In mobile ad-hoc radio networks, terminals are mobile and heterogeneous, the architecture of the network is continuously changing, communication links are packet oriented and radio resources are scarce. Therefore, mechanisms on how to access the radio channel are extremely important in order to improve network efficiency and, when needed, to guarantee QoS. However, due to these network harsh conditions, decentralized Medium Access Control (MAC) protocols designed specifically for ad hoc networks are scarce. In this paper we present a novel decentralized multiaccess MAC protocol for Ad Hoc networks. This MAC protocol is an hybrid CDMATDMA in which a cross layer approach has been followed in order to maximize network throughput. A theoretical analysis of the system is presented ending up with closed expressions for the throughput and delay of the network and some simulations are presented to evaluate the performance of the system.