High-Mobility OFDM Downlink Transmission With Large-Scale Antenna Array

Abstract

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 timevarying channel models, such as the Jakes' channel model. Index Terms-orthogonal frequency division multiplexing (OFDM), time-varying channels, high-mobility, carrier frequency offset (CFO), Doppler shifts, oscillator frequency offset (OFO), large-scale antenna array.

Angle-Domain Approach for Parameter Estimation in High-Mobility OFDM With Fully/Partly Calibrated Massive ULA

“…The cone-shaped beam pattern of ULA (as shown in Fig. 3 of [17]) can guarantee that all the signals incorporated by the beam towards θ are mainly affected by the same CFO f d cos θ + ξ. Besides, the adoption of ULA only requires to design the beamforming network along the dimension of AoA for receiving all signals dispersed in the whole space.…”

“…However, the approach in [17] must exploit a pilot sequence composed of two identical halves in the time domain, which limits its applicability to systems with other pilot sequences, and may not be optimal for channel estimation and subsequent data detection due to sparsity in the frequency domain [18].…”

“…Neither have the authors of [17] taken into account the fact that it is quite challenging and may not be possible in practice to establish a fully and entirely calibrated large-scale antenna array. Due to various uncontrollable factors such as imperfect time synchronization or communication devices aging, etc., gain and phase mismatches inevitably appear among multiple receive antennas.…”

“…• By eliminating the necessity of exploiting the two-halves pilot as in [17], the proposed joint estimation algorithms can be implemented into many practical communication systems without incurring incompatibility problem. Moreover, as the proposed algorithms can be applied to systems with optimized pilot sequences, its performance can be superior to [17].…”

Radiation Efficiency Aware High-Mobility Massive MIMO With Antenna Selection

“…More recently, the large-scale antenna array or massive multi-input multi-output (MIMO) has attracted increasing interests in dealing with richly scattered high-mobility scenarios due to its high spatial resolution [4]- [6]. For high-mobility downlink, the work in [7] separated the Doppler shifts by beamforming network with a large-scale antenna array and proposed a joint oscillator frequency offset and Doppler shift estimation scheme. For uplink transmissions, it has been demonstrated that the harmful effect of Doppler shift can be also mitigated by massive MIMO technique [8], [9].…”