Dual mode phone line networking modem utilizing conventional telephone wiring

• US 6,603,808 B1
• Filed: 07/22/1999
• Issued: 08/05/2003
• Est. Priority Date: 07/22/1999
• Status: Expired due to Term

• Current Assignee: HTC Corporation
• Original Assignee: Compaq Information Technologies Group LP (HP Inc.)
• Inventors: Watts, Robert F., Anne, Ramakrishna
• Primary Examiner(s): Tran, Khai
• Application Number:
  US09/359,018
• Time in Patent Office: 1,475 Days
• Field of Search: 375/222, 375/219, 375/261, 375/269, 375/376, 709/200, 709/220, 711/150
• US Class Current: 375/222
• CPC Class Codes: H04L 2027/0073 Detection of synchronisation state
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453

Abstract

A networking modem capable of full duplex communication over a telephone line is adapted for use as a component of a computer system. The modem comprises a digital signal processor (DSP) capable of implementing a plurality of digital modulation and demodulation techniques, including pulse position modulation (PPM), quadrature phase shift keying (QPSK), and quadrature amplitude modulation (QAM). The DSP implements a digital phase locked loop (DPLL), including a carrier NCO and a carrier detector to synchronize local demodulation timing to an incoming carrier signal. Available processing options include spectral agility for optimizing channel capacity, symbol shaping to compensate for evolving channel conditions, and echo cancellation. The digital processing provides a flexible, adaptive, programmable, and backward compatible solution to eliminate various problems with prior art systems, including timing inaccuracies, incompatibility with standard modulation techniques, the half duplex limitation, and the susceptibility to noise that increases intersymbol interference and limits throughput.

Claims

1. A computer system, comprising:

a central processing unit;

a memory array coupled to said central processing unit;

an expansion bus coupled to said central processing unit and said memory array, said expansion bus capable of interfacing peripheral devices; and

a networking modem coupled to said expansion bus, comprising;

an expansion bus interface coupled to said expansion bus;

a network interface capable of connecting to a telephone line;

a programmable digital signal processor coupling said expansion bus interface to said network interface;

said networking modem is capable of full duplex communication over the telephone line;

wherein said computer system is capable of using said networking modem to communicate with another device connected to the telephone line;

wherein said networking modem further comprises;

a CODEC disposed between said network interface and said digital signal processor, said CODEC comprising an analog to digital converter that converts analog signals received through said network interface into incoming digital data and applies the incoming digital data to said digital signal processor and a digital to analog converter that converts digital data output from said digital signal processor into outgoing analog signals and applies the outgoing analog signals to the telephone line through said network interface;

a digital phase locked loop that recovers the timing of a received pulse position modulation canrier;

a carrier detector that asserts a carrier detect signal when said networking modem receives a pulse position modulated carrier; and

a counter synchronized to said digital phase locked loop, wherein said counter counts when the carrier detect signal is deasserted;

wherein said digital signal processor demiodulates a digital data signal received from the telephone line, and wherein the digital modulation comprises at least one of the following;

pulse position modulation, pulse amplitutde modulation, quadratlire amplitude modulation, phase shift keying, and quadrature phase shift keying.

2. A computer system, comprising:

a central processing unit;

a memory array coupled to said central processing unit;

an expansion bus coupled to said central processing unit and said memory array, said expansion bus capable of interfacing peripheral devices; and

a networking modemn coupled to said expansion bus, comprising;

an expansion bus interface coupled to said expansion bus;

a network interface capable of conniectinga to a telephone line;

a programmable digital signal processor coupling said expansion bus interface to said network interface;

said networking modem is capable of full duplex communication over the telephone line;

wherein said computer system is capable of using said networking modem to communicate with another device connected to the telephone line;

wherein said networking modem further comprises a CODEC disposed between said network interface and said digital signal processor, said CODEC comprising an analog to digital converter that converts analog signals received through said network interface into incoming digital data and applies the incoming digital data to said digital signal processor and a digital to analog converter that converts digital data output from said digital signal processor into outgoing analog signals and applies the outgoing analog signals to the telephone line through said network interface; and

wherein said digital signal processor comprises a lookup table that stores a plurality of symbol waveform is, each symbol waveform corresponding to a digital symbol, and wherein said digital signal processor reads symbol waveforms from said lookup table to create outgoing data signals to be transmitted over the telephone line.

3. The computer system of claim 2, wherein the plurality of symbol waveforms includes a group of symbol waveforms corresponding to a first digital symbol, and wherein said digital signal processor selects a first one of said group of symbol waveforms during a first time, wherein the selection is based on the channel characteristics of the, telephone line at the first time.

4. The computer system of claim 3, wherein said digital signal processor selects a second one of said group of symbol waveforms during a second time, wherein the selection is based on the channel characteristics of the telephone line at said second time, and wherein the first time precedes the second time.

5. A computer system, comprising:

a central processing unit;

a memory array coupled to said central processing unit;

an expansion bus coupled to said central processing unit and said memory array, said expansion bus capable of interfacing peripheral devices; and

a networking modem coupled to said expansion bus, comprising;

an expansion bus interface coupled to said expansion bus;

a network interface capable of connecting to a telephone line; and

a programmable digital signal processor coupling said expansion bus interface to said network interface;

wherein said computer system is capable of using said networking modem to communicate with another device connected to the telephone line; and

wherein said networking modem further comprises a conventional telephone modem data pump.

6. The computer system of claim 5, wherein said networking modem further comprises a DSL modem data pump.

7. A computer system, comprising:

a central processing unit;

an input device operatively coupled to said central processing unit;

a memory device coupled to said central processing unit; and

a phone line networking modem coupled to said central processing unit and said memory device, comprising;

a computer interface coupled to said central processing unit and said memory device and that transmits and receives data within said computer system;

a phone line interface connectable to a telephone line and capable of transmitting and receiving data simultaneously over the telephone line; and

a digital signal processor coupling said computer interface to said phone line interface;

wherein said phone line modem is capable of fill duplex communication with another device connected to said telephone line; and

wherein said phone line modem further comprises a CODEC disposed between said phone line interface and said digital signal processor, said CODEC comprising;

an analog to digital converter that converts analog signals received through said phone line interface into incoming digital data and applies the incoming digital data to said digital signal processor; and

a digital to analog converter that converts digital data output from said digital signal processor into outgoing analog signals and applies the outgoing analog signals to the telephone line through said phone line interface;

wherein said digital signal processor receives and demodulates a digital data signal received from the telephone line, and wherein the digital modulation is selected from the group consisting of pulse position modulation, pulse amplitude modulation, quadrature amplitude modulation, phase shift keying, and quadrature phase shift keying; and

wherein said networking modem further comprises;

a digital phase locked loop that tracks the timing of a received pulse position modulation carrier;

a carrier detector that determines when said networking modem receives a pulse position modulated carrier; and

a counter synchronized to said digital phase locked loop, wherein said counter counts when said carrier detector does not detect a pulse position modulated carrier pulse.

8. A computer system, comprising:

a central processing unit;

an input device operatively coupled to said central processing unit;

a memory device coupled to said central processing unit; and

a phone line networking modem coupled to said central processing unit and said memory device, comprising;

a computer interface coupled to said central processing unit and said memory device and that transmits and receives data within said computer system;

a phone line interface connectable to a telephone line and capable of transmitting and receiving data simultaneously over the telephone line; and

a digital signal processor coupling said computer interface to said phone line interface;

wherein said phone line modem is capable of full duplex communication with another device connected to said telephone line; and

wherein said phone line modem further comprises a CODEC disposed between said phone line interface and said digital signal processor, said CODEC comprising;

an analog to digital converter that converts analog signals received through said phone line interface into incoming digital data and applies the incoming digital data to said digital signal processor; and

a digital to analog converter that converts digital data output from said digital signal processor into outgoing analog signals and applies the outgoing analog signals to the telephone line through said phone line interface;

wherein said digital signal processor comprises a lookup table that stores a plurality of symbol waveforms, each symbol waveform corresponding to a digital symbol, and wherein said digital signal processor reads symbol waveforms from said lookup table to create outgoing data signals to be transmitted over the telephone line.

9. The computer system of claim 8, wherein the plurality of symbol waveforms includes a group of symbol waveforms representing a first digital symbol, and wherein said digital signal processor chooses a first waveform from said group to compensate for the channel characteristics of the telephone line at said first time.

10. The computer system of claim 9, wherein said digital signal processor selects a second waveform from said first group to compensate for the channel characteristics of the telephone line at a second time, wherein the first time precedes the second time.

11. A computer system, comprising:

a central processing unit;

an input device operatively coupled to said central processing unit;

a memory device coupled to said central processing unit; and

a phone line networking modem coupled to said central processing unit and said memory device, comprising;

a computer interface coupled to said central processing unit and said memory device and that transmits and receives data within said computer system;

a phone line interface connectable to a telephone line and capable of transmitting and receiving data simultaneously over the telephone line; and

a digital signal processor coupling said computer interface to said phone line interface;

wherein said phone line modem further comprises a conventional telephone modem data pump and is capable of full duplex communication with another device connected to said telephone line.

12. The computer system of claim 11, wherein said phone line modem further comprises a DSL modem data pump.

13. A networking modem, comprising:

a programmable digital signal processor;

a digital to analog converter coupled to said digital signal processor; and

telephone line coupling magnetics;

wherein if a telephone line is coupled to said coupling magnetics, said digital signal processor is configured to transmit digital data signals to another networking device coupled to the same telephone line using one of the following modulation techniques;

pulse position modulation, pulse amplitude modulation, quadrature amplitude modulation, phase shift keying, and quadrature phase shift keying;

a bus interface attachable to a computer system and configured to receive digital data, wherein the digital data signals represent the digital data received through said bus interface;

wherein said networking modem comprises an internal computer modem and wherein said bus interface is configured to mate with an expansion bus card slot within a computer system; and

wherein said networking modem is capable of full duplex, multidrop communications over the telephone line.

14. A networking modem, comprising:

a programmable digital signal processor;

a digital to analog converter coupled to said digital signal processor; and

telephone line coupling magnetics;

wherein if a telephone line is coupled to said coupling magnetics, said digital signal processor is configured to transmit digital data signals to another networking device coupled to the same telephone line using one of the following modulation techniques;

pulse position modulation, pulse amplitude modulation, quadrature amplitude modulation, phase shift keying, and quadrature phase shift keying;

wherein said digital signal processor comprises a lookup table that stores a plurality of symbol waveforms, each symbol waveform corresponding to one data symbol, and wherein said digital signal processor reads symbol waveforms from said lookup table to create the outgoing digital data signal.

15. The networking modem of claim 14, wherein the plurality of symbol waveforms includes a group of symbol waveforms corresponding to a first digital symbol, and wherein said digital signal processor selects a first one of said group of symbol waveforms during a first time, based on the channel characteristics of the telephone line at said first time.

16. The networking modem of claim 15, wherein said digital signal processor selects a second one of said group of symbol waveforms at a second time, based on the channel characteristics of the telephone line at said second time, and wherein the first time precedes the second time.

17. The networking modem of claim 16, further comprising a POTS data pump.

18. The networking modem of claim 17, further comprising a DSL data pump.

19. A networking modemn, comprising:

telephone line coupling magnetics;

an analog to digital converter coupled to said telephone line coupling magnetics and that samples an analog signal received from said coupling magnetics; and

a programmable digital signal processor that receives the sampled signal from said analog to digital converter and demodulates the sampled signal to produce digital data;

wherein said digital signal processor is configured to communicate with another networking device over a telephone line that couples said networking device to said networking modem and is configured to transmit an outgoing digital data signal to the other networking device;

a digital phase locked loop that recovers the timing of a received carrier;

a carrier detector that asserts a carrier detect signal when said networking modem receives a carrier; and

a counter synchronized to said digital phase locked loop, wherein said counter counts when the carrier detect signal is deasserted.

20. The networking modem of claim 19, wherein said digital signal processor comprises a lookup table that stores a plurality of symbol waveforms, each symbol waveform corresponding to a data symbol, and wherein said digital signal processor reads symbol waveforms from said lookup table to create the outgoing digital data signal.

21. The networking modem of claim 20, wherein the plurality of symbol waveforms includes a group of symbol waveforms corresponding to a first digital symbol, and wherein said digital signal processor selects a first one of the group of symbol waveforms at a first time according to the channel characteristics of the telephone line at said first time.

22. The networking modem of claim 21, wherein said digital signal processor selects a second one of the group of symbol waveforms during a second time according to the channel characteristics of the telephone line at said second time, wherein the first time precedes the second time.

23. A networking modem, comprising:

telephone line coupling magnetics;

an analog to digital converter coupled to said telephone line coupling magnetics and that samples an analog signal received from said coupling magnetics;

a programmable digital signal processor that receives the sampled signal from said analog to digital converter and demodulates the sampled signal to produce digital data and said digital signal processor is configured to communicate with another networking device over a telephone line that couples said networking device to said networking modem; and

a POTS data pump.

24. The networking modem of claim 23, further comprising a DSL data pump.

25. A networking modem, comprising:

a coupling means for transmitting and receiving signals over a telephone line;

a conversion means for converting incoming analog signals received via said coupling means into incoming digital signals and for converting outgoing digital signals into outgoing analog signals which are sent to said coupling means;

a processing means for creating and demodulating digitally modulated signals, said processing means coupled to said conversion means; and

a means for interfacing a computer bus, said means for interfacing coupled to said processing means and for transferring data between a computer bus and said processing means;

wherein said processing means creates digitally modulated outgoing digital signals and transmits the outgoing digital signals to the telephone line via said conversion means and said coupling means;

wherein said modem is capable of full duplex communications over the attached telephone line; and

wherein said digital signal processor comprises a storage means that holds a plurality of symbol waveforms, each symbol waveform corresponding to a data symbol, and wherein said digital signal processor reads symbol waveforms from said storage means to create the outgoing digital data signals.

26. The networking modem of claim 25, wherein the plurality of symbol waveforms includes a group of symbol waveforms corresponding to a first digital symbol, and wherein said digital signal processor selects a first one of the group of symbol waveforms during a first time according to the channel characteristics of the telephone line at said first time.

27. The networking modem of claim 26, wherein said digital signal processor selects a second one of the group of symbol waveforms during a second time according to the channel characteristics of the telephone line at said second time, wherein the first time precedes the second time.

28. A networking modem, comprising:

a coupling means for transmitting and receiving signals over a telephone line;

a conversion means for converting incoming analog signals received via said coupling means into incoming digital signals and for converting outgoing digital signals into outgoing analog signals which are sent to said coupling means;

a processing means for creating and demodulating digitally modulated signals, said processing means coupled to said conversion means; and

a means for interfacing a computer bus, said means for interfacing coupled to said processing means and for transferring data between a computer bus and said processing means; and

a POTS data pump;

wherein said processing means creates digitally modulated outgoing digital signals and transmits the outgoing digital signals to the telephone line via said conversion means and said coupling means.

29. The networking modem of claim 28, further comprising a DSL data pump.

30. A method of networking computers, comprising:

connecting a telephone line between a first computer and a second computer;

supplying data to a first programmable digital signal processor within said first computer;

creating within said first programmable digital signal processor a carrier signal that is digitally modulated with the data;

transmitting the modulated carrier signal from said first computer to said second computer over said telephone line;

sampling the transmitted modulated cannier signal within said second computer;

demodulating the sampled carrier signal within a second digital signal processor in said second computer;

generating a local timing signal;

comparing the phase of the local timing signal with the sampled carrier signal;

adjusting the frequency of the local timing signal until the local timing signal is phase locked with the sampled carrier signal; and

incrementing a counter on each cycle of the local timing signal if no carrier signal is detected.

31. The method of claim 30, including:

generating an error voltage indicative of the phase comparison;

asserting a carrier detect signal if the error voltage falls within a predetermined range; and

incrementing the counter if the carrier detect signal is deasserted.

32. The method of claim 31, wherein the value of the counter represents the time delay between carrier pulses in a pulse position modulation system.