KR100964215B1 - Method and apparatus for transmitting/receiving channel quality information in a communication system using orthogonal frequency division multiplexing scheme - Google Patents

Abstract

The present invention relates to a method and apparatus for transmitting and receiving channel quality information (called CQI) for subcarriers from a terminal to a base station in a communication system using an orthogonal frequency division multiplexing scheme. The terminal measures channel quality information (CQI) values for each of bands of a preset number of contiguous subcarriers, and combines the CQI values for at least one specific band with the band indices of the specific bands. Generate as absolute channel quality information (CQI), select at least two bands of all bands according to the absolute value CQI, measure CQI values for the selected bands, and measure the CQI measurements of the selected bands A differential CQI is generated by comparing the previous CQI measurements of the selected bands, respectively. Thereafter, the terminal transmits one of the information about the absolute value CQI and the differential CQI to the base station (BS).

Description

TECHNICAL AND APPARATUS FOR TRANSMITTING / RECEIVING CHANNEL QUALITY INFORMATION IN A COMMUNICATION SYSTEM USING ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SCHEME}

The present invention relates to a communication system using Orthogonal Frequency Division Multiplexing (hereinafter, referred to as 'OFDM'), and in particular, channel quality information for subcarriers from a subscriber station to a base station. (Hereinafter, referred to as 'CQI').

As the mobile communication system develops rapidly, the amount of data required and its processing speed also increase rapidly. In general, high-speed data transmission over a wireless channel has a high bit error rate (BER) due to effects of multipath fading and doppler spread. Therefore, a radio access method suitable for a radio channel is required, and a spread spectrum (SS) method, which has advantages of relatively low transmission power and relatively low detection probability, is widely used.

The spread spectrum method is classified into a direct sequence spread spectrum (DSSS) method and a frequency hopping spread spectrum (FHSS) method. .

The DSSS scheme can actively cope with multipath phenomena occurring in a wireless channel using a rate receiver using path diversity of the wireless channel. However, the DSSS method can be efficiently used up to a transmission rate of 10 Mbps, but when transmitting high-speed data of 10 Mbps or more, hardware complexity increases rapidly as the chip-to-chip interference increases, and due to multi-user interference The disadvantage is that there is a limit on the capacity of the user that can be accommodated.

Since the FHSS scheme transmits data while moving frequency by a random sequence, the FHSS scheme can reduce the effects of multi-channel interference and narrow band impulse noise. However, the FHSS scheme has a disadvantage in that accurate synchronization between the transmitter and the receiver is a very important factor, and thus it is difficult to acquire synchronization when transmitting relatively high speed data.

On the other hand, the recent research on the OFDM scheme as a suitable method for high-speed data transmission in wired and wireless channels. The OFDM method is a method of transmitting data using a multi-carrier. A plurality of subcarriers, each of which is a relatively narrow frequency band having mutually orthogonality, are converted in parallel by sequentially converting symbol strings input in series. It is a type of multi-carrier modulation (MCM) that modulates and transmits data to sub-carriers. Here, the subcarriers in a specific time period are called tones.

As described above, the OFDM scheme uses a plurality of subcarriers having mutual orthogonality, thereby increasing frequency usage efficiency. Since the modulation and demodulation of the plurality of subcarrier signals is the same as performing an Inverse Discrete Fourier Transform (IDFT) and a Discrete Fourier Transform (DFT), the transmitter and the receiver are called an Inverse Fast Fourier Transform (IFFT). And fast fast Fourier transform (hereinafter referred to as 'FFT') to perform demodulation of subcarrier signals at high speed.

Because the OFDM scheme is suitable for high-speed data transmission, IEEE (Institute of Electrical and Electronics Engineers) 802.11a, HIPELAN / 2 high-speed wireless local area network (hereinafter referred to as "LAN"), and IEEE 802.16 And the standard method of Digital Audio Broadcasting (DAB), Digital Terrestrial Television Broadcasting (DTTB), Asymmetric Digital Subscriber Line (ADSL) and Veri-high data rate Digital Subscriber Line (VDSL). Was adopted.

In a communication system using the OFDM scheme (hereinafter, referred to as an 'OFDM communication system'), the structure of a frequency domain of a symbol is defined as subcarriers. The subcarriers include a data subcarrier used for data transmission, a pilot subcarrier used for transmitting a predetermined pattern of symbols for various estimation purposes, and a guard interval. ) And three types of null subcarriers for static components. Here, remaining subcarriers other than the null subcarrier, that is, data subcarriers and pilot subcarriers, become effective subcarriers.

On the other hand, the multiple access scheme based on the OFDM scheme is an Orthogonal Frequency Division Multiple Access (hereinafter, referred to as 'OFDMA') scheme. In the OFDMA scheme, the effective subcarriers are divided into a plurality of subcarrier sets, that is, sub-channels. Here, the subchannel means a channel composed of at least one subcarrier, and the subcarriers constituting the subchannel may or may not be adjacent to each other. A communication system using the OFDMA scheme (hereinafter, referred to as an 'OFDMA communication system') may provide a service to a plurality of users at the same time.

Next, a subchannel allocation structure of a general OFDMA communication system will be described with reference to FIG. 1.

Referring to FIG. 1, subcarriers used in an OFDMA communication system include a DC subcarrier representing a static component in a time domain, and a high frequency band, that is, protection of a time domain, in a frequency domain. It consists of subcarriers indicating an interval and effective subcarriers. The effective subcarriers are composed of a plurality of subchannels, and in FIG. 1, the effective subcarriers are composed of three subchannels, namely, subchannels 1 to 3.

In the OFDMA system, adaptive modulation and coding (hereinafter, referred to as 'AMC') is particularly used to support high-speed data transmission through a wireless channel. The AMC scheme determines different modulation schemes and coding schemes according to channel conditions between a cell, that is, a base station (BS) and a mobile subscriber station (hereinafter referred to as MSS). Thus, a data transmission method for improving the use efficiency of the entire cell.

The AMC scheme has a plurality of modulation schemes and a plurality of coding schemes, and modulates and codes a channel signal by combining the modulation schemes and coding schemes. In general, each of the combinations of modulation schemes and coding schemes is called a modulation and coding scheme (hereinafter, referred to as 'MCS'), and may be referred to as a level from level 1 according to the number of MCSs. up to N) A plurality of MCSs are defined. One of the levels of the MCS is adaptively determined according to the channel state between the MSS and the base station that is currently wirelessly connected.

In order to use the AMC scheme, the MSS must inform the base station of a channel state of downlink, that is, channel quality information (CQI). Currently, in the IEEE 802.16 communication system, the MSS reports a report request (REP-REQ: REP-REQ) / Report Response (REP-RSP). It is prescribed to notify the base station of the CQI of the downlink using the method.

That is, the base station transmits a REP-REQ message to a specific MSS, and in response to the REP-REQ message, the MSS transmits a REP-RSP message including a downlink CQI to the base station. For example, the CQI may be an average value and a standard deviation value of a carrier to interference and noise ratio (CINR) or a received signal strength indicator (RSSI).

However, since the REP-REQ message does not contain any information on uplink resource allocation for the MSS to transmit the REP-RSP message, the MSS first allocates uplink resources to the base station. A random access is attempted to request The random access may delay transmission of the REP-RSP message, and thus has a disadvantage in that the correct CQI is not applied in applying the AMC scheme. In addition, the REP-RSP message transmission has a disadvantage that it acts as a signaling overhead (signalling overhead). Therefore, there is a need for a method of transmitting accurate CQI in real time while minimizing signaling overhead.

The present invention proposes a method and apparatus for transmitting and receiving CQI by minimizing signaling overhead in an OFDM / OFDMA communication system.

The present invention proposes a method and apparatus for transmitting and receiving real-time CQI in an OFDM / OFDMA communication system.

The present invention proposes a method and apparatus for constructing and transmitting and receiving a CQI suitable for a diversity mode and a band AMC mode of an OFDM / OFDMA communication system.

The present invention proposes a method and apparatus for transmitting and receiving that can reduce CQI-related overhead for MSS in a band AMC mode of an OFDM / OFDMA communication system.

The present invention proposes a method and apparatus for differentially transmitting and receiving a predetermined band having an optimal state among a plurality of bands in an OFDM / OFDMA communication system.

Method according to a preferred embodiment of the present invention; A method for transmitting channel quality information (CQI) by a terminal (MSS) in a wireless communication system using a cross frequency division multiplexing (OFDM) scheme or an orthogonal frequency division multiple access (OFDMA) scheme,

Measuring channel quality information (CQI) values for each of bands of a predetermined number of contiguous subcarriers, and comparing the CQI measurements for at least one particular band with band indices of the specific bands; Generating together absolute channel quality information (CQI), transmitting the absolute CQI to a base station, selecting at least two bands of all bands according to the absolute CQI, and selecting the selected band Measuring the CQI values of the selected bands and comparing the CQI measurements of the selected bands with previous CQI measurements of the selected bands, respectively, to generate a differential CQI; and receiving information about the differential CQI from the terminal. Including the process of transmitting.

Method according to another embodiment of the present invention; A method of receiving channel quality information (CQI) by a base station (BS) in a wireless communication system using an orthogonal frequency division multiplexing (OFDM) scheme or an orthogonal frequency division multiple access (OFDMA) scheme,

Receives an absolute value CQI report indicating channel quality information (CQI) values measured for specific bands among bands of a preset number of adjacent subcarriers from the MSS and stores each of the specific bands And selecting at least two bands of all bands according to the absolute value CQI, receiving information on differential CQI indicating increase or decrease of previous CQI measurement values for the selected bands; And updating the absolute value CQI stored for the specific bands by referring to the information on the differential CQI.

Apparatus according to a preferred embodiment of the present invention; An apparatus for transmitting channel quality information (CQI) by a terminal (MSS) in a wireless communication system using an orthogonal frequency division multiplexing (OFDM) scheme or an orthogonal frequency division multiple access (OFDMA) scheme,

Measure channel quality information (CQI) values for each of a band of a preset number of contiguous subcarriers, and determine the CQI values for at least one particular band together with the band indices of the particular bands Generate as channel quality information (CQI), select at least two bands of all bands according to the absolute value CQI, measure CQI values for the selected bands, and measure the CQI measurements of the selected bands A CQI generator for generating a differential CQI by comparing each of the previous CQI measurements of the bands,

And a transmitter for transmitting one of the information on the absolute value CQI and the differential CQI to a base station (BS).

Apparatus according to another embodiment of the present invention; An apparatus for receiving channel quality information (CQI) by a base station (BS) in a wireless communication system using Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA)

Receives an absolute value CQI report indicating channel quality information (CQI) values measured for specific bands among bands of a preset number of adjacent subcarriers from the MSS and stores each of the specific bands A controller configured to select at least two bands of all bands according to the absolute value CQI, and to update the absolute value CQI stored for the specific bands by referring to the information on the differential CQI received from the terminal;

And a receiver for receiving information on the differential CQI indicative of a change in previous CQI measurements for the selected bands.

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

The present invention has the advantage that the CQI is reflected in real time by transmitting the CQI every frame with a minimum signaling overhead in the OFDMA communication system. In addition, the present invention proposes a method for configuring CQI information suitable for the characteristics of the diversity mode and the band AMC mode and its operation method.

1 is a diagram illustrating a subchannel allocation structure of a general OFDMA communication system.
2 is a diagram illustrating an example of an OFDM frame structure including bands and bins in an OFDMA communication system.
3 is a diagram schematically illustrating a transmitter structure of an orthogonal frequency division multiple access (OFDMA) communication system applied to the present invention.
4 illustrates the encoder and modulator structure of FIG. 3 in more detail.
5 is a diagram illustrating an example of configuration of a global CQI.
6 is a diagram illustrating an example of a configuration of a differential CQI.
7 is a flowchart illustrating the operation of a mobile subscriber station according to a preferred embodiment of the present invention.

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.

One of the methods for transmitting accurate CQI in real time while minimizing signaling overhead in transmitting downlink channel quality information in order to support AMC scheme in an OFDMA communication system includes a CQI channel in a predefined section of an uplink frame. CQICH) area is allocated and each MSS carries CINR information of downlink measured by each MSS through the allocated CQICH area. In this case, CINR information measured by each MSS is displayed in every uplink frame, thereby enabling real-time AMC application. The allocation of the CQICH region is as defined in each system. As an example, channel information represented by n bits is converted into M CQI symbols and transmitted on M tones allocated to CQICH by OFDM modulation. Every MSS may be assigned a respective CQICH region.

In addition, frequency resources in subchannel units or bin units are allocated to each MSS. Here, the bin consists of at least one OFDM symbol on at least one subcarriers. In addition, when an MSS is allocated resources in subchannel units, the MSS is considered to be in diversity mode, and when another MSS is allocated frequency resources in empty units, the MSS is considered to be in band AMC mode.

Here, a band is defined as a bundle of a plurality of adjacent subcarriers, unlike a subchannel defined by a bundle of a plurality of subcarriers which may not be adjacent. As a result, the diversity mode and the band AMC mode have a difference between whether subcarriers allocated to an MSS are spaced or adjacent in frequency. In the following description, for convenience of description, subchannels will be regarded as a bundle of non-contiguous subcarriers, and bands will be regarded as a bundle of adjacent subcarriers.

2 illustrates an example of an OFDM frame structure including bands and bins in an OFDMA communication system.

Referring to FIG. 2, one downlink (DL) OFDM frame and one uplink (UL) OFDM frame are shown here, followed by a transmission transition gap (TGT) after the downlink frame. After the uplink frame, a reception transition gap (RTG) follows. The downlink and uplink OFDM frames each consist of B bands on frequency, each of which includes contiguous subcarriers. The small blocks constituting each frame represent bins. The bins may consist of two subcarriers and three OFDM symbols.

In the downlink frame, the first to third time periods are areas allocated for control. That is, the first and second time intervals are allocated to the downlink preamble for downlink (DL) control, and the third time interval is allocated to the system information channel (SICH). In the uplink frame, the first to third time periods are allocated to the ACK / NACK (ACKnowledge / NACKnowledge) channel and CQICH for Hybrid Automatic Repeat Request (HARQ) support.

On the other hand, whether the MSS operates in the diversity mode or the band AMC mode is determined according to the state of the channel. Each MSS knows the state of the down channel that it is receiving through the downlink preamble and analyzes the channel's CINR and the rate of channel change in the frequency and time dimension through the accumulated channel state information. When the MSS determines that the channel state is stable as a result of the analysis, the MSS operates in the band AMC mode, and otherwise operates in the diversity mode. In this case, the stable channel state refers to a case in which the CINR of the channel is high overall and the change of the channel does not change rapidly with time.

The criteria for channel state analysis that determine diversity mode and band AMC mode are as defined by the system. In addition, a specific operation process of determining the operation mode may also be different depending on the implementation of each system. That is, the mode conversion may be performed by a request of the MSS for tracking the reception channel state, or may be made by the determination of the base station that has reported the channel state information of the MSS. Importantly, if the channel condition is good and the change is slow, it operates in band AMC mode, otherwise it operates in diversity mode.

In the diversity mode, since the resources allocated to each MSS are in units of subchannels, and the subcarriers constituting the subchannels are spaced apart from each other in frequency, the channel CINR information necessary for AMC is sufficient as an average value for the entire frequency band. . The CINR measured by each MSS is converted into n-bit information so that a CQI symbol having an M symbol size is mapped to a CQICH. That is, when the number of _MSS is N _MSS , the amount of CQI-related overhead to be allocated to the uplink is M * N _MSS .

In the band AMC mode, since resources allocated to each MSS are in units of bins, and the bins are adjacent in frequency, each MSS is allocated a limited portion of all frequency bands. Therefore, each MSS enables more sophisticated AMC by measuring and transmitting the average CINR for the limited period (or the band to which the limited period belongs) not the entire frequency band to the base station. In this case, in order to indicate the CINR measured by each MSS, n bit information is required for each band, and B * n bit information for each MSS is converted into P CQI symbols. As a result, the amount of CQI-related overhead to be allocated to the uplink is P * M * N _MSS . This means that a significant amount of uplink resources should be devoted to CQI related control information. Therefore, the present invention proposes a technique that can significantly reduce the CQI-related overhead, especially for the MSS of the band AMC mode as follows.

Prior to describing the CQICH operating technique according to the preferred embodiment of the present invention, a method and apparatus for transmitting and receiving CQI in an OFDMA system will be briefly described with reference to FIGS. 3 and 4. Here, the description is based on the CQICH configuration adopted by HPi.

3 is a diagram schematically illustrating a transmitter structure of an orthogonal frequency division multiple access (OFDMA) communication system according to the present invention.

Referring to FIG. 3, the transmitter includes an encoder 211, a modulator 213, a serial to parallel converter 215, and a sub-channel allocator. an allocator 217, an Inverse Fast Fourier Transform (IFFT) 219, a parallel to serial converter 221, and a guard interval insertion A guard interval inserter 223, a digital-to-analog converter 225, and a radio frequency processor (227). do.

As shown in FIG. 3, when channel quality information CQI to be transmitted is generated, a bit indicating the CQI (hereinafter referred to as a 'CQI bit') is input to the encoder 211. The CQI may be, for example, an average value and a standard deviation value of a carrier to interference and noise ratio (CINR) or a received signal strength indicator (RSSI). The encoder 211 inputs the CQI bits, codes them in a predetermined coding scheme, and then outputs them to the modulator 213. Here, the coding scheme may be, for example, a block coding scheme having a preset coding rate.

The modulator 213 modulates the coded bits output from the encoder 211 by using a preset modulation method, generates modulated symbols, and outputs the modulated symbols to the serial / parallel converter 215. Here, the modulation method is differential phase shift keying (hereinafter referred to as "DPSK") method, for example, differential binary phase shift keying (hereinafter referred to as "DBPSK") method. Or differential quadrature phase shift keying (hereinafter, referred to as 'DQPSK'). The serial / parallel converter 215 receives the serial modulation symbols output from the modulator 213, converts them in parallel, and outputs them to the sub-channel allocator 217.

The sub-channel allocator 217 assigns the parallel-converted modulated symbols output from the serial / parallel converter 215 to subcarriers of a preset CQICH and outputs them to the IFFT unit 219. Here, the CQICH becomes at least one non-contiguous subcarrier in the diversity mode and at least one contiguous subcarrier in the band AMC mode. The IFFT unit 219 performs an N-point IFFT using the signal output from the sub-channel allocator 217 and outputs the N-point IFFT to the parallel / serial converter 221. The parallel / serial converter 221 inputs the signal output from the IFFT device 219 and serially converts the signal, and outputs the serial signal to the guard section inserter 223.

The guard interval inserter 223 inputs a signal output from the parallel / serial converter 221 to insert a guard interval signal and outputs the signal to the digital / analog converter 225. Here, the guard interval is inserted to remove interference between the OFDM symbol transmitted at the previous OFDM symbol time and the current OFDM symbol transmitted at the current OFDM symbol time when the OFDM symbol is transmitted in the OFDMA communication system. In addition, the guard interval is a 'cyclic prefix' method of copying the last constant samples of the OFDM symbol in the time domain and inserting them into a valid OFDM symbol, or copying the first constant samples of the OFDM symbol in the time domain. It is inserted in any one of the 'cyclic postfix (cyclic postfix)' which is inserted into the effective OFDM symbol.

The digital-to-analog converter 225 inputs the signal output from the protection section inserter 223 to perform analog conversion, and then outputs the analog signal to the RF processor 227. The RF processor 227 includes components such as a filter, a mixer, an amplifier, and the like, and transmits the signal output from the digital-to-analog converter 225 after being RF-processed to be transmitted on air. Transmission on the air through an antenna (Tx antenna).

FIG. 4 is a diagram illustrating the structure of the encoder 211 and the modulator 213 of FIG. 3 in more detail. As shown in FIG. 4, the encoder 211 includes a (m, n) block encoder. The modulator 213 includes a switch 411 and a DBPSK modulator 413. And a DQPSK modulator 415.

Referring to FIG. 4, n bits of CQI bits are input to the (m, n) block encoder 211. The (m, n) block encoder 211 blocks-codes the n-bit CQI bit to generate m symbols and outputs the m symbols to the switch 411. The switch 411 outputs the signal output from the (m, n) block encoder 211 to the DBPSK modulator 413 when the transmitter uses the DBPSK scheme according to a modulation scheme applied by the transmitter. In contrast, when the transmitter uses the DQPSK scheme, the transmitter outputs the DQPSK modulator 415.

The DBPSK modulator 413 modulates the signal output from the (m, n) block encoder 211 by the DBPSK method and outputs m + 1 modulation symbols (m + 1 symbols). In addition, the DQPSK modulator 415 modulates the signal output from the (m, n) block encoder 211 by the DQPSK scheme and outputs modulation symbols.

Hereinafter, the configuration of the CQI and the CQICH operating method according to the operation mode of the MSS will be described.

First, the diversity mode will be described. As described above, the diversity mode is a case where a frequency band is divided into subchannels, which are sets of non-adjacent subcarriers, and each MSS has a number of subchannels according to the amount of transmission information. ) Will be assigned. In this case, since each MSS receives information allocated to subcarriers evenly distributed over the entire system frequency band, the MSS measures the average CINR value of the entire frequency band of the downlink preamble and generates the CQI information.

If the CQICH allocated to each MSS can accommodate n bits of CQI information, the MSS may represent one of the predetermined 2 ⁿ CINR intervals. As a result, each MSS transmits the interval to which the average CINR value of the entire frequency band belongs to the CQICH to the base station. In the diversity mode, since the average CINR value of the entire frequency band becomes CQI information, this is called global CQI (full CQI). At this time, when the number of the MSS as N _MSS, the number of tones allocated to a CQICH in an uplink becomes a M * N _MSS. The allocation region of the CQICH is located in a predetermined section of the uplink control signal interval, so that no separate control signal for CQICH positioning is required. CQICH is allocated for every uplink frame.

5 is a diagram illustrating an example of a configuration of a global CQI.

Referring to FIG. 5, when two MSSs exist in a cell, each MSS receives downlink signals on different subcarriers. In this case, it is assumed that the MSS includes a CQICH transmitter that receives 5 bits of information and converts the information into 12 CQI symbols.

First, each MSS calculates an average CINR for the entire frequency band through the preamble of the downlink frame. As an example, assume that MSS 1 gets 8.7 dB and MSS 2 gets 3.3 dB. Here, since the values are average values for the entire frequency band, there may be a difference from the actual values of the respective subcarriers. Since the measured value of 8.7 dB of the MSS 1 is a value of the interval between 8 and 9 dB, it is converted into the 5-bit CQI information 10010 representing the corresponding interval, and similarly, the 3.3 dB of the measured value of the MSS 2 is converted into the CQI information 01101. The CQI information is encoded by the CQICH transmitter of each MSS and then modulated into 12 ton CQI symbols. In each MSS, the CQI symbols are mapped to a CQICH region allocated for the corresponding MSS in the UL control symbol region.

Next, the band AMC mode will be described. In the band AMC mode, all frequency bands are divided into bands which are sets of adjacent subcarriers, and each MSS is allocated a set of bins which are basic units constituting the band. The bin is a bundle of subcarriers adjacent in frequency and time, and when allocated to the MSS, adjacent bins in frequency and time are allocated, resulting in the MSS being allocated contiguous resources in frequency and time.

In addition, the MSS in the band AMC mode should CQI information the frequency band average CINR value of each of the B bands constituting the entire system frequency band, not the average CINR of the entire frequency band of the system. In this case, when the average CINR value of the frequency bands to which each band belongs is represented by n bit information, if all CINR values for all B bands are reported, the number of uplink tones required for the CQICH is P * M * N. _{Becomes MSS} . Since this can occupy most of the uplink resources, it can be seen that a special CQI information configuration method and a CQICH operating method for the band AMC mode is required.

Accordingly, the MSS in the band AMC mode transmits CQI information indicating whether to increase or decrease from the previous value to the base station for the average CINR value of the selected n bands among the B bands constituting the entire frequency band. At this time, since the difference from the previous value for the average CINR value of the bands becomes CQI information, this is called differential CQI (differential CQI).

When the number of MSSs in communication in one cell is referred to as N _MSS , the number of CQICH tones allocated to the uplink is M * N _MSS . Since the allocation region of the CQICH is located in a predetermined portion of the uplink control signal interval, a separate control signal for positioning the CQICH allocation region is not necessary. The differential CQI is allocated and transmitted every frame after the CINR absolute value in the form of a message is delivered. The CINR absolute value is periodically transmitted with several to several tens of frame periods in order to update the band-specific CINR values stored in the base station.

On the other hand, the method using the differential CQI transmits the channel status of each band using a relatively small overhead. Since the base station can track the channel CINR of each band through the differential CQI, it is possible to perform the optimized AMC for each band, thereby increasing the overall system throughput.

6 is a diagram illustrating a configuration example of a differential CQI according to a preferred embodiment of the present invention.

Referring to FIG. 6, when there are two MSSs in a cell, each MSS receives downlink signals on different subcarriers. The MSSs calculate the average CINR for the corresponding frequency band of the downlink preamble for each allocated band of all frequency bands of the uplink.

As an example, the entire frequency band is divided into a total of six bands, and the average CINR absolute value of each band is transmitted to the base station in the form of a message through a previous uplink frame.

As shown in FIG. 6, the MSS1 selects five bands # 0, 1, 3, 4 and 5 having a high average CINR per band in the previous frame. Then, the MSS 1 compares the average CINR value for each band measured in the previous frame (indicated by the dotted line in FIG. 6) and the currently measured CINR value (indicated by the solid line in FIG. 6) for each of the selected five bands. Determine the differential CQI for. At this time, if the current value is increased from the previous value, the bit of the corresponding band is set to 1, and if it is decreased, it is set to 0. In FIG. 6, the differential CQI value for the selected five bands is '11010', and the differential CQI value is an input of a CQI symbol modulator. Likewise, MSS 2 generates differential CQI value 01010 for the five bands # 1, 2, 3, 4, 5 and symbolizes CQI.

The two differential CQI values are mapped to a CQICH region allocated to each MSS among UL control symbol regions. Then, the base station updates the average CINR absolute value of each band previously stored based on the received differential CQI information for each band, and obtains an average CINR value of each band at the present time. Through this, the base station can perform more sophisticated band-specific AMC based on the channel-specific channel information. In the above example, band # 0 is selected for the MSS 1 and band # 4 is selected for the MSS 2. Since the selected bands have a high CINR, the base station selects an AMC level capable of high-speed transmission, and transmits downlink data for MSS1 and downlink data for MSS 2 through bands # 0 and # 4, respectively. .

Here, each MSS need not separately inform which band each bit of the differential CQI information corresponds to when transmitting the differential CQI information. This is because, since the MSS is operating in the band AMC mode, it is very unlikely that the rank of the measured bands will change before the next absolute value CINR is transmitted when the absolute value CINR for each band is transmitted. If the channel state changes significantly, each MSS transitions to the diversity mode and operates, only the global CQI is used, not the differential CQI.

In other words, when operating in the band AMC mode, the speed at which the channel changes over time is slow, which means that the channel state of each band does not change significantly for a certain time. In the band AMC mode, a band having a high average CINR is likely to continue to have a high CINR within the predetermined time period, and a band having a low average CINR is likely to have a low CINR. On the other hand, there is a small probability that the channel state of a band showing a high average CINR changes rapidly and has a low CINR within a certain time.

On the other hand, the "schedule time" that ensures the stability of the channel is a system parameter determined by computer simulation and measurement results, the "schedule time" is also used as the CQICH reporting period in the band AMC mode. Here, the CQICH period means a time interval between a frame in which the MSS reports the absolute value of the average CINR value for each band in a message form, and the next absolute value reporting frame. Between successive absolute value report frames, differential CQI values that are not absolute CINR values are repeatedly transmitted at shorter time intervals.

7 is a flowchart illustrating the operation of an MSS according to a preferred embodiment of the present invention. For the operation described below, the MSS includes a controller that controls the CQI operation and a transceiver that performs the CQI operation under the control of the controller.

Referring to FIG. 7, in step 700, the MSS starts a CQI reporting operation. In step 710, the MSS determines whether the current frame is a frame to which an average CINR absolute value of each band is transmitted or a frame transmitting differential CQI. Here, the transmission of the absolute CINR value should be made periodically, and the period is determined by the system parameter as described above. Also, for efficiency of uplink resources, the CINR absolute value is transmitted less frequently than the differential CQI.

As a result of the determination, if the frame is to transmit the absolute CINR value, the process proceeds to step 721. In step 721, the MSS measures average CINR values per band for each of all B bands constituting the entire frequency band. In step 722, the MSS selects N bands according to the measured CINR values. In this case, N is equal to or greater than n, which is the number of bits allocated to the CQICH, and equal to or less than B, which is the total number of bands. Here, the reason for selecting the N bands is for a case where it is impossible to measure CINR values for all B bands due to limited uplink resources. The N selected bands may be the bands with the highest CINR, but in other cases as determined by the system.

The MSS also reselects n bands of the N bands to report a CINR increase or decrease using a differential CQI. The selection algorithm for the n bands is an algorithm that uses only the CINR information for the N bands as an input variable, which is shared by both the MSS and the base station. That is, the base station can know the n bands selected by the MSS through the N band CINR information. Likewise, the n bands may be bands having the highest CINR values among the N bands.

Next, in step 723, the MSS generates a message containing CINR values of the selected N bands and indices of the selected N bands. Thereafter, in step 724, the generated message is mapped to an uplink frame and transmitted to the base station. Then, the base station determines the modulation scheme and coding rate for each MSS band according to the CINR values for the N bands and the band-specific CINR values of other MSSs.

On the other hand, if the transmission frame of the differential CQI in step 710, the process proceeds to step 711. The MSS measures average CINR values of respective bands in step 711. Here, the reason for measuring the band-specific CINR values for all B bands is to track the channel change situation for each band. In other words, when the channel changes drastically, it is necessary to switch from the band AMC mode to the diversity mode.

Next, in step 712, CINR values of bands previously stored in the previous frame are read for the n bands selected when the previous absolute value CINR is transmitted among the B bands. In step 713, the MSS compares the measured values with corresponding band CINR values in the read previous frame, respectively. In step 714, the MSS codes n bits of differential CQI information by coding a bit of the corresponding band among the differential CQI values to 1 when the measured CINR values are increased or equal to each other through the comparison. Create

In step 715, the measured CINR values for each band are stored for use as reference values in the next frame. In step 716, the n-bit differential CQI information is modulated into a CQICH symbol and then mapped to an uplink frame in step 717 to be transmitted to the base station.

Then, the base station is composed of a controller for controlling the CQI operation corresponding to the MSS and a transceiver for performing the CQI operation under the control of the controller, and estimates the change trend of the n bands based on the differential CQI information. That is, the absolute value CINR values of the n bands among the absolute value CINR values for each band received and stored from the MSS are increased or decreased by a predetermined value according to each bit of the differential CQI information. In this case, since the differential CQI only informs whether the corresponding CINR is increased or decreased, the exact difference from the previous frame's CINR is not known. However, when the band AMC mode is considered to be an operation mode for a stable channel change for each band, the resulting The degree of performance degradation is small compared to the degree of uplink resource efficiency improvement due to the use of differential CQI.

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 defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

Claims (32)

A method for transmitting channel quality information (CQI) by a terminal (MSS) in a wireless communication system using an orthogonal frequency division multiplexing (OFDM) scheme or an orthogonal frequency division multiple access (OFDMA) scheme,
Measuring channel quality information (CQI) values for each of bands of a preset number of adjacent subcarriers;
Generating the CQI measurements for at least one particular band together with the band indices of the particular bands as absolute channel quality information (CQI),
Transmitting the absolute value CQI to a base station;
Selecting at least two bands of all bands according to the absolute value CQI;
Measuring CQI values for the selected bands and comparing the CQI measurements of the selected bands with previous CQI measurements of the selected bands, respectively, to generate a differential CQI;
And transmitting the information on the differential CQI from the terminal to the base station. The method of claim 1,
The information on the differential CQI is transmitted in a period in which the absolute value CQI is not transmitted. The method of claim 1,
The information on the differential CQI is transmitted with a period shorter than the absolute value CQI. The method of claim 1,
And the information on the differential CQI indicates an increase or a decrease with respect to the previous CQI measurement values, respectively. The method of claim 1,
The selecting step, the channel quality information transmission method, characterized in that for selecting the number of bands equal to the number of bits of the information on the differential CQI. The method of claim 1,
And wherein the selected bands have the highest CQI measurements among all the bands. The method of claim 1,
Each bit of the information about the differential CQI corresponds to each of the selected bands, and when the CQI measurement value for the corresponding one of the selected bands is increased or equal to the previous CQI measurement value of the corresponding band, '1' And '0' when the number is decreased. The method of claim 1,
The information on the differential CQI is transmitted through the allocated control region of the uplink frame. The method of claim 1,
The CQI measurements include at least one of an average carrier-to-interference noise ratio (CINR) and an average received field strength (RSSI) of subcarriers for the downlink preamble of each of the bands. . A method of receiving channel quality information (CQI) by a base station (BS) in a wireless communication system using an orthogonal frequency division multiplexing (OFDM) scheme or an orthogonal frequency division multiple access (OFDMA) scheme,
Receives an absolute value CQI report indicating channel quality information (CQI) values measured for specific bands among bands of a preset number of adjacent subcarriers from the MSS and stores each of the specific bands Process,
Selecting at least two bands of all bands according to the absolute value CQI;
Receiving information on the differential CQI representing the increase and decrease of previous CQI measurements for the selected bands;
And updating the absolute value CQI stored for the specific bands with reference to the information on the differential CQI. The method of claim 10,
And the information on the differential CQI is received in a cycle in which the absolute value CQI is not transmitted. The method of claim 10,
And the information on the differential CQI is received with a period shorter than the absolute value CQI. The method of claim 10,
The selecting step, the channel quality information receiving method, characterized in that for selecting the same number of bands as the number of bits of the information on the differential CQI. The method of claim 10,
And wherein the selected bands have the highest measurement values among all the bands. The method of claim 10,
And information on the differential CQI is received through an allocated control region of an uplink frame. The method of claim 10,
The CQI measurements include at least one of an average carrier-to-interference noise ratio (CINR) and an average received field strength (RSSI) of subcarriers for the downlink preamble of each of the bands. . An apparatus for transmitting channel quality information (CQI) by a terminal (MSS) in a wireless communication system using an orthogonal frequency division multiplexing (OFDM) scheme or an orthogonal frequency division multiple access (OFDMA) scheme,
Measure channel quality information (CQI) values for each of a band of a preset number of contiguous subcarriers, and determine the CQI values for at least one particular band together with the band indices of the particular bands Generate as channel quality information (CQI),
Selecting at least two bands of all bands according to the absolute value CQI,
A CQI generator for measuring CQI values for the selected bands and comparing the CQI measurements of the selected bands with previous CQI measurements of the selected bands, respectively, to generate a differential CQI;
And a transmitter for transmitting one of the information on the absolute value CQI and the differential CQI to a base station (BS). The method of claim 17,
And the information on the differential CQI is transmitted in a period in which the absolute value CQI is not transmitted. The method of claim 17,
And the information on the differential CQI is transmitted with a period shorter than the absolute value CQI. The method of claim 17,
And the information on the differential CQI indicates an increase or decrease with respect to the previous CQI measurement values, respectively. The method of claim 17,
And the CQI generator selects the same number of bands as the number of bits of the information on the differential CQI in order of having the highest CQI measurements. The method of claim 17,
And wherein the selected bands have the highest CQI measurements among all the bands. The method of claim 17,
Each bit of the information about the differential CQI corresponds to each of the selected bands, and when the CQI measurement value for the corresponding one of the selected bands is increased or equal to the previous CQI measurement value of the corresponding band, '1' And '0' when it is decreased, the channel quality information transmitting apparatus characterized by the above-mentioned. The method of claim 17,
And the information on the differential CQI is transmitted through an allocated control region of an uplink frame. The method of claim 17,
The CQI measurement values include at least one of an average carrier-to-interference noise ratio (CINR) and an average received field strength (RSSI) of subcarriers for a downlink preamble of each of the bands. . An apparatus for receiving channel quality information (CQI) by a base station (BS) in a wireless communication system using Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA)
Receives an absolute value CQI report indicating channel quality information (CQI) values measured for specific bands among bands of a preset number of adjacent subcarriers from the MSS and stores each of the specific bands A controller configured to select at least two bands of all bands according to the absolute value CQI, and to update the absolute value CQI stored for the specific bands by referring to the information on the differential CQI received from the terminal;
And a receiver for receiving the information on the differential CQI representing the increase and decrease of previous CQI measurement values for the selected bands. The method of claim 26,
And the information on the differential CQI is received in a period in which the absolute value CQI is not transmitted. The method of claim 26,
And the information on the differential CQI is received with a period shorter than the absolute value CQI. The method of claim 26,
And the controller selects the same number of bands as the number of bits of the information on the differential CQI. The method of claim 26,
And the selected bands have the highest measurement values among the entire bands. The method of claim 26,
And the information on the differential CQI is received through an allocated control region of an uplink frame. The method of claim 26,
The CQI measurements may include at least one of an average carrier-to-interference noise ratio (CINR) and an average received field strength (RSSI) of subcarriers for a downlink preamble of each of the bands. .

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