Channel tracking in an OFDM wireless receiver
First Claim
1. An apparatus comprising:
- a receiver configured to wirelessly receive a packet of information that includes a known transmitted part and to digitize the received signal, the known transmitted part having subcarriers with known values;
a signal-to-tone transformer to determine the modulated subcarriers of a received signal corresponding to the received packet;
a channel storage unit coupled to the signal-to-tone transformer including;
an initial channel calculator to calculate a function of the initial channel response of subcarriers from the known part of the received packet;
a memory subsystem configured to at a first time store a function of an initial channel response corresponding to the known part of the received packet, and at later times to store additionally or instead updates to or of previous version or versions of the channel response;
a channel corrector coupled to the channel storage unit and to the signal-to-tone transformer configured to correct the modulated subcarriers of the received signal for the respective channel using the contents of the memory subsystem;
the channel corrector configured to form channel corrected constellation values for the received signal;
a decision and channel drift circuit coupled to the channel corrector to form post-decision constellation values corresponding to the channel corrected constellation values and to form a measure of the channel drift from the post decision constellation values and the pre-decision constellation values; and
an updating circuit coupled to the channel storage unit to update the memory subsystem with an updated value determined from previous contents of the memory subsystem and an update, the update determined from the memory subsystem contents and the measure of the channel drift between symbols,such that drift of the channel response is tracked.
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Abstract
An apparatus and a method to track the channel response for subcarriers in an OFDM receiver for a packet of information that includes a known transmitted part. The receiver has a signal-to-tone transformer to determine subcarriers corresponding to a received packet. The method stores a function of an initial estimate of the channel response for a subcarrier, and accepts a pre-decision constellation point value that is a post channel correction using a first estimate of the channel response. The method includes: makes a decision using the pre-decision constellation point value, re-modulates the decision to form a post-decision constellation point value, and forms a complex valued product of the function of the first estimate for the subcarrier and the complex-valued ratio of the pre-decision and post-decision values. This complex valued product forms a measure of the current channel estimate to use for updating the stored quantity.
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Citations
20 Claims
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1. An apparatus comprising:
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a receiver configured to wirelessly receive a packet of information that includes a known transmitted part and to digitize the received signal, the known transmitted part having subcarriers with known values; a signal-to-tone transformer to determine the modulated subcarriers of a received signal corresponding to the received packet; a channel storage unit coupled to the signal-to-tone transformer including; an initial channel calculator to calculate a function of the initial channel response of subcarriers from the known part of the received packet; a memory subsystem configured to at a first time store a function of an initial channel response corresponding to the known part of the received packet, and at later times to store additionally or instead updates to or of previous version or versions of the channel response; a channel corrector coupled to the channel storage unit and to the signal-to-tone transformer configured to correct the modulated subcarriers of the received signal for the respective channel using the contents of the memory subsystem;
the channel corrector configured to form channel corrected constellation values for the received signal;a decision and channel drift circuit coupled to the channel corrector to form post-decision constellation values corresponding to the channel corrected constellation values and to form a measure of the channel drift from the post decision constellation values and the pre-decision constellation values; and an updating circuit coupled to the channel storage unit to update the memory subsystem with an updated value determined from previous contents of the memory subsystem and an update, the update determined from the memory subsystem contents and the measure of the channel drift between symbols, such that drift of the channel response is tracked. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of operating an apparatus comprising a wireless receiver and a signal-to-tone transformer, the method comprising:
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the wireless receiver wirelessly receiving a signal corresponding to a packet of information, the packet being an OFDM packet that includes a known transmitted part having subcarriers with known values; transforming the received signal corresponding to the packet using the signal-to-tone transformer carrying out a signal-to-tone transformation to determining the subcarriers of the received signal corresponding to the packet; calculating a function of a channel response of subcarriers from the known part of the packet; storing the function of the channel response; channel correcting the modulated subcarriers of the received signal for the channel using the stored initial or updated function of the channel response to form channel-corrected constellation values for the received signal; forming post-decision values corresponding to the channel corrected constellation values; and forming a measure of the channel drift from the post decision values and the channel-corrected constellation values, wherein initially the function of an initial value of the channel response is stored and, as more packets are received, updates to the function or updated values of the function of the channel response are stores, the difference between a pre-update stored function of the channel response and updated values of the function of the channel response being dependent on the pre-update stored function of the channel response and on the measure of the channel drift between symbols, such that the stored function of the channel response tracks the drift of the channel response as more packets are received. - View Dependent Claims (17, 18, 19)
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20. An apparatus comprising:
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means for wirelessly receiving a signal corresponding to a packet of information, the packet being an OFDM packet that includes a known transmitted part having subcarriers with known values; means for signal-to-tone transforming the received packet to determining the subcarriers of a signal corresponding to the received packet; means for calculating a function of a channel response of subcarriers from the known part of the received packet; means for storing configured to store the function of the channel response; means for channel correcting the modulated subcarriers of the received signal for the channel using the stored initial or updated function of the channel response to form channel-corrected constellation values for the received signal; means for forming a decision to determine post-decision values corresponding to the channel corrected constellation values; and means for forming a measure of the channel drift from the post decision values and the channel-corrected constellation values, wherein initially the function of an initial value of the channel response is stored and, as more packets are received, updates to the function or updated values of the function of the channel response are stores, the difference between a pre-update stored function of the channel response and updated values of the function of the channel response being dependent on the pre-update stored function of the channel response and on the measure of the channel drift between symbols, such that the stored function of the channel response tracks the drift of the channel response as more packets are received.
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Specification