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Efficient utilisation of bandwidth and high data rates have a great impact on the performance of ad hoc wireless networks. The use of cooperative diversity, where neighbouring stations may act as relay nodes to transfer the source data to the desired destination node through an independent relay channel, has shown to provide diversity gain and consequently improve the achievable bit rate. However, this is usually attained at the expense of loosing some wireless resources such as bandwidth. On the other hand, the use of directional antennas has shown to offer an effective way for efficient bandwidth utilisation. Here, the authors propose a new channel access protocol for transmission over cooperative ad hoc networks. The proposed protocol, which aims at minimising the number of blocked nodes and consequently improving the system throughput, employs directional antennas at both the source and relay stations. The network performance under the proposed settings is modelled using continuous Markov chains. The steady-state transmission blocking probability and the average network throughput are obtained by analysing the derived Markov model. The analytical results, which are validated through simulations, show the improvement in performance compared to the carrier sense multiple access with collision avoidance protocol that employs omnidirectional antennas.