(en)The present invention overcomes various problems by defining two upstream masks (U 1 , U 2 ) and two downstream masks (D 1 , D 2 ) and using a mask selectable system for the long reach digital subscriber line (LDSL), in which a unique modem feature is activated during handshake to automatically check for physical layer status in terms of spectral compatibility and, thus, automatically optimize the boosted mode with the use of the mask selectable system choose the best combination of upstream/downstream masks in any physical layer noise scenario.

1.ApplicationNumber: US-84961807-A
1.PublishNumber: US-7496135-B2
2.Date Publish: 20090224
3.Inventor: DUVAUT PATRICK
LANGBERG EHUD

4.Inventor Harmonized: DUVAUT PATRICK(US)
LANGBERG EHUD(US)

5.Country: US
6.Claims:
(en)The present invention overcomes various problems by defining two upstream masks (U 1 , U 2 ) and two downstream masks (D 1 , D 2 ) and using a mask selectable system for the long reach digital subscriber line (LDSL), in which a unique modem feature is activated during handshake to automatically check for physical layer status in terms of spectral compatibility and, thus, automatically optimize the boosted mode with the use of the mask selectable system choose the best combination of upstream/downstream masks in any physical layer noise scenario.

7.Description:
(en)RELATED APPLICATIONS
The present invention is a continuation of U.S. application Ser. No. 10/714,907, filed Nov. 18, 2003, now U.S. Pat. No. 7,272,172, which claims priority to U.S. Provisional Application Nos. 60/441,351 filed Jan. 22, 2003 and 60/426,796 filed Nov. 18, 2002, all of which are incorporated herein by reference in their entirety.
This application is related to copending U.S. patent applications titled “ENHANCED SMART DSL FOR LDSL,” , “ENHANCED SMART DSL FOR LDSL,” which claim priority to U.S. Provisional Application No. 60/488,804 filed Jul. 22, 2003 and “POWER SPECTRAL DENSITY MASKS FOR IMPROVED SPECTRAL COMPATIBILITY” which claims priority to U.S. Provisional Application No. 60/491,268 filed Jul. 31, 2003, all filed concurrently herewith.


BACKGROUND OF THE INVENTION
The present invention relates generally to electronic communication systems, and in particular, to systems and methods for transmitting and receiving information from such systems over a computer network.
With the increasing popularity of the Internet and other content-heavy electronic communication systems, there has been a substantial need for reliable and affordable high bandwidth mediums for facilitating data transmissions between service providers and their customers. In relation to the requirement that such mediums be affordable to consumers, it was determined that the most cost-effective manner for providing service to customers was by using infrastructure already present in most locations. Accordingly, over recent years, the two such mediums most widely meeting these requirements include the cable television (CATV) and the conventional copper wire telephone systems (plain old telephone system or POTS).
Relating specifically to the adaptation of POTS telephone lines to carry data at high bandwidth or ‘broadband’ data rates, a number of Digital Subscriber Line (DSL) standards and protocols have been proposed. DSL essentially operates by formatting signals using various Time Domain Equalization techniques to send packets over copper wire at high data rates. A substandard of conventional DSL is known as Asymmetric Digital Subscriber Line (ADSL) and is considered advantageous for its ability to provide very high data rates in the downstream (i.e., from service provider to the user) direction by sacrificing speed in the upstream direction. Consequently, end user costs are minimized by providing higher speeds in the most commonly used direction. Further, ADSL provides a system that applies signals over a single twisted-wire pair that simultaneously supports (POTS) service as well as high-speed duplex (simultaneous two-way) digital data services.
Two of the proposed standards for ADSL are set forth by the International Telecommunications Union, Telecommunication Standardization Section (ITU-T). A first, conventional, ADSL standard is described in ITU-T Recommendation G.992.1—“Asymmetric Digital Subscriber Line (ADSL) Transceivers”. A second, G.992.3, ADSL2 is a new standard recently completed and approved by the International Telecommunications Union (ITU) in 2002 that will supersede existing ADSL standards. Work being done under the headings of “G.dmt.bis” and “G.lite.bis” is nearing completion to designate G.992.3 and G.992.4 for full-rate ADSL and splitterless ADSL, respectively. Much has been learned over the past three years of ADSL deployments, including areas where improvements in the technology would be particularly valuable. There is a wide variety of improvements included in ADSL2, each with very different implications; some make the transceivers operate more efficiently, some make them more affordable, and some add functionality.
As briefly described above, all DSL system operate in essentially the following manner. Initial digital data to be transmitted over the network is formed into a plurality of multiplexed data frames and encoded using special digital modems into analog signals which may be transmitted over conventional copper wires at data rates significantly higher than voice band traffic (e.g., ˜1.5 Mbps (megabits per second) for downstream traffic, ˜150 kbps (kilobits per second) for upstream traffic). The length and characteristics of wire run from a customer's remote transceiver to a central office transceiver may vary greatly from user to user and, consequently, the possible data rates for each user also vary. In addition, the physical channel (i.e., the wires themselves) over which the system communicates also vary over time due to, for example, temperature and humidity changes, fluctuating cross-talk interference sources. The distribution of signal energy over frequency is known as the power spectral density (PSD). Power spectral density is simply the average noise power unit of bandwidth (i.e. dBm/Hz). All transmission systems have a finite power and bandwidth and, therefore, the power and bandwidth of each system is used in a manner so as not to disturb other adjoining systems. A PSD mask is used which is defined as the maximum allowable PSD for a service in presence of any interference combination. The transmit spectrum for a service refers to the PSD of the transmitted signal. Spectral compatibility of the system using a modem boosted modes for improved modem rates and extended reach solutions into existing services may either be without distance limitations or partially limited distance when the spectral compatibility impact is higher than the existing service disturbance beyond a specific reach. The choice between limited and unlimited distance boosted modes are done at the network management level which requires a costly procedure from the telephone company (Telco) to provide physical layer information that also covers how the existing services are deployed, and because of the costs involved, broadband services providers shy away from all the boosted mode solutions, specially the limited distance boosted modes, thereby, restraining the coverage and performance of the underlying service deployment.
SUMMARY OF THE INVENTION
The present invention relates generally to the field of telecommunications and, more particularly, to data communications over telephone networks and more specifically the invention addresses some of the fundamental issues in coping with the performance objectives for LDSL (Long reach digital subscriber Line) systems which is sometimes called last mile DSL.
The present invention overcomes all of the aforementioned problems by defining two upstream masks (U 1 , U 2 ) and two downstream masks (D 1 , D 2 ) and using a mask selectable system for the long reach digital subscriber line (LDSL), in which a unique modem feature is activated during handshake to automatically check for physical layer status in terms of spectral compatibility and, thus, automatically optimize the boosted mode with the use of the mask selectable system choose the best combination of upstream/downstream masks in any physical layer noise scenario.
Crosstalk noise environments are varied, which include NEXT and FEXT disturbance from ISDN, HDSL, SHDSL, T1, and Self-disturbers at both the CO and CPE ends. NEXT from HDSL and SHDSL tend to limit the performance in the upstream channel while NEXT from T1 systems tend to severely limit the downstream channel performance. Also, loops containing bridged taps will degrade performance on the ADSL downstream channel more so than the upstream channel. It appears almost impossible that only one single pair of Upstream and Downstream masks will maximize the performance against any noise-loop field scenario, while ensuring spectral compatibility and at the same time, keeping a desirable balance between Upstream and Downstream rates. A realistic approach for LDSL relies on different Upstream and Downstream masks exhibiting complementary features. Realistically, all these chosen masks are available on any LDSL Platform. At the modem start up, based on a certain protocol, the best Upstream-Downstream pair of masks are automatically chosen. Whether the best pair is manually chosen is at the discretion of the operator, or it is automatically selected, this concept is identified as “smart DSL for LDSL”.
It is emphasized that other rationales advocate for smart DSL: The use of a single mask may prevent to provide some areas in the US dominated by T1 noise for instance; A spectrally compatible mask can't be ruled out; One can't prevent service providers to have access to an array of mask/tools provided as long as they are spectrally compatible; Service providers may decide to use only one mask according to the physical layer conditions, or any combination for the same reasons. The present invention defines two upstream masks (U 1 , U 2 ) and two downstream masks (D 1 , D 2 ) and using a mask selectable system as well as a tunable mask system for the long reach digital subscriber line (LDSL), in which a unique modem feature is activated during handshake to automatically check for physical layer status in terms of spectral compatibility and, thus, automatically optimize the boosted mode with the use of the mask selectable system choose the best combination of upstream/downstream masks in any physical layer noise scenario.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plot of U 1 and D 1 PSD nominal templates according to embodiments of the invention; and
FIG. 2 is an average values plot of U 2 and D 2 PSD templates according to embodiments of the invention.
FIG. 3 is a flowchart illustrating the top-level operations of an embodiment of the invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The performance of a “single mask” system and a “selectable mask” system for long reach DSL (LDSL) according to the agreements described in T1E1.4/2002-292R2 define eight different noise cases and 10 different loops, for a total of 80 test scenarios. The objective minimum bit rates for LDSL systems are 192 kb/s downstream and 96 kb/s upstream in each of the 80 test scenarios. We find a significant performance advantage for the selectable mask system in a number of test cases.
The “single Mask system” uses a single upstream and a single downstream mask, based on 0J-074, and are respectively referred to as U 2 and D 2 herein. This is a non-overlapped PSD scenario where the upstream channel ends at tone 23 and the downstream begins at tone 33 . The “mask-selectable system” uses two upstream masks, U 1 and U 2 , and two downstream masks, D 1 and D 2 . Upstream mask U 1 ends at tone 13 and the downstream mask, D 1 , is a shaped overlap mask derived from spectrum management class 5 in T1.417. The “mask-selectable system” selects the best Upstream and Downstream mask combination for each test case according to some criteria. Optimality criterion is left to the discretion of the operator who may want to force a mask set up according to the operator's field knowledge, or give priority to Upstream minimum rate, or Downstream minimum rate, up to certain margin, etc. This degree of freedom is a keystone of the selectable mask system. In the same spirit, ADSL overlap mode is left today to the discretion of the operator. Neither G.992.1 nor G.992.3 define criteria to select overlap mode. In actual deployment, the mask selection may be performed at initialization based on loop and noise conditions and criteria determined by operators and vendors.
Simulation results show that a mask-selectable system offers significant advantages over the single mask system under certain channel and noise conditions. Specifically, the single mask system (U 2 , D 2 } is judged subjectively “best” on approximately 60% of the test cases. The selectable mask system meets the data rate objectives for LDSL on approximately 90% of the test scenarios.
Mask-Selectable System for LDSL
Two Upstream masks, U 1 and U 2 , and two downstream masks, D 1 and D 2 , are used in what follows to define a mask-selectable system for LDSL.
In any physical layer noise scenario, the mask-selectable system chooses the best Upstream/Downstream masks combination according to some criteria. It is possible to prove that the four possible US/DS masks combinations defined hereafter are indeed spectrally compatible, according to method B (i.e. Annex A) of T1.417.
Although we show the masks in pairs, we do not place restrictions on mask combinations. Therefore, mask U 1 can be used with mask D 1 or D 2 for example.
Masks U 1 and D 1
U 1 and D 1 PSD nominal templates are plotted in FIG. 1 and explicitly defined in Tables 1 and 2. As defined by the standards, the PSD templates, or average PSD values, are 3.5 dB lower than the mask values. As shown in FIG. 1 , D 1 PSD overlaps the ADSL Upstream bandwidth.





TABLE 1



U1 PSD Nominal Templates






Frequency (kHz)
PDS (dBm/Hz)





0 ≦ f < 4
−101.5


4 ≦ f < 25.875
−96 + 23.4*log2(f/4)


25.875 ≦ f < 60.375
−32.9


60.375 ≦ f < 686
max {−32.9 − 95 × log 2 (f/60.38), 10 ×



log10[0.05683 × (f × 10 3 ) −1.5 ] − 3.5}


686 ≦ f < 1411
−103.5


1411 ≦ f < 1630
−103.5 peak, −113.5 average in any



[f, f + 1 MHz] window


1630 ≦ f < 12000
−103.5 peak, −115.5 average in any



[f, f + 1 MHz] window





Note 1.


The 95 dB/octave slope will be replaced by the ADSL + standardized roll off.



































TABLE 2



DI PSD Nominal Templates




Frequency (kHz)
PDS (dBm/Hz)



0 ≦ f < 4
−101

4 ≦ f < 25.875
−96 + 20.79*log 2 (f/4)

25.875 ≦ f < 91
−40

91 ≦ f < 99.2
−44

99.2 ≦ f < 138
−52

138 ≦ f < 353.625
−40.2 + 0.0148*(f − 138)

353.625 ≦ f < 552
−37

552 ≦ f < 1012
−37 − 36*log 2 (f/552)

1012 ≦ f < 1800
−68.5

1800 ≦ f < 2290
−68.5 − 75*log 2 (f/1800)

2290 ≦ f < 3093
−93.500

3093 ≦ f < 4545
−93.5 peak, average −40 − 36*log 2 (f/1104)


in any [f, f + 1 MHz] window

4545 ≦ f < 12000
−93.5 peak, average −113.500 in any


[f, f + 1 MHz] window



Note 2.

U1 Total power is equal to 12.47 dBm. D1 total power is equal to 19.43 dBm.



































Masks U 2 and D 2
Tables 3 and 4 give the breakpoints of U 2 and D 2 PSD Nominal Templates. U 2 and D 2 are derived from OJ-074. To minimize self NEXT due to the side lobes, the low frequency edge of OJ-074 downstream PSD and the high frequency edge of 0J-074 upstream PSD have been sharpened according to ADSL+ recommendations and exhibit 95 dB/octave slope.





TABLE 3



U2 PSD Nominal Template, average values.






Frequency (kHz)
PDS (dBm/Hz)





0 ≦ f < 4
−101.5


4 ≦ f < 25.875
−96 + 32.5*log2(f/4)


25.875 ≦ f < 103.5
−36.4


103.5 ≦ f < 686
max {−36.3 − 95 × log 2 (f/103.5), 10 ×



log10[0.05683 × (f × 10 3 ) −1.5 ] − 3.5}


686 ≦ f < 1411
−103.5


1411 ≦ f < 1630
−103.5 peak, −113.5 average in any



[f, f + 1 MHz] window


1630 ≦ f < 12000
−103.5 peak, −115.5 average in any



[f, f + 1 MHz] window





Note 3.


The 95 dB/octave slope will be replaced by the ADSL + standardized roll off.



































TABLE 4



D2 PSD Nominal Template, average values.




Frequency (kHz)
PDS (dBm/Hz)



0 ≦ f < 4
−101.5

4 ≦ f < 80.000
−96 + 4.63*log 2 (f/4)

80 ≦ f < 138.000
−76 + 36*log 2 (f/80)

138 ≦ f < 276.000
−42.95 + 0.0214*f

276 ≦ f < 552.000
−37

552 ≦ f < 1012
−37 − 36*log 2 (f/552)

1012 ≦ f < 1800
−68.5

1800 ≦ f < 2290
−68.5 − 75*log 2 (f/1800)

2290 ≦ f < 3093
−93.500

3093 ≦ f < 4545
−93.5 peak, average −40 − 36*log 2 (f/1104)


in any [f, f + 1 MHz] window

4545 ≦ f < 12000
−93.5 peak, average −113.500 in any


[f, f + 1 MHz] window



Note 4.

U2 total power is equal to 12.5 dBm. D2 total power is equal to 19.30 dBm.

































Performance of Selectable Masks System for LDSL
ADSL2 Performance
Table 5 gives the ADSL2 Upstream and downstream performance for calibration purposes. Noise scenarios are numbered from 1 to 8 according to T1.E1.4/292-R2. Numbers shown in bold indicate those that do not meet the LDSL performance objective of 192 kbps downstream and 96 kbps upstream.
TABLE 5 ADSL2 simulation results. Data rates in kbps. upstream case 1 case 2 case 3 case 4 case 5 case 6 case 7 case 8 Self Nex ADSL ISDN SHDSL HDSL T1 MIX TIA ADSL xDSL 10 963 963 623 344 357 982 597 665 2 xDLS 11 682 682 340 142 156 692 315 378 xDLS 12 633 633 294 109 122 642 270 331 xDLS 13 470 470 151 58 67 478 123 175 xDLS 160 770 770 424 168 180 786 398 463 xDLS 165 719 719 377 140 150 736 347 415 xDLS 170 668 668 328 115 124 684 299 364 xDLS 175 620 619 283 93 105 634 259 316 xDSL 180 576 576 241 77 88 585 217 275 xDLS 185 531 530 199 63 69 542 179 233 downstream case 1 case 2 case 3 case 4 case 5 case 6 case 7 case 8 Self Nex ADSL ISDN SHDSL HDSL T1 MIXT TIA ADSL xDSL 10 1260 1260 1168 1354 1348 194 1218 186 2 xDLS 11 207 207 101 250 250 0 131 0 xDLS 12 418 418 325 462 461 0 365 0 xDLS 13 164 194 148 199 199 0 165 0 xDLS 160 979 979 875 1057 1051 115 928 113 xDLS 165 774 774 657 847 844 72 718 66 xDLS 170 598 598 500 659 658 35 543 29 xDLS 175 447 471 357 500 500 0 412 8 xDSL 180 320 352 260 365 365 0 304 0 xDLS 185 218 248 195 256 256 0 220 0
Modified 0J-074 Single mask Performance, Combination (U 2 , D 2 )

Table 6 displays the results of the Modified 0J-074 (U 2 , D 2 }. These results will be taken as references for LDSL.





TABLE 6



Performance results for the a single upstream and single downstream PSD mask









upstream














case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8



Self Nex
ADSL
ISDN
SHDSL
HDSL
T1
MIX
TIA



Single
xDSL 10
837
838
515
330
345
842
480
531

Mask
xDLS 11
663
664
338
170
182
665
303
352

(U2,
xDLS 12
619
619
295
134
144
620
261
309

D2)
xDLS 13
492
492
182
71
82
493
152
193


xDLS 160
705
705
375
201
218
707
340
389


xDLS 165
670
671
341
169
181
673
306
355


xDLS 170
636
636
308
141
151
638
274
322


xDLS 175
602
602
275
116
125
603
242
289


xDSL 180
567
567
244
94
106
569
211
256


xDLS 185
533
532
213
77
88
534
182
225







downstream














case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8



Self Nex
ADSL
ISDN
SHDSL
HDSL
T1
MIXT
TIA



Single
xDSL 10
2402
1661
1869
2048
2039
467
1658
240

Mask
xDLS 11
991
407
505
872
911
97
380
0

(U2,
xDLS 12
1195
643
694
986
1000
58
578
0

D2)
xDLS 13
848
398
489
706
793
63
368
0


xDLS 160
2049
1333
1499
1772
1769
365
1310
171


xDLS 165
1787
1086
1252
1544
1556
291
1063
109


xDLS 170
1551
879
1028
1342
1366
227
846
63


xDLS 175
1336
753
819
1158
1191
175
684
40


xDSL 180
1140
633
747
996
1035
131
604
13


xDLS 185
970
528
665
850
891
94
519
0


























































Performance of Selectable Masks system
Table 7 gives the results of the selectable masks system for LDSL, based T1E10.4/2002-292R2.
The selectable mask system optimality criteria may be left to the discretion of the operator who may want to force a mask according to deployment guidelines, or give priority to upstream minimum rate, or downstream minimum rate, up to certain margin, etc. This degree of freedom is a keystone of the selectable mask system. In the same spirit, ADSL overlap mode may be left today to the discretion of the operator. Neither G.992.1 nor G.992.3 define criteria to select overlap mode.
In presenting results for the selectable mask system, we used mask selection criteria that considers both upstream and downstream rates but weighs the downstream more heavily by a 2:1 ratio. We compare all mask combinations and derive a cost function equal to:

cost=2*( ds rate(2)− ds rate(1))/ ds rate(1)+( us rate(2)− us rate (1))/ us rate(1).

If the cost is greater than zero, we select mask 2, otherwise we select mask 1. We will always try and select a mask for which neither the upstream nor the downstream rate is 0. If all masks have an upstream or downstream rate of 0 kbps, then the mask with the highest downstream or upstream rate respectively is selected.
The results presented in this section assume that the self crosstalk includes only the PSD masks being evaluated.





TABLE 7



Performance projections for the selectable mask system. Data rates in kbps.









upstream














case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8



Self Nex
ADSL
ISDN
SHDSL
HDSL
T1
MIX
TIA



Selec-
xDSL 10
837
838
515
330
345
235
480
239

table
xDLS 11
663
664
338
170
153
169
303
173

Masks
xDLS 12
619
619
295
148
156
147
261
151


xDLS 13
492
492
182
108
115
106
152
109


xDLS 160
705
705
375
201
218
176
340
181


xDLS 165
670
671
341
169
181
163
306
167


xDLS 170
636
636
308
150
158
149
274
153


xDLS 175
602
602
275
137
145
135
242
139


xDSL 180
567
567
244
124
131
122
211
126


xDLS 185
533
532
213
111
118
110
182
113







downstream














case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8



Self Nex
ADSL
ISDN
SHDSL
HDSL
T1
MIXT
TIA



Selec-
xDSL 10
2402
1661
1869
2048
2039
1026
1658
402

table
xDLS 11
991
407
505
872
1023
375
380
61

Masks
xDLS 12
1195
643
694
986
1000
305
578
40


xDLS 13
848
398
489
706
794
173
368
19


xDLS 160
2049
1333
1499
1772
1769
726
1310
232


xDLS 165
1787
1086
1252
1544
1556
610
1063
157


xDLS 170
1551
879
1028
1342
1366
509
846
99


xDLS 175
1336
753
819
1158
1192
420
684
71


xDSL 180
1140
633
747
996
1036
333
604
38


xDLS 185
970
528
665
850
892
255
519
22































































TABLE 8



Projected reach Improvement versus ADSL2 in feet on a 26AWG

straight loop at the target data rate 192 kbls/96 kb/s.






PSD mask




noise
single mask
selectable mask
difference









s lf
1C1
3300
3300
0

ADSL
1C2
1800
1800
0

IDSN
1C3
500
500
0

SHDSL
1C4
500
1600
1100

HDSL
1C5
500
1600
1100

T1
1C6
1700
3500
1800

combo
1C7
1100
1100
0

TIA
1C8
500
900
400

































By comparing selectable masks system and single mask it is found that a single mask system cannot handle multiple physical layer/noise scenarios.
Table 9 gives the selected upstream/downstream masks according to the optimality criteria defined in section 3.3. Table 9 illustrates that different PSD masks are appropriate under different channel and noise conditions.





TABLE 9



Selectable masks system for LDSL: Upstream/Downstrearn Selection Table.












case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8


Self Nex
ADSL
ISDN
SHDSL
HDSL
T1
MIX
TIA














xDSL 10
u2d2
u2d2{grave over ( )}
u2d2
u2d2
u2d2
u1d1
u2d2
u1d1

xDLS 11
u2d2
u2d2
u2d2
u2d2
u1d1
u1d1
u2d2
u1d1

xDLS 12
u2d2
u2d2
u2d2
u1d2
u1d2
u1d1
u2d2
u1d1

xDLS 13
u2d2
u2d2
u2d2
u1d2
u1d2
u1d1
u2d2
u1d1

xDLS 160
u2d2
u2d2
u2d2
u2d2
u2d2
u1d1
u2d2
u1d1

xDLS 165
u2d2
u2d2
u2d2
u2d2
u2d2
u1d1
u2d2
u1d1

xDLS 170
u2d2
u2d2
u2d2
u1d2
u1d2
u1d1
u2d2
u1d1

xDLS 175
u2d2
u2d2
u2d2
u1d2
u1d2
u1d1
u2d2
u1d1

xDSL 180
u2d2
u2d2
u2d2
u1d2
u1d2
u1d1
u2d2
u1d1

xDLS 185
u2d2
u2d2
u2d2
u1d2
u1d2
u1d1
u2d2
u1d1


































Although all mask combinations were considered, only three combinations are required to address multiple physical layer/noise scenarios:
{U 1 , D 1 }, identified as the Overlap Combination;
{U 2 , D 2 ), identified as the FDM Combination;
{U 1 , D 2 }, identified as the Hybrid Combination.
The overlap Combination {U 1 , D 1 } is essential to handle cases noise # 8 and # 6, where T1 noise seriously limits downstream performance of the FDM combination {U 2 , D 2 ).
The hybrid combination {U 1 , D 2 ) is crucial in the presence of HDSL and SHDSL cross talks to lift the {U 2 , D 2 } Upstream performance limitations.
{U 2 , D 2 } wins ˜60% of the scenarios.
{U 1 , D 1 } wins ˜25%% of the scenarios.
{U 1 , D 2 ) wins ˜15% of the scenarios.
It has been noted that the including only the self-crosstalk from the PSD mask being tested may be overly optimistic. The reason is that if LDSL includes an overlapped and a non-overlapped mask, for example, that results using the non-overlapped mask will be overly optimistic if some crosstalk from the overlapped mask are not included.
To address this issue, we have also run simulations results assuming that there is always at least one overlapped LDSL disturber using mask D 1 in the downstream direction. In the upstream direction, therefore, we assume that the total number of NEXT self-disturbers is one less than the number given in T1E1.4/2002-292R2 and that the remaining self disturber is mask D 1 . In the downstream direction, similarly, we make the same assumption for FEXT self-disturbers. NEXT disturbers at the CPE and FEXT disturbers at the CO are left unchanged. For the case where the overlapped mask was selected previously there should be no difference in data rates.





TABLE 10



Performance results assuming that at least 1 overlap

PSD mask is always present. Data rates are in kbps.





upstream














case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8



Self Nex
ADSL
ISDN
SHDSL
HDSL
T1
MIX
TIA



Selec-
xDSL 10
505
505
410
327
341
235
404
239

table
xDSL 11
330
330
238
169
153
169
232
173

Masks:
xDLS 12
289
289
198
147
155
147
193
151

1
xDLS 13
182
182
98
107
114
106
100
109

Overlap +
xDLS 160
364
364
271
198
214
176
265
181

Self
xDLS 165
332
332
240
163
178
163
234
167


xDLS 170
300
300
209
149
156
149
203
153


xDLS 175
269
269
179
135
143
135
174
139


xDSL 180
239
239
152
122
130
122
147
126


xDLS 185
208
208
123
110
117
110
119
113







downstream














case 1
case 2
case 3
case 4
case 5
case 6
case 7
case 8



Self Nex
ADSL
ISDN
SHDSL
HDSL
T1
MIXT
TIA



Selec-
xDSL 10
2403
1661
1869
2048
2039
1026
1658
402

table
xDSL 11
991
407
505
872
1023
375
380
61

Masks:
xDLS 12
1196
643
694
986
1000
305
578
40

1
xDLS 13
856
398
489
706
794
173
368
19

Overlap +
xDLS 160
2050
1333
1499
1772
1770
726
1310
232

Self
xDLS 165
1787
1086
1252
1544
1557
610
1063
157


xDLS 170
1551
879
1028
1342
1366
509
846
99


xDLS 175
1336
753
819
1158
1192
420
684
71


xDSL 180
1140
633
747
996
1036
333
604
38


xDLS 185
970
528
665
850
892
255
519
22

























































Not surprisingly, the upstream data rate is reduced under some of the test cases. However, for the SHDSL, HDSL, T1, and TIA test cases, the upstream rate is affected very little if at all. This is because HDSL and SHDSL disturbance is no friendlier to ADSL upstream than our overlapped PSD mask proposal is. Although SHDSL and HDSL are considered spectrally compatible with ADSL, they do have a significant negative impact on ADSL upstream performance.
Like Annex A, LDSL system operates in both non overlap and overlap modes. It should be pointed out that LDSL systems always meet the 96 kb/s upstream rate objective, against any loop/noise scenario defined in T1E1.4/2002-292R2, even in the presence of one LDSL overlap disturber.
An operator who deploys T1, HDSL, or SHDSL should have no issue deploying overlapped LDSL. However, if a loop bundle if generally free of other disturbers, then it would not make sense to deploy overlapped LDSL. Therefore, the operator should be able to select any subset of LDSL PSD masks.
We note also that even if the overlapped LDSL mask were allowed on loops that are free of SHDSL, HDSL, and T1, any reasonable selection criteria would never choose the overlapped mask. Therefore, the concern over the overlapped mask is not warranted even if the operator does not specifically prohibit it.
The performance of a “single mask” system and a “selectable mask” system for LDSL are shown that a selectable mask system offers considerable data rate or equivalently reach advantage under certain noise and loop conditions. The selectable mask system, with a choice from three upstream/downstream combinations namely (U 1 , D 1 ), (U 2 , D 2 ), and (U 1 , D 2 ), meets the LDSL minimum data rate requirements for approximately 90% of test scenarios.
Reference is now made to FIG. 3 , which is a flowchart illustrating the top-level operations of an embodiment of the invention. Specifically, FIG. 3 illustrates a method for selecting a spectral mask for use with a DSL system. The illustrated method comprises obtaining a weighted ratio of upstream rates and downstream rates 302 . The method also determines whether a cost function, based in part upon the weighted ratio, is greater than a predetermined value 304 . Finally, the method selects a spectral mask based in part upon the determination of whether the cost function is greater than a predetermined value 306 .
Like Annex A, LDSL system operates in both non overlap and overlap modes. It should be pointed out that LDSL systems always meet the 96 kb/s upstream rate objective, against any loop/noise scenario defined in T1E1.4/2002-292R2, even in the presence of one LDSL overlap disturber.