LTE Air Interface Overview

(1)

Nokia Academy

LTE Air Interface Overview

(2)

2 TM51154EN04GLA2 © Nokia Solutions and Networks 2014

Copyright and confidentiality

The contents of this document are proprietary and confidential property of Nokia Solutions and Networks. This document is provided subject to confidentiality obligations of the applicable agreement(s).

This document is intended for use of Nokia Solutions and Networks customers and collaborators only for the purpose for which this document is submitted by Nokia Solutions and Networks. No part of this document may be reproduced or made available to the public or to any third party in any form or means without the prior written permission of Nokia Solutions and Networks. This document is to be used by properly trained professional personnel. Any use of the contents in this document is limited strictly to the use(s) specifically created in the applicable agreement(s) under which the document is submitted. The user of this document may voluntarily provide suggestions, comments or other feedback to Nokia Solutions and Networks in respect of the contents of this document ("Feedback"). Such Feedback may be

used in Nokia Solutions and Networks products and related specifications or other documentation. Accordingly, if the user of this document gives Nokia Solutions and Networks feedback on the contents of this document, Nokia Solutions and Networks may freely use, disclose, reproduce, license, distribute and otherwise commercialize the feedback in any Nokia Solutions and Networks product, technology, service, specification or other documentation. Nokia Solutions and Networks operates a policy of ongoing development. Nokia Solutions and Networks reserves the right to make changes and improvements to any of the products and/or services described in this document or withdraw this document at any time without prior notice.

The contents of this document are provided "as is". Except as required by applicable law, no warranties of any kind, either express or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular

purpose, are made in relation to the accuracy, reliability or contents of this document. NOKIA SOLUTIONS AND NETWORKS SHALL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THIS DOCUMENT or for any loss of data or income or any special, incidental, consequential, indirect or direct damages howsoever caused, that might arise from the use of this document or any contents of this document. This document and the product(s) it describes are protected by copyright according to the applicable laws. Nokia is a registered trademark of Nokia Corporation. Other product and company names mentioned herein may be trademarks or trade names of their respective owners.

(3)

Module Objectives

After completing this module, the participant should be able to:

• Understand the basics of the OFDM transmission technology.

• Explain different methods for Multiplexing the access with OFDM.

• Analyze the reasons for SC-FDMA selection in UL.

• Discuss about LTE/EUTRAN Subcarriers, the Frame Structure,

Resource Block and the Modulation options.

• List the frequency allocation alternatives for LTE.

• Describe the basics of MIMO.

• Identify maximum bit rates for LTE.

• Distinguish different LTE UE categories.

• Describe the basics for HARQ.

(4)

Module Contents

• Orthogonal Frequency Division Multiplexing

• OFDM Multiple Access

• OFDM implementation in LTE/EUTRAN

• SC-FDMA

• LTE/EUTRAN Radio Frames

• OFDM Resource Block

• Modulation Schemes in LTE/EUTRAN

• LTE/EUTRAN Frequency Variants

• MIMO

• DL & UL Peak Bit Rates

• LTE UE Categories

• HARQ

(5)

TDMA

f

t

f

• Time Division

FDMA

f

t

• Frequency Division

CDMA

f

t

f

• Code Division

OFDMA

f

t

• Frequency Division

• Orthogonal subcarriers

Wireless Access Technology

User 1

User 2

User 3

User ..

(6)

Multiple Access

1

2

3

4

5

2

1

2

3

4

5

4

2

1

2

3

4

5

3

1

5

3

2

4

1 P

o

w

e

r

Frequency

TDMA

Time Division

Multiple

Access,

2G e.g. GSM,

PDC

FDMA

Frequency

Division

Multiple Access

1G e.g. AMPS,

NMT, TACS

CDMA

Code Division

Multiple Access

3G e.g. UMTS,

CDMA2000

1 _{UE 1}

2 _{UE 2}

3 _{UE 3}

4 UE 4

5 UE 5

OFDMA

Orthogonal

Frequency

Division

Multiple Access

e.g. LTE

(7)

OFDM Basics

• Orthogonal Frequency Division Multiplexing (OFDM) is a

digital encoding and modulation technique

• The channel bandwidth is divided into lower bandwidth subcarriers

• Each subcarrier operates at a different, equally-spaced center

frequency

• Bits are modulated and transmitted simultaneously on each data

subcarrier during a symbol time

• LTE uses OFDMA in the DL and SC-FDMA in the UL

Channel

(8)

OFDM Basics

- Data is sent in parallel across the set of subcarriers, each subcarrier only

transports a part of the whole transmission

- The throughput is the sum of the data rates of each individual (or used)

subcarriers while the power is distributed to all used subcarriers

Power

frequency

bandwidth

(9)

Multi-Carrier Modulation

• Multiple carriers in parallel (Subcarriers).

frequency

Serial-to-Parallel

Converter

011001011100101001011101

011 001 011 100 101 001 011 101

Subcarriers

Guard Bands

(10)

Multi-Carrier Modulation

• The center frequencies must be spaced so that interference between

different carriers, known as Adjacent Carrier Interference ACI, is

minimized; but not too much spaced as the total bandwidth will be wasted.

frequency

f

₀

_f

1

f

2

f

N-2

f

N-1

(11)

OFDM: Orthogonal Frequency Division Multi-Carrier

• OFDM allows a tight packing of small carrier - called the subcarriers - into

a given frequency band.

P

o

w

e

r

D

e

n

s

it

y

P

o

w

e

r

D

e

n

s

it

y

Frequency (f/fs)

Saved

Bandwidth

(12)

OFDM Basics

• Transmits hundreds or even thousands of separately modulated

radio signals using orthogonal subcarriers spread across a

wideband channel

Orthogonality:

The peak ( centre

frequency) of one

subcarrier …

…intercepts the

‘nulls’ of the

neighbouring

subcarriers

(13)

OFDM and Multiple Access

• Up to here we have only discussed simple point-to-point or

broadcast OFDM.

• Now we have to analyze how to handle access of multiple users

simultaneously to the system, each one using OFDM.

• OFDM can be combined with several different methods to handle

multi-user systems:

1.-Plain OFDM

3.-Orthogonal Frequency Division Multiple Access OFDMA®

2.-Time Division Multiple Access via OFDM

(14)

1.- Plain OFDM

• Plain OFDM: Normal OFDM has no built-in

multiple-access mechanism.

• This is suitable for broadcast systems like

DVB-T/H which transmit only broadcast and

multicast signals and do not really need an

uplink feedback channel (although such

systems exist too).

.

Plain OFDM

time

s

u

b

c

a

rr

ie

r

...

1

2

3 common info

(may be addressed via

Higher Layers)

UE 1

UE 2

UE 3

(15)

2.- Time Division Multiple Access via OFDM

• Time Division Multiple Access via OFDM:

The simplest model to implement multiple

access handling is by putting a time

multiplexing on top of OFDM.

• The disadvantage of this simple mechanism

is, that every user gets the same amount of

capacity (subcarriers) and it is thus rather

difficult to implement flexible (high and low) bit

rate services.

• Furthermore it is nearly impossible to handle

highly variable traffic (e.g. web traffic)

efficiently without too much higher layer

signaling and the resulting delay and signaling

overhead.

1

1 .

.

2

2 .

.

3

3 .

.

Time Division Multiple

Access on OFDM

time

s

u

b

c

a

rr

ie

r

...

1

2

1

2

3 common info

(may be addressed via

Higher Layers)

UE 1

UE 2

UE 3

(16)

2.- Orthogonal Frequency Division Multiple Access

OFDMA®

• Orthogonal Frequency Division Multiple Access

OFDMA®: is a registered trademark by Runcom

Ltd.

• The basic idea is to assign subcarriers to users

based on their bit rate services. With this approach

it is quite easy to handle high and low bit rate users

simultaneously in a single system.

• But still it is difficult to run highly variable traffic

efficiently.

• The solution to this problem is to assign to a single

users so called resource blocks or scheduling

blocks.

• Such block is simply a set of some subcarriers over

some time.

• A single user can then use one or more Resource

blocks.

1

1 .

.

2 .

.

3 .

.

Orthogonal Frequency

Multiple Access

OFDMA®

time

...

1

2

3

1 s

u

b

c

a

rr

ie

r

1

3

3 Resource Block (RB)

1

2

3 common info

(may be addressed via

Higher Layers)

(17)

.

Plain OFDM

time

s

u

b

c

a

rr

ie

r

...

1

1 .

.

2

2 .

.

3

3 .

.

Time Division Multiple Access

on OFDM

time

s

u

b

c

a

rr

ie

r

...

1

2

2 OFDMA® is registered trademark of Runcom Technologies Ltd.

1

1 .

.

2

2 .

.

3

3 .

.

Plain Orthogonal Frequency

Multiple Access

OFDMA®

time

...

1

2

1

3

1

1 s

u

b

c

a

rr

ie

r

1

1 .

.

2 .

.

3 .

.

Orthogonal Frequency

Multiple Access

OFDMA®

time

...

1

2

3

1 s

u

b

c

a

rr

ie

r

1

3

3 Resource Block (RB)

1

2

3 common info

(may be addressed via HL)

UE 1

UE 2

UE 3

(18)

Channel Bandwidth

1.4 MHz

3 MHz

5 MHz

10 MHz

15 MHz

20 MHz

• LTE defines channel sizes from

1.4 MHz to 20 MHz

Channel

(19)

OFDM Challenges

High Peak-to-Average Power Ratio (PAPR) of the transmitted signal: this

results in requirements for expensive linear power amplifiers.

(20)

The transmitted power is the sum of

the powers of all the subcarriers

- Due to large number of

subcarriers, the peak to average

power ratio (PAPR) tends to have

a large range

- The higher the peaks, the greater

the range of power levels over

which the transmitter is required

to work.

- Not best suited for use with

mobile ( battery-powered)

devices

(21)

- Single Carrier Frequency Division Multiple

Access: Transmission technique used for

Uplink

• Variant of OFDM that reduces the PAPR:

• Combines the PAR of single-carrier system with the

multipath resistance and flexible subcarrier

frequency allocation offered by OFDM.

• It can

reduce the PAPR between 6…9dB

compared

to OFDMA

• TS36.201 and TS36.211 provide the mathematical

description of the time domain representation of an

SC-FDMA symbol.

- Reduced PAPR means lower RF hardware

requirements ( power amplifier)

S

C

-F

D

M

A

O

F

D

M

A

SC-FDMA in UL

(22)

SC-FDMA and OFDMA Comparison

- OFDMA transmits data in parallel across multiple subcarriers

- SC-FDMA transmits data in series employing multiple subcarriers

- In the example:

• OFDMA: 6 modulation symbols ( 01,10,11,01,10 and 10) are transmitted per

OFDMA symbol, one on each subcarrier

• SC-FDMA: 6 modulation symbols are transmitted per SC-FDMA symbol using

all subcarriers per modulation symbol.

(23)

(24)

Channel Direction

• Downlink (DL) is always from the eNodeB to the UEs

• Uplink (UL) is always from the UE(s) to the eNodeB

eNodeB

UE1

(25)

LTE FDD and TDD Modes

Uplink

Downlink

Bandwidth

up to 20MHz

Duplex Frequency

f

t

Bandwidth

up to 20MHz

Guard

Period

f

t

Uplink

Downlink

Bandwidth

up to 20MHz

(26)

TDD vs. FDD

Downlink

Uplink

FDD

TDD

Time

Frequency

Throughput

DL

UL

_DL

UL

Only this is

needed

Wasted

We get what we need

Downlink throughput

is also affected

(27)

LTE Radio Frames, Slots and Subframes

FDD mode

• The basic EUTRAN Radio Frame is 10 ms long.

• The EUTRAN Radio Frame is divided into 20 slots, each one 0.5 ms long.

• Always two slots together form a subframe. The subframe (1 ms) is the

smallest time unit the scheduler assigns to physical channels.

• In case of FDD there is a time offset between uplink and downlink

transmission.

Slot

#0

Slot

#0

Slot

#1

Slot

#1

Slot

#2

Slot

#2

Slot

#3

Slot

#3

Slot

#16

Slot

#16

Slot

#17

Slot

#17

Slot

#18

Slot

#18

Slot

#19

Slot

#19

. . .

Slot

#0

Slot

#0

Slot

#1

Slot

#1

Slot

#2

Slot

#2

Slot

#3

Slot

#3

Slot

#16

Slot

#16

Slot

#17

Slot

#17

Slot

#18

Slot

#18

Slot

#19

Slot

#19

. . .

f

DL carrier

UL carrier

radio frame 10 ms

subframe 0

subframe 1

subframe 8

subframe 9

subframe 0

subframe 1

subframe 8

subframe 9

D

L

/U

L

T

im

e

o

ff

s

e

t

time

(28)

LTE Radio Frames, Slots and Subframes

TDD mode

• If TDD mode is used, subframe 0 and subframe 5 must be downlink, all

other subframes can dynamically be used as uplink or downlink period.

Slot

#0

Slot

#1

Slot

#2

Slot

#3

Slot

#16

Slot

#17

Slot

#18

Slot

#19

. . .

f

time

UL/DL

carrier

radio frame 10 ms

subframe 0

subframe 1

subframe 5

_{subframe 9}

. . .

(29)

LTE Physical Layer Structure – Frame Structure

- FDD Frame structure is common to both uplink and downlink.

- Divided into 20 x 0.5ms slots

• Structure has been designed to facilitate short round trip time

10 ms frame

0.5 ms slot

s

₀

s

₁

s

₂

s

₃

s

₄

s

₅

s

₆

s

₇

_…..

s

18

s

19

1 ms sub-frame

SF

0 SF

1 SF

2 …..

SF

9 sy

4

sy

0

sy

1

sy

2

sy

3

sy

5

sy

6

0.5 ms slot

SF

3 -

Frame length =10 ms

-

FDD: 10 ms sub-frame for UL and

10 ms sub-frame for DL

-

1 Frame = 20 slots of 0.5ms each

-

1 slot = 7 ( normal CP) or 6

symbols ( extended CP)

SF: SubFrame

s: slot

(30)

LTE Slot

The LTE Slot carries:

• 7 symbols with short cyclic prefix

(31)

Cyclic Prefix

Extended Symbol Time

T

_CP

Cyclic Prefix

• T

_CP

accounts for multipath delay (distance)

• Cyclic Prefix copies signal from the end of the symbol time and

attaches in front of the symbol time

• Normal T

_CP

is 4.67 µs

• Extended T

_CP

is 16.67 µs

(32)

Multi-Path Propagation and Inter-Symbol Interference

Inter Symbol Interference

BTS

Time 0 Ts

+

Time 0 Tt Ts+Tt

(33)

Multi-Path Propagation and the Guard Period

2 time

T

SYMBOL

Time Domain

1

3 time

T

_SYMBOL

time

T

_SYMBOL

T

_g

1

2

3 Guard Period (GP)

Guard Period (GP)

(34)

f

₀

f

₁

f

₂

f

₃

f

₄

15 kHz

LTE/EUTRAN Air Interface

• LTE uses a 15 kHz subcarrier spacing (fs).

Therefore the Symbol duration (Ts) is 66.67

µ

s.

• This corresponds to bandwidths from 1.4 MHz,

3 MHz, 5 MHz,10 MHz, 15MHZ and up to

20 MHz.

• Its an operator’s choice how many subcarriers

(bandwidth) a cell should get.

(35)

OFDM Key Parameters

In LTE not all the available channel bandwidth (e.g. 20 MHz) will be used. For the

transmission bandwidth typically 10% guard band is considered (to avoid the out band

emissions).

If BW = 20MHz

→

Transmission BW = 20MHz – 2MHz = 18 MHz

→

the number of subcarriers Nc = 18MHz/15KHz = 1200 subcarriers

Transmission

Bandwidth [RB]

Transmission Bandwidth Configuration [RB]

Channel Bandwidth [MHz]

R

e

s

o

u

rc

e

b

lo

c

k

C

h

a

n

e

l e

d

g

e

C

h

a

n

e

l e

d

g

e

DC carrier

Active Resource Blocks

(36)

OFDMA Parameters

- Channel bandwidth:

Bandwidths ranging from 1.4 MHz to 20 MHz

- Data subcarriers:

They vary with the bandwidth

• 72 for 1.4MHz to 1200 for 20MHz

Guard (no power)

DC (no

power)

data

Guard (no power)

(37)

Physical Resource Blocks

• In both the downlink and

uplink direction, data is

allocated to users in terms

of resource blocks (RBs).

• A resource block consists

of 12 consecutive

subcarriers in the

frequency domain, that are

reserved for the duration of

one 0.5 millisecond time

slot.

• The smallest resource unit

a scheduler can assign to a

user is a scheduling block

which consists of two

consecutive resource

blocks

..

12 subcarriers

Time

Frequency

0.5 ms slot

1 ms subframe

or TTI

Resource

block

During each TTI,

resource blocks for

different UEs are

scheduled in the

eNodeB

(38)

OFDM Resource Block for LTE/EUTRAN

• EUTRAN combines OFDM symbols in so

called resource blocks (RB).

• A single resource block is always 12

consecutive subcarriers during one slot

(0.5 ms):

• 12 subcarriers * 15 kHz= 180 kHz

• It is the task of the scheduler to assign

resource blocks to physical channels

belonging to different users or for general

system tasks.

• A single cell must have at least 6 resource

blocks (72 subcarriers) and up to 100 are

possible (1200 subcarriers).

frequency

time

Subcarriers

Subframe

1ms

Subcarrier

Bandwidth

15kHz

B

a

n

d

w

id

th

1

8

0 k

H

z

Slot

R

e

s

o

u

rc

e

B

lo

c

k

(39)

OFDM resource Grid for LTE/EUTRAN

frequency

time

…

Slot = 0.5 ms

1

2 s

u

b

c

a

rr

ie

rs

6 or 7 Symbols/slot

OFDM Symbol

Scheduling Resource Block

(SRB)

• OFDM symbols are arranged in a 2 dimensional matrix called the resource grid:

–

One axis of the grid is the subcarrier index

–

The other axis is the time.

• Each OFDM symbol has its place in the resource grid.

(40)

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 6

Subcarrier 1

Subcarrier 12

1

8

0 K

H

z

1 slot

1 ms subframe

• 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

(41)

(42)

OFDMA Parameters

- Frame duration:

10ms created from slots and subframes

- Subframe duration ( TTI):

1 ms ( composed of 2 x 0.5slots)

- Subcarrier spacing:

Fixed to 15kHz ( 7.5 kHz defined for MBMS)

Varies with the bandwidth but always factor

or

multiple of 3.84 to ensure compatibility with

WCDMA by using common clocking

Frame Duration

Subcarrier Spacing

Resource Block

Data Subcarriers

Symbols/slot

CP length

1.4MHz

3 MHz

5 MHz

10 MHz

15 MHz

20 MHz

10 ms

15 kHz

Normal CP=7, extended CP=6

Normal CP=4.69/5.12

µ

sec., extended CP= 16.67

µ

sec.

6

15

25

50

75

100

72

180

300

600

900 1200

(43)

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

1 slot

1 ms subframe

OFDM resource Grid for LTE/EUTRAN

• Reference symbols helps the

UE to keep the synchronization

with the network over the air

interface, both in term of time

and frequency synchronization.

Subcarrier 1

Subcarrier 12

1

8

0 K

H

z

OFDM Symbols/ Time Domain

Reference Symbols

(44)

b

₀

b

₁

QPSK

Im

Re

10

11

00

01 b

₀

b

₁

b

₂

b

₃

16QAM

Im

Re

0000

1111

Im

Re

64QAM

b

₀

b

₁

b

₂

b

₃

b

₄

b

₅

• Each OFDM symbol even within a resource block can have a different

modulation scheme.

• EUTRAN defines the following options: QPSK, 16QAM, 64QAM.

Not every physical channel will be allowed to use any modulation scheme:

Control channels to be using mainly QPSK.

• In general it is the scheduler that decides which form to use depending on

carrier quality feedback information from the UE.

(45)

LTE Modulation Techniques

• Modulation techniques supported:

• BPSK

– 1 bit per symbol

QPSK

– 2 bits per symbol

16QAM – 4 bits per symbol

64QAM – 6 bits per symbol

• BPSK used for preambles

• DL traffic uses QPSK, 16QAM, 64QAM

(46)

Modulation

(47)

Downlink Peak Bit Rate

• 2x2 MIMO (2 antennas for TX, 2 Antennas for RX)

• 64QAM

• Control & Reference symbol overhead 14.8%

• 172 Mbps in 20 MHz and 86 Mbps in 10 MHz

Resource blocks

6

15

25

50

100 Subcarriers

72

180

300

600 1200

Modulation coding

1.4 MHz

3.0 MHz

5.0 MHz

10 MHz

20 MHz

QPSK 1/2

Single stream

0.9

2.2

3.6

7.2

14.4 16QAM 1/2

Single stream

1.7

4.3

7.2

14.4

28.8 16QAM 3/4

Single stream

2.6

6.5

10.8

21.6

43.2 64QAM 3/4

Single stream

3.9

9.7

16.2

32.4

64.8 64QAM 4/4

Single stream

5.2

13.0

21.6

43.2

86.4 64QAM 3/4

2x2 MIMO

7.8

19.4

32.4

64.8

129.6 64QAM 1/1

2x2 MIMO

10.4

25.9

43.2

86.4

172.8

(48)

Resource blocks

5

14

24

49

99 Subcarriers

60

168

288

588 1188

Modulation coding

1.4 MHz

3.0 MHz

5.0 MHz

10 MHz

20 MHz

QPSK 1/2

Single stream

0.7

2.0

3.5

7.1

14.3 16QAM 1/2

Single stream

1.4

4.0

6.9

14.1

28.5 16QAM 3/4

Single stream

2.2

6.0

10.4

21.2

42.8 16QAM 1/1

Single stream

2.9

8.1

13.8

28.2

57.0 64QAM 3/4

Single stream

3.2

9.1

15.6

31.8

64.2 64QAM 1/1

Single stream

4.3

12.1

20.7

42.3

85.5 64QAM 1/1

V-MIMO (cell)

8.6

24.2

41.5

84.7

171.1 Uplink Peak Bit Rate

• Single stream transmission with 64QAM assumed

• Reference symbol overhead 14.3%

(49)

LTE UE Categories

Qualcomm first chipset has 50 Mbps downlink and 25 Mbps uplink

• All categories support 20 MHz

• 64QAM mandatory in downlink, but not in uplink (except Class 5)

• 2x2 MIMO mandatory in other classes except Class 1

Class 1

Class 2

Class 3

Class 4

Class 5

10/5 Mbps

50/25 Mbps

100/50 Mbps

150/50 Mbps

300/75 Mbps

Peak rate DL/UL

20 MHz

RF bandwidth

20 MHz

64QAM

Modulation DL

64QAM

16QAM

Modulation UL

16QAM

64QAM

Yes

Rx diversity

Yes

1-4 tx

BTS tx diversity

Optional

MIMO DL

2x2

4x4

(50)

3GPP LTE Spectrum

Band MHz Uplinks MHz Downlink MHz Region or typical name

1 2x60 1920-1980 2110-2170 FDD UMTS core, “2.1GHz” 2 2x60 1850-1910 1930-1990 US PCS, “1900MHz” 3 2x75 1710-1785 1805-1880 “1800MHz” 4 2x45 1710-1755 2110-2155 US AWS

5 2x25 824-849 869-894 “850MHz”; US, Korea, APAC, MEA, Africa 7 2x70 2500-2570 2620-2690 “2.6GHz”

8 2x35 880-915 925-960 GSM 900 9 2x35 1749-1784 1844-1879 Japan 1700 10 2x60 1710-1770 2110-2170 Extended AWS 11 2x20 1427.9-1447.9 1475.9-1495.9 Japan 1500

12 2x17 699-716 729-746 US 700 MHz Lower (Band A,B,C)

13 2x10 777-787 746-756 US 700 MHz Upper (Band C) – Verizon

14 2x10 788-798 758-768 US 700 MHz Upper (Band D+)

17 2x12 704-716 734-746 US 700 MHz Lower (Band B, C) – AT&T

18 2x15 815-830 860-875 Japan 800 – new 19 2x15 830-845 875-890 Japan 800 – new

20 2x30 832-862 791-821 „800MHz“; European Digital Dividend band

21 2x15 1448-1463 1496-1511 Japan (upper 1500) 22 2x80 3410-3490 3510-3590 3,5 GHz band FDD 23 2x20 2000-2020 2180-2200 US S-band 24 2x34 1626.5-1660.5 1525-1559 US L-band 25 2x65 1850-1915 1930-1995 US ext. 1900 26 2x35 814-849 859-894 Korea, US: Extended 850 27 2x17 807-824 852-869 Latin America, 850 28 2x45 703-748 758-803 “APAC 700”; mainstream 33 1x20 1900-1920 TDD UMTS core TDD 34 1x15 2010-2025 UMTS core TDD 35 1x60 1850-1910 US (possible TDD alternative to FDD) 36 1x60 1930-1990 US (possible TDD alternative to FDD) 37 1x20 1910-1930 US

38 1x50 2570-2620 “2.6GHz - TDD part”, China, Europe, Lat.Am

39 1x40 1880-1920 China UMTS TDD

40 1x100 2300-2400 China TDD, APAC ,MEA, RUS,….

41 1x194 2496-2690 US TDD 42 1x200 3400-3600 TDD global 43 1x200 3600-3800 TDD global 44 1x90 703-803 “APAC700”; alternative

(51)

MIMO

• MIMO stands for Multiple Input Multiple Output.

• It is a key technology to increase a channel’s capacity by using multiple transmitter

and receiver antennas.

• The very basic ideas behind MIMO have been established already 1970 , but have

not been used in radio communication until 1990.

Air Interface

Transmission antennas

(52)

MIMO

• MIMO is currently used in 802.11n, 802.16d/e to increase the channel

capacity.

• LTE supports 2x2 and 4x4 MIMO configurations.

• Two kinds of MIMO techniques:

• Multistream transmission (also known as spatial multiplexing) MIMO

• Transmit Diversity (or space-time coding) MIMO.

TX

RX

(53)

Examples of MIMO Usage

Spatial

multiplexing

Transmission

diversity

Typically, close to the eNodeB Spatial multiplexing could be used to improve the throughput

At the cell edge Transmission diversity could be used to improve the coverage

(54)

Dynamic MIMO mode

Depending on Radio Conditions:

switch between Diversity and Spatial Multiplexing

Spatial

Multiplex

(55)

Scope of RRM

• Management

and optimized utilization of the (scarce) radio resources:

• Provision for each service/bearer/user an adequate QoS

(if applicable)

• Increasing

the overall radio network capacity

and optimizing quality

• RRM is located in eNodeB

LTE-UE

Evolved Node

B

(eNB)

X2

LTE-Uu

eNB

(56)

Radio Admission Control ( RAC)

Objective:

To admit or to reject the requests for establishment of Radio Bearers

(RB) on a cell basis

- Based on number of RRC connections

and number of active users per cell

• Non QoS aware

- Operator configures both max. number of established RRC connections and

max. number of active users per cell.

• RRC connection is established when the

SRBs

have been admitted and

successfully configured.

(57)

LTE vs. R99 Scheduling

NodeB Rel. 99

eNodeB LTE

Fast pipe is shared among UEs

Dedicated pipe for every UE

(58)

Scheduler Types

A variety of scheduling strategies is available.

Examples are:

- Round-Robin

No quality indication is taken into consideration. The resources are mainly shared in an equal

manner.

- Max C/I.

The UE with the best channel conditions gets the highest priority. The cell throughput is

maximised. Starvation of UEs with channels of low quality may be a disadvantage.

- Proportional Fair.

This algorithm defines priorities based on the quality and the averaged scheduled rate.

- QoS

Different strategies exist to get QoS related information integrated.

E.g. Depending on the priority of the service and/or the UE, RT/NRT service type. a scheduling

weight can be introduced.

(59)

Link Adaptation by AMC (UL/DL)

• Motivation of link adaptation:

Modify the signal transmitted to and by a

particular user according to the signal quality variation to improve the system

capacity and coverage reliability.

• If SINR is good then higher MCS can be used -> more bits per byte ->

more throughput.

• If SINR is bad then lower MCS should be use ( more robust)

(60)

Handover Types

E-UMTS micro cells

Intra-frequency HO

(intra eNB)

intra-frequency HO

(inter eNB, inter MME)

1a

interfrequency HO

other RAT

E-UMTS macro cell

intersystem HO

triggered by e.g.

-

coverage of E-UMTS

-

service load

1b

3

2 intersystem HO

triggered by other

RAT

(61)

RRM differences between LTE & UMTS

• The main difference reflects decentralized RRM control

moved to the edge of E-UTRAN (RRM resides at eNB) as

opposed to the centralized RRM control in UMTS (RNC

entity performs most RRM functions).

• Softer and Soft handovers are not supported by the LTE

system

• LTE requirements on power control are much less

stringent due to the different nature of LTE radio interface

i.e. OFDMA (WCDMA requires fast power control to

address the “Near-Far” problem and intra-frequency

interferences)

• On the other hand LTE system requires much more

stringent timing synchronization for OFDMA signals.

(62)

(63)

Radio Protocols Architecture

MAC

RLC

PDCP

Physical Layer

RRC

L

1 L

2 L

3 Radio Bearer

Logical Channel

Transport Channels

Control Plane

User Plane

(64)

Radio Protocols Architecture (1/2)

The EUTRAN radio protocol model specifies the protocols terminated between UE and eNB. The

protocol stack follows the standard guidelines for radio protocol architectures (ITU-R M1035)

and is thus quite similar to the WCDMA protocol stack of UMTS.

The protocol stack defines three layers: the physical layer (layer 1), data link and access layer

(layer 2) and layer 3 hosting the access stratum and non-access stratum control protocols as

well as the application level software (e.g. IP stack).

physical layer: The physical layer forms the complete layer 1 of the protocol stack and provides

the basic bit transmission functionality over air. In LTE the physical layer is driven by OFDMA

in the downlink and SC-FDMA in the uplink. FDD and TDD mode can be combined (depends

on UE capabilities) in the same physical layer. The physical layer uses physical channels to

transmit data over the radio path. Physical channels are dynamically mapped to the available

resources (physical resource blocks and antenna ports). To higher layers the physical layer

offers its data transmission functionality via transport channels. Like in UMTS a transport

channel is a block oriented transmission service with certain characteristics regarding bit

rates, delay, collision risk and reliability. Note that in contrast to 3G WCDMA or even 2G GSM

there are no dedicated transport or physical channels anymore, as all resource mapping is

dynamically driven by the scheduler.

MAC (Medium Access Control): MAC is the lowest layer 2 protocol and its main function is to

drive the transport channels. From higher layers MAC is fed with logical channels which are

in one-to-one correspondence with radio bearers. Each logical channel is given a priority and

MAC has to multiplex logical channel data onto transport channels. In the receiving direction

obviously demultiplexing of logical channels from transport channels must take place. Further

functions of MAC will be collision handling and explicit UE identification. An important function

(65)

Radio Protocols Architecture (2/2)

RLC (Radio Link Control): Each radio bearer possesses one RLC instance working in either of the

three modes: UM (Unacknowledged), AM (Acknowledged) or TM (Transparent). Which mode is

chosen depends on the purpose of the radio bearer. RLC can thus enhance the radio bearer with

ARQ (Automatic Retransmission on reQuest) using sequence numbered data frames and status

reports to trigger retransmission. Note that it shall be possible to trigger retransmissions also via

the HARQ entity in MAC. The second functionality of RLC is the segmentation and reassembly that

divides higher layer data or concatenates higher layer data into data chunks suitable for transport

over transport channels which allow a certain set of transport block sizes.

PDCP (Packet Data Convergence Protocol): Each radio bearer also uses one PDCP instance. PDCP

is responsible for header compression (ROHC RObust Header Compression; RFC 3095) and

ciphering/deciphering. Obviously header compression makes sense for IP datagram's, but not for

signaling. Thus the PDCP entities for signaling radio bearers will usually do ciphering/deciphering

only.

RRC (Radio Resource Control): RRC is the access stratum specific control protocol for EUTRAN. It

will provide the required messages for channel management, measurement control and reporting,

etc.

NAS Protocols: The NAS protocol is running between UE and MME and thus must be transparently

transferred via EUTRAN. It sits on top of RRC, which provides the required carrier messages for

NAS transfer.

(66)

FDD | TDD - Layer 1

( DL: OFDMA, UL: SC-FDMA )

Medium Access Control (MAC)

Physical Channels

Transport Channels

RLC

Control)

RLC

(Radio Link Control)

…

PDCP’

Convergence Protocol)

PDCP’

(Packet Data Convergence Protocol)

…

RLC

Control)

RLC

PDCP’

RLC

Control)

RLC

PDCP

RLC

Control)

RLC

(Radio Link Control) Convergence

PDCP

RLC

Control)

RLC

(Radio Link Control) Convergence

PDCP

Logical Channel

(E-)RRC

(Radio Resource Control)

IP / TCP | UDP | …

Application 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/…)

(67)