Performance Enhancement in LTE-based D2D Networks

Abstract

Recently, Device-to-Device (D2D) communication has attracted much attention as an emerging solution to cope with heavy cellular traffic caused by the proliferation of mobile devices such as smartphones and tablet PCs along with the increased demands for high data rate services. D2D communication is a promising technique which is introduced to one of the technology in Fifth Generation (5G) mobile network. In this scenario, allowing User Equipments (UEs) to reuse cellular resources can boost up the network performance in terms of the system capacity. In addition, reduced number of hops and shorter communication distance via direct communication between proximity UEs implies reduced energy consumption and communication delay. Moreover, D2D communications can help offload cellular traffic and avoid congestion in cellular network.

This dissertation dealt with various aspects of problems under D2D network. For performance enhancement, various schemes and algorithms for D2D discovery and communication are proposed and evaluated via simulation.

First of all, we investigate the interference problem occurring during D2D discovery. Every D2D-UE (D-UE) chooses the discovery resource randomly. Therefore, if the same resource is selected by more than one D-UE, mutual interference by collision is inevitable. Moreover, the collided D-UEs can not recognize the collision event in distributed D2D network. To reduce such mutual interference, interference mitigation technique is necessary. This study proposes two schemes to improve the discovery performance by alleviating the mutual interference. Since the proposed schemes are considered to operate in distributed manner, additional signaling or resources are not needed. In addition, performance evaluation of the proposed schemes and algorithm are conducted by incorporating in recent specification.

Secondly, this study proposes the D2D discovery and link setup protocol model working in an LTE network. In addition, propose discovery synchronization, beacon resource and energy efficient RRC IDLE state discovery. These proposed model and discovery design in LTE-based is the first study in academia. Even though, the demand for D2D communication has increased, energy consumption is a growing concern as well. A device has to support both cellular and D2D communication, meaning that additional energy is required. Due to the energy concerns, we comparatively analyze the performance of the D2D discovery and link setup in RRC CONNECTED and RRC IDLE states. The performance analysis is conducted by utilizing the real measurement results with commercialized LTE smartphones.

Lastly, we design a spatial reuse scheme which is well-known as one of the advantages in proximity D2D communication. The spatial reuse scheme is allowed to reuse one resource by sharing multiple transmitters. However, sharing the spectrum is carefully allowed due to the generating interference mutually. Especially, when two (or more than) devices reuse in proximity. This study investigate the spatial reuse problem under D2D multicast transmission and solve it with distributed manner. Moreover, this study proposes novel resource reusing schemes by multiple transmitters to increase spectrum efficiency. The performance evaluation of the proposed schemes are conducted by incorporating in recent specification, thus the simulation results demonstrate that proposed schemes outperform the baseline scheme.