BB / ESP32: Network Architecture Survey

[remtrib]

The goal is to allow both the device running the application and the targeted device to easily connect over the air with the less effort required by the user for the setup. We first describe in a survey each possible method according to available hardware, and then propose a trade-off solution.

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• 👨🏻‍💻 To communicate remotely between a device and a Blinky Block, we assess 4 wireless modes : Ad-hoc, Access Point, Mesh, and Station, considering we use an ESP32/8266 based on Arduino framework for implementation.

• Ad-hoc mode is useful for peer to peer communication without considering WiFi complexity. Unfortunately WiFi 802.11 Ad Hoc mode is not available for the ESP32 WiFi Stack Libraries developed by Espressif company.

• A traditional infrastructure Wi-Fi network is a point-to-multipoint network where a single central node known as the access point (AP) is directly connected to all other nodes known as stations. The AP is responsible for arbitrating and forwarding transmissions between the stations. Some APs also relay transmissions to/from an external IP network via a router. Traditional infrastructure Wi-Fi networks suffer the disadvantage of limited coverage area due to the requirement that every station must be in range to directly connect with the AP. Furthermore, traditional Wi-Fi networks are susceptible to overloading as the maximum number of stations permitted in the network is limited by the capacity of the AP. source

  WiFi-UART Serial Bridge Using ESP8266 or ESP32 - Atadiat

• ESP-MESH differs from traditional infrastructure Wi-Fi networks in that nodes are not required to connect to a central node. Instead, nodes are permitted to connect with neighboring nodes. Nodes are mutually responsible for relaying each others transmissions. This allows an ESP-MESH network to have much greater coverage area as nodes can still achieve interconnectivity without needing to be in range of the central node. Likewise, ESP-MESH is also less susceptible to overloading as the number of nodes permitted on the network is no longer limited by a single central node. source

  painlessMesh / painlessMesh

  espressif/esp-mdf

• Trade-off solutions:

  1. Considering requirements of our system, I choose to use the ESP32 in access point mode, additionally listening on a specific port to UDP datagrams. The remote device willing to control a module (i.e. the ESP32) over Wi-Fi first connects to the advertised SSID and sends a broadcast datagram on the same port as the one listened by the ESP32, which is acknowledged by that same ESP32. The device uses the ack datagram to retrieve the IP address to open a TCP socket with the remote ESP32 and thus establish a bidirectional communication.
  2. Another solution, would be to connect both devices on the same Wi-Fi network, thus using station mode, but this requires to have access to a low security network or a personal modem, and to modify the code on the ESP32 with the correct credentials each time you change of network, which is not really user friendly.
  3. A third solution, is to both subscribe the ESP32 and device to the same filters on a MQTT server online that will act as a relay between systems using publish and subscribe protocol. But the downside is you would need a connection to internet to interact with a module within the same room.

  We could gather that ad-hoc networks for ESPs works roughly as an AP, as it involves the same code than AP mode.