lte call flow, radio link failure and drx

1. LONG TERM EVOLUTION 1
TOPICS
● CALL FLOW
● RADIO LINK FAILURE
● DRX ,
● PAGING
● SCHEDULING
● RACH PROCDURE
● SON
● QoS(quality of service)
●

2. LONG TERM EVOLUTION 2
1. CALL FLOW
When UE power switched on :
●
UE scan RSSI (rssi is simply measure the whatever energy/power of frequency
channel) for each and every frequency channel.
● This time UE does not know about network.
● UE make a list and compare with the threshold value.(threshold value is just
depend on UE chipset.not part of 3GPP.

3. LONG TERM EVOLUTION 3
CALL FLOW
UE search pss then ue determine
(a) exact carrier frequency
(b) cyclic prefix length
(c) one out of three PCI group(3*168)
(d) sub frame timing
UE search SSS then ue determine
(a) Frame timing
(b) Exact PCI value from 1 out of 3 group
Now UE decode MIB then UE Determine
(a) SFN,PHICH, bandwidth based on PLMN and PCI ,frequency channel
and ue sim info. UE will figure out the real candidate
Now UE able to read SIB 1.
(a) PLMN ID,TAC,Frequency Band indicator,cell selection info,other SIB's info.
<check cell selection criteria>Decode other SIB's.
RRC RACH procedure..2 types
(a) Contention based.
(b) non contention based

4. LONG TERM EVOLUTION 4
non contention based & Contention based Rach procedure
UE send to ENB RRC connection request.
(a) UE id (S-TMSI) value
(b) random value (0....2^40-1)
(c) stablishment cause

5. LONG TERM EVOLUTION 5
CALL FLOW
● ENB send to UE RRC connection setup
– Radio resource configuration Dedicated
(a) srb to add mod list
(b) drb to add mod list
(c) drb to release list
– MAC main configuration
(a) Sps configuration
– Physical config dedicated
(a) pusch ,pdsch,pucch config dedicated
(b) uplink power control dedicated
(c) CQI reporting
● UE send to ENB RRC connection setup complete + NAS attach request +ESM
(a) Selected PLMN id
(b) Registered MME
(c) Dedicated info NAS

6. LONG TERM EVOLUTION 6
CALL FLOW
ENB send inital UE S1AP message to MME
(a) ENB-UE-S1AP-ID
(b) TAC
(c) Attach request(EPS encryption /intergrity algo. Info.)
(d) connection request ( PDN type)
MME send to HSS AUC. Config request via Diameter protocol
(a) command code ,application ID,user name ,RAT type ,visited PLMN id .
HSS response to MME via diameter protocol
(a) result code success,subscriber status, APN config. Info
MME send DL NAS Transport s1ap to ENB
(a) MME-UE-S1AP-ID
(b) ENB-UE-S1AP ID
(c) Rand value,auc no.& key selection id also include in this message

7. LONG TERM EVOLUTION 7
CALL FLOW
● ENB send RRC DL info tranfer to UE
There are three main componenet of this authentication process
(a) input parameter (b) authentication algo (c)output value
Both ue and enodeB use same input and same authentication algo for same output value either
its fail
● UE send RRC UL info transfer to ENB
(a) security header type
(b) EPS mobility management protocol
(c) security mode complete message id
● ENB send UL NAS Transport s1ap to MME
(a) MME-UE-S1AP ID
(b) ENB-UE-S1AP ID
(c) Ue send RES value back to MME,TAC.

8. LONG TERM EVOLUTION 8
CALL FLOW
● MME send a create session request to SGW,SGW forward to PGW
(a) MME initiate the default route establishment by asking the SGW to create a GTP tunnel.
Message contains
(b) RAT type,PDN type,bearer context ,MS-ISDN,TAI,PGW S5/S8 address,APN address
allocation
● MME send A S1AP Initial context setup request +NAS attach accept+activate
default bearer request to ENB
This message contains
(a) MME-UE-S1AP ID,ENB-UE-S1AP ID,AMBR,E-RAB to be setup,UE security capability
(b) EPS attach,TAI list ,GUTI,GPRS ready timer
(c) EPS bearer id ,EPS QoS,access point name ,PDN address
● ENB send a AS security mode command to UE
(a) This is the same step as NAS security mode command the only diffrence is
Its only for RRC.(integrity & ciphering algo info).

9. LONG TERM EVOLUTION 9
CALL FLOW
● ENB send a initial context setup response S1AP to MME
(c) MME-UE-S1AP ID
(b) ENB-UE-S1AP ID,
(a) E-RAB setup list
● Complete attach and Default bearer activation
(a) ENB transport attach complete and bearer accep the message was
received from ue .

10. LONG TERM EVOLUTION 10
RADIO LINK FAILURE
●
Radio link failure means UE suddenly lost the connection with the network in other words
“break physical layer”. when UE is in connected state .
●
When RLF happens ;
●
Layer 1 monitors down link quality and report problem to RRC.
●
RRC filter L1 indicates and start a timer .
●
If no recovery then layer 2 monitors random access attempts and indicate problem to RRC
●
If no recovery then possible recovery through an RRC connection Re-establishment
procedure .
●
Re-establishment may be performed in any cell to which the UE”s context is made available .
●
If no recovery then UE go back into IDLE state.

11. 11
DRX
DRX functionality that controls UE’s PDCCH monitoring activity.
If DRX is configured the UE is allowed to
monitor PDCCH discontinuously .
DRX Cycle specifies the periodic repetition
of the on-duration followed by a possible
period of inactivity .
DRX Inactivity Timer :
Specifies the number of consecutive PDCCH sub frame(s) after successfully decoding a PDCCH
indicating an initial UL or DL user data transmission
DRX Re transmission Timer :
Specifies the number of consecutive PDCCH sub frame(s) for as soon as DL retransmission is
expected by the UE .
DRX Short Cycle Timer: UE should follow the DRX short cycle timer after the inactivity timer has
expired.
On Duration Timer: Specifies the number of consecutive PDCCH sub frame(s) at the beginning of
DRX cycle.

12. 12
PAGING
Paging is a network initiated connection setup .
Paging relies on PDCCH ,monitored at predefined time according to DRX cycle .
If the UE detect its Paging group ID on PDCCH ,its demodulate and decode the PDSCH and forward
the decoded data on PCH to MAC layer the PCH transport block contains the exact identity of the
terminal being paged.
Paging can be used for :
(1) To initiate mobile terminated to PS call
(2) To initiate mobile terminated to CSFB call
(3) To re-acquire system info.
(4) To provide ETWS notification.
There are also two more concept in paging which is :
Paging Occasion (PO): is a sub frame where there may be P-RNTI transmitted on PDCCH
addressing the paging message .
Paging Frame (PF): is a one radio frame ,which may contains one or multiple paging occasions .

13. LONG TERM EVOLUTION 13
MAC
● Scheduling types
1. Dynamic scheduling
2. Persistence scheduling
3. Semi-persistence schuding
1. The first OFDMA symbol in each
and every subframe consist of a CFI
information.CFI info. Basically tells
about how many OFDMA symbol
used by PDCCH .PDCCH has DCI
Information with the help of DCI
UE decode the data from PDSCH.
now when UE download a set of file from the internet ,each and every subframe has PCFICH and
PDCCH data in first 3-4 symbol.the data is robust and adaptive in nature when its web data so its
essential to send control information in each sub frame along with it this type of scheduling is called
dynamic scheduling.

14. LONG TERM EVOLUTION 14
MAC
2. Persistence scheduling :
Consider a case where a voice data in the form of small packets and it comes in a regular
interval. which is network dependent, sending a control information of every subframe plays a
vital role in the bandwidth utilization. This kind of scheduling is called persistance scheduling where
the control information sent across the subframe is retained for every nth subframe coming after it
until unnotified.
3. Semi Persistence Scheduling :
In order to support more allocation
without increase in the size of PDCCH
, SPS can be used. UE is pre
configured by the ENB with in
SPS-RNTI and a periodicity.
Once its preconfigured UE will
Recieve allocation using sps-RNTI
instead of C-RNTI.

15. LONG TERM EVOLUTION 15
HARQ
● HARQ is a combination of high-rate forward error-correcting coding and ARQ is a error control
for detectable-but-uncorrecttable errors.
● In HARQ a code is used that can perform both forward error correction (FEC) in addition to
error detection (ED) such as reed solomon code , convolutional code or turbo code.
● Round trip timing is 8ms
● HARQ only support DLSCH and ULSCH
● Multiple 8 parallel stop and wait process
● Asynchronous Protocol : - No fixed timing relationship between DL packet transmited and the
ACK/NACK sent by UE.
● Synchronous Protocol :- Fixed timing relationship between dl packet transmitted and
ACK/NACK sent by UE .
● Adaptive Protocol :- the frequency location and the more detailed transmission format can be
changed between transmission.
● Non Adaptive Protocol :- retransmission must occur at the same frequency resource and with
the same transmission formate as the initial transmission.

16. LONG TERM EVOLUTION 16
RACH Procedure
● Objective :- its for UL synchronization and also get unique identity to UE and timing correction
information for uplink
● Two Types :
(1) Contention(collision) based
(a) RRC idle to RRC connected
(b) UL data transfer(synchronization lost)
(c) RRC connection re-establishment
(2) Non-Contention(non-collision) based :-
(a) intra sys handover
(b) DL data arrival(synchronization lost)
● Contention based :-
Step 1:- Random acess preamble transmission
Network broadcast info to all UE s.

17. LONG TERM EVOLUTION 17
RACH Procedure
● preamble transmission info. allowed in SIB 2.in each cell there are 64 preamble sequence
available.UE randomly select a 1 sequence,transmission of random acess preamble for ENB to
estimate the UE transmission timing .power ramping can be applied until preamble is received .
● Step 2 :- Random Access Response
After ENB detect the preamble it send a transmission on PDCCH identified using RA-RNTI.
Actual RAR is on PDCCH pointed by PDCCH with RA-RNTI.
Message contains index of the random acess preamble ,timing correction calculated at the
network,temporary identity TC-RNTI.
● Step 3 :- Terminal Identification
● UE adjust timing correction info. UE start a contention resolution timer , each UE will transfer it
unique UL-CCCH SDU on ULSCH transmitting the uplink message.its allow to use HARQ to
enhance receiving performance.
● Step 4:- Contention Resolution
ENB will only receive ULSCH from UE those timing adjustment was suitable . Then ENB send a
PDCCH with a TC-RNTI orignally included in RAR and then the contention message on PDSCH
where a contention resolution id which match the CCCH SDU of only of the UE s is included.
each UE receiving the downlink message will compare the contention resolution id. Only UE
which observe a match between the ID received in contention resolution and the CCCH SDU
will declare the random access procedure successfull.

18. LONG TERM EVOLUTION 18
RACH Procedure
● Non Contention Based :-
● Step 1:- random access preamble assignment via
dedicated signaling in DL .
● Step 2 :- random access preamble on PRACH
in uplink. Power ramp can be applied until
preamble is received.the amount of power
increase is depend on .
● Step 3 :- ENB send a transmission on pdcch idntified
using RA-RNTI actual RAR is on pdsch pointed by
PDCCH with RA-RNTI ,no HARQ,RAR include
RA preamble ID .If UE find the same preamble id in RAR .
UE consider random access response was successful.

19. LONG TERM EVOLUTION 19
SON
SON aim to configure and optimize the network automatically so that the human intraction can be
reduce and the capacity of network should be increase.
Main functions of SON
Self Configuration
Self Optimization
Self Healing
● Self configure :- where newly deployed ENB are configure by automatic installation. process is ...
● An ip address allocated to newly deployed ENB and the information of self configuration sub system
of OAM is given to the ENB.
● A gate way is configure to newly deployed ENB so that the ENB can exchange IP packet with other
internet nodes.
● ENB provides its information including type hardware etc to the self configuration sub-system for
authentication purpose .
● The new ENB is configured based on the transport and radio configuration data .
● The new ENB connect to the normal OAM sub system to the other management system.

20. LONG TERM EVOLUTION 20
SON
● Self Optimization :- Is a process where UE & ENB measurement and performance
measurement are used to auto-tune the network.its start when RF interface is switch on its
collects UE & ENB measurement information and then with the help of external optimization
tool.it auto tune the configure data to optimize the network.
● Self Healing :- Its aim at automatic detection and localization of most of the failure and applies
self healing mechanism to solve several failure classes.
● SON Architechture :- it can be divided into three classes
(a) Centralised SON
(b) Distributed SON
(c) Hybrid SON
● SON use case :-
● ANR
● Coverage and Capacity optimization
● Mobility Roboust optimization
● Mobility Load Balancing Optimization etc.

21. QoS
In LTE Quality of service is applied on radio bearer .
In LTE QoS applied on two types of radio bearer Dedicated bearer and Default bearer.
Default Bearer : when UE attach to the network for the first time it will be assigned default
bearer which remains as long as UE attached . each default bearer comes with an IP
address ,UE can have additional default bearer as well . each default bearer will have a
separate IP address. default bearer only Non GBR . QCI (5-9) assigned to default bearer .
Non GBR does not provide a guaranteed bit rate
Parameter of default bearer : APN-AMBR,UE-AMBR,APN ,IP address,ARP.
APN-AMBR : is the max. allowed total Non-GBR through put to specific APN.
UE-AMBR: is max. allowed total Non-GBR throughput among all APN to a specific UE.
ARP: allocation and retention priority is basically used for deciding whether new bearer
modification or establishment request should be accepted.

22. QoS
Dedicated Bearer : dedicated bearer provides dedicated tunnel to one or more specific traffic
(i.e. voip ,video,etc) dedicated bearer acts as an additional bearer on top of the default
bearer .its does not require a separate IP address .due to the fact only additional default
bearer need an IP address and dedicated bearer always linked to one of the default bearer
established previously .
Dedicated bearer can be sub divided into GBR QCI (1-4) or Non GBR (5-9).
Parameter of dedicated bearer:
Non-GBR: APN-AMBR,UE-AMBR,TFT,ARP,L-EBI.
GBR: GBR,MBR,TFT,ARP,L-EBI.
GBR: Provide guaranteed bit rate per EPS bearer .specified independently for UL/DL.
MBR: The maximum guaranteed bit rate per EPS bearer .specified independently for UL/DL
Traffic Flow Template (TFT) : its always associated with dedicated bearer and while default
bearer may or may not have TFT.

23. QoS
TFT define rules so that UE and network knows which IP packet should be sent on particular
dedicated bearer .its usually has rules on the basis of IP packet destination /source or
protocol used.
L-EBI : Its stands for linked EPS bearer ID .each dedicated bearer always linked to one of
default bearer .L-EBI tells dedicated bearer which default bearer it is attached to.