In addition, various PHY-Layer authentication efforts have been undertaken, which can be considered as a complement or extension of the higher level authentication mechanisms. In general, existing Phy-Layer authentication schemes can be divided into key or no key , depending on whether a common secret key between legitimate parties is used to authenticate each other or not. In some practical cases, it may be difficult to implement keyless authentication schemes [21-23]. This is because the functions of the specific transmitter or channel must be identified between the legitimate users used to authenticate the transmission. Instead, authentication schemes based on the common key between two legitimate users [25-27] are closer to traditional authentication protocols for challenges. In , an authentication algorithm was used for the spatial and temporally specific fading channel between the transmitter and the receiver. The authors of  proposed a PHY-Response Response authentication mechanism, which exploits the randomness and recipiation of wireless signal amplitude for authentication. A PHY-PCRAS (PHY-PCRAS) authentication scheme was proposed in . He took advantage of the coincidence and reciprocity of the channel`s live reaction to protect the common key from possible interceptions and obtain authentication. If nodes 412 and opposing nodes 422 are located at a comparable distance from nodes 402, a secret parcel transmission may take place with sufficient probability. However, if an opposing node 422 is near 402 nodes relative to the distance between nodes 402 and 412, node 422 is more favourable with higher SINR values. This reduces the likelihood of secret packet transmission between nodes 402 and nodes 412. This is called the distant case.
The cooperative jamming technique solves the almost distant case: when node 402 transmits a package, the second antenna (or auxiliary node near 402) transmits a random signal (or noise) on the wireless channel. This increases the noise in the environment, which decreases with distance. While the opposing node 422 receives a stronger signal, it also receives a louder noise. On the other hand, node 412 is not very affected by this artificial noise, because node 412 is further away. This is how the use of cooperative jamming works by intersecting the difference between the SINR values of node 412 and node 422. The use of a second antenna as a collaborative lament in a multi-antenna system requires very limited additional complexity. 3 is an exemplary block diagram of a wireless communication device in which this invention can be implemented. The 300 wireless communication device includes a 302 processor to control the operation of the 300 wireless communication device and a 304 memory.