JP2011049842A - Base station, and channel allocation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allocate a radio channel suitable for an MIMO method. <P>SOLUTION: This base station 12 includes: a transmission capacity estimation section 32 for selecting, as communication channel candidates, radio channels capable of forming, for each of the numbers of space streams formable between a mobile station corresponding to an MIMO method and itself, space streams of the number, and estimating the total transmission capacity of the communication channel candidates when the space streams of the number are formed; a stream number determination section 34 for determining the number of space streams formed between the mobile station and itself based on a result obtained by comparing the total transmission capacity of the communication channel candidates estimated by the transmission capacity estimation section 32; and a channel allocation section 36 for allocating, to the mobile station, all or part of the communication channel candidates selected for the number of space streams determined by the stream number determination section as communication channels. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a base station and a channel allocation method, and more particularly to a mobile communication system employing a MIMO (Multiple-Input Multiple-Output) scheme.

  2. Description of the Related Art Mobile communication systems are known that maintain or improve communication quality by determining or changing the position (frequency band, time slot, etc.) and number of radio channels that a base station allocates to mobile stations in accordance with radio wave conditions. .

  For example, in XGP (eXtended Global Platform) conforming to the standard described in Non-Patent Document 1, the base station assigns at least a part of a plurality of radio channels as communication channels to the mobile station, and then assigns the assigned radio channel to 1 It can be changed for each frame.

“ARIB STD-T95 Version 1.2“ OFDMA / TDMA TDD Broadband Wireless Access System (Next GenerationPHS) ””, March 18, 2009, Japan Radio Industry Association

  If a plurality of spatial streams are formed in a radio section between a base station and a mobile station using a MIMO scheme such as SM (Spatial Multiplexing) or SDM (Space Division Multiplexing), a radio channel is formed. The transmission capacity per hit can be increased.

  However, in the mobile communication system such as XGP, a method for assigning a radio channel to a mobile station corresponding to the MIMO scheme has not been established yet. In particular, in SM and SDM, it is not possible to form different numbers of spatial streams at the same time between a base station and a mobile station, and the characteristics of spatial streams formed on the same radio channel are all the same. It is desirable to assign a radio channel in consideration.

  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 and a channel allocation method capable of performing radio channel allocation suitable for the MIMO scheme.

  In order to solve the above-described problem, a base station according to the present invention is a base station that allocates at least a part of a plurality of radio channels as communication channels to a mobile station that supports the MIMO scheme. For each of the number of spatial streams that can be formed, a radio channel that can form the number of spatial streams is selected as a communication channel candidate, and the total transmission capacity of the communication channel candidates when the number of spatial streams is formed Transmission capacity estimation means for estimating the total transmission capacity of the communication channel candidates estimated for each of the number of spatial streams by the transmission capacity estimation means, and based on the comparison result, A stream number determining means for determining the number of spatial streams to be formed in between, and the stream number determining means Channel allocating means for allocating all or part of the communication channel candidates selected for the number of spatial streams to the mobile station as communication channels, the number of spatial streams determined by the stream number determining means, and the channel Means for notifying the mobile station of the communication channel assigned by the assigning means.

  According to the present invention, it is possible to assign a radio channel in consideration of a transmission capacity that increases in accordance with the number of spatial streams formed by the MIMO scheme. For this reason, it is possible to assign a radio channel suitable for the MIMO scheme.

  Also, in one aspect of the present invention, the base station associates the number of space streams with detection means for detecting a channel quality value representing the channel quality of each of the plurality of radio channels, and each of the plurality of spatial streams. Storage means for storing a threshold of channel quality required to form a stream, wherein the transmission capacity estimation means includes channel quality values for each of the plurality of radio channels detected by the detection means, and the storage The communication channel candidates may be selected for each of the number of spatial streams based on the comparison result with the threshold value stored in the means.

  Also, in one aspect of the present invention, the transmission capacity estimation unit may determine each of the communication channel candidates when the number of spatial streams is formed for each number of spatial streams that can be formed with the mobile station. May be determined, and the total transmission capacity of the communication channel candidates when the number of spatial streams is formed may be estimated based on the determination result.

  According to this aspect, it is possible to more accurately estimate the transmission capacity that increases in accordance with the number of spatial streams formed by the MIMO scheme.

  In the aspect of the invention, each of the plurality of radio channels may include one of a plurality of subchannels defined in a predetermined frequency band and a plurality of time slots defined in a frame having a predetermined time width. Any of the above, the selection of communication channel candidates by the transmission capacity estimation means, the estimation of the total transmission capacity of the communication channel candidates, the determination of the number of spatial streams by the number of stream determination means, and the communication channel by the channel allocation means May be performed for each time slot.

  According to this aspect, it is possible to improve the use efficiency of radio resources as compared to the case where the same number of spatial streams are uniformly formed in a plurality of time slots.

  In one aspect of the present invention, the type of the MIMO scheme may be SM or SDM.

  Further, the channel allocation method according to the present invention is a channel allocation method of a base station that allocates at least a part of a plurality of radio channels as communication channels to a mobile station compatible with the MIMO scheme. For each of the number of spatial streams that can be formed, radio channels that can form the number of spatial streams are selected as communication channel candidates, and the total transmission capacity of the communication channel candidates when the number of spatial streams is formed is The total transmission capacity of the communication channel candidates estimated for each of the number of spatial streams in the transmission capacity estimation step and the estimated transmission capacity estimation step are compared with each other based on the comparison result. Stream number determining step for determining the number of spatial streams to be formed, and the number of streams A channel assignment step of assigning all or part of the communication channel candidates selected for the number of spatial streams determined in the determination step to the mobile station as communication channels, and the number of spatial streams determined in the number of streams determination step And a step of notifying the mobile station of the communication channel assigned in the channel assignment step.

It is a figure which shows the structure of the mobile communication system which concerns on embodiment of this invention. It is a figure which shows the radio channel structure in the mobile communication system which concerns on this embodiment. It is a functional block diagram of the base station which concerns on this embodiment. It is an example of the table which shows the correspondence of the number of spatial streams, and the threshold value of channel quality. It is a figure which shows an example of the communication channel candidate elected about the number of 1 spatial streams, and its total transmission capacity (total number of PRUs). It is a figure which shows an example of the communication channel candidate elected about the number of spatial streams 2, and its total transmission capacity (total number of PRUs). It is a figure which shows an example of the communication channel candidate elected about the number of spatial streams 4, and its total transmission capacity (total number of PRUs). It is a figure which shows an example of the communication channel candidate elected for every time slot about the number of spatial streams, and its total transmission capacity (total number of PRUs). It is a figure which shows an example of the communication channel candidate elected for every time slot about the number of spatial streams, and its total transmission capacity (total number of PRUs). It is a figure which shows an example of the communication channel candidate elected for every time slot about the number of spatial streams, and its total transmission capacity (total number of PRUs). FIG. 7 is a diagram showing communication channels assigned to mobile stations in the examples shown in FIGS. 6A to 6C. It is a figure which shows an example of the communication channel candidate elected about the number 1 of spatial streams, and its total transmission capacity (total number of PRUs). It is a figure which shows an example of the communication channel candidate elected about the number 2 of spatial streams, and its total transmission capacity (total number of PRUs). FIG. 9A is a diagram illustrating a total transmission capacity (total transmission rate) of communication channel candidates in consideration of a modulation scheme applicable to each communication channel candidate in the example illustrated in FIGS. 8A and 8B. It is a flowchart which shows an example of the channel allocation process which concerns on this embodiment.

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

  FIG. 1 is a diagram showing a configuration of a mobile communication system 10 according to an embodiment of the present invention. As shown in FIG. 1, 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 performs a plurality of movements using an OFDMA (Orthogonal Frequency Division Multiple Access) method and a TDMA / TDD (Time Division Multiple Access / Time Division Duplex) method. Multiplex communication with the station 14 is performed.

  FIG. 2 is a diagram showing a radio channel configuration in the mobile communication system 10. As shown in the figure, in the mobile communication system 10, a TDMA frame having a predetermined time width (here, 5 ms) is divided into an upstream subframe (2.5 ms) and a downstream subframe (2.5 ms). Each frame is equally divided into a plurality of time slots (here, Slot 1 to Slot 4). A plurality of OFDMA subchannels (here, Sch1 to Sch18) are defined in a predetermined frequency band. The minimum unit of the radio channel that the base station 12 allocates to the mobile station 14 is called a PRU (Physical Resource Unit), and each PRU is either one of time slots (Slot 1 to Slot 4) and one of subchannels (Sch 1 to Sch 18). , Belonging to. All 72 PRUs are defined to be identified by consecutive PRU numbers (1, 2, 3,..., 72) starting from 1.

  Of these 72 PRUs, four PRUs (PRU1 to PRU4) belonging to a specific subchannel (here, Sch1) are used as a CCH (Common Channel) shared by one or more mobile stations 14. . On the other hand, the other 68 PRUs (PRU5 to PRU72) are used as ICH (Individual Channel) individually assigned to each mobile station 14. In principle, one ICH is assigned to each mobile station 14 and is mainly used for transmission of control information, and one or more communication channels are assigned to each mobile station 14 and are mainly used for transmission of communication data. EXCH (Extra Channel) or the like. Note that the base station 12 can change the PRU (particularly EXCH) assigned to the mobile station 14 as ICH for each frame.

  Further, at least a part of the mobile station 14 and the base station 12 are each provided with a plurality of antenna elements, and by forming a plurality of spatial streams for each PRU using the MIMO scheme (SM or SDM), the PRU The transmission capacity per hit can be increased. In this SM or SDM, different numbers of spatial streams cannot be formed simultaneously between the base station 12 and the mobile station 14, the characteristics of the spatial streams formed on the same radio channel are all the same, etc. There are features.

  In the mobile communication system 10, when the base station 12 allocates a communication channel to the mobile station 14 compatible with the MIMO scheme, the transmission increases according to the number of spatial streams formed between the base station 12 and the mobile station 14. Capacity is taken into account.

  For example, when the base station 12 assigns a communication channel to the mobile station 14 corresponding to the MIMO scheme (up to four spatial streams), the number of spatial streams (1, 2, 4) that can be formed with the mobile station 14 is allocated. ) Are selected as communication channel candidates for PRUs that can form that number of spatial streams. Specifically, it can be assigned to the mobile station 14 when the number of spatial streams is 1, based on the availability of PRU, the amount of data transmitted / received to / from the mobile station 14, the radio quality of each PRU, and the like. A communication channel candidate A, a communication channel candidate B that can be assigned to the mobile station 14 when the number of spatial streams is 2, a communication channel candidate C that can be assigned to the mobile station 14 when the number of spatial streams is 4, Is elected.

  Next, the base station 12 estimates the total transmission capacity of the selected communication channel candidates A to C. For example, a value obtained by multiplying the number of PRUs included in the communication channel candidate A by the number of spatial streams 1 is estimated as the total transmission capacity of the communication channel candidate A. Similarly, the value obtained by multiplying the number of PRUs included in communication channel candidate B by the number of spatial streams 2 is used as the total transmission capacity of communication channel candidate B, and the number of PRUs included in communication channel candidate C is multiplied by the number of spatial streams 4. Is estimated as the total transmission capacity of the communication channel candidate C.

  Then, the base station 12 compares the estimated total transmission capacities of the communication channel candidates A to C, and determines the number of spatial streams formed with the mobile station 14 based on the comparison result. For example, if the total transmission capacity of the communication channel candidate B is the largest among the three communication channel candidates, the number of spatial streams formed with the mobile station 14 is two. Further, the base station 12 assigns the communication channel candidate B (or part thereof) corresponding to the determined number of spatial streams 2 to the mobile station 14 as a communication channel.

  Thus, in the mobile communication system 10, the base station 12 allocates a communication channel to the mobile station 14 in consideration of the transmission capacity that increases in accordance with the number of spatial streams.

  Below, the structure with which the base station 12 is provided in order to implement | achieve the said process is demonstrated concretely.

  FIG. 3 is a functional block diagram of the base station 12. As shown in FIG. 3, the base station 12 includes a plurality of antenna elements 20 (here, antenna elements 20-1 to 20-4), a radio communication unit 22, a baseband unit 24, a signal processing unit 26, and a control unit 28 ( A line quality detection unit 30, a transmission capacity estimation unit 32, a stream number determination unit 34, a channel allocation unit 36, a channel notification unit 38), and a storage unit 40 are configured.

  The antenna elements 20-1 to 20-4 receive a radio signal from the mobile station 14 and output the received radio signal to the radio communication unit 22. Further, the antenna elements 20-1 to 20-4 transmit 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 converter, a band pass filter, an A / D converter, and a D / A converter. The radio communication unit 22 amplifies the radio signals input from the antenna elements 20-1 to 20-4 with a low noise amplifier, then down-converts the radio signals to an intermediate frequency signal, converts the signal to a digital signal, and then converts the signal to a baseband unit. 24. The radio communication unit 22 converts the digital signal input from the baseband unit 24 into an analog signal, then up-converts the signal to a radio signal, amplifies the signal to a transmission output level with a power amplifier, and then transmits the antenna element 20-1. To ~ 20-4.

  The baseband 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 unit 24 performs GI (Guard Interval) removal, serial parallel conversion, discrete Fourier transform, and the like on the digital signal input from the wireless communication unit 22 and outputs the obtained complex symbol sequence to the signal processing unit 26. To do. The baseband unit 24 also performs inverse discrete Fourier transform, parallel-serial conversion, GI addition, and the like on the complex symbol sequence input from the signal processing unit 26 and outputs the obtained digital signal to the wireless communication unit 22. .

  The signal processing unit 26 performs separation, demodulation, decoding, error detection, and the like on the complex symbol sequence input from the baseband unit 24 into signal components corresponding to each spatial stream, and controls the obtained reception data To the unit 28. Further, the signal processing unit 26 obtains the transmission data input from the control unit 28 to the mobile station 14 by adding an error detection code, encoding, modulation, signal distribution to each spatial stream, and the like. The complex symbol sequence is output to the baseband unit 24.

  The control unit 28 includes, for example, a CPU and a program that controls the operation of the CPU, and controls each unit of the base station 12. In particular, the control unit 28 functionally includes a channel quality detection unit 30, a transmission capacity estimation unit 32, a stream number determination unit 34, a channel allocation unit 36, and a channel notification unit 38, and is formed between the mobile station 14. Determination of the number of spatial streams, determination of PRU to be allocated to the mobile station 14, notification of the determined number of spatial streams and PRU, and the like are performed.

  The line quality detection unit 30 detects a line quality value representing the line quality of each PRU. As the channel quality value of each PRU, for example, RSSI (Received Signal Strength Indication) detected by carrier sense (jamming wave measurement) or SNR (Signal to Noise Ratio) is used. Can do.

  When the mobile station 14 is compatible with the MIMO scheme, the transmission capacity estimation unit 32, for each of the number of spatial streams that can be formed with the mobile station 14, is the PRU that can form that number of spatial streams. Are selected as communication channel candidates, and the total transmission capacity of the communication channel candidates when the number of spatial streams is formed is estimated. The number of streams to which the mobile station 14 is compatible with the MIMO scheme is identified by, for example, the protocol version number notified from the mobile station 14 at the start of communication. In SM and SDM, the upper limit of the number of spatial streams that can be formed between the base station 12 and the mobile station 14 depends on the number of antenna elements provided in each.

  Here, assuming that the number of spatial streams that can be formed with the mobile station 14 is 1, 2 or 4, the transmission capacity estimation unit 32 moves when the number of spatial streams is 1, 2, 4. PRUs that can be assigned to the station 14 are selected as communication channel candidates. Selection of these communication channel candidates includes, for example, the availability of the PRU channel, the amount of data transmitted / received to / from the mobile station 14, the communication type (voice communication, data communication, etc.), the contract information of the mobile station 14 (the movement thereof) Based on at least one of information relating to the upper limit number of radio channels that can be allocated to the station 14), radio quality of each PRU, and the like.

  In particular, the selection of communication channel candidates when the number of spatial streams is two or more is determined by selecting the channel quality value of each PRU detected by the channel quality detection unit 30 and the channel quality threshold value stored in the storage unit 40 (FIG. 4). And the reference result). Of course, the selection of communication channel candidates when the number of spatial streams is two or more may be further based on other indices.

  FIG. 4 is an example of a table showing a correspondence relationship between a plurality of spatial streams (here, 1, 2, and 4) and a threshold of channel quality required to form each number of spatial streams. Here, when the channel quality value of each PRU detected by the channel quality detection unit 30 is RSSI (the channel quality is higher as the RSSI is lower), the transmission capacity estimation unit 32 sets the PRU whose RSSI is less than γ to 4 It is determined that the PRU is capable of forming one spatial stream, the PRU having an RSSI of γ or more and less than β is determined to be a PRU capable of forming two spatial streams, and the PRU having an RSSI of β or more and less than α is 1 It is determined that the PRU is capable of forming two spatial streams (that is, the MIMO scheme cannot be applied) (in this case, α> β> γ). On the other hand, when the channel quality value of each PRU detected by the channel quality detection unit 30 is an SNR (the higher the SNR, the higher the channel quality), the transmission capacity estimation unit 32 selects four PRUs having an SNR of γ or more. It is determined that the PRU is capable of forming a spatial stream, a PRU having an SNR of β or more and less than γ is determined to be a PRU capable of forming two spatial streams, and one PRU having an SNR of α or more and less than β It is determined that the PRU is capable of forming a spatial stream (that is, the MIMO scheme cannot be applied) (in this case, α <β <γ).

  5A, FIG. 5B, and FIG. 5C are examples of communication channel candidates for user A's mobile station 14 selected for each of the number of spatial streams (1, 2, 4) and their total transmission capacity (total number of PRUs). FIG. In the example shown in the figure, the number of PRUs of communication channel candidates when the number of spatial streams is 1, 2, and 4 is 17 PRU, 9 PRU, and 4 PRU, respectively (see the bold frame). In comparison with the number of PRUs, among the three communication channel candidates, the number of PRUs (17 PRUs) of communication channel candidates when the number of spatial streams is 1 is the largest.

  However, the transmission capacity estimation unit 32 does not simply estimate the total transmission capacity of each communication channel candidate only by the number of PRUs, but based on the transmission capacity that increases according to the number of spatial streams formed in each PRU, Estimate the total transmission capacity of each communication channel candidate.

  For example, as shown in FIGS. 5A to 5C, the transmission capacity estimation unit 32 estimates a value (total number of PRUs) obtained by multiplying the number of PRUs by the number of spatial streams as the total transmission capacity of communication channel candidates. In the example shown in the figure, the total transmission capacities of communication channel candidates when the number of spatial streams is 1, 2, 4 are 17 PRU (17 PRU × 1), 18 PRU (9 PRU × 2), and 16 PRU (4 PRU × 4), respectively. It becomes. For this reason, when compared with the total number of PRUs, among the three communication channel candidates, the total transmission capacity (18 PRU) of the communication channel candidates when the number of spatial streams is 2 is maximized.

  The number-of-streams determination unit 34 compares the total transmission capacities of the communication channel candidates estimated for each of the number of spatial streams by the transmission capacity estimation unit 32, and forms between the mobile station 14 based on the comparison result. Determine the number of spatial streams.

  For example, in the example illustrated in FIGS. 5A to 5C, the stream number determination unit 34 may calculate the number of spatial streams that form the maximum total transmission capacity (total number of PRUs) 2 with the mobile station 14 as the number of spatial streams. Good. However, as in the example shown in the figure, when there is not much difference between the total transmission capacities of the respective communication channel candidates (for example, when the difference between the total transmission capacities is equal to or less than a predetermined value), the PRU occupancy is minimum. The number of spatial streams 4 may be the number of spatial streams assigned to the mobile station 14. By doing so, it is possible to achieve both improvement in communication throughput of the mobile station 14 and improvement in the number of users accommodated in the base station 12.

  The channel allocation unit 36 allocates all or part of the communication channel candidates selected for the number of spatial streams determined by the stream number determination unit 34 to the mobile station 14.

  For example, in the example shown in FIGS. 5A to 5C, when the number-of-streams determination unit 34 determines that the number of spatial streams 2 is to be allocated to the mobile station 14, the channel allocation unit 36 sets the number of spatial streams to 2 Communication channel candidates (see the thick line frame in FIG. 5B) are determined as PRUs to be assigned to the mobile station 14.

  The channel notification unit 38 notifies the mobile station 14 of the number of spatial streams determined by the stream number determination unit 34 and the communication channel allocated to the mobile station 14 by the channel allocation unit 36. That is, the channel notification unit 38 generates a channel notification message of a predetermined format including the number of spatial streams determined by the stream number determination unit 34 and the PRU allocated to the mobile station 14 as a communication channel by the channel allocation unit 36. Then, the channel notification message is notified to the mobile station 14 by outputting to the signal processing unit 26.

  5A to 5C show an example in which the number of spatial streams formed between the base station 12 and the mobile station 14 is uniformly determined without distinction of time slots. Selection, estimation of the total transmission capacity of communication channel candidates, determination of the number of spatial streams, and allocation of communication channels may be performed for each time slot. In the mobile communication system 10 employing SM or SDM, different numbers of spatial streams cannot be formed simultaneously between the base station 12 and the mobile station 14, but the number of spatial streams can be changed for each time slot. (For example, it is possible to set the number of spatial streams in Slot 1 to 2 and the number of spatial streams in Slot 2 to 4).

  6A, 6B, and 6C show communication channel candidates for the mobile station 14 of user A selected for each time slot for each of the number of spatial streams (1, 2, 4) and their total transmission capacity (total number of PRUs). It is a figure which shows an example. In the example shown in the figure, the number of PRUs of communication channel candidates in Slot 1 when the number of spatial streams is 1, 2, and 4 is 6 PRU, 6 PRU, and 4 PRU, respectively (see the bold line frame in Slot 1). Comparing by the number of PRUs, among the three communication channel candidates, the number of PRUs (4 PRU) of communication channel candidates in Slot 1 when the number of spatial streams is 4 is the smallest.

  However, as in FIGS. 5A to 5C, if the total transmission capacity of communication channel candidates in Slot 1 is estimated by multiplying the number of PRUs by the number of spatial streams (total number of PRUs), in the example shown in FIGS. 6A to 6C, When the number of spatial streams is 1, 2, and 4, the total transmission capacity of communication channel candidates in Slot 1 is 6 PRU (6 PRU × 1), 12 PRU (6 PRU × 2), and 16 PRU (4 PRU × 4), respectively. For this reason, when compared with the total number of PRUs, among the three communication channel candidates in Slot 1, the total transmission capacity (16 PRU) of the communication channel candidates when the number of spatial streams is 4 is the maximum.

  Similarly, when comparing the total number of PRUs in other time slots, the total transmission capacity (12 PRU) of communication channel candidates when the number of spatial streams is 2 in Slot 2 is the communication channel when the number of spatial streams is 2 in Slot 3 The total transmission capacity (6PRU) of the candidate is the maximum when the number of spatial streams is 1 in Slot 4 and the total transmission capacity (4PRU) of the candidate communication channel is maximum.

  For this reason, in the example shown in FIGS. 6A to 6C, the number of spatial streams formed between the mobile station 14 and the stream number determination unit 34 is 4, 2, 2, 1 in Slots 1, 2, 3, and 4, respectively. If the channel assignment unit 36 assigns the communication channel candidates when the number of spatial streams is 4, 2, 2, 1 to the mobile station 14 as communication channels, the total transmission of communication channels assigned to the mobile station 14 The capacity is 38 PRUs in terms of the total number of PRUs (see FIG. 7). This is larger than the total transmission capacity 32 PRU (total PRU number conversion, see FIG. 6B) when the number of spatial streams formed between the base station 12 and the mobile station 14 is uniformly 2 without distinction of time slots.

  As described above, if the base station 12 selects a communication channel candidate, estimates the total transmission capacity of the communication channel candidate, determines the number of spatial streams, and assigns a communication channel for each time slot, the base station 12 assigns a plurality of time slots. Compared with the case where the same number of spatial streams are uniformly formed, the utilization efficiency of radio resources can be improved.

  5A to 5C and FIGS. 6A to 6C show examples in which the total number of PRUs is regarded as the total transmission capacity of communication channel candidates. However, the total transmission considering the modulation scheme applicable to each of the communication channel candidates is shown. The rate may be regarded as the total transmission capacity of the communication channel candidates.

  8A and 8B are diagrams illustrating examples of communication channel candidates selected for each of the number of spatial streams (1, 2) and their total transmission capacity (total number of PRUs). In the example shown in the figure, the number of PRUs of communication channel candidates when the number of spatial streams is 1 and 2 is 4 PRU and 1 PRU, respectively (see the thick line frame), and the total transmission capacity is 4 PRUs in terms of the total number of PRUs. (4PRU × 1), 2PRU (1PRU × 2).

  On the other hand, FIG. 9 is a diagram showing the total transmission capacity (total transmission rate) of communication channel candidates in consideration of the modulation scheme applicable to each communication channel candidate in the examples shown in FIGS. 8A and 8B. In the mobile communication system 10 that employs SM or SDM, the characteristics of the spatial streams formed in the same PRU are all the same, so that the modulation schemes applied to the spatial streams formed in the same PRU are usually all the same. .

  The modulation scheme applicable to each PRU when the number of spatial streams is 1 is BPSK, and the modulation scheme applicable to each PRU when the number of spatial streams is 2 is also BPSK (see the left column in FIG. 9). ), The total transmission capacity of communication channel candidates when the number of spatial streams is 1 is 4 (bit / symbol), and the total transmission capacity of communication channel candidates when the number of spatial streams is 2 is 2 (bit / symbol). Become. In this case, the total transmission capacity increases when the number of spatial streams is 1.

  When the number of spatial streams is 1, the modulation scheme applicable to each PRU is BPSK, and when the number of spatial streams is 2, the modulation scheme applicable to each PRU is QPSK (see the middle column in FIG. 9). ), The total transmission capacity of communication channel candidates when the number of spatial streams is 1 is 4 (bit / symbol), and the total transmission capacity of communication channel candidates when the number of spatial streams is 2 is 4 (bit / symbol). Become. In this case, since there is no difference in the total transmission capacity, it is preferable to set the number of spatial streams to 2, for example, so that the PRU occupancy rate becomes smaller.

  The modulation scheme applicable to each PRU when the number of spatial streams is 1 is BPSK, and the modulation scheme applicable to each PRU when the number of spatial streams is 2 is 64QAM (see the right column in FIG. 9). ), The total transmission capacity of communication channel candidates when the number of spatial streams is 1 is 4 (bit / symbol), and the total transmission capacity of communication channel candidates when the number of spatial streams is 2 is 12 (bit / symbol). Become. In this case, the total transmission capacity increases when the number of spatial streams is two.

  Thus, if the total transmission capacity of communication channel candidates is estimated based on the modulation scheme applicable to each PRU, the transmission capacity that increases according to the number of spatial streams formed by the MIMO scheme can be estimated more accurately. be able to.

  The storage unit 40 is composed of, for example, a semiconductor memory element, and stores a program executed by the control unit 28, a table shown in FIG.

  Next, the operation of the base station 12 will be described.

  FIG. 10 is a flowchart showing an example of channel assignment processing executed by the base station 12. This process is executed for each frame, for example. Here, it is assumed that the number of spatial streams that can be formed with the mobile station 14 is 1, 2 or 4.

  As shown in FIG. 10, the base station 12 detects the channel quality value (RSSI, SNR, etc.) of each PRU (S100). Based on the comparison result between the detected channel quality value of each PRU and the channel quality threshold value stored in the storage unit (see FIG. 4), the base station 12 Communication channel candidates to the mobile station 14 are selected for each (S102).

  Here, when there are communication channel candidates for two or more spatial streams (S104: Y), the base station 12 considers the total number of PRUs and the total transmission rate as the total transmission capacity, for example, and selects the selected communication channel candidate. Are estimated (S106). Then, the base station 12 determines the number of spatial streams to be formed with the mobile station 14 based on the comparison result of the estimated total transmission capacity (S108). For example, the base station 12 may set the number of spatial streams with the maximum estimated total transmission capacity as the number of spatial streams formed with the mobile station 14.

  On the other hand, when there are no communication channel candidates for two or more spatial streams (S104: N), the base station 12 determines the number of spatial streams formed with the mobile station 14 as 1 (S110). That is, the base station 12 determines not to apply the MIMO scheme to the communication with the mobile station 14.

  When the number of spatial streams is determined in S108 or S110, the base station 12 assigns all or part of the communication channel candidates selected for the determined number of spatial streams to the mobile station 14 as communication channels (S112). . Then, the base station 12 notifies the mobile station 14 of the number of spatial streams determined in S108 or S110 and the PRU assigned as a communication channel in S112 (S114).

  Note that the base station 12 may perform the processes from S102 to S112 in a plurality of time slots at once or may be performed separately for each time slot.

  According to the mobile communication system 10 described above, the base station 12 can allocate a communication channel to the mobile station 14 in consideration of a transmission capacity that increases in accordance with the number of spatial streams formed by the MIMO scheme.

  The present invention is not limited to the above embodiment.

  For example, the present invention is not limited to a base station using both the TDMA scheme and the OFDMA scheme, and can be widely applied to a base station that allocates at least a part of a plurality of radio channels to mobile stations that support the MIMO scheme. In the MIMO scheme here, SM and SDM cannot be formed at the same time with different numbers of spatial streams between the base station and the mobile station, and the characteristics of the spatial streams formed on the same radio channel are all the same. Any type that has similar characteristics to the above may be used.

  DESCRIPTION OF SYMBOLS 10 Mobile communication system, 12 Base station, 14 Mobile station, 20 Antenna element, 22 Wireless communication part, 24 Baseband part, 26 Signal processing part, 28 Control part, 30 Channel quality detection part, 32 Transmission capacity estimation part, 34 Stream Number determination unit, 36 channel allocation unit, 38 channel notification unit, 40 storage unit.

Claims (6)

A base station that allocates at least a part of a plurality of radio channels as communication channels to a mobile station that supports the MIMO scheme,
For each of the number of spatial streams that can be formed with the mobile station, a radio channel that can form the number of spatial streams is selected as a communication channel candidate, and the communication when the number of spatial streams is formed is selected. Transmission capacity estimation means for estimating the total transmission capacity of channel candidates;
The total transmission capacity of the communication channel candidates estimated for each of the number of spatial streams by the transmission capacity estimation means is compared, and based on the comparison result, the number of spatial streams formed with the mobile station is determined. A means for determining the number of streams to be determined;
Channel allocating means for allocating all or part of the communication channel candidates selected for the number of spatial streams determined by the stream number determining means to the mobile station as a communication channel;
Means for notifying the mobile station of the number of spatial streams determined by the stream number determining means and the communication channel allocated by the channel allocating means;
A base station comprising: In the base station according to claim 1,
Detecting means for detecting a line quality value representing the line quality of each of the plurality of radio channels;
Storage means for storing a line quality threshold required to form the number of spatial streams in association with each of a plurality of spatial streams;
Further including
The transmission capacity estimation unit is configured to determine the number of spatial streams based on a comparison result between a channel quality value of each of the plurality of radio channels detected by the detection unit and a threshold value stored in the storage unit. Selecting the communication channel candidates;
A base station characterized by that. In the base station according to claim 1 or 2,
The transmission capacity estimation means determines, for each of the number of spatial streams that can be formed with the mobile station, a modulation scheme applicable to each of the communication channel candidates when the number of spatial streams is formed. In addition, based on the determination result, the total transmission capacity of the communication channel candidates when the number of spatial streams is formed is estimated.
A base station characterized by that. In the base station according to any one of claims 1 to 3,
Each of the plurality of radio channels belongs to one of a plurality of subchannels defined in a predetermined frequency band and one of a plurality of time slots defined in a frame having a predetermined time width,
Selection of communication channel candidates and estimation of the total transmission capacity of communication channel candidates by the transmission capacity estimation means, determination of the number of spatial streams by the stream number determination means, and allocation of communication channels by the channel allocation means For each slot,
A base station characterized by that. In the base station according to any one of claims 1 to 4,
The type of the MIMO scheme is SM or SDM.
A base station characterized by that. A channel allocation method of a base station that allocates at least part of a plurality of radio channels as a communication channel to a mobile station compatible with the MIMO scheme,
For each of the number of spatial streams that can be formed with the mobile station, a radio channel that can form the number of spatial streams is selected as a communication channel candidate, and the communication when the number of spatial streams is formed is selected. A transmission capacity estimation step for estimating a total transmission capacity of channel candidates;
The total transmission capacity of the communication channel candidates estimated for each of the number of spatial streams in the transmission capacity estimation step is compared, and based on the comparison result, the number of spatial streams formed with the mobile station is determined. Determining the number of streams to be determined;
A channel assignment step of assigning all or part of the communication channel candidates selected for the number of spatial streams determined in the stream number determination step to the mobile station as a communication channel;
Notifying the mobile station of the number of spatial streams determined in the stream number determining step and the communication channel allocated in the channel allocation step;
A channel assignment method comprising:

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