Iterative channel estimation for high mobility MIMO-OFDM systems

Summary

Multiple-input multiple-output and orthogonal frequency division multiplexing (MIMO-OFDM) techniques have been adopted in 3GPP LTE and WiMAX standards to achieve very high data rates (> 10Mbps). In these standards, high mobility users, moving at speeds higher than 300Km/h, need to be supported. Accurate channel state information (CSI) is required for reliable signal detection at the receiver. Pilot symbols are inserted among sub-carriers before transmission to accurately estimate the wireless channel. In a high mobility environment, the wireless channel is time-variant and frequency-selective causing the symbol transmission to be impaired by the Doppler spread. The Doppler spread destroys the orthogonality and creates inter-carrier interference (ICI) between OFDM sub-carriers. In addition, the channel changes significantly within one OFDM symbol. As a consequence, the Standard channel estimation methods cannot be used in 3GPP LTE and WiMAX to support high mobility users.
We propose a novel pilot-aided iterative receiver, based on pilot symbols and iterative soft-estimate of data symbols. The channel is estimated by time-domain interpolation and least-square (LS) methods. Soft-estimates for data symbols are obtained by a maximum-a-posteriori (MAP) decoder and improved subsequently. The simulation results show that the performance of the proposed iterative receiver outperforms the existing schemes. The performance degradation of the proposed receiver structure when users move at speed of up to 324Km/h compared to the performance of a perfect CSI system with a zero Doppler shift is shown to be very marginal.

Supervisor(s)

Professor Branka Vucetic, Professor Yonghui Li

Research Location

Electrical and Information Engineering

Program Type

PHD

Synopsis

Multiple-input multiple-output and orthogonal frequency division multiplexing (MIMO-OFDM) techniques have been adopted in 3GPP LTE and WiMAX standards to achieve very high data rates (> 10Mbps). In these standards, high mobility users, moving at speeds higher than 300Km/h, need to be supported. Accurate channel state information (CSI) is required for reliable signal detection at the receiver. Pilot symbols are inserted among sub-carriers before transmission to accurately estimate the wireless channel. In a high mobility environment, the wireless channel is time-variant and frequency-selective causing the symbol transmission to be impaired by the Doppler spread. The Doppler spread destroys the orthogonality and creates inter-carrier interference (ICI) between OFDM sub-carriers. In addition, the channel changes significantly within one OFDM symbol. As a consequence, the Standard channel estimation methods cannot be used in 3GPP LTE and WiMAX to support high mobility users.
We propose a novel pilot-aided iterative receiver, based on pilot symbols and iterative soft-estimate of data symbols. The channel is estimated by time-domain interpolation and least-square (LS) methods. Soft-estimates for data symbols are obtained by a maximum-a-posteriori (MAP) decoder and improved subsequently. The simulation results show that the performance of the proposed iterative receiver outperforms the existing schemes. The performance degradation of the proposed receiver structure when users move at speed of up to 324Km/h compared to the performance of a perfect CSI system with a zero Doppler shift is shown to be very marginal.

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Keywords

MIMO, OFDM, Multi-user, WiMax, LTE, Channel Estimation, Iterative decoder

Opportunity ID

The opportunity ID for this research opportunity is: 1037

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