Transmission system for reduction of amateur radio interference
First Claim
1. A transmitter for transmitting a modulated signal across a transmission medium, the transmitter comprising:
- an encoder for encoding a digital data stream into one or more encoded digital signals;
one or more substantially identical baseband notching filters connected to the encoder, for respectively receiving the one or more encoded digital signals, each baseband notching filter having a notch at zero frequency; and
a modulator connected to the one or more baseband notching filters, for producing the modulated signal centered about a carrier frequency, wherein the carrier frequency is approximately equal to the center frequency of an interference band.
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Accused Products
Abstract
The invention is a novel method and transmission system for mitigating the adverse effects of amateur (HAM) radio interference on digital signals transmitted across a twisted pair and reducing the interference caused by the digital signals to amateur radio communications. At the heart of the invention is strategical placement of the frequency spectrum of the transmitted signal relative to the center frequency of the HAM bands. In particular, the signal spectrum is permitted to straddle one or more HAM bands, which permits the transport of high data rates with a single carrier. At the transmitter, the signal is filtered with a real-valued symmetric baseband filter in order to remove signal content in the HAM bands. At the receiver, the signal undergoes adaptive interference cancellation, followed by processing through a decision feedback equalizer. In some cases, the signal is filtered at baseband with a real-valued filter to remove interference in the HAM bands. In the context of a telecommunications access system, the inventive technique can be applied to either or both directions of traffic flow, i.e., downstream and upstream, and multiple carriers can be added to increase capacity in any given direction.
83 Citations
18 Claims
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1. A transmitter for transmitting a modulated signal across a transmission medium, the transmitter comprising:
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an encoder for encoding a digital data stream into one or more encoded digital signals;
one or more substantially identical baseband notching filters connected to the encoder, for respectively receiving the one or more encoded digital signals, each baseband notching filter having a notch at zero frequency; and
a modulator connected to the one or more baseband notching filters, for producing the modulated signal centered about a carrier frequency, wherein the carrier frequency is approximately equal to the center frequency of an interference band. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A transmitter for transmitting a modulated signal across a transmission medium, the transmitter comprising:
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an encoder for encoding a digital data stream into one or more encoded digital signals having a symbol rate fS;
one or more substantially identical baseband notching filters connected to the encoder, for respectively receiving the one or more encoded digital signals, each baseband notching filter having a pair of notches symmetrically disposed about zero frequency at frequencies approximately equal to ±
fS/4; and
a modulator connected to the one or more baseband notching filters, for producing the modulated signal centered about a carrier frequency fC;
wherein fS and fC are related to the center frequencies fH1 and fH2 of two interference bands by fC being approximately equal to ½
(fH1+fH2) and fS being approximately equal to 2|fH2−
fH1|.- View Dependent Claims (8, 9, 10, 11, 12)
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13. A method of transmitting digital data, comprising the steps of:
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encoding the data into one or more baseband digital signals;
filtering the one or more baseband digital signals with respective baseband filters having notches at zero frequency;
modulating the filtered baseband digital signals about a carrier frequency, thereby to produce a modulated signal; and
transmitting the modulated signal across a transmission medium;
wherein the carrier frequency is approximately equal to the center frequency of an interference band. - View Dependent Claims (14, 15)
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16. A method of transmitting digital data, comprising the steps of:
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encoding the data into one or more baseband digital signals;
filtering the one or more baseband digital signals with respective baseband filters having notches at frequencies approximately equal to ±
Δ
f;
modulating the filtered baseband digital signals about a carrier frequency fC, thereby to produce a modulated signal; and
transmitting the modulated signal across a transmission medium;
wherein fC+Δ
f is approximately equal to the center frequency of a first interference band and fC−
Δ
f is approximately equal to the center frequency of a second interference band.- View Dependent Claims (17, 18)
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Specification