This paper presents a comprehensive analysis of the impact of a generic power amplifier’s (PA’s) output power on the bit-error-rate (BER) in a transceiver employing a 4Mquadrature amplitude modulation (QAM) scheme. The study highlights the dual effects of excessive and insufficient output power on system performance. On one hand, low output power reduces the signal-to-noise ratio (SNR) at the receiver, leading to increased BER. On the other hand, high output power pushes the PA into its nonlinear region, similarly degrading BER. A quantitative analysis is conducted to examine the combined influence of noise and nonlinearity on BER. From this analysis, the globally optimal PA output power that minimizes BER for a wireless system is derived. Theoretical insights are validated through system-level simulations, demonstrating the effectiveness and high accuracy of analytical expressions.

The new philosophy of realizing high-order modulation schemes directly in the RF domain enables the generation of spectrally efficient$4^{M}$quadrature-amplitude-modulated$(4^{M}$QAM) symbols using the vectorial summation of$M$quadrature phase-shift keying (QPSK) signals. As will be shown in this paper, this approach, called RF-QAM, leads to several remarkable advantages in power amplification and signal formation in terms of both performance and power consumption. This paper presents a study of the RF-QAM transmitter (TX) and a comparison with the conventional architecture, as well as analytical studies and simulations to verify the superior performance of the RF-QAM transmitter compared to the conventional counterpart.

Realization of high-order modulation schemes directly in the RF domain enables the generation of spectrally efficient$4^M$quadrature-amplitude-modulated ($4^M$QAM) symbols using the vectorial summation of$M$quadrature phase-shift keying (QPSK) signals whose amplitudes are progressively scaled by a constant factor of two. Called RF-QAM, this approach leads to numerous advantages including the elimination of power-hungry digital-to-analog converter (DAC) and the mitigation of stringent linearity requirement of the front-end power amplifier (PA). This paper presents a comprehensive comparative study of RF-QAM and conventional transmitters. The design issues associated with the front end and the mixed-signal blocks for both architectures are investigated, and the performance of these two designs is compared. Various circuit-and system-level simulations verify the superior performance of the RF-QAM transmitter compared to the conventional counterpart.

A phase-locked-based frequency synthesizer – ubiquitously used to generate local oscillation in a communication transceiver – exhibits phase noise and jitter which considerably degrades bit-error rate (BER) and error vector magnitude (EVM) of a digital communication link. This paper presents an analytical study of EVM and BER degradation for a variety of widely used digital modulation schemes. Phase noise and jitter of a generic integer-N phase-locked loop (PLL) as a local oscillator feeding an RF mixer are derived, while accounting for the reference spurs and cyclo-stationarity of the mixer operation as well as the additive noise of the communication link. This jitter model is then utilized to directly study its impact on digital modulation constellations. Specifically, the EVM and BER degradation due to the PLL jitter in communication systems incorporating M-ary phase-shift keying (M-PSK) and${4^{M}}$quadrature amplitude modulation (${4^{M}}$QAM) are analyzed. Comparison between analytical models and system-level simulations verifies an excellent accuracy of these models.