JP3618719B2 - Communication control method and apparatus in mobile communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a communication control method and apparatus in a mobile communication system, and more particularly, in a mobile communication system, based on a so-called space division multiple access (SDMA), between a base station and a mobile station. The present invention relates to a communication control method for controlling communication.
[0002]
[Prior art]
Conventionally, a communication control method for space division multiple access (hereinafter referred to as SDMA) has been proposed. When the SDMA communication control method is employed as communication control between a base station and a mobile station in a cellular mobile communication system, for example, as shown in FIG. 15, communication areas (cells) E1, E2, E3 are Each base station 20 ₁ , 20 ₂ , 20 ₃ Does not radiate a radio wave covering the entire communication area, but forms a radio wave beam B extending in the direction in which the mobile station exists to communicate with the mobile station.
[0003]
In a cellular mobile communication system in which communication control between a base station and a mobile station is performed according to the SDMA communication control method, the direction of each radio wave beam B formed if the direction from the base station to the mobile station is different. Is different. Therefore, communication at the same frequency is possible in adjacent communication areas, and an improvement in frequency utilization efficiency can be expected.
[0004]
[Problems to be solved by the invention]
However, as the number of mobile stations located in the communication area of each base station increases, the opportunity to form radio beams at the same timing in the same direction or in the opposite direction in a plurality of adjacent communication areas, Opportunities of overlapping radio wave beams formed toward the mobile station increase, and the radio wave beams interact with each other as interference waves.
[0005]
Accordingly, an object of the present invention is to provide a communication control method based on SDMA (space division multiple access) capable of reducing interference caused by radio wave beams radiated from each base station to a mobile station in a mobile communication system, and Is to provide a device.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a mobile station that includes a base station in a cellular mobile communication system capable of emitting a radio beam in a plurality of directions from each base station. In the communication control method when each base station communicates with a mobile station at the same frequency by radiating a radio beam toward the base station, it is expected that the radio beam will interfere with the timing of radiating the radio beam from the base station. Configured to be controlled so as to be different from the radiation timing of the radio wave beam radiated from another base station with respect to the direction that matches is there When the reception level at the mobile station of the signal by the radio beam from the direction of the base station facing the mobile station decreases, the mobile station To a mobile station different from the mobile station Directing the radio beam in the direction of arrival of the other radio beam having the best reception quality among the other radio beams radiated and arriving at the mobile station, requesting allocation of time slots in the other radio beam, the base station, The time slot is assigned so as to be different from the radiation timing of the radio beam radiated from another base station in the direction matching the direction in which the interference by the other radio beam is expected.
In such a communication control method, the radiation of a radio beam radiated from another base station with respect to a direction in which the timing of radiating a radio beam from each base station matches the direction in which the interference by the radio beam is expected. It is controlled differently from the timing. For this reason, radio beams are not radiated from a plurality of base stations simultaneously in the direction in which the interference is expected. In addition, the problem of narrowing the beam can be solved and a communication path with less interference can be secured.
In addition, from the viewpoint of always ensuring good communication, the present invention, as described in claim 2, is there The mobile station receives a signal from the first radio wave beam from the direction of the base station facing the mobile station, and from the base station To a mobile station different from the mobile station The radio station directs the radio beam in the direction of arrival of the second radio beam that is radiated and arrives at the mobile station, and requests allocation of a time slot in the second radio beam. The mobile station assigns the time slot so as to be different from the radiation timing of the radio wave beam radiated from another base station with respect to the direction matching the direction in which the interference by the radio wave beam 2 is expected. The reception signal by one radio wave beam and the reception signal by the second radio beam can be combined.
From the viewpoint of securing a communication path with less interference on the base station side, when the reception level at the base station of the signal by the radio beam from the direction of the mobile station facing the base station decreases, the base station It is also possible to secure a path by directing a radio beam in the direction of arrival of another radio beam having the best reception quality among other radio beams radiated from the mobile station and arriving at the base station.
In the case where the mobile station has an omnidirectional antenna instead of a directional antenna, the present invention provides the same effect as that of the first aspect of the invention. 3 As described in is there When the reception level at the mobile station of the signal by the radio beam from the direction of the base station facing the mobile station decreases, the mobile station To a mobile station different from the mobile station The other radio beam having the best reception quality is selected from the other radio beams radiated and arriving at the mobile station, and the time slot is requested to be allocated by the other radio beam. The time slot may be allocated so that the radio wave radiated from other base stations is emitted in a direction that matches the direction in which interference is expected.
Further, in the case where the mobile station has an omnidirectional antenna instead of a directional antenna, the present invention provides the above as described in claim 4 from the viewpoint of obtaining the same effect as the invention of claim 2. In the communication control method, is there The mobile station receives a signal from the first radio wave beam from the direction of the base station facing the mobile station, and from the base station To a mobile station different from the mobile station Requesting time slot allocation in the second radio wave beam, which is another radio beam radiated and arriving at the mobile station, and the base station matches the direction in which the interference by the second radio beam is expected The mobile station assigns the time slot to be different from the radiation timing of the radio wave beam radiated from another base station, and the mobile station uses the received signal from the first radio wave beam and the second radio beam. It can be configured to synthesize the received signal.
[0008]
The present invention claims 5 As described above, in the communication control method, another base station that should consider interference of a radio beam from the base station is determined in advance with respect to the base station, and the other base station is determined with respect to the base station. The direction of the radio beam radiated from the radio station and the radiation timing thereof are notified, and based on the notified information, the timing of the radio wave beam radiated from the own station is expected to interfere with the radio beam. It can be configured so as to be controlled to be different from the radiation timing of the radio wave beam radiated from another base station with respect to the direction matching the direction.
[0009]
From the viewpoint of considering a base station in a range where the influence of the interference by the radio wave beam from each base station is stronger, the present invention claims 6 As described in the above, in the communication control method, the other base station that should consider the interference of the radio beam from the base station to the base station may be a base station adjacent to the base station. it can.
[0010]
From the standpoint of enabling mobile station handover, the present invention claims 7 As described in the above, in each of the communication control methods, the radio beam emitted from the base station that communicates with the mobile station is switched from the first radio beam to the second radio beam as the mobile station moves. In this case, the radiation timing of the first radio wave beam and the radiation timing of the second radio wave beam can be made different.
[0011]
From the viewpoint that the frequency can be used more efficiently when the radio wave beam radiated from the base station covers a plurality of mobile stations, the present invention claims 8 As described in the above, in each of the communication control methods, when the radio beam emitted from the base station covers a plurality of mobile stations, the radiation timing of the radio beam is configured to be different for each mobile station. be able to.
[0012]
The present invention claims 9 In the communication control method described above, the radio wave beam radiation timing is controlled so that the radio wave beam is radiated from the base station to the mobile station in a plurality of time zones at predetermined intervals. can do.
[0013]
The plurality of time zones for each predetermined period can be defined by time slots constituting a time frame, for example.
[0014]
From the viewpoint that it is possible to control the amount of communication to the mobile station according to the communication state in each base station, the present invention claims 10 As described above, the communication control method can be configured to determine the number of time zones for each predetermined period for radiating the radio wave beam based on a communication state in the base station.
[0015]
The communication state at the base station may be either an individual communication state for each mobile station (communication amount for the mobile station) or an overall communication state (traffic state) at the base station. .
[0023]
The mobile station of the present invention is also claimed 11 A mobile station in a cellular mobile communication system in which each base station communicates with a mobile station at the same frequency by radiating a radio beam from each base station toward the mobile station. When the reception level at the mobile station of the signal due to the radio beam from the direction of the opposite base station decreases, the base station To a mobile station different from the mobile station Means for directing a radio beam in the direction of arrival of another radio beam having the best reception quality among other radio beams radiated and arriving at the mobile station, and requesting allocation of a time slot in the other radio beam; The base station is configured to assign the time slot so that the radio beam radiated from another base station is different from the emission timing with respect to the direction matching the direction in which the interference from the other radio beam is expected. be able to.
[0024]
The mobile station of the present invention is also claimed 12 And receiving a signal by the first radio beam from the direction of the base station facing the mobile station, and from the base station To a mobile station different from the mobile station Means for directing a radio wave beam in the direction of arrival of a second radio wave beam that is radiated and arriving at the mobile station, and requesting allocation of a time slot in the second radio beam; After the station assigns the time slot so that it differs from the radiation timing of the radio beam radiated from another base station in the direction matching the direction in which the interference by the second radio beam is expected The first radio wave beam reception signal and the second radio wave beam reception signal may be combined.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment and a second embodiment of the invention will be described with reference to the drawings. The first embodiment is an embodiment showing a basic configuration of the present invention, and the second embodiment is a configuration in which the mobile station emits a beam in the reflected wave direction in the configuration in the first embodiment. In this embodiment, a time slot allocation is requested and a path is secured.
[0026]
<First Embodiment>
A mobile communication system in which communication control between a base station and a mobile station is performed according to a communication control method according to an embodiment of the present invention is configured, for example, as shown in FIG.
[0027]
In FIG. 1, a base station 20 that supervises each communication area (cell) E0, E1, E2, E3, E4, E5, E6. ₀ , 20 ₁ , 20 ₂ , 20 ₃ , 20 ₄ , 20 ₅ , 20 ₆ Are connected to the control station 30. A mobile station (mobile phone terminal, PHS terminal, personal digital assistant (PDA), etc.) 10 located in the communication area E0 is connected to a base station 20 ₀ Wireless communication with the base station 20 ₀ Then, communication (voice communication, data communication) is performed with another communication terminal via the control station 30 and a predetermined communication network (not shown). In addition, mobile stations located in other communication areas E1 to E6 are similarly configured to base stations 20 that control the communication areas. ₁ , 20 ₂ , 20 ₃ 20 ₄ , 20 ₅ , 20 ₆ And wireless communication. Each base station 20 ₀ , 20 ₁ , 20 ₂ , 20 ₃ , 20 ₄ , 20 ₅ , 20 ₆ Uses the same frequency when performing wireless communication with a mobile station.
[0028]
Each base station 20 ₀ , 20 ₁ , 20 ₂ , 20 ₃ , 20 ₄ , 20 ₅ , 20 ₆ (Hereinafter, reference numeral 20 is used when referring to base stations generically) basically performs radio communication with a mobile station according to SDMA (space division multiple access). The configuration is as shown in FIG. become.
[0029]
In FIG. 2, this base station 20 has an antenna array 21 composed of a plurality of antenna elements, a combiner 22, a direction detector 23, a beam former 24, a transceiver 25, and a base station controller 26. Yes. The direction detector 23 detects the direction of the mobile station 10 that communicates with the base station 20 based on the received signal at each antenna element of the array antenna 21 input via the combiner 22. The beam former 24 sets predetermined parameters so that a radio wave beam is formed at the radiation timing instructed by the base station controller 26 in the direction of the mobile station 10 detected by the direction detector 23.
[0030]
The transceiver 25 transmits and receives signals to and from the mobile station 10 using the radio wave beam formed as described above via the array antenna 21, the combiner 22, and the beam former 24. Arbitrary division multiple access (TDMA, CDMA, etc.) can be applied when sending and receiving the signal. As described above, the base station controller 26 can indicate the radiation timing of the radio wave beam to the beam former 26, and controls the transceiver 25 to transfer the signal received by the transceiver 25 to the communication network. The signal from the communication network is supplied to the transceiver 25.
[0031]
The base station 20 configured as described above forms a radio wave beam in the direction of the mobile station 10 by a so-called adaptive array antenna control technique, and is allocated to the mobile station 10 according to a predetermined division multiple access (TDMA, CDMA, etc.). Communicates on other channels (time slot, code, etc.). For example, as shown in FIG. 3, each direction (0 °, 30 °, 60 °, 90 °, 120) obtained by dividing the omnidirectional (2π = 360 °) of the communication area E into m (in this case, 12). It is possible to form beams B1 to Bm (in this case, B1 to B12) directed to (°, 150 °, 180 °, 210 °, 240 °, 270 °, 300 °, 330 °, 360 °). Each formed radio wave beam partially overlaps an adjacent radio wave beam.
[0032]
Returning to FIG. 1, the control station 30 includes each base station 20. ₀ , 20 ₁ , 20 ₂ , 20 ₃ , 20 ₄ , 20 ₅ , 20 ₆ The direction in which the radio wave beam is formed and the radiation timing (time) of the radio wave beam are managed. Details of this management will be described later.
[0033]
For example, as shown in FIG. 4, in the communication area E0, the mobile station 10 is oriented in the direction of 30 °. ₁ , Mobile station 10 in the direction of 90 ° ₂ , Mobile station 10 in the direction of 240 ° ₃ And the mobile station 10 in the direction of 300 ° ₄ 10 ₅ Is located, base station 20 ₀ Radiates radio beams B1, B2, B3, B4 in those directions, ie, 30 ° direction, 90 ° direction, 240 ° direction and 300 ° direction, respectively. And base station 20 ₀ The (base station control device 26) controls the radiation timing (timing at which each radio beam is formed) of each radio beam B1, B2, B3, B4. Control of the radiation timing of each radio wave beam B1, B2, B3, B4 is performed by the base station 20 ₀ Each base station 20 that supervises the communication areas E1 to E6 adjacent to the communication area E0 ₁ ~ 20 ₆ The radio waves B1, B2, B3, and B4 are radiated at a timing different from the radiation timing of the radio beams in the direction in which interference by the radio waves B1, B2, B3, and B4 is expected. I try to do it. In this example, the base station 20 ₀ Radio waves from the adjacent base station 20 due to propagation attenuation. ₁ ~ 20 ₆ It shall not interfere with radio wave beams from other base stations.
[0034]
Base station 20 ₀ Adjacent base station 20 that is expected to be interfered by a radio wave beam radiated in each direction of ₁ ~ 20 ₆ The radio wave beam from is expected, for example, as shown in FIG.
[0035]
In FIG. 5, the base station 20 ₀ The radio wave beam radiated in the direction of 0 ° from the adjacent base station 20 ₁ From the direction of 240 ° from the adjacent base station 20 ₆ The base station 20 is expected to act as an interference wave for each communication using a radio wave beam radiated in a direction of 120 ° from the base station 20. ₀ Radio waves radiated in the direction of 30 ° from the adjacent base station 20 ₁ It is expected to act as an interference wave for each communication using radio wave beams radiated in the 210 ° direction (directly facing direction) and 30 ° direction (same direction). Moreover, the radio wave beam radiated in the direction of 60 ° from the base station 200 was a radio wave beam radiated in the direction of 180 ° from the adjacent base station 201 and the direction of 300 ° from the adjacent base station 202. The base station 20 is expected to act as an interference wave for each communication. ₀ Radio waves radiated in the direction of 90 ° from the adjacent base station 20 ₂ It is expected to act as an interference wave for each communication using radio wave beams radiated in the 270 ° and 90 ° directions.
[0036]
Hereinafter, similarly, the base station 20 ₀ The radio wave beams radiated in the directions of 120 °, 150 °, 180 °, 210 °, 240 °, 270 °, 300 °, and 330 ° from the adjacent base stations 20 ₂ , 20 ₃ , 20 ₄ And 20 ₅ Therefore, it is expected to act as an interference wave for each communication using a radio wave beam radiated in the direction as shown in FIG.
[0037]
The control station 30 is radiated from each base station based on the prediction of the interference situation with respect to communication using the radio beam radiated from the base station adjacent to the radio beam radiated from each base station. Management of the direction of the radio wave beam and its radiation timing is performed as follows.
[0038]
Each base station (base station control device 26) controls the radiation timing of the radio beam in each direction in units of time frames formed by a plurality of time slots defined in advance in the system. By such control, the radio beam in each direction is radiated at the timing of the time slot assigned to it. Each base station sequentially reports to the control station 30 the time slot assigned to the radio beam in each direction. The control station 30 receiving such a report manages the time slots assigned to the radio wave beams radiated in the respective directions from the respective base stations.
[0039]
Then, based on the report, the control station 30 determines whether the base station (for example, the base station 20 ₀ ) In the direction corresponding to each direction (see FIG. 5) where radio wave beam interference is expected (see FIG. 5). ₁ ~ 20 ₆ The time slot already assigned to the radio beam radiated from is determined. As a result, the control station 30 creates an interference management table for each base station as shown in FIG.
[0040]
FIG. 6 shows the base station 20 ₀ The interference management table with respect to is shown.
[0041]
This interference management table is stored in the base station 20 ₀ Adjacent base station 20 corresponding to the direction of 0 ° from ₁ Are already assigned time slots for electron beams emitted in the direction of 240 ° from the base station 20 ₀ Adjacent base stations 20 corresponding to the same direction ₆ This means that the time slot already assigned to the radio wave beam radiated in the direction of 120 ° from S1 is S1. The interference management table is stored in the base station 20. ₀ Adjacent base station 20 corresponding to the direction of 30 ° from ₁ S2 and S6 are already assigned time slots for a radio wave beam radiated in the direction of 210 ° from the adjacent base station 20 ₁ This means that the time slot already assigned to the radio wave beam radiated in the direction of 30 ° from S3 is S3. Further, this interference management table is stored in the base station 20. ₀ Adjacent base station 20 corresponding to the direction of 60 ° from ₁ S4 and S5 are already assigned time slots for the radio wave beam radiated in the direction of 180 ° from the base station 20 ₀ Adjacent base stations 20 corresponding to the same direction ₂ This indicates that the time slot already assigned to the radio wave beam radiated in the direction of 300 ° from S2 is S2.
[0042]
Further, the interference management table corresponds to each direction (90 °, 120 °, 150 °, 180 °, 210 °, 240 °, 270 °, 300 °, 330 °) from the base station 20 as described above. It represents what time slot has already been allocated for the radio wave beam radiated from each adjacent base station.
[0043]
In the interference table, the base station 20 ₀ Adjacent base station 20 corresponding to the direction of 300 ° from ₅ 60 ° from and adjacent base station 20 ₆ In the 180 ° direction, no mobile station exists and no radio wave beam is emitted.
[0044]
The content of such an interference management table is updated each time a time slot assigned to radiate the radio beam from each base station is reported to the control station 30. Then, every time the content of the interference management table is updated, the control station 30 transfers the interference management table to each base station.
[0045]
Each base station that has received such an interference management table refers to the interference management table and controls the radiation timing of the radio wave beam to be formed in each direction. That is, radiation is performed for each direction in which interference is expected (0 °, 30 °, 60 °, 90 °, 120 °, 150 °, 180 °, 210 °, 240 °, 270 °, 300 °, 330 °). To the radio wave beam to be transmitted, a time slot other than the time slot already assigned to the radio wave beam radiated from the adjacent base station in a direction corresponding to the direction is assigned according to a predetermined rule. In addition, when a radio beam is not radiated from an adjacent base station in a direction corresponding to each direction from each base station, or even if a radio beam is radiated from an adjacent base station in a direction not corresponding thereto, the adjacent base station Regardless of the radiation beam from, a time slot is assigned to a radio beam to be radiated in each direction from each base station according to a predetermined rule.
[0046]
Each base station, eg, base station 20 ₀ As a result of assigning time slots to radio waves radiating in each direction as described above, for example, radio wave radiation timing control is performed as shown in FIG.
[0047]
In FIG. 7, the base station 20 ₀ Is a mobile station 10 ₁ Radio wave beam B1 in the direction of 30 ° for communication with the adjacent base station 20 corresponding to the direction of 30 °. ₁ Mobile station 10 in the direction of 210 ° from ₁₁ And 10 ₁₂ In order to communicate with the neighboring base station 20 ₁ Is radiated at the timing of a time slot S1 different from the time slots S2 and S6 of the radio wave beam B11 radiated from. In addition, the base station 20 ₀ Is a mobile station 10 ₂ Radio wave beam B2 in the direction of 90 ° to communicate with the adjacent base station 20 corresponding to the direction of 90 °. ₃ Mobile station 10 in the direction of 270 ° from ₂₁ In order to communicate with the neighboring base station 20 ₃ Is radiated at the timing of a time slot S3 different from the time slot S2 of the radio wave beam B21 radiated from. Furthermore, the base station 20 ₀ Is a mobile station 10 ₃ Radio wave beam B3 in the direction of 210 ° to communicate with the adjacent base station 20 corresponding to the direction of 210 °. ₄ Mobile station 10 in the direction of 30 ° from ₄₁ And 10 ₄₂ In order to communicate with the neighboring base station 20 ₄ Is radiated at a timing of a time slot Sn different from the time slots S1 and Sm of the radio wave beam B41 radiated from.
[0048]
Base station 20 ₀ Adjacent base station 20 corresponding to 300 ° from ₅ 60 ° from and adjacent base station 20 ₆ Since no radio wave beam is emitted in the direction of 180 ° from the base station 20, ₀ Is a mobile station 10 ₄ And 10 ₅ Radio wave beam B4 in the direction of 300 ° to communicate with the adjacent base station 20 ₅ , 20 ₆ Irradiates at the time slots Si and Sj determined regardless of the radio wave beam radiated from.
[0049]
The time frame defined in the system for controlling the emission timing of the radio beam as described above is a control time slot for a control signal such as a signal (time slot designation signal) for notifying the mobile station of the time slot. And a communication time slot for a communication signal including information to be communicated. Each base station transmits a type of time slot (control time slot or communication) to be allocated to a radio beam radiated according to the purpose of communication (transmission / reception of control signals or transmission / reception of communication signals) with a mobile station as a communication partner. Switching signal time slot).
[0050]
The mobile station 10 includes an array antenna, and directs the beam radiation direction in the direction in which the radio wave from the base station 20 is most strongly received. Then, when the radio beam is emitted from the base station 20 at the timing of the control time slot, the mobile station 10 receives the communication time slot designation signal from the base station 20 and designates it by the designation signal. When a radio wave beam is emitted from the base station 20 at the timing of the communication time slot, a communication signal transmitted from the base station 20 is received. Further, the mobile station 20 transmits a communication signal to the base station 20 at the timing of the designated communication time slot, and the base station 20 receives the communication signal from the mobile station 10 at the timing of the communication time slot. To do. Thus, communication between each base station 20 and the mobile station 10 is performed.
[0051]
According to the radio wave beam radiation timing control as described above, radio wave beams are radiated from the base stations in different time zones (time slots) of each time frame in the direction in which interference is expected. Therefore, when each base station radiates a radio beam in the direction of each mobile station and performs communication at the same frequency as each mobile station, interference with communications using other radio beams is further reduced. be able to.
[0052]
In the above example, the base station 20 ₀ A plurality of mobile stations (10 ₄ 10 ₅ ) Is included (see FIG. 7), the base station changes the radiation time zone (time slot) in each time frame of the radio beam for communication with those mobile stations. The communication may be performed by different channels (TDMA time slot, CDMA code) by radiating in a single time zone.
[0053]
Further, when the number of mobile stations included in one radio beam exceeds a predetermined threshold, the radio beam is emitted in a single time slot (time slot) so that communication can be performed on different channels. be able to.
[0054]
Furthermore, in the above example, the time frame defined in the system is composed of a control time slot and a communication time slot, but the control signal and the communication signal are transmitted and received through different channels (frequency, code). Different time frames can be formed in each of the control time slot and the communication time slot. In this case, the emission timing of the radio beam for transmitting and receiving the control signal and the emission timing of the radio beam for transmitting and receiving the communication signal are controlled in separate time frame units.
[0055]
Also, it is possible to control the number of time slots to be allocated to the radio beam for the mobile station in accordance with the communication amount between the base station and the mobile station and the communication status such as traffic (time slot allocation status) in the base station. Is possible.
[0056]
For example, in FIG. ₀ Or when the base station 20 ₀ And mobile station 10 ₁ When the amount of communication with the base station 20 increases ₀ Is a mobile station 10 ₁ Radio wave beam B1 in the direction of 30 ° for communication with the adjacent base station 20 corresponding to the direction of 30 °. ₁ Mobile station 10 in the direction of 210 ° from ₁₁ And 10 ₁₂ The base station 20 to communicate with ₁ Are radiated at timings of a plurality of time slots S1, S3 and Sn different from the time slots S2 and S6 of the radio wave beam B11 radiated from.
[0057]
Furthermore, when the mobile station moves and moves from an area covered by a radio wave beam radiated in a certain direction to an area covered by an adjacent radio wave beam, for example, handover control is performed as shown in FIG. The
[0058]
In FIG. 9, the base station 20 communicates with the mobile station 10 at the position P1 by radiating a radio beam B1 in a certain direction in a time slot Sn-x. When the mobile station 10 moves while communicating with the base station 20 and reaches a position P2 in the common part of the area covered by the radio wave beam B1 and the area covered by the radio beam B2, the base station 20 detects the time slot Sn. The radio beam B1 is emitted at -x and the radio beam B2 is emitted at the time slot Sn-i to continue communication with the mobile station 10 at the position P2. Further, when the mobile station 10 moves and reaches a position P3 in an area covered only by the radio wave beam B2, the base station 20 emits the radio beam B2 in the time slot Sn-i, and the mobile station at the position P3. Communication with 10 continues.
[0059]
The example shown in FIG. 5 represents an expected interference situation when communication is performed at the same frequency in all communication areas (cells). For example, as shown in FIG. 10, even when each cell is divided into sectors to which three frequencies F1, F2, and F3 are assigned, the base station that manages each cell (communication area) has the same frequency. In each allocated area (sector), radio wave beam radiation timing control in each direction as described above can be performed.
[0060]
In this case, as shown in FIG. ₀ The radio wave beam radiated from the assigned sector of frequency F1 to each adjacent base station 20 ₆ , 20 ₁ , 20 ₂ , 20 ₃ The sector assigned with the frequency F1 may be affected as an interference wave. Specifically, the base station 20 ₀ A radio beam radiated in the direction of 0 ° from the adjacent base station 20 ₆ The base station 20 is expected to act as an interference wave for communication using a radio wave beam emitted in the direction of 120 ° from the base station 20 ₀ Radio waves radiated in the direction of 30 ° from the adjacent base station 20 ₁ It is expected to act as an interference wave for communication using a radio wave beam radiated in the direction of 30 °. In addition, the base station 20 ₀ Radio waves radiated in the direction of 90 ° from the adjacent base station 20 ₂ The base station 20 is expected to act as an interference wave for communication using a radio wave beam emitted in the direction of 90 ° from the base station 20 ₀ Radio waves radiated in the direction of 120 ° from the adjacent base station 20 ₃ It is expected to act as an interference wave for communication using a radio wave beam radiated in the direction from 0 ° to 0 °.
[0061]
Similarly to the above, the base station 20 ₀ The radio wave beam radiated to the assigned sector of frequency F2 from each adjacent base station 20 ₂ , 20 ₃ , 20 ₄ , 20 ₅ It is possible to influence the sector assigned with the frequency F2 as an interference wave. In addition, the base station 20 ₀ In the same manner as described above, the radio wave beam radiated to the sector to which the frequency F3 is allocated from each adjacent base station 20 ₄ , 20 ₅ , 20 ₆ , 20 ₁ The sector to which the frequency F3 is assigned may be affected as an interference wave.
[0062]
From the prediction of the interference situation with respect to the communication using the radio wave beam radiated from the base station adjacent to the radio wave beam emitted from each base station, the control station 30 determines each radio wave reported from each base station. Based on the time slot assigned to the beam, for example, an interference management table as shown in FIGS. 11A, 11B, and 11C is created.
[0063]
11 (a), (b) and (c) show the base station 20 ₀ The interference management table with respect to is shown.
[0064]
The interference management table shown in FIG. 11A manages time slots assigned to each radio wave beam radiated to the sector to which the frequency F1 is assigned. In FIG. 11A, the base station 20 ₀ The time slot already assigned to radiate the radio beam in the direction of 120 ° from the adjacent base station 206 corresponding to the direction of 0 ° from the base station 200 is S4, and the adjacent base station corresponding to the direction of 30 ° of the base station 200 is Bureau 20 ₁ The time slot already assigned to radiate the radio beam in the direction of 30 ° from is S2. In addition, the base station 20 ₀ Adjacent base station 20 corresponding to the direction of 90 ° from ₂ S4 and S6 are already assigned time slots for radiating a radio beam in the direction of 90 ° to the radio beam in the direction of 0 ° from the adjacent base station 203 corresponding to the direction of 120 ° from the base station 200. The time slot already assigned to radiate is S1.
[0065]
The interference management table shown in FIG. 11 (b) manages time slots assigned to each radio beam emitted to the sector to which the frequency F2 is assigned. The interference management table shown in FIG. The time slot allocated to each radio wave beam radiated to the sector to which the frequency F3 is allocated is managed. Each interference management table shown in FIGS. 11B and 11C also manages the time slot assigned to each radio wave beam radiated to the sector to which the frequency F1 is assigned (see FIG. 11A). As with the base station 20 ₀ It represents what time slot has already been allocated to radiate a radio beam from an adjacent base station in a direction corresponding to each direction of the radio beam emitted from the base station.
[0066]
The base station 20 that has received the interference management table as described above ₀ In the same manner as in the example described above, with reference to the interference management table, in each sector, the radiation timing of the radio beam in each direction where interference is expected is radiated in the corresponding direction from each adjacent base station. The timing is controlled to be different from the radiation timing of the radio wave beam.
[0067]
By dividing the cell managed by each base station into a plurality of cells in this way, the number of radio beams from adjacent base stations that are expected to be affected as interference by radio beams emitted from each base station is reduced. Thus, the control of the radiation timing of the radio wave beam using the interference management table can be further simplified.
[0068]
In each example described above, the control station 30 creates an interference management table and transfers it to each base station. However, the present invention is not limited to this, and time slots assigned to radio beams radiated in each direction for communication with a mobile station are sequentially transferred between base stations, and each base station is based on the information as described above. In consideration of interference (based on information corresponding to the contents of the interference management table), the radiation timing (time slot) of the radio wave beam for each direction can be determined.
[0069]
In each of the above examples, the control station 30 and the base station 20 ₀ The timing control means which comprises a communication control apparatus with the function of is implement | achieved.
[0070]
<Second Embodiment>
Next, a second embodiment of the present invention will be described.
[0071]
In a method using a thin beam such as SDMA, radio waves from the base station are often blocked by buildings around the mobile station, and it is difficult to secure a path with the target base station. There is a case. On the other hand, the beam radiated in the other direction may be reflected on the building and so on to reach the mobile station (radiating radio waves in various directions using a broad beam and many thin beams Since it is equivalent to radiating in various directions), the mobile station can secure a path by directing the beam in the direction of the reflected wave or the like, not in the direction of the opposing base station.
[0072]
However, in SDMA that continuously uses a beam in one direction, when communication is performed in the beam direction, a slot cannot be assigned to communication in the other direction. Even when CDMA is used in combination, the amount of interference increases, which puts pressure on the system capacity. In any case, communication quality is degraded in SDMA.
[0073]
Here, in the time division multiple access (TSDMA) system using the beam in time division multiplexing as described in the first embodiment, a slot different from the slot used in the beam is used for other communication. Can be assigned.
[0074]
From the above viewpoint, in this embodiment, when a beam is directed toward the base station facing the mobile station and a null is formed in the reflected wave direction from the other beam, the path is blocked and received by the building or the like. When the level drops, the beam is directed in the direction of arrival of the radio wave from the strongest other beam, and the base station is requested to allocate a slot with that beam to secure a path. As a result, so-called path diversity can be performed, the above-mentioned problems caused by narrowing the beam can be solved, and a communication path with less interference can be secured.
[0075]
Here, in order to detect the strongest other beam by the mobile station, for example, there is a method of grasping the reception level in each direction by polling. In response to the slot allocation request, the base station allocates time slots with reference to the interference management table as shown in FIG.
[0076]
In addition, the mobile station receives the designated slot by directing the beam in the direction of the opposite base station, receives the designated slot by requesting slot assignment in the beam in the direction of arrival of radio waves from the strongest other beam, It is also possible to perform selective synthesis of these slots.
[0077]
Next, FIG. 12 shows the configuration of a mobile station having an adaptive array antenna (directional antenna) for realizing the above functions.
[0078]
This mobile station includes an antenna array 31 composed of a plurality of antenna elements, a combiner 32, a direction detector 33, a beam former 34, and a transceiver 35. The direction detector 33 detects the direction of the strongest beam based on the received signal at each antenna element of the array antenna 31 input via the combiner 32. The beam former 34 sets predetermined parameters so that a radio wave beam is formed in the direction of the base station detected by the direction detector 33 or in the direction of a strong beam.
[0079]
The transceiver 35 transmits and receives signals to and from the base station using the radio wave beam formed as described above via the array antenna 31, the combiner 32, and the beam former 34. Arbitrary division multiple access (TDMA, CDMA, etc.) can be applied when sending and receiving the signal.
[0080]
The mobile station configured as described above forms a radio wave beam in the direction of the strongest beam (reflected wave) by a so-called adaptive array antenna control method, and is assigned according to a predetermined division multiple access (TDMA, CDMA, etc.) Communication is performed using (time slot, code, etc.).
[0081]
Next, when the path is interrupted by a building or the like and the reception level decreases, the mobile station directs the beam in the direction of arrival of radio waves from the strongest other beam and requests slot allocation in that beam to secure the path. A specific operation will be described with reference to FIG.
[0082]
A mobile station normally directs a beam in the direction of the opposing base station and forms a null in the direction of reflection from other beams. Base station 20 ₀ When the beam A is directed in the direction of 270 ° in the communication area E0, the mobile station #j and the base station 20 ₀ When there is a shielding object SA such as a building between ₀ The radio wave radiated by the beam A from the A is attenuated, and the received signal level is lowered at the mobile station #j.
[0083]
At this time, the base station 20 ₀ If there is a radio wave propagation path in which the radio wave of the beam B radiated in the direction of 300 ° from the reflector SB is reflected by the shield SB and reaches the mobile station #j, the mobile station #j ₀ The strength of each radio beam radiated from the base station 20 is measured by an adaptive array antenna or a directional antenna owned by the mobile station #j, and the reception quality, for example, the received signal level is the best (maximum). ₀ Select the beam. At this time, the directivity of the antenna of the mobile station #j is not necessarily geometrically the base station 20. ₀ 13, and as shown in FIG. 13, the direction (here, the direction of the building SB as viewed from the mobile station #j) in which the reception quality (in this case, the radio wave intensity) is maximized is indicated. Be controlled. Mobile station #j then directs the beam in that direction, requests time slot assignment with that beam, and secures a path.
[0084]
The allocation of time slots at this time will be described using the interference management table of FIG.
[0085]
As shown in the interference management table of FIG. ₀ Adjacent base station 20 corresponding to 270 ° ₅ Sk is assigned in the direction of 270 ° of the adjacent base station 20 ₅ Si is assigned to the 90 ° direction of the base station 20 and the direction of the beam B is the base station 20. ₀ Adjacent base station 20 corresponding to the direction of 300 ° from ₅ 60 ° and adjacent base station 20 ₆ Since no time slot is assigned in the direction of 180 °, a time slot Sm other than Sk and Si is assigned for communication by the beam B of the mobile station.
[0086]
Communication with mobile station #j is managed as a time slot in the direction of beam A and in the direction of beam B, and information on the assignment of this time slot is notified to the control station, and the interference management table in each base station is updated. Is done.
[0087]
Next, a specific operation in the case of selectively combining the time slot of the beam in the direction of the opposite base station and the time slot of the strongest other beam due to reflection will be described with reference to FIG.
[0088]
In FIG. 14, the base station 20 ₀ When the beam A is directed in the direction of 270 ° in the communication area E0 of the mobile station #j and the base station 20 ₀ A radio wave propagation path is formed between the two to communicate. At this time, even when a radio wave is radiated in the beam direction B by the reflective building or the like SB in the direction of another beam (here, the beam B in the direction of 300 °), the radio wave propagation path between the reflective building SB and the mobile station #j. May be formed and communication may be possible. That is, the base station 20 ₀ Communication between the mobile station #j and the reflection building SB and the mobile station #j.
[0089]
Here, the characteristics of the radio wave propagation paths formed by the beam A and the beam B are generally different, and the time fluctuation characteristics of the radio wave propagation formed in these beam directions (when the mobile station #j moves) Different. In such a case, rather than selecting and using either the beam A or the beam B, if there is a vacancy in the radio wave emission time slot for each beam, Communication quality can be ensured by providing time slots, forming antenna beams of mobile station #j in a plurality of directions from which these radio waves arrive, and combining and receiving radio waves coming from both. .
[0090]
At this time as well, in the interference management table shown in FIG. ₀ Adjacent base station 20 corresponding to 270 ° ₅ Sk is assigned in the direction of 270 ° of the adjacent base station 20 ₅ Si is assigned to the 90 ° direction of the base station 20 and the direction of the beam B is the base station 20. ₀ Adjacent base station 20 corresponding to 300 ° ₅ 60 ° and adjacent base station 20 ₆ Since no time slot is assigned in the direction of 180 °, beam A is assigned a time slot Sm excluding Sk and Si, and beam B is assigned a time slot Sn excluding Sk, Si and Sm. Assigned. The time slot Sm assigned to the beam A can be considered as a time slot assigned from the beginning. As the above synthesis method, any one of selection synthesis, maximum ratio synthesis, and equal gain synthesis can be used.
[0091]
Similarly to the operation of the mobile station described above, the base station directs the beam toward the opposite mobile station, and if the path is blocked by a building or the like, the base station starts from the strongest other beam from the mobile station. The path can be secured by directing the beam in the direction of arrival of the radio wave. Further, this operation can be performed based on slot allocation request information from the mobile station.
[0092]
Now, even when the mobile station has an omnidirectional antenna instead of a directional antenna such as an adaptive array antenna, it is possible to perform the beam switching and the combined reception as described above.
[0093]
Base station 20 ₀ Mobile station #j having an omnidirectional antenna in the situation as shown in FIG. ₀ The intensity of each radio beam emitted from the mobile station #j is measured by an antenna owned by the mobile station #j, and the beam having the best (maximum) reception quality, for example, the received signal level (in this case, irradiated and shielded in the direction of 300 °) Radio wave reflected by the object SB) is selected. Thereby, the communication by the beam B can be performed similarly to the case where a directional antenna is used. The time slot assignment is the same as when a directional antenna is used.
[0094]
Next, a case will be described in which time slots of beams from a plurality of directions as shown in FIG. 14 are combined when the mobile station has an omnidirectional antenna without a directional antenna.
[0095]
When the state of the beam from the base station is as shown in FIG. 14, when either one of the beam A and the beam B is not selected and used, the radio wave emission time slot in each beam is empty. Provides a time slot for radio wave radiation in both beams and synthesizes and receives radio waves coming from both. Time slot assignment is the same as in the case of using the directional antenna.
[0096]
At this time, the mobile station #j receives radio waves arriving from a plurality of directions, but there is a difference in arrival time to the mobile station #j between these incoming waves. In a receiver using a CDMA system, by applying a RAKE receiver, signals from a plurality of paths having arrival time differences can be combined and a path diversity effect can be used. Even in other digital communication systems that do not perform code spreading, by using a transversal filter that is set at a plurality of transmission signal symbol time intervals or an integer time interval thereof, a plurality of receptions that reach through a plurality of paths The signal can be configured to equalize and synthesize, and the reception characteristic can be improved by using the path diversity effect.
[0097]
The present invention is not limited to the above-described embodiments, and various modifications and applications can be made within the scope of the claims.
[0098]
【The invention's effect】
As described above, according to the present invention, radio beams are not radiated from a plurality of base stations at the same time in a direction in which interference is expected, so that radiation is radiated from each base station toward the mobile station in the mobile communication system. It is possible to realize a communication control method and apparatus based on SDMA (space division multiple access) that can reduce interference caused by a radio wave beam.
[0099]
In addition, even when the communication path from the base station to the mobile station is interrupted by a building, etc., by assigning the time slot with the strongest other radio wave beam, it is possible to secure the path and improve communication reliability Can be made.
[0100]
Further, when receiving radio waves from the base station from a plurality of directions, the communication quality can be improved by combining the received signals.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of a mobile communication system to which a communication control method according to an embodiment of the present invention is applied.
FIG. 2 is a block diagram illustrating a configuration example of each base station.
FIG. 3 is a diagram illustrating an example of a radio wave beam that can be radiated from each base station.
FIG. 4 is a diagram illustrating a state of each radio wave beam formed when a base station communicates with a mobile station in its communication area.
FIG. 5 is a diagram illustrating an example of a relationship between each radio beam emitted from a base station and each radio beam emitted from an adjacent base station that is expected to receive interference from each radio beam.
FIG. 6 is a diagram illustrating an example of an interference management table.
FIG. 7 is a diagram illustrating an example of a time slot assigned to a radio wave beam radiated from each base station.
FIG. 8 is a diagram illustrating another example of a time slot allocated to a radio wave beam emitted from a certain base station.
FIG. 9 is a diagram illustrating an operation example when a mobile station performs handover.
FIG. 10 is a diagram showing another example of the relationship between each radio wave beam radiated from a base station and each radio beam radiated from an adjacent base station that is expected to receive interference from each radio wave beam; .
FIG. 11 is a diagram illustrating another example of the interference management table.
FIG. 12 is a block diagram illustrating a configuration example of a mobile station.
FIG. 13 is a diagram for explaining an operation when a path is blocked by a building or the like.
FIG. 14 is a diagram for explaining an operation when signals are received from two directions and combined.
FIG. 15 is a diagram illustrating an example of a conventional mobile communication system in which communication control according to SDMA (space division multiple access) is performed.
[Explanation of symbols]
10 Mobile station
20 (20 ₀ , 20 ₁ , 20 ₂ , 20 ₃ , 20 ₄ , 20 ₅ , 20 ₆ ) base station
21, 31 Antenna array
22, 32 Synthesizer
23, 33 direction detector
24, 34 Beamformer
25, 35 Transceiver
26 Base station controller
30 Control station

Claims (12)

In a cellular mobile communication system capable of radiating radio wave beams in a plurality of directions from each base station, radio waves are emitted from each base station toward the mobile station, and each base station communicates with the mobile station at the same frequency. When communicating, the timing of radiating a radio beam from a base station differs from the radiation timing of the radio beam radiated from another base station with respect to a direction that matches the direction in which interference by the radio beam is expected. A communication control method in a mobile communication system for controlling
The mobile station is radiated from the base station toward a mobile station different from the mobile station when the reception level at the mobile station of the signal by the radio beam from the direction of the base station facing the mobile station decreases. Directing the radio beam in the direction of arrival of the other radio beam having the best reception quality among the other radio beams arriving at the mobile station, requesting allocation of a time slot in the other radio beam,
In a mobile communication system in which a base station assigns a time slot so that a radio beam radiated from another base station is different from a radiation timing radiated from another base station in a direction that coincides with a direction in which interference by the other radio beam is expected. Communication control method. In a cellular mobile communication system capable of radiating radio wave beams in a plurality of directions from each base station, radio waves are emitted from each base station toward the mobile station, and each base station communicates with the mobile station at the same frequency. When communicating, the timing of radiating a radio beam from a base station differs from the radiation timing of the radio beam radiated from another base station with respect to a direction that matches the direction in which interference by the radio beam is expected. A communication control method in a mobile communication system for controlling
A certain mobile station receives a signal from a first radio beam from the direction of the base station facing the mobile station, and is emitted from the base station toward a mobile station different from the mobile station and arrives at the mobile station. Directing the radio wave beam in the direction of arrival of the second radio wave beam, which is another radio beam, and requesting time slot allocation in the second radio beam, the base station may cause interference by the second radio beam. The time slot is assigned to a direction that matches the expected direction so as to be different from the radiation timing of the radio beam radiated from another base station, and the mobile station receives the received signal by the first radio beam. And a communication control method in a mobile communication system for combining a received signal by the second radio wave beam. In a cellular mobile communication system capable of radiating radio wave beams in a plurality of directions from each base station, radio waves are emitted from each base station toward the mobile station, and each base station communicates with the mobile station at the same frequency. When communicating, the timing of radiating a radio beam from a base station differs from the radiation timing of the radio beam radiated from another base station with respect to a direction that matches the direction in which interference by the radio beam is expected. A communication control method in a mobile communication system for controlling
The mobile station is radiated from the base station toward a mobile station different from the mobile station when the reception level at the mobile station of the signal by the radio beam from the direction of the base station facing the mobile station decreases. Selecting another radio beam having the best reception quality among other radio beams arriving at the mobile station, requesting allocation of a time slot in the other radio beam,
In a mobile communication system in which a base station assigns a time slot so that a radio beam radiated from another base station is different from a radiation timing radiated from another base station in a direction that coincides with a direction in which interference by the other radio beam is expected. Communication control method. In a cellular mobile communication system capable of radiating radio wave beams in a plurality of directions from each base station, radio waves are emitted from each base station toward the mobile station, and each base station communicates with the mobile station at the same frequency. When communicating, the timing of radiating a radio beam from a base station differs from the radiation timing of the radio beam radiated from another base station with respect to a direction that matches the direction in which interference by the radio beam is expected. A communication control method in a mobile communication system for controlling
A certain mobile station receives a signal from a first radio beam from the direction of the base station facing the mobile station, and is emitted from the base station toward a mobile station different from the mobile station and arrives at the mobile station. Request time slot allocation in the second radio beam, which is the other radio beam to
The base station assigns the time slot so as to be different from the radiation timing of the radio wave beam radiated from another base station in the direction matching the direction in which the interference by the second radio beam is expected, A communication control method in a mobile communication system, wherein a mobile station synthesizes a reception signal by the first radio beam and a reception signal by the second radio beam. In the communication control method in the mobile communication system according to any one of claims 1 to 4,
Predetermine another base station that should consider the interference of the radio beam from the base station to the base station,
Notifying the base station of the direction of the radio wave radiated from the other base station and its radiation timing,
Based on the information notified by the base station, the timing of the radio beam radiated from the own station is set to the radio wave radiated from another base station in a direction matching the direction in which the interference by the radio beam is expected. A communication control method for a mobile communication system which is controlled so as to be different from the radiation timing of the beam. In the communication control method in the mobile communication system according to claim 5 ,
A communication control method for a mobile communication system, in which another base station that should consider interference of a radio beam from the base station is a base station adjacent to the base station. In the communication control method in the mobile communication system according to any one of claims 1 to 6 ,
When the radio beam emitted from the base station communicating with the mobile station is switched from the first radio beam to the second radio beam as the mobile station moves, the radiation timing of the first radio beam and the second A communication control method in a mobile communication system in which radiation timings of two radio wave beams are made different. In the communication control method in the mobile communication system according to any one of claims 1 to 7 ,
A communication control method in a mobile communication system in which when a radio wave beam radiated from a base station covers a plurality of mobile stations, the radiation timing of the radio wave beam is different for each mobile station. In the communication control method in the mobile communication system according to any one of claims 1 to 8 ,
A communication control method in a mobile communication system, wherein a radio wave beam emission timing is controlled so that a radio wave beam is emitted from a base station to a mobile station in a plurality of time zones at predetermined intervals. The communication control method in the mobile communication system according to claim 9 ,
A communication control method in a mobile communication system, wherein the number of time zones for each predetermined period for radiating the radio wave beam is determined based on a communication state at the base station. A mobile station in a cellular mobile communication system in which each base station communicates with a mobile station at the same frequency by radiating a radio beam from each base station to the mobile station,
Another radio beam radiated from the base station toward a mobile station different from the mobile station and arriving at the mobile station when the reception level of the signal by the radio beam from the direction of the opposing base station is lowered at the mobile station Means for directing the radio beam in the direction of arrival of the other radio beam having the best reception quality and requesting time slot allocation in the other radio beam,
The base station assigns the time slot differently from the radiation timing of the radio beam radiated from the other base station in the direction matching the direction in which the interference by the other radio beam is expected. Mobile station to be. A mobile station in a cellular mobile communication system in which each base station communicates with a mobile station at the same frequency by radiating a radio beam from each base station to the mobile station,
Other radio beams radiated from the base station toward a mobile station different from the mobile station and arriving at the mobile station while receiving a signal from the first radio beam from the direction of the base station facing the mobile station Means for directing the radio wave beam in the direction of arrival of the second radio wave beam and requesting allocation of a time slot in the second radio wave beam,
The base station assigns the time slot so that it differs from the radiation timing of the radio beam radiated from another base station in the direction matching the direction in which the interference by the second radio beam is expected. A mobile station characterized by comprising means for combining the received signal by the first radio wave beam and the received signal by the second radio wave beam.

Images