Patent Application
20050259663
1. Field of the Invention
The present invention relates to a radio base station and a mobile communication system, and in particular to a radio (wireless) base station and a mobile communication system utilizing for example W-CDMA (Wideband-Code Division Multiple Access) and the like.
2. Description of the Related Art
Recently, developments of W-CDMA are expected as one of the high-speed packet communication methods in the next generation mobile communication system.
In a mobile communication system using packets such as W-CDMA, the standards have been reviewed in 3GPP (3rd Generation Partnership Project), where with protocols prescribed thereby, packet communications are performed between a radio base station (hereinafter occasionally referred to as a base station) and a terminal (a mobile phone etc.).
At present, in 3GPP, the HSDPA (High Speed Down Link Packet Access) method has been reviewed for performing a higher speed packet communication.
1.1 Concerning HSDPA
The HSDPA is a technology for making downward packet communication (communication from base station to terminal) at 10 Mbps and higher, and has been reviewed to be standardized by Release 5 3GPP standards as above-mentioned. Comparing with Release 99 of the conventional standards, there is a large modification in the radio channel configuration, and the introduction of a retransmission (resending) control and a scheduler.
Hereinafter, the radio channel configuration will be briefly described and a scheduler related to the present invention will be described as follows:
1.2 Concerning HSDPA Radio Channel
As shown in
Retransmission controls in the conventional Release 99 are performed by a radio channel control station or radio network controller (RNC) in an upper side of a base station. Namely, as shown in
Meanwhile, in 3GPP Release 5, the following two points are to be executed in order to realize a high speed packet transmission, namely to enhance an effective transmission speed (throughput);
(2) A scheduler is introduced to set and transmit the priority (order) of transmission depending on the contents of services to be transmitted or the condition of a terminal.
Hereinafter, these points will be briefly described:
(1) Concerning Retransmission Control
The flow of retransmission control is the same as in
In the terminal MS, as shown in
To the contrary, if it is found that there is an error, the retransmission controller 36 transmits a NACK (retransmission request) signal with UL HS-DPPCH likewise to the base station BTS for the retransmission request. At this time, the retransmission request is repeated until no error reception is achieved, for example.
Furthermore, in the base station BTS, as shown in
Having received the NACK signal, the scheduler 10 retransmits data stored in a retransmission buffer 3 through a modulator 4 and a transmitter 5. Also, having received the ACK signal, the scheduler 10 discards information stored in the retransmission buffer 3, takes out data from an ordinary buffer 2 to be stored in the retransmission buffer 3, and transmits them through the modulator 4 and the transmitter 5.
It is to be noted that while a retransmission controller may be substituted for the scheduler 10 and the transmission buffer 3 may be provided within the modulator 4, the following description, as shown in the figures, is applied to an example where the retransmission control is performed by the scheduler 10 and the retransmission buffer 3 is provided at the former stage of the modulator 4.
(2) Concerning Scheduler
The function of the above scheduler will be described in the following:
Data toward terminals transmitted from an upper layer are held in the ordinary buffer 2 provided per each terminal. Then, by a terminal-receiving-state-information extractor 9, a receiving status such as C/I transmitted from the terminal is extracted from the demodulated signal of the demodulator 7 and is transferred to the scheduler 10 (C the power of a desired wave (Carrier) and I interference waves).
The scheduler determines to which terminal the transmission should be prioritized or preferential by using the receiving-state-information, thereby controlling a switch (not shown). Then, ordinary data whose transmission order has been determined are re-stored in the retransmission buffer 3 from the ordinary buffer 2 and modulated by the modulator 4 to be transmitted from the transmitter 5.
As a method determining to which terminal the transmission should be prioritized or preferential, a Max C/I method, Round Robin method, Proportional Fairness method or the like is known. Particularly, when a method using C/I such as the Max C/I method is selected, a terminal with a better C/I is preferentially selected. For example, the Max C/I method is for determining a priority of transmission or an assigned time in order from a terminal which has the best receiving condition or the best C/I, in view of C/I of each terminal.
At this time, as shown in
1.4 Concerning Problems on Scheduling
As above-described, a terminal positioned in the vicinity of the cell border generally has a bad receiving status (for example C/I). This is because “C”, namely the power of desired wave (Carrier) is attenuated due to a far distance from the base station to the terminal while “I”, namely interference waves are made unchanged or larger in the presence of interference waves from other base stations BTS so that the C/I is reduced.
At this time when the scheduler of the base station preferentially performs assignments in order from a terminal with a better C/I, a terminal in the vicinity of the cell border has a bad C/I as above-described, so that no opportunity of transmission is given, or the assigned time becomes short even if it is given. As a result, it is disadvantageous that the throughput of the terminal is deteriorated or any communication is disabled at the worst case.
1.5 Concerning Problems at Hand-Over Time
(1) Concerning Hand-Over and Retransmission Control
A hand-over generally refers to an operation when the terminal MS changes its destination, as being moved from a cell CL 1 of a base station BTS 1 to a cell CL 2 of a base station BTS 2 as shown in
It is to be noted that HS-DSCH, based on the standards (3GPP Release 5), performs a cell change, not performing the conventional soft hand-over or hard hand-over. The cell change is the same as the hard hand-over in that a channel is once disconnected followed by a movement between cells and reconnected in a cell of the moved destination.
On the other hand, UL A-DPCH and DL A-DPCH enable a soft hand-over to be performed as well, which is a method for performing a hand-over only by changing spreading codes without changing the frequency, enabling a hand-over to be made without disconnecting the channel.
A hand-over in W-CDMA system is controlled by a radio channel control station (RNC) as shown in
The operation of this hand-over will be described in a case where the base station having the arrangement shown in
It is now presumed that communications are being performed between the terminal MS and the base station BTS 1, a hand-over to a base station BTS 2 is determined by the radio channel control station RNC and a retransmission is being made so that retransmission data are stored in the retransmission buffer 3 shown in
For performing the hand-over, the following three alternatives are conceivable:
The above hand-over method a) cannot be selected because the data are lost. The method b) is the most practical method which, however, requires data transmission between base stations, different from the conventional method. This will be hereinafter described referring to
At first, a hand-over request is sent from the radio channel control station RNC to the hand-over controller 11 (step S141 in
Then, the scheduler 10 requests the normal buffer 2 for the hand-over object terminal to transfer the data stored similarly to the base station BTS 2 (step S146). The buffer 2 performs transferring the data through the radio channel control station RNC (step S147), and after the transfer, reports the transfer completion to the scheduler 10 (step S148).
In response, the scheduler 10 reports the entire transfer completion to the hand-over controller 11 (step S149), which then reports the hand-over having been prepared to the radio channel control station RNC (step S150). After this, the hand-over is implemented (step S151).
On the other hand, it is understood that the method c) is a simple one because it may use the conventional control, however, as above-noted a hand-over terminal exists in the vicinity of the border of ordinary cells, having a bad C/I so that the priority set by the scheduler 10 is low and the time is short (not assigned at the worst case).
Accordingly, it is disadvantageous that when a hand-over is performed after the retransmission is completed, the operation time is lengthened or the hand-over cannot be performed for a long time because of no sufficient time for the hand-over at the worst case.
Such a problem at a hand-over time has arisen not only for the retransmission data stored in the retransmission buffer but also ordinary data stored in the ordinary buffer.
Also as another conventional technology, a preferential call connecting device for radio communication system has been proposed in which in the absence of space for radio channels with respect to preferential call (a call with a high priority or a call with a high priority for QoS), the radio channels are preferentially assigned when a space is generated (for example, see patent document 1 being Japanese patent application laid open number 11-8876 (abstract,
However, in case of the conventional technology, a preferential call is assigned without any hand-over or channel disconnection for the purpose of keeping restrictions such as transmission speed, so that a preferential assignment is performed to a call with a high priority (i.e. service attribute), in which the communication call is made preferential in any case unless the service is changed
It is accordingly an object of the present invention to provide a radio base station and a mobile communication system wherein in the above-noted method c), the transmission time of retransmission data or ordinary data at hand-over time is shortened, thereby securing a transmission assignment time.
In order to achieve the above-mentioned object, a radio base station according to the present invention, comprises, a buffer holding communication data to a terminal, an extractor extracting a communication request signal from a received signal, and a scheduler controlling a transmission of the communication data based on an output signal of the extractor, the scheduler, upon detection of a hand-over request, controlling the buffer so as to preferentially perform the data transmission by raising an order of the data transmission for a hand-over object terminal before executing the hand-over.
Namely, in the present invention, an output signal of the extractor is a NACK signal in case a received signal includes a retransmission request or an ACK signal in case ordinary data are requested, so that based on the output signal the scheduler controls the transmission of communication data to a terminal which is held in a buffer.
At this time, upon detecting a hand-over request, the scheduler raises or elevates the order of data transmission to a hand-over object terminal (terminal to be handed over) which the scheduler itself knows, thereby preferentially performing the data transmission from the buffer.
Thus, regardless of a reception status or service indicated by C/I etc of the hand-over object terminal, the order of data transmission at the scheduler is raised or advanced, which is equivalent to the transmission assignment time being relatively increased, whereby the data transmission to the hand-over object terminal is completed before the hand-over to shorten the time required for the hand-over.
In the above, the communication data may be retransmission data or ordinary data, so that the above buffer may be a retransmission buffer or an ordinary buffer.
In case the above buffer is the retransmission buffer storing the retransmission data, this radio base station may further comprise an ordinary buffer, in which the scheduler, upon detection of the retransmission buffer being empty, preferentially transmits ordinary data for the hand-over object terminal among from ordinary data held in the ordinary buffer.
Namely, after the retransmission data is preferentially transmitted at hand-over time, the ordinary data held in the ordinary buffer are also preferentially transmitted.
This radio base station may further comprise an inflow controller, in which the scheduler, upon detection of the hand-over request, stops an inflow of data for the hand-over object terminal from an upper side by controlling the inflow controller.
Namely, since data are flowed into the radio base station even at hand-over time, a preferential data transmission at hand-over time is made possible more surely by suppressing the data inflow at the inflow controller preliminarily.
The above hand-over request may be provided from for example a radio channel control station (RNC).
On the other hand, the base station may detect the hand-over request similarly by the following various methods before it is provided from the radio channel control station.
This radio base station may further comprise a propagation time calculator calculating a signal propagation time between the terminal and the base station from a data transmission time to a reception time of the output signal of the extractor, and a terminal distance calculator calculating a distance between the terminal and the base station from the propagation time; the scheduler detecting the hand-over request by comparing the distance with a threshold.
In this case, the propagation time calculator and the terminal distance calculator may be included in the scheduler.
Namely, data transmission is performed from the base station to the terminal, a time of an ACK or NACK signal returned from the terminal, i.e. a signal propagation time between terminal-base station (BS) is calculated, a distance between terminal-base station is calculated from the propagation time, and the calculated distance is compared with a threshold value of a distance required for the hand-over, whereby the scheduler regards it as the terminal approaching to the border of cells so that a hand-over request will be generated shortly or as the hand-over request being detected.
Thus, after the detection of the hand-over request, it is made possible likewise to raise the order of data transmission to a hand-over object terminal and to complete the data transmission before the hand-over.
Alternatively, this radio base station may further comprise a terminal receiving-electric-field-strength (intensity)-information extractor extracting a receiving-electric-field-strength-information calculated from a received signal, and transmitted by the terminal; the scheduler detecting the hand-over request by comparing the receiving-electric-field-strength with a threshold.
Also in this case, the terminal-receiving-electric-field-strength-information extractor may be included in the scheduler.
Namely, a receiving-electric-field-strength (or reception power) detected on the terminal side is extracted in the radio base station, and the scheduler compares the receiving-electric-field-strength with a threshold value, thereby regarding it as the detection of the hand-over request.
Alternatively, this radio base station may further comprise a terminal-position-information extractor extracting terminal-position-information measured and transmitted by the terminal, a position information memory storing position information of the station itself, and a terminal distance calculator calculating a distance between the terminal and the base station from the terminal-position-information and the position information of the station itself; the scheduler detecting the hand-over request by comparing the distance with a threshold.
Also in this case, the terminal-position-information extractor and the position information memory and the terminal distance calculator may be included in the scheduler.
Namely, in this case, the scheduler calculates a distance between terminal-base station from terminal-position-information obtained from the terminal and position information of the base station itself preliminarily obtained, and prepares the distance with a threshold value, thereby regarding it as the detection of the hand-over request as in the above.
Also, this radio base station may further comprise a connected-BS-number-information extractor extracting connected-BS-number-information detected and transmitted by the terminal or provided from an upper side; the scheduler detecting the hand-over request by comparing the connected-BS-number with a threshold.
Also in this case, the connected-BS-number-information extractor may be included in the scheduler.
Namely, connected-BS-number-information detected on the terminal side or provided from an upper side such as the radio channel control station is extracted on the side of the radio base station to be compared with a threshold value, whereby the scheduler may regard it as the detection of the hand-over request.
Also, this radio base station may further comprise a terminal-position-information extractor extracting terminal-position-information measured and transmitted by the terminal, a memory storing past one of the terminal-position-information extracted by the terminal-position-information extractor, and a moving direction calculator calculating a moving direction of the terminal from present one of the terminal-position-information extracted by the terminal-position-information extractor and the past terminal-position-information stored in the memory; the scheduler detecting the hand-over request from the moving direction.
Also in this case, the terminal-position-information extractor, the memory and the moving direction calculator may be included in the scheduler.
Namely, in this case, terminal position information measured at the terminal is extracted at the base station, and the scheduler calculates the moving direction of the terminal with a present value and a past value of the terminal position information, thereby regarding it as a substantial handover request based on the moving direction in which the terminal is moving toward the cell border.
Furthermore, this radio base station may further comprise a terminal-position-information extractor extracting terminal-position-information measured and transmitted by the terminal, and a terminal-moving-direction extractor extracting moving-direction-information of the terminal measured and transmitted by the terminal; the scheduler detecting the handover request from the terminal-position-information and the moving-direction-information.
Also in this case, the terminal-position-information extractor and the terminal-moving-direction extractor may be included in the scheduler.
Namely, in this case, the terminal position information measured at the terminal and the moving direction information of the terminal also calculated at the terminal are both extracted at the base station, and the scheduler regards it as the detection of the handover request from the terminal position information and the moving direction information as extracted.
Also, this radio base station may further comprise a terminal-position-information extractor extracting terminal-position-information measured and transmitted by the terminal, a memory storing past one of the terminal-position-information extracted by the terminal-position-information extractor, and a moving speed calculator calculating a moving speed of the terminal from present one of the terminal-position-information extracted by the terminal-position-information extractor and the past terminal-position-information stored in the memory; the scheduler detecting the handover request by comparing the moving speed with a threshold.
Also in this case, the terminal-position-information extractor, the memory and the moving speed calculator may be included in the scheduler.
Namely, in this case, by using a past value and a present value of the terminal position information measured at the terminal, the moving speed of the terminal is calculated at the base station to be compared with a threshold value, thereby regarding it as the detection of the handover request.
Also according to the present invention, various kinds of mobile communication systems including the above radio base station are provided as follows:
A mobile communication system comprising, a terminal calculating receiving-electric-field-strength-information from a reception signal (received signal) to be transmitted and the above-noted radio base station; the radio base station extracting the receiving-electric-field-strength-information, and detecting the handover request by comparing the receiving-electric-field-strength with a threshold;
The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which the reference numerals refer to like parts throughout and in which:
To the demodulator 7, an ACK/NACK extractor 8 and a terminal-reception-condition-information extractor 9 are connected. These are also connected to a scheduler 10. The scheduler 10 is mutually connected with the ordinary buffer 2 and the retransmission buffer 3, and mutually connected with a handover controller 11.
At first, it is supposed that a handover request is provided to the base station BTS from a radio channel control station (not shown) with respect to a terminal connected to the base station BTS. This handover request is received by the handover controller 11 (step S1), which then requests a handover control to the scheduler 10 (step S2). At this time, it is also supposed that a terminal to be handed over performs a retransmission control.
Also, the scheduler 10 prioritizes each terminal for scheduling the transmission order on the basis of receiving condition of each terminal (for example, C/I), service contents, maximum delay time or the like as in the Max C/I method.
The scheduler 10 requested with a handover control sets the retransmission of handover object terminal on the top (highest) priority (step S3), and informs it to the retransmission buffer 3.
Then, the scheduler 10 monitors the output signal of the ACK/NACK extractor 8, i.e. an ACK signal or a NACK signal (step S4), controls to retransmit retransmission data from the retransmission buffer 3 when the NACK signal is extracted (step S5), and confirms the completion of retransmission to the terminal when the ACK signal is returned from the terminal.
After the retransmission has been thus finished, the scheduler 10 makes a transfer request of ordinary data to the ordinary buffer 2 (step S7). This makes the ordinary buffer 2 transfer the ordinary data to the base station of a handover destination through the radio channel control station (step S8).
When the transfer of the ordinary data has been finished, the ordinary buffer 2 reports the completion of transfer to the scheduler 10 (step S9), which responsibly reports the completion of handover preparation to the handover controller 11 (step S11). Therefore, the handover controller 11 reports the completion of handover preparation to the radio channel station (step S11), so that the handover is going to be executed (step S12).
Thus, the scheduler 10 performs the retransmission on a priority or the top priority until a new transmission request (ACK signal) is returned from the terminal. As a result, for a handover object terminal, the retransmission is to be completed in a shorter time in comparison with a case where the priority order is not raised. It is to be noted that a new transmission request means that data transmission has been made to a terminal with a predetermined quality or more, or without errors. The retransmission control is finished at the time when the ACK signal is returned from the terminal.
Thus, by raising the priority order, the retransmission to handover object terminal can be made smoothly, making the retransmission buffer 3 empty in the earliest manner. Also, in the past, data stored in the retransmission buffer for the terminal were required to be transferred to the base station that is a handover destination, which is illuminated by the present invention.
It is to be noted that in the above embodiment, the scheduler may perform the handover control by itself. Also, a transfer controller for transferring data in the buffer may be provided. Furthermore, the transfer of data in the ordinary buffer and the handover are performed in this order for the sake of simplified description, however, the handover may be executed during the data transfer of the ordinary buffer.
At first, steps S21-S25 shown in
At step S26, the transmission order not only for the retransmission buffer 3 but also ordinary data toward the handover object terminal stored in the ordinary buffer 2 is set on the top priority. It is to be noted that in this case a predetermined priority level or degree may be raised, instead of the top priority.
Then, it is determined whether or not the ordinary buffer 2 of the handover object terminal is empty (step S27). If it is not empty, the ordinary data in the ordinary buffer 2 is stored in the retransmission buffer 3 and transmitted through the modulator 4 and the transmitter 5 (step S28).
Since the result of the transmission of the ordinary data is returned from the terminal, it is monitored at the ACK/NACK extractor 8 through the receiver 6 and the demodulator 7 (step S29). When the output signal of the ACK/NACK extractor 8 indicates an ACK signal the process returns to step S27 while when it is a NACK signal indicating a presence of an error in the received packet, the scheduler 10 retransmits the transmission data stored in the retransmission buffer 3 (step S30). Then, steps S29 and S30 are repeated until an ACK signal is returned as to the data.
Returning to step S27, it is found that the ordinary buffer 2 of the handover object terminal becomes empty, a preparation finish is reported to the handover controller 11 in the same manner as step S10 in
Thus, data transfer of ordinary data to a base station as a handover destination through a radio channel control station as well as its control become unnecessary. Furthermore, a signal line therefore being not required enables the circuit scale to be reduced. Also, in the absence of data transfer in a network between the radio channel control station and the base station, the network load can be lightened.
It is to be noted that as will be described later, a unified arrangement of the retransmission buffer 3 and the ordinary buffer 2 can be made possible.
At first, after having received a handover request, in the same manner as step S1 in
This enables an increase of the ordinary data in the ordinary buffer 2 to be stopped.
After this, steps S43-S53 are executed corresponding to steps S2-S12 in
Thus, since the data amount in the ordinary buffer 2 is not increased, the data transferring time or the time up to the transfer completion can be shortened, enabling the ordinary buffer to be surely empty. Furthermore, between the radio channel control station and the radio base station, it becomes possible to lighten the network load because unnecessary data transfer is eliminated.
While in the above embodiments, it is supposed that the handover request is provided from an upper radio channel control station, this embodiment treats a case with no handover request. Namely, a case is supposed where the terminal exists in the vicinity of the border of cells so that the handover request for executing a handover is going to be generated in the near future with a high possibility.
Starting the reception of a signal (step S61), the propagation time calculator 12 calculates the propagation time T of the signal (step S62). The calculation of this propagation time will be described as follows:
The base station BTS carries the packet P2 on HS-DSCH, and stores the transmission time received from the transmitter 5. Having received this packet P2, the terminal confirms whether or not this packet P2 includes an error, in which if it includes an error, a NACK signal that is a retransmission request is returned while if includes no error an ACK signal requesting a new transmission is carried on HS-DPCCH and returned to the base station.
The base station BTS having received the signal by HS-DPCCH extracts an ACK/NACK signal at the ACK/NACK extractor 8 through the receiver 6 and the modulator 7, and notifies the propagation time calculator 12 of the time extracted.
This enables the propagation time calculator 12 to calculate a reciprocated propagation time T by subtracting a predetermined time required for the system from a response time from the signal transmission time to the signal reception time.
On the basis of this result, a terminal distance calculator 13 calculates a distance L between the base station and the terminal (step S63).
The scheduler 10 compares the inputted distance L with a threshold value Lth corresponding to a predicted distance in which a handover can arise (step S64), and determines that the terminal is positioned in the vicinity of the border of cells if the distance L exceeds the threshold value Lth.
Thus, the processing of steps S65-S74 are executed by regarding the handover request as one provided from the radio channel control station. Namely, these steps S65-74 correspond to steps S3-S12 shown in
It is also to be noted that in this embodiment, like the embodiment (2) in
It is to be noted that while the comparison between the distance L and the threshold value is performed by the scheduler 10, it may be done inside the terminal distance calculator 13, or the propagation time calculator 12 and the terminal distance calculator 13 may be included in the scheduler 10.
Furthermore, according to 3GPP the above-noted transmission timing is prescribed including a delay due to the propagation, so that it can be easily made to calculate the propagation time.
From the above, a priority order can be determined regardless of the receiving status (C/I) of the terminal. Also, by raising the priority (order), the throughput or the transmission delay of the terminal can be improved, enabling services requiring a high-speed transmission to be offered.
Also, since a handover can be performed in the near future with a high possibility when the terminal exists in the vicinity of the border of cells, by raising the transmission priority order in the scheduler like the above embodiments before the handover request is provided from an upper side, and transmitting the ordinary data stored in the ordinary buffer, it becomes possible to perform a handover more quickly compared with a case where an actual handover request is received and executed.
Starting the reception of a signal (step S81), the terminal-receiving-electric-field-strength-information extractor 14 shown in
This receiving-electric-field-strength-information is calculated as information of receiving-electric-field-strength E of a received signal, transmitted from the terminal, which the receiving-electric-field-strength calculator 38 receives through the modulator 34 and demodulator 35 in the terminal MS shown in
Then, the receiving-electric-field-strength-calculator 38 transmits the calculated receiving-electric-field-strength E to the base station BTS shown in
The receiving-electric-field-strength-information thus extracted is forwarded to the scheduler 10 to be compared with a threshold value Lth (step S83). As a result, if it is found that the receiving-electric-field-strength E is larger than the threshold value Eth (E>Eth), it is determined that the terminal MS exists in the vicinity of the border of cells so that the possibility of a handover is high (step S84).
Then, in the same way as the embodiment shown in
It is to be noted that upon calculating the receiving-electric-field-strength at the terminal, a moving average can be used to decrease fading effects. Also, by controlling a time interval for calculating the average, it becomes possible to lessen the fading effects by similarly.
Also, in this embodiment, the scheduler 10 may include the terminal-receiving-electric-field-strength-information extractor 14. Also, after the calculation of the receiving-electric-field-strength at the terminal, the terminal may determine the possibility of handover by itself, in which determining that there is a possibility, the terminal may return the result to the base station. In this case, the terminal receiving-electric-field-strength-information extractor 14 in the base station BTS may be a handover determination result extractor.
While in the embodiment (5) shown in
To this end, in the embodiment (6) shown in
The operation of the embodiment (6) shown in
At first, the terminal-position-information extractor 16 shown in
The BS position information memory 15 has preliminarily stored therein the position information of itself. The terminal distance calculator 17 having inputted the BS-position-information stored in the BS-position-information memory 15 and terminal-position-information extracted by the terminal-position-information extractor 16 can calculate a distance L between the terminal-base station from the position information Pt1 of the terminal and the position-information Pt0 of the base station.
The scheduler 10 compares the inputted distance L with the threshold value Lth like the embodiment (4) shown in
Namely, the scheduler 10 raises the priority order of data retransmission for the retransmission buffer 3, and transmits the data stored in the ordinary buffer 2.
Thus, it becomes possible to realize a handover at a high speed. It is to be noted that in view of the base station which does not move, a position measurement or direct input may be pre-stored in the position information memory.
Also, in this embodiment, the scheduler 10 may include the BS-position-information memory 15, the terminal-position-information-extractor 16 and the terminal distance calculator 17.
While in the above embodiments, the detection of handover request is simulated by using a distance between BS-terminal or receiving-electric-field-strength, the number of base station connected will increase as the terminal approaches to the border of cells. Therefore, it is possible to detect a substantial handover request by such a connected-BS-number.
Here, site diversity used for detecting connected-BS-number will be briefly described.
Site diversity is a method for transmitting the same data toward a certain terminal from a plurality of base stations, in which as shown in
An embodiment (7) using such a site diversity is shown in
Hereinafter the operation of the embodiment (7) will be described referring to the flowchart shown in
At first, in case the terminal MS is positioned in a relatively near place to the base station BTS 1 or BTS 2, a receiving-electric-field-strength E forwarded to the site diversity controller 39 from the receiving-electric-field-strength-calculator 37 in the terminal MS is high so that the site diversity controller 39 dose not perform the above site diversity. Therefore, the connected-BS-number-calculator 40 dose not calculate the connected-BS-number either. In case the terminal MS is positioned in the vicinity of the border of cells, the receiving-electric-field-strength E becomes low to the contrary so that a control with site diversity is performed.
When performing the site diversity, the site diversity controller 39 gives the complex wave signal of DLA-DPCH at this time to the connected-BS-number calculator 40, whereby a BS number N indicating the number of the current connection is detected at the connected-BS-number calculator 40 and transmitted to the base station through the modulator 32 and the transmitter 33.
At the base station BTS, the connected-BS-number information N thus transmitted from the terminal MS is extracted at the connected-BS-number-information extractor 18 (step S102).
Then, the scheduler having received the connected-BS-number-information compares the connected-BS-number N with the threshold value Nth (step S103), in which if the connected-BS-number N detected exceeds the threshold value Nth, it is determined that the terminal is positioned in the vicinity of the border of cells and steps S65-S74 are executed in the same manner as
This connected-BS-number-information N may be notified to the terminal or base station from an upper side such as the radio channel control station.
Also, in this embodiment, the scheduler 10 may include the connected-BS-number-information extractor 18.
In addition to a distance between BS-terminal, receiving-electric-field-strength, or connected-BS-number in the above embodiments, it is possible to detect a state where the terminal exists near the border of cells by detecting a moving direction of the terminal.
In an embodiment (8) of a radio base station according to the present invention as shown in
Hereinafter, the operation of the base station shown in
At first, the terminal-position-information-extractor 16 shown in
Then, the terminal-position-information extractor 16 extracts the next terminal-position-information Pt2 (step S114), at which the terminal-moving-direction calculator 20 calculates a moving direction D of the terminal by inputting present terminal-position-information Pt2 extracted by the terminal-position-information extractor 16 and past terminal-position-information Pt1 having been stored in the memory 19 (step S115).
The scheduler 10 having inputted the terminal moving direction D calculated by the moving direction calculator 20 determines whether or not the moving direction D is toward the border of cells (step S116), whereby it can be determined from the moving direction D and the terminal-position-information Pt2 that the terminal is directing toward the cell border so that in such a determination, steps S65-S74 are executed like
To the contrary, if it is found that the moving direction D is not directing toward the cell border, the present terminal-position-information Pt2 is stored in the terminal-position-information memory 19 as the past terminal-position-information Pt1 (step S117).
Thus, it is also possible to realize a high-speed handover.
Also, in this embodiment, the scheduler 10 may include the terminal-position-information extractor 16, the memory 19 and the terminal-moving-direction calculator 20.
While the above embodiment (8) calculates the moving direction of the terminal, this embodiment (9) of a radio base station according to present invention shown in
To this end, the base station BTS does not include the memory 19 and the terminal-moving-direction calculator 20 in the embodiment (8) shown in
The operation of this embodiment (9) will now be described referring to the flow chart shown in
At first, in the terminal MS, position information Pt1 detected at the GPS portion 38 is once stored in the memory 41. By comparing the present position information and the past position information at the moving direction calculator 42, the moving direction D of the terminal MS is calculated and transmitted to the base station BTS together with the position information Pt1 through the modulator 32 and the transmitter 23.
In the base station BTS, terminal position information Pt1 is extracted at the terminal-position-information extractor 16 (step S122), thereby extracting terminal-moving-direction information D at the terminal-moving-direction-information extractor 21 (step S123).
As a result, in the same manner as step S116 in
Thus, it is determined from the moving direction D and the terminal-position-information Pt1 that the terminal is directing toward the cell border, the priority order of data retransmission in the scheduler 10 is raised and the ordinary data stored in the ordinary buffer is transmitted, thereby realizing a high speed handover.
Also, in this embodiment, the scheduler 10 may include the terminal-position-information extractor 16 and the terminal-moving-direction-information extractor 21.
While the embodiments (8) and (9) make controls by using the moving direction of the terminal, a similar determination is made possible by using a moving speed of the terminal.
An embodiment (10), performing such a control, is shown in
Namely, the base station BTS shown in
In the flow chart shown in
V=(Pt2−Pt1)/(T2−T1)
where T1 and T2 indicate times respectively added to the terminal-position-information detected at the terminal, to be transmitted.
As a result, if it is found that the calculated terminal speed V is larger than a threshold value Vth (step S136), steps S65-74 are executed similarly to
To the contrary, if it is found that the terminal moving speed V is equal to or lower than the threshold value Vth, new present terminal-position-information Pt2 is stored in the terminal-position-information memory 19 as past-terminal-position-information Pt1 (step S137).
Also, in this embodiment, the scheduler 10 may include the terminal-position-information extractor 16, the terminal-position-information memory 19 and the terminal-moving-speed calculator 22.
As in the above, according to the present invention, by raising a priority of a handover object terminal at the time of handover, it becomes unnecessary to transfer retransmission data stored in a retransmission buffer during retransmission to a base station of a handover destination. Also, it becomes unnecessary to transfer ordinary data stored in an ordinary buffer similarly. The transferring operation being not required makes it unnecessary for the corresponding control.
Also, when a handover is performed, an inflow of data for the terminal to the base station is stopped, thereby smoothly and surely executing the transfer operation within the buffer.
If it is found that the terminal is positioned near the cell border by using a propagation time, position information or connected-BS-number, by raising the order of data transmission to the terminal, it is facilitated that the throughput of the terminal is improved and the maximum delay time is maintained. Also, similar effects to the above are obtained upon handover.
This application is a continuation of International Application PCT/JP03/01710 filed on Feb. 18, 2003, now pending, the contents of which are herein wholly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP03/01710 | Feb 2003 | US |
| Child | 11191352 | Jul 2005 | US |
