Energy Saving in HetNet Network Using eNB Parameters Tuning
Abstract
Power consumption represents an exciting subject in the field of mobile communication networks. In the last decades, the radio access networks have witnessed a denoting augmentation in power consumption, and this has indirect drawbacks on both environment and economic sides. The increase of power consumption conduct to both a substantial growth in CO2 emissions and on the operational expenditure of network operators. For this reason, minimizing power consumption in mobile cellular networks has become mandatory. In this paper, we suggest a power saving scheme in LTEAdvanced based Heterogeneous Networks (HetNet) by the mean of switching ON/OFF eNodeB (eNB) and tilt modification of neighbors.
1 Introduction
Long Term Evolution (LTE), designed by 3GPP, is enhanced by the use of new access techniques and by the improvement of architecture that combines different new services. New methods are included to LTE to migrate to LTE Advanced such as Coordinated Multipoint (CoMP), Massive MIMO, carrier aggregation and HetNet. The notion of LTE Advanced based on HetNet aims to ameliorate spectral efficiency. HetNet is a combination between various cell types: microcells, picocells and femtocells, and separate access technology [1].
In recent years, data traffic in the wireless mobile network has gained considerable growth. Consequently, energy consumption of Information and Communication Technology (ICT) is rising with a staggering rate. This significant increase in ICT energy consumption has many environmental and economic effects. Thus, on the ecological side, ICT is responsible practically for 2% of CO2 emissions [2]. Moreover, on the economic side, the percentage of ICT energy consumption varies from 2% to 10% of the annual worldwide energy consumption [3].
Several researches are proposed to reduce energy consumption in cellular networks, the most wellknown are the Switch ON/OFF algorithms. The condition to apply the Switch ON/OFF procedure is different from one technique to another. The main aim is to reduce the energy consumption by optimizing the use of the power of BSs with guaranteed QoS.
In [5], according to the traffic variation, the authors switch ON/OFF dynamically the BSs by respecting certain conditions of blocking probability in order to guarantee the QoS. In [6], BSs are switched ON/OFF randomly to minimize energy consumption in a UMTS cellular network. An improvement of this work is given in [7] where authors proposed a Switch ON/OFF algorithm using a uniform and a hierarchical scenario.
Algorithms of Switch ON/OFF are also applied in LTE and LTEA networks through some researches. Notably, in [8], Alexandra et al. try to come up with an optimum combination of switching ON/OFF eNBs in order to guarantee the maximum of energy saving. In [9], Narjes et al. implemented a Switch ON/OFF scheme in LTE network especially during low traffic period and QoS is guaranteed using a power up/down procedure. An improvement of this work is detailed in [10], where the algorithm of switch ON/OFF is implemented in an LTEA based HetNet. In this work, the switch ON/OFF procedure is performed based on the SINR values of UEs. QoS and coverage are maintained using femtocells and CoMP techniques.
In all works mentioned above, researchers are concentrated on power consumption issue in UMTS, LTE and LTEA networks. They all use the Switch ON/OFF procedure that aims to raise the power saving by minimizing the number of active eNBs during low traffic periods.
In this paper, we are interested by applying algorithms of Switch ON/OFF in LTEA based HetNet. Our contribution is to switch off an eNB when the number of their attached UEs is lower than a given threshold. UEs of Switched off eNB are assigned after the Switch OFF depending on their measured SINR (Signal to Interference plus Noise Ratio) value. Femtocells will serve UEs with good SINR value and neighbors eNBs will serve UEs with bad SINR value. Coverage is maintained by applying a tilt variation procedure for the neighboring eNB.
The rest of the paper is organized as follows: Sect. 2, describes the Network architecture. Section 3, introduces the eNodeB power model. In Sect. 4, we describe the proposed algorithm. Results of simulation are the subject of Sects. 5 and 6 concludes the paper.
2 Network Architecture
In our topology, we focused on two main concepts used in LTEAdvanced.
2.1 Femtocells
Due to the use of HetNet, we benefit from the use of femtocells to reduce power consumption. At first, femtocells are developed to raise capacity and guarantee coverage for highly densified areas [1]. Moreover, Femtocells are small, inexpensive and are characterized by low energy consumption of BSs [11]. For this reason, in our work, femtocells are disposed around the eNB to compensate switched off procedure.
2.2 Antenna Tilt
3 Power Calculation Model
4 Proposed Power Saving Algorithm
Our energy saving algorithm is based on the concept of Switch ON/OFF especially during low traffic periods when eNBs are little used. We add to this concept some new features that significantly reduce energy consumption in the network.
Our algorithm behaves as follow: At first, all macro eNBs are activated, and all femtocells are deactivated. When the number of active UEs attributed to an eNB i is smaller than a given threshold T, a Switch OFF procedure is applied to eNB i, at the same time, femtocells existing in the cell range of switched off eNB are activated to serve UEs surrounding the deactivated eNB. For UEs located at the cell extremity, they are allowed to the nearest active eNB neighbor.

Step 1: At first, we start by calculating the number of active UEs \(N_i(t)\) attributed to eNB i.
 Step 2: The second step is to compare the value of calculated number \(N_i(t)\) to a fixed threshold T. We can meet two possible cases described in the algorithm below: Noting that \(S_f(t)\) is the state of the femtocell at an instant t given by:$$\begin{aligned} S_f(t) = \left\{ \begin{array}{rl} 1 &{} \text{ if } ON \\ 0 &{} \text{ if } OFF \end{array} \right. \end{aligned}$$(10)
 Step 3: After taking the decision of Switch ON/OFF, we should specify new assignment of UEs of switched off eNB i. The allocation of a UE j is taken depending on its SINR value. The SINR of a UE j is calculated using the following formula:Where, \(P_{RX} (j)\) is the power received at UE j, given in Eq. 8, \( \sum _{i \ne j}^{N} P_{RX} (i)\) is the interference average power. \(KT_pW\) indicate the background noise, where K is the Boltzmann constant, \(T_p\) is the temperature and W is the bandwidth used by UE.$$\begin{aligned} SINR(j)= \frac{P_{RX} (j)}{\sum _{i \ne j}^{N} P_{RX}(i)+ KT_pW} \end{aligned}$$(11)The decision to allocate each UE to the correct cell is done referring to the Table 1.The best femtocell \(\widetilde{f}\) is chosen according to the following hypothesis:Table 1.
SINR value according to UE position in LTEA
UE position
SINR (dB)
Around the eNB
\(\ge \)13
Middle of cell
From 0 to 13
End of cell
\(\le \)0
Where, \(N_{femtocells}(i)\) is the number of femtocells existing in the cell range of eNB i and \(P_{RX}\) is the received power at user side j coming from the femtocell f.$$\begin{aligned} \widetilde{f} = \arg \max _{f \in N_{femtocells}} (P_{RX}^ {(f)} (i, j)) \end{aligned}$$(12)The right eNB neighbor \(\widetilde{n}\) is chosen according to the following hypothesis:Where, \(N_{neighbors}(i) \) is the number of eNB i’s neighbors and \(P_{RX}\) is the power received at user side j coming from eNB neighbor n.$$\begin{aligned} \widetilde{n} = \arg \max _{n \in N_{neighbors}} (P_{RX} ^{(n)}(i,j)) \end{aligned}$$(13)When we activate femtocells and attribute to them UEs of deactivated eNB, a new amount of power denoted \(\delta P_{femto}\) is added to the total power \(P_{total}\). \(\delta P_{femto}\) is given by:\(P_{f} \) is the power of one femtocell and \(S_f(t)\) indicate its state defined in Eq. 10.$$\begin{aligned} \delta P_{femto}(t) =\sum _{f=1}^{N_{femto}} S_f (t).P_{f} \end{aligned}$$(14)The assignment of UEs is described in more details in the following algorithm: 
Step 4: After allocation of UEs to femtocells, UEs in the cell borders are attributed to their nearest neighbor \(\widetilde{n}\). Two mechanisms are performed to ensure coverage: a power adjustment procedure is applied in parallel with a tilt variation of the antenna tilt of eNB neighbor \(n_0\). The antenna tilt variation’s process is performed in order to achieve coverage continuity and raise cells coverages.
The better value of \(\theta \) should be chosen to offer coverage for UEs located in the cell extremity of deactivated eNB. Thus the choice of \(\theta \) should respect the following condition:If the previous condition is false, no tilt variation and no power addition is performed.$$\begin{aligned} P_{RX}(\theta ) < P_{min} \end{aligned}$$(15)When we apply the tilt variation procedure, an amount of power \(\delta P_{tilt}\) is added. \(\delta P_{tilt}\) depends on distance between the deactivated eNB and its neighbors:$$\begin{aligned} \delta P_{tilt}(t) = \max P_{min}  P_{RX}(\theta ) \end{aligned}$$(16)  Step 5: After the procedure of Switch ON/OFF and power adjustment and tilt variation, the next step is to calculate the total power at instant t. \(\varDelta P \) in Eq. 7 is calculated as:Then, the total power \(P_{total} (t)\) at time t is given by:$$\begin{aligned} \varDelta P (t) = \delta P_{femto} (t) + \delta P_{tilt} (t) \end{aligned}$$(17)$$\begin{aligned} P_{total}(t) = \sum _i^{N} [ P_{OP} (i) + P_{TX}(i). S_i(t)]+ \sum _f^{N_{femto}} S_f (t). P_{f} + \sum _{k=1} ^ {M} [P_{min}  P_{RX}(\theta , k)] \end{aligned}$$(18)
5 Perfermance Evaluation
5.1 Simulation Scenario

43 dBm for a bandwidth of 1.25, 5 MHz.

46/49 dBm for a bandwidth of 10, 20 MHz.
Simulation parameters
Parameters  Values 

Bandwidth [MHz]  20 
Frequency [MHz]  2140 
Propagation model  Pathloss model 
Distribution of user  non uniform 
Transmitted power for macro cell [dBm]  35–46 
Transmitted power for femto cell [dBm]  5 
Distance between macro eNBs [m]  500 
Number of resource blocks (RBs) in macro cell  100 
Number of resource blocks (RBs) in femto cell  20 
5.2 Simulation Results
In this section, we will present simulation results and evaluation of the proposed scheme.
Looking at the Fig. 6, we notice that in high traffic hours, our proposed algorithm gives almost the same results as the low traffic algorithm, but in periods of low traffic, our proposed approach realizes the better power saving than the case of no switch ON/OFF technique is performed and the cases of low traffic and random schemes.
The use of femtocells improves the amount of energy saving; thus, femtocells are characterized by their low amount of energy consumption. Better yet, the use of the tilt variation technique increase the amount of power saving after applying the switch ON/OFF algorithm, thus, it improves the QoS by guarantying an acceptable coverage to UEs.
6 Conclusion
The purpose of our work in this paper is to find a better method that can reduce energy consumption in a LTEA based HetNet network. Our algorithm is based on two concept: the first one is the use of femtocells that can help to reduce the energy consumption in the network thanks to their low energy consumption. The second concept is the tilt variation technique that ensures an acceptable coverage and maintains QoS. According to the SINR values before and after Switch ON/OFF, we can say that our algorithm does not affect the QoS of the network.
Notes
Acknowledgment
This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 761579 (TERAPOD).
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