Two-way cable television system with enhanced signal-to-noise ratio for upstream signals

• US 3,924,187 A
• Filed: 05/14/1974
• Issued: 12/02/1975
• Est. Priority Date: 05/14/1974
• Status: Expired due to Term

• Current Assignee: Magnavox Electronic Systems Company
• Original Assignee: Paul M. Dormans
• Inventors: Dormans, Paul M.
• Primary Examiner(s): Libman, George H.
• Application Number:
  US05/469,713
• Time in Patent Office: 567 Days
• Field of Search: 178/DIG.13 179/17R,17A 340/147R,151,147SY,147C,183,408 325/308,478,52
• US Class Current: 725/125
• CPC Class Codes: H04B 3/04 Control of transmission; Equalising
• CPC Class Codes: H04H 20/78 CATV [Community Antenna Television] systems
• CPC Class Codes: H04H 60/97 using uplink of the CATV systems
• CPC Class Codes: H04N 7/173 with two-way working, e.g. subscriber sending a programme selection signal

Abstract

A cable television system having a bidirectional, downstream and upstream, signal transmission network capable of providing downstream signal paths between a central station and each of a plurality of subscriber terminals simultaneously with upstream signal paths between each of the subscriber terminals and the central station, utilizes controllable signal gates in series with the upstream paths. Each gate is associated with one or more of the subscriber terminals and a portion of the upstream network common thereto. Each gate is activated at appropriate times to allow transmission of upstream signals from the subscriber terminals to the central station; and at other times, to isolate both the subscriber terminals and the common network portion from the remainder of the system'"'"''"'"'s upstream network and the central station without affecting the transmission of downstream signals to the subscriber terminals. The system operates for providing a reduction in the level of undesired noise which normally accompanies desired upstream signals to the central station by reducing the number of noise contributing sources in the system'"'"''"'"'s upstream network. Certain subscriber terminals and portions of the upstream network which are not, at the time, active in upstream signal transmission are removed from the upstream network. Activation of the gates can be controlled by the presence of an actual upstream signal at each gate or by other types of either downstream or upstream signals which are indicative of, or referenced to, time periods during which it is desirous to have the gate activated.

Claims

1. A two-way cable television system for providing an enhanced signal-to-noise ratio for upstream signals comprising:

a bidirectional signal transmission network for providing simultaneous downstream and upstream signal paths and having a single downstream source node in common with a single upstream sink node and a plurality of downstream sink nodes in common with a plurality of upstream source nodes;

first signal generating and receiving means connected to the common downstream source node and upstream sink node for providing transmission of downstream signals and a master reference signal and for reception of upstream signals;

second signal generating and receiving means connected to each one of the common downstream sink nodes and upstream source nodes for providing transmission of upstream signals and reception of downstream signals, each one of said second signal generating means having a predetermined and different time period for the transmission of the upstream signals which time period is commenced by said master reference signal; and

gating means associated with one or more of the second signal generating and receiving means and inserted in series into the signal path of the signal transmission network and controlled by the signals therein for gating the last mentioned one or more second signal generating and receiving means to the upstream signal path during said time period of each one of said one or more second signal generating means whereby there is a selective reduction of the number of second signal generating and receiving means connected to the upstream signal path and the first signal receiving means.

2. In a cable television system having a central station and a plurality of subscriber terminals, a signal transmission network interconnecting the central station and the subscriber terminals for providing downstream and upstream signal paths to and from the subscriber terminals and the central station, the system being capable of providing simultaneous transmission of downstream signals from the central station to the subscriber terminals and upstream signals from the subscriber terminals to the central station, each subscriber terminal being assigned to a predetermined and uniqUe time slot period for the transmission of upstream signals, the downstream signals including a time slot reference signal for use by all the subscriber terminals to establish their predetermined time slot periods, the improvement comprising:

means at the central station for transmitting downstream time slot reference signals to each of the plurality of subscriber terminals;

means connected to the signal transmission network for receiving the transmitted time slot reference signals and including timing means responsive to the received signals for providing an enabling signal, said timing means adapted to provide said enabling signal only during the time slot periods assigned to a preselected one or more of the subscriber terminals; and

means inserted in series into the signal paths of said last mentioned subscriber terminals and including a gating means responsive to said enabling signal for continuously providing a downstream signal path and for providing an upstream signal path only during the time slot periods assigned to said terminals.

3. A method of reducing the noise in an upstream signal network for enhancing the signal-to-noise ratio of upstream signals in a time slot organized two-way cable television system having a central station and a plurality of subscriber terminals interconnected by simultaneous downstream and upstream signal paths, the subscriber terminals having a predetermined time slot period for transmitting upstream signals, the predetermined time slot period being different for different subscriber terminals, the method comprising:

transmitting a master timing reference signal;

receiving the master timing reference signal at all bidirectional control units;

generating at each bidirectional control unit upon receipt of the reference signal an enabling signal having a predetermined time interval corresponding to the said different time slot periods of said bidirectional control unit; and

gating each bidirectional control unit to the upstream signal path during its predetermined time interval.