PN scrambler for peak-to-average power ratio reduction in OFDM systems for range extension and lower power consumption

Orthogonal Frequency Division Multiplexing (OFDM) 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). Multicarrier waveforms for digital communications require the summation of multiple frequency-spaced single-carrier signals prior to transmission through a power amplifier (PA). OFDM is a spectral-efficient, multicarrier technique that utilizes hardware efficient IFFT in order to modulate each individual subcarrier with a QAM symbol and sum the carriers together to produce a single time-domain waveform. The addition of multiple sinusoids modulated with random amplitude and phase produces a Gaussian distributed time-domain signal with a large peak-to-average power ratio (PAPR). As a result, the average power into the PA must be backed-off to avoid clipping of the time-domain signal peaks. Clipping of the signal significantly increases in-band noise (IBN) and out-of-band noise (OBN) which adversely increases the bit-error rate (BER) and adjacent channel interference (ACI), respectively. The large backoff required to avoid clipping and provide operation in the linear region of the PA requires use of higher power amplifiers at the transmitter which greatly increases the system's DC power consumption. The methods described in this document allow for PAPR reduction of an OFDM signal by more than 3 dB using a novel pseudo-noise (PN) scrambler technique.;The goal of the research is to improve system power efficiency, while reducing distortion effects. First, an overview of OFDM waveform theory and the PAPR reduction method is provided. Second, extensive probabilistic methods of signals are used to derive new comprehensive analytical equations to predict performance, and allow a system designer to determine the parameters for the PN scrambler technique. Third, an innovative efficient IFFT is presented to allow implementation of the technique with reduced implementation complexity and latency. Fourth, a unique low PAPR preamble is described to provide a complete OFDM packet with PAPR reduction. Finally, a novel power amplifier linearization technique is presented to allow further system power efficiency increase. The simulations and measurements demonstrate significant benefits of the proposed techniques for long-range wireless communications applications.