This dissertation addresses cooperative communications and proposes multi-layer solu-
tions for wireless local area networks, focusing on cooperative MAC design. The coop-
erative MAC design starts from CSMA/CA based wireless networks. Three key issues
of cooperation from the MAC layer are dealt with: i.e., when to cooperate (opportunistic
cooperation), whom to cooperate with (relay selection), and how to protect cooperative
transmissions (message procedure design). In addition, a cooperative MAC protocol that
addresses these three issues is proposed. The relay selection scheme is further optimized
in a clustered network to solve the problem of high collision probability in a dense
network. The performance of the proposed schemes is evaluated in terms of through-
put, packet delivery rate and energy efficiency. Furthermore, the proposed protocol is
verified through formal model checking using SPIN. Moreover, a cooperative code allo-
cation scheme is proposed targeting at a clustered network where multiple relay nodes
can transmit simultaneously. The cooperative communication design is then extended to
the routing layer through cross layer routing metrics. Another part of the work aims at
enabling concurrent transmissions using cooperative carrier sensing to improve the per-
formance in a WLAN network with multiple access points sharing the same channel