Wireless communication systems are traditionally conceptualized such that users individually commu-

nicate with the associated base station and vice versa. Cooperation is referred to as any architecture

that deviates from this traditional approach, that is where a user’s communication link is enhanced in

a supportive way by relays or in a cooperative way by other users. Due to the many available degrees

of freedom of such systems, that is the many ways in which supportive relays and cooperative users

can be deployed, an enormous amount of different architectures exist. Some canonical architectures

are briefl y introduced below, after having discussed the wireless channel they experience and the gains

one can expect from such deployments.