Joint Time-Domain Tracking of Channel and Frequency Offsets for MIMO OFDM Systems

Abstract

In this paper we address the problem of joint channel and frequency offset estimation and tracking in multiple-input multiple-output (MIMO) OFDM systems for mobile users. The proposed method stems from extended Kalman filtering and is suitable for time-frequency-space selective channels. Separate offset for each MIMO channel branch is considered because of the mobility and rich scattering. The channel taps and the frequency offsets are estimated in time-domain while the equalization is performed in frequency domain. Simulation results demonstrate that the proposed method tracks time-varying channels and frequency offsets with high fidelity. Realistic channel models are used in mobile scenarios. The proposed time-domain approach has improved performance and robustness in comparison to purely frequency domain processing. Computational complexity is lower as well.

Joint Carrier Frequency Offset and Channel Estimation for OFDM Systems via the EM Algorithm in the Presence of Very High Mobility

“…In this section, we compare our proposed algorithm with the algorithm of [9]. This algorithm is based on the extended Kalman filtering to carry out channel taps and CFO estimation together with data detection.…”

“…Note that it operates on equivalent discrete channel model only, and not on the parametric channel model. The simulations presented in [9] have been carried out in Decision-Directed (DD) mode only (after the acquisition step), i.e. only decoded data symbols are used to perform the filtering.…”

“…only decoded data symbols are used to perform the filtering. However, when introducing their algorithm, the authors also stated that in case of high mobility, pilot signals are also needed [9] [29]. So to compare both algorithms, we insert pilots in the algorithm following the pilot scheme of our tracking algorithm [15].…”

“…We propose to address the problem of joint CFO and channel estimation via the EM algorithm in the context of OFDM systems with very high mobility. Note that there are other approaches for estimating both CFO and channel, like the extended Kalman filter used in [9].…”

Blind Frequency Synchronization in OFDM via Diagonality Criterion

“…Semi-blind approaches proposed in the literature aim at improving bandwidth efficiency [11]- [13]. Those usually rely on various assumptions such as the usage of a single pilot symbol, two identical consecutive OFDM data blocks [11], decision-directed processing [13], or some specific structure within the OFDM symbol [14].…”