Direct Line Of Sight Path Research Articles

Mobility aware resource allocation for millimeter-wave D2D communications in presence of obstacles

The device-to-device (D2D) communication is envisioned as the solution to the bandwidth scarcity problem in the era of exponentially growing smart handheld devices. Although D2D communication in high frequency millimeter wave (mmWave) band offers high data rate, it requires obstacle free line-of-sight (LOS) communication path due to high propagation and penetration losses. The relay selection problem in D2D communication deals with careful selection of relay devices in order to establish a communication link when the direct LOS path is blocked or suffers from high interference from neighboring devices. With the limited number of available frequency channels, the channel allocation problem aims to judicially allocate the frequency channels to the activated D2D communication links. Due to the interdependence of the aforesaid two problems, it is a challenging task to optimally allocate frequency channels to the requesting D2D pairs along with proper selection of relay devices, specially in the presence of obstacles and user mobility. In this paper, we have proposed a mobility and obstacle aware base-station controlled centralized framework which jointly deals the channel allocation and relay selection problems for mmWave D2D communication. After proving the hardness of this joint problem, we provide a greedy solution along with its approximation bound. Our proposed algorithm has been shown to outperform an existing work through extensive simulations.

Optimum Distance and Power allocation Strategies for Quantum-limited Inter-Relayed FSO Communication System

In this work, we analyze the performance of a uni-directional quantum-limited inter-relay assisted free space optical link. We assume that there is no direct line of sight path between source and destination. The influence of path loss, atmospheric turbulence and pointing error impairments is considered for the analysis. The turbulence induced fading is modeled by independent but not necessarily identically distributed Gamma-Gamma fading statistics. The proposed system employs decode and forward relaying protocol assisted with channel state information. The approximate analytical expression for the probability of error is derived and illustrated by numerical plots. The asymptotic analysis for minimizing error probability in order to find optimum distance between the nodes for uniform power transmission, and for optimizing power allocated to different links, has been performed. It is shown that either distance between the nodes can be optimized for minimizing error probability when uniform power allocation is done, or optimum power allocation can be done for minimizing probability of error. Further, it helps to increase the distance for transmission between source and destination, and can make transmission possible in situations where direct link between source and destination can’t be established due to high rise buildings and other obstacles, while keeping the total transmitted power within permissible levels.