# High-Mobility OFDM Downlink Transmission with Large-Scale Antenna Array

## TL;DR

This paper introduces a novel receiver design for high-mobility OFDM downlink systems with large-scale antenna arrays, effectively handling fast time-varying channels caused by Doppler shifts and CFOs without complex channel estimation.

## Contribution

A new receiver architecture that separates CFOs spatially and jointly estimates Doppler shifts and CFOs, simplifying high-mobility OFDM reception with large antenna arrays.

## Key findings

- Effective separation of multiple CFOs using beamforming.
- Joint estimation method for Doppler shifts and CFOs.
- Applicable to standard time-varying channel models like Jakes'.

## Abstract

In this correspondence, we propose a new receiver design for high-mobility orthogonal frequency division multiplexing (OFDM) downlink transmissions with a large-scale antenna array. The downlink signal experiences the challenging fast time-varying propagation channel. The time-varying nature originates from the multiple carrier frequency offsets (CFOs) due to the transceiver oscillator frequency offset (OFO) and multiple Doppler shifts. Let the received signal first go through a carefully designed beamforming network, which could separate multiple CFOs in the spatial domain with sufficient number of receive antennas. A joint estimation method for the Doppler shifts and the OFO is further developed. Then the conventional single-CFO compensation and channel estimation method can be carried out for each beamforming branch. The proposed receiver design avoids the complicated time-varying channel estimation, which differs a lot from the conventional methods. More importantly, the proposed scheme can be applied to the commonly used time-varying channel models, such as the Jakes' channel model.