Wi-Fi Nodes Research Articles

Coexist WiFi for ZigBee Networks With Fine-Grained Frequency Approach

The widely deployed WiFi APs and ZigBee devices make the coexistence for these two networks more pervasive than ever. Previous solutions focus on the contention resolution in time domain, but would lead to the underutilized frequency resources. However, for frequency domain schemes, to enable efficient coexistence for WiFi and ZigBee networks, the WiFi nodes or ZigBee nodes have to select the appropriate channel for transmission. Such scheme will need strict cooperations among these two independent systems, and could not work with the conventional legacy systems seamlessly. In this paper, we propose a frequency overlay approach named COFFEE (COexist wiFi For zigbEE networks), where subcarriers interfering with ZigBee transmissions are nullified by WiFi. According to our basic evaluations, due to the relatively robust feature in WiFi/OFDM design, nullifying small portion of subcarriers would affect the WiFi performance slightly, but could improve the capability for coexistence significantly. Thus by using COFFEE, WiFi and ZigBee nodes can transmit their packets concurrently without any coordination. Also, COFFEE and conventional legacy WiFi systems could work together seamlessly. Furthermore, we implement COFFEE with USRP software radio platform and evaluate the performance under real wireless network scenarios. The extensive evaluations show that compared to the coexistence schemes in time domain, COFFEE is able to increase the network throughput by more than 300%. Even when the ZigBee node never knows the transmission time of WiFi packet, it still can provide concurrent lossless transmission by using COFFEE with only 10% to 15% WiFi throughput reduction.

Cooperative LBT Design and Effective Capacity Analysis for 5G NR Ultra Dense Networks in Unlicensed Spectrum

With the rapidly increasing demand of data traffic in fifth-generation (5G) wireless systems, various sophisticated techniques have been developed to cope with the demand. New radio-unlicensed (NR-U) technology is one of the most promising techniques to address the exponential growth of data traffic. At the same time, NR base stations are densely deployed in 5G. Therefore, large numbers of NR-U base stations attempt to access the unlicensed spectrum. Although listen before talk (LBT) with random backoff can guarantee fairness, it can also increase the collision probability. For the IEEE 802.11 Wi-Fi networks, a contention-based random access protocol is adopted, which cannot guarantee the Quality of Service (QoS). To overcome these problems, a new LBT protocol, referred to as cooperative LBT, is designed, in which zero forcing (ZF) precoding is applied to suppress the multi-user interference. Based on the new LBT protocol, a (N+3)-state semi-Markovian model is established to characterize the effective capacity of NR-U in unlicensed bands, where N is the number of NR-U base stations. An expression for the effective capacity is obtained, which is a function of QoS, instantaneous transmit rate, the number of Wi-Fi nodes, and NR-U base stations. The influences of the finite backhaul and transmit power on the effective capacity are also analyzed in this paper. The simulation results show that the usage of cooperative communication can reduce the collision probabilities from 0.4928 to 0.1632 and increase the effective capacities by 220.04%. The cooperative LBT protocol has a more compelling advantage for 5G NR ultradense deployment scenarios.

Precision local positioning mechanism in underground mining using IoT-enabled WiFi platform

ABSTRACTInternet of Things (IoT) connects many physical devices to many individuals from earth to space. This new concept covers almost all applications such as smart cities, industries, autonomous systems, and underground setups. This article summarizes the application of IoT-driven wireless nodes and IoT decision support platform in underground mining areas where location estimation of the miners is a critical task for the mining administrators. The underground mining accident is one of the most critical environmental disasters where life risk of the miners is a very crucial factor to be addressed. There are very few research work reported to find real-time location of the miner without any Global Positioning System (GPS) and mobile signals. This work demonstrates an efficient local positioning mechanism where low-cost and high battery capacity WiFi nodes are used to find the location of the miner during crude environmental conditions. The whole local positioning system works on the basis of Receiver Signal Strength Indicator (RSSI) value of the miner nodes. This article also demonstrates the useful technique to increase the battery life more than one year. Apart from all the above technological uses, it has been proposed that the localization algorithm can be used as potential technological key for local positioning in underground mines.

Spatial and Time Domain Model for LAA/Wi-Fi Coexistence

In Release 13 of the 3rd Generation Partnership Project standard, the deployment of long-term evolution (LTE)/ LTE-advanced to the unlicensed spectrum called licensed-assisted access (LAA) was introduced to satisfy the high demand of traffic data with a new type of services mostly multimedia streams. The unlicensed spectrum is a shared resource between different radio access terminals such as Wi-Fi and radar system, and listen before talk (LBT) in LTE side makes this coexistence possible. In this letter, we propose a new framework to model and evaluate the performance of LAA/Wi-Fi coexistence based on marked Poisson point process (MPPP) and Markov chain model. The proposed model captures the back-off procedure in the spatial and time domain to provide a more realistic analysis of the channel busy probability and the signal to interference plus noise ratio coverage probability. Numerical results show the validity of the proposed model with the overestimation of the LAA and Wi-Fi nodes density in MPPP model.

E-LBT: an Enhanced Listen Before Talk Mechanism for Collision Avoidance in an LTE-U and WiFi Coexistence System

This paper considers the hidden-node problem in downlink transmission of an LTE-U and WiFi coexistence system operating in unlicensed bands. An enhanced LTE-U node structure is first presented, in which a WiFi module is introduced in an LTE-U eNB, and the RRC and MAC functional blocks in both LTE-U eNB and LTE-U UE are redefined. The purpose is to enable information exchange between an LTE-U node and a WiFi node in order to handle the hidden-node problem. Based on the enhanced LTE-U node structure, an enhanced listen-before-talk (e-LBT) mechanism is further presented, which incorporates an RTS/CTS handshaking procedure in the basic LBT mechanism. To support RTS/CTS handshaking, the relevant information that needs to be exchanged between e-MACWiFi in the WiFi module and e-RRC in the LTE-U module of an LTE-U node is identified, and the message format to be exchanged between e-MACWiFi and e-RRC is defined. Simulation results show that the proposed e-LBT mechanism can significantly improve the performance of the coexistence system in terms of the LTE-U system throughput and WiFi system throughput as compared with the basic LBT mechanism.

Shape adaptive DCT compression for high quality surveillance using wireless sensor networks

Wireless surveillance networks consists of numerous camera and sensor node to transmit the surveillance details from a remote location to the user nodes. Large amount of information transmitted via the sensor nodes are non-priority information like the background which never changes throughout the surveillance time. This non priority information requires more space and is of no use in transmitting so this information can be compressed to the maximum level without affecting the quality of the image transmitted. For efficient transmission of the input data it is important that only Region of Interest (ROI) is transmitted with lower compression ratio and the non ROI regions to be compressed as much as possible. In this proposed work a shape adaptive DCT compression and Decompression scheme is proposed for efficient image data transmission over the wireless sensor networks. The frames from the surveillance sensor networks are acquired and the ROI is calculated using dynamic saliency maps. The image is then divided into two parts, the transmitting node performs the shape adaptive DCT on the image and transmits the image to the user node where the decompression is done using the inverse shape adaptive DCT. The performance of the proposed algorithm is tested on the set of video images and performance is tabulated for the quality of image and current consumption when the compressed image is transmitted by sender ENTDEV019 ESP 8266 WiFi MCU node and received by receiver ENTDEV019 ESP 8266 WiFi node.

Self-interference suppression improvement by employing circular polarized antennas

This paper presents a novel method for suppressing the self-interference due to multipath in WiFi nodes of full-duplex systems based on employing two circular polarized antennas. Three different techniques have been used in order to suppress the interference generated by the direct wave: antenna separation, antenna pattern and analogue cancellation circuit comprised of a balun, a phase shifter and a variable attenuator. As a result, an initial isolation of 90dB was achieved inside an anechoic chamber. In order to beat the multipath interference circular polarization was employed. With the aim of analyzing the robustness of the circular polarization in comparison with the linear one, the self-interference between transmitter and receiver was measured in nine different environments. The measured level of self-interference was also compared with the results achieved inside the anechoic chamber. In this way, the degradation of the self-interference suppression due to multipath was evaluated. Results show better isolation when employing circularly polarized antennas in seven of nine environments. In addition, with the circular polarization self-interference suppression higher than 70dB was achieved independently of the environment.

Embedding LTE-U within Wi-Fi Bands for Spectrum Efficiency Improvement

Driven by growing spectrum shortage, Long-term Evolution in unlicensed spectrum (LTE-U) has recently been proposed as a new paradigm to deliver better performance and experience for mobile users by extending the LTE protocol to unlicensed spectrum. In the paper, we first present a comprehensive overview of the LTE-U technology, and discuss the practical challenges it faces. We summarize the existing LTE-U operation modes and analyze several means for LTE-U coexistence with Wi-Fi medium access control protocols. We further propose a novel hyper access-point (HAP) that integrates the functionalities of LTE small cell base station and commercial Wi-Fi AP for deployment by cellular network operators. Our proposed LTE-U access embedding within the Wi-Fi protocol is non-disruptive to unlicensed Wi-Fi nodes and demonstrates performance benefits as a seamless and novel LTE and Wi-Fi coexistence technology in unlicensed band. We provide results to demonstrate the performances advantage of this novel LTE-U proposal.

Development of WiFi Mesh Infrastructure for Internet of Things Applications

This paper described the design of WiFi mesh infrastructure in order to improve the performance of an ad hoc network, WLAN, and WMAN so that the interconnection becomes easier and cheaper. The built system consisting of some WiFi routers were configured to form a WiFi mesh network so that it can build the Internet cloud. The operating system used in this research is quick mesh project (QMP). In addition, the WiFi node as a client developed for the internet of things (IoT) applications. These nodes using message queuing protocol telemetry transport (MQTT) based publish and subscribe. WiFi mesh infrastructure is working well with the average value of the measured throughput was 110.5 kbps.

A Stochastic Optimization Framework for Adaptive Spectrum Access and Power Allocation in Licensed-Assisted Access Networks

Licensed-assisted access (LAA) has been becoming a promising technology to the supplementary utilization of the unlicensed spectrum. However, due to the densification of small base stations (SBSs) and the dynamic variation of the number of Wi-Fi nodes in the overlapping areas, the licensed channel interference and the unlicensed channel collision could seriously influence the quality of service and the energy consumption. In this paper, jointly considering time-variant multi-wireless-channel conditions and random numbers of Wi-Fi nodes, we address an adaptive spectrum access and power allocation problem that enables the minimization of the system power consumption under a certain queue stability constraint in the LAA-enabled SBSs and Wi-Fi networks. The complex stochastic optimization problem has been decomposed as a modified Hungarian algorithm and a difference of two convex algorithm in the framework of Lyapunov optimization. We also characterize the performance bounds of the proposed algorithm with a tradeoff of [O(1/V), O(V)] between power consumption and delay theoretically. The numerical results verify the tradeoff and show that our scheme can reduce the power consumption over the existing scheme by up to 73.3% under the same traffic delay.

A Framework for Co-Channel Interference and Collision Probability Tradeoff in LTE Licensed-Assisted Access Networks

Small cell deployment in heterogeneous networks, whereby small cell base stations (SBS) are deployed alongside traditional macro-cell base stations, is a proven solution for enhancing spatial frequency reuse across licensed spectrum in long-term evolution (LTE) networks. In order to mitigate the shortage of licensed spectrum resources, licensed-assisted access (LAA) has been introduced to allow LTE SBSs to share the unlicensed channel with WiFi nodes. As such, a complex yet interesting optimization problem results from the joint utilization of licensed and unlicensed spectrum resources by the SBSs to meet the quality-of-service (QoS) requirements of small cell users (SUEs). In this paper, we highlight the fundamental tradeoff induced by the SBSs between the amount of co-channel interference (CI) resulting from the reuse of licensed spectrum resources and the collision probability (CP) imposed on the co-existing WiFi nodes due to the sharing of unlicensed spectrum resources in such a coexisting LTE LAA-WiFi heterogeneous network deployment. We find that this fundamental tradeoff can be analyzed by developing a power allocation rule with double water-filling lines and the complete set of Pareto optimal solution can be achieved by the weighted Tchebycheff method. Our simulation results show that the proposed joint resource allocation algorithm can achieve a flexible and suitable tradeoff between the licensed spectrum CI and the WiFi CP according to the QoS requirements of SUEs in LTE LAA networks.

Integration of Wi-Fi mobile nodes in a Web of Things Testbed

Abstract The Internet of Things (IoT) is supposed to connect billions of devices to the Internet through IP-based communications. The main goal is to foster a rapid deployment of Web-enabled everyday objects, allowing end users to manage and control smart things in a simple way, by using Web browsers. This paper focuses on the integration of Wi-Fi nodes, hosting HTTP resources, into a Web of Things Testbed (WoTT). The main novelty of the proposed approach is that the WoTT integrates new nodes by using only standard mechanisms, allowing end-users to interact with all Smart Objects without worrying about protocol-specific details.

Wireless sensor node modelling for energy efficiency analysis in data-intensive periodic monitoring

Data-intensive wireless sensor applications, such as remote visual inspection using high-resolution video sensors, require a special design approach in order to save energy and prolong lifetime of a battery-powered wireless sensor node. This study is motivated by searching for the most efficient communication protocol for high-resolution image transmission in environmental monitoring sensor networks, where data should be transmitted periodically, but relatively rarely (usually once or twice per day). Some previous publications propose ZigBee or Wi-Fi as suitable candidates for data-intensive wireless transmission, but the literature lacks a systematic study that would provide a guidance for designing such systems. We construct a measurement-based model of a wireless sensor node with emphasis on the communication unit. We measured the energy consumption of commercially available wireless ZigBee and Wi-Fi modules, as well as the influence of the interface bandwidth limitation that reduces their energy efficiency. The model includes real-world communication channel properties that at high bit-rates reduce the communication range and increase the energy consumption due to a higher susceptibility to noise.Our results show that in scenarios when the node sends up to 64kB of data per session once per day, the estimated lifetime of a ZigBee node is up to 10% longer than of a Wi-Fi node. However, when the amount of data per session increases, the Wi-Fi wins due to its higher energy efficiency during data transfer. When the data amount reaches 10MB, the lifetime of a Wi-Fi node using UDP protocol is 5 times longer than that of a ZigBee node. On the other hand, the Wi-Fi node lifetime decreases with increasing number of sessions per day, because the connection establishment with the access point is very energy consuming. As a result, when 5 sessions per day are required the ZigBee node can offer 40% longer lifetime than the Wi-Fi node when 10kB of data is transmitted per session.

Taming Cross-Technology Interference for Wi-Fi and ZigBee Coexistence Networks

Recent studies show that Wi-Fi interference has been a major problem for low power urban sensing technology ZigBee networks. Existing approaches for dealing with such interferences often modify either the ZigBee nodes or Wi-Fi nodes. However, massive deployment of ZigBee nodes and uncooperative Wi-Fi users call for innovative cross-technology coexistence without intervening legacy systems. In this work, we investigate the Wi-Fi and ZigBee coexistence when ZigBee is the interested signal. Typically, the duration of transmitting a ZigBee data packet is longer than that of a Wi-Fi packet. Mitigating short duration Wi-Fi interference (called flash ) in long duration ZigBee data (called smog ) is challenging. To address these challenges, we propose ZIMO: a sink-based MIMO design for harmony coexistence of ZigBee and Wi-Fi networks with the goal of protecting the ZigBee data packets from being interfered by high-power cross-technology signals. The key insight is to properly exploit opportunities resulted from differences between Wi-Fi and ZigBee, and bridge the gap between interested data and cross technology signals. Also, extracting the channel coefficient of Wi-Fi and ZigBee will enhance other coexistence technologies such as TIMO [1] . We implement a prototype in GNURadio-USRP N200, and our extensive evaluations under real wireless conditions show that ZIMO can improve ZigBee network throughput up to 1.9 $\times$ , with 1.5 $\times$ in media, and 1.1 $\times$ to 1.9 $\times$ for Wi-Fi network as byproduct in ZigBee signal recovery.

Lifetime Bounds of Wi-Fi Enabled Sensor Nodes

Wireless sensor and actuator networks are often deployed in areas that already have a wireless infrastructure. Coexisting in this infrastructure is a challenge, as the used communication techniques interfere. Instead of fighting to fit in, one could try to tap into the existing infrastructure. This solves the coexistence problem, does not require new infrastructure and makes the integration of systems trivial. To determine the feasibility of such a solution, our work focuses on analysing energy consumption and power management policies of Wi-Fi enabled nodes based on recent hardware. Our analysis shows that for some tasks, Wi-Fi nodes are becoming a viable option and it may not be necessary to retain the current practice of deploying and maintaining specialised wireless sensor and actuator networks.

WizSync: Exploiting Wi-Fi Infrastructure for Clock Synchronization in Wireless Sensor Networks

Time synchronization is a fundamental service for wireless sensor networks (WSNs). Although a number of message passing protocols can achieve satisfactory synchronization accuracy, they suffer poor scalability and high transmission overhead. An alternative approach is to utilize the global time references such as those induced by GPS and timekeeping radios. However, they require the hardware receiver to decode the out of band clock signal, which introduces extra cost and design complexity. This paper proposes a novel WSN time synchronization approach by exploiting the existing Wi-Fi infrastructure. Our approach leverages the fact that 802.15.4 sensors and Wi-Fi nodes often occupy the same or overlapping radio frequency bands in the 2.4 GHz unlicensed spectrum. As a result, a 802.15.4 node can detect and synchronize to the periodic beacons broadcasted by Wi-Fi access points (APs). A key advantage of our approach is that, due to the long communication range of Wi-Fi, a large number of 802.15.4 sensors can synchronize clock rates to the same beacons without any message exchange. This paper makes several key contributions. First, we experimentally characterize the spatial and temporal characteristics of Wi-Fi beacons in an enterprise Wi-Fi network consisting of over 50 APs deployed in a 300,000 square foot office building. Motivated by our measurement results, we design a novel synchronization protocol called WizSync. WizSync employs digital signal processing (DSP) techniques to detect periodic Wi-Fi beacons and use them to calibrate the frequency of native clocks. WizSync can intelligently predict the clock skew and adaptively schedules nodes to sleep to conserve energy. We implement WizSync in TinyOS 2.1.1 and conduct extensive evaluation on a testbed consisting of 19 TelosB motes. Our results show that WizSync can achieve an average synchronization error of 0.12 milliseconds over a period of 10 days with radio power consumption of 50.9 microwatts/node.

Wi-Fi multi-floor indoor positioning considering architectural aspects and controlled computational complexity

This paper focuses on the positioning of Wi-Fi nodes in multi-floor indoor environments. A target radio-frequency (RF) fingerprint – measured by the MS to be localized – is compared with georeferenced RF fingerprints, previously stored in a correlation database (CDB). Therefore, this strategy lies within the so-called Database Correlation Methods (DCM) used to locate mobile stations (MS) in wireless networks. To obtain best matches in terms of architectural structures such as floors, doors, aisles, among others, the authors apply two combined techniques that improve localization accuracy: unsupervised clustering (K-medians and Kohonen layer) and majority voting committees of backpropagation artificial neural networks (ANNs). The unsupervised clustering is employed to allow collected data (the fingerprints) to group freely in their natural space, without precluding – through the imposition of architectural constraints – any natural arrangement of the collected fingerprints. The proposed combined strategy improves floor identification accuracy, which in indoor multi-floor positioning must be high. The effects of the proposed solution on the DCM positioning accuracy are experimentally evaluated using actual measured data. In the trial the floor identification accuracy ranged from 91% to 97%, and the average 2D positioning error ranged from 4.5 to 1.7m, depending on the size of the measurement window (from 1 to 25 samples).

Comparison of two routing metrics in OLSR on a grid based mesh network

Predicting the performance of ad hoc networking protocols for mesh networks has typically been performed by making use of software based simulation tools. Experimental study and validation of such predictions is a vital to obtaining more realistic results, but may not be possible under the constrained environment of network simulators. This paper presents an experimental comparison of OLSR using the standard hysteresis routing metric and the ETX metric in a 7 by 7 grid of closely spaced Wi-Fi nodes to obtain more realistic results. The wireless grid is first modelled to extract its ability to emulate a real world multi-hop ad hoc network. This is followed by a detailed analysis of OLSR in terms of hop count, routing traffic overhead, throughput, delay, packet loss and route flapping in the wireless grid using the hysteresis and ETX routing metric. It was discovered that the ETX metric which has been extensively used in mesh networks around the world is fundamentally flawed when estimating optimal routes in real mesh networks and that the less sophisticated hysteresis metric shows better performance in large dense mesh networks.

Comparison of MANET Routing Protocols Using a Scaled Indoor Wireless Grid

Predicting the performance of ad-hoc networking protocols has typically been performed by making use of software based simulation tools. Experimental study and validation of such predictions is vital to obtaining more realistic results, but may not be possible under the constrained environment of network simulators. This paper presents experimental comparisons of routing protocols using a 7×7 grid of closely spaced WiFi nodes. It firstly demonstrates the usefulness of the grid in its ability to emulate a real world multi-hop ad-hoc network. It specifically compares hop count, routing traffic overhead, throughput, delay and packet loss for three protocols which are listed by the Internet Engineering Task Force Mobile Ad-hoc Networks (MANET) working group. These are the Ad-hoc on demand distance vector routing protocol (AODV), the optimized link state routing protocol (OLSR) and the dynamic MANET on demand routing protocol (DYMO).