Patent Application
20100035542
The present application claims priority from Japanese patent application JP2008-205760 filed on Aug. 8, 2008, the content of which is hereby incorporated by reference into this application.
A technology disclosed in the present specification relates to a radio communication system including a repeater apparatus and a repeater control unit as constituent elements.
First, the background of a radio mobile communication system is described.
In the radio communication system, a base station device connected to a backbone network and a mobile station device having only a radio I/F transmit data signals (also including audio signals) wirelessly to each other.
As an interface standard of the radio portion, there is known, for example, Ultra Mobile Broadband (UMB). The UMB belongs to a so-called 3.9-th generation mobile communication system. In a standards document, the rule of a method of transmitting the data signal, a control signal, and so on, is defined for each of the base station and the mobile station.
The UMB adopts an orthogonal frequency division multiple access (OFDMA) system and a code division multiple access (CDMA) system in order to transmit the data signal and the control signal. The CDMA signal is mapped on a resource block of the OFDMA after the discrete Fourier transform (DFT) has been performed, and thus the UMB is allowed to be regarded as an OFDMA-based system. Long Term Evolution (LTE) being a communication system of the same generation as the UMB also adopts the OFDMA system, and the OFDMA system is a mainstream after the 3.9-th generation.
As of 2008, the standardization activity on the standard of IMT-Advanced which is considered as the fourth generation has started in earnest. When the 3.9-th generation is treated as a migration generation to the fourth generation, there is the high possibility that the OFDMA will be adopted as the communication system.
Prior to the standardization activity, in 2007, a frequency band allocation for the fourth generation mobile communication has been determined in the World Radiocommunication Conference 2007 (WRC07). The highlight is 3.5 GHz band that enables the band width of 100 MHz to be ensured in both of uplink and downlink.
In the conventional mobile communication system including the 3.9-th generation, the use of an 800 MHz band and a 2 GHz band is mainstream. On the contrary, the 3.5 GHz band is a high frequency band, and there is concern that the propagation distance of radio waves is shortened. In other words, in order to ensure the conventional coverage area of the mobile communication system, there is a need to install several times more base stations than in the conventional art.
Subsequently, the background of the repeater apparatus is described.
In a cellular system in which the base station devices are spread, there frequently occurs an area (dead zone) in which arrival of radio waves is difficult. The dead zone is liable to occur in underground cities, indoors, and in high-rises. In order to solve the above-mentioned problem, there is installed a repeater apparatus that relays radio waves with respect to the base stations.
As a method of realizing the repeater apparatus, there can be applied, in principle, a method involving performing digital signal processing to remove unnecessary interference, or a method involving decoding packets once to reconfigure a transmit signal, and transmitting the transmit signal to thereby enhance the performance of the repeater apparatus. However, the buffering or repeating process of the signal makes processing time long, and accordingly the transmit signal is delayed by several frames to several tens frames with respect to a signal used for the base station and the mobile station to directly communicate with each other. With the above-mentioned delay, for example, a repeat request of hybrid automatic repeat request (ARQ) is not made in time, and a requirement for the radio interface standard (UMB and so on) of the mobile communication cannot be achieved. Hence, as the repeater apparatus, a system of amplifying a radio frequency (RF) signal is general.
JP 2005-252938 A discloses a repeater apparatus having a directional antenna. A desired signal to be subjected to relay amplification, and an undesired signal not to be subjected to relay amplification arrive at the repeater apparatus, but the undesired signal can be suppressed by the directional antenna to execute the relay amplification.
3GPP2, C30-20060327-023R2, Naga Bhushan, “QUALCOMM Proposal for 3GPP2 Air Interface Evolution Phase 2, Rev. 2”, p.125, 2006/3 discloses a technology of reducing an interference between cells.
3GPP2, C. S0084-001-0, Version 2.0, “Physical Layer for Ultra Mobile Broadband (UMB) Air Interface Specification”, p.4-41, 2007/8 discloses a technology of controlling an interference between sectors.
An ultimate object of this invention is to reduce the number of installed base stations which are costly.
A reduction in the number of installed base stations causes two problems. In other words, (1) a reduction in coverage area, and (2) a deterioration in throughput per mobile station. The problem (1) can be eliminated by installation of a repeater apparatus. The problem (2) can be further classified into two problems. In other words, (A) a deterioration in throughput which is caused by a shortage of an absolute number of base stations, and (B) a deterioration in throughput which is accompanied by an increase in the number of mobile stations connected to the base station.
Solving the problem (A) is out of the scope of this invention. In order to solve the problem (A), the number of base stations should be increased. The problem (B) can be solved by an ingenuity and is to be solved by this invention.
The problem (B) is described in more detail. The throughput per mobile station is a result of dividing the throughput when the mobile stations occupy all of communication resources of the base station by the occupancy. The occupancy is in reverse proportion to the number of mobile stations connected to the base station. In other words, the throughput per mobile station is reduced more as the number of mobile stations connected to the base station increases more.
The number of mobile stations connected to the base station is unequal among the base stations, and hence the throughputs of the mobile stations connected to the base station originally having a larger number of connected mobile stations are improved when the number of mobile stations is made uniform among the base stations. As a result, the throughputs of a smaller number of mobile stations are reduced whereas the throughputs of a larger number of mobile stations can be improved.
Further, the number of mobile stations connected to the base station varies with time, and hence it is necessary to control the number thereof to be uniform while adjusting to connection environment.
In summary, this invention has been made to achieve the following three objects.
To make efficient use of a repeater apparatus to cover a decrease in number of installed base stations.
To make uniform the number of connected mobile stations among the base stations.
To control the number of connected mobile station to be uniform while adjusting to its time variation number of connected mobile station.
According to a representative invention disclosed in this application, there is provided a radio communication system, comprising: a plurality of base stations; and a repeater apparatus, wherein the repeater apparatus is configured to: amplify and transmit a radio signal received from at least one of the plurality of base stations; and control a domain in which the radio signal is transmitted based on a traffic amount of each of the plurality of base stations.
With the radio communication system and the repeater apparatus according to one embodiment of this invention, the number of connected mobile stations can be made uniform dynamically among the base stations. As a result, though a decrease in the throughputs of a smaller number of mobile stations is induced, the throughputs of a larger number of mobile stations can be improved. Further, the loads are uniformed among the base stations, whereby idle or almost-nonoperating base stations can be reduced, and the cost-effectiveness of the base station installation can be enhanced. Further, the number of installed base stations can be reduced by introduction of the repeater apparatus so that the costs necessary for the system construction can be suppressed.
There is provided a method of realizing an increase in coverage area of base stations and load distribution among the base stations with the use of a repeater in a radio communication system.
Base stations (BS) 101 cover areas (domains surrounded by heavy lines in the example of
A mobile station (MS) 107 implements data communication with a base station 101-2 (desired base station). The mobile station 107 is located at an edge of a sector 103-2 that is covered with the desired base station, and thus the mobile station 107 receives interference from other base stations 101-1 and 101-3 in a downlink traffic with substantially the same electric power as that of a radio signal from the desired base station. As a result, a desired signal to undesired signal power ratio (DUR) is deteriorated, resulting in such a problem that the communication quality is deteriorated by interference in addition to deterioration due to the propagation attenuation.
In the radio communication system, there is a need to consider the equality of the communication capacity among the mobile stations. However, in order to ensure the equality of the mobile stations including a mobile station low in DUR, there is a need to sacrifice the communication capacity of the entire system. This is not preferable in view of the efficiency of the system.
This problem does not induce no problem on the mobile station located in the vicinity of the base station. This is a problem only on the mobile station located on the boundary of the sectors. In order to eliminate the above-mentioned problem, there is a need to reduce the interference among the sectors or the base stations.
A mobile station 107-1 communicates with the base station 101-2 with the sector 103-2 as a serving sector (SS). Likewise, three mobile stations 107-2, 107-3, and 107-4 communicate with the base station 101-1 with a sector 103-1 as the SS, and four mobile stations 107-5, 107-6, 107-7, and 107-8 communicate with the base station 101-3 with a sector 103-3 as the SS. In other words,
The throughput of the mobile station is in inverse proportion to the number of mobile stations belonging to the sector. In other words, the throughput per mobile station is reduced more as the number of mobile stations increases. As a result, there arises a problem that services (guaranteed bandwidth) enjoyed by the mobile station are dispersed depending on the sector to be connected.
Further, when the guaranteed bandwidths of the respective mobile stations are identical with each other, there occurs a difference in operating rate among the sectors. In other words, under the condition that the guaranteed bandwidth is held constant, a larger amount of free communication resources occur in the sector as a smaller number of mobile stations belong to the sector. The operating rate is more deteriorated as the amount of free communication resources is larger, and hence there arises a problem that the operating rate (performance) to the base station installation costs is deteriorated.
In order to solve the problems posed in
A repeater 108 is installed on boundaries of the sector 103-1, the sector 103-2, and the sector 103-3. The repeater 108 receives a transmit signal from the base station 101-2 by a directional antenna, and receives signals from the base stations 101-1 and 101-3 after reducing gains thereof by the directional antenna (that is, blocks the signals). The repeater 108 amplifies only a signal from the base station 101-2, and radiates the signal toward an area 109 produced by the repeater 108.
As a result, the same signal as that in the sector 103-2 is radiated in coverage area 109 of the repeater. In other words, an area of the sector 103-2 can be broadened. Strictly speaking, the propagation path length is extended via the repeater 108, and a delay caused by processing inside of the repeater occurs. For that reason, a time at which a signal routed through the repeater 108 is received at the mobile station is delayed with respect to a signal that is transmitted from the base station 101-2 to directly reach the mobile station. The reason that the delay time causes no problem under a given condition is described later with reference to
Further, as a result that the repeater 108 amplifies the signal in the sector 103-2, the problem on the interference among the cells at the positions being originally the sector boundaries is eliminated. However, it is perceivable that the boundaries between the sector 103-2 and other sectors 103-1 and 103-3 are merely moved, but the problem on the interference among the sectors which is posed in
An increase in coverage area of the sector 103-2 is implemented by using the repeater 108 as illustrated in
More specifically, three mobile stations 107-1, 107-4, and 107-5 communicate with the base station 101-2 via the sector 103-2, and two mobile stations 107-2 and 107-3 communicate with the base station 101-1 via the sector 103-1. Further, three mobile stations 107-6, 107-7, and 107-8 communicate with the base station 101-3 via the sector 103-3.
As a result, the number of mobile stations connected to the base stations 101-1, 101-2, and 101-3 is 1:3:4 in the example of
In order to realize the load distribution, there is a need to relatively increase coverage area of the sector that is relatively small in traffic as compared with other sectors.
The repeater 108 receives downlink signals from the base stations by using a directional beam 110. The directional beam 110 blocks downlink signals from the base stations 101-1 and 101-3, and relatively emphasizes the signal from the base station 101-2. As a result, the repeater 108 can amplify only a desired downlink signal without amplifying useless interference within coverage area 109 of the repeater 108.
Further, the repeater 108 transmits uplink signals from the mobile stations to only the base station 101-2 by using the above-mentioned directional beam 110. As a result, unnecessary interference is not affected to the base stations 101-1 and 101-3.
The repeater 108 transmits a downlink signal from the base station by using a directional beam 111. The directional beam 111 allows the amplified downlink signal to be transmitted over the entire coverage area 109 of the repeater 108. The downlink signal to be transmitted depends on the directional beam 110 to the base station as illustrated in
On the other hand, in the uplink traffic, the repeater 108 receives the uplink signals in all directions viewed from the repeater 108 by means of the directional beam 111, amplifies the received signals, and transmits the amplified signals to the base station 101-2, for example, by means of the directional beam 110 illustrated in
In the above-mentioned method, in the uplink traffic, there can occur a phenomenon that the uplink signal transmitted to a destination of the base station 101-1 is amplified by the repeater 108 and then received by the base station 101-2. In other words, there is concern about the occurrence of interference between the base stations or interference between the sectors in the uplink traffic. This problem is eliminated by using a signal (F-IOTCH, forward interference over thermal channel, refer to 3GPP2 , C. S0084-001-0, Version 2.0, “Physical Layer for Ultra Mobile Broadband (UMB) Air Interface Specification”, p. 4-41, 2007/8 cited as the background) for controlling interference between the sectors, as with normal interference between the base stations and between the sectors through no repeater 108.
The above-mentioned method illustrated in
A signal transmitted by the base station 101 includes a first signal directly received by the mobile station 107, and a second signal received by the mobile station 107 via the repeater 108. This example is a downlink traffic example, and in the uplink traffic, a difference resides in that the base station 101 and the mobile station 107 illustrated in
Arrival times of the first and second signals on the receiving side (the mobile station 107 in the downlink traffic, and the base station 101 in the uplink traffic) are different depending on the propagation path length of the radio signal and a processing delay within the repeater 108. In general, the first signal is first received.
An example in which the first signal is received at an upper timing, and the second signal is received at a lower timing is described. In an orthogonal frequency division multiplexing (OFDM) system, respective subcarriers are multiplexed so that an OFDM symbol length becomes the integral multiple of a cycle of the subcarriers, to ensure orthogonality among the subcarriers. For that reason, a part of the second half of each OFDM symbol is allocated to a head of the OFDM symbol to prevent interference among the OFDM symbols which is caused by the delay time difference without impairing the periodicity. A loop signal allocated in this example is called “cyclic prefix (CP)”.
When the receive timing difference between the first signal and the second signal is within a length of the CP as illustrated in the example of
In a code division multiple access (CDMA) system, receivers that are in synchronism with the respective receive timings of the first signal and the second signal are prepared for the first signal and the second signal, and a delay time between those signals are uniformed and synthesized, thereby enabling the two signals to be synthetically received. This method is called “RAKE reception”.
In an example of
It is understood from comparison of
With the above-mentioned description, the problems on the radio communication system and the effect of eliminating the problems according to this invention have been confirmed. A method of realizing this invention is described below.
The base stations 101-1, 101-2, and 101-3 exchange data with another base station or another communication system via the base station control unit 104 and the packet data serving node (PDSN) 105. The base stations 101-1, 101-2, and 101-3 exchange data with another communication system over the IP network 106. A route communicating traffic data is indicated by thin lines in
A repeater control unit (RCU) 201 collects information necessary to control the repeater 108 from the base stations 101-1, 101-2, and 101-3, and exchanges information for controlling the repeater with the repeater 108. A route used for controlling the repeater 108 is indicated by thick lines in
The repeater control unit 201 can be arranged anywhere as long as a wired or wireless communication path to the base stations 101-1, 101-2, 101-3, and the repeater 108 can be ensured. For example, the repeater control unit 201 may be located in the base station 101-1, 101-2, or 101-3, or the base station control unit 104, or may be located in the repeater 108. Alternatively, the repeater control unit 201 may be located at another place independently. In any cases, the advantages of this invention are not affected.
First, the repeater control unit 201 requests a report on a repeater state from the repeater 108 (Step 901). The repeater 108 that has received the request transmits the repeater state information to the repeater control unit 201 (Step 902). More specifically, the repeater state information includes an identifier (ID) unique to the repeater, the number of repeater sectors, and an ID of the base station sector which is most strongly received by the respective repeater sectors. A format example of the repeater state information to be transmitted is illustrated in
The repeater sector is a sector realized by the directional beams 110 and 111 from the repeater 108. In the following description, the repeater sector is also referred to as “repeater sector 110” or “repeater sector 111”.
The repeater sector includes a repeater sector on a base station side in use for a communication between the repeater 108 and the base station 101, and a repeater sector on a mobile station side in use for a communication between the repeater 108 and the mobile station 107. In the example of
On the other hand, the section provided by the base station 101 is referred to as “base station sector 103” (for example, the base station sector 103-1 of
Further, the repeater control unit 201 requests the transmission of traffic information from the base station 101 (Step 903). The base station 101 that has received the request transmits the traffic information to the repeater control unit 201 (Step 904). More specifically, the traffic information includes an ID unique to the sector, and the total throughput of the sector or the operating rate of the sector (that is, the utilization of the resource). A format example of the traffic information to be transmitted is illustrated in
When managing a plurality of sectors, the base station 101 transmits the traffic information for each sector. For decision of the data size to be reported, the number of sectors may be inserted before the field of the sector ID. A format example of the traffic information when the number of sectors is inserted before the field of the sector ID is illustrated in
The repeater control unit 201 produces control information to be transmitted to the respective repeaters based on the traffic information of the respective base stations and the state information of the respective repeaters which have been recorded in the above-mentioned steps (Step 906), and transmits the control information to the respective repeaters (Step 907).
After transmitting the traffic information to the repeater control unit 201, the base station 101 adds up the traffic information in background that executes data communication (Step 908). More specifically, information for updating the sector throughput or the resource utilization is collected.
After transmitting the state information to the repeater control unit 201, the repeater 108 executes processing of updating the state (Step 909). More specifically, the repeater 108 updates the ID of the base station sector which is most strongly received by the respective repeater sectors.
Upon receiving the control information transmitted in Step 907, the repeater 108 controls transmission and reception according to the control information (Step 910). The details of the control are described later (refer to Step 407, etc. of
Subsequently, the repeater 108 transmits a notification indicating that the control has been completed to the repeater control unit 201 (Step 911).
After receiving the notification transmitted in Step 911, the repeater control unit 201 again transmits the traffic information request at given timing (for example, after a standby time has elapsed in Step 301 of
More specifically,
As illustrated in
For example, when the repeater control unit 201 receives the repeater state information illustrated in
Likewise, when the repeater control unit 201 receives the repeater state information from another repeater (for example, a repeater identified by a repeater ID “1001”, or a repeater identified by a repeater ID “1002”), the contents of the received repeater state information are recorded.
More specifically,
More specifically,
As illustrated in
Likewise, when the repeater control unit 201 receives the traffic information measured in another base station sector (for example, the base station sector identified by the base station sector ID “652”, or the base station sector identified by the base station sector ID “896”), the contents of the received traffic information are recorded.
The repeater control unit 201 waits until a clock counter within the repeater control unit reaches a constant value because the repeater control unit 201 operates in a given cycle (Step 301). The above-mentioned given cycle can be arbitrarily set, but typically follows a macro traffic variation, and therefore it is conceivable that a cycle of about 1 minute to 1 hour is appropriate.
In Step 302, the repeater control unit 201 requests state information transmission from the respective repeaters 108, collects the state information from the respective repeaters 108, and records the collected state information in the repeater control unit 201. In this stage, the ID of the base station sector which is affected by a change in coverage area by controlling the repeater 108 is specified as illustrated in
In Step 303, the repeater control unit 201 requests traffic information transmission from the respective base stations 101, collects the traffic information from the respective base stations 101, and records the collected traffic information in the repeater control unit 201. The traffic information may be collected from all of the base stations 101 within the system. However, the data volume to be collected is huge, and thus the repeater control unit 201 may request the traffic information transmission from only the base station that manages the base station sector ID having the repeater state information recorded therein based on the repeater state information (
In Step 304, the repeater control unit 201 initializes the repeater counter because the repeater control unit 201 controls all of the repeaters 108.
In Step 305, the repeater control unit 201 compares traffic among a plurality of base station sectors recorded in the repeater state information for each repeater. An example of an evaluation index is represented by the following formula.
In the numerical formula (1), reference r is an index of the repeater, S is an index of the repeater sector being a target, Tr(r, x) is a traffic amount of a repeater sector x of a repeater r (refer to
Calculated through the numerical formula (1) is a ratio of the traffic of the base station sector which is most strongly received by the repeater sector S of the repeater r to the traffic average of the base station sectors that are most strongly received by the repeater sectors other than the repeater sector S of the repeater r, respectively. In other words, a value calculated by the numerical formula (1) is an index indicating how larger or smaller the traffic of the base station sector which is most strongly received by the repeater sector S is than the traffics of other base station sectors around the repeater.
In Step 305, the repeater control unit 201 determines whether or not a value calculated by the numerical formula (1) is larger than a given threshold value (arbitrary value of 0 to 1).
When the value calculated by the numerical formula (1) is smaller than the threshold value (that is, when determination is yes in Step 305 of
Increasing the output of that repeater sector is realized by amplifying a signal from the base station sector which has been received by the repeater sector to thereby enlarge an area to be transmitted. As a result, coverage area of the base station sector whose traffic is determined to be relatively small is enlarged by means of the repeater whose transmission area is enlarged, thereby eliminating the imbalance of the traffics.
Then, in Step 307, the repeater control unit 201 adds 1 to the repeater counter in order to process a subsequent repeater because processing has been completed for one repeater.
When the value calculated through the numerical formula (1) is equal to or larger than the threshold value, the repeater control unit 201 executes Step 307 without execution of Step 306.
In Step 308, the repeater control unit 201 determines whether or not processing for all the repeaters 108 has been completed. If processing has not been completed, the repeater control unit 201 returns to Step 305 to execute processing for the subsequent repeater. If processing has been completed, the repeater control unit 201 transmits the control information to the respective repeaters 108 in Step 309.
In the example of
For example, in Step 305 of
In the example of
As in the example of
Processing for actually increasing or decreasing the output of the repeater sector based on the above-mentioned control information is executed in Step 406 of
First, the repeater 108 updates the state of the repeater 108 in Step 401 immediately after its activation. More specifically, the repeater 108 specifies the signal of the base station sector which is most strongly received by the respective repeater sectors, and determines the base station sector ID for each of the repeater sectors.
In Step 402, the repeater 108 waits to receive the state information transmission request from the repeater control unit 201.
In Step 403, the repeater 108 transmits the results of the state update executed in Step 401 or Step 404 (to be described later) in the previous loop to the repeater control unit 201 according to the format of
Step 404 is the same processing as that of Step 401.
In Step 405, the repeater 108 waits to receive the control information transmitted from the repeater control unit 201.
In Step 406, the repeater 108 controls the input and output of the repeater 108 based on the control information illustrated in
In Step 407, the repeater 108 notifies the repeater control unit 201 that processing of Step 406 has been completed.
A network I/F 501 is an interface for communicating the control information with the repeater control unit 201, and is realized by a wired or wireless interface device.
An input-output control unit 502 has a function of exchanging a control message with the repeater control unit 201, and a function of controlling the input/output of the repeater 108 based on the control information from the repeater control unit 201. For control of the input/output, the input-output control unit 502 controls a downlink switch 507, a downlink power amplifier 508, an uplink switch 512, and an uplink power amplifier 513. The input-output control unit 502 can be realized by a CPU or a DSP because the input-output control unit 502 is an arithmetic unit.
An antenna for base station 503 is an antenna for performing uplink and downlink radio communications with the base station 101, and at least one antenna is disposed for each of the repeater sectors. A plurality of the antennas are equipped for each repeater sector, thereby enabling multi-antenna communication within the repeater sector.
Duplexers 504 and 509 each have a function of distributing an uplink radio signal and a downlink radio signal by a filter in order that the antenna is shared between the uplink traffic and the downlink traffic.
Low noise amplifiers 505 and 511 are amplifiers used in an initial stage of the receiving side on which applied noises are small.
A state measurement unit 506 has a function of executing cell search for searching a base station sector which is most strongly received for each of the repeater sectors in baseband processing. More specifically, the state measurement unit 506 includes an A/D converter and a logic circuit or arithmetic unit (CPU or DSP) which executes synchronization and cell search.
The downlink switch 507 is made up of a switch and a multiplexer, changes over a connection between the receiving sector on the base station side and the transmitting sector on the mobile station side, and synthesizes the switch output. The switch is controlled by the input-output control unit 502.
The power amplifiers 508 and 513 each have a function of amplifying a transmit signal. The input-output control unit 502 controls the power amplifier 508 to control the transmit power for each of the sectors.
An antenna for mobile station 510 is an antenna for implementing the uplink and downlink radio communications with the mobile station 107, and the antenna is disposed for each of the repeater sectors. A plurality of the antennas are disposed for each of the repeater sectors, thereby enabling multi-antenna communication within the repeater sector.
The uplink switch 512 is made up of a switch and a multiplexer, changes over a connection between the receiving sector on the mobile station side and the transmitting sector on the base station side, and synthesizes the switch output. The configuration of the uplink switch 512 is identical with that of the downlink switch 507, and controlled by the input-output control unit 502.
The state measurement unit 506 executes analog-digital conversion by each ADC 514 in response to the output of the low noise amplifier 505 for each of the repeater sectors according to the downlink receive signal from the base station 101. Thereafter, the state measurement unit 506 executes frame synchronization processing using a matched filter in a synchronizer 515, and then inputs a receive signal establishing frame synchronization to a cell searcher 516.
In the case of a CDMA receiver, the cell searcher 516 executes correlation calculation by means of the matched filter while changing a sector specific spreading code of the base station, and records the ID of the base station sector having the largest calculated value in a memory 517. In the case of an OFDM receiver, the cell searcher 516 converts the receive signal into a frequency domain by FFT calculation. The cell searcher 516 reads the base station sector specific ID from a broadcast signal which is transmitted from the base station 101 into the base station sector, and records the read ID in the memory 517. The above-mentioned matched filter and FFT calculation can be realized by a logic circuit, a CPU, a DSP, or the like.
When recording in the memory 517, the base station sector ID is recorded for each of the repeater sectors, for example, as illustrated in
More specifically,
The output of the low noise amplifier 505 or 511 is a receive signal of each repeater sector.
Switches 518 each change over a connection between the receiving side repeater sector and the transmitting side repeater sector. More specifically, each switch 518 controls passing or blocking of a signal communicated between each receiving side repeater sector and each transmitting side repeater sector. Each of the switches 518 is in any one of “on” state and an “off” state. The switch 518 being in the “on” state allows the signal to pass therethrough, but the switch 518 being in the “off” state blocks the signal.
Multiplexers 519 each synthesize the outputs of the plurality of switches 518. The output of each multiplexer 519 corresponds to the output of the transmitting side repeater sector, and is transmitted from the transmission antenna of each repeater sector through the power amplifier 508 or 513 for each repeater sector.
In the example illustrated in
In the case of the downlink traffic, the number of receive signals (corresponding to the base station transmit signal) to be amplified and output among the receive signals in the plurality of repeater sectors is one. For that reason, as illustrated in
In the case of the uplink traffic, the switches are controlled as illustrated in
A method of connecting the switches and a method of controlling the power amplifier output for both of the uplink traffic and the downlink traffic is described below. A main difference between the uplink traffic and the downlink traffic is that, in the former, one sector on the base station side being the output side may be connected with a plurality of sectors on the mobile station side being the input side, whereas, in the latter, one sector B on the mobile station side the output side is connected with only one sector on the base station side being the input side. In other words, the number of connections of input with respect to output may be plural in the uplink traffic whereas the number thereof is only one in the downlink traffic.
First, in Step 601, the input-output control unit 502 waits to receive the control information from the repeater control unit 201.
Subsequently, in Step 602, the input-output control unit 502 selects a repeater sector A on the base station side whose coverage area is to be enlarged from the received control information according to the format illustrated in
For example, when the repeater sector #1 is selected as the repeater sector A as illustrated in
In Step 603, the input-output control unit 502 selects a repeater sector B on the mobile station side which is newly connected to the repeater sector A determined in Step 602. The selecting method is described later with reference to
In Steps 604 to 609, the input-output control unit 502 controls the downlink traffic. With regard to the input-output control unit 502 according to this embodiment, the input is the repeater sector on the base station side whereas the output is the repeater sector on the mobile station side.
In Step 604, the input-output control unit 502 determines whether or not the power amplifier output of the above-mentioned repeater sector B can be decreased. More specifically, when the following two conditions are met, it is determined that the output can be decreased.
(a) The power amplifier output is larger than a minimum value.
(b) The repeater sector B is not connected with the repeater sector A.
When the result in Step 604 is yes (that is, when the power amplifier output can be decreased), the input-output control unit 502 decreases the power amplifier output of the repeater sector B in Step 605. In this situation, when the power amplifier output is decreased from the maximum value to the minimum value at once, though the input-output control unit 502 does not fail as the system, the mobile station connected to the base station with the aid of the repeater suddenly loses the base station being the connection destination. This induces the fear that the line is disconnected. In other words, the quality of the service is deteriorated, and hence it is not preferable to decrease the output at once as described above. Conversely, it is desirable that the output be gradually decreased (for example, 1 dB per one second) to naturally effect the hand-off of the mobile station in this embodiment.
When the result in Step 604 is no, the input-output control unit 502 does not execute Step 605.
In Step 606, the input-output control unit 502 determines whether or not there is room to decrease the output of the repeater sector B. The determination contents per se are identical with those in Step 604, but a difference from Step 604 resides in that the result in Step 605 is reflected. More specifically, when the power amplifier output of the repeater sector B is the minimum, it is determined that there is no room to further decrease the output of the repeater sector B.
When it is determined that there is no room to decrease the output of the repeater sector B in Step 606, the input-output control unit 502 changes over the switch 507 input to the repeater sector B so as to connect only to the repeater sector A in Step 607.
When it is determined that there is room to decrease the output of the repeater sector B in Step 606, the input-output control unit 502 does not execute processing of Step 607.
In Step 608, the input-output control unit 502 determines whether or not the output of the power amplifier 508 in the repeater sector B can be increased. More specifically, when the following two conditions are met, it is determined that the output can be increased.
(c) The power amplifier output is smaller than a maximum value.
(d) The repeater sector B is being connected with the repeater sector A.
When the result in Step 608 is yes, the input-output control unit 502 increases the output of the power amplifier 508 in the repeater sector B in Step 609. In this situation, when the power amplifier output is increased from the minimum value to the maximum value at once, the interference appears to rapidly increase in relation to the mobile stations around the repeater apparatus. Therefore, there is a risk that no communication is made until the mobile stations are adjusted to the rapidly increased interference, which is not preferable. As in Step 605, it is desirable that the output be gradually increased (for example, 1 dB per one second) to naturally effect the hand-off of the mobile station in this embodiment.
When the result in Step 608 is no, the input-output control unit 502 does not execute Step 609.
In Steps 610 to 615, the input-output control unit 502 controls the uplink traffic. The input is the repeater sector on the mobile station side, and the output is the repeater sector on the base station side in relation to the input-output control unit 502 of this embodiment.
In Step 610, the input-output control unit 502 determines whether or not the output of the power amplifier 513 in the repeater sector A can be decreased. More specifically, when all of the following three conditions are met, it is determined that the output can be decreased.
(e) The power amplifier output is larger than a minimum value.
(f) The repeater sector A is not connected with the repeater sector B.
(g) The repeater sector A is not connected to the repeater sectors on the mobile station side other than the repeater sector B.
The conditions (f) and (g) mean that the power amplifier output can be decreased only when the repeater sector A is connected to none of the repeater sectors on the mobile station side. When the power amplifier output is decreased in a state where the condition (g) is not met, a communication via the repeater sectors except for the repeater sectors to be controlled (that is, the repeater sector A, the repeater sector B, and the repeater sector on the base station side C originally connected with the repeater sector B) is destabilized more than necessary, which is undesirable.
If the condition (g) is excluded, equivalently, the propagation attenuation of the transmission path that reaches the base station via the repeater sector A from the repeater sectors on the mobile station side other than the repeater sector B gradually increases. As a result, the mobile stations that conduct the uplink traffic by using the repeater sectors on the mobile station side except for the repeater sector B are handed off at the same time, and hence the fear becomes high that the delay time of the hand-off time increases, or that the line is disconnected. Hence, it is not preferable that the condition (g) be excluded.
When the result in Step 610 is yes (that is, when it is determined that the output of the power amplifier 513 in the repeater sector A can be decreased), the input-output control unit 502 decreases the power amplifier output of the repeater sector A in Step 611. In this situation, when the power amplifier output is decreased from the maximum value to the minimum value at once, there is the fear that the line of the mobile station connected to the base station with the aid of the repeater is disconnected as in Step 605. In other words, the quality of the service is deteriorated, which is not preferable. Conversely, it is desirable that the output be gradually decreased (for example, 1 dB per one second) to naturally effect the hand-off of the mobile station in this embodiment.
When the result in Step 610 is no, the input-output control unit 502 does not execute Step 611.
In Step 612, the input-output control unit 502 determines whether or not there is room to decrease the output of the repeater sector A. The determination contents per se are identical with those in Step 610, but a difference from Step 610 resides in that the result in Step 611 is reflected. More specifically, when the power amplifier output of the repeater sector A is the minimum, it is determined that there is no room to further decrease the output of the repeater sector A.
When it is determined that there is no room to decrease the output of the repeater sector A in Step 612, the input-output control unit 502 changes over the switch 512 of the repeater sector B input to the repeater sector A from “disconnected” (that is, off) to “connected” (that is, on).
When it is determined that there is room to decrease the output of the repeater sector A in Step 612, the input-output control unit 502 does not execute processing of Step 613.
In Step 614, the input-output control unit 502 determines whether or not the output of the power amplifier 513 in the repeater sector A can be increased. More specifically, when the following two conditions are met, it is determined that the output can be increased.
(h) The power amplifier output is smaller than a maximum value.
(j) The repeater sector A is being connected with the repeater sector B.
When the result in Step 614 is yes (that is, when it is determined that the output can be increased), the input-output control unit 502 increases the output of the power amplifier 513 in the repeater sector A in Step 615. In this situation, when the power amplifier output is increased from the minimum value to the maximum value at once, the interference appears to rapidly increase in relation to the base station. Therefore, there is a risk that no communication is made until the base station is adjusted to the rapidly increased interference, which is not preferable. As in Step 611, it is desirable that the output be gradually increased (for example, 1 dB per one second) to naturally effect the hand-off of the mobile station in this embodiment.
Upon completion of Step 615, the processing returns to Step 601.
When the result in Step 614 is no, the input-output control unit 502 returns to Step 601 without executing processing of Step 615.
In an example of
A state of the switch 518 illustrated in
A sector on the mobile station side directed toward the same direction as that of the sector A on the base station side being a target;
A sector on the mobile station side which is minimum in power amplifier (PA) output among the plurality of candidates;
A sector on the mobile station side connected to the repeater sector on the base station side (
A sector on the mobile station side selected at random when the candidates cannot be narrowed in the above-mentioned manners.
The first item realizes a state in which the base station sector and the repeater sector A sandwich the mobile station. With this configuration, the receive power at the mobile station of the base station sector within the base station sector is improved. When a traffic among the base station sectors around the repeater is balanced, a resistance to the inter-section interference of the respective base station sectors is enhanced, whereby one stable configuration in this invention is realized (which is described with reference to
The second item means that the sector on the mobile station side which is estimated to be smallest in an impact on the system due to the changeover of the switch is to be controlled. When the downlink switch 507 changes over, the transmit output of the repeater sector to be controlled is decreased once as illustrated in a flow of
The third item means that the repeater control unit 201 selects the repeater sector on the mobile station side related to the base station sector whose output may be decreased as illustrated in
In the selected sector on the mobile station side, the input-output control unit 502 controls the input/output in the following procedure.
(i) The PA output of the subject sector on the mobile station side is minimized.
(ii) A connection with the sector on the base station side being connected to the subject sector on the mobile station side is switched off.
(iii) A connection with the sector on the base station side newly connected to the subject sector on the mobile station side is switched on.
(iv) The PA output of the subject sector on the mobile station side is maximized.
Among the above-mentioned controls, the results of executing the items (i) to (iii) are illustrated in
The repeater 108 amplifies radio signals related to the base station sectors (that is, the base station sectors 103-1, 103-2, and 103-3) opposite to the respective repeater sectors 110-1, 110-2, and 110-3. The mutual interference in signals received or transmitted by the repeater 108 is suppressed by the directional antenna, whereby the respective mobile stations that communicate with the respective base station sectors or the respective base station sectors can suppress interference from the other base station sectors. When the traffic is balanced among the base station sectors, the state of
The state of the switch 518 illustrated in
In the sector on the base station side related to the selected sector on the mobile station side, the input-output control unit 502 controls the input/output in the following procedure.
(I) The PA output of the sector on the base station side being connected to the subject sector on the mobile station side is minimized.
(II) A connection with the sector on the base station side being connected to the subject sector on the mobile station side is switched off.
(III) A connection with the sector on the base station side newly connected to the subject sector on the mobile station side is switched on.
(IV) The PA output of the newly connected sector on the base station side is maximized.
Among the above-mentioned controls, the results of executing the items (I) to (III) are illustrated in
In the procedure of the above-mentioned item (I), when the sector on the base station side is connected to another sector on the mobile station side in addition to the subject sector on the mobile station side, there may be a case in which the PA output cannot be minimized as described in Step 601 of
Then, a second embodiment for avoiding the above-mentioned concern is described.
The second embodiment is the same as the first embodiment except for the difference described below.
The basic configuration of the second embodiment is similar to that of the first example illustrated in
A difference from the control (
In Step 616, the input-output control unit 502 maximizes the attenuation of the attenuator 520 that connects the sector B on the mobile station side selected in Step 603 and the sector on the base station side connected to that sector B on the mobile station side, and minimizes the attenuation of the attenuator 520 that connects the sector A on the base station side selected in Step 602 and the above-mentioned sector B on the mobile station side. As a result, the sector B on the mobile station side changes over the sector on the base station side being a connection destination. In this example, the rapid changeover of the attenuation is not desirable because the rapid changeover induces the rapid increase of interference or base station loss as has been already described. It is desirable that the attenuation be gradually changed (for example, 1 dB per one second) to naturally effect the hand-off of the mobile station in this embodiment.
In the sector on the base station side related to the selected sector on the mobile station side, the input-output control unit 502 controls the input/output in the following procedure. The control example of the items (II) and (III) is illustrated in
(I) The PA output of the sector on the base station side being connected to the subject sector on the mobile station side is minimized.
(II) The attenuation of the connection attenuator with the sector on the base station side being connected to the subject sector on the mobile station side is maximized.
(III) The attenuation of the connection attenuator with the sector on the base station side newly connected to the subject sector on the mobile station side is minimized.
(IV) The PA output of the newly connected sector on the base station side is maximized.
Among the above-mentioned controls, the results of executing the items (II) and (III) are illustrated in
More specifically,
Before Step 616 starts, the attenuation of the attenuator 520 that connects the sector #2 on the mobile station side and the sector #1 on the base station side is 0 dB. On the other hand, the attenuation of the attenuator 520 that connects the sector #2 on the mobile station side and the sector #2 on the base station side is 100 dB. This state corresponds to the result of executing the above-mentioned item (I).
When Step 616 starts, the input-output control unit 502 increases the attenuation of the attenuator 520 that connects the sector #2 on the mobile station side and the sector #1 on the base station side at a given change rate (for example, 1 dB per one second). This processing corresponds to the above-mentioned item (II).
When the attenuation of the attenuator 520 that connects the sector #2 on the mobile station side and the sector #1 on the base station side reaches 100 dB, the input-output control unit 502 decreases the attenuation of the attenuator 520 that connects the sector #2 on the mobile station side and the sector #2 on the base station side at a given change rate (for example, 1 dB per one second) while maintaining the attenuation of the attenuator 520 that connects the sector #2 on the mobile station side and the sector #1 on the base station side. The processing corresponds to the above-mentioned item (III).
At a time point when the attenuation of the attenuator 520 that connects the sector #2 on the mobile station side and the sector #2 on the base station side reaches 0 dB, Step 616 is completed. Thereafter, the input-output control unit 502 maintains the attenuation of the respective attenuators 520. This state corresponds to the results of executing the above-mentioned item (IV).
This invention is applied to a radio communication system, in particular, a cellular system, thereby enabling plane development of service with the arrangement of a smaller number of base stations. Further, the load balance between the base stations is made, thereby enabling the service satisfaction degree among the mobile station devices to be equalized, and the investment cost-benefit performance of the base station installation to be enhanced.
While the present invention has been described in detail and pictorially in the accompanying drawings, the present invention is not limited to such detail but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-205760 | Aug 2008 | JP | national |
