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We propose two schemes to perform multiuser detection (MUD) for multiuser multiple-input multiple-output (MIMO) systems under overload. Typically linear MUD algo rithms fail to perform under overload and maximum likelihood detection is often prohibitively complex. In this paper, we use hybrid automatic repeat request (HARQ) retransmissions to transform an overloaded system into a critically or underloaded system based on the concept of virtual receive antennas. Hence, low complexity linear MUD algorithms can be used and achieve diversity gains. Simulation results clearly highlight the advan tages obtained by the proposed schemes.Index Terms-MIMO, HARQ, Multiuser detection. I. IN TRODUCTIONThe performance and reliability of wireless communication systems can be improved by employing multiple antennas at both ends, thereby creating multiple-input multiple-output (MIMO) channels. However, once multiple co-channel users are added to the system it can be difficult to provide as many receive antennas, Nn as transmit antennas, N t , resulting in an overloaded (Nr < N t ) condition. Multiuser detection (MUD) algorithms are used to detect the data transmitted from all co-channel users. Co-channel inter ference (CCI) introduced by multiple users severely degrades the performance of linear MUD algorithms under overloaded conditions compared to critically loaded (Nr = N t ) and underloaded (Nr > N t ) conditions [1], [2]. Joint maximum likelihood (JML) [3] detection works well under overloaded conditions. However, there is an exponential growth in com plexity with the number of transmit antennas, making it less feasible for practical applications. To overcome this limitation, reduced-complexity MUD algorithms have been developed for overloaded scenarios [4], [5], [6]. These algorithms demand sophisticated implementation and still have quite high com putational complexity. Furthermore, these algorithms exhibit error floors at high signal-to-noise ratio (SNR). The primary focus of this paper is to combine hybrid automatic repeat request (HARQ) [7] with the use of virtual receive antennas [8] and a simple MUD algorithm resulting in a simple and novel multiuser transmission approach that works well under overloaded conditions. Most previous research on MIMO HARQ systems [9] -[10] has focused on critically or underloaded conditions. In [9], a symbol-level packet combining scheme was proposed, based on uncertainty processing to improve the decoding performance in MIMO HARQ systems. In [10], a linear MIMO HARQ precoder was designed to optimize the mutual information, and joint HARQ detection was performed by stacking the received vectors from all (re-)transmissions. The same signal vector was transmitted from all antennas during all (re-)transmissions. To the best of our knowledge, research to date has not considered MIMO HARQ in overloaded conditions. Here we consider MUD and HARQ techniques for overloaded systems. We describe two new schemes which stack the received vector from all (re-)transmissions. Unlike the work of [10], sta...

Several studies have attempted to uncover the impact of weather parameters on the coronavirus (COVID-19) pandemic during the initial stage of its outbreak. However, they reported contradicting findings due to limited data available at an earlier stage of the outbreak. Therefore, in this study, we investigate the impact of regional temperature on the pandemic in 34 different locations of the globe by defining two main objectives. The first objective is focused on pattern analysis of an earlier stage of the pandemic. The conducted analysis suggests that the spread of the COVID-19 outbreak during its initial stage was slower in the regions experiencing extreme temperatures. The second objective is about understanding the impact of temperature on new cases (NC) and new deaths (ND) of COVID-19 reported per day by using linear regression (LR) as a statistical tool. For most of the locations, under simple LR analysis, a significant inverse relationship has been observed between average temperature and NC or ND. However, a few locations, including Pakistan, India, Singapore, Bahrain, and Qatar, have shown a significant positive relationship between average temperature and NC with a 99.9% confidence level. Furthermore, Pakistan, Thailand, Bahrain, and Qatar have shown a significant positive relationship between average temperature and ND with a 95% confidence level. Although most of these locations experienced temperatures with a mean greater than 22 °C and standard deviation greater than 5 °C, excluding India, the number of total COVID-19 cases reported in these locations is small. Moreover, the results of multiple LR analysis reveal a significant inverse relationship between average temperature and NC or ND with a 95% confidence level.

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In this paper, an 8-element Ultra-wideband Multiple-Input-Multiple-Output (UWB-MIMO) antenna system is proposed. This MIMO system has novel miniaturized antenna elements that are evolved from a conventional monopole patch antenna. These antennas incorporate various impedance matching features including but are not limited to smoothly tapered fed lines, split and truncated ground configuration, semicircles arches, and inverted p-shaped slots. The antenna pairs are arranged in the cuboidal form to achieve a 3D-arrangement whereas customized decoupling structures achieve the desired isolation levels for three configurations including side-by-side, orthogonal, and across. These three distinct isolation mechanism offers isolation ranges from 20-30 dB for the proposed configurations. More importantly, a diamond eye structure (DES) as a parasitic element is also designed and optimized to improve the impedance matching owing to the lossy nature of isolation structures. The proposed antenna system has compact dimensions of 26.9 × 26 × 26.9 mm and its investigated MIMO performance proves its suitability for communication devices operating in the whole UWB spectrum of 3.1-10.6 GHz. INDEX TERMS Frequency selective surfaces (FSS), Multiple-input-multiple-output (MIMO), Mutual coupling, Ultra-Wideband (UWB) antennas.

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xCalamities such as earthquakes and tsunami affect communication services by devastating the communication network and electrical infrastructure. Multihop relay networks can be deployed to restore the communication environment quickly in catastrophe-stricken areas. However, performance in terms of throughput is affected by deploying the relay networks. In wireless local area networks (WLANs), the primary purpose of multiband transmission employing multihop relay networks is to increase the throughput and reduce the latency. In the future, wireless networks are believed to carry high throughput, more data rates, and less latency by expanding bandwidth-demanding applications. Simultaneous multiband transmission in WLAN systems is considered to increase the coverage area without power escalation. Due to the inherent characteristics of different bands and channel conditions, transmission rates tend to be different. The impact of such conditions may cater to the disproportional distribution of data among bands, causing some of the bands to be overwhelmed, which incurs buffer overflow and packet loss. In contrast, the channel capacity of some of the bands remains underutilized. In this paper, we consider the channel conditions and transmission rates of each band on either side of the relay to address the problems mentioned above. Furthermore, this paper proposes a load distribution-based end-to-end traffic scheduling technique to improve system performance. The simulation results demonstrate the effectiveness of our proposed method with maximizing throughput and minimizing end-to-end delay.