AIRCOM LTE Webinar 2 - Air Interface

Graham
Whyley
Lead LTE
Technical
Trainer

The webinar will start shortly.

AIRCOM LTE Webinar Series:

LTE Air-Interface (Part 1)
1

© 2013 AIRCOM International Ltd

Graham
Whyley
Lead LTE
Technical
Trainer

www.aircominternational.com/Webinars

AIRCOM LTE Webinar Series:

LTE Air-Interface (Part 1)
2


About the Presenters
Graham Whyley – Lead Technical Trainer

AIRCOM Technical Master Trainer since 2005

Currently responsible for all LTE training
course creation and delivery

Over 20 years of training experience at
companies including British Telecom and
Fujitsu

Adam Moore – Learning & Development
Manager

With AIRCOM since 2006

Member of CIPD

Contact us at training@aircominternational.com
3


About AIRCOM
AIRCOM is the leading provider of mobile network planning,
optimisation and management software and consultancy services.







Founded in 1995
14 offices worldwide
Over 150 LTE customers
Acquired Symena in 2012
Products deployed in 159
countries
Comprehensive Tool and
technology training portfolio

Find out more at www.aircominternational.com
4


Agenda- LTE Air-Interface (Part 1)
 LTE Air-Interface
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5

What is own cell Interference?
What is other cell Interference?
What is SINR?
What is Physical Resource Block
cyclic prefix
Time Transmission Interval (TTI)
Normal & Extended

PRACH PARAMETERS- LTE TROUBLE SHOOTING COURSE

Unlikely to get own cell interference:
Same time/Same Frequency

However
If you lose timing advance
Frequency

PRACH

Different Time
UE 2

Frequency

UE 1

Timing Av

RRC
CONNECTED

Time Slot

Data

Evolved
Node B
(eNB)

Time Slot

Packet
Scheduling

PS allocates
frequency and Time
to the UE
6

Data

UE 1

UE 2


PRACH PARAMETERS- LTE TROUBLE SHOOTING COURSE
PRACH Parameters effect
coverage
UPLINK THROUGHPUT

Unlikely to get own cell interference:

Same time/Same Frequency

PRACH Parameters affect
coverage

However
If you lose timing advance
Frequency

PRACH

Different Time
UE 2

Frequency

UE 1

Timing Av

RRC
CONNECTED

An other reason for
own Interference
Inter-symbol
This effects
coverage/Capacity
7

Time Slot

Data

Timing Advance effect
coverage

Evolved
Node B
(eNB)

Time Slot

Packet
Scheduling

PS allocates
frequency and Time
to the UE

Data

UE 1

UE 2


Function Evolved Node B (eNB)
Evolved
Node B

SINR ave =

S
I+N
I = Iown + Iother

(eNB)

RRC
CONNECTED
UE at cell edge
Same time slot
Same Frequency

PS allocates
frequency and
Time to the UE

Packet
Scheduling

Data

Other Cell
Interference
Evolved
Node B
(eNB)
Packet
Scheduling

Data

PS allocates frequency and
Time to the UE

8


Traffic SINR
SINR ave = S
I+N
I = Iown + Iother

There are a number of ways of
controlling other cell Interference

9


Channel Quality Indicator
CQI=15

The CQI indicates the downlink
channel quality

CQI=10

Evolved
Node B

RF conditions will change as the user moves
CQI=1

(eNB)

CQI=8

Packet
Scheduling

Downlink
16-QAM

User reports CQI index8, it informs the eNB that, for the CQI bandwidth being
reported, it can support a transport block using 16-QAM modulation
and a coding rate of approximately 0.48 with a block error of less than
10%.
10


Channel Quality Indicator
The CQI indicates the downlink
channel quality

Coding Rate

PS takes the decision to
OPSK
16QAM
assign a particular MCS
64QAM
2bits/Hz
4bits/Hz
6bits/Hz
(modulation and coding
scheme) for a particular
modulation and coding scheme
Evolved
UE.
Node B

CQI

CQI

(eNB)

CQI
QPSK for noisy channels

Physical Uplink Control Channel (PUCCH)
Packet Scheduling

CQI
Physical Uplink Shared Channel(PUSCH)

The CQI mainly depends on the received signal to interference plus noise ratio,
because a high data rate can only be received successfully at a high SINR.
Periodic Reporting
Normally on PUCCH,
PUSCH used when
multiplexed with data
11

Aperiodic Reporting
When requested by eNodeB
(DCI format 0 on PDCCH)
Always on PUSCH

SINR - Signal to Interference & Noise
Ratio
S: indicates the power of
measured usable signals.
SINR ave = S
I+N
I = Iown + Iother

Path Loss

12


SINR - Signal to Interference & Noise
Ratio
CQI Modulation
Actual
coding rate

Required
SINR

I: interference signals from other cells in the
current system plus own cell
N: indicates background noise, which is related
to measurement bandwidths and receiver
noise coefficients
UEs typically use SINR to calculate the CQI
(Channel Quality Indicator) they report to the
network
13

QPSK

0.11719

-3.75

QPSK

0.18848

-2.55

4

QPSK

308/1024

-1.15

QPSK

449/1024

1.75

6

QPSK

602/1024

3.65

7

16QAM

378/1024

5.2

8

16QAM Quality Indicator 6.1
Channel 490/1024

9

16QAM

616/1024

7.55

10

64QAM

466/1024

10.85

11

64QAM

567/1024

11.55

12

S: indicates the power of measured usable
signals.

-4.46

5

The components of the SINR calculation can be
defined as:

SINR ave = S
QPSK
I + N 0.07618
I = Iown + Iother

64QAM

666/1024

12.75

13

64QAM

772/1024

14.55

14

64QAM

873/1024

18.15

15

64QAM

948/1024

19.25

1
2
3

not defined in the 3GPP specs but defined by the UE vendor.


Function Evolved Node B (eNB)
SINR

SINR = 19db

SINR=-4.46dB
SINR ave =

S
I+N
I = Iown + Iother

QPSK
2bits/Hz

Evolved
Node B
16QAM
4bits/Hz

64QAM
6bits/Hz

(eNB)

Data

Packet
Scheduling

By improving SINR you will increase coverage and
throughput
SINR

SINR = 19db

SINR=-4.46dB

QPSK
2bits/Hz

14

Evolved
Node B
16QAM
4bits/Hz

64QAM
6bits/Hz

(eNB)

Packet Scheduling

Data


Traffic SINR

Point of
interest

15


Poll

What is meant by adaptive modulation
and coding (AMC)?

16


Poll
Link adaptation, or adaptive modulation and coding (AMC), is a term used in wireless
communications to denote the matching of the modulation, coding and other signal
and protocol parameters to the conditions on the radio link

If the base station receives the data correctly

Sends the mobile a positive acknowledgement
on the physical hybrid ARQ indicator channel
(PHICH).

17


Poll
If the base station receives the data with errors
Two ways for it to respond

1. The base station can trigger a
non adaptive re-transmission by sending the mobile a
negative acknowledgement on the PHICH.
The mobile then re-transmits the data with the same
parameters that it used first time around.
Scheduling grant
Change parameters like uplink modulation scheme
QPSK for noisy channels
2. Alternatively, the base station can trigger an adaptive re-transmission by
explicitly sending the mobile another scheduling grant. It can do this to change the
parameters that the mobile uses for the re-transmission, such as the resource block
allocation or the uplink modulation scheme.
18


What is a time slot?
Physical Resource Block

time slot
0

You need allot of frequencies

Block of
Frequencies

19

Same Time-Different Frequency
Own cell interference zero

time slot
1
Same Frequency -Different time
Own cell interference zero

Block of
Frequencies

Block of
Frequencies

Block of
Frequencies

SINR ave = S
I+N
I = Iown + Iother

Block of
Frequencies


What is a time slot?

10ms

0.5ms

time slot
0

time slot
1

You need allot of frequencies

Block of
Frequencies

Block of
Frequencies

Block of
Frequencies

Block of
Frequencies

Block of
Frequencies
20

time slot
2

time slot
19

UE1

TTI = 1ms
10 sub channels in 10mS
Physical Downlink Control Channel (PDCCH)

TTI = 1mS
UE3


Physical downlink control channel (PDCCH)
10ms

0.5ms

sub channel
time slot
0
Block of
I need to read the PDCCHFrequencies
Is it QPSK, 64 QAM, 16QAM
What is the size of the
transport Block?
Do I do hopping?
What about Power control
What is my uplink/Down link
resources?

time slot
1

time slot
2

time slot
3

time slot
19

UE1

Physical Downlink Shared Channels

Physical downlink control channel
(PDCCH)

I cannot change my MCS
till I see another PDCCH

Scheduling grant
I need to change MCS

At the start of each subframe, a few symbols are reserved for the control information that
the base station transmits on the PCFICH, PDCCH and PHICH. The number of control
symbols can vary from one subframe to the next, depending on how much control
information the base station needs to send.
21


What is Physical Resource Block?
100 Physical Resource Blocks

0.5ms

time slot
0

Frequencies 1200

12 subcarriers
12 subcarriers

Block of
Frequencies

12 subcarriers

Block of
Frequencies

12 subcarriers

Block of
Frequencies

12 subcarriers
22

Block of
Frequencies

Block of
Frequencies

In LTE the Physical
Resource Block is
made up of 12
subcarriers
If there are 100
Physical Resource
Blocks you would
require 1200
frequencies

Master Information Block
Bandwidth 1.4
(MHz)
# of RBs

6

3

5

10

15

20
LTE-Uu
Air-Interface

15

25

50

75

100

MIB

Evolved
Node B
(eNB)

20MHz
15MHz

10MHz
5MHz
3MHz

Subcarriers

72

180

300

600

900

1200

1.4MHz

Channel Bandwidth
in Resource Blocks

6 x 12 = 72 Subcarriers
50 x 12 = 600 Subcarriers
23


Master Information Block
Logical

BCCH

Transport

PCCH

CCCH

DCCH

DTCH MCCH

MTCH

BCH
PCH

DL-SCH

MCH

PHYS.
PBCH

PDSCH

PMCH

REFERENCE
SIGNALS

R
R

R
R

R

0

24


Physical Resource Block
12 subcarriers

0.5ms

Physical
Resource
Block

time slot
0

Normal Frame
84 OFDM symbols (12x7)

cyclic prefix
In the time domain, a guard interval may be added to
each symbol to combat inter-OFDM-symbol-interference
due to channel delay spread
Normal 7
Extended 6

12 subcarriers

Resource Element(RE) : The smallest
unit made up of 1 symbol x 1
subcarrier
QPSK = 2bits
16 QAM = 4bits
64 QAM = 6bits

Extended
72 OFDM symbols(12x6)
25

7 symbols


Channel Bandwidth
Carrier spacing 15 kHz

12 subcarriers in the frequency domain x
Carrier spacing 15 kHz = 180 kHz

100 x 180khz= 18Mhz

12 subcarriers = 180 kHz

Frequency Domain

Normal Cyclic Prefix

Normal Frame
84 OFDM symbols
(12x7

)

7 symbols = 0.5 ms
Time Domain

Channel Bandwidth
in Resource Blocks

50 x 180khz= 9Mhz

26


Channel Bandwidth
Channel Bandwidth (MHz)

1.4

3

5

10

15

20

Transmission Bandwidth Config. (RB)

6

15

25

50

75

100

Number of Subcarriers

72

180

300

600

900

1200

Occupied Bandwidth (MHz)

1.08

2.7

4.5

9.0

13.5

18.0

20 MHz
Channel Bandwidth (20MHz)
Transmission Bandwidth Configuration (RB)

100 x 180khz= 18Mhz

27

12 subcarriers
in the
frequency
domain x
Carrier spacing
15 kHz = 180
kHz


Any questions?

28


Delay spread

Greater the Delay spread
Greater the Guard period
Extended

Evolved
Node B
(eNB)

2
1
3

If we
sample
here

Direct signal

If we
sample
here

Reflection 1

Last Reflection

Guard Period

29

Sampling Window


Delay spread
radio waves travel at speed of light =
300 000000m/s

For LTE, the normal CP length has been set at 4.69 μs, enabling the system to
cope with path delay variations up to about 1.4 km.

300m× 4.69 =1.4km
Extended cyclic prefix of 16.7 μs for highly dispersive environments.
variations up to about 5km
300mx 16.7 =5km
30


Summary so far

Frequency Domain


Normal Frame
84 OFDM symbols
(12x7)

Resource Element
7 symbols = 0.5 ms
2 bits
Time Domain
4 bits
Extended Cyclic Prefix
6 bits

Resource Block represents the basic unit
of resource for LTE
Resource Block is a grid:
12 subcarriers in the frequency domain
(180 kHz)
6 or 7 symbols in the time domain (0.5 s)

72 or 84 Resource Elements per Resource
Block
Each Resource Element can accommodate
1 modulation symbol, e.g. QPSK, 16QAM,
64QAM
Bandwidth 1.4
(MHz)

3

5

10

15

20


# of RBs

31

Extended
72 OFDM
symbols(12x6)

6 symbols = 0.5 ms

6

15

25

50

75

100

Subcarriers

72

180

300

600

900

1200


LTE is about 300Mbps 25%
(4x4)
Overhead about

20 Mhz-100PRB



12 subcarriers x 7
OFDMA symbols= 84

How do we get 300Mbps?
PDCCH
Assume 20 MHz channel bandwidth, normal CP, 4x4
MIMO. 64 QAM modulation and no coding. 25%
overhead
64 QAM

20 MHz

reference signal
Calculate the number of resource elements (RE) in a
sub-frame with 20 MHz channel bandwidth:
7 symbols = 0.5 ms

84x100= 8400

Time Domain


Each RE can carry a modulation symbol: 2bits/4bits/6bits

8400x2=16800RE’s per subframe

32

12 subcarriers x 7 OFDMA symbols x 100 resource
blocks x 2 slots= 16800 REs per sub-frame.

7 symbols = 0.5 ms

16800REs per sub-frame x 6 = 100800bits per ms
100800 x 1000 = 100800000 bits per second
About 100 Mbits per transmitter (1x1)
4x4 MIMO about 400Mbits/s

Time-Division Duplexing (TDD)
Normal / Extended

Multicast-broadcast singlefrequency network (MBSFN)
is a communication channel
defined in Long Term
Evolution (LTE). It can deliver
services such as mobile TV
using the LTE infrastructure

33

Normal Cyclic
Prefix

7 symbols = 0.5 ms

Frequency-division duplexing(FDD)
Normal / Extended


Frame Structures


6 symbols = 0.5 ms
Time Domain


Multicast Traffic Channel (MTCH)

Physical Downlink Shared
Channels is shared

Dedicated Traffic Channel (DTCH)
Dedicated Control CHannel
Logical

BCCH

PCCH

DCCH

DTCH

MCCH

MTCH

SIB’s

MIB

Transport

CCCH

BCH
PCH

Physical Downlink Control Channel

DL-SCH

MCH

SIB’s

PDCCH

PHYS.
PBCH

PDSCH

PMCH

REFERENCE
SIGNALS

Physical Downlink Shared Channels
7 symbols = 0.5 ms

7 symbols = 0.5 ms

DCCH
SIB’s

7 symbols = 0.5 ms

34

7 symbols = 0.5 ms



Frame Structures

7 symbols = 0.5 ms

For LTE, the normal CP length has been set at 4.69 μs, enabling the
system to cope with path delay variations up to about 1.4 km.

35


Frame Structures



Extended cyclic prefix of 16.7 μs for highly dispersive
environments. variations up to about 5km

6 symbols = 0.5 ms
Time Domain

36


Next Topic

LTE Carriers
•
•
•
•
•

RSRP, RSSI, RSRQ
Frequency-division duplexing(FDD)
Re-Farming
Time-Division Duplexing (TDD)
TDD- Standard sub-frames & Special
sub-frames.
• CQI reports

37


LTE RAN Portfolio

Contact us on training@aircominternational.com
38


In Closing
 Thank you for attending
 Webinars webpage – keep up to date and
register to receive email alerts on new
webinars
http://www.aircominternational.com/Webinars.aspx

39


Questions?

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