Post on 23-Dec-2015
LTE Protocol Principle
ZTE University
Objectives
After the course,you will: Understand the Protocol Structure of Control Plane and
User Plane Understand the Frame Structure Understand the Channel Know the MAC Layer Function Know the RLC Layer Function Know the PDCP Layer Function
Contents
Protocol Structure Physical Layer Protocol MAC Layer Protocol RLC Layer Protocol PDCP Layer Protocol
Protocol Structure on Control-Plane
UE eNodeB MME
eNB
PHY
UE
PHY
MAC
RLC
MAC
MME
RLC
NAS NAS
RRC RRC
PDCP PDCP
NAS functions: Certification Authentication, Security controlMobility processing in Idle modePaging launch in Idle mode
RRC functions: Broadcast Paging Link managementWireless bearing control MobilityUE measurement report and control
PDCP performs the function of encryption and integrity protectionRLC functions: PDU transmissionARQPacket assembly and disassembly
MAC functions: Scheduling HARQLogic channel priority processing PDU packetizing and demultiplexingPhysical layer
(L1) functions: Wireless access Power control MIMO
Protocol Structure on User-Plane
UE eNodeB MME
eNB
PHY
UE
PHY
MAC
RLC
MAC
PDCPPDCP
RLC
SAE Gateway
RLC performs the following functions: PDU transmissionARQPacket assembly and disassembly
PDCP performs the following functions: Header compression Encryption
MAC performs the following functions: Scheduling HARQLogic channel priority processing PDU multiplexing and de-multiplexing
Physical layer (L1) performs the following functions: Wireless access Power control MIMO
Contents
Protocol Structure Physical Layer Protocol
Basic Concepts Uplink and Downlink Physical Layer process Physical Procedure
MAC Layer Protocol RLC Layer Protocol PDCP Layer Protocol
Frame Structure
FDD frame structure
TDD frame structure
#0 #1 #2 #3 #19#18
A wireless frame, Tf = 307200Ts = 10 ms
A timeslot, Tslot = 15360Ts = 0.5 ms
A sub-frame
One slot, Tslot=15360Ts
GP UpPTSDwPTS
One radio frame, Tf = 307200Ts = 10 ms
One half-frame, 153600Ts = 5 ms
30720Ts
One subframe, 30720Ts
GP UpPTSDwPTS
Subframe #2 Subframe #3 Subframe #4Subframe #0 Subframe #5 Subframe #7 Subframe #8 Subframe #9
Physical Resource Block
One physical resource block (RB) contain OFDM symbols on the time-domain and
sub-carriers on frequency-domain.
The number of and
are determined by the CP type and the subcarrier interval.
DLsymbN OFDM symbols
One downlink slot slotT
0l 1DLsymb Nl
RB
scD
LR
BN
N
subc
arri
ers
RB
scNsu
bcar
rier
s
RBsc
DLsymb NN
Resource block
resource elements
Resource element ),( lk
0k
1RBsc
DLRB NNk
DLsymbN
RBscN
DLsymbN
RBscN
Resource Grouping
RE (Resource Element): The minimum resource unit which is a symbol in time-domain and a subcarrier in frequency-domain
RB (Resource Block): A resource unit allocated by service channel resource. It is a timeslot in time-domain and 12 subcarriers in frequency-domain.
REG (Resource Element Group): a resource unit and it is allocated for control channel resource, it composed of 4 REs
CCE (Channel Control Element): A resource unit allocated by PDCCH resource, it composed of 9 REGs
RBG (Resource Block Group): A resource unit and it is allocated for the service channel resource, it composed of a group of RBs.
Concept of REG
l = 0
RS
RS
RS
RS
l = 1
k = 77
k = 72
k = 78
k = 83
l = 2
1Tx or 2Tx configured
l = 0 l = 1
k = 77
k = 72
k = 78
k = 83
l = 2
4Tx configured
7261212 PRB0 nk6min,
PRB DLRBNn
RS
RS
RS
RS
RS
RS
RS
RS
REG Diagram
464 – 110
327 – 63
211 – 26
1≤10
(P)
RBG SizeSystem Bandwidth
DLRBN
Concept of RBG
RBG is used for resource allocation of service channel One RBG is composed of a group of RBs. The number of RBG is related with the system bandwidth.
Concept of CCE
CCE is used in PDCCH allocation. PDCCH allocation is made after PCFICH and
PHICH. One CCE include 9 REGs. CCE is numbered from
0. Total number of CCEs is determined by the
number of PDCCH-occupied symbols.
CP,Subcarrier interval and OFDM Symbol
Relations between CP Type and Subcarrier Interval and OFDM Symbols
Subcarrier Interval
Number of OFDM Symbols (one slot)
Number of RB-Occupied Subcarriers
Corresponding REs in One RB
Normal CP 15KHz 7 12 84
Extended CP
15KHz 6 12 72
7.5KHz 3 24 72
One RB is composed of 12 subcarriers in the frequency-domain, i.e. 180KHz=15 x 12
(for normal CP)
RB and Bandwidth
The Number of RBs in Different Bandwidths
Occupied bandwidth = subcarrier interval x number of subcarriers in one RB x number of RBs
Subcarrier Interval = 15KHz The Number of subcarriers in one RB = 12 Remark: Maximum number of RBs is 110 in current protocols
Nominal bandwidth
(MHz)
1.4 3 5 10 15 20
Number of RBs 6 15 25 50 75 100
Actually occupied
bandwidth
(MHz)
1.08 2.7 4.5 9 13.5 18
Contents
Protocol Structure Physical Layer Protocol
Basic Concepts Uplink and Downlink Physical Layer process Physical Procedure
MAC Layer Protocol RLC Layer Protocol PDCP Layer Protocol
Physical Downlink Channel and Signal
The LTE downlink includes the following physical channels: Physical-control-format indication channel (PCFICH) Physical broadcast channel (PBCH) Physical Hybrid-ARQ indicator channel (PHICH) Physical downlink control channel (PDCCH) Physical downlink shared channel (PDSCH) Two physical-layer signals: RS (reference signal) P (S) -SCH (synchronized channel)
Resource Allocation
Remark:This diagram is to display the effect of the resource allocation. Each square indicates “time-domain length of a symbol x resource of 12 subcarriers”. It is neither RE nor RB.
SCH (synchronization channel)
SCH includes P_SCH and S_SCH. The frequency-domain is located in the 72 subcarriers near direct current. Only 62 subcarriers are actually occupied. Other 10 subcarriers do not hold synchronization sequences.
There are two same P-SCHs in a wireless frame. Their time-domain is located in the last symbol of the slot no.0 and the slot no. 10.
There are also two S-SCHs in a wireless frame. Their time-domain is located in the penultimate symbol of the slot no.0 and the slot no. 10.
0 1 2 3 4 5 6 0 1 2 3 4 5 6
Slot no. 0
10ms radio frame
S-SCHP-SCH
Slot no. 10
Location of PSS and SSS
PBCH (physical broadcast channel)
PBCH bears the BCH-contained system information such as downlink system bandwidth, system frame number (SFN), PHICH duration, and resource-size indication information.
Each No.0 sub-frame has four PBCH signals of OFDM symbols.
Physical resource mapping on each antenna
port
OFDM modulation
OFDM modulation
OFDM modulation
An 1
An 0
An P
Cell interference enhancing
Modulation mapping
Layer mapping
Pre-programming
BCH TB
CRC adding
Signal program-
ming
Rate matching
PCFICH (physical-control-format indication channel)
PCFICH and E-Node B are transmitted in each sub-frame, informing UE of the OFDM symbols that PDCCH occupies in a sub-frame. The OFDM symbols are indicated by CFI which can be valued as 1, 2, 3, 4 (4 is reserved).
Signal program-
ming
Interference enhancing
Modulation mapping
Layer mapping
Pre-programming
RE mapping
OFDM symbol generating
CFI
PHICH (physical HARQ indication channel)
PHICH Channel bearing the NAK/ACK responding information of the eNodeB.
Two PHICH durations in one sub-frame : 1. short PHICH 2. long PHICH; This duration is indicated by 1 bit in PBCH.
In each downlink sub-frame, PHICH needs to be sent. Multiple PHICH groups can be sent at the same time. Define one PHICH group to be mapped from multiple ones to a PHICH in the same RE.
Repetition(RF=3)
ModulationLayer
MappingPrecoding RE mapping
OFDM modulation
Spreading & scrambling
ACK/NACK
PDCCH (physical downlink control channel)
PDCCH bearing scheduling and other control information: Transmission format, resource allocation, uplink scheduling permission, power control and uplink-transmission-related ACK/NACK;
All the information can group multiple types of control information (DCI) format which is mapped to the first n (n<=4) OFDM symbols in each sub-frame. The value of n is indicated by CFI in the PCFICH channel.
In a sub-frame, we can transmit multiple PDCCHs. One UE can monitor one group of PDCCH. Each PDCCH is sent in one or more control channel elements (CCE) to achieve the different PDCH encoding rates by integrating various numbers of CCEs.
PDCCH supports 4 types of physical-layer formats which occupy one, two, four, and eight CCEs respectively.
CRC adding
User interference enhancing
Channel encoding
Rate matching
Merge the
PDCCH channels inside the
cell
CRC adding
User interference enhancing
Channel encoding
Rate matching
CRC adding
User interference enhancing
Channel encoding
Rate matching
Physical resource mapping on each antenna
port
OFDM modulation
OFDM modulation
OFDM modulation
An 1
An 0
An P
Cell interference enhancing
Modulation mapping
Layer mapping
Pre-coding
PDCCHDCIn
1DCI
2DCI
PDSCH (physical downlink service channel)
CRCadding
Bit block division
Turbo coding Bit block
cascading
1st data flow
Bit flow Interference
enhancing
Modulation mapping
Bit block cascadin
g
Bit flow Interference
enhancing
Modulation mapping
Layer mapping
1. Single antenna 2. Multiplexing 3. Diversity
Pre-coding
1. Single antenna 2. Multiplexing 3. Diversity
RE mapping
RE mapping
OFDM signal generating
OFDM signal generating
Symbol flow
Symbol flow
E-Node B baseband – Service channel processing link Antenna
port0
Antenna port
P
Turbo coding
Rate matching
Rate matching
CRCadding
Bit block division
Turbo codingM data
flow Turbo coding
Rate matching
Rate matching
Power factor
Power factor
Physical Uplink Channel and Signal
The LTE uplink includes the following physical channels: Physical random access channel (PRACH) Physical uplink control channel ( PUCCH) Physical uplink shared channel (PUSCH)
Two physical-layer signal: Demodulation reference signal (DRS) Sounding reference signal (SRS)
Enhance interference
ModulateTransfer pre-
programmed codesMap resource
Generate SC-FDMA signal
PUSCH (Physical Uplink Shared Channel)
Bearing uplink service information Adding interference: Using UE dedicated interference code Performing modulation: Supporting QPSK, 16QAM and
64QAM modulation Transmitting pre-programmed codes: Divide the input
symbols into groups and pre-program codes, i.e. DFT
Mapping to RE: From the 1st timeslot of the sub-frame, map k and I in turn.
Generating SC-FDMA signal: IDFT
PUSCHscsymb MM
PUCCH (Physical uplink control channel)
6 formats used to bear HARQ-ACK, CQI, SR information
For the same UE, PUCCH does not transmit with PUSCH.
Supports multiple formats: Different formats determine different modulations and different bytes in each sub-frame
PUCCH
formats
Modulati
on
Number of bytes in each
sub-frame
1 N/A N/A
1a BPSK 1
1b QPSK 2
2 QPSK 20
2aQPSK+BP
SK21
2bQPSK+Q
PSK22
PUCCH (Continuing)
Format 1 transfers SR information and sends constant 1.
Format 1a/1b transfers HARQ-ACK, BPSK modulation in 1 byte, and QPSK modulation in 2 bytes.
Format 2 transfers CQI information. Program CQI to 20 bit and performs QPSK modulation.
Format 2a/2b transfers the hybrid information of CQI and HARQ-ACK. Program CQI signal to 20 bit and perform QPSK modulation. For HARQ-ACK, perform BPSK/QPSK modulation.
PRACH (physical random access channel)
Frame structure
Different Preambles
Preamble generation Generated by the
Zadoff-Chu sequence in zero-related region
SequenceCP
CPT SEQT
6RB
10, ZC
)1(
ZC
Nnenx N
nunj
u
)mod)(()( ZCCS, NvNnxnx uvu
LTE Uplink/Downlink Mapping
BCCH PCCH CCCH DCCH DTCH MCCH MTCH
PCH DL-SCH MCHBCH
PBCH PDSCH PMCH
Logical Channel
Transmission Channel
Physical Channel
CCCH DCCH DTCH
UL-SCH
PRACH PUSCH
RACH
PUCCH
Downlink
Downlink
Logical Channel
Transmission Channel
Physical Channel
Contents
Protocol Structure Physical Layer Protocol
Basic Concepts Uplink and Downlink Physical Layer process Physical Procedure
MAC Layer Protocol RLC Layer Protocol PDCP Layer Protocol
Physical-layer process – Cell SearchStart
End
Symbol timing, frequency shift estimating, sector ID
identifying
Frame synchronizing, cell group ID identifying, CP-
type blind detecting
RS identifying, cell identifying, antenna
configuration identifying
complete
with
primary
synchroni
zation
signal
and time-
domain
complete
with
secondar
y
synchroni
zation
signal
and
frequency
-domain
Physical-layer process –Power Control
Open-loop power control: Decide a starting transmit power of UE transmit power as the basis for closed-loop control adjustment.
Closed-loop power control: eNodeB measures SINR of PUCCH/PUSCH/SRS signal, then compares SINR with SINRtarge to determine the TPC command (what’s informed is power step size.), finally informs UE through PDCCH to determine the transmit power of uplink signal on the corresponding sub-frame.
Outer-loop power control: Controlled by the upper layer Inner-loop power control
Physical-layer process –Random Access
Random access process can be used in the following situations: Access at RRC_IDLE status Access when the wireless link fault occurs Access in handover Access at RRC_Connected status
When there are downlink data (eg. The uplink is at non-synchronization status.)
When there are uplink data (eg. The uplink is at non-synchronization status or no PUCCH resource can be used for scheduling request.)
Physical-layer process –Random Access
Random access based on competitiveness Used in the five mentioned situations UE selects a preamble sequence randomly in the
available preamble set in a competitive way. Possible collision: two UEs use the same preamble
sequence. Perform the synchronization process through four steps.
The fourth step is used to solve the collision. Random access based on non-competitiveness
In handover or when the downlink data arrive The BS allocates a preamble sequence. Perform the synchronization through three steps without
solving the collision.
Random Access Process (Based on Competitiveness)
Step1: UE sends Msg1 through PRACH, (RACH
-》 PRACH) eNB measures the distance between UE and BS
according to the received preamble, and generates timing adjustment quantity.
Step2: eNB sends Msg2 and Msg2 through PDSCH (DL-
SCH -》 PDSCH) The location is indicated by PDCCH, no HARQ. Msg2 is the grant of Msg4. If UE fails to receive the
RA respondence in a time window, this RA process is terminated; otherwise it goes to step3.
Step3: UE sends Msg3 and through PUSCH (UL-SCH
-》 PUSCH), HARQ eNB detects Msg3 and generates ACK/NACK.
Step4: eNB sends Msg4 for collision detection, HARQ UE finds that the UE of its own NAS-layer ID is
sending ACK.
UE eNB
MSG1
MSG2
MSG3
MSG4
1
2
3
4
Contents
Protocol Structure Physical Layer Protocol MAC Layer Protocol RLC Layer Protocol PDCP Layer Protocol
Structure of Layer 2
PDCP
RLC
MAC
RRC
PHY
Layer 2 is split into the following sub layers : MAC, RLC and PDCP.
Layer 2
Layer 3
Layer 1
Introduction to MAC
Resides on layer 2 of LTE wireless protocols (L2 ; L2 also includes RLC and PDCP)
Used to allocate the wireless resources (time, frequency (number of RBs and location), number of emission layers, number of antenna, and transmit power) to users
Resides in both E-Node B and UE, but has different functions.
Random Access Control
PCCH BCCH CCCH DCCH DTCH MAC-control
Upper layers
PCH BCH DL-SCH UL-SCH RACH
Lower layer
(De-) Multiplexing
Logical Channel Prioritization (UL only)
HARQ
Control
MAC structure overview, UE sideMAC structure overview, UE side
RLCRLC
PHYPHY
The Overview of MAC Structure
Functions of MAC sub layer
MAC
MultiplexingMultiplexing
UE priority handlingUE priority handling
TX Format SelectionTX Format Selection
De-multiplexingDe-multiplexing
Logical channels priorityLogical channels priority
Error correction (HARQ)Error correction (HARQ)
Scheduling Info ReportingScheduling Info Reporting
Mapping of ChannelsMapping of Channels
MAC Function
At UE side Mapping between the logic channel and transmission channel MAC SDUs multiplexing/de-multiplexing MAC PDU HARQ Buffer status report (BSR)
At eNodeB side Mapping between the logic channel and transmission channel MAC SDUs multiplexing/de-multiplexing MAC PDU HARQ Scheduling among UE of different priorities (dynamic scheduling,
semi-persistent scheduling) Selecting transmission format (MCS) Priority processing among different logic channels in the same UE
Functions of MAC sub layer
Services related to MAC sub layer
Data transfer Signalling of HARQfeedbackSignalling of Scheduling RequestMeasurements
RLCMACData transferRadio resource allocationPHY
Services expected from physical layer
Services provided to upper layers
Key Technology at MAC Layer- Fast Scheduling
Basic concept: Fast scheduling means fast service.
LTE FDD: 1ms. LTE TDD downlink: 1ms - 4ms
(related with uplink/downlink configuration)
LTE TDD uplink: 1ms - 10ms (related with uplink/downlink configuration) UMB: 1ms.
WiMAX TDD: 5ms. WCDMA HSDPA: 2ms. CDMA 2000 1x EV-DO:
1.667ms.
Scheduling modes: TDM, FDM, SDM
Key Technology at MAC Layer- Fast Scheduling-Classification
According to resource-occupied time:
Persistent scheduling (static scheduling)
Semi-persistent scheduling (semi-static scheduling)
Dynamic schedulingEvery M x TTI occupies N x RB. It turns to dynamic
scheduling in retransmission. For VoIP, every 20 TTIs occupies 2
RBs.
Determined according to channel status, buffer status, and remained resources.
Constantly occupies resources
Key Technology at MAC Layer- Fast Scheduling-Classification
According to resource-occupied time: Persistent scheduling (static
scheduling) Semi-persistent scheduling (semi-
static scheduling) Dynamic scheduling
Constantly occupies resources
Every M x TTI occupies N x RB. It turns to dynamic
scheduling in retransmission. For VoIP, every 20 TTIs occupies 2
RBs.
Determined according to channel status, buffer status, and remained resources.
Key Technology at MAC Layer- Fast Scheduling-Classification
Dynamic scheduling is classified according to multiplexing modes:
Time-domain scheduling (TDM) Frequency-domain scheduling
(FDM) Space-domain scheduling
(SDM)
Occupies part or all of RBs.
Occupies part or all of TTIs.
Occupies a part or all of RBs/TTIs but only a part of antenna resources.
Dynamic scheduling is classified according to fairness and throughput rate:
Polling (RR) MAX-C/I (MAX-TB). General proportional fairness (G-PF) Torsten proportional fairness (T-PF)
Best fairness but low
throughput
Better fairness and
higher throughput
Worse fairness but highest throughput
Better fairness and better throughput than G-PF
Key Technology at MAC Layer- Fast Scheduling-Classification
Key Technology at MAC Layer- Fast Scheduling-Classification
Dynamic scheduling is classified according to fairness and throughput rate:
Polling (RR) MAX-C/I (MAX-TB). General proportional
fairness (G-PF) Torsten proportional fairness
(T-PF)
Best fairness but low
throughput
Worse fairness but
highest throughput
oughputHistoryThr1
)(12
1
i
iTBFF
ngMultiplexi SpaceFor , oughput_2HistoryThr
)2(
oughput_1HistoryThr
)1(
Diversity TX , oughput_1HistoryThr
)1(
TBTB
ForTB
FF
Select the UE with the best fair factor (FF):
Round robin (RR)
MAX-C/I (MAX-TB).
General proportional fairness (G-PF)
Torsten proportional fairness (T-PF)
ngMultiplexi SpaceFor , oughput_2HistoryThr
)2(
oughput_1HistoryThr
)1(
Diversity TX , oughput_1HistoryThr
)1(
TBTB
ForTB
FFoughputHistoryThr1
)(12
1
i
iTBFF
2
1
)(i
iTBFFgtSchedulinI_SinceLasNumberOfTTFF
Key Technology at MAC Layer- Fast Scheduling-Classification, Algorithm
Dynamic scheduling is classified
according to the frequency selection
(FS):
Broadband scheduling (non-FS)
Sub-band scheduling (FS)
Operation is complicated but it can fully use the channel status. The
system performance is good.
Operation is simple but it cannot fully use the channel status.
The system performance is poor.
Key Technology at MAC Layer- Fast Scheduling-Classification
Dynamic scheduling is classified according to QoS:
QoS scheduling
BE scheduling
Can guarantee the QoS.
Cannot guarantee the QoS.
Key Technology at MAC Layer- Fast Scheduling-Classification
Key Technology at MAC Layer: AMC
Time-domain AMC
Frequency-domain
AMC
Space-domain AMC
SINR
Time
UE 1
UE 2
UE 3
TTI 1 TTI 2 TTI 3 TTI k TTI m
SINR
Frequency
UE 1
UE 2
UE 3
SubBand 1 SubBand 2 SubBand 3 SubBand k SubBand m
Key Technology at MAC Layer: AMC Principle
QPSK, 16QAM and 64QAM
“Continuous” encoding rate (0.07 - 0.93)
eNode B
UE
2. To check buffer.
3. To schedule a UE4. To issue a HARQ Process
UE
5. To set modulation, RBs, Layer, RV, etc.
0 5 10 15 20 25 300
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5x 10
7
Th
rou
gh
pu
t [b
ps
]
SNR [dB]
SCM-C 2x2, 50 RBs
chan_est ideal; 0.5 QPSK chan_est ideal; 0.5 16QAM chan_est ideal; 0.5 64QAM chan_est mmse; 0.5 QPSK chan_est mmse; 0.5 16QAM chan_est mmse; 0.5 64QAM
Key Technology at MAC Layer: HARQ
HARQ = FEC + ARQ. In LTE, FEC is a Turbo code attached with QPP.
SAW N-Channel (FDD uplink: 8; FDD downlink: 1 – 8; TDD uplink: related with timeslot configuration and a fixed number; TDD downlink: related with timeslot configuration).
Merging way of HARQ: CC/FIR/PIR. Synchronous HARQ and asynchronous HARQ Self-adaptive HARQ and non-self-adaptive HARQ
Key Technology at MAC Layer: HARQ Downlink Asynchronous Self-Adaptation
In order to make full use of channels, eNodeB can send new data blocks before receiving UE’s ACK/NACK.
P1 P2P1 P2P1 P2
P1
UE1 UE2 UE3 UE4
Key Technology at MAC Layer: HARQ Uplink Synchronous Self-Adaptation
Synchronous self-adaptation: When eNodeB sends UE NACK and PDCCH Format 0, it indicates that UE should resend in on this newly allocated RB.
PUSCH PHICH: sends NACK
PDSCH
>= 3ms
PDCCH Format 0: sends new authorization
Key Technology at MAC Layer: HARQ Uplink Synchronous Non-Self-Adaptation
Synchronous non-self-adaptation: When eNodeB sends UE NACK and does not send PDCCH Format 0, it indicates that UE should resend on the previously allocated RB.
PUSCH PHICH: sends NACK
PDSCH
>= 3ms
CCCH DTCHDCCH
RACH UP-SCH PCH DL-SCHBCH
PCCH DTCHBCCH CCCH DCCH
Transport CH
Logical CH
DOWN LINK UP LINK
MCH
Mapping between Logical CHs & Transport CHs
Contents
Protocol Structure Physical Layer Protocol MAC Layer Protocol RLC Layer Protocol PDCP Layer Protocol
Overview of RLC
Overview model of the RLC sub layer
Functions of RLC
TM data transfer
UM data transfer
AM data transfer
Deliver indication
Data transfer
Transmissionopportunity
Total size of the RLC PDU(s)
MAC RLC PDCP
Services related to RLC sub layer
Transparent Mode
An RLC entity in transparent mode can send/receive RLC PDU through the logic channels, such as BCCH, DL/UL CCCH and PCCH
Transmissionbuffer
Transmitting TM-RLC entity
TM-SAP
radio interface
Receiving TM-RLC
entity
TM-SAP
UE/E-Node B E-Node B/UE
BCCH/PCCH/CCCH BCCH/PCCH/CCCH
Non-Confirmation Mode
An RLC entity in non-confirmation mode can send/receive RLC PDU through the logic channels, such as DL/UL DCCH, DL/UL DTCH, MCCH/MTCH.
Compared with 3G, the UM mode does not support the encryption/decryption function which is processed in PDCP.
Transmissionbuffer
Segmentation &Concatenation
Add RLC header
Transmitting UM-RLC entity
UM-SAP
radio interface
Receiving UM-RLC
entity
UM-SAP
UE/E-Node B E-Node B/UE
DCCH/DTCH/MCCH/MTCH DCCH/DTCH/MCCH/MTCH
Receptionbuffer & HARQ
reordering
SDU reassembly
Remove RLC header
Confirmation Mode
An RLC entity in confirmation mode can send/receive RLC PDU through the logic channels, such as DL/UL DCCH, DL/UL DTCH
Transmissionbuffer
Segmentation &Concatenation
Add RLC header
Retransmission buffer
RLC control
Routing
Receptionbuffer & HARQ
reordering
SDU reassembly
DCCH/DTCH DCCH/DTCH
AM-SAP
Remove RLC header
Contents
Protocol Structure Physical Layer Protocol MAC Layer Protocol RLC Layer Protocol PDCP Layer Protocol
Overview of PDCP
The E-UTRAN protocol structure involves two layers: radio network layer (RNL) and transmission network layer (TNL).
PDCP separates the transmission technology on TNL from the air-interface processing technology on E-UTRAN.
PDCP maps the upper-layer protocol characteristics to the lower-layer air interface protocol characteristics and thus enables the LTE protocol to bear IP packets between UE and E-Node B through transparent transmission provides for the upper layer.
PDCP Structure
ROHC ROHC Integrity protection
Encryption Encryption
User Plane Control Plane
EPC Data from S-GW NAS Signal from MMERRC Signal from eNodeB
Structure of PDCP Entity
PDCP Functions
PDCP serves SRB and DRB mapped on the logic channels DTCH and DCCH. The functions provides on DTCH and DCCH are as follows:
DTCH channel PDCP packet transmission SN sequence number maintenance Header compression and decompression of IP data flow Encryption and decryption Resorting of lower-layer PDU data in switch-over
DCCH channel PDCP packet transmission SN sequence number maintenance Integrity protection Encryption and decryption
Transfer of user plane data
Transfer of control plane data
Header compression
Ciphering &integrity protection
Acknowledged data transfer
Unacknowledged data transfer
in-sequence delivery
Duplicate discarding
RLC PDCP RRC
Services related to PDCP sub layer