US 7,397,758 B1Granted

Channel tracking in a OFDM wireless receiver

AssigneeCisco Technology, Inc.

InventorsBrian Hart, David J. Pignatelli, Eldad Perahia, Paul C. P. Dankoski

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Abstract

An apparatus and a method to estimate the channel response for a set of subcarriers in an OFDM receiver. The receiver receives a packet of information that includes a known transmitted part having known subcarrier values, and includes a signal-to-tone transformer to determine the subcarriers of a signal corresponding to a received packet. For each subcarrier, the method stores a function of an initial estimate of the channel response for the subcarrier, and accepts a post-channel correction pre-decision constellation point value for the subcarrier. The method further includes making a decision using the pre-decision constellation point value, re-modulating the decision to form a post-decision constellation point value, and forming 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 to forms a measure of the current channel estimate to use for updating the stored quantity.

Claims51

Dependent claims

In an OFDM receiver to wirelessly receive a packet of information that includes a known transmitted part, the receiver including a signal-to-tone transformer to determine the modulated subcarriers of a received signal corresponding to the received packet, an apparatus comprising:

a channel storage unit coupled to the signal-to-tone transformer including:
an initial channel calculator to calculate a function of an initial channel response of subcarriers from the known part of the received packet;
a memory subsystem coupled to the initial channel calculator initially to store the function of the initial channel response, and then to store updates of the function of the initial channel response;
a channel corrector coupled to the channel storage unit and to the signal-to-tone transformer to channel correct the modulated subcarriers of the received signal, the correcting using the latest updates from the contents of the memory subsystem;
the channel corrector to form channel corrected constellation values for the received signal;
a decision and channel drift circuit coupled to the channel corrector to make decisions to form post-decision values corresponding to the channel corrected constellation values and to form a measure of the channel drift using the formed post decision constellation values and the constellation values prior to the post-decision values being formed;
and
a weighting and summing circuit coupled to the channel storage unit to update the memory subsystem with a weighted sum of the pre-update function in the memory subsystem and a quantity determined from the pre-update function and the measure of the channel drift between symbols,
such that the memory subsystem contents track channel drift from symbol to symbol, the tracking according to the relative weightings of the weighted sum.

6 more elements

In an OFDM receiver to wirelessly receive a packet of information that includes a known transmitted part, the receiver including a signal-to-tone transformer to determine the subcarriers of a signal corresponding to the received packet, a method comprising:

accepting the subcarriers of the known part of the received packet;
calculating a function of the initial channel response of subcarriers from the known part of the received packet;
storing the function of the initial channel response;
storing updates of the function of the channel response as more data is accepted to form, as modulated subcarriers of the received packet are determined, updated stored function of the channel response, the storing updates including:
channel correcting the modulated subcarriers of the received packet for the channel using the stored initial or updated function of the channel response to form channel-corrected constellation values for the received signal;
decision making using the channel-corrected constellation values to form post-decision values corresponding to the channel corrected constellation values;
forming a measure of the channel drift from the post decision values and the channel-corrected constellation values;
forming a weighted sum of the stored function of the channel response and a quantity determined from the stored function of the channel response and the formed measure of the channel drift;
and
storing the weighted sum as an updated stored function of the channel response,
such that the stored function of the channel response track channel drift from symbol to symbol, the tracking according to the relative weightings of the weighted sum.

8 more elements

Dependencies are inferred from the claim text.