Spectral optimization and joint signaling techniques with upstream/downstream separation for communication in the presence of crosstalk

• US 6,292,559 B1
• Filed: 09/01/1998
• Issued: 09/18/2001
• Est. Priority Date: 12/19/1997
• Status: Expired due to Term

• Current Assignee: Rice University
• Original Assignee: Rice University
• Inventors: Baraniuk, Richard G., Gaikwad, Rohit V.
• Primary Examiner(s): WOO, STELLA L
• Application Number:
  US09/145,349
• Time in Patent Office: 1,113 Days
• Field of Search: 375/260, 375/254, 375/285, 375/296, 375/346, 379/417, 379/416, 370/201
• US Class Current: 379/417
• CPC Class Codes: H04L 27/00 Modulated-carrier systems
• CPC Class Codes: H04L 27/2614 Peak power aspects
• CPC Class Codes: H04L 27/2646 using feedback from receiver for adjusting OFDM transmission parameters, e.g. transmission timing or guard interval length
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: H04W 52/346 distributing total power among users or channels

Abstract

A system and method for determining transmission characteristics for a communications channel and for transmitting data on the communications channel. In one embodiment, the method starts by determining the channel'"'"'s transfer function and determining interference characteristics for the channel. The interference characteristics preferably include transfer functions describing the channel'"'"'s susceptibility to cross talk from neighboring channels. The channel transfer function and the interference characteristics are then examined and a transmit spectrum (or power spectral density function) is constructed for the channel. The transmit spectrum preferably uses orthogonal separation of upstream and downstream communications to increase channel capacity. This method is useable in communicating data when the channel is subject to interference from one or more other communications channels, including near-end cross talk (NEXT) and far-end cross talk (FEXT), from other channels carrying the same service and/or different services. The present invention may be used in digital subscriber-line (xDSL) communications or in a variety of other applications, such as in well-logging and in systems involving multiple interfering radio transmitters.

Claims

1. A method for determining a transmit spectrum for use in communicating data on a communications channel, wherein the communications channel is subject to interference from one or more other communications channels,

wherein the communications channel carries a first type of service, wherein the one or more other communications channels includes a first subset of communications channels that carry the first type of service, and wherein the communications channel is subject to self-NEXT and self-FEXT interference from the first subset of communications channels that carry the first type of service;

wherein the communications channel is subject to uncorrelated interference in addition to the self-NEXT and self-FEXT interference; and

wherein the communications channel is constrained to carry a total average power P_max;

the method comprising;

determining a self-NEXT transfer function and a self-FEXT transfer function for interference from the first subset of communications channels that carry the first type of service;

determining an amount of uncorrelated interference into the communications channel;

determining the transmit spectrum in response to the self-NEXT transfer function, the self-FEXT transfer function, and the amount of uncorrelated interference, wherein the transmit spectrum is useable in communicating data on the communications channel, wherein said determining the transmit spectrum comprises;

dividing the channel into a plurality of frequency bins;

identifying frequency bins M_E and M_F in response to the self-NEXT transfer function and the self-FEXT transfer function, wherein EQPSD signaling leads to a greater channel capacity than FDS signaling for bins lower in frequency than M_E, and wherein FDS signaling leads to a greater channel capacity than EQPSD signaling for bins greater in frequency than M_F;

identifying a crossover frequency bin M_E2F after said identifying frequency bins M_E and M_F, wherein M_E<

M_E2F<

M_F;

calculating an amount of power transmitted in each of the plurality of frequency bins after said identifying the crossover bin M_E2F, wherein said calculating the amount of power transmitted in each of the plurality of frequency bins is performed in response to the channel transfer function, the self-NEXT transfer function, the self-FEXT transfer function, and the amount of uncorrelated interference;

using EQPSD signaling in a first set of frequency bins, wherein each bin in the first set of frequency bins has a frequency less than or equal to the frequency of the crossover frequency bin M_E2F;

using FDS signaling in a second set of frequency bins, wherein each bin in the second set of bins has a frequency greater than or equal to the frequency of the crossover bin M_E2F.

2. The method of claim 1, wherein said identifying the crossover bin M_E2F includes using frequency bin M_E as an initial estimate of the crossover bin M_E2F;

and wherein said calculating an amount of power transmitted in each of the plurality of frequency bins comprises;

(a) choosing a first amount of power P_E for transmission in the first set of frequency bins and a second amount of power P_F for transmission in the second set of frequency bins, wherein P_E+P_F=P_max;

(b) performing a first water-filling calculation for the first set of frequency bins with a constraining total power P_E;

(c) performing a second water-filling calculation for the second set of frequency bins with a constraining total power P_F;

(d) computing the channel capacity in response to the first and second water-filling calculations;

(e) modifying the values of P_E and P_F;

(f) repeating steps (b)-(e) until the channel capacity is substantially maximized;

(g) identifying a new crossover bin M_E2F; and

(h) repeating steps (a)-(g) until the channel capacity is substantially maximized.

3. The method of claim 2, wherein said modifying the values of P_E and P_F is performed such that the channel capacity is increased.

4. The method of claim 2, wherein said identifying a new crossover bin M_E2F is performed such that the channel capacity is increased.

5. The method of claim 1,

wherein said identifying the crossover bin M_E2F comprises using frequency bin M_E as the crossover bin M_E2F;

and

wherein said calculating an amount of power transmitted in each of the plurality of frequency bins comprises;

(a) choosing a first amount of power P_E for transmission in the first set of frequency bins and a second amount of power P_F for transmission in the second set of frequency bins, wherein P_E+P_F=P_max;

(b) performing a first water-filling calculation for the first set of frequency bins with a constraining total power P_E;

(c) performing a second water-filling calculation for the second set of frequency bins with a constraining total power P_F;

(d) computing the channel capacity in response to the first and second water-filling calculations;

(e) modifying the values of P_E and P_F;

(f) repeating steps (b)-(e) until the channel capacity is substantially maximized;

6. The method of claim 5, wherein said modifying the values of P_E and P_F is performed such that the channel capacity is increased.

7. A method for determining a transmit spectrum for use in communicating data on a communications channel, wherein the communications channel is subject to interference from one or more other communications channels;

wherein the communications channel carries a first type of service, wherein the one or more other communications channels includes a first subset of M-1 communications channels that carry the first type of service, wherein M is two or more;

the method comprising;

determining a channel transfer function H₁(f) of the communications channel;

determining a self-NEXT transfer function X₁(f) for self-NEXT interference into the communications channel from the first subset of communications channels that carry the first type of service;

determining a self-FEXT transfer function F₁(f) for self-FEXT interference into the communications channel from the first subset of communications channels that carry the first type of service;

determining a SNR G₁(f) of the communications channel;

determining other SNRs G_i(f) of the communications channels in the first subset of communications channels, wherein i ε

; and

examining the channel transfer function H₁(f), the self-NEXT transfer function X₁(f), the self-FEXT transfer function F₁(f), the SNR G₁(f), and the other SNRs G_i(f),

determining the transmit spectrum in response to said examining, wherein the transmit spectrum is useable in communicating data on the communications channel.

8. The method of claim 7, wherein said determining the transmit spectrum comprises determining an EQPSD transmit spectrum in a first frequency range of the communications channel;

wherein the SNR G₁(f) is greater than a SNR limit over the first frequency range; and

wherein the SNR limit depends on at least two of the channel transfer function H₁(f), the self-NEXT transfer function X₁(f), the self-FEXT transfer function F₁(f), and the other SNRs G_i(f).

9. The method of claim 7, wherein said determining the transmit spectrum comprises determining an FDS transmit spectrum in a second frequency range of the communications channel;

wherein the SNR G_i(f) is less than a SNR limit over the second frequency range; and

wherein the SNR limit depends on at least two of the channel transfer function H₁(f), the self-NEXT transfer function X_i(f), the self-FEXT transfer function F₁ (f), and the other SNRs G_i(f).

10. The method of claim 8 or of claim 9,

wherein the SNR limit is given by the following expression, $\frac{{(\sum _{}^{}}^{}}{}$

i=1M

Gi

(f))2

(X12

(f)-F12

(f))+2

(∑

i=2M

Gi

(f))

(X1

(f)-F1

(f))(∑

i=2M

Gi

(f))

F1

(f)

H1

(f)+H1

(f).

11. The method of claim 7, wherein the one or more other communications channels are located proximate to the communications channel.

12. The method of claim 7, wherein the transmit spectrum is determined so that the communications channel has equal upstream and downstream capacities.

13. The method of claim 7, wherein the transmit spectrum is determined in response to (1) a predetermined average power on the communications channel, or to (2) a predetermined peak power constraint in frequency, or to (3) a predetermined peak power constraint in frequency and a predetermined average power on the communications channel.

14. The method of claim 7, wherein the transmit spectrum is spectrally compatible with the one or more other communications channels.

15. The method of claim 7, wherein the transmit spectrum operates to substantially maximize a data transmission rate for the communications channel and is spectrally compatible with the one or more other communications channels.

16. The method of claim 7, wherein said determining the transmit spectrum comprises using a water-filling technique or a peak constrained water-filling technique to determine a power spectral density function.

17. The method of claim 7, wherein the communications channel is divisible into a plurality of frequency bins;

wherein the transmit spectrum is operable to selectively allocate transmission power to different ones of the plurality of frequency bins.

18. A method for transmitting data in a digital communications channel,

wherein the channel has a transmission bandwidth B, a channel transfer function, a self-NEXT transfer function, and a self-FEXT transfer function;

wherein the channel can be divided into a set of K frequency bins with bandwidth W, wherein W is substantially smaller than B, and wherein the frequency bins are indexed by an index k ε

in order of increasing center frequencies f_k;

the method comprising;

a) transmitting data on the communications channel using equal power densities for upstream and downstream signaling in a first subset of the frequency bins; and

b) transmitting data on the communications channel using frequency-division signaling for duplexing upstream and downstream signals in a second set of the frequency bins;

wherein each frequency bin in the set of frequency bins has a first characteristic quantity, wherein the first characteristic quantity of the kth frequency bin is given by the expression,

19. The method of claim 18, further comprising,

c) transmitting data on the communications channel using frequency-division signaling for duplexing upstream and downstream signals in a third subset of frequency bins (M_E, M_F).

20. The method of claim 18, further comprising,

c) transmitting data on the communications channel using equal power densities for upstream and downstream signaling in a third subset of frequency bins ?(M_E, M_E2F), wherein M_E<

M_E2F<

M_F; and

d) transmitting data on the communications channel using frequency-division signaling for duplexing upstream and downstream signals in a fourth subset of frequency bins (M_E2F, M_F);

wherein M_E2F is chosen by successive approximations of a water-filling technique or a peak constrained water-filling technique to optimize a power spectral density transmit spectrum of the channel.

21. The method of claim 18, wherein W is sufficiently narrow that channel noise in each of the frequency bins is substantially additive Gaussian noise, that the interference noise in each of the frequency bins is substantially equal to additive colored Gaussian noise, and that within each of the frequency bins the channel is substantially a linear time-invariant system.

22. A method for determining a signaling strategy for communicating data on a communications channel subject to interference from one or more other communications channels, wherein the method comprises:

determining a channel transfer function of the communications channel;

determining interference characteristics of the communications channel, wherein said determining interference characteristics includes;

determining an amount of interference that results from said one or more other channels, and

determining an amount of uncorrelated interference;

determining in response to the channel transfer function and the interference characteristics, a substantially optimum signaling strategy for duplex communications across the communications channel and the one or more other communications channels, wherein determining the substantially optimum signaling strategy includes;

allocating a first portion of the frequency spectrum for EQPSD signaling across the communications channels;

allocating a second, distinct portion of the frequency spectrum for orthogonal duplex signaling, wherein the second portion consists of an integer number of equally divided frequency bins;

grouping the equally divided frequency bins to form no more than three continuous, contiguous frequency bands that together make up the whole of the second portion; and

designating each of the frequency bands in the second portion as upstream signaling only or downstream signaling only.

23. The method of claim 22, wherein the first portion consists of an integer number of equally divided frequency bins, and wherein the center frequency f of each of the frequency bins in the first portion satisfies $\frac{H}{}$

(f)-2

(X

(f)-F

(f))X

(f)2-F

(f)2-H

(f)

F

(f)<

0,

wherein H(f)≡

|H_c(f)|² is the channel transfer function, X(f)≡

|H_N(f)|² is the self-NEXT transfer function, and F(f)≡

|H_F(f)|² is the self-FEXT transfer function.

24. The method of claim 22, wherein each of the bins for which the center frequency f satisfies $\frac{H}{}$

(f)-2

(X

(f)-F

(f))X

(f)2-F

(f)2-H

(f)

F

(f)>

0

is one of the bins in the second portion, wherein H(f)≡

|H_c(f)² is the channel transfer function, X(f)≡

|H_N(f)|² is the self-NEXT transfer function, and F(f)≡

|H_F(f)|² is the self-FEXT transfer function.

25. The method of claim 22, wherein the grouping is designed to provide equal upstream and downstream capacities.

26. The method of claim 22, wherein the grouping is designed to provide equal performance margins with equal upstream and downstream average powers.

27. The method of claim 22, wherein the determining the substantially optimum signaling strategy further includes allocating a third portion of the frequency spectrum distinct from the first and second portions for orthogonal channel signaling.

28. The method of claim 27, wherein code division multiplexing is used for orthogonal channel signaling in the third portion.

29. The method of claim 27, wherein the third portion consists of an integer number of equally divided frequency bins, and wherein each of the frequency bins in the third portion are designated for exactly one of the set of communications channels that includes said communications channel and said one or more other communications channels, wherein an equal number of frequency bins in the third portion is designated for each of the set of communications channels.