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doc.: IEEE 802.15- 15-09-0485-03-004gJuly 2009
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: Future Proof Platform for SUN – Technical OverviewDate Submitted: July 6, 2009Source: Steve Shearer, IndependentAddress: Pleasanton, CA, USA Voice: (408) 417 1137 , FAX: [], E-Mail: Shearer_inc @ yahoo.comRe: [802.15.4g] TG4g Call for Proposals, 2 February, 2009
Ab t t T h i l O i f h d OFDM l f S Sh L di &G M i dAbstract: Technical Overview of the merged OFDM proposals of Steve Shearer, Landis&Gyr, Maxim and ETRI. This document highlights key signal processing areas of the proposal that make this a good choice for the new SUN PHY.
Purpose: Technical Proposal to be discussed by IEEE 802 15 TG4gPurpose: Technical Proposal to be discussed by IEEE 802.15 TG4gNotice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right t dd d ithd t i l t i d h ito add, amend or withdraw material contained herein.Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
Submission Steve Shearer (Independent)Slide 1
doc.: IEEE 802.15- 15-09-0485-03-004gJuly 2009
A Future Proof Platform for Smart Utility Networks
Top Level Technical Overview
Steve ShearerJuly 2009
Supporters: Roberto Aiello [Independent], Sangsung Choi [ETRI], Bob Fishette [Trilliant], Michel Veillette [Trilliant], David Howard [On-Ramp], Rishi Mohindra [MAXIM],Michel Veillette [Trilliant], David Howard [On Ramp], Rishi Mohindra [MAXIM],
Emmanuel Monnerie [Landis & Gyr], Partha Murali [Redpine Signal], Shusaku Shimada [Yokogawa Electric Co.], Kendall Smith [Aclara], Mark Wilbur [Aclara], Mark Thomson
[Aclara] , John Buffington [Itron], Rodney Hemminger [Elster], Elad Gottlib [Silver Springs Networks], Jay Ramasastry [Silver Springs Networks], Xing Tao [Chinese Academy of
Submission Steve Shearer (Independent)Slide 2
Networks], Jay Ramasastry [Silver Springs Networks], Xing Tao [Chinese Academy of Science], Betty Zhao [Huawei]
doc.: IEEE 802.15- 15-09-0485-03-004g
IntroductionJuly 2009
Introduction• The purpose of this presentation is to introduce key technical aspects
of the Future Proof Platform merged OFDM proposal– Demonstrates that an OFDM system, properly configured to the
application at hand, can lead to a highly efficient, low complexity PHY
• This presentation shows how the combination of several simple signal p p gprocessing methods have been used to create the SUN OFDM PHY proposal– And shows how this proposal is compatible with the existing standard
and some new proposals
• We believe that this proposal is worthy of consideration as a candidate for new Smart Utility Networks PHY standardcandidate for new Smart Utility Networks PHY standard.
Submission Steve Shearer (Independent)Slide 3
doc.: IEEE 802.15- 15-09-0485-03-004g
ContentsJuly 2009
Contents• Proposal meets the requirements of the PAR
• Some common concerns about OFDMSome common concerns about OFDM
• Key aspects of this proposal– Data rates / Bandwidth– Compatibility with existing MAC– Modulation– Soft decisions– Convolutional coding– Time and Frequency Spreading– Data structure– Reference Transmitter Diagram
• How Multicarrier systems maximize the use of the radio channel– Inter Symbol InterferenceInter Symbol Interference– Frequency selective fading– Spatial/Geographic nulls– Rayleigh fading– Performance Advantage Snapshot
Submission
Performance Advantage Snapshot
• Conclusions
Slide 4 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
Requirements of the PARJuly 2009
Requirements of the PAR• Operation in any of the regionally available license exempt frequency bands, such as
700MHz to 1GHz, and the 2.4 GHz band.
• Data rate of at least 40 kbits per second but not more than 1000 kbits per second
• Carrier Grade Reliability
• Achieve the optimal energy efficient link margin given the environmental conditions• Achieve the optimal energy efficient link margin given the environmental conditions encountered in Smart Metering deployments.
• Principally outdoor communications– “highly obstructed, high multipath locations with inflexible antenna orientation”
– “Applications for Wireless Smart Metering Utility Network further intensify the need for maximum range”
– “Wireless Smart Metering Utility Network requirement of 100% coverage”
– “ability to provide long‐range point‐to‐point circuits available for meshing”
• PHY frame sizes up to a minimum of 1500 octets• PHY frame sizes up to a minimum of 1500 octets
• Simultaneous operation for at least 3 co‐located orthogonal networks
• Connectivity to at least one thousand direct neighbors characteristic of dense urban
Submission
• Connectivity to at least one thousand direct neighbors characteristic of dense urban deployment
Steve Shearer (Independent)Slide 5
doc.: IEEE 802.15- 15-09-0485-03-004g
This Proposal meets the PARJuly 2009
This Proposal meets the PAR• It is applicable to the 700, 800, 900 MHz and 2.4Ghz bands
• Scalable data rates from 780 kbps down to 46 kbps– Enables accessing “difficult‐to‐get‐to” nodes
• Achieves excellent energy efficient link margin (Eb/N0) to achieve Carrier Grade reliability without wasting power
• Designed for outdoor environments because it addresses:‐– Multipath by using long symbol times and a cyclic prefix
– Spatial nulls by using slow frequency hopping or Frequency Diversity
– Fading by employing channel coding and Time Diversity for improved packet errorFading by employing channel coding and Time Diversity for improved packet error performance
– Provides long range where necessary
• Supports packet sizes up to 2047 octets with low PER in outdoor environments
• Is adjacent channel friendly to allow co‐located orthogonal networks
• Supports connectivity to multiple neighbors
• In addition battery consumption can be shown to be as low or lower than single
Submission
• In addition, battery consumption can be shown to be as low, or lower, than single carrier systems
Steve Shearer (Independent)Slide 6
doc.: IEEE 802.15- 15-09-0485-03-004g
Common concerns about OFDMJuly 2009
Common concerns about OFDM• More complicated MAC?
– Intended to re‐use current 802.15.4e MAC
Hi h SNR?• High SNR?– This proposal shows reliable operation in negative SNR conditions
• High PAPR?– Low order modulation allows PA back‐off to be 3dB or less
• High TX Power?– 15 to 30dB link margin advantage allows lower TX power
(same data rate on the same link)
• Complexity?Complexity?– Orders of magnitude lower than popular WLAN systems
• Cost?– System cost can be as low as single carrier systems
• Accurate Xtal oscillators?– 20 ppm is sufficient, 40 ppm can be tolerated
• High Power consumption?– Analysis shows superior performance for battery operated devices
Submission
y p p y p
• ‘Brick wall’ analog filters?– Not necessary
Steve Shearer (Independent)Slide 7
doc.: IEEE 802.15- 15-09-0485-03-004g
Key ParametersJuly 2009
Key Parameters• Several configurations to suit different Regulatory b/w
requirements– Option 1 1060 kHz 128 pt FFT
• Channel Coding derived from ½ rate convolutional mother code
• Coding rates from 3/4 through to 1/8p p
– Option 2 518 kHz 64 pt FFT
– Option 3 264 kHz 32 pt FFT
– Option 4 146 kHz 16 pt FFT
– Option 5 68 kHz 8 pt FFT
Coding rates from 3/4 through to 1/8 using
– Puncturing
– Frequency Repetition
– Time Repetition
• Common parameters for all options– Symbol time 128us
– Cyclic prefix 25.6us
– Tone spacing 9.7kHz
• Soft decision decoding for higher performance
– Multipath tolerance > 25us at all data rates
– Low order modulation BPSK, QPSK, 16QAM
• Supports low packet‐by‐packet frequency hopping to mitigate spatial nulls
OFDM Option 1
OFDM Option 2
OFDM Option 3
OFDM Option 4
OFDMOption 5
Unit
FFT size 128 64 32 16 8Active Tones 108 52 26 14 6# Pilots tones 8 4 4 2 2hopping to mitigate spatial nulls
• Non hopping mode to ease concerns on battery consumption
• Complexity is orders of magnitude
# Data Tones 100 48 22 12 4
Approximate Signal BW 1064.45 517.58 263.67 146.48 68.36 kHzBPSK 1/2 rate coded and 4x repetition 97.66 46.88 21.48 11.72 3.91 kbpsBPSK 1/2 rate coded and 2x repetition 195.31 93.75 42.97 23.44 7.81 kbpsBPSK 1/2 rate coded 390.63 187.50 85.94 46.88 15.63 kbpsBPSK 3/4 rate coded 585.94 281.25 128.91 70.31 23.44 kbpsQPSK 1/2 rate coded 781 25 375 00 171 88 93 75 31 25 kbps
Submission
• Complexity is orders of magnitude lower than WLAN
Slide 8 Steve Shearer (Independent)
QPSK 1/2 rate coded 781.25 375.00 171.88 93.75 31.25 kbps
QPSK 3/4 rate coded 1171.88 562.50 257.81 140.63 46.88 kbps16‐QAM 1/2 rate coded 1562.50 750.00 343.75 187.50 62.50 kbps16‐QAM 3/4 rate coded 2343.75 1125.00 515.63 281.25 93.75 kbps
doc.: IEEE 802.15- 15-09-0485-03-004g
Scalable Data Rates / BandwidthJuly 2009
Scalable Data Rates / Bandwidth
• P id l bili i• Provides scalability in a highly structured way– Avoids a wide array of
Submission
yindependent parameters
Steve Shearer (Independent)Slide 9
doc.: IEEE 802.15- 15-09-0485-03-004g
Multicarrier ModulationJuly 2009
Multicarrier Modulation
• This proposal modulates each carrier using BPSK, QPSK, or 16‐QAMThis proposal modulates each carrier using BPSK, QPSK, or 16 QAM
• The PSK symbols are mapped onto individual tones in the frequency domaindomain
• Several frequencies are nulled outh ll d h l i h i l i f h– The nulled DC component helps in the implementation of cheap, zero‐IF receivers (does not exclude passband receivers)
– The nulled frequencies at the band edges significantly ease filtering complexity for adjacent channel performancecomplexity for adjacent channel performance
• An appropriate size Inverse FFT produces the time domain samples for transmission
Submission
for transmission
Slide 10 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
Modulation and PAPRJuly 2009
Modulation and PAPR• PA nonlinearity causes two issues
– Spectral regrowth from compression of the peaks100
200
300
ProbabilityDistribution
Function
– High EVM from signal distortion
• The amplitude of an OFDM signal is approximately Rayleigh distributed
0 0.5 .85 1 1.5 1.7 2 2.5 30
80
100
X: 57Y: 96.17
Only 4% of samples
CumulativeDistributionapproximately Rayleigh distributed
– Fortunately the peaks don’t happen very often thus minimizing average spectral regrowth
0 1 2 30
20
40
60
Amplitude
Only 4% of samplesgreater than 2 sigma
DistributionFunction
EVM = -9dB
• This proposal uses only low order modulations which can withstand much higher EVM without loss of performance
1
EVM = -9dB
• Therefore PA linearity requirements for this proposal id bl d d
-1
0
Submission
are considerably reduced– See IEEE 802.15‐15‐09‐0483‐00‐004g for details
Steve Shearer (Independent)Slide 11
-1 0 1
doc.: IEEE 802.15- 15-09-0485-03-004g
CompatibilityJuly 2009
Compatibility• The basic concept of this PHY is directly compatible with the current
802.15.4e work– It does not impose any further requirements on the MAC
– Allows the entire upper s/w stack to be re‐used
• All modes can use packet‐by‐packet frequency hopping– Although this is probably only necessary for narrowband modes
– Wider band modes allow Battery efficient non‐hopped operation in many popular bands (e g 900MHz)bands (e.g. 900MHz)
• The time domain waveform leaving the antenna is different in nature to that of FSK or DSSS systems, but this is invisible to the upper layersof FSK or DSSS systems, but this is invisible to the upper layers
Submission Steve Shearer (Independent)Slide 12
doc.: IEEE 802.15- 15-09-0485-03-004g
OFDM enables simple Soft decisionJuly 2009
OFDM enables simple Soft decision generation
Th d d l t f h t t t th bit ‘ fid l l ’• The demodulator for each tone outputs the bits as ‘confidence levels’ based on an estimate of the channel quality– Bits demodulated during a fade will have small +/‐ confidence levels
– Bits demodulated in a peak will have larger +/‐ confidence levelsBits demodulated in a peak will have larger +/ confidence levels
• Provides additional information about where errors may lie– Decoder can concentrate its error correction capabilities on the bits that are p
most likely in error
100 strong 1's data is likely to be in errorlow confidence 1's & 0's
-100
0
Soft Decision demodulator output for each tonestrong 0's
Submission
• Allows Maximal Ratio Combining for Frequency Spreading and Time Spreading modes
Steve Shearer (Independent)Slide 13
doc.: IEEE 802.15- 15-09-0485-03-004g
Frequency SpreadingJuly 2009
Frequency Spreading• Frequency spreading is a method of replicating PSK symbols on different carriers
• The diagram indicates how the left half of the spectrum is replicated using conjugated versions of the PSK symbols
• Protects against frequency selective fading by providing Frequency Diversity– Enhances SNR performance
Submission Slide 14 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
Frequency De‐spreadingJuly 2009
Frequency De‐spreading• Frequency diversity relies on the fact that fading on
separate carriers is independentseparate carriers is independent– While one is fading the other may be strong
• Soft decision PSK symbols 100 faded section non-faded section• Soft decision PSK symbols can be optimally combined at the receiver with little computational overhead
-100
0
100
Tone(n)
faded section non faded section
p
• Diversity gain offers significant improvement in -100
0
100
Tone(n+j)
+
faded sectionnon-faded section
significant improvement inperformance as shown by the quality of the combined data
( j)
0
100combination combination
Submission
– No ‘dead ‘ spots
Steve Shearer (Independent)Slide 15
-100
doc.: IEEE 802.15- 15-09-0485-03-004g
Time SpreadingJuly 2009
Time Spreading• Time spreading is a method of replicating OFDM symbols at different
timestimes
• The diagram indicates how symbols are repeated
• Protects against Rayleigh fading by providing Time Diversity– Enhances SNR performance
• Frequency Spreading and Time Spreading can be used together for additional robustness
Submission Steve Shearer (Independent)Slide 16
doc.: IEEE 802.15- 15-09-0485-03-004g
Convolutional CodeJuly 2009
Convolutional Code• Convolutional Codes are well know for their ability to effectively use
soft decisions to correct errorssoft decisions to correct errors– Coding gain is normally quoted as Eb/N0
– SNR improvement at a normalized net information rate
– And with modern hardware, they are easy to implementAnd with modern hardware, they are easy to implement
• This proposal uses a constraint length 7, ½ rate codeWell known generator polynomials G [133 171]– Well known generator polynomials G1,2 = [133, 171],
• Offers a coding gain of 6 dB for the same information rate(9dB SNR)– (9dB SNR)
Submission Steve Shearer (Independent)Slide 17
doc.: IEEE 802.15- 15-09-0485-03-004g
Puncturing for Flexible data ratesJuly 2009
Puncturing for Flexible data rates• Puncturing is a process of removing redundancy to increase the coding rate
– Bits are removed before transmissionBits are removed before transmission– And replaced with dummy bits on reception
• This is a well researched area (Hagenauer et al.)– Used in many systems
• Easy to implement using array indexing operations
• Provides very flexible data rates with no computational overheadcomputational overhead
Submission Slide 18 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
InterleavingJuly 2009
Interleaving• Interleaving is used to spread bits in frequency over one symbol
– Still investigating if interleaving over more symbols gives a performanceStill investigating if interleaving over more symbols gives a performance advantage
• Interleaving equation for 32‐FFT shown below
• Details for other n‐FFT’s given in detailed document IEEE 802.15‐15‐09‐0489‐00‐004g
Submission Steve Shearer (Independent)Slide 19
doc.: IEEE 802.15- 15-09-0485-03-004g
Data StructureJuly 2009
Data Structure
P k d f• Packets are made up of:‐– Synchronization sequence
– PHY header coded for maximum robustness
– Variable length data payload coded according to data rate
Submission Slide 20 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
Synchronization SequenceJuly 2009
Synchronization Sequence
• RF carrier reference and signal processing clock are derived from the same source– Frequency correction also corrects the symbol timing
• Synchronization sequence is made up of two sections
f d b k i/4
STF
– Set of tones spaced by 38.8 kHz for coarse frequency and time sync
- pi/4
+ pi/4
itude
Tone spacing38.8 kHz
Good Frequencyauto correlation
properties
– Set of closely spaced tones for channel estimation and fine frequency/time sync
+ pi/2
LTF
- 260 kHz + 260 kHz0 Hz
Pha
se /
Am
pli
fine frequency/time sync
• This scheme allows simultaneous correction of timebase and frequency error for
- 260 kHz 0 Hz + 260 kHz
- pi/2
Tones spaced by9.7 kHz
Submission
• This scheme allows simultaneous correction of timebase and frequency error for very loose tolerance Xtals.
Slide 21 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
PHY HeaderJuly 2009
PHY Header
• The PHY header contains 5 fields– Rate field specifies the data rate of the payload frame– Length specifies the length of the payload– Scrambling seed for the PSDU
• helps with Regulatory compliance• helps with Regulatory compliance
– Header Check sequence• 8 bit CRC taken over the data fields only• Avoids erroneous decoding of payloads and saves power consumption
– Tail bits for Viterbi decoder flushing
• Encoded at the lowest data rate for robustness
Submission Slide 22 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
Data Unit (PSDU)July 2009
Data Unit (PSDU)
• Frame PayloadFrame Payload– 8 to 2047 octets
• CRC– 32 bit IEEE CRC for error detection
• Tail and Pad bits– Used to clear encoder memory
Submission Slide 23 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
Reference Transmitter DiagramJuly 2009
Reference Transmitter Diagram
• Summary of transmitter signal processingSummary of transmitter signal processing
• Constellation Mapping block determines mapping of symbols and number of tones
Submission Slide 24 Steve Shearer (Independent)
doc.: IEEE 802.15- 15-09-0485-03-004g
Representative SUN ChannelsRepresentative SUN Channels• Simple two tap channel models used for performance evaluation
– ETSI ETSI EN 300 392‐2 V3.2.1 (2007‐09)
• Performance simulations currently use only Pseudo Static methodology• Performance simulations currently use only Pseudo Static methodology– Realistic fading rates still need to be defined for this application
Channel Models taken from ETSI ETSI EN 300 392‐2 V3.2.1 (2007‐09)
Propagation ModelTap
NumberRelative delay (us)
Average relative
power (dB)Rural Area (Rax) 1 0 0Typical Urban (Tux) 1 0 0
2 5 ‐22.3Bad Urban (Bux) 1 0 0
2 5 ‐3Hilly Terrain (HTx) 1 0 0
2 15 ‐8.6
Submission
doc.: IEEE 802.15- 15-09-0485-03-004g
Key Channel ImpairmentsJuly 2009
Key Channel Impairments• Amplitude fading due to non LOS path
• Multipath due to reflections – Frequency selective fading
I t S b l I t f
Spectral analysis of 300 kHz channel. Two ray channel, 5us multipath
0
B)
– Inter Symbol Interference
• Spatial propagationll ( t h )
-40
-20
Am
plitu
de (d
Bnulls (not shown)
• How does OFDM
0
-150 kHz
Frequency
overcome these problems?
Submission
+150 kHzTime
Frequency
Steve Shearer (Independent)Slide 26
doc.: IEEE 802.15- 15-09-0485-03-004g
Multipath ‐ ISIJuly 2009
Multipath ‐ ISI• Multipath introduces Inter Symbol Interference
– Every previous bit degrades every current bity p g y
• OFDM overcomes ISI by – making the symbol much longer than the multipath
– And using a cyclic prefix to contain the ISI
• OFDM retains the data rate by adding more carriers in the same proportion h l h i f h b las the lengthening of the symbol
• Frequency hopping is very useful to mitigate spatial nulls but doesn’t helpmitigate spatial nulls but doesn’t help with ISI
The delayed multipath components are contained in this prefix at the receiver and d t t i t th d d l ti
Submission Steve Shearer (Independent)Slide 27
do not contaminate the demodulation process.
doc.: IEEE 802.15- 15-09-0485-03-004g
Multipath – Frequency selective fadingJuly 2009
Multipath – Frequency selective fading• Multipath also causes frequency nulls in the received spectrum
• OFDM overcomes frequency nulls by dividing up the channel into individual carriers– So if one is knocked out, at least Frequency selective
the others aren't affected
• Frequency Diversity
Damaged carrier
fade
combining, or interleaving across frequency, togetheri h FEC h l
0
20
40
ude
(dB
)
with FEC, help to‘fill in the gaps’
68
1012
-40
-20
Time
Am
plit
Submission Steve Shearer (Independent)Slide 28
02
4Frequency (Carrier #)Soft decision streams
out of each carrier
doc.: IEEE 802.15- 15-09-0485-03-004g
Visualization of OFDM’s advantageJuly 2009
Visualization of OFDM s advantage• Notice how the multiple carrier soft decision streams accurately
convey channel quality information in both Time and Frequencyconvey channel quality information in both Time and Frequency– Re‐creating the previous spectral analysis
• This valuable information allows
Surface of 300 kHz channel constructed using demodulated soft decisions.
Two ray channel, 5us multipath
20
40
B)
effective combination of Time and Frequency diversity
-60
-40
-20
0
20
Am
plitu
de (d• This is a key to
why OFDM systems have such a
f
4
6
8
10
12
Frequency(carrier #)
performance advantage
Submission
0
2 TimeIndividual carrier
soft decisionsSteve Shearer (Independent)Slide 29
doc.: IEEE 802.15- 15-09-0485-03-004g
Performance Advantage SnapshotJuly 2009
Performance Advantage Snapshot• FS10 and TN19 propagation channels as measured by L&G in low rise urban area
– 1.6us multipath
• Bu0 and Ht0 channels as defined by ETSI for “Bad Urban” and “Hilly Terrain”
100100kbps OFDM and 100kbps MSK for 125 byte packets in various channels
MSK TN19MSK FS10
Bu0 and Ht0 channels as defined by ETSI for Bad Urban and Hilly Terrain– 5us and 15us multipath
respectively
OFDM h 18 29 dB
10-1
MSK AWGNMSK Bu0MSK Ht0OFDM Bu0OFDM Ht0OFDM AWGNOFDM FS10
• OFDM shows 18 – 29 dB advantage even in benign1.6us multipath channels with short 125 byte
10-2
PE
R
OFDM FS10OFDM TN19
FS10TN1929 dB
ypackets
10AWGN4dB
FS1018 dB
29 dB
• The advantage is even greater– for Bu0 and Ht0
– Longer packets
Submission
4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 38 40 40 42 44 4610-3
EbN0 (dB)
Steve Shearer (Independent)Slide 30
doc.: IEEE 802.15- 15-09-0485-03-004g
ConclusionsJuly 2009
Conclusions• This Proposal adequately meets all the requirements of the PAR
– Wide applicability in a range of Regulatory requirements
– Wide range of data rates
– Superior performance in the outdoor channels defined in the PAR
– Carrier Grade Reliabilityy
– Wide range of packet lengths
– Excellent link margin and efficiency
Add d b OFDM• Addressed some common concerns about OFDM
• Detailed the key Technical aspects that make up the proposal
Sh d h OFDM hi it f i th h h l• Showed how OFDM achieves its performance in the chosen channels– Hinted at some results
– See later presentations for more details
Submission
• Provides flexibility is a consistent, highly structured waySteve Shearer (Independent)Slide 31