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1. Low-Complexity MISO Cache-Aided Communication via Meta-User Scheduling

   Mohajer, Soheil; Bergel, Itsik (January 2021, International ITG Workshop on Smart Antennas WSA)

   We present a novel low-complexity scheme for cache-aided communication, where a multi-antenna base station serves multiple single-antenna mobile users. The scheme is based on dividing the users into meta-users, where all users in the same meta-user store the same content during the placement phase. The inter meta-user interference is mitigated by using the cache as well as zero forcing, while the interference between users of the same meta-user is mitigated by zero forcing. Compared to the current state of the art, this scheme is feasible for a wider range of parameters. Moreover, while still achieving the optimal number of degrees of freedom (DoF), the proposed scheme imposes the same or less complexity compared to all the known schemes for each set of parameters. Consequently, the proposed scheme enables practical implementation of cache-aided communication for a large number of users. 

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2. FASURA: A Scheme for Quasi-Static Massive MIMO Unsourced Random Access Channels

   https://doi.org/10.1109/SPAWC51304.2022.9833940  

   Gkagkos, Michail; Narayanan, Krishna R; Chamberland, Jean-Francois; Georghiades, Costas N (July 2022, IEEE)

   This article considers the massive MIMO unsourced random access problem on a quasi-static Rayleigh fading channel. Given a fixed message length and a prescribed number of channel uses, the objective is to construct a coding scheme that minimizes the energy-per-bit subject to a fixed probability of error. The proposed scheme differs from other state-of-the-art schemes in that it blends activity detection, single-user coding, pilot-aided and temporary decisions-aided iterative channel estimation and decoding, minimum-mean squared error (MMSE) estimation, and successive interference cancellation (SIC). We show that an appropriate combination of these ideas can substantially outperform state-of-the-art coding schemes when the number of active users is more than 100, making this the best performing scheme known for this regime. 

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3. Simple Caching Schemes for Non-homogeneous MISO Cache-Aided Communication via Convexity

   https://doi.org/10.1109/ICASSP40776.2020.9053936  

   Bergel, Itsik; Mohajer, Soheil (May 2020, ICASSP 2020 - 2020 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP))

   We present a novel scheme for cache-aided communication over multiple-input and single output (MISO) cellular networks. The presented scheme achieves the same number of degrees of freedom as known coded caching schemes, but, at much lower complexity. The scheme is derived for communication systems with heterogeneous rates and finite signal-to-noise ratio, in which links are modeled by wideband fading channels. The base station is serving multiple users simultaneously, by sending a combination of several packets, each intended for one user. The interference is either suppressed using the cache content or nulled by zero-forcing at the unintended users. We focus on efficient coding schemes, which allow for a maximum number of users to be served throughout the course of communication. An achievable rate region is characterized by determining the extreme rate vectors satisfying an efficient transmission. The analysis results in a simple scheduling scheme and in a closed-form performance analysis. 

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4. Backhauling Many Devices: Relay Schemes for Massive Random Access Networks

   https://doi.org/10.1109/GLOBECOM42002.2020.9322431  

   Ogbe, Dennis; Love, David J.; Wang, Chih-Chun (December 2020, 2020 IEEE Global Communications Conference (GLOBECOM))

   null (Ed.)

   The number of devices connected to Internet of Things (IoT) and massive machine-type communication (mMTC) networks is expected to increase exponentially in the next generation of wireless communication systems, resulting in a new type of “massive” random access network. However, most of the work in this emerging field considers the single-hop setting with direct communication between the users and a fully-equipped base station. In contrast, this work explores the massive random access problem in a two-hop relay setting where users access the network through a femto- or pico-cell relay which itself only has a limited amount of bandwidth/power. We present two low-complexity relaying schemes designed to minimize power consumption and discuss their tradeoffs using numerical simulations. 

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5. On Secrecy Performance of RIS-Assisted MISO Systems Over Rician Channels With Spatially Random Eavesdroppers

   https://doi.org/10.1109/TWC.2023.3348591  

   Shi, Wei; Xu, Jindan; Xu, Wei; Yuen, Chau; Lee_Swindlehurst, A; Zhao, Chunming (August 2024, IEEE Transactions on Wireless Communications)

   Reconfigurable intelligent surface (RIS) technology is emerging as a promising technique for performance enhancement for next-generation wireless networks. This paper investigates the physical layer security of an RIS-assisted multiple-antenna communication system in the presence of random spatially distributed eavesdroppers. The RIS-to-ground channels are assumed to experience Rician fading. Using stochastic geometry, exact distributions of the received signal-to-noise-ratios (SNRs) at the legitimate user and the eavesdroppers located according to a Poisson point process (PPP) are derived, and closed-form expressions for the secrecy outage probability (SOP) and the ergodic secrecy capacity (ESC) are obtained to provide insightful guidelines for system design. First, the secrecy diversity order is obtained as 2α2 , where α2 denotes the path loss exponent of the RIS-to-ground links. Then, it is revealed that the secrecy performance is mainly affected by the number of RIS reflecting elements, N, and the impact of the number of transmit antennas and transmit power at the base station is marginal. In addition, when the locations of the randomly located eavesdroppers are unknown, deploying the RIS closer to the legitimate user rather than to the base station is shown to be more efficient. Moreover, it is also found that the density of randomly located eavesdroppers, λe , has an additive effect on the asymptotic ESC performance given by log2(1/λe) . Finally, numerical simulations are conducted to verify the accuracy of these theoretical observations. 

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