WO2009104826A1 - Apparatus and method for determining a feedback channel of ofdma communication system - Google Patents

Apparatus and method for determining a feedback channel of ofdma communication system Download PDF

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Publication number
WO2009104826A1
WO2009104826A1 PCT/KR2008/000973 KR2008000973W WO2009104826A1 WO 2009104826 A1 WO2009104826 A1 WO 2009104826A1 KR 2008000973 W KR2008000973 W KR 2008000973W WO 2009104826 A1 WO2009104826 A1 WO 2009104826A1
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Prior art keywords
channels
denotes
fed back
channel
allocated
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PCT/KR2008/000973
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French (fr)
Inventor
Chung Gu Kang
Jin Woo Kim
Young Jin Park
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Korea University Industrial & Academic Collaboration Foundation
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Priority to PCT/KR2008/000973 priority Critical patent/WO2009104826A1/en
Publication of WO2009104826A1 publication Critical patent/WO2009104826A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0003—Two-dimensional division
    • H04L5/0005—Time-frequency
    • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
    • H04L1/0028—Formatting
    • H04L1/0029—Reduction of the amount of signalling, e.g. retention of useful signalling or differential signalling
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems

Definitions

  • the present invention relates to an apparatus and method for determining a feedback channel of orthogonal frequency-division multiple access (OFDMA) communication system and more particularly, to an apparatus and method for determining a feedback channel of OFDMA communication system using an improved version of an opportunistic feedback scheme in which the number of channels to be fed back is selectively determined by considering the number of channels allocated to a receiving terminal so as to reduce an overhead generated in a transmitter due to feedback channel information.
  • OFDMA orthogonal frequency-division multiple access
  • An orthogonal frequency-division multiple access (OFDMA) scheme is generally defined as a scheme in which effective sub-carrier sets are differently allocated to a plurality of users employing a typical orthogonal frequency division mul- tiplexing(OFDM) scheme.
  • OFDM orthogonal frequency division mul- tiplexing
  • the OFDM scheme is a 2-dimensional access scheme combining conventional time division access and frequency division access techniques.
  • data is transmitted using the OFDM scheme, respective OFDM symbols are carried on sub-carriers in a distributed manner and are transmitted through a predetermined sub-channel.
  • the OFDM scheme provides excellent spectral efficiency since spectrums of sub-channels overlap with one another while maintaining mutual orthogonality. Further, the OFDM scheme enables effective digital implementation of a modulator/demodulator since OFDM modulation/demodulation is implemented using inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT).
  • IFFT inverse fast Fourier transform
  • FFT fast Fourier transform
  • FIG. 1 is a block diagram illustrating a structure of a mobile communication system using a conventional OFDM scheme.
  • Input bits are binary signals.
  • the input bits are input to a channel coder 11.
  • the channel coder 11 codes the input bits and outputs coded symbols.
  • the coded symbols are input to a serial/parallel convertor (i.e., S/P unit) 12.
  • the SP unit 12 converts the input coded symbols (i.e., serial symbols) into parallel symbols, and delivers the parallel symbols to a modulator 13.
  • the modulator 13 performs symbol-mapping on input coded symbols by using a symbol mapping constellation.
  • the modulator 13 can use various modulation schemes, such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-phase shift keying (PSK), 16-quadrature amplitude modulation (QAM), 62-QAM, etc.
  • BPSK binary phase shift keying
  • QPSK quadrature phase shift keying
  • PSK 8-phase shift keying
  • QAM 16-quadrature amplitude modulation
  • 62-QAM etc
  • Modulation symbols output from the modulator 13 are input to an IFFT unit 14.
  • Parallel input symbols are allocated to respective sub-carriers by performing an IFFT.
  • the modulation symbols are input to a parallel/serial convertor (i.e., P/S unit) 15 and are converted into a symbol stream having a serial format.
  • the symbols converted into the serial format are transmitted through a transmit (Tx) antenna.
  • Symbols transmitted from the Tx antenna are received by a receive (Rx) antenna.
  • the symbols received by the Rx antenna are converted into symbols having a parallel format by an S/P unit 26, and the converted symbols are delivered to an FFT unit 25.
  • the FFT unit 25 extracts modulated symbols from the respective sub-carriers.
  • the demodulator 24 After performing an FFT, the symbols are input to a demodulator 24.
  • the demodulator 24 has a symbol mapping constellation which is the same as the symbol mapping constellation of the modulator 13, and converts a de-spread symbol into a symbol having a binary bit according to the symbol mapping constellation. That is, a demodulation scheme is determined depending on a modulation scheme.
  • the binary symbols demodulated by the demodulator 24 are channel-estimated by a channel estimator 23.
  • the channel estimation enables effective data reception by estimating various situations that can be generated in a wireless channel environment.
  • the binary symbols which are channel-estimated by the channel estimator 23 are converted into a symbol stream having a serial format by a P/S unit 22, and thereafter are decoded by a decoder 21.
  • the binary symbols input to the decoder 21 are output as binary bits by performing a decoding process.
  • a base station estimates a channel condition for an Rx signal transmitted through a specific channel by utilizing feedback information provided from a receiving terminal in a process of allocating sub-carriers, and selectively allocates sub-carriers having excellent efficiency according to the estimated channel condition. Therefore, transfer efficiency of the mobile communication system can be increased.
  • the OFDMA system allocates the sub-carriers to a plurality of receiving- side terminals.
  • feedback information of each receiving- side terminal is measured in a sub- carrier unit through the uplink communication. In this case, if each receiving-side terminal transmits its feedback information, waste of uplink radio resources is significant, and an unnecessary feedback overhead is increased.
  • the opportunistic feedback scheme is extended to multiple channels.
  • the opportunistic feedback scheme is a scheme in which feedback is opportunistically performed only on users having a good channel condition.
  • the number of feedbacks is determined according to the number of channels averagely allocated to users.
  • the first feedback method does not consider resource allocation information, and the second feedback method determines the number of feedbacks irrespective of the total number of users. Therefore, there is a problem in that systematic allocation of sub-carriers is not achieved since it is difficult to obtain effective channel information. Disclosure of Invention
  • the present invention provides an apparatus and method for determining feedback channel of OFDMA communication system using an orthogonal frequency-division multiple access (OFDMA) scheme, whereby a feedback overhead caused by feedback information on a channel is reduced.
  • the feedback information is generated since the total number of feedbacks is increased in proportion to the total number of users as the total number of users is increased in an OFDMA system.
  • OFDMA orthogonal frequency-division multiple access
  • the present invention also provides an apparatus and method for determining feedback channel of OFDMA communicatin system using an OFDMA scheme, whereby an opportunistic feedback scheme using channel allocation information is applied to a transmitting side when a receiving-side terminal provides feedback information so that a communication throughput can be improved and the total number of feedbacks is the same as that used in the opportunistic feedback scheme.
  • an apparatus for determining a feedback channel of an orthogonal frequency-division multiple access (OFDMA) communication system in which a transmitter including a communication unit that com- municates with at least one mobile station according to an OFDMA scheme selectively receives feedback information on the mobile station by using the communication unit, the apparatus comprising: a packet scheduler that allocates transport channels for packets to be transmitted using the communication unit; a channel operator that obtains the number of channels averagely allocated to the mobile station according to the number of channels instantaneously allocated to the mobile station by using the packet scheduler; a feedback channel determining unit that determines the number of channels to be fed back from the mobile station on the basis of the number of averagely allocated channels; and an evaluator that evaluates whether the number of channels to be fed back is a proper number.
  • OFDMA orthogonal frequency-division multiple access
  • S i denotes the number of instantaneously allocated channels
  • the number of channels to be fed back is calculated according to:
  • ⁇ i denotes the number of averagely allocated channels
  • the feedback channel determining unit determines the number of channels to be fed back by using both the number of averagely allocated channels and the number of instantaneously allocated channels.
  • the number of channels to be fed back is calculated according to:
  • JV denotes the total number of channels
  • the scaling factor is 0.5, 1.0, 1.5, or 2.0.
  • the evaluator corrects the number of channels to be fed back to the total number of channels, when the number of channels to be fed back is less than T, the evaluator corrects the number of channels to be fed back to T, and otherwise, the evaluator outputs the number of channels to be fed back without alteration.
  • a method of determining a feedback channel of an orthogonal frequency-division multiple access (OFDMA) communication system in which a transmitter that communicates with at least one mobile station according to an OFDMA scheme selectively receives feedback information on the mobile station, the method comprising: a first step in which a transport channel is allocated for a packet to be transmitted to the mobile station; a second step in which the number of averagely allocated channels is obtained according to the number of channels instantaneously allocated to the packet; a third step in which the number of channels to be fed back is obtained according to the number of averagely allocated channels; and a fourth step in which the number of channels to be fed back is evaluated.
  • OFDMA orthogonal frequency-division multiple access
  • a feedback transport channel is determined by using channel allocation information allocated during communication.
  • the total number of feedbacks can be maintained to be equal to that of an opportunistic feedback scheme while performing channel resource allocation more systematically than the opportunistic feedback scheme.
  • usage efficiency of channel resources can be increased, and a transport channel speed can also be increased.
  • a feedback channel is configured based on channel information allocated to each user by considering that the total number of feedbacks is increased in proportion to the total number of users.
  • feedback information can be provided through a channel having high efficiency.
  • whether receiving- side feedback is provided is effectively controlled to reduce a channel allocation overhead in a receiving side and a transmitting side, thereby increasing a system throughput.
  • FIG. 1 is a block diagram illustrating a structure of a mobile communication system using a conventional orthogonal frequency-division multiple access (OFDMA) scheme;
  • OFDMA orthogonal frequency-division multiple access
  • FIG. 2 is a schematic view of an apparatus for determining feedback channel of
  • OFDMA communication system according to an embodiment of the present invention
  • FIG. 3 is a flowchart of a method for determining feedback channel of OFDMA communication system according to an embodiment of the present invention
  • FIG. 4 is a graph illustrating a system throughput for all users when a scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention
  • FIG. 5 is a graph illustrating the total number of feedbacks for all users when a scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention
  • FIG. 6 is a graph illustrating a communication throughput for all users when the total number of channels is 24 according to an embodiment of the present invention.
  • FIG. 7 is a graph illustrating the total number of feedbacks for all users when the total number of channels is 24 according to an embodiment of the present invention. Best Mode for Carrying out the Invention
  • FIG. 2 is a schematic view of an apparatus for determining feedback channel of
  • the apparatus includes a transmitter 110.
  • the transmitter 110 includes a communication unit 111 that communicates with at least one user terminal (i.e., mobile station (MS)) 100 according to an orthogonal frequency-division multiple access (OFDMA) scheme, a packet scheduler 112 that allocates a plurality of transport channels for data packets to be transmitted from the transmitter 110 through the communication unit 111, a channel operator 113 that receives channel allocation information used in the MS 100 from the packet scheduler 112 and calculates various parameters required to obtain the number of channels to be fed back, a feedback determining unit 114 that determines the number of channels to be fed back according to the operation result of the channel operator 113, and an evaluator 115 that evaluates the number of channels to be fed back.
  • OFDMA orthogonal frequency-division multiple access
  • the packet scheduler 112 can allocate the channels to be fed back in a descending order of channel efficiency according to the number of channels to be fed back, thereby increasing a communication speed.
  • the channel allocation information provided by the packet scheduler 112 includes the number of channels instantaneously allocated to the MS 100.
  • the channel operator 113 calculates the number of averagely allocated channels by using the number of instantaneously allocated channels.
  • T denotes the MS
  • the channel operator 113 calculates the number of averagely allocated channels according to the following equation.
  • the feedback determining unit 114 can calculate the number of channels to be fed back according to the following equation.
  • IHT f round(K' ⁇ l -( l -p) ⁇ 's t )
  • the feedback determining unit 114 can also calculate the number of channels to be fed back according to the following equation in consideration of both the number of instantaneously allocated channels and the number of averagely allocated channels. [39] Math Figure 3
  • JV denotes the total number of channels
  • the number of channels to be fed back calculated as described above is evaluated by the evaluator 115 to determine whether the number of channels is a proper number. This will be described in brief with reference to FIG. 3. If the calculated number
  • a of channels to be fed back is less T, the calculated number is corrected to be T and if the calculated number
  • a of channels to be fed back is greater than the total number
  • the maximum number of channels to be fed back is limited within the total number of channels while the minimum number of channels to be fed back is guaranteed. Therefore, a channel overhead caused by excessive feedback information can be reduced.
  • the calculated number of channels to be fed back is greater than T and less than the total number of channels, the calculated number is maintained so that a proper amount of feedback information can be received. Therefore, channel resources can be effectively used.
  • the packet scheduler 112 determines a channel for receiving feedback information according to a specific number of channels to be fed back, wherein the specific number is calculated by the feedback determining unit 114 and is evaluated by the evaluator 115. Further, the packet scheduler 112 performs scheduling by using the received feedback information so that a channel having high efficiency is allocated with priority for a data packet to be transmitted. As a result, communication efficiency can be increased. Furthermore, the channel having high efficiency can be determined as a channel to be fed back in order to receive the feedback information. Therefore, feedback channels and transport channels can be effectively allocated.
  • the number of instantaneously allocated channels varies according to the number of instantaneously allocated channels.
  • the number of averagely allocated channels varies according to the number of instantaneously allocated channels. Therefore, the number of channels to be fed back can vary in response to a communication condition. Accordingly, even if the total number of MSs changes, the packet scheduler can easily allocate channel resources in response to the changes in the communication state of the MS.
  • the number of channels to be fed back varies according to the number of instantaneously allocated channels and the number of averagely allocated channels, it is possible to reduce an overhead which is generated when feedback information is received due to configuration of unnecessary feedback channel.
  • the feedback information includes various channel measurement values for the feedback channel.
  • the feedback information may include a signal to interference power ratio (SIR) or a channel to noise ratio (CNR).
  • SIR signal to interference power ratio
  • CNR channel to noise ratio
  • the feedback information can be utilized as information regarding channel allocation for data packets of the packet scheduler and information regarding configuration of a channel to be fed back.
  • FIG. 4 is a graph illustrating a system throughput for all users when the scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention.
  • the graph of FIG. 4 is obtained through experimentation whereby the number
  • a of channels to be fed back is determined using the number
  • the system throughput can be different according to the scaling factor depending on the total number of users.
  • a scaling factor for maximizing the system throughput is increased in proportion to the total number
  • FIG. 5 is a graph illustrating the total number of feedbacks for all users when the scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention.
  • a of channels to be fed back is determined using the number
  • the total number of feedbacks can be different according to the scaling factor depending on the total number of users.
  • FIG. 6 is a graph illustrating a communication throughput for all users when the total number of channels is 24 according to an embodiment of the present invention.
  • the graph of FIG. 6 is obtained through experimentation according to a full feedback scheme, an instantaneous allocation-based opportunistic feedback (IAOF) scheme of the present invention, an efficiency-based opportunistic feedback (EOF) scheme of the present invention, and an opportunistic feedback (OF) scheme.
  • the full feedback scheme feeds back all channels.
  • the IAOF scheme determines the number
  • the EOF scheme determines the number
  • the communication throughput is almost the same as that of the full feedback scheme as the total number of users increases.
  • a communication throughput is more increased than the OF scheme.
  • FIG. 7 is a graph illustrating the total number of feedbacks for all users when the total number of channels is 24 according to an embodiment of the present invention.
  • the graph of FIG. 7 is obtained through experimentation according to the full feedback scheme, the IAOF scheme, the EOF scheme, and the OF scheme.
  • the total number of feedbacks becomes the same as that of the OF scheme as the total number of users increases.
  • the total number of feedbacks is the same as that of the OF scheme.
  • a first feedback method proposed in the present invention that is, the IAOF method
  • the total number of feedbacks becomes equal to that of the OF scheme as the total number of users increases, and the communication throughput is almost the same as that of the full feedback scheme.
  • the second feedback method proposed in the present invention that is, the EOF scheme
  • the total number of feedbacks is the same as that of the OF scheme but the communication throughput increases to be higher than that of the OF scheme. That is, by using the two methods of the present invention, the communication throughput can be maintained to be almost the same level as the full feedback scheme while the total number of feedbacks is maintained to be the same level as the conventional OF scheme. Therefore, smooth communication can be achieved.

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Abstract

Provided are an apparatus and method for determining a feedback channel of OFDMA communication system. Specifically, provided are an apparatus and method for determining feedback channel of OFDMA communication system using an OFDMA scheme that is an improved version of an opportunistic feedback scheme in which the number of channels to be fed back is selectively determined by considering the number of channels allocated to a receiving terminal so as to reduce an overhead generated in a transmitter due to feedback channel information. Accordingly, a feedback transport channel is determined by using channel allocation information allocated during communication. Thus, the total number of feedbacks can be maintained to be equal to that of an opportunistic feedback scheme while performing channel resource allocation more systematically than the opportunistic feedback scheme, thereby reducing unnecessary feedback information. In addition, a feedback channel is configured based on channel information allocated to each user by considering that the total number of feedbacks is increased in proportion to the total number of users. Thus, feedback information can be provided through a channel having high efficiency. Further, whether receiving- side feedback is provided is effectively controlled to reduce a channel allocation overhead in a receiving side and a transmitting side, thereby increasing a system throughput.

Description

Description
APPARATUS AND METHOD FOR DETERMINING A FEEDBACK CHANNEL OF OFDMA COMMUNICATION
SYSTEM
Technical Field
[1] The present invention relates to an apparatus and method for determining a feedback channel of orthogonal frequency-division multiple access (OFDMA) communication system and more particularly, to an apparatus and method for determining a feedback channel of OFDMA communication system using an improved version of an opportunistic feedback scheme in which the number of channels to be fed back is selectively determined by considering the number of channels allocated to a receiving terminal so as to reduce an overhead generated in a transmitter due to feedback channel information. Background Art
[2] An orthogonal frequency-division multiple access (OFDMA) scheme is generally defined as a scheme in which effective sub-carrier sets are differently allocated to a plurality of users employing a typical orthogonal frequency division mul- tiplexing(OFDM) scheme.
[3] The OFDM scheme is a 2-dimensional access scheme combining conventional time division access and frequency division access techniques. When data is transmitted using the OFDM scheme, respective OFDM symbols are carried on sub-carriers in a distributed manner and are transmitted through a predetermined sub-channel. The OFDM scheme provides excellent spectral efficiency since spectrums of sub-channels overlap with one another while maintaining mutual orthogonality. Further, the OFDM scheme enables effective digital implementation of a modulator/demodulator since OFDM modulation/demodulation is implemented using inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT).
[4] Furthermore, by transmitting data while maintaining orthogonality among a plurality of sub-carriers, the OFDM scheme is characterized in that optimal transfer efficiency can be obtained when data is transmitted at a high speed. In addition, the optimal transfer efficiency can be obtained when high-speed data transmission is performed since the OFDM scheme provides excellent frequency usage efficiency and has characteristics robust to multi-path fading. In particular, frequency spectrums are used in an overlap manner to achieve effective frequency usage, frequency selecting fading, and multi-path fading. In addition, inter-symbol interference can be minimized by using a guard interval, and a structure of an equalizer can be simplified in a hardware manner. [5] FIG. 1 is a block diagram illustrating a structure of a mobile communication system using a conventional OFDM scheme. Input bits are binary signals. The input bits are input to a channel coder 11. The channel coder 11 codes the input bits and outputs coded symbols. The coded symbols are input to a serial/parallel convertor (i.e., S/P unit) 12. The SP unit 12 converts the input coded symbols (i.e., serial symbols) into parallel symbols, and delivers the parallel symbols to a modulator 13. The modulator 13 performs symbol-mapping on input coded symbols by using a symbol mapping constellation. The modulator 13 can use various modulation schemes, such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-phase shift keying (PSK), 16-quadrature amplitude modulation (QAM), 62-QAM, etc. Modulation symbols output from the modulator 13 are input to an IFFT unit 14. Parallel input symbols are allocated to respective sub-carriers by performing an IFFT. After performing the IFFT, the modulation symbols are input to a parallel/serial convertor (i.e., P/S unit) 15 and are converted into a symbol stream having a serial format. The symbols converted into the serial format are transmitted through a transmit (Tx) antenna. Symbols transmitted from the Tx antenna are received by a receive (Rx) antenna. The symbols received by the Rx antenna are converted into symbols having a parallel format by an S/P unit 26, and the converted symbols are delivered to an FFT unit 25. The FFT unit 25 extracts modulated symbols from the respective sub-carriers. After performing an FFT, the symbols are input to a demodulator 24. The demodulator 24 has a symbol mapping constellation which is the same as the symbol mapping constellation of the modulator 13, and converts a de-spread symbol into a symbol having a binary bit according to the symbol mapping constellation. That is, a demodulation scheme is determined depending on a modulation scheme. The binary symbols demodulated by the demodulator 24 are channel-estimated by a channel estimator 23. The channel estimation enables effective data reception by estimating various situations that can be generated in a wireless channel environment. The binary symbols which are channel-estimated by the channel estimator 23 are converted into a symbol stream having a serial format by a P/S unit 22, and thereafter are decoded by a decoder 21. The binary symbols input to the decoder 21 are output as binary bits by performing a decoding process.
[6] In the mobile communication system using the OFDM scheme, a base station estimates a channel condition for an Rx signal transmitted through a specific channel by utilizing feedback information provided from a receiving terminal in a process of allocating sub-carriers, and selectively allocates sub-carriers having excellent efficiency according to the estimated channel condition. Therefore, transfer efficiency of the mobile communication system can be increased.
[7] Unlike the OFDM scheme in which all sub-carriers are used by only one receiving- side terminal, the OFDMA system allocates the sub-carriers to a plurality of receiving- side terminals. In a situation where high-speed packet data transmission is taken into consideration through uplink communication which is slower than downlink communication, feedback information of each receiving- side terminal is measured in a sub- carrier unit through the uplink communication. In this case, if each receiving-side terminal transmits its feedback information, waste of uplink radio resources is significant, and an unnecessary feedback overhead is increased.
[8] There are two conventional feedback methods for reducing the feedback overhead. In a first feedback method, the opportunistic feedback scheme is extended to multiple channels. The opportunistic feedback scheme is a scheme in which feedback is opportunistically performed only on users having a good channel condition. In a second feedback method, the number of feedbacks is determined according to the number of channels averagely allocated to users.
[9] However, the first feedback method does not consider resource allocation information, and the second feedback method determines the number of feedbacks irrespective of the total number of users. Therefore, there is a problem in that systematic allocation of sub-carriers is not achieved since it is difficult to obtain effective channel information. Disclosure of Invention
Technical Problem
[10] To overcome the above problems, the present invention provides an apparatus and method for determining feedback channel of OFDMA communication system using an orthogonal frequency-division multiple access (OFDMA) scheme, whereby a feedback overhead caused by feedback information on a channel is reduced. The feedback information is generated since the total number of feedbacks is increased in proportion to the total number of users as the total number of users is increased in an OFDMA system.
[11] The present invention also provides an apparatus and method for determining feedback channel of OFDMA communicatin system using an OFDMA scheme, whereby an opportunistic feedback scheme using channel allocation information is applied to a transmitting side when a receiving-side terminal provides feedback information so that a communication throughput can be improved and the total number of feedbacks is the same as that used in the opportunistic feedback scheme. Technical Solution
[12] According to an aspect of the present invention, an apparatus for determining a feedback channel of an orthogonal frequency-division multiple access (OFDMA) communication system, in which a transmitter including a communication unit that com- municates with at least one mobile station according to an OFDMA scheme selectively receives feedback information on the mobile station by using the communication unit, the apparatus comprising: a packet scheduler that allocates transport channels for packets to be transmitted using the communication unit; a channel operator that obtains the number of channels averagely allocated to the mobile station according to the number of channels instantaneously allocated to the mobile station by using the packet scheduler; a feedback channel determining unit that determines the number of channels to be fed back from the mobile station on the basis of the number of averagely allocated channels; and an evaluator that evaluates whether the number of channels to be fed back is a proper number. [13] Preferably, when
Z denotes the mobile station, the number of averagely allocated channels is calculated according to:
Figure imgf000006_0001
, where
denotes the number of averagely allocated channels,
S i denotes the number of instantaneously allocated channels, and
denotes a window size. [14] Preferably, when
denotes the mobile station, the number of channels to be fed back is calculated according to:
1/K, frroιmd{K- { l -( l -p) }-^)
, where
^i denotes the number of averagely allocated channels,
denotes the total number of mobile stations, and
P denotes a predetermined usage efficiency of the transmitter. [15] Preferably, the feedback channel determining unit determines the number of channels to be fed back by using both the number of averagely allocated channels and the number of instantaneously allocated channels. [16] Preferably, when i denotes the mobile station, the number of channels to be fed back is calculated according to:
f ]— round {Ni l- (l-p) llK)} h +wsc(K,NyioBe^ si
, where
denotes the number of averagely allocated channels,
denotes the number of instantaneously allocated channels,
JV denotes the total number of channels, and
denotes a scaling factor by which allocated channel information has an effect on channel information to be fed back.
[17] Preferably, the scaling factor is 0.5, 1.0, 1.5, or 2.0.
[18] Preferably, when the number of channels to be fed back is greater than the total number of channels, the evaluator corrects the number of channels to be fed back to the total number of channels, when the number of channels to be fed back is less than T, the evaluator corrects the number of channels to be fed back to T, and otherwise, the evaluator outputs the number of channels to be fed back without alteration.
[19] According to another aspect of the present invention, a method of determining a feedback channel of an orthogonal frequency-division multiple access (OFDMA) communication system, in which a transmitter that communicates with at least one mobile station according to an OFDMA scheme selectively receives feedback information on the mobile station, the method comprising: a first step in which a transport channel is allocated for a packet to be transmitted to the mobile station; a second step in which the number of averagely allocated channels is obtained according to the number of channels instantaneously allocated to the packet; a third step in which the number of channels to be fed back is obtained according to the number of averagely allocated channels; and a fourth step in which the number of channels to be fed back is evaluated.
Advantageous Effects
[20] According to the present invention, a feedback transport channel is determined by using channel allocation information allocated during communication. Thus, the total number of feedbacks can be maintained to be equal to that of an opportunistic feedback scheme while performing channel resource allocation more systematically than the opportunistic feedback scheme. As a result, by reducing unnecessary feedback information, usage efficiency of channel resources can be increased, and a transport channel speed can also be increased.
[21] In addition, according to the present invention, a feedback channel is configured based on channel information allocated to each user by considering that the total number of feedbacks is increased in proportion to the total number of users. Thus, feedback information can be provided through a channel having high efficiency. Further, whether receiving- side feedback is provided is effectively controlled to reduce a channel allocation overhead in a receiving side and a transmitting side, thereby increasing a system throughput. Brief Description of Drawings
[22] FIG. 1 is a block diagram illustrating a structure of a mobile communication system using a conventional orthogonal frequency-division multiple access (OFDMA) scheme;
[23] FIG. 2 is a schematic view of an apparatus for determining feedback channel of
OFDMA communication system according to an embodiment of the present invention;
[24] FIG. 3 is a flowchart of a method for determining feedback channel of OFDMA communication system according to an embodiment of the present invention;
[25] FIG. 4 is a graph illustrating a system throughput for all users when a scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention;
[26] FIG. 5 is a graph illustrating the total number of feedbacks for all users when a scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention;
[27] FIG. 6 is a graph illustrating a communication throughput for all users when the total number of channels is 24 according to an embodiment of the present invention; and
[28] FIG. 7 is a graph illustrating the total number of feedbacks for all users when the total number of channels is 24 according to an embodiment of the present invention. Best Mode for Carrying out the Invention
[29] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[30] FIG. 2 is a schematic view of an apparatus for determining feedback channel of
OFDMA communication system according to an embodiment of the present invention. Referring to FIG. 2, the apparatus includes a transmitter 110. The transmitter 110 includes a communication unit 111 that communicates with at least one user terminal (i.e., mobile station (MS)) 100 according to an orthogonal frequency-division multiple access (OFDMA) scheme, a packet scheduler 112 that allocates a plurality of transport channels for data packets to be transmitted from the transmitter 110 through the communication unit 111, a channel operator 113 that receives channel allocation information used in the MS 100 from the packet scheduler 112 and calculates various parameters required to obtain the number of channels to be fed back, a feedback determining unit 114 that determines the number of channels to be fed back according to the operation result of the channel operator 113, and an evaluator 115 that evaluates the number of channels to be fed back.
[31] The packet scheduler 112 can allocate the channels to be fed back in a descending order of channel efficiency according to the number of channels to be fed back, thereby increasing a communication speed. The channel allocation information provided by the packet scheduler 112 includes the number of channels instantaneously allocated to the MS 100. The channel operator 113 calculates the number of averagely allocated channels by using the number of instantaneously allocated channels.
[32] That is, if
T denotes the MS, the channel operator 113 calculates the number of averagely allocated channels according to the following equation. [33] MathFigure 1
[Math.l]
sfj)
Figure imgf000009_0001
[34] Herein,
denotes the number of instantaneously allocated channels, and
denotes the number of averagely allocated channels. In addition,
denotes a window size for calculating
S
[35] Thereafter, by using the number of averagely allocated channels calculated by the channel operator 113, the feedback determining unit 114 can calculate the number of channels to be fed back according to the following equation.
[36] MathFigure 2
[Math.2]
1 IHT f = round(K' { l -( l -p) } 'st)
[37] Herein,
denotes the total number of MSs, and
P denotes a predetermined usage efficiency of the transmitter. [38] In addition, the feedback determining unit 114 can also calculate the number of channels to be fed back according to the following equation in consideration of both the number of instantaneously allocated channels and the number of averagely allocated channels. [39] MathFigure 3
[Math.3]
fj— round {Ni l - (1 -p)
Figure imgf000010_0001
[40] Herein,
JV denotes the total number of channels, and
denotes a scaling factor by which the channel allocation information has an effect on channel information to be fed back.
[41] The number of channels to be fed back calculated as described above is evaluated by the evaluator 115 to determine whether the number of channels is a proper number. This will be described in brief with reference to FIG. 3. If the calculated number
A of channels to be fed back is less T, the calculated number is corrected to be T and if the calculated number
A of channels to be fed back is greater than the total number
JV of channels, the calculated number is corrected to be the total number
JV of channels. Accordingly, the maximum number of channels to be fed back is limited within the total number of channels while the minimum number of channels to be fed back is guaranteed. Therefore, a channel overhead caused by excessive feedback information can be reduced.
[42] In addition, if the calculated number of channels to be fed back is greater than T and less than the total number of channels, the calculated number is maintained so that a proper amount of feedback information can be received. Therefore, channel resources can be effectively used.
[43] The packet scheduler 112 determines a channel for receiving feedback information according to a specific number of channels to be fed back, wherein the specific number is calculated by the feedback determining unit 114 and is evaluated by the evaluator 115. Further, the packet scheduler 112 performs scheduling by using the received feedback information so that a channel having high efficiency is allocated with priority for a data packet to be transmitted. As a result, communication efficiency can be increased. Furthermore, the channel having high efficiency can be determined as a channel to be fed back in order to receive the feedback information. Therefore, feedback channels and transport channels can be effectively allocated.
[44] In addition, according to a communication state of the MS and according to changes in the communication state of the MS such as changes in data packet capacity, the number of instantaneously allocated channels varies. At the same time, the number of averagely allocated channels varies according to the number of instantaneously allocated channels. Therefore, the number of channels to be fed back can vary in response to a communication condition. Accordingly, even if the total number of MSs changes, the packet scheduler can easily allocate channel resources in response to the changes in the communication state of the MS. Moreover, since the number of channels to be fed back varies according to the number of instantaneously allocated channels and the number of averagely allocated channels, it is possible to reduce an overhead which is generated when feedback information is received due to configuration of unnecessary feedback channel.
[45] The feedback information includes various channel measurement values for the feedback channel. The feedback information may include a signal to interference power ratio (SIR) or a channel to noise ratio (CNR). The feedback information can be utilized as information regarding channel allocation for data packets of the packet scheduler and information regarding configuration of a channel to be fed back.
[46] FIG. 4 is a graph illustrating a system throughput for all users when the scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention. The graph of FIG. 4 is obtained through experimentation whereby the number
A of channels to be fed back is determined using the number
of channels averagely allocated to the MS
T and the number
S i of channels instantaneously allocated to the MS
Z
. Referring to FIG. 4, the system throughput can be different according to the scaling factor depending on the total number of users. In addition, a scaling factor for maximizing the system throughput is increased in proportion to the total number
of users. [47] FIG. 5 is a graph illustrating the total number of feedbacks for all users when the scaling factor is 0.5, 1.0, 1.5, or 2.0 and the total number of channels is 24 according to an embodiment of the present invention.
[48] The graph of FIG. 5 is obtained through experimentation whereby the number
A of channels to be fed back is determined using the number
of channels averagely allocated to the MS
Z and the number
S i of channels instantaneously allocated to the MS
Z
. Referring to FIG. 5, the total number of feedbacks can be different according to the scaling factor depending on the total number of users.
[49] FIG. 6 is a graph illustrating a communication throughput for all users when the total number of channels is 24 according to an embodiment of the present invention. The graph of FIG. 6 is obtained through experimentation according to a full feedback scheme, an instantaneous allocation-based opportunistic feedback (IAOF) scheme of the present invention, an efficiency-based opportunistic feedback (EOF) scheme of the present invention, and an opportunistic feedback (OF) scheme. The full feedback scheme feeds back all channels. The IAOF scheme determines the number
A of channels to be fed back by using the number
S , of channels averagely allocated to the MS
Z and the number
S 1- of channels instantaneously allocated to MS T
. The EOF scheme determines the number
of channels to be fed back by using the number
of channels averagely allocated to the MS
Z
. Referring to FIG. 6, in the IAOF scheme of the present invention, the communication throughput is almost the same as that of the full feedback scheme as the total number of users increases. In the EOF scheme of the present invention, a communication throughput is more increased than the OF scheme.
[50] FIG. 7 is a graph illustrating the total number of feedbacks for all users when the total number of channels is 24 according to an embodiment of the present invention. The graph of FIG. 7 is obtained through experimentation according to the full feedback scheme, the IAOF scheme, the EOF scheme, and the OF scheme. Referring to FIG. 7, in the IAOF scheme, the total number of feedbacks becomes the same as that of the OF scheme as the total number of users increases. In the EOF scheme, the total number of feedbacks is the same as that of the OF scheme.
[51] As described above with reference to FIGs. 6 and 7, according to a first feedback method proposed in the present invention, that is, the IAOF method, the total number of feedbacks becomes equal to that of the OF scheme as the total number of users increases, and the communication throughput is almost the same as that of the full feedback scheme. In addition, according to a second feedback method proposed in the present invention, that is, the EOF scheme, the total number of feedbacks is the same as that of the OF scheme but the communication throughput increases to be higher than that of the OF scheme. That is, by using the two methods of the present invention, the communication throughput can be maintained to be almost the same level as the full feedback scheme while the total number of feedbacks is maintained to be the same level as the conventional OF scheme. Therefore, smooth communication can be achieved.
[52] The description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The word "exemplary" is used exclusively herein to mean "serving as an example, instance, or illustration". Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects.
[53] Accordingly, while aspects of an apparatus and method for determining a feedback channel of orthogonal frequency-division multiple access (OFDMA) communication system have been illustrated and described herein, it will be appreciated that various changes can be made to the aspects without departing from their spirit or essential characteristics. Therefore, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Claims

Claims
[1] An apparatus for determining a feedback channel of an orthogonal frequency- division multiple access (OFDMA) communication system, in which a transmitter including a communication unit that communicates with at least one mobile station according to an OFDMA scheme selectively receives feedback information on the mobile station by using the communication unit, the apparatus comprising: a packet scheduler that allocates transport channels for packets to be transmitted using the communication unit; a channel operator that obtains the number of channels averagely allocated to the mobile station according to the number of channels instantaneously allocated to the mobile station by using the packet scheduler; a feedback channel determining unit that determines the number of channels to be fed back from the mobile station on the basis of the number of averagely allocated channels; and an evaluator that evaluates whether the number of channels to be fed back is a proper number.
[2] The apparatus of claim 1, wherein, when
Z denotes the mobile station, the number of averagely allocated channels is calculated according to:
S ,i(f+ i)= 1 -— W/)+— s /U)
, where
denotes the number of averagely allocated channels,
S i denotes the number of instantaneously allocated channels, and
denotes a window size.
[3] The apparatus of claim 1, wherein, when denotes the mobile station, the number of channels to be fed back is calculated according to: ft = round(K' { l -( l -p) 1^}-^)
, where
denotes the number of averagely allocated channels,
denotes the total number of mobile stations, and
P denotes a predetermined usage efficiency of the transmitter.
[4] The apparatus of claim 1, wherein the feedback channel determining unit determines the number of channels to be fed back by using both the number of averagely allocated channels and the number of instantaneously allocated channels.
[5] The apparatus of claim 4, wherein, when
Z denotes the mobile station, the number of channels to be fed back is calculated according to:
ff— round [N-( I -
Figure imgf000017_0001
, where
denotes the number of averagely allocated channels,
denotes the number of instantaneously allocated channels,
JV denotes the total number of channels, and
denotes a scaling factor by which allocated channel information has an effect on channel information to be fed back.
[6] The apparatus of claim 5, wherein the scaling factor is 0.5, 1.0, 1.5, or 2.0.
[7] The apparatus of claim 1, wherein, when the number of channels to be fed back is greater than the total number of channels, the evaluator corrects the number of channels to be fed back to the total number of channels, when the number of channels to be fed back is less than T, the evaluator corrects the number of channels to be fed back to T, and otherwise, the evaluator outputs the number of channels to be fed back without alteration.
[8] A method of determining a feedback channel of an orthogonal frequency- division multiple access (OFDMA) communication system, in which a transmitter that communicates with at least one mobile station according to an OFDMA scheme selectively receives feedback information on the mobile station, the method comprising: a first step in which a transport channel is allocated for a packet to be transmitted to the mobile station; a second step in which the number of averagely allocated channels is obtained according to the number of channels instantaneously allocated to the packet; a third step in which the number of channels to be fed back is obtained according to the number of averagely allocated channels; and a fourth step in which the number of channels to be fed back is evaluated.
[9] The method of claim 8, wherein, when
Z denotes the mobile station, the number of averagely allocated channels in the second step is calculated according to:
Figure imgf000018_0001
, where
denotes the number of averagely allocated channels,
denotes the number of instantaneously allocated channels, and
denotes a window size.
[10] The method of claim 8, wherein, when
Z denotes the mobile station, the number of channels to be fed back in the second step is calculated according to: frround(K- { l -( l -p) 1^}-^)
, where
denotes the number of averagely allocated channels,
denotes the total number of mobile stations, and
P denotes a predetermined usage efficiency of the transmitter.
[11] The method of claim 8, wherein, in the third step, the number of channels to be fed back is obtained by using both the number of averagely allocated channels and the number of instantaneously allocated channels.
[12] The method of claim 11, wherein, when
T denotes the mobile station, the number of channels to be fed back is calculated according to:
fj— round (,V-( I- (I -P) 1^)J - l+Wje(*,Λ0-log,
Hi
, where
denotes the number of averagely allocated channels,
S i denotes the number of instantaneously allocated channels,
JV denotes the total number of channels, and
Figure imgf000020_0001
denotes a scaling factor by which allocated channel information has an effect on channel information to be fed back.
[13] The method of claim 12, wherein the scaling factor is 0.5, 1.0, 1.5, or 2.0.
[14] The method of claim 8, wherein, in the fourth step, when the number of channels to be fed back is greater than the total number of channels, the number of channels to be fed back is corrected to the total number of channels, when the number of channels to be fed back is less than T, the number of channels to be fed back is corrected to T, and otherwise, the number of channels to be fed back is output without alteration.
PCT/KR2008/000973 2008-02-19 2008-02-19 Apparatus and method for determining a feedback channel of ofdma communication system WO2009104826A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070189199A1 (en) * 2004-03-30 2007-08-16 Matsushita Electric Industrial Co., Ltd. Base station apparatus, mobile station apparatus, and data channel scheduling method
US20070287468A1 (en) * 2006-04-21 2007-12-13 Samsung Electronics Co., Ltd Method and apparatus for transmitting and receiving channel quality information in a wireless communication system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070189199A1 (en) * 2004-03-30 2007-08-16 Matsushita Electric Industrial Co., Ltd. Base station apparatus, mobile station apparatus, and data channel scheduling method
US20070287468A1 (en) * 2006-04-21 2007-12-13 Samsung Electronics Co., Ltd Method and apparatus for transmitting and receiving channel quality information in a wireless communication system

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