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.
| 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 × log2(f/4) |
| 25.875 < f < 138 | −38 |
| 138 < f < 307 | −38 −48 × log2(f/138) |
| 307 < f < 1221 | −93.5 |
| 1221 < f < 1630 | min(−90−48 × log2(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:
where fsym 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:
| 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 | SDSLu (f) with fsym = 160,000 | 320 | 15.5 |
| TS103 | SDSLu (f) with fsym = 168,000 | 336 | 14.5 |
| TS104 | SDSLu (f) with fsym = 208,000 | 416 | 13.5 |
| TS105 | SDSLu (f) with fsym = 232,000 | 464 | 12.5 |
| TS106 | SDSLu (f) with fsym = 264,000 | 528 | 12 |
| TS107 | SDSLu (f) with fsym = 296,000 | 592 | 11.5 |
| TS108 | SDSLu (f) with fsym = 328,000 | 656 | 11 |
| TS109 | SDSLu (f) with fsym = 360,000 | 720 | 10.5 |
| TS110 | SDSLu (f) with fsym = 392,000 | 784 | 10 |
| TS111 | SDSLu (f) with fsym = 456,000 | 912 | 9.5 |
| TS112 | SDSLu (f) with fsym = 520,000 | 1040 | 9 |
| TS113 | SDSLu (f) with fsym = 552,000 | 1104 | 8.5 |
| TS114 | SDSLu (f) with fsym = 616,000 | 1232 | 8 |
| TS115 | SDSLu (f) with fsym = 712,000 | 1424 | 7.5 |
| TS116 | SDSLu (f) with fsym = 840,000 | 1680 | 7 |
| TS117 | SDSLu (f) with fsym = 936,000 | 1872 | 6.5 |
| TS118 | SDSLu (f) with fsym = 1,064,000 | 2128 | 6 |
| TS119 | SDSLu (f) with fsym = 1,128,000 | 2256 | 5.5 |
| TS120 | SDSLu (f) with fsym = 1,160,000 | 2320 | 5 |
| Line Bit Rate LBR (kbps) | KSHDSL | fsym (ksymbols) | f3dB |
|---|---|---|---|
| LBR ≠ 1544 or 1552 | 7.86 | LBR 13 | 1.0 × fsym12 |
| LBR = 1544 or 1522 | 8.32 | LBR 13 | 0.9 × fsym12 |
where fint is the intersection frequency in which the two functions in PSDSHDSL(f) intersect in the range of 10 kHz to fsym, KSHDSL is a scaling coefficient, fsym is the symbol rate, f3dB is the low-pass shaping filter cut-off frequency, and fc 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.
| 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 |
| 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.
Figure 10.14. Plot of 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 log10(f/130000) |
| 307000 < f ≤ 1221000 | −93.5 |
| 1221000 < f ≤ 1630000 | min(−90 − 48 × log2(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.