Green Cognitive and Cooperative Heterogeneous Networks (Hetnets): Current Status and Technical Persp

GRD Journals | Global Research and Development Journal for Engineering | International Conference on Innovations in Engineering and Technology (ICIET) - 2016 | July 2016

e-ISSN: 2455-5703

Green Cognitive and Cooperative Heterogeneous Networks (HetNets): Current Status and Technical Perspectives 1Bhagyalakshmi

M G 2Vaishnavi Devi S V 3Swathi V R 1 Assistant Professor 2,3B.E student 1,2,3 Department of Computer Science Engineering 1,2,3 K.L.N. College of Engineering, Pottapalayam, Sivagangai 630612, India Abstract The future generation of wireless communication technologies is expected to be energy-smart while providing rich multimedia contents with higher Quality of Service (QoS) to the end-users, which necessitates integration of various technologies. Green Cognitive and Cooperative HetNets involve optimal integration of cognitive and cooperative communication techniques in heterogeneous networks (HetNets) to increase the energy efficiency without sacrificing significantly the QoS. To reduce the energy consumption overhead introduced by cognitive and cooperative communications, there is a need to incorporate green concepts in communication technologies. Finally, design challenges in embracing green technologies to achieve Green Cognitive and Cooperative HetNets is addressed.

Keyword- HetNet, Cognitive and Cooperative communication, Green communication __________________________________________________________________________________________________

I. INTRODUCTION The idea of energy efficiency in every domain has led to the concept of green cellular networking. HetNets are typically consists of several radio access technologies (RATs) where multiple low power, low cost user/operator deployed base stations are complementing the existing network. In network communication base stations are most energy consuming area according to technical analysts. The rapid development in networking has led to the increase of emission of CO2 [1]. So by reducing power consumption at base stations energy efficiency could be achieved. Meanwhile the users should be guaranteed of quality service and coverage. These aspects could be achieved by designing base station hardware in an energy efficient manner, protocols that could be used in sleep modes, cell zooming and usage of renewable energy sources [2].

Fig. 1: Power Consumption by cellular network

A. Heterogeneous Networks (HetNets) The new generation of wireless user equipment and the proliferation of bandwidth-intensive applications, user data traffic and their corresponding network load are increasing in an exponential manner [5]. Most of these new data traffic requires increased link budget and coverage extension to provide good user experience. This leads to an increasing interest to deploy distributed antennas, relays and small cellular access points (such as picocells and femtocells) in homes, offices and subways. These network architectures, that may be either operator-deployed or consumer-deployed consists of a mix of low power cells underlying the macro-cell network that are commonly referred to as heterogeneous networks (HetNets) [7]. By installing additional network nodes within the local-area and bringing the network closer to users, HetNets can improve spatial reuse and provide improved coverage that allows future cellular systems to achieve higher data rates, while retaining the seamless connectivity and mobility [8].

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Green Cognitive and Cooperative Heterogeneous Networks (HetNets): Current Status and Technical Perspectives (GRDJE / CONFERENCE / ICIET - 2016 / 065)

B. Cognitive Radio Cognitive radio (CR) is a technology that addresses critical challenges in spectrum efficiency, interference management, and coexistence of heterogeneous networks and thereby enables next generation intelligent wireless communications [3]. CR technology aims at the development of an intelligent and adaptive wireless communication system that can work in an environmentaware manner [4]. Cognitive radio networks enables opportunistic spectrum access, which aims at solving the imbalance created between spectrum scarcity and spectrum under-utilization [7].

II. RELATED WORKS A. Cognitive and cooperative communications in hetNet In HetNet architecture, the coexistence of macro and small cells paves way to reduce the energy consumption by reducing the distance between the end user equipment andeNodeBs [2]. For the cooperative schemes in homogeneous and heterogeneous networks, different user equipment or eNodeBs are allowed to share resources and channel information to implement collaboration.

For the cognitive schemes in homogeneous and heterogeneous networks, the cognitive radio technique enables utilization of intelligent and adaptive transmission strategies with a distributed transmission manner [8].

In HetNet architecture, the conflict between the low resources utilization and scarcity of spectrum resource increases the energy consumption and reduces the energy efficiency seriously. Because of the intra tier and inter tier interference, the independent performance optimization in the isolated and homogeneous cell cannot provide converge to the global optimal solution of HetNet [2]. Further, the coordination schemes among the heterogeneous nodes have a strong impact on the performance and complexity of the network, which must be designed carefully [7].

In an attempt to solve these challenges more efficiently, the cognition of the complicated scenario and the cooperation of the multidimensional radio resource in HetNet should be investigated thoroughly. Cognitive and cooperative network are new paradigms in wireless communications technology that aims at enhancing the utilization of limited spectrum resources and enhance the overall performance [8]. Although the cooperative and cognitive radio networks could be integrated and implemented together between different nodes in HetNet, a higher degree of cognition and cooperation brings a higher degree of cost and complexity in terms of energy consumption and network operation [2].

B. Energy Efficiency Improvements with Cooperative HetNet In HetNet architecture, there's two-tier cooperation used to optimize the performance: intertier and intratier cooperation [5]. These two cooperative structures are deployed individually or together with the constraints on complexity and blackhull link [2]. It's a very desirable characteristic for interference-limited networks where full spectrum reuse is exploited to enhance the data rate and increase the use of resource, particularly in heterogeneous network where amounts of different nodes are deployed in an overlapping space [8].

Fig. 2: Energy efficiency in full reuse HetNets with different MBS load [8].

The energy efficiency versus density of low-power nodes in HetNet architecture is shown in Figure 2, where the spectrum resources are reutilized among MeNBs and SeNBs [2]. In order to minimize the interference and increase the energy potency in HetNet, whereas increasing the resource utilization according to the load condition and small cells density, a hierarchical cooperation in the spectrum allocation is presented. Based on the received interference, load condition, and the number of small cells installed within the network, the factor of spectrum utilization and the frequency allocation is optimized between the heterogeneous nodes in a cooperative manner. With the framework of intratier and intertier cooperation, the proposed scheme is performed in the following two steps.

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Green Cognitive and Cooperative Heterogeneous Networks (HetNets): Current Status and Technical Perspectives (GRDJE / CONFERENCE / ICIET - 2016 / 065)

In the primary step, the intratier cooperation strategy is deployed between the MeNBs to exclude the intratier interference according to the fluctuation of MeNBs load. When there is some idle resource, the cooperation schemes may cause very serious interference to others that is the spectrum is orthogonally allocated among the MeNBs .In the second step, the intertier cooperation is explored between the MeNB and SeNB within the same macrocell to improve the utilization of spectrum while maintaining the QoS of macrocell UEs (MUEs) [8].

When there is large density of SeNBs, the reused frequency resource should be decreased for reducing the interference to MUEs. More frequency resources is reused for increasing the resource utilization efficiency when there's small number of SeNBs set in the macrocell [7]. The reused spectrum resource ought to be optimized in an exceedingly cooperated manner to determine the trade-off between the impact of resource and interference on the energy efficiency.

Fig. 3: Energy efficiency in cooperative HetNet with different MBS load [8]

Figure 3 shows that the energy efficiency is improved by the cooperative scheme in HetNet. Compared to the energy efficiency in full reuse scheme depicted in Figure 2, higher energy efficiency can be obtained by the cooperation, especially when higher data transmission rate requirement is supported in macro cells. It is claimed that the energy efficiency increases first and then sharply decreases with the increasing number of SeNBs [8]. In a cooperative manner, the spectrum resource can be allocated adaptively between the heterogeneous nodes, by which high utilization efficiency of resource is explored. When lesser number of SeNBs are deployed in the network, more frequency can be reutilized between the MeNB and SeNB. On the other hand, the energy efficiency can be increased significantly with a reasonable density of SeNBs when more amount of resources are idle in MeNBs, because SeNB is much suitable in the energy efficient networking strategies [7].

Hence, the more practical cost estimation method and power consumption model in cooperative and cognitive HetNet shall be investigated, in an attempt to give some useful suggestions while designing energy efficient communication networks.

III. GREEN COGNITIVE AND COOPERATIVE COMMUNICATIONS IN HETNET All Corporate Responsibilities target to reduce CO2 emissions and environmental impacts of networks. It could be achieved by green cellular networks, green sensor networks and green machine to machine communication [4]. The existing wireless communication system derives its base from conventional “command-and-control� spectrum usage model and it does not support the adaptive exploitation of spectrum opportunities which could improve the energy efficiency by more effective and efficient interference management, better spatial and temporal reuse. Next, the existing wireless communication systems use traditional layered approach which is borrowed from the wired networking technology [6].However, the necessity to operate the wireless medium in such a way that resembles wired communication links for compatibility with traditional higher-layer protocols couldn't be achieved without sacrificing communication reliability and energy efficiency [3].

With cognitive and cooperative communication, the opportunistic adaptation of the spectrum use and the use of larger spectrum band lead to more effective interference management, better temporal and spatial reuse, thus reducing the power consumption [1].

IV. CONCLUSION Green networking, Cognitive and cooperative communications are promising techniques for better utilization of radio resources and also guarantee quality of services (QoS) in wireless heterogeneous networks (HetNet). Integration of green networking in cognitive cooperative HetNets can greatly improve the system performance.

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Green Cognitive and Cooperative Heterogeneous Networks (HetNets): Current Status and Technical Perspectives (GRDJE / CONFERENCE / ICIET - 2016 / 065)

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