Packet combining considerations for random-access networks

If the channel is particularly poor, a radio may be unable to decode any individual packet reception. Packet combining utilizes retransmission diversity to improve the probability that a message can be decoded. In cases where the transmitter is known to the receiver (e.g., communication using a dedicated time slot), the receiver can request that the transmitter resend the message. However, in random access networks, a receiver may hear packets from many transmitters. If a received message is not decodable, the receiver may not know the identity of the transmitter and thus be unable to request a retransmission directly. The lack of a positive acknowledgment may cause the transmitter to eventually repeat the message, but without any explicit control signaling between the two radios, the receiver may be unaware that the new attempt can be combined with one of its previous receptions. In this paper, techniques to identify which received packets should be combined are considered. The packet matching techniques are limited to those utilizing information contained only in the individual receptions and so are suitable for random-access networks.