Data transmission via multi-path channels using orthogonal multi-frequency signals with differential phase shift keying modulation
First Claim
1. A data communications system, for use over a multi-path channel, comprising:
- an orthogonal frequency division multiplexing (OFDM) sub-carrier signal generator that outputs a plurality of OFDM sub-carrier signals;
a differential quadrature phase shift keying (DQPSK) modulator that modulates each OFDM sub-carrier signal in response to input data, and forms a plurality of modulated OFDM sub-carrier signals in response to input data;
a summer that combines the plurality of modulated OFDM sub-carrier signals to form a transmitted signal;
a receiver to output a received signal in response to the transmitted signal transmitted through the multi-path channel;
an OFDM sub-carrier reference generator that outputs a plurality of OFDM sub-carrier reference signals;
a synchronizer that synchronizes an OFDM symbol interval to a demodulating interval by minimizing a length of a vector formed by correlating the received signal and the plurality of OFDM sub-carrier reference signals; and
a demodulator, using a DQPSK multi-carrier detector, that demodulates the received signal to form an output signal.
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Accused Products
Abstract
A method and an apparatus relating to an OFDM data communications system where the sub-carriers are modulated using differential quadrature phase-shift keying (DQPSK). The multi-carrier transmitted signal is directly generated using a summation of pre-computed sample points. As part of the multi-carrier signal generation, a signal for the guard interval is established. In an acoustic application of this approach, direct radiation of the sub-carrier approach is facilitated. Symbol synchronization in the receiver is based on signal correlation with the missed sub-carrier. Separation of the sub-carriers in the receiver uses a correlation of the received signal and reference signals that are derived from a table of pre-computed values. Optimal non-coherent processing of the sub-carriers without any phase tracking procedures is achieved.
211 Citations
15 Claims
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1. A data communications system, for use over a multi-path channel, comprising:
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an orthogonal frequency division multiplexing (OFDM) sub-carrier signal generator that outputs a plurality of OFDM sub-carrier signals; a differential quadrature phase shift keying (DQPSK) modulator that modulates each OFDM sub-carrier signal in response to input data, and forms a plurality of modulated OFDM sub-carrier signals in response to input data; a summer that combines the plurality of modulated OFDM sub-carrier signals to form a transmitted signal; a receiver to output a received signal in response to the transmitted signal transmitted through the multi-path channel; an OFDM sub-carrier reference generator that outputs a plurality of OFDM sub-carrier reference signals; a synchronizer that synchronizes an OFDM symbol interval to a demodulating interval by minimizing a length of a vector formed by correlating the received signal and the plurality of OFDM sub-carrier reference signals; and a demodulator, using a DQPSK multi-carrier detector, that demodulates the received signal to form an output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A data transmitter, for use over a multi-path channel, comprising:
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an orthogonal frequency division multiplexing (OFDM) sub-carrier signal generator that outputs a plurality of OFDM sub-carrier signals; a differential quadrature phase shift keying (DQPSK) modulator that modulates each OFDM sub-carrier signal in response to input data, and forms a plurality of modulated OFDM sub-carrier signals in response to input data, the plurality of modulated OFDM sub-carrier signals being pilot-free and comprising a sequence of equally-spaced modulated OFDM sub-carrier signals having a single missing modulated OFDM sub-carrier signal located at a median frequency of the plurality of modulated OFDM sub-carrier signals, wherein the DQPSK modulator comprises a decimal transformation device, a modulo-4 summation device, and a switch controller device; and a summer that combines the plurality of modulated OFDM sub-carrier signals to form a transmitted signal.
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9. A data receiver, for use over a multi-path channel, comprising:
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a receiver to output a received signal in response to a transmitted signal transmitted through the multi-path channel; an orthogonal frequency division multiplexing (OFDM) sub-carrier reference generator that outputs a plurality of OFDM sub-carrier reference signals; a synchronizer that synchronizes an OFDM symbol interval to a demodulating interval by minimizing a length of a vector formed by correlating the received signal and the plurality of OFDM sub-carrier reference signals, wherein the plurality of OFDM sub-carrier reference signals are associated with a missed sub-carrier; and a demodulator, using a differential quadrature phase shift keying (DQPSK) multi-carrier detector, that demodulates the received signal to form an output signal. - View Dependent Claims (10, 11)
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12. A method for data communications, comprising the steps of:
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generating a plurality of orthogonal frequency division multiplexing (OFDM) sub-carrier transmitter signals; modulating, using differential quadrature phase shift keying (DQPSK), each OFDM sub-carrier transmitter signal to forma plurality of modulated OFDM sub-carrier signals; summing the plurality of modulated OFDM sub-carrier signals to form a transmitted signal; transmitting the transmitted signal through a multi-path channel; receiving the transmitted signal to form a received signal; generating a plurality of OFDM sub-carrier reference signals; synchronizing an OFDM symbol interval and a demodulating interval by minimizing a length of a vector formed by correlating the received signal and the plurality of OFDM sub-carrier reference signals; and demodulating, using a DQPSK multi-carrier detector, the received signal to form an output signal, wherein the generating, modulating, summing, transmitting, receiving, generating, synchronizing and demodulating are performed by one or more circuits. - View Dependent Claims (13, 14, 15)
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Specification