The Open Radio Access Network (O-RAN) initiative, characterized by open interfaces and AI/ML-capable RAN Intelligent Controller (RIC), facilitates effective spectrum sharing among RANs. In this context, we introduce AdapShare, an ORAN-compatible solution leveraging Reinforcement Learning (RL) for intent-based spectrum management, with the primary goal of minimizing resource surpluses or deficits in RANs. By employing RL agents, AdapShare intelligently learns network demand patterns and uses them to allocate resources. We demonstrate the efficacy of AdapShare in the spectrum sharing scenario between LTE and NR networks, incorporating real-world LTE resource usage data and synthetic NR usage data to demonstrate its practical use. We use the average surplus or deficit and Jain's fairness index to measure the RL system's performance in various scenarios. AdapShare outperforms a quasi-static resource allocation scheme based on long-term network demand statistics, particularly when available resources are scarce or exceed the aggregate demand from the networks. Lastly, we present a high-level O-RAN-compatible architecture using RL agents, which demonstrates the seamless integration of AdapShare into real-world deployment scenarios.

The Open Radio Access Network (O-RAN), an industry-driven initiative, utilizes intelligent Radio Access Network (RAN) controllers and open interfaces to facilitate efficient spectrum sharing between LTE and NR RANs. In this paper, we introduce the Proactive Spectrum Adaptation Scheme (ProSAS), a data-driven, O-RAN-compatible spectrum sharing solution. ProSAS is an intelligent radio resource demand prediction and management scheme for intent-driven spectrum management that minimizes surplus or deficit experienced by both RANs. We illustrate the effectiveness of this solution using real-world LTE resource usage data and synthetically generated NR data. Lastly, we discuss a high-level O-RAN-compatible architecture of the proposed solution.

Sidelink in cellular networks enables direct exchange of data packets between devices without the need for network infrastructure, resulting in various benefits, including communication in out-of-coverage areas and possible decrease in latency by a considerable extent. Thus, sidelink is a favorable choice for applications like public safety communications and Vehicle-to-Everything (V2X) communications. As 4G Long Term Evolution (LTE) advanced to 5G New Radio (NR) under the Third Generation Partnership Project (3GPP), several new features were introduced to sidelink, such as two-stage Sidelink Control Informations (SCIs), data and control multiplexing, and feedback-based Hybrid Automatic Repeat Request (HARQ) with a configurable maximum number of transmissions. To conduct extensive NR sidelink link-level evaluations, a comprehensive simulation platform is essential. In this paper, we introduce the first publicly accessible 5G NR Link-Level Simulator (LLS) that supports major 5G NR sidelink features and complies with the 3GPP standards. This MATLAB-based simulator allows for flexible control over various Physical Layer (PHY) configurations, facilitating customized simulations on algorithm development and performance evaluations. We discuss the simulator’s structure and the sidelink features implemented in detail and evaluate the 5G NR sidelink performance using the developed simulator. Our simulation results indicate that the Block Error Rate (BLER) curves are insensitive to error-prone 2nd-stage Sidelink Control Information (SCI2) and number of Resource Blocks (RBs) allocated; however, the sidelink communication range is sensitive to the deployment environment. We also highlight the need for a careful choice of numerology, device power class and HARQ configuration to balance performance metrics for a variety of services based on 5G NR sidelink deployment scenarios.

Since the Third Generation Partnership Project (3GPP) specified 5G New Radio (NR) sidelink in Release 16, researchers have been expressing increasing interest in sidelink in various research areas, such as Proximity Services (ProSe) and Vehicle-to-Everything (V2X). It is essential to provide researchers with a comprehensive simulation platform that allows for extensive NR sidelink link-level evaluations. In this paper, we introduce the first publicly accessible 5G NR link-level simulator that supports sidelink. Our MATLAB-based simulator complies with the 3GPP 5G NR sidelink standards, and offers flexible control over various Physical Layer (PHY) configurations. It will facilitate researcher's exploration in NR sidelink with a friendly access to the key network parameters and great potential of customized simulations on algorithm developments and performance evaluations. This paper also provides several initial link-level simulation results on sidelink using the developed simulator.

With the need to serve multiple users intended for the same content, especially in mission-critical applications, multicast has long been studied with evolving standards. Compared with its counterpart unicast, multicast has an apparent advantage of sending one copy instead of multiple copies. However, in Long Term Evolution (LTE) Multicast-Broadcast Single-Frequency Network (MBSFN), multicast does not support Multiple Input Multiple Output (MIMO) technology, which is one major technology that improves unicast performance significantly. Multicast also differs from unicast in other aspects that have major performance impacts, such as constructive signals and significant interference reduction, no retransmissions, less available subframes, extended cyclic prefix, and denser reference signals, to name a few. While almost all existing work focuses on a single factor and few addresses MIMO, in this paper we study multicast and unicast in detail with all these factors included, together with their integrated impact on performance. Profound analysis reveals that, contrary to what is commonly assumed in existing studies, multicast and unicast would not share the same modulation and coding scheme, but rather differ significantly in how efficiently they use resources. In addition, the balance among various factors mentioned above leads to a switch point where multicast or unicast outperforms, and the switch point changes upon system configurations and the performance metric of interest. Given that multicast configuration is semi-static in LTE, the results provide insightful guidelines in unicast or multicast deployment in serving user traffic. The work can also be easily extended to other Single-Frequency Network (SFN) based multicast technologies.

The Third Generation Partnership Project (3GPP) defines various pre-configured channel parameters for the Long-Term Evolution (LTE) Device-to-Device (D2D) communications with Physical Sidelink (SL) Channels. In this paper, we investigate the impacts of channel parameter settings on the performance of content deliveries for Public Safety Network (PSN) applications in Out-of-Coverage (OOC) scenario. We first measure the reliability of the SL channels under various sets of channel parameters using Monte Carlo simulations. Then, for a given PSN application, the acquired reliability results are utilized to help determining the amount of delay that is to be introduced to the system, such that the throughput requirement for the application is assured during the transmissions. To the best of our knowledge, this is the first LTE D2D work that focuses on OOC mission-critical communications performance in group traffic settings. Our results are valuable to both network operators, for using them as references in selecting a best set of channel parameters, and to future studies on more complex transmission patterns and network scenarios using D2D communications in PSNs.

Public safety incidents typically involve a significant amount of group traffic and have a stringent requirement of connection reliability. Hence multicast could potentially improve network and user performance significantly, which triggered our study on Long-Term Evolution (LTE) Multicast Broadcast Single Frequency Network (MBSFN). In this paper, we first derive a realistic MBSFN Signal-to-Interference-plus-Noise Ratio (SINR) analytical model, with multiple antennas, multipath channel, and equalizer considered. Then through comprehensive system level simulations, we compare MBSFN and unicast in terms of resource efficiency v.s. throughput, as well as outage probability. We also study the impacts of MBSFN size and quantify the MBSFN SINR improvement due to diversity combining and interference reduction, respectively.

Proximity Services (ProSe) and Wi-Fi are two promising technologies that may provide support for Mission Critical Voice (MCV) applications in remote and rural areas by enabling Device-to-Device (D2D) communication. In this paper, several performance metrics of ProSe and Wi-Fi are evaluated and compared side-by-side under various configurations. The ns-3 simulation results show that ProSe outperforms Wi-Fi in terms of coverage range and access time with a medium traffic load, while Wi-Fi has a shorter access time under a light traffic load. In addition, with various user densities, ProSe offers better coverage range and access time a majority of the time. The evaluation in this paper provides insights to first responders on what to expect with either technology and how to improve the performance by adjusting different system parameters.

In many public safety scenarios, Device-to-Device (D2D) communication should be capable of handling out-of-coverage situations, ensuring that D2D devices can communicate directly without the aid of network infrastructure. In this paper, we investigate a set of distributed resource allocation schemes for out-of-coverage D2D group communication. Particularly, we first provide guidelines concerning how to allocate D2D resources based on Modulation and Coding Scheme (MCS), Physical Resource Block (PRB) size, and Time Resource Pattern (TRP) to meet the Quality of Service (QoS) requirements of applications. We then design three distributed resource allocation schemes that select PRBs in the resource pool and/or adjust the transmitting power based on the level of available information about the network. To evaluate the designed distributed resource allocation schemes, we conduct extensive performance evaluation, validating their effectiveness in a variety of deployment scenarios.

Public safety incidents typically involve significant amount of group traffic. This paper initializes our study in exploring the potential spectrum savings and improvement in first responders experience by using Multicast Broadcast Single Frequency Network (MBSFN) to serve group traffic among first responders. Towards this goal, this paper proposes a comprehensive methodology that closely follows The 3rd Generation Partnership Project (3GPP) specifications and considers unicast multiple-input multiple-output (MIMO) and MBSFN without MIMO. High fidelity Block Error Rate (BLER) curves for both MBSFN and unicast are generated, and Signal-to-noise ratio (SNR) points to switch Channel Quality Indicators (CQIs) are extracted and analyzed. Several simulation scenarios have been designed and the empirical results are analyzed.

Public safety organizations around the world started migrating toward Long-Term Evolution (LTE) networks to support the increasing needs for video and data. To address the unique voice communication requirements of first responders, the 3rd Generation Partnership Project (3GPP) introduced new capabilities that aim at providing similar functionalities as the traditional Land Mobile Radio (LMR) systems, namely, Direct Mode communication and mission critical push-to-talk (MCPTT). Direct Mode communication, also called Proximity Services (ProSe), allows public safety users to communicate directly with each other regardless of the network status. MCPTT was the first mission critical service, and first application, standardized by 3GPP to provide both on- and off-network voice capability. Assessing the performance of those capabilities is critical to accelerate their deployment and adoption by first responders. In this study, we evaluate the performance of an off-network mode MCPTT device over ProSe by focusing on the access time, a measure of the delay incurred before a user can talk. We develop analytical models for various types of calls and verify the accuracy of the predicted access time using ns-3 simulations. We perform sensitivity analysis to show the validity of the models for various scenarios. Finally, we show how the models can be used to guide parameter configuration for both MCPTT and ProSe to optimize the performance.

In order to support the increasing demand for capacity in cellular networks, Long Term Evolution (LTE) introduced Proximity Services (ProSe) enabling Device-to-Device (D2D) communications, defining several services to support such networks. We are interested in the performance in out-of-coverage scenarios of one of these services: direct discovery. As defined in the standard, network and configuration parameters for direct discovery are predefined and do not change over time, which creates an inability to adjust to variations in topologies, number of operating devices, and/or users' mobility during the discovery process. In this paper we propose an enhanced discovery algorithm that, building on previous works, allows users to adapt to potential variations in the discovery group, using optimized transmission probabilities and transmission success probabilities. The performance of this algorithm is evaluated, and we demonstrate gains in the accuracy of the discovery information, and in the time required for discovery.

This paper examines the performance of the Long Term Evolution (LTE) Physical Sidelink Shared Channel (PSSCH) in out-of-coverage (OOC) device- to-device (D2D) communication scenarios. We develop a closed form expression for the distribution of the number of User Equipments (UEs) that successfully decode a message sent on the PSSCH, given the number of UEs that received the transmitter's Sidelink Control Information (SCI) message over the Physical Sidelink Control Channel (PSCCH). We validate our results using Monte Carlo simulations of the PSSCH and network simulations in ns-3, and discuss some of the effects of system parameters on performance.

In this paper, we access the performance of a Device-to-Device (D2D) communication link. Particularly, we design a framework to evaluate performance with respect to coverage probability and average throughput. Our modeling framework considers a variety of D2D deployment scenarios (i.e., Outdoor-to-Outdoor, Outdoor-to-Indoor, and Indoor-to-Indoor), channel effects (i.e., path loss, shadowing, and small-scale fading), and system parameters (i.e., resource block size, fixed Modulation and Coding Scheme (MCS) versus adaptive MCS, and transmit power). For the defined scenarios, we derive mathematical expressions for the coverage probability and average throughput as a function of the distance between two D2D user equipments. Based on the designed framework, we conduct an extensive performance evaluation of the D2D communication link under various D2D deployment scenarios with varying channel effects. We also evaluate the impact of system parameters, including Physical Resource Block (PRB) size, fixed/adaptive MCS, and transmit power, on the performance of D2D communication links. Our results demonstrate the expected performance that can be achieved in practical D2D scenarios.

Long Term Evolution Advanced (LTE-A) introduces a new feature called Proximity Services (ProSe) that enables device-to-device (D2D) communication between User Equipment (UE), including the capability to operate out-of-coverage. In order to establish a D2D communication link the UEs need to be synchronized. In out-of-coverage scenarios, the synchronization is performed in a distributed manner by the UEs. In this paper, we studied problems associated with the simultaneous execution of the synchronization procedure by LTE-A D2D-enabled UEs operating out-of-coverage. In particular, we focused on detection and convergence problems resulting from the half-duplex constraint and periodic scheduling. We showed that if two transmitter UEs are acting as synchronization references and they perform the procedure too close in time, convergence to a synchronized state is not possible. Moreover, the periodic triggering of the procedure will make the problematic condition persistent in time. We proposed an effective algorithm that prevent these problems, or resolve them in a reasonable time. We considered the protocol and requirements specified in the LTE-A standard, and we evaluated the performance of the proposed algorithm using system level simulations.

User Equipments (UEs) that send data must advertise the upcoming transmission by broadcasting signaling messages over the Physical Sidelink Control Channel (PSCCH). Thus, it is important for the network operator to define the PSCCH resource pool to maximize the probability that each UE will be able to successfully decode all of the control messages that appear on the PSCCH. For UEs operating in Mode 2 (i.e., outside the coverage area of an eNodeB), this is especially challenging because there is no base station present that can assign PSCCH resources. UEs must choose pool resources randomly, which can lead to collisions of transmitted messages. In addition, UEs are half-duplex and a poorly designed control channel resource pool can create a significant risk that a signaling message and its duplicate will be missed by a UE that transmits its own signaling message in the same pair of subframes. In this paper, we present an analytical model that allows us to develop closed form expressions for the distribution of the number of UEs that successfully receive a transmitted message on the PSCCH. This model can support PSCCH design by network operators, and can be used to investigate other aspects of D2D communications.

Device-to-device (D2D) communications for Long Term Evolution (LTE) networks relies on a discovery process to enable User Equipment (UE) to determine which D2D applications and services are supported by neighboring UEs. This is especially important for groups of UEs that operate outside the coverage area of any base station. The amount of time required for discovery information to reach every UE in a group depends on the number of UEs in the group and the dimensions of the discovery resource pool associated with the Physical Sidelink Discovery Channel (PSDCH); an additional factor is the half-duplex property of current UEs. In this paper, we use a Markov chain to characterize the performance of Mode 2 direct discovery. The resulting analytical model gives the distribution of the time for a UE to discover all other UEs in its group. We validate the model using Monte Carlo and network simulations.

In this paper we study and improve one service used for Proximity Services and Device-to-Device (D2D) communications: D2D Direct Discovery. As defined in the Third Generation Partnership Project, for both in-coverage and out-of-coverage cases, resource pool parameters, including the transmission probability (in UE-Selected mode), are configured in advance. This means that they are independent of the network conditions and the number of users. Thus, we propose an adaptive algorithm which takes into account the available resources and the number of nearby users as they are being discovered, and adapts the transmission probability accordingly. This algorithm improves the overall performance of the discovery process. It reduces the time needed to complete the discovery within a group of UEs and makes it dynamic and adaptable to changing environments.

The introduction of Proximity services (ProSe) in Long Term Evolution Advanced (LTE-A) allows User Equipments (UEs) to communicate directly without routing the data through the LTE access network. This is a major step towards supporting mission-critical communication for first responders who need the ability to communicate ubiquitously. To properly receive data, the UEs must be synchronized. Thus, reducing the synchronization delays is important to avoid service disruption. When operating outside of the network coverage, UEs cannot rely on the synchronization information provided by the base station. In such cases, a distributed protocol is required to announce and detect the synchronization information within devices in proximity. In this paper, we present an adaptive algorithm that reduces the out-of-coverage synchronization delays while meeting the requirements specified in the LTE-A standard. The algorithm takes into account the UE traffic and synchronization conditions to achieve these goals. We evaluate the algorithm performance using our ns-3 ProSe implementation and show that fast convergence time to a synchronized state can be achieved using the proposed algorithm while satisfying the standard performance constraints.

The National Public Safety Telecommunications Council (NPSTC) has defined resiliency as the ability of a network to withstand the loss of assets and to recover quickly from such losses. How to measure the resiliency of a base station deployment is an important consideration for network planners and operators. In this paper, we propose a resiliency measurement method in conjunction with a performance metric such as coverage or supported throughput, where we define the resiliency as the maximum number of sites that can fail before the metric falls below a minimum acceptable threshold. Because the number of combinations of failures increases exponentially with respect to the number of sites in a given deployment, we introduce an algorithm that generates estimates of the lowest, highest, and average values of the metric for a given failure count while examining a subset of the possible failure combinations. We use an example deployment to demonstrate how the resiliency metric can be used to identify sites that have a disproportionate impact on performance; the network planner can harden these sites or, for a future deployment, adjust the site placement to reduce the effect of the high-impact sites.

In this paper we study the performance of the authentication process in media independent handovers and consider the impact of using IEEE 802.21 link triggers to achieve seamless mobility. We describe all interactions between the 802.21 services and the authentication in order to achieve timely and seamless handovers.

We explore the use of the Media Independent Information Service (MIIS) in the IEEE 802.21 Media Independent Handover (MIH) framework to improve handover performance for Fast Mobile IPv6 by providing Authentication information. We explore the tradeoffs of Pre-Authentication before joining a new network versus authentication after connecting to a new network during a Fast Mobile IPv6 handover. We discuss our implementations of services available from the MIIS in simulation using the ns-2 simulation system and evaluate their performance.

The media independent handover (MIH) architecture is designed to facilitate the signaling and enable seamless handovers in heterogeneous networks. In this paper, we propose a solution using the stream control transmission protocol (SCTP) to efficiently carry MIH messages. The solution uses SCTPpsilas multihoming and multistreaming capabilities along with cross-layer information available through the MIH. We analyze the performance of the proposed solution for various packet loss conditions.