Sami Hakola

Device-To-Device (D2D) Communication in Cellular Network - Performance Analysis of Optimum and Practical Communication Mode Selection

In a cellular network system one way to increase its capacity is to allow direct communication between closely located user devices when they are communicating with each other instead of conveying data from one device to the other via the radio and core network. The problem is then when the network shall assign direct communication mode and when not. In previous works the decision has been done individually per communicating device pair not taking into account other devices and the current state of the network. We derive means for getting optimal communication mode for all devices in the system in terms of system equations. The system equations capture information of the network such as link gains, noise levels, signal-to-interference-and-noise-ratios, etc., as well as communication mode selection for the devices. Using the derived equations performance bounds for the cellular system where D2D communication is an additional communication mode are illustrated via simulations. Further, practical communication mode selection algorithms are used to evaluate their system performance against the achievable bounds. Analysis show the usability of the system equations and the potential of having D2D operation integrated into a cellular system when there is enough local communication occurring.

The investigation of power control schemes for a device-to-device communication integrated into OFDMA cellular system

Power control is one of the key functions which are able to co-ordinate the system interference. In this paper, several power control schemes are investigated for a hybrid LTE system, which combines the direct device-to-device (D2D) mode communication and the normal cellular mode communication. In the system study, the power control for the D2D mode communication is emphasized. In general, the utilization of local area transmission for D2D communications provides a better SINR than normal cellular communications. In this case, the proper power control for D2D communications can be a flexible way to improve (and balance) the overall system performance. Naturally, the low power transmission of D2D communications leads to many potential advantages, such as low interference level (to normal cellular users) and low power consumption. From the power control point of view, the low power transmission provides more freedom to tune the Tx power. However, power control is not an efficient solution to avoid the strong mutual (co-channel) interference between different types of UEs. In this case, the join consideration of mode selection, resource scheduling, link adaption and power control is needed.

Network controlled Device-to-Device (D2D) and cluster multicast concept for LTE and LTE-A networks

In this paper we introduce a reliable multicast concept for Device-to-Device (D2D) communication integrated into cellular network. In addition to the introduction of the basic concept, initial simulation results are presented as well. Clustering closely located devices which have local communication needs is a feasible and efficient way of solving the increasing data traffic requirements in the future cellular network. Reliable D2D multicast concept introduced in this paper is designed to be scalable and efficient solution for local communication needs such as file transfer and even streaming services. Due to the network involvement in controlling the local D2D communication, sufficient quality of service can be guaranteed. In addition, due to the flexible mode switching between direct and cellular modes in the integrated operation the service continuity can be provided.

Clustering Concept Using Device-To-Device Communication in Cellular System

We study how direct communication within a group of devices, cluster, can improve the performance of a conventional cellular system. The clusters are formed from devices that are close and communicating with each other, for example, sharing data. The clusters share the radio resources among other devices in the system thus creating a mixed network system comprising directly communicating devices and devices having radio links to and from the base stations. In this kind of a system the additional challenge is to decide when clusters shall use direct communication and when conventional cellular radio links to communicate with each other. Here, in addition to clustering concept description we provide new means to analyse achievable system performance when clustering communication is integrated into a cellular network and especially into an interference limited system.

Time Hopping for Device-To-Device Communication in LTE Cellular System

In this paper, we analyze the challenges of the interference environment in a hybrid network that consists of the device-to-device (D2D communication based ad-hoc connections and conventional cellular connections. Accordingly, time hopping (TH) based radio resource allocation schemes aiming to improve the robustness of the hybrid network are proposed. The performance improvement even with the simple random TH scheme is considerable, which is validated via extensive simulations. In addition, the simulation results also give some hints on the optimization of the practical TH operation in a hybrid network.

Enhancing HSUPA system level performance with dual carrier capability

The purpose of this paper is to analyze how dual carrier capability can enhance High Speed Uplink Packet Access performance in comparison to using only single carrier. Dual carrier operation gives the User Equipment the possibility to transmit simultaneously using two 5 MHz bands, theoretically doubling the peak data rates and user throughput. The analysis is conducted with a system level simulation tool. This paper first indicates with single carrier simulations that, especially in small cells, terminals have spare power available for dual carrier operation. These observations are verified with dual carrier simulations by showing that the burst throughput can be practically doubled. In the larger cells only the users in good position can fully benefit from using dual carrier.