Improvements in or relating to signal communication systems
First Claim
1. A signal broadcast system comprising a broadcast transmitter and at least one broadcast receiver, the system comprising:
- means for generating at the transmitter a first carrier of a first reference frequency N and for broadcasting that first carrier;
means for generating at the transmitter a second carrier of second frequency N/n derived from the first reference carrier where the divisor n is greater than 1, for modulating the second carrier with a digital modulating signal in accordance with the digital information to be transmitted thereby, and for broadcasting the digitally modulated second carrier;
means at the receiver for receiving the first carrier and for dividing it by the divisor n to produce a corresponding demodulating signal of frequency N/n; and
a demodulator at the receiver receiving the second digitally modulated carrier and the demodulating signal and demodulating the second digitally modulated carrier with the second demodulating signal to generate a resulting digital information signal.
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Accused Products
Abstract
The invention comprises a low power broadcast system that is applicable especially to the so-called "electronic shelf" for retail stores, wherein the shelf edge carries price displaying modules that can be addressed and controlled from a central computer operated station. The system also permits the modules to broadcast back to the central station to confirm safe receipt of data and to give information as to stock levels, etc. A broadcast system avoids the need for wiring so that location changes are facilitated. To overcome the extremely noisy environment and to conserve power consumption, and hence battery life, the system employs a low frequency (132 kHz) reference carrier transmitted by the base station in discrete segmented packages, each of which frames a base data word transmitted by the base station and a corresponding module data word transmitted by the module a fixed period after the end of the base word; the base receiver then has precise time information for receipt of the module word and can "look" for it among the noise. The carrier received by the module is divided and the lower frequency used to demodulate the information-carrying transmission from the base station of the same frequency, avoiding the need for a phase locked loop detector; this lower frequency is also used for the module transmission. The module employs an air-cored loop antenna coil for the lower frequency and a ferrite-cored loop antenna for the higher reference frequency, while the store antenna is segmented for selection of the group of modules to be addressed; the antenna contacts the metal shelving to provide electromagnetic coupling thereto. Each module contains a microprocessor which controls the operation. Each module has "concealed" buttons which can be enabled and used to insert data to be transmitted therefrom. A charging circuit can be used as the power source employing the received RF carrier energy.
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Citations
26 Claims
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1. A signal broadcast system comprising a broadcast transmitter and at least one broadcast receiver, the system comprising:
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means for generating at the transmitter a first carrier of a first reference frequency N and for broadcasting that first carrier; means for generating at the transmitter a second carrier of second frequency N/n derived from the first reference carrier where the divisor n is greater than 1, for modulating the second carrier with a digital modulating signal in accordance with the digital information to be transmitted thereby, and for broadcasting the digitally modulated second carrier; means at the receiver for receiving the first carrier and for dividing it by the divisor n to produce a corresponding demodulating signal of frequency N/n; and a demodulator at the receiver receiving the second digitally modulated carrier and the demodulating signal and demodulating the second digitally modulated carrier with the second demodulating signal to generate a resulting digital information signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A signal communication system comprising a base transmitter including transmitting means and also including receiving means, and comprising a plurality of module receivers, each of which includes a respective receiving means and also a respective transmitting means;
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the transmitting means of the base transmitter including means for generating a first carrier of a first reference frequency N and for transmitting that first carrier respectively to the receiving means of the module receivers; each transmitting means of the base transmitter and the module receiver also including means for generating when transmitting a second carrier of second frequency N/n derived from the first reference carrier, where the divisor n is greater than 1, means for modulating the respective second carrier with a respective digital modulating signal in accordance with digital information to be transmitted respectively from the base transmitter and the module receivers, and means for transmitting the digitally modulated second carrier therefrom; dividing means at each receiving means receiving the first carrier from the respective transmitting means and dividing it by the divisor n to produce a corresponding demodulating signal of frequency N/n; and a demodulator at each receiving means receiving the respective second digitally modulated carrier and the demodulating signal and demodulating the second digitally modulated carrier with the demodulating signal to generate a resulting digital information signal. - View Dependent Claims (15, 16, 17, 18, 19)
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20. A signal communication system comprising a base transmitter including transmitting means and also including receiving means, and comprising a plurality of module receivers, each of which includes a respective receiving means and also a respective transmitting means;
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the transmitting means of the base transmitter including means for generating a first carrier of a first reference frequency N and for transmitting that first carrier respectively to the receiving means of the module receivers, wherein the said first carrier is generated at the base transmission means and transmitted therefrom in the form of sequential discrete envelopes; each transmitting means of the base transmitter and the module receiver also including means for generating when transmitting a second carrier of second frequency N/n derived from the first reference carrier, where the divisor n is greater than 1, for generating a data word to be transmitted thereby, means for modulating the second carrier with the said data word, and means for transmitting the resultant modulated second carrier therefrom; dividing means at each receiving means receiving the first carrier from the respective transmitting means and dividing it by the divisor n to produce a corresponding demodulating signal of frequency N/n; and a demodulator at each receiving means receiving the respective second digitally modulated carrier and the demodulating signal and demodulating the second digitally modulated carrier with the demodulating signal to generate a resulting data word; the receiving means at each module receiver detecting each received data word and the module receiver in response t its termination generating a timing period of length such that the sum of the length of the received data word, the length of the timing period and the length of a module data word to be transmitted by the module transmitting means is equal to the length of a respective envelope of said first carrier frequency; the transmitting means at the module receiver modulating the respective second carrier with its data word to be transmitted and transmitting the resultant, modulated second carrier at the termination of the said timing period. - View Dependent Claims (21, 22, 23, 24, 25, 26)
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Specification