Mode selection for energy efficient D2D communications in dynamic TDD systems

Abstract

Abstract-Network-assisted Device-to-Device (D2D) communication is a promising technology for improving the performance of proximity-based services. This paper demonstrates how D2D communication can be used to improve the energy-efficiency of cellular networks, leading to a greener system operation and a prolonged battery life of the mobile devices. Assuming a flexible TDD system, we develop optimal mode selection policies for minimizing the energy cost (either from the system or from the device perspective) while guaranteeing a certain rate requirement. The jointly optimal transmit power and time allocation, as well as the optimal mode selection, is found by solving a small convex optimization problem. Special attention is given to the geometrical interpretation of the obtained results. We show that when network energy is the primary concern, D2D mode is preferable in a large portion of the cell. When the device energy consumption is most important, on the other hand, the area where D2D mode is preferable shrinks and becomes close to circular. Finally, we investigate how network parameters affect the range where direct communication is preferred.Index Terms-Network-assisted Device-to-Device, Mode Selection, TDD-LTE, Energy Efficient Communications I. INTRODUCTION During the last decade, the number of mobile subscribers and their traffic demand has increased tremendously, resulting in a larger energy consumption for cellular networks. Furthermore, the battery lifetime of mobile devices has been reduced considerably. Network-assisted Device-to-Device (D2D) communication is a promising technology to improve energy efficiency in future wireless networks: when mobile users in proximity to each other need to exchange data at high rate (e.g. media sharing, gaming, and other proximity-based services [1,2]), direct communication can potentially offload the BS and improve throughput, delay and energy consumption [3,4].A natural question in the context of D2D communication is under which condition two users should communicate through a direct link rather than via the BS. We call this problem the mode selection problem. The optimal mode selection naturally depends on the performance measure that we would like to optimize. For example, the authors in [5] select the transmission mode to maximize user rate in both single-cell and multiple-cell scenarios, while satisfying SINR constraints on active cellular links. In [6] and [7], the authors focus on maximizing the power-efficiency of the network. A joint mode selection and resource allocation problem in a multicell scenario is presented in [8] and shown to be NP-Hard. In [9], the authors address the mode selection problem of

Energy Efficient D2D Communications in Dynamic TDD Systems

“…However, they do not account for the mode selection and they mainly focus on the adaptive UL/DL slot allocation to D2D pairs, so to balance the traffic load, coordinate the interference, improve coverage probability and sum-rate. This paper extends our previous study [21] to a more realistic multi-link scenario. We consider two possible spectrum allocation strategies: one where each D2D pair is assigned its own frequency channel, and one where all D2D connections share the same channel.…”

“…In this case, E CELL ll (t ul ) is given by (11) and the expression for κ(D 0l ) gets a bit more involved [21]. Fig.…”

“…In this section, we present a heuristic algorithm that achieves a near-optimal solution to (21) in a more practical and scalable way than the B&B approach. Again, we focus on the UE case.…”

Fundamental Green Tradeoffs: Progresses, Challenges, and Impacts on 5G Networks

“…Therefore, an energy efficient NOA implementation using reconfigurable platform is promising [73] and the associated unified frame structure design [74] and low-overhead protocol [75] to reduce the switching latency of multiple NOA schemes are also important. April 28, 2016 DRAFT D2D communications have been envisioned as a key technology for 5G networks [75]- [81].…”

Potential games for subcarrier allocation in multi-cell networks with D2D communications

“…We assume that mode selection to determine if each user should communicate in cellular or D2D mode has already been performed [14], and focus on the allocation of timefrequency resources to users.…”