5.LTE Protocol Principle-44

8/18/2019 5.LTE Protocol Principle-44

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Principles of LTE Protocol

Course objectives:

Understand the architecture of the LTE protocol

Understand the frame structure of the LTE system

Understand functions of each LTE system layer


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Contents

1 System Overview...........................................................................................................................................1

1.1 Overall Architecture of LTE ystem...................................................................................................1

1.! "rotocol Architecture of LTE ystem..................................................................................................!

2 Physical Layer Protocol................................................................................................................................7

!.1 #unctions of "hysical Layer................................................................................................................$

!.! tructure of %adio #rame &%#'............................................................................................................(

!.) "hysical Channel...............................................................................................................................1*

!.+ Transmission Channel........................................................................................................................1*

!., -appin /et0een Transmission Channel and "hysical Channel.....................................................11

3 Data Link Layer..........................................................................................................................................13

).1 Overvie0 of ata Lin2 Layer............................................................................................................1)

).! -AC ub3layer "rotocol...................................................................................................................1,

).!.1 #unctions of -AC ub3layer.................................................................................................1,

).!.! Loical Channel......................................................................................................................1,

).!.) -appin bet0een Loical Channel and Transmission Channel............................................14

).!.+ 5ey Technoloies of -AC Layer..........................................................................................1$

).) %LC ub3layer "rotocol....................................................................................................................1(

).).1 T- -ode................................................................................................................................!*

).).! U- -ode................................................................................................................................!1

).).) A- -ode................................................................................................................................!!

).).+ %LC "U tructure................................................................................................................!)

).+ "C" ub3layer "rotocol..................................................................................................................!+

).+.1 #unctions of "C" Layer.......................................................................................................!+


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).+.! "C" Entity............................................................................................................................!4

).+.) tructure of "C" "U.........................................................................................................!$

4 RRC Layer Protocol...................................................................................................................................29

+.1 #unctions of %%C Layer....................................................................................................................!(

+.! %%C tate..........................................................................................................................................)*

+.) inalin "rocess of %%C Layer.......................................................................................................)1

+.).1 /roadcast "rocess...................................................................................................................)1

+.).! "ain "rocess........................................................................................................................)!

+.).) %%C Connection etup...........................................................................................................)!

+.).+ %%C Connection %econfiuration..........................................................................................))

+.)., %%C Connection %eestablishment.........................................................................................))

+.).4 %%C Connection %elease.......................................................................................................)+

!"S Layer Protocol....................................................................................................................................3

,.1 A and 6A -odel...........................................................................................................................),

,.! 6A Layer "rotocol tates and tate Transition..............................................................................)$

,.) /asic "rocedures of 6A..................................................................................................................)(

,.).1 /asic "rocedures of 6A.......................................................................................................)(

,.).! -appin %elationship bet0een 6A Layer #unctions and /asic "rocedures......................)(


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1 System Overview

Knowledge points:

Overall architecture of the LTE system

Access stratum &A' and non3access stratum &6A'

User plane protocol architecture

Control plane protocol architecture

1.1 Overall Arcitect!re of LTE System

The fiure belo0 is the net0or2 topoloy of the LTE system.

#iure 1.131 Overall architecture of the LTE system

Compared 0ith the U-T system7 the 0ireless transmission technoloy7 air interface

protocol and system architecture of the LTE8AE net0or2 have been revolutioni9ed.

The correspondin 0ireless net0or2 and pac2et core net0or2 are called as E3UT%A6

and Evolved "ac2et Core &E"C' respectively. The 0hole net0or2 system is named as

Evolved "ac2et ystem &E"'.

n the E3UT%A67 " transmission is adopted in the bottom layer communication

bet0een e6ode/s 0hich are interconnected throuh the ;! interface loically. t is


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also often 2no0n as -esh type net0or2. uch net0or2 architecture desin can

effectively support the movability of UE in the 0hole net0or2 to ensure seamless

handover of the user. Each e6ode/ is connected to the --E83


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Chapter , 6A Layer "rotocol

#iure 1.!3! User plane protocol stac2 of the air interface

The follo0in fiure sho0s the control plane protocol stac2.

#iure 1.!3) Control plane protocol stac2 of the air interface

The control plane protocol stac2 contains the non3access stratum &6A'7 %%C7 "C"7

%LC7 -AC and "B layers. Amon them7 the "C" layer provides encryption and

interality protection functions. #unctions e@ecuted by the control plane in %LC and

-AC layers are consistent 0ith those of the user plane. The %%C layer protocol ends at

the e6ode/ and reali9es functions such as broadcastin7 pain7 %%C connection

manaement7 %adio /earer &%/' control7 mobility manaement7 UE measurementreport and control. The 6A layer ends at the --E and achieves functions such as

E" bearer manaement7 authentication7 mobility manaement in idle state7 pain

messae and security control.

The follo0in fiure briefly describes the LET protocol architecture of different layers7

functions and the interaction process bet0een layers. The follo0in fiure presents the

protocol architecture of the e6ode/ side7 0hich is similar to that of the UE side.

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"rinciple of LTE "rotocol

#iure 1.!3+ "rotocol architecture of the LTE system &do0nlin2'

Li2e the U-T system and most mobile communication systems7 the data processin

of the LTE system is divided into different protocol layers. The fiure above describes

the overall protocol architecture of the LTE system in do0nlin2 transmission. The

do0nlin2 data is transmitted in " pac2et. /efore bein transmitted by the air interface7

the " pac2et 0ill be processed throuh multiple protocol layer entities. The follo0in

describes the process in detail.

? "C" layer: The "C" layer e@ecutes the header compression to reduce the bit

stream that must be transmitted by the radio interface. The header compression

mechanism is based on %OC 0hich is a standard header compression

alorithm and has been applied in the U-T and multiple mobile

communication specifications. The "C" layer is also responsible for

encryption and interity protection of transmit data. At the receivin end7 the

"C" protocol e@ecutes decryption and decompression. #or a terminal7 each

radio bearer has a "C" entity.

? %LC layer: The %LC layer is responsible for sementation and connection7

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retransmission process and transmission of hih3level data in seuence.

ifferent from the U-T system7 the %LC protocol of the LTE system is at the

e6ode/7 because the architecture of the radio access net0or2 is flattened at the

LTE system and has only one layer of node>e6ode/. The %LC layer provides

service to the "C" layer in radio bearer mode. Amon them7 an %LC entity is

allocated for each radio bearer of a terminal.

? -AC layer: The -AC layer is responsible for A%D retransmission and

uplin28do0nlin2 schedulin. The -AC layer provides service to the %LC layer

in loical channel mode.

? "B layer: The "B layer is responsible for codin7 decodin7 modulation7demodulation7 multi3antenna mappin and other functions of the telecom

physical layer. The "B layer provides service to the -AC layer in

transmission channel mode.

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" Pysical Layer Protocol

Knowledge points:

#unctions of the physical layer

#rame structure of the physical layer

"hysical resource allocation

"hysical layer channel and mappin relations

".1 #!nctions of Pysical Layer

The physical layer of the air interface in the LTE system is mainly responsible for

providin the lo0er3layer data transmission service to the upper layer. To provide the

data transmission service7 the physical layer shall have the follo0in functions:

? etectin errors of the transmission channel and providin instructions to the

upper layer

? #or0ard error correction EC' and codin of the transmission channel

? ybrid Automatic %epeat %euest &A%D' soft combinin

? %ate matchin and mappin bet0een the transmission channel and the physical

channel

? "o0er30eihtin of the physical channel

? -odulation and demodulation of the physical channel

? Time and freuency synchronism

? -easurin %# characteristics and providin instructions to the upper layer

? --O antenna processin

? Transmit diversity

? /eamformin

? %# processin

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The follo0in briefly introduces the 2ey technical solutions of the physical layer in the

LTE system.

? ystem band0idth: The carrier spacin of the LTE system is 1, 29. The

minimum resource bloc2 of uplin2 and do0nlin2 is 1* 29F that is7 the

band0idth of 1! sub3carriers. The mappin from the data to the resource bloc2

can be in centrali9ed or distributed mode. Throuh reasonable number allocation

of sub3carriers7 the system can achieve fle@ible band0idth confiuration of

1.+G!* -9.

? O#-A and C3#-A: The basic do0nlin2 transmission of the LTE system

adopts the Orthoonal #reuency ivision -ultiple Access &O#-A' mode.The cyclic prefi@ &C"' in the O#- transmission mode is mainly used to

eliminate intersymbol interference effectively. ts lenth determines the anti3

multipath capability and coverae capability of the O#- system. To reach the

coverae reuirements of the cell 0ith the radius of 1** 2m7 the LTE adopts t0o

C" prorams>lon C" and short C" 0hich can be selected accordin to specific

scenario. The short C" proram is basic option7 and the lon C" proram is used

to support lare3rane cell coverae and multi3cell broadcast service. n the

uplin2 direction7 the LTE system adopts the C"3based inle3Carrier #reuency

ivision -ultiple Access &C3#-A' technoloy. The main reason of selectin

the C3#-A as the uplin2 sinal access mode of the LTE system is to reduce

the pea23to3averae po0er ratio&"A"%' of the transmittin terminal and then to

reduce the si9e and cost of the terminal.

? uple@ mode: The LTE system supports t0o basic 0or2 modes>#reuency

ivision uple@ ' and Time ivision uple@ &T' and t0o 2inds of

radio frame structure. The frame lenth is 1* ms in averae

? -odulation systems: The LTE system supports the follo0in modulation

systems: D"57 14DA- and 4+DA-.

? Channel codin: n the LTE system7 the channel codin proram used for the

transport bloc2 is Turbo codin 0ith the codin rate of %H18). t consists of t0o

3state sub3coders and one internal interleaver of Turbo codes. Amon them7 the

Trellis termination proram is adopted in Turbo codin.

? -ulti3antenna technoloy: The LTE system has introduced the --O

technoloy. The simultaneous confiuration of multiple antennas at the

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transmittin terminal and the receivin terminal can reatly enhance the 0hole

capacity of the system. The basic --O confiuration of the LTE system is !I!

antennas in do0nlin2 and 1I! antennas in uplin2. To confiure more antennas

can also be considered &up to +I+'. #or the do0nlin27 the --O technoloy

adopted by the LTE system includes transmit diversity7 spatial multiple@in7

space division multiple access &-A' and precodin. #or the uplin27 the LTE

system adopts the virtual --O technoloy to increase the capacity.

? "hysical layer process: The LTE system covers multiple physical layer

processes7 includin cell search7 po0er control7 uplin2 synchronism7 do0nlin2

timin control7 random access relevant process and A%D. Throuh physical

resource control in the time domain7 freuency domain and po0er domain7 the

LTE system also supports the interference coordination function implicitly.

? "hysical layer measurement: The LTE system supports the physical layer

measurement bet0een the UE and the e6ode/ and reports the correspondin

measurement results to the upper layer. The measurement inde@es are

measurement of co3pilot and inter3pilot handoff7 measurement of handoff

bet0een different radio access technoloies7 timin measurement and

measurement of radio resource manaement.

"." Str!ct!re of $adio #rame %$#&

The structure of the LTE system time domain frame is as sho0n in the fiure belo0.

The total lenth of each %# is T frame H 1* ms7 0hich can be further divided into 1* sub3

frames 0ith the lenth of Tsubframe H 1 ms each. To provide consistent and precise

definition of time7 the LTE system ta2es TsH 18)*$!**** s as the basic time unit. All

time slots in the system are inteer multiples of the basic unit. The time slot in the

follo0in fiure can be represented as T frame H )*$!** Ts and Tsubframe H )*$!* Ts.

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#iure !.!3, tructure of the LTE system time domain frame

Each 1* ms %# contains t0o half3frames 0ith the lenth of , ms. Each half3frame

consists of four data sub3frames and one special sub3frame. The special sub3frame

contains three special slots: 0"T7


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? o0nlin2 hared Channel &L3C': t supports transmittin data 0ithin the

0hole coverae area of the cell and A%D. Lin2 adaptation can be achieved

throuh multiple modulation modes7 encoded modes and transmit po0er. t

supports beamformin7 dynamic or semi3dynamic resource allocation7

discontinuous receivin &%;' of the UE to save po0er and transmission of the

-/- service.

? "ain Channel &"C': t supports transmittin data 0ithin the 0hole coverae

area of the cell. t can be mapped to the physical resources that for the use of

services and other dynamic channel. t supports discontinuous receivin &%;'

of the UE to save po0er and transmission of the -/- service.

? -ulticast Channel &-C': t supports transmittin data 0ithin the 0hole

coverae area of the cell. #or sinle freuency point net0or2 &-/#6'7 it

supports transport combination of multi3cell -/- and adopts semi3static

resource allocation.

? Correspondinly7 the uplin2 transmission channel of the LTE system has the

follo0in types:

? Uplin2 hared Channel &UL3C': t can achieve dynamic lin2 self3adaptation

by adjustin the transmittin po0er and modulation8codin format. t supports

beamformin7 A%D7 dynamic or semi3dynamic resource allocation.

? %andom Access Channel &%AC': t can bear limited control information and

supports the conflict8collision resolution mechanism.

".) *apping +etween Transmission Cannel and Pysical Cannel

The mappin relationship bet0een the transmission channel and physical channel in

the LTE system is as sho0n in the fiure belo0.


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#iure !.,34 Uplin2 and do0nlin2 channel and mappin relationship

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' ,ata Lin- Layer

Knowledge points:

Uplin2 and do0nlin2 L! architecture of the LTE system

-AC sub3layer protocol

%LC sub3layer protocol

"C" sub3layer protocol

'.1 Overview of ,ata Lin- Layer

The data lin2 layer mainly consists of the -AC7 %LC and "C" sub3layers. The

follo0in fiure sho0s the uplin2 and do0nlin2 L! architecture of the LTE system.

#iure ).13$ o0nlin2 L! architecture of the LTE system

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#iure ).13 Uplin2 L! architecture of the LTE system

As sho0n in the fiure above7 the ervice Access "oints &A"' is adopted bet0een

layers as the end3to3end communication interface. The "C" layer provides radio

bearer service to the upper layer7 as 0ell as %obust eader Compression &%OC' and

security protection. The A" bet0een the physical layer and the -AC layer is the

transmission channel. The A" bet0een the -AC layer and the %LC layer is the

loical channel. Therefore7 the -AC layer is mainly responsible for mappin bet0een

the loical channel and the transmission channel and multiple@in multiple loical

channels &such as the radio bearer' to a unified transmission channel &such as the

transport bloc2'.

n the uplin2 and do0nlin2 architecture of the LTE system7 the functions of each sub3

layer are basically the same. The main difference is that the do0nlin2 reflects the

situation of the net0or2 side and processes multiple users 0hile the uplin2 reflects the

situation of the terminal side and only processes one user.

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'." *AC S!/layer Protocol

'.".1 #!nctions of *AC S!/layer

The -AC protocol sub3layer of the LTE system mainly provides effective connection

bet0een the %LC layer service and physical layer. #rom this perspective7 the -AC

layer supports the follo0in functions:

? -appin bet0een the loical channel and transmission channel

? electin transport format7 for instance7 selectin the transport bloc2 si9e and

modulation scheme as the input parameters and providin them to the physical

layer

? "riority manaement of the loical channel in one UE or multiple UEs

? Error correction throuh the A%D mechanism

? "addin

? %LC "U multiple@in and demultiple@in

? -easurin and reportin the service volume

Compared 0ith the -AC layer in the e@istin U-T system7 the -AC layer of the

LTE system has ne0 feature. That is7 each cell has only one -AC entity to achieve all

functions relevant to the -AC layer.

n conclusion7 the service provided to the upper layer by the -AC layer mainly

includes data transmission and radio resource allocation. The service provided to the

-AC layer by the physical layer includes data transmission7 A%D ac2no0ledement

sinalin7 schedulin reuest sinalin and measurement.

'."." Logical Cannel

The -AC layer can provide data transmission service over the loical channel. n this

0ay7 a roup of loical channels are defined by the -AC layer for different types of

data service. Each loical channel has the type definition of transmitted messaes.

Accordin to the type of transmitted messae in each channel7 the loical channel is

divided into t0o cateories: control channel and traffic channel.

1. Control channel: The control channel is responsible for transmittin the control

plane messaes. The control channels provided by the -AC layer have the

follo0in types:

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? /roadcast Control Channel &/CC': The /CC is a do0nlin2 channel used to

broadcast the system control messaes

? "ain Control Channel &"CC': The "CC is a do0nlin2 channel used to

transmit the pain messaes. This channel is used 0hen the net0or2 is una0are

of the cell position of the UE

? Common Control Channel &CCC': The CCC is an uplin2 and do0nlin2 t0o3

0ay channel used to transmit the control messaes bet0een the UE and net0or2.

This channel is used 0hen there is no %%C connection bet0een the UE and

net0or2

? -ulticast Control Channel &-CC': The -CC is a point3to3multipoint

&"T-"' do0nlin2 channel used to transmit the -/- schedulin and control

messaes from the net0or2 to the UE. This channel is only used for the UE to

receive the -/- service.

? edicated Control Channel &CC': The CC is a point3to3point &"T"' t0o3

0ay channel used to transmit the dedicated control messaes bet0een the UE

and net0or2. This channel is used 0hen there is %%C connection in the UE.

!. Traffic channel: The traffic channel is responsible for transmittin the user plane

messaes. The traffic channels provided by the -AC layer have the follo0in

types:

? edicated Traffic Channel &TC': The TC is a "T" channel and is used to

transmit the user plane messaes by a UE. t can be a conte@t t0o30ay channel.

? -ulticast Traffic Channel &-TC': The -TC is a "T-" do0nlin2 channel

used to transmit data from the net0or2 side to the UE. This channel is only used

for the UE to receive the -/- service.

'.".' *apping etween Logical Cannel and Transmission Cannel

Compared 0ith the U-T system7 types of the loical channel and transmission

channel in the LTE system decrease reatly. The mappin relationship is simpler.

The mappin relationship bet0een the loical channel and transmission channel is as

sho0n in the fiure belo0. #or the loical channel in uplin27 the CCC7 CC and

TC are all mapped to the UL3C in transmission channel. #or the loical channel

in do0nlin27 the "CC is mapped to the "C7 the /CC is mapped to the /C or

L3C7 and the CCC7 CC and TC are all mapped to the L3C in the

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transmission channel.

#iure ).!3( -appin relationship bet0een the loical channel and transmission channel

'.".( Key Tecnologies of *AC Layer

'.".(.1 Priority Processing

"riority processin is a main function of the -AC layer. The process of priority

processin is to select one pac2et from different 0aitin ueues and transfer it to the

physical layer 0hich then transmits it throuh the radio interface. n vie0 of the

transmission of different information flo0s such as pure user data7 E3UT%A6 sinalin

&TC loical channel' and E"C sinalin &CC loical channel'7 the process is

very complicated. f the transmitted data is not correctly received7 0hether to

retransmit the data is related to priority processin. Therefore7 the process of priority

processin is closely relevant to the A%D.

/esides7 the -AC layer of the net0or2 side is responsible for priority processin of the

uplin2 since it needs to select from all uplin2 schedulin reuest messaes of multiple

terminals sharin the UL3C transmission channel7 as sho0n in the fiure belo0.

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#iure ).!31* "riority processin of the e6ode/ -AC layer

n uplin2 transmission7 the -AC layer at the terminal side just multiple@es its o0n

multiple uplin2 data flo0s and decides 0hether to transmit the uplin2 schedulin

reuest or the uplin2 data. o0ever7 in the shared channel of the do0nlin27 the e6ode/

shall consider flo0s &or loical channel' transmitted to all users in the cell.

'.".(." +asic Principle of 0A$

The basic principle of A%D is to buffer the data that are not correctly received and

combine the retransmission data and oriinal data. The soft combination mode adopted

in practice depends on the A%D Combinin mechanism. n the Chase Combinin

&CC' proram7 the data sent for the first time is the same as the retransmitted data and

the receivin end combines the 0hole data bloc2. n the ncremental %edundancy &%'

proram7 some ne0 verification information is added to the error bloc2 and the codedsymbols received by the terminal end contain the information different from the data

transmitted for the first time.

n the E3UT%A67 the A%D adopts multiple parallel channels in processin &63

"rocess'. =hen one process 0aits for the AC586AC5 messae7 other processes 2eep

transmittin data.

The A%D adopts the self3adaptation asynchronous retransmission mechanism for the

do0nlin2 and the synchronous retransmission mechanism for the uplin2. n the

synchronous mechanism7 the data can only be retransmitted accordin to the subframe

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6o. transmitted for the first time. n the asynchronous retransmission mechanism7 the

retransmitted data can be transmitted at any time.

The adoption of the synchronous mode in uplin2 is to reduce the protocol overhead.

ince the receivin end can acuire the subframe 6o. 0hen the synchronous mode is

adopted7 there is no need to mar2 the channel 6o. for A%D processin.

The A%D of the E3UT%A6 and that of )< "A and E3C8U"A are similar.

'.' $LC S!/layer Protocol

The %adio Lin2 Control &%LC' protocol is to deliver the data to the peer3end %LC

entity. Therefore7 the %LC has three modes: Transparent -ode &T-'7 Unac2no0leded

-ode &U-' and Ac2no0leded -ode &A-'. The overall architecture of the %LC layer

in fiure belo0 reflects the three transmission modes.

TransmittingT* $LC entity

receivingT* $LC entity

receivingT* $LC entity

TransmittingT* $LC entity

Transmitting2* $LC entity

$eceiving 2*$LC entity

$eceiving 2*$LC entity

Transmitting2* $LC entity

A* $LC entity

A* $LC entity

e3+

2E

SAP.etween

!pperlaters

Logicalcanne

l

Logicalcanne

l

SAP.etween

!pperlaters

2pper layer

Lower layer

2pper layer

Lower layer

#iure ).)311 Overall architecture of the %LC layer

The T- mode is the simplest and does not chane any upper layer data. This mode is

typically applied in the transmission of the /CC or "CC loical channel. t needs

not to ma2e any special process on the %LC layer. The transparent mode entity of the

%LC layer receives the data from the upper layer and transmits it to the lo0er -AC

layer 0ithout any chane. There is no increase in %LC header7 data sementation or

concatenation.

The U- mode can detect the loss of data pac2et7 order and reassemble the data pac2et.

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The U- mode can be used in any dedicated or multicast loical channel. The specific

usae depends on the type of application and e@pected Do. %eorderin the data pac2et

is to order the received disordered data.

The A- mode is the most complicated mode. /esides features supported by the U-

mode7 the A- %LC entity can reuire its peer entity to retransmit the data pac2et 0hen

detectin pac2et lossF that is7 the A%D mechanism. Therefore7 the A- mode is only

applied in the CC or TC loical channel.


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=hen the transmittin T- %LC entity forms the %LC U to the T- &transparent

mode data' "U7 it 0ill not sement or concatenate the %LC U7 nor add any %LC

header. =hen the receivin T- %LC entity receives the T- "U7 it 0ill deliver the

T- "U &%LC U in fact' to the upper layer.

'.'." 2* *ode

The U- %LC entity can deliver8receive the %LC "U throuh the L8UL CC7

L8UL TC7 -CC or -TC loical channel7 as sho0n in the fiure belo0.

#iure ).)31) U- mode transmission

=hen the transmittin U- %LC entity forms the %LC U to the U-

&unac2no0leded mode data' "U7 it 0ill sement or concatenate the %LC U so

that the U- "U fits for the total si9e of %LC "U indicated by the lo0er layer. t

0ill indicate the total si9e of %LC "U 0hen the do0nlin2 notifies the specific

transmission opportunity and add %LC header to the U- "U.

=hen the receivin U- %LC entity receives the U- "U7 it detects if the U-

"U has been received as a duplicate and discards the duplicated U- "U. f the

received one is disordered7 the entity reorders the U- "U. At the same time7 it

detects the lo0er layer. f it finds that the U- "U is lost7 to avoid overmuch delay

in reorderin7 the entity reassembles the %LC U from the ordered U- "U and

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delivers the %LC U in seuence to the upper layer. f it detects that a U- "U

pac2et of a specific %LC U is lost and the received U- "U cannot be

encapsulated to the %LC U7 the entity discards these U- "U pac2ets.

'.'.' A* *ode

The A- %LC entity can deliver8receive the %LC "U throuh the L8UL CC or

L8UL TC loical channel7 as sho0n in the fiure belo0.

#iure ).)31+ A- mode transmission

=hen the transmittin A- %LC entity forms the %LC U to the A-

&ac2no0leded mode data' "U7 it 0ill sement or concatenate the %LC U so that

the A- "U fits for the total si9e of %LC "U indicated by the lo0er layer in

specific occasion. =hen the transmittin A- %LC entity sements and retransmits the

A- "U formed from the upper layer %LC U or the A- "U formed from the

%LC "U7 it 0ill contain relevant %LC header in the %LC "U.

=hen the receivin A- %LC entity receives the %LC "U7 it detects if the %LC "U

has been received as a duplicate and discards the duplicated %LC "U. f the received

one is disordered7 the entity reorders the %LC "U. At the same time7 it detects the

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lo0er layer. f it finds that the %LC "U is lost7 it reuires the peer3end A- %LC

entity to retransmit the %LC "U. ubseuently7 it assembles the ordered %LC "U to

the %LC U and delivers the %LC U in seuence to the upper layer.

'.'.( $LC P,2 Str!ct!re

The format and parameters of the %LC "U are as sho0n in the fiure belo0.

#iure ).)31, tructure of the %LC "U

The %LC header contains the 6. of the %LC "U 0hich is different from that of theU.

One %LC "U consists of the follo0in sements: The last sement of 6o. i U

concatenates n complete Us and then concatenates the first sement of 6o. iKnK1

U &n shall be an inteer reater than or eual to *'.

ifferent from the si9e of the "LC "U in the U-T system 0hich is uasi3static7 the

si9e of the %LC "U in the LTE system can vary dynamically. #or the hih3speed data7

to adopt a bi "U can acuire smaller overheadF 0hile for the lo03speed data7 adopt a

small "U. Therefore7 supportin dynamic "U in the LTE system can achieve the

variation of data rate from thousands bits per second to hundreds meabits per second.

ince the %LC schedulin and rate self3adaptation mechanism are at the e6ode/7 the

LTE system can easily support the dynamic "U mechanism.

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'.( P,CP S!/layer Protocol

'.(.1 #!nctions of P,CP Layer

The "C" protocol layer of the LTE system mainly transmits or receives the pac2et

data of the peer "C" entity. This sub3layer mainly completes the follo0in functions:

" header compression and decompression7 data and sinalin encryption7 and interity

protection of sinalin. The fiure belo0 sho0s the main function model of the "C"

layer user plane and control plane.

#iure ).+314 "C" layer protocol model

On the control plane7 encryption and interity protection are reuired functions. On the

user plane7 robust header compression is reuired function. ata encryption is optional.

The data here can either be the user data or application layer sinalin7 such as " and

%TC".

The "C" provides service to the %%C at the UE side and the upper layer of user plane

or the relay at the e6ode/ side7 includin user plane data transmission7 control plane

data transmission7 header compression7 encryption and interity protection.

The service provided to the lo0er layer by the "C" layer includes transparent data

transmission service7 ac2no0leded data transmission service &includin indication of

successful "C" "U transmission'7 and unac2no0leded data transmission service

&transmission in seuence7 pac2et copyin or discardin'.

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pecifically spea2in7 the user plane of the "C" layer has the follo0in functions:

? eader compression and decompression7 only supportin one compressionalorithm7 that is7 the %OC alorithm

? User plane data transmissionF that is7 transmittin the "C" U data received

from the 6A sub3layer to the %LC layer7 and vice versa

? eliverin the upper3layer "U in seuence in the "C" re3construction

process of the %LC A-

? etectin the lo0er3layer U repeatedly in the "C" re3construction process

of the %LC A-

? %etransmittin the "C" U durin %LC A- handover

? ata encryption

? iscardin U in uplin2 based on the timer

? The "C" layer control plane has the follo0in functions:

? Encryption and interity protection

? Control plane data transmissionF that is receivin the "C" U data from the

%%C layer and for0ardin it to the %LC layer7 and vice versa

? Compared 0ith the "C" layer in the U-T system7 the "C" layer in the LTE

system has the follo0in features:

? imple compression alorithm7 only supportin one compression alorithm

? 6ot supportin none3loss relocation

? upportin encryption

'.(." P,CP Entity

The "C" entity is at the "C" layer. #or a UE7 multiple "C" entities can be

defined. Each "C" entity carryin the user plane data can be confiured to use the

header compression technoloy. Each "C" entity carries the data of a radio bearer. n

the current protocol version7 only the %OC protocol is supported. Each "C" entity

can use one %OC instance at most.

=hether a "C" entity is relevant to the control plane or user plane depends on 0hat

2ind of radio bearer the entity carries the data for. The follo0in fiure sho0s the

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functional schematic diaram of the "C" layer.

#iure ).+31$ #unctional schematic diaram of the "C" layer

'.(.' Str!ct!re of P,CP P,2

The fiure belo0 sho0s the structure of the "C" "U.

#iure ).+31 tructure of the "C" "U

Amon them7 the lenth of the "C" "U is an inteer multiple of a byte and the

lenth of the "C" header can be one or t0o bytes.

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( $$C Layer Protocol

Knowledge points:

#unctions of the %%C layer

%%C layer protocol states and state transition

Typical sinalin process of the %%C layer

(.1 #!nctions of $$C Layer

The radio resource control &%%C' layer is the most important sinalin protocol

supportin multiple functions bet0een the terminal and e6ode/s. #unctions of the

%%C layer include:

? ystem messae bet0een the broadcast 6A layer and the A layer

? "ain function &e@ecuted throuh the "CC loical channel'

? %%C connection setup7 maintenance and release7 includin the allocation of

temporary s bet0een the UE and the E3UT%A67 and the radio bearin

confiuration of sinalin

? ecurity function7 includin 2ey manaement

? Establishment7 modification and release of end3to3end radio bearin

? -obility manaement7 includin UE measurement report7 report control for

inter3cell mobility and inter3%AT mobility7 inter3cell handover7 UE cell selection

and reselection7 and %%C conte@t transmission durin handover

? -/- service notification7 and radio bearin establishment7 modification and

release of the -/- service

? Do manaement function

? UE measurement report and measure control

? Transmission of the 6A messae

? nterality protection of the 6A messae

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(." $$C State

The main function of the %%C protocol is to manae the connection bet0een the

terminal and the E3UT%A6 access net0or2. The follo0in fiure sho0s the state of

the %%C protocol.

#iure +.!31( %%C tate

n fact7 each %%C protocol state represents a 2ind of connection status and describes

ho0 the net0or2 and terminals process the mobility of terminal7 pain messaes and

system information broadcast.

The follo0in table describes specific features of the idle and connected states of the

%%C layer.

Table +.!31 escription of LTE %%C layer state

#eatures of the idle state &%%C3LE state' #eatures of the connected state &%%C3

CO66ECTE'

"L-6 selectionF

ystem information broadcastF

iscontinuous receivin painF

The cell reselects the mobilityF

The UE has a uniue 0ithin the trac2in

area &TA' raneF

6o %%C communication conte@t is saved in

the e6ode/.

The UE has an %%C connection.

The UE has communication conte@t in the E3

UT%A6.

The E3UT%A6 2no0s 0hich cell the UE belons to.

ata can be transmitted and received bet0een the

net0or2 and terminal.

-obility manaement of net0or2 control7 includin

handover or net0or2 assisted cell chane &6ACC' to


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#eatures of the idle state &%%C3LE state' #eatures of the connected state &%%C3

CO66ECTE'

The terminal can monitor and control the channel to

confirm 0hether the net0or2 has confiured shared

channel resources for it.

The e6ode/ can confiure the discontinuous

receivin &%;' period accordin to the active

situation of the terminal7 0hich saves the battery and

raises the utili9ation of radio resource.

n the U-T system7 the UE has five states: idle7 CELL3C7 CELL3#AC7 CELL3

"C7 and U%A3"C. Compared 0ith the %%C state in the U-T system7 the %%C

state in the LTE system is reatly reduced7 0hich indicates that the %%C state machine

in the LTE system is simpler and the comple@ity of the system is further reduced.

Li2e the U-T system7 after the startup7 the terminal selects a proper cell from the

desinated "L-6 to reside. =hen the UE resides in a cell7 it can receive system

information and cell broadcast messaes. 6ormally7 the UE needs to e@ecute the

reistration process for the startup for the first time7 0hich completes mutual

authentication and enables the net0or2 to acuire the basic information of the UE.

After that7 the UE can be in idle state all the time until the %%C connection is

established. The UE can enter into the connected state only after the %%C connection is

set up. ere7 the UE can interact data 0ith the net0or2. After the UE releases the %%C

connection7 the UE transits from the %%C3CO66ECTE state to the %%C3LE state.

(.' Signaling Process of $$C Layer

(.'.1 +roadcast Process

The UE acuires the A and 6A system information broadcasted by the E3UT%A6

throuh the system information reuest process.

E3UT%A6

MasterInformationBlock

UE

SystemInformationBlockType1

SystemInformation

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=hen the e6/ cell is established successfully7 the e6/ sends the system information at

the air port: -asternformation/loc27 ystemnformation/loc2Type17

ystemnformation7 mainly includin the cell selection and reselection information of

the UE in idle state.

(.'." Paging Process

"ain is used to notify the UE in LE or CO66ECTE state of the chane of

system information.

After the pain information is submitted to the upper layer7 the %%C connection setup

process may be initiated subseuently.

(.'.' $$C Connection Set!p

This process is used to set up the %%C connection7 includin conflict resolution and

%/1 setup. At the same time7 the initial 6A messae is send from the UE to the E3

UT%A6.

(.'.( $$C Connection $econfig!ration

This process is used to modify the %%C connection and mainly achieves the follo0in

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functions:

? %/ setup7 modification and release

? E@ecute s0itchover

? Transparent transmit the 6A messae from the E3UT%A6 to the UE.

(.'.) $$C Connection $eestalisment

This process is used to reestablish the %%C connection.

Application scenarios:

? %adio lin2 failure

? 0itchover failure

? nter3%AT failure

? nterity chec2in failure

? %%C connection reconfiuration failure

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(.'.4 $$C Connection $elease

This process is used to release the %%C connection and mainly achieves the follo0in

functioins:

? %elease the radio resource

? %elease the established radio bearer

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) 3AS Layer Protocol

Knowledge points:

A model and 6A model

6A layer protocol states and state transition

-appin relationship bet0een 6A layer functions and basic procedures of the 6A

layer

).1 AS and 3AS *odel

The follo0in fiure sho0s the A and 6A model. The model is divided into t0o

layers>A and 6A and crosses multiple entities such as the terminal7 radio access

net0or2 and pac2et core net0or2.

#iure ,.13!* A and 6A -odel

The A layer is mainly responsible for connection 0ith the 0ireless interface. t is not

limited to the 0ireless part of the radio access net0or2 and terminal7 but also supports

some special functions relevant to the core net0or2.


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supports the follo0in functions:

? %adio bearer manaement: includin the allocation7 setup7 modification andrelease of radio bearer

? %adio channel processin: includin channel codin and modulation

? Encryption: t only refers to its o0n encryption process. The initiali9ation of

encryption and selection of security alorithm are responsible by the 6A layer.

/esides7 the end3to3end encryption dependin on the application may also be

used7 such as J"6.

? -obility manaement: such as handover7 cell selection and reselection

/y contrast7 the 6A layer is mainly responsible for access irrelevant or radio access

independence functions and process and achieves the follo0in functions:

? ession manaement: includin session setup7 modification and release7 as 0ell

as Do neotiation.

? User manaement: includin user data manaement7 adherence and de3

adherence

? ecurity manaement: includin the authentication bet0een the user and

net0or2 and encryption initiali9ation

? Charin

n the


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&E--' 0hich supports


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UT%A6 system and transition bet0een states.

#iure ,.!3!1 "rotocol states in the E3UT%A6

The above fiure sho0s that the LTE3LE state corresponds to the UE in the %%C3

LE state7 the LTE3ACTJE state corresponds to the UE in the %%C3CO66ECTE

state and the LTE3ETACE state corresponds to the UE 0ithout the %%C entity.

=hen po0er3on7 the terminal enters the LTE3ETACE state. Later7 the terminal

e@ecutes the reistration process and enters the LTE3ACTJE state. Throuh this

process7 the terminal can acuire the C3%6T7 TA3 and " address and set up security

contacts throuh the authentication process. f there is no other service7 the terminal

can release the C3%6T. t enters the LTE3LE state after acuirin the discontinuous

receivin &%;' period assined to the user to receive pain channel. =hen the user

has ne0 service reuirement7 it can acuire the C3%6T throuh %%C connection

reuest &random access process'. The terminal then transits from the LTE3LE state to

the LTE3ACTJE state. n the LTE3ACTJE state7 if the terminal moves to the

unac2no0leded "L-6 area or the de3reistration process is e@ecuted7 the C3%6T7

TA3 and " address of the user 0ill be 0ithdra0n and the terminal enters the LTE3

ETACE state. #or the user in the LTE3LE state7 if the TA rene0al process

e@ecuted by the user periodically times out7 the TA3 and " address 0ill be

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0ithdra0n and the user terminal 0ill be s0itched to the LTE3ETACE state.

).' +asic Proced!res of 3AS

).'.1 +asic Proced!res of 3AS

The basic procedures of 6A is as sho0n in the table belo0.

Table ,.)31 /asic procedures of the 6A

/asic procedure nitial messae %esponse messae

uccessful Unsuccessful

Authentication

procedure

AUTE6TCATO6

%EDUET

AUTE6TCATO6

%E"O6E

AUTE6TCATO6

%EECT

Attach procedure for

E" services

ATTAC %EDUET ATTAC ACCE"T ATTAC %EECT

etach procedure ETAC %EDUET ETAC ACCE"T

"ain procedure %EDUET "A


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etach procedure UE reuested "6 connectivity procedure

Trac2in area updatin procedure UE reuested "6 disconnect procedure

ervice reuest procedure UE reuested bearer resource allocation procedure

"ain procedure UE reuested bearer resource modification procedure

Transport of 6A messaes procedure E- information reuest procedure

5.LTE Protocol Principle-44

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