Uplink Power Control in LTE Relay Enhanced Cells

1. Uplink Power Control in LTE Relay Enhanced Cells Masters Thesis Presentation Department of Communications and Networking Student: Aydin Karaer Supervisor: Prof. Jyri Hämäläinen / HUT Instructor: Doc. Simone Redana / NSN

2. Agenda • LTE Advanced • Why Relaying? • Relay Enhanced Cell (REC) Scenario • LTE Uplink Power Control • Simulation Parameters • Power Control Optimization and System Performance Evaluation in REC

3. LTE Advanced (LTE-A) • First set of requirements were addressed in June 2008 • Not a revolution but an evolution of LTE • Promises to support peak data rates of 1 Gbps in downlink and 500 Mbps in uplink • Bandwidth scalability up to 100 MHz • Improved user and control plane latencies • Improved cell edge performance

4. Why Relaying? (1)Reasons • Future wireless communication systems are operating carrier frequencies over 2 GHz • Heavy pathloss in radio transmission • Aggressive propagation conditions restrict the radio coverage especially in urban areas • Possible solutions: • Power increase? => Interference, decreased battery lifetime • More base stations? => Deployment and maintenance costs, possibly not enough subscribers, no cell edge performance enhancement • Relay nodes (RN) provide an attractive solution • to satisfy tough throughput and coverage requirements for LTE-A

5. Why Relaying? (2)Benefits • Reasoning • Result Relays can save costs • Less eNBs and smaller OPEX Relaying and LTE technology fit • OFDMA flexible enough to fine tune e.g. resource allocation Relay OPEX will be very low • Easier to find sites, no backhaul costs, easier installation Relays will be cheap • Due to low TX power, no auxiliary equipment

6. Why Relaying? (3)Drawbacks • Relays introduce extra delay and overhead • Resource partitioning and interference management becomes important • Deployment is challenging • Additional set of signaling protocols are needed in case of Layer 2 and Layer 3 relays • Increasing number of hops introduce more complexity and overhead in the system

7. Relay Enhanced Cell (REC) Scenario • Simple infrastructure multi-hop scenario is considered with decode-and-forward relays • Idea is to deploy the relay nodes in the cell edges in order to improve the low SINR experienced by users and minimize the cell outage Two-hop relay based deployment Downlink received signal power in REC

8. LTE Uplink Power Control (1)Rationale • Full frequency reuse (reuse one) is highly desirable for future communication systems so as to exploit the spectrum efficiently • Intra-cell interference was the limiting factor in WDCMA uplink • LTE uplink transmission scheme SC-FDMA mitigates • intra-cell interference • near far effect • However, the LTE system is sensitive to inter-cell interference

9. LTE Uplink Power Control (2)Analysis • Standardized LTE uplink power control formula is simple and robust: • Fractional power control (FPC) utilizes a compensation factor for the pathloss and it is introduced to improve the performance of cell center users by inducing an acceptable inter-cell interference • Open loop power control is considered in this work, thus closed loop corrections are omitted • Used formula is given as:

10. Power Control in REC (1)Motivation • REC requires detailed dimensioning and planning • New cell edges introduced by RNs will lead to severe intra-cell and inter-cell interference • in particular when high number of relay nodes are deployed in the cell with reuse one • Power control becomes an important means in the uplink transmission of REC • to mitigate the interference and increase the cell edge and system capacity • Approved LTE uplink power control scheme should be re-investigated in REC to achieve an optimal performance • in this work, approved LTE uplink power control formula is applied in each relay node

11. Power Control in REC (2)Main Simulation Parameters Ref.1: TR 36.814 v0.3.1 (2008-09), Further Advancements for E-UTRA, Physical Layer Aspects, 3GPP TR 25.942, 3GPP R1-084026

12. Power Control in REC (3)Parameter Configuration in a Macro Cell Scenario • Rationale is based on the cell capacity and cell coverage with considering the corresponding average interference over thermal (IoT) level in the system adopted from Ref.2 • Acceptable IoT level is decided according to the eNB receiver dynamic range (see Appendix A) Ref.2: C. Castellanos, D. L. Villa, C. Rosa, I. Z. Kovacs, F. Frederiksen, and K. I. Pedersen, ‘’Performance of Fractional Power Control in UTRAN LTE Uplink’’, The 2008 IEEE, ICC, Beijing, China, May 2008 Disclaimer: Resulting Po values are not same with the Ref.2 due to that shadowing is not considered.

13. Power Control in REC (4)Suboptimal Settings for REC • Macro cell scenario parameter configurations are named as full compensation power control (FCPC) and fractional power control (FPC) according to coverage and capacity priorities respectively • The eNB-only deployment with optimal parameter settings for cell capacity prioritized scenario by FPC was assumed as reference case for the performance evaluation in REC scenario. Notations are as following: • FPC: optimal parameter setting for fractional power control in eNB-only deployment • FCPC (eNB and RN): optimal parameter setting for FCPC in eNB-only deployment is applied in relay based deployment both at eNB and RN • FPC (eNB and RN):optimal parameter setting for FPC in eNB-only deployment is applied in relay based deployment both at eNB and RN

14. Power Control in REC (5)Results of Suboptimal Settings • Very high throughput at RNs • FCPC outperforms FPC up to 50% ile • 80 % of the UEs connected to eNB experience higher throughput compared to FPC • FPC boosts the performance of UEs served by RNs • Do we need high capacity at RNs? • it should be noted that an ideal relay link is assumed (see Appendix B) • Parameter settings should be re-adjusted to achieve an optimal performance CDF of Throughput per UE at sector for FCPC (eNB and RN) vs. FPC (eNB and RN) in 1 tier (9 RNs deployed at the cell edges) REC scenario

15. Power Control in REC (6)Analysis of Po at eNB and RNs • Analysis of Po at eNB in REC => Optimum cell edge performance can be maintained with suboptimal settings found in eNB-only scenario • Analysis of Po at RNs in REC => Feasible SINR threshold at RNs (-15 dBm), 12 dB lower Po value can be used in FPC case • Po value can be set as small as possible for the UEs served by RNs in order to improve the performance of UEs served by eNBs

16. Power Control in REC (7)Analysis of No Power Control at RNs • Performing a power control scheme might still be regarded as an extra overhead at RNs • No power control by considering fixed maximum allowed transmit power for UEs at RNs • Scheme maintains the SINR performance of the cell edge users connected to RNs with a fixed maximum Tx power • leads to higher throughput for the cell center UEs at RNs • simpler RN design without penalizing the UEs served by eNB • 18 dBm illustrates similar performance to FCPC • 15 dBmresultsin better performance for the UEs at eNB

17. Power Control in REC (8)Power control with Maximum Allowed Tx Power Setup • Po configuration with fixed maximum allowed transmit power can be still re-adjusted to reduce the experienced high throughput for the UEs served by RNs and enhance the UEs served by eNBs • 5% ile user throughput improved by • 9 % for FCPC • 25 % for FPC • Average user throughput improved by • 17 % for FCPC • 40 % for FPC • compared to non-adjusted suboptimal settings

18. Power Control in REC (9)Results of Optimized Parameter Settings • It is observed that FPC outperforms FCPC after parameter optimization • For the UEs at eNB in the REC • FPC provides: • 70 % better cell edge user throughput (5 %ile) than eNB-only • 55 % better average user throughput than eNB-only • For the same cell edge performance FPC provides: • 23 % better average user throughput at eNB than FCPC • 13 % better average user throughput at RNs than FCPC • 15 % better average user throughput at sector than FCPC

19. Summary & Conclusions • Relaying is a promising solution for the demands of LTE-A • REC provides performance enhancement in the cell edge throughput and the system capacity compared to Macro cell scenario • Standardized LTE UL Power control scheme is feasible to use in REC scenarios • Parameter optimization and transmit power setup is important to achieve optimal performance • FPC outperforms traditional FCPC with an appropriate parameter configuration and transmit power setup in REC scenarios

20. Appendix AeNB Receiver Dynamic Range vs. Average IoT • Assuming a maximum allowed receiver dynamic range of 35 dBm, compensation factors lower than 0.6 do not seem suitable to use because of non-acceptable eNB receiver dynamic ranges

21. Appendix BRelay Link Overhead • This study assumes an ideal relay link (can be maintained via Microwave transmission) • However, a possible resource allocation scheme is also studied to see the overhead that is introduced by relay link given as in Fig.1: where half duplex transmission is applied to define the signal reception between direct link and relay link. • End-to-end user throughput is calculated according to a minimum formula given as: • It is observed that excessive user throughput experienced from the access link is limited by the relay link • Described resource allocation scheme only improves the cell edge users while it does not increase the average user throughput and system capacity compared to an eNB-only scenario • This can be achieved with bandwidth scalability of 100 MHz by LTE-A andmore efficient resource allocation and frequency reuse scheme Fig.1

22. THANK YOU!