Abstract: A RF tag reader may use spatial averaging to compensate for the limitations of performing multi-frequency continuous-wave ranging (MFCW) in a bandwidth-limited environment. Although MFCW provides an estimate of the separation distance between a RF tag and the tag reader with errors that vary widely, the error values form a pattern based on the separation distance. That is, as the separation distance increases or decreases, the error values oscillate between maximum and minimum values centered on the correct separation distance. Accordingly, in one embodiment, the receiver uses spatial averaging to average out this oscillating error (e.g., the maximum errors are counter-balanced by the minimum errors). The more accurate, spatially-averaged MFCW estimate may then be used to resolve the cycle ambiguity in continuous-wave ranging to identify the separation distance between the RF tag and the tag reader.

Abstract: Techniques are presented for adaptively increasing power delivered to an RF tag. In one embodiment, a tag reader uses multiple transmit antennas to increase the power delivered to an RF tag without increasing the transmission power. The tag reader may perform transmit diversity (or a related antenna diversity schema) to ensure that transmitted signals from the multiple transmit antennas constructively interfere at the location of the RF tag. The tag reader may transmit a pilot signal and measure a phase associated with a received signal from the RF tag. The tag reader may then use the phase to determine a phase shift for each of the plurality of antennas. The phase shift may then be applied to any subsequent signals transmitted by the antennas to ensure that the signals interfere at the RF tag's location.

Abstract: A RF tag reader may use spatial averaging to compensate for the limitations of performing multi-frequency continuous-wave ranging (MFCW) in a bandwidth-limited environment. Although MFCW provides an estimate of the separation distance between a RF tag and the tag reader with errors that vary widely, the error values form a pattern based on the separation distance. That is, as the separation distance increases or decreases, the error values oscillate between maximum and minimum values centered on the correct separation distance. Accordingly, in one embodiment, the receiver uses spatial averaging to average out this oscillating error (e.g., the maximum errors are counter-balanced by the minimum errors). The more accurate, spatially-averaged MFCW estimate may then be used to resolve the cycle ambiguity in continuous-wave ranging to identify the separation distance between the RF tag and the tag reader.

Abstract: Techniques are presented for adaptively increasing power delivered to an RF tag. In one embodiment, a tag reader uses multiple transmit antennas to increase the power delivered to an RF tag without increasing the transmission power. The tag reader may perform transmit diversity (or a related antenna diversity schema) to ensure that transmitted signals from the multiple transmit antennas constructively interfere at the location of the RF tag. The tag reader may transmit a pilot signal and measure a phase associated with a received signal from the RF tag. The tag reader may then use the phase to determine a phase shift for each of the plurality of antennas. The phase shift may then be applied to any subsequent signals transmitted by the antennas to ensure that the signals interfere at the RF tag's location.