AIRCOM LTE Webinar 5 - LTE Capacity

© 2013 AIRCOM International Ltd
AIRCOM LTE Webinar Series:
What affects LTE Cell throughput

2 © 2013 AIRCOM International Ltd
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
Contact us at training@aircominternational.com
Adam Moore – Learning & Development
Manager
 With AIRCOM since 2006
 Member of CIPD

About AIRCOM
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 14 offices worldwide
 Over 150 LTE customers
 Acquired Symena in 2012
 Products deployed in 159 countries
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 TEOCO offer very complimentary assurance an optimisation solutions as
well as an excellent analytics portfolio.
 Significantly stronger combined offering for customers
 Find out more at www.aircominternational.com

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(5 days inc exam)

Agenda-What affects LTE Cell throughput
 Maximizing the data rate and spectral
efficiency are the main targets in LTE
cellular systems.
 Transport Block Size
 Codewords
 LTE UE categories
 What effects Cell throughput

What affects Cell throughput
L1/L2
IP
UDP
GTP-U
eNode B
L1
MAC
RLC
PDCP
Relay
L1
MAC
RLC
PDCP
UE
IP
Application
TCP/UDP
DATA
DATA
DATA
DATA
DATA
DATA

User Plane
Application ApplicationApplication Rate
TCPoverhead UDP
Real TimeNon Real
Time
TCPoverhead UDP
Real TimeNon Real
Time
IPoverhead IPoverhead
RLC layer will concatenate or segment the data coming
from PDCP layer into correct block size
RLC
PDCP
overhead RLC
PDCP
overhead

WHAT IS A TRANSPORT BLOCK
RLC
HEADER
RLC
HEADER
RLC
MAC MAC HEADER
TRANSPORT BLOCK
RLC
MAC
IP
TCP
/UDP

User Plane
Application ApplicationApplication Rate
TCPoverhead UDP
Real TimeNon Real
Time
TCPoverhead UDP
Real TimeNon Real
Time
IPoverhead IPoverhead
RLC
PDCP
overhead RLC
PDCP
overhead
L1
MAC
UE
overhead
overhead L1
MAC
UE
overhead
overhead
MAC layer selects the modulation and coding scheme
configures the physical layer
QPSK
2 bits
16QAM
4 bits
64QAM
6bits
Different coding Rates

LTE UE categories
Normal Cyclic Prefix
7 symbols = 0.5 ms
FrequencyDomain
12subcarriers=180kHz
Time Domain
Resource Element
2 bits
4 bits
6 bits

Now how many bits are
transferred in this 1ms
transport block size?
Modulation and coding scheme (MCS): The
MCS index (0…31) is used by the base station
to signal to the terminal the modulation and
coding scheme to use for receiving or
transmitting a certain transport block. Each
MCS index stands for a certain modulation
order and transport block size index

RRC Connection Reconfiguration
Message
Since the size of
transport block is
not fixed
MCS Index
|UE ID/RNTI Type |C-RNTI |
|Subframe Number |2 |
|UE ID/RNTI Value |'8627'H ||
|Transport Block Indicator |single TB info |
|Modulation Order DL 1 |QAM64 |
|New Data Indicator DL 1 |new data |
|Redundancy Version DL 1 |0 |
|Reserved |0 |
|Modulation Scheme Index DL |24 |
RRC Connection Reconfiguration Message
Modulation Scheme Index DL 24

How much bits are transferred in this
1ms transport block size?
It depends on:
The MCS (modulation and coding scheme)
The number of resource blocks assigned to the
UE
7 symbols = 0.5 ms
FrequencyDomain
Time Domain
Extended Cyclic Prefix
6 symbols = 0.5 ms
Time Domain
Resource Element
2 bits
4 bits
6 bits

Transport Block Size Tables
 Look-up table is referenced by the TBS Index and the number of
allocated Resource Blocks
RRC Connection Reconfiguration Message
Modulation Scheme Index DL 24

POLL
eNB assigns MCS index 12 and 2 resource blocks
(RBs). What is the transport block size?
1. 56
2. 144
3. 616
4. 376
5. 440

Table 7.1.7.2.1-1 Look-up table is referenced by the TBS Index and the number of
allocated Resource Blocks

What affects LTE Cell throughput

Coding Rate

Coding rate
L1
MACoverhead
overhead L1
MACoverhead
overhead
MAC layer selects the modulation and coding scheme
configures the physical layer
Code rate: The code rate is defined as the ratio between the transport block size
and the total number of physical layer bits per subframe that are available for
transmission of that transport block. The code rate is an indication for the
redundancy that has been added due to the channel coding process

CQI Modulation Efficiency Actual
coding rate
Required
SINR
1 QPSK 0.1523 0.07618 -4.46
2 QPSK 0.2344 0.11719 -3.75
3 QPSK 0.3770 0.18848 -2.55
4 QPSK 0.6016 308/1024 -1.15
5 QPSK 0.8770 449/1024 1.75
6 QPSK 1.1758 602/1024 3.65
7 16QAM 1.4766 378/1024 5.2
8 16QAM 1.9141 490/1024 6.1
9 16QAM 2.4063 616/1024 7.55
10 64QAM 2.7305 466/1024 10.85
11 64QAM 3.3223 567/1024 11.55
12 64QAM 3.9023 666/1024 12.75
13 64QAM 4.5234 772/1024 14.55
14 64QAM 5.1152 873/1024 18.15
15 64QAM 5.5547 948/1024 19.25
The coding rate indicates
how many real data bits
are present out of 1024
while the efficiency
provides the number of
information bits per
modulation symbol.
602/1024 = 0.5879
QPSK = 2bits
Efficiency=
2x0.5879=1.1758 data
bits per symbol
Coding Rate

Coding Rate 602/1024 = 0.5879
QPSK = 2bits
Efficiency=
2x0.5879=1.1758 data
bits per symbol
DL BEARER – 64QAM, Efficiency 5.5
SINR +19,25
High cell throughput
DL BEARER – QPSK Efficiency 0.1523
SINR -4.46
Low cell throughput

Coding Rate

CQI
Modulation Efficiency
Actual
coding rate
Required
SINR
1 QPSK 0.1523 0.07618 -4.46
2 QPSK 0.2344 0.11719 -3.75
3 QPSK 0.3770 0.18848 -2.55
4 QPSK 0.6016 308/1024 -1.15
5 QPSK 0.8770 449/1024 1.75
6 QPSK 1.1758 602/1024 3.65
7 16QAM 1.4766 378/1024 5.2
8 16QAM 1.9141 490/1024 6.1
9 16QAM 2.4063 616/1024 7.55
10 64QAM 2.7305 466/1024 10.85
11 64QAM 3.3223 567/1024 11.55
12 64QAM 3.9023 666/1024 12.75
13 64QAM 4.5234 772/1024 14.55
14 64QAM 5.1152 873/1024 18.15
15 64QAM 5.5547 948/1024 19.25
Coding Rate
CQI = 15
Terminal
Density
High
throughput

Code word
L1
MACoverhead
overhead
TRANSPORT BLOCK
• 24 bit checksum (CRC) to the transport block
This CRC is used to determine whether the
transmission was successful or not, and triggers
Hybrid ARQ to send an ACK or NACK
codeword
Transmitter
Transport Block
Transport Block CRC
Compute CRC
Modulation
Receiver
Error detection
Demodulation
Transport Block CRC
NACK
Transport Block CRC
NACK
L1 converts the transport
block into a code-word
Re-transmissions will reduce throughput

Adaptive re-transmission
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.
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 modulation scheme.
Scheduling grant maximum number of re-transmissions without receiving a positive response
Change parameters like uplink modulation scheme
QPSK for noisy channels

Code word If the transport block is too small, it is padded up to
40 bits
If the Transport Block is too big, it is divided into
smaller pieces, each of which gets an additional 24 bit
CRC
A codeword, then, is essentially a transport block with
error protection.
Note that a UE may be configured to receive one or
two transport blocks (and hence one or two
codewords) in a single transmission interval
Maximum of 2 codewords used to limit signalling
requirement (CQI reporting, HARQ
acknowledgements, resource allocations)
L1
MAC
TRANSPORT BLOCK
codeword
L1
MAC
TRANSPORT BLOCK
codeword

Codeword
• Maximum of 2 codewords used to limit signalling
requirement (CQI reporting, HARQ acknowledgements,
resource allocations)
• Transmit diversity provides the fallback when only a
codeword is transferred
The number of layers is always less than or equal to the number of antenna ports
(transmit antennas).
Layer 1
Layer 2
Codeword 1

Transmit Diversity
 Transmit diversity requires multiple antenna elements at the transmitter,
and one or more antenna elements at the receiver
 3GPP has specified transmit diversity schemes based upon using either 2
or 4 antenna elements at the transmitter
 Transmit diversity transfers a single code word during each 1 ms
subframe
Modulated
Codeword
Layer 1
Layer 2
Layer mapping for 2 layers
Modulated
Codeword
Layer 3
Layer 4
Layer mapping for 4 layers
Layer 1
Layer 2

4 Layers
Codewords Layers Mapping
2 4 The first codeword is split (odd/even) between the first
two layers , the second codeword is split between the
second two layers. Each codeword same length
Layer 1
Layer 2
Layer 3
Layer 4
4 layers – 2 codewords
Codeword 1
Codeword 2
Note that the number of layers is always
less than or equal to the number of
antenna ports (transmit antennas).
The number of layers used in any
particular transmission depends (at least
in part) on the Rank Indication (RI)
feedback from the UE

MIMO
 MIMO can transfer either 1 or 2 code words during each 1 ms sub-frame
 CQI reporting, link adaptation and HARQ run independently for each
code word
Resource Allocation Type (0 or 1)
Resource Block Assignment
TPC Command for PUCCH
HARQ Process Number
Modulation and Coding Scheme
New Data Indicator
Redundancy Version
Modulation and Coding Scheme
New Data Indicator
Redundancy Version
Precoding Information
Transport Block 1 information
Transport Block 2 information
DCI Format 2
The scheduling commands for downlink
transmissions are more complicated, and are handled
in Release 8 by DCI formats 1 to 1D and 2 to 2A

Cell throughput
CQI = 1
CQI = 15
10Mhz
Maximizing the data rate
and spectral efficiency are
the main targets in LTE
cellular systems.
CQI
Modulation Efficiency
Actual
coding rate
Required
SINR
1 QPSK 0.1523 0.07618 -4.46
2 QPSK 0.2344 0.11719 -3.75
3 QPSK 0.3770 0.18848 -2.55
4 QPSK 0.6016 308/1024 -1.15
5 QPSK 0.8770 449/1024 1.75
6 QPSK 1.1758 602/1024 3.65
7 16QAM 1.4766 378/1024 5.2
8 16QAM 1.9141 490/1024 6.1
9 16QAM 2.4063 616/1024 7.55
10 64QAM 2.7305 466/1024 10.85
11 64QAM 3.3223 567/1024 11.55
12 64QAM 3.9023 666/1024 12.75
13 64QAM 4.5234 772/1024 14.55
14 64QAM 5.1152 873/1024 18.15
15 64QAM 5.5547 948/1024 19.25

Spectral efficiency
Evolved
Node B
(eNB)
modulation and coding scheme
64QAM
6bits/Hz
64QAM
6bits/Hz
64QAM
6bits/Hz
64QAM
6bits/Hz
A 64 QAM the spectral efficiency cannot exceed N = 6 (bit/s)/Hz
If a forward error correction (FEC) code with code rate 1/2 is added, meaning
that the encoder input bit rate is one half the encoder output rate, the spectral
efficiency is 50% of the modulation efficiency
Different Coding Rates
(Bit/s)/Hz per cell
It is a measure of the quantity
of users or services that can be
simultaneously supported by a
limited radio frequency
bandwidth
Efficiency
5.5547
Efficiency
5.1152
Efficiency
4.5234
Efficiency
3.9023

Maximum data rate for CQI bearer 1
Assumptions:
10 Mz Bandwidth
Normal Prefix
Coding rate 0.07618
MIMO 1x1
Bandwidth
(MHz)
1.4 3 5 10 15 20
# of RBs 6 15 25 50 75 100
Subcarriers 72 180 300 600 900 1200Normal Cyclic Prefix
7 symbols = 0.5 ms
FrequencyDomain
Time Domain
CQI bearer 1
All 50 PRB
MIMO 1x1

0 1 2 3 19
One Sub-frame = 1 mS
10 ms
Number of Traffic symbols bits in a TTI = (4
x12) + (7x12)-6 =126
If QPSK bearer =126 x 2 =252 bits in 1ms
4 x12 7x12
7 symbols = 0.5 ms
FrequencyDomain
Time Domain

0 1 2 3 19
10 ms
Number of Traffic symbols bits in a TTI = (4 x12) +
(7x12)-6 =126
In10Mhzyouhave50PRBin1mS
In one TTI (1mS)you have
50 x 252 bits = 12600 bits
per 1mS

0 1 2 3 19
10 ms
Number of Traffic symbols bits in a TTI = (4 x12) +
(7x12)-6 =126
In10Mhzyouhave50PRBin1mS
In one TTI (1mS)you have
50 x 252 bits = 12600 bits per 1mS
Coding Rate
12600 bits x 0.07618=959.104 bits in 1ms
Bits per second
=959.104 x 1000= 959104 kb/s
=0.975 Mb/s in 10Mhz

What have we not taken into account?

Each Bearer has a maximum data rate
Antenna 1
1 ms
12sub-carriersBits per second
=959.104 x 1000= 959104 kb/s
=0.975 Mb/s in 10Mhz
WithoutMIMO
CQI 15
CQI 1
Low throughput
High throughput
WithoutMIMO

BearersWithoutMIMO

Physical OverheadWithoutMIMO
Antenna 1 Antenna 2

Coverage/Capacity
CQI 1
CQI 15
CQI 14
CQI 13
CQI 12
CQI 11
CQI 10
CQI 9
CQI 8
CQI 7
CQI 6
CQI 5
CQI 4
CQI 1CQI 3
CQI 2

Summary
Cell throughput is dependant on:
• Modulation and coding scheme (MCS) (0…31)
and Transport block size
• Bandwidth
• Normal / Extended Prefix
• Transmission modes TX diversity, Su-MIMO etc.
• LTE UE categories
CQI
(MCS) (0…31)
7 symbols = 0.5 ms
FrequencyDomain
Time Domain

Next Topic
Comparison between GSM, UMTS & LTE

In Closing
 Thank you for attending
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AIRCOM LTE Webinar 5 - LTE Capacity

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