Low power two-way wireless communication system for electronic shelf labels
First Claim
1. A communications system for communicating a serial data stream from a first device to a second device, the first and second device being physically separate from each other;
- the second device comprising a transmitter transmitting an RF signal modulated by a spread-spectrum modulation;
the first device comprising an antenna coupled to a two-terminal nonlinear component, an oscillator, the oscillator having an output defining an offset frequency; and
a mixer responsive to the serial data stream for selectively coupling the oscillator output to the nonlinear component in response thereto; and
the second device further comprising a receiver receiving RF energy present at a sideband offset from the transmitted signal by the offset frequency, and a spread-spectrum demodulator demodulating the received RF energy with respect to the spread-spectrum modulation of the transmitter, and a second demodulator demodulating the demodulated signal, yielding the serial data stream.
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Accused Products
Abstract
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.
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Citations
10 Claims
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1. A communications system for communicating a serial data stream from a first device to a second device, the first and second device being physically separate from each other;
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the second device comprising a transmitter transmitting an RF signal modulated by a spread-spectrum modulation; the first device comprising an antenna coupled to a two-terminal nonlinear component, an oscillator, the oscillator having an output defining an offset frequency; and
a mixer responsive to the serial data stream for selectively coupling the oscillator output to the nonlinear component in response thereto; andthe second device further comprising a receiver receiving RF energy present at a sideband offset from the transmitted signal by the offset frequency, and a spread-spectrum demodulator demodulating the received RF energy with respect to the spread-spectrum modulation of the transmitter, and a second demodulator demodulating the demodulated signal, yielding the serial data stream. - View Dependent Claims (2, 3, 4, 5)
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6. A method for communicating a serial data stream from a first device at which the serial data stream originates to a second device, the first and second device being physically separate from each other, the first device compising an antenna and a nonlinear component coupled thereto, the method comprising the steps of:
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generating at the second device a spread-spectrum modulation; transmitting from the second device an RF signal modulated by the spread-spectrum modulation; receiving energy of the spread-spectrum-modulated RF signal at the antenna of the first device; generating at the first device an offset signal at a frequency defining an offset frequency; selectively coupling at the first device the offset signal to the nonlinear component in response to the serial data stream; receiving at the second device RF energy at a sideband offset from the transmitted signal by the offset frequency; spread-spectrum demodulating at the second device the received RF energy with respect to the spread-spectrum modulation generated at the second device; and further demodulating the demodulated signal at the second device, yielding at the second device the serial data stream that originated at the first device. - View Dependent Claims (7, 8, 9, 10)
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Specification