AU2005209644B2 - System and method for enabling two-pair E1 delivery with spectrally compatible signals - Google Patents

Description

S&FRef: 735764

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant Actual Inventor(s): Address for Service: Invention Title: Adtran, Inc., of 901 Explorer Boulevard, Huntsville, Alabama, 35806, United States of America Marc Kimpe Robert Barrett Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) System and method for enabling two-pair El delivery with spectrally compatible signals The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c SYSTEM AND METHOD FOR ENABLING TWO-PAIR El DELIVERY WITH SPECTRALLY COMPATIBLE SIGNALS CROSS REFERENCE TO RELATED APPLICATION This application claims priority to U.S. Provisional Application No. 60/608,560, entitled "Spectral Shaping of 2-Pair El Delivery to Achieve Longer Reach and Allow Repeaters While Remaining Spectrally Compatible," and filed on September 10, 2004, which is incorporated herein by reference.

FIELD OF THE INVENTION The invention relates generally to communication systems, and in particular to a system and method for enabling two-pair El delivery with spectrally compatible signals.

BACKGROUND

Segments of telecommunication lines are usually bundled in cables that extend over large distances from transceivers at a central office to transceivers at remote locations, sometimes referred to as "customer premises." Signals communicated across telecommunication line segments bundled within the same cable couple from line-to-line causing crosstalk. The crosstalk between signals using the same frequencies may degrade signal performance and may limit the cable's capacity or data rate.

A wide variety of telecommunication technologies may be used to communicate across telecommunication line segments bound by the same cable. In order to allow signals from different technologies to co-exist in the same cable, spectrum management standards T1.417-2001 Spectrum Managementfor Loop Transmission applicable to North America or ACIF C559.2005 applicable to Australia) have been developed. Such [R:\L1Boo]07072.D0C:GYC standards specify crosstalk limits to ensure that crosstalk will not reduce signal quality below a specified level. A telecommunication service provider must ensure that signals communicated by its equipment satisfy the limits imposed by applicable country-specific spectrum management standards.

Signals that violate the spectrum management standards by causing an unacceptable amount of crosstalk to affect other signals communicated through the same cable are referred to as "spectrally incompatible" with such other signals. Signals that adhere to the spectrum management standards and, therefore, do not induce an unacceptable amount of crosstalk are referred to as "spectrally compatible" with the other signals communicated through the same cable.

Digital subscriber line (DSL) services, such as high-data-rate digital subscriber line, second generation 2-wire (HDSL2), high-data-rate digital subscriber line, second generation 4-wire HDSL (HDSL4), single-pair high-data-rate digital subscriber line (SHDSL) and asymmetric digital subscriber line (ADSL) services, are very popular due to the relatively high data rates and relatively low costs associated with these types of services. HDSL2, HDSL4, SHDSL and ADSL transceivers communicate over conventional copper loops and, therefore, are able to utilize a substantial portion of the vast telecommunication copper infrastructure that has been in place for decades.

Second-generation HDSL has two deployment technologies, HDSL2 and HDSL4.

HDSL2 transmits a 1.544 Mega-bits per second (Mbps) DS1 payload on a single copper loop (2 wires). HDSL4 uses a similar transmission technology as HDSL2 but uses two copper loops (4 wires) each carrying half of the 1.544 Mbps DS1 payload. In general, HDSL2 signals communicated in accordance with existing standards can be transmitted with acceptable signal quality up to approximately 9,000 feet (ft) on 26 AWG. In general, [R:\..IBOO107072.DOC:GYC 3 HDSL4 signals communicated in accordance with existing standards can be transmitted with acceptable signal quality up to approximately 12,000 feet (ft) on 26 AWG before O being regenerated. Both HDSL2 and HDSL4 have shaped PSDs in order to improve spectral compatibility with ADSL. In addition, HDSL4 allows the use of spectrally compatible repeaters.

SHDSL is a multi-rate symmetric technology using a transmission technology Ssimilar to HDSL2 and HDSL4. It can transmit data rates from 192 kilo-bits per second (kbps) to 2320 kbps, trading-off data rate for reach. While HDSL2/HDSL4 is a technology geared towards North American use because it only supports DS1 transport, SHDSL is used internationally because it can also support El and TU-12 transport. ETSI ETR 152 standardizes the transport of an El payload using 2B1Q HDSL technology. While El refers to a payload of 2.048 Mbps, HDSL adds overhead. Therefore, El transport over HDSL currently requires 2.304 Mbps on a single pair or 1.168 Mbps on each of two pairs. Some countries, such as Germany, make use of the overhead, but some other countries, such as Australia, do not. While HDSL is a fixed rate technology, SHDSL is variable rate. Hence, countries using the overhead may replace HDSL two-pair by SHDSL two-pair running at 1.168 Mbps on each wire pair, and countries not using the overhead may replace HDSL two-pair by SHDSL two-pair operating at a payload rate of 1.024 Mbps resulting in a line rate of 1.032 Mbps on each wire pair. For the sake of simplicity, 1032 kbps and 1168 kbps over each of two pairs will both be referred to herein as El transport. It is understood that although both carry an El payload, the overhead is different.

ADSL is a ubiquitous DSL technology used by telecommunication operators throughout the world to deliver broadband. ADSL signals can often be transmitted up to approximately 18,000 ft on AWG 26 or 5 kilometers (km) on 0.4 millimeter (mm) PIUT [R:\LIBOO]07072.DOC:GYC without regeneration. The deployment of ADSL is protected in order to achieve a minimum performance for ADSL.

Moreover, SHDSL signals transmitted at 1032/1168 kbps and ADSL signals transmitted in accordance with existing standards are spectrally compatible and, therefore, can be transmitted in the same cable up to a specified deployment limit for SHDSL. The limit is defined in the country specific spectrum management document. For example, table 16 of T1.417 limits the deployment reach of SHDSL at 1168 kbps to approximately 11 kilo-feet (kft) of EWL AWG 26 and Table A-1 class 9d of C559:2005 limits the deployment reach of SHDSL 1032 and 1168 kbps to 2.8 km of PIUT 0.4 mm cable in Australia. Although C559:2005 does not explicitly cover repeaters, Table A-1 class 9a allows SHDSL repeaters up to 584 kbps while class 9b describes a non-standard reduced power version of SHDSL that allows repeaters up to 784 kbps. If an SHDSL 1032/1168 kbps signal is regenerated beyond approximately 2.8 km in Australia, then unacceptable interference occurs with ADSL signals communicated in the same cable, and the repeatered SHDSL 1032/1168 kbps signal is, therefore, spectrally incompatible with such ADSL signals. Thus, deployment of SHDSL 1032/1168 kbps is often limited approximately to the first 2.8 km of a cable that extends from a central office so that regeneration of SHDSL signals is unnecessary. Such a limitation ensures spectral compatibility between SHDSL 1032/1168 kbps and ADSL signals but undesirably limits the deployment distance of SHDSL 1032/1168 kbps services.

SUMMARY OF THE DISCLOSURE Generally, embodiments of the present disclosure pertain to systems and methods for enabling two pair El delivery with spectrally compatible signals.

[R:\LIBOO]07072.DOC:GYC A system in accordance with one exemplary embodiment of the present disclosure comprises a telecommunication line segment, a first transceiver and a second transceiver.

O The first transceiver is configured to transmit a first signal across the telecommunication line segment and to receive a second signal from the telecommunication line segment. The first transceiver is further configured to spectrally shape the first signal such that the first t signal has a first power spectral density (PSD). The second transceiver is configured to Stransmit the second signal across the telecommunication line segment and to receive the first signal from the telecommunication line segment. The second transceiver is further configured to spectrally shape the second signal such that the second signal has a second PSD that is dissimilar to the first PSD. The first and second signals provide at least onehalf of El delivery over the telecommunication line segment and are spectrally compatible.

The second PSD has a passband more narrow than a passband of the first PSD, and the passband of the second PSD extends from about 0 kHz to a range between approximately 138 kHz to approximately 200 kHz. A total power of the first PSD within the passband of the second PSD is less than a total power of the second PSD within the passband of the second PSD.

A method in accordance with one embodiment of the present disclosure comprises the steps of: transmitting a first signal from a first transceiver to a second transceiver across a telecommunication line segment; spectrally shaping the first signal such that the first signal has a first power spectral density (PSD); transmitting a second signal from the second transceiver to the first transceiver across the telecommunication line segment; and spectrally shaping the second signal such that the second signal has a second PSD that is dissimilar to the first PSD.

[R:\LIBOO]07072.DOC:GYC The first and second signals enable at least one-half of El delivery over the telecommunication line segment and are spectrally compatible, and the second PSD has a passband more narrow than a passband of the first PSD. The passband of the first PSD extends from about 0 kHz to a range between approximately 138 kHz to approximately 200 kHz, and a total power of the first PSD within the passband of the second PSD is less than a total power of the second PSD within the passband of the second PSD.

BRIEF DESCRIPTION OF THE DRAWINGS The invention can be better understood with reference to the following drawings.

The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Furthermore, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a block diagram illustrating a conventional communication system.

FIG. 2 is a block diagram illustrating a communication system in accordance with an exemplary embodiment of the present disclosure.

FIG. 3 is a graph illustrating exemplary power spectral density (PSD) functions for SHDSL transceivers communicating across one of the tele-communication lines of FIG. 2.

FIG. 4 is a block diagram illustrating a repeater depicted in FIG. 2.

FIG. 5 is a block diagram illustrating an exemplary embodiment of a transceiver that may be used to implement one or more transceivers depicted in FIGS. 2 and 4.

FIG. 6 is a block diagram illustrating an exemplary embodiment of a transmitter depicted in FIG. FIG. 7 is a block diagram illustrating an exemplary embodiment of a receiver depicted in FIG. [R:\LIB00107072.DOC:GYC FIG. 8 is a graph illustrating exemplary power spectral density (PSD) functions for SHDSL transceivers communicating across one of the tele-communication lines of FIG. 2.

FIG. 9 is a graph illustrating another exemplary power spectral density (PSD) functions for SHDSL transceivers communicating across one of the tele-communication lines of FIG. 2.

DETAILED DESCRIPTION Embodiments of the present disclosure pertain to systems and methods for spectrally shaping power spectral densities (PSDs) on a single or multiple links to deliver at least an El payload on 2 pairs and remain spectrally compliant.

A system in accordance with an exemplary embodiment of the present disclosure comprises a telecommunication line that provides a communication channel between a central office transceiver and a remote transceiver. Segments of the telecommunication line can be coupled to one or more repeaters, which regenerate signals communicated along the telecommunication line.

FIG. 1 depicts a conventional telecommunication system 15. The system 15 of FIG. 1 comprises a Single-Pair High Speed Digital Subscriber Line (SHDSL) transceiver 18 and an asymmetric digital subscriber line (ADSL) transceiver 21 residing at a central office 23 of a telecommunication network. The SHDSL transceiver 18 of FIG. 1 communicates with a remote SHDSL transceiver 27 via a telecommunication line 29. The telecommunication line 29 depicted in FIG. 1 has two repeaterless segments 31 and 32, each of which comprises a twisted wire pair, sometimes referred to as a "loop." Segment 31 couples the SHDSL transceiver 18 of the central office 23 to a repeater 35, and segment 32 couples the repeater 35 to the remote SHDSL transceiver 27. Note that the remote SHDSL transceiver [R:\LIBOO]07072.DOC:GYC 8 27 may reside at a customer premises or may reside within another repeater in the event that telecommunication line 29 extends beyond the remote SHDSL transceiver 27.

The ADSL transceiver 21 communicates with a remote ADSL transceiver 39 over a repeaterless telecommunication line segment 41, which comprises a twisted wire pair. The ADSL transceiver 39 resides at a customer premises.

For illustrative purposes, assume that each of the transceivers 27 and 39, as well as the repeater 35, are positioned at their maximum respective distances from the central office 23, as allowed by the applicable standard, such as T1.417 in North America and C559:2005 in Australia.

In the instant example in which SHDSL signals are communicated across telecommunication line 29, trellis coded pulse amplitude modulation (TC-PAM) is used to form such signals. However, other types of signals may be communicated across telecommunication line 29 in other examples, and these signals may be formed using other types of modulation schemes, such as quadrature amplitude modulation (QAM) or Discrete Multi-tone (DMT). For example, the signals communicated over telecommunication lines 29 and 41 may be in accordance with HDSL2, HDSL4, G.SHDSL.bis, SDSL, or other known or future-developed standards. In amplitude modulation, such as PAM or QAM, a constellation is used to map digital data words to points or levels, referred to as "symbols," corresponding to the values of the digital data words. In this regard, a constellation defines different symbols to which digital data words can be mapped, and the total number of symbols within a constellation controls the size of the data words that may be mapped by the constellation.

It is generally well known that a constellation density of a little less than (payload bits/symbol) provides an optimum solution for PAM considering the factors of [R:\LIBOO]07072.DOC:GYC 9 bandwidth, signal quality, and reach. Thus, conventional PAM transceivers are typically configured to communicate using constellations providing constellation densities of O Higher constellations can beused. However, for a given length of a telecommunication line segment, increasing the constellation density reduces the signal quality of the signals transmitted over the line segment. Thus, to keep the signal quality of such signals within t an acceptable range, the acceptable maximum length of a repeaterless telecommunication line segment is often significantly reduced as the constellation density for the signals communicated over the segment is increased. Moreover, in selecting the constellation density, significant trade-offs exist between bandwidth, signal quality, and reach maximum possible repeaterless line length). Accordingly, the transceivers 18 and 27 depicted by FIG. 1, as well as transceivers (not shown) included in the repeater 35, are configured to transmit symbols that contain three bits of payload information.

In some embodiments, it is possible for the telecommunication line segments 32 and 41 to be positioned in close proximity to one another bound within the same cable or other binder). When the segments 32 and 41 extending across distance d are bound within the same cable, crosstalk induced by the regenerated signals transmitted across segment 32 may interfere with the signals transmitted across segment 41. Indeed, if the regenerated SHDSL signals transmitted across segment 32 induce an unacceptable amount ofcrosstalk, as defined by the applicable standard, such as T1.417 in North America or C559:2005 in Australia, then the regenerated SHDSL signals are spectrally incompatible with the ADSL signals transmitted across segment 41.

Significant effort has been expended to modify the regenerated SHDSL signals in order to make these signals spectrally compatible with ADSL signals transmitted through the same cable. For example, various techniques for spectrally shaping and adjusting the power [R:\LIBOO]07072.DOC:GYC levels of the SHDSL signals transmitted by repeaters have been employed in an effort to make these signals spectrally compatible. In this regard, spectral shaping generally refers to processes that modify the spectral shape of transmitted signals, and power back-off generally refers to processes that reduce the transmission power of transmitted signals. Such spectral shaping and/or power back-off techniques may be used to lower crosstalk effects within selected bandwidths in an effort to make transmitted signals spectrally compatible.

Spectrally shaping and power back-off techniques have been successfully performed for HDSL4, which can be used to transmit a T1 payload over 2 wire pairs or "pairs" for short.

However, despite great effort, spectral shaping and power back-off techniques have not been successfully performed in the past for an El payload rate over 2 pairs. Thus, in general, regenerated SHDSL signals, such as those generated by the repeater 35 of FIG. 1, as well as non-regenerated SHDSL signals transmitted over certain distances, have not been spectrally compatible with ADSL signals communicated through the same cable.

Given that service providers have to comply with all provisions of the countryspecific spectrum management document, they cannot deploy 2-pair El transport beyond the allowed deployment reach defined in the applicable spectrum management document.

Accordingly, to provide 2-pair El services to the SHDSL transceiver 27, service providers are limited to a certain reach 11 kft in North America and 2.8 km in Australia). Service providers could offer El-transport over more than two pairs. For example, using 584 kbps on each pair, a service provider could offer El over four pairs in Australia and not be limited by spectrum management. However, doubling the number of pairs per El is not often a very attractive solution.

FIG. 2 depicts a telecommunication system 100 in accordance with an exemplary embodiment of the present disclosure. As can be seen by comparing FIGS. 1 and 2, the [R:\LIBOO]07072.DOC:GYC 11 system 100 may be similar to the conventional communication system 15 described above.

Indeed, components having the same reference number in FIGS. 1 and 2 are identically configured. However, the configuration of repeater 135 and SHDSL transceivers 118 and 127 of FIG. 2 are different than the configuration of repeater 35 and SHDSL transceivers 18 and 27, respectively, of FIG. 1. In this regard, rather than communicating signals across segment 31 using the standard 1168 kbps power spectral density (PSD) described in G.991.2, tailored PSDs are preferably used at both ends of segment 31 and both ends of segment 32.

For example, the SHDSL transceiver 118 at the central office 23 can be configured to spectrally shape its signals to be transmitted such that these signals have the PSD 137 shown by FIG. 3. Further, the other transceivers (not specifically shown in FIG. 2) of the repeater 135 and the transceiver 127 can be configured to spectrally shape their signals to be transmitted such that these signals have the PSD 138 shown by FIG. 3. Note that current SHDSL standards specify that the PSD 136 can be used in both the upstream and downstream directions. Also note that PSD 137 may violate spectrum management if used on segment 32. The use of tailored PSDs 137 and 138, as described above, has at least two measurable impacts. First, if no repeater is used, a regular SHDSL 1168 kbps PSD 136 will be more limited in terms of reach relative to the tailored set of PSDs 137 and 138. For example, a regular 1168 kbps PSD 136 in Australia is limited to approximately 2.8 km per C559:2005 while the tailored PSDs 137 and 138, as described above, are not so limited.

Further, if a repeater is used, a regular SHDSL 1168 kbps PSD 136 is not spectrally compatible beyond the deployment limit defined in spectrum management while the tailored PSDs 137 and 138 on segments 31 and 32, as described above, can be used in conjunction with a repeater while still remaining spectrally compatible.

[R:\LIBOO]07072.DOC:GYC 12 By shaping the various PSDs of the signals transmitted across segments 31 and 32, as described herein, it is possible for such signals to remain spectrally compatible. Indeed, by using the PSDs 137 and 138 depicted in FIG. 3, it is possible, to transmit signals across segment 31 and 32 at a rate of at least at 1032/1168 kbps over long distances much greater than 1.8 km) such that these signals are spectrally compatible, as defined by T1.417 and C559:2005, with the ADSL signals transmitted across segment 41 even when the telecommunication line segments 32 and 41 are in close proximity bound within the same cable). Moreover, the deployment restrictions affecting service providers, such as SHDSL providers, in conventional systems can be avoided. Note that, depending on the desired reach, the transmit power of the signals transmitted across segments 31 and 32 may be lowered across some or all frequencies with the PSDs 137 and 138 remaining spectral compatible with ADSL signals. However, lowering the transmit power will likely reduce the maximum possible reach.

FIG. 4 depicts an exemplary configuration of the repeater 135. The repeater 135 of FIG. 4 comprises an SHDSL transceiver 148 coupled to telecommunication line segment 31 and an SHDSL transceiver 152 coupled to telecommunication line segment 32. Further, each of the SHDSL transceivers 148 and 152 is coupled to a set of buffers 155 and 156. As noted above, the telecommunication line segment 31 of the instant example comprises a twisted wire pair or "loop," and the telecommunication line segment 32 of the instant embodiment also comprises a twisted wire pair or "loop." In the instant example, at least one-half of El delivery is provided by the transceivers 118, 127, 148, and 152 over telecommunication line 29. An additional line (not specifically shown) and additional transceivers (not specifically shown) configured similar to the line 29 and transceivers 118, 127, 148, and 152 can be [R:\LIBOO]07072.DOC:GYC 13 employed to achieve full El delivery across both the line 29 and the additional line (not shown).

The SHDSL transceiver 118 (FIG. 2) at the central office 23 spectrally shapes its signals to be transmitted so that these signals have the PSD 137 of FIG. 3. These signals are received from the segment 31 by the SHDSL transceiver 148 and are demodulated by the transceiver 148 to recover data originally transmitted by the central office transceiver 118.

Such data is then transmitted to buffer 155, which buffers the data before transmitting it to SHDSL transceiver 152. SHDSL transceiver 152 then modulates the data to form a signal that is transmitted across segment 32. Before transmitting such signal, the transceiver 152 spectrally shapes the signal such that it has the PSD 138 of FIG. 3.

Similarly, the remote SHDSL transceiver 127 transmits across segment 32 signals having the PSD 138 of FIG. 3. Such signals are received from the segment 32 by the SHDSL transceiver 152 and are demodulated by the transceiver 152 to recover digital data. This digital data is buffered by buffer 156 and then modulated by transceiver 148 to form signals that are then transmitted across segment 31. Such signals are spectrally shaped by the transceiver 148 such that they each have the PSD 138 of FIG. 3.

By having tailored PSDs as described above, the signals transmitted across segment 31 are spectrally compatible with the ADSL signals on segment 41 even if segments 31 and 41 are located in the same cable. Further, by having tailored PSDs as described above, the signals transmitted across segment 32 are spectrally compatible with the ADSL signals on segment 41 even if segments 32 and 41 are located in the same cable.

As indicated above, FIG. 3 depicts exemplary PSDs for the transceivers 118, 127, 148, and 152. PSD 136 can be expressed as follows.

[R:\LIBOO]07072.DOC:GYC 2 -PBO K 1 1 f2 10 Xrnsm f fin, ^01 x ,x 7 PSD(f) 135 j xorer f 2 n \3dB 0.5683x 10 4 x f-5, fi,, f 1.1MH where Ktnsmit, order, fsym, and f3dB are specified below in Table 1 and where fint is the frequency at which the two expressions defining the PSD intersect.

Table 1 PSD parameters Kransm,, order fsym (kHz) F3dB 7.86 6 1168/3 fym/2 Based on T1.417 in North America and C559:2005 in Australia, spectrally compatible signals having non-tailored PSD 136 can be transmitted over a repeaterless telecommunication line if such line is less than approximately 11 kft in North America and approximately 2.8 km in Australia.

Note that spectrum management documents, such as T1.417 in North America and C559:2005 in Australia, define the PSD template of the system as the nominal PSD generated on the loop, and the PSD mask as the maximum values for the PSD. At each respective frequency, the mask PSD value is always greater than or equal to the template PSD value.

The difference between the template and the mask depends on the various systems. An SHDSL system generally has about 1 dB difference between the template PSD and the mask PSD, and a DMT system generally has about 3.5 dB difference. Spectrum management documents usually base their spectral compatibility studies on the template.

[R:\LIBOO]07072.DOC:GYC In one embodiment, the transceiver 118 at the central office 23 transmits signals having the PSD 137, and each of the other transceivers 127, 148, and 152 transmits signals having the PSD 138. The PSDs 137 and 138 can be expressed by the following equation.

f f 2 I IOXogjO 2 2 I f HZ]

P

2 -97.5 dBrn Hz f r I1MHz ]MHz f :5 Am, where: f Freq frequency in Hz P(f) is defined below in Table 1 for the downstream PSD 137 and upstream PSD 138 1350 f, is the transformer cut-off frequency, assumed to be 5 kHz f.a 11,040 MHz Table 2 for the Table 1 Freq. (Hz) Downstream PSD (dBm/Hz) (Freq 1.2e3) (Freq<=95.8e3) &(Freq>11.2e3) (Freg <=10763) (Freq >95.8e3) -50-2*(Freg -95.8e3) /1 1.2e3 (Freg <=125e3) (Freq >107e3) -52 (Freg 190e3) (Freg 12 5e3) -52+1 1.5*(Freg -125e3) /65e3 (Freg <=405 e3) (Freg 190e3) -40.5 (Freg <=60063) (Frpg >405e3) -40.5-32*(Freg -405e3) /195e3 (Freq <=876e3) (Freq >60063) -72.5-21*(Freg -600e3) /276e3 (Freq >876e3) -93.5 Table 2 [R:\LIBOO]07072.DOC:GYC (Freq <=2e3 (Freq >200) -50-PBO+10*(Freg -200) /1.8e3 (Freg <=563) (Freg >2e3) -40-PBO+4*(Freg -2e3) /3e3 (Freg <=50e6) (Freg >563) -36-PBO (Fre 12 5e3) (Freg >50Oe3) (Fe 50 /75e3 (Freg <=152.5e3) (Freg >125e3) -37-PBO- 1. 1*(Freq -1 25e3) /27.5e3 (Freg <=326e3) (Freg >1 52.5e3) -38. 1 -PBO- 165*logl 0(Freg/1 52.5e3) (Freg >326e3) -93.5 Although other tolerances may be possible, about 1 dB tolerance for the PSIs 137 and 138 should ensure that spectral compatibility is maintained. Note that power back-off (PBO) can be assumed to be equal to 1. Additional power restrictions, such as mandating that the power in a given bandwidth be within half of a dB of the power under the template may also be defined. Further, in the nomenclature used herein, ey shall mean 1 x Thus, e3 equals 1 X 10 3 The mask of PSIs 137 and 138 can be expressed by the following equation.

.0 Pj P(f) MaskOffsetdB(f)[dBnI Hz] f :5 1MHz {P2 =-9OdBm Hz peak witiz max innun power in a[f, MHz] window of 37.5 dBrn 1MHz f fma where: f frequency in Hz P(f) is defined above in Table 1 for the downstream PSD 137 and Table 2 for the upstream PSD 138 135 02 MkOffstdB~f) fI 0,4X fnask f [w4 f fmsk 1i [ms dBlf fmask =ms 150 kHz =11,040 MHz [R:\LIBOO]07072.DOC:GYC 17 FIG. 5 depicts an exemplary transceiver 170 that may be used to implement any of the SHDSL transceivers 118, 127, 148, or 152 of FIGS. 2 and 4. The transceiver 170 of FIG. comprises a pair of digital data ports 174 and 176. If the transceiver 170 is used to implement SHDSL transceiver 152 of FIG. 4, then the digital data port 174 is coupled to and receives digital data from the buffer 155. Further, the digital data port 176 is coupled to and transmits digital data to the buffer 156. If the transceiver 170 is used to implement SHDSL transceiver 148 of FIG. 4, then the digital data port 174 is coupled to and receives digital data from the buffer 156. Also, the digital data port 176 is coupled to and transmits digital data to the buffer 155.

As shown by FIG. 5, the transceiver 170 comprises a transmitter 181 and a receiver 183. The transmitter 181 has a mapper 184 for mapping the digital data from the digital data port 174 to symbols using a selected constellation. Thus, the transmitter 181 outputs a data signal that comprises the digital data received from the digital data port 174. A digital filter 185 receives and filters the data signal output by transmitter 181 to provide a filtered digital signal to a digital-to-analog converter 188. The D/A converter 188 converts the filtered digital signal into an analog signal, which is filtered by an analog filter 191. Note that the spectral shaping performed to achieve the tailored PSDs described herein may be performed by digital filter 185, by analog filter 191, or by a combination of digital filter 185 and analog filter 191.

The filtered analog signal from filter 191 is applied, via a hybrid network 194 and a line-coupling transformer 196, to the telecommunication line segment 31 or 32 that is coupled to the transformer 196. In this regard, if the transceiver 170 is used to implement SHDSL transceiver 127 or 152, then the transformer 196 is coupled to telecommunication [R:\LIBoo]07072.DOC:GYC 18 line segment 32. If the transceiver 170 is used to implement SHDSL transceiver 118 or 148, then the transformer 196 is coupled to telecommunication line segment 3 1.

An analog signal on the telecommunication line segment 31 or 32 is coupled through transformer 196 and hybrid network 194 and is applied to an analog filter 202, which filters the received analog signal and provides a filtered analog signal to an analog-to-digital (A/D) converter 204. The A/D converter 204 converts the filtered analog signal into a digital signal, which is filtered by a digital filter 207. A differential summer. 209 combines this filtered digital signal with an echo cancellation signal from an echo canceller 212 in order to cancel, from the filtered digital signal, echoes of signals transmitted by the transceiver 170 over the telecommunication line segment 31 or 32 that is coupled to the transformer 196. The combined signal from the differential sumnmer 209 is then coupled through a channel equalizer 208 to remove intersymbol interference (ISI) and then received by the receiver 183.

The receiver 183 has a decoder 213, such as a Viterbi decoder, for example, although other types of decoders may be used in other examples. The decoder 213 has an inverse mapper 214, which maps the symbols received from the equalizer 208 to digital data using a selected constellation. Suich digital data is transmitted to the digital data port 176, which outputs this digital data from the transceiver 170.

FIGS. 6 and 7 depict exemplary embodiments of the transmitter 181 and receiver 183, respectively. For illustrative purposes, transmitter 181 will be described hereafter as performing Trellis coded PAM (TC-PAM) to provide code words of three payload bits and one error checking bit. Such code words can be mapped into symbols using a constellation that provides a constellation density of 3.0. However, in other examples, other configurations of the transmitter 181 and receiver 183 are possible. For example, it is unnecessary for error correction encoding to be performed, and data words of other bit lengths may be used.

[R:\LIBOO]07072.DOC:GYC 19 Further, other types of coding may be used to encode and decode code words, and constellations having different constellation densities may be used in other embodiments.

Digital data from the data port 174 (FIG. 5) is respectively framed and scrambled by framer 242 and scrambler 244. A serial-to-parallel converter 247 converts the serial stream of data from scrambler 244 to three-bit data words. A Trellis encoder 249 encodes each three-bit data word with an additional error checking bit to provide a four-bit data word. The mapper 184 maps each four-bit data word into a symbol. In such an embodiment, the constellation has sixteen different symbols one symbol for each possible value of the four-bit encoded data words). Note that encoding techniques other than Trellis encoding may be employed by encoder 249 in other embodiments.

In FIG. 7, the signals received by receiver 183 are decoded into four bit code words by decoder 213. Each code word comprises three payload bits and one error correction bit.

The decoder 213 outputs the three payload bits of each code word to a parallel-to-serial converter 255 that converts the data words into serial data. In other embodiments, it is unnecessary for the code words to have error correction information, and the code words may be decoded into other numbers of bits. A descrambler 257 and deframer 259 respectively descramble and deframe the data from the parallel-to-serial converter 255.

It should be noted that repeater 135 has generally been described as operating in an SHDSL delivering 2-pair El payload environment. However, the techniques described herein for making SHDSL signals spectrally compatible with ADSL signals may be employed in other types of environments to make other types of signals non- 168 kbps signals and/or non-SHDSL signals) spectrally compatible with other signals communicated through the same cable. In addition, the transceivers 118, 148, 152, and 127 have been described herein as using TC-PAM. However, in other embodiments, other types of [R:\LIBOO]07072.DOC:GYC modulation may be employed such as quadrature amplitude modulation (QAM) or discrete multitone (DMT), for example.

O As an example, FIG. 8 depicts other exemplary PSDs 237 and 238 that may be used by the transceivers 118, 127, 148, and 152 for other embodiments, including when these transceivers are communicating at 1032 kbps. In particular, the central office transceiver 118 is configured to transmit signals having the PSD 237, and each of the other transceivers 127, S148, and 152 is configured to transmit signals having the PSD 238. By spectrally shaping the transmitted signals in this way, such signals are spectrally compatible with ADSL signals communicated over segment 41 even when the segment 31 is located in the same cable as segment 41 and when the segment 32 is located in the same cable as segment 41. Note that FIG. 8 also depicts the mask PSD 247 for template PSD 237 and the mask PSD 248 for template PSD 238.

The PSDs 237 and 238 can be expressed by the following equation.

2 P 10X log 1 0 2 f2 f <MHz f /c [dBm/Hz]

P

2 -97.5dBm Hz MHz where: f Freq frequency in Hz P(f) is defined below in Table 3 for the downstream PSD 237 and Table 4 for the upstream PSD 238 Rs= 1359 fc is the transformer cut-off frequency, assumed to be 5 kHz fmax 11,040 MHz Table 3 [R:\LIBOO]07072.DOC:GYC Freq. (Hz) Downstream PSD (dBmIHz) (Freq <=6263) -42 (Freg <=8063) (Freg >62e3) -42-1 *(Freq -0.62e5) /18e3 (Freg <=10563) (Freg >8063) -43-4*(Freg -0.8e5) /25e3 (Freg <=155e3) (Freg >105e3) -47 (Freg 170e3) (Freg 15 5e3) -47+5*(Freg -1.55e5) /15e3 (Freg <=18003) (Freg >17063) -42+2*(Freg -1.70e5) /I10e3 (Freg <=375e3) (Freg >180e0) -40.0 (Freg <=395e3) (Freg >375e3) -40- 1 *(Freg -3.75e5) /20e3 (Freg <=435e3) (Freg >395e3) -50-10*(Freg -3.95e5) A4Me (Freg <=670e6) (Freg >435e3) -60-35*(Freg -4.35e5) /235e3 (Freg <=74063) (Freg >670e0) -95-2.5*(Freg -6.70e5) /70e3 (Freg <=I1e6) (Freg >740e3) -97.5 Table 4 Freq. (Hz) Upstream PSD (dBmIHz) (Freq <=200) -50.5 (Freg <=2e3) (Freg >200) -40.5+10*(Freq -2000) /1800 (Freg <=563) (Freg 2e3) -36.5+4*(Freg -5e3) /3e3 (Freg <=50e6) (Freq >5e3) -36.5 (Freg <=125e3) (Freg >5063) -36.5-*(Freq -5063) /75e3 (Freg 15 2e3) (Freg 12 5e3) -37.5- 1. 1*(Freg -125e3) /27e3 (Freg <=34063) (Freg >152e3) -38.6-158*logio(Freg/152e3) (Freq <=365e3) (Freq >340e3) -93.84-3.66*((Freq -340e0) /25e3) (Freg e6) (Freq >365e3) -97.5 Although other tolerances may be possible, about 1 dB tolerance for the PSDs 237 and 238 should ensure that spectral compatibility is maintained.

The respective masks 247 and 248 of template PSDs 237 and 238 can be expressed by the following equation.

Pff) MaskoffsetdB(f)[dBin Hz] f 5 1 MHz P(f) -9OdBm Hz peak withi max imnum power in a~,f M~]window of 37.5 dBm 'MHz <f :5 f a where: [R:\LIBOO]07072.DOC:GYC f= Freq frequency in Hz P(f) is defined above in Table 3 for the downstream PSD 237 and Table 4 for the upstream PSD 238 Rs 135 0 MaskOffsetdB(f f 1 ,4X f s k f [dB f fmask 1L [dBl f 2 fmask fmask =150 kHz f, =11,040 MHz Further, FIG. 9 depicts other exemplary PSDs 337 and 338 that may be used by the transceivers 118, 127, 148, and 152 for yet other embodiments. In particular, the central office transceiver 118 is configured to transmit signals having the PSD 337, and each of the other transceivers 127, 148, and 152 is configured to transmit signals having the PSD 338.

By spectrally shaping the transmitted signals in this way, such signals are spectrally compatible with ADSL signals communicated over segment 41 even when the segment 31 is located in the same cable as segment 41 and when the segment 32 is located in the same cable as segment 41. Note that FIG. 9 also depicts the mask PSD 347 for template PSD 337 and the mask PSD 348 for template PSD 338.

The PSDs 337 and 338 can be expressed by the following equation.

f 2 P(f) P(f)+10x logl 2 2 f f IMHz i c [dBml Hz] IMHz f fma

P

2 -97.5dBm Hz MHz f fmax where: f Freq frequency in Hz P(f) is defined below in Table 5 for the downstream PSD 337 and Table 6 for the upstream PSD 338 Rs= 1350 fc is the transformer cut-off frequency, assumed to be 5 kHz [R:\LIBOO]07072.DOC:GYC C. 11,040 MHz Table Freg. (Hz) Downstream PSD (dBnilHz) (Freq <=110e3) -49.5 (Freq <=1.45e3) (Freq (-49.5+2*(Freq-110e3)/35e3) >110e3) (Freq <=190e3) (Freq (-47.5+7.5*(Freq-145e3)/45e3) >145e3) (Freq <=400e3) (Freg -40.0 >190e3) (Freq <=460e3) (Freq C-40-15*(Freq-40Oe3)/6Oe3) >400e3) (Freq <=740e3) (Freq (-55-39*(Freq-46Oe3)/280e3) >460e3) (Freq <=800e3) (Freq (-94-3.5*(Freq-740e3)/60e3) >740e3) (Freq <=le6) &(Freq -97.5 >800e3) Table 6 Freg. (Hz) Upstream PSD (dBmJ/Hz) (Freq<=200) -50.5 (Freq<=2e3) -4O.5+10*(Freq-2000)/180Q) (Freq>200) (Freq<=5e3) 4*(Freq.5e3)/3e3) (Freq>2e3) (Freq<=50e3) -36.5 (Freq>5e3) (Freq<=125e3) (-36.5-(Freq-50e3)/75e3) (Freq>50e3) (Freq<=152e3) (-37.5-1.1*(Freq-125e3)/27e3) (Freq>125e3) (Freq<=340e3) 8. 6 158*logio (Freq/152e3)) (Freq>152e3) (Freq<=365e3) (-93.84-3.66*((Freq-340e3)/25e3)) (Freq<~=1e6) (Freq -97.5 >365e3) Although other tolerances may be possible, about I dB tolerance for the PSDs 337 and 338 should ensure that spectral compatibility is maintained.

The respective masks 347 and 348 of template PSDs 337 and 338 can be expressed by the following equation.

[R:\LIBOO]07072 .DOC:GYC P P(f) MaskOffsetdB(f)[dBm Hz] f

P

2 -90dBm Hz peak with max imum power in a[f, f MHz] window of 37.5dBm 1MHz where: f Freq frequency in Hz P(f) is defined above in Table 5 for the downstream PSD 337 and Table 6 for the upstream PSD 338 Rs 135 0 MaskOffsetdB(f)= 4X fm [dBf fdask 1 [dB,f fmas fmask =150 kHz fx 11,040 MHz As can be seen by comparing FIGS. 3, 8, and 9, tailored PSDs, such as those shown by FIGS. 3, 8, and 9, in accordance with several embodiments of the present disclosure have several common characteristics. In general, the tailored PSDs are designed to comply with two conflicting constraints. First, the tailored PSDs are designed to comply with applicable spectrum management and excess power requirements associated with protected or basis systems. For example, C559:2005, which applies in Australia, has minimum performance requirements for ADSL, ADSL2+, SHDSL, El, ISDN and HDSL-2p. Such requirements are captured in Table 4-1 and Table 4-2 of C559:2005 Part 2. Excess power is defined section 2.4. Second, the tailored PSDs achieve a reach that is greater than the allowed deployment reach for SHDSL 1032 or 1168 kbps in the current spectrum management documents. For Australia, the reach is computed using the loop, noise, and PSD models of section 5 of C559:2005 Part 2. The interferer is assumed to be (4 self 4 interferers) where self is the proposed PSD and interferer is each of the basis systems.

[R:\LIBOO]07072.DOC:GYC Moreover, by examining FIGS. 3, 8, and 9, it can be seen that the tailored PSD, such as PSD 137, 237, or 337, of the transceiver 118 at the central office 23 is dissimilar relative to the tailored PSDs, such as PSDs 138, 238, or 338, of the other transceivers 148, 152, and 127.

Note that the tailored PSDs are specifically defined for 16 or 32 TC-PAM and carry a symmetric payload greater than or equal to 1024 kbps and smaller than 1168 kbps for 16- TCPAM and greater than or equal to 1024 kbps and smaller than 1600 for 32-TCPAM, although such PSDs may be used for other transmission schemes and other data rates. For each line segment, the tailored PSDs in the upstream and the downstream directions are partially overlapped (refer to U.S. Patent No. 6,246,716, which is incorporated herein by reference). The upstream is narrow with a passband from about 0 kHz to a frequency within a range of approximately 100-200 kHz. The downstream passband is wider than the upstream passband. Preferably, as shown in FIGS. 3, 8, and 9, the downstream passband extends from about 0 kHz to approximately 400 kHz with a notch from about 0 kHz to a frequency within a range of approximately 138-152 kHz. Although the notch can have various shapes, it is generally desirable for the notch to be below approximately -40 dBm/Hz across the range of the notch. Although, as shown by FIG. 3, it is possible for portions of the notch to be close to -40 dBm/Hz, it is generally desirable for at least a portion of the notch to be significantly below -40 dBm/Hz, as shown from about 100 kHz to the end of the notch to about 138-152 kHz) in FIG. 3 and as shown from about 0 kHz to the end of the notch to about 138-152 kHz) in FIGS. 8 and 9. If fp is the bandwidth of the upstream passband, then the total power in f, of the downstream PSD is lower than the total power of the upstream PSD in fp. If a repeater is used, then the downstream PSD is used on the first segment and an upstream PSD is used on all other segments.

[R:\LIBoo]07072.DOC:GYC

Claims (15)

1. A communication system for enabling two pair El delivery with spectrally compatible signals, comprising: a telecommunication line segment; a first transceiver coupled to the telecommunication line segment, the first transceiver configured to transmit a first signal across the telecommunication line segment and to receive a second signal from the telecommunication line segment, the first transceiver configured to spectrally shape the first signal such that the first signal has a first power spectral density (PSD); and a second transceiver coupled to the telecommunication line segment, the second transceiver configured to transmit the second signal across the telecommunication line segment and to receive the first signal from the telecommunication line segment, the second transceiver configured to spectrally shape the second signal such that the second signal has a second PSD that is dissimilar to but overlaps, at least partially, the first PSD, wherein the first and second signals provide at least one-half of El delivery over the telecommunication line segment and are spectrally compatible, wherein the second PSD has a passband more narrow than a passband of the first PSD, the passband of the second PSD extending from about 0 kHz to a range between approximately 138 kHz to approximately 200 kHz, and wherein a total power of the first PSD within the passband of the second PSD is less than a total power of the second PSD within the passband of the second PSD.

2. The system of claim 1, wherein the second transceiver demodulates the first signal to recover digital data, and wherein the system further comprises a third transceiver [R:\LIBOO]07072.DOC:GYC 27 configured modulate a third signal with the digital data thereby regenerating the first signal, the third transceiver configured to spectrally shape the third signal such that the third signal has a PSD corresponding to the second PSD.

3. The system of claim 2, wherein the first transceiver is located at a central office of a telecommunication network.

4. The system of claim 1, wherein the first and second signals are modulated via trellis coded pulse amplitude modulation (TC-PAM). The system of claim 1, wherein the first and second PSDs have shapes in accordance with Figure 8.

6. The system of claim 1, wherein the first transceiver has a first transformer and the first PSD is defined by the following equation: PSD(f) P(f) 10 loglo(f/(f 2 fc2)) wherein fc is a cutoff frequency of the first transformer, wherein P(f) is approximately equal to -42 .62e5)/18e3 dBm/Hz for f above 62e3 Hz and below 80e3 Hz, wherein P(f) is approximately equal to -43 .8e5)/25e3 dBm/Hz for f above 80e3 Hz and below 105e3 Hz, wherein P(f) is approximately equal to -47 dBm/Hz for f above 105e3 Hz and below 155e3 Hz, wherein P(f) is approximately equal to -47 1.55e5)/15e3 dBm/Hz for f above 155e3 Hz and below 170e3 Hz, wherein P(f) is approximately equal to -42 1.70e5)/10e3 dBm/Hz for f above 170e3 Hz and below 180e3 Hz, wherein [R:\LIBOO]07072.DOC:GYC 28 P(f) is approximately equal to -40.0 dBm/Hz for f above 180e3 Hz and below 375e3 Hz, wherein P(f) is approximately equal to -40 10*(f- 3.75e5)/20e3 dBm/Hz for f above 375e3 Hz and below 395e3 Hz, wherein P(f) is approximately equal to -50 3.95e5)/40e3 dBm/Hz for f above 395e3 Hz and below 435e3 Hz, wherein P(f) is approximately equal to -60 35*(f- 4.35e5)/235e3 dBm/Hz for f above 435e3 Hz and below 670e3 Hz, and wherein P(f) is approximately equal to -95 6.70e5)/70e3 dBm/Hz for f above 670e3 Hz and below 740e3 Hz.

7. The system of claim 6, wherein the second transceiver has a second transformer and the second PSD is defined by the following equation: PSD(f) P 2 10 loglo(f 2 fc22)) wherein fc2 is a cutoff frequency of the second transformer, wherein P 2 is approximately equal to -40.5 10*(f- 2000)/1800 dBm/Hz for f above 200 Hz and below 2e3 Hz, wherein P 2 is approximately equal to -36.5 5e3)/ 3e3 dBm/Hz for f above 2e3 Hz and below 5e3 Hz, wherein P 2 is approximately equal to -36.5 dBm/Hz for f above 5e3 Hz and below 50e3 Hz, wherein P 2 is approximately equal to -36.5 50e3)/ 75e3 dBm/Hz for f above 50e3 Hz and below 125e3 Hz, wherein P 2 is approximately equal to -38.6 158*logio(f/152e3) dBm/Hz for f above 152e3 Hz and below 340e3 Hz, and wherein P 2 is approximately equal to -93.84 340e3)/ 25e3) dBm/Hz for f above 340e3 Hz and below 365e3 Hz.

8. The system of claim 1, wherein the second transceiver has a transformer and the second PSD is defined by the following equation: PSD(f) P(f) 10 loglo(ft/(fI fc 2 [R:\LIBOO]07072.DOC:GYC wherein fc is a cutoff frequency of the second transformer, wherein P(f) is approximately equal to -40.5 10*(f- 2000)/1800 dBm/Hz for f above 200 Hz and below 2e3 Hz, wherein P(f) is approximately equal to -36.5 5e3)/ 3e3 dBm/Hz for f above 2e3 Hz and below 5e3 Hz, wherein P(f) is approximately equal to -36.5 dBm/Hz for f above 5e3 Hz and below 50e3 Hz, wherein P(f) is approximately equal to -36.5 50e3)/ 75e3 dBm/Hz for f above 50e3 Hz and below 125e3 Hz, wherein P(f) is approximately equal to -38.6 158*logio(f/152e3) dBm/Hz for f above 152e3 Hz and below 340e3 Hz, and wherein P(f) is approximately equal to -93.84 340e3)/ 25e3) dBm/Hz for f above 340e3 Hz and below 365e3 Hz.

9. The system of claim 1, wherein the first PSD has a notch from about 0 kHz to a frequency within a range of approximately 138-152 kHz. The system of claim 9, wherein the notch is below approximately -40 dBm/Hz.

11. A communication method for enabling two pair El delivery with spectrally compatible signals, comprising the steps of: transmitting a first signal from a first transceiver to a second transceiver across a telecommunication line segment; spectrally shaping the first signal such that the first signal has a first power spectral density (PSD); transmitting a second signal from the second transceiver to the first transceiver across the telecommunication line segment; and [R:\LIBOO]07072.DOC:GYC c spectrally shaping the second signal such that the second signal has a second PSD that is dissimilar to but overlaps, at least partially, the first PSD, wherein the first and second signals enable at least one-half of El delivery over the telecommunication line segment and are spectrally compatible, wherein the second PSD 5 has a passband more narrow than a passband of the first PSD, the passband of the first PSD extending from about 0 kHz to a range between approximately 138 kHz to approximately O 200 kHz, and wherein a total power of the first PSD within the passband of the second PSD is less than a total power of the second PSD within the passband of the second PSD.

12. The method of claim 11, further comprising the steps of: demodulating the first signal at the second transceiver to recover digital data; modulating a third signal with the digital data thereby regenerating the first signal; and spectrally shaping the third signal such that the third signal has a PSD corresponding to the second PSD.

13. The method of claim 12, wherein the first transceiver is located at a central office of a telecommunication network. [R:\LIBOO]07072.DOC:GYC

14. The method of claim 11, wherein the first and second signals are modulated via trellis coded pulse amplitude modulation (TC-PAM). The method of claim 11, wherein the first and second PSDs have shapes in accordance with Figure 8.

16. The method of claim 11, wherein the first transceiver has a first transformer and the first PSD is defined by the following equation: PSD(f) P(f) 10 logo(fl/( f2)) wherein fc is a cutoff frequency of the first transformer, wherein P(f) is approximately equal to -42 .62e5)/18e3 dBm/Hz for f above 62e3 Hz and below 80e3 Hz, wherein P(f) is approximately equal to -43 .8e5)/25e3 dBm/Hz for f above 80e3 Hz and below 105e3 Hz, wherein P(f) is approximately equal to -47 dBm/Hz for f above 105e3 Hz and below 155e3 Hz, wherein P(f) is approximately equal to -47 1.55e5)/15e3 dBm/Hz for f above 155e3 Hz and below 170e3 Hz, wherein P(f) is approximately equal to -42 1.70e5)/10e3 dBm/Hz for f above 170e3 Hz and below 180e3 Hz, wherein P(f) is approximately equal to -40.0 dBm/Hz for f above 180e3 Hz and below 375e3 Hz, wherein P(f) is approximately equal to -40 10*(f- 3.75e5)/20e3 dBm/Hz for f above 375e3 Hz and below 395e3 Hz, wherein P(f) is approximately equal to -50 3.95e5)/40e3 dBm/Hz for f above 395e3 Hz and below 435e3 Hz, wherein P(f) is approximately equal to -60 35*(f- 4.35e5)/235e3 dBm/Hz for f above 435e3 Hz and below 670e3 Hz, and wherein P(f) is approximately equal to -95 6.70e5)/70e3 dBm/Hz for f above 670e3 Hz and below 740e3 Hz. [R:\LIBOO]07072.DOC:GYC

17. The method of claim 16, wherein the second transceiver has a second transformer and the second PSD is defined by the following equation: PSD(f) P 2 10 loglo/(fl( fc22)) wherein fc2 is a cutoff frequency of the second transformer, wherein P 2 (f) is approximately equal to -40.5 10*(f- 2000)/1800 dBm/Hz for f above 200 Hz and below 2e3 Hz, wherein P 2 is approximately equal to -36.5 5e3)/ 3e3 dBm/Hz for f above 2e3 Hz and below 5e3 Hz, wherein P 2 is approximately equal to -36.5 dBm/Hz for fabove 5e3 Hz and below 50e3 Hz, wherein P 2 is approximately equal to

36.5 50e3)/ 75e3 dBm/Hz for f above 50e3 Hz and below 125e3 Hz, wherein P 2 is approximately equal to -38.6 158*logio(f/152e3)/ dBm/Hz for f above 152e3 Hz and below 340e3 Hz, and wherein P 2 is approximately equal to -93.84 340e3)/ 25e3) dBm/Hz for f above 340e3 Hz and below 365e3 Hz. 18. The method of claim 11, wherein the second transceiver has a transformer and the second PSD is defined by the following equation: PSD(f) P(f) 10 logo(f/(f fc2 wherein f, is a cutoff frequency of the second transformer, wherein P(f) is approximately equal to -40.5 10*(f- 2000)/1800 dBm/Hz for f above 200 Hz and below 2e3 Hz, wherein P(f) is approximately equal to -36.5 5e3)/ 3e3 dBm/Hz for f above 2e3 Hz and below 5e3 Hz, wherein P(f) is approximately equal to -36.5 dBm/Hz for f above 5e3 Hz and below 50e3 Hz, wherein P(f) is approximately equal to -36.5 50e3)/ 75e3 dBm/Hz for f above 50e3 Hz and below 125e3 Hz, wherein P(f) is approximately equal to -38.6 158*loglo(f/152e3)/ dBm/Hz for f above 152e3 Hz and [R:\LIB300]07072. DO GYC 33 below 340e3 Hz, and wherein P(f) is approximately equal to -93.84 340e3)/ 25e3) dBm/Hz for f above 340e3 Hz and below 365e3 Hz. 19. The method of claim 11, wherein the first PSD has a notch from about 0 kHz to a frequency within a range of approximately 138-152 kHz. The method of claim 19, wherein the notch is below approximately -40 dBm/Hz. 21. A communication system substantially as described herein with reference to any of the embodiments, as that embodiment is illustrated in any of the accompanying drawings. 22. A communication method substantially as described herein with reference to any of the accompanying drawings. DATED this fifth Day of May, 2006 Thomas Kayden Horstemeyer Risley LLP Patent Attorneys for the Applicant SPRUSON FERGUSON [R:\LIBoo]07072.DOC:GYC