Interactive television and data transmission system

A bidirectional wireless digital communication system comprising

• a television broadcast station for transmitting ordinary television programming including vertical sync and horizontal sync signals and associated blanking intervals on a preassigned television channel and associated video carrier;
• broadcast means for controllably transmitting downlink digital data signals;
• a plurality of subscriber receiver-transmitters distributed about an area within the broadcast range of said television broadcast station and said broadcast means, each subscriber receiver-transmitter having a subscriber receiving means for receiving said video signal and detecting sync signals, and for receiving and detecting said downlink digital data signals, each subscriber receiver transmitter having modulating means for modulating uplink digital data signals on an uplink carrier of a frequency within the frequency band of a television channel adjacent said preassigned television channel, each subscriber transmitting means coupled to said subscriber receiving means for transmitting the modulated uplink digital data signals during at least some of the blanking intervals of the received video signal;
• and
• a plurality of central receivers, each central receiver being located and having a directional antenna to predominately receive the modulated uplink digital data signals from a respective subarea within said area, each said central receiver being a means for receiving and detecting said uplink digital data signals transmitted by the respective subscriber transmitting means within the respective subarea.

A method of communicating information from a plurality of remote locations to a central location served by a television station broadcasting ordinary television programming in the frequency band of a first preassigned television channel, the television programming including horizontal and vertical sync signals and associated blanking intervals, comprising the steps of:

• (i) at each remote location;
• (a) receiving the ordinary television programming and detecting the horizontal sync signals thereof,
• (b) modulating the information to be communicated from each remote location onto a carrier having a frequency in the frequency band of a preassigned television channel adjacent the frequency band of the first preassigned television channel,
• (c) transmitting the modulated information during at least some of the horizontal blanking intervals of the received television programming, and
• (ii) at at least one central location
• (d) receiving the transmissions of step (c) and detecting the information therein.

In an interactive television system, a method of communicating information from a plurality of remote receiver locations, each connected to a cable television system, to a central location, the cable television system receiving ordinary television programming over the air and providing the same over a cable having amplifiers at various points along the cable, each serving a plurality of remote locations, comprising the steps of:

• (i) at each remote location;
• (a) modulating the information to be communicated from each remote location onto a carrier having a frequency in the frequency band of an unused cable television channel;
• (b) transmitting the modulated information on the cable only during at least some of the horizontal blanking intervals of an adjacent cable channel carrying ordinary television programming:
• (ii) adjacent each cable amplifier
• (c) detecting the horizontal sync signals of a television channel broadcasting ordinary television programming over the air
• (d) transmitting the modulated information received on the cable over the air and in the frequency band of a television channel adjacent the channel referred to in step (c) only during at least some of the horizontal blanking intervals associated with the detected horizontal sync signals of the channel referred to in step (c);
• and
• (iii) at at least one central location
• (e) receiving the transmissions of step (d) and detecting the information therein.

A method of information communication within an area utilizing the frequency band of a television channel adjacent to as well as that of a television channel serving the same area and broadcasting ordinary television programming, the programming including horizontal and vertical sync signals and associated blanking intervals, comprising the steps of:

• (a) modulating information on a plurality of subcarriers;
• (b) modulating the modulated information of step (a) onto the carrier of the television channel broadcasting the ordinary television programming, the subcarriers causing the modulation of this step (b) to result in frequency components within the frequency band of the television channel adjacent that of the television channel broadcasting ordinary television programming;
• (c) broadcasting the modulated information only during the horizontal blanking intervals of the ordinary television programming;
• (d) receiving the transmitted modulated information at a distant location and detecting the information therein.

A method of determining the location of a mobile unit within an area utilizing the frequency band of a television channel adjacent to or the same as that of a television channel serving the same area and broadcasting ordinary television programming, including horizontal and vertical sync signals and associated blanking intervals, comprising the steps of:

• (a) modulating identification information on a carrier within the frequency band of the television channel adjacent to or the same as that of the television channel broadcasting ordinary television programming;
• (b) transmitting the modulated information only during the horizontal blanking intervals of the ordinary television programming;
• (c) receiving the transmitted modulated information at the mobile unit and transponding the received information;
• and
• (d) receiving the transponded informtion and the television programming at at least two different central locations and determining the location of the mobile unit by differences in the transmission times of the received signals.