---
title: "A Solar-Powered and Multi-Tiered Mesh Node for a Portable in Situ Emergency Response System"
url: "https://maker.wiznet.io/mayuri/projects/a-solar-powered-and-multi-tiered-mesh-node-for-a-portable-in-situ-emergency-response-system/"
markdown_url: "https://maker.wiznet.io/mayuri/projects/a-solar-powered-and-multi-tiered-mesh-node-for-a-portable-in-situ-emergency-response-system/md"
type: "UCC: User Created Content"
author: "Adam Matthews"
author_url: "https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=2021&context=etd"
editor: "WIZnet"
editor_url: "https://maker.wiznet.io/"
original_author: "Adam Matthews"
original_url: "https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=2021&context=etd"
published: "2022-10-12"
language: "en"
hardware: ["WIZnet WizFi220"]
likes: 10
views: 905
comments: 0
source: "WIZnet Makers (https://maker.wiznet.io/)"
---

# A Solar-Powered and Multi-Tiered Mesh Node for a Portable in Situ Emergency Response System

> The aftermath of a natural disaster is typically characterized by lack of a reliable medium for dissemination of information to survivors.

Original author: Adam Matthews (source: https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=2021&context=etd)

## Components

- **WIZnet WizFi220** x 1 ([docs](https://docs.wiznet.io/Product/Wi-Fi-Module/WizFi210))

## Article

I. INTRODUCTION With natural disasters and other calamities on the rise in recent years, there is a growing need for a reliable post-disaster communication infrastructure to provide survivors with emergency relief information. Disasters such as earthquakes, tornados, hurricanes, snow storms, and floods claim the lives of thousands of people (and rising) in the United States every year [11]. The majority of these casualties reportedly occur after the disaster has taken place [61], many of which could be avoided with an appropriate emergency response system in place to provide survivors with pertinent information such as what has happened, when they can expect relief, and how they can escape safely if possible

Objective The objective of this research project has been to design and construct a solar-powered mesh that can be used in the aftermath of a natural disaster to supply survivors via Wi-Fi interface with relief information such as maps, locations and routes to safe zones, and any other pertinent information which could assist survivors in finding safety. In order to successfully remedy the existing problems with current emergency information services, several criteria must met for our design.

Design Challenges The design and implementation of a practical system for post-disaster information dissemination presents several major challenges. Since such a system must be available in the absence of power grid access, it must be made self-sustainable by using an alternative power source such as solar energy. Since solar energy harvesting is known to be unpredictable and difficult to model [27], [28], [30], a significant challenge is to balance system functionality and availability with an unpredictable energy supply, especially for a system which has power hungry resources such as PERPETUU.

Motivation for a Multi-Tiered Architecture The tasks of distributing GIS information among the nodes and to mobile clients require high-bandwidth radios which consume a large amount of energy. Since scavenged solar energy is sparse, a careful plan must be developed that conserves energy by only turning on the highpower radios when absolutely necessary. This need for ultra-low-power consumption by the system is in direct conflict with the need to maximize availability to the users by keeping the system always on. While optimization techniques exist for reducing power consumption such as CPU Dynamic Voltage and Frequency Scaling (DVFS) [62] and Power Saving Modes (PSM) [3], these techniques cannot eliminate the irreducible power draw of the system sourced by the CPU clock, RAM, and onboard oscillators.

II. BACKGROUND In this chapter we describe some of the background work from which our research emerged. We describe previous and current methodologies for designing low-power photovoltaic systems, future energy prediction, Wi-Fi sensing, and the infrastructure for contemporary emergency alert systems.

Low-Power Photo-Voltaic Systems Several factors have led to research in finding new methods for improving energy efficiency in wireless LANs and meshes. First, available energy is limited by the size of costly solar panels and batteries, while the prevalence of solar-powered wireless systems has grown in recent years due to the spread of smart mobile devices. Secondly, there is no inherent mechanism in the 802.11 standard which allows for any power saving method at an access point [70]. This shortcoming of IEEE 802.11 has been a hindrance to the development of practical power saving methods for WLAN infrastructure [69], [70].

III. HARDWARE ARCHITECTURE The hardware architecture for PERPETUU is built around five basic hardware pieces needed to achieve the design goals for the project: 1) a multi-tiered, multi-radio platform allowing for a wide range of power states, 2) a PIC micro-controller and its peripheral devices and supporting hardware for operation control, 3) a means of energy harvesting and energy 13 storage, 4) power gating techniques for minimizing power consumption, and 5) the ability to make fine-grained current and voltage measurements.

![](https://maker.wiznet.io/upload/ckeditor5/704233387%5F1665585188%2Epng)

SOFTWARE ARCHITECTURE The design principles for the software architecture of PERPETUU are two-fold: 1) Virtualize the high-power subsystem residing on the Gumstix at the low-power subsystem existing between the PIC and WizFi radio, to achieve nearly always-on operation at a minimal energy cost. 2) Utilize high-energy demanding resources intelligently by balancing solar energy harvested with the allotted energy for each resource. PERPETUU succeeds in meeting the software design goals by using the following essential software modules, an illustrated in Figure 2.

![](https://maker.wiznet.io/upload/ckeditor5/704233387%5F1665585216%2Epng)

Portable Map Stack The Gumstix module hosts a portable custom designed map stack module, while the PIC micro-controller runs a virtualized version of the map stack. Map layers are retrieved from a residing postgresql database by the map stack, which also runs mapserver, an apache webserver, and custom software modules that adaptively send different map layers to Wi-Fi clients. The map stack is a key component to making the PERPETUU system low-power, adaptive, and accessible to users. Figure 3 shows the viewable map using off-the-shelf wireless devices. The map stack residing on the Gumstix was designed and implemented by Bill Johnston (University of Arkansas).

![](https://maker.wiznet.io/upload/ckeditor5/704233387%5F1665585249%2Epng)

Wi-Fi Sensing The PERPETUU node utilizes a relatively low-power Wi-Fi module (WizFi220) to sense the presence of a Wi-Fi client. This low-power Wi-Fi module is used to sense whether or not a user is present without waking up the Gumstix. The low-power module sends out the same ESSID as the Gumstix Wi-Fi. A Wi-Fi user can connect to the low-power module, which indicates to the PIC a user is present. If a user is detected, the PIC uses the wakeup controller algorithm to determine whether or not the Gumstix should be woken up to serve map data. This is a critical component to the system – providing the nearly always-on availability criteria while 20 consuming only a fraction of the power of the Gumstix. While the WizFi220 has a boot time of only 20ms, it takes about ten seconds, from beginning to end, to boot, broadcast its ESSID, allow for a client to connect to its Wi-Fi server, and notify the PIC that a client has been detected.

![](https://maker.wiznet.io/upload/ckeditor5/704233387%5F1665585279%2Epng)

Wakeup Controller The wakeup controller plays a vital role in maximizing the number of users served during an emergency scenario, as will be shown in Chapter VI. It uses the predicted energy, hardware measurements on residual battery SOC, and energy consumption of different components of the system to calculate whether the low power Wi-Fi module and the Gumstix should be woken up to serve maps. It also determines the period of time that the Gumstix should remain on to serve users (TWait).

IMPLEMENTATION The PERPETUU node is implemented on a custom designed power supply PCB which houses the PIC micro-controller, energy harvester/battery charger, light sensor, and interfaces to the three radios. The system can be powered using a solar panel, Li-ion batteries, an external power supply, or any combination of those. Some key features of the board include: 1) hardware implemented temperature-controlled maximum power point tracking, 2) the ability to power the system directly from the solar panel when the battery is near full, 3) the ability to make fine-grained power measurements, 4) power gating certain subsections of the board to reduce power leakage, 5) the ability to survive a wide range of temperatures, 6) a weatherresistant utility box to protect the susceptible components from outdoor conditions.

![](https://maker.wiznet.io/upload/ckeditor5/704233387%5F1665585330%2Epng)

FUTURE WORK Our ultimate objective for this project is to save lives, by developing the self-sufficient infrastructure needed to provide survivors with proper post-disaster relief information. Such a problem requires an extensive knowledge base, innovation, and expertise in many different areas of computing. Given the potential societal impact of the project, the problem is worthy of continuation. Due to the broad scope of the problem(s), some of the barriers standing in between our current system and an ideal emergency mesh have yet to be fully worked out.

CONCLUSION We have presented PERPETUU, a solar-powered GIS micro-server mesh node that uses a multi-tiered hardware and software architecture for serving information-rich maps to survivors of disasters. PERPETUU combines a computationally weak but low-power micro-controller device with a computationally capable Gumstix platform to explore tradeoffs between energy consumed, system availability, and computational capability. Through the use of energy prediction, power profiling capabilities, and an intelligent wakeup controller, the system can 56 balance energy harvested from solar panels with energy consumed by different subsystems. Our evaluation of PERPETUU shows the system can last near perpetually while serving a large number of survivors during an emergency.

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Source: https://maker.wiznet.io/mayuri/projects/a-solar-powered-and-multi-tiered-mesh-node-for-a-portable-in-situ-emergency-response-system/