National Instruments Corporation

Krishna Bharadwaj

Vijaya Yajnanarayana

I Zakir Ahmed

Ramesh Krishnan

A low complexity system and method for operating a receiver in order to estimate an offset between the actual sample clock rate 1/T' of a receiver and an intended sample clock rate 1/T. The receiver captures samples of a received baseband signal at the rate 1/T&#x2032;, operates on the captured samples to generate an estimate for the clock rate offset, and fractionally resamples the captured samples using the clock rate offset. The resampled data represents an estimate of baseband symbols transmitted by the transmitter. The action of operating on the captured samples involves computing an error vector signal and then estimating the clock rate offset using the error vector signal. The error vector signal may be computed in different ways depending on whether or not carrier frequency offset and carrier phase offset are assumed to be present in the received baseband signal.

Estimation of sample clock frequency offset based on error vector magnitude

A mechanism for jointly correcting carrier phase and carrier frequency errors in a demodulated signal. A computer system may receive samples of a baseband input signal (resulting from QAM demodulation). The computer system may compute values of a cost function J over a grid in a 2D angle-frequency space. A cost function value J(&#x3b8;,&#x3c9;) is computed for each point (&#x3b8;,&#x3c9;) in the grid by (a) applying a phase adjustment of angle &#x3b8; and a frequency adjustment of frequency &#x3c9; to the input signal; (b) performing one or more iterations of the K-means algorithm on the samples of the adjusted signal; (c) generated a sum on each K-means cluster; and (d) adding the sums. The point (&#x3b8;, &#x3c9;) in the 2D angle-frequency space that minimizes the cost function J serves an estimate for the carrier phase error and carrier frequency error. The estimated errors may be used to correct the input signal.

Blind estimation of frequency and phase offsets for received signals

Using error vector magnitude to estimate sample clock frequency offset

A mechanism for jointly correcting carrier phase and carrier frequency errors in a demodulated signal. A computer system may receive samples of a baseband input signal (resulting from QAM demodulation). The computer system may compute values of a cost function J over a grid in a 2D angle-frequency space. A cost function value J(&#x3b8;,&#x3c9;) is computed for each point (&#x3b8;,&#x3c9;) in the grid by (a) applying a phase adjustment of angle &#x3b8; and a frequency adjustment of frequency &#x3c9; to the input signal; (b) performing one or more iterations of the K-means algorithm on the samples of the adjusted signal; (c) generated a sum on each K-means cluster; and (d) adding the sums. The point (&#x3b8;,&#x3c9;) in the 2D angle-frequency space that minimizes the cost function J serves an estimate for the carrier phase error and carrier frequency error. The estimated errors may be used to correct the input signal.

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Bengaluru, India

Krishna Bharadwaj