System Architecture Evolution (SAE) in 3GPP

•Targets for System Architecture Evolution:•Optimization for PS services, No longer CS Core network•Support for higher throughput (more capacity, higher data rates)•Decrease the response time for activation and bearer set-up (Control plane latency)•Decrease packet delivery delay (User plane latency)•Architecture simplification when comparing with existing cellular networks•Inter-working with 3GPP access networks•Inter-working with other wireless access networks

LTE/SAE Requirements Summary1.- Simplify the RAN:

- Reduce the number of different types of RAN nodes, and their complexity.

- Minimize the number of RAN interface types.2.- Increase throughput: Peak data rates of uplink/downlink 50/100 Mbps 3.- Reduce latency (which is a prerequisite for CS replacement).4.- Improve spectrum efficiency. Capacity 2-4 times higher than with Release 6 HSPA5.- Frequency flexibility and bandwidth scalability: Frequency Refarming6.- Migrate to a PS only domain in the core network.7.- Provide efficient support for a variety of different services. Traditional CS services will be supported via VoIP, etc.8.- Minimise the presence of single points of failure in the network above the evolved Node Bs (eNBs):S1-Flex interface9.- Support for inter-working with existing 3G system and non-3GPP specified systems10.- Operation in FDD and TDD modes 11.- Improved terminal power efficiency A more detailed list of the requirements and objectives for LTE can be found in TR25.913 from 3GPP.

Evolved Packet System (EPS) Architecture - Subsystems

LTE or EUTRAN SAE or EPC

LTE/EPS Interworking with 2G/3G Networks

LTE-UE

Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)

MME

S6a

ServingGateway

S1-U

S11S1-MME

PDNGateway

PDN

PCRF

Gx Rx+

SGiS5/S8

HSS

SGSN

S3UTRAN

Iu-PS

S4

EvolvedNode B(eNB)

cell

LTE-Uu

GERANGb

S6d: diameter Based Gr: MAP Based

GGSNGnPDN

Gi

S12

Direct Tunnels from Serving GW

to RNC (User Plane)

Radio Resource Management (RRM)

Radio Bearer Control: setup, modifications and release of Radio Resources

Connection Mgt. Control: UE State Mgmt. MME-UE Connection

Radio Admission Control

eNode B Measurements Collection and evaluation

Dynamic Resource Allocation (Scheduler)

eNB Functions

IP Header Compression/ de-compression

Access Layer Security: ciphering and integrity protection on the radio interface

MME Selection at Attach of the UE

User Data Routing to the SAE GW.

Transmission of Paging Message coming from MME

Transmission of Broadcast Info (System info, MBMS)

EvolvedNode B(eNB)cell

LTE-Uu

LTE-UE

•It is the only network element defined as part of EUTRAN. •It replaces the old Node B / RNC combination from 3G.•It terminates the complete radio interface including physical layer.•It provides all radio management functions•An eNB can handle several cells. •To enable efficient inter-cell radio management for cells not attached to the same eNB, there is a inter-eNB interface X2 specified. It will allow to coordinate inter-eNB handovers without direct involvement of EPC during this process.

Evolved Node B (eNB)

EvolvedNode B(eNB)

MME

ServingGateway

S1-U

S1-MME

S11

HSS

S6a

MME Functions

Non-Access-Stratum (NAS)Signalling

Idle State Mobility Handling

Tracking Area updates

Security (Authentication, Ciphering, Integrity protection)

Trigger and distribution of Paging Messages to eNB

Roaming Control (S6a interface to HSS)

Inter-CN Node Signaling (S10 interface), allows efficient inter-MME tracking area updatesand handovers

Signalling coordination for SAE Bearer Setup/Release & HO

Subscriber attach/detach

Control plane NE in EPC

Mobility Management Entity (MME)

• It is a pure signaling entity inside the EPC.• SAE uses tracking areas to track the position of idle UEs. The basic principle is identical to 2G/3G LA or RA. • MME handles attaches and detaches to the SAE system, as well as tracking area updates. • Therefore it possesses an interface towards the HSS (home subscriber server) which stores the subscription relevant information and the currently assigned MME in its permanent data base.• A second functionality of the MME is the signaling coordination to setup transport bearers (SAE bearers) through the EPC for a UE.• MMEs can be interconnected via the S10 interface.• It generates and allocates temporary ids for UEs.• VLR-like functionality

LTE FDD and TDD Modes

Uplink Downlink

Bandwidth

up to 20MHz

Duplex Frequency

f

t Bandwidth

up to 20MHz

GuardPeriod

f

t

Uplink

Downlink

Bandwidth

up to 20MHz

LTE Air Interface Key Features

OFDM is the state-of-the-art and most efficient and robust air interface and could be used for both FDD and TDD modes

Fast Link Adaptationdue to channel behaviour

Short TTI = 1 msTransmission time interval

Advanced SchedulingTime & Freq.

TX RX

Tx RxMIMO

Channel

DL: OFDMA

UL: SC-FDMA

scalable

ARQ Automatic Repeat Request

64QAMModulation

Radio Protocols Architecture

MAC

RLC

PDCP

Physical Layer

RRC

L1

L2

L3

Radio Bearer

Logical Channel

Transport Channels

Control Plane User Plane

Physical Channels

FDD | TDD - Layer 1( DL: OFDMA, UL: SC-FDMA )

FDD | TDD - Layer 1( DL: OFDMA, UL: SC-FDMA )

Medium Access Control (MAC)Medium Access Control (MAC)

Physical Channels

Transport Channels

RLC(Radio Link

Control)

RLC(Radio Link

Control)

…

PDCP’(Packet DataConvergence

Protocol)

PDCP’(Packet DataConvergence

Protocol)

…

RLC(Radio Link

Control)

RLC(Radio Link

Control)

PDCP’(Packet DataConvergence

Protocol)

PDCP’(Packet DataConvergence

Protocol)

RLC(Radio Link

Control)

RLC(Radio Link

Control)

PDCP(Packet DataConvergence

Protocol)

PDCP(Packet DataConvergence

Protocol)

RLC(Radio Link

Control)

RLC(Radio Link

Control)

PDCP(Packet DataConvergence

Protocol)

PDCP(Packet DataConvergence

Protocol)

RLC(Radio Link

Control)

RLC(Radio Link

Control)

PDCP(Packet DataConvergence

Protocol)

PDCP(Packet DataConvergence

Protocol)

Logical Channel

(E-)RRC(Radio Resource Control)

(E-)RRC(Radio Resource Control)

IP / TCP | UDP | …IP / TCP | UDP | …

Application LayerApplication Layer

Radio Bearer

ROHC (RFC 3095)

Security

Segment./Reassembly

ARQ

Scheduling /Priority Handling

HARQ

De/Multiplexing

CRC

Coding/Rate Matching

Interleaving

Modulation

Resource Mapping/MIMO

NAS Protocol(s)(Attach/TA Update/…)NAS Protocol(s)

(Attach/TA Update/…)

Challenges for the Air Interface Design

The usage of the pulse leads to other challenges to be solved:

1. ISI = Intersymbol InterferenceDue to multipath propagation → solution: use cyclic prefix

2. ACI = Adjacent Carrier Interference Due to the fact that FDM = frequency division multiplexing will be used

→ solution: orthogonal subcarriers

3. ICI = Intercarrier Interference Losing orthogonality between subcarriers because of effects like e.g. Doppler→ solution: use reference signals – will be explained in chapter 7

Resource Block and Resource Element

• 12 subcarriers in frequency domain x 1 slot period in time domain.0 1 2 3 4 5 6 0 1 2 3 4 5 6Subcarrier

1

Subcarrier 12

180

KHz

1 slot 1 slot

1 ms subframe

RB

• Capacity allocation is based on Resource Blocks

• Resource Element ( RE): – 1 subcarrier x 1 symbol period– Theoretical minimum capacity

allocation unit.– 1 RE is the equivalent of 1

modulation symbol on a subcarrier, i.e. 2 bits for QPSK, 4 bits for 16QAM and 6 bits for 64QAM.

Resource Element

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

6. Physical Resource Block or Resource Block (PRB or RB)

OFDM Key Parameters for FDD and TDD Modes

Bandwidth(NC×Δf)

1.4 MH 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz

Subcarrier Fixed to 15 kHz (7.5kHz defined for MBMS)Spacing (Δf)

Symbol Tsymbol = 1/Δf = 1/15kHz = 66.67μsduration

Sampling rate, fS (MHz)

1.92 3.84 7.68 15.36 23.04 30.72

DataSubcarriers (NC)

72 180 300 600 900 1200

NIFFT (IFFT Length)

128 320 512 1024 1536 2048

Number of Resource Blocks

6 15 25 50 75 100

Symbols/slot Normal CP=7; extended CP=6

CP length Normal CP=4.69/5.12μsec., Extended CP= 16.67μsec

Data Rate Calculation

1. Maximum channel data rate

The maximum channel data rate is calculated taking into account the total number of the available resource blocks in 1 TTI = 1msMax Data Rate = Number of Resource Blocks x 12 subcarriers x (14 symbols/ 1ms)

= Number of Resouce Blocks x (168 symbols/1ms)

2. Impact of the Channel Bandwith: 5, 10, 20 MHz

For BW = 5MHz -> there are 25 Resource Blocks-> Max Data Rate = 25 x (168 symbols/1ms) = 4,2 * Msymbols/sBW = 10MHz -> 50 Resource Blocks -> Max Data Rate = 8,4 Msymbols/s BW = 20MHz -> 100 Resource Blocks -> Max Data Rate =16,8 Msymbols/s

3. Impact of the Modulation: QPSK, 16QAM, 64QAM

For QPSK – 2bits/symbol; 16QAM – 4bits/symbol; 64QAM – 6 bits/symbol QPSK: Max Data Rate = 16,4 Msymbols/s * 2bits/symbol = 32,8 Mbits/s (bandwith of 20 MHz)16QAM: Max Data Rate = 16,4 Msymbols/s * 4 bits/symbols = 65,6 Mbits/s64QAM: Max Data Rate = 16,4 Msymbols/s * 6 bits/symbols = 98,4 Mbits/s

Data Rate Calculation

4. Impact of the Channel Coding

Channel Coding will be discussed in chapter 6. In LTE Turbo coding of rate 1/3 will be used. The effective coding rate is dependent on the Modulation and Coding Scheme selected by the scheduler in the eNodeB. In practice several coding rates can be obtained. Here it is considered 1/2 and 3/41/2 coding rate: Max Data rate = 98,4 Mbits/s * 0,5 = 49,2 Mbits/s 3/4 coding rate: Max Data rate = 98,4 Mbits/s * 0,75 = 73,8 Mbits/s

5. Impact of MIMO = Multiple Input Multiple Output

MIMO is discussed in chapter 9. If spatial diversity it is used (2x2 MIMO) then the data rate will be doubled since the data is sent in parallel in 2 different streams using 2 different antennas2x2 MIMO: Max Data Rate = 73,8 Mbit/s * 2 = 147,6 Mbits/s

6. Impact of physical layer overhead and higher layers overhead

The real data rate of the user will be further reduced if the physical layer overhead is considered. Also the higher layers may introduce overhead as shown in chapter number 2. For example IP , PDCP , RLC and MAC are introducing their own headers. This type of overheads are not discussed here

CRC Coding and Segmentation

CRCCRC

CodingCoding + Rate Matching

CodingData Modulation

CodingResource Mapping

Antenna Mapping

MA

C s

ched

uler

MA

C s

ched

uler

HARQ

ModulationScheme

Resource/Power AssignmentAntennaAssignment

RedundancyVersion

. . .

. . .

TBTB

Transport Blocks(variable sizes)

ACK | NACK

HARQ Info

QPSK,16QAM,64QAM

3GPP TS 36.302 v8.1.0

Presentation / Author / Date

b0 b1

QPSK

Im

Re10

11

00

01

b0 b1b2b3

16QAM

Im

Re

0000

1111

Im

Re

64QAM

b0 b1b2b3 b4 b5

• 3GPP standard defines the following options: QPSK, 16QAM, 64QAM in both directions ( UL and DL)- UL 64QAM not supported in RL10

• Not every physical channel is allowed to use any modulation scheme:

• Scheduler decides which form to use depending on carrier quality feedback information from the UE

Modulation Schemes

QPSK:

2 bits/symbol

16QAM:

4 bits/symbol

64QAM:

6 bits/symbol

Physical channel

Modulation

PDSCH QPSK, 16QAM, 64QAM

PMCH QPSK, 16QAM, 64QAM

PBCH QPSK

PDCCH (PCFICH, PHICH)

QPSK

PUSCH QPSK, 16QAM, 64QAM

PUCCH BPSK and/or QPSK

LTE Physical Layer Structure – Frame Structure (TDD)

– TDD has a single frame structure: same as FDD but with some specific fields to enable also TD-SCDMA co-existence (China):

• Common frame structure and slot duration allows to parameterize the LTE TDD mode of operation so that the site can have compatible UL and DL split (static parameter)

– Each half frame carries six subframes and three specialized fields ( inherited from TD-SCDMA): DwPTS, GP, UpPTS

– Subframe 0 and DwPTS are reserved for downlink; subframe1 and UpPTS are reserved for UL. Remaining fields are dynamically assigned between UL and DL.

– Also called Frame Type 2. TDD may change between UL and DL either with 5 or 10 ms period

SF#0SF#0

. . .f

time

UL/DL carrier

radio frame 10 ms

subframe 0

Dw

PTS

Dw

PTS

GPGP

UpP

TSU

pPTS SF

#1SF#1

SF#5SF#5

subframe 1subframe 5

SF#0SF#0

. . .

Dw

PTS

Dw

PTS

GPGP

UpP

TSU

pPTS SF

#1SF#1

SF#5SF#5

subframe 0 subframe 1 Subframe 5

half frame

DwPTS: Downlink Pilot time Slot

UpPSS: Uplink Pilot Time Slot

GP: Guard Period to separate between UL/DL

Downlink Subframe

Uplink Subframe

TDD frame structure (1/2)There are 7 frame configurations, according to different DL/UL partition

1 frame = 10ms

1 subframe = 1ms

DL

DL

DL

DL

DL

DL

DL

DL

DLDL

DL DLDL

DL DL DL DL DL

DL

DLDL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DLDL

UL

UL

UL

UL

UL

UL

UL UL UL UL UL

ULUL

UL

UL

UL

UL

UL

UL

UL

UL

UL

UL

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

0

1

2

3

4

5

6

DL – Downlink subframeUL – Uplink subframeSS – Special Switching subframe

Special subframeUE always needs a guard period in order to switch from receiver to transmitter. The guard period includes RTD (Round Trip Delay).

eNodeB

UE

PT PTSP

Downlink

Downlink Uplink

Uplink

eNodeB ends

transmitting

End of DL subframe has reached at the

UE

UE has switched to transmission and has begun UL subframe

Start of UL subframe reaches

at eNodeB

PT = Propagation TimeSP = Switching PeriodRTD = Round Trip DelayGP = Guard Period

GP

RTD = 2 x PTGP = RTD + SP

Spatial Multiplexing or Multi-Stream 2x2 MIMO

•Multi-Stream or Spatial Multiplexing MIMO case:

•1.- Each transmit antenna transmits a different data stream.•2.- This technique significantly increases the peak data rate over the radio link. (For instance, 4x4 MIMO effectively increases the peak data rate by a factor of four.)•3.- It requires high signal-to-noise-plus-interference ratio (SNIR) radio conditions in order to be effective.

eNodeB

Laptop with two antennas

Data stream 1

Data stream 2

Spatial multiplexing 2x2 MIMO

• Increases peak data rate• High SNIR required

•MIMO stands for Multiple Inputs - Multiple Outputs•The LTE initially supports 2x2 (and later 4x4) •Only in the downlink.•Two kinds of MIMO techniques:– Multistream transmission (also known as spatial multiplexing) MIMO– Diversity (or space-time coding) MIMO.

3GPP MODE 1•Single antenna port; port 0 •1 TX antenna transmitting always on port 0

3GPP Mode 4•Closed Loop spatial multiplexing •Multiple antennas transmitting different signals •Feedback from the UE used•Improves user data rate

3GPP MODE 2•Transmit diversity •Multiple antennas transmit same signal •Improves SINR

3GPP Mode 3•Open loop spatial multiplexing •Multiple antennas transmitting different signals •No feedback from the UE used •Improves user data rate

Transmission Modes in 3GPP (1/2)

Tracking Area• Tracking areas are used for EPS (Evolved Packet System) Mobility Management (EMM)

• Paging messages are broadcasted across the tracking areas within which the UE is registered

• UE can be registered within more than a single tracking area• Each eNode B can contain cells belonging to different

tracking areas• Each cell can only belong to a single tracking area• A tracking area can be shared by multiple MME• Tracking Area Identity (TAI):

TAI = MCC + MNC + TAC ( Tracking Area Code)

• The TAC, MCC and MNC are broadcast within SIB 1

Tracking areas are the equivalent of Location Areas and Routing Areas for LTE

TAI2TAI2

TAI1

TAI1TAI1

TAI1

TAI1 eNB

Tracking Area

Tracking Area Planning Guidelines• Tracking areas should be planned to be relatively large (100 eNode B) rather than

relatively small• Their size should be reduced subsequently if the paging load becomes high• Existing 2G and 3G location area and routing area boundaries should be used as a

basis for defining LTE tracking area boundaries• Tracking areas should not run close to and parallel to major roads nor railways.

Likewise, boundaries should not traverse dense subscriber areas• Cells which are located at a tracking area boundary and which experience large

numbers of updates should be monitored to evaluate the impact of the update procedures