Add Hardware and networking description

doc/smart_home_technical_paper

@@ -21,3 +21,17 @@ Keywords: Smart Home, Presence detection, Node-red, mqtt, gateway, raspberry pi
   The used software, why the software was used and how it works is described in section 3 and in section 3 
   Section 2 contains the outline of the setup used and we will describe the specific components and explain why they are used in Section 3
 
+2. THE GATEWAY's HARDWARE AND NETWORK COMMUNICATION
+  A Raspberry Pi is used as the basis of the smart home gateway. 
+  It provides a full linux installation with raspbian lite which is well equipped to run headless, has only basic applications preinstalled and uses few resources by passing on a graphical user interface.
+  
+  To make the project controllable a graphical user interface will be provided, which is accessible over the university's network.
+  For this, the gateway uses a static ip-address in the university's lan-network, which makes the gui accessible in the entire university's network.
+  
+  Additionally, the sensors developed in the scope of this project will communicate with the gateway via wifi.
+  This would ideally be done by using the universitv's provided network as well, but the networks configuration does not allow for this, since the used security protocol used by eduroam is not supported by the used microcontroller ESP8266 and ESP32.
+  To circumvent this limitation, the raspberry pi is used as a wireless access point running a standalone network.
+  the sensors will connect to this standalone network, in which the gateway is the host with a static ip-address, and send their gathered data via the network to the gateway for further processing.
+  
+3. THE SETUPS SOFTWARE
+  [IMAGE]