Modulation and demodulation system employing AM-PSK and QPSK communication system using digital signals

A method for transmitting information in a bit pattern from a source node to a target node in a communication system having a unidirectional transmitting medium terminating at a head end said information being translated at said head end onto a unidirectional receiving medium originating from said head end, comprising the steps of:

• transmitting said information as an offset quadrature phase shift keyed (OQPSK) signal on a carrier on said transmitting medium from said source node;
• receiving said OQPSK with an OQPSK receiver at said head end to obtain a received signal;
• hard limiting said received signal with a limiter circuit means to obtain a limited signal within a defined dynamic range;
• transmitting continuously a class one, three-level partial response signal on a continuous carrier on said receiving medium from said head end;
• modulating said continuous carrier with said bit pattern of said information when said bit pattern of said information is present and modulating said continuous carrier with a repetitive bit pattern when said bit pattern of said information is not present;
• receiving said continuous carrier at said target node on said receiving medium;
• detecting said modulated continuous carrier with an envelope detector means;
• and
• extracting said bit pattern of said information from said modulated continuous carrier by strobing said bit pattern in synchronism with a system clock.

A communication system for transmitting a unit of information in a bit pattern from a source node to a set of target nodes comprising:

• a head end;
• a unidirectional transmitting medium coupling each node in a source path to and terminating at said head end;
• a unidirectional receiving medium originating from said head end and coupling to each said target node;
• means at said source node for transmitting said information as an offset quadrature phase shift keyed (OQPSK) signal on a carried on a transmitting bus from said node;
• said head end comprising:
• a) head end receiving means at said head end for receiving said OQPSK signal with an OQPSK receiver at said head end to obtain a received signal, said head end receiving means including a limiter circuit means for hard limiting said received signal to obtain a limited signal within a defined range;
• and
• b) head end translating means for transferring signals received at said head end of said transmitting medium to said receiving medium;
• c) means for transmitting continuously a class one, three-level partial response signal on a continuous carrier on said receiving medium from said head end;
• and
• d) means for modulating said continuous carrier with said bit pattern of said information when said bit pattern of said information is present and modulating said continuous carrier with a repetitive bit pattern when said bit pattern of said information is not present;
• and target node receiving means for receiving said continuous carrier at said target node on said receiving medium, said target node receiving means including:
• a) envelope detector means for detecting said modulated continuous carrier;
• and
• b) analog to digital converting means for extracting said bit pattern of said information from said carrier by strobing said bit pattern in synchronism with a system clock.