10.7 Technology-Specific Guidelines

   


10.7 Technology-Specific Guidelines

In addition to the technology-independent SM classes described, the SM standard T1.417 also contains technology-specific guidelines. In the first issue of T1.417, there is one specific underlying technology, namely, pulse amplitude modulation; however, there are three distinct families of technology specific guidelines. The technology specific guidelines include 2B1Q-based SDSL, PAM per G.991.2 Annex A, and PAM per HDSL4 using 776/784 kb/s asymmetric PSDS.

Table 10.10. Spectrum Management Class 9 Upstream Template Definition

Frequency Band (kHz)

PSD (dBm/Hz)

0 < f < 4

-101, with max power in the in 0 “4 kHz bands of + 15 dBm

4 < f < 25.875

-96 + 21.5 x log 2 ( f /4)

25.875 < f < 138

-38

138 < f < 307

-38 -48 x log 2 ( f /138)

307 < f < 1221

-93.5

1221 < f < 1630

min(-90-48 x log 2 ( f /1221), -93.5)

1630 < f < 11040

-110


10.7.1 2B1Q SDSL

Although this is a nonstandard technology in North America, there have been many systems deployed using multirate 2B1Q SDSL in the loop plant. 2B1Q is four-level pulse amplitude technology whose bandwidth is directly proportional to the bit rate of the system. The spectral compatibility of 2B1Q SDSL with the basis systems is computed using the following mathematical expression for the PSD:

graphics/10equ02.gif


where f sym is the symbol rate in units of symbols per second, the symbol rate is one-half the bit rate, and f is the frequency in Hz. Because this is a variable bit rate, hence variable bandwidth transmission system, the spectral compatibility with the basis systems will vary with the symbol rate of SDSL. We therefore need to define a deployment guideline for each of the symbol rates supported by SDSL so that there is no degradation to the services provided by the basis systems. Complying with the 2B1Q SDSL template at a specific symbol rate assures spectral compatibility with the basis systems if deployed according to the deployment guidelines associated with that symbol rate. A complete list of deployment guidelines is provided in Table 10.11.

10.7.2 G.shdsl

G.shdsl (i.e., G.991.2) defines a multirate transmission system based on trellis -coded pulse amplitude modulation (TC-PAM). Annex A of G.shdsl defines a family of symmetric PSDs that is a function of the symbol rate. As with 2B1Q SDSL, the spectral compatibility of G.shdsl with the basis systems will be vary with the symbol rate of G.shdsl-based systems. To compute the spectral compatibility of the G.shdsl systems with the basis systems, the following mathematical expression for the G.shdsl PSD is used:

Table 10.11. SDSL Deployment Guidelines

Designation

PSD

Maximum 2B1Q SDSL line bit rate (kbps)

2B1Q SDSL deployment guideline, EWL (kft)

TS101

SMI PSD template

300

all non-loaded loops

TS102

SDSL u ( f ) with f sym = 160,000

320

15.5

TS103

SDSL u ( f ) with f sym = 168,000

336

14.5

TS104

SDSL u ( f ) with f sym = 208,000

416

13.5

TS105

SDSL u ( f ) with f sym = 232,000

464

12.5

TS106

SDSL u ( f ) with f sym = 264,000

528

12

TS107

SDSL u ( f ) with f sym = 296,000

592

11.5

TS108

SDSL u ( f ) with f sym = 328,000

656

11

TS109

SDSL u ( f ) with f sym = 360,000

720

10.5

TS110

SDSL u ( f ) with f sym = 392,000

784

10

TS111

SDSL u ( f ) with f sym = 456,000

912

9.5

TS112

SDSL u ( f ) with f sym = 520,000

1040

9

TS113

SDSL u ( f ) with f sym = 552,000

1104

8.5

TS114

SDSL u ( f ) with f sym = 616,000

1232

8

TS115

SDSL u ( f ) with f sym = 712,000

1424

7.5

TS116

SDSL u ( f ) with f sym = 840,000

1680

7

TS117

SDSL u ( f ) with f sym = 936,000

1872

6.5

TS118

SDSL u ( f ) with f sym = 1,064,000

2128

6

TS119

SDSL u ( f ) with f sym = 1,128,000

2256

5.5

TS120

SDSL u ( f ) with f sym = 1,160,000

2320

5


Table 10.12. Values of the G.shdsl PSD Parameters

Line Bit Rate LBR (kbps)

K SHDSL

f sym (ksymbols)

f 3dB

LBR 1544 or 1552

7.86

LBR 13

1.0 x f sym 12

LBR = 1544 or 1522

8.32

LBR 13

0.9 x f sym 12


graphics/10equ03.gif


where f int is the intersection frequency in which the two functions in PSD SHDSL ( f ) intersect in the range of 10 kHz to f sym , K SHDSL is a scaling coefficient, f sym is the symbol rate, f 3dB is the low-pass shaping filter cut-off frequency, and f c is the high-pass transformer cut-off frequency. The values for the G.shdsl PSD parameters are given in Table 10.12. Because G.shdsl is a variable bit rate resulting in a variable bandwidth transmission system, the spectral compatibility with the basis systems will vary with its symbol rate. As with SDSL, the deployment guidelines for G.shdsl need to be defined as a function of symbol rate. Complying with the G.shdsl template at a specific symbol rate assures spectral compatibility with the basis systems if deployed according to the deployment guidelines associated with that symbol rate. A complete list of deployment guidelines is provided in Table 10.13.

Table 10.13. Deployment Guidelines for G.shdsl

Designation

G.shdsl Line Bit Rate (kbps)

G.shdsl deployment guideline, EWL (kft)

TS201

LBR 592

All non-loaded loops

TS202

600 LBR 616

15.0

TS203

624 LBR 648

14.5

TS204

656 LBR 688

14.0

TS205

696 LBR 800

13.5

TS206

808 LBR 832

12.5

TS207

840 LBR 896

12.0

TS208

904 LBR 952

13.0

TS209

960 LBR 1000

12.5

TS210

1008 LBR 1088

12.0

TS211

1096 LBR 1160

11.5

TS212

1168 LBR 1320

11.0

TS213

1328 LBR 1472

10.5

TS214

1480 LBR 1536

10.0

TS215

1544 LBR 1552

10.5

TS216

1560 LBR 1664

10.0

TS217

1672 LBR 1880

9.5

TS218

1888 LBR 2008

9.0

TS219

2016 LBR 2320

8.5


Table 10.14. PSD Template for HDSL4 Downstream Channel

Frequency (kHz)

PSD (dBm/Hz)

Frequency (kHz)

PSD (dBm/Hz)

Frequency (kHz)

PSD (dBm/Hz)

0.2

-51

110

-58

250

-51.5

2

-41

135

-46.5

400

-46.5

5

-37.5

145

-40.5

600

-70

50

-37.5

150

-38.5

1000

-89.2

80

-40.5

155

-37.5

2000

-99.7

90

-45

200

-40.25

3000

-108

105

-58

210

-43

3100

-110


10.7.3 776/784 HDSL4 Asymmetric Spectra Using TC-PAM

HDSL4 technology is designed to transport a 1.544 Mb/s (DS1) payload on two twisted wire pairs using TC-PAM. This is the same core technology as that for G.shdsl, where the bit rate and transmission spectrum are fixed to transport 784 kb/s or 776 kb/s on each wire pair end-to-end.

To obtain optimum reach and spectral compatibility with other services in the cable, HDSL4 uses a set of asymmetric PSDs for transmission of the upstream and downstream channels. The downstream channel template is listed in Table 10.14 and the corresponding PSD plot is shown in Figure 10.13. In the construction of the PSD, linear interpolation of the frequency and PSD points is used. The upstream channel template is listed in Table 10.15 and the corresponding plot is given in Figure 10.14.

Figure 10.13. Plot of PSD template for HDSL4 downstream channel.

graphics/10fig13.jpg

Figure 10.14. Plot of PSD template for HDSL4 upstream channel.

graphics/10fig14.jpg

Table 10.15. PSD Template for HDSL4 Upstream Channel

Frequency Band (kHz)

PSD (dBm/Hz)

0 < f 200

-51

200 < f 2000

-41 + 10( f -2000)/1800

2000 < f 5000

-37 + 4( f -5000)/3000

5000 < f 50000

-37

50000 < f 125000

-37-(( f -50000)/75000)

125000 < f 130000

-38

130000 < f 307000

-38-142 log 10 ( f /130000)

307000 < f 1221000

-93.5

1221000 < f 1630000

min(-90 - 48 x log 2 ( f /1221000), -93.5)

f < 1630000

-110


Given the optimized spectral shaping for the given bit rates, signals of HDSL4 technology are considered to be spectrally compatible with the basis system when deployed on any nonloaded loop facility. The only restriction is that an HDSL4 transceiver is not located near the customer end with the downstream spectrum traveling in the downstream direction. The far-end crosstalk may cause a spectral incompatibility with other systems served directly from the central office.


   
Top


DSL Advances
DSL Advances
ISBN: 0130938106
EAN: 2147483647
Year: 2002
Pages: 154

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net