Wifi Cicada: Open Source Design and Implementation

A Case Study

By Oscar Aitchison
June 06, 2022
Modern off-grid energy solutions require an internet connection, so communities without mobile data coverage are often deprioritized.
— It’s about to get technical! For easier navigation of this post, browse the index below.

Index

  • Executive Summary
  • Background
  • Wifi Cicada – Hardware & Firmware
  • Implementation Site
  • Communications Network Design
  • VSAT Uplink
  • Wifi Local Area Network (LAN)
  • Bill of Materials
  • Technical Design Notes
  • Implementation
  • Providing Internet-as-a-Service
  • Impact
  • Lessons
  • Conclusion
  • Annex A – Antennat Test Results

Executive Summary

In the energy access space it is well-known that there are around 770Mn people living without access to electricity worldwide, and that number is used constantly. But statistics around mobile internet access are less discussed. GSMAs 2021 figures indicate that there are around 450Mn people who still lack mobile internet coverage (3G+). The exact degree to which these two populations overlap is unknown, but from our 5 years experience deploying 35 mesh-grids in 7 countries and talking to energy developers, regulators and communities all over the world, we believe the overlap is significant. Conservatively, we’d estimate that at least 10% of the world’s off-grid population has neither electricity nor mobile internet coverage of any kind (including 2G), and that the figure could be much higher. If that wasn’t bad enough, these communities are often deprioritized for electrification, even if they’re otherwise good candidates, given that network coverage is critical for operating modern energy solutions like microgrids and PAYGo SHS.

Okra Solar, in partnership with ATE Co Philippines and with the generous support of EnAccess Foundation, has designed, manufactured, field-tested, and now open-sourced an IoT communications solution which we believe will help to address this problem. This consists of:

  • A hardware and firmware design for the “Wifi Cicada” – an IoT communications module to be installed in devices such as meters, sensors, etc.
  • Ready-to-use PCBAs available on demand from the Seed Studio marketplace
  • A field implementation design based on a VSAT uplink with 2.4GHz LAN distributed throughout site (the subject of this document)

The result is a field-proven product and approach, providing internet access to a remote Philippines community of 100 households for the first time, realising the mutually supporting goals of operating an IoT-enabled solar energy service and providing general purpose internet access into the community. It is our hope that this proof of concept will set the stage for other similar projects to be developed at scale using our open source design.

Background

In 2017 Okra began development of a product that would primarily use the 2G GSM network to remotely monitor and bill energy usage in a decentralised “mesh grid”. This prototype product worked well as a proof of concept, but we were relying on off-the-shelf, low-quality, unreliable cellular modules that gave us endless headaches in the field, especially in areas of weak or no connectivity in Cambodia and the Philippines. Additionally, many countries around the world began setting “sunset dates” for the decommissioning of 2G networks. The need for another solution became irrefutable. With the help of EnAccess Foundation, in 2019 we developed (and open-sourced) an embedded module from the ground up which was 2G, 3G and 4G compatible – the Cicada communications module. We’ve manufactured thousands of Cicadas and they have facilitated communities getting access to IoT-operated electricity services all over the world, but still network connectivity was a limiting factor. With support from EnAccess, again, we focused on a solution for areas with zero connectivity, and we’re proud to now introduce it to the world: the Wifi Cicada.

Wifi Cicada can pair with VSAT satellite technology to provide internet access to remote communities, both for the purposes of IoT device communication and for general community access.

Wifi Cicada – Hardware & Firmware Design

Cicada IoT comms modules are a plug-and-play PCBA, and are attached to the main PCBA of all Okra Pods

The Wifi Cicada PCBA design is based around an ESP-07S ESP8266 Serial Wifi MCU, which can be inserted into a “host” device (in our case the Okra Pod, shown right) via a standard 2×10 2.54mm female header. Host devices may be any device using the STM32F1 family of STM MCUs.

The ESP32/ESP8266 module is controlled via AT commands. The ESP works as a Wi-Fi adapter, receiving commands via UART serial communication from the host MCU. The ESP runs Espressif AT binaries firmware based on the Espressif IoT Development Framework (ESP-IDF) repository.

The core hardware specifications of the Wifi Cicada are as follows:

Frequency range

2.4GHz

Wifi protocols

802.11b/g/n

Power supply

5V 500mA

Avg power consumption

0.45W Tx, 0.04W Rx, <1mW standby

Security

WPA/WPA2

Output Power

+20dBm in 802.11b mode

Wifi Cicada module block schematic

Further details including source code, schematics, and manufacturing files can be found in the Enaccess github repository.

The Implementation site

Our partners, ATE Co, have been operating Okra Mesh Grids since 2019, energising more than 500 houses in the Quezon and Northern Samar provinces of the Philippines. One of these communities is the village of Maybuho, a small fishing community of 100 households, located on Palasan, a small island off the east coast of Luzon.

Small communities like Maybuho are geographically isolated from many forms of centrally distributed infrastructure, including mobile internet coverage

Due to the lack of cellular signal in Maybuho, ATE Co has been operating a mesh grid of 31 households completely offline. They manually collect flat monthly payments for the electricity, and the local maintenance agent living in the community must climb a nearby mountain to get cell service to communicate with ATE Co staff. These conditions made Maybuho a perfect site for the field test of wifi cicada with a VSAT uplink.

Communications Network Design

Clearly an IoT-enabled device that uses 2.4GHz Wifi to communicate is useless in a remote area without two things:

  1. A local wifi network (LAN) to connect to
  2. A way for that LAN to communicate with the outside world (uplink)

In the off-grid context, the uplink tends to almost universally be a cellular connection. Wifi Cicada can still be used with a cellular (2/3/4G) uplink and a Wifi LAN, but since we were focused on solving the problem for an area with no cellular signal for miles around, this project focused on a VSAT uplink instead.

Wifi Local Area Network (LAN)

Once the VSAT dish provides the uplink to the internet, a simple LAN must be constructed to provide connectivity to the IoT devices (i.e. meters, Okra Pods, or any smart devices) installed around the community.

Wifi Cicada network diagram

The community LAN is distributed throughout the site through a series of Outdoor Wireless Access Points (APs) mounted on poles that can “mesh” together and wirelessly daisy-chain, provided they have some range overlap. This architecture eliminates the need for PtP bridges or other complex network designs. Given the importance of line of sight to maintain the maximum range, the APs are mounted on poles to raise them above roof level (see below).

AP range overlap

Bill of Materials

The following table is a rough breakdown of the costs and quantities of materials used in the project. Internal costs (e.g. Okra and ATE Co staff travelling to site, meals, etc) are excluded, as are the costs of the new wifi cicada Pods retrofitted in the homes, to give a picture of what just the VSAT + LAN costs alone look like.

ITEM

QTY

UNIT

UNIT COST

TOTAL COST

TP-Link EAP225 Outdoor w/POE adapter

2

pcs

$70

$140

18dBi 2.4GHz Yagi Antennas

2

pcs

$10

$20

Steel pole 20ft

4

pcs

$10

$40

Okra Pod ED-WF (Wifi comms)

2

pcs

$125

$250

VSAT BUC Satellite Dish

1

pcs

$350

$350

TP-Link Omada OC200 Hardware Controller

1

pcs

$50

$50

TP-Link Omada ER605 Router

1

pcs

$50

$50

VSAT modem - Newtec MDM2510

1

pcs

$50

$50

Concrete footing

1

pcs

$50

$50

Solar panel 370Wp

2

pcs

$111

$222

Gel Batteries 12V 150Ah

3

pcs

$180

$540

500W MSW Inverter

2

pcs

$80

$160

BOS components (screws, connectors, cables)

1

pcs

$50

$50

Installation Labour

1

pcs

$1,600

$1,600

*A full breakdown of every line item was not available, and some costs are estimates extrapolated from the total.

Technical Design Notes

The following table gives a brief overview of the technical considerations that led to the specific model and quantities of equipment chosen for the project

ITEM

DESIGN NOTES

TP-Link EAP225 Outdoor w/POE adapter

Chosen for its low cost, simple setup and “mesh wifi” features, making it easy to extend the same network SSID and daisy chain new APs without any custom engineering. Although range is limited (300m at best), we found that large omnidirectional APs (e.g. Cambium XVT2-2T) capable of very large area coverage were much more expensive (>$600/pc) and complex than simply daisy-chaining several wifi APs together.


Given that most off-grid communities tend to be <3sqkm in area, this indicates with a coverage of roughly 0.3sqkm, there should be no more than 10 APs required to distribute wifi around any given site.


The AP is technically capable of dual band 2.4/5GHz, but as range is more important than speed in this application, 2.4GHz was chosen for better range and obstacle penetration.

18dBi 2.4GHz Yagi Antennas

Okra staff tested the range of 3 different antennas - a 20cm 5dbi Omni Antenna, a 45cm 15dbi Omni Antenna, and an 18dbi Yagi (directional) Antenna. Test results can be seen in Annex A. We chose to use the one with the best demonstrated results,  however we now believe based on field experience that a smaller gain omnidirectional antenna would have likely worked just as well given a clear line of sight to the AP.

Steel pole 20ft

Chosen by installation contractors to raise the APs above the level of all buildings so that it could be clearly seen from all houses.

Okra Pod ED-WF (Wifi comms)

Required for each house needing power, and also to provide power to the VSAT equipment.

VSAT BUC Satellite Dish

Standard 1.2m dish and “Block UpConverter” provided by supplier.

TP-Link Omada OC200 Hardware Controller

Technically optional. This controller is like a mini-PC that sits on the LAN and stores configuration details, as well as allowing for remote login and diagnosis of the network. It makes it easier to operate and debug remotely but is not strictly necessary for the network to work. It is also valuable if there is an intention to sell internet access (e.g via vouchers), where there is a need to authenticate which devices are owned by “paid users”.

TP-Link Omada ER605 Router

Also technically optional, but required if the VSAT modem does not also have router capabilities and sufficient LAN ports to connect the AP and Hardware Controller. A future design could likely remove this component.

VSAT modem - Newtec MDM2510

Standard modem for the VSAT provided by the VSAT supplier. It may be possible to find a modem-router combo device that removes the need for two separate components.

Concrete footing

Required for smooth, stable mounting surface. It must be ensured that the dish cannot move, as this will heavily impact performance. The footing was 1.5*1.5*0.12m dimensions with a 7.6cm OD 2mm steel pole set in the centre for antenna mounting. The location of the footing must be no more than 30m from the VSAT modem.

Solar panel 370Wp

Additional power required for the various communications devices (modems, routers, APs). Altogether the power consumption of this equipment is ~55W continuous for 24hrs, so ~1.3kWh/day. With a design month PSH of 3.5, this is equivalent to ~370Wp of additional PV capacity. Further system reliability is gained through connection to the Okra Mesh Grid, such that any shortfalls in generation can be supplemented from nearby households.

Gel Batteries 12V 150Ah

To accommodate 1.3kWh/day with 2 days autonomy, at an average design DOD of 36%, gives roughly 3.6kWh of battery capacity required (2x12V 150Ah)

500W MSW Inverter

Required to convert 12VDC output from the Pod to 220VAC output required for device power. Although technically no more than 100W of inverter capacity was required to power the communications equipment, 500W was procured simply due to availability. Modified Sine Wave type can work, but generally Pure Sine Wave is preferred to minimise the risk of transient voltage spikes damaging sensitive equipment.


A future optimisation could potentially do away with this inverter entirely and power the equipment from 24VDC directly.

BOS components (screws, connectors, cables)

Derived from equipment already available from the main mesh grid installation. Includes things like:

- 4sqmm PV cable + MC4 to connect solar panel to Pod
- 10sqmm battery cable + terminal lugs to connect battery to Pod
- AC power strip to power comms equipment from inverter
- Mounting screws
- Wood backing board
- Solar panel flush mounting kit (rails, tin feet, end clamps)

Installation Labour

VSAT suppliers Apocomm provided installation and commissioning support on site. Experienced personnel are generally needed for the setup and orientation of the VSAT dish (although again, technology is making this easier with setup smartphone apps to guide through the process)

Implementation

The community is approximately 300m in diameter. For this size, one Access Point should be suitable, but out of an abundance of caution we purchased equipment to set up 2 meshed APs, and set them up in the locations shown on the map below.

The first step was to position the VSAT dish. This involved pouring a concrete footing with a steel pole in the centre for the dish to be mounted on.

Next, the communications equipment and the accompanying power system was installed in the house of the Local Maintenance Agent.
Power system block diagram
Final wired installation

Once the VSAT uplink was commissioned and successfully transmitting data, the next step was to install the APs on poles and erect them. Poles were installed with 4 guy wires for stabilisation, buried and attached to concrete beams inside the house for additional support. The poles were each a total length of 40’, which we now believe is excessive.

With the APs erected in both locations and with clear line of sight between them, the Pods were ready to be connected to the network. Yagi antennas were mounted outside each house and effort was made to point them to the closest AP as directly as possible and with minimal obstruction.

These yagi antennas turned out to not be wholly necessary, as staff on the ground were able to easily connect to the outdoor AP using their phones, even at distances of >130m.

Ultimately, 29/31 mesh grid households were able to be connected to the Wifi LAN, with 2 standalone houses not connected as they were >1km away, and additional APs to cover the distance were not within the project budget. ATE Co intends to connect these houses at a later date when the mesh grid is expanded to the full community.

Providing an Internet Service

We have demonstrated that installing a VSAT uplink is technically feasible and relatively affordable, but when used only for IoT device communications (it could be difficult to justify the ongoing costs). The VSAT service installed in Maybuho costs 200USD/month for:

  • 10mbps down / 30mbps up
  • 50GB/month (after which bandwidth is throttled)

To recoup this amount, ATE Co is looking to offer general-purpose internet to the community, who will purchase vouchers for specific amounts of data (the TP-Link Hardware Controller supports this function). Split between the roughly 100 households in the community, this means ATE Co must earn ~2USD/HH/month from offering the internet service in order to sustainably operate it. Over time we’ll see if the community is willing to pay $2/month for ~0.5GB of internet on an ongoing basis, but anecdotal evidence on the ground suggests that the community is very eager and able to pay this.

Overall the costs of providing an internet service via VSAT can be recovered through additional revenue from internet sales, provided the community is sufficiently large, and monthly fees are in the ranges ATE Co have been able to procure.

Impact

The immediate impact of this project is clear and measurable – 29 houses that ATE Co operated for more than 2 years without any form of remote monitoring or control, have now been consistently reporting data. We expect this visibility will lead to reduced operational costs (avoiding unnecessary site visits by assessing issues remotely), and reduced rates of payment default (remote control means non-payers can be automatically cut off from access). Building on this success, ATE Co intends to expand their service in Maybuho to the entire community later in 2022.

On a community level, we expect the impact to be even more significant. Instead of climbing a nearby mountain just to send and receive SMS, community members will be able to smoothly use all forms of internet communication, for business, entertainment, and education. Initial community feedback suggests the biggest impact will be in the area of education. Many students in the Philippines were forced to move to online learning due to the COVID-19 pandemic, and for those in no-connectivity areas such as Maybuho, this has made continuing their studies incredibly difficult. Students in the community are very excited to begin to use the internet for their studies (although, when asked, they were most excited about being able to play the online video game “Mobile Legends”).

Additionally, it is hard to overstate the value of reliable communications for disaster response. Island communities such as Maybuho are prone to damaging typhoons and typically almost completely cut off from support during such storms, as the winds make sea travel treacherous. It is our hope that when such an event next arises in Maybuho, the residents will be able to rely on the VSAT uplink to communicate with loved ones and authorities, and in doing so perhaps even save lives in a crisis.

Lessons

Overall, the performance of the EAP225 APs exceeded expectations in terms of range, and this meant that several of the components purchased were not necessary or over-specced. We believe a single AP could have covered the entire range, and a smaller, cheaper antenna would have been sufficient for the Pods to pick up the signal.

The AP installation could also be dramatically simplified whilst still achieving similar results. Installation contractors mounted the APs using 40ft steel poles, secured by 4 guy wires. This was done to ensure the signal would reach every household, but in practice such a tall pole introduces safety concerns. We are working with the installation contractors to find ways to increase structural stability and reduce the risk of any safety hazards during tropical storms (which the area is prone to). Further, the APs are now quite difficult to access should any maintenance be required. In general the aim should be to mount the APs at the minimum effective height to clear the majority of obstructions. Considering that the APs are relatively cheap, it may also be worth simply purchasing more, and dealing with the loss of range incurred by mounting at a lower height (say, 4m), for the sake of simplicity and safety.

Conclusion

Overall this implementation was a success for ATE Co – they can see usage data from their Okra pods and people in the community are able to use the internet, both for the first time. We are actively working with ATE Co to plan for an expansion of these networks to other mesh grids.

We believe that similar implementations of a VSAT uplink, 2.4GHz LAN, and Wifi Cicada-enabled smart devices should be possible in many applications, whether it be for microgrid metering, SHS monitoring, or any asset that requires remote control (e.g. kiosk, communal cold room). Provided there is a supplier of VSAT services in-country, the remaining equipment is readily available online, including the wifi cicada , which we hope engineers will find simple to incorporate into their own product designs.

Distributing 2.4GHz Wifi throughout a community for the purpose of IoT device monitoring presents a clear opportunity to also provide internet services to the community. The additional revenue gained from providing this service to the community can be used to offset the costs of maintaining the VSAT connection, and our research suggests that these costs will continue to trend downwards, making it not just viable but profitable to serve such communities with satellite internet.

Annex A – Antenna Test Results

  • Test Parameters
  • Used TL-XAP1801GP as the Access Point
  • Used this app to measure the dBm WiFi Analyzer – Apps on Google Play
  • If the WiFi could not connect connect, the comms loop was retested at least 4 times to confirm failure
  • Each test was done with clear line of sight on flat ground
  • Antennas tested (left to right):
    • 20cm 5dbi Omni Antenna
    • 45cm 15dbi Omni Antenna
    • 18dbi Yagi Antenna

DISTANCE

20cm Omni Antenna 5dBi

45cm Omni Antenna 5dBi

Yagi Antenna

5m

Connects ✅ (-49 dBm)

Connects ✅ (-52 dBm)

Connects ✅ (-47 dBm)

10m

Connects ✅ (-51 dBm)

Connects ✅ (-50 dBm)

Connects ✅ (-50 dBm)

25m

Connects ✅ (-60 dBm)

Connects ✅ (-62 dBm)

Connects ✅ (-55 dBm)

50m

Connected after 3 attempts 🟨 (-62 dBm)

Connected after 2 attempts 🟨 (-63 dBm)

Connects ✅ (-66 dBm)

75m

Could not connect ❌ (-68 dBm)

Connected and got NTP time after 4 attempts, but could not connect to MQTT 🟨 (-67 dBm)

Connected after 3 attempts 🟨 (-69 dBm)

100m

-

Could not connect ❌ (-76 dBm - measurement was spotty and only momentarily would display 76 dBm)

Connected after 3 attempts 🟨 (-76 dBm - measurement was spotty and only momentarily would display 76 dBm)

125m

-

-

Could not connect ❌ (not measurable by phone)

Other Notes

  • Doing the ‘Self Test’ would always produce an RSSI = 143 when in range (self test passed) and 0 when not in range (self test failed)
  • The % signal strength shown on the pods display was always 100% when in range and 0% when not in range
    dBm measurements done by phone don’t seem to be very reliable as they tend to bounce up and down +/- 5dBm each second
  • Shenzhen has a lot of wifi and bluetooth signal which may have interfered with our signal strength

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