A Low Overhead Frame Configuration for Improved Preamble Based Channel Estimation in FBMC-OQAM

In a wireless communication system, the channel estimation (CE) is a crucial step of receiver design. Notably, in a filterbank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) system, CE is a complicated task due to the presence of intrinsic interference arising from the neighboring symbols. The intrinsic interference arises due to the use of per sub-carrier filtering based on so-called localized prototype filters, which also gives FBMC it's high spectral efficiency. However, in reality, any filter's time-frequency (TF) response is not strictly localized, and thus the preamble pilot sequence gets contaminated by the interference from random neighboring data symbols, which results in an irreducible CE error floor. A straight forward solution to this problem is to transmit multiple symbols of nulls or zeros after the preamble, which effectively reduces the number of data symbols interfering with pilots, and results in a better CE mean squared error (CE-MSE) and bit error rate (BER), but induces a significant overhead in a fixed-length FBMC-OQAM frame. This paper presents an alternative low overhead solution for the above problem, in which instead of transmitting symbols of nulls, data symbols derived from lower energy subset of full QAM constellation are transmitted, consequently, improving the CE-MSE and BER. Through extensive simulations and calculations, it is shown that the proposed configuration can recover the increased overhead through enhanced BER performance when used in a fixed-length FBMC-OQAM frame.