Up-sampling and cross-correlation for time of arrival determinations in passive entry/passive start systems

An access method for a vehicle, the method comprising:

• transmitting a first wireless signal from the vehicle to a portable access device via one or more antennas;
• receiving a second wireless signal transmitted from the portable access device to the vehicle via the one or more antennas;
• determining a phase via a control module based on the first wireless signal and the second wireless signal, wherein the second wireless signal indicates a phase delay of the first wireless signal;
• determining a location via the control module of the portable access device relative to the vehicle based on the phase;
• and
• determining the location of the portable access device based on the phase delay.

An access system for a vehicle, the access system comprising:

• a transmitter configured to transmit a first signal at each of a plurality of frequencies from the vehicle to a portable access device;
• a receiver configured to receive a second signal transmitted from the portable access device to the vehicle, and receive at the vehicle the second signal at each of the plurality of frequencies;
• and
• a control module configured to
• determine a first phase for a first one of the plurality of frequencies based on the first signal and the second signal,
• determine a second phase for a second one of the plurality of frequencies based on the first signal and the second signal, and
• determine at least one of a location or a distance of the portable access device relative to the vehicle based on the first phase and the second phase.

An access system for a vehicle, the access system comprising:

• a transmitter configured to transmit a first signal from the vehicle to a portable access device;
• a receiver configured to receive a second signal transmitted from the portable access device to the vehicle;
• and
• a control module configured to determine a phase based on the first signal and the second signal, and to determine at least one of a location or a distance of the portable access device relative to the vehicle based on the phase,
• wherein
• the first signal includes a first continuous wave tone,
• the second signal includes a second continuous wave tone, and
• the control module is configured to determine the phase based on the first continuous wave tone and the second continuous wave tone.