Aligning the Upstream DMT Symbols of Multiple Lines in a TDD DSL System

• US 20130294597A1
• Filed: 05/02/2013
• Published: 11/07/2013
• Est. Priority Date: 05/02/2012
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Shi, Cao, Fazlollahi, Amir H., Liu, Jianhua
• Granted Patent: US 9,331,840 B2
• Time in Patent Office: Days
• US Class Current: 379/406.01
• CPC Class Codes: H04B 3/32 Reducing cross-talk, e.g. by compensating
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 25/14 Channel dividing arrangements , i.e. in which a single bit stream is divided between several baseband channels and reassembled at the receiver
• 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 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: H04L 5/1469 using time-sharing
• CPC Class Codes: H04L 7/0041 Delay of data signal
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

A method comprising transmitting a delay value to each of a plurality of digital subscriber line (DSL) transceivers, by a distribution point unit (DPU), and receiving a plurality of signals at substantially the same time, wherein each of the plurality of signals is from a different DSL transceiver in the plurality of DSL transceivers and transmitted at different times based on the delay value and a corresponding propagation delay.

Claims

1. A method comprising:

transmitting a delay value to each of a plurality of digital subscriber line (DSL) transceivers, by a distribution point unit (DPU); and

receiving a plurality of signals at substantially the same time, wherein each of the plurality of signals is from a different DSL transceiver in the plurality of DSL transceivers and transmitted at different times based on the delay value and a corresponding propagation delay.

2. The method of claim 1, further comprising:

transmitting at least one symbol to each of the plurality of DSL transceivers, wherein the corresponding propagation delay is estimated based on a corresponding attenuation of the at least one symbol.

3. The method of claim 2, wherein each of the different times is computed as the difference between the delay value and two times the corresponding propagation delay.

4. The method of claim 3, wherein the delay value is a desired gap time between the end of a transmitted signal from the DPU and the beginning of a received signal at the DPU, wherein a time-division duplex (TDD) frame comprises the transmitted signal, the received signal, the desired gap time, and a second gap time, wherein the transmitted signal comprises a first plurality of discrete multitone modulation (DMT) symbol periods, wherein the received signal comprises a second plurality of DMT symbol periods, and wherein the desired gap time plus the second gap time equals a DMT symbol period.

5. The method of claim 2, further comprising:

transmitting an upper bound on switching time to each of the plurality of DSL transceivers, wherein the delay value is an upper bound on propagation delay, and wherein each of the different times is computed based on the upper bound on switching time, the delay value, and the corresponding propagation delay.

6. The method of claim 5, wherein each of the different times is computed according to:

T_g1′

(i)=ST_U+2×

D_max−

2×

D(i), where T_g1′

(i) represents the time the ith DSL transceiver from the plurality of DSL transceivers waits to transmit its signal in the plurality of signals from the end of receiving a downstream signal, where ST_U represents the upper bound on switching time, D_max represents the upper bound on propagation delay, and D(i) represents the corresponding propagation delay for the ith different DSL transceiver.

7. The method of claim 2, wherein the corresponding propagation delay is estimated based on the corresponding loop length, and wherein the corresponding loop length is estimated based on the corresponding attenuation.

8. A method comprising:

synchronizing transmitters of a plurality of digital subscriber line (DSL) remote terminals, by a distribution point unit (DPU) comprising a plurality of collocated transceivers, such that the signals received at a U-interface of the collocated transceivers arrive at substantially the same time,

wherein the synchronization is based on an assumed longest DSL line that may be connected to the DPU.

9. The method of claim 8, further comprising:

transmitting at least one symbol to each of the plurality of DSL remote terminals, wherein each of the plurality of DSL remote terminals estimates its corresponding propagation delay based on a corresponding attenuation of the at least one symbol, and wherein each of the signals received at the U-interface was transmitted at a different time based on the propagation delay of the assumed longest DSL line and the corresponding propagation delay.

10. The method of claim 8, further comprising:

receiving at least one symbol from each of the plurality of DSL remote terminals by corresponding DPU transceivers based on an initial transmit time delay;

estimating the corresponding propagation delay, by the DPU, based on a corresponding attenuation of the at least one symbol,

for each of the DPU transceivers, computing a new transmit time delay based on the initial delay value, the propagation delay of the assumed longest DSL line, and the corresponding propagation delay and transmitting the new transmit time delay to the corresponding DSL transceiver,

wherein each of the signals received at the U-interface of the DPU transceivers is transmitted at a different time based on the corresponding new transmit time delay of the DSL remote terminal.

11. The method of claim 9, wherein synchronizing transmitters of the plurality of DSL remote terminals comprises transmitting a delay value to each of the plurality of DSL remote terminals, wherein the delay value is a desired gap time between the end of a transmitted signal from the DPU and the beginning of the signals received at the U-interface, wherein a time-division duplex (TDD) frame comprises the transmitted signal, the received signals, the desired gap time, and a second gap time, wherein the transmitted signal comprises a first plurality of discrete multitone modulation (DMT) symbol periods, wherein each of the received signals comprises a second plurality of DMT symbol periods, and wherein the desired gap time plus the second gap time equals a DMT symbol period.

12. The method of claim 11, wherein synchronizing transmitters of the plurality of DSL remote terminals further comprises:

transmitting an upper bound on switching time to each of the plurality of DSL transceivers, wherein the delay value is an upper bound on propagation delay, and wherein each of the different times is computed based on the upper bound on switching time, the delay value, and the corresponding propagation delay.

13. A distribution point unit (DPU) comprising:

a plurality of digital subscriber line (DSL) transceivers; and

a processor coupled to the DSL transceivers and configured to;

synchronize transmitters of a plurality of DSL remote terminals such that the signals received at a U-interface of the plurality of DSL transceivers arrive at substantially the same time, wherein the synchronization is based on an assumed longest DSL line that may be connected to the DPU.

14. The DPU of claim 13, wherein the plurality of DSL transceivers is configured to:

transmit at least one symbol to each of the plurality of DSL remote terminals, wherein each of the plurality of DSL remote terminals estimates its corresponding propagation delay based on a corresponding attenuation of the at least one symbol, and wherein each of the signals received at the U-interface was transmitted at a different time based on the propagation delay of the assumed longest DSL line and the corresponding propagation delay.

15. The DPU of claim 14, wherein synchronizing transmitters of the plurality of DSL remote terminals comprises requesting the plurality of DSL transceivers to transmit a delay value to each of the plurality of DSL remote terminals, wherein the delay value is a desired gap time between the end of a transmitted signal from the DPU and the beginning of the signals received at the U-interface, wherein a time-division duplex (TDD) frame comprises the transmitted signal, the received signals, the desired gap time, and a second gap time, wherein the transmitted signal comprises a first plurality of discrete multitone modulation (DMT) symbol periods, wherein each of the received signals comprises a second plurality of DMT symbol periods, and wherein the desired gap time plus the second gap time equals a DMT symbol period.

16. The DPU of claim 15, wherein synchronizing transmitters of the plurality of DSL remote terminals further comprises:

requesting the plurality of DSL transceivers to transmit an upper bound on switching time to each of the plurality of DSL transceivers,

wherein the delay value is an upper bound on propagation delay, and wherein each of the different times is computed based on the upper bound on switching time, the delay value, and the corresponding propagation delay.

17. A method comprising:

acquiring a delay value, by a first digital subscriber line (DSL) transceiver, from a second DSL transceiver at a distribution point unit (DPU); and

transmitting a signal, by the first DSL transceiver, at a time based on the delay value and an estimated propagation delay between the first DSL transceiver and the second DSL transceiver.

18. The method of claim 17, further comprising:

receiving at least one symbol, wherein the corresponding propagation delay is estimated based on a corresponding attenuation of the at least one symbol.

19. The method of claim 18, wherein the delay value is a desired gap time between the end of a received signal from the DPU and the beginning of the signal received at the DPU, wherein a time-division duplex (TDD) frame duration is equal to the sum of a duration of the transmitted signal, a duration of the received signal, the desired gap time, and a second gap time, wherein the duration of the transmitted signal comprises a first plurality of discrete multitone modulation (DMT) symbol periods, wherein the duration of the received signal comprises a second plurality of DMT symbol periods, and wherein the desired gap time plus the second gap time equals a DMT symbol period.

20. The method of claim 18, further comprising:

receiving an upper bound on switching time, wherein the delay value is an upper bound on propagation delay, and wherein the time is further based on the upper bound on switching time.

21. The method of claim 20, wherein the time is computed according to:

T_g1′

=ST_U+2×

D_max−

2×

D, where T_g1′

represents the time the first DSL transceiver waits to transmit the signal from the end of receiving a downstream signal, where ST_U represents the upper bound on switching time, D_max represents the upper bound on propagation delay, and D represents the corresponding propagation delay.