Publications

Publications

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2019

expandFully-/Partially-Connected Hybrid Beamforming Architectures for mmWave MU-MIMO
Xiaoshen Song, Thomas Kühne, Giuseppe Caire; arxiv version of journal version, submitted to IEEE in April 2019

Abstract:Hybrid digital analog (HDA) beamforming has attracted considerable attention in practical implementation of millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems due to the low power consumption with respect to its fully digital baseband counterpart. The implementation cost, performance, and power efficiency of HDA beamforming depends on the level of connectivity and reconfigurability of the analog beamforming network. In this paper, we investigate the performance of two typical architectures that can be regarded as extreme cases, namely, the fully-connected (FC) and the one-stream-per-subarray (OSPS) architectures. In the FC architecture each RF antenna port is connected to all antenna elements of the array, while in the OSPS architecture the RF antenna ports are connected to disjoint subarrays. We jointly consider the initial beam acquisition and data communication phases, such that the latter takes place by using the beam direction information obtained by the former. We use the state-of-the-art beam alignment (BA) scheme previously proposed by the authors and consider a family of MU-MIMO precoding schemes well adapted to the beam information extracted from the BA phase. We also evaluate the power efficiency of the two HDA architectures taking into account the power dissipation at different hardware components as well as the power backoff under typical power amplifier constraints. Numerical results show that the two architectures achieve similar sum spectral efficiency, while the OSPS architecture is advantageous with respect to the FC case in terms of hardware complexity and power efficiency, at the sole cost of a slightly longer BA time-to-acquisition due to its reduced beam angle resolution.


 

2018

expandAn Analog Module for Hybrid Massive MIMO Testbeds Demonstrating Beam Alignment Algorithms
Thomas Kühne, Giuseppe Caire, International ITG Workshop on Smart Antennas (WSA 2018), Bochum, Germany. March 2018.

Abstract:Hybrid analog-digital beamforming for massive MIMO is an important technology for millimeter-wave communication systems. Current experimentation of massive MIMO is based mainly on full digital solutions and in the sub-6 GHz frequency range. The technology for millimeter-wave massive MIMO systems is not yet available to the broad research community. Due to high path loss, sparsity of the channel, and restrictions of the hardware in the millimeter-wave band, new challenges in signal processing arise. One of these problems is the initial link acquisition also called beam alignment (BA). We present a hybrid analog-digital massive MIMO sub-6 GHz testbed with 64 antennas. This testbed enables the investigation of challenges connected to a hybrid analog-digital architecture like the BA problem. We demonstrate multiple BA algorithms to show their advantages and disadvantages. The testbed is based on a self-developed analog module with a high resolution of phase and amplitude settings. Our module can be connected to standard software defined radios (SDRs) and supports different types of hybrid architectures


 

expandFully-Connected vs. Sub-Connected Hybrid Precoding Architectures for mmWave MU-MIM
Xiaoshen Song, Thomas Kühne, Giuseppe Caire; arxiv version of the ICC conference paper, October 2018

Abstract:Hybrid digital analog (HDA) beamforming has attracted considerable attention in practical implementation of millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems due to its low power consumption with respect to its digital baseband counterpart. The implementation cost, performance, and power efficiency of HDA beamforming depends on the level of connectivity and reconfigurability of the analog beamforming network. In this paper,weinvestigatetheperformanceoftwotypicalarchitectures for HDA MU-MIMO, i.e., the fully-connected (FC) architecture where each RF antenna port is connected to all antenna elements of the array, and the one-stream-per-subarray (OSPS) architecturewheretheRFantennaportsareconnectedtodisjoint subarrays. We jointly consider the initial beam acquisition phase and data communication phase, such that the latter takes place by using the beam direction information obtained in the former phase. For each phase, we propose our own BA and precoding schemes that outperform the counterparts in the literature. We also evaluate the power efficiency of the two HDA architectures taking into account the practical hardware impairments, e.g., the power dissipation at different hardware components as well as the potential power backoff under typical power amplifier (PA) constraints. Numerical results show that the two architectures achievesimilarsumspectralefficiency,buttheOSPSarchitecture outperforms the FC case in terms of hardware complexity and power efficiency, only at the cost of a slightly longer time of initial beam acquisition.