Shannon Wireless’ Post

#Stacked #intelligent #metasurfaces (#SIM) represents an advanced signal processing paradigm that enables over-the-air processing of electromagnetic waves at the speed of light. Its multi-layer structure exhibits customizable increased computational capability compared to conventional single-layer reconfigurable intelligent surfaces and metasurface lenses. In this paper, the authors deploy SIM to improve the performance of multi-user #multiple-#input #single-#output (#MISO) wireless systems with low complexity transmit #radio #frequency (#RF) chains. In particular, an optimization formulation for the joint design of the SIM phase shifts and the transmit power allocation is presented, which is efficiently solved via a customized #deep #reinforcement #learning (#DRL) approach that continuously observes pre-designed states of the SIM-parametrized smart wireless environment. The presented performance evaluation results showcase the proposed method's capability to effectively learn from the wireless environment while outperforming conventional precoding schemes under low transmit power conditions. Finally, a whitening process is presented to further augment the robustness of the proposed scheme. ---- 刘昊, Jiancheng An, Derrick Wing Kwan Ng, George Alexandropoulos, Lu Gan More details can be found at this link: https://lnkd.in/gBgs5aZe

In this paper, the authors adopt #vector-#wise and #element-#wise compression on the raw or pre-processed received signal vectors to store them in the memory. They investigate the impact of the limited memory capacity in the #access #points (#APs) on the optimal number of APs. They show that with no memory constraint, having single-antenna APs is optimal, especially as the number of users grows. However, a limited memory at the APs restricts the depth of the sequential processing pipeline. Furthermore, they investigate the relation between the memory capacity at the APs and the rate of the fronthaul link. ---- Vida Ranjbar, Robbert Beerten, Marc Moonen, Sofie Pollin More details can be found at this link: https://lnkd.in/ep2cd_XW

This paper leverages model pruning and proposes a #pruning-#enabled #hierarchical #federated #learning (#PHFL) in #heterogeneous #networks (#HetNets). The authors first derive an upper bound of the convergence rate that clearly demonstrates the impact of the model pruning and wireless communications between the clients and the associated BS. Then they jointly optimize the model pruning ratio, #central #processing #unit (#CPU) frequency and transmission power of the clients in order to minimize the controllable terms of the convergence bound under strict delay and energy constraints. However, since the original problem is not convex, they perform #successive #convex #approximation (#SCA) and jointly optimize the parameters for the relaxed convex problem. ---- Ferdous Pervej, Richeng Jin, Huaiyu Dai More details can be found at this link: https://lnkd.in/eveBgZB8

This letter introduced a novel #optical #DACs (#oDAC) parallelizing a pair of optimized 2-segment MZMs, remarkably fed by 4 uncoupled NRZ signals. Based on a pair of IQ-nested new oDACs, the resulting DAC-less QAM #Transmitters (#Tx) is fed by 8 uncoupled NRZ drivers. The energy efficiency, photonic efficiency and resolution of the flexible oDAC and QAM Tx are at their utmost. ---- Moshe Nazarathy, Dr. Ioannis Tomkos More details can be found at this link: https://lnkd.in/eBQJs8KZ

In this article, the authors show that #Reservoir #Computing (#RC) can universally approximate a general #linear #time-#invariant (#LTI) system. Specifically, they present a clear signal processing interpretation of RC and utilize this understanding in the problem of approximating a generic LTI system. Under this setup, they analytically characterize the optimum probability density function for configuring (instead of training and/or randomly generating) the recurrent weights of the underlying #recurrent #neural #network (#RNN) of the RC. ---- Shashank Jere, Lizhong Zheng, Karim Said, Lingjia Liu More details can be found at this link: https://lnkd.in/eVnTTxVH

In this paper, the application of #integrated #access and #backhaul (#IAB) technique in #millimeter-#wave (#mmWave) #cell-#free (#CF) massive MIMO systems is investigated. The access and backhaul links share a frequency spectrum in the mmWave bands, and in both, hybrid beamforming techniques are adopted for signal transmission. The bandwidth allocation (division) parameter between the two link types as well as the beamforming matrices are optimized to maximize the end-to-end data rate. This leads to a non-convex optimization problem for which an efficient solution method is proposed. ---- Ali Hosseinalipour jazi, S. Mohammad Razavizadeh, Tommy Svensson More details can be found at this link: https://lnkd.in/eB_q8BTJ

This letter design a low-complexity #minimum #mean #square #error (#MMSE) receiver for a practical rectangular pulse-shaped #orthogonal #time #frequency #space (#OTFS) #massive #multiple-#input #multiple-#output (#mMIMO) system. The proposed receiver is designed by exploiting the OTFS channel sparsity, and the structure of matrices involved in the MMSE receiver. The authors show that the sparse OTFS channel matrix is multi-banded, and has a high bandwidth. This is because its non-zero elements, which occur in multiple bands, are scattered throughout the matrix. They reduce its bandwidth by using the Reverse Cuthill-Mckee algorithm. The proposed MMSE receiver does not use any approximation, and thus has the same #bit #error #rate (#BER) as that of its conventional counterpart. ---- Mudasir Ahmad sheikh, Prem Singh, Rohit Budhiraja More details can be found at this link: https://lnkd.in/ezpXv7S4

This article presents the designs of ultrawideband microwave flat #gradient #index (#GRIN) #lenses, which realizes over a 108% fractional bandwidth (12-40 GHz). The frequency-independent ray optics method is employed to determine the radially varying permittivity profile of the lenses. The challenge of realizing such a radially varying profile and the limitations in dielectric material choices are overcome by two additive-manufacturing-aided approaches: 1) partially infilled dielectrics with a varied periodicity, which ensures the lens performance at the higher end of the frequency range and 2) #artificially #engineered #dielectrics (#AED) with subwavelength-scale metallic inclusions, which enables-high permittivity dielectrics and leads to benefits of thickness and mass reduction for the GRIN lenses. ---- Shiyu Zhang, Ravi Kumar ARYA ,Prof. Will Whittow, Darren Cadman, Raj Mittra, J. C. Vardaxoglou More details can be found at this link: https://lnkd.in/eaHHDtV8

This article investigates the double-#reconfigurable #intelligent #surfaces (#RISs) channel characteristics and propose a #geometry-#based #triple-#cylinder #model, where the RIS subsurface/tile is enabled to assist #vehicle-#to-#vehicle (#V2V) systems and other elements are turned off. To determine tile locations on RIS surface, they formulate an optimization problem by maximizing the end-to-end channel gain and solve it using the #gradient #ascent (#GA) method. Following this, channel correlation function, channel capacity, and outage probability are derived according to the proposed model. Five typical mobile scenarios are discussed to validate the convergence of proposed GA algorithm, where the results show that channel gain can converge to its maximum with optimized tile locations.----@Guiqi Sun, Ruisi He, Jiancheng An, @Bo Ai, @Yaxin Song, @Yong Niu, @Gongpu Wang, Chau Yuen More details can be found at this link: https://lnkd.in/gMskqEPg