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An editorial is presented on Cybertwin supporting advanced vehicle-to-everything (V2X) applications in the future intelligent and securing vehicular 6G network. Topics include becoming the personal AI assistant and acting as a security agent through customizing the visibility of recorded data; and proposing scheme good security performances in terms of symbol error rate (SER) and secrecy outage probability.

Non-orthogonal multiple access (NOMA) is an effective way to improve the spectrum efficiency of multiple-input multiple-output (MIMO) systems, where this advancement can be fully exploited by employing a proper user selection strategy in the multiuser MIMO system. However, for multiuser scenarios, information-theoretic throughput may not be properly used as the performance indicator since the constraints at the receiver (e.g., suboptimal detectors) are not taken into consideration. In this paper, we adopt the error probability (EP) as the performance metric, which is equivalent to the practical throughput efficiency and can take the critical constraints into consideration. We analyze the pair-wise error probability (PEP) performance of different detectors and propose two kinds of user selection methods to minimize the PEP. To facilitate the detection performance evaluation, we further investigate the multiuser diversity of the proposed selection methods and derive a tight lower PEP bound for the case with randomly selected users. From the analytical and numerical results, we demonstrate that the proposed multiuser selection methods can suppress the inter-user interference effectively and achieve better performance than that of the state-of-the-art method. [ABSTRACT FROM AUTHOR]

In this paper, we study the multiuser detection in a millimeter-wave (mm-wave) wireless communication system using hybrid beamformers, where uplink transmissions are considered under limited scattering. For a base station, with the condition that the number of radio-frequency (RF) chains is relatively smaller than that of users, we consider opportunistic beamforming with analog beams for multiple-signal detection and derive a closed form expression for system sum rate. By applying the minimum mean square error (MMSE)-filter with the proposed opportunistic hybrid beamforming algorithm, the system performance can be further improved. Through simulation results, it is shown that the proposed MMSE-based multiuser detection approaches are attractive for hybrid mm-wave systems to support a large number of users with a small number of RF chains. [ABSTRACT FROM AUTHOR]

Based on the zero prefix (ZP) structure, we propose an efficient block transmission algorithm using distributed space-time codes in the asynchronous cooperative communication systems. To accomplish the new frame, ZP is inserted in front of the data block to combat the relative delay between the asynchronous relays, while zero suffix (ZS) is appended at the end of the block to remove the interblock interference caused by the time dispersing channel; so, we employ this ZP–ZS precoding form to make the coded frames synchronous. It should be noted that single carrier transmission and orthogonal frequency division multiplexing (OFDM) are both compatible with the frame. For single carrier transmission, conventional space-time equalizers can be investigated at the destination node to cancel the multipath interference. To further improve the performance, an improved QR decomposition-based recursive interference cancellation (QRD-RIC) detector is employed, where joint QRD is adopted on the combination of channel matrices from different relays, and then spatial-and-multipath diversity combinations are introduced and improved into the proposed system, where the spatial and multipath diversities are acquired. For OFDM, the fractionally spaced frequency-domain MMSE diversity receiver is employed, since the guard interval in our framing scheme implies oversampling in the frequency domain. Numerical simulations show that the proposed algorithms are effective for the asynchronous transmissions under frequency selective fading channels. [ABSTRACT FROM AUTHOR]

In the fifth-generation (5G) system, millimeter-wave (mmWave) communication has been recognized as a candidate technique. To overcome the high transmission loss of mmWave, distributed antenna systems that consist of a base station (BS) connecting with multiple remote radio units (RRUs) were studied to improve the energy efficiency. In this letter, by utilizing the propagation characteristics of mmWave, we propose a cooperative multiuser beamforming method for energy-efficient transmissions in mmWave distributed antenna systems. The RRUs first decide the local serving group separately and the BS makes an optimization globally with limited data exchange. From simulation results, compared to the state-of-the-art method, it is shown that higher energy efficiency can be realized by the proposed method for the multiuser mmWave distributed system. [ABSTRACT FROM AUTHOR]

With the significant advance of connected vehicles, future demand for vehicular infotainment services will be greatly increased. Traditional content distribution approaches based on typical cellular architecture suffer from long latency and unstable connections in high-dynamic vehicular environments and even may cause congestion on the backhaul network due to a large amount of requested data. In this paper, we propose a novel content delivery framework by leveraging the 5G edge networks, in which the content caching and data prefetching techniques are exploited accordingly. We investigate the comprehensive dynamic link utilization problem in 5G edge networks from the perspectives of vehicle users and network operator, respectively. For the vehicle users’ perspective, our aim is to maximize the vehicular content distribution throughput through optimal scheduling of vehicular access link slots, and also the utilization problem of backhaul link slots in edge networks is studied to reduce the data access delay of vehicles. For the network operator's perspective, the objective is to maximize the total profit of the network operator, and therefore, the auction model is utilized for the vehicular access link slot scheduling and the backhaul link utilization is analyzed in terms of compensations and costs. Finally, extensive simulations are conducted to demonstrate the efficiency of the proposed solutions for edge content delivery of connected vehicles. [ABSTRACT FROM AUTHOR]

A software-defined wireless local area network (SDWLAN) has gained significant interest recently from both the academic and industrial communities and initiated a paradigmatic reconsideration on the stereotyped management and control of current WLAN due to its flexibility and programmability. However, with the proliferation of mobile devices, efficient client association with quality of service (QoS) guarantees in the high-density SDWLAN is a very challenging issue. In this paper, we study the client association problem in the SDWLAN with new features, including centralized association, global network state awareness, seamless handoff, and flow-level association. We formulate the client association in a high-density scenario as an optimization problem aiming to minimize the interpacket delay of individual flows, based on an unsaturated and heterogeneous Markovian analytical model. Furthermore, we interpret the optimization problem as an NP-hard supermodular set function minimization problem, which is solved by two low-complexity heuristic methods, namely the greedy algorithm and the bounded local search algorithm. Through simulations, we demonstrate the effectiveness of our proposed client association solution. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the performance of a dual-hop multiple-input–multiple-output (MIMO) amplify-and-forward (AF) relay network, where the source, relay, and destination are all equipped with multiple antennas. By using maximum ratio transmission (MRT) at the transmitter and maximum ratio combining (MRC) at the receiver, we first obtain the output signal-to-interference-plus-noise ratio (SINR) of the dual-hop AF relay system, considering multiple cochannel interferences (CCIs), as well as noise at the relay. Then, we derive an exact closed-form expression for the outage probability (OP), and the asymptotic result of OP at high SNR, which can be used to calculate the array gain and diversity order. Finally, computer simulations are conducted to validate the performance analysis. Our new analytical expressions not only provide a fast and efficient method to evaluate the system performance but enable us to gain valuable insights into the effects of key parameters on the MIMO AF relaying network performance that benefits from implementing multiple antennas at each of the three nodes as well. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the performance of a multiple-input–multiple-output (MIMO) maximal ratio combining (MRC) system with feedback delay and channel estimation error. By taking these practical imperfect factors into account, we first formulate the system model and derive the moment-generating function of the output signal-to-noise ratio (SNR), which serves as the basis for further system performance analysis. Then, we compute the probability density function (pdf) and the cumulative distribution function (cdf) of the output SNR. Furthermore, we derive the analytical expressions of the exact and approximate average symbol error rates (SERs) of the MIMO MRC system, which are used to investigate the performance loss in terms of the array gain and diversity order. Finally, computer simulations are conducted to show the efficacy of the analytical results and the effect of feedback delay and channel estimation error on the system performance. [ABSTRACT FROM PUBLISHER]