Spread spectrum bit allocation algorithm

• US 20020044597A1
• Filed: 05/25/2001
• Published: 04/18/2002
• Est. Priority Date: 12/31/1997
• Status: Active Grant

• Current Assignee: Ranjan V. Sonalkar, Richard Robert Shively
• Original Assignee: Ranjan V. Sonalkar, Richard Robert Shively
• Inventors: Sonalkar, Ranjan V., Shively, Richard Robert
• Granted Patent: US 6,418,161 B1
• Time in Patent Office: Days
• US Class Current: 375/222
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

High transmission capacity in a twisted pair signal line, where power is limited by a power spectral-density mask and an aggregate signal power constraint, is obtained by: (1) allocating data to multitone sub-bands according to a lowest marginal power-cost per bit scheme and (2) in an environment where an aggregate power budget remains after all bits have been allocated to all sub-bands with sufficient margins to carry a bit, assigning additional bits to sub-bands with otherwise insufficient power margins to carry a single bit, by frequency-domain-spreading a single bit across several sub-bands at correspondingly reduced power levels, to permit the otherwise unacceptable noise levels to be reduced on average by despreading at the receiving end. Another feature of the invention, applicable in an environment in which multiple interfering channels are employed, provides increased signal throughput by (3) transmitting coherently in a number of multitone sub-bands, identical blocks of data, with the number of multitone sub-bands being equal to a number of interfering channels and multiplying the signal carried by corresponding sub-bands in the separate interfering channels by a different respective vector from an orthonormal basis set so that near-end cross-talk is eliminated upon despreading at the receiving end.

Claims

1. A transmitting modem receiving digital data from a data source, modulating carriers to represent said digital data, and applying a resulting modulated signal to a channel connectable to a receiving modem, said channel being subject to a power spectral density mask said transmitting modem comprising:

first, second, and third signal modulators, each with an input;

a signal combiner with a combined output connected to said channel;

a serial-to-parallel converter connected to said data source and to each of said first, second, and third signal modulator inputs such that said digital data from said data source is converted to multiple parallel streams applied respectively to said first, second, and third signal modulators;

each of said first, second, and third signal modulators having a respective output connected to said signal combiner such that a sum of output signals of said first, second, and third signal modulators is applied to said channel;

a transfer characteristic of said channel being such that a first minimum power required to represent a specified minimum number of bits by modulating in a first frequency sub-band falls below said power spectral density mask and such a that a second minimum power required to represent a second specified minimum number of bits by modulating in each of second and third frequency sub-bands exceeds said power spectral density mask;

said serial-to-parallel converter being programmed to feed a first bit of said digital data to said first signal modulator to represent said first bit by modulating in said first frequency sub-band at a first power level at least as high as said first minimum power;

said serial-to-parallel converter being programmed to feed a second bit of said digital data to said second and third modulators to represent said second bit by coherently modulating in both said second and said third frequency sub-bands at a second power level below said first power level, whereby resulting signals applied in said second and third frequency sub-bands may be combined by said receiving modem to retrieve said second bit;

said first and second minimum number of bits both being equal to one in the absence of some other specified constraint.

2. A modem as in claim 1, further comprising fourth and fifth modulators, said serial-to-parallel converter being programmed to feed said second bit to said fourth and fifth modulators, whereby said resulting signals applied in said second through fifth frequency sub-bands may be coherently combined by said receiving modem to retrieve said second bit.

3. A modem as in claim 2, wherein said second through fifth frequency sub-bands are substantially adjacent in frequency such that they form a continuous spectrum.

4. A modem as in claim 1, wherein said second and third frequency sub-bands are substantially adjacent in frequency such that they form a continuous spectrum.

5. A frequency division multiplexor transmitting data from a data source over a channel, comprising:

a signal modulator with an input and first, second, and third outputs, each transmitting data in a respective one of first, second, and third frequency bands;

a channel response detector connected to said channel to detect a transfer characteristic of said channel, said transfer characteristic including a noise power level and an attenuation of said channel;

a controller connected to said signal modulator to control an allocation of first and second blocks of data from said data source for transmission in said first, second, and third frequency bands;

said controller being programmed to transmit said first block of data in said first frequency band and transmit said second block redundantly in each of said second and third frequency bands at a first power level when said channel transfer characteristic is such that a power level required to transmit said second block, at a specified bit error rate, in said second frequency band alone is a first power level and to transmit said second block in said second frequency band alone when said channel transfer characteristic is such that a power level required to transmit said second block, at said specified bit error rate, in said second frequency band alone at a second power level, said second power level being higher than said first power level.

6. A frequency division multiplexor as in claim 5, wherein said controller transmits said second block redundantly in said second and third frequency bands when an amount of power required to transmit a single bit in said second frequency band exceeds a power spectral density mask limit stored by said controller.

7. A frequency division multiplexor as in claim 6, wherein said controller is programmed to transmit said second data block in said second frequency band alone when a power required to transmit said second data block in said second frequency band is less than a power spectral density mask limit stored by said controller and greater than an aggregate power limit for all said first, second, and third frequency bands stored by said controller.

8. A frequency division multiplexor as in claim 5, wherein said controller is programmed to calculate an array of values each indicating an amount of power required to transmit a minimum number of bits in each of said second and third frequency bands and to sort said array according to said power, said controller being further programmed to transmit said second block in said second and third frequency bands responsively to one of said second and said third frequency bands appearing in said sorted array at a position indicating that said second bin requires a minimum amount of power to transmit said minimum number of bits.

9. A frequency division multiplexor as in claim 5, wherein said controller is programmed to calculate an array of values each indicating an amount of power required to transmit a minimum number of bits in each of said second and third frequency bands and to sort said array according to said power, said controller being further programmed to transmit said second block in said second and third frequency bands responsively to said sorted array.

10. A modem, comprising:

a frequency-division modulator with a controller, said modulator transmitting input data in frequency channels;

said controller having a memory storing a power spectral density (PSD) mask specifying a respective maximum power level permitted for a signal transmitted in each of said frequency channels;

said controller memory storing an aggregate power limit specifying a total permitted power for all of said signals;

said controller being programmed to measure and store in said memory a measured channel transfer characteristic of a communications channel through which said input data is to be transmitted;

said controller being programmed to transmit respective unique portions of said input data in said each of said frequency channels, responsively to said stored aggregate power limit, said PSD mask, and said measured transfer characteristic being a first transfer characteristic and to transmit a same portion of said data in at least two of said frequency channels responsively to said stored aggregate power limit, said PSD mask, and said measured transfer characteristic being a second transfer characteristic.

11. A modem as in claim 10, wherein said respective transfer characteristic is responsive to a specified error rate.

12. A modem as in claim 10, wherein said first transfer characteristic is characterized by at least one of a lower aggregate noise level and a lower aggregate attenuation than said second transfer characteristic.

14. A method as in claim 13 wherein said step of allocating bits is responsive to a channel transform characteristic sensitive to a noise power level of said channel and an attenuation of said channel and includes allocating bits to each channel frequency by allocating bits to the channel frequency having the lowest marginal power requirement to transmit an additional bit.

15. A method as in claim 13 wherein said step of further allocating includes selecting a channel frequency from a among a set of frequency channels for which no data allocated in said step of allocating.

16. A method as in claim 15, wherein said step of further allocating includes selecting a channel frequency from among said set based on a lowest marginal power requirement for transmitting a further bit.

17. A method as in claim 13, wherein said step of allocating includes allocating according to a minimum number of bits per channel frequency.

18. A method as in claim 13, wherein said step of allocating includes storing an array of length equal to a number of frequency bins, the value of each element being a maximum number of bits to be transmitted.

19. A method as in claim 13, wherein said step of further allocating includes storing an array of length equal to a number of frequency bins remaining unallocated in said step of allocating, the value of each element being an amount of power required to transmit a minimum number of bits in a frequency corresponding to a respective one of said frequency bins remaining.

13. A method for use in a data modulator for allocating bits to data channel frequencies comprising the steps of:

storing mask power data representing a respective maximum power level for each of said data channel frequencies;

storing aggregate power data representing a total amount of signal power to be applied in all of said channel frequencies;

allocating bits, such that bits are allocated up to said respective maximum power level for each of said channel frequencies and such that each of said bits is allocated to a single respective one of said channel frequencies; and

when said aggregate power level is not substantially reached in said step of allocating, further allocating bits to multiples of said channel frequencies for transmission at reduced power rates per channel frequency, to permit further bits to be allocated, until one of said aggregate power limit is substantially reached and said respective maximum power level is reached.

20. Apparatus for allocating bits for data transmission via a plurality of discrete frequencies comprising tone ordering circuitry, gain scaling circuitry and an inverse discrete Fourier transform modulator, the circuitry in combination to:

allocate initial bits to frequencies on a per frequency basis, such that said initial bits are successively allocated until a maximum power level for each frequency is at least substantially reached, each of said initial bits being unique to a given frequency;

calculate a stored total power level for said initial bits allocated to a plurality of transmit frequencies, and

if the stored total power level is not exceeded, allocate further bits to frequencies for which no initial bits are allocated, such that each of said further bits is redundantly allocated to more than one of said frequencies.

21. Apparatus as in claim 20, wherein said further bits are allocated sequentially according to the frequency requiring the least power to transmit an single bit.

22. A frequency-division multiplex (FDM) transmission system for a channel having multiple subchannels, each of said subchannels being susceptible to cross-talk interference from another of said subchannels, said system comprising:

a transmitting modem with a programmable FDM modulator connected to modulate first and second frequency carriers, representing an input data stream, in each of first and second subchannels of said channel;

a receiving modem connected to said channel;

a modulator programmed to modulate said first and second frequency carriers coherently to represent a first subportion of said data stream in said first and second frequency bands to form first and second signals in said first subchannel;

said modulator being programmed to modulate said first and second frequency carriers coherently to represent a second subportion of said data stream in said first and second frequency bands to form third and fourth signals in said second subchannel;

said receiving modem having a demodulator configured to combine coherently said first and second signals;

said modulator being further programmed to form said third and fourth signals such that when said demodulator combines coherently said first and second signals, cross-talk interference in said first subchannel, caused by concurrent transmission of said third and fourth signals in said second channel is diminished in a combined signal resulting therefrom.

23. A system as in claim 22, wherein said receiving modem combines said first and second signals such that an incoherent distortion of said first and second signals in said first subchannel is attenuated relative to said subportion of said data stream.

24. A system as in claim 22, wherein said modulator is programmed to weight said first and second signals by a respective one of a set of codes forming an orthogonal set.

25. A system as in claim 24, wherein said modulator is programmed to weight said second and third signals by a another one of said set of codes.

27. A method as in claim 24, wherein said step of combining includes deweighting said first and second signal and then summing deweighted versions of said first and second signals.

28. A method as in claim 24, wherein said orthogonal set of codes are Walsh codes.

29. A method as in claim 24, wherein first and second channels are twisted pairs of conductors in a metallic telecommunications network.

31. A system as in claim 28, wherein said modulator is programmed to modulate a third frequency carrier to represent a second subportion of said data stream, said demodulator being configured to extract said second subportion without combining said a signal corresponding to said third frequency carrier with another signal corresponding to another frequency carrier modulated in said channel.

26. A method for reducing near end cross talk comprising the steps of:

forming first and second signals in respective first and second tones redundantly representing first data to form a first multi-tone signal such that said first and second signals are weighted by a first vector of an orthogonal set of codes;

applying said first multi-tone signal to a first interfering channel;

forming third and fourth signals in said respective first and second tones redundantly representing second data to form a second multi-tone signal such that said third and fourth signals are weighted by a second vector of an orthogonal set of codes;

applying said second multi-tone signal to a second interfering channel;

combining said first and second multitone signals such that a distortion in said first data caused by near end cross talk in first interfering channel is diminished.

30. A frequency division multiplex (FDM) transmission system for transmitting an input data stream through a channel, comprising:

a transmitting modem with a programmable FDM modulator connected to modulate first and second frequency carriers, representing an input data stream, in said channel;

a receiving modem connected to said channel;

a modulator programmed to modulate said first and second frequency carriers coherently to represent a first subportion of said data stream in said first and second frequency bands to form first and second signals;

said receiving modem having a demodulator configured to combine coherently said first and second signals to extract said first subportion such that an incoherent distortion of said first and second symbols in said first channel is, on average, reduced in said extracted first subportion.

32. A method for increasing a data rate in a communication channel subject to a power spectral density mask, comprising:

detecting a transfer characteristic indicating a required minimum power of a respective carrier modulated to transmit one bit in each of a plurality of multitone subchannels of said channel;

supplying a data stream to a modulator;

modulating a first set of respective carriers to represent respective unique portions of said data stream in at least a subset of those of said multitone subchannels for which, in said step of detecting indicates said minimum power falls below a power limit imposed by said power spectral density mask;

modulating a second set of respective carriers to represent redundantly at least one portion of said data stream in at least a subset of those of said multitone subchannels for which said step of detecting indicates said minimum power exceeds a power limit imposed by said power spectral density mask;

receiving said at least first and second symbols at a receiving end of said communication channel;

combining said at least first and second symbols received at said receiving end in such a way as to increase a signal power of said at least first and second symbols and, on average, reduce incoherent distortion of said at least first and second symbols;

reconstructing said same portion of said data stream at said receiving end from a combination of said at least first and second symbols, resulting from said step of combining.

33. A communications system for communicating data in a channel having multiple subchannels, comprising:

a modulator having an output for each of said subchannels; and

a demodulator having an input for each of said subchannels;

said modulator having an input connected to receive data from a data source;

said modulator being programmed to modulate separate sets of carriers in each of said subchannels to represent respective portions of said data;

said modulator being programmed to modulate n separate frequency carriers coherently in each of said subchannels to represent a one of said respective portions of said data;

n modulated signals resulting from a modulation of said modulator being output by said modulator;

each of said n modulated signals, upon being received at said demodulator, including an incoherent component resulting from attenuation and/or noise in said channel, a first coherent component resulting from near-end cross talk from said n modulated signals in the subchannels other than said each, and a second coherent component output which is the original n modulated signals output by said modulator;

said modulator modulating said n separate frequency carriers such that when said demodulator demodulates said n modulated signals upon being received at said demodulator, by linearly combining said received n modulated signals, in a signal resulting from said linearly combining, said incoherent component and said first coherent component are, on average, suppressed and said second coherent component is, on average, amplified.

37. A method as in claim 34, wherein said first encoded signal is a CDMA signal.

38. A method as in claim 35, further comprising the step of applying a second encoded signal to said channel, said second signal being a CDMA signal with a code orthogonal to a code of said first encoded signal.

39. A method as in claim 34, wherein said first and said other channels are adjacent wires forming a cable bundle.

34. A transmitting modem receiving digital data from a data source, modulating carriers to represent said digital data, and applying a resulting modulated signal to a channel connectable to a receiving modem, said transmitting modem comprising:

first, second, and third signal modulators, each with an input;

a signal combiner with a combined output connected to said channel;

a serial-to-parallel converter connected to said data source and to each of said first and second signal modulator inputs such that said digital data from said data source is converted to multiple parallel streams applied respectively to said first and second signal modulators;

each of said first and second signal modulators having a respective output connected to said signal combiner such that a sum of output signals of said first and second signal modulators is applied to said channel;

said serial-to-parallel converter being programmed to feed a bit of said digital data to said first and second modulators to represent said second bit by coherently modulating in both said first and second frequency sub-bands, whereby resulting signals applied in said first and second frequency sub-bands may be coherently linearly combined by said receiving modem to retrieve said bit and such that incoherent components and coherent but at least partially orthogonal components of said resulting signals are attenuated and coherent component of a modulated signal applied by said first and second modulators is amplified.

35. A method for transmitting data through a channel subject to a power spectral density mask limit and an aggregate power constraint, comprising the steps of:

detecting a frequency-dependent transmission characteristic of said channel;

defining fist and second sub-bands of an aggregate transmission band responsively to a result of said step of detecting, said aggregate power constraint, and said power spectral density mask limit;

generating a first modulated signal with a first power dynamic range permitted by said power spectral density mask limit, said first modulated signal representing said first portion of said data;

generating a second modulated signal with a second power dynamic range permitted by said power spectral density mask limit, said second modulated signal representing said second portion of said data.

36. A method of communicating a signal through a first channel in which interfering signals are generated by other channels, comprising the steps of:

modulation said signal to generate a first encoded signal that is orthogonal to signals in said other channels; and

applying said first encoded signal to said first channel.

40. A method for communicating information through a cable containing a plurality of wires, comprising the steps of:

dividing the plurality of wires into groups; and

modulating signals that are to be communicated over different wires within a group with a modulation technique such that the modulated signal communicated over any wire in the group is orthogonal to the modulated signal communicated over any other wire in the group.

41. An apparatus for placement on a customer premises and for connecting premises communication devices to a wire pair leading to a communication network, comprising:

a network port for connecting to the wire pair;

a set of premises ports, containing at least one premises port, for connecting premises communication devices to said apparatus;

means for creating a CDM signal by modulating a source signal supplied by said premises devices with a code-division-multiplexing code that arranges for the spectrum of the CDM signal to occupy substantially all of the useful bandwidth of the wire pair; and

means for applying the CDM signal to the wire pair.

42. The apparatus of claim 41 where the means for applying forms the primary termination of the wire pair at the customer premises.

43. The apparatus of claim 41 where the means for applying forms the sole termination of the wire pair at the customer premises.

44. The apparatus of claim 41 further comprising

a TVRC modem that develops the CDM signal, and

a controller for coupling the premises devices to the TVRC modem.

45. The apparatus of claim 44 where the TVRC modem comprises:

a hybrid circuit connected to the network port,

a D/A converter and an A/D converter connected to the hybrid circuit,

an active echo canceler coupled to the output of the A/D converter,

an output processing unit for outputting digital signals representative of signals received at the network port, and

an input processing unit for developing signals applied to the D/A converter.

46. The apparatus of claim 44 further including:

at least one premises port in said set of premises ports for connecting ISDN phones to said apparatus, and

an ISDN interface module interposed between the controller and the port for connecting ISDN phones.

47. The apparatus of claim 44 further including

at least one premises port in said set of premises ports for connecting digital premises devices to said apparatus, and

a digital devices interface module interposed between the controller and the port for connecting digital premises devices.

48. The apparatus of claim 44 where the CDM signal comprises a plurality of modulated tones, and a preselected number of said tones are devoted by the controller to control functions.

49. The apparatus of claim 48 where at least one of the premises devices connected to said set of premises ports is asynchronous, and at least one is synchronous, and where the controller assigns the tones of the CDM signal to the asynchronous premises devices and to the synchronous premises devices, as necessary.

50. The apparatus of claim 49 where the controller assigns the tones of the CDM signal to the asynchronous premises devices and to the synchronous premises devices as necessary to satisfy the needs of the asynchronous premises devices.

51. The apparatus of claim 50 where the controller assigns the tones of the CDM signal dynamically, as the needs change.

52. The apparatus of claim 50 where the controller increases the tones of the CDM signal that are assigned to the asynchronous premises devices when an additional asynchronous premises device becomes active, and reduces the tones of the CDM signal that are assigned to the asynchronous premises devices when an active asynchronous premises device ceases to be active.

53. The apparatus of claim 50 where the tones are assigned by the controller to form groups of tones that are assigned to asynchronous and synchronous premises devices.

54. The apparatus of claim 44 where at least some of the premises devices connected to said at least one premises port are asynchronous, and some are synchronous.

55. The apparatus of claim 54 where the controller includes a module for directing information of the synchronous premises devices and the asynchronous premises devices to different routes.

56. The apparatus of claim 44 where said set of premises ports includes:

at least one analog port, and

a POTS interface interposed between the at least one analog port and the controller.

57. The apparatus of claim 56 where the POTS interface includes a current sensing circuit coupled to the controller and arranged to sense the current flowing through the analog port, and where the controller includes a current computation module that, based on the sensed current, determines whether a premises device connected to the analog port is active.

58. The apparatus of claim 57 where the current computation module determines which of a number of premises devices connected to the analog port is active.