Cooperative Automatic Retransmission Request (C-ARQ) schemes exploit the broadcast nature of the radio channel by allowing those users which overhear a transmission to act as spontaneous relays when a packet has been received with errors at destination. Transmission takes place in two phases. First, the source transmits to the destination. In the case of error, retransmissions are then executed by the relays, providing the system with cooperative diversity. In this paper we analyze how the addition of these relays to the communication modifies the well-known hidden and exposed terminal problems associated to any medium access control protocol based on carrier sensing. This work is focused on Carrier Sensing Multiple Access (CSMA) protocols, such as the one defined in the IEEE 802.11 Standard. The theoretical study presented in this paper has been supported by computer-based simulations.

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