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2. 2 Wireless Information Network Laboratory 23 Sponsors, NSF, DARPA, State of NJ
7 profs, 35 grad students, 15 undergrads
3. 3 WINLAB: Research with a broad systems viewpoint
4. 4 Why simulate? Because I have no choice!
Wireless systems are complicated
and getting more complicated
algorithms are part of integrated systems
Interactions are hard to predict
5. 5 Example: Bad Interactions SIR Handoff
When SIR too low
SIR Power Control
Use min power to meet SIR target
6. 6 Picoradio Networks(Jan Rabaey) “versatile, self-organizing, dynamically reconfigurable”
“adaptive and programmable”
“consume a minimum amount of energy”
7. 7 Wireless Basics Every transmitter needs
a receiver
a radio channel
CDMA code? frequency hop? transmit power?
Transmit bits and packets
Support applications
8. 8 Wireless Network Adaptation Given
received signal
feedback from RX to TX
Adaptation:
link setup/reconfig
power control
channel (code) assignment, RX filtering
rate adjustment
9. 9 Adaptation Layers
10. 10 Wireless Time Scales
11. 11 Wireless Simulation Flavors
12. 12 Mobile Computing Simulation Mobile users running network, transport, application layer protocols
Simple models for:
packet transmission/reception
link quality
13. 13 Signal Processing Simulation Decode bits from signal at RX i : ri(t)=?j hij(t)*sj(t) +N(t)
14. 14 Wireless System Simulation No Radios
link quality based on models
15. 15 Simulation Types: Summary
16. 16 Models Mobile Computing
simple model of physical layer
links up and down, packet errors sometimes
Signal Processing
simple model of application traffic
steady stream of bits
Wireless System
simple model of radio + traffic
17. 17 Picoradio Models? “Ensuring and verifying that these distributed and embedded systems will behave in a correct manner is especially hard”
Appropriate Model Abstractions?
Which layers can be ignored or simplified?
Example: Power Control
18. 18 Interference Constraints Power Vector: p = [p1 p2 pN ]
N = number of transmitters!
SIR Constraints: p ? Hp + ?
Matrix H includes
data rates, QoS targets, CDMA cross-correlations, path losses, terminal locations, receiver filters
Feasibility iff ?(H) < 1
19. 19 Wireless Power Control Use SIR (Signal to Interference Ratio) for QoS
SIR Balancing Power Control
SIR too low ? Raise transmit power
SIR too high ? Reduce transmit power
800 iterations/s in IS-95
Stability iff P-F eigenvalue ?(H) < 1
20. 20 CDMA System Instability
21. 21 Cellular Outage Response Cellular goal: maintain connections
Backoff by lowering SIR targets
Look for handoff
CDMA: go into soft handoff
22. 22 Picoradio Outage Response
23. 23 Unlicensed Interferers System-specific modulation formats
How to model interferers objectives?
Cordless Phones: maintain connection
Meter reading: unreliable data delivery
Wireless Lan: Reliable data
with backoff and retransmission
System-specific simulations
24. 24 Picoradio Simulation Issues What protocol layers really matter?
How do we model unlicensed interferers?
Which really matter?
Does modulation format depend on application?
What’s the (pico)radio channel?
25. 25 Picoradio Simulations?
26. 26 Interprotocol Interactions Models that capture interactions are extremely difficult.
Need simulation across layers
27. 27 Simulation at WINLAB
28. 28 Scalable Simulation Framework (SSF) Parallel discrete event simulation API
C++ and Java versions
Base SSF objects - Entity, Event, Process, Channel
Events pass via SSF channels between entities.
www.ssfnet.org
Andy Ogielski (Dartmouth)
29. 29 SSF Simulation
30. 30 WiPPET WiPPET = Wireless Propagation and Protocol Evaluation Testbed
Built on SSF
Inheritance of base SSF objects - Entity, Event, Process, Channel to create higher entities - Mobile, Base, RadioChannel, Mobility, Geography
Versions:
WiPPETsession + WiPPETpacket+ WiPPETsignal
31. 31 WiPPETSIGNAL
32. 32 WiPPETSIGNAL Design
33. 33 RCH Propagation and Interference
34. 34 RCH Properties Multicell Interference
Independent of framing/coding structure
Geography/Mobility embedded in channels
Distance path loss and shadow fading based on geography
Path and RxAntenna diversity
Independent Rayleigh fading process for each multipath component of each Tx/Rx antenna pair
35. 35 WiPPET WCDMA Multi Cell Results
36. 36 WCDMA Multi Cell Power Profiles
37. 37 WCDMA Directions Multicell Evaluation of WCDMA enhancements
channel estimation
SIR estimation
Downlink Interference Suppression
Integrated Soft Handoff + interference cancellation algorithms
Integration with Internet access
38. 38 WiPPETSIGNAL:More Systems GSM/GPRS/EDGE
in progress at winlab
Infostations
Ad Hoc Networks
Picoradio Sensor Networks
39. 39 More Systems=More Issues CDMA
integer-chip timing for multipath delay, asynchronism
signal = sampled vector, 1 sample/chip
Narrowband (including FH) systems
how many samples/symbol?
real RX? In simulation?
Efficient RCH depends on modulation
Building a universal RCH is not trivial
40. 40 RCH Data Structures Fixed receivers (Base stations)
precompute path loss and shadow fading
G geography pts, B bases ? GB entries in radio topology database
Mobile Receivers (Ad hoc networks)
G geography points ? G 2 entries!
41. 41 Visualization! Mobile connected to base
Small sign error
link gain increasing with distance...
System works great!
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