Silent polarity reversal in a communication system

A method for reversing polarity in a communication system comprising the steps of:

• receiving a polarity reversal request from a central office;
• sampling direct current flowing in a subscriber loop of the communication system;
• storing a discrete time version, Idc(n) of the sampled direct current in a memory;
• modulating the stored Idc(n) over discrete time intervals with respective portions of a predetermined discrete time waveform;
• converting the modulated discrete time waveform into a continuous time control signal;
• and
• providing a continuous time current to the subscriber loop in accordance with the continuous time control signal having substantially the same frequency components as the predetermined discrete time waveform.

A method of reversing polarity of A and B conductors of a plurality of subscriber loops, the method comprising the steps of:

• providing a respective direct current, Idc(N), to each of N subscriber loops, where N is an integer;
• detecting each Idc(N);
• sampling each Idc(N);
• storing each Idc(N) in a memory coupled to a processor;
• executing a computer program, for each of the of the N subscriber loops, with the processor, wherein the computer program is stored in a memory coupled to the processor and includes processor executable instructions for:
• monitoring for polarity reversal requests for respective subscriber loops from a central office;
• if a polarity request is monitored which requests positive polarity with respect to conductor B, the method comprises the steps of:
• a) multiplying the stored Idc(N) by a value derived from a first look up table entry of M look up table entries stored in a memory coupled to the processor to generate a discrete time control signal;
• b) multiplying the stored Idc(N) by a value derived from a subsequent look up table entry to generate a following discrete time control signal;
• c) converting the successive discrete time control signals into a continuous time waveform control signal;
• d) generating a current waveform on the respective subscriber loop with approximately the same frequency components as the discrete time waveform control signal;
• and
• e) repeating the steps of b), c), and d) for each of the M look up table entries;
• if a polarity request is monitored which requests positive polarity with respect to conductor A, the method comprises the steps of:
• f) multiplying the stored Idc(N) by a value derived from a last look up table entry of the M look up table entries to generate a discrete time control signal;
• g) multiplying the stored Idc(N) by a value derived from a preceding look up table entry to generate a following discrete time control signal;
• h) converting the successive discrete time control signals into a continuous time waveform control signal;
• i) generating a current waveform on the respective subscriber loop with approximately the same frequency components as the discrete time waveform control signal;
• and
• j) repeating the steps of g), h), and i) for each of the M look up table entries.

A communication system comprising:

• circuitry for sampling a first continuous time signal on a subscriber loop in response to a request for a polarity reversal of the first continuous time signal;
• a line card having a processor and a memory and coupled to the sampling circuitry, the memory storing code for execution by the processor, the code including instructions for modulating the sampled first continuous time signal with predetermined discrete time waveform components stored in the memory to generate a discrete time control signal;
• and
• circuitry coupled to the processor responsive to the discrete time control signal to drive a second continuous time signal on the subscriber loop, wherein the second continuous time signal has at least approximately the same frequency component(s) as the predetermined discrete waveform.

A communication system comprising:

• a subscriber line interface circuit having input terminals coupled to respective subscriber loop terminal pairs to detect a direct current signal and having output terminals to receive a continuous time control signal;
• analog to digital converter coupled to an output terminal of the subscriber line interface circuit to sample the direct current signal;
• a processor coupled to the analog to digital converter for receiving a sample of the direct current signal;
• a digital to analog converter coupled between the processor and the subscriber loop;
• a memory coupled to the processor and storing code for execution by the processor, the code including instructions for retrieving waveform shaping factors from the memory, for generating a discrete time control waveform, for reversing polarity of the subscriber loop terminal pairs, from a product of the waveform shaping factors and the direct current signal sample, and for providing the discrete time control waveform to the digital to analog converter wherein the code further includes instructions for multiplying the direct current signal sample and a first order of the waveform shaping factors to reverse polarity of the subscriber loop terminal pairs in a first direction and for multiplying the direct current signal sample and a reverse order of the waveform shaping factors to reverse polarity of the subscriber loop terminal pairs in a reverse direction;
• wherein the subscriber line interface circuit is responsive to a continuous time control input signal from the digital to analog converter corresponding to the discrete time control waveform.

A communication system comprising:

• means for receiving a polarity reversal request from a central office;
• means for sampling direct current flowing in a subscriber loop of the communication system;
• means for storing a discrete time version, Idc(n) of the sampled direct current;
• means for modulating the stored Idc(n) over discrete time intervals with respective portions of a predetermined discrete time waveform;
• means for converting the modulated discrete time waveform into a continuous time control signal;
• and
• means for providing a continuous time current to the subscriber loop in accordance with the continuous time control signal having substantially the same frequency components as the predetermined discrete time waveform.