3G & 4G Mobile Communication Systems - Chapter IV

Dr. Stefan BrückQualcomm Corporate R&D Center Germany

3G/4G Mobile Communications Systems

Chapter IV: Radio Interface and Application Protocols

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Protocols

Slide 2

Radio Interface and Application Protocols

� Logical, Transport and Physical Channels

� Channel Mapping in UMTS and LTE

� Layer 3 Control Plane Protocol� Radio Resource Control (RRC)

� Layer 2 Protocols� Radio Link Control (RLC)

� Medium Access Control (MAC)

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� Medium Access Control (MAC)

� MAC Architecture in HSPA and LTE� PDU Formats for MAC-hs, MAC-ehs, LTE MAC (DL-SCH)

� Stop and Wait Hybrid Automatic Repeat Request Protocol

� Example of an Application Protocol: X2 Application Protocol

Slide 3

UMTS and LTE Channels

� Downlink – transmitted by UTRAN, received by UE

� Uplink – transmitted by UE, received by UTRAN

� Common – carriers information to/from multiple UEs

� Dedicated – carries information to/from a single UE using dedicated resources

� Shared – carries information to/from a single UE using shared resources

� Logical – defined by what type of information is transferred, e.g., signaling or

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� Logical – defined by what type of information is transferred, e.g., signaling or user data

� Transport – defined by how data is transferred over the air interface, e.g., multiplexing of logical channels

� Physical – defined by physical mapping and attributes used to transfer data over the air interface, e.g. spreading rate

Slide 4

Channel Mapping – UMTS Release 99 Channels

5 Slide 5

Channel Mapping – UMTS Dedicated Channels

� These channels carry user and signaling data between UTRAN and an individual UE

� DCCH carries RRC and NAS signaling

� The number of DTCH assigned is determined by the application, e.g. for voice three DTCHs are assigned to one UE

� DCCHs and DTCHs are mapped to a

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� DCCHs and DTCHs are mapped to a single DCH or may be assigned an individual DCH

� In R99 deployments all DCHs are mapped to a single DPDCH

� The DPCCH carries information generated at PHY such as pilot, power control bits. There is always exactly one DPCCH

Slide 6

Typical UMTS R99 Service Combinations

Service Combination Uplink Service Combination Downl ink

3.4kbps signalling + PS I&B 64kbps + AMR Voice 12.2kbps


3.4kbps signalling + PS I&B 128kbps 3.4kbps signalling + PS I&B 384kbps

3.4kbps signalling + PS I&B 8kbps + PS Strm64kbps+ AMR Voice 12.2kbps

3.4kbps signalling + PS I&B 8kbps + PS Strm16kbps+ AMR Voice12.2kbps

3.4kbps signalling + AMR Voice 12.2kbps 3.4kbps signalling + AMR Voice 12.2kbps

7 Slide 7

3.4kbps signalling + AMR Voice 12.2kbps 3.4kbps signalling + AMR Voice 12.2kbps

3.4kbps signalling + CS 64kbps 3.4kbps signalling + CS 64kbps

I&B ≡ Interactive & BackgroundStrm ≡ Streaming

HSDPA and HSUPA Channel Mapping

8 Slide 8

Typical UMTS HSPA Service Combinations

Service Combination Uplink Service Combination Downl ink

3.4kbps signalling + PS I&B 64kbps 3.4kbps signalling + PS I&B HSDSCH

3.4kbps signalling + PS I&B 64kbps + CS 64kbps

3.4kbps signalling + PS I&B HSDSCH + CS 64kbps

3.4kbps signalling + PS I&B 384kbps 3.4kbps signalling + PS I&B HSDSCH


3.4kbps signalling + PS I&B HSDSCH + AMR Voice 12.2kbps

9 Slide 9

Voice 12.2kbps Voice 12.2kbps

3.4kbps signalling + PS Strm 32kbps +PS I&B 8kbps+ AMR Voice 12.2kbps

3.4kbps signalling + PS Strm HSDSCH 32kbps + PS I&B HSDSCH + AMR Voice 12.2kbps

3.4kbps signalling + PS I&B EDCH 3.4kbps signalling + PS I&B HSDSCH

EDCH signalling + PS I&B EDCH 3.4kbps signalling + PS I&B HSDSCH

Channel Mapping – LTE Downlink

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� Most DL data is carried on the DL-SCH and its corresponding PDSCH

� In contrast to UMTS, there are no dedicated transpo rt channels in LTE

Slide 10

Channel Mapping – LTE Uplink

� Most UL data is carried on the UL-SCH and its corresponding PDSCH

� In contrast to R99 UMTS, there are no dedicated transport channels in LTE

11 Slide 11

Layer 2 Overview

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� The Layer 2 consists of the following sublayers� Packet Data Convergence Protocol (PDCP) – performs header compression and

decompression of IP streams

� Broadcast/Multicast (BMC) – supports cell broadcast functions

� Radio Link Control (RLC) – performs segmentation, reassembly, concatenation and provides various data transfer mode

� Medium Access Control – maps logical channels onto transport channels, performs traffic volume reporting, scheduling

Slide 12

Layer 2 Overview – SDUs and PDUs

� Protocol Data Unit� Unit of data exchanged between

peer layers in a network

� May contain information, addressing, and data

� Service Data Unit� Set of data sent by a user of the

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� Set of data sent by a user of the services of a given layer

� Transmitted to the peer service semantically unchanged

Slide 13

Layer 2 Overview – Data Flow Example (UMTS)

14 Slide 14

UMTS Protocol Stack – Control Plane

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Radio Resource Control (RRC)• Access stratum control• System information processing• Paging and notification• RRC connection management• NAS layer message routing• Ciphering and integrity protection control• Radio Bearer management• RRC mobility• Measurement control and reporting

Slide 15

UMTS Protocol Stack – User Plane

Physical Layer (PHY)• Error detection on transport channels• Forward error correction encoding/decoding• Interleaving/deinterleaving of transport channels• Multiplexing/demultiplexing of transport channels• Rate matching• Modulation/demodulation • Spreading/despreading• Measurements (e.g., FER, transmit power)

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Radio Link Control (RLC)• Segmentation, reassembly, concatenation, padding• Retransmission control, flow control• Duplicate detection, in-sequence delivery• Error correction• Ciphering – acknowledged and unacknowledged mode

Medium Access Control (MAC)• Mapping and multiplexing of logical to transport channels• Priority handling of data flows• UE identification on common channels • Traffic volume measurements• Random Access Channel procedure• Scheduling• Ciphering – transparent mode

Slide 16

RLC Overview – Functions (TS 25.322, TS 36.322)

� Radio Link Control Functions� Transfer of user data and signaling

� Segmentation and reassembly

� Concatenation

� Padding

� Error correction

� In-sequence delivery of upper layers PDUs

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� In-sequence delivery of upper layers PDUs

� Duplicate detection

� Flow control

� Sequence number check

� Protocol error detection and recovery

� Ciphering (UM and AM only)

� SDU discard

Slide 17

RLC Overview – Architecture

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� The primary function of the RLC is to transfer user data and signaling

� Data flow to and from upper layers are carried by Radio Bearers and may carry either signaling data (Signaling Radio Bearer) or user data (Radio Access Bearer)

� Each Radio Bearer is mapped to a RLC entity, which operates in of the three data transfer modes: transparent mode (TM), unacknowledged mode UM, or acknowledge mode (AM)

Slide 18

RLC Overview – Data Transfer Modes

� Transparent Mode (TM)� Unreliable service

� Separate receive and transmit entities

� Supports a set of fixed SDU sizes configured by RRC

� Unacknowledged Mode (UM)� Unreliable service


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� Supports arbitrary SDU sizes

� Acknowledged Mode (AM)� Reliable service

� Bidirectional entity

� Supports arbitrary SDU sizes

Slide 19

RLC Overview – Data Transfer Modes (cntd.)

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� Radio Bearers using RLC TM: BCCH, PCCH, CS Voice DTCH

� Radio Bearers using RLC UM: one DCCH, PS DTCH used for error tolerant and delay sensitive applications

� Radio Bearers using RLC AM: one DCCH, PS DTCH used for error sensitive and delay tolerant applications

Slide 20

RLC Transparent Mode

� In TM Mode, PDUs are transferred with little interaction by RLC� No header is added

� Segmentation and reassembly� If the SDU size is too large to fit into a

single PDU, it may segmented at Tx and reassembled at Rx side

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and reassembled at Rx side

� Ciphering for logical channels is performed by the MAC

Slide 21

RLC Unacknowledged Mode

� A small header containing information about segmentation, concatenation and sequence number is added


� Sequence number check� Used during reassembly to detect

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� Used during reassembly to detect corrupted SDUs

Slide 22

RLC Acknowledged Mode

� AM Mode provides reliable service based on ACKs and NACKs


� Error correction� PDUs received in error are

retransmitted

� In-sequence delivery

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� In-sequence delivery� PDUs are delivered to upper layers

in the same order as they were submitted to the transmitted RLC

� Flow control� Configurable transmit and receive

window sizes

� Ciphering of logical channels is performed by RLC

Slide 23

U-Plane Protocol Stack (System Simulator)

24 Slide 24

Example: Parameters for DL 384 kbps / PS RAB

RLC SDU Size

25 Slide 25

Table taken from 3GPP TS 34.108, v5.3.0

MAC Overview – Functions (TS 25.321, TS 36.321)

� Medium Access Control (MAC) Functions� Logical and transport channel mapping

� Identification of UEs on common transport channels

� Prioritizing logical channels

� Multiplexing/de-multiplexing of logical channels

� Transport format combination selection

� (Scheduling)

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� (Scheduling)

� Ciphering (for RLC TM only)

� (Segmentation)

� (Reordering)

� (HARQ)

Slide 26

UTRAN MAC Overview – Architecture I/III

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� The MAC in R99 consists of three parts� MAC-c/sh: controls access to the common transport channels

� MAC-b: controls access to the broadcast channel

� MAC-d: controls access to the dedicated channels

Slide 27

UTRAN MAC Overview – Architecture II/III

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� The MAC in R5 was extended to support HSDPA� MAC-hs: This part of the MAC resides in the Node B to allow fast Hybrid ARQ. It is

also responsible for scheduling of the HS-DSCH

Slide 28

UTRAN MAC Overview – Architecture III/III

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� The MAC in R6 was extended to support HSUPA� MAC-e: provides fast retransmissions by HARQ

� MAC-es: provides reordering functionalities

� On the UTRAN the MAC is split between the Node B (MAC-e) and the RNC (MAC-es)

Slide 29

MAC Entity and HARQ Entity in 3GPP

� Common definitions in LTE and HSDPA� There is one MAC entity per cell� There is one HARQ entity per supported UE

� The HARQ entity handles the hybrid ARQ functionality for one user� A number of parallel HARQ processes are used to support the HARQ entity� The HARQ processes are of stop and wait type

� The HARQ process can be re-used if the associated ACK/NACK is received again

� Definitions in HSDPA

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� Definitions in HSDPA � There is one HARQ process per TTI for single stream transmission � There two HARQ processes per TTI for dual stream transmission

� This definition applies for MAC-ehs only

� Definitions in LTE� A HARQ process is associated with one or two MAC PDUs

Slide 30

� The queues store MAC-d PDUs which are also called MAC-hs SDUs

� In the MAC-hs only entire MAC-d PDUs from one priority queue can be mapped into one MAC-hs PDU

� Multiplexing and segmentation of MAC-d PDUs is not offered in the

MAC-hs

MAC – Control

Priority Queuedistribution

MAC-d flows

Priority Queuedistribution

PriorityQueue

PriorityQueue

PriorityQueue

PriorityQueue

Scheduling/Priority handling

MAC-hs Entity in the UTRAN (Rel5, Rel6)

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MAC-d PDUs is not offered in the MAC-hs

� The MAC-hs header indicates the queue ID, the TSN and the MAC-d PDU sizes. The smallest size 21 bits

HS-DSCH

TFRC selection

Associated DownlinkSignalling

Associated UplinkSignalling

HARQ entity

Slide 31

� The queues store MAC-d PDUs which are also called MAC-ehs SDUs

� A reordering SDU is a complete or a segment of a MAC-ehs SDU

� A reordering PDU consists of several reordering SDUs of the same priority queue

� Finally, a MAC-ehs PDU consists of one or several reordering PDUs from

MAC-ehs

MAC – Control

MAC-d flows

Priority Queue

Scheduling/Priority handling

Priority Queue

LCH-ID MUX

Segment Segment

LCH-ID MUX

MAC-ehs Entity in the UTRAN (Rel7)

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Finally, a MAC-ehs PDU consists of one or several reordering PDUs from up to three priority queues

� The MAC-ehs offers multiplexing and segmentation

� The MAC-ehs header indicates the logical channel ID, the TSN, segmentation and SDU sizes. The smallest size is 24 bits

HS-DSCH

TFRC selection

Associated Downlink Signalling

Associated Uplink Signalling

Segmentation

HARQ entity

Segmentation

Slide 32

MAC-hs and MAC-ehs Entities in the UE

� The disassembly unit removes the MAC-hs/MAC-ehs header and potential padding bits� Padding is introduced since a finite set of

MAC-hs/MAC-ehs PDUs is allowed

� New ‘octed-aligned’ PDU sizes have been introduced together with MAC-ehs, i.e. the PDU sizes are multiples of one byte

� The reordering queue distribution routes

MAC-hs

MAC – Control


To MAC-d

Associated Downlink Signalling

HS-DSCH

HARQ

Reordering Reordering

Re-ordering queue distribution

Disassembly Disassembly

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� The reordering queue distribution routes the received MAC-hs PDUs or the reordering PDUs to the correct reordering queues � based on the queue ID or received logical

channel identifier

� The reordering entity reorders received MAC-hs PDUs/reordering PDUs according to the received TSN

� The reassembly entity reassembles segmented MAC-ehs SDUs

M AC-ehs

M AC – Contro l


To M AC-d

Associated Downlink Signa lling

HS-DSC H

HARQ

Reordering Reordering

Re-o rdering queue distributio n

LCH-ID D em ux LCH-ID D em ux

Reassembly

Disassembly

Reassembly

Associated Uplink SignallingAssociated Downlink Signalling

Slide 33

� In Rel. 5 – 6 the RLC PDU sizes was either fixed to 336 bits or 656 bits

� The RLC protocol applies a window based ARQ mechanism with a window size W of up to 4095 PDUs� The RLC protocol can send at most 4095 PDUs before a status report is

received from the UE.

� Some UEs only support a window size of 2047 PDUs

� In the RLC protocol the maximal throughput T is limited to

[bits] Size PDU W ⋅

Why MAC-ehs Segmentation in HSDPA

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� The RLC round trip time is typically in the order of 80ms – 120ms in real world

� The timer status prohibit should be set to similar values as the RLC RTT

� Therefore it is very difficult to achieve 14.4 Mbps in HSDPA with realistic parameter settings and window sizes of 2047 PDUs

� The flexible RLC PDU size (up to 1500 bytes) introduced in Rel. 7 together with MAC-ehs segmentation overcomes this bottleneck

Prohibit StatusTimer RTT RLC TT

[bits] Size PDU WT

+⋅≤

Slide 34

Differences of MAC-hs/ehs and LTE MAC

� MAC-hs does not support segmentation

� MAC-ehs segmentation needed in HSDPA � The RLC protocol resides in the RNC

� The RLC does not have fast information about required MAC-ehs SDU sizes in the Node B

� In LTE both RLC and MAC reside in the Node B � The MAC can inform the RLC about required MAC SDU sizes per TTI.

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� Segmentation is done in the RLC

� Additionally, no re-ordering is supported in the LTE MAC� Reordering to higher layers is done in the RLC

Slide 35

MAC PDU Formats

Queue ID TSN SID1 N1 F1 SID2 N2 F2 SIDk Nk Fk

MAC-hs header MAC-hs SDU Padding (opt) MAC-hs SDU

Mac-hs payload

VF

SI1 LCH-ID1 TSN1 L1 TSNk Lk LCH-IDk SIk F1 Fk

MAC-hs PDU

MAC-ehs PDU

36 Slide 36

MAC-ehs header Reordering PDU Padding (opt) Reordering PDU

Mac-ehs payload

MAC-ehs PDU

LTE MAC PDU(DL-SCH)

DL transmissionat NodeB

DL receptionat UE

DL processingat UE

HARQprocess #1

HARQprocess #2

HARQprocess #3

HARQprocess #4

HARQprocess #5

HARQprocess #6

2 ms

HARQprocess #1

HARQprocess #2

HARQprocess #3

HARQprocess #4

HARQ process #1

HARQ process #2

HARQprocess #1

ACK/NACK

feedb

ack t

o Node

B

...

HARQprocess #2

......

...

Stop and Wait HARQ Protocol in HSDPA and LTE

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� A HARQ process is in charge of the transmission (and possible subsequent re-transmission) of one MAC PDUs

� Once the MAC PDU is sent the HARQ process waits for the ACK/NACK from the UE to decide whether to schedule a re-transmission or a new MAC-hs PDU transmission.

� The round trip time delay is typically 6 TTI = 12 ms in HSDPA

� In LTE the round trip time is 8 TTI = 8 ms

Slide 37

Horizontal Layers – Vertical Planes

� The protocol structure consists of two main layers, Radio Network Layer and Transport Network Layer� Vertically, the protocols are separated in control and user plane

� All (E)-UTRAN related issues are visible only in the Radio Network Layer � The Transport Network Layer applies standard transport technology that is

selected for (E)-UTRAN without any (E)-UTRAN specific requirements

� Application protocols (AP) are control plane protocols in the Radio Network Layer of entities

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Layer of entities� They control the signaling to other entities

� Examples of Applications Protocols in UTRAN� NBAP: Node B – RNC

� RANAP: RNC – SGSN/MSC

� RNSAP: RNC – RNC

� Examples for Applications Protocols in E-UTRAN� X2AP: eNB – eNB

� S1AP: eNB – MME

Slide 38

LTE X2 Protocol Structure (TS 36.423)

X2-AP

Transport Network Layer

User Transport Network

Plane

Control Plane User Plane

Transport

User

Network

Plane

Radio Network Layer

GTP-U

UDP

User Plane PDUs

SCTP

Signaling Transport

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UDP

IP

Data link layer

Physical layer

SCTP

IP

Data link layer

Physical layer

� Clear separation between radio network and transport network layers

� The radio network layers defines interaction between eNBs

� The transport network layer provides services for user plane and signaling transport

Data Transport

Slide 39

X2 Application Protocol (X2AP)

� The X2AP is responsible for providing signaling between eNBs

� X2AP functions are executed by so called Elementary Procedures� Rel. 8 defines eleven EPs related to different X2AP functions

� In Rel. 9 four additional EPs have been defined

� Class 1: EPs with response (success or failure)

� Class 2: EPs without response

� In LTE Rel. 8/9 limited load management functionality is supported� Its functionality is extended in Rel. 10

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� Its functionality is extended in Rel. 10

Function Elementary Procedure(s) Mobility Management a) Handover Preparation

b) SN Status Transfer c) UE Context Release d) Handover Cancel

Load Management a) Load Indication b) Resource Status Reporting Initiation c) Resource Status Reporting

Reporting of General Error Situations Error Indication Resetting the X2 Reset Setting up the X2 X2 Setup eNB Configuration Update eNB Configuration Update Mobility Parameters Management Mobility Settings Change Mobility Robustness Optimisation a) Radio L ink Failure Indication

b) Handover Report Energy Saving Cell Activation

Release 8

Release 9

Slide 40

X2 AP Load Management

� The X2AP load management function is used by the eNBs to indicate resource status, overload and traffic load to each other

� The load management function consists of the EPs � Load Indication (class 2)

� Purpose: Transfer load and interference coordination information between eNBs

� An eNB initiates the procedure by sending LOAD INFORMATION message to another eNB

eNB1

LOAD INFORMATION

eNB2

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INFORMATION message to another eNB

� Resource Status Reporting Initiation (class 1)� Purpose: Request the reporting of load measurements to

another eNB

� The procedure is initiated with a RESOURCE STATUS REQUEST message sent from eNB1 to eNB2 and eNB2 answers with RESOURCE STAUS RESPONSE message

� Resource Status Reporting (class 2)� Purpose: Report the result of measurements admitted by

eNB2 following a successful Resource Status Reporting Initiation procedure

� The eNB2 reports the results of the measurements in RESOURCE STATUS UPDATE message

Slide 41

eNB1 eNB2

RESOURCE STATUS UPDATE

eNB1 eNB2

RESOURCE STATUS REQUEST

RESOURCE STATUS RESPONSE

Information Elements of LOAD INFORMATION

� UL Interference Overload Indication IE: � Indicates the interference level experienced by the indicated cell on all resource

blocks, per PRB.

� Values: High Interference, Medium Interference, Low Interference

� UL High Interference Indication IE: � Indicates, per PRB, the occurrence of high interference sensitivity, as seen from

the sending eNB.

� The receiving eNB should try to avoid scheduling cell edge UEs in its cells for the concerned PRBs

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concerned PRBs

� Values: High Interference Sensitivity, Low Interference Sensitivity

� Relative Narrowband Tx Power (RNTP) IE:� Indicates, per PRB, whether downlink transmission power is lower than the value

indicated by the RNTP Threshold IE

� Values: Tx power exceeding RNTP threshold, Tx power not exceeding RNTP threshold

� Detailed definition of interference, interference sensitivity are implementation specific

Slide 42

RESOURCE STATUS REQUEST Message

� The reporting can be periodic or event based

� In case of periodic reporting request, the RESOURCE STATUS UPDATE message is used � Periodicity is either 1s, 2s, 5s, 10s

� Supported measurements� Radio Resource Status IE indicates the usage of the PRBs in Downlink and Uplink

� DL GBR PRB usage, UL GBR PRB usage, DL non-GBR PRB usage, UL non-GBR PRB usage, DL Total PRB usage, UL Total PRB usage

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usage, DL Total PRB usage, UL Total PRB usage

� The report is an integer value ranging from 0 to 100

� S1 TNL Load Indicator IE indicates the status of the S1 Transport Network Load experienced by the cell� Low Load, Medium Load, High Load, Overload

� Hardware Load Indicator IE indicates the status of the Hardware Load experienced by the cell� Low Load, Medium Load, High Load, Overload

� Composite Available Capacity Group IE indicates the overall available resource level in the cell in Downlink and Uplink.

� Detailed definition of measurements are implementation specific

Slide 43

3G & 4G Mobile Communication Systems - Chapter IV

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