From Pre-Planned to Self-Organizing and Green Wireless Networks

1. From Pre-Planned to Self-Organizing and Green Wireless Networks Antonio Capone The 10th INFORMS Telecommunications Conference Concordia University, May 5 - 7, 2010

2. Disclaimer:Engineers and Mathematicians Picture borrowed from: A. Eisenblätter, H.-F. Geerdes, Wireless Network Design: Solution-oriented Modeling And Mathematical Optimization, IEEE Wireless Communications, December 2006

3. Summary • Wireless networks • Radio planning evolution (2G and 3G) • Coverage Planning • Capacity Planning • Self-organizing networks (4G) • Complexity of network management • 4G systems (LTE) • Concept of SON • Dynamic resource management • Wireless Green networks • Energy consumption • Green energy management • Conclusion

4. Phones …

5. Mobile phones

6. Cellular subscribers vs fixed lines Source: www.etforecasts.com

7. Mobile vs fixed vs internet • 60 mobile subscribers per 100 inhabitants • 19 fixed lines per 100 inhabitants • 23 internet users per 100 inhabitants • 9 broadband users per 100 inhabitants Source: ITU Data: 2008

8. Mobile subscribers by country

9. Radio planning • The deployment of mobile radio networks required so far HUGE investments • The extension of existing network, new data services, and new technologies are continuing to require a lot of money • This has stimulated mobile operators to use automatic tools for the design and the optimization of their networks • In the last ~15 years the research community has proposed a large number of approaches for designing and optimizing wireless access networks (more than 16000 results in Google Scholar)

10. Network planning tools Main Planning Tools: • Aircom Asset • Mentum Planet • Atoll FORSK • ATDI • WinProp • EDX Signal Pro • CelPlan • Siradel • Pathloss Main Optimization Engines • Actix • Capesso

11. What is radio planning? • The basic decisions that must be taken during the radio planning phase are: • Where to install base stations (or access points, depending on the technology) • How to configure base stations (antenna type, height, sectors orientation, tilt, maximum power, device capacity, etc.) X X X X

12. FDMA POWER TIME FREQUENCY TDMA POWER FREQUENCY TIME CDMA POWER FREQUENCY TIME What is radio planning? • This is, however, not enough … • Multiple access techniques are used to define communication channels on the available radio spectrum • Radio resources for wireless systems are limited and must be reused in different areas (cells) • Resource reuse generates interference

13. Interference • Interference is the key parameter that drives network planning and optimization processes • Interference can be tolerated (good communication quality) if the Signal-to-Interference and Noise Ratio (SINR) is high enough • SIR constraint limits the number of simultaneous communications per cells, i.e. the system capacity GOAL: minimize costs maximize covered traffic

14. 2G Planning • FDMA/TDMA cellular systems adopt a two phases radio planning • Coverage planning • Capacity planning (frequency assignment) • Coverage planning: • Select where to install base stations • Select antenna configurations • s.t. constraints on signal level in the area • Capacity planning: • Define which radio resources can be used by each cell • s.t. SINR (quality) constraints

15. Coverage Planning • Many different models have been proposed for the coverage planning • Basically all of them are based on the classical set covering problem • With several specific features that have been added depending on technology and service mix Objective function: total network cost Full coverage constraints One configuration per site Integrality constraints

16. Coverage Planning • Example: Cell overlap • Cell overlap may be required for mobility management • Overlap can negatively affect capacity (e.g. in WLANs) Note that: zih = 1 if i and h are covered by a same BS

17. F2 F2 F7 F3 F7 F3 F1 F1 F6 F4 F6 F4 F5 F2 F5 F2 F7 F3 F2 F7 F3 F1 F7 F3 F1 F6 F4 F1 F6 F4 F5 F6 F4 F5 F2 F5 F2 F7 F3 F7 F3 F1 F1 F6 F4 F6 F4 F5 F5 Capacity planning(aka frequency assignment) • After coverage planning, capacity planning is in charge of defining which radio resources can be used by each cell • The amount of resources (frequencies) assigned to cells determines system capacity • Frequencies can be reused, but SINR (quality) constraints must be enforced

18. Frequency assignment • Maximizing the simultaneous transmission with SINR constraints is a key problem is all wireless networks i j SINRij>t • However, the most popular models for frequency assignment have been based on compatibility graphs • Frequency assignment problems are modeled as variants of the graph coloring problems cij i j

19. Frequency assignment • Since Graph based models do not consider SINR constrains explicitly the cumulative effect of interference is not accouter for • Minimum Interference Frequency Assignment Problem (MI-FAP) and its variants models directly interference effect Compatible?

20. 3G Planning • 3rd Generation Systems are based on W-CDMA (UMTS) • Two-phases approach not suitable because: • Channels are shared and there is no frequency planning for CDMA • Coverage depends on SINR values • Joint coverage and capacity planning • SINR constraints make the problem a generalization of the capacitated facility location problems

21. Network management & control • Network configuration and optimization is becoming far too complex for mobile operators

22. 4G – Long Term Evolution • The need to plan, configure, manage a new wireless network from scratch • … with up to 10 times more base stations • … and many more parameters to set • simply worries mobile operators

23. 4G – Long Term Evolution

24. LTE architecture • The radio architecture of LTE is more complex • Base stations (eNodeB) are connected also among them (mesh topology) • and they have computation capability to perform advances functions • The presence of femto-cells can make the network management even more complicated

25. LTE radio interface • More similar to 2G than to 3G

26. Self Organizing Network (SON) • “self-organizing network is a cellular network in which the tasks of configuring, operating, and optimizing are largely automated.”

27. Self Organizing Network (SON) CentralizedArchitecture DistributedArchitecture

28. Self Organizing Network (SON) • Most of the SON features are aimed at simplifying preoperational and operational procedures • HW configuration • SW installation and configuration • Radio basic parameters • Transport parameters • Etc. • However, the most interesting issues from our perspective are related to the configuration and management of radio resources Load balancing Automatic carrier selection Fractional reuse

29. Dynamic assignment • The idea of self-configuring and self-optimizing wireless network is not new! • Several Dynamic Channel Assignment (DCA) schemes have been proposed and analyzed for 2G • Channel/frequency assigned on demand based on compatibility or interference constraints • … but they have never been used in real networks

30. Resourceassignment in LTE • LTE-advanced offers several instruments to make configuration and dynamic management of radio resources possible • eNBs can make measurements over the radio interface before first resource configuration • User terminals can provide measurements to eNBs during system operation to dynamically select resources

31. Resource assignment in LTE • Defining both centralized and distributed self-configuration and self-optimization models and algorithms for LTE is still an open problem • Automatic carrier selection • Channel assignment based on position in the cell (fractional reuse) • Load balancing among cells forcing handover • Etc.

32. Green Wireless Networks • In addition to configuration, energy consumption of wireless network is another issue that concerns of operators • The power consumption of cellular networks infrastructure (base stations and core network) doubles every 4-5 years - to 60 TWh in 2008 • Energy consumption of mobile telephony operators in Italy is 0,7% of total national electric consumption, 55% of whole communications sector, with bills of more than 300M€ per year

33. Energy consumption Radio access and core network Mobile Stations Mobile Network 20% Base Stations 80% User Terminals 10% Network 90%

34. Energy consumption

35. Traffic load • Wireless access networks are dimensioned for estimated peak demand using dense layers of cell coverage • Traffic varies during the day • Energy consumption is almost constant Network capacity Traffic Load Day 1 Day 2 Day 3

36. Energy Savings • Significant energy savings can be achieved if parts or all components of some wireless network devices are powered off when traffic is low, and powered on based on the volume and location of user demand

37. Energy Savings • It is also possible to partially switch off internal modules of base stations Base Station Cabinet Air Conditioner TRXs

38. Green Network Management • Switching on and off network elements based on traffic level • Re-planning of the network based on different traffic scenarios

39. Green Network Management • Radio Planning models can be “re-used” • But some additional features need to be modeled like: • Coverage and capacity constraints • Cost of network reconfiguration • Performance – Energy trade off • Etc. • Energy saving is one of the issues that is being considered as part of Self Organizing Network by standardization bodies and manufacturers

40. Conclusion • The need to plan and manage new generation wireless network in a cost effective way is even more acute now than in the past • Network complexity is increasing • Network re-planning is required more often also for energy saving • New design and management approaches are required • Don’t let engineers play alone with these new challenging problems

41. From Pre-Planned to Self-Organizing and Green Wireless Networks Antonio Capone Thanks