Transmission system for reduction of amateur radio interference

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 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|.

A receiver for extracting a digital data stream from a modulated signal, said modulated signal being centered about a carrier frequency, the receiver comprising:

• adaptive interference cancellation (AIC) means for controllably reducing narrowband interference present in the modulated signal around the carrier frequency, thereby to produce an interference-reduced signal;
• a demodulator connected to the AIC means for receiving and demodulating the interference-reduced signal, thereby to produce one or more baseband demodulated signals;
• a power estimator connected to the demodulator and to the AIC means, for receiving the one or more baseband demodulated signals, calculating the power of residual interference present in the one or more baseband demodulated signals around the carrier frequency and providing the AIC means with an interference estimate signal;
• one or more substantially identical baseband notching filters connected to the demodulator, for receiving the one or more baseband demodulated signals and producing respective filtered demodulated signals, each baseband notching filter having a notch at zero frequency;
• and
• a decision-feedback equalizer (DFE) connected to the one or more baseband notching filters, for receiving the filtered demodulated signals, decoding digital data embedded therein and producing the digital data stream.

A receiver for extracting a digital data stream from a modulated signal, said modulated signal being centered about a carrier frequency fC and having a bandwidth fS, the receiver comprising:

• adaptive interference cancellation (AIC) means for controllably reducing narrowband interference present in the modulated signal around frequencies fC±fS/4, thereby to produce an interference-reduced signal;
• a demodulator connected to the AIC means for receiving and demodulating the interference-reduced signal, thereby to produce one or more baseband demodulated signals;
• a power estimator connected to the demodulator and to the AIC means, for receiving the one or more baseband demodulated signals and providing the AIC means with an estimate of residual interference in the one or more baseband demodulated signals around frequencies fC±fS/4;
• one or more substantially identical baseband notching filters connected to the demodulator, for receiving the one or more baseband demodulated signals and producing respective filtered demodulated signals, each baseband notching filter having a pair of notches symmetrically disposed about zero frequency at frequencies approximately equal to ±fS/4;
• and
• a decision-feedback equalizer (DFE) connected to the one or more baseband notching filters, for receiving the filtered demodulated signals, decoding digital data embedded therein and producing the digital data stream.

A receiver for extracting a digital data stream from a modulated signal, said modulated signal being centered about a carrier frequency, the receiver comprising:

• adaptive interference cancellation (AIC) means for controllably reducing narrowband interference present in the modulated signal around the carrier frequency in accordance with first and second residual interference estimates, thereby to produce an interference-reduced signal;
• a demodulator connected to the AIC means for receiving and demodulating the interference-reduced signal, thereby to produce one or more baseband demodulated signals, and for providing the AIC means with the first estimate of residual interference in the one or more baseband demodulated signals around the carrier frequency;
• one or more substantially identical baseband notching filters connected to the demodulator, for receiving the one or more baseband demodulated signals and producing respective filtered demodulated signals, each baseband notching filter having a notch at zero frequency;
• and
• a decision-feedback equalizer (DFE) connected to the one or more baseband notching filters, for receiving the filtered demodulated signals, decoding digital data embedded therein and producing the digital data stream, wherein the DFE is further connected to the AIC means for providing the AIC means with the second estimate of residual interference in the filtered demodulated signals around the carrier frequency;

A method of transmitting digital data, comprising the steps of:

• 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.

A method of transmitting digital data, comprising the steps of:

• 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 ±Δf;
• 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+Δf is approximately equal to the center frequency of a first interference band and fC−Δf is approximately equal to the center frequency of a second interference band.

A method of recovering a digital data stream from a received signal modulated about a carrier frequency, comprising:

• demodulating the modulated signal, thereby to produce one or more baseband demodulated signals;
• filtering the one or more baseband demodulated signals with respective baseband filters having notches at zero frequency;
• and
• decoding the filtered baseband demodulated signals, thereby to recover the digital data;
• wherein the carrier frequency is approximately equal to the center frequency of an interference band.

A method of recovering a digital data stream from a received signal modulated about a carrier frequency fC, comprising:

• demodulating the modulated signal, thereby to produce one or more baseband demodulated signals;
• filtering the one or more baseband demodulated signals with respective baseband filters having notches at frequencies ±Δf;
• and
• decoding the filtered baseband demodulated signals, thereby to recover the digital data;
• wherein fC±Δf is approximately equal to the center frequency of a first interference band and fC−Δf is approximately equal to the center frequency of a second interference band.

A modem for transmitting a first modulated signal onto a twisted pair and for receiving a second modulated signal from the twisted pair, comprising:

• a hybrid for interfacing with the twisted pair;
• a transmitter connected to the hybrid, for producing the first modulated signal from a first digital data stream, the transmitter comprising an encoder for encoding the first 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 first modulated signal centered about a carrier frequency, wherein the carrier frequency is approximately equal to the center frequency of an interference band;
• and
• a receiver connected to the hybrid, for extracting a digital data stream from the second modulated signal, the receiver comprising adaptive interference cancellation (AIC) means for controllably reducing narrow band interference present in the second modulated signal around the carrier frequency, thereby to produce an interference-reduced signal;
• a demodulator connected to the AIC means for receiving and demodulating the interference-reduced signal, thereby to produce one or more baseband demodulated signals;
• a power estimator connected to the demodulator and to the AIC means, for receiving the one or more baseband demodulated signals and providing the AIC means with an estimate of residual interference in the one or more baseband demodulated signals around the carrier frequency;
• one or more substantially identical baseband notching filters connected to the demodulator, for receiving the one or more baseband demodulated signals and producing respective filtered demodulated signals, each baseband notching filter having a notch at zero frequency;
• and a decision-feedback equalizer (DFE) connected to the one or more baseband notching filters, for receiving the filtered demodulated signals, decoding digital data embedded therein and producing the second digital data stream.