The present disclosure provides a method and a system to estimate LO leakage and quadrature error parameters for a transmitter RF front end, such as a direct up-conversion transmitter RF front end, in a joint fashion. The proposed method utilizes a PN sequence inserted at the transmitter baseband. At the observation receiver side, an RX accumulator is implemented to sum receiver signals to take advantage of a despreading gain using the same PN sequence from transmitter side. Through the despreading process, the receiver-transmitter channel may be estimated and used to extract the quadrature error parameters. The estimated channel may also be used to eliminate user data interference presented within the RX accumulator output, which may further be used to compute the LO leakage.

An apparatus for wireless communication is disclosed that performs zero-crossing-avoidance encoding for quadrature amplitude modulation. In an example aspect, the apparatus includes a polar transceiver configured to be coupled to an antenna. The polar transceiver is configured to transmit, via the antenna, data including multiple symbols associated with quadrature amplitude modulation. The multiple symbols include multiple sets of two consecutive symbols. An absolute value of a phase difference between the two consecutive symbols within each set of the multiple sets is substantially different than 180 degrees.