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Transcript of 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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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
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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
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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
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List of Tables
Table1 PI-to- PICH mapping ..................................................................................................12 Table2 Paging traffic statistics indices....................................................................................24
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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
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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
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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.
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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:
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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
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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].
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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.
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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.
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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
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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
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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.
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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.
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Figure 8 CCH setup request signaling resolution
2.1.5 System Information Block Type 1
Figure 9 System message 1 signaling resolution
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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:
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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.
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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.
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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
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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
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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.
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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
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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].
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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
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