This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2012-235559, filed on Oct. 25, 2012, the entire contents of which are incorporated herein by reference.
The embodiments discussed herein are related to a wireless communication apparatus, a wireless communication circuit, a wireless communication system, and a wireless communication method.
A femto base station (Home eNB: HeNB), also referred to as low power base station, is often installed in a personal residence or the like to extend indoors coverage of a cellular network, such as Universal Mobile Telecommunication System (UMTS). A coverage area of a femto base station is commonly referred to as a femto cell, a low power cell or a small cell. In the femto base station, for example, access restriction is implemented so that users other than a registered user are restricted from connecting to the femto base station.
When using a femto base station, for example, a user who is close to the femto base station but is not able to connect to the femto base station may receive interference from the femto base station, so that the throughput may be degraded or the connection may be disconnected. To cope with this, a method is known in which transmission power from the femto base station is reduced when such a user is detected (for example, see Japanese Laid-open Patent Publication No. 2010-283826).
When two femto base stations are close to each other, the femto base stations may interfere with each other, so that the throughput may be degraded. To cope with this, a method is known in which the femto base station performs bandwidth control (for example, see Japanese Laid-open Patent Publication No. 2010-103753).
According to an aspect of the invention, a wireless communication apparatus, includes: a processor configured to: perform a first detection to detect another wireless communication apparatus that shares given frequency bands with the wireless communication apparatus and that causes interference with the wireless communication apparatus, perform a second detection to detect a second wireless terminal that has communication quality lower than or equal to a given value from a first wireless terminal that communicates with the wireless communication apparatus, and select a frequency band from the given frequency bands for communication with the first wireless terminal based on a combination of detection result of the first detection and the second detection; and a transmitter coupled to the processor and configured to transmit a signal to the first wireless terminal using the selected frequency band.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
Hereinafter, embodiments of to a base station, a communication system, and a communication method will be described in detail with reference to the drawings.
While inventing the present embodiments, observations were made regarding a related art. Such observations include the following, for example.
In a communication system of the related art, there is a case in which the throughput of a user terminal that receives interference from a femto base station or the like and a user terminal connected to the femto base station or the like is difficult to be improved.
Therefore, the embodiments disclosed herein, for example, provide wireless communication apparatus, a wireless communication circuit, a wireless communication system, and a wireless communication method that may improve the throughput. The wireless communication apparatus includes a base station, for example.
The first base station 110 and the second base station 120 can use given frequency bands (hereinafter referred to as the “common frequency band”) in each cell thereof and form cells adjacent to each other. In other words, the first base station 110 and the second base station 120 form cells which may interfere with each other. Each of the first base station 110 and the second base station 120 is, for example, a Home eNodeB (HeNB) that forms a femto cell.
The wireless terminals 101 and 102 are wireless terminals that are connected to the cell of the first base station 110. The wireless terminal 102 is a low quality terminal whose communication quality with the first base station 110 is lower than or equal to a given value because of the reasons that the distance between the wireless terminal 102 and the first base station 110 is long or the wireless terminal 102 receives interference from the second base station 120 because the distance from the second base station 120 is short.
The wireless terminal 103 is a wireless terminal that is connected to the cell of the second base station 120. Although the wireless terminal 104 is connected to none of the first base station 110 and the second base station 120, the wireless terminal 104 is located close to the first base station 110 and is an interfered terminal (also referred to herein as a victim terminal) which is interfered by transmission signals from the first base station 110 to the wireless terminals 101 and 102. Each of the wireless terminals 101 to 104 is, for example, a user equipment (UE).
The first base station 110 wirelessly transmits a downlink signal to the wireless terminals 101 and 102 that are connected to the cell of the first base station 110. Specifically, the first base station includes first detection unit 111, second detection unit 112, third detection unit 113, a selection unit 114, and a transmission unit 115.
The first detection unit 111 detects presence or absence of an adjacent base station that is performing communication among adjacent base stations such as the second base station 120. For example, the first detection unit 111 detects presence or absence of an adjacent base station that is performing communication based on a signal transmitted from adjacent base stations. The first detection unit 111 outputs the detection result to the selection unit 114.
The second detection unit 112 detects presence or absence of a low quality terminal such as the wireless terminal 102. For example, the second detection unit 112 detects a low quality terminal based on communication quality notified from wireless terminals connected to the first base station 110. The second detection unit 112 outputs the detection result to the selection unit 114.
The third detection unit 113 detects presence or absence of an interfered terminal such as the wireless terminal 104. For example, the third detection unit 113 measures radio frequency (RF) power of an uplink signal transmitted from wireless terminals connected to other cells and detects presence or absence of an interfered terminal based on the measurement result. The third detection unit 113 outputs the detection result to the selection unit 114.
The selection unit 114 selects a frequency band used for the first base station 110 to transmit a downlink signal from the common frequency band based on a combination of the detection results outputted from the first detection unit 111, the second detection unit 112, and the third detection unit 113. Then, the selection unit 114 notifies the transmission unit 115 of the selected frequency band.
For example, the selection unit 114 extracts candidates of the frequency band corresponding to the combination of the detection results based on correspondence information between the combination of the detection results and candidates of the frequency band included in the common frequency band. Then the selection unit 114 calculates the throughput between the base station 110 and the wireless terminals (for example, the wireless terminals 101 and 102) that are connected to the cell of the base station 110 for each of the extracted candidates of the frequency band and selects the frequency band from the extracted candidates of the frequency band based on the calculated throughputs. Thereby, it is possible to select a frequency band in which the throughput is most improved from the candidates of the frequency band corresponding to the combination of the detection results.
The transmission unit 115 wirelessly transmits a downlink signal to the wireless terminals 101 and 102 that are connected to the cell of the first base station 110 by using the frequency band notified by the selection unit 114. However, the transmission unit 115 does not have to use all of the frequency band notified by the selection unit 114, but may use a part of the frequency band notified by the selection unit 114.
The second base station includes first detection unit 121, second detection unit 122, third detection unit 123, a selection unit 124, and a transmission unit 125. The configurations of first detection unit 121, the second detection unit 122, the third detection unit 123, the selection unit 124, and the transmission unit 125 of the second base station 120 are the same as those of the first detection unit 111, the second detection unit 112, the third detection unit 113, the selection unit 114, and the transmission unit 115 of the second base station 110, respectively.
In the example illustrated in
For example, when an adjacent base station is detected by the first detection unit 111 and a low quality terminal is detected by the second detection unit 112, the selection unit 114 of the first base station 110 selects a part of the common frequency band. Thereby, in the example illustrated in
Thereby, the first base station 110 urges the second base station to use a frequency band that is not used by the first base station 110 in the common frequency band, so that it is possible to reduce the interference from the second base station 120 to the wireless terminal 102.
When an interfered terminal is detected by the third detection unit 113, even if at least either one of an adjacent base station and a low quality terminal is not detected, the selection unit 114 of the first base station 110 may select a part of the common frequency band. Thereby, in the example illustrated in
Thereby, the first base station 110 urges the wireless terminal 104 to use a frequency band that is not used by the first base station 110 in the common frequency band, so that it is possible to reduce the interference from the first base station 110 to the wireless terminal 104.
In this way, in the communication system 100, the first base station 110 and the second base station 120 adjacent to each other autonomously control the transmission frequency band according to the combination of the detection results of the victim UE by the cell thereof, the low quality UE of the cell thereof, and the adjacent base station. Thereby, it is possible to improve the throughput of the victim UE and the low quality UE and improve the throughput of the entire communication system 100.
The base station 200 includes a receiving antenna 201, a receiver 202, a received signal processing unit 203, a victim UE detection unit 204, an adjacent HeNB detection unit 205, a low quality UE detection unit 206, a UE quality information acquisition unit 207, and a transmission pattern table storage unit 208. The base station 200 further includes a transmission pattern candidate extraction unit 209, a throughput estimation unit 210, a transmission pattern determination unit 211, a UE scheduler 212, a transmission signal creation unit 213, a transmitter 214, and a transmission antenna 215.
Each of the first detection units 111 and 121 illustrated in
Each of the selection units 114 and 124 illustrated in
The receiver 202 receives a signal wirelessly transmitted from another wireless communication apparatus (for example, a wireless terminal or another base station) through the receiving antenna 201. Then, the receiver 202 outputs the received signal to the received signal processing unit 203.
The received signal processing unit 203 performs channel estimation and received signal processing such as decoding on the signal outputted from the receiver 202. Then, the received signal processing unit 203 outputs the signal obtained by the received signal processing to the victim UE detection unit 204, the adjacent HeNB detection unit 205, the low quality UE detection unit 206, and the UE quality information acquisition unit 207.
The victim UE detection unit 204 detects a victim UE (an interfered terminal), which is not connected to the cell of the base station 200 and receives interference of a signal transmitted from the base station 200, based on the signal outputted from the received signal processing unit 203. For example, the victim UE detection unit 204 measures electric power of an uplink signal transmitted from UE connected to another cell and if the measurement result is greater than or equal to a certain value, the victim UE detection unit 204 determines that there is a victim UE.
The electric power of an uplink signal transmitted from UE connected to another cell can be measured by, for example, detecting a signal of a known pattern of the uplink signal transmitted from the UE connected to the other cell and measuring electric power of the detected signal. Or, the electric power of an uplink signal transmitted from UE connected to another cell can be measured based on interference power to an uplink signal received from UE that is connected to the base station 200. The victim UE detection unit 204 outputs the detection result of the victim UE to the transmission pattern candidate extraction unit 209.
The adjacent HeNB detection unit 205 detects an adjacent HeNB that forms an adjacent cell which can share a common frequency band with the cell of the base station 200 and generates interference between the adjacent cell and the cell of the base station 200, based on the signal outputted from the received signal processing unit 203. For example, the for cell search can detect an adjacent HeNB by measuring electric power of a downlink signal transmitted from the adjacent HeNB for cell search in the adjacent cell. The for cell search outputs the detection result of the adjacent HeNB to the transmission pattern candidate extraction unit 209.
The low quality UE detection unit 206 detects a low quality UE (a low quality terminal), which is connected to the cell of the base station 200 and whose communication quality is lower than or equal to a given value, based on the signal outputted from the received signal processing unit 203. For example, the low quality UE detection unit 206 acquires CQI (Channel Quality Indicator: channel quality information), which is transmitted from UE in the cell of the base station 200 and which indicates a downlink communication quality of the UE in the cell of the base station 200, and calculates an average of the acquired CQIs in a certain period of time. When the calculated average of the CQIs is smaller than or equal to a certain value, the low quality UE detection unit 206 determines that the UE that transmits the CQIs is a low quality UE. The low quality UE detection unit 206 outputs the detection result of the low quality UE to the transmission pattern candidate extraction unit 209.
The UE quality information acquisition unit 207 acquires quality information, which indicates downlink communication quality of each UE that is connected to the cell of the base station 200, based on the signal outputted from the received signal processing unit 203. For example, the UE quality information acquisition unit 207 acquires CQI for each frequency band transmitted from UE in the cell of the base station 200 as the quality information. Then, the UE quality information acquisition unit 207 outputs the acquired quality information to the throughput estimation unit 210.
The transmission pattern table storage unit 208 stores a transmission pattern table (correspondence information) that associates a combination of the detection results of the victim UE detection unit 204, the adjacent HeNB detection unit 205, and the low quality UE detection unit 206 with candidates of transmission pattern. The transmission pattern is information that indicates a frequency band used for the base station 200 to transmit a signal to UE. In the transmission pattern table, one or a plurality of candidates of transmission pattern are associated with each combination of the detection results.
The transmission pattern candidate extraction unit 209 acquires the detection results of the victim UE detection unit 204, the adjacent HeNB detection unit 205, and the low quality UE detection unit 206. Further, the transmission pattern candidate extraction unit 209 acquires one or a plurality of candidates of transmission pattern associated with the combination of the acquired detection results from the transmission pattern table storage unit 208. Then, the transmission pattern candidate extraction unit 209 notifies the throughput estimation unit 210 and the transmission pattern determination unit 211 of the acquired candidates of transmission pattern.
The throughput estimation unit 210 calculates estimation value of downlink throughput of each UE that is connected to the cell of the base station 200 for each candidate of transmission pattern notified from the transmission pattern candidate extraction unit 209 based on the quality information outputted from the UE quality information acquisition unit 207. Then, the throughput estimation unit 210 outputs the calculated estimation values of the throughput to the transmission pattern determination unit 211. The calculation of the estimation value of the throughput by the throughput estimation unit 210 will be described later.
The transmission pattern determination unit 211 determines a transmission pattern used to transmit a signal to UE from among the candidates of transmission pattern notified from the transmission pattern candidate extraction unit 209. For example, the transmission pattern determination unit 211 determines a transmission pattern whose estimation value of throughput notified from the throughput estimation unit 210 is the greatest among the notified candidates of transmission pattern to be the transmission pattern used to transmit a signal to the UE. The transmission pattern determination unit 211 notifies the UE scheduler 212 of the determined transmission pattern.
The UE scheduler 212 performs scheduling to assign a wireless resource to the UE so that a frequency band indicated by the transmission pattern notified from the transmission pattern determination unit 211 is used. The wireless resource includes, for example, a frequency resource and a time resource. The UE scheduler 212 outputs the result of the scheduling to the transmission signal creation unit 213.
The transmission signal creation unit 213 creates a signal to be transmitted to the UE based on the result of the scheduling outputted from the UE scheduler 212. Then, the transmission signal creation unit 213 outputs the created signal to the transmitter 214. The transmitter 214 wirelessly transmits the signal outputted from the transmission signal creation unit 213 to the UE through the transmission antenna 215.
For the digital circuit 231, for example, a digital signal processor (DSP), a field programmable gate array (FPGA), or the like can be used. In this case, for example, the receiver 202 includes an analog/digital converter (ADC) that converts an analog signal outputted from the receiving antenna 201 into a digital signal and outputs the digital signal to the digital circuit 231. Further, for example, the transmitter 214 includes an digital/analog converter (DAC) that converts a digital signal outputted from the digital circuit 231 into an analog signal and outputs the analog signal to the transmission antenna 215.
The transmission pattern table storage unit 208 illustrated in
First, the transmission pattern candidate extraction unit 209 acquires the detection result of the victim UE from the victim UE detection unit 204 (step S301). Further, the transmission pattern candidate extraction unit 209 acquires the detection result of the adjacent HeNB from the adjacent HeNB detection unit 205 (step S302). Further, the transmission pattern candidate extraction unit 209 acquires the detection result of the low quality UE from the low quality UE detection unit 206 (step S303). The order of the steps S301 to S303 can be changed.
Next, the transmission pattern candidate extraction unit 209 extracts candidates of the transmission pattern based on a combination of the detection results acquired by the steps S301 to S303 (step S304). Next, the transmission pattern determination unit 211 acquires an estimation value of the throughput from the throughput estimation unit 210 for each candidate of the transmission pattern extracted by the step S304 (step S305).
Next, the transmission pattern determination unit 211 determines the transmission pattern from among the candidates extracted by the step S304 based on the estimation value of the throughput acquired by the step S305 (step S306), and completes the series of operations.
By the steps described above, it is possible to extract candidates of the transmission pattern based on the combination of the detection results of the victim UE, the adjacent HeNB, and the low quality UE and select a transmission pattern whose throughput is high from among the extracted candidates.
The transmission pattern P1 illustrated in
The transmission pattern P2 illustrated in
The transmission pattern P3 illustrated in
In this way, in the transmission patterns P2 and P3 that use a part of the common frequency band 410, the power density is greater than that of the transmission pattern P1 that uses the entire band of the common frequency band 410. Thereby, when a part of the common frequency band 410 is used, it is possible to wirelessly transmit a signal by using a power density greater than that used when the entire band of the common frequency band 410 is used. Thereby, it is possible to suppress degradation of the throughput when only a part of the common frequency band 410 is used.
Calculation of Estimation Value of Throughput
The calculation of the estimation values of the throughput of the transmission patterns P1, P2, and P3 by the throughput estimation unit 210 will be described. For example, it is assumed that CQIs of the lower frequency side of UE#i (i=1, 2, 3, and so on) are CQI_L[i] and CQIs of the upper frequency side of UE#i are CQI_H[i]. In this case, the estimation values of the throughput of the UE#i TP1[i] to TP2[i] when the patterns P1, P2, and P3 are used can be calculated by, for example, the formulas (I) below.
T
P1
[i]=log2(1+f(CQI—L[i]))
+log2(1+f(CQI—H[i]))
T
P2
[i]=log2(1+f(CQI—L[i]))
T
P3
[i]=log2(1+f(CQI—H[i])) (1)
In the above formulas (I), Shannon's channel capacity formula, C=log2(1+SINR) is used. Further, f(CQI) is a conversion formula from CQI to a signal to interference and noise ratio (SINR).
The throughput estimation unit 210 calculates the estimation values TP1[i] to TP2[i] of the throughput for each UE#i (i=1, 2, 3, and so on) of the base station 200. Then, throughput estimation unit 210 calculates an average value of the estimation values of the throughput for each of the patterns P1, P2, and P3 and outputs the calculation results to the transmission pattern determination unit 211. However, throughput estimation unit 210 may calculate not only the average value of the estimation values of the throughput, but also other indexes based on the estimation values of the throughput such as the minimum value and the logarithmic mean of the estimation values of the throughput.
In this way, it is possible to calculate an estimated throughput for each frequency band by using CQI for each frequency band transmitted by UE, so that it is possible to calculate the throughput of each user for each transmission pattern including the increase of the power density.
When Victim UE is Detected
For example, when a victim UE is detected, it is desirable to secure a frequency band in which interference is small in order to help the victim UE. Therefore, in the transmission pattern table 500, records where the detection result of the victim UE is “DETECTED” are associated with the transmission patterns P2 and P3 whose frequency band is halved. In this case, the base station 200 selects a transmission pattern by which the throughput is the highest from the transmission patterns P2 and P3.
When Both Low Quality UE and Adjacent HeNB are Detected
When both a low quality UE and an adjacent HeNB are detected, it is desirable to limit the frequency band of the adjacent HeNB. Therefore, in the transmission pattern table 500, records where the detection results of the low quality UE and the adjacent HeNB are “DETECTED” are associated with the transmission patterns P2 and P3 whose frequency band is halved. In this case, the base station 200 selects a transmission pattern by which the throughput is the highest from the transmission patterns P2 and P3.
Other Cases
In the transmission pattern table 500, records where the detection result of the victim UE is “NOT DETECTED” and the detection result of at least either one of the low quality UE and the adjacent HeNB is “NOT DETECTED” are associated with the transmission patterns P1, P2, and P3 including the transmission pattern P1. In this case, the base station 200 selects a transmission pattern by which the throughput is the highest from the transmission patterns P1, P2, and P3.
When the transmission patterns P2 and P3 are selected in an adjacent cell, one-half of the entire frequency band is not used in the adjacent cell. Therefore, it is highly probable that the estimation value of the throughput of either one of the transmission patterns P2 and P3 is the greatest among the candidate transmission patterns P1, P2, and P3. As a result, it is possible to improve the throughput by automatically selecting different frequency bands between the base stations 200 adjacent to each other.
The cell 611a of the HeNB 611 and the cell 612a of the HeNB 612 are adjacent to each other. Therefore, the HeNB 611 detects the HeNB 612 as an adjacent HeNB. Also, the HeNB 612 detects the HeNB 611 as an adjacent HeNB.
Although the HUE 621 (Home UE) is connected to the HeNB 611, the HUE 621 is away from the HeNB 611 and further the HUE 621 is close to the HeNB 612 to receive interference from the HeNB 612, so that the HUE 621 is a low quality terminal whose quality of communication with the HeNB 611 is low. Therefore, the HeNB 611 detects the HUE 621 as a low quality UE.
The HUE 622 is connected to the HeNB 612.
The Macro UEs (MUEs) 631 and 632 are located in a range of the cell 613a of the Macro eNB (MeNB) 613 and connected to the MeNB 613. Although the MUE 631 is not connected to the HeNB 611, the MUE 631 is close to the HeNB 611, so that the MUE 631 is a victim UE that receives interference from the HeNB 611. Therefore, the HeNB 611 detects the MUE 631 as a victim UE.
The transmission pattern 621a represents a frequency band of a downlink signal transmitted from the HeNB 611 to the HUE 621. In a state illustrated in
The transmission pattern 631a represents a frequency band of a downlink signal transmitted from the HeNB 613 to the HUE 631. In the state illustrated in
The HeNB 611 detects the adjacent HeNB (HeNB 612), the victim UE (MUE 631), and the low quality UE (HUE 621), so that the HeNB 611 selects a pattern where the throughput is high from the patterns P2 and P3 in which the frequency band is halved. Here, as illustrated in
Thereby, the interference to the MUE 631 from the HeNB 611 decreases in the upper side of the frequency band, so that as illustrated in
Since the HeNB 612 detects only the adjacent HeNB (HeNB 611), the HeNB 612 selects any one of the patterns P1, P2, and P3. Here, the interference from the HeNB 611 decreases in the upper side of the frequency band, so that the throughput is the greatest by the pattern P3 that uses only the upper side of the frequency band. Therefore, as illustrated in
In this way, the HeNBs 611 and 612 can autonomously performs interference control in the communication system 600 in which a macro base station (MeNB 613) and femto base stations (HeNBs 611 and 612) coexist. Thereby, it is possible to help the victim UE (MUE 631) and improve the throughput of the femto users (HUEs 621 and 622), so that it is possible to improve the throughput of the entire communication system 600.
As described above, according to the first embodiment, each femto base station adjacent to each other can autonomously control the transmission frequency band according to a combination of the detection results of a victim UE affected by the femto base station, a low quality UE in the cell of the femto base station, and an adjacent femto base station. Thereby, it is possible to improve the throughput of both the victim UE and the low quality UE and improve the throughput of the entire system.
Differences of the base station 200 according to a second embodiment from the base station 200 according to the first embodiment will be described. For example, in LTE, Synchronization Signal (SS) is transmitted at a given timing twice per 10 [ms] in frequency bands of six resource blocks (RBs) at the center of the common frequency band 410. The SS includes, for example, synchronization information.
Further, for example, in LTE, Physical Broadcast Channel (PBCH) is transmitted at a given timing once per 10 [ms] in frequency bands of six resource blocks at the center of the common frequency band 410. The PBCH includes, for example, system information. The SS and PBCH are channels which UE receives when starting communication.
The central frequency band 710 indicates a frequency band including a frequency band in which control signals such as the SS and the PBCH are transmitted in the common frequency band 410. For example, the central frequency band 710 is a frequency band occupying the central ⅛ of the common frequency band 410. The transmission patterns P1, P2, and P3 illustrated in
The transmission pattern P4 illustrated in
The transmission pattern P5 illustrated in
The transmission pattern P6 illustrated in
In this way, in the transmission patterns P4, P5, and P6 illustrated in
Further, in the transmission patterns P4, P5, and P6 that use a part of the common frequency band 410, the power density is greater than that of the transmission pattern P1 that uses the entire band of the common frequency band 410. Thereby, when a part of the common frequency band 410 is used, it is possible to wirelessly transmit a signal by using a power density greater than that used when the entire band of the common frequency band 410 is used. Thereby, it is possible to suppress degradation of the throughput when only a part of the common frequency band 410 is used.
For example, when a victim UE is detected, to help the victim UE, it is desirable to secure a frequency band in which the control signals such as the SS and the PBCH are transmitted. Therefore, in the transmission pattern table 500 illustrated in
As described above, according to the second embodiment, a plurality of candidate frequency bands associated with a combination in a case in which an interfered terminal is detected are frequency bands, from which given frequency bands in which given control signals are transmitted by another communication apparatus is removed. Thereby, it is possible to reduce interference to the control signals.
Further, the signal transmitting timing may be synchronized among the MeNB 613 and the HeNB 611 and 612, and transmission patterns may be transmitted for every time period. Thereby, it is possible to avoid that a transmission pattern which generates interference to the control signals such as the SS and the PBCH continues, so that it is possible to efficiently avoid the interference to the control signals such as the SS and the PBCH.
Differences of the base station 200 according to a third embodiment from the base station 200 according to the first embodiment will be described.
The selection unit 114 of the first base station 110 selects a frequency band used for the first base station 110 to transmit a downlink signal from the common frequency band based on a combination of the detection results outputted from the first detection unit 111 and the second detection unit 112.
The selection unit 124 of the second base station 120 selects a frequency band used for the second base station 120 to transmit a downlink signal from the common frequency band based on a combination of the detection results outputted from the first detection unit 121 and the second detection unit 122.
The transmission pattern table storage unit 208 stores a transmission pattern table that associates a combination of the detection results of the adjacent HeNB detection unit 205 and the low quality UE detection unit 206 with candidates of transmission pattern. The transmission pattern candidate extraction unit 209 acquires one or a plurality of candidates of transmission pattern associated with the combination of the detection results of the adjacent HeNB detection unit 205 and the low quality UE detection unit 206 from the transmission pattern table storage unit 208.
First, the transmission pattern candidate extraction unit 209 acquires the detection result of the adjacent HeNB from the adjacent HeNB detection unit 205 (step S1101). Further, the transmission pattern candidate extraction unit 209 acquires the detection result of the low quality UE from the low quality UE detection unit 206 (step S1102). The order of the steps S1101 and S1102 can be changed.
Next, the transmission pattern candidate extraction unit 209 extracts candidates of the transmission pattern based on a combination of the detection results acquired by the steps S1101 to S1102 (step S1103). Next, the transmission pattern determination unit 211 acquires an estimation value of the throughput from the throughput estimation unit 210 for each candidate of the transmission pattern extracted by the step S1103 (step S1104).
Next, the transmission pattern determination unit 211 determines the transmission pattern from among the candidates extracted by the step S1103 based on the estimation value of the throughput acquired by the step S1104 (step S1105), and completes the series of operations.
By the steps described above, it is possible to extract candidates of the transmission pattern based on the combination of the detection results of the adjacent HeNB and the low quality UE and select a transmission pattern whose throughput is high from among the extracted candidates.
As illustrated in
The HeNB 611 detects the adjacent HeNB (HeNB 612) and the low quality UE (HUE 621), so that the HeNB 611 selects a pattern where the throughput is high from the patterns P2 and P3 in which the frequency band is halved. Here, as illustrated in
On the other hand, the HeNB 612 detects only the adjacent HeNB (HeNB 611), the HeNB 612 selects any one of the patterns P1, P2, and P3. Here, the interference from the HeNB 611 decreases in the upper side of the frequency band, so that the throughput is the greatest by the pattern P3 that uses only the upper side of the frequency band. Therefore, as illustrated in
In this way, also in the third embodiment in which the detection of the victim UE is omitted, the HeNBs 611 and 612 can autonomously performs interference control in the communication system 600 in which a macro base station (MeNB 613) and femto base stations (HeNBs 611 and 612) coexist. Thereby, it is possible to improve the throughput of the femto users (HUEs 621 and 622), so that the throughput of the entire communication system 600 can be improved.
Thereby, for example, when the first base station 110 and the second base station 120 select the transmission patterns P2 and P3 respectively, it is possible to suppress interference to each other. Further, in each of the first base station 110 and the second base station 120, a plurality of frequency bands which do not overlap each other are used, so that it is possible to further improve the throughput by a frequency diversity effect.
In this way, each of the transmission patterns P2 and P3 which use a part of frequency bands of the common frequency band 410 among the transmission patterns P1, P2, and P3 includes a plurality of frequency bands which do not overlap each other, so that the throughput can be further improved.
As described above, according to the base station, the communication system, and the communication method, it is possible to improve the throughput.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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2012-235559 | Oct 2012 | JP | national |