A digital transmission system includes a transmitter configured to transmit an orthogonal frequency division multiplexing (OFDM) signal along a signal path, a receiver for receiving the OFDM signal from the transmitter and extracting OFDM symbols from the received OFDM signal, and a diagnostic unit configured to (i) demodulate the received OFDM signal to create an ideal signal, (ii) compare the received OFDM signal with the ideal signal to calculate an error signal, (iii) cross-correlate the error signal with the ideal signal, and (iv) determine a level nonlinear distortion from one of the transmitter and the signal path based on the correlation of the error signal with the ideal signal.

Methods and systems are provided for using error related feedback during signal processing. During handling of an input signal, each of a plurality of sub-carriers in the input signal is processed, and error-related information for each one of the plurality of sub-carriers is determined based on the processing. Aggregate error-related information is generated based on error-related information of each of one of the plurality of sub-carriers, and subsequent processing of at least one of the sub-carriers is adjusted based on the aggregate error-related information. The error-related information may comprise phase error-related information. Adjustments to subsequent processing of one or more of the sub-carriers may be determined based on processing-related information corresponding to different stages during processing of each of the plurality of sub-carriers.

The present disclosure provides a method implemented in a wireless communication device for estimating a frequency offset between a carrier frequency of a received signal and a frequency of a local oscillator as well as the wireless communication device. The method comprises determining a plurality of phase change candidates for a phase change between a data symbol and a first reference symbol in the signal. The method further comprises generating a collection of constellation symbols from the data symbol and rotating the collection of constellation symbols by the plurality of phase change candidates. Then, one of the phase change candidates corresponding to one of the rotated collections of constellation symbols is selected in such a manner that said one of the rotated collections of constellation symbols matches a set of constellation points best. Next, the frequency offset is determined based on the selected phase change candidate.

A robust frequency drift tracking receiver. The received signal is translated to an intermediate frequency in the RF stage by a quadrature demodulator, and is then brought into the base band by a digital mixer made by a CORDIC. A base band processing, stage allows for a synchronisation of the receiver relative to the data frame, to estimate data and to output a counter-reaction signal to the CORDIC, obtained by integration of successive frequency corrections with a predetermined step.

A method for estimating a time offset of a transmitted signal which comprises pilot symbols and data symbols, the method comprising: receiving the transmitted signal to produce a received signal; and processing an optimizing function of the received signal at a finite number of possible time offsets to produce an estimator of the time offset.

A device may demodulate a set of OFDM data-pilot symbols and select a subset of based at least in part on the position of each data pilot on a constellation map (e.g., how close the data pilot symbol is to an actual constellation point). The device may then perform a data-pilot-based phase estimation based at least in part on the selected subset. The device may also reduce the number of data pilots by partitioning a set of subcarriers into groups and selecting a representative subcarrier from each group. The phase estimation may then be based on the data pilots received on the selected subcarriers. In some cases, the device may also generate a smooth phase signal based on a linear regression algorithm including a phase averaging and a phase offset estimation and perform the phase estimation using the smooth phase signal.

Methods, apparatus and systems for reference signal configuration in a wireless communication are disclosed. In one embodiment, a method performed by a wireless communication device is disclosed. The method comprises: generating a pilot signal occupying N symbol resources, wherein the pilot signal includes at least one most sparse reference signal (RS) port that is determined from a predetermined pool of most sparse RS ports, wherein the predetermined pool includes at least N most sparse RS ports, wherein N is an integer larger than one; and transmitting a signal comprising the pilot signal to a wireless communication node.