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1. On Multicast Throughput in Multi-hop MIMO Networks with Interference Alignment

   https://doi.org/10.1109/TVT.2018.2817365  

   Zeng, Huacheng; Qin, Xiaoqi; Yuan, Xu; Tian, Feng; Hou, Thomas; Lou, Wenjing; Midkiff, Scott (January 2018, IEEE Transactions on Vehicular Technology)

   Interference alignment (IA) is widely regarded as a promising interference management technique for wireless networks and its potential is most profound in interference-intensive environments. This motivates us to study IA for multicast communications in multi-hop MIMO networks, which are rich in interference by nature. We develop a set of linear constraints that can characterize a feasible design space of IA for multicast communications. The set of linear constraints constitutes a simple mathematical model of IA that allows us to conduct cross-layer multicast throughput optimization in multi-hop MIMO networks, but without getting involved into the onerous signal design at the physical layer. Based on the mathematical model of IA, we formulate a multicast throughput maximization problem and develop an approximation solution that can achieve (1−ϵ)-optimality. Simulation results show that the use of IA can significantly increase the multicast throughput in multi-hop MIMO networks and the throughput gain increases with the volume of multicast traffic and the number of antennas. 

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2. Interferometry Based Integrated Sensing and Communications with Imperfect Synchronizations

   https://doi.org/10.1109/GLOBECOM46510.2021.9685228  

   Guo, Terry N.; MacKenzie, Allen B.; Li, Husheng (December 2021, IEEE Global Communications Conference)

   Interferometry is a powerful tool for estimating the incident angle of electromagnetic (EM) waves by calculating the correlation of received signals at different antennas. Motivated by very-long-baseline interfereometry (VLBI) in radio astronomy, an interferometry based sensing scheme is proposed as integrated sensing and communications (ISAC). It reuses the communication signal from base stations (BSs), similarly to passive radars, which improves the sensing precision and spectrum efficiency. Different from the almost-perfect synchronization in VLBI realized by atomic clocks, the synchronization in BSs of cellular communication networks (usually based on GPS signals) could have significant errors. Therefore, algorithms for compensating for synchronization errors in both time and frequency are proposed. Numerical simulations demonstrate that the proposed algorithms can substantially alleviate the synchronization errors. 

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3. UD-MIMO: Uplink Distributed MIMO for Wireless LANs

   https://doi.org/10.1109/SECON52354.2021.9491622  

   Pirayesh, Hossein; Sangdeh, Pedram Kheirkhah; Yan, Qiben; Zeng, Huacheng (July 2021, 2021 18th Annual IEEE International Conference on Sensing, Communication, and Networking (SECON))

   null (Ed.)

   Wireless local area networks (WLANs) are a key component of the telecommunications infrastructure in our society. While many solutions have been produced to improve their downlink throughput, the techniques for enhancing their uplink throughput remain limited. The stagnation can be attributed to the lack of fine-grained inter-node synchronization due to the hardware limitation of most devices. In this paper, we present an uplink distributed multiple-input-and-multiple-output scheme (termed UD-MIMO) for WLANs to enable concurrent uplink transmission in the absence of fine-grained inter-node synchronization. The enabling technique behind UD-MIMO is a practical solution to decoding uplink packets from asynchronous users. UD-MIMO makes it possible for WLANs to significantly improve their uplink throughput while not requiring tight internode synchronization. We have built a prototype of UD-MIMO on a wireless testbed and demonstrate its compatibility with commercial off-the-shelf Atheros 802.11 client devices (with modified Linux driver). Our experimental results show that, for a WLAN with 8 APs in a conference room, UD-MIMO offers 3.4× throughput compared to interference-avoidance approach. 

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4. Comparative Performance Evaluation of mmWave 5G NR and LTE in a Campus Scenario

   Tehrani-Moayyed, M.; Restuccia, F.; Basagni, S. (October 2020, Proceedings of IEEE VTC 2020 Fall)

   The extremely high data rates provided by communications in the millimeter-length (mmWave) frequency bands can help address the unprecedented demands of next-generation wireless communications. However, atmospheric attenuation and high propagation loss severely limit the coverage of mmWave networks. To overcome these challenges, multi-input-multi-output (MIMO) provides beamforming capabilities and high-gain steer- able antennas to expand communication coverage at mmWave frequencies. The main contribution of this paper is the per- formance evaluation of mmWave communications on top of the recently released NR standard for 5G cellular networks. Furthermore, we compare the performance of NR with the 4G long-term evolution (LTE) standard on a highly realistic campus environment. We consider physical layer constraints such as transmit power, ambient noise, receiver noise figure, and practical antenna gain in both cases, and examine bitrate and area coverage as the criteria to benchmark the performance. We also show the impact of MIMO technology to improve the performance of the 5G NR cellular network. Our evaluation demonstrates that 5G NR provides on average 6.7 times bitrate improvement without remarkable coverage degradation. 

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5. Detection Performance of RIS-AIDED MIMO Radar with Asynchronous Propagation

   https://doi.org/10.1109/CAMSAP58249.2023.10403510  

   Wang, Fangzhou; Swindlehurst, A Lee; Li, Hongbin (December 2023, Proc. IEEE 9th International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP))

   This paper explores the use of reconfigurable intelligent surfaces (RISs) for moving target detection in multi-input multi-output (MIMO) radar. Unlike previous related works that ignore the propa-gation delay difference between the direct path and the RIS-reflected path, we examine the detection problem in RIS-assisted MIMO radar by taking into account the effect of asynchronous propagation. Specifically, we first develop a general signal model for RIS-aided MIMO radar with multiple asynchronous RISs and arbitrary wave-forms. Next, we formulate the RIS design problem by maximizing the overall received signal energy. The resulting optimization problem is non-convex, which is solved with semidefinite relaxation (SDR) techniques. A coherent detector is introduced for target detection. Finally, numerical results are presented to demonstrate the performance of the RIS-aided MIMO radar in comparison with the conventional MIMO radar. 

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