Transceiver Pipeline and Radio Modeling

Copyright © 2000 MIL 3, Inc. Modeling Custom Wireless Effects– 1

OPNET UNIVERSITY

2000

Transceiver Pipeline and Radio Modeling


OPNET UNIVERSITY

2000Goals

• Introduce the OPNET Transceiver Pipeline– Capabilities

– Defaults

• Modify pipeline– Show openness and extensibility

– Model custom wireless effects


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


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


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


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)


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


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


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


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


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.


OPNET UNIVERSITY

2000Point-to-Point Pipeline Models

• Execution for one transmission

receiver

transmitter

TransmissionDelay

0

PropagationDelay

1

ErrorAllocation

ErrorCorrection

23


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


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


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



InterferenceNoise

Bit ErrorRate

Bit ErrorRate


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


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


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:


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:


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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



OPNET UNIVERSITY


• View Results– Pulldown menu: Results View Results

– Select Statistics- Object Statistics:Closure:Transmitter:Radio Transmitter: Link Closure Failure (failures/sec)


• Conclusion– Closure is failing, causing undesired packet loss


OPNET UNIVERSITY

2000Lab: Closure - Stage Modification Overview

• Goal– Modify the link closure model to eliminate closure failure

• Approach– Update Models

- Project: Create new scenario



– View results


OPNET UNIVERSITY

2000Lab: Closure - Duplicate Scenario


- Scenario name: Zero_Antenna_Height_Success


OPNET UNIVERSITY

2000Lab: Closure - Update Node Model


- Node model: closure_stats_rt

• Change module attribute– Right click transmitter module

– Change attribute- closure model: dra_closure_all


- Filename: closure_all_rt

• Close node model


OPNET UNIVERSITY

2000Lab: Closure - Closure All Stage

• Open pipeline stage– Return to Windows NT Explorer


– 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


OPNET UNIVERSITY

2000Lab: Closure - Update Network Model


• Change Transmitter object– Right click Transmitter node

- Edit Attributes


- Select closure_all_rt



OPNET UNIVERSITY



- Object Statistics:Closure:Transmitter:Radio Transmitter: Traffic Sent (bits/sec)

- Object Statistics:Closure:Receiver:Radio Receiver: Traffic Received (bits/sec)


• Conclusion– Traffic is being generated by transmitter– Traffic is being received by receiver– Closure was failing due to occlusions


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.


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


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


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


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:


OPNET UNIVERSITY

2000Stage 5: Propagation Delay


• 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


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


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


OPNET UNIVERSITY

2000Lab: Doppler - Project/Scenario


• Open project– Doppler

• View scenario– No_Doppler_Shift

- Transmitter - aircraft

- Receiver


OPNET UNIVERSITY

2000Lab: Doppler - Choose Results / Simulation




- Node Statistic:Radio Transmitter: Transmission Frequency - Unshifted (Hz)

- Node Statistic:Radio Transmitter: Transmission Frequency - Shifted (Hz)



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)


• Conclusion– Default behavior observed

– No shift in frequency

– No Doppler shift computations


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



– View results


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


OPNET UNIVERSITY

2000Lab: Doppler - Open Pipeline Stage



– Double click to open file- opnetwork_chanmatch_no_doppler.ps.c


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


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

*


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


OPNET UNIVERSITY

2000Lab: Doppler - Duplicate Scenario





– Scenario name: Doppler_Shift

• Include external file– Pulldown menu: File Declare External Files

- Change doppler_shift status to included


OPNET UNIVERSITY

2000Lab: Doppler - Update Node Model


- Node model: no_doppler_rt

• Change transmitter module attribute– Right click transmitter module

– Change attribute- chanmatch model: opnetwork_chanmatch_doppler


- Filename: doppler_rt

• Close node model


OPNET UNIVERSITY

2000Lab: Doppler - Update Network Model

• Return to the Project/Scenario– Doppler-Doppler_Shift

• Change Transmitter node attribute– Right click Transmitter node



- Select doppler_rt




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)


• Conclusion– Frequency shifts +/- 40 Hz


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


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


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:


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


OPNET UNIVERSITY

2000Stage 7: Receiver Power


• 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


OPNET UNIVERSITY

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


OPNET UNIVERSITY

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


OPNET UNIVERSITY

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


OPNET UNIVERSITY

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


OPNET UNIVERSITY

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


OPNET UNIVERSITY

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:


OPNET UNIVERSITY

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:


OPNET UNIVERSITY

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


OPNET UNIVERSITY

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:


OPNET UNIVERSITY

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


OPNET UNIVERSITY

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


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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


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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


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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%


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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


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2000Lab: Capture Mode - Project/Scenario


• Open project– Capture_Mode

• View scenario– Signal_Lock

- High powered transmitter- Low powered transmitter- Receiver


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2000Lab: Capture Mode - Choose Results / Simulation




- Node Statistic:Radio Receiver: Traffic Received High Powered Tx (bits/sec)

- Node Statistic:Radio Receiver: Traffic Received Low Powered Tx (bits/sec)



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2000Lab: Capture Mode - View Results


- 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)


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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


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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


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2000Lab: Capture Mode - Open Pipeline Stage



– Double click to open file- opnetwork_capture_mode_power.ps.c


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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


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2000Lab: Capture Mode - Modify Pipeline Stage (cont.)



– 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


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2000Lab: Capture Mode - Modify Pipeline Stage (cont.)



– 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


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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


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2000Lab: Capture Mode - Duplicate Scenario





– Scenario name: Power_Lock


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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


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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 capture_mode_power_lock_rr




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2000Lab: Capture Mode - View Results


- 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)


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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


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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


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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


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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

Transceiver Pipeline and Radio Modeling

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