Efficient Design of Selective Mapping and Partial Transmit Sequence Using T-OFDM

Selective mapping (SLM) and partial transmit sequence (PTS) are attractive schemes for mitigating the high peak power inherent in orthogonal frequency division multiplexing (OFDM) signals. However, the high computational complexity and redundant side information (SI) bits have been identified as the main limitations for such techniques. The high computational complexity is mainly due to the need to perform several inverse fast Fourier transforms (IFFTs), and phase optimization process at the transmitter side. Therefore, this paper presents new SLM and PTS designs using a low complexity T-transform rather than IFFT. The use of the T-transform with SLM achieves a considerable computational complexity and peak-to-average power ratio (PAPR) reduction. Furthermore, we apply the T-transform to PTS and derive two different configurations that compromise the SI requirements and PAPR reduction. All the proposed schemes do not affect the original power spectrum of OFDM signals. The complexity analysis show that the proposed schemes have much lower complexity as compared to conventional schemes. Moreover, simulation results demonstrate that the proposed schemes are resilient to dispersion arising from multipath propagation, which is due to the frequency diversity introduced by the T-transform.

I. Introduction

Due to its spectral efficiency and immunity to intersymbol interference (ISI) caused by multipath signal propagation, orthogonal frequency division multiplexing (OFDM) has been adopted by various high data rate standards for communication systems [1]. The spectral efficiency of OFDM is due to the spectra overlapping of adjacent subcarriers, and the immunity to ISI is gained by using the cyclic prefix (CP) as time-domain guard bands. Because the bandwidth of each subcarrier is much smaller than the coherence bandwidth of the channel, then each subcarrier experiences a flat fading even though the overall channel response is frequency-selective. Consequently, certain subcarriers can be severely attenuated by deep fades, and thus, OFDM signals do not offer any bit error rate (BER) improvement over single carrier systems. However, as described in [2] and [3], OFDM can be exploited to provide full diversity without spectral losses by using the T-transform, which spreads each data symbol over all subcarriers.