Communication system with CRC checks for packet header and payload and use of explicit or hashed acknowledgements

A transmitter identification (604) and a first cyclic redundancy code (CRC)(606) are added to a header (608) of a packet to be transmitted. A second CRC is added to a data portion (612) of the packet. A receiver decodes a received packet and returns positive or negative acknowledgements depending on whether the decoding was successful. In an explicit mode, the acknowledgement contains the identification of the receiver and the first CRC from the received packet (fig.8, not shown). In an implicit mode, the acknowledgement contains a hashed response comprising an acknowledgement hashed with the identification of the receiver (fig.9, not shown). A negative acknowledgement may also contain an indication of resources reserved for retransmission of a packet. The transmitter identification in the transmitted packet may be hashed with control information and/or a CRC (fig.7, not shown), or be replaced by a hash of control information, a key and/or a CRC.