WO2005013634A1

WO2005013634A1 - Timer-controlled channel switching in a umts communications system

Info

Publication number: WO2005013634A1
Application number: PCT/GB2004/003250
Authority: WO
Inventors: Nektaria Efthymiou
Original assignee: Hutchison Whampoa Three G Ip (Bahamas) Limited
Priority date: 2003-07-28
Filing date: 2004-07-27
Publication date: 2005-02-10
Also published as: WO2005013634A8; GB2404528A; GB0317621D0

Abstract

In a 3G communication system a method of controlling a radio communication channel between user equipment and a base station is provided. The communication channel is caused to operate in DCH operation to permit data transfer between the radio network and the user equipment, and thereafter to switch to operate in FACH operation at the end of a time interval after the data transfer is complete, that time interval being variable and dynamically determined according to conditions in said communication system.

Description

TIMER-CONTROLLED CHANNEL SWITCHING IN A UMTS COMMUNICATIONS SYSTEM

The present invention relates to mobile communication systems and in particular to the management of switching between different types of communication channel established between network equipment and mobile devices or user equipment (UE). The invention has particular application in the context of 3G mobile telephone systems but may also have application in other systems where multiple channel types are provided at different times for different purposes.

Background to the Invention

In 3G mobile telephone systems facilities are provided to enable a user of a mobile telephone or other user equipment to browse pages of data on their phones. These pages of data are provided from one or more servers to which access may be had by way of the telephone network system and, as is well known, such pages typically have links from one page to another to enable users to view a sequence of pages as they wish. During such browsing it will be appreciated that there are times when a high volume of data transfer is called for, such as when the user as just indicated that they wish to view a particular page and the data representing that page must be downloaded to the user equipment, and other times when a low amount of data is being transferred, such as when a user is spending time viewing a downloaded page but has not yet called for a further page, but during these times it is still necessary to maintain the communication link so as to enable the user to call for the next page. In 3G mobile telephone systems it is known to provide two kinds of channels or radio links from the user equipment to the base stations to deal with these various requirements. Firstly, a direct channel (DCH) may be established when a high data volume is required in order to download a page of information. Secondly, common channels may be used (i.e. forward access channel (FACH) for the downlink and Random Access Channel (RACH) for the uplink) that simply maintain the communication link between the user equipment and the base station but such a channel does not have as high a data transfer capacity as a DCH. During a browsing session, the communication link established by the user equipment is switched between a DCH and a RACH/FACH according to the required usage of the communication channel from time to time. This control is typically undertaken on the network side by the radio network control (RNC) according to traffic measurement or other criteria. In the basic current implementation a timer is provided which simply causes the channel to switch from DCH to RACH/FACH at a fixed time after the main data transfer has concluded. If the time to switch from DCH to RACH/FACH is fixed and short there are a number of disadvantages associated to this. For example, if the time to switch from RACH/FACH is the same as the maximum time to allowed by the UE to trigger event 4b and equal to a value of 5 seconds when browsing, the communication channel to the user equipment will switch back to a RACH/FACH 5 seconds after the completion of the download of each page. When a user indicates a desire to view another page the channel must be switched back to DCH so as to provide the capacity to download that further page. It has been found that users generally spend more than 5 seconds viewing each page before deciding to download a further page and, typically, it has been found that users may view each page for around 23 seconds. Because of this, it is virtually always the case that between downloading pages to the user equipment, the communication channel will have switched from DCH to FACH and therefore must be switched back again in order to go ahead with the next download. Although the switching back to lower capacity channels is efficient from the point of view of not unnecessarily tying up network capacity, it is found that this system is inefficient in that it requires a significant number of switching events to control the type of communication channel established to the user equipment.

Summary of the Invention

The present invention provides a method of controlling a radio communication channel between user equipment and a base station in a mobile communication system in which the communication channel may operate in one of at least a first mode which permits high volume data transfer between the user equipment and the radio network and a second mode, the method comprising: causing said communication channel to operate in said first mode when the user equipment indicates that data should be transferred between the radio network and the user equipment; monitoring said communication channel to determine when the data transfer is complete; causing said communication channel to switch to operate in said second mode at the end of a time interval after the data transfer is complete, that time interval being variable and dynamically determined according to conditions in said communication system. Preferably there are set minimum and maximum values of the time interval defining a window before which said communication channel is not switched to operate in said second mode and after which the communication channel is switched to operate in said second mode regardless of said conditions in said communication system. The conditions according to which the time interval is determined may comprise overall network resource usage or demand. In particular, the communication channel may be caused to switch to operate in said second mode when the overall network usage exceeds a predetermined threshold, which may be represented as a predetermined proportion of maximum network capacity. The method may be advantageously implemented in a CDMA communication system, in which said first mode of operation is Direct Channel (DCH) operation and said second mode of operation is common channel (DACH/RACH) operation. In particular, the invention has particular application to 3G mobile telephone systems. Additionally, the system may include additional algorithms which cause the communication channel to operate in said second mode when any type of congestion is detected in the system regardless of whether the end of said time interval has been reached. The present invention therefore advantageously controls the timing of switching between high and low capacity data channels on a dynamic basis so as to make better overall use of the network while improving performance for users.

Brief Description of the Drawings

The present invention will be better understood from the following description of a preferred embodiment which is given by way of example and with reference to the accompanying Figures in which: Fig 1 illustrates typical operation of switching between FACH and DCH channels; and Fig 2 illustrates a preferred embodiment of the present invention. Detailed description of the preferred embodiments of the invention

In general terms, the preferred embodiment is a 3G communication system in which a method of controlling a radio communication channel between user equipment and a base station is provided. The communication channel is caused to operate in DCH operation to permit data transfer between the radio network and the user equipment, and thereafter to switch to operate in FACH operation at the end of a time interval after the data transfer is complete, that time interval being variable and dynamically determined according to conditions in said communication system. The Figures illustrate two schemes for switching between FACH and DCH in a 3G mobile telephone system according to the activity of the user and in particular when a user calls for the download of a page of data for viewing. As will be explained in more detail below, in Figure 1, the prior art is shown as providing an inactive time period after which the communication channel is switched from DCH to FACH while Figure 2 illustrates the embodiment of the invention in which the switching from DCH to FACH is managed based on other parameters such as the overall usage of the network in addition to the question of how long the user has been inactive. Figure 1 is a schematic diagram of a prior art arrangement for switching between FACH and DCH. In this diagram it is assumed that a communication channel between user equipment and a base station is already established and is operating as FACH 10. At time Tl the user of the equipment indicates that they wish to view a new page of data and accordingly, under the control of the radio network controller (R-NC) the communication channel is switched to a high capacity DCH 12. The required data is downloaded across this communication channel and the transfer of the data is completed at time T2. As far as the communication channel is concerned, the user at this time starts to be inactive in both Uplink and Downlink, in that no further substantial amount of data is being transferred over the communication channel. The inactivity of the Uplink is notified at that moment by the UE with event 4b. The inactivity of the Downlink is detected in the RNC by measuring the Downlink buffer usage. (Of course the user may actually be active at the user equipment in reading the data on the page or navigating around the downloaded page but this does not present any data load to the communication channel.) At time T2 then the RNC starts a timer which is set to time a period Tdch- fach of inactivity on the communication channel. At time T3, assuming there has been no further activity on the channel which would reset to time Tl in Figure 1, the Tdch-fach time expires and the communication channel is switched back to FACH 14. It has been observed that keeping an inactive user only for a short time on DCH (a relatively short Tdch-fach) will result in unnecessary switching between DCH and RACH/FACH and degrade the performance of browser application since in most cases the timer almost always expires before the user calls for the next page such that between the download of consecutive pages, the channel has had two switching events which may be unnecessary from the point of view of the overall network usage. Furthermore, Tdch-fach should not be a very long fixed value because allocation of dedicated resources for inactive users may result to unnecessary shortage of radio resource. Figure 2 is a schematic illustration of the operation of a presently preferred embodiment of the present invention in which again the switching between FACH and DCH is illustrated. As with Figure 1, it is assumed initially that a communication channel is set up between a user equipment and a radio network which is operating as FACH 20. At time Tl the user calls for a download of a page of data and the channel switches to DCH 22. At time T2 the download of the page is complete and, as discussed above, the user is then inactive so far as the communication channel is concerned. At that time instance the inactivity in the UL is established by the reception of event 4a by the network and the inactivity in the Downlink is confirmed by measuring the buffer usage. In this embodiment the time at which the communication channel is switched back to FACH 24 is dynamically controlled within a minimum and a maximum boundary. The minimum time after T2 for which the communication channel will be maintained as DCH is designated Tdch_inactive_min and a timer set to time this time period is started at time T2. Although Tdch_inactive_min may be set to be 0, efficient operation of the network will normally require some finite value for this minimum so as to ensure that the communication channels do not immediately switch back to FACH even in the event that a second page is immediately called for by a user. The maximum time which may expire before the channel switches back to FACH is designated Tdch_inactive_max and a timer to time this period is also started at time T2. It is important to have a maximum time after which the communication channel will switch from DCH to FACH not least because maintaining a DCH channel uses considerably more battery power in the user equipment than maintaining an FACH channel and so this constraint requires that the communication channel should be switched back to FACH after a period even if there are no other calls for the network capacity. The appropriate value for Tdch_inactive_max may depend on a large number of conditions including network environment, expected number of users and base station capacity, but it is currently thought that a suitable value would be between 40 and 120 seconds. However, this invention does not necessarily fix the timer values (Tdch_inactive_min and Tdch_inactive_max) but may allow dynamic setting of their values. The setting can be either controlled by an external parameter which will be set on per DCH type or will be controlled and dynamically set internally by the system. As is illustrated in Figure 2 between the expiry of Tdch_inactive_min and Tdch_inactive_max switching from DCH to FACH may be triggered dynamically by a radio resource management algorithm 26 which makes a decision based on overall network resource usage and the user equipment inactivity behaviour. In this context resource usage on the network a typically mean channelisation code utilisation such that the system should start switching users to FACH when they are inactive on DCH for longer than Tdch_inactive_min and the resource utilisation is above a threshold value set for the channelisation codes available for the particular spreading factor (SF) used by the user equipment. In general terms then this algorithm takes into account whether the network capacity is required by many other users or not. If the network capacity is being called for by other users on the system then a user which is inactive may be switched back to FACH quite soon after the expiry of Tdch_inactive_min. However, if there are no or few other calls for network capacity then the inactive user may be permitted to remain on DCH for longer and possibly until the expiry of Tdch_inactive_max. It should be noted that there may be other control algorithms within the overall system which may take precedence over the control algorithm of this embodiment. In this case it would be the case that any indication by such other algorithms (e.g. admission control , congestion control, scheduling, load control), external to this function, that there is shortage on resources with respect to radio or processing resource usage all the timers are re-set and the user is given back to the scheduling algorithm to be scheduled by the relevant algorithms of the system which are not part of this invention. As in the arrangement of Figure 1, if the user becomes active before the channel is switched back to FACH, the system resets to time Tl with that activity and the Tdch_inactive_min and Tdch_inactive_max timers start again at new time T2. The maximum resource allocation for each SF will generally be set by the operator within the network, and then resource utilisation is expressed as a function of the ratio between the number of codes in use or unavailable on the SF in question and the total codes available for this SF. The threshold used by the algorithm 26 is expressed in the same terms and is used in the decision making as described above. The resource usage is related to the codes used by this SF over the total available codes because for each SF there is a certain number of codes that are available for use. Since the user is inactive during Tdch-inactive timer this user most probably does not occupy radio or processing resources but only codes. Therefore, if there are radio and processing resources available then the shortage that will trigger the premature switching of this user to FACH will be due to codes unavailability on this SF. If a user with higher priority or a user with data to transmit is using the same SF as the inactive user on DCH then the system should provision to switch the inactive user to FACH and allocate his code to the user that needs this code. As it was mentioned before any type of congestion or overload for any type of resources should re-set all timers and handover the PS user to the relevant algorithms to schedule him according to his priority class. As mentioned above, the actual values of Tdch_inactive_min and Tdch_inactive_max can be either set by the network operator on fixed values or can be dynamically adjustable by relevant algorithms according to network conditions. This system is found to improve browsing performance in general for users who find that, in particular in times of low network usage, access to subsequent pages is accelerated by the removal of the need to switch the communication channel before a subsequent page can be downloaded, while not substantially affecting overall network efficiency because in times of high usage users are quickly switched back to FACH.

Claims

CLAIMS:

1. A method of controlling a radio communication channel between user equipment and a base station in a mobile communication system in which the communication channel may operate in one of at least a first mode which permits high volume data transfer between the user equipment and the radio network and a second mode, the method comprising: causing said communication channel to operate in said first mode when the user equipment indicates that data should be transferred between the radio network and the user equipment; monitoring said communication channel to determine when the data transfer is complete; causing said communication channel to switch to operate in said second mode at the end of a time interval after the data transfer is complete, that time interval being variable and dynamically determined according to conditions in said communication system.

2. The method according to claim 1 in which said time interval has a minimum value before which said communication channel is not switched to operate in said second mode.

3. The method according to claim 1 or 2 in which said time interval has a maximum value at which, if reached, the communication channel is switched to operate in said second mode regardless of said conditions in said communication system.

4. The method according to claim 1, 2 or 3 in which said conditions comprise overall network resource usage or demand.

5. The method according to claim 1, 2 or 3 in which said communication channel is caused to switch to operate in said second mode when the overall network usage exceeds a predetermined threshold.

6. The method according to claim 5 in which said threshold is a predetermined proportion of maximum network capacity.

7. The method according to any preceding claim in which said communication system is a CDMA communication system.

8. The method according to claim 7 in which said first mode of operation is Direct Channel (DCH) operation.

9. The method according to claim 7 or 8 in which said second mode of operation is common channel (DACH/RACH) operation.

10. The method according to claim 7, 8 or 9 in which said communication system is a 3G mobile telephone system.

11. The method according to any preceding claim further comprising causing said communication channel to operate in said second mode when any type of congestion is detected in the system regardless of whether the end of said time interval has been reached.