Systems and methods for signaling for vectoring of DSL systems
View Patent ↗The measurement of far-end crosstalk (FEXT) in a Digital Subscriber Line communications is instrumental in the ability of using a multiple input multiple output (MIMO) pre-coder to cancel FEXT. A reliable robust back channel for transmission of error is instrumental to provide error samples for the proper operation of a MIMO pre-coder. Bins can be dedicated to insure bandwidth from the customer premises equipment (CPE) to the central office (CO). By increasing the margin used in the bins, robustness can be added to this back channel between the CPE and CO.
1. A method for dedicated back channel communications for communicating error samples in a Digital Subscriber Line (DSL) system comprising: measuring errors in downstream data communicated on the DSL; forming error samples corresponding to the measured errors; reserving a plurality of bins from among a total number of bins available for upstream communication over the DSL for the dedicated back channel communications; encoding the error samples onto the plurality of bins; and simultaneously transmitting upstream the error samples using the plurality of reserved bins over the DSL and transmitting encoded user data using bins not reserved for the dedicated back channel communications from a customer premises equipment (CPE), wherein the error samples enable Far-End Crosstalk (FEXT) pre-coder coefficients to be derived.
2. The method of claim 1 , wherein the error samples are measured in a downstream sync symbol and the error samples are transmitted over an upstream back channel message block corresponding to the downstream sync symbol.
3. The method of claim 1 , wherein the reserving the plurality of bins comprises allocating a number of bits per bin for each bin in the plurality of bins wherein the allocating uses an additional signal to noise ratio (SNR) margin over a margin used in bins not reserved for the dedicated back channel communications.
4. The method of claim 3 , wherein the additional SNR margin is 6 dB or 12 dB.
5. The method of claim 1 , wherein the reserving the plurality of bins comprises allocating a number of bits per bin for each bin in the plurality of bins wherein the allocating uses a bit loading profile and allocates bits based on the number of bits specified for a bin in the bit loading profile.
6. The method of claim 1 , wherein each bin has a SNR and the reserving the plurality of bins comprises selecting the bins with the highest SNR.
7. The method of claim 1 , wherein the errors are measured between received sync symbols and the constellation points corresponding to the received symbols.
8. A Digital Subscriber Line (DSL) modem comprising: a processor; a line driver; and a memory comprising instructions wherein the instructions cause the processor to: receive an orthogonal pilot sequence during downstream sync symbols; measure an error sample based on the received orthogonal pilot sequence; format the error sample into a message block; encode the message block onto a plurality of bins from among a total number of bins available for communication over the DSL, the plurality of bins reserved for dedicated back channel communications for communicating error samples; and simultaneously cause the line driver to transmit upstream the message block using the plurality of bins over the DSL and to transmit encoded user data using bins not reserved for the dedicated back channel communications from a customer premises equipment (CPE), wherein the error samples enable Far-End Crosstalk (FEXT) pre-coder coefficients to be derived.
9. The DSL modem of claim 8 , wherein the instructions further cause the processor to process the reception of a command relating to the error samples; and add acknowledgement information into the message block.
10. The DSL modem of claim 9 , wherein the command specifies a resolution of each error sample, or specifies a bin group for error measurement or combination thereof.
11. The DSL modem of claim 10 , wherein the acknowledgement information specifies the resolution of the error samples that the DSL modem is capable of transmitting.
12. The DSL modem of claim 9 wherein the message block comprises error detection data.
13. The DSL modem of claim 12 wherein the error detection data is a cyclic redundancy code.
14. The DSL modem of claim 8 , wherein the DSL modem is a vectoring enabled Very High Speed Digital Subscriber Line (VDSL) modem.
15. The DSL modem of claim 8 , wherein the instructions further cause the processor to measure the error sample based on received orthogonal pilot sequence and its corresponding constellation point.
16. A method of measuring downstream errors comprising: transmitting a first orthogonal pilot sequence downstream to a first customer premises equipment (CPE) during a first downstream sync symbol; receiving a first back channel message block corresponding to the first downstream sync symbol from the first CPE, said first back channel message block encoded on a plurality of bins from among a total number of bins available for upstream communication over a Digital Subscriber Line (DSL), the plurality of bins reserved for dedicated back channel communications for simultaneously communicating error samples derived from the first orthogonal pilot sequence while communicating encoded user data using bins not reserved for the dedicated back channel communications; extracting the error samples from the first back channel message block; and deriving pre-coder coefficients using the extracted error samples, wherein the pre-coder coefficients comprise Far-End Crosstalk (FEXT) pre-coder coefficients.
17. The method of claim 16 further comprising:
transmitting a second orthogonal pilot sequence that is orthogonal to the first orthogonal sequence to a second CPE during a second downstream sync symbol which is synchronized to the first downstream sync symbol;
receiving a second back channel message block corresponding to the first downstream sync symbol from the second CPE, said second back channel message block encoded on a second plurality of bins from among the total number of bins available for communication over the DSL subscriber line, the second plurality of bins reserved for the dedicated back channel communications; and
extracting error samples from the second back channel message block.
18. The method of claim 16 further comprising transmitting a command specifying a bin group for error measurement, where the command comprises a unique identifier associated with the bin group.
19. The method of claim 16 further comprising transmitting a command specifying the resolution for the error samples.
20. The method of claim 16 wherein each bin in the plurality of bins has an associated number of bits, wherein the associated number of bits is allocated using an additional signal to noise ratio (SNR) margin over a margin used in bins not reserved for the dedicated back channel communications.
21. The method of claim 16 wherein each bin in the plurality of bins has an associated number of bits, wherein the associated number of bits is derived from an existing bit loading profile.
22. The method of claim 16 , wherein each bin has a SNR and the plurality of bins is selected from the bins with the highest SNR.
23. The method of claim 16 further comprising deriving the error samples from the first orthogonal pilot sequence and the constellation points corresponding to the first orthogonal pilot sequence.