JP2013138440A - Wireless communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which suppresses an influence of a mobile terminal interfering with neighboring cells in a wireless communication system.SOLUTION: A first base station corresponding to a first cell receives a measurement result report on neighboring cells from a mobile terminal, determines whether the neighboring cells are interfered with by the mobile terminal or the neighboring cells interfere with the mobile terminal, allocates a resource to the first cell, and notifies a second base station corresponding to a second cell of the allocated resource. To the second cell, the second base station allocates a resource other than the resource allocated to the first cell.

Description

  The present invention relates to a radio communication system, and more particularly to resource allocation in a radio communication system.

  A wireless communication system typically has a cellular telephone structure in which a plurality of base stations define each communication cell and a mobile terminal in those cells communicates with a corresponding base station. The base station allocates communication resources (typically time-frequency blocks) to each mobile terminal in the cell in order to enable communication between the mobile terminal and the base station.

  As the mobile terminal moves within the cell, the radio situation in which the mobile terminal is placed changes. In some places, such as the edge region of a cell, strong transmission power is required in order to successfully transmit data between the mobile terminal and the base station.

  However, as the mobile terminal approaches the cell boundary, strong transmission power can cause the mobile terminal to interfere with communication in neighboring cells. In addition, communication from the mobile terminal may be disturbed by communication in neighboring cells.

  In addition, a handover from one base station to another base station will force the mobile terminal to asynchronous random access in the destination cell. Random access increases handover interruption time.

  Furthermore, it is difficult to plan the frequency of mobile terminals at cell boundaries, whether a static distribution (eg, 1/3) reuse scheme or a partial load scheme is used. On the other hand, both schemes can achieve optimal performance.

  Therefore, it is desired to provide a technique capable of suppressing the influence of mobile terminals that interfere with neighboring cells.

  According to an aspect of the present invention, a first communication cell is defined, a first base station that communicates with a mobile terminal located in the first communication cell, a second communication cell is defined, and the first communication cell is defined. A second base station that communicates with a mobile terminal located in the second communication cell, a resource assignment unit that assigns communication resources in the second cell, and a communication quality in the first cell that has a threshold level. A detecting unit that detects a mobile terminal that is lower than the mobile terminal and transmits information on the mobile terminal to the resource allocation unit, wherein the resource allocation unit receives and receives information on the mobile terminal from the detection unit A wireless communication system is provided that allocates resources to the second communication cell using information.

  The detection unit may be provided in the first base station, and the resource allocation unit may be provided in the second base station. The first base station may transmit information on the detected mobile terminal to the second base station.

  The resource allocation unit may allocate communication resources to the second cell while avoiding resources allocated to the mobile terminal detected in the first communication cell.

  The second resource allocation unit may be provided in the first base station, and may allocate communication resources to the first communication cell while avoiding resources allocated in the second communication cell.

  The resource allocation unit may allocate communication resources to the second cell without referring to information on the detected mobile terminal.

  The resource allocation unit allocates resources to the second communication cell using received information and using either a frequency hopping technique or a best effort technique. The wireless communication system described.

  According to an aspect of the present invention, a first base station that defines a first communication cell and communicates with a mobile terminal in the first communication cell, and a second communication cell that defines the second communication cell are defined. A communication resource allocation method in a wireless communication system comprising: a second base station that communicates with a mobile terminal in a cell, wherein a mobile terminal whose communication quality is below a threshold level in the first communication cell is detected. There is provided a communication resource allocation method for allocating communication resources to the second communication cell using information on detected mobile terminals.

  The detection of the mobile terminal may be performed by the first base station. The allocation of resources to the second communication cell may be performed by the second base station. The method may further include transmitting information about the detected mobile terminal from the first base station to the second base station.

  The allocation of communication resources may consist of allocating resources to mobile terminals in the second cell avoiding resources allocated to the mobile terminals detected from the first cell.

  The allocation of communication resources may use the first base station and avoid resources allocated in the second communication cell.

  The allocation of communication resources may consist of allocating communication resources to mobile terminals in the second cell without referring to information about detected mobile terminals.

  The information related to the detected mobile terminal may be information related to a communication schedule for the mobile terminal in the first cell.

  Information on the detected mobile terminal may be transmitted from the first base station to the second base station using an X2 communication interface.

  The information related to the detected mobile terminal may be information related to a possible interference of the second communication cell of the mobile terminal.

  According to another aspect of the present invention, information relating to a mobile terminal (4) that is used in a wireless communication system that defines a communication cell and communicates with a mobile terminal in the communication cell and operates in another communication cell is received. Then, a base station is provided that includes a resource allocation unit that allocates resources in the communication cell using the received information.

  The base station may include a detection unit that detects a mobile terminal whose communication quality is below a threshold level in the communication cell, and transmits information on the detected mobile terminal to another base station.

  The resource allocation unit may allocate a communication resource in the communication cell while avoiding a resource allocated to the mobile terminal detected from the other communication cell.

  According to another aspect of the present invention, a communication cell is defined and used in a wireless communication system that communicates with a mobile terminal in the communication cell, and the communication quality in the communication cell is lower than a threshold level. A base station is provided that includes a detection unit that detects a terminal and transmits information on the detected mobile terminal to another base station.

  A mobile terminal with low radio conditions and / or strong transmission power is subjected to different processing from a mobile terminal close to the base station.

According to the embodiment of the present invention, the following effects can be obtained.
• No cell edge reserved frequency pool for 1/3 or similar reuse is required. Cell edge blocks are prepared and released depending on the load.
The second base station can select whether to accept the reservation while avoiding the use of the corresponding resource block, or to reject it when the load is heavy.
-Since signaling includes quality of service (QoS), etc., better control of the processing of the second target base station is possible compared to a simple opportunistic approach.
The mobile terminal is also a top candidate for further handover to the second base station. The second base station may have the opportunity to measure the mobile terminal to allow synchronized handover.

1 is a schematic diagram showing a wireless communication system. It is a block diagram which shows the base station which embodies one viewpoint of this invention. Fig. 6 is a flow chart illustrating steps in a method embodying many aspects of the invention. Fig. 6 is a flow chart illustrating steps in a method embodying many aspects of the invention. Fig. 6 is a flow chart illustrating steps in a method embodying many aspects of the invention. 2 shows resource allocation in a wireless communication system. 2 shows resource allocation in a wireless communication system. 2 shows resource allocation in a wireless communication system. 2 shows resource allocation in a wireless communication system. 2 shows resource allocation in a wireless communication system.

FIG. 1 is a schematic diagram of a wireless communication system 1 operable in accordance with one aspect of the present invention. The system 1 of FIG. 1 includes a core network (CN) resource 2, a first base station 6, and a second base station. The first base station 6 defines a first communication cell in which communication with the mobile terminal is controlled by the first base station 6. Similarly, the second base station 8 defines a second communication cell in which communication with the mobile terminal is controlled by the second base station 8. In FIG. 1, an exemplary mobile terminal (or user equipment UE) 4 is shown. Each base station can communicate with the core network resource 2 for call routing and other roles using the signal links S1 ₁ and S1 ₂ as is well known and understood. Furthermore, the first and second base stations 6 and 8 can communicate with each other using a communication path (or interface) X2.

  It should be readily understood that the above system of FIG. 1 has been simplified and, in practice, the system has many base stations, each defining a communication cell. Such a system can provide communication to many mobile terminals.

  As described above, the mobile terminal 4 always communicates with the signal base station, and when the mobile terminal moves within the area covered by the system, the mobile terminal needs to cross the cell boundary and the communication needs to be switched to the next base station. is there. This process is known as handover.

  In the following description, it is assumed that the mobile terminal 4 is located at the outer boundary of the communication cell defined by the first base station 6 and therefore communication with the mobile terminal 4 is relatively low. The mobile terminal 4 is considered to be in a “bad” wireless environment that requires high output power to enable normal transmission. However, this high output power means that the mobile terminal 4 tends to interfere or interfere with communication in neighboring cells, for example the second cell defined by the second base station 8. Additionally or alternatively, the mobile terminal 4 may be prevented from communicating with the first base station by communication in the second cell.

  Embodiments of the present invention are intended to suppress these disturbances.

  The configuration of a base station that embodies one aspect of the present invention will be described with reference to FIG. Usually, in a wireless communication system, each base station is substantially the same as follows. Accordingly, the description of the base station shown in FIG. 2 applies to both the first and second base stations of FIG. The base station in FIG. 2 includes a control unit 10 that controls the overall operation of the base station. The control unit 10 can communicate with the core network resource. The base station also includes a radio frequency (RF) transmission (Tx) / reception (Rx) unit 12 that communicates with the mobile terminal via an antenna 18 in a known manner.

  In the embodiment of the present invention, the base station includes a detection unit 14 and a resource allocation unit 16. It should be readily appreciated that the detector 14 and resource allocator can be operated by the controller 10 or other suitable means. The control unit 10 can communicate with other base stations using the interface connection X2 (20).

  Here, the operation of the base station of FIG. 2 will be described with reference to FIGS. 1 and 2 and the flowcharts of FIGS.

  FIG. 3 is a flowchart showing a process executed in the first radio base station 6. In steps 101 and 103, the detection unit 14 detects communication with the mobile terminal in the first cell and determines the quality of downlink communication (communication from the mobile terminal to the base station). Judge the quality level. This is achieved by interpreting downlink (DL) measurement results reported from mobile terminals with poor radio conditions in the first cell. This DL radio status can be known from the number of retransmissions. This retransmission requires the output power used for these retransmissions along with the data in order to achieve normal transmission. This information can be known by the first base station. Also, the DL radio status can be obtained from the mobile terminal quality measurement result reported to the base station. The determination of uplink (UL) radio conditions can be realized by various methods. For example, it is conceivable that the DL radio situation gives the correct reality of the UL situation to the first base station. Alternatively, the first radio base station 6 can also detect the number of transmissions required by the mobile terminal 4 for the base station to receive data normally. This information may be combined with the power level indicated to the mobile terminal and the quality measurement result of the first base station. In this way, the expected interface contribution in the cell for a particular mobile terminal is obtained. As a result, it is possible to determine whether or not the mobile terminal 4 interferes with a neighboring cell.

  In step 105, it is determined whether the quality level is below a threshold value. That is, it is determined whether or not the communication with the mobile terminal is of sufficiently high quality. If so, the detection unit returns to Step 101, and the detection unit detects another mobile terminal.

  If the communication does not reach the required quality, for example, when the mobile terminal is located at the end of the first cell and requests high output power, the details of the mobile terminal are stored as part of the candidate list. Is done. This candidate list indicates mobile terminals that block or can block one or more neighboring cells. In this example, since it is assumed that the mobile terminal 4 is located at the end of the first cell that is the boundary with the second cell, interference is likely to occur between the mobile terminal 4 and the second cell. .

  In a practical embodiment of the invention, this candidate list will contain many mobile terminals since many mobile terminals communicate in each cell.

  For each mobile terminal on the candidate list, in step 107, the control unit 10 obtains measurement results of neighboring cells from the mobile terminal. Such a measurement result is obtained by measuring a pilot channel signal from a neighboring cell. This measurement result is sent back to the base station by the mobile terminal, preferably in the form of an RRC message. From this information, the cell interference level (to and from the mobile terminal) is determined (step 109).

  Then, cells that are likely to be disturbed or are likely to be disturbed (so-called target cells) are added to the cell list (step 111). A cell list is generated for each confirmed mobile terminal.

  Subsequently, the control unit 10 transmits information on the mobile terminal to be disturbed or disturbed to an appropriate base station for the target cell on the cell list associated with the mobile terminal. In the example described, the details of the mobile terminal 4 are sent by the first base station 6 to the second base station 8 via the interface X2.

  FIG. 5 is a flowchart illustrating a process performed in the base station of the target cell. For the sake of brevity, one operation at the second base station 8 for one mobile terminal 4 will be described. It should be readily understood that such a process is performed as necessary in many mobile terminals and cells.

  In step 115, the second base station 8 receives information regarding the mobile terminal 4 from the first base station 6. This information preferably includes at least schedule and resource allocation information for the mobile terminal 4. In step 117, the resource allocation unit 16 of the second base station evaluates scheduling information for the mobile terminal 4 in order to confirm whether the mobile terminal 4 interferes with the second communication cell. Details of this evaluation will be described later. Then, the resource allocation unit 16 allocates resources for the second cell using the received information (step 119).

  If it is determined that the mobile terminal 4 does not actually disturb this cell or is not disturbed by this cell, the received information is discarded, and the resource allocation to the second cell refers to it. Done without.

  On the other hand, if the mobile terminal 4 is determined to be disturbed by the second cell or to interfere with the second cell, there are several options for resource allocation for the second cell.

  For example, the resource allocation unit 16 ends any scheduling of the mobile terminal that uses the time / frequency period in which the interference occurs. This is possible by rescheduling the mobile terminal to a time / frequency period different from the time / frequency period of the mobile terminal 4 to be disturbed / disturbed.

  Another method is that the second base station schedules only mobile terminals with good radio conditions during the jamming time / frequency period. Since a good radio situation indicates that low transmission power is being used, this suppresses interference and also reduces the possibility of interference.

  Further, the second base station 8 may suppress the possibility of further interference by taking a means for scheduling a new user while avoiding the interference time / frequency period.

  This approach requires that scheduling be deterministic over at least a few tens of ms ahead. Deterministic assignment requires significant latency (10-100 ms) to ensure that all affected base stations are aware of the intended schedule prior to its occurrence.

  The influence of latency is dealt with differently depending on the transmission situation.

・ Best effort Best effort data is less susceptible to latency. The resource allocation decision may be made several milliseconds ahead.
Voice / video phone The voice / video codec is very foreseeable and resource allocation is done for long periods, ie the mobile terminal sets X basic resource blocks at 20 ms intervals according to a specific frequency hopping scheme. Assigned. Although one or more communications scheduled for the first time are not known to other base stations, the other base stations can suppress the influence once the scheme is received.
Quality of service (QoS) non-predictive service This is a service that is unknown but requires high QoS. It is considered that the amount of data transmitted is not small. Such communication is performed by each base station reserving a part of the bandwidth (or time domain) to a high-interference mobile terminal. In some techniques, this is a static part of the bandwidth, meaning "1 reuse at the cell center> 1 reuse at the cell boundary". In accordance with the essence of the present invention, this reserved area can be increased or decreased as needed in the actual cell. When QoS non-predictive service is initiated, the assumed corresponding bandwidth is “reserved” and communicated to neighboring cells. This can be done either by reserving part of the bandwidth or by reserving a frequency hopping scheme of a certain bandwidth.

  Here, in order to explain resource allocation according to one aspect of the present invention, FIGS. In these figures, the grid represents an exemplary basic resource block, the horizontal axis shows the duration of the block, and the horizontal axis shows the frequency width of the block. Each mobile terminal has one or more consecutive blocks allocated for communication.

  FIG. 6 shows an example of resource block allocation to the mobile terminal 4 by the base station 6. A block A in FIG. 6 indicates a block assigned to the mobile terminal 4.

  As described above, if the first base station determines that the second cell is blocked by the mobile terminal 4 or the mobile terminal 4 is blocked by the first base station, the first base station moves to the mobile terminal 4. Send information about resources that are intended to be allocated.

  FIG. 7 shows an example of resources that are intended to be allocated by the second base station in the second cell. As can be seen from FIG. 7, mobile terminals B, C, D, E, F and G are allocated resources in the second cell.

  FIG. 8 shows how the intended assignment to mobile terminal 4 (indicated by block A) collides with the intended assignment to existing mobile terminals in the second cell. Since it is considered that the second base station 8 determines that the mobile terminal 4 interferes with communication of at least one of the existing mobile terminals in the second cell, the second base station reallocates resources to avoid the interference. Would do.

  FIG. 9 shows a possible reallocation scheme for the second cell. Here, the resources allocated to the existing mobile terminal and the mobile terminal 4 are arranged so as not to overlap each other or to interfere with each other.

  The second base station 8 reallocates its resources in order to ensure suitable communication with existing mobile terminals in the second cell. Furthermore, the second base station 8 can detect at least the envelope of the signal from the mobile terminal 4 in order to determine the amount of interference that can be caused by the mobile terminal 4. Normally, since the second base station 8 cannot decode the signal from the mobile terminal 4, it can only measure the signal envelope. However, in a variant, the second base station 8 can decode the communication from the mobile terminal 4, so that the timing (offset from ideal), signal quality (eg signal to noise ratio), and / Or signal strength can be measured.

  In addition to the second base station 8 reallocating resources in the second communication cell, the first base station also uses the information collected for the mobile terminal 4 to allocate resources for the first cell. Can be reassigned. Resource reallocation in the first and second communication cells can contribute to the optimization of the capacity of these cells.

  In allocating resources to the first and / or second communication cell, a frequency hopping technique can be utilized to obtain frequency diversity. The frequency hopping scheme is particularly suitable for long-term resource allocation.

  It is preferable to schedule resource blocks contiguous in the time domain to the mobile terminal rather than in the frequency domain so that the disturbing or disturbed mobile terminal is not synchronized with the second cell in the time domain. Such an assignment is shown in FIG. Since assignment B is continuous in the frequency domain, it can be seen that this assignment disturbs many blocks in the time domain. On the other hand, allocation C only disturbs 2 blocks in the time domain.

  Each base station may maintain a “buffer” of resource blocks for the hopping sequence. This is similar to a static configuration, but the allocated bandwidth (BW) is set to a small value. This is because a substantial part is not allocated, so that a moving mobile terminal can obtain a “protected” bandwidth faster and less demand on the interface X2. This “buffer” is updated from time to time to minimize bandwidth waste and maintain a small margin for new mobile terminals with poor signal quality. The buffer update may include processing the latest sequence to take into account the timing of pre-measurements by possible target cells.

  As an example, the second base station 8 can report the measurement result obtained for the mobile terminal 4 to the first base station 6 via the communication interface X2. For example, if the second communication cell is heavily disturbed by the mobile terminal 4, the second base station 8 may propose a handover of the mobile terminal from the first base station 6 to the second base station 8. it can. Alternatively, the first base station 6 would be able to reduce the data rate that can be assigned to the mobile terminal 4, suppress the required transmission power, and suppress possible interference to the second cell. .

  As another possibility, the second base station 8 transmits the data supplied from the first base station 6 to the second base station 8 via the communication interface X2 to the mobile terminal 4. Such data transmission results in downlink macro diversity. The first base station 6 provides the payload data to be transmitted and the channel coding, modulation and scrambling used. The second base station 8 outputs data according to the channel coding, modulation, and scrambling. The mobile terminal 4 will receive the same signal from both the first and second base stations. However, scheduling control and retransmission control are transmitted only from the first base station 6. Uplink macro diversity is realized by the second base station 8 sending data received from the mobile terminal 4 to the first base station 6. If the data received by the receiver of the first base station 6 is insufficient to successfully decode the uplink information of the mobile terminal 4, the first base station 6 transmits from the second base station 8. Data can be used. The reception confirmation or retransmission request is transmitted to the mobile terminal 4 by the first base station 6 based on one or a plurality of received data. The drawback of the uplink macro diversity described here is the additional delay imposed by the communication path between the first and second base stations. This delay is a total of several hundred microseconds until data is received from the second base station 8 and ready for use by the first base station 6 until a reception confirmation or retransmission request is transmitted to the mobile terminal 4. Will be an additional delay. This additional delay will not severely degrade the system.

Both uplink and downlink macrodiversity is such that the difference in path delay between each base station and the terminal is within the range required to be compensated by the receiver of each terminal and base station. Works best when distance is short. For example, a distance of 2 km between base stations is easily dealt with. For longer distances, the communication of the second base station 8 with the mobile terminal 4 has a different timing (early or late) than the mobile terminal in the cell controlled by the second base station.

Claims (25)

A method performed by a first base station (6) operating for a first cell having at least two neighboring cells to which at least one second base station corresponds:
Receiving a measurement result report for one or more neighboring cells from at least one mobile terminal (107);
Based on the measurement result report, determine whether the reported one or more cells are blocked by the mobile terminal or the mobile terminal (109);
Scheduling resources for communication with the mobile terminal of the first cell;
Informing the resource scheduled for the mobile terminal to one or more second base stations operating for a cell determined to be disturbed.   The method according to claim 1, wherein the first cell and the two or more neighboring cells are assigned at least partially overlapping frequency regions for scheduling to a mobile terminal operating by each cell. .   The method according to claim 1 or 2, wherein the resource scheduled for the mobile terminal is a resource block in a time-frequency domain.   The method according to claim 1, 2 or 3, wherein the resource scheduled for the mobile terminal is a frequency hopping pattern.   Transmitting the user data to the one or more second base stations determined to be disturbed in order for the one or more second base stations to transmit user data to the mobile terminal. The method of claim 1, 2 or 3, further comprising:   The method according to any one of claims 1, 2, 3 or 5, further comprising receiving user data originating from a mobile terminal of the first cell from the second base station. A method performed by a second base station (8) operating for communication with a mobile terminal in a second cell, the first cell to which the first base station (6) corresponds is a neighboring cell, ;
Scheduling communication resources between the mobile terminals (4) in the second cell;
further,
Receiving information on resources scheduled in the first cell from the first base station to a first mobile terminal that is or has been determined to interfere with communication in the second cell;
Avoiding scheduling resources scheduled for the first mobile terminal in the first cell in the second cell to at least one or two or more cell edge mobile terminals .   The step of determining whether or not the first mobile terminal interferes with the second cell, and the process proceeds to the avoidance step when the second base station evaluates that the first mobile terminal interferes The method according to claim 7.   8. The method according to claim 7, wherein the second and first cells are assigned at least partially overlapping frequency regions for scheduling to mobile terminals operating by each cell.   The second base station (8) can communicate with the first mobile terminal (4) without registering the first mobile terminal with the second base station (8). 10. The method according to 7 or 9.   11. The second base station (8) according to claim 7 or 10, wherein the second base station (8) is capable of receiving data for transmission to the first mobile terminal (4) from the first base station (6). The method described.   The said 2nd base station (8) can receive the data for transmitting to said 1st base station (6) from said 1st mobile terminal (4), According to claim 7 or 11 The method described.   The determination as to whether or not the one or more mobile terminals are located at a cell edge is performed based on transmission power used for communication with each of the mobile terminals of the second cell. Item 8. The method according to Item 7. A base station utilized in a wireless communication system and arranged to support communication with at least a mobile terminal of a first cell:
An interface (X2) that communicates with one or more second base stations and contributes to communication in one or more second cells that are neighbors of the first cell;
A detector (14) for detecting that one or more second cells are disturbed or obstructed by a first mobile terminal (4) operating in the first cell;
A resource allocation unit (16) that schedules resources for communication with the mobile terminal of the first cell;
Controlling the operation of the base station and operating the resource information scheduled for the first mobile terminal for one or more of the second cells determined to be disturbed A control unit provided for transmission to the base station;
A base station.   The base station according to claim 14, wherein the base station operates in a frequency band commonly used in the first and second cells.   The base station according to claim 14 or 15, wherein the resource allocation unit schedules resources in a resource block format in a time-frequency domain.   User data is transmitted to the one or more second base stations (8) determined to be disturbed so that the one or more second base stations can transmit user data to the mobile terminal. The base station according to claim 14, 15, or 16, wherein the base station is transmitted via the interface.   The base station according to claim 14, 15, 16, or 17, wherein user data generated from the first mobile terminal is received from the second base station via the interface. A base station (8) utilized in a wireless communication system and arranged to support communication with a mobile terminal of at least a second cell comprising:
An interface for communicating with at least one first base station that contributes to communication in a first cell that is a neighboring cell of the second cell;
A resource allocator (16) for scheduling resources among mobile terminals in the second cell;
With
Depending on the block resource information received from the first base station and scheduled for the mobile terminal of the first cell that interferes with or is expected to interfere with the second cell, the resource allocation unit In the second cell, a base station that avoids scheduling of the block resources to at least one or two or more mobile terminals assumed to be located at cell edges.   The base station according to claim 19, which operates in a frequency band commonly used in the first and second cells.   The base station according to claim 19 or 20, wherein the block resource is a block in a time-frequency domain.   The base station according to claim 19 or 20, wherein the mobile terminal of the first cell communicates with the first mobile terminal (4) without registering with the base station (8).   23. The base station according to claim 19, 20 or 22, which receives data for transmission from the first base station (6) to a mobile terminal (4) of the first cell.   24. The base station according to claim 19, 20, 22 or 23, which receives data for transmission from the mobile terminal (4) of the first cell to the first base station (6). The determination as to whether or not the one or more mobile terminals are located at a cell edge is performed based on transmission power used for communication with each of the mobile terminals of the second cell. 19. A base station according to 19.

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