Carrier frequency recovery in wireless transceivers with transient impairments

Switching operation happens extensively in nowadays wireless devices between various functional modules. The transient responses during the hardware switching are non-ideal due to the non-ideal behavior of hardware components. The non-ideal transient may cause distortion on signals and degenerate system performance before the transient effect is settling down. We explore the advanced solutions to compensate the transient impairments rather than, as the conventional treatment, inserting guard intervals. In this paper, we present the transient carrier frequency offset (CFO) observed in hardware testbeds built for wireless communications research, which are configured working in time division duplexing (TDD) mode. The transient CFO arises as a result of the switching between transmission and reception radio functions. The transient CFO cannot be estimated by the conventional CFO estimators because it is time varying. We present the modeling and estimation of the transient CFO in this paper. A weighted KumaresanTufts (KT) algorithm is proposed by exploiting both low-rank approximation and subspace structure to optimize the estimation of the transient CFO. We compare the proposed algorithm with the existing methods as well as the Crámer-Rao bound (CRB). The proposed algorithm is also confirmed by the experimental results obtained from the hardware testbed.