AM-compatible digital broadcasting method and system

A method of receiving an in-band on-channel (IBOC) digital broadcast radio frequency (RF) signal that is at least partially redundantly transmitted in upper and lower outer sidebands of a mask, the method comprising the steps of:

• receiving via a receiver the IBOC digital broadcast signal that has a first portion of codeword information replicated in each of an upper outer sideband and a lower outer sideband that are positioned relative to a center frequency, and receiving a second portion of codeword information in at least one of an upper inner sideband and a lower inner sideband;
• determining, in the receiver, whether the source bit information for the codeword at least partially in the upper outer sideband is less likely to have errors in a determined source bit estimate than the replicated source bit information for the codeword that is at least partially in the lower outer sideband;
• and
• selecting, in the receiver, the source bit information for the codeword determined in said determining step to be less likely to have source bit errors, whereby the method of receiving is robust against adjacent channel interference.

An in-band on-channel (IBOC) digital audio broadcast (DAB) communication system including a transmitter and at least one IBOC DAB receiver, the IBOC DAB system comprising:

• signal generator means in the transmitter including analog AM-compatible monophonic signal generator means, upper outer sideband digital signal generator means, lower outer sideband digital signal generator means, and at least one of upper inner sideband digital signal generator means and lower inner sideband digital signal generator means, said transmitter for combining an analog AM-compatible monophonic signal generated by said AM-compatible signal generator means together with digital sideband signals from said upper outer sideband generator means, said lower outer sideband generator means, and said at least one of upper inner sideband digital signal generator means and lower inner sideband digital signal generator means, into a composite signal to be transmitted to said one receiver, and wherein said sideband digital signals each include source bit information;
• means for transmitting said composite signal to said receiver;
• said IBOC DAB receiver for receiving said composite signal, said receiver including analog AM monophonic demodulator means, upper outer sideband digital demodulator means, lower outer sideband digital demodulator means, and at least one of upper inner and lower inner sideband digital demodulator means;
• said receiver further including a comparing device for determining which of i) recovered source bit information from demodulation of inner sideband IBOC DAB signals and upper outer sideband IBOC DAB signals, and (ii) recovered source bit information from demodulation of said inner sideband IBOC DAB signals and lower outer sideband IBOC DAB signals, is less likely to be erroneous;
• and
• said receiver further including a selector for selecting, for further processing and forwarding to a user, recovered source bit information determined by said comparing device to be less likely to be erroneous.

A method of receiving a digitally modulated signal including at least partially redundantly transmitted codeword information, the method comprising the steps of:

• receiving the digitally modulated signal which has a first part of the codeword information redundant in modulation of signals in each of an upper outer sideband and a lower outer sideband relative to a center frequency of a predetermined mask so as to result in redundancy of at least part of the codeword information, and receiving a second part of the codeword information in only one of an upper inner sideband and a lower inner sideband, whereby the codeword information in said upper outer sideband is redundant to the codeword information in the lower outer sideband;
• demodulating received signals from said upper outer, said lower outer, and said one inner sidebands;
• determining which of source bit information from recovered at least partially redundant codewords, from (i) demodulation of said one inner sideband and upper outer sideband signals, and (ii) demodulation of said one inner sideband and lower outer sideband signals, is less likely to be erroneous;
• and
• selecting recovered source bit information determined in said determining step as being less likely to be erroneous.

A method of transmitting a redundant IBOC-DAB radio frequency (RF) signal in an IBOC DAB RF communication system which is robust to certain deleterious effects, the method comprising the steps of:

• providing a source message which is to be at least partially redundantly transmitted to a corresponding receiver;
• using the source message to generate codeword information, a first part of which is used to redundantly data-modulate a set of subcarrier signals in each of an upper outer sideband and a lower outer sideband of a predetermined RF mask over a plurality of baud intervals so that the respective outer sideband signals include redundant codeword information thus providing frequency diversity, and a second part of the codeword information is used to data-modulate a set of subcarrier signals in at least one of an upper inner and a lower inner sideband resulting in at least one inner sideband signal;
• time-delaying the codeword information used for the modulation of only one of the upper outer and lower outer sideband digital signals relative to the other;
• generating an analog AM-compatible monophonic signal to be transmitted;
• and
• transmitting together, via an antenna, the analog AM-compatible monophonic signal, the inner sideband signal, and the redundant outer sideband digital signals to an IBOC-DAB receiver.

A method of receiving a digitally modulated signal including codeword information, the method comprising the steps of:

• receiving the digitally modulated signal that has a first part of the codeword information redundant in an upper outer sideband and a lower outer sideband relative to a center frequency of a predetermined mask, and a second part of the codeword information non-linearly modulated in inner sidebands of the mask;
• demodulating received signals from the upper outer, lower outer, and non-linearly modulated inner sidebands;
• determining which of recovered duplicated codewords from (i) demodulation of the inner sideband signals and upper outer sideband signals, and (ii) demodulation of the said inner sideband signals and lower outer sideband signals, is less likely to be erroneous;
• and
• selecting recovered source bit information from the demodulated codeword determined in said determining step has to be likely to be erroneous.

An in-band on-channel (IBOC) digital broadcast receiver comprising:

• receiving means for receiving a redundantly transmitted IBOC digital RF signal including encoded source bit information, said receiving means for receiving a first portion of said encoded source bit information that is duplicated by modulation of signals in each of an upper outer and a lower outer sideband of a predetermined mask, and for receiving a second portion of said encoded source bit information that is used to non-linearly modulate signals in each of an upper inner sideband and a lower inner sideband, whereby the upper outer sideband signal is redundant to the lower outer sideband signal;
• demodulation means for demodulating the received IBOC digital signal in the upper outer sideband, the lower outer sideband, the upper inner sideband, and the lower inner sideband in order to determine at least partially duplicated demodulated source bit information for each at least partially redundantly transmitted codeword made up of said source bit information;
• determination means for determining whether the source bit information for the codeword having a portion thereof in the at least partially upper outer sideband or the at least partially duplicate codeword having a similar portion thereof in the lower outer sideband is less likely to be erroneous;
• and
• selection means for selecting the source bit information determined by said determination means to be less likely erroneous.