A 423.5-450 MHz low-power OOK/FSK/QPSK wireless transmitter is proposed with multi-phase injection locking and frequency multiplication techniques. A low-frequency phase-rotation-based frequency synthesizer is employed to provide multichannel support and FSK modulation. The far-out phase noise caused by the quantization noise of the$\Delta \Sigma $modulator is filtered through a proposed N-path filter and two-stage injection-locked ring oscillators (ILROs). Phase modulation is achieved by changing the offset frequency between the oscillator free-running frequency and the injected frequency to control the steady-state phase offset of the injection-locked oscillator. Finally, a current mode class-D edge-combining power amplifier with high energy efficiency is used to achieve 5X frequency multiplication to generate the required carrier frequency. A prototype transmitter is fabricated in TSMC 90 nm CMOS process. It is shown that the device delivers an output power of −7 dBm with a power consumption of$870 \mu \text{W}$under a 0.75 V supply voltage and supports data rates of 40/5/80 Mbps under OOK/BFSK/QPSK modulation, respectively, achieving the energy efficiency of 11 pJ/bit and 23% global efficiency.

In-station Wi-Fi AP deployment provides opportunistic Wi-Fi access in underground Mass Rapid Transit (MRT) system. But such vehicular network faces the obstacle of limited connection time from the MS on the train to the BS at the station. Therefore, maximizing the throughput during the tens of second intervals becomes crucial to overcome such hindrance. To achieve the goal, we propose Accelerometer-Assisted Rate Adaptation (AARA) to divide the motion of the train into four phases; each adopts a specific rate adaptation mechanism. The experiments show that the average throughput of AARA outperforms that of the conventional scheme.