Acorn Technologies, Inc.

Fernando Lopez De Victoria

Steven C Thompson

Roee Kalinksy

A wireless receiver receives location pilots embedded in received symbols and uses the location pilots to detect the first path for every base station the network has designated for the receiver to use in time of arrival estimation. The receiver preferably applies matching pursuit strategies to offer a robust and reliable identification of a channel impulse response's first path. The receiver may also receive and use estimation pilots as a supplement to the location pilot information in determining time of arrival. The receiver can use metrics characteristic of the channel to improve the robustness and reliability of the identification of a CIR's first path. With the first path identified, the receiver measures the time of arrival for signals from that path and the receiver determines the observed time difference of arrival (OTDOA) to respond to network requests for OTDOA and position determination measurements.

Communication system determining time of arrival using matching pursuit

An OFDM system generates a channel estimate in the time domain for use in either a frequency domain equalizer or in a time domain equalizer. Preferably channel estimation is accomplished in the time domain using a locally generated reference signal. The channel estimator generates an initial estimate from a cross correlation between the time domain reference signal and an input signal input to the receiver and generates at least one successive channel estimate. Preferably the successive channel estimate is determined by vector addition (or subtraction) to the initial channel estimate. The at least one successive channel estimate reduces the minimum mean square error of the estimate with respect to a received signal.

Least squares channel identification for OFDM Systems

An OFDM communication system performs time domain channel estimation responsive to received symbols before the symbols are processed by a fast Fourier transform. The communication system generates virtual pilots from actual pilots to improve the stability and quality of channel estimation. The system generates a reference signal from the actual and virtual pilots and correlates the resulting reference signal with a signal responsive to the received symbol to generate an initial channel impulse response (CIR) and to determine statistics about the channel. In some circumstances, the resulting reference signal is correlated with a modified symbol in which the actual and virtual pilot locations are emphasized and the data locations are deemphasized. Time domain channel estimation iteratively improves on the initial CIR. The system determines channel estimates for data only symbols through averaging such as interpolation.

OFDM receiver with time domain channel estimation

An OFDM receiver receives OFDM symbols in the frequency domain and comb filters and then punctures the OFDM symbols to leave symbols with actual pilot information and with null values at the data symbols. The receiver provides the punctured OFDM symbols to an OFDM symbol queue. A virtual pilot interpolator is coupled to the punctured OFDM symbol storage to generate virtual pilot information introduced to OFDM symbols. The interpolator may be a two dimensional Wiener filter. The receiver also includes a time domain channel estimator that processes a first OFDM symbol including virtual pilot information to generate a channel impulse response for the first OFDM symbol. A frequency equalizer equalizes the OFDM symbol in response to the channel impulse response for the first OFDM symbol.

Block time domain channel estimation in OFDM system

An OFDM receiver generates an initial channel impulse response in response to a received OFDM signal. The receiver determines the time span within the initial channel impulse response in which significant paths are present. An intermediate channel impulse response estimator identifies paths within the initial channel impulse response and generates an improved intermediate channel impulse response. A channel impulse response estimator performs a second non-linear process to generate a channel impulse response. An equalizer responds to the channel impulse response and the OFDM symbol to equalize the OFDM symbol. Metrics are generated that can be used for effectively stopping the second iterative non-linear process.

Non-linear time domain channel estimation in OFDM systems

A receiver performs interference mitigation under blind or semi-blind conditions using diversity present in the signal of interest or in the interferer. A first path interference mitigation procedure extracts training information from received signals, performs interference mitigation on the training information and estimates the channel. The second path interference mitigation procedure uses data extracted from the received signal and the channel estimate to perform interference mitigation. Each interference mitigation process can take the form of a lossy compression followed by decompression.

Communication system and method using subspace interference cancellation

Least squares channel identification for OFDM systems

A communication system includes a channel shortening filter to reduce intersymbol interference and facilitate recovery of communications. The channel shortening filter preferably includes a energy concentration filter that optimizes SNR or SINR or other performance criterion and a impulse response tail canceller filter that eliminates energy or, equivalently, cancels coefficients outside the allowed delay-spread window for the channel. Preferably the filters are calculated using signal decomposition.

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San Francisco, CA, United States of America

Fernando Lopez De Victoria