Improving UE SINR and Networks Energy Efficiency based on Femtocell Self-Optimization Capability報告人：陳柏偉日期： 2015.6.9

指導老師：林永松

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AGENDA INTRODUCTIONSYSTEM MODEL AND SELF-CONFIGURATIONSELF-OPTIMIZATION MECHANISMSIMULATION RESULTSCONCLUSION

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AGENDA INTRODUCTIONSYSTEM MODEL AND SELF-CONFIGURATIONSELF-OPTIMIZATION MECHANISMSIMULATION RESULTSCONCLUSION

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INTRODUCTIONThe ITU organization confirms that by the end of 2011 the number of mobile services subscribers reached 6 billion around the world, with a penetration factor of 86% [1] and recent surveys show that in the near future in-building generated phone calls and data traffic are expected to account for 50 and 70 of total volume, respectively [2].

Users are requiring an ever-higher data rates and a better coverage, especially in low coverage areas, such as macrocell edges and indoor environment.

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INTRODUCTIONTo cope with these challenges, femtocells were integrated with existing macrocells to increase their capacity, to maintain their coverage and to meet the requirement of quality of service (QoS) [3].

As femtocells are user-deployed, their proper operation relies on their self-configuration and self-optimization capabilities.

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INTRODUCTION In view of this, SONs constitute a novel approach that empowers operators to reduce the amount of manual intervention involved in network planning by relying on self-analysis, self-configuration and self-healing [5].

Using SON-enabling mechanisms, small cells can sense, learn from their environment and autonomously adjust their transmission strategies towards an optimal performance [8].

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INTRODUCTIONNowadays, an extensive deployment of femtocells has been implemented, resulting in two main concerns.

One is the inevitable co-channel interference between macrocell and femtocells, which is one of the main factor limiting achievable spectral efficiency and system coverage.

The other one is the resultant substantial energy consumption of femtocells.

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INTRODUCTION In this paper, self-configuration of transmit power for femtocells is adopted to guarantee the power leaked out of the home under a low level.

After self-configuration, we find that there exists a femtocell-centered region in the room.

When UE is outside the region, macrocell will provide a higher SINR for UE than the femtocell on condition that femtocell turns off radio transmission and UE swithes to macrocell.

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INTRODUCTIONThe proposed self-optimization method calculates the virtual cell size and allows the femtocell to turn on radio transmission when distance between UE and femtocell doesn’t exceed virtual cell size, and turn off on the contrary.

This mechanism has the advantages that it can improve indoor SINR and reduce the energy consumption of femtocell’s transmission power.

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AGENDA INTRODUCTIONSYSTEM MODEL AND SELF-CONFIGURATIONSELF-OPTIMIZATION MECHANISMSIMULATION RESULTSCONCLUSION

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A. System Model the downlink SINR of femtocell UE i in femtocell j can be represented as

The obtainable throughput for UE in each location of femtocell is calculated as

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B. Self-Configuration for Transmit Power In self-configuration, the transmit power for each femtocell is set to a value that is on average equal to the strongest power received from macrocell at the target cell radius of r=10m.

Then the femtocell transmit power can be calculated (in dB) as

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AGENDA INTRODUCTIONSYSTEM MODEL AND SELF-CONFIGURATIONSELF-OPTIMIZATION MECHANISMSIMULATION RESULTSCONCLUSION

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A. Concept of Virtual Cell SizeAssume that femtocell j is located in macrocell M, and UE i is in the edge of femtocell j.

If UE i is attached to femtocell j, the received SINR of UE is calculated as

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A. Concept of Virtual Cell Size If UE i is attached to macrocell M, the received SINR of UE is calculated as

Based on the self-configuration scheme in Section II, pMi is the roughly the same as pji because UE i is located in the edge of the femtocell.

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A. Concept of Virtual Cell SizeNow if femtocell j switches off its radio transmission, the received SINR of UE i in the same condition is calculated as

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A. Concept of Virtual Cell SizeSo we define virtual cell size as a distance to femtocell, where SINR of UE attached to macrocell with femtocell turning off is equal to that attached to femtocell in the direction of connection between macrocell and femtocell.

From the definition of virtual cell size, we can deduce that:

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Then virtual cell size can be written as

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B. Calculation of Virtual Cell SizeThe way to calculate virtual cell size in (8) needs to know received power from macrocells and femtocells in advance, which is hard to realize.

Initially, the femtocell turns off radio transmission and value of virtual cell size is set to 5 meters (half of cell radius). The

UE located in femtocell is connected to macrocell and sends its SINR to femtocell as SINR threshold.

The UE located in femtocell is connected to macrocell and sends its SINR to femtocell as SINR threshold.

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B. Calculation of Virtual Cell SizeThen, femtocell starts self-configuration and UE switches to femtocell as signal from femtocell is stronger.

Every 500ms, femtocell detects its distance from UE and compares it with value of virtual cell size.

In the case that distance exceeds virtual cell size, if SINR of UE attached to femtocell is larger than threshold, the value of virtual cell size will be updated to the distance.

With time going on and UE moving, virtual cell size will get closer to the actual value.

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C. Power Control MethodBased on the virtual cell size obtained above, the power control method allows a femtocell to turn on or turn off its radio transmissions through comparing the distance detected between UE and itself with virtual cell size every 500 ms.

If distance exceeds virtual cell size, femtocell will switch off radio transmission during next detection cycle and UE will switch to macrocell to obtain a higher SINR.

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AGENDA INTRODUCTIONSYSTEM MODEL AND SELF-CONFIGURATIONSELF-OPTIMIZATION MECHANISMSIMULATION RESULTSCONCLUSION

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SIMULATION RESULTS

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SIMULATION RESULTSScheme 1: Femtocell turns off radio transmission and UEs in femtocell coverage connect to macrocell all the time.

Scheme 2: Femtocell turns on radio transmission and UEs in femtocell coverage connect to femtocell all the time.

Scheme 3: self-optimization mechanism described in Section III.

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A. Accuracy of Virtual Cell Size

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A. Accuracy of Virtual Cell Size

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B. SINR Improvement

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B. SINR Improvement

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B. SINR Improvement

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B. SINR Improvement

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C. Energy EfficiencyHere the performance about energy efficiency of scheme 3 is evaluated by examining the resultant reduction in femtocell’s transmit power consumption.

The average reduction in femtocell’s transmit power consumption can be characterized as a percentage of the total energy:

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C. Energy Efficiency

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AGENDA INTRODUCTIONSYSTEM MODEL AND SELF-CONFIGURATIONSELF-OPTIMIZATION MECHANISMSIMULATION RESULTSCONCLUSION

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CONCLUSIONA method to calculate virtual cell size for each femtocell and a novel power-control scheme were proposed based on femtocell’s self-optimization capability.

It can make full use of femtocells and reduce the transmit power consumption of femtocells.

The evaluation results have proved that the self-optimization mechanism improves the SINR obtained indoor without increasing transmit power of femtocell and introduces an average reduction of approximately 58.5% in femtocell’s transmit power consumption.