Software-Defined Metasurfaces (SDMs) have ad-vanced from basic theoretical ideas to a key enabler for next generation wireless systems. When massively deployed in a wireless environment, they can realize precise, software-defined propagation of signals and wireless channel customizations. A plethora of studies have thoroughly investigated the physical design of the SDMs and their wireless channel engineering capa-bilities. This work introduces a novel architecture and associated processes for integrating SDMs into existing networked wireless systems. First, the integration architecture and the according complex underlying physics of the SDMs are presented. Then the software abstractions are proposed that enable the interaction of the surfaces in a physics-agnostic manner. These software abstractions require an SDM profile to operate in real-time, i.e., a database that accurately describes the capabilities of a given metasurface. Thus, the manufacturing time workflows are suggested to produce such a profile. The proposed solutions are evaluated in an actual physical setup/testbed.

Programmable wireless environments (PWEs) utilize internetworked intelligent metasurfaces to transform wireless propagation into a software-controlled resource. In this article, the interplay is explored between the user devices, the metasurfaces, and the PWE control system from the theory to the end-to-end implementation. This article first discusses the metasurface hardware and software, covering the complete workflow from the user device initialization to its final service via the PWE. Furthermore, to be compatible with the 5G and 6G wireless systems, the software-defined networking (SDN) paradigm is extended to achieve scalable internetworking and central control in PWE deployments with multiple metasurfaces and multihop communication. Subsequently, the set of SDN foundations is exploited in order to abstract the physics behind PWEs and a theoretical framework is established to describe and manipulate them in an algorithmic form. This can lead to smart radio environments that are readily accessible from various engineering disciplines, facilitating their integration into existing networks, wireless systems, and applications. This article is concluded by outlining strategies for the optimal placement of metasurfaces within a PWE-controlled space, open challenges in PWE security, specialized SDN integration issues, and theoretical problems toward the graph-driven modeling of PWEs.

Programmable wireless environments (PWEs) utilize electromagnetic metasurfaces to transform wireless propagation into a software-controlled resource. In this work we study the effects of user device mobility on the efficiency of PWEs. An analytical model is proposed, which describes the potential misalignment between user-emitted waves and the active PWE configuration, and can constitute the basis for studying queuing problems in PWEs. Subsequently, a novel, beam steering approach is proposed which can effectively mitigate the misalignment effects. Ray-tracing-based simulations evaluate the proposed scheme.

Intelligent surfaces exert deterministic control over the wireless propagation phenomenon, enabling novel capabilities in performance, security and wireless power transfer. Such surfaces come in the form of rectangular tiles that cascade to cover large surfaces such as walls, ceilings or building facades. Each tile is addressable and can receive software commands from a controller, manipulating an impinging electromagnetic wave upon it by customizing its reflection direction, focus, polarization and phase. A new problem arises concerning the orchestration of a set of tiles towards serving end-to-end communication objectives. Towards that end, we propose a novel intelligent surface networking algorithm based on interpretable neural networks. Tiles are mapped to neural network nodes and any tile line-of-sight connectivity is expressed as a neural network link. Tile wave manipulation functionalities are captured via geometric reflection with virtually rotatable tile surface norm, thus being able to tunable distribute power impinging upon a tile over the corresponding neural network links, with the corresponding power parts acting as the link weights. A feedforward/backpropagate process optimizes these weights to match ideal propagation outcomes (normalized network power outputs) to wireless user emissions (normalized network power inputs). An interpretation process translates these weights to the corresponding tile wave manipulation functionalities.

The traditional cycle of industrial products has been linear since its inception. Raw resources are acquired, processed, distributed, used and ultimately disposed of. This linearity has led to a dangerously low efficiency degree in resource use, and has brought forth serious concerns for the viability of our natural ecosystem. Circular economy is introducing a circular workflow for the lifetime of products. It generalizes the disposal phase, reconnecting it to manufacturing, distribution and end-use, thus limiting true deposition to the environment. This process has not been extended so far to software. Nonetheless, the development of software follows the same phases, and also entails the use-and waste-of considerable resources. This include human effort, as well as human and infrastructure sustenance products such as food, traveling and energy. This paper introduces circular economy principles to the software development, and particularly to network management logic and security. It employs a recently proposed concept-the Socket Store-which is an online store distributing end-user network logic in modular form. The Store modules act as mediators between the end-user network logic and the network resources. It is shown that the Socket Store can implement all circular economy principles to the software life-cycle, with considerable gains in resource waste.

Programmable, intelligent surfaces can manipulate electromagnetic waves impinging upon them, producing arbitrarily shaped reflection, refraction and diffraction, to the benefit of wireless users. Moreover, in their recent form of HyperSurfaces, they have acquired inter-networking capabilities, enabling the Internet of Material Properties with immense potential in wireless communications. However, as with any system with inputs and outputs, accurate sensing of the impinging wave attributes is imperative for programming HyperSurfaces to obtain a required response. Related solutions include field nano-sensors embedded within HyperSurfaces to perform minute measurements over the area of the HyperSurface, as well as external sensing systems. The present work proposes a sensing system that can operate without such additional hardware. The novel scheme programs the HyperSurface to perform compressed sensing of the impinging wave via simple one-antenna power measurements. The HyperSurface can jointly be programmed for both wave sensing and wave manipulation duties at the same time. Evaluation via simulations validates the concept and highlight its promising potential.

Programmable wireless environments enable the software-defined propagation of waves within them, yielding exceptional performance. Several building-block technologies have been implemented and evaluated at the physical layer in the past. The present work contributes a network-layer solution to configure such environments for multiple users and objectives, and for any underlying physical-layer technology. Supported objectives include any combination of Quality of Service and power transfer optimization, eavesdropping, and Doppler effect mitigation, in multi-cast or uni-cast settings. In addition, a graph-based model of programmable environments is proposed, which incorporates core physical observations and efficiently separates physical and networking concerns. The evaluation takes place in a specially developed simulation tool, and in a variety of environments, validating the model and reaching insights into the user capacity of programmable environments.

Wireless communication environments are unaware of the ongoing data exchange efforts within them. Moreover, their effect on the communication quality is intractable in all but the simplest cases. The present work proposes a new paradigm, where indoor scattering becomes software-defined and, subsequently, optimizable across wide frequency ranges. Moreover, the controlled scattering can surpass natural behavior, exemplary overriding Snell's law, reflecting waves towards any custom angle (including negative ones). Thus, path loss and multi-path fading effects can be controlled and mitigated. The core technology of this new paradigm are metasurfaces, planar artificial structures whose effect on impinging electromagnetic waves is fully defined by their macro-structure. The present study contributes the software-programmable wireless environment model, consisting of several HyperSurface tiles controlled by a central, environment configuration server. HyperSurfaces are a novel class of metasurfaces whose structure and, hence, electromagnetic behavior can be altered and controlled via a software interface. Multiple networked tiles coat indoor objects, allowing fine-grained, customizable reflection, absorption or polarization overall. A central server calculates and deploys the optimal electromagnetic interaction per tile, to the benefit of communicating devices. Realistic simulations using full 3D ray-tracing demonstrate the groundbreaking potential of the proposed approach in 2.4GHz and 60GHz frequencies.

A developer of mobile or desktop applications is responsible for implementing the network logic of his software. Nonetheless: i) Developers are not network specialists, while pressure for emphasis on the visible application parts places the network logic out of the coding focus. Moreover, computer networks undergo evolution at paces that developers may not follow. ii) From the network resource provider point of view, marketing novel services and involving a broad audience is also challenge for the same reason. Moreover, the objectives of end-user networking logic are neither clear nor uniform. This constitutes the central optimization of network resources an additional challenge. As a solution to these problems, we propose the Socket Store. The Store is a marketplace containing end-user network logic in modular form. The Store modules act as intelligent mediators between the end-user and the network resources. Each module has a clear, specialized objective, such as connecting two clients over the Internet while avoiding transit networks suspicious for eavesdropping. The Store is populated and peer-reviewed by network specialists, whose motive is the visibility, practical applicability and monetization potential of their work. A developer first purchases access to a given socket module. Subsequently, he incorporates it to his applications under development, obtaining state-of-the-art performance with trivial coding burden. A full Store prototype is implemented and a critical data streaming module is evaluated as a driving case.

Nanonetworks comprise numerous wireless nodes, assembled at micro-to-nano scale. The unique manufacturing challenges and cost considerations of these networks make for minimal complexity solutions at all network layers. From a networking aspect, packet retransmissions should be kept minimal, while ensuring communication between any two nanonodes. In addition, assigning unique addresses to nanonodes is not straightforward, since it can entail a prohibitively high number of packet exchanges. Thus, efficient data routing is considered an open issue in nanonetworking. The present paper proposes a routing system which can be dynamically deployed within a nanonetwork. Static, dense topologies with numerous, identical nodes are examined. These attributes are especially important in the context of recently proposed applications of nanonetworks. The proposed scheme incurs a trivial setup overhead and requires integer processing capabilities only. Once deployed, it operates efficiently, inducing lower packet retransmission rates than related schemes.

Wireless networks of nano-nodes will play a critical role in future medical, quality control, environmental monitoring and military applications. Nano-nodes are invisible/marginally visible to the human eye, ranging in size from approximately 100 μm to few nanometers. Nano-networking poses unique challenges, requiring ground-breaking solutions. First, the nano-scale imposes severe restrictions to the computational and communication capabilities of the nodes. Second, nano-nodes are not accessible for programming, configuration and debugging in the classical sense. Thus, a nano-network should be self-configuring, resilient and adaptive to environmental changes. Finally, all nano-networking protocols should be ultra-scalable, since a typical nano-network may comprise billions of nodes. The study contributes a novel paradigm for data dissemination in networking nano-machines, addressing these unique challenges. Relying on innovative analytical results on lattice algebra and nature-inspired processes, a novel data dissemination method is proposed. The nano-nodes exploit their environmental feedback and mature adaptively into network backbone or remain single network users. Such a process can be implemented as an ultra-scalable, low complexity, multi-modal nano-node architecture (physical layer), providing efficient networking and application services at the same time. Requiring existing manufacturing technology, the proposed architecture constitutes the first candidate solution for realizable nano-networking.

The Web offers abundant amounts of information anytime, anyplace. Multimedia provision companies bloom and die, seeking to attract a viable share of the data dissemination market. More often than not, failure is attributed to unsuitable content orientation. The present work contributes a novel content specialization scheme for periodic, push-based data streaming services. Its goal is to maximize the ratio of user requests served within their respective deadlines. In this sense, optimality is proven to be achievable only by discarding all requests for certain data items, focusing solely on the streaming of the remaining ones. Thus, the service achieves the content specialization that yields the most clients. The methodology workflow is as follows. By means of mathematical analysis we quantify data compatibility in terms of boosting the system’s service ratio. A data selection algorithm is then proposed, which follows a sort-and-segment approach. Through simulations, the algorithm is shown to surpass related solutions, while coinciding with bruteforce results and analytical expectations.

The continuous increase of Internet users worldwide, as well as the extensive need to support real-time traffic and bulk data transfers simultaneously, has directed research towards service differentiation schemes. These schemes either propose techniques that provide users with the necessary quality guarantees or follow a "better-than-best-effort" approach to satisfy broadly the varying needs of different applications. We depart from our new service principle called Less Impact Better Service (LIBS) and propose a novel service differentiation method, namely size-oriented dropping policies, which uses packet size to categorize time-sensitive from delay-tolerant flows and prioritize packet dropping probability, accordingly. Unlike existing proposals, the distinction of flows is dynamic and the notion of packet size is abstract and comparative; a packet size is judged as a unit within a dynamic sample space, that is, current queue occupancy. We evaluate size-oriented dropping policies both analytically and experimentally; we observe a significant increase on the perceived quality of real-time applications. Delaysensitive flows increase their bandwidth share, to reach a state of system fairness, regulating the dominant behavior of bulk-data flows.

We evaluate selected research proposals towards the efficient real-time QoS management over wireless links. We mainly focus on real-time performance of link-and transport-level mechanisms that bind operationally wired and wireless links. Employing a new metric for the evaluation of real-time performance we demonstrate that there are occasions where increased goodput does not correspond to real-time performance gains. In the sequel, we exploit further the potential of transport layer approaches