Power loading for CP-OFDM over frequency-selective fading channels

We compare cyclic prefix (CP) based single and multicarrier block transmission schemes in frequency-selective fading channels. Analytical comparison shows that at moderate-to-high signal-to-noise ratio (SNR), the uncoded error rate performance of multicarrier transmission is inferior to that of single carrier. We propose new minimum bit error rate (MBER) power loading algorithms for multicarrier transmission. It is also shown that a simpler approximate MBER (AMBER) power loading method has performance close to that of the optimum MBER scheme. Performance of a variety of methods is compared analytically and verified by simulations.

I. Introduction

Broadband wireless communication signals suffer from serious intersymbol interference (ISI) due to time-dispersive frequency-selective channels. Multicarrier modulation (MC), especially Orthogonal Frequency Division Multiplexing (OFDM) using a cyclic prefix (CP) has been receiving growing interest in recent years as countermeasures of frequency selectivity of wireless channels due to simplified equalization in the frequency domain [1]. The time-domain equalization of conventional single carrier (SC) transmission usually has much higher complexity (especially when the channel delay spread is large). Recently, it has been shown that block SC transmission with similar block structure and frequency-domain equalization to CP-OFDM, has similar equalization complexity and performance as OFDM [2].