Wireless System Simulation

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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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