Frequency Offset and Phase Noise

Abstract

Multicarrier systems are widely used due to their high spectral efficiency and robustness against frequency-selective channels. However, the performance of these systems is highly affected by carrier frequency offset (CFO) and phase noise (PN), since the orthogonality between carriers is lost. As these imperfections are mostly related to local oscillator quality and user mobility, low-cost and high-speed applications are critical. The estimation of CFO and phase noise is divided into two steps, acquisition and tracking, where known sequences (or pilot symbols) are used to estimate the parameters at the receiver. The multiuser case is more challenging since the problem is multi-parametric, i.e., it is necessary to estimate the CFO and phase noise of each user. While the compensation of these imperfections is quite simple in the single user case (downlink), it is more elaborated in a multiuser access condition (uplink). Successive interference cancellation or linear suppression techniques are therefore used for CFO and phase noise cancellation in the multiuser case. In this chapter we first describe the effects of the CFO and the phase noise in the system performance, paying special attention to critical applications, such as low-cost unstable oscillators and high-speed vehicles. Then, we introduce several CFO estimation techniques for the downlink (single user case), based on statistical properties of the sequence of pilot symbols. Finally, we present estimation and compensation strategies for the uplink (multiuser case) of orthogonal frequency division multiple access (OFDMA) and multiuser filter bank multicarrier (FBMC), using direct and successive interference cancellation algorithms. The performance of the compensation is evaluated considering high and low mobility scenarios.