The document discusses the LTE attach call flow process, including: 1. An overview of the evolution of cellular systems and the introduction of 5G. 2. The decoding processes involved in LTE attach which include frequency scanning, decoding the PSS, SSS, MIB, PDCCH, and SIBs. 3. The steps in the LTE attach process such as the random access channel process, sending an RRC connection request, receiving an RRC connection setup, and responding with an RRC connection setup complete message.

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LTE Attach Call
Flow Discussion
Surinder Salyan
RF Quality_Haryana

2. C2 – Vodafone Idea Internal
Content of Discussion
1. Evolution of Cellular system
2. Coverage Pattern of Different Bands
3. 5G introductions for Coverage point of view
4. Sites Connectivity diagram
5. LTE/EPS Network Elements & architecture
6. Massage flow overview to attach in LTE network
7. Frequency scanning
8. PSS & SSS Decoding
9. MIB decoding
10. PDCCH decoding
11. SIB Decoding
12. RACH process
13. RRC connections request
14. RRC connections Setup
15. RRC connections Setup complete

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Evolution of Cellular system
Voice Service in 1979
Voice & Data (40 kbit/s)in 1991
Voice & Data (171 kbit/s)in 1999
Voice & Data (384 kbit/s)in 1999
Voice & Data (2 Mbps/s) in 2001
Voice & Data (14 Mbps/s) in
2005
Voice & Data (42Mbps/s) in 2007
Volte & Data (200mbps-1 Gbps) in 2008
Volte & Data (10Gbps-100Gbps) in 2019
3.75G HSPA+
To be launch in 2027-28
6G
2G
2.5G
2.75G EDGE
3G UMTS
3.5G HSPA
5G NR
4G LTE /LTE-A
1G

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Coverage Pattern of Different Bands
900 MHz
2500 MHz
2100 MHz
1800 MHz
RANGE

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5G Introductions for Coverage point of view
Macro Cells Small Cells

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PoP
A
D
C
B
E
Ring Topology
F
PoP
A
D
C
B
E
Chain Topology
F
PoP
A
D
C
B
E
Tree Topology
F
PoP
H
G
P
K
K
L
M
N
H
Sites/MW Connectivity diagram demo
1
.
2. 4.
A
D
C
B
E
Loop Topology
PoP
F
3.
Fiber
Fiber
Fiber
Fiber
PoP

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LTE/EPS Network Elements & architecture
LTE-UE
Evolved UTRAN (E-UTRAN)
MME S10
S6a
Serving
Gateway
S1-U
S11
PDN
Gateway
IMS/PDN
Evolved Packet Core (EPC)
S1-MME
PCRF
Gx or S7 Rx
SGi
S5/S8
Evolved
Node B
(eNB)
cell
X2
LTE-Uu
HSS
MME: Mobility Management Entity
PCRF:Policy & Charging Rule Function
SAE
Gateway
HSS Home Subscriber Server

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MIB-SIB Decoding
Freq Scaning
RA Request
RA Response
RRC Conncetions Req
RRC Conncetions Setup
RRC connection Setup complete
Intial UE msg Attach PDN Req Authentication info Req
Authentication info Response
Authentication Req
Authentication Response
Security Mode Command
Security Mode Command Complete
Location update Req
Location update Response
Create session Req Create session Req
Create session Response
Create session Response
Intial Context Req
UE Capability inquiry
UE Capability information's UE Capability info indications
UE Security Mode
UE Security Mode Complete
RRC reconfigurations
RRC reconfigurations Complete Initial Context setup complete
Modify Bearer Request
Modify Bearer Response
End to End GPRS Tunnel

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Frequency scanning
1. SLS (Stored list search) UE have some stored list because UE was earlier attached with
network, if we are going to restart mobile / aroplane mode so it don’t need to scan
Frequency
2. DBS (Deviated band stand) if SLS data is invalid than UE will start searching which
Frequency band UE supporting & according to RAT priority & RSSI,RSRP,RSRQ
 Frequency Band Supported
 RAT Priority
There is two type of Frequency Scanning

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PSS & SSS Decoding (LTE Synchronization)
After power-up, the UE tries to obtain time and frequency synchronization with the system. For this, UE needs to detect signals to find out
where the frame begins and ends. LTE define two type of synchronization signals:
 Primary synchronization signal (PSS) PSS helps to achieve subframe, slot and symbol synchronization in the time domain, identify the center of the channel
bandwidth in the frequency domain and deduce a pointer towards 1 of 3 Physical layer Cell Identities (PCI)
 Secondary synchronization signal (SSS) SSS helps to achieve radio frame synchronization
UE uses the Synchronization Signals to:
•Achieve radio frame, subframe, slot and symbol synchronization in the time domain
•Identify the center of the channel bandwidth in the frequency domain
•Deduce the Physical layer Cell Identity (PCI)
PSS:- 0,1,2
SSS:- 0 to 167
Total PCI :-503 in LTE
PSS to be radiate on central 62 Carrier (6RB)

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MIB (Master information block) decoding
MASTER INFORMATION BLOCK (MIB) is the broadcast information transmitted by eNodeB at periodically. After
Decoding the PSS and SSS information UE have the information of Physical cell ID and not it can descramble the further
information which Master information Block, which will provide the System bandwidth, Antenna configuration , System
frame number & periodicity of MIB is 40ms.
Bits and Bytes of Master information blocks:
•Size of Master Information Block – 24 Bits (3 Bit for Radio Bandwith,3 Bit for PHICH Configurations,8 bit for SFN & rest 10
for future use)
•Resource Block Requirement – MIB require 6 RBs (72 subcarriers) in Frequency domain
•Modulation – QPSK

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PDCCH (Physical downlink control channel) decoding
PDCCH is a physical channel that carries downlink control information (DCI), PDSCH channel to be use
to send this information's, we also have UCI format which is to be use through PUSCH ,
PDCCH has following formats..
 Resource block assignment information ( number of RBG allocated to UE)
 New data indicator value ( indications its new data of old data means part of retransmission)
 TPC command for PUCCH (transmit power control).
 Redundancy version (LTE utilizes incremental-redundancy HARQ with a 1/3 turbo encoder used for FEC)
 Modulation and coding scheme.

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SIB ( System information Block) Decoding
System Information Blocks in LTE, SIBs carry relevant information for the UE, which helps
UE to access a cell, perform cell re-selection, information related to INTRA-frequency,
INTER-frequency, and INTER-RAT cell selections. SIB1 & 2 required for initial attach, 80ms
periodicity In LTE there are 13 types of SIBs
SIB 1 : Cell Selection (eCGI), Cell access status
SIB 2 : RACH preamble infomations, Access Barring, UL frequency Information, 40ms periodicity
SIB 3 : Intra Frequency Cell Reselection
SIB 4 : Intra Frequency Neighbor Cell
SIB 5 : Inter Frequency Neighbor Cell
SIB 6 : UTRAN Neighbour Cell
SIB 7 : GERAN Neighbour Cell
SIB 8 : CDMA Neighbour Cell
SIB 10/SIB11 : ETWS (earhquick & tsunami warning system)
SIB 19 :-SIB19 for FRLTE
SIB 24 : NR Neighbour Cell

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RACH process (random access channels)
•Random Access Procedure:- RACH procedure is used be synchronized with the network through Uplink & to obratin the resource for
RRC connections req. There are total of 64 preambles available which are divided into two groups Group A and Group B. UE decides the preamble
index from a group on the basis of parameters received in SIB2, Suppose a UE wants to access the network, so first it will try to attach or
syncronise with the network. In LTE a separate channel PRACH ( Physical Random Access Channel) is provided for initial access to the network. 6
PRB to be use by UE to send RACH preabble
When does UE need to perform Random Access Procedure :-
. Initial Access.
•Handover
•When uplink synchronization is lost :- It means from a certain duration network has not received anything from UE in uplink.
•Radio link lost.
•During RRC connection re-establishment procedure .
•When UE does not have any PUCCH resources available for SR(Scheduling Request) .
•When timing advance is needed for positioning purpose in RRC connected state for UE

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RRC connections request
RRC CONNECTION REQUEST message is used to request the E-UTRAN for the establishment of an
RRC connection. It is transferred using SRB0 on the Common Control Channel (CCCH)..
IEs in RRC CONNECTION REQUEST message are given below:
ue-Identity (Initial UE-Identity): This IE is included to facilitate contention resolution by lower layers. It can
be either S-TMSI (40-bits) or a bit string of randomValue (40-bits). If the upper layers provide S-TMSI, then
S-TMSI is used as the ue-Identity; else a random value in the range of 0 … 240-1 is drawn and used as
the ue-Identity. Upper layers provide the S-TMSI if the UE is registered in the TA of the current cell
establishmentCause:The main cause values and the corresponding NAS procedure whichtriggers the
RRC connection establishment are presented below:
emergency: This corresponds to NAS Procedure “MO-CS fallback Emergency call”
mt-Access: Corresponding NAS procedures are“Service Request” (paging response for PS domain) or
“Extended Service Request”(MT-CS fallback)
mo-Signalling: Corresponding NAS procedures are Attach, Detach, and TAU
mo-Data: Corresponding NAS Procedures are“Service Request” and “Extended Service Request”

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RRC connections Setup
Direction: E-UTRAN => UE
Signalling Radio Bearer: SRB0
RLC Mode: TM
Logical Channel: CCCH
Transport Channel: DL-SCH
The RRC CONNECTION SETUP message is used to establish SRB1. It contains configuration information for SRB1. This
allows subsequent signaling to use the DCCH logical channel. The configuration for SRB1 can be a specific configuration
or the default configuration.
The RRC CONNECTION SETUP message may also contain configuration for PUSCH, PUCCH, PDSCH channels and
information regarding uplink power control, CQI reporting, the SRS, antenna configuration and scheduling requests

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RRC connections Setup Complete
Direction: UE => E-UTRAN
Signalling Radio Bearer: SRB1
RLC Mode: AM
Logical Channel: DCCH
Transport Channel: UL-SCH
The RRC CONNECTION SETUP COMPLETE message is used to confirm the successful completion of an RRC connection establishment. Some of the IEs in this message
are explained below:
selectedPLMN-Identity: This IE points to a PLMN-Id in the plmn-IdentityList of SIB1. The IE plmn-IdentityList is transmitted in SIB1 when the cell belong to more
than one PLMN.The value of this IE equals to ‘1’ if the 1st PLMN is selected from the plmn-IdentityList included in SIB1, ‘2’ if the 2nd PLMN is selected from the plmn-
IdentityList included in SIB1 and so on
registeredMME: This IE is optional, and is included when available. This is the identity of the MME with which the UE is (previously) registered with. If upper layers
provide the 'Registered MME', then the IE registeredMME is set as follows:
If the PLMN identity of the 'Registered MME' is different from the PLMN selected by the upper layers (selectedPLMN-Identity) then include the plmnIdentity in
the registeredMME and set the mmegi and the mmec to the value received from upper layers
dedicatedInfoNAS: This IE includes the initial NAS message from the UE

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Thank you…