**5. Numerical results**

68 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

10. BCCH (CGI, TAI, CSG ID)

14. Access control based on reported ECGI

17. HO Required (Access Mode\*

16. HO decision

12. HO decision triggering

> 15. HO Context Report (ECGI)

13. HO Context Request (ECGI, timestamp, DL RS Tx Power, Received Interference Power)

23. HO Command

, CSG ID\*

**Figure 4.** Network signaling procedure for the proactive handover approach

) 18. HO Request (CSG ID\*

, Membership Status\*

22. HO Request Ack

) 19. HO Request (CSG ID\*

, Membership Status\*

21. HO Request Ack

Legend Cell search and measurement reporting signaling Handover decision signaling Handover execution signaling

3. HO Context Report

)

20. Validate CSG ID, Admission Control

accordingly.

UE MME Serving eNB

5. Reconfiguration (Report Proximity Config) 6. Proximity Indication 7. Reconfiguration (Measurement Config)

> 9. Reconfiguration (SI Request)

8. Measurement Report (PCI, timestamp)

11. Measurement Report (CGI, TAI, CSG ID, Member Indication)

24. HO Command

access status of the tagged UE on the target ECGI in steps 10 and 14, respectively. If the tagged user is not allowed to access the target eNB, the MME notifies the serving LTE cell

The key difference between the reactive and the proactive approaches is that in the former the MME forwards the HO context request towards the target eNB (steps 11-15), while in the latter the MME may directly provide the required HO context by utilizing the reports derived in steps 1-4 (Fig.4). It should be noted that the proactive context derivation signaling phase is indicatively located in steps 1-4, since it can be performed asynchronously with respect to the rest HO signaling procedure. In the absence of HO context close to the required measurement timestamp, the MME may decide to forward the HO context request towards the target eNB as in the reactive approach. Upon HO context acquisition, the HO decision algorithm in the serving eNB proceeds to a HO execution whenever necessary. In that case, a common HO execution signaling follows for both approaches (steps 17-24) [6].

> HeNB GW\*

Report Config) 2. Reconfiguration

(ECGI, timestamp) 4. HO Context Report

(ECGI, timestamp)

1. Reconfiguration (ECGI, HO Context Target HeNB

(HO Context Report Config) Proactive

Cell search and measurement

HO context derivation

HO context derivation / Handover decision

Handover execution

This section includes selected numerical results to evaluate the performance of the proposed UTPR HO decision policy in the macrocell – femtocell LTE network. The simulation scenario is based on the evaluation methodology described in [22], while the proposed HO decision policy is compared against a strongest cell based policy, referred to as SCB policy in the following.

A conventional hexagonal LTE network is considered, including a main LTE cluster composed of 7 LTE cells, where each LTE cell consists of 3 hexagonal sectors. The wraparound technique is used to extend the LTE network, by copying the main LTE cluster symmetrically on each of the 6 sides. A set of blocks of apartments, referred to as femtoblocks, are uniformly dropped within the main LTE cluster according to the parameter ���, which indicates the femtoblock deployment density within the main LTE cluster, i.e., the percentage of the main LTE cluster area covered with femtoblocks. Each femtoblock is modeled according to the dual stripe model for dense urban environments in [22]. According to it, each femtoblock consists of two stripes of apartments separated by a 10 m wide street, while each stripe has two rows of �� = �� apartments of size 10 × 10 m. For a tagged femtoblock, femtocells are deployed with a femtocell deployment ratio parameter ���, which indicates the percentage of apartments with a femtocell [22]. Each femtocell initially serves one associated user, while in general, it can serve up to 4 users. Femtocells and femtocell users are uniformly dropped inside the apartments. Each LTE user is member of up to one CSG, where the CSG ID per user and femtocell is uniformly picked from the set {1, 2, 3}. Each LTE sector initially serves ten macrocell users, which are uniformly distributed within it. Unless differently stated, it is assumed that �̅= 3 km/h and �� = 1 km/h.

The macrocell stations operate in a LTE band centered at 2000MHz, divided into � RBs of width 180 KHz and utilizing a 5MHz bandwidth. The macrocell inter-site distance is set to


Energy Efficient Mobility Management for the Macrocell – Femtocell LTE Network 73

UE RSSI, SCB, *r*

UE RSSI, SCB, *r*

UE RSSI, UTPR, *r*

UE RSSI, UTPR, *r*

Cell R.I.P., SCB, *r*

Cell R.I.P., UTPR, *r*

Cell R.I.P., SCB, *r*

Cell R.I.P., UTPR, *r*

*fc=0.1*

*fc=0.3*

*fc=0.1*

*fc=0.3*

*fc=0.1*

*fc=0.3*

*fc=0.1*

*fc=0.3*

**Figure 7.** Average LTE cell transmit power versus the ݀ி

SCB, *r*

SCB, *r*

UTPR, *r*

UTPR, *r*

*fc=0.1*

*fc=0.3*

*fc=0.1*

*fc=0.3*

0






Average Interference Power (dBm)




5

10

15

Average LTE Cell Transmit Power (dBm)

20

25

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Femtoblock deployment density *dFB*

**Figure 8.** Average UE RSSI and Cell Received Interference Power versus the ݀ி

0 0.1 0.2 0.3 0.4 0.5

Femtoblock deployment density *dFB*

**Figure 6.** Average UE energy consumption per bit versus the ���

Fig. 5 and 6 depict the performance of the SCB and UTPR decision policies in terms of UE average transmit power and average energy consumption per bit, owing to transmit power, respectively. Notice that an increased femtoblock deployment density ��� corresponds to an increased number of femtocells and UEs within the main LTE cluster. The same implies for an increased femtocell deployment ratio ���, which corresponds to an increased femtocell and UE density within each femtoblock. As expected, an increasing femtoblock deployment density ��� or femtocell deployment ratio ��� results in lower UE power and energy consumption per bit for both approaches. However, a higher femtocell deployment ratio ��� is required in order for the SCB policy to benefit from the LTE femtocell presence, both in terms of UE power and energy consumption per bit. On the contrary, the UTPR policy's awareness on the downlink RS and received interference power enables mobility towards LTE cells with lower UE power consumption, while maintaining the tagged user's SINR target. In more detail, for ��� = 0.1 and ��� = 0.3 the proposed policy results in significantly lower UE power consumption compared to the SCB policy, varying from 1 to 16 dB and 1 to 20 dB respectively. Significantly lower UE energy consumption per bit is also achieved, varying from 10 to 85% compared to the SCB policy, in accordance with the femtoblock deployment density and the femtocell deployment ratio.

**Figure 7.** Average LTE cell transmit power versus the ݀ி

**Figure 6.** Average UE energy consumption per bit versus the ���

SCB, *r*

SCB, *r*

UTPR, *r*

UTPR, *r*

*fc=0.1*

*fc=0.3*

*fc=0.1*

*fc=0.3*

0

0.2

0.4

0.6

0.8

Average Energy Consumption per Bit (joules/bit)

1

1.2

1.4

1.6

x 10-7

deployment density and the femtocell deployment ratio.

Fig. 5 and 6 depict the performance of the SCB and UTPR decision policies in terms of UE average transmit power and average energy consumption per bit, owing to transmit power, respectively. Notice that an increased femtoblock deployment density ��� corresponds to an increased number of femtocells and UEs within the main LTE cluster. The same implies for an increased femtocell deployment ratio ���, which corresponds to an increased femtocell and UE density within each femtoblock. As expected, an increasing femtoblock deployment density ��� or femtocell deployment ratio ��� results in lower UE power and energy consumption per bit for both approaches. However, a higher femtocell deployment ratio ��� is required in order for the SCB policy to benefit from the LTE femtocell presence, both in terms of UE power and energy consumption per bit. On the contrary, the UTPR policy's awareness on the downlink RS and received interference power enables mobility towards LTE cells with lower UE power consumption, while maintaining the tagged user's SINR target. In more detail, for ��� = 0.1 and ��� = 0.3 the proposed policy results in significantly lower UE power consumption compared to the SCB policy, varying from 1 to 16 dB and 1 to 20 dB respectively. Significantly lower UE energy consumption per bit is also achieved, varying from 10 to 85% compared to the SCB policy, in accordance with the femtoblock

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Femtoblock deployment density *dFB*

**Figure 8.** Average UE RSSI and Cell Received Interference Power versus the ݀ி

The UTPR policy reduces the average transmit power in the LTE cells as well (Fig. 7), as a result of the substantial interference mitigation achieved in the LTE downlink in terms of RSSI and in the LTE uplink in terms of Received Interference Power at the LTE cells (Fig. 8). These are a direct outcome of the proposed policy's tendency to facilitate mobility towards cells which utilize bands with lower Received Interference Power. The latter reduces the number of UE interferers in congested LTE bands and condenses the overall UE power transmissions per band. Although the incorporation of the proposed UTPR policy achieves substantial energy consumption and interference mitigation gains, an increased HO probability is observed compared to the SCB policy (Fig. 9). This follows from the proposed policy's tendency to extend the femtocell utilization time, resulting to an increased sensitiveness on user mobility. To this end, the HO execution events are even more frequent when the femtocell deployment ratio per femtoblock increases. As in the SCB case, standard mobility-centric HO margin ��������� ���� adaptation techniques can be utilized [10-12] to moderate the network-wide number of HO execution events (Fig. 10). The following results are derived for ��� = 0.05 and ��� = 0.2, while three different mean user speed values are considered i.e. 3, 60 and 125 km/h.

Energy Efficient Mobility Management for the Macrocell – Femtocell LTE Network 75

Mean speed=3km/h, UTPR Mean speed=3km/h, SCB Mean speed=60km/h, UTPR Mean speed=60km/h, SCB Mean speed=125km/h, UTPR Mean speed=125km/h, SCB

user speed raises the HO probability for both policies. However, it can be seen that for a

moderated and converge to the number of HO execution events corresponding to the SCB

The random femtocell deployment may result in degraded SINR performance, increased outage probability, and enlarged network signaling, if the interference-agnostic strongest cell policy is employed during the HO decision phase. This chapter discussed the key feature of femtocell deployment and presented a novel HO decision policy for reducing the UE transmit power in the macrocell – femtocell LTE network given a prescribed mean SINR target for the LTE users. This policy is fundamentally different from the strongest cell HO policy, as it takes into account the RS power transmissions and the RF

0 2 4 6 8 10 12 14 16 18 20

*UTPR (dB)*

Handover Margin *HHMc(dB)*

்ோ parameter adaptation, the HO execution events for the UTPR policy are

்ோ value. As expected, an increasing

Fig. 10 illustrates the HO probability versus the ܯܪܪǡሺௗሻ

்ோ values.

**Figure 10.** HO probability versus the Handover Margin

**6. Conclusion** 

0

0.05

0.1

0.15

HO probability

0.2

0.25

suitable ܯܪܪǡሺௗሻ

policy with lower ܯܪܪǡሺௗሻ

**Figure 9.** HO probability versus the ���

Fig. 10 illustrates the HO probability versus the ܯܪܪǡሺௗሻ ்ோ value. As expected, an increasing user speed raises the HO probability for both policies. However, it can be seen that for a suitable ܯܪܪǡሺௗሻ ்ோ parameter adaptation, the HO execution events for the UTPR policy are moderated and converge to the number of HO execution events corresponding to the SCB policy with lower ܯܪܪǡሺௗሻ ்ோ values.

**Figure 10.** HO probability versus the Handover Margin

#### **6. Conclusion**

74 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

mobility-centric HO margin ���������

*r*

*r*

*r*

*r*

*fc=0.3, UTPR*

*fc=0.1, UTPR*

*fc=0.3, SCB*

*fc=0.1, SCB*

considered i.e. 3, 60 and 125 km/h.

**Figure 9.** HO probability versus the ���

0

0.05

0.1

0.15

0.2

0.25

HO probability

0.3

0.35

0.4

0.45

The UTPR policy reduces the average transmit power in the LTE cells as well (Fig. 7), as a result of the substantial interference mitigation achieved in the LTE downlink in terms of RSSI and in the LTE uplink in terms of Received Interference Power at the LTE cells (Fig. 8). These are a direct outcome of the proposed policy's tendency to facilitate mobility towards cells which utilize bands with lower Received Interference Power. The latter reduces the number of UE interferers in congested LTE bands and condenses the overall UE power transmissions per band. Although the incorporation of the proposed UTPR policy achieves substantial energy consumption and interference mitigation gains, an increased HO probability is observed compared to the SCB policy (Fig. 9). This follows from the proposed policy's tendency to extend the femtocell utilization time, resulting to an increased sensitiveness on user mobility. To this end, the HO execution events are even more frequent when the femtocell deployment ratio per femtoblock increases. As in the SCB case, standard

moderate the network-wide number of HO execution events (Fig. 10). The following results are derived for ��� = 0.05 and ��� = 0.2, while three different mean user speed values are

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

Femtoblock deployment density *dFB*

���� adaptation techniques can be utilized [10-12] to

The random femtocell deployment may result in degraded SINR performance, increased outage probability, and enlarged network signaling, if the interference-agnostic strongest cell policy is employed during the HO decision phase. This chapter discussed the key feature of femtocell deployment and presented a novel HO decision policy for reducing the UE transmit power in the macrocell – femtocell LTE network given a prescribed mean SINR target for the LTE users. This policy is fundamentally different from the strongest cell HO policy, as it takes into account the RS power transmissions and the RF

interference at the LTE cell sites. The proposed policy is backwards compatible with the standard LTE handover decision procedure, as it is employed by adapting the HHM with respect to the user's mean SINR target and standard link quality measurements describing the status of the candidate cells. Even though employing the proposed policy necessitates an enhanced network signaling between cells, numerical results demonstrate greatly lower network-wide RF interference, and reduced UE power consumption owing to transmit power, compared to the strongest cell HO policy. The impact of using an increased HHM for mobility mitigation has also been investigated in terms of HO probability.

Energy Efficient Mobility Management for the Macrocell – Femtocell LTE Network 77

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