wcdma rno paging procedure analysis guidance

Product name Confidentiality level WCDMA RNP For internal use only Product version

V100R001 Total 27 pages

WCDMA RNO Paging Procedure

analysis Guidance

For internal use only

Prepared by: URNP-SANA Date: 2003-11-03 Reviewed by: Date: Reviewed by: Date: Approved by: Date:

HUAWEIHUAWEI

Huawei Technologies Co., Ltd. All rights reserved

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WCDMA RNO Paging Procedure Analysis Guidance For internal use only

2004-07-06 Confidential of 27

Revision Record

Date Revision version

Description Author

2003-11-03 1.00 Initial transmittal Jiao Anqiang 2003-12-18 2.00 Revision based on the review comments Jiao Anqiang





Table of Contents

1 Paging Process Analysis ..........................................................................................................7 1.1 Paging Initiation ..................................................................................................................7 1.2 Paging Flow ........................................................................................................................7

1.2.1 Paging Type 1 .........................................................................................................................7 1.2.2 Paging Type 2 .........................................................................................................................8 1.2.3 Actions of UE Received Paging ...........................................................................................9

1.3 DRX Process of UE ..........................................................................................................10 1.3.1 DRX Cycle Length and Paging Occasion .........................................................................10 1.3.2 Association between PICH and SCCPCH ........................................................................11 1.3.3 Paging Channel Selection ...................................................................................................13 1.3.4 Example of UE DRX.............................................................................................................13

2 Paging Signaling Analysis ......................................................................................................14 2.1 L3 Signaling Analysis .......................................................................................................14

2.1.1 IU Interface Paging...............................................................................................................14 2.1.2 Paging Type 1 .......................................................................................................................16 2.1.3 Paging Type 2 .......................................................................................................................17 2.1.4 Common Transport Channel (CCH) Setup Request of IUB ..........................................17 2.1.5 System Information Block Type 1 ......................................................................................18 2.1.6 System Information Block Type 5 ......................................................................................19

2.2 L2 Signaling Analysis .......................................................................................................19 3 Paging Performance Analysis ................................................................................................21 3.1 Paging Scheduling............................................................................................................21 3.2 Paging Parameter Analysis ..............................................................................................22

3.2.1 DRX Paging Cycle Coefficient ............................................................................................22 3.2.2 Paging Re-transmission Times and Interval.....................................................................23

3.3 Traffic Statistics and Alarm for Paging .............................................................................24 3.4 Paging Abnormity Handling ..............................................................................................25

3.4.1 System Abnormity ................................................................................................................25 3.4.2 Paging Channel Capacity Restriction ................................................................................26





List of Figures

Figure 1 PAGING TYPE 1 ..........................................................................................................8 Figure 2 PAGING TYPE 2 ..........................................................................................................9 Figure 3 Schematic diagram of UE paging occasion ...............................................................11 Figure 4 Structure of Paging Indicator Channel (PICH) ...........................................................12 Figure 5 Time sequence relation between PICH and SCCPCH ..............................................13 Figure 6 IU interface paging signaling resolution .....................................................................16 Figure 7 Paging Type 1 Signaling Resolution ..........................................................................17 Figure 8 CCH setup request signaling resolution .....................................................................18 Figure 9 System message 1 signaling resolution .....................................................................18 Figure 10 CCH layer structure...........................................................................................19 Figure 11 PCH FP frame structure....................................................................................20





List of Tables

Table1 PI-to- PICH mapping ..................................................................................................12 Table2 Paging traffic statistics indices....................................................................................24





WCDMA RNO Paging Procedure Analysis Guidance

Key words: Paging, process analysis, signaling analysis, performance analysis

Abstract: This document describes basic process of paging, and analyzes the relevant key

parameters, signaling and performance of paging.

List of abbreviations:

Abbreviations Full spelling DRX Discontinuous Reception

LA Location Area

PCH Paging Channel

PI Paging Indication

PICH Page Indication Channel

RA Routing Area

RAN Radio Access Network

RNC Radio Network Controller

RNP Radio Network Planning

WCDMA Wideband Code Division Multiple Access





1 Paging Process Analysis

1.1 Paging Initiation

In the paging process, paging massage is transmitted to the UE in the idle,

CELL_PCH or URA_PCH state on the paging control channel. The core network

(CN) may request paging, to e.g. establish a signaling connection. UTRAN can also

initiate pagingfor UEs in CELL_PCH or URA_PCH state to trigger the cell update

procedure. In addition, UTRAN may initiate paging for UEs in idle mode, CELL_PCH

and URA_PCH state to trigger reading of updated system information. To be specific,

paging are initiated on the network side in the following cases:

ü For CN originated paging:

In order to request UTRAN connect to UE, CN initiates the paging

procedure .transmites paging message to the UTRAN through Iu interface, and

UTRAN transmites the paging message from CN to UE through the paging

procedure on

When the cell system message is updated: When system messages change,

the UTRAN will trigger paging process in order to inform UE in the idle,

CELL_PCH or URA_PCH state to carry out the system message update, so that

the UE can read the updated system message.

ü UE state transition: In order to trigger UE in the CELL_PCH or URA_PCH

state to carry out state transition (for example, transition to the CELL_FACH

state), the UTRAN will perform a paging process. Meanwhile, the UE will

initiate a cell update or URA update process, as a reply to the paging.

1.2 Paging Flow

1.2.1 Paging Type 1

To setup a call, the CN transmites the paging message to the UTRAN on Iu

interface. Then the UTRAN transmites the paging message from CN to UE through

the paging procedure on Uu interface, which will have the UE initiate a signaling

connection setup process with the CN.

The PAGING message is transmitted on Iu interface in the connectionless

message mode. After RNC receives paging message from the CN, if the information

element (IE) of Non Searching Indication in the PAGING message is set to

“non-searching” [1] (that is not to check whether the UE is in the connection state or

not), or set to “searching”, but the UTRAN cannot find SRNTI (indicating the UE is in





the idle state). The RNC delivers the PAGING TYPE 1 message through the PCCH

channel. If the PAGING message at the Iu interface carries LAI or RAI, the RNC will

deliver the PAGING TYPE 1 message to all the cells within the location areas or

routing areas. If there is no LAI or RAI, the RNC will deliver PAGING TYPE 1

message to all the cells of this RNC. In addition, the UTRAN will deliver the PAGING

TYPE 2 message through the DCCH channel, which is called collaboration paging.

As shown in Figure 1, the CN initiates paging in a location area (LA), which is

covered by two RNCs. After receiving a paging message, the RNC searches all the

cells corresponding to the LAI, and then calculates the paging time, at which it will

send the PAGING TYPE 1 message to these cells through the PCCH.

CN RNC1 RNC2 NODEB1.1 NODEB2.1 UE

RANAPRANAP

RANAP RANAP

PCCH: PAGING TYPE 1

PAGING

PAGING

PCCH: PAGING TYPE 1

Figure 1 PAGING TYPE 1

The UTRAN can initiate PAGING TYPE 1 directly without the CN. When the UE

is in the CELL_PCH or URA_PCH state, if the UTRAN needs to exchange

information (including signaling and data, as described in Section 2.1) with the UE, it

is necessary to send PAGING TYPE 1 message through the PCCH channel to notify

the UE to transit to the CELL_FACH state from the URA_PCH or URA_PCH state.

Then the state of the UE is transited by means of the cell updating process.

1.2.2 Paging Type 2

As shown in Figure 2, if the UTRAN determines it is a collaboration paging,

indicating the UE is in the CELL_DCH or CELL_FACH state, the UTRAN will

immediately transmite PAGING TYPE 2 message to the paged UE on DCCH

channel.





If UE is in CELL_PCH or URA_PCH state, the UTRAN transmits the paging

information in PAGING TYPE 1 message to UE. After received paging message, UE

performs a cell update procedure to transit state to CELL_FACH.

In conclusion, if the UE is in CELL_FACH or CELL_DCH state, PAGING TYPE

2 message is delivered on the network side; otherwise, PAGING TYPE 1 message is

delivered.

CN SRNC UE

RANAPRANAP

PAGING

RRCRRCDCCH: PAGING TYPE 2

Figure 2 PAGING TYPE 2

1.2.3 Actions of UE Received Paging

UTRAN may page several UEs in the same paging occasion by including one

IE “Paging record” for each UE in the PAGING TYPE 1 message. When the UE

receives a PAGING TYPE 1 message. it shall perform the actions as specified

below.

If the UE is in the idle state, for each occurrence of the IE “Paging record”

included in the message the UE shall:

1. If the IE “Used paging identity paging originator” is a CN identity:

- compare the IE “UE identity” with all of its allocated CN UE identities:

- If one match is found, indicate reception of paging; and forward the IE of

“CN domain identity”, the IE“UE identity" and the IE "Paging cause" to the upper

layers;

2．Otherwise, UE ignores this paging record.

If the UE is in connection mode, for each occurrence of the IE “Paging record”

included in the message the UE shall:





1) If the IE “Used paging identity” is a UTRAN identity and if this U-RNTI is with

the same as the U-RNTI allocated to the UE:

- If the optional IE “CN originated page to connected mode UE” is

included, indicate reception of paging; and forward the IE “CN domain identity",

the IE "Paging cause" and the IE "Paging record type identifier" to the upper

layers.

- If the optional IE “CN originated page to connected mode UE” is not

included, the UE performs a cell update procedure with cause “Paging record” as

response.

2) If the IE “Used paging identity” is not UTRAN, the UE ignores this paging

record.

If the IE "BCCH modification info" is included, any UE in idle mode, CELL_PCH

or URA_PCH state shall re-read the system message, ignoring the contents of

"Paging record".

1.3 DRX Process of UE

1.3.1 DRX Cycle Length and Paging Occasion

In idle mode, the UE can monitor the paging in two modes: one is to decode

SCCPCH directly every 10ms, the other is to decode the PICH periodically. Only

when the Page Indicator (PI) exists will the associated SCCPCH information be

decoded, that is the Discontinuous Reception (DRX), which can reduce the power

consumption.

Calculation formula [1] for the DRX paging cycle length when the UE is in idle

state:

DRX cycle length = 2K x PBP frames

Where: K represents the IE of “CN domain specific DRX cycle length coefficient”,

which is broadcast in the system information. At present, the K value of CS and that

of PS are 8. PBP, the paging block periodicity, is 1 for the FDD mode.

Then the formula is simplified as:

DRX cycle length =2K (1)

The value of the Paging Occasion is determined as follows:

Paging Occasion(CELL SFN) = {(IMSI mod M) mod (DRX cycle length div

PBP)} * PBP + n * DRX cycle length + Frame Offset





When n=0,1,2……. As long as SFN is below its maximum value 4096, for FDD,

Frame Offset = 0. M represents the number of the SCCPCHs bearing PCH, which is

1 in generally cases.

The above formula is simplified as:

SFN = IMSI mod 2K + n*2K (2)

The UE needs to monitor the PI on these PICH frames only. As shown in Figure

3, the UE needs to monitor the frames (paging occasions) indicated by the red dots,

and then decodes the qth PI of this frame. The formula for the value of q is formula

(3).

。。。

0

2^K-1

0 4095

。。。

P I P I P I P I。。。。。。

0 1 q NP-1

One DRX cycle

Figure 3 Schematic diagram of UE paging occasion

1.3.2 Association between PICH and SCCPCH

The Page Indication Channel (PICH) is a fixed rate (SF=256) physical channel used

to carry the paging indicators. The PICH is always associated with an S-CCPCH to which a

PCH transport channel is mapped

Figure 4 illustrates the frame structure of the PICH. One PICH radio frame of length 10

ms consists of 300 bits (b0, b1, …, b299). Of these, 288 bits (b0, b1, …, b287) are used to carry

paging indicators. The remaining 12 bits are not formally part of the PICH and shall not be

transmitted. The part of the frame with no transmission is reserved for possible future use

[1].





b1b0

288 bits for paging indication12 bits (transmission

off)

One radio frame (10 ms)

b287 b288 b299

Figure 4 Structure of Paging Indicator Channel (PICH)

Each PICH frame carries NP PIs. NP (the number of paging indications per

frame) defines the maximum number of PIs supported by each frame on the PICH

channel. The UE obtains the value of NP in the cell system message, including 18,

36, 72 and 144, that means to divide the 288 bit by NP, with each part constituting a

PI. The mapping from {PI0, .., PIN-1} to PICH bits {b0,..,b287} are according to Table 1:

Table1 PI-to- PICH mapping

Number of PI per frame (NP)

PIp = 1 PIp = 0

NP=18 {b16p, .. b16p+15} ={1,1,..,1} {b16p, .. b16p+15} = {0,0,..,0} NP=36 {b8p, .. b8p+7} = {1,1,..,1} {b8p, .. b8p+7} = {0,0,..,0} NP=72 {b4p, .. b4p+3} = {1, 1,1,1} {b4p, .. b4p+3} = {0, 0,0,0} NP=144 {b2p, b2p+1} = {1,1} {b2p, b2p+1} = {0,0}

The UE determines to associate the qth part of bits by calculating the suffix p of

its IP.

( )( )( ) NpNpSFNSFNSFNSFNPIq mod144

144mod512/64/8/18

×+++×+= (3)

Where, PI = DRX index mod NP = (IMSI div 8192) mod NP

SFN is the paging time of the UE, it is the SFN of the PCCPCH once the PICH

appears.

Based on formula (3), the UE can get the suffix of itself. Thus, the UE can

monitor the bits associated with itself in the PICH. Once they are assigned to 1, the

UE knows that it is paged. Then it starts to receive the paging message from the

7680th chip after the radio frame of this PICH ends, and then resolves the paging

message. The time sequence relation between PICH and SCCPCH is shown in

Figure 4. The end part of the radio frame of PICH is 7680 chips ahead of the

associated SCCPCH.





τPICH

Associated S-CCPCH frame

PICH frame containing paging indicator

Figure 5 Time sequence relation between PICH and SCCPCH

1.3.3 Paging Channel Selection

The system information block type 5 (SIB5) defines commom channel to be

employed in the idle mode. In a cell, a single or several PCHs may be established.

Each SCCPCH indicated to the UE in system information may carry up to one PCH.

Thus, for each defined PCH there is one uniquely associated PICHalso indicated.

If case that more than a single PCH and associated PICH are defined in the

SIB5, the UE shall perform a selection according to the following rule:

- The UE shall select a SCCPCH from the ones listed in SIB5 based on

IMSI as follows:

Index of selected SCCPCH = (IMSI div (( “DRX cycle length”div PBP)*Np*NPICH))

mod K,

Where K is equal to the number of listed SCCPCHs which carry a PCH

(e.g.SCCPCHs carrying FACH only shall not counted). These SCCPCH shall be

indexed in the order of their occurrence in SIB5 from 0 to k-1.

“Index of selected SCCPCH” identifies the selected SCCPCH with the PCH

and the uniquely associated PICH to be used by the UE.

At present, Huawei realizes the scheme of one cell being configured with one

PICH and one SCCPCH, with the SCCPCH carry two FACHs and one PCH.

1.3.4 Example of UE DRX

After a cell is set up, the parameters of paging in the broadcast system

information are set as follows:

l IE “CN domain specific DRX cycle length coefficient”: 7

l IE “Number of PI per frame”: 36

After receiving this information, the UE calculates the paging time, the PI and

the p value of itself.





For example, a user whose IMSI is 448835805669362, the calculation is as

follows:

DRX cycle length = 28 = 256

Cell SFN ＝ 448835805669362 mod 28+ n*28 = 242 + 256*n (n = 0,1,2,...)

PI = (448835805669362 div 8192) mod 36 = 14

q = (14 + [((18*(242 + [242/8] + [242/64] + [242/512])) mod 144) *0.25]) mod 36

= 27

It can be learnt from the above data that the PICH of this cell carries 36 PIs in

each frame, with each PI composed of 288/36 bits, that is 8 bits. The UE needs to

monitor bit 216 (27x8)–bit223 of each PICH radio frame. If these 8 bits is changed to

1, the UE learns that it is paged, and needs to receive the paging message at the

SCCPCH.

2 Paging Signaling Analysis

2.1 L3 Signaling Analysis

The signaling related to paging include paging IU, paging type 1, paging type 2,

as well as the common transport channel setup request (IUB) for configuring the

PCH and PICH parameters, system information 1 and system information 5.

2.1.1 IU Interface Paging

If the CN needs to set up signaling connection with the UE, it shall initiate the

paging procedure at Iu interface. The signaling resolution is shown in Figure 6.

The CN initiates the procedure by sending a PAGING message, this message

shall contain information necessary for RNC to be able to page the UE,like:

ü The CN Domain Indicator IE shall be used by the RNC to identify from which CN

domain the PAGING message originates.

ü The Permanent NAS UE Identity IE (i.e. IMSI) shall be used by the UTRAN

paging co-ordination function to check if a signalling connection towards the other

CN domain already exists for this UE. In that case, the radio interface paging

message shall be sent via that connection instead of using the paging broadcast

channel.

ü DRX Cycle Length Coefficient: Represented by K, for calculating the DRX

period (2K*PBP) of the UE. If this IE contains UTRAN, the K value will be

transferred to the UE transparently. The UE may probably receives the K





values configured by the CS, PS or the UTRAN, and will take the smallest

one. This IE is optional.

ü The Temporary UE Identity IE (e.g. TMSI) is the temporary identity of the user

(allocated by that CN Domain) which can be used in a radio interface paging

message. If the Temporary UE Identity IE is not included in the PAGING message,

the RNC shall use the Permanent NAS UE Identity instead – if no signalling

connection exists.

ü The Paging Area IE shall be used by the RNC to identify the area in which the

radio interface paging message shall be broadcast in case no signalling connection,

as described above, already exists for the UE. If the Paging Area IE is not included

in the PAGING message, the whole RNC area shall be used as Paging Area – if no

signalling connection exists for that UE

The Paging Cause IE shall indicate to the RNC the reason for sending the

PAGING message. The paging cause is transferred transparently to the

UE.

ü .The Non Searching Indication IE shall, if present, be used by the RNC to

decide whether the UTRAN paging co-ordination function needs to be

activated or not. In the absence of this IE, UTRAN paging co-ordination

shall be performed.

ü





Figure 6 IU interface paging signaling resolution

2.1.2 Paging Type 1

The UTRAN can page several UEs in one PAGING TYPE 1 message through

the paging packet. Figure 7 illustrates the signaling resolution of paging type 1.

Paging type 1 contains the following IEs:

Paging record list: It is specified in the protocol that a maximum of 8 UEs,

corresponding to 8 paging records containing the paging resource, can be paged at

the same paging occasion. If the CN initiates paging, the information such as domain

ID of the CN, the NAS layer ID of the UE and the paging cause should be specified.

If the UTRAN initiates paging, the UE ID of the AS layer, URNTI, should be

specified.

BCCH modification info: Identifies the system information changes with the

value tag. If this IE exists, the UE will read the system information, ignoring the

Paging record list.





Figure 7 Paging Type 1 Signaling Resolution

2.1.3 Paging Type 2

For the UE in CELL_DCH or CELL_FACH state, the UTRAN sends the PAGING

TYPE 2 message with AM RLC on DCCH channel to initiate the paging procedure.

The UTRAN may send the PAGING TYPE 2 message in other processes, without

influence on the state in that process, unless otherwise specified.

UTRAN should set the IE "Paging cause" to the cause for paging received from upper

layers. If no cause for paging is received from upper layers, UTRAN should set the value

"Terminating – cause unknown".

2.1.4 Common Transport Channel (CCH) Setup Request of IUB

The RNC notifies the NODEB PCH transport channel parameters and the

relevant parameters of PICH through the Iub interface signaling of “Common

Transport Channel Setup Request”. In Figure 8, we can see that the two transport

block formats of the PCH (0x240 and 1x240), whose power is 2 dB greater than that

PCPICH; the NP value of PICH is 36, whose power is 3 dB smaller than PCPICH.





Figure 8 CCH setup request signaling resolution

2.1.5 System Information Block Type 1

Figure 9 System message 1 signaling resolution





The UTRAN notifies UE DRX cycle coefficient with the system information block

type 1. As shown in Figure 9, the cycle coefficients of CS and PS are 8.

2.1.6 System Information Block Type 5

The UE gets the PCH transport format and the NP value of the PICH by reading

the system information block type 5.

2.2 L2 Signaling Analysis

MACC

F ACH

FP

F ACH

F P

RA C

H F P

RAC

H F P

FAC

H FP

FA C

H FP

PC

H FP

SCCPCH SCCPCH PRACH PRACH

……

PCCHCCCH CCCH

RLC RLC

MACD MACD

AAL2

(DL) (DL)CCCH(UL)

(UM) (UM)

Figure 10 CCH layer structure

Figure 10 shows the mapping relation among PCCH, MACC, PCH FP and

SCCPCH. The PCCH adopts the TM mode at the RLC layer. The MACC schedule

the paging packets. The relevant features of the PCH are represented in the PCHFP

frame.

The PCH data frames include the PI information and paging message. To page

an UE, two continuous PCH data frames are sent with continuous CFNs: the first

frame contains the PI information, and the other contains the paging message.

For NODEB, except NP that is obtained by means of CCH setup, other

parameters are present in the PCH FP frame delivered from the upper layer. The PI

is contained in the PI bitmap; DRX Cycle length is determined by the time interval of

the PCH FP with the same PI; paging time can be worked out based on the CFN in

the PCH FP. The frame structure of the PCH FP frame is shown below:





Header CRC

CFN

First TB

Header

Payload

FT

First TB

Pad

7 0

Payload CRC

Payload CRC (cont)

Last TB

Last TB

Pad

CFN (cont)

TFI

Not Used

PI-bitmap

PI-bitmap

Pad

PI

Spare Extension

Spare

Figure 11 PCH FP frame structure

The units in the data frame are described as follows:

Header CRC: The polynomial of cyclic redundancy is calculated according to

the header of a data frame by means of the polynomial of (X^7+X^6+X^2+1). The

calculation of the CRC should include all the bits in the header, that is, from bit 0 in

the first byte (FT field) to the end of the header. The field is 7 bits in length, with the

value range of (0–127).

Frame type: Indicates it is a data frame or control frame, 0 for data frame and 1

for control frame. It is 1 bit in length.

Connection frame number (CFN): Indicates the radio frame of which the first

data to be received in the uplink or to be sent at the downlink. The value range and

length depends on the transport channel used by the CFN. In the case of PCH, the

value range is (0-4095), and the length (PCH) is 12 bits. In the case of other

channels, the value range is (0-255).

Transport format indicator (TFI): It is the indicator of the transport format used to

transport a TTI. It is 5 bits in length, ranging from 0 to 31.





Transport block: It is a data block to be transported or that has been received

through the radio interface. The transport format indicated by the TFI describes the

transport block length and the transport block set size.

Pay load CRC: The polynomial of cyclic redundancy is calculated according to

the payload of a data frame by means of the polynomial of (X^16+X^15+X^2+1). The

calculation of the CRC should include all the bits in the payload, that is, from bit 7 in

the first byte to the byte before the payload CRC. It is 16 bits in length.

Page instruction (PI): Describes whether the PI Bitmap is present in the payload,

with 0 for no and 1 for yes. It is 1 bit in length.

PI-bitmap: Bit map of PI0..PIN-1. Bit 7 of the first byte contains PI0, and Bit 6 of

the first byte contains PI1,,…, Bit 7 of the send byte contains PI8, and so on. The

value range is 18, 36, 72 or 144 PIs). It is 3, 5, 9 or 18 in length. If PI-bitmap is 1, it

indicates the UE at the PI monitored is paged.

3 Paging Performance Analysis

3.1 Paging Scheduling

The paging scheduling is performed in the MACC. After receiving the paging

message from the CN, the L3 of the RNC judges whether the system is overload. If

no, it sends the paging message to the MACC; if yes, it discards the paging

message. After the MACC receives the paging message from the upper layer, it

works out the paging time, and then stores the paging record at the corresponding

location of the paging cycle closest to the current CFN. For the MACC, a maximum

of 8 paging records can be stored at one paging time, and the excessive ones will be

discarded. When each paging time comes, the MACC codes the paging records

corresponding to this paging time, and delivers them to the NODEB, and then clears

them. NODEB delivers the paging records through the cell paging channel. However,

for the paging caused by system message update, the MACC will immediately code

them and deliver them, and clears all the paging records.

At present, the transport block of the PCH supported by the MACC is 240 bits.

The coded paging message supported by each frame cannot exceed 240 bits.

According to the signaling structure and ASN.1 PER coding rule of PAGING TYPE 1,

if the UE ID of the paging message is IMSI, a maximum of 3 UEs can be paged at

each paging time. If the UE ID is TMSI or PTMSI, a maximum of 5 UEs is supported.

Refer to [3] for details.





Therefore, with the current coding mode of PCH, the number of UEs paged at

one paging frame cannot reach the protocol value 8. If the number of UEs paged at

the same paging time is beyond the processing capacity of the system, it will lead to

paging loss, and consequently call loss. In the configuration of IMSI, the detailed

planning should be made according to the calculation formula for paging time, IMSI

mod 2k+n*2k, so as to ensure the paging times of every UE are evenly distributed on

the frames of a paging cycle.

On the other hand, the network can improve the paging success rate by means

of re-transmission. After the paging timer is time-out, the CN will re-transmit the

paging message at the Iu interface, and the UTRAN can also re-transmit during the

scheduling of the MACC, but in different paging cycles, as shown in Figure 3.

3.2 Paging Parameter Analysis

3.2.1 DRX Paging Cycle Coefficient

The DRX paging cycle coefficient K determines the DRX cycle length. The

bigger the K value, the longer the DRX cycle, and the lower the UE power

consumption. If the K value is too small, the paging period will be short, and the

paging processing overhead and consumption will be increased. The protocol value

range is 2-12. Huawei takes the value of 8, that is, the DRX paging cycle is 2.56

seconds.

The DRX paging cycle coefficient may comes from system message, CN paging

message or Uu interface signaling of UTRAN. The processing modes of CS and PS

are different.

For PS domain, The DRX paging cycle coefficient is negotiated by the UE and

the SGSN through the NAS layer message (attach process). No matter the UE is in

the idle or connection state, the data of the negotiation result will be the reference,

and the data of the CS domain in the case of negotiation failure.

For the CS domain, if the UE is in the idle state, the DRX paging cycle

coefficient adopts the minimum value in the system message and paging message

from the CN. If the UE is in the connection state, it will adopt the minimum value in

the system message, the paging message and the Uu interface signaling of UTRAN.

The RNC has two MML commands to modify the DRX paging cycle coefficient.

1. SET FRC modifies the DRX paging cycle coefficient of UTRAN, and notifies

the UE through the following signaling:

² UU_CELL_UPDATE_CONFIRM





² UU_URA_UPDATE_CONFIRM

² UU_PH_CH_RECFG

² UU_TR_CH_RECFG

² UU_RB_SETUP

² UU_RB_REL

² UU_RB_RECFG

2. MOD CNDOMAIIN modifies the DRX paging cycle coefficient of the CS and

PS, and then sends the PAGING TYPE 1 message to notify the UE to read the

updated system message.

NP value

Np is the number of PIs delivered by PICH in one frame, in the value range of

(18, 36, 72, 144). This parameter is indicated by Number of PI per frame in the

system message. The UE receives the PI frame sent by the PICH at the specified

paging occasion. Only when the PI is valid will the UE demodulate the subsequent

S-CCPCH frame.

Meanings of in the actual network: This parameter divides all the UEs into Np

groups, with all the UEs in the same group using the same PI. The influence of the

Np on the network: If the value of Np is too small, the number of UEs in each group

are more, thus the occurrence probability of PI is high for each UE, and the waken

times are more; if the value of Np is too big, the number of UEs in each group are

less, the occurrence probability of PI is low for each IMSI, and the waken times are

less. On the other hand, the bigger the Np is, the performance requirement on the

PICH demodulation is higher [2].

3.2.2 Paging Re-transmission Times and Interval

To increase the paging success rate, the CN and RCN will re-transmit the

paging message. However, paging re-transmission leads to some negative effect,

namely, paging volume increase, especially when the downlink channel of the air

interface is congested, the paging re-transmission will double increase the paging

volume, which wastes the downlink channel resource at a large degree, and thus the

new paging message cannot be delivered promptly. To consider both paging

success rate and paging efficiency, the CN re-transmission times and interval should

be considered together with the re-transmission of the UTRAN.

At present, Huawei realizes the scheme of RNC re-transmits tow PAGING

TYPE 1 message at the time interval of one paging cycle , , that is 2560ms (with the





DRX cycle length coefficient of 8). The CN supports 4 times of paging

re-transmission at the maximum (excluding the first transmission), that is, the CN

supports 5 time of paging transmission. The paging re-transmission interval of the

CN can be set by soft parameter. It is fixed to [2, 2, 2, 3s] presently.

Generally, the UTRAN re-transmits the paging in a DRX cycle (2560ms). If the

CN re-transmits the paging for once, the time interval can be considered as follows

[2]:

If the UTRAN does not re-transmit, the re-transmission interval of the CN should

be greater than a DRX cycle (2560ms), 3s can be adopted. As described in Section

3.1 “Paging Scheduling”, when a paging message is sent by the CN to the UTRAN,

the UTRAN calculates that the paging time CFN is a DRX cycle (2560ms) away from

the maximum time interval of the current PCH CFN. If another one paging message

is sent within this interval before the previous one is sent out from the UTRAN, this

will cause unnecessary channel bandwidth waste.

If the UTRAN re-transmits once, the re-transmission time should be greater than

tow DRX cycles.

Under this rule, the CN should re-transmit the second paging message after the

UTRAN re-transmits the former one. For this, the parameters of re-transmission

times and interval of the CN, the re-transmission times of the UTRAN and the DRX

paging cycle can be adjusted for this rule.

3.3 Traffic Statistics and Alarm for Paging

Table 2 shows the traffic statistics indices for paging in the RNC. Among which,

the two main indices CN_PAGE_IDLE_UE_SUCC_RATE and

UTRAN_PAGE1_SUCC_RATE indicate the paging performance. The paging

success rate, the first paging success rate and second paging success rate at the

CN side can be measured. Based on these indices, the network paging indices can

be optimized specially.

Table2 Paging traffic statistics indices

Traffic statistics index name Meaning Statistics point of time

CN_PAGE_REQ Measures the times of paging at the Iu interface

When the PAGING message initiated by the CN is terminated

CN_PAGE_IDLE_UE_REQ Measures the times of paging idle UEs at the Iu interface

When the PAGING message initiated by the CN is terminated by an idle UE.





CN_PAGE_IDLE_UE_SUCC Measures the times of paging idle UEs successfully

When the RRC connection request message of UE is received, with the request cause being a called type cause, for example, Terminating Conversational Call.

UTRAN_PAGE1_REQ Measures the number of PAGING TYPE 1 messages initiated by the UTRAN

When the UTRAN initiates a PAGING TYPE 1 message

UTRAN_PAGE1_SUCC

Measures the times of successful response from the UE after the UTRAN initiates the PAGING TYPE 1 message

When the UTRAN receives the paging response message from the UE

CN_PAGE_IDLE_UE_SUCC_RATE Measures the success rate of paging to idle UEs initiated by the CN

A calculation index, calculated with the formula of

[CN_PAGE_IDLE_UE_SUCC]/ [CN_PAGE_IDLE_UE_REQ]

UTRAN_PAGE1_SUCC_RATE Measures the success rate of PAGING TYPE 1

A calculation index, calculated with the formula of

[UTRAN_PAGE1_SUCC]/[UTRAN_PAGE1_REQ]

At present, Huawei does not provide the paging-related alarm function at

present. In the actual running process of the network, flow control or paging capacity

restriction will lead to paging loss. If the paging loss volume reaches the pre-set

threshold, it is recommended to output paging loss alarm, with the main loss cause.

3.4 Paging Abnormity Handling

If the UTRAN does not buffer paging messages, all the paging messages will be

discarded in case abnormity occurs in the paging process.

3.4.1 System Abnormity

To ensure the stability of the system and avoid impact on the system caused by

burst message storm, the RNC performs flow control on the messages (including

paging messages) with high processing frequency. When the RNC receives the

paging message of the CN, it will judge whether the system is overload. If yes, it will

discard the paging message, and record the number of paging message discarded.

If the loss proportion reaches a specific threshold, the RNC will send overload





message to the CN, and then the CN will control the message transmission flow by

decreasing the flow based on a certain step length. Thereafter, if the CN does not

receive the Overload message within a certain period of time, the message flow of

the Iu interface will increase to the normal state step by step.

In addition, if some failure occurs in the system, for example, the Iub interface

transmission layer failure or cell in abnormal state, it may cause paging message

loss.

NodeB will not process the paging message packet when it is overload, either.

To minimize the call loss caused by paging loss, the network side adopts the

measure of call message re-transmission. Refer to Section 3.2.3 for details.

3.4.2 Paging Channel Capacity Restriction

Due to the restriction of the PCH capacity, the number of UEs that can be paged

at the same paging time is limited. If the number of UEs exceeds this limit, paging

message will be discarded. This will occur in two cases:

1) The number of UEs paged at the same paging time exceeds eight (the

protocol value), beyond the processing capability of the MACC (The MACC applies a

memory area for eight paging records at each paging time.).

2) As the transport block of each frame after coding is 240 bits at the maximum,

even if the number of UEs of each paging time is smaller than 8, paging loss cannot

be avoided. If the UE ID of the paging record is IMSI, the paging message of each

frame can process the paging records of 3 UEs only. If the UE ID of the paging

record is TMSI or PTMSI, the paging message of each frame can process the

paging records of 5 UEs only. If this limit is exceeded, the excessive paging records

will be discarded. For the calculation of paging capacity, refer to Reference [3].





List of references:

[1] 3GPP R1999 25_series, 2002/09

[2] Zhang Jiayi, WCDMA Paging Strategy Study, 2003/11

[3] Miao Jiashu, WCDMA RNP Paging Area Planning Guide, 2003/03



wcdma rno paging procedure analysis guidance

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