Patent ID: 8794517

Claim:
A computer-implemented method of communication between a card reader and a user device, comprising: receiving, from a read head of the card reader coupled to the user device through an audio jack of the user device, card information encoded on a payment card; encoding the card information in a fast format packet to be sent to the user device at a first data rate; encoding the card information in a slow format packet to be sent to the user device at a second data rate lower than the first data rate including generating a preamble segment for the slow format packet that is longer than a preamble segment of the fast format packet; modulating the fast format packet and the slow format packet into a signal and sending the signal over an audio channel of the user device; initiating, at the user device, a demodulation process on a portion of the signal that corresponds to the fast format packet; determining that the demodulation process on the portion of the signal that corresponds to the fast format packet has failed; in response to determining that the demodulation process on the portion of the signal that corresponds to the fast format packet has failed, demodulating a portion of the signal that corresponds to the slow format packet; and decoding the card information from the demodulated portion of the signal that corresponds to the slow format packet.