Wire loops extending from a telephone company central office to a customer premises are a ubiquitous part of the existing communications infrastructure. These wire loops form a communications network often referred to as the plain old telephone service' (POTS) network. The POTS network originated to support analog voice phone service.
The POTS network currently supports a wide range of communications services in addition to analog voice phone calls. These services include digital data transmissions from facsimile (FAX) machines and computer modems. Voice calls, FAX connections, and computer modem transmissions all operate within the frequency spectrum of traditional POTS calls, thus ensuring compatibility with the existing wire loop infrastructure and allowing transport of these services end-to-end through the POTS phone network. However, the use of POTS-compatible transmission frequencies severely limits the maximum information carrying capacity of the wire loop.
Certain transmission technologies may use carrier frequencies greater than those required for POTS services to exceed the information capacity limits of POTS calls over wire loops. However, since the existing POTS loop infrastructure was not designed for carrying such high frequency signals, severe impediments to such transmission exist. In particular, as a result of electromagnetic coupling among wire loops, electromagnetic noise signals are induced on the loops. This electromagnetic coupling may occur among the large number of loops in the wire bundles that extend from the central office to various customer distribution points.
Noise signals induced on the loops by electromagnetic coupling may not be perceptible on POTS voice calls. However, such signals may significantly interfere with wide-bandwidth modulated data transmissions that use high frequency signals. To reduce interference problems, sophisticated signal processing circuitry, such as digital signal processors (DSPs), are used within modulated data receiver and transmitter units to remove noise, to encode and decode desired signals, and to perform error correction functions.
To minimize the number of wire loops needed to service a customer's premises, POTS signals and modulated data transmission signals may be combined on a single wire loop. To combine POTS and wide-bandwidth modulated data transmission signals, the wide-bandwidth modulated data is transported using frequencies (spectrum) greater than those of POTS services. This spectrum usage allows a POTS service connection to be supported by its traditionally allocated spectrum while simultaneously supporting high frequency modulated data transmission. Thus, current technology permits POTS and high bandwidth data may be carried between customer premise equipment (CPE) and a central office (CO) on a single wire loop. At the central office, the POTS signal frequencies are separated from the high frequency data signal; the POTS signal is then handled by the existing POTS switch and network, while the high frequency spectrum is directed to separate processing components.
Signal processing, transmitting, and receiving circuitry for such high frequency modulated data signals requires a substantial amounts of power, typically up to 5 watts per loop served. For a large central office, potentially serving many thousands of such data connections, this power usage is substantial.