3G & 4G Mobile Communication Systems - Chapter IV

ant.uni.bremen.de

3G & 4G Mobile Communication Systems - Chapter IV

3G/4G Mobile Communications Systems

Dr. Stefan Brück

Qualcomm Corporate R&D Center Germany


Chapter IV:

Radio Interface and Application

Protocols

2

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)

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

3

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

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

4

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

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

6

Slide 6


Typical UMTS R99 Service Combinations

Service Combination Uplink

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

Voice 12.2kbps

3.4kbps signalling + PS I&B 128kbps

3.4kbps signalling + PS I&B 8kbps + PS Strm

64kbps+ AMR Voice 12.2kbps

3.4kbps signalling + AMR Voice 12.2kbps

3.4kbps signalling + CS 64kbps

Service Combination Downlink

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

Voice 12.2kbps

3.4kbps signalling + PS I&B 384kbps

3.4kbps signalling + PS I&B 8kbps + PS Strm

16kbps+ AMR Voice12.2kbps

3.4kbps signalling + AMR Voice 12.2kbps

3.4kbps signalling + CS 64kbps

I&B

Strm

≡ Interactive & Background

≡ Streaming

7

Slide 7


HSDPA and HSUPA Channel Mapping

8

Slide 8


Typical UMTS HSPA Service Combinations

Service Combination Uplink

3.4kbps signalling + PS I&B 64kbps

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

64kbps

3.4kbps signalling + PS I&B 384kbps

3.4kbps signalling + PS I&B 8kbps + AMR

Voice 12.2kbps

3.4kbps signalling + PS Strm 32kbps +

PS I&B 8kbps+ AMR Voice 12.2kbps

3.4kbps signalling + PS I&B EDCH

EDCH signalling + PS I&B EDCH

Service Combination Downlink

3.4kbps signalling + PS I&B HSDSCH

3.4kbps signalling + PS I&B HSDSCH + CS

64kbps

3.4kbps signalling + PS I&B HSDSCH

3.4kbps signalling + PS I&B HSDSCH + 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 HSDSCH

3.4kbps signalling + PS I&B HSDSCH

9

Slide 9


Channel Mapping – LTE Downlink

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

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

10

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

12

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

services of a given layer

Transmitted to the peer service

semantically unchanged

13

Slide 13


Layer 2 Overview – Data Flow Example (UMTS)

14

Slide 14


UMTS Protocol Stack – Control Plane

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

15

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)

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

16

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

Duplicate detection

Flow control

Sequence number check

Protocol error detection and recovery

Ciphering (UM and AM only)

SDU discard

17

Slide 17


RLC Overview – Architecture

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)

18

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

Separate receive and transmit entities

Supports arbitrary SDU sizes

Acknowledged Mode (AM)

Reliable service

Bidirectional entity

Supports arbitrary SDU sizes

19

Slide 19


RLC Overview – Data Transfer Modes (cntd.)

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

20

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

Ciphering for logical channels is

performed by the MAC

21

Slide 21


RLC Unacknowledged Mode

A small header containing information

about segmentation, concatenation

and sequence number is added

Segmentation and reassembly

Sequence number check

Used during reassembly to detect

corrupted SDUs

22

Slide 22


RLC Acknowledged Mode

AM Mode provides reliable service

based on ACKs and NACKs

Segmentation and reassembly

Error correction

PDUs received in error are

retransmitted

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

23

Slide 23


U-Plane Protocol Stack (System Simulator)

24

Slide 24


Example: Parameters for DL 384 kbps / PS RAB

RLC SDU Size

Table taken from 3GPP TS 34.108, v5.3.0

25

Slide 25


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)

Ciphering (for RLC TM only)

(Segmentation)

(Reordering)

(HARQ)

26

Slide 26


UTRAN MAC Overview – Architecture I/III

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

27

Slide 27


UTRAN MAC Overview – Architecture II/III

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

28

Slide 28


UTRAN MAC Overview – Architecture III/III

The MAC in R6 was extended to support HSUPA

MAC-e: provides fast retransmissions by HARQ

MAC-es: provides reordering functionalities

29

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

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

30

Slide 30


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

MAC-d flows

MAC-hs

Priority

Queue

Priority Queue

distribution

Priority

Queue

Scheduling/Priority handling

Priority Queue

distribution

Priority

Queue

HARQ entity

TFRC selection

Priority

Queue

MAC – Control

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

The MAC-hs header indicates the

queue ID, the TSN and the MAC-d

PDU sizes. The smallest size 21 bits

Associated Uplink

Signalling

HS-DSCH

Associated Downlink

Signalling

31

Slide 31


MAC-ehs Entity in the UTRAN (Rel7)

MAC-d flows

MAC-ehs

LCH-ID MUX

Scheduling/Priority handling

LCH-ID MUX

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

Priority

Queue

Priority

Queue

MAC – Control

A reordering PDU consists of several

reordering SDUs of the same priority

queue

Segment

ation

Segment

ation

Finally, a MAC-ehs PDU consists of

one or several reordering PDUs from

up to three priority queues

Associated Uplink

Signalling

HARQ entity

TFRC selection

HS-DSCH

Associated Downlink

Signalling

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

32

Slide 32


MAC-hs and MAC-ehs Entities in the UE

To MAC-d

M AC-hs

Disassembly Disassembly

Reordering

Reordering

Re-ordering queue distribution

HARQ

HS-DSCH

Associated Downlink Signalling

To M AC-d

M AC-ehs LCH-ID D em ux

Reasse mbly

Reo rdering

Associated Uplink Signalling

LCH-ID D em ux

Reassembly

Reordering

Re-o rdering queue distributio n

Disassembly

HARQ

HS-DSC H

Associated Downlink Signalling

Associated Uplink Signalling

MAC – Control

M AC – Contro l

The disassembly unit removes the MAChs/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

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

33

Slide 33


Why MAC-ehs Segmentation in HSDPA

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

T


W


PDU Size [bits]

T RLC

+ T

RTT

Timer Status Prohibit

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

34

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.

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

35

Slide 35


MAC PDU Formats

VF

Queue ID TSN SID 1 N 1 F 1 SID 2 N 2 F 2 SID k N k F k

MAC-hs PDU

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

Mac-hs payload

LCH-ID 1 L 1 TSN 1

SI 1

F 1 LCH-ID k L k TSN k SI k F k

MAC-ehs PDU

MAC-ehs header Reordering PDU

Reordering PDU

Mac-ehs payload

Padding (opt)

LTE MAC PDU

(DL-SCH)

36

Slide 36


Stop and Wait HARQ Protocol in HSDPA and LTE

2 ms

DL transmission

at NodeB

...

HARQ

process #1

HARQ

process #2

HARQ

process #3

HARQ

process #4

HARQ

process #5

HARQ

process #6

HARQ

process #1

HARQ

process #2

...

DL reception

at UE

...

HARQ

process #1

HARQ

process #2

HARQ

process #3

HARQ

process #4

...

ACK/NACK

feedback to NodeB

DL processing

at UE

HARQ process #1

HARQ process #2





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

37

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

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

38

Slide 38


LTE X2 Protocol Structure (TS 36.423)

Radio

Network

Layer

Control Plane

X2-AP

User Plane

User Plane

PDUs

Transport

Network

Layer

Transport Network

User Plane

Signaling

Transport

Transport Network

User Plane

SCTP

IP

Data link layer

Physical layer

Data

Transport

GTP-U

UDP

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

39

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

Function

Mobility Management

Load Management

Reporting of General Error Situations

Resetting the X2

Setting up the X2

eNB Configuration Update

Mobility Parameters Management

Mobility Robustness Optimisation

Energy Saving

Elementary Procedure(s)

a) Handover Preparation

b) SN Status Transfer

c) UE Context Release

d) Handover Cancel

a) Load Indication

b) Resource Status Reporting Initiation

c) Resource Status Reporting

Error Indication

Reset

X2 Setup

eNB Configuration Update

Mobility Settings Change

a) Radio Link Failure Indication

b) Handover Report

Cell Activation

Release 8

Release 9

40

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

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 eNB 1 to eNB 2 and eNB 2

answers with RESOURCE STAUS RESPONSE message

Resource Status Reporting (class 2)

Purpose: Report the result of measurements admitted by

eNB 2 following a successful Resource Status Reporting

Initiation procedure

The eNB 2 reports the results of the measurements in

RESOURCE STATUS UPDATE message

eNB1

eNB2

LOAD INFORMATION

eNB 1 eNB 2

RESOURCE STATUS REQUEST

RESOURCE STATUS RESPONSE

eNB 1 eNB 2

RESOURCE STATUS UPDATE

41

Slide 41


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

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

42

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

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

43

Slide 43

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