Method for controlling transmission capacity and mobile communication system

Abstract: A mobile communication system implements packet communication by allocating efficiently a transmission capacity to a wired line and a wireless line, wherein a practical transmission speed of data communication between a radio base station 2 and a mobile terminal 1 is measured in a call. A transmission capacity required for transmitting data at the minimum level of the transmission speed is determined as a target transmission capacity and, in a relay station 3 and a mobile switching station 4, an allocated transmission capacity with which transmission of data is permitted in the wired line is allowed to decrease in the case where the allocated transmission capacity is larger than the target transmission capacity. The allocated transmission capacity is allowed to increase in the case where the allocated transmission capacity is smaller than the target transmission capacity. A transmission speed in the wired line is controlled so as to be equal to or less than the allocated transmission capacity.

Description: FIELD OF THE INVENTION The present invention relates to a mobile communication system wherein data communication is implemented in accordance with a packet system, and particularly to a mobile communication system wherein a transmission capacity is allocated efficiently to each call in data communication in accordance with a packet system. BACKGROUND OF THE INVENTION Recently, calls to the Internet by means of a mobile terminal such as cellular phone and a hand-held information appliance through a mobile communication system have increased. In the case where data communication is performed in order to access home pages or to transmit and receive emails in a mobile communication system, a system has been heretofore employed in which a transmission capacity that has been previously determined in accordance with circuit switching connection is allocated to each call. Referring to FIG. 1, there is shown an example of a conventional mobile communication system for effecting data communication in accordance with a circuit switching system, comprising a mobile terminal 11, a radio base station 12, and a radio communication control unit 13, wherein a connection is established with respect to the Internet 20 through a packet switching station (PDSN) 14, and a packet gateway switching station (PDGN) 15. The mobile terminal 11 is a user terminal for mobile communication by the use of a cellular phone or a hand-held information terminal. The radio base station 12 communicates with the mobile terminal 11 by means of transmission and reception of radio signals. The radio communication control unit 13 is a control unit for controlling a plurality of radio base stations 12. The packet switching station 14 is equipment to be connected with a call intending to link to the Internet among calls to be connected with the radio communication control unit 13, which has a translating function between a communication switching system and a packet switching system. The packet gateway switching system 15 is an interconnecting gateway switching station for connecting a data communication in a mobile communication system to the Internet. In case of a data communication through an Internet link in a conventional mobile communication system, data is transmitted by means of a communication switching system inside the mobile communication system; then, the system is switched into a packet switching system in a packet switching system 14, and it is linked to the Internet 20 in a packet gateway switching station 15. Data communications such as Internet connections exhibit such characteristics that signals are transmitted and received for a short period of time in a burst mode different from voice communications, and no signal is transmitted and received other than the above-described period of time. In a communication switching system, a fixed band remains allocated when no signal is being transmitted and received in the same way as when signals are transmitted and received in data communication; this means that a transmission capacity allocated is uselessly occupied in the case where no signal is transmitted and received. Accordingly, such situation as described above is a factor for preventing efficient use of a transmission capacity in data communication, and in this respect, improvements are demanded. In place of such communication switching system, there is a packet system wherein a transmission capacity is efficiently used in data communication. According to a packet system, a transmission capacity in a network is held in common with a plurality of terminals, so that packets are transmitted on the network only in cases where signals are transmitted and received by the terminals, and no transmission is effected other than the case described above. Therefore, such packet system is a system wherein a transmission capacity maintained by a network is efficiently utilized in accordance with statistical multiplexing effect in data communication, which has such characteristic that signals are transmitted and received in a burst mode. Hence, utilization of the packet system increase also in a mobile communication system. Also in such packet system, packets transmitted from terminals and the like are restricted by means of an average value or a peak value in order to prevent convergence due to a concentration of the packets. A mobile communication system involves a wireless line and a wired line wherein data is retransmitted frequently in order to transmit correctly the data, since a wireless line exhibits a higher error rate than that of a wired line. Furthermore, the lower quality in a wireless line brings about a slower practical data transmission speed. Besides, a larger amount of information for detecting errors and processing retransmission of signals is added to a wireless line than that of a wired line, so that a ratio of transmission capacity that can be actually utilized with respect to a line speed is lower in the wireless line than in the wired line. In this connection, since a substantially equal amount of transmission has been allocated to a wired line and a wireless line in a conventional mobile communication system, there was either a case where a transmission capacity in the wired line became useless when quality in the wireless line becomes poor, or a case where loss of data arose in a part linked from the wired line to the wireless line. "A Flow Control Framework For ABR Services in Wireless/Wired ATM Networks"; Francis, M et al; Vehicular Technology Conference, 1999 IEEE 49th Houston, Texas, USA; 16-20 May 1999; Piscataway, New Jersey, USA; IEEE, US 16 May 1999; pages 1156-1160; XP010342144; (ISBN: 0-7803-5565-2) proposes a flow control framework for available bit rate (ABR) traffic in wireless/wired ATM networks. A base station calculates the rate of transmission for all the ABR sources that communicate through that base station, and the result is used in an uplink protocol. A fair share allocation scheme is disclosed, based on the quality of the wireless channels from the ABR sources to the base station and also on bandwidth availability from the base station to destinations. WO 99/05830 (Ericsson) discloses an enhanced internetworking function (E-IWF) that supports a method of direct digital inter-working between a radio telecommunications network and standard Internet Protocol (IP) routers. It is stated that the IWF provides translation functions between digital radio link protocols and land-line analog modems, ISDN terminals, terminal adapters, and packet data networks. SUMMARY OF THE INVENTION An object of the preferred embodiment of the present invention is to provide a mobile communication system wherein each of transmission capacities to a wired line and a wireless line is allocated to efficiently implement a packet communication. A method for controlling a transmission capacity according to the present invention corresponds to a method for controlling a transmission capacity for allocating efficiently the transmission capacity on a wired line in every call in a data communication wherein the data communication relates to a mobile communication system in which data is transmitted in a wireless line and the wired line in accordance with a packet system, including the steps of: measuring a practical transmission speed of the data on the wireless line in a call; determining, as a target transmission capacity of the wired line, a minimum transmission capacity that is required for transmitting through the wired line the data at the practical transmission speed in the call; and, changing an allocated transmission capacity usable for transmission of the data through the wired line, so as to reduce a difference between the allocated transmission capacity and the target transmission capacity of the wired line. Preferably, the step of changing the allocated transmission capacity includes the steps of: decreasing the allocated transmission capacity in the case where the allocated transmission capacity is larger than the target transmission capacity; and, increasing the allocated transmission capacity in the case where the allocated transmission capacity is smaller than the target transmission capacity. Accordingly, the optimum permissible transmission capacity determined on the basis of a practical transmission speed in a wireless line is allocated to each call, so that a transmission capacity can be allocated efficiently to a call in data communication. Furthermore, an amount of data in a packet from a wired line is restricted by a permissible transmission capacity based on a practical transmission speed in a wireless line, so that data having a higher speed that a transmission speed in the wireless line does not flow thereinto. Moreover, since allocation of a transmission capacity is controlled on the basis of a practical transmission speed of data transmitted through a wireless line, processing of the control is not dependent upon a protocol applied to the wireless line. Preferably, the step of changing the allocated transmission capacity of the wired line includes the steps of: decreasing the allocated transmission capacity in the case where the allocated transmission capacity exceeds the target transmission capacity by less than a predetermined first threshold; and, increasing the allocated transmission capacity in the case where the allocated transmission capacity exceeds the target transmission capacity by more than a predetermined second threshold. Preferably, in the foregoing methods, the allocated transmission capacity is periodically updated. A mobile communication system according to the present invention corresponds to a mobile communication system implementing data communication by transmitting data through a wireless line and a wired line in accordance with a packet system, and includes: a radio base station that includes: means for measuring a practical transmission speed of the data on the wireless line in a call; means for determining, as a target transmission capacity of the wired line, a minimum transmission capacity that is required for transmitting through said wired line the data at the practical transmission speed in the call; and, means for generating a transmission-capacity-demanding signal for changing an allocated transmission capacity, available for transmission of the data through the wired line, according to a difference between the allocated transmission capacity and the target transmission capacity; a relay station that includes means for receiving the transmission-capacity-demanding signal from the radio base station to change the allocated transmission capacity set up inside said relay station in the call, and for transmitting the transmission-capacity-demanding signal; and, a mobile switching station that includes means for receiving the transmission-capacity-demanding signal from the relay station to change the allocated transmission capacity set up inside the mobile switching station in the call. Preferably, the radio base station also includes means controlled by the transmission-capacity-demanding signal for decreasing the allocated transmission capacity in the case where the allocated transmission capacity is larger than the target transmission capacity, and for increasing the allocated transmission capacity in the case where the allocated transmission capacity is smaller than the target transmission capacity. Alternatively, the radio base station preferably also includes means controlled by said transmission-capacity-demanding signal for decreasing the allocated transmission capacity in the case where the allocated transmission capacity exceeds the target transmission capacity by less than a predetermined first threshold, and for increasing the allocated transmission capacity in the case where the target transmission capacity exceeds the allocated transmission capacity by more than a predetermined second threshold. In the foregoing mobile communication systems, the radio base station may further include means for measuring periodically the transmission speed to determine the allocated transmission capacity, and for transmitting the transmission-capacity-demanding signal as occasion demands. A further aspect of the invention is an apparatus for allocating transmission capacity on a wired line for data communication calls in a mobile communication system in which data is transmitted in a wireless line and the wired line in accordance with a packet system, the apparatus including: means for measuring a practical transmission speed of the data on the wireless line in a call; means for determining, as a target transmission capacity of the wired line, a minimum transmission capacity of the wired line that is required for transmitting through the wired line the data at the practical transmission speed in the call; and, means for changing an allocated transmission capacity usable for transmission of the data through the wired line, so as to reduce a difference between the allocated transmission capacity and the target transmission capacity of the wired line. BRIEF DESCRIPTION OF THE DRAWINGS Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- FIG. 1 is a systematic block diagram showing a conventional mobile communication system wherein data communication is implemented in accordance with a communication switching system; FIG. 2 is a systematic block diagram showing a constitution of a mobile communication system according to an embodiment of the present invention; FIG. 3 is a sequential diagram illustrating a sequence in the case when the mobile communication system according to the present embodiment controls a transmission capacity; and FIG. 4 is an explanatory view for explaining an example of an algorithm for calculating a transmission capacity to be demanded with respect to a relay station 3 and a mobile switching station 4 from a radio base station 2 in the present embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENT Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Referring to FIG. 2, a mobile communication system according to the embodiment of the present invention comprises a mobile terminal 1, a radio base station 2, a relay station 3, and a mobile switching station 4. The mobile terminal 1 is a cellular phone or a hand-held information terminal movable over an area covered by the radio base station 2, and which can communicate with the radio base station 2 by means of radio signals. In a data communication, data is transmitted and received in accordance with a packet system wherein packets containing the data are transmitted. The radio base station 2 communicates with a mobile terminal within an area that is covered thereby by means of radio signals, and terminates a radio interface thereof. In a data communication, data is transmitted and received in accordance with a packet system. In the case when there is a call being in a data communication, the radio base station 2 measures a practical transmission speed in a wireless line established with respect to the mobile terminal 1 in every call, calculates a target transmission capacity that is the optimum transmission capacity for a wired line of the call in the data communication based on the data transmission speed measured, and requests with respect to the relay station 3 to the effect that a permissible transmission capacity, which is permitted for transmission of data in the call at present, is made to coincide with the target transmission capacity. In this case, it is required that a permissible transmission capacity in each call must be a capacity sufficient for transmitting data at the transmission speed obtained by the measurement, and it is desired that such capacity is small as much as possible in order to utilize practically the wired line. The relay station 3 contains a plurality of radio base stations 2, and relays a data transmission between the radio base stations 2 and the mobile switching station 4 wherein data is transmitted and received in accordance with a packet transmission system in a data communication, When it is requested by a radio base station 2 to change a permissible transmission capacity into its target transmission capacity, the relay station 3 changes a permissible transmission capacity in a corresponding call in a data communication, and at the same time, notifies of the same request to the mobile switching station 4. The mobile switching station 4 is a switching station constituting a mobile communication network, and contains at least one relay station 3. The mobile switching station 4 connects the relay station 3, another relay station, another mobile switching station, a gateway switching station (not shown) linked to the internet with each other to transmit and receive data. In a data communication, data is transmitted and received in accordance with a packet transmission system. When the mobile switching station 4 receives a request for changing a permissible transmission capacity into its target transmission capacity from the relay station 3, the mobile switching station 4 changes the permissible transmission capacity of a corresponding call in a data communication in accordance with such request. FIG. 3 is a sequential diagram illustrating a sequence in the case when a mobile communication system according to the present embodiment controls a transmission capacity. Before applying the sequence, a call is established between a mobile terminal 1 and a device of another party in communication (not shown) through a route composed of a radio base station 2, a relay station 3, and a mobile switching station 4 wherein a data communication is started. Referring to FIG. 3, packet data signals derived from the device of another party in communication (not shown) are transmitted from the mobile switching station 4 to the relay station 3; the packet data signals thus transmitted are transmitted from the relay station 3 to the radio base station 2, and further transmitted from the radio base station 2 to the mobile terminal 1. Quality in a wireless line between the radio base station 2 and the mobile terminal 1 varies with time dependent upon movement in the mobile terminal 1, influence of an obstacle, fading and the like. In this respect, there are generally many cases where line quality is inferior in a wireless line to that of a wired line. Unlike a voice communication, it is requested to transmit data without any accompanying error in a data communication, so that there is a case where data is retransmitted when any error occurs. As a result, there is a case where a practical data transmission speed varies. A practical transmission speed of a data transmission in a wireless line established between a radio base station 2 and a mobile terminal 1 is measured in the radio base station 2. For instance, an amount of data transmitted within a predetermined time is measured, and it may be determined in accordance with an equation (practical transmission speed) = (amount of data)/(predetermined time). A target transmission capacity in a wired line is determined on the basis of a practical transmission speed in a wireless line; and a transmission capacity demanding signal, which is requested to increase or decrease a permissible transmission capacity as a target based on the target transmission capacity thus determined, is transmitted from the radio base station 2 to the relay station 3. Then, when the transmission capacity demanding signal is received by the relay station 3, a permissible transmission capacity for restricting transmission of packets is updated in accordance with the demand from the radio base station 2. Then, such transmission capacity demanding signal is transmitted to the mobile switching station 4 from the relay station 3. A permissible transmission capacity for restricting transmission of packets is updated in the mobile switching station 4 based on the transmission capacity demanding signal. In the relay station 3 and the mobile switching station 4, transmission of packets is controlled such that a data transmission speed of packets in a wired line is limited to the permissible transmission capacity or less. For instance, these stations are provided with buffers each accumulating tentatively data received, respectively; data thus received are accumulated in these buffers; and thereafter the data are read in response to a permissible transmission capacity to transmit the same, whereby control for transmission of packets can be achieved. On one hand, it is also possible to control a data transmission speed by effecting flow control in apparatuses between which packets are transmitted and received. FIG. 4 is an explanatory view for explaining an example of algorithm for calculating a transmission capacity to be demanded with respect to a relay station 3 and a mobile switching station 4 from a radio base station 2 in the present embodiment. As shown in FIG. 4, a difference BWt (= BWo - BWi) between a practical transmission speed BWo in a wireless line and a practical transmission speed BWi in a wired line is calculated; and when the difference BWt exceeds a predetermined threshold BWt1, a transmission capacity is allowed to increase by RQ1, while when the difference BWd reaches below the predetermined threshold BWt2, the transmission capacity is allowed to decrease by RQ2. As a practical transmission speed in a wired line, a theoretical value, which is determined from a ratio or the like in a part other than data such as a line speed and a packet header, may be used, or a measured value, which is obtained by measuring a practical transmission speed on a wired line in a radio base station 2, may be employed. Since a practical transmission speed in a wireless line varies with time, it is desirable to measure periodically such practical transmission speed, and to update a permissible transmission capacity in a wired line. Therefore, the optimum permissible transmission capacity determined on the basis of an practical transmission speed in a wireless line is allocated to a wired line in each call, so that a transmission capacity in a wired line can be allocated to a call in a data communication, whereby calls in a data communication can be efficiently multiplexed. Furthermore, an amount of data in a packet that is to be received by a radio base station 2 from a wired line is restricted by a permissible transmission capacity based on an practical transmission speed in a wireless line, so that a buffer overflow due to deterioration of quality in a wireless line is prevented. Moreover, since allocation of a transmission capacity is controlled on the basis of an practical transmission speed of data transmitted through a wireless line, a transmission speed of data on a wireless line can be matched with that of a wired line irrespective of a protocol applied to the wireless line. Besides, a transmission capacity demanding signal transmitted from a radio base station 2 or a relay station 3 is transmitted in only the case where a transmission capacity in a wired line is needed to change, so that a decrease in a transmission capacity based on which data can be transmitted that is derived from transmission of such transmission capacity demanding signal is suppressed to the required minimum level. As a method for controlling a transmission capacity in a data communication in accordance with a packet system, there are a method for controlling an average value of transmission capacities, a method for controlling a peak value of transmission capacities, a method for controlling an average value and a peak value of transmission capacities and the like methods. According to the present invention, a transmission capacity can be efficiently allocated to a call in a data communication, whereby calls in a data communication can be efficiently multiplexed. Furthermore, according to the present invention, data at a speed more than a transmission speed in a wireless line does not flow thereinto, so that a buffer overflow due to deterioration of quality in the wireless line is prevented. Moreover, according to the present invention, a transmission speed of data on a wireless line can be matched with that of a wired line irrespective of a protocol applied to the wireless line. It will be appreciated by those of ordinary skill in the art that the present invention can be embodied in other specific forms without departing from the essential characteristics thereof. The presently-disclosed embodiment is therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all that changes that come within the meaning and range of equivalents thereof are intended to be embraced therein. Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. The text of the abstract filed herewith is repeated here as part of the specification. A mobile communication system implements packet communication by allocating efficiently a transmission capacity to a wired line and a wireless line, wherein a practical transmission speed of data communication between a radio base station and a mobile terminal is measured in a call. A transmission capacity required for transmitting data at the minimum level of the transmission speed is determined as a target transmission capacity and, in a relay station and a mobile switching station, an allocated transmission capacity with which transmission of data is permitted in the wired line is allowed to decrease in the case where the allocated transmission capacity is larger than the target transmission capacity. The allocated transmission capacity is allowed to increase in the case where the allocated transmission capacity is smaller than the target transmission capacity. A transmission speed in the wired line is controlled so as to be equal to or less than the allocated transmission capacity.

Claims: A method for allocating transmission capacity on a wired line for data communication calls in a mobile communication system in which data is transmitted in a wireless line and said wired line in accordance with a packet system, the method being characterized by comprising the steps of: measuring a practical transmission speed of said data on said wireless line in a call; determining, as a target transmission capacity of the wired line, a minimum transmission capacity that is required for transmitting through said wired line said data at said practical transmission speed in said call; and, changing an allocated transmission capacity usable for transmission of said data through said wired line, so as to reduce a difference between said allocated transmission capacity and said target transmission capacity of the wired line. A method for allocating transmission capacity as claimed in claim 1, wherein the step of changing the allocated transmission capacity comprises the steps of: decreasing (RQ2) the allocated transmission capacity in the case where said allocated transmission capacity is larger than said target transmission capacity; and, increasing (RQ1) the allocated transmission capacity in the case where said allocated transmission capacity is smaller than said target transmission capacity. A method for allocating transmission capacity as claimed in claim 1, wherein the step of changing the allocated transmission capacity comprises the steps of: decreasing (RQ2) the allocated transmission capacity in the case where said allocated transmission capacity exceeds said target transmission capacity by less than a predetermined first threshold; and, increasing (RQ1) the allocated transmission capacity in the case where said allocated transmission capacity exceeds said target transmission capacity by more than a predetermined second threshold. A method for allocating transmission capacity as claimed in claim 1, 2 or 3, wherein said allocated transmission capacity is periodically updated. A mobile communication system implementing data communication by transmitting data through a wireless line and a wired line in accordance with a packet system, the mobile communication system being characterized by comprising: a radio base station (2) comprising: means for measuring a practical transmission speed of said data on said wireless line in a call; means for determining, as a target transmission capacity of the wired line, a minimum transmission capacity that is required for transmitting through said wired line said data at said practical transmission speed in said call; and, means for generating a transmission-capacity-demanding signal for changing an allocated transmission capacity, available for transmission of said data through said wired line, according to a difference between said allocated transmission capacity and said target transmission capacity of the wired line; a relay station (3) including: means for receiving the transmission-capacity-demanding signal from said radio base station to change said allocated transmission capacity set up inside said relay station in said call, and for transmitting said transmission-capacity-demanding signal; and, a mobile switching station (1) including: means for receiving the transmission-capacity-demanding signal from said relay station to change said allocated transmission capacity set up inside said mobile switching station in said call. A mobile communication system as claimed in claim 5, wherein said radio base station also comprises means controlled by said transmission-capacity-demanding signal for decreasing the allocated transmission capacity in the case where said allocated transmission capacity is larger than said target transmission capacity, and for increasing the allocated transmission capacity in the case where the allocated transmission capacity is smaller than said target transmission capacity. A mobile communication system as claimed in claim 5, wherein said radio base station also comprises means controlled by said transmission-capacity-demanding signal for decreasing the allocated transmission capacity in the case where said allocated transmission capacity exceeds said target transmission capacity by less than a predetermined first threshold, and for increasing the allocated transmission capacity in the case where said target transmission capacity exceeds said allocated transmission capacity by more than a predetermined second threshold. A mobile communication system as claimed in claim 5, 6 or 7, wherein said radio base station further comprises means for measuring periodically said transmission speed to determine said allocated transmission capacity, and for transmitting said transmission-capacity-demanding signal as occasion demands. An apparatus for allocating transmission capacity on a wired line for data communication calls in a mobile communication system in which data is transmitted in a wireless line and said wired line in accordance with a packet system, the apparatus being characterized by comprising: means for measuring a practical transmission speed of said data on said wireless line in a call; means for determining, as a target transmission capacity of the wired line, a minimum transmission capacity that is required for transmitting through said wired line said data at said practical transmission speed in said call; and, means for changing an allocated transmission capacity usable for transmission of said data through said wired line, so as to reduce a difference between said allocated transmission capacity and said target transmission capacity of the wired line.

Inventors: TAKETSUGU MASANORI, TAKETSUGU, MASANORI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 2001
Main classification: H04Q7
IPC codes: H04L12, H04B7, H04M3, H04W28, H04W92