Uplink Power Control in LTE Relay Enhanced Cells
Masters Thesis PresentationDepartment of Communications and Networking
Student: Aydin Karaer
Supervisor: Prof. Jyri Hämäläinen / HUTInstructor: Doc. Simone Redana / NSN
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
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
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
Less eNBs and smaller OPEX
OFDMA flexible enough to fine tune e.g. resource allocation
Reasoning Result
Due to low TX power, no auxiliary equipment
Relays can save costs
Relaying and LTE
technology fit
Relays will be cheap
Easier to find sites, no backhaul costs, easier installation
Relay OPEX will be very
low
Why Relaying? (2)Benefits
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
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
Downlink received signal power in RECTwo-hop relay based deployment
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
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:
)}()(log,min{ max ifiLMPPP TF 100 10
)log,min{ max LMPPP 100
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
Power Control in REC (2)Main Simulation Parameters
PARAMETER (Ref.1) ASSUMPTIONS
System Layout 19 cells & 3 sectors/cell & 1 tier (9 RNs) of RNs/sector
Carrier Frequency 2 GHz
Propagation Scenario Macro 1 (500m ISD)
Frequency Planning Reuse one (each eNB and RN uplink transmission interferes with each other)
System Bandwidth 10 MHz (48 PRBs for data)
Channel Models eNB-UE => (R in km) eNB height/location = 25 m (above rooftop)
eNB-RN => (R in km) RN height/location = 5 m (below rooftop)RN-UE => (R in km) UE height/location = 1.5 m
Antenna Configurations(Pattern & Number of Ant.)
eNB antennas per sector = 2 tx, 2 rx
RN antennas per sector = 2 tx, 2 rx
UE antennas = 1 tx, 2 rx
UE Transmit Power 23 dBm
eNB Transmit Power 46 dBm
RN Transmit Power 30 dBm
Extra Margins 0 dB (No shadow fading, fast fading)
User Drop 48 users per Sector / 200 iterations
UE Scheduling/Traffic Model Round robin, full buffer
Simulation Window 1 TTI
RL 106371128 log.. RL 106375124 log.. RL 107367140 log..
m
dB
AA ,min)(2
3
12
odB 703
dB 25mA
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
Power Control in REC (3)Parameter Configuration in a Macro Cell Scenario
Cell coverage prioritized Cell capacity prioritized
Po & Alpha -83 dBm & 1 -42 dBm & 0.6
Average IoT 5.4 dB 5.1 dB
Cell capacity 9354 kbps 11032 kbps
Cell coverage 3757 kbps 3382 kbps
• 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
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
• Acceptable IoT level is decided according to the eNB receiver dynamic range (see Appendix A)
Disclaimer: Resulting Po values are not same with the Ref.2 due to that shadowing is not considered.
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
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
Power Control in REC (6)Analysis of Po at eNB and RNs
• 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
• Analysis of Po at eNB in REC => Optimum cell edge performance can be maintained with suboptimal settings found in eNB-only scenario
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 dBm results in better performance for the UEs at eNB
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
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
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
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
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 toa 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 improvesthe 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-Aand more efficient resource allocation and frequency reuse scheme
f
t
UE - eNB
UE - RNRN - eNB
)RNby served UEsofNumber
RNper ThroughputLink Relay , per UE ThroughputLink (Access 2 minThroughputUEee
Fig.1
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