Spatial Resource Allocation for Spectrum Reuse in Unlicensed LTE Systems

TL;DR

This paper proposes a spatial resource allocation method for unlicensed LTE systems that balances throughput with Wi-Fi coexistence by optimizing the use of spatial degrees of freedom through zero-forcing beamforming, considering CSI errors.

Contribution

It introduces a novel DoF allocation scheme for LTE-U that accounts for imperfect CSI, enhancing coexistence with Wi-Fi and balancing throughput.

Findings

The scheme effectively balances LTE-U and Wi-Fi throughput.

Residual interference due to CSI errors is analytically characterized.

Simulation results confirm the scheme's effectiveness.

Abstract

In this paper, we study how to reuse the unlicensed spectrum in LTE-U systems while guaranteeing harmonious coexistence between the LTE-U and Wi-Fi systems. For a small cell with multiple antennas at the base station (SBS), some spatial degrees of freedom (DoFs) are used to serve small cell users (SUEs) while the rest are employed to mitigate the interference to the Wi-Fi users by applying zero-forcing beamforming (ZFBF). As a result, the LTE-U and Wi-Fi throughput can be balanced by carefully allocating the spatial DoFs. Due to the channel state information (CSI) estimation and feedback errors, ZFBF cannot eliminate the interference completely. We first analyze the residual interference among SUEs, called intra-RAT interference, and the interference to the Wi-Fi users, called inter-RAT interference after ZFBF, due to imperfect CSI. Based on the analysis, we derive the throughputs of the small cell and the Wi-Fi systems, respectively. Accordingly, a spatial DoF allocation scheme is proposed to balance the throughput between the small cell and the Wi-Fi systems. Our theoretical analysis and the proposed scheme are verified by simulation results.