JP5199149B2 - Radio base station and communication control method - Google Patents

Description

  The present invention relates to a radio base station that transmits signals to and from a plurality of radio terminals, and a communication control method in the radio base station.

  In a wireless communication system that performs time division duplex (TDD) and time division multiplexing (TDMA) communication between a plurality of wireless terminals and a wireless base station, the distance between each wireless terminal and the wireless base station is different for each wireless terminal. Different. For this reason, even though different time slots are assigned to the respective radio terminals, the radio base station may simultaneously receive burst signals from the respective radio terminals due to a propagation delay caused by a difference in distance. is there.

  In order to prevent such simultaneous reception (collision) of burst signals, for example, in the techniques described in Patent Literature 1 and Patent Literature 2, a radio base station transmits a control signal for preventing collision to each radio terminal. . Each wireless terminal forcibly adjusts the transmission timing of the burst signal based on the received control signal. Such control is referred to as time alignment control.

JP 2001-169343 A JP 2002-77087 A

  However, when the wireless terminal moves from the vicinity to the distance with respect to the wireless base station, the time position (reception window) of the burst signal received by the wireless base station becomes the time even if the time alignment control as described above is performed. It may come off to the rear of the slot.

  Thus, when there is a burst signal whose reception timing at the radio base station is extremely delayed, the burst signal collides with the next burst signal, and normal demodulation becomes difficult.

  In particular, in a PHS (Personal Handy Phone System) wireless communication system, a change in the distance between a wireless terminal and a wireless base station is large due to the macro cell formation, so that the above-described signal collision is likely to occur.

  In view of the above problems, an object of the present invention is to provide a radio base station and a communication control method that prevent collision of signals from each radio terminal.

  In order to solve the above-described problems, the present invention has the following features. A first feature of the present invention is that a frame including a plurality of uplink time slots obtained by dividing an uplink time slot used for uplink communication is configured, and the uplink time slots are divided into a plurality of radio terminals (radio terminals 2A to 2D). And a radio base station (radio base station 1) that transmits signals to and from the plurality of radio terminals by time division multiplexing, and receives a signal from each of the plurality of radio terminals ( A wireless communication unit 106), a collision detection unit (collision detection unit 154) that detects a collision between the two signals received by the reception unit, and a transmission source of the two signals from which the collision is detected by the collision detection unit Reducing the number of uplink time slots allocated per unit time to a plurality of wireless terminals, and in the frames different from each other with respect to the wireless terminal that is the transmission source of the two signals And summarized in that and a reallocation section (allocation section 152) that allocates time slots Ri.

  When a collision between two signals from a wireless terminal is detected, such a wireless base station reduces the number of uplink time slots allocated per unit time to the wireless terminal that is the transmission source of the two conflicting signals. In other words, by reducing the uplink transmission rate, it is possible to assign uplink time slots in different frames to the radio terminals that are the sources of the two conflicting signals. Further, the radio base station assigns uplink time slots in different frames to the radio terminals that are the sources of the two signals that have collided with each other, so that the radio terminals that are the sources of the two signals that have collided with each other Is prevented from being assigned an upstream time slot, and further, collision of signals from two wireless terminals is prevented.

  A second feature of the present invention relates to the first feature of the present invention, wherein the reallocation unit is a radio that is a transmission source of a front signal among the two signals in which a collision is detected by the collision detection unit. The gist is that assignment of the uplink time slot next to the uplink time slot assigned to the terminal is prohibited.

  A third feature of the present invention relates to the first feature or the second feature of the present invention, wherein the reallocation unit is provided only when the two signals whose collision is detected by the collision detection unit are voice signals. Reducing the number of uplink time slot allocations per unit time for the radio terminals that are the transmission source of the two audio signals, and the uplink in the frames that are different from each other for the radio terminals that are the transmission sources of the two audio signals The gist is to assign time slots.

  A fourth feature of the present invention relates to any one of the first to third features of the present invention, wherein the reallocation unit is configured such that one of the two signals in which a collision is detected by the collision detection unit is an audio signal. And when the other is a data signal, the number of uplink time slots assigned per unit time to the wireless terminal that is the transmission source of the voice signal is reduced, and the per-unit time for the wireless terminal that is the transmission source of the data signal The gist is to maintain the number of uplink time slots allocated and to allocate the unused uplink time slots to the wireless terminal that is the transmission source of the data signal.

  A fifth feature of the present invention relates to the first to fourth features of the present invention, and it is assumed that the collision detection unit detects a collision of two signals before assigning the uplink time slot to the wireless terminal. The number of uplink time slots allocated per unit time to the wireless terminal that is the transmission source of the two signals is less than or equal to ½ of the number of frames per unit time, and the transmission source of the two signals The present invention includes an initial allocating unit (allocation unit 152) that allocates the uplink time slots in the different frames to the wireless terminals.

  A sixth feature of the present invention is that a frame including a plurality of uplink time slots obtained by dividing an uplink time slot used for uplink communication is configured, and the uplink time slots are allocated to a plurality of radio terminals to perform time division multiplexing. A communication control method in a radio base station for transmitting signals to and from the plurality of radio terminals, wherein the radio base station receives signals from each of the plurality of radio terminals; and A station detecting a collision between two received signals, and a number of uplink time slots allocated per unit time to a wireless terminal that is a source of the two signals from which the wireless base station has detected a collision. And assigning the uplink time slots in the frames different from each other to the wireless terminal that is the transmission source of the two signals. The gist be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to prevent the collision of the signal from each wireless terminal in a wireless base station.

1 is an overall schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. It is a figure which shows the structure of the flame | frame which concerns on embodiment of this invention. It is a block diagram of the radio base station which concerns on embodiment of this invention. It is a figure which shows an example of allocation of the uplink time slot in the wireless base station which concerns on embodiment of this invention. It is a figure which shows the structure of the reception data in the wireless base station which concerns on embodiment of this invention. It is a figure which shows an example of reallocation of the uplink time slot in the radio base station which concerns on embodiment of this invention. It is a flowchart which shows the operation | movement of the wireless base station which concerns on embodiment of this invention. It is a flowchart which shows the operation | movement of the collision signal detection in the wireless base station which concerns on embodiment of this invention. It is a flowchart which shows the operation | movement of signal discrimination | determination in the radio base station which concerns on embodiment of this invention. 6 is a flowchart showing an operation of reassigning uplink time slots in the radio base station according to the embodiment of the present invention. 5 is a flowchart showing an operation for monitoring allocation of uplink time slots in the radio base station according to the embodiment of the present invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. Specifically, (1) the configuration of the radio communication system, (2) the operation of the radio base station, (3) the operation and effect, and (4) other embodiments will be described. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) Configuration of Radio Communication System First, the configuration of the radio communication system according to the embodiment of the present invention will be described in the order of (1.1) Overall schematic configuration of radio communication system, (1.2) Configuration of radio base station. To do.

(1.1) Overall Schematic Configuration of Radio Communication System FIG. 1 is an overall schematic configuration diagram of a radio communication system 10 according to an embodiment of the present invention.

  As shown in FIG. 1, the radio communication system 10 is a PHS radio communication system. The radio communication system 10 includes a radio base station 1, a radio terminal 2A, a radio terminal 2B, a radio terminal 2C, and a radio terminal 2D. In FIG. 1, wireless terminals 2 </ b> A and 2 </ b> B are located in a cell 3 provided by the wireless base station 1.

  Prior to communication with the radio terminals 2A and 2B, the radio base station 1 allocates time slots in a frame to be described later to the radio terminals 2A and 2B, and the radio base station 1 and the radio terminals 2A and 2B In 2B, signals are transmitted by TDD and TDMA.

(1.2) Configuration of Radio Base Station Next, the configuration of the radio base station 1 will be described. FIG. 3 is a configuration diagram of the radio base station 1. As illustrated in FIG. 3, the wireless base station 1 includes a control unit 102, a storage unit 103, a wired communication unit 104, a wireless communication unit 106, and an antenna 108.

  The control unit 102 is configured by a CPU, for example, and controls various functions provided in the radio base station 1. The storage unit 103 is configured by a memory, for example, and stores various types of information used for control and the like in the radio base station 1.

  The wired communication unit 104 communicates with a gateway server or the like in an upper network (not shown). The wireless communication unit 106 includes an RF circuit, a baseband circuit, etc., performs modulation and demodulation, encoding and decoding, etc., and transmits and receives wireless signals to and from the wireless terminals 2A and 2B via the antenna 108. I do.

  The control unit 102 includes an allocation unit 152 and a collision detection unit 154.

  The assigning unit 152 assigns time slots in the frame to the wireless terminals 2A and 2B.

  FIG. 2 is a diagram illustrating a frame configuration. As shown in FIG. 2, the frame includes an upstream time zone used for communication in the upstream direction (direction from the wireless terminal 2 to the wireless base station 1) and a downstream direction (direction from the wireless base station 1 to the wireless terminal 2). The downlink time zone is divided into four uplink time slots U1 to U4, and the downlink time zone is divided into four downlink time slots D1 to D4.

  The assigning unit 152 assigns the first uplink time slot U1 and the first downlink time slot D1 in each frame to the radio terminal 2A. Also, the assigning unit 152 assigns the second uplink time slot U2 and the second downlink time slot D2 in each frame to the radio terminal 2B. As a result, the transmission rate between the radio base station 1 and the radio terminals 2A and 2B is full in both the uplink direction and the downlink direction. FIG. 4 is a diagram illustrating an example of uplink time slot allocation.

  Thereafter, the radio terminals 2A and 2B transmit signals to the radio base station 1 using the assigned uplink time slots, and receive signals from the radio base station 1 using the assigned downlink time slots.

  The collision detection unit 154 detects a collision of radio signals transmitted from the radio terminals 2A and 2B using the uplink time slot. Specifically, the collision detection unit 154 receives received data corresponding to two radio signals (a radio signal from the radio terminal 2A and a radio signal from the radio terminal 2B) in successive uplink time slots from the radio communication unit 106. Enter.

  Next, the collision detection unit 154 deteriorates the SNR of the two received data corresponding to the two consecutive radio signals (the radio signal from the radio terminal 2A and the radio signal from the radio terminal 2B) to a first predetermined level or less. Determine whether or not. When the SNRs of the two received data have deteriorated below the first predetermined level, the collision detection unit 154 further detects the SNR of the tail part in the front received data and the SNR of the header part in the rear received data. To detect.

  FIG. 5 is a diagram showing a configuration of received data. The received data shown in FIG. 5 has a bit length of 240 bits. The received data includes, in order from the top, a 4-bit long ramp time for transient response (R), a 2-bit long start symbol (SS), a 6-bit long preample (PR), a 16-bit long unique word (UW). ), A 180-bit information part, a 16-bit CRC (Cyclic Redundancy Check), and a 16-bit guard. The header part is composed of a ramp time (R) for transient response, a start symbol (SS), a pre-ample (PR), and a unique word (UW), and the tail part is composed of CRC.

  Next, in the collision detection unit 154, the SNR of the tail portion in the front reception data has deteriorated to a second predetermined level or less, and the SNR of the header portion in the rear reception data has deteriorated to a third predetermined level or less. It is determined whether or not.

  When the SNR of the tail part in the front reception data deteriorates to a second predetermined level or less and the SNR of the header part in the rear reception data deteriorates to a third predetermined level or less, the collision detection unit 154 It is determined that the front radio signal corresponding to the received data collides with the rear radio signal corresponding to the rear received data.

  For example, in the example of FIG. 1, the wireless terminal 2 </ b> A is located far from the wireless base station 1. Therefore, as shown in FIG. 4, the radio signal from the radio terminal 2A received by the radio base station 1 is delayed and deviates behind the first uplink time slot U1, and the second uplink time slot U2 Collides with a radio signal from the radio terminal 2B corresponding to

  When the front radio signal and the rear radio signal collide, the assignment unit 152 determines whether or not these two consecutive radio signals (collision signals) are audio signals. For example, the assigning unit 152 can determine whether or not the corresponding wireless signal is an audio signal by analyzing the information part in the received data.

  When two consecutive collision signals are voice signals, the assigning unit 152 reassigns the uplink time slots to the wireless terminals 2A and 2B that are the transmission sources of these two signals.

  Specifically, the assigning unit 152 assigns the first uplink time slot U1 in the odd-numbered frame to the wireless terminal 2A that is the transmission source of the forward audio signal among the two consecutive collision signals. . The assigning unit 152 assigns the second uplink time slot U2 in the even-numbered frame to the wireless terminal 2B that is the transmission source of the backward audio signal among the two consecutive collision signals.

  Thereby, the transmission rate in the uplink direction between the radio base station 1 and the radio terminals 2A and 2B becomes a half rate. In addition, since the uplink time slot U1 assigned to the radio terminal 2A and the uplink time slot U2 assigned to the radio terminal 2B are located in different frames, the radio base station 1 receives the signal from the radio terminal 2A, The collision of signals from the terminal 2B is prevented. FIG. 6 is a diagram illustrating an example of reassignment of uplink time slots.

  Thereafter, the radio terminal 2A transmits a signal to the radio base station 1 using the first uplink time slot U1 in the allocated odd-numbered frame, and the radio terminal 2B transmits the signal in the allocated even-numbered frame. A signal is transmitted to the radio base station 1 using the second uplink time slot U2.

  Next, the assigning unit 152 determines whether or not the wireless terminal 2C or 2D, which is a wireless terminal other than the wireless terminals 2A and 2B, has entered the cell 3 and a call connection request has been made from the wireless terminal 2C or 2D. judge. When a call connection request is made from the wireless terminal 2C or 2D, the allocation unit 152 corresponds to the second uplink time slot U2 in the odd-numbered frame, that is, the wireless signal from the wireless terminal 2A that is delayed. Allocation of the second uplink time slot U2 next to the first uplink time slot U1 to be performed is prohibited.

  In this case, the assigning unit 152 assigns the third uplink time slot U3 or the fourth uplink time slot U4 that is an unused uplink time slot to the wireless terminal 2C or 2D.

(2) Operation of Radio Base Station Next, the operation of the radio base station 1 will be described. FIG. 7 is a flowchart showing the operation of the radio base station 1.

  In step S101, the radio base station 1 performs signal collision detection. FIG. 8 is a flowchart showing a signal collision detection operation. In step S201, the radio base station 1 acquires reception data corresponding to two consecutive radio signals (front radio signal and rear radio signal) received from the radio terminals 2A and 2B, and receives these two consecutive receptions. It is determined whether the SNR of the data has deteriorated below a first predetermined level.

  When the SNRs of the two received data deteriorate below the first predetermined level, in step S202, the radio base station 1 detects the SNR of the tail part in the front received data and detects the header part in the rear received data. SNR is detected, and it is determined whether the SNR of the tail part in the front reception data has deteriorated to a second predetermined level or less and the SNR of the header part in the rear reception data has deteriorated to a third predetermined level or less. judge.

  When the SNR of the tail part in the front received data deteriorates to a second predetermined level or lower and the SNR of the header part in the rear received data deteriorates to a third predetermined level or lower, The radio signal and the radio signal behind the radio terminal 2B collide with each other.

  In this case, in step S102 of FIG. 7, the radio base station 1 performs signal discrimination.

  FIG. 9 is a flowchart showing the signal discrimination operation. In step S301, the radio base station 1 determines whether or not two continuous collision signals are audio signals. If the two consecutive collision signals are not audio signals, the series of operations ends.

  On the other hand, if the two consecutive collision signals are audio signals, the radio base station 1 performs reassignment processing of uplink time slots in step S103 of FIG.

  FIG. 10 is a flowchart showing an uplink time slot reassignment process. In step S401, the radio base station 1 assigns the first uplink time slot U1 in the odd-numbered frame to the radio terminal 2A that is the transmission source of the forward audio signal.

  In step S402, the radio base station 1 allocates the second uplink time slot U2 in the even-numbered frame to the radio terminal 2B that is the source of the rear audio signal.

  Thereafter, in step S104 of FIG. 7, the radio base station 1 performs assignment monitoring processing.

  FIG. 11 is a flowchart showing the assignment monitoring process. In step S501, the radio base station 1 determines whether a call connection request from the radio terminal 2C or 2D has been made. When a call connection request is made from the wireless terminal 2C or 2D, in step S502, the wireless base station 1 prohibits assignment of the second uplink time slot U2 in the odd-numbered frame.

(3) Operation / Effect In the radio communication system 10 according to the embodiment of the present invention, the first uplink time slot U1 is allocated to the radio terminal 2A, and the second uplink time slot U2 is allocated to the radio terminal 2B. In the state, when the radio base station 1 detects a collision of radio signals from the radio terminals 2A and 2B, the radio base station 1 allocates the first uplink time slot U1 in the odd-numbered frame to the radio terminal 2A and A second uplink time slot U2 in the even-numbered frame is assigned to 2B.

  As a result, the uplink transmission speeds of the wireless terminals 2A and 2B become half rate, and it is possible to allocate uplink time slots in different frames to the wireless terminals 2A and 2B. In addition, the radio base station 1 assigns uplink time slots in different frames to the radio terminals 2A and 2B, so that the radio terminals 2A and 2B that are the transmission sources of the two radio signals that collide with each other are assigned. Thus, it is possible to prevent adjacent uplink time slots from being assigned, and to prevent collision of signals from the radio terminals 2A and 2B.

  Further, in the radio base station 1, the radio signal from the radio terminal 2A is delayed and deviates behind the first uplink time slot U1, and the radio signal from the radio terminal 2B corresponding to the second uplink time slot U2 In view of the collision, the radio base station 1 uses the first uplink time slot U1 assigned to the radio terminal 2A that is the transmission source of the radio signal ahead of the two radio signals that are colliding. By prohibiting assignment of the next uplink time slot U2, it is possible to prevent another collision.

  In addition, when the two radio signals that are colliding are audio signals, the radio base station 1 collides with the fact that even if the uplink transmission rate is lowered, it is considered that quality degradation is allowed. By performing the reassignment process described above only when the two existing radio signals are audio signals, deterioration of quality other than the audio signals is prevented.

(4) Other Embodiments As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in the above-described embodiment, the radio base station 1 performs the reassignment process of the uplink time slot only when the two radio signals colliding are voice signals. If one of them is an audio signal and the other is a data signal, the following processing may be performed.

  For example, the allocation unit 152 in the control unit 102 of the radio base station 1 analyzes whether the corresponding radio signal is an audio signal or a data signal by analyzing the information unit in the received data. Determine.

  Next, the assigning unit 152 reassigns the odd-numbered or even-numbered uplink time slot to the wireless terminal that has transmitted the audio signal. On the other hand, the assigning unit 152 assigns an uplink time slot in each frame to the wireless terminal that is the transmission source of the data signal. At this time, the assigning unit 152 assigns an unused uplink time slot that is an uplink time slot other than the uplink time slot that has been assigned to the wireless terminal that has transmitted the data signal.

  Thereby, the transmission rate of the data signal is maintained, and the deterioration of the quality of the data signal is prevented.

  Further, the allocation unit 152 in the control unit 102 of the radio base station 1 is assumed to detect a collision of radio signals from the radio terminals 2A and 2B before the first uplink time slot is allocated to the radio terminals 2A and 2B. In this case, the first uplink time slot U1 in the odd-numbered frame is assigned to the wireless terminal 2A in advance, and the second uplink time slot U2 in the even-numbered frame is assigned to the wireless terminal 2B. You may do it.

  For example, the assigning unit 152 acquires the positions of the wireless terminals 2A and 2B, and when the position of one of the wireless terminals is far away, that is, close to the outer edge of the cell 3, detection of collision of two signals is assumed. Can be determined.

  As described above, the radio base station 1 assigns uplink time slots for collision avoidance in advance, so that the re-assignment can be reduced as much as possible to suppress the variation in quality.

  In the above-described embodiment, the radio base station 1 changes the uplink transmission rate of the radio terminals 2A and 2B from the full rate to the half rate in the reassignment of the uplink time slot, but further changes from the half rate to the quarter rate. Alternatively, the full rate may be changed to the quarter rate.

  Further, in the above-described embodiment, the radio base station 1 determines the collision between the two radio signals based on the SNR of the tail part in the front reception data and the SNR of the header part in the rear reception data. The collision determination method is not limited to this. For example, the radio base station 1 determines that the difference between the time position of the UW (see FIG. 5) in the reception data corresponding to the front radio signal and the time position of the UW in the reception data corresponding to the rear radio signal is a predetermined time. If it is within the range, it may be determined that the two radio signals collide.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  INDUSTRIAL APPLICABILITY The radio base station and communication control method of the present invention can prevent signal collision from each radio terminal, and are useful as a radio base station and a communication control method.

  DESCRIPTION OF SYMBOLS 1 ... Wireless base station, 2A-2D ... Wireless terminal, 3 ... Cell, 10 ... Wireless communication system, 102 ... Control part, 103 ... Memory | storage part, 104 ... Wired communication part, 106 ... Wireless communication part, 108 ... Antenna, 152 ... allocation unit, 154 ... collision detection unit

Claims (6)

A frame including a plurality of uplink time slots obtained by dividing an uplink time slot used for uplink communication is configured, and the uplink time slots are allocated to a plurality of radio terminals, and are communicated with the plurality of radio terminals by time division multiplexing. A radio base station for transmitting signals on
A receiving unit that receives signals from each of the plurality of wireless terminals;
A collision detection unit for detecting a collision between two signals received by the reception unit;
While reducing the number of uplink time slots allocated per unit time to the wireless terminal that is the source of the two signals for which a collision has been detected by the collision detector, the wireless terminals that are the source of the two signals A radio base station comprising: a reallocation unit that allocates the uplink time slots in different frames.   The reallocation unit allocates the uplink time slot next to the uplink time slot allocated to the wireless terminal that is the transmission source of the preceding signal, of the two signals in which the collision is detected by the collision detection unit. The radio base station according to claim 1, which is prohibited.   The reallocation unit is configured so that the uplink time slot per unit time with respect to a wireless terminal that is a transmission source of the two audio signals is only when the two signals in which a collision is detected by the collision detection unit are audio signals. The radio base station according to claim 1 or 2, wherein the number of allocations is reduced, and the uplink time slots in the frames different from each other are allocated to radio terminals that are transmission sources of the two audio signals.   The reallocation unit is configured such that when one of the two signals in which a collision is detected by the collision detection unit is a voice signal and the other is a data signal, the unit per unit time for the wireless terminal that is the transmission source of the voice signal Reducing the number of uplink time slots assigned to the data signal transmission source wireless terminal, maintaining the number of uplink time slot assignments per unit time for the data signal transmission source wireless terminal, The radio base station according to claim 1, wherein the uplink time slot for use is allocated.   When it is assumed that the collision detection unit detects a collision of two signals before allocating the uplink time slot to the wireless terminal, the uplink per unit time for the wireless terminal that is the transmission source of the two signals An initial allocation unit that allocates the uplink time slots in the frames that are different from each other to the wireless terminal that is the transmission source of the two signals, while setting the number of time slots to be ½ or less of the number of frames per unit time The radio base station according to claim 1, comprising: A frame including a plurality of uplink time slots obtained by dividing an uplink time slot used for uplink communication is configured, and the uplink time slots are allocated to a plurality of radio terminals, and are communicated with the plurality of radio terminals by time division multiplexing. A communication control method in a radio base station that transmits a signal using
The radio base station receiving signals from each of the plurality of radio terminals;
The radio base station detecting a collision of two received signals;
The radio base station reduces the number of allocation of the uplink time slot per unit time to the radio terminal that is the transmission source of the two signals in which a collision is detected, and for the radio terminal that is the transmission source of the two signals Allocating the uplink time slot in the frame different from each other.

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