1. Resource Allocation and Reuse in LTE

2. Mobile Communication 2 Markus Laner Seminar, SS 2008 0325687 Contents Introduction History of Resource Reuse Proposals and Specification for LTE Inter-cell Interference Soft Frequency Reuse Conclusion

3. Mobile Communication 3 Markus Laner Seminar, SS 2008 0325687 Introduction Resource reuse to enhance capacity -use expensive spectrum acquired by providers most efficiently -minimize number of BS but maximize number of users -leads to interference limited systems

4. Mobile Communication 4 Markus Laner Seminar, SS 2008 0325687 Contents Introduction History of Resource Reuse Proposals and Specification for LTE Inter-cell Interference Soft Frequency Reuse Conclusion

5. Mobile Communication 5 Markus Laner Seminar, SS 2008 0325687 History of Resource Reuse GSM -digital because higher SIR supported -clusters of cells -frequency reuse factor between 3 and 9 -not very efficient

6. Mobile Communication 6 Markus Laner Seminar, SS 2008 0325687 History of Resource Reuse UMTS -real freq reuse 1 through spreading and scrambling -no more freq planning -Macro diversity => connections to 1 or more BS Scrambling A Spreading 1,2,3 Scrambling B Spreading 1,2,3

7. Mobile Communication 7 Markus Laner Seminar, SS 2008 0325687 Contents Introduction History of Resource Reuse Proposals and Specification for LTE Inter-cell Interference Soft Frequency Reuse Conclusion

8. Mobile Communication 8 Markus Laner Seminar, SS 2008 0325687 Proposals and Specifications no specifications defined jet ( necessary? ) frequency reuse 1 proposed hard handover, no macro diversity many proposals to combat ICI (3GPP TR 25.814) –ICI cancellation –ICI co-ordination –ICI randomization

9. Mobile Communication 9 Markus Laner Seminar, SS 2008 0325687 Contents Introduction History of Resource Reuse Proposals and Specification for LTE Inter-cell Interference Soft Frequency Reuse Conclusion

10. Mobile Communication 10 Markus Laner Seminar, SS 2008 0325687 Inter-cell Interference ICI cancellation multiple antennas can be used to suppress interferer - demodulation and subtraction (Blast) - IRC (Interference rejection combining) instead of MRC (Maximum ratio combining) - optimum combining - uplink: multiple BS can be seen as giant MIMO system drawback: extremely high complexity

11. Mobile Communication 11 Markus Laner Seminar, SS 2008 0325687 Inter-cell Interference ICI randomization similar to the method used in UMTS -cell specific scrambling -cell specific interleaving (IDMA) (interleave-division multiple access) the UE can identify the transmitting BS via different patterns, interference is spread over multiple channels

12. Mobile Communication 12 Markus Laner Seminar, SS 2008 0325687 Inter-cell Interference ICI co-ordination most promising methods for LTE - soft frequency reuse (SFR) reuse 1 -> cell-centre users (CCU) reuse 3 -> cell-edge users (CEU) - co-ordination between BSs TLA (two level allocation scheme) (see graphic) UFR (universal frequency reuse) -> static DMA (dynamic major-group allocation scheme) -> dynamic

13. Mobile Communication 13 Markus Laner Seminar, SS 2008 0325687 Inter-cell Interference adaptive modulation and coding (AMC) users with different SIR get different modulation and coding schemes assigned -modulation schemes up to 64-QAM -Turbo coding with different code rates drawback: wasting of resources

14. Mobile Communication 14 Markus Laner Seminar, SS 2008 0325687 Inter-cell Interference beam forming at eNodeB BSs track their active subscribers with the antenna beam

15. Mobile Communication 15 Markus Laner Seminar, SS 2008 0325687 Inter-cell Interference Muting -> UE tracks the scheduling information of neighboring cells -> UE recognizes when co-channel interferer are active -> in this case the UE is ‘mute’, doesn’t transmit drawback: wasting of resources

16. Mobile Communication 16 Markus Laner Seminar, SS 2008 0325687 Contents Introduction History of Resource Reuse Proposals and Specification for LTE Inter-cell Interference Soft Frequency Reuse Conclusion

17. Mobile Communication 17 Markus Laner Seminar, SS 2008 0325687 Soft Frequency Reuse TLA (two level allocation scheme) CRA (cell-level resource allocation) - static, major- & minor-group URA (user-level resource allocation) - division in CEU (high priority) and CCU by geometry factor

18. Mobile Communication 18 Markus Laner Seminar, SS 2008 0325687 Soft Frequency Reuse benefits: -CQI (channel quality information) has to be available at BS anyway, can be used for partitioning users -low complexity -better cell-edge performance drawbacks: -signaling overhead -reuse partitioning is suboptimal from information theoretical point of view -overall loss of throughput (see next slides)

19. Mobile Communication 19 Markus Laner Seminar, SS 2008 0325687 Soft Frequency Reuse Impact of ICI on capacity, reuse 1 y-axis Cell Throughput: whole cell [bits/second] x-axis arrival rate: poisson distriubuted [erlang / number of servers]

20. Mobile Communication 20 Markus Laner Seminar, SS 2008 0325687 Soft Frequency Reuse Impact of ICI on capacity: reuse 1/3 Throughput per cell-edge userThroughput of the whole cell

21. Mobile Communication 21 Markus Laner Seminar, SS 2008 0325687 Soft Frequency Reuse Types of traffic Narrow-band services (calls) will perform better than wide-band services (FTP) reason: narrow-band services allow more flexibility in resource allocation Served traffic of user X circles mark the link utilization factor: 0.2 / 0.4 / 0.6 / 0.8 / 1

22. Mobile Communication 22 Markus Laner Seminar, SS 2008 0325687 Soft Frequency Reuse UFR (Ki Tae Kim, 2007) (universal frequency reuse) -special patterns (sequences) for frequency allocation coordinated with neighboring cells -lower interference for small LF (loading factor) -static configuration, low complexity Loading factor three different algorithms for three different cells C0, C1, C2

23. Mobile Communication 23 Markus Laner Seminar, SS 2008 0325687 Soft Frequency Reuse DMA (Fan, Qian, Zheng, Wang, 2007) (dynamic major-group allocation scheme) dynamic allocation of major group sub carriers depending on the number of CEU (sectors per site) -benefits depending on major- to minor-group power-ratio -high complexity

24. Mobile Communication 24 Markus Laner Seminar, SS 2008 0325687 Contents Introduction History of Resource Reuse Proposals and Specification for LTE Inter-cell Interference Soft Frequency Reuse Conclusion

25. Mobile Communication 25 Markus Laner Seminar, SS 2008 0325687 Conclusion Specifications / Suggestions: -reuse 1 -no macro-diversity -hard handover ICI overcoming: -cancellation: too complex -mitigation / coordination: will be supported in LTE -randomization: no real improvement -beam forming at eNodeB: will be supported in LTE -AMC (adaptive modulation and coding): will be supported in LTE

26. Mobile Communication 26 Markus Laner Seminar, SS 2008 0325687 Conclusion Soft Frequency Reuse: -also called reuse 1/3 -partitioning of users in CEU and CCU through geometry factor -good performance for CEU -low complexity -overall loss of throughput -further improvements through different scheduling / resource assignment methods possible (UFR, DMA)

27. Mobile Communication 27 Markus Laner Seminar, SS 2008 0325687 The End Thank you, Questions ?

28. Mobile Communication 28 Markus Laner Seminar, SS 2008 0325687 Appendix References, Specifications: -3GPP TR 25.892, Feasibility Study for OFDM for UTRAN enhancement, 2004-06 -3GPP TR 25.814, Physical layer aspects for eUTRA, 2006-09 -3GPP R1-050764, Ericsson, Inter-cell Interference Handling for eUTRA, 2005-08-29, London -3GPP R1-050763, Ericsson, Muting – Further Discussion and Results, 2005-08-29, London -3GPP R1-060864, Texas Instruments, Overview of Resource Management Techniques for Interference Mitigation in eUTRA, 2006-03-27, Athens

29. Mobile Communication 29 Markus Laner Seminar, SS 2008 0325687 Appendix References, Papers: -Bin Fan, A Dynamic Resource Allocation Scheme Based on Soft Frequency Reuse for OFDMA Systems, 2007 -Elayoubi, On frequency allocation in 3G LTE systems, 2006 -Fan, An Inter-Cell Interference Coordination Technique Based on User's Ratio and Multi-Level Frequency Allocations, 2007 -Jorguseski, Downlink Resource Allocation in Beyond 3G OFDMA Cellular Systems, 2007 -Ki Tae Kim, A Universal Frequency Reuse System in Mobile Cellular Environment, 2007 -Simonsson, Frequency Reuse and Inter-cell Interference Co- ordination in eUTRA, 2007

30. Mobile Communication 30 Markus Laner Seminar, SS 2008 0325687 Appendix References, Books: -Dahlman, Parkvall, Sköld, Beming, 3G Evolution – HSPA and LTE for Mobile Broadband, Academic Press, 2007 -Molisch, Wireless Communications, Wiley & Sons, 2005