JP2011139402A - Base station, communication system, and base station exclusion determining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the deterioration of reception quality in a terminal of a second communication system while suppressing interference imparted to a radio station of the second communication system from a base station of the second communication system even if first and second communication systems of different kinds using the same frequency bands are used together. <P>SOLUTION: A power difference calculator 109 calculates a power difference between minimum reception power and reception power other than minimum reception power out of reception power in a radio station of a reference signal transmitted from a plurality of base stations, and the power difference is obtained from a channel estimate value estimated using the reference signals transmitted from the plurality of base stations where a sensor station near a radio station of the first communication system belongs to a base station group of the second communication system. A determination section 110 determines whether the base station corresponding to the minimum reception power should be excluded from the base station group based on the power difference calculated by the power difference calculator 109. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  As typified by IMT-Advanced, which is being studied for standardization, in the next-generation mobile communication system, it is necessary to secure a wide frequency band in order to perform high-speed and large-capacity communication. For example, in IMT-Advanced, the International Telecommunication Union Radiocommunications Department (ITU-R) has decided to use the 3.4 GHz-3.6 GHz band as a frequency band.

  However, in recent wireless communication systems in general, demand for expansion of communication capacity is increasing, and expansion of frequency bands is desired, but available frequency resources are being depleted.

  Moreover, the frequency band currently considered for next-generation mobile communication systems such as IMT-Advanced may be used in existing communication systems represented by a fixed satellite communication system (FSS). Many. That is, the frequency band used in IMT-Advanced and the frequency band used in the existing communication system overlap.

  Accordingly, since the frequency is shared with such an existing system (for example, FSS), a later new system (for example, IMT-Advanced system) provides services by suppressing interference with the existing system. There must be.

  As a conventional technique for suppressing interference, by controlling transmission directivity so that a plurality of base stations (or a plurality of antennas) cooperate to direct a null in a specific direction, the interference in that specific direction is reduced. A mitigating interference suppression technique using base station cooperation simultaneous transmission has been proposed (see Non-Patent Document 1, for example).

  According to Non-Patent Document 1, a plurality of base stations connected by ROF (Radio Over Fiber) links simultaneously transmit signals multiplied by a weight (NULL weight), thereby transmitting the same frequency to a plurality of terminals. I do. At this time, if a plurality of base stations transmit signals to the desired terminal at the same time, the received power (reception level) decreases at the positions of terminals other than the desired terminal (that is, a null point is formed). That is, it is possible to suppress the interference by reducing the reception level at the position of the terminal other than the desired terminal while maintaining the reception level above a certain level at the desired terminal.

IEICE Technical Report on Radio Communication Systems RCS2002, Vol.102 No.86, pp.7-12, May.2002. “Same Frequency Spatial Multiplexing in Downlink of Unidirectional Antenna System with Pre-weighted Multiple Station Simultaneous Transmission (Technical report of IEICE, RCS 102 (86), pp.7-12, May.2002, "Proposal of Space Division Multiplexing of Co-channel Signals by Pre-Weighting Simultaneous Transmission in Ubiquitous Antenna System")

  However, the above prior art is premised on interference suppression in the same system. Therefore, it is conceivable to apply the above-described conventional technique in order to suppress interference that a new system gives to an existing system in a heterogeneous communication system.

  In the following description, as an example, as shown in FIG. 1, a case where the above-described IMT-Advanced system (new system) and FSS (existing system) coexist will be described. That is, a case where an IMT-Advanced system, which is a system different from FSS, is operated at the same frequency as FSS will be described.

  In FIG. 1, in FSS, an FSS radio station (hereinafter referred to as FSS ES: FSS Earth Station) communicates with an FSS satellite station. In FIG. 1, in the IMT-Advanced system, a plurality of base stations (IMT BS1 to 4) transmit signals to a terminal (IMT UE) by base station cooperative simultaneous transmission (base station cooperative MIMO transmission by multi-antenna processing). Send. That is, a plurality of base stations (IMT BS1 to 4 in FIG. 1) that perform base station cooperative simultaneous transmission form one base station group. A plurality of base stations belonging to the base station group are connected to each other by, for example, an ROF link.

  Here, in the FSS earth station shown in FIG. 1, since the reception power of the signal transmitted from the FSS satellite station is very small, interference from the IMT BSs 1 to 4 to the FSS earth station becomes a big problem. On the other hand, in the FSS earth station, since the transmission directivity is controlled so that the signal is directed in the direction of the FSS satellite station (above the FSS earth station), interference from the FSS earth station to the IMT BS1 to 4 is almost a problem. Don't be.

  Therefore, in the following description, the above-described conventional technique is applied as a frequency sharing technique in the IMT-Advanced downlink. That is, the plurality of base stations of the IMT-Advanced system performs null point control (that is, interference suppression technology by simultaneous base station cooperation transmission) that makes the interference power to the band used in the FSS earth station equal to or less than a predetermined value. .

Therefore, as shown in FIG. 1, in the IMT-Advanced system, a sensor station (an IMT UE for channel estimation) is provided in the vicinity of the FSS earth station. The sensor station estimates a channel estimation value using a reference signal from each base station (a signal known by the base station and the sensor station, sometimes referred to as a reference signal or a pilot signal), and feeds back the estimation result to the IMT BS. To do. Thereby, in the IMT-Advanced system shown in FIG. 1, the respective channel estimation values h _{1 to} h ₄ between the IMT BSs _{1 to 4} and the FSS earth station can be obtained.

The base station group to which the IMT BSs 1 to 4 shown in FIG. 1 belong has NULL weights generated based on channel estimation values (h ₁ to h ₄ shown in FIG. 1) between each base station and the FSS earth station. Is used to form a null point in the FSS earth station.

Specifically, an arbitrary base station among the IMT BSs 1 to 4 shown in FIG. 1 uses all channel estimation values h _{1 to} h ₄ between the base station and the FSS earth station to A NULL weight that minimizes the received power (reception level) is generated. The generated NULL weight is notified from each base station to each base station. Then, the IMT BSs 1 to 4 shown in FIG. 1 multiply the generated NULL weight by the signal and transmit the multiplied signals, respectively. Accordingly, the IMT UE (desired terminal) shown in FIG. 1 can maintain the reception level above a certain level and suppress the interference by reducing the reception level at the position of the FSS earth station.

  Here, the NULL weight is set so that the reception power (reception level) of the signal from each base station (IMT BS1 to 4 shown in FIG. 1) received by the FSS earth station is approximately the same. Moreover, the upper limit of the transmission power in each base station (IMT BS1-4 shown in FIG. 1) is preset.

  Therefore, when there is a difference between a plurality of base stations in the magnitude of the channel estimation value estimated by the sensor station, that is, the reception power (reception level) of the reference signal in the FSS earth station, transmission processing using a NULL weight is performed. If this is done, the transmission power at the base station may be reduced.

Specifically, as shown in FIG. 1, compared with the distance between IMT BS1,2,4 and FSS earth station (or sensor station), IMT BS3 and FSS earth station (or sensor station) The distance between them is very long (the distance shown in FIG. 1 is large). In this case, the magnitude | h ₃ | of the channel estimate h ₃ between the IMT BS 3 and the FSS earth station is much smaller than the magnitude of the channel estimate between the other IMT BSs and the FSS earth station. . In other words, the received power at the FSS earth station of the reference signal transmitted from the IMT BS 3 is much smaller than the received power at the FSS earth station of the reference signal transmitted from another IMT BS.

  Therefore, in order to make the reception power (reception level) of the signals from the base stations (IMT BS1 to 4) received by the FSS earth station shown in FIG. 1 comparable, the transmission power of IMT BS3 is set to IMT BS1. , 2 and 4 are preferably larger than the transmission power. However, since an upper limit value is set for the transmission power of each base station, the transmission power of IMT BS1, 2, and 4 must be relatively reduced to the extent that the transmission power of IMT BS3 can only be increased to the upper limit value. It may not be possible. In this case, the cover area (service area that can be received by the IMT UE) covered by the IMT BSs 1, 2, and 4 is reduced as much as the transmission power of the IMT BSs 1, 2, and 4 decreases.

  In this way, when the first communication system (for example, FSS) and the second communication system (for example, IMT-Advanced system) using the same frequency band coexist, the second communication system is the first communication system. When the interference given to the second communication system is suppressed, the cover area covered by the base station of the second communication system may be reduced. If the coverage area covered by a base station becomes small, there is a high possibility that a terminal that receives a signal from the base station is located outside the coverage area (outside the reception area), and the reception quality at the terminal deteriorates. End up. For example, if the cover area (not shown) of the IMT BSs 1, 2, and 4 shown in FIG. 1 becomes small, the IMT UE shown in FIG. 1 is likely to be located outside the cover area of the IMT BSs 1, 2, and 4. End up.

  An object of the present invention is to suppress interference caused by the second communication system to the first communication system when different types of the first communication system and the second communication system using the same frequency band coexist. It is to provide a base station, a communication system, and a base station removal determination method capable of preventing deterioration of reception quality in a terminal of the communication system 2.

  The base station of the present invention is a second communication system that uses the same frequency band as the first communication system, and a base station group that forms a null point at the position of the radio station of the first communication system, Estimate channel estimation values using reference signals transmitted from a plurality of base stations belonging to the base station group provided near the radio station and a terminal that receives signals transmitted in cooperation with the base station group A base station in the second communication system having a sensor station, wherein the reference signal transmitted from the plurality of base stations obtained from the channel estimation value is received power in the radio station, Calculating means for calculating a power difference between the minimum received power and other received power other than the minimum received power; and a base station corresponding to the minimum received power based on the power difference Exclude from Taking a determination unit configured to whether a configuration comprising.

  The communication system of the present invention is a communication system that uses the same frequency band as another communication system, and a base station group that forms a null point at a position of a radio station of the other communication system, and the base station group includes A terminal that receives a signal to be transmitted in cooperation; a sensor station that is provided in the vicinity of the wireless station and estimates a channel estimation value using reference signals transmitted from a plurality of base stations belonging to the base station group; And the base station obtains the minimum received power and the minimum received power among the received power of the reference signal transmitted from the plurality of base stations obtained from the channel estimation values at the radio station. Calculating means for calculating a power difference with other received power other than the above, and determining means for determining whether to exclude a base station corresponding to the minimum received power from the base station group based on the power difference And comprising A configuration.

  The base station exclusion determination method of the present invention is a second communication system that uses the same frequency band as the first communication system, and forms a null point at the position of the radio station of the first communication system. Group, a terminal receiving a signal transmitted in cooperation with the base station group, and a channel estimation using reference signals provided in the vicinity of the radio station and transmitted from a plurality of base stations belonging to the base station group A base station exclusion determination method in the second communication system, comprising: a sensor station that estimates a value, the radio station of the reference signal transmitted from the plurality of base stations obtained from the channel estimation value And calculating a power difference between the minimum received power and other received power other than the minimum received power, and a base corresponding to the minimum received power based on the power difference The adopts a configuration having a, a determination step of determining whether to exclude from the base station group.

  According to the present invention, even when different first communication systems (for example, FSS) and second communication systems (for example, IMT-Advanced system) using the same frequency band coexist, the base of the second communication system It is possible to prevent deterioration of reception quality at the terminal of the second communication system while suppressing interference from the station to the radio station of the second communication system. Therefore, for example, even in an area where FSS radio stations are already installed, it is possible to newly install an IMT-Advanced system that uses the same frequency band as the FSS.

A diagram showing different types of communication systems using the same frequency band The figure which shows the heterogeneous communication system which uses the same frequency band concerning one embodiment of this invention The block diagram which shows the structure of the base station (primary base station) in the IMT-Advanced system which concerns on one embodiment of this invention

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

  In this embodiment, as an example of different types of communication systems using the same frequency band, a case where the IMT-Advanced system and the FSS system shown in FIG. 2 coexist as in FIG. 1 will be described.

  In FIG. 2, the IMT-Advanced system has four base stations (IMT BS1-4), one terminal (IMT UE), and one sensor station. In FIG. 2, the FSS includes an FSS earth station (FSS ES) and an FSS satellite station. The sensor station shown in FIG. 2 is provided in the vicinity of the FSS earth station. Moreover, IMT BS1-4 shown in FIG. 2 form the base station group which performs base station cooperation simultaneous transmission.

In the IMT-Advanced system using the same frequency band as the FSS, the base station group forms a null point at the position of the FSS earth station. Moreover, IMT UE receives the signal which a base station group transmits in cooperation. The sensor station is provided in the vicinity of the FSS earth station, and estimates channel estimation values h _{1 to} h ₄ using reference signals transmitted from a plurality of base stations belonging to the base station group. In FSS, the FSS earth station communicates with the FSS satellite station.

Further, in the IMT-Advanced system shown in FIG. 2, any one of the IMT BSs 1 to 4 is determined as a primary base station (Primary BS, IMT BS1 in FIG. 2). The primary base station acquires the channel estimation values h _{1 to} h ₄ between the IMT BSs _{1 to 4} and the FSS earth station measured by the sensor station, and uses NULL in the base station group based on the channel estimation values. Generate weights.

  FIG. 3 is a block diagram showing a configuration of base station 100 which is a primary base station (IMT BS1 in FIG. 2) according to the present embodiment.

  In base station 100 shown in FIG. 3, radio receiving section 102 performs reception processing such as down-conversion and A / D conversion on the signal received via antenna 101, and the received signal is subjected to GI (Guard Interval). The data is output to the removal unit 103. Note that the signal received by the wireless reception unit 102 includes each of a plurality of base stations belonging to the base station group of the IMT-Advanced system and the sensor stations (that is, FSS earth stations) estimated by the sensor station. Control information indicating a channel estimation value or a data signal from the IMT UE is included.

  The GI removal unit 103 removes the GI added to the signal input from the wireless reception unit 102 and outputs the signal after the GI removal to an FFT (Fast Fourier Transform) unit 104.

  The FFT unit 104 performs FFT on the signal after the GI removal to obtain a frequency domain signal. Then, FFT section 104 outputs the signal after FFT to demapping section 105.

  The demapping unit 105 extracts, from the signal input from the FFT unit 104, a portion corresponding to a frequency band to which control information indicating a channel estimation value and a data signal from the IMT UE are allocated. Then, demapping section 105 outputs the extracted signal to demodulation section 106.

  Demodulation section 106 demodulates the signal input from demapping section 105 and outputs the demodulated signal to decoding section 107.

  The decoding unit 107 extracts a data signal and control information by decoding the signal input from the demodulation unit 106 (for example, error correction decoding). Decoding section 107 then outputs the extracted data signal as received data, and outputs the channel estimation value corresponding to each base station included in the extracted control information to power calculation section 108.

  Based on the channel estimation value input from the decoding unit 107, the power calculation unit 108 receives the reception power (reception level) at the FSS earth station of the reference signal transmitted from a plurality of base stations belonging to the base station group of the IMT-Advanced system. ) Is calculated. Then, the power calculation unit 108 outputs information indicating the calculated received power to the power difference calculation unit 109.

  First, the power difference calculation unit 109 includes the reference signal transmitted from a plurality of base stations belonging to the IMT-Advanced base station group indicated in the information input from the power calculation unit 108, in the received power at the FSS earth station. Identify the minimum received power. Next, the power difference calculation unit 109 calculates an average value of received power other than the minimum received power among the received power. Then, the power difference calculating unit 109 calculates a power difference between the specified minimum received power and the calculated average value. Then, the power difference calculation unit 109 outputs information indicating the calculated power difference and the base station corresponding to the minimum received power to the determination unit 110.

  Based on the power difference indicated in the information input from the power difference calculation unit 109, the determination unit 110 determines whether or not to exclude the base station corresponding to the minimum received power from the base station group of the IMT-Advanced system. judge. In other words, the determination unit 110 determines whether or not a plurality of base stations belonging to the base station group include base stations to be excluded from simultaneous base station cooperation transmission. Specifically, the determination unit 110 excludes the base station corresponding to the minimum received power from the base station group when the power difference calculated by the power difference calculation unit 109 is larger than a preset threshold value. Then, the determination unit 110 outputs a determination result indicating whether or not to exclude the base station corresponding to the minimum received power from the base station group to the notification data generation unit 111.

  When the determination result indicating that the base station corresponding to the minimum received power is excluded from the base station group is input from the determination unit 110, the notification data generation unit 111 excludes the base station corresponding to the minimum received power Notification data indicating an instruction to perform is generated. The generated notification data is notified to a plurality of base stations belonging to the base station group.

  Then, a plurality of base stations belonging to the IMT-Advanced base station group receives notification data from the base station 100 (primary base station), and when it corresponds to the base station indicated in the notification data, transmission to the IMT UE To stop. That is, the base station indicated in the notification data is excluded from the base station group to which the base station belongs.

  In addition, after the base station exclusion determination process in the determination unit 110 is completed, the base station 100 corresponds to a plurality of base stations belonging to the current base station group (that is, a base station group not including the excluded base station). Based on the estimated value, a NULL weight is generated (not shown). A plurality of base stations belonging to the base station group transmit signals (base station cooperative simultaneous transmission) using NULL weights notified from the base station 100 (primary base station).

  As described above, a plurality of base stations belonging to the base station group (including the base station 100 (primary base station) shown in FIG. 3) use a reference signal known between each base station and the sensor station. Send to sensor station. Then, the sensor station uses the reference signal transmitted from each base station to calculate the channel estimation value between each base station and the sensor station, that is, the channel estimation value between each base station and the FSS earth station. presume. Then, the sensor station feeds back control information indicating the estimated channel estimation value to the base station 100 (primary base station) shown in FIG.

  Further, among the plurality of base stations belonging to the base station group, base stations other than the primary base station perform only reception processing of signals transmitted from the IMT UE. Specifically, base stations other than the primary base station have the same components as the antennas 101 to 107 shown in FIG. 3 and obtain received data (signals from the IMT UE).

  Next, details of the base station exclusion determination process in base station 100 (primary base station) shown in FIG. 3 will be described.

  In the following description, the distance between the IMT BS3 and the FSS earth station (or sensor station) shown in FIG. 2 is much greater than the distance between the IMT BS1,2,4 and the FSS earth station (or sensor station). Long. The distances between the IMT BSs 1, 2, 4 and the FSS earth station (or sensor station) are approximately the same.

  Also, the IMT BS1 is determined as the primary base station (base station 100 shown in FIG. 3) from the IMT BSs 1 to 4 belonging to the base station group of the IMT-Advanced system shown in FIG.

Further, the IMT BSs 1 to 4 shown in FIG. 2 transmit channel estimation reference signals (signals to which transmission weights are not applied) to the sensor station. At this time, the IMT BSs 1 to 4 transmit the reference signal with the same transmission power. When the sensor station shown in FIG. 2 receives the reference signals respectively transmitted from the IMT BSs _{1 to 4, the} channel estimation values h _{1 to} h ₄ between the IMT BSs _{1 to 4} and the sensor station (that is, the FSS earth station). Is estimated. Then, the sensor station feeds back the estimated channel estimation values h _{1 to} h ₄ to the IMT BS 1 that is the primary base station.

IMT BS1 (primary base station) receives the channel estimates _h 1 to h _4, which is fed back from the sensor station performs base station exclusion determination process.

Specifically, the power calculation unit 108 of the IMT BS1 uses the channel estimation value magnitude | h ₁ | to | h ₄ | to receive the reference signal transmitted from the IMT BSs ₁ to _{4 at} the FSS earth station. (Reception level) is calculated.

Next, the power difference calculation unit 109 of the IMT BS1 specifies the minimum received power among the received powers at the FSS earth stations of the reference signals transmitted from the IMT BS1 to BS4. In FIG. 2, the distance between the IMT BS3 and the FSS earth station (or sensor station) is much longer than the distance between the IMT BS1,2,4 and the FSS earth station (or sensor station). Therefore, the magnitude | h ₃ | of the channel estimation value shown in FIG. 2 is much smaller than the magnitudes | h ₁ |, | h ₂ |, | h ₄ | of other channel estimation values. Therefore, the power difference calculation unit 109 of the IMT BS1 uses the received power corresponding to the IMT BS3 (that is, the channel estimation) as the minimum received power among the received powers of the reference signals transmitted from the IMT BS1 to BS4 at the FSS earth station. identifying a power value _{h 3).}

  Next, the power difference calculation unit 109 of the IMT BS1 calculates an average value of received power other than the minimum received power. That is, the power difference calculation unit 109 calculates the average value of the received power corresponding to the IMT BSs 1, 2, and 4 other than the IMT BS3 corresponding to the minimum received power in FIG.

  Then, power difference calculation section 109 calculates the power difference between the received power (minimum received power) corresponding to IMT BS3 and the average value of the received power corresponding to IMT BS1,2,4.

  Next, based on the power difference calculated by the power difference calculation unit 109, the determination unit 110 of the IMT BS1 determines whether to exclude the IMT BS3 corresponding to the minimum received power from the base station group to which the IMT BS1 to 4 belong. Determine whether. For example, when the power difference is larger than a preset threshold value, the determination unit 110 determines to exclude the IMT BS3 from the base station group. On the other hand, the determination unit 110 determines that the IMT BS3 is not excluded from the base station group when the power difference is equal to or less than a preset threshold value.

  Then, the notification data generation unit 111 of the IMT BS1 generates notification data indicating an instruction to exclude the IMT BS3 from the base station group when the power difference is larger than a preset threshold, and other data belonging to the base station group Transmit to the base station (IMT BS2-4).

  Therefore, when the IMT BS3 shown in FIG. 2 is notified of an instruction to be excluded from the base station group, the base station formed by the IMT BS1 to BS4 is stopped by stopping signal transmission (base station cooperative simultaneous transmission). Excluded from the group. As a result, in the IMT-Advanced system shown in FIG. 2, IMT BSs 1, 2, and 4 belong to the base station group.

Accordingly, IMT BS1 is the primary base station (base station 100) deletes the channel estimate _{h 3} corresponding to the IMT BS3. Then, the IMT BS1 generates NULL weights based on the remaining channel estimation values h ₁ , h ₂ , and h _4, and uses the generated NULL weights as other base stations IMT BSs 2 and 4 (that is, To the base station that transmits simultaneously with the base station cooperation).

  The IMT BSs 1, 2, and 4 shown in FIG. 2 form a null point for the FSS earth station by transmitting a signal multiplied by a NULL weight.

  At this time, since the power difference of the channel estimation value in the propagation path between the IMT BSs 1, 2, 4 and the FSS earth station is small, the amount of reduction in transmission power by multiplying the signal by the NULL weight at each base station is Get smaller. Thereby, it is possible to prevent the cover area covered by the IMT BSs 1, 2, and 4 shown in FIG. For this reason, it is less likely that the IMT UE that receives signals from the IMT BSs 1, 2, 4 is located outside the coverage area of the IMT BSs 1, 2, 4, and it is possible to suppress degradation of reception quality at the IMT UEs. .

  Further, in FIG. 2, by removing IMT BS3, the number of base stations belonging to the base station group is decreased by one to three. However, the remaining three IMT BSs 1, 2, 4 can also form null points for the FSS earth station. That is, the decrease in the number of base stations belonging to the base station group due to the base station exclusion process hardly affects the interference suppression process for the FSS earth station. In other words, by performing the base station exclusion process on the base station group of the IMT-Advanced system, it is possible to prevent degradation of reception quality at the IMT UE while maintaining the interference suppression effect on the FSS earth station. .

  In this manner, a plurality of base stations belonging to the base station group of the IMT-Advanced system performs base station exclusion determination processing before performing interference suppression processing by base station cooperative simultaneous transmission. Specifically, the base station 100 (primary base station) receives the minimum received power and other received power (of the received signals at the FSS earth station of the reference signal transmitted from a plurality of base stations belonging to the base station group ( If the power difference from the average value here is larger than the threshold, it is determined that the base station corresponding to the minimum received power is excluded from the base station group.

  That is, the base station 100 causes a base area that causes the coverage area covered by other base stations to become extremely small by multiplying a signal by a NULL weight among a plurality of base stations belonging to the base station group. And the specified base station is excluded from the base station group. As a result, when performing interference suppression processing by base station cooperative simultaneous transmission, it is possible to reduce the cover area (service area) covered by the base station by preventing a decrease in transmission power in the base stations belonging to the base station group. Can be prevented.

  Therefore, according to the present embodiment, when different types of first communication systems (for example, FSS) and second communication systems (for example, IMT-Advanced system) using the same frequency band coexist, While suppressing interference from the base station of the communication system to the radio station of the second communication system, it is possible to prevent deterioration of reception quality at the terminal of the second communication system. Therefore, for example, even in an area where an existing system (FSS) radio station is installed, a new system (IMT-Advanced system) using the same frequency band as that of the existing system (FSS) can be newly installed.

  In the present embodiment, as shown in FIG. 3, base station 100 (power calculation unit 108), which is a primary base station, calculates received power at the FSS earth station of reference signals transmitted from a plurality of base stations. Explained when to do. However, in the present invention, the sensor station may calculate the received power at the FSS earth station of the reference signal transmitted from a plurality of base stations. In this case, the sensor station has the same configuration as the power calculation unit 108 of the base station 100 shown in FIG. 3, and the primary base station uses the power calculation unit 108 of the base station 100 shown in FIG. The omitted configuration is adopted. In other words, the sensor station feeds back control information indicating the received power at the FSS earth station of the reference signals transmitted from a plurality of base stations to the primary base station, so that the primary base station has the received power obtained from the channel estimation value. Arithmetic processing becomes unnecessary. Even in this case, the primary base station can perform the base station exclusion determination process in the same manner as in the above embodiment.

  Further, in the present embodiment, power difference calculation section 109 of base station 100 (primary base station) shown in FIG. 3 receives the received power at the FSS earth station of the reference signal transmitted from a plurality of base stations belonging to the base station group. Among these, the case where the power difference between the minimum received power and the average value of other received power other than the minimum received power is calculated has been described. However, in the present invention, the base station 100 (primary base station) has the minimum received power and the minimum received power among the received power at the FSS earth station of the reference signal transmitted from a plurality of base stations belonging to the base station group. A power difference with other received power other than power may be calculated individually for each base station. That is, power difference calculation section 109 receives each received power at the FSS earth station of the reference signal transmitted from a base station other than the base station corresponding to the minimum received power among the plurality of base stations belonging to the base station group. And the difference between the minimum received power and the minimum received power may be calculated.

  For example, the power difference calculation unit 109 of the base station 100 (primary base station) performs the IMT BSs 1, 2, 4 other than the IMTBS3 corresponding to the minimum received power among the IMT BSs 1 to 4 belonging to the base station group illustrated in FIG. And the power difference (that is, three power differences) between the received power corresponding to 1 and the received power corresponding to IMT BS3, respectively. Then, determination section 110 of base station 100 (primary base station) compares a plurality of (three in FIG. 2) power differences calculated by power difference calculation section 109 with preset threshold values. Here, when the power difference corresponding to another base station (IMT BS1, 2, 4 in FIG. 2) other than the base station corresponding to the minimum received power is larger than the threshold, the determination unit 110 is greater than the threshold. The base station (IMT BS3 in FIG. 2) corresponding to the minimum received power is excluded from the base station group. That is, in a plurality of base stations belonging to the base station group, when there is at least one base station set in which the difference in received power at the FSS earth station exceeds the threshold, the corresponding base station (minimum Base stations corresponding to received power) are excluded from the base station group. That is, the base station 100 can perform the base station exclusion determination process more strictly than in the case of calculating the average received power described above. For example, when calculating the power difference from the minimum received power, the base station 100 (primary base station) calculates the power difference between the minimum received power and the average value of the other received power according to the communication environment. Alternatively, whether to calculate the power difference between the minimum received power and other received power for each base station may be switched.

  Also, in the present invention, when it is determined that the primary base station is excluded from the base station group as a result of the base station exclusion determination process by the primary base station, another base station belonging to the base station group is determined as a new primary base station. The At this time, the base station to be excluded (old primary base station) is a base station that becomes a newly determined primary base station (new primary base station), information indicating that it is set as a primary base station, And the information which shows the determination result (determination result which excludes an old primary base station) is notified. Then, the new primary base station notifies notification data for excluding the old primary base station from the base station group to the base stations belonging to the base station group.

  Further, in the present embodiment, the case has been described in which the primary base station (base station 100) performs the base station exclusion determination process only once (that is, the exclusion determination process for one base station). However, the primary base station includes a plurality of base stations whose power difference calculated by the power difference calculation unit 109 is larger than a threshold (that is, a base station whose power of the channel estimation value is very small compared to other base stations). If present, the base station exclusion determination process may be repeated. However, in order to perform base station cooperation simultaneous transmission by the base station group, at least two base stations need to belong to the base station group. Therefore, the base station exclusion determination process is performed when the number of base stations belonging to the base station group is 3 or more (that is, when the number of base stations belonging to the base station group after the base station is excluded is 2 or more). Preferably, it is done. Thereby, the power difference of the channel estimation value becomes small between a plurality (two or more) of base stations belonging to the base station group after the base station exclusion determination process. Therefore, as in the above-described embodiment, it is possible to prevent the reception quality of the terminal from deteriorating without reducing the cover area covered by each of the plurality of base stations belonging to the base station group.

  In this embodiment, an IMT-Advanced system is given as an example of a mobile communication system. However, the mobile communication system is not limited to an IMT-Advanced system, and the present invention may be applied to other communication systems. Good. In the present embodiment, a satellite communication system (FSS) is given as an example of a communication system that coexists with a mobile communication system, but the same may be considered between other types of communication systems.

  Further, in the present embodiment, a case has been described in which base station cooperation simultaneous transmission (base station cooperation MIMO transmission) in which a plurality of base stations cooperate is performed. However, the present invention may be applied to array antenna processing by a base station having a plurality of transmission antennas instead of base station cooperation simultaneous transmission. That is, a plurality of antennas respectively correspond to the plurality of base stations in the above embodiment. That is, in a base station having a plurality of antennas, an antenna exclusion determination process is performed based on each channel estimation value (received power) between the plurality of antennas and the sensor station.

  The present invention is useful, for example, when a mobile communication system and a satellite communication system sharing the same frequency coexist.

DESCRIPTION OF SYMBOLS 100 Base station 101 Antenna 102 Wireless reception part 103 GI removal part 104 FFT part 105 Demapping part 106 Demodulation part 107 Decoding part 108 Power calculation part 109 Power difference calculation part 110 Determination part 111 Notification data generation part

Claims (7)

A second communication system that uses the same frequency band as the first communication system, wherein a base station group that forms a null point at a position of a radio station of the first communication system and the base station group cooperate with each other. A terminal that receives a signal to be transmitted, and a sensor station that is provided in the vicinity of the wireless station and estimates a channel estimation value using reference signals transmitted from a plurality of base stations belonging to the base station group. A base station in the second communication system,
Of the received power at the radio station of the reference signal transmitted from the plurality of base stations, obtained from the channel estimation value, the power of the minimum received power and other received power other than the minimum received power A calculating means for calculating the difference;
Determining means for determining whether to exclude, from the base station group, a base station corresponding to the minimum received power based on the power difference;
A base station. The determination means excludes, from the base station group, a base station corresponding to the minimum received power when the power difference is larger than a preset threshold.
The base station according to claim 1. The calculating means is the power that is a difference between the minimum received power and an average value of the other received powers of the received power of the reference signal transmitted from the plurality of base stations at the wireless station. Calculate the difference,
The base station according to claim 1. The calculation means includes the reception power at the radio station of the reference signal transmitted from a base station other than the base station corresponding to the minimum reception power among the plurality of base stations, and the minimum reception. Calculating the difference between the power and the power,
The determination unit excludes the base station corresponding to the minimum received power from the base station group when any one of the power differences corresponding to the other base stations is larger than the threshold.
The base station according to claim 1. The first communication system is a satellite communication system, and the second communication system is a mobile communication system;
The base station according to claim 1. A communication system using the same frequency band as other communication systems,
A base station group for forming a null point at a position of a radio station of the other communication system;
A terminal that receives signals transmitted in cooperation with the base station group;
A sensor station that is provided in the vicinity of the wireless station and that estimates a channel estimation value using reference signals transmitted from a plurality of base stations belonging to the base station group, and
The base station
Of the received power at the radio station of the reference signal transmitted from the plurality of base stations, obtained from the channel estimation value, the power of the minimum received power and other received power other than the minimum received power A calculating means for calculating the difference;
Determination means for determining whether to exclude, from the base station group, a base station corresponding to the minimum received power based on the power difference,
Communications system. A second communication system that uses the same frequency band as the first communication system, wherein a base station group that forms a null point at a position of a radio station of the first communication system and the base station group cooperate with each other. A terminal that receives a signal to be transmitted, and a sensor station that is provided in the vicinity of the wireless station and estimates a channel estimation value using reference signals transmitted from a plurality of base stations belonging to the base station group. A base station exclusion determination method in the second communication system,
Of the received power at the radio station of the reference signal transmitted from the plurality of base stations, obtained from the channel estimation value, the power of the minimum received power and other received power other than the minimum received power A calculation step for calculating the difference;
A determination step of determining whether to exclude, from the base station group, a base station corresponding to the minimum received power based on the power difference;
A base station exclusion determination method comprising:

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