Coexistence Capability Research Articles

Autonomous Interference Mapping for Industrial Internet of Things Networks Over Unlicensed Bands: Identifying Cross-Technology Interference

The limited coexistence capabilities of current Internet-of-things (IoT) wireless standards produce inefficient spectrum utilization and mutual performance impairment. The entity of the issue escalates in industrial IoT (IIoT) applications, which instead have stringent quality-of-service requirements and exhibit very-low error tolerance. The constant growth of wireless applications over unlicensed bands mandates then the adoption of dynamic spectrum access techniques, which can greatly benefit from interference mapping over multiple dimensions of the radio space. In this article, the authors analyze the critical role of real-time interference detection and classification mechanisms that rely on IIoT devices only, without the added complexity of specialized hardware. The trade-offs between classification performance and feasibility are analyzed in connection with the implementation on low-complexity IIoT devices. Moreover, the authors explain how to use such mechanisms for enabling IIoT networks to construct and maintain multidimensional interference maps at run-time in an autonomous fashion. Lastly, the authors give an overview of the opportunities and challenges of using interference maps to enhance the performance of IIoT networks under interference.

Spectrum Sharing for Massive Access in Ultra-Narrowband IoT Systems

Ultra-narrowband (UNB) communications has become a signature feature for many emerging low-power wide-area (LPWA) networks. Specifically, using extremely narrowband signals helps the network connect more Internet-of-things (IoT) devices within a given band. It also improves robustness to interference, extending the coverage of the network. In this article, we study the coexistence capability of UNB networks and their scalability to enable massive access. To this end, we develop a stochastic geometry framework to analyze and model UNB networks on a large scale. The framework captures the unique characteristics of UNB communications, including the asynchronous time-frequency access, signal repetition, and the absence of base station (BS) association. Closed-form expressions of the transmission success probability and network connection density are presented for several UNB protocols. We further discuss multiband access for UNB networks, proposing a low-complexity protocol. Our analysis reveals several insights on the geographical diversity achieved when devices do not connect to a single BS, the optimal number of signal repetitions, and how to utilize multiple bands without increasing the complexity of BSs. Simulation results are provided to validate the analysis, and they show that UNB communications enables a single BS to connect thousands of devices even when the spectrum is shared with other networks.

An Experimental Study of Sub-1 GHz Frequency-Hopping-Based 6LoWPAN Mesh Networking for Smart-Grid Applications

This paper presents an experimental study of a multihop Internet Protocol Version 6 over Low-Power Wireless Personal Area Networks (6LoWPAN)-based mesh system that uses un-slotted channel hopping (USCH) medium access control (MAC). Designers of wireless smart-grid networks are using (or looking to use) the Sub-1 GHz spectrum, given its longer radio range compared to the traditional 2.4 GHz spectrum used in Wi-Fi® or Bluetooth® low energy. The frequency-hopping (FH) technique is attractive in this area, as it provides improved robustness and longer range owing to the higher transmission power that regulatory requirements allow. Although Sub-1 GHz allows for a longer range, smart-grid networks deployed over a large geographic area still require multiple hops to provide the required coverage. Many proprietary and standards-based solutions have been proposed to implement such a networking protocol. Notable specifications in this area include the Field Area Networks (FAN) specification from the Wi-SUN (smart utility networks) Alliance and the JupiterMesh specification from the Zigbee Alliance. Little is known about the performance of FH systems over a multihop network, however. This paper presents an implementation of an FH-based multihop networking protocol based on the Texas Instruments (TI) SimpleLink™ TI 15.4-stack, with an experimental study of such a system over multiple hops compared to a non-frequency-hopping (non-FH) system. Results show that the proposed FH-based 6LoWPAN mesh system significantly improves network coverage, network capacity, and communication robustness to interference while demonstrating coexistence capabilities.

Dense Deployment of BLE-Based Body Area Networks: A Coexistence Study

The issues of cross-technology interference and coexistence in the unlicensed 2.4-GHz spectrum band among various technologies including WiFi, ZigBee, and classic Bluetooth have been studied extensively. However, it remains relatively understudied for Bluetooth low energy (BLE), especially in densely deployed scenarios. In this paper, we develop a testbed to conduct our experimental studies, focusing on BLE and its coexistence capabilities when being deployed in a dense environment, under possible interference from WiFi and ZigBee/IEEE 802.15.4. One scenario of interest is a network of several co-located BLE-based BANs, each of which is designed in a star topology with one gateway and multiple BLE sensor nodes. The second scenario represents a highly heterogeneous network where each BAN now carries both BLE and ZigBee sensors, while being exposed to interference from external WiFi transmission. Experiments are carried out on our testbed, which are built based on low-cost, light-weight off-the-shelf components and state-of-the-art BAN protocols. Our results show that the performance of BLE is relatively robust to interference from other BLE transmissions as well as those from nearby ZigBee and WiFi devices. In addition, the deployment of the testbed on human bodies results in no performance degradation for the network.

Methodology of cooperative spectrum sensing and dynamic access to the channels in WSN

Cognition into wireless sensors is a current paradigm to improve the performance of wireless sensor networks (WSN) and the efficient use of the radio frequency spectrum. The classic static allocation of the radio frequency bands causes coexistence problems or underutilization of resources. This issue could be addressed using cognitive sensors with dynamic spectrum allocation. Therefore, a novel methodology for cooperative spectrum sensing and dynamic access to the channels (MSDAC) for a cluster of a WSN is proposed in this article. The MSDAC proposal aims the asynchronous coordination and communication between the cluster sensors in a simple way based on reinforcement-learning for home automation applications. Additionally, a set of experiments are formulated to evaluate and to compare the proposal. The experiments are based on a case study with a wireless local area network acting as primary user and a secondary network with burst traffic formed by IEEE 802.15.4 devices performing the MSDAC. The results show an improvement in the message delivery ratio and in the coexistence capability when MSDAC is used. In addition, the lowest amount of message retransmissions causes a reduction in the sensor active time when compared with other approaches, which is beneficial for energy saving.

Extending LTE into the Unlicensed Spectrum: Technical Analysis of the Proposed Variants

The commercial success of LTE and the resulting growth in mobile data demand have urged cellular network operators to strive for new innovations. LTE in unlicensed spectrum has been proposed to allow cellular network operators to offload some of their data traffic by accessing the unlicensed 5 GHz frequency band. Currently, there are three proposed variants for LTE operation in the unlicensed band, namely LTE-U, licensed assisted access (LAA), and MulteFire. This article provides a comparative analysis of these variants and explains the current regulations of the 5 GHz band in different parts of the world. We present the technical details of the three proposed versions and analyze them in terms of their operational features and coexistence capabilities to provide an R&D perspective for their deployment and coexistence with legacy systems.

A Study on Coexistence Capability Evaluations of the Enhanced Channel Hopping Mechanism in WBANs.

As an important coexistence technology, channel hopping can reduce the interference among Wireless Body Area Networks (WBANs). However, it simultaneously brings some issues, such as energy waste, long latency and communication interruptions, etc. In this paper, we propose an enhanced channel hopping mechanism that allows multiple WBANs coexisted in the same channel. In order to evaluate the coexistence performance, some critical metrics are designed to reflect the possibility of channel conflict. Furthermore, by taking the queuing and non-queuing behaviors into consideration, we present a set of analysis approaches to evaluate the coexistence capability. On the one hand, we present both service-dependent and service-independent analysis models to estimate the number of coexisting WBANs. On the other hand, based on the uniform distribution assumption and the additive property of Possion-stream, we put forward two approximate methods to compute the number of occupied channels. Extensive simulation results demonstrate that our estimation approaches can provide an effective solution for coexistence capability estimation. Moreover, the enhanced channel hopping mechanism can significantly improve the coexistence capability and support a larger arrival rate of WBANs.

A wireless communication system for energy and environmental monitoring

Abstract. Custom-fit communication systems are key elements in modern cyber-physical sensor systems. Therefore a wireless communication system (WCS) for sensor/actuator communication has been developed to facilitate energy and environmental monitoring on the shop floor of industrial production sites. Initially, the distinct demands and requirements are described. As the WCS has been designed for new installations as well as for retrofitting already installed facilities, the WCS has to be able to coexist with other wireless communication systems already allocated in the same frequency band. The WCS handles measurement data from both, energy-autarkic sensors and fast line-powered sensors. Mobile users in the field equipped with mobile devices are served by the system, too. A modular hardware concept has been chosen for easy system modification or for the integration of new wireless standards. Finally, measured results for the coexistence capability are presented.

Implementation of a noise-coexistence threshold logic architecture on a GaAs-based nanowire FET network

Toward reconfigurable and noise-coexistence information processing system utilizing nanostructures, we study a threshold logic circuit and a double threshold function using a GaAs-based nanowire field-effect transistor (FET) network. A noise coexistence capability is based on a noise-assisted state transition in a threshold function in a threshold logic element. We fabricate a circuit reconfigurable between NAND and NOR functions. A hysteresis transfer characteristic with double threshold is realized in the GaAs nanowire by using a silicon nitride (SiN) as the gate insulator. We introduce a unique inverter design using the SiN-gate FET as a load to achieve the transfer characteristic with clockwise hysteresis, similar to a Schmitt trigger.

Adaptive data distribution technique for enhancing MB-OFDM UWB link performance in detect and avoid environments

Detect-and-avoid (DAA) mechanisms were developed to minimise potential interference caused by ultra wideband (UWB) systems to in-band active narrowband links. Interference is reduced by minimising emitted power in overlapping bands to create a spectral notch, which provides a certain level of isolation between both systems. Although it has been proved that this procedure deteriorates UWB link performance significantly, no research suggested any scheme to mitigate it. In this paper, we introduce the adaptive data distribution (ADD) technique, which we developed to enhance UWB link performance upon employment of DAA. ADD technique is confined to the physical layer and is fully transparent to the MAC sub-layer. Results have shown a significant reduction in error rates that could provide an SNR gain of at least 4 dB for most covered scenarios. In addition, ADD technique renders performance less sensitive to transmission mode variation and augments its coexistence capability by enabling a UWB device to safely notch 16-55% of its bandwidth.

Performance Evaluation of WiMAX Broadband from High Altitude Platform Cellular System and Terrestrial Coexistence Capability

The performance obtained from providing worldwide interoperability for microwave access (WiMAX) from high altitude platforms (HAPs) with multiple antenna payloads is investigated, and the coexistence capability with multiple-operator terrestrial WiMAX deployments is examined. A scenario composed of a single HAP and coexisting multiple terrestrial WiMAX base stations deployed inside the HAP coverage area (with radius of 30 km) to provide services to fixed users with the antenna mounted on the roof with a directive antenna to receive signals from HAPs is proposed. A HAP cellular configuration with different possible reuse patterns is established. The coexistence performance is assessed in terms of HAP downlink and uplink performance, interfered by terrestrial WiMAX deployment. Simulation results show that it is effective to deliver WiMAX via HAPs and share the spectrum with terrestrial systems.