Zhengxiang Ma

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Power amplifiers (PAs) are inherently nonlinear devices and are used in virtually all communications systems. Digital baseband predistortion is a highly cost-effective way to linearize PAs, but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA)(More)
Conventional radio-frequency (RF) power amplifiers operating with wideband signals, such as wideband code-division multiple access (WCDMA) in the Universal Mobile Telecommunications System (UMTS) must be backed off considerably from their peak power level in order to control out-of-band spurious emissions, also known as "spectral regrowth." Adapting these(More)
Impairments in the analog quadrature modulator can adversely impact the performance of a digital predistortion linearization system. In this paper, we focus on modeling and compensation of frequency-dependent gain/phase imbalance and dc offset when the input and output of the direct upconverter are available. We first propose channel models to describe the(More)
Power amplifiers (PAs) are essential in communication systems, but are inherently nonlinear. To achieve linearity with good efficiency, PA linearization is necessary. Digital baseband predistortion is a highly cost-effective way to linearize PAs, but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth(More)
In the recent years, power line communication technology has seen a rapid development. However, due to the unsteadiness of the power line channels, there are still some problems of obstruction and attenuation in this field which decrease the prospect and scope of this technology. This paper which is based on previous basic studies about spread spectrum(More)
Relay technology is an effective and efficient physical layer solution to the recent challenges in telecommunication. To be brief, a relay acts as a service station for wireless signal between source and destination. By employing relays, the reliability and quality of service (QoS) of a communication network can be improved significantly without much(More)
The transformer is a pivotal device in substations, and its operational state is highly correlated to the security and reliability of a power system. Especially with the development of smart grid, the faults in transformers would have a severe negative impact, not only on the local power network, but also on the holistic power system and power grid. In this(More)
A transformer is a pivotal component over the electrical power grid and provides a series of indispensable functions for the normal operation of the whole power system. Hence once even a transformer in a local substation goes abnormal, it will result in several chain reactions and eventually degrade the power quality and electricity service. Therefore, in(More)