JP5384470B2 - Communication system, base station device - Google Patents

Description

  The present invention relates to a technology for performing communication between a base station apparatus and a radio communication terminal using a plurality of radio resources provided by a technique such as frequency division multiplexing or time division multiplexing, and in particular, the radio resources are divided into a plurality of sections. The present invention relates to a technique for leveling the number of radio communication terminals assigned to each section.

  Generally, in a wireless Internet access system, when data communication is performed, a random access channel (RACH: Random) is transmitted from a user terminal (UT: User Terminal (wireless communication terminal used by a user)) to a base station (BS: BaseStation). A connection request (RA: Request Access) is transmitted using Access Channel. When the base station receives the connection request RA transmitted from the user terminal, the base station uses the same radio resources as the connection request RA (for example, the same frequency and time slot in the case of time division multiplexing) A connection assignment (AA) indicating that communication may be started is transmitted, and permission to use a traffic channel (TCH) is given. Thereafter, the same radio resource is transferred to the traffic channel and communicated.

  Further, when the amount of data in communication between the base station and the user terminal is large, communication is performed by assigning a plurality of radio resources as traffic channels to one user. Furthermore, when the amount of communication between the base station and user terminals increases and the number of radio resources available in the random access channel or traffic channel exceeds, the base station activates the radio resource fair distribution function, etc. Control is performed to equalize the amount of radio resource usage.

  Moreover, there exists a thing described in patent document 1 as this kind of conventional technology. In the technique described in this document, in a wireless communication system, the reception strength and download status are monitored on the terminal side and the monitoring result is transmitted to the base station. By referring to the monitoring result on the base station side and reflecting the radio resource in the allocation control, interruption of data transfer is suppressed and the throughput of the sector is improved.

JP 2002-291042 A

  Here, the number n of available radio resources in the entire base station has a maximum value, and the maximum value is always independent of the number of users connected to the session and the number of users (active users) in communication. Maintained constant. That is, assuming that the number of radio resources of the entire base station is N, the number n of available radio resources is maintained such that “N> n”. The reason is that it is necessary to always reserve a free channel to some extent in the random access channel so that a user terminal newly starting communication can always access the base station.

  As described above, conventionally, since it is necessary to secure a free channel in a random access channel, radio resources of the entire base station have not been effectively used. Further, when radio resources are divided into a plurality of sections and managed in the base station according to the carrier frequency or the like, there is a problem that the radio resources cannot be leveled between the sections.

  In other words, when radio resources are sectioned for each modem board that performs signal processing according to the carrier frequency, for example, the user terminal connected to the base station is assigned to the user terminal from among the radio resources handled by the modem board Once radio resources are allocated, the user terminal cannot move between the modem boards unless reassignment is performed by reconnection, and thus the user may be biased to a specific modem board. In other words, the radio resources that each modem board can provide are limited. Therefore, if the user is biased to one modem board, the radio resources of other modem boards can be connected to the modem board even though there is room. Since the total number of resources of a plurality of user terminals is limited, there has been a problem of affecting the bandwidth (throughput) of each user terminal.

  In view of such circumstances, it is an object of the present invention to provide a technique that can level the use rate of radio resources and effectively use radio resources.

The communication system according to the present invention is a communication system that performs data communication using a communication slot that is a unit of a communication period between a wireless communication terminal and a base station apparatus by a time division multiplexing method, wherein the base station apparatus includes the wireless communication A plurality of sections that transmit and receive signals to and from the terminal, and a control unit that selects an empty communication slot corresponding to the section, the control unit, in response to a connection request from the wireless communication terminal, Notifying the wireless communication terminal of waiting for the connection request based on the number of registered wireless communication terminals, selecting one section according to the number of empty communication slots corresponding to each section, and further supporting the selected section The base station apparatus receives the retransmission of the connection request from the wireless communication terminal after the notification of the standby. When the communication is performed, the control unit of the base station apparatus starts data communication in the selected communication slot.

The control unit of the base station apparatus specifies a first mode for starting data communication in the selected communication slot when receiving the retransmission , and a connection request according to a connection request from the wireless communication terminal. And switching to a second mode in which a connection assignment for using the same communication slot as the transmitted communication slot is transmitted to the wireless communication terminal.

  The control unit of the base station apparatus switches to the first mode when the number of registrations of the wireless communication terminal is greater than a predetermined value.

  The control unit of the base station apparatus monitors the number of empty communication slots in the plurality of sections, and switches to the first mode when the difference in the number of empty communication slots in each section exceeds a threshold value. It is characterized by that.

A base station apparatus according to the present invention transmits / receives a signal to / from a wireless communication terminal in a base station apparatus that performs data communication with a wireless communication terminal using a communication slot that is a unit of a communication period by time division multiplexing. A plurality of sections, and a control unit that selects an empty communication slot corresponding to the section, the control unit according to the number of registrations of the wireless communication terminal according to a connection request from the wireless communication terminal Notifying the wireless communication terminal of waiting for a connection request, selecting one section according to the number of empty communication slots corresponding to each section, further selecting an empty communication slot corresponding to the selected section, upon receiving the retransmission of the connection request by the wireless communication terminal after the notification of the waiting, to initiate data communication with the selected communication slot It is characterized in.

  According to the present invention, when performing data communication using a communication slot which is a unit of a communication period by a time division multiplexing method using a plurality of frequencies, the usage status of the communication slot is determined in determining a communication slot to be allocated to the communication device. Since it can be reflected, it is possible to efficiently use radio resources. Therefore, the total throughput of the entire base station is improved, and there is an advantage that smooth data communication can be maintained even when radio resources are congested. Moreover, there is an advantage that the number of user terminals that can be registered in the base station can be increased as the utilization efficiency of radio resources is improved. In particular, since smooth data communication can be maintained, it is advantageous for setting up VoIP (Voice over Internet Protocol) and a dedicated line. Further, there can be obtained an advantage that packets per transmission / reception device in the base station can be distributed.

It is a flowchart which shows the procedure of extended RA / AA exchange mode. 1 is a block diagram showing an outline of a wireless Internet access system according to an embodiment of the present invention. It is a block diagram which shows the structure around the modem of a base station. It is a block diagram which shows the internal structure of each modem board. It is a block diagram which shows the internal structure of each processing system. It is a communication flowchart which shows the procedure of normal RA / AA exchange mode. It is a flowchart which shows the outline of the algorithm performed in the base station at the time of receiving the request access signal RA.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 is a block diagram showing an outline of a wireless Internet access system according to an embodiment of the present invention. As shown in the figure, a user terminal (wireless communication terminal: UT) 1 is a terminal having a function capable of wirelessly communicating with a base station (base station: BS) 2. The user terminal 1 includes general components such as a CPU, a main memory, and an input / output device as information processing terminals, and a wireless communication unit for communicating with the base station 2. The wireless communication unit includes a transmission unit that transmits a connection request to the base station 2, and a reception unit that receives a connection standby instruction transmitted from the base station 2. The CPU receives the connection standby instruction, A standby unit for instructing to resend the connection request after waiting for a predetermined time is included. The wireless communication unit includes a retransmission unit that retransmits the connection request.

  The base station 2 is connected to an IP (Internet Protocol) network 3 by wire and provides an Internet access service to the user terminal 1. The base station 2 can be connected to a large number of user terminals 1, and a plurality of base stations 2 can be recognized from the user terminal 1 in a normal form.

  FIG. 3 is a block diagram showing a configuration around the modem in the base station 2. FIG. 4 is a block diagram showing the internal configuration of each modem board. FIG. 5 is a block diagram showing an internal configuration of each processing system. As shown in these drawings, the base station 2 is configured as a multi-antenna multi-carrier type. The main control unit 4 controls the base station 2, and each component shown in the figure operates under the instruction of the main control unit 4. The data input / output interface 5 is a circuit for performing data input / output with an internal circuit of the base station 2 (not shown) such as an interface for performing data input / output with the IP network 3 (see FIG. 2).

  The modem unit 6 is a circuit that performs modulation / demodulation, and includes a plurality (two in this example) of modem boards (sections) 6-1 and 6-2. The path control unit 7 controls the configuration of a data transmission path between the modem unit 6 and the wireless communication unit 8 (8-1 to 8-n). The wireless communication unit 8 (8-1 to 8-n) includes an antenna 801, a high frequency circuit unit (RF: Radio Frequency) 802, a digital down converter (DDC) 803, and a digital up converter (DUC) 804, respectively. Composed. The antenna 801 and the high-frequency circuit unit 802 transmit and receive radio waves. The digital down converter 803 digitizes the received signal (analog signal). The digital up converter 804 converts the transmission signal (digital data) into an analog form.

  In the modem unit 6, the modem boards 6-1 and 6-2 are respectively responsible for modulation / demodulation of a plurality of carrier frequencies (in this example, f 1 to f 4 and f 5 to f 8). The modem board 6-1 has a processing system 60 (60-1 to 60-4) for each carrier frequency. Each processing system 60 has a plurality of digital signal processors (DSPs) 600 (600-1 to 600-3) corresponding to the number of divisions by time division multiplexing (in this example, three divisions). Each digital signal processing unit 600 stores a program for performing modulation / demodulation processing in a main memory (not shown). When the digital signal processing unit 600 operates based on such a program, it performs modulation / demodulation processing of data of the carrier frequency / slot in charge. The Tx / Rx buffer 601 is a buffer that temporarily holds transmission / reception data for each carrier frequency. The modem board 6-2 has the same configuration as the modem board 6-1.

  2 to 5, in the wireless Internet access system according to this embodiment, when the user terminal 1 is connected to the base station 2, the base station 2 connects the user terminal 1 to the modem boards 6-1 and 6-2. And a request access signal (connection request) RA is transmitted from the user terminal 1 to the base station 2 through a random access channel, and an access allocation signal (connection allocation) AA is transmitted from the base station 2 to the user terminal 1. (Hereinafter referred to as “RA / AA exchange”) to allocate radio resources (traffic channel TCH) used for data communication.

  Here, radio resources that can be used in this system are, for example, channels for communication, and are provided by adopting frequency division multiplexing, time division multiplexing, space division multiplexing (SDMA), etc. It is assumed that Among these N radio resources, a predetermined number is used for broadcast channel (BCH: Broadcast Channel) or PPP (Point to Point Protocol) alive signal (signal for confirming connection), for fair distribution function ( And the remaining n radio resources are allocated to a random access channel and a traffic channel (TCH). : Traffic Channel).

  In assigning the above radio resources, first, the user terminal 1 transmits a request access signal RA to the base station 2. Upon receiving this request access signal RA, the base station 2 determines a radio resource to be allocated to the user terminal 1 and returns an access allocation signal AA indicating the allocated radio resource to the user terminal 1. When determining the radio resource to be allocated, the radio resource in the modem board in which the user terminal 1 is registered is selected. This speeds up the process of selecting a radio resource, and the layer 2 can use the same channel in the same frame to make a radio resource allocation notification of a connection request called RA / AA exchange.

  Here, in this embodiment, a management process (hereinafter referred to as “radio resource manager task”) for leveling radio resources between the modem boards 6-1 and 6-2 is introduced, and radio resources are mixed. Whenever a radio resource is allocated to the user terminal 1 (or every time the radio resource allocation process is executed a predetermined number of times), the same task is activated. It is also possible to monitor the number of free resources of the modem boards 6-1 and 6-2 and start the task when the difference between the two exceeds a threshold value and becomes unbalanced. In any form, the radio resources of the modem boards 6-1 and 6-2 are leveled, so that the use efficiency of the radio resources as the entire base station 2 is improved.

  However, since the radio resource manager task needs to perform processing based on the usage status of both modem boards 6-1 and 6-2, it is assumed that processing is performed in layer 3. For this reason, it is necessary to achieve consistency with RA / AA exchange performed in layer 2. In this embodiment, a procedure (hereinafter referred to as “extended RA / AA exchange”) for exchanging control signals (described later) that is not included in the normal RA / AA exchange is set to ensure the above-described consistency. . In the following description, a mode for performing normal RA / AA exchange is referred to as “normal RA / AA exchange mode”, and a mode for performing extended RA / AA exchange is referred to as “extended RA / AA exchange mode”.

  FIG. 6 is a communication flowchart showing the procedure of the normal RA / AA exchange mode. FIG. 1 is a flowchart showing the procedure of the extended RA / AA exchange mode. Referring to FIGS. 1 to 6, the base station 2 optimizes the number of free random access channels according to two parameters of the number of radio resources currently used and the number of registrations, and further performs normal RA / AA exchange. Select whether to enter the mode or the extended RA / AA exchange mode. This algorithm (described later) needs to be synchronized with the timing of each frame.

  In the extended RA / AA exchange mode, the base station 2 does not notify the user terminal 1 of the normal access allocation signal AA, but instead notifies the user terminal 1 of an access allocation pending signal (connection waiting instruction) AA_Pending. Upon receiving the access allocation pending signal AA_Pending, the user terminal 1 proceeds to a standby process for a predetermined time. Here, the access allocation pending signal AA_Pending may include a wait value, and the standby process may be executed according to the wait value. This wait value is set to a value of about several frames, and is appropriately set according to the expected time required for the radio resource manager task described later, whereby the waiting time of the user terminal 1 can be shortened and optimized.

  FIG. 7 is a flowchart showing an outline of an algorithm executed in the base station when the request access signal RA is received in this embodiment. As shown in FIGS. 1, 2, and 7, when receiving the request access signal RA, the base station 2 first checks the number of resources currently used (S1). That is, first, the number of resources is compared with the first threshold value α, and if the number of used resources is smaller than the first threshold value (S1: No), the aggregation permission mode is selected (S2). If the number of used resources is larger than the first threshold value α (S1: Yes), the process proceeds to the aggregation prohibition mode (S3).

  The aggregation prohibition mode is a mode in which the number of resources allocated to one user is limited to, for example, one resource, and resources used by the user are suppressed with such limitation. Furthermore, the base station 2 compares the number of used resources with the second threshold value β (α <β) (S4). As a result, when the number of used resources does not exceed the second threshold β (S4: No), the process proceeds to the next without starting the radio resource fair distribution function (Fairness MAC function) (S5). If the number of used resources exceeds the second threshold β (S4: Yes), the wireless resource fair distribution function is enabled (S6). This function is a function for fairly allocating the same radio resources as much as possible to the entire user by releasing a part of the connection of the user terminals 1 during data communication. Then, detailed explanation is omitted.

  Next, the base station 2 checks the number of user terminals 1 currently registered with itself (hereinafter referred to as “registration number”) (S7). When the number of registrations exceeds the third threshold γ (S7: No), the process proceeds to a process of reducing the number of free random access channels (S8). On the other hand, if the registered number is below the third threshold γ (S7: Yes), the process proceeds to a process of increasing the number of free random access channels (S9). The third threshold value γ is not provided by only one point, but the processing is branched with a plurality of threshold values, and the number of random access channels is controlled by correlating with the number of registrations to optimize. You can also.

  Furthermore, the base station 2 compares the number of registrations with a fourth threshold value φ (φ <γ) (S10). If the number of registrations is below the fourth threshold φ (S10: No), processing in the normal RA / AA exchange mode is performed (S11). When the number of registrations exceeds the fourth threshold φ (S10: Yes), the base station 2 selects the processing in the extended RA / AA exchange mode. (S12).

  In this extended RA / AA exchange mode, the base station 2 transmits the access allocation pending signal AA_Pending to the user terminal 1 as described above, while moving to layer 3 and inquiring the radio resource manager task. The radio resource manager task executes a resource selection process considering radio resource leveling.

  In this process, first, the radio resource usage status of each modem board is confirmed, and a modem board with many free resources is selected regardless of which modem board the user terminal 1 is registered to. A radio resource to be allocated is appropriately selected from the radio resources to which the radio terminal belongs, and a radio resource to be allocated to the user terminal 1 is returned, and a notification to that effect is sent to the modem board related to the radio resource. Upon receiving this notification, the modem board executes predetermined preprocessing. That is, it notifies the DSP (modulation / demodulation circuit) related to the radio resource that the user terminal 1 has been allocated, and waits for a communication request from the user terminal 1.

  The base station 2 stores the radio resource returned from the radio resource manager task in a predetermined memory area (storage means), and when the request access signal RA reaches the base station 2 from the user terminal 1 that has completed the wait process. The base station 2 notifies the user terminal 1 of an access assignment signal AA for allocating the radio resource obtained by the radio resource manager task. When the user terminal 1 receives the access allocation signal AA, the user terminal 1 starts data communication using the traffic channel using the allocated radio resource. Upon receiving a request for starting data communication from the user terminal 1, the DSP related to the radio resource starts data communication immediately.

  As described above, according to this embodiment, the base station 2 is determined to be congested based on the fact that the number of registrations with respect to the base station 2 exceeds the threshold value φ. Regardless of whether the board is registered or not, select a modem board that has sufficient radio resources for all modem boards, select a radio resource from the selected modem boards, and assign it to the user terminal 1 . Therefore, the imbalance in the usage state of the radio resources between the modem boards is corrected, and the situation where the radio resources of the other modem board are insufficient even though the radio resources of one modem board have room can be avoided.

  In addition, the base station 2 moves to layer 3 when taking the mode of selecting a radio resource without being defined by the registered modem board described above, but by placing the user terminal 1 on standby in the extended RA / AA exchange mode. It becomes possible to match the response immediacy of the RA / AA exchange in layer 2 with the redundancy of the radio resource manager task in layer 3. Further, the radio resource manager task precedes the communication start procedure by the traffic channel from the user terminal 1, notifies the modem board related to the assigned radio resource, and waits for the radio resource, thereby starting the communication start procedure by the traffic channel. Can be performed quickly, and the standby processing time due to the extended RA / AA exchange can be compensated to some extent.

  The embodiment of the present invention has been described in detail above, but the specific configuration is not limited to this embodiment, and includes a design and the like within a range not departing from the gist of the present invention.

  In addition, a user terminal (wireless terminal) is registered in a section of radio resources set in the base station (base station) (in the above embodiment, a modem board), and radio resources in the section are allocated and the user terminal is assigned. When connecting, determine when the base station is congested based on criteria such as the number of registrations (registration number) of the user terminal with the base station exceeding the threshold, and when there is a connection request from the user terminal Regardless of the section in which the user terminal is registered, select a section with a lot of free radio resources and shift to a mode in which the radio resources of the section are allocated to the user terminal. Use of radio resources The rate it is possible to equalize. When shifting to the same mode, in addition to the normal connection control procedure in which the connection assignment is immediately returned to the connection request between the base station and the user terminal, a procedure for notifying the connection request of standby and connection request retransmission is added. Accordingly, it is possible to achieve both the high speed required for radio resource allocation to the user terminal and the redundancy generated when performing the radio resource allocation process across sections. Further, by adopting a form in which the base station designates the waiting time of the user terminal, the waiting time of the user terminal can be shortened and optimized within a range defined by the processing capacity of the base station at that time. Further, following the above-described radio resource allocation process, the allocation of the user terminal is notified to the allocated radio resource without waiting for a re-connection request from the user terminal, and the radio resource is set in a standby state. As a result, the communication procedure of the user terminal can be simplified and speeded up, and the redundancy at the start of communication due to standby can be compensated to some extent.

  For example, when executing RA / AA exchange processing at a user terminal or a base station, such processing is performed by incorporating a predetermined program into a CPU (Central Processing Unit) type arithmetic device or a computer system equipped with CPU type arithmetic. A form in which a function to be executed is constructed is common, but in such a form, it is an item that can be arbitrarily selected by design to execute a series of processes appropriately distributed not only to the main CPU but also to the local CPU. Further, the above-described program can be recorded and distributed on a computer-readable recording medium, and may be distributed in a form that realizes a part of the functions. For example, it may be distributed in the form of application software using basic functions provided by an OS (operation system). Further, it is possible to adopt a form in which a predetermined function can be realized in combination with a program of an existing system already recorded in a computer system, that is, a so-called differential program.

  The computer-readable recording medium includes a storage device such as a hard disk and other nonvolatile storage devices in addition to a storage medium such as a portable magnetic disk and a magneto-optical disk. Furthermore, the form provided from another computer system via arbitrary transmission media, such as the internet and other networks, may be sufficient. In this case, the “computer-readable recording medium” includes a medium that holds a program for a certain period of time in a transmission medium such as a volatile memory inside a computer system serving as a host or client on a network.

  In the above description, the configuration in which the control unit is constructed by the distributed processing method using the main CPU or the sub CPU has been described. However, at least a part of the processor may be constructed by FPGA (Field Programmable Gate Array). In this case, the distribution of the circuit program information to be incorporated into the FPGA can take various forms in the same manner as the distribution of the program.

  DESCRIPTION OF SYMBOLS 1 ... User terminal, 2 ... Base station, 3 ... IP network, 4 ... Main control part, 5 ... Data input / output interface, 6 ... Modem part, 6-1, 6-2 ... Modem board, 60 (60-1- 60-4) ... Processing system, 600 (600-1 to 600-3) ... DSP, 601 ... Tx / Rx buffer, 7 ... Path control unit, 8 (8-1 to 8-n) ... Wireless communication unit, 801 ... Antenna, 802 ... High frequency circuit part, 803 ... DDC, 804 ... DUC

Claims (5)

In a communication system that performs data communication using a communication slot that is a unit of a communication period between a wireless communication terminal and a base station apparatus by time division multiplexing,
The base station device
A plurality of sections for transmitting and receiving signals to and from the wireless communication terminal;
A control unit for selecting an empty communication slot corresponding to the section,
In response to a connection request from the wireless communication terminal, the control unit notifies the wireless communication terminal of waiting for the connection request based on the number of registrations of the wireless communication terminal, and an empty communication slot corresponding to each section. Select one section according to the number, and select an empty communication slot corresponding to the selected section,
When the base station apparatus receives a retransmission of the connection request from the wireless communication terminal after notification of the standby, the control unit of the base station apparatus starts data communication in the selected communication slot. A communication system. The control unit of the base station apparatus,
A first mode for starting data communication in the selected communication slot upon receipt of the retransmission ;
In response to a connection request from the wireless communication terminal, the mode is switched to a second mode in which connection assignment for using the same communication slot as the communication slot specified in the connection request is transmitted to the wireless communication terminal. The communication system according to claim 1.   The communication system according to claim 2, wherein the control unit of the base station apparatus switches to the first mode when the number of registrations of the wireless communication terminal is larger than a predetermined value. The control unit of the base station apparatus monitors the number of empty communication slots in the plurality of sections, and when the difference in the number of empty communication slots in each section exceeds a threshold,
The communication system according to claim 2, wherein the communication mode is switched to the first mode. In a base station apparatus that performs data communication with a wireless communication terminal using a communication slot that is a unit of a communication period by time division multiplexing,
A plurality of sections for transmitting and receiving signals to and from the wireless communication terminal;
A control unit for selecting an empty communication slot corresponding to the section,
In response to a connection request from the wireless communication terminal, the control unit notifies the wireless communication terminal of waiting for the connection request based on the number of registrations of the wireless communication terminal, and an empty communication slot corresponding to each section. When one section is selected according to the number, an empty communication slot corresponding to the selected section is selected, and when the retransmission of the connection request by the wireless communication terminal is received after notification of the standby , the selected communication A base station apparatus which starts data communication in a slot.

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