transceiver pipeline and radio modeling
DESCRIPTION
Transceiver Pipeline and Radio Modeling. Goals. Introduce the OPNET Transceiver Pipeline Capabilities Defaults Modify pipeline Show openness and extensibility Model custom wireless effects. Overview. Wireless modeling overview Transceiver pipeline - PowerPoint PPT PresentationTRANSCRIPT
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 1
OPNET UNIVERSITY
2000
Transceiver Pipeline and Radio Modeling
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 2
OPNET UNIVERSITY
2000Goals
• Introduce the OPNET Transceiver Pipeline– Capabilities
– Defaults
• Modify pipeline– Show openness and extensibility
– Model custom wireless effects
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 3
OPNET UNIVERSITY
2000Overview
• Wireless modeling overview
• Transceiver pipeline
• Pipeline architecture and default stages– Lab: Closure - Custom Pipeline Statistic
– Break
– Lab: Channel Match - Doppler Shifts
– Break
– Lab: Power, Inoise, ECC - Signal Lock vs. Power Lock
• Conclusion
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 4
OPNET UNIVERSITY
2000Wireless Modeling Overview
• Wireless communications– Broadcast medium
– Communication more likely to be problematic
– Less of a controlled environment than wireline
• Wireless channels need to be characterized appropriately– Model real-world channel behavior
- Frequencies, power, line-of-sight, interference, etc.
– Channel characteristics affect higher layer protocol behavior
• Simulation tool must support wireless modeling– Node mobility
- Car, ship, aircraft, satellite, etc.
– Link-budget-analysis computation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 5
OPNET UNIVERSITY
2000Transceiver Pipeline
• Models packet transmission across communications channel
• Implements physical layer characteristics
• Divided into multiple stages
• Determines if packet can be received
Tx Rx
S1 S2 S3 S13. . .Each stage models an aspect of the channel’s behavior
Packet
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 6
OPNET UNIVERSITY
2000Pipeline Stages
• Sequence of ‘C’ or ‘C++’ procedures– Computes line-of-sight, signal strength, bit errors, etc.
– Can indicate packet is not receivable
• Each procedure has a defined interface (prototype)– Argument is typically a packet
– Information typically obtained and stored as Transmission Data Attributes (TDA)
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 7
OPNET UNIVERSITY
2000Transmission Data Attributes (TDA)
• Scope– Special packet storage areas
- Part of every packet
– Carry numerical values- Integer, Object ID, floating point, or pointer
– Initialized by kernel at start of transmission– Readable during a packet’s life– Writable only in pipeline
• Purpose– Carry pipeline information
- Kernel to pipeline stage- Pipeline stage to kernel- Between pipeline stages
User-DefinedPre-Defined TDA
Tx Rx
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 8
OPNET UNIVERSITY
2000Pipeline Models
• Scope– Each stage uses a pipeline model– Stages are referenced via a pipeline model object attributes
- Point-to-Point - link attributes- Bus -Bus attributes- Radio - transceiver attributes
– Stages must be compiled prior to reference
• Modeling method– Create stage in context of the pipeline model– Compile stage into object form– Change pipeline model object attribute to reference stage
• NOTE: Stage and procedure (pipeline model context) can be used interchangeably
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 9
OPNET UNIVERSITY
2000Pipeline Model Attributes
• Point-to-point– 4 stages
– Specified as link attributes
• Bus– 6 stages
– Specified as bus attributes
• Radio– 14 stages
– Specified as transceiver attributes
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 10
OPNET UNIVERSITY
2000Default Pipeline Stage Location
• Default stages– <mil3_dir>/<rel_dir>/models/std/links
• Default stage prefixes– dpt_* - default point-to-point– dbu_* - default bus– dra_* - default radio
• NOTE: OPNET can access pipeline stages from any path in mod_dirs
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 11
OPNET UNIVERSITY
2000Pipeline Stage Conventions
• File naming– <name>.ps.c - C procedure– <name>.ps.cpp - C++ procedure– <name>.ps.o - object form
• Procedure naming– Same as file name w/o extension
• Compilation– op_mko -type ps -m <name>– Generates <name>.ps.o
• NOTE: Choices for pipeline stages in OPNET are taken from the set of .ps.o files located in mod_dirs.
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 12
OPNET UNIVERSITY
2000Point-to-Point Pipeline Models
• Execution for one transmission
receiver
transmitter
TransmissionDelay
0
PropagationDelay
1
ErrorAllocation
ErrorCorrection
23
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 13
OPNET UNIVERSITY
2000Bus Pipeline Models
• Execution sequence for one transmission
multiple receivers
transmitter
TransmissionDelay
ClosurePropagation
DelayPropagation
DelayPropagation
DelayClosureClosureClosure
CollisionCollisionCollisionCollision
ErrorAllocation
ErrorAllocation
ErrorAllocation
ErrorAllocation
ErrorCorrection
ErrorCorrection
ErrorCorrection
PropagationDelay
ErrorCorrection
01 2
345
stage 0 executed once per transmission
stages 2 and up are executed separately for each receiver
collision stage may be executed zero or more times
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 14
OPNET UNIVERSITY
2000Radio Pipeline Models
• Execution sequence for one transmission
transmitter
(Continued on the next slide)
ReceiverGroupReceiverGroupReceiverGroupReceiverGroup
TransmissionDelay
LinkClosure
LinkClosure
LinkClosure
LinkClosure
ChannelMatchChannelMatchChannelMatch
Tx AntennaGain
Tx AntennaGain
Tx AntennaGain
Tx AntennaGain
PropagationDelay
PropagationDelay
PropagationDelay
PropagationDelay
ChannelMatch1
2 3
45
0
executed once at the start of simulation for each pair of transmitter and receiver channels
stage 1 executed once per transmission
stages 2-6 executed separately for each receiver
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 15
OPNET UNIVERSITY
2000Radio Pipeline Models (cont.)
• Execution sequence for one transmission (cont.)
multiple receivers
ReceivedPower
BackgroundNoise
InterferenceNoise
Signal-to-NoiseRatio
Bit ErrorRate
ErrorAllocation
ErrorAllocation
ReceivedPowerReceived
PowerRx Antenna
Gain
BackgroundNoise
BackgroundNoiseReceived
Power
InterferenceNoise
InterferenceNoise
Signal-to-NoiseRatio
Signal-to-NoiseRatio
InterferenceNoise
Bit ErrorRate
Bit ErrorRate
Signal-to-NoiseRatio
ErrorAllocation
ErrorAllocation
ErrorAllocation
ErrorAllocation
ErrorAllocation
BackgroundNoise
Bit ErrorRate
6 8 8
91011
12
Stages 9-11 may be executed zero or more times
Stages 10-12 may be executed one or more times
Rx AntennaGain
Rx AntennaGain
Rx AntennaGainError
Correction13
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 16
OPNET UNIVERSITY
2000Radio Pipeline Model Attributes
Radio Transmitter Radio Receiver
8 Stages (6-13) Associated with Radio Receiver
6 Stages (0-5) Associated with Radio Transmitter
•Receiver Group•Transmission Delay•Link Closure•Channel Match•Tx Antenna Gain•Propagation Delay
•Rx Antenna Gain•Received Power•Background Noise•Interference Noise•Signal-to-Noise Ratio•Bit Error Rate•Error Allocation•Error Correction
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 17
OPNET UNIVERSITY
2000Stage 0: Receiver Group
• Invocation– Once at start of simulation
• Purpose– Filter out ineligible receiver channels
- Simulation runtime improvements
– Possible uses- Disjunct frequency bands- Excessive physical separation- Antenna Nulls
• Requirements– Return value of OPC_TRUE or OPC_FALSE
• Results– Defines destination channel set for each transmitting channel
Tx
Rx 0
Rx 1
Rx 2
Rx 3
Rx 0Rx 1Rx 3
Example:
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 18
OPNET UNIVERSITY
2000Stage 0: Receiver Group (default)
• Name– dra_rxgroup
• Computation– None
• Result– All receivers are potential destinations
- Returns OPC_TRUE
Tx
Rx
Rx
RxRx
Default:
Tx
Rx
Rx
RxRx
Custom:
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 19
OPNET UNIVERSITY
2000Stage 1: Transmission Delay
• Invocation– First dynamic stage
– Start of packet transmission
– Single invocation for all destination channels
• Purpose– Computes time required to transmit packet
• Requirements– Sets TX_DELAY TDA
• Results– Kernel schedules end-of-transmission event
- Signals start of transmission of next packet in transmitter queue
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 20
OPNET UNIVERSITY
2000Stage 1: Transmission Delay (default)
• Name– dra_txdel
• Computation– Based on channel data rate and packet length
- Data rate (bits/sec) from TX_DRATE TDA
- Packet length (bits) from op_pk_total_size_get ()
• Result– Places computed delay value in TX_DELAY TDA
TxTx
TimeTx Start Tx End
Tx Delay
Default:
Data Rate
gthPacket LenDelay
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 21
OPNET UNIVERSITY
2000Stage 2: Closure
• Invocation– Once for each destination channel– Called immediately after stage 1 - no intervening events
• Purpose– Determines if signal can reach destination– Allows dynamic enabling/disabling of links
• Requirements– Sets PROP_CLOSURE TDA
• Results– Occlusion (obstruction)
- Packet destroyed by kernel- No further stages are called for packet
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 22
OPNET UNIVERSITY
2000Stage 2: Closure (default)
• Name– dra_closure
• Computation– Based on ray-tracing line of sight model
– Assumes Earth is spherical
– Three occlusion checks- Case 1: 90o
- Case 2: 90o , < 90o
- Case 3: 90o, 90o, d Earth Radius
• Result– If any case fails, occlusion exists
- PROP_CLOSURE set to OPC_FALSE
Tx
Rx
T
> 90
D
R
Case 1:
Case 2:
Case 3:
TxRx
T
< 90
D
R
> 90
d
Tx
Rx
T
< 90
D
R
< 90
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 23
OPNET UNIVERSITY
2000Lab: Link Closure - Overview
• Problem– Higher layer protocols implemented and tested to operate over wireline
– Models were updated to include wireless transceivers
– Results show no traffic received
• Goals– Determine link closure status
- Modify closure stage to record statistic
– Eliminate any occlusions- Use closure stage that guarantees link closure is met
• Purpose– Show how stages can be modified
– Guarantee link closure
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 24
OPNET UNIVERSITY
2000Lab: Link Closure - Project/Scenario
• Start OPNET Modeler (Radio)– Double desktop icon
• Open project– Closure
• View scenario– Zero_Antenna_Height_Failure
- Transmitter
- Receiver
• NOTE: When OPNET is not being used, minimize application
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 25
OPNET UNIVERSITY
2000Lab: Link Closure - Choose Results / Simulation
• Observe chosen results– Pulldown menu: Simulation Choose Individual Statistics
- Node Statistics:Radio Receiver: Traffic Received (bits/sec)
- Node Statistics:Radio Transmitter: Traffic Sent (bits/sec)
- Node Statistic:Radio Transmitter: Link Closure Failure (failures/sec)
• Execute simulation– Pulldown menu: Simulation Run Simulation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 26
OPNET UNIVERSITY
2000Lab: Closure - View Results
• View Results– Pulldown menu: Results View Results– Select statistics
- Object Statistics:Closure:Transmitter:Radio Transmitter: Traffic Sent (bits/sec)
- Object Statistics:Closure:Receiver:Radio Receiver: Traffic Received (bits/sec)
• Show results– Click Show
• Conclusion– Traffic is being generated by transmitter– Traffic is not being received by receiver
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 27
OPNET UNIVERSITY
2000Lab: Closure - Stage Modification Overview
• Goal– Modify the link closure stage
– Collect a custom statistic
• Approach– Modify the pipeline stage
- Add code to collect new statistic
– Update Models- Project: Create new scenario
- Node: Update node model
– Execute simulation
– View results
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 28
OPNET UNIVERSITY
2000Lab: Closure - Open Pipeline Stage
• Open pipeline stage– Open Windows NT Explorer
- Double click desktop icon
– Go to directory containing file- c:\users\student\op_models
– Double click to open file- opnetwork_closure_stats.ps.c
– Pipeline stage should open in Microsoft Development Studio
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 29
OPNET UNIVERSITY
2000Lab: Closure - Modify Pipeline Stage
• Modify stage– Observe code block at end of file
- Line 99 through 142
– Cut lines- Line 103: #if 0- Line 142: #endif
– Save file
• NOTE: When Microsoft Development Studio is not being used, minimize application
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 30
OPNET UNIVERSITY
2000Lab: Closure - Compile Pipeline Stage
• Compile the pipeline stage– Open a Command Prompt window
- Double click desktop icon
– Execute the compile command- op_mko -type ps -m opnetwork_closure_stats
• NOTE: When Command Prompt is not being used, minimize application
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 31
OPNET UNIVERSITY
2000Lab: Closure - Duplicate Scenario
• Return to OPNET Modeler (Radio)– Maximize application
• Refresh model directories– Pulldown menu: File Refresh Model Directories
– Required for OPNET to know about new files
• Duplicate scenario– Pulldown menu: Scenarios Duplicate Scenario
– Scenario name: Zero_Antenna_Height_Failure_Stats
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 32
OPNET UNIVERSITY
2000Lab: Closure - Update Node Model
• Open Transmitter node model– Double click Transmitter object
- Node model: closure_rt
• Change transmitter module attribute– Right click transmitter module
– Change attribute- closure model: opnetwork_closure_stats
– Save node model- Pulldown menu: File Save As
- Filename: closure_stats_rt
• Close node editor
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 33
OPNET UNIVERSITY
2000Lab: Closure - Update Network Model
• Change Transmitter node attribute– Right click Transmitter node
- Select Edit Attributes
– Change model attribute value- Select Edit...
- Select closure_stats_rt
– Close attribute edit box- Select Close
• Execute simulation– Pulldown menu: Simulation Run Simulation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 34
OPNET UNIVERSITY
2000Lab: Closure - View Results
• View Results– Pulldown menu: Results View Results
– Select Statistics- Object Statistics:Closure:Transmitter:Radio Transmitter: Link Closure Failure (failures/sec)
• Show results– Click Show
• Conclusion– Closure is failing, causing undesired packet loss
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 35
OPNET UNIVERSITY
2000Lab: Closure - Stage Modification Overview
• Goal– Modify the link closure model to eliminate closure failure
• Approach– Update Models
- Project: Create new scenario
- Node: Update node model
– Execute simulation
– View results
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 36
OPNET UNIVERSITY
2000Lab: Closure - Duplicate Scenario
• Duplicate scenario– Pulldown menu: Scenarios Duplicate Scenario
- Scenario name: Zero_Antenna_Height_Success
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 37
OPNET UNIVERSITY
2000Lab: Closure - Update Node Model
• Open Transmitter node model– Double click Transmitter object
- Node model: closure_stats_rt
• Change module attribute– Right click transmitter module
– Change attribute- closure model: dra_closure_all
– Save node model- Pulldown menu: File Save As
- Filename: closure_all_rt
• Close node model
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 38
OPNET UNIVERSITY
2000Lab: Closure - Closure All Stage
• Open pipeline stage– Return to Windows NT Explorer
– Go to directory containing file- c:\users\student\op_models
– Double click to open file- dra_closure_all.ps.c
• Closure All– Performs no computation
– Link closure met for all destination channels
– Sets CLOSURE TDA to OPC_TRUE
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 39
OPNET UNIVERSITY
2000Lab: Closure - Update Network Model
• Return to OPNET Modeler (Radio)– Maximize application
• Change Transmitter object– Right click Transmitter node
- Edit Attributes
– Change model attribute value- Select Edit...
- Select closure_all_rt
• Execute simulation– Pulldown menu: Simulation Run Simulation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 40
OPNET UNIVERSITY
2000Lab: Closure - View Results
• View Results– Pulldown menu: Results View Results– Select statistics
- Object Statistics:Closure:Transmitter:Radio Transmitter: Traffic Sent (bits/sec)
- Object Statistics:Closure:Receiver:Radio Receiver: Traffic Received (bits/sec)
• Show results– Click Show
• Conclusion– Traffic is being generated by transmitter– Traffic is being received by receiver– Closure was failing due to occlusions
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 41
OPNET UNIVERSITY
2000Lab: Closure - Summary
• Zero antenna height (altitude)– common problem of packet loss
• Pipeline stage modification– Record custom statistic
- Helps assess problem
– Use of dra_closure_all- Eliminates closure computations
- Causes no link failures due to occlusions
• NOTE: Another common problem of packet loss in the pipeline is due to the ECC threshold. The same approach as above can be applied to isolate the problem and counter with a pipeline modification.
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 42
OPNET UNIVERSITY
2000Stage 3: Channel Match
• Invocation– Once for each destination channel satisfying stage 2– Called immediately after stage 2 - no intervening events
• Purpose– Classifies the transmission
- Valid, noise, or ignore- Based on frequency, bandwidth, data rate, spreading code, etc.
• Requirements– Sets MATCH_STATUS TDA
• Results– Kernel destroys ignored packets– If ignore, no further stages are called for packet
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 43
OPNET UNIVERSITY
2000Stage 3: Channel Match (default)
• Name– dra_chanmatch
• Computation– Accounts for frequency overlap, data rate,
modulation, and spreading code
– Three cases- Case 1: No frequency overlap - ignored
- Case 2: Partial characteristic match - noise
- Case 3: Full characteristic match - valid
• Result– Sets MATCH_STATUS TDA based on case
Case 1:
Case 2:
Case 3:
ModTx ModRx
DRTx DRRx
FTx FRx
DRTx DRRx
ModTx ModRx
FTx FRx
FTx FRx
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 44
OPNET UNIVERSITY
2000Stage 4: Transmitter Antenna Gain
• Invocation– Once for each destination channel satisfying stage 2 and stage 3
– Called immediately after stage 3 - no intervening events
• Purpose– Computes transmitter antenna gain in the direction of the receiver
• Requirements– Sets TX_GAIN TDA
• Results– Typically used by stage 7 for receiver power computation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 45
OPNET UNIVERSITY
2000Stage 4: Transmitter Antenna Gain (default)
• Name– dra_tagain
• Computation– Distance vector between tx and rx
– Aligns all entities w.r.t. same coordinate system- Antenna patterns / pointing directions, node locations
- Majority of the computation
– Determines lookup angles
– Performs table lookup to obtain gain (dB)
• Result– Value placed in TX_GAIN for use by stage 7
Gain (dB)
Tx
Rx
Default:
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 46
OPNET UNIVERSITY
2000Stage 5: Propagation Delay
• Invocation– Once for each destination channel– Called immediately after stage 4 - no intervening events
• Purpose– Calculates signal propagation time from transmitter to receiver– Usually dependent on distance and propagation velocity
• Requirements– Sets START_PROPDEL and END_PROPDEL TDAs
• Results– Kernel schedules
- Start of reception event- End of reception event
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 47
OPNET UNIVERSITY
2000Stage 5: Propagation Delay (default)
• Name– dra_propdel
• Computation– Based on distance and propagation velocity– Computed for start and end of transmission
- Takes into account mobility
– Obtains distances (in meters)- START_DIST and END_DIST TDAs
• Result– Places computed values in START_PROPDEL and END_PROPDEL TDAs– Kernel schedules start and end reception events
Default:
Rx
TimeRx Start Rx End
Prop Delay
Rx
Velocity
DistanceDelay
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 48
OPNET UNIVERSITY
2000Lab: Doppler Shifts - Overview
• Problem– Doppler shifts - caused by transceiver mobility
– Receiver must handle frequency effects
– Default stages assume no frequency shift
• Goals– Determine appropriate stage location
– Implement Doppler shifting and record frequency shift statistic
• Purpose– Show pipeline stage modifications to account for Doppler shifts
– Show use of external files
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 49
OPNET UNIVERSITY
2000Lab: Doppler - Project/Scenario
• Return to OPNET Modeler (Radio)– Maximize application
• Open project– Doppler
• View scenario– No_Doppler_Shift
- Transmitter - aircraft
- Receiver
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 50
OPNET UNIVERSITY
2000Lab: Doppler - Choose Results / Simulation
• Observe chosen results– Pulldown menu: Simulation Choose Individual Statistics
- Node Statistics:Radio Receiver: Traffic Received (bits/sec)
- Node Statistics:Radio Transmitter: Traffic Sent (bits/sec)
- Node Statistic:Radio Transmitter: Transmission Frequency - Unshifted (Hz)
- Node Statistic:Radio Transmitter: Transmission Frequency - Shifted (Hz)
• Execute simulation– Pulldown menu: Simulation Run Simulation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 51
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2000Lab: Doppler - View Results
• View Results– Pulldown menu: Results View Results
– Select statistics- Object Statistics:Doppler:Transmitter:Radio Transmitter: Transmission Frequency - Unshifted (Hz)
• Show results– Click Show
• Conclusion– Default behavior observed
– No shift in frequency
– No Doppler shift computations
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 52
OPNET UNIVERSITY
2000Lab: Doppler - Stage Modification Overview
• Goal– Modify the pipeline to compute Doppler shifts
– Record the shifted frequency
• Approach– Find the appropriate pipeline location
– Modify the pipeline stage- Add code to compute Doppler shift
– Update Models- Project: Create new scenario
- Node: Update node model
– Execute simulation
– View results
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 53
OPNET UNIVERSITY
2000Lab: Doppler - Stage Location
• Stage Location dependencies– Requires computed results from previous stages
– Prior to computations in future stages
– Similar computations already exist
• Stage Location Possibilities– Channel match model obtains frequency information
- Results could be used for MATCH_STATUS TDA
– Computations require start and end distance computations- START_DIST and END_DIST TDAs
- Initialized by kernel at start of transmission
• Stage Location– Channel match model
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 54
OPNET UNIVERSITY
2000Lab: Doppler - Open Pipeline Stage
• Open pipeline stage– Return to Windows NT Explorer
– Go to directory containing file- c:\users\student\op_models
– Double click to open file- opnetwork_chanmatch_no_doppler.ps.c
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 55
OPNET UNIVERSITY
2000Lab: Doppler - Modify Pipeline Stage
• Modify stage– Change procedure name and FIN
- Lines 17 and 26- opnetwork_chanmatch_doppler
– Cut lines- Line 45: #if 0- Line 47: #endif
– Save file- opnetwork_chanmatch_doppler
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 56
OPNET UNIVERSITY
2000Lab: Doppler - Doppler Shift Computation
• Required values– Start and end distances
- START_DIST and END_DIST TDAs
– Propagation velocity- Transmitter module extended attribute
– Transmission delay- TX_DELAY TDA
• Computation
• Result
– Values placed in user-definable TDAs- MAX_INDEX + 1- MAX_INDEX + 2
unshiftednpropagatio
npropagatiorelativeshifted
tx
startendrelative
FV
VVF
D
ddV
*
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 57
OPNET UNIVERSITY
2000Lab: Doppler - Compile Stage / External File
• Compile the pipeline stage– Return to a Command Prompt
– Execute the compile command- op_mko -type ps -m opnetwork_chanmatch_doppler- op_mko -type ex -m doppler_shift
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 58
OPNET UNIVERSITY
2000Lab: Doppler - Duplicate Scenario
• Return to OPNET Modeler (Radio)– Maximize application
• Refresh model directories– Pulldown menu: File Refresh Model Directories
– Required for OPNET to know about new files
• Duplicate scenario– Pulldown menu: Scenarios Duplicate Scenario
– Scenario name: Doppler_Shift
• Include external file– Pulldown menu: File Declare External Files
- Change doppler_shift status to included
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 59
OPNET UNIVERSITY
2000Lab: Doppler - Update Node Model
• Open Transmitter node model– Double click Transmitter object
- Node model: no_doppler_rt
• Change transmitter module attribute– Right click transmitter module
– Change attribute- chanmatch model: opnetwork_chanmatch_doppler
– Save node model- Pulldown menu: File Save As
- Filename: doppler_rt
• Close node model
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 60
OPNET UNIVERSITY
2000Lab: Doppler - Update Network Model
• Return to the Project/Scenario– Doppler-Doppler_Shift
• Change Transmitter node attribute– Right click Transmitter node
- Select Edit Attributes
– Change model attribute value- Select Edit...
- Select doppler_rt
– Close attribute edit box- Select Close
• Execute simulation– Pulldown menu: Simulation Run Simulation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 61
OPNET UNIVERSITY
2000Lab: Doppler - View Results
• View Results– Pulldown menu: Results View Results– Select Statistics
- Object Statistics:Doppler:Transmitter:Radio Transmitter: Transmission Frequency - Unshifted (Hz)
- Object Statistics:Doppler:Transmitter:Radio Transmitter: Transmission Frequency - Shifted (Hz)
• Show results– Click Show
• Conclusion– Frequency shifts +/- 40 Hz
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 62
OPNET UNIVERSITY
2000Lab: Doppler - Summary
• Doppler shifts– Common problem in mobile systems
– Potential packet loss due to receivers inability to lock onto shifting frequency
• Pipeline stage modification– Computed Doppler shifts
– Did not use computed shift, but recorded shift statistic- Observed that a shift does exist
– Use of external file- Shows how procedures can be called from within a stage
- Useful for interfacing to other applications
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 63
OPNET UNIVERSITY
2000Stage 6: Receiver Antenna Gain
• Invocation– Once for each destination channel
– First stage after start of reception event
• Purpose– Computes receiver antenna gain in the direction of the transmitter
• Requirements– Sets RX_GAIN TDA
• Results– Typically used by stage 7 for receiver power computation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 64
OPNET UNIVERSITY
2000Stage 6: Receiver Antenna Gain (default)
• Name– dra_ragain
• Computation– Distance vector between tx and rx
– Aligns all entities w.r.t. same coordinate system- Antenna patterns / pointing directions, node locations
- Majority of the computation
– Determines lookup angles
– Performs table lookup to obtain gain (dB)
• Result– Value placed in TX_GAIN for use by stage 7
Gain (dB)
Tx
Rx
Default:
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 65
OPNET UNIVERSITY
2000Signal Lock
• Scope– Attribute of each destination channel
– Provides ability for receiver to lock onto arriving packet
– Lock is maintained for duration of transmission
• Procedure– First valid packet arrival at destination channel
- Signal lock obtained
– Subsequent valid packet arrivals- Match status changed to noise
– First valid packet completes arrival- Signal lock released
RxTx
Tx
1
2
Valid
Valid
RxTx
Tx
1
2
Valid
Noise
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 66
OPNET UNIVERSITY
2000Stage 7: Receiver Power
• Invocation– Once for each destination channel– Called immediately after stage 6 - no intervening events
• Purpose– Computes signal power level at receiver– Typically based on transmitter power and frequency, distance, and antenna gains– Computed only for valid and noise packets
• Requirements– Sets RCVD_POWER TDA
• Results– Kernel uses value to record receiver power channel statistic– Places packets in separate lists based on match status
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 67
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2000Stage 7: Receiver Power (default)
• Name– dra_power
• Computation– Determines if signal lock is active
– Computes received power- valid and noise packets
- Computes path loss - free space
- Determines in-band transmission power
- Obtains tx and rx antenna gains
• Result– Value placed in RCVD_POWER for use by stage 9
(watts) GainAntenna Receiver
(watts) GainAntenna r Transmitte
(watts) Power Received
Bandwidth
(Hz) FrequencyMinimum
(Hz) FrequencyMaximum
(watts) Power dTransmitte
FrequencyInband
quencyCenter Fre
Lightof Speed
Distance
Wavelength
Pathloss
rx
tx
min
max
G
G
P
B
f
f
P
P
f
C
D
L
rx
tx
i
c
p
rxptxir
tx
c
p
GLGPB
ffPP
f
C
DL
x
minmaxi
2
P
4
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 68
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2000Stage 8: Background Noise
• Invocation– Called immediately after stage 7 - no intervening events
• Purpose– Represents effects of all background noise sources– Typically includes
- thermal or galactic noise- neighboring electronics emissions- other unmodeled radio transmissions (commercial/amateur radio, TV)
• Requirements– Sets BKGNOIS TDA
• Results– Typically used by stage 10 in signal-to-noise computation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 69
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2000Stage 8: Background Noise (default)
• Name– dra_bknoise
• Computation– Constant ambient noise
– Constant background noise
– Constant thermal noise
• Result– Value placed in BKGNOISE for use by stage 10 in signal-to-noise computation
ab
rxa
rxbkrxb
bk
rx
NNN
BN
kBTTN
k
T
NFT
26
23
E0.1
E379.1
0.290
0.290*)0.1(
NoiseN
N
N
B
k
T
T
NF
a
b
rx
bk
rx
NoiseAmbient
Noise Background
andwidthReceiver B
Constant sBoltzmann'
eTemperatur Background
eTemperaturReceiver
FigureNoise
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 70
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2000Packet Segments
• Portion of packet with constant signal-to-noise– Segmentation performed by kernel
– SNR computation performed by pipeline model
– Upon packet completion, kernel subtracts SNR of completing packet
SNR Variations
1 2 3 4 1SNR Variations
1 2 3 2 1
SNR Variations1 2 3 2 1
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 71
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2000Stage 9: Interference Noise
• Invocation– Only if packet collision occurs
• Purpose– Accounts for concurrent transmissions– Compute the effect of noise on valid packets
• Requirements– Sets NOISE_ACCUM TDA– Sets NUM_COLLS TDA
• Results– Accumulates noise of interfering packets– Noise from packet completing reception is subtracted by kernel– Typically used in stage 10 for signal-to-noise ratio computations
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 72
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2000Stage 9: Interference Noise (default)
• Name– dra_inoise
• Computation– Increments collision count
– Adds received power of colliding packet- Obtains power from RCVD_POWER TDA
• Result– Places accumulated noise in NOISE TDA
– Value used in stage 10 in signal-to-noise computation
RxTx
Tx
1
2
Valid
Valid
RxTx
Tx
1
2
Noise
Valid
RxTx
Tx
1
2
Valid
Noise
Case 1:
Case 2:
Case 3:
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 73
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2000Stage 10: Signal-to-Noise Ratio
• Invocation (only for valid packets)– Operates on valid packets - those in valid list
– Does not require collision for invocation
• Purpose– Computes the current average SNR
– Typically based on received power and noise
• Requirements– Sets SNR TDA
• Results– Used by kernel to update receiver channel statistics
– Used by later stages
RxTx
Valid
RxTx
Tx
1
2
Noise
Valid
RxTx
Tx
1
2
Valid
Noise
Case 1:
Case 2:
Case 3:
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 74
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2000Stage 10: Signal-to-Noise Ratio (default)
• Name– dra_snr
• Computation– Obtains received power from RCVD_POWER TDA
- Computed in stage 7
– Obtains background noise from BKGNOISE_TDA- Computed in stage 8
– Obtains interference noise from NOISE_ACCUM TDA- Computed in stage 9
– Computes signal-to-noise ratio (in dB)
• Result– Places in SNR TDA– Value used in stage 11 in bit-error-rate computation
)/(log10 10 ibr PPPSNR
(watts) Noise eInterfernc
(watts) Noise Backgroun
(watts) Power Received
i
b
r
P
P
P
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 75
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2000Stage 11: Bit Error Rate
• Invocation– Operates on valid packets - those in valid list– Does not require collision for invocation
• Purpose– Derives the probability of bit errors– Computed for each packet segment - constant SNR– Value typically obtained from modulation curve
• Requirements– Sets BER TDA
• Results– Used by the kernel to record BER statistic– Typically used in stage 12 for allocating errors
RxTx
Valid
RxTx
Tx
1
2
Noise
Valid
RxTx
Tx
1
2
Valid
Noise
Case 1:
Case 2:
Case 3:
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 76
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2000Stage 11: Bit Error Rate (default)
• Name– dra_ber
• Computation– Obtains signal-to-noise ratio from SNR TDA
- Computed in stage 10
– Obtains processing gain from PROC_GAIN TDA- Attribute of receiver channel
– Computes effective SNR
– Determines expected bit-error-rate- Modulation table lookup
• Result– Records BER TDA for use in stage 12 in error allocation computation
pactualeffective GSNRSNR Gain ProcessingpG
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 77
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2000Stage 12: Error Allocation
• Invocation– Called immediately after stage 11 - no intervening events
• Purpose– Estimates bit errors for packet segment
• Requirements– Sets bit-error accumulation in NUM_ERRORS TDA
– Sets empirical bit error rate in ACTUAL_BER TDA
• Results– Kernel maintains a bit accumulator - NUM_ERRORS TDA
– Kernel updates BER statistic - ACTUAL_BER TDA
– Typically used in stage 13 for error correction
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 78
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2000Stage 12: Error Allocation (default)
• Name– dra_error
• Computation– Does not perform bit-by-bit error computations
- Cannot retain bit-error location
– Obtains probability of error - BER TDA
– Computes probability of k errors
– Generates uniform random number: r = (0 1]
– Integrates probability mass over possible outcomes
• Result– Records NUM_ERRORS TDA
N
kk
kNkk
rP
k
NppP
0
)1(
ErrorsofNumber
)1(__
(bits) gthPacket Len
Errorofy Probabilit
Errors ofy Probabilit
k
uniformdistopr
N
p
kPk
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 79
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2000Stage 13: Error Correction
• Invocation– Once for each valid packet– Called immediately after stage 12 - no intervening events
• Purpose– Determines acceptability of arriving packet
• Requirements– Sets PK_ACCEPT TDA
• Results– Rejected
- destroyed by Kernel
– Accepted- forwarded on output stream
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 80
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2000Stage 13: Error Correction (default)
• Name– dra_ecc
• Computation– Obtains threshold from ECC_TRESH TDA
- Percentage of packet in error that still yields acceptability
– Obtains packet length from op_pk_total_size_get ()– Obtains number of errors from NUM_ERRORS TDA
– Computes the percent error
• Result– Packet accepted or rejected depending on threshold and error
– Releases signal lock
length
errors
P
NError%
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 81
OPNET UNIVERSITY
2000Lab: Capture Mode - Overview
• Problem– Default pipeline stages use signal lock
– Systems can lock on to lowest power signal- Higher power signal does not have lock, but dominates channel
- Drowns out lower powered signal
- Causes both communications to fail
• Goals– Modify stages to incorporate signal lock and power lock
– Compare results between the two capture modes
• Purpose– Show additional stage modification
– Incorporate power lock capability
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 82
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2000Lab: Capture Mode - Project/Scenario
• Return to OPNET Modeler (Radio)– Maximize application
• Open project– Capture_Mode
• View scenario– Signal_Lock
- High powered transmitter- Low powered transmitter- Receiver
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 83
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2000Lab: Capture Mode - Choose Results / Simulation
• Observe chosen results– Pulldown menu: Simulation Choose Individual Statistics
- Node Statistics:Radio Transmitter: Traffic Sent (bits/sec)
- Node Statistics:Radio Receiver: Traffic Received (bits/sec)
- Node Statistic:Radio Receiver: Traffic Received High Powered Tx (bits/sec)
- Node Statistic:Radio Receiver: Traffic Received Low Powered Tx (bits/sec)
• Execute simulation– Pulldown menu: Simulation Run Simulation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 84
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2000Lab: Capture Mode - View Results
• View Results– Pulldown menu: Results View Results– Select statistics
- Object Statistics:Capture Mode:High Powered Transmitter:Radio Transmitter: Traffic Sent (bits/sec)
- Object Statistics:Capture Mode:Low Powered Transmitter:Radio Transmitter: Traffic Sent (bits/sec)
- Object Statistics:Capture Mode:Receiver:Radio Receiver: Traffic Received (bits/sec)
- Object Statistics:Capture Mode:Receiver:Radio Receiver: Traffic Received High Powered Tx(bits/sec)
- Object Statistics:Capture Mode:Receiver:Radio Receiver: Traffic Received Low Powered Tx(bits/sec)
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 85
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2000Lab: Capture Mode - View Results (cont.)
• Show results– View mode
- Statistics Overlaid
– Filter- As Is
- Average
– Click Show
• Conclusion– Low powered transmission dominating
- Longer packet lengths - longer signal lock retention
– High powered transmission loss- Short packet lengths - shorter signal lock retention
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 86
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2000Lab: Capture Mode - Stage Modification Overview
• Goal– Modify three pipeline stages to model power lock– Modifications will eliminate signal lock
• Approach– Modify the pipeline stages
- power model- inoise model- ecc model
– Update Models- Project: Create new scenario- Node: Update node model
– Execute simulation– View results
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 87
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2000Lab: Capture Mode - Open Pipeline Stage
• Open pipeline stage– Return to Windows NT Explorer
– Go to directory containing file- c:\users\student\op_models
– Double click to open file- opnetwork_capture_mode_power.ps.c
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 88
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2000Lab: Capture Mode - Modify Pipeline Stage
• Modify stage– Observe code block in middle of file
- Line 59 through 91
– Cut entire else statement- Line 59: start cutting
- Line 91: end cutting
– Save file
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 89
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2000Lab: Capture Mode - Modify Pipeline Stage (cont.)
• Open pipeline stage– Return to Windows NT Explorer
– Go to directory containing file- c:\users\student\op_models
– Double click to open file- opnetwork_capture_mode_inoise.ps.c
• Modify stage– Modifications already complete
– Observe code block at end of file- Line 69
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 90
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2000Lab: Capture Mode - Modify Pipeline Stage (cont.)
• Open pipeline stage– Return to Windows NT Explorer
– Go to directory containing file- c:\users\student\op_models
– Double click to open file- opnetwork_capture_mode_ecc.ps.c
• Modify stage– Modifications already complete
– Observe code block at end of file- Line 60
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 91
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2000Lab: Capture Mode - Compile Stages
• Compile the pipeline stage– Return to a Command Prompt
– Execute the compile command- op_mko -type ps -m opnetwork_capture_mode_power- op_mko -type ps -m opnetwork_capture_mode_inoise- op_mko -type ps -m opnetwork_capture_mode_ecc
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 92
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2000Lab: Capture Mode - Duplicate Scenario
• Return to OPNET Modeler (Radio)– Maximize application
• Refresh model directories– Pulldown menu: File Refresh Model Directories
– Required for OPNET to know about new files
• Duplicate scenario– Pulldown menu: Scenarios Duplicate Scenario
– Scenario name: Power_Lock
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 93
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2000Lab: Capture Mode - Update Node Model
• Open Receiver node model– Double click High Powered Receiver object
- Node model: no_doppler_rt
• Change receiver module attribute– Right click receiver module– Change attribute
- power model: opnetwork_capture_mode_power- inoise model: opnetwork_capture_mode_inoise- ecc model: opnetwork_capture_mode_ecc
– Save node model- Pulldown menu: File Save As- Filename: capture_mode_power_lock_rr
• Close node Model
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 94
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2000Lab: Capture Mode - Update Network Model
• Return to the Project/Scenario– Capture_Mode-Power_Lock
• Change Receiver node attribute– Right click Receiver node
- Select Edit Attributes
– Change model attribute value- Select Edit...
- Select capture_mode_power_lock_rr
– Close attribute edit box- Select Close
• Execute simulation– Pulldown menu: Simulation Run Simulation
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 95
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2000Lab: Capture Mode - View Results
• View Results– Pulldown menu: Results View Results– Select statistics
- Object Statistics:Capture Mode:High Powered Transmitter:Radio Transmitter: Traffic Sent (bits/sec)
- Object Statistics:Capture Mode:Low Powered Transmitter:Radio Transmitter: Traffic Sent (bits/sec)
- Object Statistics:Capture Mode:Receiver:Radio Receiver: Traffic Received (bits/sec)
- Object Statistics:Capture Mode:Receiver:Radio Receiver: Traffic Received High Powered Tx(bits/sec)
- Object Statistics:Capture Mode:Receiver:Radio Receiver: Traffic Received Low Powered Tx(bits/sec)
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 96
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2000Lab: Capture Mode - View Results (cont.)
• Show results– View mode
- Statistics Overlaid
– Filter- As Is
- Average
– Click Show
• Conclusion– High powered transmission dominating
- Obtaining power lock
– Low powered transmission loss
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 97
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2000Lab: Capture Mode - Summary
• Signal lock– Representative of most systems– Locks on to first arriving signal– All other signals are noise, regardless of power level
• Power lock– Locks on to highest power signal– All other signals are noise– Example: IS-95
- Mobile unit moving between cells- Soft handoff process- Constantly demodulates 3 incoming signals in parallel- Monitors 4th incoming signal- Any of 3 active signals become weak, mobile can switch to high-powered signal
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 98
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2000Conclusion
• Transceiver pipeline– Scope– Capabilities– Default
• Pipeline Modifications– Closure model– Channel match model– Power, Inoise, and ECC models
• Pipeline stages– Flexible– Open– Extensible
Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 99
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2000Further Information
• Documentation– Modeling Concepts
- Communication Mechanisms
– General Models- Pipeline Stages / Bus Link
- Pipeline Stages / Point-to-Point Link
- Pipeline Stages / Radio Link