Coded Auxiliary Pilots for Channel Estimation in FBMC-OQAM Systems

In this paper, we propose a novel scattered pilot method for channel estimation in filter-bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) systems. We refer to this as the coded auxiliary pilot (CAP) method. It builds on the idea of using a few auxiliary pilot (AP) symbols to eliminate the imaginary interference on each scattered pilot. At the same time, to keep the spectral efficiency of transmission high, the AP symbols are coded to also carry information symbols. Theoretical analysis and numerical results show that the CAP method can maintain high spectral efficiency and high power efficiency, while achieving complete imaginary interference cancelation. Taking the spectral and power efficiency, the imaginary interference cancelation performance, and the coding/decoding complexity into consideration, the CAP method with two to four AP symbols is identified as a good compromised choice for practice.

I. Introduction

Filter-BANK multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) [1]– [7] is considered to be a promising alternative to the conventional orthogonal frequency-division multiplexing (OFDM) technique [8], [9]. However, channel estimation in FBMC-OQAM, in general, is more complicated than in OFDM. Scattered pilots are commonly inserted among data symbols in the time–frequency space of an OFDM waveform for channel estimation and its tracking over the length of each data packet. The orthogonality of subcarriers in OFDM allows separation of pilot subcarriers from data subcarriers; hence, channel estimation at the pilot positions can be performed trivially. Unfortunately, this is not the case in FBMC-OQAM, as subcarrier orthogonality is limited to the real field only (not the complex field) [1].