Community Research and Development Information Service - CORDIS

Final Report Summary - CODEC (Cellular Network based Device-to-Device Wireless Communications)

1.1 Project objectives
Densely expanded mobile network has driven proximity-based applications, such as information exchange between friends in neighbourhoods and location-based advertisements, to be very important social network elements and traffic contributor in future mobile networks, with a market expected to grow to € 48.91 billion by 2022. Device-to-device (D2D) communication in cellular networks enables user equipments (UEs) in proximity to communicate directly with each other, which results in improved network throughput and significantly reduced transmission latency, thanks to short distances between UEs. Furthermore, D2D connections can also benefit cellular networks by offloading traffic from base stations (BSs) to D2D links, or serve as relays to extend the communication range for cellular users. The CODEC project focuses on resource management (RM) in cellular D2D communications, which is indispensable for achieving spectral and energy efficiencies, and providing quality of service (QoS) to different applications. The main objectives of the CODEC project are: 1) Provide a generic analytical framework for investigating the performance of D2D communications as an underlay to cellular network, in terms of spectral efficiency and energy efficiency. 2) Based on the analytical framework, develop RM schemes for D2D communications to optimise the network performance under practical constraints, such as power constraint, data rate requirement and QoS requirement, for different kinds of applications. 3) Extend the proposed analytical framework to accompany an important emerging technology, fractional frequency reuse (FFR), in wireless cellular networks. 4) Setup the testbed and carry out experimental evaluation for the proposed RM schemes.

1.2 Work performed and main results achieved in the project
The global work plan of the CODEC project has been split into four work packages (WPs) for a lifespan of two years. Above objectives were achieved by carrying out the following research activities in the CODEC project:
1) In Task 1.1, a generic analytical framework was developed for D2D communications in order to develop RM schemes under WP2 and WP3. 2) Task 1.2 focused on abstracting the characteristics of D2D nodes and virtual D2D nodes modelling. 3) In Task 2.1, based on the analytical framework achieved in WP1, with target of increasing the energy and the spectral efficiencies of the cellular networks, RM schemes were developed in a single cell environment. 4) Then, in Task 2.2, RM schemes were proposed in multicellular networks considered inter-cell interference in the RM with frequency being reused in different cells. 5) In WP3, analytical framework developed in WP1 was extended to FFR-based cellular networks to develop suitable resource management for this structure. 6) Considering that traffic offloading is an important function of D2D communication, D2D based content caching was investigated. 7) In order to verify the proposed resource management schemes, a software-based simulation platform was set up to simulate and evaluate the proposed schemes in terms of spectral efficiency and energy efficiency, and 8) a hardware-based testbed was also set up to test the D2D communication under a central control.
Research activities 1)-3) were mainly performed in Year 1 (15/12/2014-14/12/2015) of the project, and activities 4), 5) and 7) started from Year 1 and were carried on in Year 2 (15/12/2015-14/12/2016) of the project. The research activities 6) and 8) were mainly carried out in Year 2.
The main results achieved during the two years of the CODEC project are listed as follows:
1) In Task 1.1, a sub-cell based framework was proposed. Under the framework, analytical results of the spectral and energy efficiencies of D2D communications and the performance gain for adopting D2D communications in cellular networks were evaluated by simulation results, which were shown as Milestones 1.2 and M1.3. The results are used for carrying out the tasks in WP2.
2) Task 1.2 focused on abstracting the characteristics of D2D nodes, and the results were shown as Milestone 1.1 to model the characteristics of virtual D2D nodes for unicast, broadcast and multicast applications and D2D relays. The statistic characteristics of the transmit power per subcarrier was obtained to model the interference from one sub-cell to another sub-cell, which can be used in the development of RM schemes with low complexity.
3) In Task 2.1, based on the analytical framework and statistical model achieved in WP1, in order to increase the energy and the spectral efficiencies of the cellular networks, RM schemes in a single cell environment were explored by formulating the RM problem into an optimisation problem with multiple constraints. The main contributions from this task include: a) investigation of RM problems under multiple practical requirements from BS and UE. In this part, two related journal papers and two related conference papers have been accepted; b) analytical study of spectral efficiency and energy efficiency for cellular systems. In this part, one related journal paper and one conference paper have been accepted; c) development of RM scheme for multiple D2D pairs in cellular networks, which was shown as the outcome for Milestone 2.1 (RM methods for one cell environment). A conference paper on this work was accepted and will be extended to a journal paper.
4) In Task 2.2, under the topology with multiple sub-cells, which can be easily extended to multiple cells, frequency reuse was taken into account under the consideration of inter-cell interference. Given the density of D2D pairs in a unit area, how to divide the unit area into multiple sub-cells was theoretically analysed in order to achieve the optimal spectral efficiency when frequency reuse is allowed among different sub-cells. The analysis-based numerical results were compared with simulation results to show the optimal number of sub-cells per unit area for achieving the optimal spectral efficiency, which is input to Milestone 2.2. In this task, one interference management related journal paper and one related conference paper were accepted.
5) In Task 3.1, the spectral efficiency of D2D communications in an FFR based two-layer cellular model has been analysed as a function of radius ratio of the central area to the edge area, which is also shown as the outcome for Milestone 3.1 (performance of D2D communications in FFR-based cellular networks).
6) In Task 3.2, the resource allocation (RA) between cellular users and D2D users are analysed in the FFR based cellular network. The outcome is included in Milestone 3.2. A journal paper based on research achievement in WP3 is under preparation.
7) As traffic offloading is an important function of D2D communication, D2D based content caching was also investigated by considering users’ content preference and willingness of sharing the content. One related journal paper and two conference papers have been accepted were accepted.
8) In Task 4.1, a software based test platform has been set up to simulate and evaluate the proposed D2D communication algorithms under single-cell and multi-cell scenarios. The platform and all the simulation results are shown in Milestones 4.1 and 4.2.
9) In Task 4.2, a hardware-based testbed is set up to connect two mobile devices under a central controller.

1.3 The potential impact and use of final results
In CODEC, an innovative concept of grouping D2D nodes and providing a generic analytical framework was introduced to ensure that the optimal resource management schemes can be developed with the consideration of various proximity-based applications in a systematic way, and performance gain from cellular D2D can be quantified. Practically, during the two-year project time, CODEC has obtained the following outcomes to contribute to researches related with D2D communications : 1) established a novel framework for developing practical resource management schemes with high spectrum and energy efficiencies for both cellular networks and mobile devices; 2) developed practical resource management schemes for D2D communications in single-cell, multi-cell and FFR scenarios; 3) evaluated the improvement of QoS especially for real-time video transmission when adopting D2D communications; 4) investigated D2D content caching, and proposed interference management scheme and content pushing scheme for D2D content caching; 5) demonstrated the feasibility of implementing D2D in cellular networks. The results can be applied to provide high quality of service (QoS) for proximity-based mobile social networking.
During the project period, Dr Zhu has visited several operators, including EE, BT, 3UK and Telekom Slovenije. They have shown great interest in adopting D2D communications into their cellular networks as statistics have shown there are a considerable amount of communications existing in a small area covered by one cell. Offloading traffic from BSs to D2D communications can benefit operators by saving energy and providing better customer services. Also, D2D underlaying cellular network enables direct data transmission between mobile devices in proximity and can guarantee QoS for multimedia applications with high spectral and energy efficiencies. Hence, the research work carried out in CODED is of great importance for the valuable market of mobile social networking.
The CODEC project has also contributed significantly to the career development for the fellow, Dr Zhu, through the following successful trainings: 1) Training in research areas has enhanced the fellow’s skills in video transmission via D2D communications, cooperative communications and testbed development for the experimentation of D2D communications. 2) Training in transferable skills also benefit the fellow significantly. During the project period, she has delivered two talks and participated in two industrial workshops and one international conference, and made visit to several key technology companies in related field and operators. She is also currently supervising five PhD students. She has led a proposal submitted to EU Horizon 2020 EU Horizon 2020 Marie Sklodowska-Curie Innovative Training Networks.
As a TPC co-chair, Dr Zhu also participated in the organisation of an IEEE Global Communications Conference (Globecom) 2016 workshop -Workshop on Trends of Future Mobile Networks - Self-organization Networks for 5G wireless communications and Internet of Things, which was held on 8th December 2016, Washington, DC, USA.

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