Christopher D. Moffatt

Linearization of EER RF power amplifiers using an adaptive subband predistorter

Power amplifiers are a fundamental component for nearly all communications systems. Long-range wireless communications require high-power radio frequency (RF) amplifiers that are by far the most power consuming devices in the entire system. It is well known that efficient power amplifiers are highly nonlinear. However, highly efficient amplifiers such as the envelope elimination and restoration (EER) amplifiers as described herein are critical to mobile communications systems that require low power consumption for increased battery life and reduced size, weight, and power (SWAP), such as cell phones and military radios. The non-linearity of amplifiers generates both in-band noise (IBN) and out-of-band noise (OBN) which causes an increased bit error rate (BER) and adjacent channel interference (ACI), respectively. This degradation in performance has become a critical issue in recent years as newly emerging spectrally-efficient digital waveforms are being used for high-data rate communications. Linearization is necessary to comply with adjacent channel spectral mask requirements, to reduce BER, and to achieve acceptable amplifier efficiency. Predistortion can be used to convert a nonlinear amplifier into a linear amplifier. This paper describes a novel method for linearizing EER RF power amplifiers using adaptive subband predistortion.

Practical implementation of PN scrambler for PAPR reduction in OFDM systems for range extension and lower power consumption

Orthogonal Frequency Division Modulation (OFDM) is an efficient multi-carrier modulation scheme. It is used in many wireless communication systems due to its robustness towards fading channel behavior and a relative ease of implementation coming from computationally efficient Inverse Fast Fourier Transforms (IFFT). However, the OFDM waveform has a very large Peak-to-Average Power Ratio (PAPR). Therefore, to avoid clipping plus nonlinear distortion, the Power Amplifier (PA) needs to be backed off significantly. This paper proposes a novel implementation and analysis of a Pseudorandom Noise (PN) scrambling technique allowing a significant reduction of the OFDM signalpsilas PAPR. The theoretical basis for the technique is presented, and a particular implementation of the technique for the IEEE 802.11a standard is discussed. Both simulations and measurements demonstrate significant benefits of the proposed technique in longer range wireless communications applications that use OFDM.

High-Data-Rate, Network Radio for Wireless Communications in Military Environments

This paper discusses the development of communication technologies to dynamically manage and insure interoperability with high capacity connectivity for military communication platforms. Many advanced sensing devices are being utilized in a wide array of data collection platforms including autonomous vehicles, both on the surface of the water and under it. The volume of data from these platforms is increasing significantly. The data is usually required to be disseminated, processed and displayed to the user in a real-time fashion. This paper introduces and describes an IP-based network radio system, called Harris WetNet¿, as a Line-Of-Sight (LOS) long-range communication solution for marine platforms. This paper discusses the ongoing technology innovations of WetNet¿ in the area of range extension, power management, protocol modifications, frequency conversion, network modeling, advanced encryption, and ocean RF propagation analysis (channel charactization) in the UHF band. The technical solution discussed herein involves the integration of an innovative OFDM wireless architecture and bandwidth efficient protocol.