It is about amplification and transfer, decoding and transfer and compression and transfer. Amplification and transfer (AF) is the simplest and fastest of the three. It acts as an analog repeater and was introduced in 2004. Whenever this type of relay receives a signal, it only amplifies the signal received from the source and transmits it to the destination. The destination receives two independent versions of the information so it can make better decisions. Errors will obviously occur using this strategy. No encoding or decoding takes place here and the noise gained by the signal from the source to the relay will also be amplified! The decode and forward strategy (DF, can also be described as regenerative digital repeaters) decodes the message received at the relay. It works very well here but when it fails to decode correctly, an error propagation phenomenon is observed. To counter this, methods have been introduced where the relay detects and transmits information from the source only in the case of a high instantaneous signal-to-noise ratio between the source and relay.