Network slicing is a key enabler for providing differentiated service support to heterogeneous use cases and applications in 5G and beyond networks through creating multiple logical slices. Resource management for satisfying diverse requirements of slices is a highly challenging task under time-varying traffic and wireless channel conditions. This paper presents a deep reinforcement learning (DRL) based xApp for dynamically managing the service level agreements (SLAs) of network slices, eliminating the need for human-in-the-loop decision-making. The proposed xApp is implemented within an open source mobile network emulator to create an O-RAN compliant end-to-end 5G network capable of dynamic resource management capabilities. The intelligent resource management xApp operates on the RAN Intelligent Controller (RIC), enabling monitoring and dynamic resource control of the gNodeB through the E2 interface. The proof-of-concept experiment results demonstrate that the trained DRL model deployed on the RIC platform is successfully utilized to manage the key performance indicators of the network slices.

This paper evaluates the performance of reconfigurable intelligent surface (RIS) optimization algorithms, which utilize channel estimation methods, in ray tracing (RT) simulations within urban digital twin environments. Beyond Sionna's native capabilities, we implement and benchmark additional RIS optimization algorithms based on channel estimation, enabling an evaluation of RIS strategies under various deployment conditions. Coverage maps for RIS-assisted communication systems are generated through the integration of Sionna's RT simulations. Moreover, real-world experimentation underscores the necessity of validating algorithms in near-realistic simulation environments, as minor variations in measurement setups can significantly affect performance.

There is a growing interest in codebook-based beam-steering for millimeter-wave (mmWave) systems due to its potential for low complexity and rapid beam search. A key focus of recent research has been the design of codebooks that strike a trade-off between achievable gain and codebook size, which directly impacts beam search time. Statistical approaches have shown promise by leveraging the likelihood that certain beam directions (equivalently, sets of phase-shifter configurations) are more probable than others. Such approaches are shown to be valid for static, non-rotating transmission stations such as base stations. However, for the case of user terminals that are constantly changing orientation, the possible phase-shifter configurations become equally probable, rendering statistical methods less relevant. On the other hand, user terminals come with a large number of possible steering vector configurations, which can span up to six orders of magnitude. Therefore, efficient solutions to reduce the codebook size (set of possible steering vectors) without compromising array gain are needed. We address this challenge by proposing a novel and practical codebook refinement technique, aiming to reduce the code book size while maintaining array gain within$\gamma\ \mathbf{dB}$of the maximum achievable gain at any random orientation of the user terminal. We project that a steering vector at a given angle could effectively cover adjacent angles with a small gain loss compared to the maximum achievable gain. We demonstrate experimentally that it is possible to reduce the codebook size from 102416to just a few configurations (e.g., less than ten), covering all angles while maintaining the gain within$\gamma=3\ \mathbf{dB}$of the maximum achievable gain.

arinc664 is one of the most popular Ethernet-based deterministic network(dtn)technologies for safety-critical avionics systems. A typicalarinc 664network can support several thousands of Virtual Links (vls), each of which has hundreds of thousands of combinations for its configuration. Orthogonal Arrays (oas) method is a formalism to generate a test suite with a feasible size and a desired coverage of features for complex systems. Since the test space fordtnfeatures is prohibitively large, a single application ofoas may inadvertently eliminate many combinations of two-way interactions. In this paper, we propose to develop a test automation system that uses multiple and consecutive applications ofoas to generate test configurations fordtn. The test factors representingdtnconfiguration parameters are divided into two groups, where the first group includes the number ofvls passing through each port while the second group includes the configuration parameters forvls. Then,oas are constructed sequentially for each group such that an output element of the firstoais used as one of the inputs for the secondoa. We present a system architecture for a test automation system capable of verifying real-time network operations, where the outputs of the chainedoas are utilized to generate executable test scripts includingdtnconfigurations and traffics. As a case study, a test automation system is successfully implemented forarinc 664switch. Note to Practitioners—Safety-critical avionics networks with a large number of configuration parameters need to be tested rigorously. Exhaustive testing of all possible configurations is not realistic since there are time and resource constraints. Therefore, a chained orthogonal array is proposed to create different sub-configuration spaces of the test parameters fordtn. An automation system is mandatory to generate the repeatable test cases fast and make them simpler to implement and run. In this article, a test automation system from generating the test cases using the chained orthogonal arrays to carrying out the tests on the prototype system is presented. We believe that the concepts presented in this article can be utilized by other researchers developing a test automation for complex systems having a large number of parameters.

This paper investigates the error performance of Reconfigurable Intelligent Surfaces (RIS) assisted communication systems employing two prominent space-time coding techniques, namely Space-Time Block Coding (STBC) and Space-Time Line Coding (STLC), under time-selective fading channels. The STBC (STLC) network comprises a single base station (BS) with two (one) transmit antenna(s) and a user equipment (UE) with one (two) receive antenna(s), respectively. A RIS with N elements facilitates communication between the BS and the UE, particularly in scenarios without Line-of-Sight (LOS) channels. Simulation results reveal that time-selective fading significantly degrades the error performance of space-time coding techniques. However, utilizing RIS in "Intelligent" mode mitigates these adverse effects by applying necessary phase shift adjustments, thereby improving system reliability in fast-fading environments. In contrast, in "Blind" mode, the results indicate that the RIS has a minimal impact on improving error performance under fast-fading channel conditions.

The utilization of millimeter wave frequency bands is expected to become prevalent in the following communications systems. However, generating and transmitting communication signals over these frequencies are not as straightforward as in sub-6 GHz frequencies due to complex transceiver structures. As an alternative to conventional transmitter architectures, this paper investigates the implementation of time modulated arrays to effectively modulate and transmit high-quality communication signals at millimeter wave frequencies. By exploiting the array structures and analog beamformers, which are the fundamental components of millimeter wave transmitters, secure and low-cost transmission can be achieved. Though, harmonics of theoretically infinite bandwidth arise as fundamental problem in this approach. Thus, this paper presents a frequency analysis tool for the time-modulated arrays with hardware impairments and shows how controlling the sampling period can reduce the harmonics. Furthermore, the derived results are experimentally verified at 25 GHz with two important remarks. First, the phase error of received signals can be reduced by 32% using the proposed architecture. Second, the harmonics can be significantly suppressed by the correct choice of sampling period for the given hardware.

Reconfigurable holographic surfaces (RHSs) for multi-beam steering applications have been receiving significant attention due to their low fabrication cost and power consumption. RHSs have the advantage of exploiting more antenna elements by configuring only their radiation levels, as opposed to the typical phased antenna arrays which enable the control of each element's phase and amplitude. RHSs can be utilized to realize holographic beamforming with single-feed or multi-feeds, where digital beamforming can also be implemented using multi-feeds. In this paper, first, the holographic beamforming problem is formulated by means of the conventional beamforming expressions using the array factor and the holographic beamforming weights. Then, a zero-forcing beamforming method is developed for a single-feed RHS to generate multi-beam and multi-null patterns. Additionally, a bisectional null scanning approach for beam sweeping is presented to exploit the advantages of RHS for forming wide nulls in the beamspace. Simulation results imply a substantial advantage of such single-feed RHS for high-accuracy beam sweeping.

Reconfigurable Intelligent Surfaces (RISs) are becoming one of the fundamental building blocks of next-generation wireless communication systems. To that end, RIS phase configuration optimization is an important issue, where finding the most suitable configuration becomes a challenging and resource-consuming task, especially as the number of RIS elements increases. Since exhaustive search is not practical, iterative algorithms are utilized to determine the RIS configuration by sequentially considering all RIS elements, where the best-performing phase shift configuration is obtained for each element. However, each configuration attempt requires receiver performance feedback, leading to higher delay and signaling overhead. Thus, in this paper, a convolutional neural network (CNN) based solution is formulated to rapidly find the phase configurations of the RIS elements. The simulation results for a RIS with 40×40 elements imply that the proposed algorithm reduces the number of steps dramatically e.g., from 3200 to 160 for the particular setup. Furthermore, such improvement in complexity is achieved with a slight degradation in performance.

This paper presents field measurement-based channel characterization for air–to–ground (A2G) and air–to– air (A2A) wireless communication systems using two drones equipped with lightweight software-defined radios. A correlation-based channel sounder is employed such that the transmitting drone broadcasts the sounding waveform with a pseudo-noise sequence and the receiving drone captures the sounding waveform together with the location information for the post-processing analysis. The path loss results demonstrate that the measurement and flat-earth two-ray results have similar trends for A2G while the measurement and free space path loss are similar to each other for A2A. The time delays between the direct path and multipath components are widely spread for A2A while the multipath components are mostly concentrated around the direct path for A2G generating a more challenging communication environment. We observe that the reflections from several buildings having metal roofs and claddings on the measurement site cause sudden peaks in the root-mean-square delay spread. The results indicate that the A2A channel has better characteristics than the A2G under similar mobility conditions.

There have been recently many studies demonstrating that the performance of wireless communication systems can be significantly improved by a reconfigurable intelligent surface (RIS), which is an attractive technology due to its low power requirement and low complexity. This paper presents a measurement-based characterization of RISs for providing physical layer security, where the transmitter (Alice), the intended user (Bob), and the eavesdropper (Eve) are deployed in an indoor environment. Each user is equipped with a software-defined radio connected to a horn antenna. The phase shifts of reflecting elements are software controlled to collaboratively determine the amount of received signal power at the locations of Bob and Eve in such a way that the secrecy capacity is aimed to be maximized. An iterative method is utilized to configure a Greenerwave RIS prototype consisting of 76 passive reflecting elements. Computer simulation and measurement results demonstrate that an RIS can be an effective tool to significantly increase the secrecy capacity between Bob and Eve.

ARINC 664, which is a heavily used protocol for modern avionics networks, is preferred due to its simplicity although its mixed-criticality support is limited. Time Triggered Ethernet (TTEthernet), and IEEE Time Sensitive Networking (TSN), which utilize time synchronized schedule, are more suitable for supporting mixed-criticality applications; however, both require a fault tolerant time synchronization that makes the certification process more challenging. In this paper, we propose a novel dynamic priority assignment (DPA) concept together with the burst limiting shaper (BLS) from the IEEE TSN standard to enhance the schedulability and the mixed-criticality support of ARINC 664. The decision of flow re-assignment to a new priority class is done by calculating the high priority (HP) and low priority (LP) class worst-case delays using the network calculus framework. The numerical results show that the class utilization rates can be significantly increased by using the DPA concept with and without the BLS while the deadline constraints for all classes are satisfied. Thus, the DPA can improve the schedulability and mixed-criticality of ARINC 664 without using any time synchronization mechanism.

The strict Quality of Service requirements of real-time services in communication networks necessitate the fast recovery from link/node failures by activating alternate paths which avoid the failed component. Multi Topology Routing (MTR) based IP Fast Re-Route (IPFRR) technologies rely on virtual topologies (VTs) to seamlessly forward the IP packets during network failures. In this paper, we implement a new MTR based IPFRR technique for Software Defined Networks (SDN) which uses the Multiple Routing Configurations method to construct VTs. Our approach leads to self-recovering SDN against failures. Out preliminary results show that our approach considerably reduces the failure recovery time compared to the reactive recovery process in SDN.

Network Function Virtualization (NFV) is utilized to simplfy the deployment and management of constantly evolving and highly complex networking services. In this paper, we propose a dynamic load management framework for IMS networks using NFV, where IMS functions are created within a single virtual machine (VM) instance and moved to the cloud environment. Requests coming from the IMS clients are first processed by a Load Balancer module to efficiently distribute the incoming load over a pool of IMS VMs. The decision of switching an IMS VM instance on or off is performed by the VM provisioning service using the resource utilization information periodically received from the IMS VMs. The proof-of-concept experiments using a realistic testbed demonstrate that the proposed framework increases the scalability of the IMS networks when there are sudden significant increases in traffic.

Along with the widespread usage of mobile devices supporting multiple radio interfaces, users can connect to the mobile operator's network using different access technologies such as UMTS, WLAN and WiMAX/LTE. Depending on the network conditions and the QoS requirements of users, the usage of the right technology at the right time can provide more effective networking with higher data rate, lower cost, longer battery duration, and higher coverage area. To enable this networking effectiveness, a seamless handover mechanism to minimize service disruption is required. IEEE 802.21, which defines a set of standards for media independent handover, is capable of realizing both horizontal and vertical handovers. In this paper, a new algorithm is proposed to provide energy efficient handovers among UMTS, WiMAX, and WLAN networks. The proposed algorithm is implemented within the IEEE 802.21 framework and its performance analysis is performed using the ns-2.29 simulator. Simulation results show that the proposed algorithm significantly increases the service duration and hence decreases packet losses by dynamically changing the video downloading rate according to handover decisions and the remaining battery power levels.

To seamlessly support real-time services such as voice and video over next generation IP networks, routers must continue their forwarding tasks in case of link/node failures by limiting the service disruption time to sub-100 ms. IETF Routing Area Working Group (RTGWG) has been working on standardizing IP Fast Reroute (IPFRR) methods with a complete alternate path coverage. In this paper, a trade-off analysis of Multi Topology Routing (MTR) based IPFRR technologies targeting full coverage, namely Multiple Routing Configurations (MRC) and Maximally Redundant Trees (MRT), are presented. We implemented a comprehensive analysis tool to evaluate the performance of MRC and MRT mechanisms on various synthetic network topologies. The performance results show that MRT's alternative path lengths are not scalable with respect to the network size and density while the alternative path lengths of MRC only slightly change as the network size and density vary. We believe that this is an important scalability result providing a guidance in the selection of MTR-based IPFRR mechanism for improving the availability in ISP networks.

Time varying channel conditions with high bit error rate causes frequent packet corruptions in wireless communication networks. Cyclic Redundancy Checks (CRCs) and Automatic Repeat reQuest (ARQ) mechanisms are heavily used for effective error detection and recovery, respectively. In previous studies, the performance of CRC generator polynomials is evaluated solely based on Undetected Error (UE) probability without taking retransmission and overhead dynamics into account. This paper presents a new performance evaluation criterion (i.e., link layer goodput) which takes both CRC coding and ARQ dynamics into account. The proposed criterion is used as an objective function to compute the best polynomial and message length pairs corresponding to varying network conditions. We, then, propose an adaptive CRC coding mechanism which dynamically updates the CRC polynomial and message length pair at run-time in accordance with the time varying conditions. Simulation experiments show that dynamic selection of CRC polynomial and message length pair yields significant performance gains.

We present a force-based genetic algorithm for self-spreading mobile nodes uniformly over a geographical area. Wireless mobile nodes adjust their speed and direction using a genetic algorithm, where each mobile node exchanges its genetic information of speed and direction encoded in its chromosomes with the neighboring nodes. Simulation experiments show encouraging results for the performance of our force-based genetic algorithm with respect to normalized area coverage..

The existing naming schemes for pooling resources are suitable only for static networks. We propose dynamic survivable resource pooling (DSRP) that provides a survivable naming scheme to the pool users in mobile ad-hoc networks. DSRP dynamically places the name servers (NSs) on a virtual backbone (VB): a highly distributed, scalable, and survivable mesh network formed and maintained through one-hop beacons. In this paper, DSRP focuses on pooling resources such as servers and services that are common in robotics and battlefield applications. It provides an abstraction of all the functionally equivalent servers, whereby the client can access these servers as a single entity, termed server pool. A distributed backbone mesh of NSs is used to propagate service registrations, requests, and replies.