System and Method for Selectable Mask for LDSL

Abstract

The present invention overcomes various problems by defining two upstream masks (U1, U2) and two downstream masks (D1, D2) 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.

Description

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 (U1, U2) and two downstream masks (D1, D2) 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 (U1, U2) and two downstream masks (D1, D2) 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 U1 and D1 PSD nominal templates according to embodiments of the invention; and

FIG. 2 is an average values plot of U2 and D2 PSD templates according to embodiments 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 OJ-074, and are respectively referred to as U2 and D2 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, U1 and U2, and two downstream masks, D1 and D2. Upstream mask U1 ends at tone 13 and the downstream mask, D1, 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 {U2, D2} 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, U1 and U2, and two downstream masks, D1 and D2, 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 U1 can be used with mask D1 or D2 for example.

Masks U1 and D1

U1 and D1 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, D1 PSD overlaps the ADSL Upstream bandwidth.

TABLE 1
U1 PSD Nominal Templates
Frequency (kHz)     PSD (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 × log2(f/60.38), 10 ×
                    log10[0.05683 × (f × 103)−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
D1 PSD Nominal Templates
Frequency (kHz)   PSD (dBm/Hz)
0 ≦ f < 4         −101
4 ≦ f < 25.875    −96 + 20.79*log2(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*log2(f/552)
1012 ≦ f < 1800   −68.5
1800 ≦ f < 2290   −68.5 − 72*log2(f/1800)
2290 ≦ f < 3093   −93.500
3093 ≦ f < 4545   −93.5 peak, average −40 − 36*log2(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
Note2.
U1 Total power is equal to 12.47 dBm. D1 total power is equal to 19.43 dBm.

Masks U2 and D2

Tables 3 and 4 give the breakpoints of U2 and D2 PSD Nominal Templates. U2 and D2 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 OJ-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)    PSD (dBm/Hz)
0 ≦ f < 4          −101.5
4 ≦ f < 25.875     −96 + 21.5 × log2(f/4)
25.875 ≦ f < 103.5 −36.4
103.5 ≦ f < 686    max{−36.3 − 95 × log2(f/103.5), 10 ×
                   log10[0.05683 × (f × 103)−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 f (kHz) PSD (dBm/Hz)
0 ≦ f < 4         −101.5
4 ≦ f < 80.000    −96 + 4.63*log2(f/4)
80 ≦ f < 138.000  −76 + 36*log2(f/80)
138 ≦ f < 276.000 −42.95 + 0.0214*f
276 ≦ f < 552.000 −37
552 ≦ f < 1012    −37 − 36*log2(f/552)
1012 ≦ f < 1800   −68.5
1800 ≦ f < 2290   −68.5 − 72*log2(f/1800)
2290 ≦ f < 3093   −93.500
3093 ≦ f < 4545   −93.5 peak, average −40 − 36*log2(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.
	upstream
		case 1	case 2	case 3	case 4	case 5	case 6	case 7	case 8
		Self Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
ADSL2	xDSL 10	963	963	623	344	357	982	597	665
	xDSL 11	682	682	340	142	156	692	315	378
	xDSL 12	633	633	294	109	122	642	270	331
	xDSL 13	470	470	151	58	67	478	123	175
	xDSL 160	770	770	424	168	180	786	398	463
	xDSL 165	719	719	377	140	150	736	347	415
	xDSL 170	668	668	328	115	124	684	299	364
	xDSL 175	620	619	283	93	105	634	259	316
	xDSL 180	576	576	241	77	88	585	217	275
	xDSL 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 Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
ADSL2	xDSL 10	1260	1260	1168	1354	1348	194	1218	186
	xDSL 11	207	207	101	250	250	0	131	0
	xDSL 12	418	418	325	462	461	0	365	0
	xDSL 13	164	194	148	199	199	0	165	0
	xDSL 160	979	979	875	1057	1051	115	928	113
	xDSL 165	774	774	657	847	844	72	718	66
	xDSL 170	598	598	500	659	658	35	543	29
	xDSL 175	447	471	357	500	500	0	412	8
	xDSL 180	320	352	260	365	365	0	304	0
	xDSL 185	218	248	195	256	256	0	220	0
Data rates in kbps.

Modified OJ-074 Single Mask Performance, Combination {U2, D2}

Table 6 displays the results of the Modified OJ-074 {U2, D2}. These results will be taken as references for LDSL.

TABLE 6
Performance results for the a single upstream and single downstream PSD mask (U2, D2).
	upstream
		case 1	case 2	case 3	case 4	case 5	case 6	case 7	case 8
		Self Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
SINGLE	xDSL 10	837	838	515	330	345	842	480	531
MASK	xDSL 11	663	664	338	170	182	665	303	352
(U2, D2)	xDSL 12	619	619	295	134	144	620	261	309
	xDSL 13	492	492	182	71	82	493	152	193
	xDSL 160	705	705	375	201	218	707	340	389
	xDSL 165	670	671	341	169	181	673	306	355
	xDSL 170	636	636	308	141	151	638	274	322
	xDSL 175	602	602	275	116	125	603	242	289
	xDSL 180	567	567	244	94	106	569	211	256
	xDSL 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 Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
SINGLE	xDSL 10	2402	1661	1869	2048	2039	467	1658	240
MASK	xDSL 11	991	407	505	872	911	97	380	0
(U2, D2)	xDSL 12	1195	643	694	986	1000	58	578	0
	xDSL 13	848	398	489	706	793	63	368	0
	xDSL 160	2049	1333	1499	1772	1769	365	1310	171
	xDSL 165	1787	1086	1252	1544	1556	291	1063	109
	xDSL 170	1551	879	1028	1342	1366	227	846	63
	xDSL 175	1336	753	819	1158	1191	175	684	40
	xDSL 180	1140	633	747	996	1035	131	604	13
	xDSL 185	970	528	665	850	891	94	519	0
Data rates in kbps.

Performance of Selectable Masks System

Table 7 gives the results of the selectable masks system for LDSL, based on T1E1.4/2002-292R2.

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*(dsrate(2)−dsrate(1))/dsrate(1)+(usrate(2)−usrate(1))/usrate(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.
	upstream
		case 1	case 2	case 3	case 4	case 5	case 6	case 7	case 8
		Self Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
SELECTABLE	xDSL 10	837	838	515	330	345	235	480	239
MASKS	xDSL 11	663	664	338	170	153	169	303	173
	xDSL 12	619	619	295	148	156	147	261	151
	xDSL 13	492	492	182	108	115	106	152	109
	xDSL 160	705	705	375	201	218	176	340	181
	xDSL 165	670	671	341	169	181	163	306	167
	xDSL 170	636	636	308	150	158	149	274	153
	xDSL 175	602	602	275	137	145	135	242	139
	xDSL 180	567	567	244	124	131	122	211	126
	xDSL 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 Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
SELECTABLE	xDSL 10	2402	1661	1869	2048	2039	1026	1658	402
MASKS	xDSL 11	991	407	505	872	1023	375	380	61
	xDSL 12	1195	643	694	986	1000	305	578	40
	xDSL 13	848	398	489	706	794	173	368	19
	xDSL 160	2049	1333	1499	1772	1769	726	1310	232
	xDSL 165	1787	1086	1252	1544	1556	610	1063	157
	xDSL 170	1551	879	1028	1342	1366	509	846	99
	xDSL 175	1336	753	819	1158	1192	420	684	71
	xDSL 180	1140	633	747	996	1036	333	604	38
	xDSL 185	970	528	665	850	892	255	519	22
Data rates in kbps.

TABLE 8
Projected reach Improvement versus ADSL2 in feet on a 26AWG
straight loop at the target data rate 192 kb/s/96 kb/s.
	PSD mask
noise	single mask	selectable mask	difference
s lf	IC1	3300	3300	0
ADSL	IC2	1800	1800	0
IDSN	IC3	500	500	0
SHDSL	IC4	500	1600	1100
HDSL	IC5	500	1600	1100
T1	IC6	1700	3500	1800
combo	IC7	1100	1100	0
TIA	IC8	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/Downstream Selection Table.
	case 1	case 2	case 3	case 4	case 5	case 6	case 7	case 8
	Self Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
xDSL 10	u2d2	u2d2	u2d2	u2d2	u2d2	u1d1	u2d2	u1d1
xDSL 11	u2d2	u2d2	u2d2	u2d2	u1d1	u1d1	u2d2	u1d1
xDSL 12	u2d2	u2d2	u2d2	u1d2	u1d2	u1d1	u2d2	u1d1
xDSL 13	u2d2	u2d2	u2d2	u1d2	u1d2	u1d1	u2d2	u1d1
xDSL 160	u2d2	u2d2	u2d2	u2d2	u2d2	u1d1	u2d2	u1d1
xDSL 165	u2d2	u2d2	u2d2	u2d2	u2d2	u1d1	u2d2	u1d1
xDSL 170	u2d2	u2d2	u2d2	u1d2	u1d2	u1d1	u2d2	u1d1
xDSL 175	u2d2	u2d2	u2d2	u1d2	u1d2	u1d1	u2d2	u1d1
xDSL 180	u2d2	u2d2	u2d2	u1d2	u1d2	u1d1	u2d2	u1d1
xDSL 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:

{U1, D1}, identified as the Overlap Combination;

{U2, D2}, identified as the FDM Combination;

{U1, D2}, identified as the Hybrid Combination.

The overlap Combination {U1, D1} is essential to handle cases noise # 8 and # 6, where T1 noise seriously limits downstream performance of the FDM combination {U2, D2}.

The hybrid combination {U1, D2} is crucial in the presence of HDSL and SHDSL cross talks to lift the {U2, D2} Upstream performance limitations.

{U2, D2} wins ˜60% of the scenarios.

{U1, D1} wins ˜25%% of the scenarios.

{U1, D2} 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 D1 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 D1. 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.
	upstream
		case 1	case 2	case 3	case 4	case 5	case 6	case 7	case 8
		Self Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
SELECTABLE	xDSL 10	505	505	410	327	341	235	404	239
MASKS: 1	xDSL 11	330	330	238	169	153	169	232	173
OVERLAP +	xDSL 12	289	289	198	147	155	147	193	151
SELF	xDSL 13	182	182	98	107	114	106	100	109
	xDSL 160	364	364	271	198	214	176	265	181
	xDSL 165	332	332	240	163	178	163	234	167
	xDSL 170	300	300	209	149	156	149	203	153
	xDSL 175	269	269	179	135	143	135	174	139
	xDSL 180	239	239	152	122	130	122	147	126
	xDSL 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 Next	ADSL	ISDN	SHDSL	HDSL	T1	MIX	TIA
SELECTABLE	xDSL 10	2403	1661	1869	2048	2039	1026	1658	402
MASKS: 1	xDSL 11	991	407	505	872	1023	375	380	61
OVERLAP +	xDSL 12	1196	643	694	986	1000	305	578	40
SELF	xDSL 13	856	398	489	706	794	173	368	19
	xDSL 160	2050	1333	1499	1772	1770	726	1310	232
	xDSL 165	1787	1086	1252	1544	1557	610	1063	157
	xDSL 170	1551	879	1028	1342	1366	509	846	99
	xDSL 175	1336	753	819	1158	1192	420	684	71
	xDSL 180	1140	633	747	996	1036	333	604	38
	xDSL 185	970	528	665	850	892	255	519	22
Data rates are in kbps.

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 (U1, D1), (U2, D2), and (U1, D2), meets the LDSL minimum data rate requirements for approximately 90% of test scenarios.

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.

Claims

1. A DSL system comprising: mask selection criteria, the criteria comprising: a weighted ratio of upstream rates and downstream rates; anda cost function based in part upon the weighted ratio; anda mask-selectable operator configured to select a spectral mask based on the mask selection criteria, wherein the mask-selectable operator selects a spectral mask based in part upon a determination of whether the cost function is greater than a predetermined value.