JP2014232991A - Communication system, base station, and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system, a base station, and a communication control method that speed up communication by securing the bandwidth of carriers in a communication system such as TD-LTE, and can prevent radio wave interference with another system by keeping the carriers within a frequency band (for example, a 9 MHz band) allocated to the communication system.SOLUTION: A communication system 1 comprises a plurality of base stations that perform radio communication by arranging a plurality of carriers in a second frequency band in which the bandwidth of the carries will exceed the bandwidth of the predefined second frequency band when the carriers with first frequency bandwidth are arranged consecutively. The communication system 1 arranges the carriers by overlapping part of the carriers in the second frequency band. A first base station 10a using one carrier A of carriers part of which are overlapped and arranged, and a second base station 10b using the other carrier B control radio resource allocation in the overlapped part on the basis of the MCS of a mobile station.

Description

  The present invention relates to a communication system, a base station, and a communication control method.

  For example, in a TD-LTE communication method, a carrier wave used for transmission can have a frequency bandwidth (hereinafter referred to as a bandwidth) of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, and 20 MHz (non-bandwidth). Patent Documents 1 and 2). The number of resource blocks (RB) included in each bandwidth is 6 RB, 15 RB, 25 RB, 50 RB, and 100 RB, respectively, and the communication speed increases as the bandwidth increases. However, since it is not possible to share the frequency band allocated for other current communication methods (digital cordless telephone etc.), an appropriate bandwidth is set within the range of the available frequency band.

3GPP TS 36.101 Ver. 9.0.0 “LTE; Evolved Universal Terrestrial Radio Access (U-UTRA); User Equipment (UE) radio transmission and reception” 3GPP TS 36.211 Ver. 9.0.0 “LTE; Evolved Universal Terrestrial Radio Access (U-UTRA); Physical channels and modulation”

  An area having a bandwidth of 9 MHz (hereinafter referred to as 9 MHz band or second frequency band) from 1884.5 MHz to 1893.5 MHz is allocated as the frequency band of the public PHS. For example, when a TD-LTE communication method is used in the 9 MHz band, the carrier bandwidth is set to 5 MHz (hereinafter also referred to as a first frequency bandwidth) so as to be within the bandwidth of 9 MHz, and one carrier is arranged. Conceivable. However, if the bandwidth is 5 MHz, the communication speed will be lower than when the bandwidth is 10 MHz. Moreover, since only the bandwidth of 9 MHz, which is the bandwidth, is used for communication, the use efficiency of communication resources is deteriorated.

  On the other hand, if two 5 MHz carriers are continuously arranged in the 9 HMz band, the bandwidth exceeds 9 MHz, and it protrudes into the band of another adjacent system (digital cordless telephone band). More specifically, although the effective band occupied when two carriers of 5 MHz (effective band is 4.5 MHz) are continuously arranged is 9 MHz, the leaked power protrudes into the frequency band of the digital cordless telephone, Radio interference will occur.

  Accordingly, an object of the present invention made in view of the above-described problems is to secure a carrier bandwidth in a communication system such as TD-LTE so as to increase communication speed and to be assigned to the communication system. Another object of the present invention is to provide a communication system, a base station, and a communication control method that can prevent a radio wave interference with other systems by placing a carrier in a frequency band (for example, 9 MHz band).

In order to solve the above problems, a communication system according to the present invention provides:
A plurality of bases that perform radio communication by arranging a plurality of the carriers in the second frequency band that exceeds the bandwidth of the second frequency band defined in advance when the carriers of the first frequency bandwidth are continuously arranged. A communication system comprising a station,
The communication system is arranged by overlapping a part of each carrier in the second frequency band,
The first base station that uses one of the carriers that is partially overlapped and the second base station that uses the other carrier allocate radio resources in the overlapping portion based on the MCS of the mobile station. It is characterized by controlling.

Moreover, the communication system according to the present invention includes:
When the MCS of the mobile station connected to the first base station and the second base station is equal to or greater than a predetermined first threshold, the first base station and the second base station allocate the overlapping portion of radio resources to the mobile station. It is characterized by lowering the priority.

Moreover, the communication system according to the present invention includes:
Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is less than a predetermined second threshold The first base station does not transmit user data, and the second base station transmits a reference signal.

Moreover, the communication system according to the present invention includes:
Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is equal to or greater than a predetermined second threshold The first base station transmits user data, and the second base station does not transmit a reference signal.

Further, the base station according to the present invention is:
A plurality of bases that perform radio communication by arranging a plurality of the carriers in the second frequency band that exceeds the bandwidth of the second frequency band defined in advance when the carriers of the first frequency bandwidth are continuously arranged. A base station in a communication system comprising a station,
In the second frequency band, a part of each carrier is arranged in an overlapping manner, and one carrier in which the part is arranged in an overlapping manner is used,
The radio resource allocation in the overlapping part is controlled based on the MCS of the mobile station.

Further, the base station according to the present invention is:
When the MCS of the mobile station connected to the local station is equal to or greater than a predetermined first threshold, the priority for allocating the overlapping radio resources to the mobile station is lowered.

Further, the base station according to the present invention is:
In the radio resource in which the reference signal of the other base station using the other carrier and the user data of the own station collide,
When the MCS of the mobile station connected to the local station is equal to or greater than a predetermined second threshold, user data is transmitted,
When the MCS of the mobile station connected to the own station is less than a predetermined second threshold, user data is not transmitted.

Further, the base station according to the present invention is:
In radio resources where user data of another base station using the other carrier collides with the reference signal of the own station,
If the MCS of the mobile station connected to the other base station is equal to or greater than a predetermined second threshold, the reference signal is not transmitted,
A reference signal is transmitted when the MCS of the mobile station connected to the other base station is less than a predetermined second threshold.

Further, the communication control method according to the present invention includes:
A plurality of bases that perform radio communication by arranging a plurality of the carriers in the second frequency band that exceeds the bandwidth of the second frequency band defined in advance when the carriers of the first frequency bandwidth are continuously arranged. A communication control method of a communication system including a station,
The communication system is arranged by overlapping a part of each carrier in the second frequency band,
The first base station that uses one of the carriers that is partially overlapped and the second base station that uses the other carrier allocate radio resources in the overlapping portion based on the MCS of the mobile station. It is characterized by controlling.

Further, the communication control method according to the present invention includes:
When the MCS of the mobile station connected to the first base station and the second base station is equal to or greater than a predetermined first threshold, the first base station and the second base station allocate the overlapping portion of radio resources to the mobile station. It is characterized by lowering the priority.

Further, the communication control method according to the present invention includes:
Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is less than a predetermined second threshold The first base station does not transmit user data, and the second base station transmits a reference signal.

Further, the communication control method according to the present invention includes:
Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is equal to or greater than a predetermined second threshold The first base station transmits user data, and the second base station does not transmit a reference signal.

  According to the communication system, base station, and communication control method of the present invention, in a communication system such as TD-LTE, the carrier bandwidth is ensured to increase the communication speed, and the frequency allocated to the communication system It is possible to prevent radio wave interference with other systems by placing the carrier in the band (for example, 9 MHz band).

1 is a schematic diagram of a communication system according to Embodiment 1 of the present invention. It is a block diagram of the base station which concerns on Embodiment 1 of this invention. FIG. 2 is a block diagram of a mobile station according to Embodiment 1 of the present invention. It is an arrangement | positioning schematic diagram of the carrier which concerns on Embodiment 1 of this invention. It is a figure which shows the example of the radio | wireless resource allocation in the downlink which concerns on Embodiment 1 of this invention. FIG. 6 is a diagram illustrating an example of radio resource allocation in the first ODFM symbol of FIG. 5. It is a flowchart which shows operation | movement of the communication system which concerns on Embodiment 1 of this invention. It is a figure which shows the example of the radio | wireless resource allocation in the downlink which concerns on the modification of Embodiment 1 of this invention. It is a block diagram of the base station which concerns on Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the communication system which concerns on Embodiment 2 of this invention.

  Embodiments of the present invention will be described below.

(Embodiment 1)
FIG. 1 is a schematic diagram of a communication system 1 according to Embodiment 1 of the present invention. The communication system 1 according to Embodiment 1 of the present invention includes a plurality of communication devices. For example, as shown in FIG. 1, the communication system 1 includes a communication device 10a (base station 10a) and a communication device 10b (base station 10b), each of which includes a communication device 11a (mobile station 11a) and a communication device 11b (mobile station 11b). ) Is connected. Although FIG. 1 shows an example in which two base stations and two mobile stations are provided, the present invention is not limited to this, and there may be two or more base stations and mobile stations. The communication system 1 is configured to be able to communicate with the base station 10a and the base station 10b.

  The communication system 1 is a system that employs a communication method such as TD-LTE or LTE. Hereinafter, in the present embodiment, the communication system 1 will be described assuming that a TD-LTE communication method is employed. The communication system 1 performs wireless communication by arranging two carriers having a bandwidth (first frequency bandwidth) of 5 MHz (effective bandwidth is 4.5 MHz) in the 9 MHz band (second frequency band). Hereinafter, the two carriers arranged in the second frequency band are referred to as carrier A and carrier B. For example, the base station 10a and the communication device 11a communicate using the carrier A, and the base station 10b and the communication device 11b communicate using the carrier B.

  2 (a) and 2 (b) are block diagrams of base station 10a and base station 10b according to Embodiment 1 of the present invention. As shown in FIG. 2A, the base station 10a includes a base station communication unit 101a, a base station baseband unit 102a, and a base station control unit 103a. The base station communication unit 101a and the base station baseband unit 102a are connected to the base station control unit 103a.

  The base station communication unit 101a transmits and receives radio signals (data) to and from the mobile station 11a via an antenna. The base station communication unit 101a performs amplification and down-conversion with low noise on the received radio signal (reception signal), and sends the processed signal to the base station baseband unit 102a. Further, the base station communication unit 101a performs up-conversion and amplification on the baseband signal received from the base station baseband unit 102a, and generates a radio signal (transmission signal). Then, the base station communication unit 101a transmits the radio signal to the mobile station 11a via the antenna.

  The base station baseband unit 102a demodulates the received signal by performing AD conversion, fast Fourier transform, and the like on the signal received from the base station communication unit 101a, and extracts the baseband signal. Then, the base station baseband unit 102a sends a baseband signal to the base station control unit 103a. The base station baseband unit 102a modulates the baseband signal by performing inverse fast Fourier transform, DA conversion, and the like on the baseband signal generated by the base station control unit 103a. Then, the modulated baseband signal is sent to the base station communication unit 101a. Further, the base station baseband unit 102a extracts a CQI (Channel Quality Indicator) indicating channel quality from a radio signal (CQI report) received from the mobile station 11a. Then, the base station baseband unit 102a sends the extracted CQI to the base station control unit 103a.

  The base station control unit 103a controls and manages the entire base station 10a including each functional block of the base station 10a. The base station control unit 103a is configured as software executed on any suitable processor such as a CPU (central processing unit), or by a dedicated processor (for example, DSP (digital signal processor)) specialized for each process. It can also be configured.

  The base station control unit 103a uses the carrier A having the first frequency bandwidth in order to realize wireless communication between the base station 10a and the mobile station 11a. Specifically, the base station control unit 103a allocates used downlink radio resources and used uplink radio resources, which are part of the carrier A, to the mobile station 11a (and other mobile stations connected to the base station 10a). The used downlink radio resource is a radio resource that the base station uses in downlink communication (downlink) with the mobile station. The used uplink radio resource is a radio resource used by the mobile station in uplink communication (uplink) with the base station. Then, the base station control unit 103a communicates with the mobile station 11a using the allocated use downlink radio resource and use uplink radio resource. In addition, the base station control unit 103a transmits the information on the assigned downlink radio resources and uplink uplink radio resources to the mobile station 11a (and other mobile stations connected to the base station 10a) via the base station communication unit 101a. Send.

  Allocation of radio resources to each mobile station connected to the base station 10a is performed based on a scheduling algorithm such as PF (Proportional Fair) using the CQI extracted by the base station baseband unit 102a. PF is a scheduling method for assigning an RB to a mobile station having a large instantaneous SINR with respect to an average SINR (Signal to Interference plus Noise power Ratio) for each RB. Also, the base station control unit 103a determines the most efficient MCS (Modulation and Coding Scheme) that satisfies a predetermined BLER (Block Error Rate) with the assigned radio resource. MCS is a value from 0 to 28 indicating a combination of a data modulation scheme and a channel coding rate used for transmission of a radio signal. While the efficiency is higher as the MCS value is larger, the coding strength of the radio signal is lowered. The allocation of radio resources according to the type of radio signal transmitted by the base station 10a will be described later with reference to FIGS.

  As shown in FIG. 2B, the base station 10b has the same configuration as the base station 10a. The base station communication unit 101b and the base station baseband unit 102b perform the same operations as the base station communication unit 101a and the base station baseband unit 102a, respectively.

  The base station control unit 103b of the base station 10b uses the carrier B having the first frequency bandwidth in order to realize wireless communication between the base station 10b and the mobile station 11b. Specifically, the base station control unit 103b allocates the used downlink radio resources and the used uplink radio resources that are part of the carrier B to the mobile station 11b (and other mobile stations connected to the base station 10b). Then, the base station control unit 103b communicates with the mobile station 11b using the allocated use downlink radio resource and use uplink radio resource. In addition, the base station control unit 103b sends the information on the assigned downlink radio resources and uplink uplink radio resources to the mobile station 11b (and other mobile stations connected to the base station 10b) via the base station communication unit 101b. Send.

  The radio resource allocation performed for each mobile station connected to the base station 10b is performed based on a scheduling algorithm such as PF, for example, using the CQI extracted by the base station baseband unit 102b. Further, the base station control unit 103b determines the most efficient MCS that satisfies a predetermined BLER with the assigned radio resource. The allocation of radio resources according to the type of radio signal transmitted by the base station 10b will be described later with reference to FIGS.

  3 (a) and 3 (b) show block diagrams of mobile station 11a and mobile station 11b according to Embodiment 1 of the present invention, respectively. As shown in FIG. 3A, the mobile station 11a includes a mobile station communication unit 111a, a mobile station baseband unit 112a, and a mobile station control unit 113a. The mobile station communication unit 111a and the mobile station baseband unit 112a are connected to the mobile station control unit 113a.

  The mobile station communication unit 111a transmits and receives radio signals (data) to and from the base station 10a via an antenna. The mobile station communication unit 111a performs amplification and down-conversion with low noise on the received radio signal (reception signal), and sends the processed signal to the mobile station baseband unit 112a. In addition, the mobile station communication unit 111a performs up-conversion and amplification on the baseband signal received from the mobile station baseband unit 112a to generate a radio signal (transmission signal). Then, the mobile station communication unit 111a transmits the radio signal to the base station 10a via the antenna.

  The mobile station baseband unit 112a demodulates the received signal by performing AD conversion, fast Fourier transform, and the like on the signal received from the mobile station communication unit 111a, and extracts the baseband signal. Then, the mobile station baseband unit 112a sends a baseband signal to the mobile station control unit 113a. The mobile station baseband unit 112a modulates the baseband signal by performing inverse fast Fourier transform, DA conversion, and the like on the baseband signal generated by the mobile station control unit 113a. The modulated baseband signal is sent to the mobile station communication unit 111a.

  The mobile station control unit 113a controls and manages the entire mobile station 11a including each functional block of the mobile station 11a. The mobile station control unit 113a is configured as software executed on an arbitrary suitable processor such as a CPU (Central Processing Unit), or by a dedicated processor (for example, DSP (Digital Signal Processor)) specialized for each process. It can also be configured.

  The mobile station control unit 113a determines the radio resource to be used, the modulation scheme, and the coding rate based on the allocation information of the used downlink radio resource and the used uplink radio resource in the carrier A received from the base station 10a. . Then, the mobile station control unit 113a performs radio communication with the base station 10a through the mobile station communication unit 111a and the mobile station baseband unit 112a using the determined radio resource, modulation scheme, and coding rate. Further, the mobile station control unit 113a generates a CQI report as information related to channel quality at a predetermined cycle. Preferably, when generating the CQI report, the mobile station control unit 113a uses higher layer-configured subband feedback (Mode 3-0, Mode 3-1) or UE- Use selected subband feedback (Mode 2-0, Mode 2-2).

  As shown in FIG. 3B, the mobile station 11b has the same configuration as the mobile station 11a. The mobile station communication unit 111b and the mobile station baseband unit 112b perform the same operations as the mobile station communication unit 111a and the mobile station baseband unit 112a, respectively.

  The mobile station control unit 113b of the mobile station 11b uses the radio resources to be used, the modulation scheme, and the encoding based on the allocation information of the used downlink radio resources and the used uplink radio resources in the carrier B received from the base station 10b. Determine the rate. Then, the mobile station control unit 113b performs radio communication with the base station 10b by the mobile station communication unit 111b and the mobile station baseband unit 112b using the determined radio resource, modulation scheme, and coding rate. Further, the mobile station control unit 113b generates a CQI report as information related to channel quality at a predetermined cycle. Preferably, the mobile station control unit 113b generates higher layer-configured subband feedback (Mode 3-0, Mode 3-1) or UE- in order to eliminate the influence of overlapping channel quality when generating the CQI report. Use selected subband feedback (Mode 2-0, Mode 2-2).

  Here, when the carrier A and the carrier B having the first frequency bandwidth (5 MHz) are continuously arranged in the second frequency band (9 MHz band), the total becomes 10 MHz and exceeds 9 MHz. Therefore, the communication system 1 according to the first embodiment of the present invention arranges a part of the bands of the carrier A and the carrier B overlapping (overlapping) in the 9 MHz band. FIG. 4 shows a schematic diagram in which a part of the carrier A and the carrier B are overlapped. As shown in FIG. 4, as a peripheral band of the 9 MHz band, a 1.7G mobile phone band, a guard band band, a public PHS band (9 MHz band), a digital cordless telephone band, a public PHS band, a guard band band, and a 2G mobile phone Bandwidth is less than 1879.9 MHz, 1879.9 MHz to 1884.5 MHz, 1884.5 MHz to 1893.5 MHz, 1893.5 MHz to 1906.1 MHz, 1906.1 to 1915.7 MHz, 1915.7 MHz to 1920 MHz, 1920 MHz or more, respectively. Assigned. As shown in FIG. 4, in the communication system 1, the carrier A and the carrier B are partially overlapped and arranged in the 9 MHz band. Specifically, since the center frequency of the carrier is assigned in units of 0.1 MHz based on the LTE standard (Non-Patent Document 1), most of the frequency band of carrier A is between 1884.5 MHz and 1889.5 MHz. And most of the frequency band of the carrier B is arranged between 1888.5 and 1893.5 MHz. The carrier A and the carrier B are overlapped in a 1 MHz portion between 1888.5 MHz and 1889.5 MHz, for example. Hereinafter, the overlapping part is referred to as an overlapping part (or overlap band). When the base station 10a and the base station 10b transmit radio signals using radio resources that collide with each other at overlapping portions, the mobile station cannot receive the radio signals correctly due to interference. Therefore, it is desirable that only one of the base stations transmits a radio signal for each radio resource in the overlapping portion.

  Next, radio resource allocation according to the type of radio signal transmitted by the base station will be described with reference to FIGS. FIG. 5 is a diagram showing an example of radio resource allocation in the downlink according to Embodiment 1 of the present invention. As an outline, the base station 10a and the base station 10b perform radio communication by dividing radio resources preferentially used by each base station for transmission of radio signals in overlapping portions of carriers. FIG. 5A shows a state where carrier A and carrier B each having 25 RBs per slot are overlapped by 5 RBs to form a band having 45 RBs as a whole. In FIG. 5A, one subframe consisting of two slots is shown in the time axis direction, and RB numbers from 0 to 44 are assigned as index numbers. In FIG. 5A, for the sake of explanation, a control information area to which a control channel such as PDCCH (Physical Downlink Control Channel) is assigned is omitted, and a user data area to which a shared channel such as PDSCH (Physical Downlink Shared Channel) is assigned. Only shows. The PDCCH is a channel that transmits control information related to the connection between the base station and the mobile station. The PDSCH is a channel for transmitting user data related to downloading from the base station to the mobile station. In the following description, the low frequency side is assumed to be carrier A, and the high frequency side is assumed to be carrier B.

  PBCH (Physical Broadcast Channel), PSS (Primary Synchronization Signal), and SSS (Secondary Synchronization Signal) are allocated to a band corresponding to 6 RBs at the center frequency of the carrier based on the LTE standard (Non-patent Document 2). Therefore, the PBCH, PSS, and SSS transmitted by the base station 10a and the base station 10b are not assigned to overlapping portions, so there is no need to consider collision between carriers.

  Next, PDSCH will be described. The base station 10a performs scheduling by distributed RB allocation in order to reduce the influence of collision in overlapping portions. Here, since the 24th RB does not perform frequency hopping, the base station 10a uses the 0th to 23rd RBs for PDSCH allocation, and does not use the 24th RB. On the other hand, the base station 10b performs scheduling based on local RB allocation using RBs 24 to 44 for PDSCH allocation.

  As described above, regarding the allocation of PDSCH for transmitting user data, the base station 10a preferentially uses a part of the overlapping part, that is, the 20th to 23rd RBs, so that the PDSCH collides in the overlapping part. Can be prevented.

  FIG. 5B is a diagram showing details of the 19th and 20th RBs in FIG. 1 RB has 12 subcarriers in the frequency axis direction, and has 1 slot consisting of 7 OFDM symbols in the time axis direction. In a subframe consisting of two slots, the top three symbols are used as a control information area to which PDCCH and the like are allocated, and the remaining 11 symbols are used as a user data area to which PDSCH and the like are allocated.

  Next, a cell-specific reference signal (hereinafter referred to as a reference signal) will be described. The reference signal is used for channel equalization of the control channel and is transmitted for each antenna port of the carrier. FIG. 5B shows an example of assignment of reference signals corresponding to the antenna port 0 and the antenna port 1 of the base station 10a and the base station 10b. Based on the LTE standard, a reference signal is allocated to two REs (Resource Elements) with a predetermined arrangement per 6 subcarriers for each antenna port (Non-patent Document 2). Since the 19th RB is not an overlapping portion, reference signals respectively corresponding to the antenna port 0 and the antenna port 1 of the carrier A are allocated. On the other hand, since the 20th RB is an overlapping part, the reference signal of the base station 10b is further allocated. Here, the base station 10b transmits a reference signal using radio resources that do not collide with each other due to a different arrangement from the base station 10a. Specifically, the base station 10a and the base station 10b transmit reference signals using different subcarriers in 1 RB by adjusting cell IDs between carriers. That is, the base station 10a and the base station 10b differ in the arrangement of reference signals to be transmitted in the overlapping portion. Here, the cell ID is an identifier for identifying each of the base station 10a and the base station 10b, and can be appropriately changed by the base station control unit 103a and the base station control unit 103b. Then, the base station control unit 103a and the base station control unit 103b determine the initial offset of the reference signal based on the cell ID, that is, the allocation start position in the frequency axis direction.

  In this way, the base station 10a and the base station 10b can prevent the reference signals from colliding with each other in the overlapping portion by transmitting the reference signals using radio resources having different arrangements.

  Next, PDCCH will be described. The PDCCH is allocated in units of one REG (Resource Element Group) including 4 REs in the head symbol of the subframe. In 1RB, except for the RE to which the reference signal is allocated, there are a total of two REGs consisting of four subcarriers on the low frequency side (hereinafter referred to as the first half REG) and REG consisting of four subcarriers on the high frequency side (hereinafter referred to as the second half REG). REG is included. The PDCCH has four CCEs (Control Channel Elements) that use 9REG, and has a total of 36REG. Here, as will be described later in the description of FIG. 6, the base station 10a allocates PCFICH (Physical Control Format Indicator Channel) and PHICH (Physical HARQ Indicator Channel) while avoiding overlapping portions, and then PCFICH and PHICH are allocated. Interleave is performed on non-radio resources and PDCCHs are allocated in order from the low frequency side. PCFICH is a channel for transmitting information indicating the number of symbols used as a control signal area in a subframe. PHICH is a channel for transmitting delivery confirmation information of a radio signal transmitted by a mobile station. Based on the LTE standard, PCFICH has four REGs and PHICH has three REGs (Non-Patent Document 2). Accordingly, the base station 10a allocates the PDCCH from the low frequency side to 43REG, that is, the range from the first half REG of the 0th RB to the first half REG of the 21st RB. As shown in FIG. 5 (b), the 19th RB is not an overlapping portion, so the PDCCH of the base station 10a is assigned. On the other hand, since the 20th RB is an overlapping portion, the PDCCH and the reference signal of the base station 10b are further allocated. For this reason, PDCCH and a reference signal or PDCCH will collide between carriers.

  Here, the PDCCH is generally redundant and has high coding strength, and since the base station 10a assigns the PDCCH in order from the radio resource on the low frequency side, a part of the overlapping portion (20th RB and 21st) is assigned. There is a high possibility that the mobile station can demodulate even if there is some collision in the first half REG) of RB. For this reason, in RE in which PDCCH and a reference signal collide, a reference signal is transmitted preferentially and PDCCH is not transmitted. In the RE in which PDCCH collides, both base station 10a and base station 10b transmit PDCCH.

  Thus, the base station 10a and the base station 10b can prevent the reference signal from interfering with the PDCCH by transmitting only the reference signal in the RE in which the PDCCH and the reference signal collide.

  Next, PCFICH and PHICH will be described. FIG. 6 shows the first OFDM symbol of carrier A and carrier B in units of REG. In the figure, “front” means the first half REG and “rear” means the second half REG. Based on the LTE standard, the base station allocates PCFICH and PHICH to positions that divide the carrier bandwidth into four or three (non-patent document 2). Here, the initial offset of PCFICH and PHICH can be changed by adjusting the cell ID of the carrier. FIG. 6 shows an example of assignment of PCFICH and PHICH in the case where the carrier A has a cell ID = 2 and the carrier B has a cell ID = 13. That is, the base station 10a and the base station 10b allocate the PCFICH and PHICH by adjusting the cell ID and avoiding the overlapping part.

  Alternatively, the base station 10a may allocate PCFICH and PHICH while avoiding the overlapping portion, and the base station 10b may allocate PCFICH and PHICH while avoiding the PDCCH of the base station 10a in the overlapping portion. Specifically, since the base station 10a assigns the PDCCH from the first half REG of the 0th RB to the first half REG of the 21st RB, the second half REG of the 21st RB to the second half REG of the 24th RB is Null. It has become. Therefore, the base station 10b allocates PCFICH and PHICH while avoiding the radio resources (the first half REG of the 20th RB to the first half REG of the 21st RB) to which the PDCCH of the base station 10a is assigned in the overlapping portion.

  As described above, the base station 10b uses a radio resource having a different arrangement from the control channel (PDCCH, PCFICH, and PHICH) of the base station 10a for allocation of PCFICH and PHICH for transmitting a predetermined control signal. It is possible to prevent PCFICH and PHICH transmitted by 10a and base station 10b from colliding with each other.

  Next, the operation of the communication system 1 according to Embodiment 1 of the present invention will be described with reference to the flowchart shown in FIG.

  FIG. 7 (a) shows operations of base station 10a and mobile station 11a of communication system 1 according to Embodiment 1 of the present invention.

  First, the base station control unit 103a allocates the used downlink radio resources and the used uplink radio resources, which are part of the carrier A, to the mobile station 11a (and other mobile stations connected to the base station 10a) (step S101a). . Preferably, the used downlink radio resources are allocated by distributed RB allocation.

  At this time, base station control section 103a assigns PDSCH to the user data areas of RBs from 0th to 23rd in the downlink. Further, the base station control unit 103a assigns a reference signal to a subcarrier different from the base station 10b. In addition, the base station control unit 103a adjusts the cell ID and avoids an overlapping portion, and allocates PCFICH and PHICH to the control information area. In addition, after allocating PCFICH and PHICH, the base station control unit 103a performs interleaving and sequentially allocates PDCCH to radio resources to which PCFICH and PHICH are not allocated from the low frequency side.

  Next, the base station control unit 103a transmits the assigned downlink radio resource and uplink uplink resource allocation information to the mobile station 11a (and other mobile stations connected to the base station 10a) via the base station communication unit 101a. (Step S102a). The mobile station 11a receives the information (step S103a).

  Subsequently, the base station control unit 103a communicates with the mobile station 11a through the base station communication unit 101a and the base station baseband unit 102a (step S104a).

  At this time, the base station control unit 103a does not transmit the PDCCH in the RE in which the PDCCH of the local station collides with the reference signal of the base station 10b in the downlink.

  FIG. 7B shows operations of the base station 10b and the mobile station 11b. First, the base station control unit 103a allocates the used downlink radio resources and the used uplink radio resources, which are part of the carrier B, to the mobile station 11b (and other mobile stations connected to the base station 10b) (step S101b). .

  At this time, the base station control unit 103b assigns PDSCH to the user data areas of RBs 24 to 44 in the downlink by local RB assignment. In addition, the base station control unit 103b assigns a reference signal to a subcarrier different from the base station 10a. Also, the base station control unit 103b adjusts the cell ID to avoid overlapping portions or the control channel (PDCCH) of the base station 10a and allocates PCFICH and PHICH to the control information area. In addition, after allocating PCFICH and PHICH, the base station control unit 103b allocates PDCCH to radio resources to which PCFICH and PHICH are not allocated.

  Next, the base station control unit 103b assigns the assigned downlink radio resource and uplink radio resource assignment information to the mobile station 11b (and other mobile stations connected to the base station 10b) via the base station communication unit 101b. ) (Step S102b). The mobile station 11b receives the information (step S103b).

  Subsequently, the base station control unit 103b communicates with the mobile station 11b through the base station communication unit 101b and the base station baseband unit 102b (step S104b).

  As described above, according to the communication system 1 according to Embodiment 1 of the present invention, in a communication scheme such as TD-LTE, one communication apparatus (base station 10a) has the other communication apparatus (base By using some of the radio resources of the overlapping portion with higher priority than the station 10b), the carrier bandwidth is ensured to increase the communication speed, and within the frequency band assigned to the communication method. The carrier can be stored to prevent radio wave interference with other systems. Further, the base station 10a and the base station 10b use the radio resources that do not collide with each other in the overlapping portion with respect to the allocation of the reference signals, that is, the reference signals are transmitted by using different subcarriers. Interference can be prevented and communication stability can be improved. Also, the base station 10b uses the radio resources that do not collide with the control channel of the base station 10a, that is, PDCCH, PCFICH, and PHICH, with respect to the allocation of the PCFICH and PHICH, so that the PCFICH and PHICH collide with the control channel of the base station 10a. By avoiding this, the stability of communication can be improved.

(Modification of Embodiment 1)
Next, a modification of the first embodiment of the present invention will be described. The base station 10b according to the modification uses the radio resources in the control signal area and does not use the radio resources in the user data area with an arrangement different from that of the base station 10a regarding the allocation of the reference signal in the overlapping portion.

  FIG. 8 is a diagram showing the details of the 19th and 20th RBs in FIG. The 19th RB which is not an overlapping part is the same as that in the first embodiment. The reference signal of the base station 10b is assigned to the head symbol of the 20th RB that is the overlapping part. On the other hand, the reference signal of the base station 10b is not allocated to the user data area, and more PDSCHs of the base station 10a are allocated compared to the first embodiment.

  As described above, according to the communication system 1 according to the modification of the first embodiment of the present invention, the base station 10b is configured to transmit the reference signal in the overlapping portion with a radio signal in the control signal region by an arrangement different from the base station 10a. By using resources, the stability of communication can be improved. Further, the base station 10a can transmit user data more efficiently by allocating the PDSCH of the base station 10a as much as the base station 10b does not allocate the reference signal to the overlapping user data area.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. As an outline, the communication system 1 according to Embodiment 2 changes the radio resource allocation method according to the MCS of the mobile station connected to the base station.

  FIG. 9 is a block diagram of base station 10a and base station 10b according to Embodiment 2 of the present invention. As shown in FIG. 9A, the base station 10a includes a base station communication unit 101a, a base station baseband unit 102a, a base station control unit 103a, and a base station storage unit 104a. The base station communication unit 101a and the base station baseband unit 102a are the same as those in the first embodiment, and a description thereof will be omitted.

  The base station storage unit 104a stores the MCS threshold value 105a in advance. The MCS threshold 105a is a degradation of the MSCH threshold (first threshold) used by the base station control unit 103a in radio resource allocation to each mobile station connected to the base station 10a and the PDSCH BLER characteristic for one mobile station. MCS threshold (second threshold) for the ratio of collision RBs not to be included. The second threshold value can be calculated in advance by simulation.

  The base station control unit 103a allocates radio resources to the mobile station 11a based on the MCS of the mobile station 11a. Specifically, the base station control unit 103a lowers the priority of allocating the mobile station 11a to the overlapping RB when the MCS of the mobile station 11a is equal to or greater than the first threshold when RB is allocated to the mobile station. For example, in the calculation formula of allocation priority [RB] = instantaneous SINR [RB] / average SINR [RB] + α [RB, MCS], when MCS is equal to or greater than a first threshold (for example, 28), α = −. 1 and α = 0 if MCS is less than the first threshold. Note that α = 0 is always set for RBs that are not overlapping portions.

  Further, the base station control unit 103a determines whether or not to transmit the PDSCH based on the MCS of the mobile station 11a in a part of the PDSCH assigned to the overlapping part. Specifically, when the MCS of the mobile station 11a is equal to or greater than the second threshold, the base station control unit 103a transmits the PDSCH with an RE that collides with the reference signal of the base station 10b in the overlapping user data area. And notifies the base station 10b to that effect. On the other hand, when the MCS of the mobile station 11a is less than the second threshold, the base station control unit 103a determines not to transmit PDSCH using the RE, and notifies the base station 10b to that effect.

  As illustrated in FIG. 9B, the base station 10b includes a base station communication unit 101b, a base station baseband unit 102b, a base station control unit 103b, and a base station storage unit 104b. The base station communication unit 101b and the base station baseband unit 102b are the same as those in the first embodiment, and a description thereof will be omitted.

  The base station storage unit 104b stores the MCS threshold value 105b in advance. The MCS threshold 105b includes an MCS threshold (first threshold) used by the base station control unit 103b in radio resource allocation to each mobile station connected to the base station 10b.

  The base station control unit 103b assigns radio resources to the mobile station 11b based on the MCS of the mobile station 11b. Specifically, the base station control unit 103b lowers the priority of allocating the mobile station 11b to the overlapping RB when the MCS of the mobile station 11b is equal to or greater than the first threshold when RB is allocated to the mobile station. For example, in the calculation formula of allocation priority [RB] = instantaneous SINR [RB] / average SINR [RB] + α [RB, MCS], when MCS is equal to or greater than a first threshold (for example, 28), α = −. 1 and α = 0 if MCS is less than the first threshold. Note that α = 0 is always set for RBs that are not overlapping portions.

  Further, the base station control unit 103b determines whether or not to transmit a reference signal in the overlapping user data area based on the notification from the base station 10a. Specifically, when the base station control unit 103b receives a notification that the base station 10a transmits the PDSCH in an RE that collides with the reference signal of the base station 10b in the overlapping user data area, the base station control unit 103b refers to the RE. Decide not to send a signal. On the other hand, when the base station control unit 103b receives a notification indicating that the base station 10a does not transmit the PDSCH at the RE, the base station control unit 103b determines to transmit a reference signal at the RE.

  FIG. 10 shows an operation in which the base station allocates radio resources based on the MCS of the mobile station in the communication system 1 according to Embodiment 2 of the present invention. First, the base station 10a receives a CQI report from the mobile station 11a (step S201).

  Next, the base station 10a determines the MCS of the mobile station 11a based on the CQI extracted from the received CQI report (step S202).

  Next, the base station 10a determines the RB allocation priority for the mobile station 11a. Specifically, when the MCS value determined in step S202 is equal to or greater than the first threshold, the base station 10a lowers the allocation priority for overlapping RBs.

  Next, the base station 10a determines whether or not the MCS determined in step S202 is greater than or equal to the second threshold (step S204).

  When the MCS is equal to or larger than the second threshold (step S204-Yes), the base station 10a determines to transmit the PDSCH with an RE that collides with the reference signal of the base station 10b in the overlapping user data region (step S204). S205).

  Subsequently, the base station 10a notifies the base station 10b that the PDSCH is transmitted using the RE (step S206).

  When receiving the notification from the base station 10a, the base station 10b determines not to transmit the reference signal using the RE (step S207).

  On the other hand, when the MCS is less than the second threshold (step S204-No), the base station 10a determines not to transmit the PDSCH with an RE that collides with the reference signal of the base station 10b in the overlapping user data area. (Step S208).

  Subsequently, the base station 10a notifies the base station 10b that the PDSCH is not transmitted using the RE (step S209).

  Then, when receiving the notification from the base station 10a, the base station 10b determines to transmit a reference signal using the RE (step S210).

  As described above, in the communication system 1 according to Embodiment 2 of the present invention, when the MCS of the mobile station connected to the base station is high, the radio signal is reduced by lowering the priority for assigning the mobile station to the overlapping RB. It is possible to improve the stability of communication by reducing the probability of interference. In addition, the base station 10a and the base station 10b can use any of the REs in which the PDSCH (user data) of the base station 10a and the reference signal of the base station 10b collide with each other in the overlapping user data area according to the MCS of the mobile station 11a. The base station 10a preferentially transmits the PDSCH when the MCS is large, and the base station 10b preferentially transmits the reference signal when the MCS is small. Therefore, the stability of communication can be improved as the communication system 1 as a whole.

  In the above-described embodiment, the communication system 1 uses the second frequency band of 9 MHz. However, the present invention is not limited to this, and the second frequency band may be a band less than 9 MHz or more than 9 MHz. . In this case, according to the bandwidth of the second frequency band, the bandwidth of the first frequency band and the bandwidth of overlapping portions of a plurality of carriers are appropriately changed.

  In the above-described second embodiment, when the MCS of the mobile station connected to the own station is equal to or higher than the second threshold, the priority assigned to the RB of the overlapping portion is reduced. You may make it raise the priority assigned to RBs other than a part.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each means, each step, etc. can be rearranged so that there is no logical contradiction, and a plurality of means, steps, etc. can be combined or divided into one. .

1 Communication system 10a, 10b Base station (communication device)
11a, 11b Mobile station (communication device)
101a, 101b Base station communication unit 102a, 102b Base station baseband unit 103a, 103b Base station control unit 104a, 104b Base station storage unit 105a, 105b MCS thresholds 111a, 111b Mobile station communication unit 112a, 112b Mobile station baseband unit 113a 113b Mobile station controller

Claims (12)

A plurality of bases that perform radio communication by arranging a plurality of the carriers in the second frequency band that exceeds the bandwidth of the second frequency band defined in advance when the carriers of the first frequency bandwidth are continuously arranged. A communication system comprising a station,
The communication system is arranged by overlapping a part of each carrier in the second frequency band,
The first base station that uses one of the carriers that is partially overlapped and the second base station that uses the other carrier allocate radio resources in the overlapping portion based on the MCS of the mobile station. The communication system characterized by controlling.   When the MCS of the mobile station connected to the first base station and the second base station is equal to or greater than a predetermined first threshold, the first base station and the second base station allocate the overlapping portion of radio resources to the mobile station. The communication system according to claim 1, wherein the priority is lowered.   Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is less than a predetermined second threshold The communication system according to claim 1, wherein the first base station does not transmit user data, and the second base station transmits a reference signal.   Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is equal to or greater than a predetermined second threshold 4. The communication system according to claim 1, wherein the first base station transmits user data, and the second base station does not transmit a reference signal. 5. A plurality of bases that perform radio communication by arranging a plurality of the carriers in the second frequency band that exceeds the bandwidth of the second frequency band defined in advance when the carriers of the first frequency bandwidth are continuously arranged. A base station in a communication system comprising a station,
In the second frequency band, a part of each carrier is arranged in an overlapping manner, and one carrier in which the part is arranged in an overlapping manner is used,
A base station that controls radio resource allocation in the overlapping portion based on MCS of a mobile station.   6. The priority of allocating the overlapping portion of radio resources to the mobile station is lowered when the MCS of the mobile station connected to the mobile station is equal to or greater than a predetermined first threshold. Base station. In the radio resource in which the reference signal of the other base station using the other carrier and the user data of the own station collide,
When the MCS of the mobile station connected to the local station is equal to or greater than a predetermined second threshold, user data is transmitted,
The base station according to claim 5 or 6, wherein when the MCS of a mobile station connected to the own station is less than a predetermined second threshold, user data is not transmitted. In radio resources where user data of another base station using the other carrier collides with the reference signal of the own station,
If the MCS of the mobile station connected to the other base station is equal to or greater than a predetermined second threshold, the reference signal is not transmitted,
The base station according to any one of claims 5 to 7, wherein a reference signal is transmitted when an MCS of a mobile station connected to the other base station is less than a predetermined second threshold value. . A plurality of bases that perform radio communication by arranging a plurality of the carriers in the second frequency band that exceeds the bandwidth of the second frequency band defined in advance when the carriers of the first frequency bandwidth are continuously arranged. A communication control method of a communication system including a station,
The communication system is arranged by overlapping a part of each carrier in the second frequency band,
The first base station that uses one of the carriers that is partially overlapped and the second base station that uses the other carrier allocate radio resources in the overlapping portion based on the MCS of the mobile station. The communication control method characterized by controlling.   When the MCS of the mobile station connected to the first base station and the second base station is equal to or greater than a predetermined first threshold, the first base station and the second base station allocate the overlapping portion of radio resources to the mobile station. The communication control method according to claim 9, wherein the priority is lowered.   Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is less than a predetermined second threshold The communication control method according to claim 9 or 10, wherein the first base station does not transmit user data and the second base station transmits a reference signal.   Radio resource in which user data of the first base station collides with a reference signal of the second base station when the MCS of the mobile station connected to the first base station is equal to or greater than a predetermined second threshold The communication control method according to any one of claims 9 to 11, wherein the first base station transmits user data, and the second base station does not transmit a reference signal.

Images