In ad-hoc radio networks, mechanisms on how to access the radio channel are extremely important in order to improve network efficiency and, when needed, to guarantee QoS. Traditionally, Medium Access Control (MAC) protocols in ad hoc networks have been designed to face off the well known collision resolution problem. However, when using advanced signal processing techniques, general assumptions on collisions and packet loss are no longer valid. Besides, little has been reported about MAC algorithms dealing with multiaccess channels in ad hoc networks. In this paper, we present a novel decentralized multiaccess MAC protocol for Ad Hoc networks. This MAC protocol is an hybrid CDMA-TDMA in which a cross layer approach has been followed to dinamically adapt to the traffic load. Closed expressions for the throughput and delay of the network are presented as a function of the multipacket reception capability of the receiver, the number of codes and the packet retransmission probability.