Telecommunications – Interference signal transmission
Patent
1998-05-11
2000-07-18
Grant, Chris
Telecommunications
Interference signal transmission
348 13, H04J 1100
Patent
active
060919329
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a two-way point to multipoint data transmission system, such as a CATV (Cable TV) data transmission system capable of carrying data in both the upstream and downstream directions. The transmitted data can be any digital data, such as computer files or digitized audio or video, for example. The digital data is carried over an analog transmission line, such as a coaxial cable or optical fiber.
Cable TV systems have been available for many years. Until recently, they were used only as a means of distributing radio frequency TV channels to subscribers. More recently, it has been recognized that existing cable systems offer a convenient way of providing wide bandwidth data services direct to the home.
In North America, the downstream bandwidth is in the range of 50 to 550 MHz. This downstream bandwidth is being slowly upgraded to 750 MHz and eventually to 1 GHz.
Two-way systems operate upstream typically in the range of 5 to 30/42 MHz, depending on the cable system. The return band (upstream) was initially developed for telemetry systems, security systems, network monitoring, etc., which require relatively low bandwidth.
Originally, the distribution from the head end was entirely over coaxial cable with node sizes ranging up to many thousands of homes. The trend with new systems and upgrades is to use fiber to an optical node in the vicinity of a cluster of 400 to 500 homes. A reduction in the length of the coax run, and the number of amplifiers, is necessary if the upper bound is to be pushed to 750 MHz and then to 1 GHz. It is also necessary to reduce the number of homes on a node so that video on demand, interactive services and voice and data communications will not overload the available shared bandwidth. Reducing the number of homes is also important in limiting the total noise funneled into the head end that, in turn, is a factor affecting maximum data rates.
Due to the return path ingress, only the high end of the return band (18 to 35 MHz) has been considered for "reliable" data communications.
Most ingress enters the CATV plant from the customer premises, either from defective equipment, open stub cables, or poor connections. A primary ingress source is narrow band HAM, CB, and short wave audio broadcasts, in the 5-20 MHz band. Distant short-wave broadcasts tend to affect the entire CATV plant, while HAM, and CB interference are localized problems. This narrow band ingress is generally identified by interference with a slow variation with time (Seconds).
Another primary ingress source is 60/120 Hertz types of broad band impulsive emissions from electric motors. Impulsive noise is spectrally like a random comb generator, with power decreasing with increasing frequency. This broad band ingress is generally identified by interference with a fast variation with time (e.g. 1 mSec spike repeated at 120 Hz). This form of interference originates from electrical arcing or the ionization of air. Impulse interference is more of a problem at the low end of the return band (5 to 18 MHz).
Ingress can be controlled to some extent with high pass filters installed at "all" home demarcation points. However, this complicates the installation of multiple interactive services at the premises. Ingress directly into the CATV distribution plant is also a problem, but this can be monitored with CATV leakage "sniffer" devices, and becomes an ongoing plant hardening procedure.
Another serious downstream impairment is caused by reflections, or echoes, that occur whenever a signal encounters an impedance mismatch. Most CATV systems were originally one way and intended to serve analog TVs only. Even modern TV tuners change impedance when retuned. These tuners typically have poor return loss at the frequency to which they are tuned and much worse return loss, actually approaching zero, at all other frequencies.
Hybrid splitters are used to prevent analog TVs from interfering with each other. Some splitters, however, do not provide enough isolation to protect new digital services employing short symbol time
REFERENCES:
patent: 3835393 (1974-09-01), Marron
patent: 4343042 (1982-08-01), Schrock
patent: 5291289 (1994-03-01), Hulyalkar et al.
patent: 5315584 (1994-05-01), Savary
patent: 5361394 (1994-11-01), Shigihara
patent: 5406551 (1995-04-01), Saito
patent: 5444697 (1995-08-01), Leung et al.
patent: 5594726 (1997-01-01), Thompson
patent: 5687165 (1997-11-01), Daffara
patent: 5732068 (1998-03-01), Takahashi
"On the Eve of the Revolution" EBU Technical Review, Wood, Jun. 1994.
"A Multicarrier E-HDSL Transceiver System with Coded Modulation" European Transactions on Communications and Related Technologies, Chow, Al-Dhahir, Cioffi &Bingham, May 1993.
"Priciples of Modulation and Channel Coding for Digital Broadcasting for Mobile Receivers" EBU Review--Technical, Lassalle, Alard, Aug. 1987.
"Digital HDTV Broadcasting Over the CATV Distribution System" Signal Processing Image Communication, Moenceclaey & Bladel, Dec. 1993.
"Synchronization Requirements for Multi-User OFDM on Satellite Mobile and Two-Path Rayleigh Fading Channels" IEEE Transactions on Communications, Wei & Schlegel, Feb. 1995.
"High Performance Multimedia Transmission on the Cable Television Network" Information Systems Laboratory--Stanford University, Jacobson & Cioffi, May 1994.
Grant Chris
RegioCom GmbH
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