Wifi is a wireless technology designed to allow computing devices to send data to and from the Internet. Similar objectives to 3G, 4G and 5G. The main difference is that wifi is designed to work in a static environment, whereas mobile communications assume some form of mobility. A computing deviceis, if authorised, connected to a router or wireless access point that provides a named wifi signal (SSID). In a corporate environment when there may be many wireless access points with the same SSID, a user can move around the environment and the connection is kept alive as the device moves from one access point to another. However this cannot be achieved if the user moves away from that network and wished to connect to another WiFi network. The connection is broken and then restarted with the new WiFi network and with it the task the device was performing.

WiFi uses one of two frequency bands 2.4GHz and 3.5GHz, which are similar parts of the spectrum to Mobile communications

How does WiFi impact on the mobile phone :

• On most smartphones the user has the option to switch on WiFi as the mechanism to send and receive data. When WiFi is switched on the phone will connect to a known WiFi access point in preference to the mobile network. Underlying this decision in the operatig system is the belief that WiFi is cheaper and faster than mobile data. Now (2019) with unlimited data plans it is not necessarily cheaper. However data rates in WiFi can be 300Mbps and beyond although, as with mobile data, the speed depends on many factors including how many users, and the amount of data being transferred by the access point.
• WiFi can be used by the mobile when it requires a data channel and is a direct replacement to mobile data. WiFi does not directly support phone calls, or text messages although apps such as skype and whatsapp do a similar function over the data network
• On a train, or bus or car, there can be a WiFi access point available to travellers. This obviously, cannot use fibre or copper wire as the backhaul so this is achieved via mobile connection. A special router will transfer the data from the WiFi to a mobile connection using a SIM.
• In a home environment the WiFi backhaul is either copper wire or fibre. However, in areas of poor broadband, still supporting ADSL for example, this could be slower than the mobile network. So the mobile network can be used to provide the home broadband using a mobile router. Additionally some standard routers have a mobile capability to provide backup if the broadband becomes too slow.
• Phone tethering is operation where the mobile phone is used as a mobile hotspot. The phone acts as a mobile router, When this is turned on, other computing devices, laptops, tablets etc, can connect to the WiFi provided by the phone and use this in the same way as a fixed router. The phone transferes the data from WiFi signals to mobile phone signals.