National Instruments Corporation

I Zakir Ahmed

Vijaya Yajnanarayana

Krishna Bharadwaj

Craig Eugene Rupp

Ramesh Krishnan

Gerardo Orozco Valdes

Sartaj Chaudhary

Ramanujeya Lakshminarayan Narahari

A mechanism for determining an error vector magnitude EVMfor a signal transmitted by a device under test (DUT). A receiver (typically an RF signal analyzer) produces a baseband signal in response to the signal transmission. An OFDM input signal (derived from the baseband signal) is accessed from memory. The OFDM input signal includes a sequence of time-domain OFDM input symbols. A reference signal is accessed from the memory. The reference signal includes a sequence of time-domain OFDM reference symbols. EVMis computed in the time domain based on a time-domain difference signal, i.e., a time-domain difference between the sequence of time-domain OFDM input symbols and the sequence of time-domain OFDM reference symbols. The error vector magnitude EVMis determined without transforming the sequence of time-domain OFDM input symbols to the frequency domain. The error vector magnitude EVMis related to a standard-defined composite EVM by a scalar multiple.

Time-domain mechanism for computing error vector magnitude of OFDM signals

Method and system for a test process. The method may include performing tests on one or more units under test (UUTs). At least one test on one or more UUTs may be performed. A signal may be acquired from the UUT. A reference signal may be retrieved. The reference signal may be derived from a transmitted signal characteristic of the UUT. The signal may be analyzed with respect to the reference signal. Results, useable to characterize the one or more UUTs, from performing the at least one test on the one or more UUTs may be stored. The reference signal may be derived from an initial test and may be stored for subsequent retrieval. A respective reference signal may be retrieved for all UUTs of the one or more UUTs for a respective test. The signal may be a radio frequency signal. The UUT may be a wireless mobile device.

Unit testing and analysis of multiple UUTs

Unit testing and analysis using a stored reference signal

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 system and method for estimating carrier frequency offset &#x394;f and carrier phase offset &#x3c6;inherent in a received CPM signal. Samples of a continuous phase modulated (CPM) signal are received. A maximum of an objective function J is determined over a two-dimensional region parameterized by frequency offset v and phase offset w. The coordinates vand wof a maximizing point in the region represent estimates of the carrier frequency offset &#x394;f and the carrier phase offset &#x3c6;. To evaluate the objective function J at a point (v,w), apply a frequency shift of amount &#x2212;v and a phase shift of amount &#x2212;w to the received samples to obtain modified samples, and perform Viterbi demodulation on the modified samples to obtain a winning path metric value at a final time. The winning path metric value is the objective function value J(v,w).

Maximizing the viterbi winning path metric to estimate carrier frequency and phase offsets in continuous phase modulated signals

Maximizing the viterbi winning path metric to estimate carrier phase offset in continuous phase modulated signals

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 computer-implemented system and method for blind demodulation of an offset QPSK input signal, involving repeatedly performing a set of operations, including: (a) applying a phase correction to the input signal based on an estimate of a carrier phase offset of the input signal to obtain a first modified signal; (b) shifting a quadrature component of the first modified signal by half a symbol period relative to an inphase component to obtain a second modified signal; (c) extracting a first sequence of symbols from the second modified signal, where the extraction includes estimating a symbol timing offset from the second modified signal; (d) performing hard-decision demodulation on the first sequence of symbols to obtain a second sequence of reference symbols; (e) computing a phase difference between the first sequence of symbols and second sequence of reference symbols; and (f) updating the carrier phase offset estimate using the phase difference.

Blind mechanism for demodulating offset QPSK signals in the presence of carrier phase error

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

I Zakir Ahmed