapping the channel coded symbols to a predetermined physical resource group for one segment; And multiplexing the mapped symbols with data and transmitting the multiplexed symbols to the terminal. In a method for receiving a physical downlink control channel signal from a base station in a mobile communication system of an orthogonal frequency multiple access method, Receiving a physical downlink control channel signal from a base station and determining whether the received signal is a segmented and transmitted signal; When the received signal is a segmented and transmitted signal, extracting a symbol string transmitted through a physical resource group corresponding to each segment for each segment, and configuring the symbol strings into a single symbol string; If the received signal is a signal received by a single segment, extracting symbols by performing demapping from a physical resource group; And channel demodulating the single symbol string or the symbols and demodulating the control symbols into control information. A transmission apparatus for transmitting a physical downlink control channel signal to a terminal in a mobile communication system using an orthogonal frequency multiple access method, A channel decoder which decodes channel state information on the downlink channel received from a terminal; A segment unit for selectively dividing an encoded symbol string of the downlink control channel into one or more segments according to a channel state of the downlink channel; A mapping unit for mapping each of the separated symbol strings to predetermined physical resource blocks for each segment; And a multiplexer for multiplexing the mapped symbol strings with data and transmitting the multiplexed symbol strings to the terminal. A terminal receiver for receiving a physical downlink control channel signal from a base station in a mobile communication system using an orthogonal frequency multiple access method, A demultiplexer for receiving and demultiplexing a physical downlink control channel signal from a base station; A demapping unit configured to extract a symbol string transmitted from the demultiplexed signal through a physical resource group corresponding to at least one segment constituting the demultiplexed signal; A single symbol string construction unit for collecting the extracted symbol strings to form a single symbol string; And a channel decoder configured to perform channel decoding on the configured single symbol string and demodulate the channel control information.

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