[Paper Review] Compressed Channel Estimation with Position-Based ICI Elimination for High-Mobility SIMO-OFDM Systems

Xiang Ren, Meixia Tao+1 more|arXiv (Cornell University)|Mar 1, 2020

Advanced Wireless Communication Techniques31 references36 citations

TL;DR

The paper introduces a position-based intercarrier interference (ICI) elimination method for CE-BEM in high-mobility SIMO-OFDM, enabling ICI-free pilots and improved compressed sensing channel estimation with a speed-agnostic pilot pattern.

ABSTRACT

Orthogonal frequency-division multiplexing (OFDM) is widely adopted for providing reliable and high data rate communication in high-speed train systems. However, with the increasing train mobility, the resulting large Doppler shift introduces intercarrier interference (ICI) in OFDM systems and greatly degrades the channel estimation accuracy. Therefore, it is necessary and important to investigate reliable channel estimation and ICI mitigation methods in high-mobility environments. In this paper, we consider a typical HST communication system and show that the ICI caused by the large Doppler shift can be mitigated by exploiting the train position information as well as the sparsity of the conventional basis expansion model (BEM) based channel model. Then, we show that for the complex-exponential BEM (CE-BEM) based channel model, the ICI can be completely eliminated to get the ICI-free pilots at each receive antenna. After that, we propose a new pilot pattern design algorithm to reduce the system coherence and hence can improve the compressed sensing (CS) based channel estimation accuracy. The proposed optimal pilot pattern is independent of the number of receive antennas, the Doppler shifts, the train position, or the train speed. Simulation results confirms the performance merits of the proposed scheme in high-mobility environments. In addition, it is also shown that the proposed scheme is robust to the respect of high mobility.

Motivation & Objective

• Motivate reliable channel estimation in high-mobility OFDM under large Doppler-induced ICI.
• Leverage train position information to reduce the effective channel coefficient set from KL to L.
• Develop an ICI elimination technique for CE-BEM that yields ICI-free pilots at each receive antenna.
• Design a pilot pattern that minimizes average coherence to boost CS-based channel estimation accuracy.
• Ensure the optimal pilot pattern is independent of train speed, Doppler shifts, or receive-antenna count.

Proposed method

• Model the high-mobility channel with a basis expansion model (BEM) and show S-sparsity of dominant coefficients at a given train position.
• Specialize to the complex-exponential BEM (CE-BEM) to obtain a strictly banded frequency-domain representation.
• Derive a position-based ICI elimination technique for CE-BEM that reduces the channel to a dominant diagonal form with a permutation, yielding ICI-free pilots.
• Formulate a low-coherence compressed sensing pilot design problem to minimize average coherence and propose a low-complexity algorithm (Algorithm 1) to find a global-optimal pilot pattern w*.
• Prove that the optimal pilot pattern w* is independent of speed, Doppler, number of receive antennas, and train position.

Experimental results

Research questions

• RQ1 How can ICI caused by large Doppler shifts in high-mobility SIMO-OFDM be mitigated using position information?
• RQ2 Can CE-BEM-based channels be made ICI-free at the receiver via a permutation-based approach?
• RQ3 What pilot design minimizes average coherence to improve CS-based channel estimation in high-mobility scenarios?
• RQ4 Is there a global-optimal pilot pattern that does not depend on train speed, Doppler shifts, or antenna count?
• RQ5 How robust is the proposed scheme to varying mobility and system parameters?

Key findings

• ICI can be eliminated for CE-BEM by exploiting train position, resulting in ICI-free pilots at each receive antenna.
• Under CE-BEM, the dominant channel becomes a permuted diagonal matrix, enabling ICI-free reception with a subcarrier permutation.
• The optimal pilot pattern is independent of speed, Doppler shifts, receive-antenna count, and position, allowing a single global pattern to be stored and used.
• The pilot design reduces system average coherence, improving CS-based channel estimation accuracy without requiring guard pilots.
• Simulation results corroborate robustness to high mobility and demonstrate performance gains from the proposed ICI elimination and pilot design.