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US 8,411,807 B1Granted
Mid-packet clear channel assessment
AssigneeCisco Technology, Inc.
InventorsRaghuram Rangarajan, Brian Donald Hart, Paul J. Stager
Life of this patent
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Abstract
A mid-packet detection technique is provided that detects a packet with periodic repetitions of a fixed duration at a point in time of the packet other than a start-of-packet pattern, e.g., a preamble, associated with the packet. The process performs packet detection without detecting a preamble and does not require carrier frequency recovery, timing recovery (synchronization) or channel estimation. In one embodiment, a doubly differential matched filter autocorrelation of the received signal is computed and used as a metric for packet detection when the preamble is not observed or to complement preamble detection. The metric is compared to a threshold to indicate detection of a packet.
Claims24
A method comprising:
- receiving energy in a frequency band and producing a receive signal representative thereof:
- analyzing the receive signal to detect occurrence of a packet associated with a transmission by a communication device at a point in time during a payload portion of the packet, wherein the payload portion of the packet comprises a plurality of segments that occur at regular intervals throughout a duration of the packet and each of the segments comprises a first portion and a second portion that contains and repeats part of the first portion, and wherein analyzing is based on a repetition period of the segments and a duration of the second portion of the segments of the packet and comprises computing a metric representing a doubly differential matched filter autocorrelation of the receive signal and comparing the metric with a threshold, which when exceeded, indicates presence of a packet in the receive signal;
- and
- detecting an in-progress packet transmitted by the communication device in a particular frequency channel within the frequency band based on said analyzing.
1 more element
A method comprising:
- receiving energy in a frequency band and producing a receive signal representative thereof;
- analyzing the receive signal to detect occurrence of a packet associated with a transmission by a communication device at a point in time during a payload portion of the packet, wherein the payload portion of the packet comprises a plurality of segments that occur at regular intervals throughout a duration of the packet and each of the segments comprises a first portion and a second portion that contains and repeats part of the first portion, wherein the first portion comprises a data interval containing data and the second portion comprises a guard interval that includes a cyclic extension that repeats a portion of the data contained in the data interval, wherein analyzing is based on the repetition period of the segments and a duration of the guard interval of the segments of the packet by:
- delaying the receive signal by an amount equal to a duration of the data interval to produce a delayed receive signal;
- computing an autocorrelation of the delayed receive signal to produce a first autocorrelation signal;
- computing a moving average of the first autocorrelation signal to match filter peaks that may be contained in the first autocorrelation signal arising from the duration of the guard interval and produce a peak matched filtered signal representative thereof;
- computing an autocorrelation of the peak matched filtered signal at a delay corresponding to the repetition period of the segments to produce a second autocorrelation signal;
- computing an average of the second autocorrelation signal at points spaced by a period of time corresponding to the repetition period and over a plurality of segment intervals to output an average signal comprising peaks that regularly occur at a time interval corresponding to the repetition period;
- and
- comparing a magnitude of the peaks in the average signal with a threshold and generating an output indicating detection of a packet when the magnitude of any one of the peaks exceeds the threshold;
- detecting an in-progress packet transmitted by the communication device in a particular frequency channel within the frequency band based on said analyzing.
7 more elements
An apparatus comprising:
- a receiver that is configured to produce a receive signal from detected energy in a frequency band;
- a modem coupled to the receiver, wherein the modem is configured to analyze the receive signal to detect occurrence of a packet associated with a transmission by a communication device at a point in time during a payload portion of the packet;
- and
- a transmitter coupled to the modem, wherein the transmitter is configured to make a transmission based on a transmit signal received from the modem;
- wherein the modem is configured to detect an in-progress packet transmitted by the communication device in a particular frequency channel within the frequency band, wherein the payload portion of the packet comprises a plurality of segments that occur at regular intervals throughout a duration of the packet and each of the segments comprises a first portion and a second portion that contains and repeats part of the first portion, and wherein the modem is configured to analyze the received signal based on a repetition period of the segments and a duration of the second portion of the segments of the packet by computing a metric representing a doubly differential matched filter autocorrelation from the receive signal and comparing the metric to a threshold, which when exceeded, indicates presence of a packet in the receive signal.
2 more elements
An apparatus comprising:
- a receiver that is configured to produce a receive signal from detected energy in a frequency band;
- a modem coupled to the receiver, wherein the modem is configured to analyze the receive signal to detect occurrence of a packet associated with a transmission by a communication device at a point in time during a payload portion of the packet, wherein the payload portion of the packet comprises a plurality of segments that occur at regular intervals throughout a duration of the packet and each of the segments comprises a first portion and a second portion that contains and repeats part of the first portion, wherein the first portion comprises a data interval containing data and the second portion comprises a guard interval that includes a cyclic extension that repeats a portion of the data contained in the data interval, and wherein the modem is configured to analyze the receive signal on the basis of the repetition period of the segments and a duration of the guard interval of the segments of the packet by:
- delaying the receive signal by an amount equal to a duration of the data interval to produce a delayed receive signal;
- computing an autocorrelation of the delayed receive signal to produce a first autocorrelation signal;
- computing a moving average of the first autocorrelation signal to match filter peaks that may be contained in the first autocorrelation signal arising from the duration of the guard interval and produce a peak matched filtered signal representative thereof;
- computing an autocorrelation of the peak matched filtered signal at a delay corresponding to the repetition period of the segments to produce a second autocorrelation signal;
- computing an average of the second autocorrelation signal at points spaced by a period of time corresponding to the repetition period and over a plurality of segment intervals to output an average signal comprising peaks that regularly occur at a time interval corresponding to the repetition period;
- and
- comparing a magnitude of the peaks in the average signal with a threshold and generating an output indicating detection of a packet when the magnitude of any one of the peaks exceeds the threshold;
- and
- a transmitter coupled to the modem, wherein the transmitter is configured to make a transmission based on a transmit signal received from the modem;
- wherein the modem is configured to detect an in-progress packet transmitted by the communication device in a particular frequency channel within the frequency band.
9 more elements
A non-transitory computer readable media storing software instructions for execution by a processor, and when executed operable to:
- analyze a receive signal derived from energy detected in a frequency band to detect occurrence of a packet associated with a transmission by a communication device at a point in time during a payload portion of the packet, wherein the instructions operable to analyze comprise instructions operable to compute a metric representing a doubly differential matched filter autocorrelation from the receive signal and to compare the metric to a threshold, which when exceeded, indicates presence of a packet in the receive signal;
- and
- detect an in-progress packet transmitted by the communication device in a particular frequency channel within the frequency band based on the analysis.
Dependencies are inferred from the claim text.