Antti Ratilainen 22.05.2014 This work was carried out in Oy L M Ericsson Ab

1. Protocol Performance of Uplink/Downlink Separation in LTE Heterogeneous NetworksMaster’s thesis presentation Antti Ratilainen 22.05.2014 This work was carried out in Oy L M Ericsson Ab Supervisor: Professor Jyri Hämäläinen

2. Contents of presentation • Background • Problem setting – UL/DL imbalance • UL/DL separation • Simulations • Protocol simulations • System simulations • Summary

3. Demand for wireless data is increasing rapidly • The demand for mobile data traffic is expected to increase up to 11-fold by 2018 according to CISCO • Ericsson’s vision: More than 50 billion connected devices by 2020

4. Three methods for improving the cellular network capacity • Improving macro sites • Densifying macro layer • Adding Low Power Nodes (Heterogeneous Networks)

5. Uplink/Downlink Imbalance • High power and Low Power Nodes (LPNs) in heterogeneous networks cause UL/DL imbalance situations for the UEs, where the best uplink cell and the best downlink cell are not the same. • Currently the serving cell is generally chosen based on downlink measurements RSRP Macro LPN Path loss Macro LPN

6. Contents of presentation • Background • Problem setting – UL/DL imbalance • UL/DL separation • Simulations • Protocol simulations • System simulations • Summary

7. Uplink/Downlink Separation • In UL/DL separation the uplink and downlink of a UE are splitted to separate cells in order to provide the best connection for both links. • This means that for LPN cells the cell area is expanded in uplink and within this Cell Uplink Range Expansion (CURE) the UEs are connected to the pico cell in uplink while in downlink they are connected to macro cell.

8. UL/DL Separation Downlink Uplink CURE macro pico RSRP_macro == RSRP_pico

9. TCP Uplink/Downlink Separation • In this thesis the studied case is such that the UL/DL separation is done after PDCP layer. • Separate RLC and MAC layers for both cells. • Everything which comes from PDCP or above goes through macro cell in downlink and pico cell in uplink. • Pico cell still uses downlink for RLC and MAC purposes. • Likewise, macro cell still uses uplink for RLC and MAC purposes. Delay PDCP RLC RLC MAC-DL MAC-UL PUSCH PDSCH PUCCH PDSCH PUSCH PDCCH(DL assign) PDCCH(UL grants)

10. Contents of presentation • Background • Problem setting – UL/DL imbalance • UL/DL separation • Simulations • Protocol simulations • System simulations • Summary

11. Study is performed by means of simulations • Two types of simulations are performed: • Protocol simulations to verify the benefits of UL/DL separation on protocol level. • System simulations to see the behavior of UL/DL separation in a more detailed and realistic system. • One of the major challenges with the thesis was actually implementing the UL/DL separation feature to the simulators! • The feature is now implemented and functional, it can be used for future research on the matter and for further development towards a more generalized dual connectivity simulator, which actually is currently being planned.

12. UL/DL Separation protocol simulator • The simulation scenario is in a sense a “snapshot” of a user in a full, dynamic system, meaning that the simulation is stationary; the user stays in the same state during a single simulation. • Only the higher layer protocols of a connection are simulated: FTP, TCP, IP and PDCP (as an RLC UM due to reordering) layers. • Downlink traffic comes from MeNB, while uplink traffic goes through SeNB with an added backhaul delay. • Gains in FTP rate for a single user using UL/DL separation were calculated using this model to get insight of the technology potential of the UL/DL separation.

13. Without UL/DL separation FTP Server FTP Client TCP TCP IP Network IP Terminal Basic channel with delay Reordering entity in RXRLC UM, bi-direct Reordering entity in RXRLC UM, bi-direct Mux/Demux Mux/Demux Downlink Uplink Downlink Uplink MeNB

14. UL/DL separation FTP Server FTP Client TCP TCP IP Network IP Terminal Basic channel with delay Reordering entity in RXRLC UM, bi-direct Reordering entity in RXRLC UM, bi-direct Mux/Demux Mux/Demux Basic channel with delay Uplink Relay, bi-directionalhelper class Downlink SeNB MeNB

15. Simulations with protocol simulator • Simulations were run with several different parameter sets and compared to a basic case, where both uplink and downlink traffic were handled by MeNB only. • The backhaul delay was varied with different bit rates through the SeNB link. • The FTP transfer rate was recorded during the simulations and gains for using UL/DL separation according to the simulations were calculated and plotted. • Block sizes are based on averages observed in system simulations. MeNB transport block size is 8000 bits. • Uplink FTP traffic!

16. Rate gain • FTP file size = 2 MB • MeNB link block size = 8000 bits

17. Results summary with protocol simulator • It seems that increasing SeNB link bitrateincreases the gain achieved from using UL/DL separation. • With small files, the gains are smaller, or even negative. (Due to TCP slow start) • The longer the delay in the SeNB link, the less gain is achieved. • Results seemed intuitive, UL/DL separation can provide gains on protocol level with certain conditions

18. Contents of presentation • Background • Problem setting – UL/DL imbalance • UL/DL separation • Simulations • Protocol simulations • System simulations • Summary

19. System simulator - Deployment scenario • 3GPP Case 1 SIMO multi cell Hetnet • 7 macro sites, 3 sectors per site • Max Tx power = 40 W • Inter site distance = 500 m • 4 pico cells per macro cell • Co-located with hotspots • Max Tx power = 1 W • 4 hotspot per macro cell • Minimum distance between hotspots = 50 m • Minimum distance to site = 75 m • Max UeTx power = 0.25 W • Users • Poisson arrivals, arrival intensity = 3, 5, 7 and 9 users/s with 2 MB file, 0.75, 1.25, 1.75 and 2.25 users/s with 8 MB file • Clustered around hotspots probability = 0.6667 • Indoor probability = 0.8 (adds 20 dB attenuation) • Velocity 3 km/h • Data traffic • Fixed FTP traffic • Object size 2 MB and 8 MB • Offered loads 48, 80, 112 and 144 Mbps (low, medium, high, very high)

20. Other parameters/configurations • In control plane, the lower layers of RRC are bypassed to make sure RRC signaling goes through, since we are interested in the protocol performance in the user plane and wanted to eliminate the issues caused by problems in signaling. • 20 ms backhaul delay after SeNB when UL/DL separation is activatedSingle carrier • 10 MHz bandwidth • Carrier frequency 2 GHz • Mainly uplink traffic studied • 500 second simulation time

21. UL/DL separation activation/deactivation scenarios • Due to the nature of UL/DL separation, multiple handover scenarios had to be implemented macro == pico 5. 4. CURE pico macro 6. 3.

22. UL/DL separation activation/deactivation scenarios 1. macro 7. macro pico

23. UL/DL separation activation/deactivation scenarios 2. pico macro pico 8. pico

24. Best cells of the simulation area

25. System simulation results • Curves plotted: • Mean gains and gains for worst 5% users in FTP rate (uplink) • CDFs for FTP rate (uplink) • User distribution between macros, picos and split • System load (uplink) • Mean gains and gains for worst 5% users in FTP rate (downlink) • CDFs for FTP rate (downlink)

26. Uplink FTP rate, 2 MB Low load High load

27. CDFs for mean user uplink throughputs, 2 MB Low load High load

28. User distribution between macros, picos and split, high load

29. Used uplink resources, very high load, 2 MB

30. Downlink FTP rate, 2 MB Low load High load

31. CDFs for mean user downlink throughputs, low load, 2 MB Low load High load

32. Contents of presentation • Background • Problem setting – UL/DL imbalance • UL/DL separation • Simulations • Protocol simulations • System simulations • Summary

33. Uplink results summary • Considerable uplink gains are achieved in certain situations • Increasing CURE increases the achieved mean gain even up to CURE 20 dB depending on system load • The fifth percentile users benefit more than users on average • Cell-edge users in CURE area benefit from being transferred from macro cell to pico cell due to better uplink to pico • Interestingly with higher system loads, the gains are higher • In addition to some users having better uplink to the pico cell instead of serving macro cell, with higher loads the macro cells become so overloaded, that offloading becomes a significant factor in achieved gains • The system was studied also with file size of 8 MB. The results were quite similar, although the gains were somewhat smaller. This can be explained by that the macro cells did not get as overloaded in this case, so the benefit from offloading was not as large.

34. Downlink results summary • The system was also studied with 2 MB downlink FTP transmissions • As only TCP ACKs go through the SeNB uplink, no gains was to be expected • As can be seen, the results show negative gains • TCP ACKs are just small packets, and therefore do not benefit greatly from the increased bitrate in the uplink of UL/DL separation. On the contrary, the backhaul delay just increases the RTT of TCP ACKs thus slowing down the downlink transmissions as well.

35. Conclusions • UL/DL separation can provide considerable uplink gains in certain situations • The gains increase with the system load • Cell-edge users seem to benefit the most • The downlink results show slightly negative gains for using UL/DL separation • UL/DL separation is a promising technology which still needs to be researched further, for example with different deployments and traffic models

36. References • More Than 50 Billion Connected Devices, Ericsson, 2011, Available: http://www.ericsson.com/news/110214_more_than_50_billion_244188811_c • Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2013–2018, 2013, Available: http://www.cisco.com/c/en/us/solutions/collateral/service-provider/visual-networking-index-vni/white_paper_c11-520862.html • Heterogeneous networks – increasing cellular capacity, Ericsson, 2011, Available: http://www.ericsson.com/news/110211_hetnets_244188811_c

37. Questions? Thank you!