D2D User Equipments Research Articles

Relaying Robust Beamforming for Device-to-Device Communication With Channel Uncertainty

In this letter, we study robust beamforming design in the scenario that user equipments (UEs) relay the messages from a base station (BS) to a destination UE out of the cellular networks, which is considered as a high-priority device-to-device (D2D) scenario in the 3rd Generation Partnership Project (3GPP) Long-Term-Evolution (LTE) standardization. We assume that another D2D UE, which receives data from another D2D transmission group, coexists in the network, and it is interfered by D2D relay UEs. Moreover, the channel links between D2D relay UEs and the interfered UE are supposed to suffer from Gaussian errors due to low accuracy of channel estimation. Our optimization objective is to minimize the total transmission power at the BS and D2D relay UEs, while satisfying the signal-to-interference-plus-noise ratio (SINR) requirement of the destination D2D receiver and keeping the probability of low SINR event of the interfered D2D receiver smaller than a predefined threshold. Finally, we present the joint BS and D2D relay UE beamforming design, the effectiveness of which is verified by computer simulations.

Analysis of device‐to‐device communications with exclusion regions underlaying 5G networks

ABSTRACTDevice‐to‐device (D2D) communication underlaying cellular networks is an effective way to improve spectral efficiency and alleviate the traffic load of base stations, therefore it is considered as one of the key technologies in the fifth generation mobile communications, also referred to as IMT‐2020. However, it also introduces interference between D2D terminals and cellular users. In this work, we adopt both exclusion regions (ERs) and open‐loop fraction power control (OFPC) to mitigate the D2D‐to‐Cellular interference in a multicell uplink spectrum‐sharing scenario. We derive the closed‐form expressions of outage probability (OP) and area spectral efficiency (ASE) using stochastic geometry, and reveal the impact of the D2D user equipment (DUE) density versus cellular user equipment (CUE) density (in other words, how many DUEs can reuse the resource of a CUE per cell), D2D communication distance, different ER sizes, and of the compensation factor in OFPC. Numerical results show that adopting ERs could both decrease the OP of cellular users and increase the network ASE, and a proper ER radius can be selected by network operators according to their target OP, D2D users' density, and the communication distance of D2D users. Copyright © 2014 John Wiley & Sons, Ltd.

A Geometrical-Based Throughput Bound Analysis for Device-to-Device Communications in Cellular Networks

Device-to-device (D2D) communications in cellular networks are promising technologies for improving network throughput, spectrum efficiency, and transmission delay. In this paper, we first introduce the concept of guard distance to explore a proper system model for enabling multiple concurrent D2D pairs in the same cell. Considering the Signal to Interference Ratio (SIR) requirements for both macro-cell and D2D communications, a geometrical method is proposed to obtain the guard distances from a D2D user equipment (DUE) to the base station (BS), to the transmitting cellular user equipment (CUE), and to other communicating D2D pairs, respectively, when the uplink resource is reused. By utilizing the guard distances, we then derive the bounds of the maximum throughput improvement provided by D2D communications in a cell. Extensive simulations are conducted to demonstrate the impact of different parameters on the optimal maximum throughput. We believe that the obtained results can provide useful guidelines for the deployment of future cellular networks with underlaying D2D communications.

다중셀 간섭 네트워크와 중첩된 D2D 통신을 위한 효과적인 간섭 정렬 기법

K개의 셀과 각 셀에서 2개의 단말간 직접 통신(device-to-device communication: D2D communication) 링크 간에 셀룰러 하향 링크 자원을 재사용하는 다중셀 간섭 시스템에 중첩되어 있는 D2D 통신 모델을 고려한다. 본 논문에서는 현재의 셀 또는 인접 셀에 간섭을 미치지 않는 다수 개의 링크를 선택하거나 또는 전력 제어를 통해 다수 개의 링크가 어떤 기지국에도 간섭을 미치지 않는다고 가정했을 때, 간섭 정렬(interference alignment: IA)를 통해 셀간 및 셀 내의 하향링크 간섭을 효과적으로 없앨 수 있다는 것을 보인다. 특히, 2개의 D2D 통신 쌍에 대해서는 간섭채널에서 이론적으로 가능한 최대 자유도를 실현할 수 있는 방법을 제시하며, 기지국과 모든 단말의 송신 및 수신 안테나 개수가 각각 M일 때 그 자유도는 (K+1)M로 주어지는 것을 보인다. We consider the device-to-device (D2D) communication underlaying multi-cell interference system, in which the cellular downlink (DL) resource is reused by K cells and two D2D transmission links within each cell. In this paper, it has been shown that the downlink intra-cell and inter-cell interference can be effectively handled by interference alignment (IA) technique, as long as the simultaneous D2D links are properly selected or power-controlled so that they may not incur interference to the base stations in the same and neighbor cells. In particular, we provides the IA technique that can achieve the theoretically maximum possible degree of freedom (DOF), demonstrating that a total of (K+1)M degrees of freedom (DOFs) can be achieved for K-cell interference system with two underlaying D2D links, where base stations, cellular UE's, and D2D UE's all have M transmit and receive antennas.

Resource Allocation Under Channel Uncertainties for Relay-Aided Device-to-Device Communication Underlaying LTE-A Cellular Networks

Device-to-device (D2D) communication in cellular networks allows direct transmission between two cellular devices with local communication needs. Due to the increasing number of autonomous heterogeneous devices in future mobile networks, an efficient resource allocation scheme is required to maximize network throughput and achieve higher spectral efficiency. In this paper, performance of network-integrated D2D communication under channel uncertainties is investigated where D2D traffic is carried through relay nodes. Considering a multi-user and multi-relay network, we propose a robust distributed solution for resource allocation with a view to maximizing network sum-rate when the interference from other relay nodes and the link gains are uncertain. An optimization problem is formulated for allocating radio resources at the relays to maximize end-to-end rate as well as satisfy the quality-of-service (QoS) requirements for cellular and D2D user equipments under total power constraint. Each of the uncertain parameters is modeled by a bounded distance between its estimated and bounded values. We show that the robust problem is convex and a gradient-aided dual decomposition algorithm is applied to allocate radio resources in a distributed manner. Finally, to reduce the cost of robustness defined as the reduction of achievable sum-rate, we utilize the \textit{chance constraint approach} to achieve a trade-off between robustness and optimality. The numerical results show that there is a distance threshold beyond which relay-aided D2D communication significantly improves network performance when compared to direct communication between D2D peers.

Resource Management for Device-to-Device Communications in Heterogeneous Networks Using Stackelberg Game

Device-to-device (D2D) communications and femtocell systems can bring significant benefits to users’ throughput. However, the complicated three-tier interference among macrocell, femtocell, and D2D systems is a challenging issue in heterogeneous networks. As D2D user equipment (UE) can cause interference to cellular UE, scheduling and allocation of channel resources and power of D2D communication need elaborate coordination. In this paper, we propose a joint scheduling and resource allocation scheme to improve the performance of D2D communication. We take UE rate and UE fairness into account by performing interference management. First, we construct a Stackelberg game framework in which we group a macrocellular UE, a femtocellular UE, and a D2D UE to form a two-leader one-follower pair. The cellular UE are leaders, and D2D UE is the follower who buys channel resources from the leaders. We analyze the equilibrium of the game and obtain solutions to the equilibrium. Second, we propose an algorithm for joint scheduling of D2D pairs based on their utility. Finally, we perform computer simulations to study the performance of the proposed scheme.