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See detailBeam Squint-Aware Integrated Sensing and Communications for Hybrid Massive MIMO LEO Satellite Systems
You, Li; Qiang, Xiaoyu; Tsinos, Christos UL et al

in IEEE Journal on Selected Areas in Communications (2022), 40(10), 2994-3009

The space-air-ground-sea integrated network (SAGSIN) plays an important role in offering global coverage. To improve the efficient utilization of spectral and hardware resources in the SAGSIN, integrated ... [more ▼]

The space-air-ground-sea integrated network (SAGSIN) plays an important role in offering global coverage. To improve the efficient utilization of spectral and hardware resources in the SAGSIN, integrated sensing and communications (ISAC) has drawn extensive attention. Most existing ISAC works focus on terrestrial networks and cannot be straightforwardly applied in satellite systems due to the significantly different electromagnetic wave propagation properties. In this work, we investigate the application of ISAC in massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite systems. We first characterize the statistical wave propagation properties by considering beam squint effects. Based on this analysis, we propose a beam squint-aware ISAC technique for hybrid analog/digital massive MIMO LEO satellite systems exploiting statistical channel state information. Simulation results demonstrate that the proposed scheme can operate both the wireless communications and the target sensing simultaneously with satisfactory performance, and the beam-squint effects can be efficiently mitigated with the proposed method in typical LEO satellite systems. [less ▲]

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See detailMassive MIMO Hybrid Precoding for LEO Satellite Communications With Twin-Resolution Phase Shifters and Nonlinear Power Amplifiers
You, Li; Qiang, Xiaoyu; Li, Ke-Xin et al

in IEEE Transactions on Communications (2022), 70(8), 5543-5557

The massive multiple-input multiple-output (MIMO) transmission technology has recently attracted much attention in the non-geostationary, e.g., low earth orbit (LEO) satellite communication (SATCOM ... [more ▼]

The massive multiple-input multiple-output (MIMO) transmission technology has recently attracted much attention in the non-geostationary, e.g., low earth orbit (LEO) satellite communication (SATCOM) systems since it can significantly improve the energy efficiency (EE) and spectral efficiency. In this work, we develop a hybrid analog/digital precoding technique in the massive MIMO LEO SATCOM downlink, which reduces the onboard hardware complexity and power consumption. In the proposed scheme, the analog precoder is implemented via a more practical twin-resolution phase shifting (TRPS) network to make a meticulous tradeoff between the power consumption and array gain. In addition, we consider and study the impact of the distortion effect of the nonlinear power amplifiers (NPAs) in the system design. By jointly considering all the above factors, we propose an efficient algorithmic approach for the TRPS-based hybrid precoding problem with NPAs. Numerical results show the EE gains considering the nonlinear distortion and the performance superiority of the proposed TRPS-based hybrid precoding scheme over the baselines. [less ▲]

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See detailJoint Communications and Sensing for Hybrid Massive MIMO LEO Satellite Systems With Beam Squint
Qiang, Xiaoyu; You, Li; Tsinos, Christos UL et al

in 2022 IEEE International Conference on Communications Workshops (ICC Workshops) (2022)

To improve the efficient utilization of spectral and hardware resources, joint communications and sensing (JCS) has drawn extensive attention. Most existing JCS works focus on terrestrial networks and can ... [more ▼]

To improve the efficient utilization of spectral and hardware resources, joint communications and sensing (JCS) has drawn extensive attention. Most existing JCS works focus on terrestrial networks and can not be straightforwardly applied in satellite systems due to the significantly different electromagnetic wave propagation properties. In this work, we investigate the application of JCS in massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite systems. We first charac-terize the statistical wave propagation properties by considering beam squint effects. Based on this analysis, we propose a beam squint-aware JCS technique for hybrid analog/digital massive MIMO LEO satellite systems exploiting statistical channel s-tate information. Simulation results demonstrate that both the wireless communications and target sensing can be operated simultaneously with satisfactory performance, and the beam squint effects can be efficiently mitigated with the proposed method in typical LEO satellite systems. [less ▲]

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See detailHybrid Analog/Digital Precoding for Downlink Massive MIMO LEO Satellite Communications
You, Li; Qiang, Xiaoyu; Li, Ke-Xin et al

in IEEE Transactions on Wireless Communications (2022), 21(8), 5962-5976

Massive multiple-input multiple-output (MIMO) is promising for low earth orbit (LEO) satellite communications due to the potential in enhancing the spectral efficiency. However, the conventional fully ... [more ▼]

Massive multiple-input multiple-output (MIMO) is promising for low earth orbit (LEO) satellite communications due to the potential in enhancing the spectral efficiency. However, the conventional fully digital precoding architectures might lead to high implementation complexity and energy consumption. In this paper, hybrid analog/digital precoding solutions are developed for the downlink operation in LEO massive MIMO satellite communications, by exploiting the slow-varying statistical channel state information (CSI) at the transmitter. First, we formulate the hybrid precoder design as an energy efficiency (EE) maximization problem by considering both the continuous and discrete phase shift networks for implementing the analog precoder. The cases of both the fully and the partially connected architectures are considered. Since the EE optimization problem is nonconvex, it is in general difficult to solve. To make the EE maximization problem tractable, we apply a closed-form tight upper bound to approximate the ergodic rate. Then, we develop an efficient algorithm to obtain the fully digital precoders. Based on which, we further develop two different efficient algorithmic solutions to compute the hybrid precoders for the fully and the partially connected architectures, respectively. Simulation results show that the proposed approaches achieve significant EE performance gains over the existing baselines, especially when the discrete phase shift network is employed for analog precoding. [less ▲]

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See detailHybrid A/D Precoding for Downlink Massive MIMO in LEO Satellite Communications
Qiang, Xiaoyu; You, Li; Li, Ke-Xin et al

in 2021 IEEE International Conference on Communications Workshops (ICC Workshops) (2021, July 09)

In this paper, we develop hybrid analog/digital precoding based on the fully-connected architecture for massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite communications (SATCOM ... [more ▼]

In this paper, we develop hybrid analog/digital precoding based on the fully-connected architecture for massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite communications (SATCOM), by exploiting the statistical channel state information (CSI) at the transmitter. The hybrid precoder design is formulated as an energy efficiency (EE) maximization problem by considering both continuous and discrete phase shift networks for implementing the analog precoder. The resulting optimization problem is nonconvex and difficult to solve. To that end, first, we apply a closed-form tight upper bound to approximate the ergodic rate. Then, we adopt Dinkelbach's algorithm and the iteratively weighted minimum mean-square error (WMMSE) method to obtain the fully digital precoders. After that, the alternating minimization and inexact majorization-minimization (MM) algorithms are utilized to compute the hybrid precoders. Simulation results show that the proposed algorithmic solutions achieve significant performance gains when compared to existing literature ones, especially in the case where the discrete phase shift network is employed for analog precoding. [less ▲]

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