Patent Publication Number: US-6985565-B2

Title: Configurable DSL modem for high bit rates

Description:
This patent application is a continuation under 35 USC § 120 to patent application entitled CONFIGURABLE MULTI-PORT MODEM TO ACHIEVE A HIGH BIT RATE IN A DSL SYSTEM, having a Ser. No. 10/200,991, and a filing date of Jul. 23, 2002 now U.S. Pat. No. 6,754,318. 

   BACKGROUND OF THE INVENTION 
   1. Technical Field of the Invention 
   This invention relates generally to communication systems and more particularly to digital subscriber line (DSL) based communication systems. 
   2. Description of Related Art 
   Communication systems are known to enable a plurality of communication devices to communicate among themselves and with communication devices in other communication systems. Such communication devices, which may be computers, modems, facsimile machines, printers, personal digital assistants, et cetera, communicate voice, text, and/or video data. Such communication systems support the communication of data in accordance with one or more communication standards. As is known, there are a large number of communication standards for the communication of data and such standards vary from country to country. For example, there are a variety of standards governing digital subscriber line (DSL) communications and such standards vary from country to country. 
   As is further known, for a communication device to communicate via a DSL based system, the communication device includes a DSL modem. Typically, the location of the communication device with its associated DSL modem is referred to as the customer premises. The DSL modem at the customer premises is typically coupled via a twisted pair to a DSL modem at a central office.  FIG. 1  illustrates an example of a DSL modem at the customer premise (CPE) coupled to a DSL modem at the central office (CO). The coupling is achieved via a twisted pair, which supports one DSL channel, and is one of a plurality of twisted pairs in a cable binder, or bundle of wires. In this example, the frequency allocation of the DSL channel is illustrated in  FIG. 2 . 
   As shown in  FIG. 2 , the DSL channel includes 4 frequency bands (band  1  through band  4 ). Each band may be allocated for upstream transmission (i.e., from the CPE to the CO) or downstream transmission (i.e., from the CO to the CPE). For example, bands  1  and  3  may be used for upstream transmissions while bands  2  and  4  are used for downstream transmissions. The width (i.e., frequency) and height (i.e., power) of each band may vary and are typically defined by one or more standards. For example, various DSL standards prescribe a frequency, or spectral, plan that define the transmit frequencies (i.e., start frequency and width) and associated powers (i.e., height) for each band. This is done primarily to minimize near-end-cross-talk between twisted pairs within a cable binder by having each twisted pair within a cable binder using the same frequency plan. 
   To support the DSL channel illustrated in  FIG. 2 , the CO modem and CPE modem of  FIG. 1  each include two transmitters and two receivers. In addition, each modem includes a hybrid, which performs a 2-wire to 4-wire conversion, a summer, and a splitting multiplexer and a reconstruction multiplexer. Accordingly, for the example given where bands  1  and  3  are used for upstream data communications, the 1 st  transmitter of the CPE modem transmits the data in band  1  and the 2 nd  transmitter of the CPE modem transmits the data associated with band  3 . The transmitters in the CO modem transmit the data in band  2  and data in band  4 , respectively. Correspondingly, the receivers in the CPE modem receive the data in band  2  and band  4 , respectively. Similarly, the receivers in the CO modem receive the data in band  1  and band  3 , respectively. Alternatively, bands  1  and  3  may be used for downstream transmissions and bands  2  and  4  may be used for upstream transmissions. 
   The splitting multiplexers in the CO modem and CPE modem split the incoming transmit data between the respective transmitters. Conversely, the reconstructing multiplexers, reconstruct the data received from the respective receivers into a serial data stream. 
   When data can be allocated into all 4 bands, the CPE modem and CO modem are capable of transceiving data at a relatively high bit rate (e.g., greater than 5 Mbps). Typically, the shorter the twisted pair, the less cable loss and the less cross-talk the twisted pair, or loop, exhibits. Conversely, the cable loss and cross-talk increase as the length of the loop increases. When the cable loss and cross-talk increase to significant levels, the upper frequency bands (e.g., band  3  and band  4 ), become unusable. Thus, CPE modems coupled to the central office via shorter loops typically have higher bit rates than CPE modems coupled to the central office via longer loops. This creates a discontinuity in quality of service since some users have a higher bit rate than others. 
   Therefore, a need exists for a method and apparatus for a configurable modem that achieves high bit rates in a DSL system regardless of the loop length. 
   BRIEF SUMMARY OF THE INVENTION 
   The configurable DSL modem of the present invention substantially meets these needs and others. In one embodiment, a method for configuring a multi-port digital subscriber line (DSL) modem, the method begins by utilizing frequency bands of a single DSL channel to support a data communication when loop length of the single DSL channel and data rate of the data communication are favorable. The method continues by utilizing some of the frequency bands of the single DSL channel and frequency bands of at least one other DSL channel to support the data communication when the loop length of the single DSL channel is unfavorable or the data rate of the data communication is unfavorable. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram of prior art DSL modems; 
       FIG. 2  is a graphical representation of frequency band allocations of a DSL channel in accordance with one or more DSL communication standards; 
       FIG. 3  is a schematic block diagram of a DSL system in accordance with the present invention; 
       FIG. 4  is a schematic block diagram of a configurable modem in accordance with the present invention; 
       FIG. 5  is a graphical representation of an example of frequency band usage in the DSL system of  FIG. 3 ; 
       FIG. 6  is a graphical representation of a 2 nd  example of frequency band usage in the DSL system of  FIG. 3 ; 
       FIG. 7  is a graphical representation of a 3 rd  example of frequency band usage in the DSL system of  FIG. 3 ; 
       FIG. 8  is a schematic block diagram of an alternate configurable modem in accordance with the present invention; and 
       FIG. 9  is a logic diagram of a method for configuring a multi-port DSL modem in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  is a schematic block diagram of a DSL system  10  that includes a plurality of configurable modems  20 – 26  at various customer premises (CPE 1 –CPE 4 ) and a central office (CO). The central office includes a plurality of configurable modems  12 – 18 . Each configurable modem  12 – 18  of the central office is coupled via a plurality of twisted pairs with a configurable modem  20 – 26  at one of the customer premises CPE 1 –CPE 4 . The twisted pairs between the central office and the customer premises may be in one or more bundles of twisted pairs, or cable binders and may include two or more twisted pairs. 
   Each of the configurable modems  20 – 26  at the customer premises CPE 1 –CPE 4  communicates DSL signals  28 – 34  with a corresponding configurable modem  12 – 18  within the central office. For example, configurable modem  20  processes user data  1  to communicate DSL signals  28  with configurable modem  12 . Similarly, configurable modem  22  processes user data  2  to communicate DLS signals  30  with configurable modem  16 . Configurable modem  24  processes user  3  data to communicate DSL signals  32  with configurable modem  14 . Configurable modem  26  processes user  4  data to communicate DSL signals  34  with configurable modem  18 . 
   The distance between the central office and each of the customer premises may range from a few hundred feet to several kilofeet. Accordingly, the customer premises that are closer to the central office have a shorter DSL loop than customer premises that are further away. However, by including the configurable modems  12 – 26 , the same high bit rate of service may be provided to each customer premises regardless of the loop length. To achieve this, the configurable modems  20  may be implemented as shown in  FIG. 4  and/or in  FIG. 8 . 
     FIG. 4  is a schematic block diagram of a configurable modem  12 – 26  that includes multiplexers  40  and  42 , a plurality of transmitters  44 – 48 , a plurality of receivers  50 – 54 , a switching module  56 , and a plurality of hybrids  58 – 64 . Each of the plurality of hybrids is coupled to a corresponding one of twisted pairs  66 – 70 . The hybrids  58 – 64  perform a 2-wire to 4-wire conversion. As shown, the 2-wire connection is to the twisted pair and the 4-wire connection is to the switching module  56 . 
   The switching module  56  couples one or more of the transmitters and receivers to individual hybrids based on a configuration control signal  72 . For example, if the loop length is very short, all frequency bands of a DSL channel that includes multiple frequency bands are usable. As such, a single twisted pair may be used to support a DSL communication and provide a high bit rate. For example, hybrid.  58  via twisted pair  70  may support the DSL channel having multiple frequency bands (e.g., six frequency bands). When this is the case, the switching module  56  couples each of the transmitters  44 – 48  to hybrid  58  and also couples each of the receivers  50 – 54  to the hybrid  58 . With this configuration, each transmitter and each receive is allocated a frequency band. 
   For the example of short loop length and a six frequency band channel,  FIG. 5  illustrates one possible allocation of the frequency bands. In this illustration, bands  1 ,  3 , and  5  are allocated for upstream communications and bands  2 ,  4 , and  6  are allocated for down stream communications. If the configurable multi-port modem is contained at a customer premises, transmitter  44  may be allocated to process frequency band  1 ; transmitter  46  may be allocated to process frequency band  3 ; and transmitter  48  may be allocated to process frequency band  5 . Further, receiver  52  may be allocated to process frequency band  2 ; receiver  50  may be allocated to process frequency band  4 ; and receiver  54  may be allocated to process frequency band  6 . In this example, twisted pairs  66  and  68  are unused. 
   As the loop length increases, and the number of frequency bands decreases, the configuration control signal  72  may instruct the switching module  56  to use a pair of hybrids. This example is illustrated in  FIG. 6  where the high frequency bands of twisted pair  70  are unusable due to the loop loss and/or cross-talk of twisted pair  70 . As such, twisted pairs  68  and  70  are used to support a DSL communication. In this example, the switching module  56 , based on the configuration control signal  72  would couple transmitters  44  and  46  to hybrid  58  and couple transmitter  48  to hybrid  60 . In addition, the switching module  56  would couple receivers  50  and  52  to hybrid  58  and receiver  54  to hybrid  60 . 
   Depending on whether the configuration modem is at the central office site or at a customer premises, the allocation of transmitter and receiver for upstream and downstream communications would vary. For example, if the modem were at a customer premise site, the transmitters  44  and  46  would be allocated to bands  1  and  3  of twisted pair  70 . Receivers  50  and  52  would be allocated band  2  and band  4  of twisted pair  70 . Transmitter  48 , which is coupled to hybrid  60 , would be allocated band  1  of twisted pair  68  and receiver  54  would be allocated band  2  of twisted pair  68 . 
   When the loop length between the customer premise and central office is of such a length where the losses only allow bands  1  and  2  to be used, the configuration control signal  72  causes switching module  56  to use each of the hybrid  58 – 64 . Such an example is illustrated in  FIG. 7  where each of the twisted pair  66 – 70  is used, but only bands  1  and  2  of the respective twisted pairs are used. Accordingly, if the configurable modem of  FIG. 4  is at the customer premise, transmitter  44  and receiver  50  would be coupled to hybrid  58  and allocated bands  1  and  2  of twisted pair  70 , respectively. Transmitter  46  and receiver  52  would be coupled to hybrid  60  and allocated bands  1  and  2  of twisted pair  68 , respectively. Transmitter  48  and receiver  54  would be coupled to hybrid  64  and allocated bands  1  and  2  of twisted pair  66 , respectively. 
   Accordingly, the bit rate supported by the configurable modem  12 – 26  can maintain a high rate by utilizing one or more twisted pairs as illustrated in examples 1–3 depicted in  FIGS. 5–7 . As one of average skill in the art will appreciate, more or less twisted pairs, hybrids, transmitters and receivers may be included in a configurable modem to achieve higher bit rates or lower bit rates than the bit rates achievable with the 3 sets illustrated in  FIG. 4  and corresponding examples of  FIGS. 5–7 . 
   Returning to the discussion of  FIG. 4 , the configurable modem  12 – 26  also includes a splitting multiplexer  40 , or demultiplexer, that splits outbound data  74  amongst the plurality of transmitters  44 – 48 . The configurable modem  12 – 26  also includes a multiplexer  42  that combines the received data via receivers  50 – 52  and reconstructs a serial inbound data  72 . The generation of the configuration control signal  72  will be described in greater detail with reference to  FIGS. 8 and 9 . 
   As one of average skill in the art will appreciate, the switching module  56  may be implemented using jumper wires, switches, or other manual coupling means. In these instances, the configurable control signal  72  is implicit in the coupling of the jumper wires and/or the configuring of the switches. As one of average skill in the art will further appreciate, the number of bands supported by a DSL channel may be more or less than the six discussed with reference to  FIGS. 4–7 . For example, in one embodiment, four bands may be used. 
     FIG. 8  is a schematic block diagram of an alternate embodiment of the configurable modem  12 – 26 . In this embodiment, the configurable modem includes combining multiplexer  86 , splitting multiplexer  88 , splitting multiplexer  40 , combining multiplexer  42 , a plurality of transmitters  44 – 48 , a plurality of receivers  50 – 54 , a transmit switch module  80 , a receive switch module  82 , a plurality of hybrids  58 – 64 , and a control module  84 . The control module  84 , which may be included in the modem of  FIG. 4 , includes a processing module  90  and memory  92  to generate the configuration control signal  72 . The processing module  90  may be a single processing device or a plurality of processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory  92  may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module  90  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry. The memory  92  stores, and the processing module  90  executes, operational instructions corresponding to at least some of the steps and/or functions illustrated in  FIGS. 8 and 9 . 
   The functionality of multiplexers  40  and  42 , transmitters  44 – 48 , receivers  50 – 54  and hybrids  58 – 64  operate as previously discussed with reference to  FIG. 4 . The transmitter switching module  80  and receiver switching module  82  provide selective coupling between hybrids  58 – 64  and transmitters  44 – 48  and receivers  50 – 54 , respectively. Accordingly, the transmit switching module  80  and receiver switching module  82  may be a plurality of transistors, switches or combinations thereof that provide selective coupling between the transmitters  44 – 48  and hybrids  58 – 64  and receivers  50 – 54 , respectively. 
   In this embodiment, the configurable modem may support multiple connections (three are shown, but more or less may be supported). A connection is a data communication by an in-office or in-home device that includes a configurable DSL modem with a configurable DSL modem at the central office. Accordingly, if the loop length between the DSL modem at the customer premises and central office is short, three connections may be supported. To support the three connections, each hybrid is coupled to a single receiver and a single transmitter or a set of receivers and a set of transmitters depending on the desired bit rate. Accordingly, to achieve the highest bit rate possible, each hybrid would be coupled to multiple receivers and transmitters to process multiple bands of the DSL channel. As such, for a six band DSL channel and three twisted pair modem, the modem may include up to nine transmitters and nine receivers to support the highest bit rate possible for each of three connections. 
   As the loop length increases and the higher frequency bands become unusable, the configurable modem  12 – 26  may be reconfigured to support  1  or  2  connections. When 1 connection is being supported, the configurable modem  12 – 26  functions similarly to the modem of  FIG. 4  and the corresponding example illustrated in  FIG. 7 . When 2 connections are supported, the transmitters  44  and  46  and receivers  50  and  52  may be allocated to one of the two connections and transmitter  48  and receiver  54  may be allocated to the other of the two connections. Accordingly, the control module  84  determines the appropriate configuration and generates the configuration control signal  72  based thereon. Alternatively, the configuration control signal may be determined by measurements at the CPE and the switching module implemented via jumper wires and/or switches. 
     FIG. 9  is a logic diagram of a method for configuring a multi-port DSL modem in accordance with the present invention. The process begins at Step  100  where a desired data bit rate for a connection is determined. The data bit rate may range from a few hundred kilobits per second to tens of megabits per second. The process then proceeds to Step  102  where data capacity for frequency bands of a DSL channel supporting the connection are determined. Such a determination may be based on determining the loop length of the connection and based on the loop length establishing the data capacity. For a detailed discussion on determining loop length, refer to co-pending patent application entitled ADJUSTMENT OF TRANSMIT POWER BASED ON AN ESTIMATED ELECTRICAL LENGTH OF A LOOP, having a provisional filing date of May 31, 2002 and Ser. No. 60/384,469. As previously mentioned, as the loop length increases, loop loss increases as does cross-talk. Thus, the greater the loop loss and cross-talk, the less usable the higher frequency bands are. Alternatively and/or in addition to loop length estimations, signal to noise ratio may be used to determine the data bit rate. 
   The process then proceeds to Step  104  where a number of twisted pairs to support the connection is determined based on the desired data bit rate and the data capacity for the frequency bands. This was graphically illustrated and described with reference to  FIGS. 5–7 . The process then proceeds to Step  106  where at least one transceiver (i.e., transmitter/receiver) is allocated to a frequency band pair (band  1  for upstream, band  2  for downstream) for each number of twisted pairs. Such an allocation may be done as graphically illustrated and described with reference to  FIGS. 5–7 . 
   The preceding discussion has presented a method and apparatus for configuring a multi-port DSL modem to achieve a high bit rate. Accordingly, such a configurable multi-port DSL modem provides the same quality of service, i.e., high bit rate, to each customer regardless of the loop length between the customer premise and the central office. As one of average skill in the art will appreciate, other embodiments may be derived from the teaching of the present invention, without deviating from the scope of the claims.