Techniques are described for accurate tracking of a radiofrequency (RF) carrier for amplitude-modulated signals in unstable reference clock environments. For example, some embodiments operate in context of clock circuits in devices configured for near-field communication (NFC) card emulation (CE) mode. The clock circuits seek to generate an internal clocking signal by tracking a clock reference, such as an RF carrier. In some cases, the clock reference can unpredictably become unreliable for periods of time, during which continued tracking of the unreliable clock reference can yield appreciable frequency and phase errors in the generated internal clocking signal. Embodiments implement phase delta detection with time limiting to limit the magnitude of such errors in the internal clocking signal introduced while tracking an unreliable clock reference. For example, embodiments force gating of phase tracking signals to limit their duration, thereby limiting impacts of those phase tracking signals on the clock circuit output.

According to one aspect of the present disclosure, there is provided a device that includes: a first quadrature modulator configured to receive an in-phase portion of a baseband signal and a quadrature portion of the baseband signal, and to produce a first portion of an output signal according to the in-phase and quadrature portions of the baseband signal; a second quadrature modulator configured to receive a first modified signal and a second modified signal, and to produce a second portion of the output signal according to the first and second modified signals; an output circuit configured to sum the first and second portions of the output signal, and to transmit the output signal to an antenna; and a mode selection circuit configured to turn on the first quadrature modulator, to receive a control signal, and to determine whether to turn on the second quadrature modulator according to the control signal.

Embodiments of this application provide a method for sending carrier information, and the method includes: performing, by a base station, subcarrier mapping on a first carrier in a first subcarrier mapping manner, where subcarriers corresponding to the first subcarrier mapping manner have frequency offset of a first offset value relative to subcarriers corresponding to a second subcarrier mapping manner, and the subcarriers corresponding to the second subcarrier mapping manner are symmetric with respect to a carrier center frequency of the first carrier, and include no subcarrier on the carrier center frequency of the first carrier; and sending, by the base station, indication information to a terminal, where the indication information carries information about the first offset value.

According to one aspect of the present disclosure, there is provided a device that includes: a first quadrature modulator configured to receive an in-phase portion of a baseband signal and a quadrature portion of the baseband signal, and to produce a first portion of an output signal according to the in-phase and quadrature portions of the baseband signal; a second quadrature modulator configured to receive a first modified signal and a second modified signal, and to produce a second portion of the output signal according to the first and second modified signals; an output circuit configured to sum the first and second portions of the output signal, and to transmit the output signal to an antenna; and a mode selection circuit configured to turn on the first quadrature modulator, to receive a control signal, and to determine whether to turn on the second quadrature modulator according to the control signal.

A generating unit that generates phase difference-added first data obtained by adding a phase change according to second data to a first signal indicating first data and a transmitting unit that transmits the phase difference-added first data are provided, and thus the first data and the second data can be transmitted through a simple configuration.

Techniques are disclosed implementing a radio partitioning architecture using multiple data streams over a single coaxial cable that does not require external RF filtering. This provides a flexible frequency scheme (e.g., using IF frequency adjustment) that enables the avoidance of Wi-Fi and LTE harmonics. The techniques include leveraging baseband filtering, which may be integrated with the radio head in a common radio frequency intergraded circuit (RFIC).

Methods and systems for estimating a symbol timing error for an offset quadrature phase shift keying (O-QPSK) modulated signal. The method includes: receiving a plurality of complex samples representing an O-QPSK modulated signal, wherein if the O-QPSK modulated signal is sampled on time each of the plurality of samples has substantially no imaginary component; generating an early error metric and a late error metric for each sample, the early error metric based on the imaginary component for the sample and a sign of a real component of a previous sample and the late error metric based on the imaginary component for the sample and a sign of a real component of a next sample; generating a combined early error metric based on the early error metrics for the plurality of samples; generating a combined late metric based on the late error metrics for the plurality of samples; and generating an estimate of the symbol timing error based on the combined early error metric and the combined late metric.

According to one aspect of the present disclosure, there is provided a device that includes: a first quadrature modulator configured to receive an in-phase portion of a baseband signal and a quadrature portion of the baseband signal, and to produce a first portion of an output signal according to the in-phase and quadrature portions of the baseband signal; a second quadrature modulator configured to receive a first modified signal and a second modified signal, and to produce a second portion of the output signal according to the first and second modified signals; an output circuit configured to sum the first and second portions of the output signal, and to transmit the output signal to an antenna; and a mode selection circuit configured to turn on the first quadrature modulator, to receive a control signal, and to determine whether to turn on the second quadrature modulator according to the control signal.

Embodiments of this application provide a method for sending carrier information, and the method includes: performing, by a base station, subcarrier mapping on a first carrier in a first subcarrier mapping manner, where subcarriers corresponding to the first subcarrier mapping manner have frequency offset of a first offset value relative to subcarriers corresponding to a second subcarrier mapping manner, and the subcarriers corresponding to the second subcarrier mapping manner are symmetric with respect to a carrier center frequency of the first carrier, and include no subcarrier on the carrier center frequency of the first carrier; and sending, by the base station, indication information to a terminal, where the indication information carries information about the first offset value.

According to one aspect of the present disclosure, there is provided a device that includes: a first quadrature modulator configured to receive an in-phase portion of a baseband signal and a quadrature portion of the baseband signal, and to produce a first portion of an output signal according to the in-phase and quadrature portions of the baseband signal; a second quadrature modulator configured to receive a first modified signal and a second modified signal, and to produce a second portion of the output signal according to the first and second modified signals; an output circuit configured to sum the first and second portions of the output signal, and to transmit the output signal to an antenna; and a mode selection circuit configured to turn on the first quadrature modulator, to receive a control signal, and to determine whether to turn on the second quadrature modulator according to the control signal.