An ad hoc network is set up on the spot, with devices connecting directly to each other instead of through a router or access point. That flexibility comes at a price: nothing central manages the traffic, so performance depends on how far apart the devices are, how many are connected and what else is using the airwaves nearby.
Ad hoc networks have a limited range, so devices must be within range of each other, often in the same room or a small space. Move a device too far away, or place a wall between the devices, and the signal weakens. You then get a poor or intermittent signal, where the connection fades in and out. A transfer running at that moment can be cut off part way through, so the file has to be sent again from the start.
Every device on the network shares the same connection. Add three or four devices and each one gets a smaller slice, so data speeds drop for everybody, and with more devices transfers may be interrupted altogether. A device that is far from the others is slower even on its own, because a weak signal carries less data reliably. For example, four friends in a park play a multiplayer game on handheld consoles using an ad hoc connection: the two consoles nearest each other swap game maps in seconds, while the console furthest away keeps losing the connection and its download of a map stops half way. When many devices compete for the same connection, the network can become unavailable to a device trying to join.
Interference happens when other nearby devices send signals over the same channels, and it gets worse as people move around and signals cross. Ad hoc networks are also disorganised: devices join and leave as they are needed, and some may be out of range of each other. In a group of five, one device might reach the ones nearest it but not the one at the other end, so not everyone can share data with everyone else.
Pearson BTEC Digital Information Technology · Communication technologies