GB2340698A

GB2340698A - Data transmission in a mobile telephone system

Info

Publication number: GB2340698A
Application number: GB9924518A
Authority: GB
Inventors: Keijiro Take; Akira Otsuka
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1995-04-18
Filing date: 1996-04-17
Publication date: 2000-02-23
Anticipated expiration: 2016-04-17
Also published as: GB2340698B; GB9924518D0

Abstract

In a radio communication system in which radio channels between each base station and a plurality of mobile units comprise a control channel (CCH) and a plurality of traffic channels (TCHs), a base station uses a plurality of TCHs as random access channels (RACHs) for the transmission of data. A base station has means for notifying mobile units of TCHs which can be used as RACHs, means for notifying channel information concerning each such RACH on that RACH, and means for specifying another RACH to which transmission can be transferred. A RACH may be removed from the plurality of RACHs managed by a base station for use as a TCH in a telephone call, whereupon mobile units using the RACH are notified of another RACH to which they transfer.

Description

2340698 RADIO DATA TRANSMISSION SYSTEM This invention relates to a packet

data transmission system in radio communication systems centering on telephones such as a digital cellular system and a digital cordle-ss telephone system.

In a conventional radio communication system consisting of a plurality of base stations, a switching system, and a plurality of mobile stations existing in a radio zone formed by the base stations, to transmit and receive telephone and d6ta signals between the base and mobile stations, a TCH is assigred between the mobile and base stations using a CCH, then the TCH is used to execute one-to-one two-way data communication between the mobile and base stations.

For example, as described in Japanese Patent Unexamined No. Hei 6r77886, when receiving a data communication request from a mobile station, the base statibn and switching system select one or a plurality of TCHs in accordance with the channel use state and if the requested TCH can be selected, assigns the TCH to the mobile station, which then executes data communication on the assigned TCH.

on the other hand, to transmit and receive data between a plurality of mobile stations and a base station, in the radio communication system a common channel is provided for accommodating a plurality of mobile stations and data is transmitted and received by making random access in the common channel in addition to the above- mentioned method of assigning a TCH between mobile and base stations by the line switching f or providing a one-to-one two-way data communication line. The random access method is used for a CCH in the line switching.

For example, as described in Japanese Patent Unexamined No. He! 5-95358, in channel contention control in the random access system, an up link signal from a mobile station to a base station and a down link signal are put into slots on a common channel, the slots of the up and down link signals are synchronized with each other, and transmission disablelenable is information for controlling mobile station transmission is suffixed to each of the slots making up the down link signal.

In each base station, the up link channel is monitored in each slot and in the slot detecting an up link signal from a mobile station, the transmission disablelenable information suffixed to the slot of down link signal is changed to transmission disable for disabling other mobile stations from originating calls in the next slot for avoiding signal collision.

When receiving the transmission disablelenable information indicating transmission disable from the base station, the mobile station where up link information to the base station occurs continues to monitor the transmission disable/enable information until the information is changed to transmission enable. When the information is changed to transmission enable, the mobile station judges transmission start or standby in the next slot according to the transmission probability.

In the above-mentioned data communication by the line switching, one mobile station occupies one TCH and high-speed data communication can be conducted, but a connection delay occurs because of the TCH assignment process. In the data communication by the random access system, the connection delay is small, but if a plurality of mobile stations access one TCH, high traffic is handled and the throughput lowers. To use a plurality of TCHs, management among the TCHs is required.

In the invention, radio physical channels for transmitting and receiving user information are called communication channels (TCHs) and those for transmitting and receiving control information used for radio channel establishment and call connection are called control channels (CCHs). However, to use all or some of TCHs to transmit and receive the control information, all or some of the TCHs are logically called TCH attendant control channels (ACHs). Further, when a TCH is used to transmit and receive a telephone signal, it is logically called a voice channel (VCH) and when 2-5 a TCH is used for data communication using random access, it is called a random access channel (RACH).

That is, the VCH and RACH represent different channels in function, but are TCHs as radio physical channels.

It is an object of the invention to solve a problem of complicating TCH management when a plurality of TCHs are operated as RACH in a conventional 5 random access data communication system.

It is another object of the invention to solve a problem of an increase in the packet transmission wait time of a standby mobile station in the conventional data communication system by line switching because when one mobile station is communicating on a TCH, another mobile station stands by on the TCH until the communication of that mobile station ends.

According to the present invention, there is provided a radio data transmission system, comprising:

a plurality of base stations-, a plurality of mobile stations; and a base station controller; wherein radio channels between each base station and a plurality of mobile stations consist of a control channel (CCH) and a plurality of communication channels (TCHs); and wherein each base station comprises means for notifying channels that can be used as data communication channels using a random access method (RACHs) among the TCHs over the CCH, means for notifying channel information concerning each RACH on the RACH, and means for notifying another RACH to which a shift can be made.

According to another aspect of the present invention, there is provided a radio data transmission system, comprising:

a plurality of base stations; a plurality of mobile stations-, a base station controller, in which radio channels between each base station and a plurality of mobile stations consist of a control channel (CCH) and a plurality of communication channels (TCHs) wherein each of said base stations uses a plurality of TCHs as data communication channels using a random access method 15" (RACHs); means for deleting the RACH assigned to a telephone call from a managed RACH group when one of said base stations using a plurality of TCHs as RACHs and said base station controller for controlling said base station require a TCH as a new telephone call occurs; means for notifying channel information concerning each RACH on the RACH; means for sending a departure instruction notification of the RACH from said base station to mobile stations acquiring the RACH through said notification means and sending a message to the effect that the R-ACH becomes unavailable as an RACH on all other RACHs managed by said base station through said notification means; and means for changing registration of the mobile stations registered in the RACH to a shift destination RACH specified on the RACH by said base station controller.

Each of the mobile stations may comprise means for calculating shifting probability means for continuing the RACH shifting based on the calculated probability, and means for postponing the channel shifting based on the shiffing probability at the RACH shifting time of the mobile station.

The system may comprise means when a new telephone call occurs, for selecting a TCH used for the telephone call from among the TCHs operated by the base station accommodating the telephone call by the base station controller, means for deleting the TCH from-a shift RACH sequence and changing the shift RACH sequence, means for notifying the changed RACH sequence on all RACHs in the base station, and means for changing a conversion table contained in the base station controller.

The system may further comprise means for managing so as to cyclically specify an RACH to which a shift can be made for each group of RACHs operated in a single base station by the base station and the base station controller.

The system may further comprise means for calculating shift probability P at a stage where a mobile station, which has a send packet and cannot send segments on its acquired RACR has shifted one RACH to another in sequence according to a shift channel sequence notified from the corresponding base station, means for comparing the probability P with a threshold value previously stored in the mobile station, means for continuing the channel shift based on the comparison result, and means for postponing the shift for postponement time T previously stored in the base station.

Means may be provided for storing the number of times an RACH sequence has been cycled at a stage where a mobile station has shifted from one RACH to another in sequence in all the RACH sequence managed by a base station based on shift channel information notified from the base station, means for calculating cyclic probability in response to the number of times, means for comparing the calculated probability with a threshold value previously stored in the mobile station and judging continuation or postponement of the shift and means for postponing the channel for a predetermined time if postponement is judged.

Thus with the invention the base station or the base station controller notifies on the down channel of the line used as an RACI channel information concerning the RACH and information concerning other RACHs periodically or at the state transition time, and each mobile station judges packet transmission, channel shift, and detachment from RACH based on the information.

Further the base station or the base station controller can notify information containing another RACH sequence to which a shift can be made periodically or at the state transition time on the down link of RACR and each mobile station transmitting no packet starts a channel shift process upon reception of the information.

Whether channel shift is continued or postponed can be determined based on the shift probability calculated in the channel shift probability calculation section of the mobile station starting the channel shift process.

The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Figure 1 is a flowchart of TCH assignment in a conventional example; Figure 2 is a schematic diagram of RACH contention control in a conventional example; Figure 3 is a schematic drawing of a radio communication system in the invention; Figure 4 is a carrier configuration diagram to use a TDMA system for a radio line between base and mobile stations; Figure 5 is a diagram showing one embodiment of the RACH state transition; Figure 6 is a sequence chart showing one embodiment of access right acquisition on an RACH between mobile and base stations; Figure 7 is a sequence chart showing the chan'nel shift timing of mobile stations; Figure 8 is a flowchart showing the channel shift of mobile stations; Figure 9 is a block diagram showing one embodiment of the configuration of a mobile station; Figure 10 is a diagram showing one embodiment of a channel shift in the invention; Figure 11 is a flowchart of calculating the channel shift probability in the mobile station; Figure 12 is a table showing one example rerpesenting the correspondence between RACH and moble station numbers registered in a base station controller in the invention and a diagram showing one embodiment of the RACH transition state; Figure 13 is a flowchart showing one embodiment of an RACH management system in the base station controller; Figure 14 is a flowchart showing one embodiment of a mobile station channel shift method in a mobile station; Figure 15 is a flowchart showing one embodiment of a channel shift method; Figure 3 is an illustration showing a radio communication system for executing communication between base stations and mobile stations. Figure 4 is a diagram showing the carrier configuration to use a TDMA (time division multiple access) system for a radio line between base and mobile stations.

A base station controller is connected to base stations, each of which forms a radio zone for providing TCHs for mobile stations. The base stations and the base station controller always control TCHs unused for telephone calls as RACHs.

Embodiment 1:

Figure 5 is a diagram showing one embodiment of the RACH state transition in the invention. Figure6 is a sequence chart showing one embodiment of access right acquisition on an RACH between mobile and base stations.

A mobile station sends an RACH use request on an up CCH at 0201. When receiving the RACH use request, the base station selects one of RACHs and notifies the mobile station of the number of the selected RACH at 0202. The mobile station shifts to the RACH selected by the base station and receives channel information sent from the base station on the RACH at 0203. The channel information represents the channel state of the RACH by a message. The channel state is an unassigned, occupied, departure, inhibition, or idle state. When an RACH is in the unassigned state. mobile stations sending a segment on the RACH do not exist and every mobile station acquiring the RACH can send a packet. The occupied state is a state in which a mobile station is sending a packet on the RACH and other mobile stations than the mobile station are inhibited from transmitting a packet. The departure state is a state in which all mobile stations acquiring the RACH for use for a telephone call are prompted to make a channel shift. The inhibition state is a state in which all mobile stations acquiring the RACH are inhibited from emitting a radio wave. The idle state is a state in which the RACH is being set.

When determining that the channel state is an unassigned state from the received channel information, the mobile station sends a segment consisting of'synchronization bits and the identification code of the mobile station to the base station on the TCH if the radio access system is TDXA. The base station receives the segment normally, sets the channel state to the occupied state, and notifies the mobile station of channel information with the identification code of the mobile station on the down link channel, thereby granting permission of access to the TCH to the mobile station.

According to the method, if another mobile station uses the RACH specified by the base station, one mobile station having a transmission packet can omit the process of shifting to CCH and receiving assignment of another RACH from the base station and can autonomously shift from one RACH to another and detect an unassigned RACH for sending a packet.

Thus in an RACR information concerning the RACH and information concerning another RACH are notified which enables efficient and rapid RACH contention control and RACH shift in mobile stations.

Embodiment 2:

Figure 7 is a chart showing one embodiment of the channel shift timing of mobile stations in the invention.

Figure 8 is a flowchart showing one embodiment of the channel transition of mobile stations in the invention.

On each RACH controlled by a base station, a message indicating the channel state of the RACH is sent. The mobile station acquiring the RACH receives the message at step S0301 and determines whether or not sending a segment is enabled in response to the channel state. When the channel state is an unassigned state. the mobile station having send data sends the first segment. When receiving the segment normally, the base station sets the channel state to an occupied state and sends a message with a code representing the occupied state, the number of the mobile station sending the normally received segment, and a shift RACH sequence as a channel state notification message. If the mobile station receiving the message is the segment sending mobile station, the mobile station can acquire the access right to the RACH. Of the mobile stations other than that mobile station, a mobile station having send data shifts from one RACH to another based on the shift RACH sequence contained in the message at step is S0303 with reception of the message as a trigger at step S0302.

According to the method, while the state of the acquired RACH does not change. the mobile station can know the state of the RACH periodically, and at the RACH state change timing, can know the next transition state of the RACH; if a shift is made from another RACH, the shift destination RACH can also be known from a shift destination RACH notification given periodically, or if another mobile station acquires the use right, immediately the shift destination RACH can be known. Therefore, the mobile station having a transmission packet can immediately enter the RACH shift process in response to the RACH state.

Since information on RACHs to which a shift can be made is periodically notified at the RACH occupation timing and in the occupied state, mobile stations can shorten the wait time for packet transmission.

Embodiment 3:

Figure 9 is a block diagram showing one embodiment of the configuration of a mobile station in the invention. Figure is a diagram showing one embodiment of a channel shift in the invention. Figure 11 is a flowchart showing one embodiment of calculating the channel shift probability in the mobile station in the invention.

When a mobile station having send data detects the state of the acquired RACH being the occupied state based on the channel information from a base station, it calculates the shift probability Pa by a probability calculation section of the mobile station at step S0401 and compares the probability Pa with a threshold v alue stored in a storage section of the mobile station at step S0402. If Pa is greater than the threshold value, the mobile station enters an RACH shift process. If Pa is less than the threshold value, ihe mobile station waits for postponement time Tl stored in the storage section. then again receives notification information provided from the base station and checks the channel information contained in the information.

According to the method, the mobile station starts the channel shift process at the channel shift timing according to the probability calculated for each mobile station and the channel shift timings of mobile stations change, thus not all mobile stations enter the RACH shift process at the timing of receiving a packet transmission disable notification or shift destination RACH notification, and the mobile stations contending with each other at the same timing of the same RACH can be reduced. enhancing the channel use efficiency.

Embodiment 4:

Figure 12 is a table (Table 1) showing one embodiment representing the correspondence between RACH and mobile station numbers registered in the base station controller in the invention and a diagram showing one embodiment of the RACH transition state in the invention. Figure 13 is a flowchart showing one embodiment of an RACH management system in the base station controller in the invention.

A base station or the base station controller determines shift destination RACHs cyclically for the RACHs managed by the base station. for example, as a shift is destination RACH sequence of RACH1 -> RACH2 -> RACH3 -> RACH1 if the base station manages three RACHs.

As the shift destination RACH sequence, all RACHs can be cycled regularly in such a manner that one cyclic sequence is made of two cycles such as RACH1 -> RACH2 -> RACH3 -> RACH1 RACH2 RACH3 -> RACH1 or that a cyclic.sequence is made while a return is made to the shift source RACH alternately such as RACH1 -> RACH2 -> RACH1 -> RACH3 -> RACH1, or some of the RACHs are used to make a regularly cyclic seque nce such as RACH1 -> RACH2 -> RACH1.

When a mobile station originates a telephone call in the radio zone formed by the base station, the base station controller accepts the call originated f rom the mobile station at step S0101, determines whether or not TCHs that can be assigned to the mobile station exist in the base station at step S0102, and selects an available TCH at step S0104. If the TCH is operated as an RACH, the base station controller deletes the RACH operated in the TCH to be allocated to the mobile station from the shift destination RACH sequence and creates a new shift destination RACH sequence at step S0501.

That is, assuming that as in the example, the base station manages three TCHs. operates all TCHs as RACHs, notifies the shift destination RACH sequence as 1, 2, 3, and assigns TCH-3 (RACH-3) to the mobile station for the telephone call, a new created shift destination RACH sequence becomes 1, 2. The shift destination RACH sequence from which TCH-3 is assigned to the mobile station is deleted is notified as the new shift destination RACH sequence on all RACHs managed by the base station (in the example, RACH-1, RACH-2. and RACH-3) at step S0502. However, the shift destination RACH sequence is added to a. message to the effect that the channel information is changed to a departure state on RACH-3.

The base station controller holds a conversion table indicating the correspondence between the RACH number of the identification number of the RACH acquired by the mobile station and the mobile station number, and rewrites the RACH number corresponding to the mobile station number of the mobile station acquiring the RACH deleted from the shift destination AsRACH sequence according to the shift destination RACH sequence at step S0503. Further, when the mobile station ends talking at step S0110. the base station controller releases the TCH at step S0111, sets the TCH used by the mobile station for the talking to RACH to operate the TCH as RACH at step S0112, adds the RACH to the shift destination RACH sequence at step S0504. and notifies the shift destination RACH sequence on all RACHs operated by the base station at step S0505.

According to the method, a TCH used for an RACH can be assigned to a telephone call and the mobile station using the RACH can be shifted to another RACH, so that the channel use efficiency of the TCHs managed by the base station can be enhanced. In addition, if a shift destination channel among RACHs operated in a single base station is specified in a cyclic sequence and a telephone call is assigned to a TCH used for an RACH, the mobile station acquiring the RACH can autonomously shift to the shift destination RACH notified from the base station for transmitting and receiving a packet.

Further, when the mobile station makes a channel shift, if it cannot receive the RACH, the mobile station can also shift to the next RACH in the cyclic sequence for trying packet transmission.

Since a TCH used for an RACH is assigned to a telephone call and the mobile station using the RACH can be shifted to another RACH, the channel use efficiency of TCHs managed by the base station can be enhanced.

Embodiment 5:

Figure 14 is a flowchart showing one embodiment of a mobile station channel shift method in a mobile station in the invention.

- [L - When a mobile station has a transmission packet at step S0601, it determines whether or not the packet can be transmitted on the acquired RACH at step S0602. If it cannot be transmitted on the RACH (No at step S0602), a channel shift process is executed at step S0603 according to the cyclic sequence notified from the corresponding base station. After the channel shift, again whether or not the packet can be transmitted using the shift destination RACH is determined at step S0604.

If the packet cannot be transmitted (No at step S0604), whether or not the cyclic sequence notified from the base station has been once cycled is determined at step S0605. If it is not once cycled (No at step S0605), again the channel shift process is executed at step S0603. If the cyclic is sequence has been once cycled (Yes at step S0605), whether or not channel shift is immediately again repeated is aetermined at step S0606. To make this determination, for example, random numbers are generated, probability Pb is calculated, and whether or not it exceeds a threshold value is determined.

Channel shift is immediately executed at probability Pb (Yes at step S0606) or is delayed only for predetermined time Tb at probability 1-Pb (No at step S0606). While the shif t is postponed, the mobile station waits for packet transmission on the first acquired RACH. The threshold value may be changed in response to the state of each mobile station.

According to the method, since registration of mobile stations managed by the base station or the base station controller is the f irst RACH at which the mobile station starts channel shift. the time acquiring the shift start channel by the mobile station is prolonged, thereby raising the call incoming success possibility and decreasing the probability that mobile stations will execute an RACH shift at the same time. Thus, the probability that they will send a segment at the same timing on the shift destination RACH is also decre_ased, reducing the segment collision probability, resulting in an increase in the channel use efficiency.

Embodiment 6:

Figure 15 is a flowchart showing one embodiment of a channel shift method in the invention. When a mobile station attempting to transmit a packet cannot transmit it and executes a channel shift according to the cyclic sequence notified from the corresponding base station and then once cycles the cyclic sequence, the probability for immediately executing channel shift and the postponement time when the shift is postponed are changed in response to the number of times the cyclic sequence has been cycled. For example, when the cyclic sequence has been once cycled (Yes at step S0705), the number of times the cyclic sequence has been cycled is incremented by one at step S0706 and the shift probability is changed from th e resulting number of times at step S0707. Thent whether or not the shift is immediately continued is determined at step S0708 by using - 1.7 the shift probability found at step S0707. If the channel shift is not executed (No at step S0708), the shift postponement time is found from the number of times the cyclic sequence has been cycled at step S0710f and the channel shift is postponed for the postponement time at step S0711. While the channel shift is postponed, the mobile station waits for packet transmission on the first acquired RACH.

According to the method. since registration of mobile stations managed by the base station or the base station controller is the first RACH at which the mobile station starts channel shift. the time acquiring the shift start channel by the mobile station is prolonged, thereby raising the call incoming success possibility and decreasing unnecessary channel shift of the mobile stations.

CLAMS 1. A radio data transmission system, comprising:

a plurality of base stations; a plurality of mobile stations; and a base station controller; wherein radio channels between each base station and a plurality of mobile stations consist of a control channel (CCM and a plurality of communication channels (TCHs); and wherein each base station comprises means for notifying channels that can be used as data communication channels using a random access method (RACHs) among the TCHs over the CCR means for notifying channel information concerning each RACH on the RACH, and means for notifying another RACH to which a shift can be made.

2. A radio data transmission system according to claim 1 wherein channel information notifying means of the base station transmits a packet transmission disable notification and a shift destination RACH notification on one of the RACHs; and wherein said mobile station receiving the notification on the RACH shifts from the RACH to another RACH specified in the shift destination RACH notification with the notification reception as a trigger.

3. A radio data communication system as claimed in claim 2, wherein each mobile station comprises means for calculating RACH shifting probability Pa, means for comparing the probability Pa with a threshold value stored in said mobile station, means for executing RACH shifting if the probability is greater than the threshold value, and means for postponing RACH shifting for time TI if the probability is less than the threshold value.

4. A radio data transmission system, comprising: a plurality of base stations; a plurality of mobile stations; a base station controller, inwhich radio channels between each base station and a plurality of mobile stations consist of a control channel (M1) and a plurality of communication channels (TCHs) wherein each of said base stations uses a plurality of TCHs as data communication channels using a random access method (RACHs); means for deleting the RACH assigned to a telephone call from a managed RACH group when one of said base stations using a plurality of TCHs as RACHs and said base station controller for controlling said base station require a TCH as a new telephone call occurs; means for notifying channel information concerning each RACH on the RACH; 15 means for sending a departure instruction notification of the RACH from said base station to mobile stations acquiring the RACH through said notification means and sending a message to the effect that the RACH becomes unavailable as an RACH on all other RACHs managed by said base station through said notification means; and 20 means for changing registration of the mobile stations registered in the RACH to a shift destination RACH specified on the RACH by said base station controller. 5. A radio data transmission system according to claim 4 further comprising: means for cyclically determining data communication channels using the random access method (RACHs) managed by one base station to which mobile stations can shift among the RACHs managed by said management means; means for notifying mobile stations of a cyclic RACH sequence determined by said determination means through said notification means by said base station. and -21 means for shifting channels in sequence in response to the notification.

6. A radio data communication system according to claim 4 or 5 further comprising:

means for calculating probability Pb of continuing RACH shift for each mobile station when a mobile station having a send packet makes an RACH shift in sequence according to shift destination RACHs notified from the base station if an RACH acquired by the mobile station is used for packet transmission of another mobile station, and all RACHs are used for other mobile stations at a stage where all RACHs managed by the base station have been cycled in RACH shift based on the cyclic RACH specification; means for comparing the calculated probability Pb with a threshold value stored in the mobile station; and means responsive to the comparison result of said comparison means for again starting RACH shifting base on the cyclic RACH specification if the probability Pb is greater than the threshold value and for postponing RACH shifting for time T if the probability Pb is less then the threshold value.

7. A radio data communication system according to claim 4, 5 or 6 wherein each of said mobile stations comprises:

means for storing the number of times a shift channel cyclic sequence has been cycled in RACH shift base on cyclic RACH specification; means responsive to the number of times it has been cycled for calculating cyclic probability Pc at a stage where the mobile station shifts on the shift channel cyclic sequence based on shift channel information notified from the base station and has shifted all RACHs managed by the base stations; means for comparing the calculated probability Pc with a threshold value previously stored in the mobile station and judging continuation or postponement of the shifting; and means for changing postponement time T in response to the number of times if postponement is judged.

8. A radio data transmission system constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in Figures 5 to 15 of the accompanying drawings.