Flexible multimode QAM modulator
First Claim
1. A method of baseband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
- said method comprising the steps of;
generating a plurality of inphase (I) and quadrature (Q) components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation;
bandlimiting, quantizing, interpolating, and pre-compensating said I and Q components a digital signal for a sinc (sin x/x) function amplitude roll off by utilizing a Polyphase filter at a baseband frequency;
converting a plurality of digital symbols into an analog signal by using a D/A converter in each I and Q channels separately;
prefiltering by a lowpass analog antialiasing prefilter an I analog signal in an I channel, and an Q analog signal in a Q channel separately; and
complexly combining said I component and said Q component of said analog signal by an (I/Q) modulator to generate a real analog RF signal at an interpolated sampling rate.
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Abstract
A method of baseband/passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate. The method comprises the following steps: (1) generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; (2) selecting a passband or a baseband mode; and (3) generating an analog output signal in the passband or baseband mode. The step of selecting the passband or the baseband mode depends on the complexity of QAM constellation. If QAM constellation includes less than 64 QAM plant points, the passband mode is selected, and if QAM constellation includes more than 64 QAM plant points, the baseband mode is selected. If the QAM constellation includes less than 64 QAM plant points, initially selecting the passband mode until a D/A conversion speed reaches a maximum passband conversion speed, and until an output symbol rate reaches a maximum passband symbol output rate, and subsequently switching to the baseband mode in order to double the maximum passband conversion speed and to double the maximum passband symbol output rate.
66 Citations
29 Claims
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1. A method of baseband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
- said method comprising the steps of;
generating a plurality of inphase (I) and quadrature (Q) components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; bandlimiting, quantizing, interpolating, and pre-compensating said I and Q components a digital signal for a sinc (sin x/x) function amplitude roll off by utilizing a Polyphase filter at a baseband frequency; converting a plurality of digital symbols into an analog signal by using a D/A converter in each I and Q channels separately; prefiltering by a lowpass analog antialiasing prefilter an I analog signal in an I channel, and an Q analog signal in a Q channel separately; and complexly combining said I component and said Q component of said analog signal by an (I/Q) modulator to generate a real analog RF signal at an interpolated sampling rate. - View Dependent Claims (2, 3, 4, 5, 6, 7)
- said method comprising the steps of;
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8. A method of passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
- said method comprising the steps of;
generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; bandlimiting, quantizing, and interpolating said plurality of symbols by utilizing a Polyphase filter at a passband IF frequency; pre-compensating said I and Q components of a digital signal having an IF carrier signal for a sinc (sin x/x) function amplitude roll off caused by an output D/A converter by using a complex shaping filter; upconverting said I and said Q components of the digital signal to a RF carrier via a digital complex multiplier and discarding a Q output component of said digital signal; converting an I output component into an analog RF output signal using said output D/A converter; and filtering out images of a real output RF analog signal by using a lowpass analog reconstruction filter. - View Dependent Claims (9, 10, 11, 12, 13)
- said method comprising the steps of;
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14. A method of baseband/passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate:
- said method comprising the steps of;
generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; if said QAM constellation includes less than 64 QAM plant points, initially selecting a passband mode until a D/A conversion speed reaches a maximum passband conversion speed, and until an output symbol rate reaches a maximum passband symbol output rate, and subsequently switching to a baseband mode in order to double said maximum passband conversion speed and to double said maximum passband symbol output rate; and generating an analog output signal in said passband or baseband mode.
- said method comprising the steps of;
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15. A method of baseband/passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
- said method comprising the steps of;
generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; selecting a passband or a baseband mode; and generating an analog output signal in said passband or baseband mode;
wherein if said baseband mode is selected, said step of generating said analog output signal further includes the steps of;converting said plurality of digital symbols into an analog signal by using a D/A converter in each said I and Q channels separately; prefiltering by a lowpass analog antialiasing prefilter each said analog signal in each said I and Q channels separately; and complexly combining said I component and said Q component of said analog signal to generate a real analog RF signal at an interpolated sampling rate. - View Dependent Claims (16)
- said method comprising the steps of;
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17. A method of baseband/passband digital modulation for a data transmission system;
- wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
said method comprising the steps of;generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; selecting a passband or a baseband mode; and generating an analog output signal in said passband or baseband mode; said step of selecting said passband mode or said passband mode further including the following steps; bandlimiting, quantizing, and interpolating said plurality of symbols by utilizing a Polyphase filter in each said I and Q channels separately at a passband IF frequency; introducing a predistortion correction error signal in each said I and Q channels separately in order to pre-compensate for a further compression by a High Power Amplifier (HPA); pre-compensating said I and Q components of said digital signal having said IF carrier signal for a sync (sin x/x) function amplitude roll off caused by an output D/A converter by using a complex shaping filter; upconverting said I and said Q components of the digital signal to a RF carrier via a digital complex multiplier and discarding said Q output component of said digital signal; converting said I output component into an analog RF output signal using said output D/A converter; and filtering out images of said real output RF analog signal by using a lowpass analog reconstruction filter.
- wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
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18. An apparatus for baseband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
- said apparatus comprising;
a means for generating a plurality of inphase (I) and quadrature (Q) components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; a means for bandlimiting, quantizing, interpolating, and pre-compensating said I and Q components of a digital signal for a sync (sin x/x) function amplitude roll off at a baseband frequency; a means for converting a plurality of digital symbols into an analog signal; a means for prefiltering an I analog signal in an I channel, and a Q analog signal in a Q channel separately; and a means for complexly combining said I component and said Q component of said analog signal to generate a real analog RF signal at an interpolated sampling rate. - View Dependent Claims (19, 20, 21, 22, 23)
- said apparatus comprising;
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24. An apparatus for passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
- said apparatus comprising;
a means for generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; a means for bandlimiting, quantizing, and interpolating a plurality of symbols at a passband IF frequency; a means for pre-compensating said I and Q components of a digital signal having an IF carrier signal for a sinc (sin x/x) function amplitude roll off; a means for upconverting said I and said Q components of the digital signal to a RF carrier; a means for converting said I output component into an analog RF output signal; and a means for filtering out images of a real output RF analog signal. - View Dependent Claims (25, 26, 27, 28)
- said apparatus comprising;
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29. An apparatus for baseband/passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate;
- said apparatus comprising;
a means for generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; a means for selecting a passband or a baseband mode; and a means for generating an analog output signal in said passband or baseband mode; wherein said means for selecting said passband or said baseband mode further includes the following algorithm; if said QAM constellation includes less than 64 QAM plant points, initially selecting said passband mode until a D/A conversion speed reaches a maximum passband conversion speed, and until an output symbol rate reaches a maximum passband symbol output rate, and subsequently switching to said baseband mode in order to double said maximum passband conversion speed and to double said maximum passband symbol output rate.
- said apparatus comprising;
Specification