AIRCOM LTE Webinar Series:
What affects LTE Cell throughput © 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
Adam Moore – Learning & Development Manager With AIRCOM since 2006 Member of CIPD
Contact us at
[email protected] 2
© 2013 AIRCOM International Ltd
About AIRCOM AIRCOM is the leading provider of mobile network planning, optimisation and management software and consultancy services. Advise
Manage
Audit Network
Optimise
3
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
Plan
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 © 2013 AIRCOM International Ltd
LTE PORTFOLIO
ACCREDITATION COURSES A202 AIRCOM Accredited LTE Planning and Optimisation Engineer (5 days inc exam)
4
© 2013 AIRCOM International Ltd
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 5
© 2013 AIRCOM International Ltd
What affects Cell throughput DATA
Relay Application DATA
TCP/UDP
DATA
IP
PDCP
GTP-U
RLC
UDP
MAC
IP
L1
L1/L2
PDCP DATA
RLC
DATA
MAC L1
DATA
UE
6
eNode B
© 2013 AIRCOM International Ltd
User Plane Application Rate
Application
Non Real Time
overhead
Non Real Time
Real Time
TCP
overhead
Application
UDP
overhead
IP
overhead
RLC
TCP
overhead
PDCP
Real Time UDP
IP
PDCP overhead
RLC
RLC layer will concatenate or segment the data coming from PDCP layer into correct block size 7
© 2013 AIRCOM International Ltd
WHAT IS A TRANSPORT BLOCK RLC
MAC
TCP IP /UDP
RLC HEADER
RLC
RLC HEADER
MAC HEADER
MAC
TRANSPORT BLOCK
8
© 2013 AIRCOM International Ltd
User Plane Application Rate
Application
Non Real Time
overhead
Non Real Time
Real Time
TCP
overhead
Application
UDP
overhead
IP
PDCP
16QAM 4 bits
64QAM 6bits
RLC
overhead
RLC
overhead
MAC
overhead
MAC
L1 UE
Different coding Rates
UDP
IP
PDCP
overhead
overhead
TCP
overhead
QPSK 2 bits
Real Time
overhead
L1 UE
MAC layer selects the modulation and coding scheme configures the physical layer 9
© 2013 AIRCOM International Ltd
Normal Cyclic Prefix
12 subcarriers = 180 kHz
Frequency Domain
LTE UE categories
Resource Element 2 bits 4 bits 6 bits
7 symbols = 0.5 ms Time Domain
10
© 2013 AIRCOM International Ltd
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
11
© 2013 AIRCOM International Ltd
RRC Connection Reconfiguration Message |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 |
Since the size of transport block is not fixed MCS Index
RRC Connection Reconfiguration Message Modulation Scheme Index DL 24 12
© 2013 AIRCOM International Ltd
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 Time Domain 13
Extended Cyclic Prefix
12 subcarriers = 180 kHz
12 subcarriers = 180 kHz
Frequency Domain
Normal Cyclic Prefix
Resource Element 2 bits 6 symbols = 0.5 ms 4 bits Time Domain 6 bits © 2013 AIRCOM International Ltd
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
14
© 2013 AIRCOM International Ltd
POLL
15
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
© 2013 AIRCOM International Ltd
POLL
16
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
© 2013 AIRCOM International Ltd
Table 7.1.7.2.1-1 Look-up table is referenced by the TBS Index and the number of allocated Resource Blocks
17
© 2013 AIRCOM International Ltd
What affects LTE Cell throughput
18
© 2013 AIRCOM International Ltd
Coding Rate
19
© 2013 AIRCOM International Ltd
Coding rate overhead overhead
MAC L1
overhead overhead
MAC L1
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
20
© 2013 AIRCOM International Ltd
Coding Rate
21
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
© 2013 AIRCOM International Ltd
Coding Rate
602/1024 = 0.5879 QPSK = 2bits Efficiency= 2x0.5879=1.1758 data bits per symbol
SINR +19,25
High cell throughput
DL BEARER – 64QAM, Efficiency 5.5
SINR -4.46
Low cell throughput DL BEARER – QPSK Efficiency 0.1523
22
© 2013 AIRCOM International Ltd
Coding Rate
23
© 2013 AIRCOM International Ltd
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
24
CQI = 15
High throughput
Terminal Density © 2013 AIRCOM International Ltd
Code word overhead
MAC
• 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 Receiver
Transmitter Transport Block
TRANSPORT BLOCK
Error detection
Compute CRC Transport Block
overhead
CRC
Demodulation
Modulation
L1
Re-transmissions will reduce throughput Transport Block
codeword L1 converts the transport block into a code-word 25
CRC
NACK Transport Block
CRC
NACK © 2013 AIRCOM International Ltd
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. Scheduling grant maximum number of re-transmissions without receiving a positive response 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 modulation scheme. 26
© 2013 AIRCOM International Ltd
Code word MAC
MAC
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
TRANSPORT BLOCK TRANSPORT BLOCK
A codeword, then, is essentially a transport block with error protection. L1
L1
codeword
codeword
27
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)
© 2013 AIRCOM International Ltd
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 Layer 1
Codeword 1 Layer 2
The number of layers is always less than or equal to the number of antenna ports (transmit antennas).
28
© 2013 AIRCOM International Ltd
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
Layer mapping for 4 layers Layer 1
Layer mapping for 2 layers Modulated Codeword
Layer 1
Layer 2 Layer 3
Layer 2 29
Modulated Codeword
Layer 4 © 2013 AIRCOM International Ltd
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
4 layers – 2 codewords Codeword 1
Layer 1 Layer 2
Codeword 2
Layer 3 Layer 4
30
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
© 2013 AIRCOM International Ltd
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 DCI Format 2 Resource Allocation Type (0 or 1) Resource Block Assignment TPC Command for PUCCH HARQ Process Number
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
Modulation and Coding Scheme New Data Indicator
Transport Block 1 information
Redundancy Version Modulation and Coding Scheme New Data Indicator
Transport Block 2 information
Redundancy Version 31
Precoding Information
© 2013 AIRCOM International Ltd
Cell throughput 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
Maximizing the data rate and spectral efficiency are the main targets in LTE 10Mhz cellular systems.
CQI = 15
CQI = 1 32
© 2013 AIRCOM International Ltd
Spectral efficiency Different Coding Rates 64QAM 6bits/Hz
Efficiency 4.5234
64QAM 6bits/Hz
64QAM 6bits/Hz
Efficiency 5.5547
64QAM 6bits/Hz
modulation and coding scheme Efficiency 3.9023
Efficiency 5.1152
Evolved Node B (eNB)
(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
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
33
© 2013 AIRCOM International Ltd
Maximum data rate for CQI bearer 1 Assumptions: 10 Mz Bandwidth Normal Prefix Coding rate 0.07618 MIMO 1x1
Frequency Domain
12 subcarriers = 180 kHz
Normal Cyclic Prefix
Bandwidth 1.4 (MHz)
3
5
10
15
20
# of RBs
6
15
25
50
75
100
Subcarriers
72
180
300
600
900
1200
All 50 PRB CQI bearer 1 MIMO 1x1 7 symbols = 0.5 ms Time Domain
34
© 2013 AIRCOM International Ltd
Maximum data rate for CQI bearer 1 10 ms
0
1
2
3
19
One Sub-frame = 1 mS
7x12
Number of Traffic symbols bits in a TTI = (4 x12) + (7x12)-6 =126 If QPSK bearer =126 x 2 =252 bits in 1ms
12 subcarriers = 180 kHz
4 x12
Frequency Domain
Normal Cyclic Prefix
7 symbols = 0.5 ms Time Domain
35
© 2013 AIRCOM International Ltd
Maximum data rate for CQI bearer 1 10 ms
0
1
2
3
19
In 10 Mhz you have 50 PRB in 1mS
One Sub-frame = 1 mS
36
Number of Traffic symbols bits in a TTI = (4 x12) + (7x12)-6 =126 If QPSK bearer =126 x 2 =252 bits in 1ms
In one TTI (1mS)you have 50 x 252 bits = 12600 bits per 1mS © 2013 AIRCOM International Ltd
Maximum data rate for CQI bearer 1 10 ms
0
1
2
3
Number of Traffic symbols bits in a TTI = (4 x12) + (7x12)-6 =126
If QPSK bearer =126 x 2 =252 bits in 1ms
19
One Sub-frame = 1 mS
In 10 Mhz you have 50 PRB in 1mS
In one TTI (1mS)you have 50 x 252 bits = 12600 bits per 1mS
37
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 © 2013 AIRCOM International Ltd
What have we not taken into account?
38
© 2013 AIRCOM International Ltd
Each Bearer has a maximum data rate
Antenna 1
High throughput 1 ms CQI 15
Low throughput CQI 1
39
Without MIMO
12 sub-carriers
Without MIMO
Bits per second =959.104 x 1000= 959104 kb/s =0.975 Mb/s in 10Mhz
© 2013 AIRCOM International Ltd
Without MIMO
Bearers
40
© 2013 AIRCOM International Ltd
Without MIMO
Physical Overhead
41
Antenna 1
Antenna 2
© 2013 AIRCOM International Ltd
Coverage/Capacity 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 3
CQI 1 CQI 1
CQI 2
42
© 2013 AIRCOM International Ltd
Summary
(MCS) (0…31)
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
12 subcarriers = 180 kHz
Frequency Domain
Normal Cyclic Prefix
7 symbols = 0.5 ms
Time Domain
43
© 2013 AIRCOM International Ltd
Next Topic
Comparison between GSM, UMTS & LTE
44
© 2013 AIRCOM International Ltd
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/Web inars.aspx
45
© 2013 AIRCOM International Ltd