Abstract:
Systems and methods are directed to phase modulation of polar coordinates in a transmitter of wireless signals, to achieve high transmit power levels while meeting spectral mask and EVM requirements. An input signal is mapped to a sequence of modulation frequency (e.g., O-QPSK to MSK) to generate a mapped signal. A digital frequency shaping filter is applied to the mapped signal to generate a shaped signal. An adaptive rounding algorithm is applied to the shaped signal to generate a reduced bit-width signal. A digital frequency synthesizer is applied to the reduced bit-width signal to generate an analog waveform for transmission.
Abstract:
In a wireless near field communication (NFC) system, a target, such as a smart card, can communicate with an initiator, such as a card reader, by load modulating a radio frequency (RF) signal generated by the initiator. When two or more targets load modulate the RF signal generated, “collisions” can occur with the load modulation. Apparatus and methods detect the presence or absence of collisions in a lower layer or physical layer and report the presence of detected collisions to an upper layer for further handling.
Abstract:
In a wireless communication system, an initiator, such as a card reader, can communicate with a target, such as a smart card or other device emulating a smart card, by amplitude modulating a radio frequency signal. In a receiver, levels of samples of a digital baseband signal of the amplitude modulated signal can vary. Apparatus and methods associate a received sample with a hard or sliced output state (such as +1, 0, or −1) and update a value associated with the hard output state for accurate slicing of the samples. This permits the use of hard symbols in further processing rather than soft samples, which can dramatically reduce the complexity of circuitry.
Abstract:
A receiver apparatus is disclosed. In one aspect, the apparatus includes a receiverinterface configured to receive a signal from a transmitter and output an input sequence of M-bit samples. The apparatus also includes a quantizer circuit configured to convert the input sequence of M-bit samples into an output sequence of N-bit samples, wherein M and N are positive integer numbers, and wherein M is greater than N. The apparatus further includes a decoder circuit configured to decode the output sequence of N-bit samples.
Abstract:
Systems and methods are directed to low cost and low power carrier frequency offset (CFO) estimation in a receiver. In-phase (I) and quadrature (Q) samples of a wireless signal are received by the receiver and a first phase and a second phase are extracted from the outputs of a first autocorrelator with a first time-lag and a second autocorrelator with a second time-lag. The extracted first and second phases are combined to generate an estimated CFO of high accuracy and wide estimation range.
Abstract:
A method for communications is described. The method includes determining a symbol timing drift elimination amount for a received signal. The method further includes eliminating part of the symbol timing drift by adjusting a reference clock for the modem. Determining the symbol timing drift elimination amount may be based on at least one of a symbol timing drift estimate, a symbol timing error, a packet acquisition indicator, a packet validity indicator, demodulated bits or a carrier presence indicator.
Abstract:
A method for communication between near field communication (NFC) devices includes generating a transmission signal, an in-phase local oscillator signal, and a quadrature local oscillator signal from edges of an input clock signal. The method further includes mixing a load modulated signal with the in-phase local oscillator signal to generate an in-phase baseband signal. The method further includes mixing the load modulated signal with the quadrature local oscillator signal to generate a quadrature baseband signal. The method further includes adjusting a phase delay of at least one of the in-phase local oscillator signal or the quadrature local oscillator signal in response to a first signal strength of the in-phase baseband signal and a second signal strength of the quadrature baseband signal.
Abstract:
Methods, systems, and devices are described for an adaptive demodulator that supports multiple modes. An FM signal may be received at a demodulator and parameters corresponding to the FM signal may be identified. Connections between multiple modules within the demodulator may be configured, based at least in part on the parameters, to select one of multiple demodulation modes supported by the demodulator to demodulate the FM signal. The modes may include a phase differencing mode, a phase-locked loop (PLL) mode, a frequency-compressive feedback (FCF) mode, and/or a quadrature detector mode. The parameters may include one or both of a signal strength of the FM signal and a maximum frequency deviation of the FM signal. Based on the parameters, one or more signals may be generated to configure the connections within the demodulator. A switch from one mode to another may occur when one of the parameters breaches a threshold value.
Abstract:
In one aspect, a method for estimating residual carrier frequency offset (CFO) in a phase-modulated wireless signal having pseudo noise (PN) spreading is provided. The method includes receiving, at a digital transceiver, a plurality of PN spread blocks of in-phase and quadrature (I/Q) samples of the phase-modulated wireless signal and performing sample-level de-rotation, symbol-level de-spreading, and sign alignment. The method also includes estimating a phase difference and determining an estimated residual CFO based on the phase difference.
Abstract:
A method for inductively-coupled communications is described. The method includes receiving a signal. The method also includes analyzing the signal to estimate a symbol timing error. Estimating the symbol timing error may include comparing a location of a pause, a low-to-high or a high-to-low transition in the received signal with an ideal location of a pause or a transition. The method further includes adjusting symbol timing to correct for the symbol timing error.