Más contenido relacionado La actualidad más candente (20) Similar a AIRCOM LTE Webinar 2 - Air Interface (20) AIRCOM LTE Webinar 2 - Air Interface3. 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
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© 2013 AIRCOM International Ltd
4. 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
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© 2013 AIRCOM International Ltd
5. Agenda- LTE Air-Interface (Part 1)
LTE Air-Interface
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
© 2013 AIRCOM International Ltd
6. 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
© 2012 AIRCOM International Ltd
7. 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
© 2012 AIRCOM International Ltd
8. 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
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© 2012 AIRCOM International Ltd
9. Traffic SINR
SINR ave = S
I+N
I = Iown + Iother
There are a number of ways of
controlling other cell Interference
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© 2013 AIRCOM International Ltd
10. 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%.
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© 2013 AIRCOM International Ltd
11. 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
© 2013 AIRCOM International Ltd
12. SINR - Signal to Interference & Noise
Ratio
S: indicates the power of
measured usable signals.
SINR ave = S
I+N
I = Iown + Iother
Path Loss
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© 2013 AIRCOM International Ltd
13. 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.
© 2013 AIRCOM International Ltd
14. 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
© 2012 AIRCOM International Ltd
16. Poll
What is meant by adaptive modulation
and coding (AMC)?
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© 2013 AIRCOM International Ltd
17. 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).
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© 2013 AIRCOM International Ltd
18. 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.
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© 2013 AIRCOM International Ltd
19. 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
© 2013 AIRCOM International Ltd
20. 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
© 2013 AIRCOM International Ltd
21. 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.
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© 2013 AIRCOM International Ltd
22. 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
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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
© 2013 AIRCOM International Ltd
23. 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
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© 2013 AIRCOM International Ltd
25. 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
© 2013 AIRCOM International Ltd
26. 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
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© 2013 AIRCOM International Ltd
27. 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
© 2013 AIRCOM International Ltd
29. 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
© 2013 AIRCOM International Ltd
30. 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
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© 2013 AIRCOM International Ltd
31. Summary so far
12 subcarriers = 180 kHz
Frequency Domain
Normal Cyclic Prefix
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
12 subcarriers = 180 kHz
# 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
© 2013 AIRCOM International Ltd
32. LTE is about 300Mbps 25%
(4x4)
Overhead about
20 Mhz-100PRB
12 subcarriers = 180 kHz
Normal Cyclic Prefix
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
12 subcarriers = 180 kHz
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
© 2013 AIRCOM International Ltd
33. 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
12 subcarriers = 180 kHz
Frequency-division duplexing(FDD)
Normal / Extended
12 subcarriers = 180 kHz
Frame Structures
Extended Cyclic Prefix
6 symbols = 0.5 ms
Time Domain
© 2013 AIRCOM International Ltd
34. 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
© 2013 AIRCOM International Ltd
35. 12 subcarriers = 180 kHz
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
© 2013 AIRCOM International Ltd
36. Frame Structures
12 subcarriers = 180 kHz
Extended Cyclic Prefix
Extended cyclic prefix of 16.7 μs for highly dispersive
environments. variations up to about 5km
6 symbols = 0.5 ms
Time Domain
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© 2013 AIRCOM International Ltd
37. 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
© 2013 AIRCOM International Ltd
39. In Closing
Thank you for attending
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