Low power two-way wireless communication system for electronic shelf labels

摘要

A two-way low-power communication system for an electronic shelf label system uses a multiplicity of labels, each of which has an antenna and a diode. Data to be received at the label is Manchester encoded and 100% AM modulated onto a spread-spectrum RF signal, emitted from a broadcast antenna in the store ceiling. Preferably the RF is around 2.4 Ghz, and the spreading is via direct sequence phase shift keying with a chipping rate at least ten times the RF frequency. A 63-bit sequence may be used. The label detects the RF energy, and a simple comparator followed by a manchester decoder extrats the digital data stream. Data to be set from the label is communicated via a selective modulation of the diode with an offset signal, preferably in the range of 1 to 10.7 Mhz. During this time the ceiling broadcast antenna is emitting a spread-spectrum signal that is not data-modulated in any way. Energy re-emitted by the label antenna is picked up by a ceiling-mounted receiving antenna, and the energy is diverted to two sidebands during times when the diode is being modulated. The received signal is spread-spectrum demodulated and band-pass filtered so that only sideband energy is processed. The label's outbound data stream is recovered by digital signal processing techniques from the sideband energy. The result is a minimization of cost and complexity in the label and an optimal exploitation of the bandwidth given the regulatory framework thereof.