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The Moon and its surrounding cislunar space have numerous unknowns, uncertainties, or partially charted phenomena that need to be investigated to determine the extent to which they affect cislunar communication. These include temperature fluctuations, spacecraft distance and velocity dynamics, surface roughness, and the diversity of propagation mechanisms. To develop robust and dynamically operative Cislunar space networks (CSNs), we need to analyze the communication system by incorporating inclusive models that account for the wide range of possible propagation environments and noise characteristics. In this paper, we consider that the communication signal can be subjected to both Gaussian and non-Gaussian noise, but also to different fading conditions. First, we analyze the communication link by showing the relationship between the brightness temperatures of the Moon and the equivalent noise temperature at the receiver of the Lunar Gateway. We propose to analyze the ergodic capacity and the outage probability, as they are essential metrics for the development of reliable communication. In particular, we model the noise with the additive symmetric alpha-stable distribution, which allows a generic analysis for Gaussian and non-Gaussian signal characteristics. Then, we present the closed-form bounds for the ergodic capacity and the outage probability. Finally, the results show the theoretically and operationally achievable performance bounds for the cislunar communication. To give insight into further designs, we also provide our results with comprehensive system settings that include mission objectives as well as orbital and system dynamics.

Interplanetary links (IPL) serve as crucial enablers for space exploration, facilitating secure and adaptable space missions. An integrated IPL with inter-satellite communication (IP-ISL) establishes a unified deep space network, expanding coverage and reducing atmospheric losses. In order to evaluate the performance of both realistic and cost efficient IP-ISL scenario, the challenges, including irregularities in charged density, hardware impairments, and hidden celestial body brightness are analyzed with a reflectarray-based IP-ISL between Earth and Moon orbiters. In this regard, free-space channel is modeled with the charge density irregularities that disturb the angle of arrival. A discretize solution for noise temperature analyze in celestial body brightness is given with average beam occupancy. Lastly, the impact of aggregated phase noise, in-phase and quadrature imbalance and non-linear amplifier are modeled with generalized stochastic hardware impairments. As a solution, the ideal and non-ideal compensation of angle of arrival with the perfect knowledge of it is analyzed. It is observed that $10^{-8}$ order severe hardware impairments with intense solar plasma density drops an ideal system’s spectral efficiency (SE) from $\sim 38~\textrm {(bit/s)/Hz}$ down to $0~\textrm {(bit/s)/Hz}$ . An ideal full angle of arrival fluctuation recovery with full steering range achieves $\sim 20~\textrm {(bit/s)/Hz}$ gain and a limited beamsteering with a numerical reflectarray design achieves at least $\sim 1~\textrm {(bit/s)/Hz}$ gain in severe hardware impairment cases. As a result, we assess the feasibility of an integrated IP-ISL system design to establish a unified deep space network, expanding coverage and reducing atmospheric losses between the Moon and Earth in terms of spectral efficiency, addressing real-life deep space communication challenges.

Orthogonal time frequency space (OTFS) modulation is strongly considered as a promising solution for high-mobility communications. In contrast to conventional modulation techniques, wherein information symbols are multiplexed in a one-dimensional time or frequency domain, OTFS employs a two-dimensional modulation scheme by multiplexing information symbols in the delay-Doppler domain. This paper presents a comprehensive survey of OTFS. It starts with an overview of OTFS, its advantages over conventional air interface techniques, general block diagrams, and implementations. Subsequently, the paper explores the potential integration of multiple-input multiple-output and OTFS techniques. The paper further discusses the feasibility of integrating OTFS into multiple access techniques as a solution for maintaining acceptable performance in high-mobility scenarios. Then, widespread applications of OTFS in satellite communications are highlighted. Also, the potential utilization of OTFS modulation in integrated sensing and communications paradigm is thoroughly treated. In addition, the survey covers further applications of OTFS in deep learning, index modulation, underwater acoustic, and unmanned aerial vehicle communications. The paper concludes by pointing out numerous challenging and promising directions for future OTFS research.

In free-space optical satellite networks (FSOSNs), satellites can have different laser inter-satellite link (LISL) ranges for connectivity. As the LISL range increases, the number of satellites from among all the satellites in the constellation that will be needed on the shortest path between a source and a destination ground station decrease, and thereby the number of the LISLs on the shortest path decreases. Greater LISL ranges can reduce network latency of the path but can also result in an increase in transmission power for satellites on the path. Consequently, this tradeoff between satellite transmission power and network latency should be investigated, and in this work we examine it in FSOSNs drawing on the Starlink Phase 1 Version 3 (i.e., the latest version of Starlink's Phase 1) and Kuiper Shell 2 (i.e., Kuiper's biggest shell) constellations for different LISL ranges and different inter-continental connections. We use appropriate system models for calculating the average satellite transmission power (i.e., the average of the transmission power of all satellites on the shortest path) and network latency (i.e., the end-to-end latency of the shortest path). The results show that the mean network latency (i.e., the mean of network latency over all time slots) decreases and mean average satellite transmission power (i.e., the mean of average satellite transmission power over all time slots) increases with an increase in LISL range. For the Toronto–Sydney inter-continental connection in an FSOSN with Starlink's Phase 1 Version 3 constellation, when the LISL range is approximately 2,900 km, the mean network latency and mean average satellite transmission power intersect are approximately 135 ms and 380 mW, respectively. For an FSOSN with the Kuiper Shell 2 constellation in this inter-continental connection, this LISL range is around 3,800 km, and the two parameters are approximately 120 ms and 700 mW, respectively. For the Toronto–Istanbul and Toronto–London inter-continental connections, the LISL ranges at the intersection are different and vary from 2,600 km to 3,400 km. Furthermore, we analyze outage probability performance of optical uplink/downlink due to atmosphere attenuation and turbulence.

In free-space optical satellite networks (FSOSNs), satellites connected via laser inter-satellite links (LISLs), latency is a critical factor, especially for long-distance inter-continental connections. Since satellites depend on solar panels for power supply, power consumption is also a vital factor. We investigate the minimization of total network latency (i.e., the sum of the network latencies of all inter-continental connections in a time slot) in a realistic model of a FSOSN, the latest version of the Starlink Phase 1 Version 3 constellation. We develop mathematical formulations of the total network latency over different LISL ranges and different satellite transmission power constraints for multiple simultaneous inter-continental connections. We use practical system models for calculating network latency and satellite optical link transmission power, and we formulate the problem as a binary integer linear program. The results reveal that, for satellite transmission power limits set at 0.5 W, 0.3 W, and 0.1 W, the average total network latency for all five inter-continental connections studied in this work levels off at 339 ms, 361 ms, and 542 ms, respectively. Furthermore, the corresponding LISL ranges required to achieve these average total network latency values are 4500 km, 3000 km, and 1731 km, respectively. Different limitations on satellite transmission power exhibit varying effects on average total network latency (over 100 time slots), and they also induce differing changes in the corresponding LISL ranges. In the absence of satellite transmission power constraints, as the LISL range extends from the minimum feasible range of 1575 km to the maximum feasible range of 5016 km, the average total network latency decreases from 589 ms to 311 ms.

What will the wireless networks of the next generation look like? The latest advances in industrial and academic research have shed some light into that direction. With the finalization of the framework recommendation for the 6th generation (6G) networks by the International Telecommunication Union (ITU), the pillar usage scenarios, supporting capabilities and technical enablers are becoming clearer. The overarching motivation for the development of 6G is to continue to build an inclusive information society in a sustainable way. In this context, a range of user and application trends are foreseen to become an integral part of 6G, including ubiquitous intelligence, immersive multimedia and multi-sensory interactions, digital twins, digital health, smart industries, ubiquitous connectivity, integration of sensing and communication, as well as sustainability. It is worth noting that many of the trending demands do not come from the traditional markets for private mobile users and instead, they are driven by strong needs from vertical industries including manufacturing, transportation, and health care.

In the next generation (6G) wireless networks, the integration of terrestrial and non-terrestrial networks is essential to provide flawless connectivity over the globe. The vital element of this architecture is the high altitude platform station (HAPS) systems, which can provide reliable and ubiquitous connectivity among satellites, unmanned aerial vehicles (UAVs), and terrestrial users. Motivated by the importance of HAPS systems, in this paper, we provide three different use-cases for HAPS eavesdropping scenarios and investigate their physical layer security (PLS) performances. To quantify the PLS performance of the proposed setups, we perform secrecy outage probability (SOP), probability of positive secrecy (PPSC), average secrecy capacity (ASC), and secrecy throughput (ST) analyses. Furthermore, we also provide important design guidelines that can be beneficial for secure HAPS systems.

Massive swarms of low Earth orbit (LEO) satellites are poising to serve for high-speed and low-latency ubiquitous connectivity with almost global coverage. Broadband inter-satellite communication is one of the key elements of satellite communication systems that orchestrate massive satellite swarms in cooperation. Thanks to technological advancements in microelectronics and micro-systems, the terahertz (THz) band has emerged as a strong candidate for inter-satellite links (ISLs) due to its promise of wideband communication. Especially, multi-antenna systems can improve the system performance along with the wideband supported by the THz band. However, multi-antenna systems should be reconsidered due to their size, weight, and price/power (SWaP) constraints. On the other hand, as a state-of-art multi-antenna technology, reconfigurable intelligent surface (RIS) is able to relax SWaP constraints because of its passive component-based structures. However, as similar reflection characteristic throughout wideband is difficult to meet, it is possible to observe beam misalignment. In this work, we first provide an assessment of the use of the THz band for ISLs and quantify the impact of misalignment fading on error performance. Then, in order to compensate for the high path loss associated with high carrier frequencies, and to further improve the signal-to-noise ratio (SNR), we propose the use of RISs mounted on neighboring satellites to enable signal propagation. Based on a mathematical analysis of the problem, we present the error rate expressions for RIS-assisted ISLs with misalignment fading. Also, numerical results show that RIS can leverage the error rate performance and achievable capacity of THz ISLs.

The ultra-dense deployment of interconnected satellites will characterize future low Earth orbit (LEO) mega-constellations. Exploiting this towards a more efficient satellite network (SatNet), this paper proposes a novel LEO SatNet architecture based on distributed massive multiple-input multipleoutput (DM-MIMO) technology allowing ground user terminals to be connected to a cluster of satellites. To this end, we investigate various aspects of DM-MIMO-based satellite network design, the benefits of using this architecture, the associated challenges, and the potential solutions. In addition, we propose a distributed joint power allocation and handover management (D-JPAHM) technique that jointly optimizes the power allocation and handover management processes in a cross-layer manner. This framework aims to maximize the network throughput and minimize the handover rate while considering the quality-of-service (QoS) demands of user terminals and the power capabilities of the satellites. Moreover, we devise an artificial intelligence (AI)-based solution to efficiently implement the proposed D-JPAHM framework in a manner suitable for real-time operation and the dynamic SatNet environment. To the best of our knowledge, this is the first work to introduce and study DM-MIMO technology in LEO SatNets. Extensive simulation results reveal the superiority of the proposed architecture and solutions compared to conventional approaches in the literature.

The undeniable potential of computation offloading has been attracting attention from researchers for more than a decade. With advances in multi-access edge computing (MEC), computation offloading has become a more critical issue because of the heterogeneity in the computational power of edge devices and the elevated importance of extending their lifespan. Due to the apparent advantages, the use of MEC in 6G networks, where a vertical heterogeneous network composed of space, air, and ground networks is only natural. The non-terrestrial networking elements constitute effective computational resources. However, recent research investigating the potential of computational offloading in 6G networks has involved models that do not adequately reflect the complexity of the underlying processes. In this study, we propose a realistic computation model for 6G networks that considers crucial properties of the offloaded job, including the inter-dependency of the job tasks and the decomposability of the job. Our model is based on the mature application domain of MEC, where proven solutions are already studied. We also investigate the potential of a high altitude platform station (HAPS)-aided MEC platform using this model. The proposed model allows us to design offloading strategies to enable adaptive computational offloading. Through numerical analyses, we show that the proposed model provides sufficient insight to reduce the total processing time significantly.

In conventional communication systems, any interference between two communicating points is regarded as unwanted noise since it distorts the received signals. On the other hand, allowing simultaneous transmission and intentionally accepting the superposition of signals and even benefiting from it have been considered for a range of wireless applications. As prominent examples, non-orthogonal multiple access (NOMA), joint source-channel coding, and the computation codes are designed to exploit this scenario. They also inspired many other fundamental works from network coding to consensus algorithms. Especially, federated learning is an emerging technology that can be applied to distributed machine learning networks by allowing simultaneous transmission. Although various simultaneous transmission applications exist independently in the literature, their main contributions are all based on the same principle; the superposition property. In this survey, we aim to emphasize the connections between these studies and provide a guide for the readers on the wireless communication techniques that benefit from the superposition of signals. We classify the existing literature depending on their purpose and application area and present their contributions. The survey shows that simultaneous transmission can bring scalability, security, low-latency, low-complexity and energy efficiency for certain distributed wireless scenarios which are inevitable with the emerging wireless technologies.

Due to the unique channel characteristics of Terahertz (THz), comprehensive propagation channel modeling is essential to understand the spectrum and develop reliable communication systems in these bands. In this work, we propose the utilization of the hierarchical Dirichlet Process Gamma Mixture Model (DPGMM) to characterize THz channels statistically in the absence of any prior knowledge. DPGMM provides mixture component parameters and the required number of components. A revised expectation-maximization (EM) algorithm is also proposed as a pre-step for DPGMM. Kullback-Leibler Divergence (KL-divergence) is utilized as an error metric to examine the amount of inaccuracy of the EM algorithm and DPGMM when modeling the experimental probability density functions (PDFs). DPGMM and EM algorithm are implemented over the measurements taken at frequencies between 240 GHz and 300 GHz. By comparing the results of the DPGMM and EM algorithms for the measurement datasets, we demonstrate how well the DPGMM fits the target distribution. It is shown that the proposed DPGMM can accurately describe the various THz channels as well as the EM algorithm, and its flexibility allows it to represent more complex distributions better than the EM algorithm. We also demonstrated that DPGMM can be used to model any wireless channel due to its versatility.

Communications are realized as a result of successive decisions at the physical layer, from modulation selection to multi-antenna strategy, and each decision affects the performance of the communication systems. Future communication systems must include extensive capabilities as they will encompass a wide variety of devices and applications. Conventional physical layer decision mechanisms may not meet these requirements, as they are often based on impractical and oversimplifying assumptions that result in a trade-off between complexity and efficiency. By leveraging past experiences, learning-driven designs are promising solutions to present a resilient decision mechanism and enable rapid response even under exceptional circumstances. The corresponding design solutions should evolve following the lines of learning-driven paradigms that offer more autonomy and robustness. This evolution must take place by considering the facts of real-world systems and without restraining assumptions. In this paper, the common assumptions in the physical layer are presented to highlight their discrepancies with practical systems. As a solution, learning algorithms are examined by considering the implementation steps and challenges. Furthermore, these issues are discussed through a real-time case study using software-defined radio nodes to demonstrate the potential performance improvement. A cyber-physical framework is presented to incorporate future remedies.

Future integrated terrestrial, aerial, and space networks will involve thousands of low-Earth-orbit (LEO) satellites, which will form a network of mega-constellations. These mega-constellations will play a significant role in providing communication and Internet services anywhere, at any time, and for everything. Due to the large scale and highly dynamic nature of future LEO satellite networks (SatNets), their management will be a complicated process, especially the aspect of mobility management and its two components: location management and handover management. In this article, we present a comprehensive and critical review of the state-of-the-art research in location management for LEO SatNets. First, we give an overview of the Internet Engineering Task Force (IETF) mobility management standards (e.g., Mobile IPv6 and Proxy Mobile IPv6) and discuss the limitations of their location management techniques for future LEO SatNets. We highlight the mobility characteristics of future LEO SatNets and their challenging features, and we describe two unprecedented future location management scenarios. A taxonomy of existing location management solutions for LEO SatNets is also presented with solutions classified according to three approaches. The “Issues to consider” section draws attention to critical points related to each of the reviewed approaches that should be considered in future LEO SatNets location management. To identify the research gaps, the current state of LEO SatNets location management is summarized. Noteworthy future research directions are recommended. The article provides a road map for researchers and industry to shape the future of location management for LEO SatNets.

In this paper, we study the secrecy performance of mixed radio-frequency (RF) - free space optical (FSO) systems by considering both RF and FSO eavesdropper attacks. More precisely, we shed light into the design of secure mixed RF-FSO relay networks by questioning two critical design problems: 1) What are the main parameters in the design of secure RF-FSO relay networks? 2) How can we improve the confidentiality of the optical information? To do so, we derive the secrecy outage probability and the probability of positive secrecy capacity performance for mixed RF-FSO relaying schemes under RF and FSO eavesdropper attacks, respectively. To justify the problem, we consider two general fading models, Nakagami-m at the RF side and exponentiated Weibull distribution at the FSO side. The results, which are validated with the Monte-Carlo simulations, show that both the location and the size of the photo-aperture is very important in the design of RF-FSO relay networks to enhance the secrecy performance of the overall system.

Low Earth Orbit (LEO) Satellite Network (SatNet) with their mega-constellations are expected to play a key role in providing ubiquitous Internet and communications services in the future. LEO SatNets will provide wide-area coverage and support service availability, continuity, and scalability. To support the integration of SatNets and terrestrial Fifth Generation (5G) networks and beyond, the satellite communication industry has become increasingly involved with the 3rd Generation Partnership Project (3GPP) standardization activities for 5G. In this work, we review the 3GPP standardization activities for the integration of SatNets in 5G and beyond. The 3GPP use cases of SatNets are highlighted and potential requirements to realize them are summarized as well. The impacted areas of New Radio (NR) are discussed with some potential solutions. The foreseen requirements for the management and orchestration of SatNets within 5G are described. Future standardization directions are discussed to support the full integration of SatNets in Sixth Generation (6G) with the goal of ubiquitous global connectivity.

Recent advances have shown that satellite communication (SatCom) will be an important enabler for next generation terrestrial networks as it can provide numerous advantages, including global coverage, high speed connectivity, reliability, and instant deployment. An ideal alternative for radio frequency (RF) satellites is its free-space optical (FSO) counterpart. FSO or laser SatCom can mitigate the problems occurring in RF SatCom, while providing important advantages, including reduced mass, lower consumption, better throughput, and lower costs. Furthermore, laser SatCom is inherently resistant to jamming, interception, and interference. Owing to these benefits, this paper focuses on downlink laser SatCom, where the best ground station (GS) is selected among numerous candidates to provide reliable connectivity and site diversity. To quantify the performance of the proposed scheme, we derive closed-form outage probability and ergodic capacity expressions for two different practical GS deployment scenarios. Thereafter, asymptotic analysis is conducted to obtain the overall site diversity order, and aperture averaging is studied to illustrate the impact of aperture diameter on the overall performance. Furthermore, we investigate the site diversity order for a constellation of satellites that are communicating with the best GS by using opportunistic scheduling. Finally, important design guidelines that can be useful in the design of practical laser SatComs are outlined.

The fifth generation (5G) mobile networks are envisaged to enable a plethora of breakthrough advancements in wireless technologies, providing support of a diverse set of services over a single platform. While the deployment of 5G systems is scaling up globally, it is time to look ahead for beyond 5G systems. This is mainly driven by the emerging societal trends, calling for fully automated systems and intelligent services supported by extended reality and haptics communications. To accommodate the stringent requirements of their prospective applications, which are data-driven and defined by extremely low-latency, ultra-reliable, fast and seamless wireless connectivity, research initiatives are currently focusing on a progressive roadmap towards the sixth generation (6G) networks, which are expected to bring transformative changes to this premise. In this article, we shed light on some of the major enabling technologies for 6G, which are expected to revolutionize the fundamental architectures of cellular networks and provide multiple homogeneous artificial intelligence-empowered services, including distributed communications, control, computing, sensing, and energy, from its core to its end nodes. In particular, the present paper aims to answer several 6G framework related questions: What are the driving forces for the development of 6G? How will the enabling technologies of 6G differ from those in 5G? What kind of applications and interactions will they support which would not be supported by 5G? We address these questions by presenting a comprehensive study of the 6G vision and outlining seven of its disruptive technologies, i.e., mmWave communications, terahertz communications, optical wireless communications, programmable metasurfaces, drone-based communications, backscatter communications and tactile internet, as well as their potential applications. Then, by leveraging the state-of-the-art literature surveyed for each technology, we discuss the associated requirements, key challenges, and open research problems. These discussions are thereafter used to open up the horizon for future research directions.

Radio air interface identification provides necessary information for dynamically and efficiently exploiting the wireless radio frequency spectrum. In this study, a general machine learning framework is proposed for Global System for Mobile communications (GSM), Wideband Code Division Multiple Access (WCDMA), and Long Term Evolution (LTE) signal identification by utilizing the outputs of the spectral correlation function (SCF), fast Fourier Transform (FFT), auto-correlation function (ACF), and power spectral density (PSD) as the training inputs for the support vector machines (SVMs). In order to show the robustness and practicality of the proposed method, the performance of the classifier is investigated with respect to different fading channels by using simulation data. Various over-the-air real- world measurements are taken to show that wireless signals can be successfully distinguished from each other without any prior information while accounting for a comprehensive set of parameters such as different kernel types, number of in-phase/quadrature (I/Q) samples, training set size, or signal-to-noise ratio (SNR) values. Furthermore, the performance of the proposed classifier is compared to the existing well-known deep learning (DL) networks. The comparative performance of the proposed method is also quantified by classification confusion matrices and Precision/Recall/F1-scores. It is shown that the investigated system can be also utilized for spectrum sensing and its performance is also compared with that of cyclostationary feature detection spectrum sensing.

Sharing a secret key between two physically separated nodes, Alice and Bob, is possible through the use of quantum key distribution (QKD) techniques. In the presence of an eavesdropper, Alice's key may not be identical with Bob's key, due to the characteristics of a quantum channel. To obtain identical keys at Alice and Bob, we propose a block-based key verification protocol that relies on Newton's polynomial interpolation. As the nodes solely share random numbers and indices of the removed blocks, no information is revealed about the secret message, at a cost of higher computational complexity. The error propagation through the key verification process is prevented by the characteristics of the proposed approach.

Orthogonal frequency division multiplexing (OFDM) technique is the most used approach in various wireless communication technologies due to its implementation advantages. However, OFDM has also some significant drawbacks, such as the sensitivity against real-time impairments and the poor peakto-average power ratio (PAPR) performance. These drawbacks decrease the usage potential of OFDM in future networks. Recent OFDM alternatives, which have been proposed in 5G waveform research activities, can provide limited improvements and these mostly include modified filtering operations when compared to the OFDM. In this paper, as a novel and flexible approach, superposition coding is adopted to OFDM, and superposition coded-OFDM (SC-OFDM) is proposed. By exploiting superposition coding as a new transmission dimension, an adaptive waveform solution that solves the PAPR problem without creating any inefficiency is provided. At the same time, throughput or error performance, and sensitivity against realtime impairments can also be improved. Features for each problem are proposed within the SC-OFDM approach. Performances of each SC-OFDM features are measured with extensive computer simulations and real-time experiments. Real-time experiments are realized by using software defined radio nodes and these are compared with the computer simulation results. To the best of authors' knowledge, such a comprehensive waveform design is proposed for the first time in the literature. As observed with the results, SC-OFDM can meet the requirements of future communication technologies.

In this paper, to quantify the field performance of a live long term evolution (LTE) network, we design and implement a multi-layered performance monitoring system. This monitoring system delivers an accurate and thorough picture of the network behavior including switching, cellular, transmission, IP, and data networks. The designed system enables measurement results gathered from different network layers and from both user and control planes through a mediation platform, paving the way for the collection of synchronous performance measurement results, including latency, handover ratios, and throughput from network entities. Network performance metrics and the terminal-based measurement are jointly reported to reflect the subscriber perspective. Two field trials are conducted to highlight performance results of LTE networks, in a congested multi-cell with release 12 support, and a sparsely populated cell with release 14 support. Different multiple-input multiple-output (MIMO) configurations, including spatial multiplexing, transmit diversity, beamforming, and $64\times 64$ massive MIMO support, along with a selection of bandwidths and frequency bands are considered. The measurement results show that, without any significant latency cost, using more antenna elements provides higher user throughput, which also affects the overall cell throughput. However, doubling the number of antennas may not necessarily double the average data rates. Additionally, the average intrafrequency and interfrequency handover success ratios are observed to be acceptable, hence the changes among the selected the diversity and multiplexing technique does not have a visible deteriorating effect on the handover performance.

Orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM) technique has been recently proposed to provide performance improvements over conventional OFDM. OFDM-IM includes a different data transmission mechanism, where additional data bits are transmitted over subcarrier patterns by specifically activating selected subcarriers and nulling the others. However, such a mechanism inherently causes some inefficiency due to the inactive subcarriers. To improve the spectral efficiency of the OFDM-IM technique, dual-mode OFDM with index modulation (DM-OFDM) is proposed, where nulled subcarriers are activated by using a second signal constellation. With DM-OFDM, a significant data rate improvement can be obtained. As an important missing issue in the literature, OFDM-IM and its effective variations, such as DM-OFDM, have only been studied in terms of computer simulations and theoretical analysis. Therefore, their real-time performance is not yet investigated to assess their potential for next-generation networks. Addressing this gap, in this paper, OFDM-IM and DM-OFDM techniques are implemented in real-time by using software defined radio technology. National Instruments USRP-2921 nodes are used in a single-input single-output configuration. With this implementation, detailed real-time results and performance observations are provided. Moreover, a hybrid OFDM-IM (H-OFDM-IM) scheme, which can be seen as the combination of OFDM-IM and DM-OFDM, is proposed by targeting the limitations of both OFDM-IM and DM-OFDM in terms of spectral containment and error performance. With H-OFDM-IM, noticeable improvements in spectral containment and error performance can be obtained, and these observations show its suitability for real-time use and next-generation networks. With comprehensive computer simulation and test results, these claims are verified.

In this paper, we propose a novel probabilistic localization approach that relies on a Metropolis-Hastings (MH) algorithm-based Bayesian approach to visible light communication (VLC) systems. Due to the usage of the MH algorithm from Markov chain Monte Carlo methods, the positioning capability of the proposed approach becomes more robust against varying channel propagation conditions and measurement uncertainties. The validity of the proposed approach is demonstrated by numerical analyses based on simulations in 3-D indoor environments in a comparative manner with the least square (LS) and the differential LS algorithms-based localization solutions, while circumventing the shortcomings of LS-based approaches. Addressing the short range challenge in the VLC-based positioning system, an efficient hybrid localization framework is also developed for multi-tier heterogeneous networks (HetNets), jointly considering VLC and radio frequency networks. Our methodology mainly considers independent positioning solution branches that each estimate the target location by utilizing the MH-based Bayesian approach. Based on simulation results, the proposed framework for multi-tier HetNets provides a robust performance. Overall, we show that with the new VLC localization scheme, the performance in the short range is enhanced, while with HetNets the effectiveness of the localization in the long range is improved.

In forthcoming years, the Internet of Things (IoT) will connect billions of smart devices generating and uploading a deluge of data to the cloud. If successfully extracted, the knowledge buried in the data can significantly improve the quality of life and foster economic growth. However, a critical bottleneck for realizing the efficient IoT is the pressure it puts on the existing communication infrastructures, requiring transfer of enormous data volumes. Aiming at addressing this problem, we propose a novel architecture dubbed Condense which integrates the IoT-communication infrastructure into the data analysis. This is achieved via the generic concept of network function computation. Instead of merely transferring data from the IoT sources to the cloud, the communication infrastructure should actively participate in the data analysis by carefully designed en-route processing. We define the Condense architecture, its basic layers, and the interactions among its constituent modules. Furthermore, from the implementation side, we describe how Condense can be integrated into the Third Generation Partnership Project (3GPP) machine type communications (MTCs) architecture, as well as the prospects of making it a practically viable technology in a short time frame, relying on network function virtualization and software-defined networking. Finally, from the theoretical side, we survey the relevant literature on computing atomic functions in both analog and digital domains, as well as on function decomposition over networks, highlighting challenges, insights, and future directions for exploiting these techniques within practical 3GPP MTC architecture.

With the development of sensor technologies, various application areas have emerged. The usage of these technologies and exploitation of recent improvements have clear benefits on building applications. Such use-cases can improve smart functions of buildings and can increase the end-user comfort. As a similar notion, building automation systems (BAS) are smart systems that target to provide automated management of various control services and to improve resource usage efficiency. However, buildings generally contain hardware and control services from a diverse set of characteristics. The automated and central management of such functions can be challenging. In order to overcome such issues, an Emergency Evacuation Service is proposed for BAS, where requirements of such central management model are analyzed and model content and subservice definitions are prepared. A crucial scenario, which could be a necessity for future BAS, is defined and an approach for evacuation of people in the buildings at emergency situations is proposed. For real-life scenarios, the Evacuation Service is implemented by using a low-cost design, which is appropriate for Internet of Things (IoT) based BAS applications. As demonstrated, the proposed service model can provide effective performance in real-life deployments.