DSL REPEATER

Abstract: A DSL repeater includes an upstream amplifying element (314) and upstream filter (312), a downstream amplifying element (304) and a downstream filter (302). The amplifying elements and filters are disposed between a pair of electromagnetic hybrids (322, 324), which couple the repeater to the loop. The downstream filter reduces or eliminates the effect of upstream signal leakage through the hybrid on the downstream signal. Likewise, the upstream filter reduces or eliminates the effect of downstream signal leakage through the hybrid on the upstream signal. The amplifying elements may comprise amplifying equalizers, which provide more amplification to higher frequency signals than to lower frequency signals. A dedicated twisted pair may deliver DC power to the repeater from the center office.

Description: DSL REPEATER By Brian L. Hinrnan, Andrew L. Norrell, and James Schley-May CROSS REFERENCE TO RELATED APPLICATION This application relates to and claims the priority of commonly assigned U.S. Provisional Patent Application No. 60/184,392 filed on February 23, 2000 and entitled "Mid- Span Repeater for ADSL" by Brian L. Hinman, the disclosure of which is hereby incorporated by reference. BACKGROUND 1. Technical Field The present system and method relate generally to Digital Subscriber Line (DSL) technology, and more particularly to a system and method for improving ADSL (Asymmetric DSL) and VDSL (Very high data rate DSL) system performance over long local loops. 2. Description of Background Art One method of accessing the Internet is by using DSL technology, which has several varieties, including ADSL and VDSL versions. ADSL is one version of DSL technology that expands the useable bandwidth of existing copper telephone lines. ADSL is "asymmetric" in that ADSL reserves more bandwidth in one direction than in the other, which may be beneficial for users who do not require equal bandwidth in both directions. In one implementation, ADSL signals generally occupy the frequency band between about 25 kHz and 1.104 MHz. In this configuration, ADSL uses the frequency band between about 25 kHz and 120 kHz to transmit upstream signals (signals from a customer premises to a central office) and the frequency band between about 150 kHz to 1.104 MHz to transmit downstream signals (signals from the central office to a customer premises). Hence, ADSL employs Frequency Division Multiplexing (FDM) to separate upstream and downstream signals and to separate ADSL signals from POTS (Plain Old Telephone Service) band signals, which reside below 4 kHz. VDSL also uses FDM to separate downstream and upstream channels as well as to separate both downstream and upstream channels from POTS. In the past, ADSL has been used to deliver high-speed data services to subscribers up to about 18,000 feet from their serving central office or central office extension. The potential data rates range from above about 8 MBPS for short loops, but drop, off dramatically on long loops, such as local loops over about 18,000 feet, to about 0.5 MBPS or less. Conventionally, ADSL service generally employs a local loop length of about 6,000 - 14,000 feet for optimal service. Loop length is generally defined as the length of the wire between the central office, or central office extension, and the customer premises, such as a home or business. "Central office" and "central office extension" are collectively referred to herein as "central office." DSL signals generally degrade as they traverse the local loop. Hence, the longer the local loop length, the more degraded the DSL signal will tend to be upon arriving at a central office or a customer premises. While some DSL service is conventionally possible with loop lengths longer than 14,000 feet, it has been found that with loops much longer than about 14,000 feet, the DSL signal is too degraded to provide high data transfer rates. DSL signal degradation over a local loop may be caused, for example, by factors such as: signal attenuation, crosstalk, thermal noise, impulse noise, and ingress noise from commercial radio transmitters. The dominant impairment, however, is often signal attenuation. For example, a transmitted ADSL signal can suffer as much as 60 dB or more of attenuation on long loops, which substantially reduces the useable signal, greatly reducing potential data rates. Additional details regarding DSL signal degradation over long loops and regarding DSL technology more generally are described in Understanding Digital Subscriber Line Technology by Starr, Cioffi, and Silverman, Prentice Hall 1999, ISBN 0137805454 and in DSL - Simulation Techniques and Standards Development for Digital Subscriber Line Systems by Walter Y. Chen, Macmillan Technical Publishing, ISBN 1578700175, the disclosures of which are hereby incorporated by reference. SUMMARY A DSL repeater is provided along a local loop between a central office and a customer premises for amplifying DSL signals, such as Category 1 ADSL or VDSL signals, that pass between the central office and the customer premises to reduce or alleviate DSL signal degradation problems due to signal attenuation. In general, the DSL repeater amplifies upstream and downstream DSL signals to at least partially compensate for attenuation of the DSL signals as they traverse a local loop. According to one embodiment, the DSL repeater is a non-regenerative repeater and includes an upstream amplifying stage or element, an upstream filter, a downstream amplifying stage or element, and a downstream filter. The amplifying elements and filters are disposed between a pair of electromagnetic hybrids, which couple the repeater to the local loop. The upstream and downstream amplifying elements respectively amplify upstream and downstream DSL signals and may comprise, for example, amplifiers or amplifying equalizers. The downstream filter reduces or eliminates the effect of upstream signal leakage through the hybrid on the downstream signal. Likewise, the upstream filter reduces or eliminates the effect of downstream signal leakage through the hybrid on the upstream signal. Restated, the downstream filter substantially prevents upstream signals from being transmitted back to the customer premises and the upstream filter substantially prevents downstream signals from being transmitted back to the central office. Pursuant to another aspect of the present system and method, the downstream and upstream amplifying stages comprise amplifying equalizers configured to amplify higher frequency signals more than lower frequency signals. Indeed, it has been found that higher frequency signals tend to be more attenuated as they pass along the local loop than do lower frequency signals. Consequently, the DSL repeater advantageously provides increased amplification for these higher frequency DSL signals that have been more severely attenuated than lower frequency signals. For example, in one embodiment a downstream equalizer gain for about 80% compensation for about 6,000 feet of 26 AWG (American Wire Gauge) telephone cable is about 19 dB for 200 kHz downstream signals and about 37 dB for 1 MHz downstream signals. Likewise, in this embodiment, an upstream gain for about 80% compensation for about 6,000 feet of 26 AWG telephone cable is about 14.4 dB for 30 kHz upstream signals and about 17 dB for 110 kHz upstream signals. Different types and lengths of DSL transmission media will likely require different amounts of gain. In accordance with yet another aspect of the present system and method, the DSL repeater includes a set of POTS loading coils to improve the POTS, or voice, band transmission over the local loop. Conveniently, conventional POTS loading coils may be replaced with an embodiment of the present DSL repeater including POTS loading coils. Hence, pursuant to this embodiment, both POTS and DSL signal transmission over a local loop may be substantially improved through the use of a DSL repeater. Moreover, multiple DSL repeaters may be disposed in series, or in cascaded fashion, along a single local loop to amplify transmitted DSL signals multiple times as the DSL signals pass over the loop between the central office and the customer premises. By cascading multiple DSL repeaters in series along a single loop, DSL service may be effectively extended over local loops substantially longer than 18,000 feet. In a presently preferred embodiment, a DSL repeater is disposed about every 5,000 -7,000 feet and preferably about every 6,000 feet along a local loop. Accordingly, the present system and method provide for improved transmission of DSL signals over local loops. Additional features and advantages of the present system and method will be apparent to those skilled in the art from the accompanying drawings and detailed description as set forth below. BRIEF DESCRIPTION OF THE DRAWINGS FIG, 1 is a graph illustrating one example of DSL signal attenuation over a 6,000- foot length of telephone cable as a function of signal frequency; FIG. 2 illustrates multiple local loops interconnecting a central office and multiple customer premises with each local loop having at least one DSL repeater coupled thereto; FIG. 3 illustrates one embodiment of a FIG. 2 repeater; FIG. 4 illustrates another embodiment of a FIG. 2 repeater; FIG. 5 illustrates details of one embodiment of a FIG. 4 hybrid; FIG. 6 illustrates details of one embodiment of another FIG. 4 hybrid; FIG. 7 illustrates details of one embodiment of a FIG. 4 upstream filter; FIG. 8 illustrates the frequency response of the FIG. 7 filter; FIG. 9 illustrates the phase of the FIG. 7 filter; FIG. 10 illustrates details of one embodiment of a FIG. 4 downstream filter; FIG. 11 illustrates the frequency response of the FIG. 10 filter; FIG. 12 illustrates the phase of the FIG. 10 filter; FIG. 13 illustrates details of one embodiment of a FIG. 4 upstream amplifying element; FIG. 14 illustrates details of one embodiment of a FIG. 4 downstream amplifying element; FIG 15 illustrates the frequency response of the upstream amplifying element of FIG. 13; FIG. 16 illustrates the phase of the upstream amplifying element of FIG. 13; FIG 17 illustrates the frequency response of the FIG. 14 downstream amplifying element; and FIG. 18 shows the phase of the upstream amplifying element of FIG. 14. DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an example of the attenuation of a DSL signal over 6,000 feet of 26 AWG (American Wire Gauge) telephone cable. As shown, higher frequency signals are generally attenuated more than lower frequency signals. In the FIG. 1 example, a 25 kHz signal is attenuated by about 25 dB over 6,000 feet of 26 AWG telephone cable while a 1 MHz signal is attenuated by about 46 dB over 6,000 feet of 26 AWG telephone cable. As those skilled in the art will appreciate, the actual degree of attenuation will also depend on factors in addition to loop length, such as temperature. FIG. 2 illustrates a DSL network 200 that includes a central office 202, customer premises A 204, customer premises B 206, customer premises C 208, and customer premises N 210. The customer premises 204, 206, 208, and 210 are respectively coupled to the central office by local loops 214, 216, 218, and 220. Each local loop comprises a twisted pair of copper wires; commonly know in the art as a "twisted pair." Typically, the copper wires are formed of 22, 24, or 26 AWG wire. Moreover, as those skilled in the art will appreciate, the central office 202 and each of the customer premises 204, 206, 208, and 210 includes a DSL termination device, such as a DSL modem, for transmitting and receiving DSL signals over an associated local loop. A DSL repeater 224 is coupled to the local loop 214 to amplify DSL signals, such as ADSL or VDSL signals, passing over the loop 214 between the central office 202 and the customer premises 204. As discussed above, DSL signals are generally attenuated as they travel along a local loop, such as the local loop 214. The repeater 224 is disposed along the loop 214 between the central office 202 and the customer premises 204 to at least partially compensate for the DSL signal attenuation by amplifying the transmitted DSL signals. Additional details of the repeater 224 are described below with reference to FIGS. 3-18. In addition, a repeater 226 is coupled to the loop 216 between the central office 202 and the customer premises 206 to amplify DSL signals passing between the central office 202 and the customer premises 206. Likewise, a repeater 230 is disposed between the central office 202 and the customer premises 210 to amplify DSL signals passing therebetween. The repeaters 226 and 230 are configured the same as the repeater 224. Further, FIG. 2 illustrates that multiple DSL repeaters may be coupled in series, or in cascaded fashion, to a single loop for amplifying transmitted DSL signals multiple times and in multiple locations between the customer premises and the central office to permit DSL signals to be transmitted over greater distances while still maintaining an acceptable DSL signal amplitude. Specifically, a DSL repeater 228 and a DSL repeater 229 are coupled in series to the loop 218, which couples the central office 202 and the customer premises 208. Pursuant to this configuration, the repeater 228 first amplifies a downstream DSL signal transmitted from the central office 202 over the loop 218 to the customer premises 208 and the repeater 229 then amplifies the downstream signal again. Hence, the repeater 228 amplifies the downstream signal to at least partially compensate for the attenuation incurred as the downstream signal passes over the portion of the loop 218 between the central office 202 and the repeater 228. Next, the repeater 229 amplifies the downstream signal to at least partially compensate for the attenuation incurred as the downstream signal passes from the repeater 228 to the repeater 229. Likewise, for upstream DSL signals from the customer premises 208 to the central office 202, the repeater 229 amplifies the upstream signals to at least partially compensate for the attenuation that occurs between the customer premises 208 and the repeater 229. Next, the repeater 228 amplifies the upstream signal to at least partially compensate for the attenuation incurred as the upstream signal passes from the repeater 229 over the local loop 218 to the repeater 228. According to one embodiment, the loop distance between the repeaters 228 and 229 is between about 5,000 and 7,000 feet. In a preferred embodiment, the loop distance between the repeaters is about 6,000 feet. As discussed in more detail below, this loop distance between multiple repeaters disposed in series, in cascaded fashion, along a single loop may be advantageous in that pursuant to one embodiment of the present system and method, each repeater may be adapted with POTS loading coils (see FIG. 4). This embodiment may then replace conventional POTS loading coils, which are disposed about every 6,000 feet along a loop to provide both POTS loading and DSL signal amplification functionality. Additional details of this embodiment are discussed below with reference to FIG. 4. The loop 218 is illustrated as having two cascaded DSL repeaters 228 and 229 coupled thereto between the central office 202 and the customer premises 208. It should be noted, however, that additional DSL repeaters (not shown) may be disposed in series between the central office 202 and the customer premises 208 so that DSL signals may be effectively transmitted over an even longer loop 218 by being amplified multiple times by multiple DSL repeaters. In the embodiment illustrated in FIG. 2, the DSL repeaters 224, 226, 228, and 230 receive electrical power from a power supply 240, which preferably receives power over a twisted pair 242 from the central office 202. The twisted pair 242 is a dedicated twisted pair that delivers DC current to the power supply 240 in the same manner in which electrical power is conventionally provided to Tl line repeaters. While not separately illustrated, the repeater 229 may receive power from a separate dedicated twisted pair or may receive power from the power supply 240. Lastly, the power supply 240; the DSL repeaters 224, 226, 228, and 230; and the associated circuitry may be disposed in a common housing 250. FIG. 3 illustrates details of one embodiment of the repeater 224 of FIG. 1. As shown, the repeater 224 is coupled to the local loop 214 between the central office 202 and the customer premises 204. The repeater 224 is depicted as including a downstream filter 302 and a downstream amplifying element or stage 304 and an upstream filter 312 and an upstream amplifying element or stage 314. The filters 302 and 312 and the amplifying elements 304 and 314 are disposed between a pair of electromagnetic hybrid couplers 322 and 324. The amplifying elements 304 and 314 may comprise amplifiers or amplifying equalizers. In general, the hybrid coupler 322 receives downstream DSL signals from the central office 202 along the local loop 214 and outputs the downstream DSL signals to the downstream filter 302 along line 332. The hybrid coupler 322 also receives amplified upstream DSL signals from the upstream amplifying element 314 along line 334 and transmits the upstream DSL signals onto the local loop 214 for transmission to the central office 202. Similarly, the hybrid coupler 324 receives upstream DSL signals from the customer premises 204 along the local loop 214 and outputs the upstream DSL signals to the upstream filter 312 along line 342. The hybrid coupler 324 also receives amplified downstream DSL signals from the downstream amplifying element 304 along line 344 and transmits the downstream DSL signals onto the local loop 214 for transmission to the customer premises 204. As those skilled in the art will appreciate, where the hybrid coupler 322 is imperfect, at least a portion of the upstream amplified DSL signal received via the line 334 will leak through the hybrid coupler 322 onto the line 332. Likewise, where the hybrid coupler 324 is imperfect, at least a portion of the downstream amplified DSL signal received via the line 344 will leak through the hybrid coupler 324 onto the line 342. Without the presence of the filters 302 and 312, this DSL signal leakage could cause a phenomenon known in the art as "singing" - that is oscillations caused by introducing gain into a bi-directional system due to signal leakage. The signal leakage problem is overcome, or substantially alleviated, through the use of the downstream filter 302 and the upstream filter 312. One version of Category 1 ADSL upstream signals generally occupy the frequency spectrum between about 25 - 120 kHz and ADSL downstream signals generally occupy the frequency spectrum between about 150 kHz - 1.104 MHz. The downstream filter 302 substantially prevents leaked upstream signals from being transmitted back to the customer premises 204 by significantly attenuating signals between 25 kHz and 120 kHz for ADSL. Likewise, the upstream filter 312 is configured to provide significant attenuation to signals between about 150kHz - 1.104 MHz for ADSL. For other varieties of DSL, such as VDSL, the filters 302 and 312 respectively attenuate signals outside the downstream and upstream frequency bands, although the limits of these bands may be different than those for the ADSL variety. In operation, the repeater 224 receives upstream DSL signals from the customer premises 204 via the hybrid 324, filters out, or substantially attenuates, signals in the downstream frequency band with the upstream filter 312 and then passes the filtered upstream signal to the upstream amplifying element 314 via line 352 for amplification. The repeater 224 then passes the amplified upstream DSL signal onto the loop 214 for transmission to the central office 202. Similarly, the repeater 224 receives downstream DSL signals from the central office 202 via the hybrid 322, filters out, or substantially attenuates, signals in the upstream frequency band with the downstream filter 302 and then passes the amplified downstream signal to the downstream amplifying element 304 via line 354 for amplification. The repeater 224 then passes the amplified downstream DSL signal onto the loop 214 for transmission to the customer premises. FIG. 4 illustrates another embodiment of the repeater 224, which includes POTS loading coils 402. As shown, the repeater 224 of FIG. 4 includes POTS loading coils 402 coupled to the loop 214 to improve transmission of voice, or POTS, frequency signals over long loop lengths, such as those longer than about 18,000 feet. In one embodiment, the POTS loading coils 402 comprise loading coils having an inductance of about 88 mH. The hybrid 322 is illustrated as being capacitively coupled to the local loop on the central office side of the POTS loading coils 402 along lines 412 and 414. A capacitor 416 (100 nF) is disposed along the line 412 and a capacitor 418 (100 nF) is disposed along the line 414 to capacitively couple the hybrid 322 to the loop 214 on the central office side of the POTS loading coils. Similarly, the hybrid 324 is illustrated as being capacitively coupled to the local loop on the customer premises side of the POTS loading coils 402 along lines 422 and 424. A capacitor 426 (100 nF) is disposed along the line 422 and a capacitor 428 (100 nF) is disposed along the line 424 to capacitively couple the hybrid 324 to the loop 214 on the customer premises side of the POTS loading coils. The repeater 224 of FIG. 4 may be advantageously employed in circumstances where the local loop 214 already has conventional POTS loading coils coupled thereto. In this circumstance, the repeater 224 of FIG. 4 may simply replace the conventional POTS loading coil to provide both POTS loading coil and DSL signal amplification functionality. Indeed, POTS loading coils are conventionally disposed about every 6,000 feet along some long loops to improve voice frequency transmission over long loops. By replacing these conventional POTS loading coils with the DSL repeater 224 of FIG. 4, a single device, namely the DSL repeater 224 of FIG. 4, may provide both voice frequency transmission improvement and DSL signal amplification. Moreover, replacing existing POTS loading coils with the DSL repeater 224 of FIG. 4 permits the DSL repeater 224 to potentially use any housing or other hardware (not shown) associated with the previously existing POTS loading coils, thereby potentially facilitating installation of the DSL repeater 224 of FIG. 4 along the local loop 214. Additional details of the components comprising the DSL repeater 224 of FIG. 4 are discussed below with reference to FIGS. 5-18. FIGS. 5 and 6 illustrate details of one embodiment of the hybrids 322 and 324 respectively. As shown in FIG. 5, the hybrid 322 includes a winding 502 coupled to the central office side of the loop 214 (not shown) via lines 412 and 414 and a winding 504 coupled to lines 332 and 334. Line 332 couples the hybrid 322 to the downstream filter 302. Line 334 couples the hybrid 322 to the upstream amplifying element 314 via a resistor 506 (100 ohms). The winding 504 is also coupled to ground via a resistor 508 (50 ohms) along center tap line 510. The hybrid 322 also includes a conventional electromagnetic core 512. As those skilled in the art will appreciate, it is generally desirable for the hybrid 322 to substantially match the impedance of the associated loop 214 to improve transmission of DSL signals between the hybrid 322 and the loop 214. Consequently, depending on the particular application and impedance characteristics of the associated local loop 214, it may be desirable, in some instances, to replace each of the resistors 506 and 508 with an impedance network having a complex impedance to potentially better match the impedance of the associated local loop 214. The design and implementation of such impedance networks is well within the level of ordinary skill in the art. As shown in FIG. 6, the hybrid 324 includes a winding 602 coupled to the customer premises side of the loop 214 (not shown) via lines 422 and 424 and a winding 604 coupled to lines 342 and 344. Line 342 couples the hybrid 324 to the upstream filter 312. Line 344 couples the hybrid 324 to the downstream amplifying element 314 via a resistor 606 (100 ohms). The winding 604 is also coupled to ground via a resistor 608 along center tap line 510. The hybrid 322 also includes a conventional electromagnetic core 612. It is also generally desirable for the hybrid 324 to substantially match the impedance of the associated loop 214 to improve transmission of DSL signals between the hybrid 324 and the loop 214. Consequently, depending on the particular application and impedance characteristics of the associated local loop 214, it may be desirable, in some instances, to replace each of the resistors 606 and 608 with an impedance network having a complex impedance to potentially better match the impedance of the associated local loop 214. FIG. 7 illustrates details of one embodiment of the upstream filter 312 of FIG. 4. As shown, the upstream filter 312 is a circuit having a capacitor 702 (7.3 nF) in parallel with an inductor 704 (1.2 mH), which are coupled to ground via a resistor 706 (200 ohms). Adjacent to the inductor 704 is a resistor 708 (200 ohms) coupled to ground. An inductor 710 (360 uH) is disposed adjacent to the resistor 708. A capacitor 712 (4.6 nF) coupled to ground is disposed adjacent to the inductor 710 opposite the resistor 708. A capacitor 714 (16 nF) is disposed in series with the inductor 710 on the opposite side of the capacitor 712 as the inductor 710. An inductor 716 (1.5 mH) coupled to ground is disposed adjacent to the capacitor 714 opposite the capacitor 712. A capacitor 718 (45 nF) and a resistor 720 (300 ohms) are also provided in series with the capacitor 714 opposite the inductor 716. In this configuration, the upstream filter 312 is operative to attenuate signals outside the upstream frequency band. Specifically, in this embodiment, the upstream filter 312 attenuates signals in the downstream band, such as the 150 kHz -1.104 MHz band for one embodiment of downstream Category I ADSL. Those skilled in the art will appreciate that many different component configurations and component values may be employed to achieve a comparable filtering function and, therefore, the details described above in connection with FIG. 7 are to be considered in an illustrative and not restrictive sense. FIG. 8 illustrates the frequency response of the upstream filter 312 of FIG. 7. As illustrated, the upstream filter 312 attenuates signals above and below the upstream frequency band of about 25 - 120 kHz. FIG. 9 illustrates the filter phase of the upstream filter 312 of FIG. 7 and shows the locations of the poles. FIG. 10 illustrates details of one embodiment of the downstream filter 302. The downstream filter 302 is disposed between the hybrid 322 and the downstream amplifying element 304 for attenuating signals outside the downstream frequency band, such as upstream band DSL signals that have been leaked through the hybrid 322. Adjacent to the hybrid 322, the downstream filter includes a capacitor 1002 (780 pf) and an inductor 1004 (180 uH) disposed in parallel and coupled to ground via a resistor 1006 (200 ohms). A resistor 1007 (200 ohms) is also coupled to ground adjacent the inductor 1004. An inductor 1008 (42 uH) is disposed adjacent to the resistor 1007. A capacitor 1010 (410 pF) coupled to ground is disposed adjacent to the inductor 1008 opposite the resistor 1007. Another capacitor 1012 (2.7 nF) is disposed in series with the inductor 1008 and adjacent to the capacitor 1010 opposite the inductor 1008. An inductor 1014 (270 uH) coupled to ground is disposed adjacent to the capacitor 1012 opposite the capacitor 1010. Yet another capacitor 1016 (10 nF) is disposed in series with the capacitor 1012 adjacent the inductor 1014 opposite the capacitor 1012. A resistor 1018 (300 olims) is disposed in series with the capacitor 1016 between the capacitor 1016 and the line 354 leading to the downstream amplifying element 304. In this configuration, the downstream filter 302 is operative to attenuate signals outside the downstream frequency band. Specifically, in this embodiment, the downstream filter 302 attenuates signals in the upstream band, such as the 25 - 120 kHz band for downstream ADSL. Those skilled in the art will appreciate that many different component configurations and component values may be employed to achieve a comparable filtering function and, therefore, the details described above in connection with FIG. 10 are to be considered in an illustrative and not restrictive sense. FIGS. 11 and 12 respectively illustrate the downstream filter magnitude, or frequency response, and the downstream filter phase of the downstream filter 302 of FIG. 10. As shown in FIG. 11, the downstream filter 302 passes signals in the downstream band range. As discussed above, the downstream band range for one version of Categoiy I ADSL is about 150 kHz to about 1.104 MHz. Therefore, for this version of ADSL, the downstream filter 302 attenuates signals above and below this band. FIG. 12 illustrates the filter phase of the downstream filter 302 of FIG. 10 and shows the position of the filter poles. FIG. 13 illustrates details of one embodiment of the upstream amplifying element 314. As shown, the upstream amplifying element 314 is disposed between the upstream filter 312 and the hybrid 322 for amplifying upstream DSL signals and passing the amplified upstream DSL signals to the hybrid 322 to be passed to the local loop 214. In this embodiment, the upstream amplifying element comprises an amplifying equalizer having an operational amplifier 1302, a capacitor 1304 (620 pF), a resistor 1306 (10 K olims), resistors 1308 (1700 olims) and 1310 (290 ohms), and a capacitor 1312 (4.1 nF). As shown, the operational amplifier 1302 has a positive input coupled to ground and a negative input coupled to line 352, which couples the upstream amplifying element 314 to the upstream filter 312. The output of the operational amplifier 1302 is coupled to line 334, which couples the upstream amplifying element 314 to the hybrid 322. The resistors 1308 and 1310 are disposed in series with each other and in parallel with the resistor 1306 and the capacitor 1304. Moreover, the resistors 1308 and 1310 are also coupled to ground via the capacitor 1312, which is disposed between the resistors 1308 and 1310. Additional characteristics of the upstream amplifying element 314 are described below with reference to FIGS. 15 and 16. In this configuration, the upstream amplifying element 314 is operative to amplifying upstream DSL signals and to provide more amplification to upstream DSL signals according to their frequency by amplifying higher frequency upstream DSL signals more than to lower frequency upstream DSL signals. Those skilled in the art will appreciate that many different component configurations and component values may be employed to achieve a comparable or satisfactory amplifying function and, therefore, the details described above in comiection with FIG. 13 are to be considered in an illustrative and not restrictive sense. FIG. 14 illustrates details of one embodiment of the downstream amplifying element 304. In this embodiment, the upstream amplifying element comprises an amplifying equalizer having an operational amplifier 1402, a capacitor 1404 (11 pF), a resistor 1406 (44 K ohms), resistors 1408 (260 ohms) and 1410 (1600 ohms), and capacitor 1412 (4.1 nF). As shown, the operational amplifier 1402 has a positive input coupled to ground and a negative input coupled to line 354, which couples the downstream amplifying element 304 to the downstream filter 302. The output of the operational amplifier 1402 is coupled to line 344, which couples the downstream amplifying element 304 to the hybrid 324. The resistors 1408 and 1410 are disposed in series with each other and in parallel with the resistor 1406 and the capacitor 1404. Moreover, the resistors 1408 and 1410 are also coupled to ground via the capacitor 1412, which is disposed between the resistors 1408 and 1410. Additional characteristics of the downstream amplifying element 304 are described below with reference to FIGS. 17 and 18. In this configuration, the downstream amplifying element 304 is operative to amplifying downstream DSL signals and to provide more amplification to downstream DSL signals according to their frequency by amplifying higher frequency downstream DSL signals more than to lower frequency downstream DSL signals. Those skilled in the art will appreciate that many different component configurations and component values may be employed to achieve a comparable or satisfactory amplifying function and, therefore, the details described above in connection with FIG. 14 are to be considered in an illustrative and not restrictive sense. FIGS. 15 and 16 illustrate additional characteristics of the upstream amplifying element 314 shown in FIG. 13 and described above. In particular, FIG. 15 shows signal amplification as a function of signal frequency. As shown, the upstream amplifying element 314 of FIG. 13 amplifies higher upstream frequency signals more than lower upstream frequency signals to at least partially compensate for the tendency of higher frequency signals to be more attenuated as they traverse a local loop than lower frequency signals. Thus, for example, the upstream amplifying element 314 shown in FIG. 13 will amplify a 100 kHz signal more than 25 kHz signal. FIG. 16 illustrates the phase of the upstream amplifying element 314 shown in FIG. 13. FIGS. 17 and 18 illustrate additional characteristics of the downstream amplifying element 304 shown in FIG. 14 and described above. In particular, FIG. 17 shows signal amplification as a function of signal frequency. As shown, the downstream amplifying element 304 of FIG. 14 amplifies higher downstream frequency signals more than lower downstream frequency signals to at least partially compensate for the tendency of higher frequency signals to be more attenuated as they traverse a local loop than lower frequency signals. Thus, for example, the downstream amplifying element 304 shown in FIG. 14 will amplify a 1 MHz signal more than a 150 kHz signal. FIG. 18 illustrates the phase of the downstream amplifying element 304 shown in FIG. 14. The invention has been described above with reference to specific embodiments. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The foregoing description and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Claims: What is claimed is: 1. A DSL repeater adapted to be coupled to a local loop for improving transmission of DSL signals over the local loop, the DSL signals having a first frequency band for DSL signals traversing the local loop in a first direction and a second frequency band for DSL signals traversing the local loop in a second direction, the repeater comprising: a first filter for receiving DSL signals transmitted over the local loop in the first direction and attenuating signals within the second frequency band; a first amplifying element coupled to the first filter for amplifying DSL signals filtered by the first filter and passing the amplified DSL signals onto the local loop. 2. The DSL repeater of claim 1 , further comprising: a second filter for receiving DSL signals transmitted over the loop in the second direction and attenuating signals within the first frequency band; a second amplifying element coupled to the second filter for amplifying DSL signals filtered by the second filter and passing the amplified DSL signals onto the local loop. 3. The DSL repeater of claim 1 , wherein the first amplifying element further comprises an equalizer configured to amplify higher first frequency band DSL signals more than lower first frequency band DSL signals. 4. The DSL repeater of claim 1, further comprising POTS loading coils adapted to be coupled to the local loop for improving transmission of POTS band signals over the loop. 5. The DSL repeater of claim 1 , wherein the DSL signals further comprise VDSL signals. 6. The DSL repeater of claim 1 , wherein the DSL signals further comprise Category I ADSL signals. 7. The DSL repeater of claim 2, wherein the first frequency band further comprises the band between about 25 - 120 kHz and the second frequency band further comprises the band between about 150 kHz - 1.104 MHz. 8. The DSL repeater of claim 2, further comprising: a first hybrid coupled to first filter and the second amplifying element for coupling the first filter and the second amplifying element to the loop; and a second hybrid coupled to the second filter and the first amplifying element for coupling the second filter and the first amplifying element to the local loop. 9. A DSL repeater adapted to be coupled to a loop for improving transmission of DSL signals over the loop, the DSL signals having a first frequency band for DSL signals passing in a first direction and a second frequency band for DSL signals passing in a second direction, the repeater comprising: a first amplifying element for receiving first frequency band DSL signals, amplifying the first frequency band DSL signals, and passing the amplified DSL signals onto the local loop; and a second amplifying element for receiving second frequency band DSL signals, amplifying second frequency band DSL signals, and passing the amplified second frequency band DSL signals onto the local loop. 10. The DSL repeater of claim 9, further comprising: a first filter coupled to the first amplifying element for receiving DSL signals transmitted in the first direction and attenuating signals outside the first frequency band, the first filter passing the filtered signals to the first amplifying element for amplification; a second filter coupled to the first amplifying element for receiving DSL signals transmitted in the second direction and attenuating signals outside the first frequency band, the second filter passing the filtered signals to the second amplifying element for amplification. 11. The DSL repeater of claim 9, wherein: the first amplifying element further comprises an equalizer configured to amplify higher first frequency band DSL signals more than lower first frequency band DSL signals; and the second amplifying element further comprises an equalizer configured to amplify higher second frequency band DSL signals more than lower second frequency band DSL signals. 12. The DSL repeater of claim 9, further comprising POTS loading coils adapted to be coupled to the local loop for improving transmission of POTS band signals over the loop. 13. A DSL repeater adapted to be coupled to a local loop for improving DSL performance over the loop, the repeater comprising: a first hybrid for receiving downstream DSL signals from a central office over the local loop; a second hybrid for receiving upstream DSL signals from a customer premises over the local loop; a downstream filter coupled to the first hybrid for receiving downstream DSL signals from the first hybrid and attenuating signals within an upstream frequency band; a downstream amplifying element coupled to the downstream filter for receiving filtered downstream DSL signals from the downstream filter and amplifying the downstream DSL signals, the downstream amplifying element being coupled to the second hybrid for passing amplified downstream DSL signals from the downstream amplifying element onto the local loop for transmission to the customer premises; an upstream filter coupled to the second hybrid for receiving upstream DSL signals from the first hybrid and attenuating signals within a downstream frequency band; and an upstream amplifying element coupled to the upstream filter for receiving filtered upstream DSL signals from the upstream filter and amplifying the upstream DSL signals, the upstream amplifying element being coupled to the first hybrid for passing amplified upstream DSL signals from the upstream amplifying element onto the local loop for transmission to the central office. 14. The DSL repeater of claim 13, further comprising POTS loading coils adapted to be coupled to the local loop for improving transmission of POTS band signals over the local loop. 15. The DSL repeater of claim 13, wherein the DSL signals further comprise ADSL signals. 16. The DSL repeater of claim 13, wherein the DSL signals further comprise VDSL signals. 17. The DSL repeater of claim 13, wherein: the downstream amplifying element further comprises an equalizer configured to amplify higher frequency downstream frequency band DSL signals more than lower frequency first frequency band DSL signals; and the upstream amplifying element further comprises an equalizer configured to amplify higher fi-equency upstream frequency band DSL signals more than lower frequency second frequency band DSL signals. 18. A method for improving DSL service over a local loop, comprising: coupling a first DSL repeater to the local loop between a central office and a customer premises; employing the first DSL repeater to amplify upstream and downstream DSL signals passing over the local loop to at least partially compensate for DSL signal attenuation caused by the DSL signals passing over the local loop. 19. The method for improving DSL service over a local loop of claim 18, further comprising: coupling a second DSL repeater to the local loop between the central office and a customer premises, the first and second DSL repeaters being disposed in series with each other and separated by a distance; employing the second DSL repeater to amplify upstream and downstream DSL signals passing over the local loop to at least partially compensate for DSL signal attenuation caused by the DSL signals passing over the local loop. 20. The method for improving DSL service over a local loop of claim 19, wherein the distance between the first and second DSL repeaters is in the range 5,000 - 7,000 feet. 21. A method for improving DSL service over a local loop, comprising: receiving an upstream DSL signal from a customer premises; filtering the upstream DSL signal to attenuate signals outside an upstream DSL signal frequency band; amplifying the filtered upstream DSL signal to at least partially compensate for upstream DSL signal attenuation caused by the upstream DSL signal passing over the local loop; and passing the amplified upstream DSL signal onto the local loop for transmission to a central office. 22. A system for improving DSL service over a local loop, comprising: means for receiving an upstream DSL signal from a customer premises at a location along the local loop; means for filtering the upstream DSL signal to attenuate signals outside an upstream DSL signal frequency band; means for amplifying the filtered upstream DSL signal to at least partially compensate for upstream DSL signal attenuation caused by the upstream DSL signal passing over the local loop; and means for passing the amplified upstream DSL signal onto the local loop for transmission to a central office. 23. A method for improving DSL service over a local loop, comprising: receiving a downstream DSL signal from a central office; filtering the downstream DSL signal to attenuate signals outside n downstream DSL signal frequency band; amplifying the filtered downstream DSL signal to at least partially compensate for downstream DSL signal attenuation caused by the downstream DSL signal passing over the local loop; and passing the amplified downstream DSL signal onto the local loop for transmission to a customer premises. 24. A system for improving DSL service over a local loop, comprising: means for receiving a downstream DSL signal from a central office; means for filtering the downstream DSL signal to attenuate signals outside n downstream DSL signal frequency band; means for amplifying the filtered downstream DSL signal to at least partially compensate for downstream DSL signal attenuation caused by the downstream DSL signal passing over the local loop; and means for passing the amplified downstream DSL signal onto the local loop for transmission to a customer premises.

Inventors: HINMAN BRIAN, NORRELL ANDREW, SCHLEY-MAY JAMES, HINMAN, BRIAN, NORRELL, ANDREW, SCHLEY-MAY, JAMES
Applicants: 2WIRE INC, 2WIRE, INC.
Application year: 2001
Main classification: H04L25
IPC codes: H04B3, H04L5, H04L25, H04M11