Iterative channel estimation and data detection for high mobility OFDM systems
Equalization of fast time-varying channel is a challenging task, as the channel estimated using dedicated full training would be outdated when it is used for data detection. An idea to solve this problem is to insert scattered pilots among data or superimposed pilots to estimate the channel. But due to limited amount of pilot and the severe inter-carrier interference to the pilot subcarriers from neighouring data subcarriers, the estimated channel would not be accurate, and subsequently affecting the data detection performance. This leads to the need of iterative channel estimation and data detection. The idea is that estimated channel gives a tentative data estimate, which helps to refine the channel estimate in the next iteration, and so on.
This study derives iterative receivers for joint fast-fading channel estimation and data detection. The mathematical tools employed are expectation-maximization (EM) algorithm and variational inference (VI). A number of receiver impairments are also onsidered in the derivations, such as the presence of CFO, IQ imbalance, phase noise, unknown narrowband interference, etc.
Ke Zhong, Yik-Chung Wu, and Shaoqian Li, ``Signal Detection for OFDM-Based Virtual MIMO Systems under Unknown Doubly Selective Channels, Multiple Interferences and Phase Noises," IEEE Trans. on Wireless Communications, Vol. 12, no. 10, pp.5309-5321, Oct 2013. [Preprint, IEEE_Xplore]
Jingrong Zhou, Rui Min, Yik-Chung Wu, and Jiayin Qin, ``Equalizing Multihop OFDM Relay Channel under Unknown Channel Orders and Doppler Frequencies," in Proc. of IEEE International Conf. on Communications (ICC), Sydney, Australia, June 2014.
Lanlan He, Yik-Chung Wu, Shaodan Ma, Tung-Sang Ng and H. Vincent Poor, ``Superimposed Training Based Channel Estimation and Data Detection for OFDM Amplify-and-Forward Cooperative Systems under High Mobility," IEEE Trans. on Signal Processing, Vol. 60, no. 1, pp. 274-284, Jan 2012.
Lanlan He, Shaodan Ma, Yik-Chung Wu, Yiqing Zhou, Tung-Sang Ng, and H. Vincent Poor, ``Pilot-Aided IQ Imbalance Compensation for OFDM Systems Operating over Doubly Selective Channels," IEEE Trans. on Signal Processing, Vol. 59, no. 5, pp. 2223-2233, May 2011. [IEEE Xplore]
Lanlan He, Shaodan Ma, Yik-Chung Wu and Tung-Sang Ng, ``Semiblind Iterative Data Detection for OFDM Systems with CFO and Doubly Selective Channels," IEEE Trans. on Communications, Vol.56, no.12, pp.3491-3499, Dec 2010.[PDF]