We investigate rate-distortion-computing optimized live 360◦ video streaming to heterogeneous mobile VR clients in 5G networks. The client population comprises devices that feature single (LTE) or dual (LTE/NR) cellular connectivity. The content is compressed using scalable 360◦ tiling at the origin and sent towards the clients over a single backbone network link. A mobile edge server then adapts the incoming streaming data to the individual clients and their respective down-link transmission rates using formal rate-distortion-computing optimization. Single connectivity clients are served by the edge server a baseline representation/layer of the content adapted to their down-link transmission capacity and device computing capability. A dual connectivity client is served in parallel a baseline content layer on its LTE connectivity and a complementary viewport-specific enhancement layer on its NR connectivity, synergistically adapted to the respective down-links’ transmission capacities and its computing capability. We formulate two optimization problems to conduct the operation of the edge server in each case, taking into account the key system components of the delivery process and induced end-to-end latency, aiming to maximize the immersion fidelity delivered to each client. We explore respective geometric programming optimization strategies that compute the optimal solutions at lower complexity. We rigorously analyze the computational complexity of the two optimization algorithms we formulate. In our evaluation, we demonstrate considerable performance gains over multiple assessment factors relative to two state-of-the-art techniques. We also examine the robustness of our approach to inaccurate user navigation prediction, transient NR link loss, dynamic LTE bandwidth variations, and diverse 360◦ video content. Finally, we contrast our results over five popular video quality metrics and share our evaluation dataset.

Dual-connectivity streaming is a key enabler of next-generation six Degrees Of Freedom (6DOF) Virtual Reality (VR) scene immersion. Indeed, using conventional sub-6 GHz WiFi only allows to reliably stream a low-quality baseline representation of the VR content, while emerging high-frequency communication technologies allow to stream in parallel a high-quality user viewport-specific enhancement representation that synergistically integrates with the baseline representation to deliver high-quality VR immersion. We investigate holistically as part of an entire future VR streaming system two such candidate emerging technologies, Free Space Optics (FSO) and millimeter-Wave (mmWave), that benefit from a large available spectrum to deliver unprecedented data rates. We analytically characterize the key components of the envisioned dual-connectivity 6DOF VR streaming system that integrates in addition edge computing and scalable 360° video tiling, and we formulate an optimization problem to maximize the immersion fidelity delivered by the system, given the WiFi and mmWave/FSO link rates, and the computing capabilities of the edge server and the users’ VR headsets. This optimization problem is mixed integer programming of high complexity and we formulate a geometric programming framework to compute the optimal solution at low complexity. We carry out simulation experiments to assess the performance of the proposed system using actual 6DOF navigation traces from multiple mobile VR users that we collected. Our results demonstrate that our system considerably advances the traditional state of the art and enables streaming of 8K-120 frames-per-second (fps) 6DOF content at high fidelity.

In this paper, we present a novel neighbor discovery method for a wireless ad hoc network where each node is equipped with a Free-Space-Optical (FSO) transceivers capable of electronic beam switching. Directional neighbor discovery can be very challenging due to the requirement of strict line-of-sight (LOS) alignment and can result in long and impractical discovery time if the nodes in the network do not have prior information about each other’s location. Our method guarantees that a node can discover all of its neighbors within one 360◦FSO beam sweep. We present a preliminary prototype of a FSO transceiver module capable of electronic beam steering. Through experiments using the developed prototype, we demonstrate that the proposed method helps in discovering neighbor nodes with minimal delay.

In this paper, we present a novel neighbor discovery method for a Free-Space-Optical (FSO) mobile ad hoc network where the nodes do not have any prior information about each other’s location. Each node is equipped with multiple FSO transceivers and a low bit rate long-range (LoRa) omnidirectional communication channel aids in coordinating the neighbor discovery process to synchronize and establish directional FSO links among the nodes. Our proposed method guarantees that a node can discover all of its neighbors within one 360◦FSO beam scan of the surrounding environment. We also present a preliminary prototype of an FSO transceiver module capable of electronic beam steering. Through extensive simulations and real test-bed experiments using the developed prototype, we demonstrate that the proposed method can help achieve significant reductions in discovery time compared to a state-of-the-art protocol.

Virtual Reality (VR) promises immersive experiences in diverse areas such as gaming, entertainment, education, healthcare, and remote monitoring. In VR environments, users can navigate 360-degree content by moving or looking around in all directions, by rotating their heads, as in real life. A rapid head rotation can corrupt the wireless link, degrading the user experience. Due to the lack of proper head rotation models, testbeds are usually required to analyze VR systems. In this paper, we propose an open source code package that generates realistic head rotation traces. The code package is based on a simple, yet flexible, time-correlated mathematical model, which is extrapolated from a publicly available VR head rotation measurement-based dataset. We show that the probability density function of head rotation pitch and roll angles can be modeled as Gaussian distributions, while the probability density function of yaw angles can be modeled as a Gaussian mixture distribution. To introduce temporal correlation, we extrapolate the power spectral density of the angular processes, which are modeled with a bi-exponential decay. Finally, we show how the model can support and accelerate the design of future VR systems by proposing the analysis of a distributed Multiple Input Multiple Output (MIMO) system and the design of a situational awareness Machine Learning (ML) based beamforming training for millimeter wave networks.

We investigate a future WiFi-VLC dual connectivity streaming system for 6DOF multi-user virtual reality that enables reliable high-fidelity remote scene immersion. The system integrates an edge server that uses scalable 360° tiling to adaptively split the present 360° view of a VR user into a panoramic baseline content layer and a viewport-specific enhancement content layer. The user is then served the two content layers over complementary WiFi and VLC wireless links such that the delivered viewport quality is maximized for the given WiFi and VLC transmission resources. We formally characterize the actions of the server using rate-distortion optimization that we solve at low complexity. To account for the users' mobility as they explore different 360° viewpoints of the 6DOF remote scene content and maintain reliable high-quality VLC connectivity, we explore dynamic VLC transmitter steering and assignment in the system as graph bottleneck matching that aims to maximize the received VLC SNR across all users. We formulate an effective low-complexity solution to this discrete combinatorial optimization problem of high complexity. The paper also contributes a first actual 6DOF body and head movement VR navigation dataset that we collected and facilitate to assess the performance of our system via simulation experiments. These demonstrate enhanced VLC transmission performance and an up to 7 dB gain in viewport quality over a state-of-the-art VLC cellular system (LiFi), and an up to 10 dB gain in viewport quality over a state-of-the-art traditional wireless streaming method, for 12K-120fps 360° 6DOF VR content. Moreover, the synergistic WiFi-VLC dual connectivity of the proposed system augments its reliability over the reference method LiFi that comprises only VLC links. These outcomes motivate further exploration and prototype implementation of our system.

We explore a novel RF-FSO dual-path UAV net-work for remote scene aerial scalable 360° video capture and streaming, to enable future virtual human teleportation. One UAV captures the 360° video viewpoint and constructs a scalable tiling representation of the data comprising a base layer and an enhancement layer. The base layer is sent by the UAV to a ground-based remote server using a direct RF link. The enhancement layer is relayed by the UAV to the server over a multi-hop path comprising directed UAV to UAV FSO links. The viewport-specific content from the two layers is then integrated at the server to construct high fidelity content to stream to a remote VR user. The dual-path connectivity ensures both reliability and high fidelity remote immersion. We formulate an optimization problem to maximize the delivered immersion fidelity which depends on the content capture rate, FSO and RF link rates, effective routing path selection, and fast UAV deployment. The problem is mixed integer programming and we formulate an optimization framework that captures the optimal solution at lower complexity. Our experimental results demonstrate an up to 6 dB gain in delivered immersion fidelity over a state-of-the-art method and for the first time enable 12K-120fps 360° video streaming at high fidelity.

Neighbor discovery is an essential part of the communication link establishment process for any wireless ad-hoc network. This problem of discovering neighbor nodes becomes even more challenging when the transceivers are highly directional. In this paper, we consider a 3D network of unmanned-aerial-vehicles (UAVs) that uses free-space-optical (FSO) transceivers for establishing high speed highly directional communication links. We consider that each UAV is equipped with a spherical structure on which multiple FSO transceivers are placed. The UAVs can electronically steer their communication beams by switching from one transceiver to another. We provide analysis on how optimally placing the transceivers with the appropriate divergence angles can help establish an FSO link at any direction in the 3D space. We also present a neighbor discovery algorithm that ensures discovery within a limited time. We demonstrate through extensive simulations that a UAV with FSO transceivers can successfully discover its neighbor UAVs even without prior location information about them and without any additional omnidirectional radio frequency (RF) channel.

Directional Radio Frequency (RF) / Free-Space-Optical (FSO) transceivers have the potential to play a significant role in future generation wireless networks. They are advantageous in terms of improved spectrum utilization, higher data transfer rate, and lower probability of interception from unwanted sources. Despite these advantages, communications using directional transceivers require establishment and maintenance of line-of-sight (LOS). Thus, establishment of the communication link or neighbor discovery plays an important role in mobile ad hoc networks with RF/FSO directional transceivers. We consider two nodes (Unmanned Aerial Vehicles (UAVs) or quadcopters) hovering in 3D space, each with one directional transceiver mounted on a mechanically steerable spherical structure/head, with which they can scan 360 degrees in the horizontal plane and 360 degrees in the vertical plane. We propose a novel scheme that deals with the problem of automatic discovery and establishment of LOS alignment between these nodes. We performed extensive simulations to show the effectiveness of the proposed neighbor discovery method. We also developed a proof-of-concept prototype and conducted experiments with it. The results obtained from both simulations and experiments show that, using such mechanically steerable directional transceivers, it is possible to establish communication links to similar neighboring nodes within several seconds without using GPS support.

Free-Space-Optical (FSO) communication has become an attractive option over Radio Frequency (RF) communication due to having broader bandwidth, unlicensed band, higher spatial reuse, and enhanced security. In-band full-duplex FSO (IBFD-FSO) transceivers ensure, in some cases enhance, these features enabling future vision of smart communication and Internet-of-Things (IoT) applications. Even though IBFDFSO transceivers can double the network capacity theoretically, overall performance and capacity is limited by interference and optical feedback. In this paper, we present a proof-ofconcept prototype of IBFD-FSO transceiver by implementing isolation technique to reduce optical feedback. We demonstrate the effectiveness of the isolation technique and performance through test-bed experiments using off-the-shelf components.

Free-Space-Optical (FSO) communication has the potential to provide optical-level wireless communication speeds. It can also help solve the wireless capacity problem experienced by the traditional RF-based technologies. Despite its capacity advantages, FSO communication is prone to mobility. Since the FSO transceivers are highly directional, they require establishment and maintenance of line-of-sight (LOS) between each other. We consider two autonomous mobile nodes, each with one FSO transceiver mounted on a movable head capable of rotating 360 degree. We propose a novel scheme that deals with the problem of automatic maintenance of LOS alignment between the two nodes with mechanical steering of the FSO transceivers. We design protocols to maintain an FSO link between the mobiles satisfying a minimum received power or signal-to-noise ratio (SNR). We also present a prototype implementation of such mobile node with FSO transceivers. The effectiveness of the alignment protocol is evaluated by analyzing the results obtained from both simulations and also experiments conducted using the prototype. The results show that, by using such mechanically steerable transceivers and a simple auto-alignment mechanism, it is possible to maintain optical wireless links in a mobile setting with nominal disruption.

Free-Space-Optical (FSO) communication has the potential to not only deliver wireless communication links at optical-level speeds but also solve the wireless capacity problem that the traditional RF based technologies are confronting. Despite its advantages, FSO communication is prone to mobility. The highly directional FSO transceivers require establishment and maintenance of line-of-sight (LOS) between them. Facilitating continuous alignment requirements has been a major concentration of mobile FSO research to date. We consider two autonomous mobile nodes, each with one FSO transceiver mounted on a movable head capable of rotating 360 degrees. We propose a novel scheme that deals with the problem of automatic detection, establishment and maintenance of LOS alignment between the two nodes with mechanical steering of the FSO transceivers. The proposed method shows that using such mechanically steerable transceivers and a simple autoalignment mechanism, it is possible to maintain optical wireless links in a mobile setting with nominal disruption.