Symbol spreading method and device for OFDM systems
Assignee3Com Corporation
InventorsTimothy F. Murphy, Niels Van Erven
Life of this patent
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Abstract
A wired or wireless signal transmitter or receiver and methods providing improved signal-to-noise ratio (SNR) performance for the reception of data packets transmitted in the form of symbols modulated onto a signal. More particularly, apparatus and methods are disclosed for detecting the preamble and symbol boundaries of received data packets encoded with OFDM and other multi-carrier symbol transmission systems. Also disclosed are combinations of sensitive preamble detection and data payload and/or signal field encoding methods to spread data redundantly, to improve reception under a low SNR condition. This invention may be applied to a variety of standards utilizing OFDM and similar technologies, including IEEE 802.11a, Hiperlan/2 and MMAC.
Claims26
A method of receiving a packet in an input signal stream of complex samples, wherein the packet includes a preamble and a data payload, said preamble including a plurality of first symbols repeated at a first predetermined interval, the method comprising:
- digitizing a signal to obtain complex samples of the signal;
- calculating successive autocorrelation values for pairs of the complex samples separated by the first interval, by conjugating one complex sample of the complex sample pair and multiplying the complex sample pair together after conjugation to form a complex conjugate product, and determining an angle approximation from the complex conjugate product;
- filtering the successive autocorrelation values to form a time-averaged autocorrelation signal;
- detecting when said time-averaged autocorrelation signal exceeds a predetermined first threshold;
- aligning sampling of the data payload to a symbol boundary within the packet in response to the detection;
- determining whether the data payload is encoded according to a first mode or a redundantly spread second mode;
- and
- decoding the data payload.
A receiver capable of receiving an OFDM signal transmitted in any of at least two modes, including a first mode and a second mode in which the data payload has been redundantly spread relative to said first mode, operating on an input signal stream of complex samples, wherein the packet includes a preamble and a data payload, said preamble including a plurality of first symbols repeated at a first predetermined interval, the receiver including:
- an analog-to-digital converter that produces the complex samples;
- and
- logic to:
- calculate successive autocorrelation values for pairs of the complex samples separated by the first interval, by conjugating one complex sample of the complex sample pair and multiplying the complex sample pair together after conjugation to form a complex conjugate product, and determine an angle approximation from the complex conjugate product;
- filter the successive autocorrelation values to form a time-averaged autocorrelation signal;
- detect when said time-averaged autocorrelation signal exceeds a predetermined first threshold;
- align sampling of the data payload to a symbol boundary of the data packet in response to the detection;
- determine whether the data payload is encoded according to a first mode or a redundantly spread second mode;
- and
- decode the data payload.
Dependencies are inferred from the claim text.