Forward error correction for PAPR reduction in OFDM signals

The demand for high data rates in wireless communication systems has driven the need for the development of modulation schemes that can operate in harsh multipath conditions and provide high bandwidth efficiency. Orthogonal frequency division multiplexing (OFDM) has emerged as the modulation of choice in these types of environments. For OFDM to continue to fulfill its promise, inherent drawbacks, specifically high peak-toaverage power ratio (PAPR), need to be addressed and curtailed. High PAPR limits the efficiency of non-linear power amplifiers forcing them to operate at reduced average power, which in turn increases communication system costs.; This thesis proposes a new method for PAPR reduction in OFDM systems using forward error correction (FEC) to facilitate the correction of intentional errors inserted into the data stream at the transmitter. Significant PAPR reduction is achieved by changing the bits within the error correction capability of the code, calculating the corresponding PAPR, and choosing the signal with the lowest PAPR for transmission. In addition, in order to augment the benefits of FEC based PAPR reduction, a specialized bit mapping is introduced, which deviates from traditional Gray encoding of bits into modulation symbols. An optimized algorithm for the implementation of this novel scheme is developed. This approach of using FEC to reduce the PAPR rather than to exclusively combat errors in the channel is one of the unique contributions of the thesis and may form the basis for alternate applications of FEC in the future.; Performance of the proposed algorithms is verified through computer simulations. The proposed scheme exhibits low PAPR and satisfactory bit error rate (BER) performance at the expense of acceptable computational complexity. Specifically, the complementary cumulative distribution function (CCDF) of the coded signal shows about a five (5) dB improvement over the original OFDM signal. In addition, BER performance in additive white Gaussian noise (AWGN) demonstrates trade-offs between reduction in PAPR and remaining error correction capability of the deployed codes. Finally, spectral regrowth results are presented, indicating that the modified OFDM waveforms allow for a two (2) dB reduction in the input back-off (IBO) level of the power amplifier.; The simulation results are corroborated in a hardware environment based on a software defined instrumentation (SDI) platform. This hardware-software co-design methodology allows for rapid verification of the waveforms synthesized in the simulation environment using real-world non-linear amplifiers. Specifically, CCDF and spectral regrowth results are captured, demonstrating good agreement with the simulation results.; PAPR reduction techniques offer communication system design engineers greater flexibility in choosing the operating point of the transceiver. The PAPR reduction scheme proposed in this thesis operates mostly at the transmitter and requires minimal modification at the receiver. As a result, it is expected that the algorithm developed will be of particular interest in the digital audio and video broadcasting industries.