US 7,352,691 B2Granted

Double difference phase detection

AssigneeTexas Instruments Incorporated

InventorsMark D. Hagen, Mark D. Heminger

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Abstract

A method that allows a digital communications system to detect the presence of transmitted messages in noisy environments. The system includes an OFDM transmitter and an OFDM receiver. The OFDM transmitter converts a digital signal to be transmitted to a plurality of sub-signals, each corresponding to a respective sub-carrier frequency. The signal is a packet including a preamble field having a known data pattern. The transmitter pre-codes the preamble data pattern, maps the data to corresponding phase information, converts the sub-signals to the time domain, and converts the sub-signals to analog form for subsequent transmission. The OFDM receiver receives the transmitted sub-signals, converts the sub-signals to digital form, converts the sub-signals to the frequency domain, and subjects the sub-signals to preamble detection processing to detect the signals' presence. By pre-coding the preamble data pattern and defining the received sub-signals in terms of the phase difference between adjacent sub-carriers, the detection of the transmitted messages can be performed in a manner that is insensitive to phase offset.

Claims29

Dependent claims

An orthogonal frequency division multiplexing (OFDM) communications system, comprising:

an OFDM transmitter operative to transmit at least one data packet, the data packet comprising a predetermined data pattern within a preamble field, the OFDM transmitter being further operative to convert the data packet to a plurality of data packet sub-signals, each sub-signal corresponding to a respective sub-carrier frequency, to map the sub-signals to corresponding phases, to convert the sub-signals from the frequency domain to the time domain, and to convert the sub-signals from digital to analog form for subsequent transmission at the respective sub-carrier frequencies;
and
an OFDM receiver operative to receive the transmitted data packet sub-signals, to convert the received sub-signals from analog to digital form, to convert the received sub-signals from the time domain to the frequency domain, and to detect a phase of the pre-coded preamble data pattern within each received sub-signal,
wherein the OFDM transmitter includes a preamble pre-coder operative to calculate first and second cumulative phases of sub-carriers corresponding to the predetermined preamble data pattern, and
wherein the OFDM receiver includes a preamble detector operative to calculate first and second differences between adjacent ones of the second cumulative sub-carrier phases, thereby making the detection of the phase of the pre-coded preamble data pattern insensitive to phase offset misalignment between the transmitted and received data packet sub-signals.

2 more elements

A method of operating an orthogonal frequency division multiplexing (OFDM) communications system, comprising the steps of:

providing at least one data packet, the data packet comprising a predetermined data pattern within a preamble field;
encoding the predetermined preamble data pattern within the data packet by an OFDM transmitter, including calculating first and second cumulative phases of sub-carriers corresponding to the predetermined preamble data pattern;
converting the data packet to a plurality of data packet sub-signals by the OFDM transmitter, each sub-signal corresponding to a respective sub-carrier frequency;
mapping the sub-signals to corresponding phases by the OFDM transmitter;
converting the sub-signals from the frequency domain to the time domain by the OFDM transmitter;
converting the sub-signals from digital to analog form;
transmitting the sub-signals at the respective sub-carrier frequencies by the OFDM transmitter;
receiving the transmitted data packet sub-signals by an OFDM receiver;
converting the received sub-signals from analog to digital form by the OFDM receiver;
converting the received sub-signals from the time domain to the frequency domain by the OFDM receiver;
detecting a phase of the encoded preamble data pattern within each received sub-signal by the OFDM receiver;
and
calculating first and second differences between adjacent ones of the second cumulative sub-carrier phases, thereby making the detection of the phase of the pre-coded preamble data pattern insensitive to phase offset misalignment between the transmitted and received data packet sub-signals.

10 more elements

Dependencies are inferred from the claim text.