Peak-to-average power ratio suppression schemes in pi/4 QPSK, OFDM, and MC-CDMA

In this dissertation, peak-to-average power ratio (PAPR) suppression schemes for digital modulations are investigated and developed. The PAPR of a signal is the ratio of the peak signal power over the average signal power and a high PAPR signal substantially degrades the efficiency of the linear power amplifier.; In portable wireless communications, bandwidth efficiency becomes more important than power efficiency. Thus a bandwidth efficient linear amplifier and π/4 QPSK have become popular. Several PAPR suppression schemes were suggested to increase the power efficiency in π/4 QPSK but they degraded the bandwidth efficiency. Therefore, an adaptive peak suppression (APS) algorithm is introduced to suppress the PAPR without any bandwidth efficiency degradation. It adjusted the amplitudes of symbols before pulse shaping. Then, the PAPR of π/4 QPSK with root raised cosine (RRC) (roll-off 0.2) pulse was able to be suppressed from 4.8 dB to 1.9 dB.; Orthogonal frequency division multiplexing (OFDM) is an effective and popular modulation for high data rate transmission but causes very high PAPR. Most of the previous PAPR suppression schemes have weak performance or expand the bandwidth. Therefore, we developed a limiter plus APS scheme. which is the combination of an amplitude limiter and the APS algorithm. The scheme suppressed the PAPR of 128-QPSK-OFDM with RRC (roll-off 0.35) pulse shapes from 12.7 dB to 5.2 dB without any bandwidth efficiency degradation when 1 dB average power loss was allowed in an AWGN channel.; Synchronous multi-carrier code-division multiple-access (MC-CDMA) with Golay complementary spreading sequence has similar PAPR properties as OFDM. Thus, the limiter plus APS scheme was also applied to synchronous MC-CDMA and suppressed the PAPR of 128-MC-CDMA with RRC (roll-off 0.35) pulses from 12.1 dB to 3.9 dB when 1 dB average power loss was allowed. The PAPR of asynchronous MC-CDMA was determined by its spreading sequence. Zadoff-Chu sequences are currently known as the best spreading sequence for low PAPR. However, a new proposed PAPR suppressed Zadoff-Chu (PSZ) sequence causes 2–3 dB lower PAPR than Zadoff-Chu sequences without any cost.; The performances of the PAPR suppression schemes of this dissertation are very competitive when compared to previous schemes; moreover, these schemes do not sacrifice any bandwidth efficiency.