WO2007039639A1

WO2007039639A1 - Apparatus and method for providing access information in paging messages

Info

Publication number: WO2007039639A1
Application number: PCT/EP2006/067111
Authority: WO
Inventors: Joakim BERGSTRÖM; Håkan Palm; Béla RATHONYI
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2005-10-05
Filing date: 2006-10-05
Publication date: 2007-04-12

Abstract

A method and apparatus for introducing RACH access specific dynamic information into a paging message for a UE in order to reduce the delay for accessing the NW from a UE leaving the DRX-state. A UE that receives a paging message is then not required to receive additional information from the BCH before accessing the NW using a RACH. A UE that triggers a NW access receives the PCH(s) and the BCH in the cell until the first occurrence of the RACH access specific dynamic information is received and uses that when accessing the NW using a RACH.

Description

APPARATUS AND METHOD FOR PROVIDING ACCESS INFORMATION IN PAGING MESSAGES

Technical Field of the Invention

The present invention relates to communication systems, and more particularly, an apparatus and method for providing access information to User Equipment (UE) in paging messages.

Description of the Prior Art

The abbreviations used herein shall have the meanings, except as otherwise set forth herein:

DRX: Discontinues Reception

BCH: Broadcast Channel

NW: Network

PCH: Paging Channel

PoC: Push-to-talk over Cellular

RACH: Random Access Channel

UE: User Equipment

WCDMA: Wideband Code Division Multiple Access

When a UE, such as a mobile terminal/phone, in a cellular communication system does not transmit or receive any user data it is normally in a state that is designed to preserve battery life. While in this state the NW can communicate with the UE by sending a paging message at pre- determined time occurrences that normally are repeated periodically in time. The time interval between these paging messages (referred to as the periodicity) is sometimes referred to as the DRX cycle. At these paging occurrences the UE has its receiver open for a short while to be able to receive a potential paging message. This is normally the only time the receiver is open to receive messages from the NW while in the battery preserving state. The battery preserving state is referred to as the DRX-state herein. The paging message is usually transmitted on the PCH, a special type of channel in the cell. When the UE needs to communicate with the NW while in DRX-state, it normally must do so by using a RACH. The RACH is shared by several UEs and is often contention based. As a result, there can be collisions between UEs that are attempting to send on it simultaneously.

In each cell there is normally a BCH, where among other things, information about how to access the NW using the RACH is provided. This may include both static configuration for how to access the RACH and fast changing parameters like interference levels and load control information. Normally the static information sent on the BCH does not change very often and can typically also be the same in several cells within an area. The dynamic information changes quite frequently and this information normally has a validity period measured on the order of parts of a second. This information is typically not the same in several cells. The validity time is normally either pre-defined or sent along with the information on the BCH. When the validity time expires, a UE is not allowed to use the information any longer and must receive updated information from the BCH. Further, the information on the BCH is repeated periodically in time by a certain scheduling pattern that may either be predefined or transmitted on the BCH. Usually, both the static information and the dynamic information from the BCH are required to be able to transmit by a UE on the RACH.

Normally, when the UE is in the DRX-state, the information sent on the BCH is not received by the UE, as the standby time of the UE would be significantly decreased. Further, the information on the BCH is only useful if the UE should access the NW using the RACH. If important static information on the BCH is changed there is usually a special paging message sent in the cell to all UEs to trigger them to receive the updated information from the BCH. For dynamic information there is no such trigger sent to the UE since this information could potentially be changed very often, i.e. with a higher rate than the DRX cycle.

The UE normally leaves the DRX-state by one of the following actions:

1. UE originating access, for example dialing a phone call or transmitting data in a data session

2. NW initiating access, for example receiving a phone call or data from a data session

Both of these procedures require the UE to transmit a message on the RACH. The first one action is triggered, for example, by user activity such as dialing a telephone number and the second one could be triggered by an incoming telephone call. In the second case there is a paging message received at a paging occasion by the UE to trigger the access.

Before the UE can start to transmit on the RACH the dynamic information must be read from the BCH. Figure 1 below shows a simple flow chart 100 of the steps done by the UE when leaving the DRX-state by either UE triggered 101 or NW triggered 102, 103 access.

The scheduling of the dynamic information on the BCH and the paging message reception schedule is normally not synchronized in time for a UE, nor do they have the same periodicity. Typically, paging occasions are also distributed in time for different UEs so that the load on the paging channel is evened. Figure 2, for example, illustrates how the two different events can be scheduled in time. Figure 2 shows an exemplary timing diagram 200 scheduling paging occasions and dynamic RACH information.

Assume that the paging occasions for the UEs in a cell are even distributed in time and that the dynamic RACH information is repeated every X seconds on the BCH. Then a UE will on average need to wait X/2 seconds after the paging message was received until the dynamic information for the RACH is received on the BCH. For the UE originating case, the average waiting time from the internal trigger until the dynamic information is received is the same, X/2 seconds.

Most cellular communications systems today, for example GSM and WCDMA, as specified by the 3rd Generation Partnership Project (3GPP) Technical Specifications and Technical Reports for a 3rd Generation Mobile System work in accordance with the principles described above including:

1. UEs operate in DRX-states;

2. a BCH in a cell with information how to access the NW;

3. a PCH that is used to transfer paging messages for UEs that are working in DRX-state; and

4. a random access channel shared by several UEs to access the NW; The WCDMA system specified by 3GPP includes all of these referenced components where:

1. the DRX-states for a UE is called IDLE, CELL_PCH or URA_PCH;

2. the dynamic information for the NW access (i.e. the RACH) is sent on the BCH in a message called "system information block 7" (SIB7). This is repeated by a periodicity denoted "SIB7rep". The SIB7 includes the following dynamic RACH information parameters: "uplink interference" that is used by the UE to calculate the initial power to use when transmitting on the RACH, and "dynamic persistence level" that is used by the UE as input to a probability function to determine if a waiting time should be applied before a new RACH access attempt is made;

3. a UE in the DRX-state receive paging message at predefined occasions with a periodicity of the "DRX cycle"; and

4. one or several RACH exist in each cell that are shared by all UEs camped in that cell.

The primary disadvantage with the existing procedure is that there is a delay between: when the paging message is received at a UE, or a UE initiated access activity is triggered, and when the UE can access the NW by sending a message on the RACH. In currently deployed WCDMA networks, the SIB7 repetition rate is between 80-1280 ms, where 80 ms is the lowest possible value to be used. It means that the SIB7 waiting time is on average between 40-640 ms. The SIB7 repetition rate is a trade off between the capacity consumed on the BCH and the delay for UEs that wants to access the NW on the RACH.

Set forth below is a further description of how much the delay component of reading the SIB7 contributes to the overall WCDMA call/session set-up times.

In 3GPP RAN WG2 contribution R2-051916 ."Analyses of Setup Delays using CELL_FACH state", an analysis of call setup delay to Cell_DCH and Cell_FACH is presented. This analysis was also captured and introduced in 3GPP TR 25.815, vθ.3.0, " Signalling enhancements for Circuit- Switched (CS) and Packet- Switched (PS) Connections". These analysis show that the UE SIB7 reading prior to triggering the RRC connection establishment procedure contributes considerably to the total setup delay. For the Cell_DCH case, the SIB7 reading part was estimated to be 70ms of 610 ms (11%), and for Cell_FACH case 70ms of 270 ms (26%). Clearly, the delay caused by the SIB7 reading is directly dependent on the SIB7 scheduling on the BCH. The repetition rate of SIB7 can be configured to any value between 80 and 1280 ms, but the repetition is a trade off between the capacity consumed on the BCH and the delay for the RACH, so in practice the NW does not have total freedom when setting this value. Although the analysis in 3GPP RAN WG2 contribution R2-051916 was considering the RRC Connection Setup procedure (i.e. when leaving the Idle state), the delay estimations are also valid for the case of the RRC connected mode state transitions Cell_PCH/URA_PCH to Cell_DCH and Cell_PCH/URA_PCH to Cell FACH using the Cell Update procedure. The signaling and the processing in UE and UTRAN are very similar as seen in the Figures 3 and 4. Figure 3 provides an RRC connection establishment procedure 300 and Figure 4 provides a cell update procedure 400.

The analysis in 3GPP RAN WG2 contribution R2-051916 was performed for a UE-originated call setup. For network- originated "call" setup, the Paging procedure and the used DRX also must be considered. For services such as PoC, the total delay at network- initiated "call" setup is critical for the service characteristics. If a DRX cycle length of 640ms and a SIB7 scheduling period of 160ms is assumed, the maximum "call" setup delay is then estimated as seen in the following table:

As seen in the table, for Cell_FACH, the SIB7 reading contributes to 15% of the "call" setup delay and for Cell_DCH, the SIB7 reading contributes to 11% of the "call" setup delay. What is desired is an apparatus and method to reduce the delay for accessing the NW from a UE leaving the DRX-state.

Summary of the Invention

The present invention comprises a method and apparatus for introducing RACH access specific dynamic information into the paging message for a UE in order to reduce the delay for accessing the NW from a UE leaving the DRX-state. A UE that receives a paging message is then not required to receive additional information from the BCH before accessing the NW using a RACH. A UE that triggers a NW access receives the PCH(s) and the BCH in the cell until the first occurrence of the RACH access specific dynamic information is received and uses that when accessing the NW using a RACH.

For a 3GPP- WCDMA cellular system, the RACH access specific dynamic information includes information that is used to calculate the initial power to be used on the RACH, e.g. the "uplink interference", and information to determine if the RACH access is allowed to be performed, e.g. the "dynamic persistence level".

Brief Description of the Drawings

A preferred embodiment of the present invention will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 is a flow chart of a UE leaving the DRX-state at UE initiation or paging; FIG. 2 is a timing diagram for how paging occasions and dynamic RACH information is scheduled;

FIG. 3 illustrates an RRC connection establishment procedure;

FIG. 4 illustrates a cell update procedure; and

FIG. 5 is a flow chart illustrating the method of the present invention.

Detailed Description of the Embodiments

An exemplary embodiment of the invention is described with reference to the WCDMA cellular NW as the preferred embodiment of the invention. However, the present invention has a broad applicability to any apparatus and method thereof where dynamic information is needed to perform the random access attempt towards the NW.

The dynamic information for accessing the RACH in WCDMA is included in the SIB7 block transmitted on the BCH and contains three information elements. In the NW-originated "call/session" setup case, reading of SIB7 can be avoided by introducing the information carried in the SIB7 into the PAGING TYPE 1 message.

SIB7 contains three Information Elements (IEs): UL interference, dynamic persistence level and expiration time factor. The UL interference has a value range - 110..-70 dBm (6 bits)), and is usually subject to fast variations, which need to be adopted by the UE in the open loop power control. This information can be introduced into the PAGING TYPE 1 message. The Dynamic persistence level, per PRACH listed in SIB5 and SIB6, has a value range of 1..8 (3 bits). The Dynamic persistence level is used by the UE as input to the function controlling the UE transmission probability on RACH. This information could be introduced into the PAGING TYPE 1 message. In a separate embodiment of the invention, the UE uses the dynamic persistence level read from SIB7 when entering the cell. The expiration time factor, having a value range 1..8, indicates to the UE for how long it may regard the contents of SIB7 as valid. This is expressed in the number of SIB7 repetition cycles, and hence is coupled to SIB7 reading on BCH. Another embodiment of the present invention is not to introduce this IE into the PAGING TYPE 1 message, but instead to state that UE shall regard that the UL interference and dynamic persistence values as valid according to one of the following alternatives: during the following RRC procedure (if triggered by UE as a result of the paging); or until the first occurrence that the SIB7 is read from the BCH. Normally the UE knows the repletion rate of the SIB7 because it knows how the scheduling is done on the BCH through the Master Information Block (MIB). Then the UE could either use the expiration from that SIB7 and apply it to the old received values (from the paging) or use the new SIB7 all together if more RACH transmission is required. As described above, to introduce SIB7 IEs into the PAGING TYPE 1 message would primarily shorten the "call" setup time for a paged UE, i.e. for network- originated "call" setup. But since the PAGING TYPE 1 message is sent on the PCH, nothing prevents UEs also at UE-originated "call" setup from reading the PCH in parallel to the BCH, and use whichever message is received first (SIB7 on BCH or PAGING TYPE 1 (intended for another UE) on PCH). This would, on average, shorten the delay also for UE-originated "call" setup.

By introducing UL interference and dynamic persistence level in the PAGING TYPE 1 message, an additional benefit is also introduced and used. In contrast to the non UE specific SIB7 on BCH, since the PAGING TYPE 1 message is UE specific, the possibility to set UE-specific values can be introduced. In this manner, UTRAN can set UE-specific priority with UE transmit power on the RACH so as to, among other things, allow high priority UEs to start at a higher initial power (as calculated by the outer-loop power control) thus obtaining a quicker RACH transmission since the likelihood of power ramping is reduced.

Note, however, that if all UEs are allowed to read PAGING TYPE 1 messages as described above, the UL interference and dynamic persistence level should be introduced in two sets into the paging message, one set that is specific to the paged UE, and one set that is valid for all other UEs reading PCH in parallel to BCH.

Alternatively, one set of the UL interference and dynamic persistence level is introduced but in addition, a one bit indicator is also added in the PAGING TYPE 1 message to state if the values are applicable only for this UE or for any UE. In this manner, the UEs reading PAGING TYPE 1 messages sent to other UEs can determine if the UL interference and dynamic persistence level read from such a message can be used.

Figure 5 provides a flow chart 500 according to the present invention. As seen therein, the UE performs certain steps according to the method described above when leaving the DRX-state by either UE triggered access 501, 502 or NW triggered access 503, 504.

As seen therein, the UE is in the DRX state in step 501. Step 502 indicates the UE triggering activity and step 504 indicates the UE checking paging message reception at every DRX cycle. If, the UE triggers the activity, then in step 503, the UE receives BCH and PCH in parallel until the first valid RACH dynamic information is retrieved on any of the channels. Thereafter, at step 506, the UE makes NW access at step 506. Alternatively, if the UE has checked paging message reception in step 504, then in step 505 it is determined if the paging message received requires NW access. If not, then the UE returns to DRX state of step 501. If so, then the UE makes NW access at step 506. In step 506, the UE makes NW access on RACH by using dynamic RACH information retrieved in the previous step. At step 507, the UE returns to a non DRX state. By following the steps of Figure 5, the delay for call/session set-up is decreased. The present invention further comprises an apparatus adapted to perform the steps set forth in the flowchart of Figure 5.

As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed above, but is instead defined by the following claims.

Claims

1. A method for providing access information to User Equipment (UE) in paging messages, comprising the steps of: placing a UE in a discontinuous reception (DRX) state; triggering, by the UE, activity; receiving, by the UE, broadcast channel (BCH) and paging channel (PCH) in parallel until a first valid random access channel (RACH) dynamic information is retrieved on any of the channels; making, by the UE, NW access; and returning the UE to a non DRX state.

2. An apparatus in a UE for obtaining access information in paging messages, comprising: means for placing a UE in a discontinuous reception (DRX) state; means for triggering, by the UE, activity; means for receiving, by the UE, broadcast channel (BCH) and paging channel (PCH) in parallel until a first valid random access channel (RACH) dynamic information is retrieved on any of the channels; means for obtaining, by the UE, NW access; and means for returning the UE to a non DRX state.