JP2010098675A - Base station apparatus, and scheduling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the number of continuous data retransmission times in the case where an error occurs on data in a mobile communication system. <P>SOLUTION: A base station 12 performs wireless communications with a plurality of mobile stations, respectively, via at least one of a plurality of subchannels into which a frequency has been divided. The base station 12 includes: an antenna 20 and a wireless communication section 22 for receiving a wireless signal transmitted from each mobile station; a channel estimation section 30 for estimating a state of each subchannel based on the received wireless signal; an error detection section 36 for detecting an error of data included in the received wireless signal; and a scheduler 38 for allocating a subchannel having a better state than in a first transmission of the other data to retransmission of data for which an error has been detected by the error detection section 36, based on a state of each subchannel which is estimated by the channel estimation section 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a base station apparatus and a scheduling method, and more particularly to subchannel allocation by a base station apparatus that performs radio communication with each of a plurality of mobile station apparatuses via at least one of a plurality of frequency-divided subchannels.

  In data communication, error control is performed by an ARQ (Automatic Repeat Request) system (see, for example, Patent Document 1). In ARQ, when an error occurs in data in a frame received by a receiving device, the receiving device requests the transmitting device to retransmit erroneous data.

This ARQ is also employed in mobile communication systems. In particular, a base station that performs radio communication with each of a plurality of mobile stations using at least one of a plurality of frequency-divided subchannels transmits a subchannel with good radio conditions (for example, a small amount of fading fluctuation) for the first time transmission of data. And the remaining subchannels are allocated for data retransmission.
JP-A-9-284261

  However, the conventional mobile communication system has a problem that once an error occurs in the data, an error is likely to occur in the retransmitted data, that is, the number of continuous retransmissions of the data is likely to increase.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a base station apparatus and a scheduling method that can reduce the number of continuous retransmissions of data.

  In order to solve the above problems, a base station apparatus according to the present invention is a base station apparatus that performs radio communication with each of a plurality of mobile station apparatuses via at least one of a plurality of frequency-divided subchannels, Receiving means for receiving a radio signal transmitted from each mobile station apparatus, channel estimating means for estimating the state of each subchannel based on a radio signal received by the receiving means, and receiving by the receiving means Error detection means for detecting an error in data included in the radio signal to be transmitted, and retransmission of data in which an error is detected by the error detection means based on the state of each subchannel estimated by the channel estimation means Scheduling means for allocating subchannels in better condition than the initial transmission of other data.

  According to the present invention, a subchannel having a better state than the initial transmission of other data is allocated for data retransmission, so that the number of continuous data retransmissions can be reduced.

  Also, in one aspect of the present invention, the base station apparatus performs radio communication with each of a plurality of mobile station apparatuses using an orthogonal frequency division multiple access scheme, and the scheduling means uses the error detection means to store two or more data When an error is detected, the frequency interval of the subchannel allocated to each retransmission of two or more data in which the error is detected is separated by a predetermined width or more.

  According to this aspect, since the subchannels allocated to the retransmissions of two or more data in which errors are detected are not close to each other, it is difficult for errors to occur in the retransmission data even if their orthogonality is lost. For this reason, the number of continuous retransmissions of data can be further reduced.

  In each of the above aspects, the state of each subchannel may be a fading fluctuation amount in each subchannel.

  The scheduling method according to the present invention is a scheduling method of a base station apparatus that performs radio communication with each of a plurality of mobile station apparatuses via at least one of a plurality of frequency-divided subchannels. Receiving a radio signal transmitted from the apparatus; estimating a state of each of the subchannels based on the received radio signal; and detecting an error in data included in the received radio signal And, based on the estimated state of each subchannel, assigning a subchannel having a better state than the initial transmission of other data to retransmission of the data in which the error is detected, To do.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a mobile communication system 10 according to an embodiment of the present invention. As shown in the figure, the mobile communication system 10 includes a base station 12 and a plurality of mobile stations 14 (only mobile stations 14-1 to 14-3 are shown here). The base station 12 uses an OFDMA (Orthogonal Frequency Division Multiple Access) method and a TDMA / TDD (Time Division Multiple Access / Time Division Duplex) method. Multiplex communication is performed with the mobile station 14.

  FIG. 2 is a diagram illustrating an example of a frame configuration of the mobile communication system 10. As shown in the figure, in the mobile communication system 10, a downlink subframe in which the base station 12 transmits to the mobile station 14 and an uplink subframe in which the mobile station 14 transmits to the base station 12 are included in one TDMA frame. A guard time TTG (Transmit Transition Gap) for the base station 12 to switch from transmission to reception and a guard time RTG (Receive Transition Gap) for the base station 12 to switch from reception to transmission are provided.

  The minimum unit of the radio channel used for communication between the base station 12 and the mobile station 14 is called a “slot”, and is at least one continuous on the time axis with any one of a plurality of sub-channels based on OFDMA. OFDM symbol. As shown in FIG. 2, each of the downlink subframe and the uplink subframe is divided into several areas such as a data burst for data transmission and a control channel. The minimum unit for dividing these areas is a slot.

  Further, as shown in the figure, the data bursts (upstream bursts # 1 to 3) in the upstream subframe are stepped areas designated only by the number of slots. In addition to data bursts, control channel areas such as ranging, CQICH (Channel Quality Information Channel), ACK (Acknowledgement) are allocated to the uplink subframe.

  On the other hand, data bursts (downlink bursts # 1 to 5) in the downlink subframe are rectangular areas specified by a time width (the number of OFDM symbols) and a frequency width (the number of subchannels). In addition to the data burst, areas such as a preamble, an FCH (Frame Control Header), and a DL-MAP (Downlink Map) indicating downlink radio resource allocation are allocated to the downlink subframe. Note that UL-MAP (Uplink Map) indicating uplink radio resource allocation is included in the first data burst (downlink burst # 1) indicated by DL-MAP. Thereby, the base station 12 can change the downlink radio resource allocation and the uplink radio resource allocation for the mobile station 14 for each frame.

  The base station 12 receives a radio signal transmitted from the mobile station 14 via an uplink burst composed of at least one slot, and determines whether there is an error in data acquired from the radio signal. If an error in the data is detected, the base station 12 requests the mobile station 14 that has transmitted the data to retransmit the data in which the error is detected. At this time, the base station 12 allocates an uplink burst composed of slots belonging to subchannels in a better state than the initial transmission of other data for retransmission of the data. That is, in the mobile communication system 10, a subchannel having a better state than the initial transmission of other data is allocated for data retransmission, so that the number of continuous retransmissions of data by the mobile station 14 can be reduced.

  Below, the structure with which the base station 12 is provided in order to implement | achieve the said process is demonstrated. FIG. 3 is a functional block diagram of the base station 12. As shown in the figure, the base station 12 includes an antenna 20, a wireless communication unit 22, a baseband processing unit 24, an interference signal removal unit 26, a demodulation unit 28, a channel estimation unit 30, a MAC (Media Access Control) unit 32, A modulation unit 42 and a frame generation unit 44 are included.

  The antenna 20 receives a radio signal and outputs the received radio signal to the radio communication unit 22. Further, the antenna 20 transmits a radio signal supplied from the radio communication unit 22 to the mobile station 14.

  The wireless communication unit 22 includes a low noise amplifier, a power amplifier, a frequency conversion circuit, a band pass filter, an A / D converter, and a D / A converter. The radio communication unit 22 amplifies the radio signal input from the antenna 20 with a low noise amplifier, down-converts it to an intermediate frequency signal, and outputs the digitally converted signal to the baseband processing unit 24. Further, the radio communication unit 22 converts the digital signal input from the baseband processing unit 24 into an analog signal, then up-converts the signal to a radio signal, amplifies it to a transmission output level with a power amplifier, and then supplies the signal to the antenna 20 To do.

  The baseband processing unit 24 includes an FFT (Fast Fourier Transform) unit, an IFFT (Inverse Fast Fourier Transform) unit, a serial-parallel converter, and a parallel-serial converter.

  The baseband processing unit 24 performs CP (Cyclic Prefix) removal, serial-parallel conversion, discrete Fourier transform, and the like on the digital signal input from the wireless communication unit 22, and each of the obtained complex symbol sequences. The subcarrier component is classified by subchannel. Furthermore, the baseband processing unit 24 divides the complex symbol sequence for each subchannel according to the mobile station 14 according to the uplink radio resource allocation determined by the scheduler 38 of the MAC unit 32 described later, and the complex symbol sequence for each mobile station 14. Is output to the interference signal removal unit 26 and the channel estimation unit 30.

  In addition, the baseband processing unit 24 performs serial-parallel conversion, inverse discrete Fourier transform, parallel-serial conversion, CP insertion, and the like on the downlink subframes sequentially input from the frame generation unit 44 for each OFDM symbol. The digital signal is output to the wireless communication unit 22.

  The interference signal removal unit 26 removes the interference signal from the complex symbol sequence for each mobile station 14 input from the baseband processing unit 24, and supplies the demodulation unit 28 with the complex symbol sequence for each mobile station 14 from which the interference signal has been removed. Output.

  The demodulation unit 28 demodulates the complex symbol sequence for each mobile station 14 input from the interference signal removal unit 26 and outputs the data obtained by the demodulation to the MAC unit 32.

  The channel estimation unit 30 includes a known signal generation unit (not shown), and estimates the state of each subchannel based on the complex symbol sequence for each mobile station 14 input from the baseband processing unit 24. That is, the channel estimation unit 30 calculates the correlation between the complex symbol sequence for each mobile station 14 and the known signal generated by the known signal generation unit, and performs channel estimation of the fading fluctuation amount in each subchannel based on the calculation result. Get as a value. Channel estimation unit 30 then outputs the obtained channel estimation value of each subchannel to MAC unit 32. In this embodiment, the fading fluctuation amount is used as the channel estimation value. However, characteristic values (S / N ratio, interference wave level, etc.) other than the fading fluctuation amount may be used as the channel estimation value.

  The MAC unit 32 is configured by a DSP (Digital Signal Processor), for example, and controls the MAC layer. The MAC unit 32 functionally includes an error correction unit 34, an error detection unit 36, a scheduler 38, and a MAP generation unit 40.

  The error correction unit 34 performs error correction of data input from the demodulation unit 28 using a predetermined error correction algorithm. Here, if the data error is not completely corrected, the error is detected by the subsequent error detection unit 36.

  The error detection unit 36 determines whether or not the data input from the error correction unit 34 has an error, and notifies the scheduler 38 of the determination result. If no data error is detected, the error detection unit 36 outputs the data as received data to an upper layer (not shown). For example, CRC (Cyclic Redundancy Check) is used as an error detection method.

  The scheduler 38 determines uplink radio resource allocation and downlink radio resource allocation for each mobile station 14. In particular, when a data error is detected by the error detection unit 36, the scheduler 38 detects an error based on the state of each subchannel estimated by the channel estimation unit 30 (here, fading fluctuation amount in each subchannel). An uplink burst composed of slots belonging to subchannels in a better state than the initial transmission of other data is assigned to retransmission of detected data. For example, when the fading fluctuation amount in each subchannel is in the state shown in FIG. 4, the scheduler 38 has an upstream burst consisting of a slot belonging to a band whose fading fluctuation amount is smaller than a predetermined threshold, that is, either band B or band D. Is preferentially assigned to data retransmission. Thereby, the number of times of continuous retransmission of data by the mobile station 14 is reduced.

  When two or more data errors are detected by the error detection unit 36, the scheduler 38 sets the frequency interval of the uplink burst assigned to each retransmission of the two or more data in which errors are detected to a predetermined width (at least (Bandwidth for one subchannel) or more (see the shaded area in FIG. 5A). In this way, since the subchannels allocated to each of the retransmissions of two or more data in which errors are detected are not close to each other, the subchannel with low received power is not buried in the subchannel with high received power (see FIG. 6A). (See solid line). For this reason, even if the orthogonality is lost, it is difficult for an error to occur in retransmission data, and the number of continuous retransmissions of data by the mobile station 14 is further reduced.

  Conversely, if this is not done (see the shaded area in FIG. 5 (b)), the subchannels assigned to the retransmissions of two or more data in which errors are detected are close to each other. (See the solid line portion in FIG. 6B). In this case, if their orthogonality is lost, errors are likely to occur in the retransmission data.

  The MAP generation unit 40 generates UL-MAP indicating uplink radio resource allocation determined by the scheduler 38 and DL-MAP indicating downlink radio resource allocation determined by the scheduler 38, and generates the generated UL-MAP. The DL-MAP is output to the frame generation unit 44 via the modulation unit 42.

  The modulation unit 42 performs symbol mapping (assignment of amplitude and phase) to transmission data, UL-MAP, and DL-MAP addressed to each mobile station 14 input from the MAC unit 32, and obtains the obtained complex symbol sequence. The data is output to the frame generation unit 44.

  The frame generation unit 44 receives the transmission data addressed to each mobile station 14 input from the modulation unit 42, the complex symbol sequences corresponding to the UL-MAP and DL-MAP, and the downlink radio determined by the scheduler 38 of the MAC unit 32. Store in the downlink subframe according to resource allocation (see FIG. 2). Further, the frame generation unit 44 stores information for feeding back ACK or NAK to each mobile station 14 in a predetermined area of the downlink subframe, depending on whether or not data retransmission is necessary. The downlink subframes generated in this way are sequentially output to the baseband processing unit 24 for each OFDM symbol.

  Next, the operation of the base station 12 will be described. FIG. 7 is a flowchart showing an example of reception processing executed every frame in the base station 12.

  As shown in the figure, the base station 12 receives the radio signal transmitted from each mobile station 14 in the uplink subframe of the frame (S100). Next, the base station 12 estimates the state (fading fluctuation amount) of each subchannel based on the received radio signal from each mobile station 14 (S102), and transmits the radio signal from each mobile station 14 as well. By demodulating, data included in the wireless signal is acquired (S104). Then, the base station 12 performs error correction on the obtained data, and then performs a CRC check (S106), and determines whether there is an error in the data (S108).

  If no data error is detected (S108: N), the base station 12 outputs the data to the upper layer as received data (S110). On the other hand, when a data error is detected (S108: Y), the base station 12 determines the priority order for allocating radio resources (S112). Here, higher priority is given to retransmission of data in which an error is detected than to initial transmission of other data. Thereafter, the base station 12 performs a scheduling process according to the determined priority order (S120).

  FIG. 8 is a flowchart showing an example of the scheduling process of S120 in FIG. In S120, the base station 12 first identifies a subchannel whose fading fluctuation amount is equal to or less than a predetermined threshold based on the fading fluctuation amount of each subchannel estimated in S102 (S121).

  Next, the base station 12 selects a subchannel to be allocated to retransmission of data in which an error is detected in S108, from among subchannels whose fading fluctuation amount is equal to or less than a predetermined threshold (S122), and selects the selected subchannel. The uplink burst consisting of the slot to which it belongs is assigned to the retransmission of the data (S123). When two or more data errors are detected in S108, the base station 12 sets the frequency intervals of the uplink bursts assigned to the retransmissions of the two or more data in which errors are detected to a predetermined width (for example, 2 sub-channel bandwidth) or more.

  Thereafter, the base station 12 selects a subchannel to be allocated to the initial transmission of other data from the available subchannels (S124), and transmits an uplink burst composed of slots belonging to the selected subchannel to the other data. Assigned to the first transmission (S125).

  When the scheduling process of S120 ends, the base station 12 generates a UL-MAP based on the uplink burst assignment determined in S120, as shown in FIG. 7 (S130), and then generates the generated UL-MAP. By transmitting in the downlink subframe of the frame, the mobile station 14 that transmitted the data is requested to retransmit the data in which the error is detected (S132).

  According to the embodiment described above, since a subchannel having a better state than the initial transmission of other data is assigned to the retransmission of data, the number of continuous retransmissions of data by the mobile station 14 can be reduced. Thereby, it is possible to prevent a decrease in throughput due to an increase in the number of continuous retransmissions.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation implementation is possible. For example, the present invention is not limited to the base station 12 that performs radio communication with each of the plurality of mobile stations 14 according to the frame configuration illustrated in FIG. 2, but also the plurality of mobile stations via at least one of a plurality of frequency-divided subchannels The present invention can be widely applied to base stations that perform wireless communication with each.

1 is a configuration diagram of a mobile communication system according to an embodiment of the present invention. It is a figure which shows the frame structure of the mobile communication system which concerns on embodiment of this invention. It is a functional block diagram of the base station which concerns on embodiment of this invention. It is a figure which shows an example of a fading fluctuation amount. It is a figure which shows an example of UL-MAP. It is a figure which shows the example of subchannel allocation. It is a flowchart which shows an example of the reception process in the base station which concerns on embodiment of this invention. It is a flowchart which shows an example of the scheduling process of S120 in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Mobile communication system, 12 Base station, 14 Mobile station, 20 Antenna, 22 Wireless communication part, 24 Baseband process part, 26 Interference signal removal part, 28 Demodulation part, 30 Channel estimation part, 32 MAC part, 34 Error correction part 36 error detector, 38 scheduler, 40 MAP generator, 42 modulator, 44 frame generator.

Claims (4)

A base station apparatus that performs radio communication with each of a plurality of mobile station apparatuses via at least one of a plurality of frequency-divided subchannels,
Receiving means for receiving a radio signal transmitted from each mobile station device;
Channel estimation means for estimating the state of each subchannel based on a radio signal received by the reception means;
Error detecting means for detecting an error in data included in a radio signal received by the receiving means;
Scheduling means for allocating a subchannel having a better state than the initial transmission of other data to retransmission of data in which an error is detected by the error detecting means, based on the state of each subchannel estimated by the channel estimating means; ,
A base station apparatus comprising: The base station apparatus according to claim 1,
The base station device performs radio communication with each of a plurality of mobile station devices by an orthogonal frequency division multiple access method,
When the error detecting unit detects two or more data errors, the scheduling unit separates the frequency interval of the subchannel allocated to each retransmission of the two or more data in which the error is detected by a predetermined width or more. ,
A base station apparatus. In the base station apparatus according to claim 1 or 2,
The state of each subchannel is a fading fluctuation amount in each subchannel.
A base station apparatus. A base station apparatus scheduling method for performing wireless communication with each of a plurality of mobile station apparatuses via at least one of a plurality of frequency-divided subchannels,
Receiving a radio signal transmitted from each mobile station device;
Estimating a state of each subchannel based on the received radio signal;
Detecting an error in data included in the received radio signal;
Assigning subchannels in better condition than the initial transmission of other data to retransmission of data in which the error is detected based on the estimated state of each subchannel;
A scheduling method comprising:

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