The fifth generation (5G) mobile communication systems will be in use around 2020. The aim of 5G systems is to provide anywhere and anytime connectivity for anyone and anything. Several new technologies are being researched for 5G systems, such as massive multiple-input multiple-output communications, vehicle-to-vehicle communications, high-speed train communications, and millimeter wave communications. Each of these technologies introduces new propagation properties and sets specific requirements on 5G channel modeling. Considering the fact that channel models are indispensable for system design and performance evaluation, accurate and efficient channel models covering various 5G technologies and scenarios are urgently needed. This paper first summarizes the requirements of the 5G channel modeling, and then provides an extensive review of the recent channel measurements and models. Finally, future research directions for channel measurements and modeling are provided.

A Survey of 5G Channel Measurements and Models

Nonorthogonal multiple access (NOMA) exhibits superiority in spectrum efficiency and device connections in comparison with the traditional orthogonal multiple access technologies. However, the nonorthogonality of NOMA also introduces intracell interference that has become the bottleneck limiting the performance to be further improved. To coordinate the intracell interference, we investigate the dynamic user scheduling and power allocation problem in this paper. Specifically, we formulate this problem as a stochastic optimization problem with the objective to minimize the total power consumption of the whole network under the constraint of all users’ long-term rate requirements. To tackle this challenging problem, we first transform it into a series of static optimization problems based on the stochastic optimization theory. Afterward, we exploit the special structure of the reformulated problem and adopt the branch-and-bound technique to devise an efficient algorithm, which can obtain the optimal control policies with a low complexity. As a good feature, the proposed algorithm can make decisions only according to the instantaneous system state and can guarantee the long-term network performance. Simulation results demonstrate that the proposed algorithm has good performance in convergence and outperforms other schemes in terms of power consumption and user satisfaction.

Energy-Efficient User Scheduling and Power Allocation for NOMA-Based Wireless Networks With Massive IoT Devices

The modern intelligent transportation system brings not only new opportunities for vehicular Internet of Things (IoT) services but also new challenges for vehicular ad-hoc networks (VANETs). Apart from enhanced network performance, a practical and reliable security scheme is needed to handle the trust management while preserving user privacy at the same time. The emerging 5G mobile communication system is viewed as a prominent technology for ultra-reliable, low-latency wireless communication services. Furthermore, incorporating software-defined network (SDN) architecture into the 5G-VANET enables global information gathering and network control. Hence, real-time IoT services on transportation monitoring and reporting can be well supported. Both pave the way for an innovative vehicular security scheme. This paper investigates the security and privacy issue in the transportation system and the vehicular IoT environment in SDN-enabled 5G-VANET. Due to the decentralized and immutable characteristics of blockchain, a blockchain-based security framework is designed to support the vehicular IoT services, i.e., real-time cloud-based video report and trust management on vehicular messages. This paper explicitly illustrates the SDN-enabled 5G-VANET model and the scheduling procedures of the blockchain-based framework. The numerical simulation results also show that malicious vehicular nodes or messages can be well detected while the overhead and impact on the network performance are acceptable for large-scale scenarios. Through case studies and theoretical analysis, we demonstrate our design substantially guarantees a secure and trustworthy vehicular IoT environment with user privacy preserved.

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Blockchain-Based Secure and Trustworthy Internet of Things in SDN-Enabled 5G-VANETs

This paper is a tutorial on linear, state space, model-based methods for certain nonlinear estimation problems commonly encountered in signal and data analysis. A prototypical problem that is studied is that of estimating the frequencies of multiple, superimposed sinusoids from a short record of noise-corrupted data. The approach expounded however, is applicable to a vast range of nonlinear signal analysis problems and applications in direction finding and damped sinusoid retrieval are dealt with in some detail. The benefits that result from using a state space description of the signal are highlighted in this paper. It is shown that state space models provide an elegant tool for exposing the structure present in the problem. The approach also allows for robust parameterization of the model with respect to finite precision errors. The robustness of the parameter set is complemented by the availability of numerically robust tools to estimate the parameters. The resulting algorithms are compatible with multiprocessor implementations. >

Model based processing of signals : a state space approach. Prolog

At the time of writing, vehicle-to-vehicle (V2V) communication is enjoying substantial research attention as a benefit of its compelling applications. However, the ever-increasing tele-traffic is expected to result in overcrowding of the available band. As a first resort, multiple input multiple output (MIMO) can be utilized to enhance the attainable bandwidth efficiency or link reliability. However, in hostile V2V wireless propagation environments, the achievable multiple-antenna gain is eroded by the channel correlation. As a promising MIMO technique, spatial modulation (SM) only activates a single transmit antenna (TA) in any symbol interval and, hence, completely avoids the inter-antenna interference, hence showing robustness against channel correlation. As a further powerful solution, non-orthogonal multiple access (NOMA) has been proposed for improving the bandwidth efficiency. Inspired by the robustness of SM against channel correlation and the benefits of NOMA, we intrinsically amalgamate them into NOMA-SM in order to deal with the deleterious effects of wireless V2V environments as well as to support improved bandwidth efficiency. Moreover, the bandwidth efficiency of NOMA-SM is further boosted with the aid of a massive TA configuration. Specifically, a spatio-temporally correlated Rician channel is considered for a V2V scenario. We investigate the bit error ratio performance of NOMA-SM via Monte Carlo simulations, where the impact of the Rician $K$ -factor, spatial correlation of the antenna array, time-varying effect of the V2V channel, and the power allocation factor is discussed. Furthermore, we also analyze the capacity of NOMA-SM. By analyzing the capacity and deriving closed-form upper bounds on the capacity, a pair of power allocation optimization schemes are formulated. The optimal solutions are demonstrated to be achievable with the aid of our proposed algorithm. Again, instead of simply invoking a pair of popular techniques, we intrinsically amalgamate SM and NOMA to conceive a new system component exhibiting distinct benefits in the V2V scenarios considered.

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Performance Analysis of NOMA-SM in Vehicle-to-Vehicle Massive MIMO Channels

This letter presents a novel compact dual-band dual-polarized antenna with filtering structures for Sub-6 GHz base station applications. It is operating at the LTE (2500–2690 MHz) and Sub-6 GHz of 5G (3300–3600 MHz) bands, where the center frequency of upper-band (UB) is 1.32 times of lower-band (LB). Mutual coupling between LB and UB is suppressed by the introduction of the filtering stubs near the feeding lines. A sufficiently high isolation between LB and UB (>25 dB) is also obtained. The size of the proposed antenna is only 0.43 ${{\rm{\lambda }}_1} \times \text{0.43}$ ${{\rm{\lambda }}_1} \times \text{0.26}$ ${{\rm{\lambda }}_{1}}$ ( ${{\rm{\lambda }}_1}$ is the free-wavelength at 2.6 GHz). The half power beam widths are 65° ± 5° over both bands at horizontal planes. A four-element array, which consists of four hybrid antennas (the UB element is nested in the LB element) with a small array width (only 105 mm) is also studied. The proposed antenna and its array are suitable for wireless communication applications.

A Compact Dual-Band Dual-Polarized Antenna With Filtering Structures for Sub-6 GHz Base Station Applications

Massive multiple-input multiple-output (MIMO) is a key technology in fifth-generation (5G) networks. By using a large number of antenna elements placed in a 2-D array, an evolved Node B (eNB) can form multiple vertical beams in the elevation domain and adaptively track moving vehicles. Thus, the throughput and spatial multiplexing efficiency in vehicle-to-infrastructure (V2I) access can be significantly increased. However, multipath spatial propagation in wireless channels results in the angular spread of the power arrival profile, which causes intersector interference in massive-MIMO beamforming and becomes a limiting factor for the system capacity. In this paper, we investigate the channel propagation characteristics and the intervehicle interference in the elevation-domain spatial multiplexing for V2I mobile access and develop a packet-level channel model that can be used for system design and network protocol simulations. First, a measurement campaign for the urban macrocell street uplink channels was performed using a 3-D MIMO channel sounder, and the elevation power spectra (EPSs) on the eNB side were measured. Then, the intersector interference in the vertical beamforming is evaluated based on the antenna array pattern and channel EPS. Finally, a packet-level channel model in the form of a finite-state Markov chain (FSMC) is proposed for the V2I elevation multiplexing uplinks. The model describes the received signal-to-interference ratio (SIR) variation when a vehicle is moving toward an eNB. The steady-state distribution of the FSMC is analytically derived and verified by simulations. Based on the stochastic process of the SIR, the concepts of “large/small-scale multiplexing fading” are proposed. The field measurement results in this work have revealed the spatial power arrival profiles of the V2I street channels that are critical for the MIMO system design, and the proposed packet-level channel model provides an enabling tool for the analysis and simulation of the V2I elevation multiplexing links in the 5G networks.

Channel Measurement and Packet-Level Modeling for V2I Spatial Multiplexing Uplinks Using Massive MIMO

By utilizing planar antenna arrays, a base station (BS) by the roadside can exploit two-dimensional (2-D) sectorization and beamforming to connect dense pedestrians and vehicles in a street. The azimuth and elevation angular spreads of the street radio channels are critical for the spatial multiplexing performance. In this paper, by utilizing a multiple-input–multiple-output (MIMO) channel sounder equipped with two uniformed planar antenna arrays, the three-dimensional (3-D) multipath propagations in urban macrocellular street canyon environments were measured and modeled, with the focus on the dynamics of the angular spreads along the streets. The transmitter (emulating a user equipment, UE) was placed at 100 and 95 positions in two streets for the line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios, respectively. The azimuth/elevation angle-of-arrival (AoA/EoA) and the root-mean-square azimuth/elevation spread of arrivals (ASA/ESA) at each position were measured. Contrary to the expected monotonous change of the angular spreads with respect to the UE–BS distance, the measurement results show that, in the LOS scenario, ASA and ESA have a positive correlation with the UE–BS distance in an open street but a negative correlation in a closed street. In the NLOS scenario, the correlation is positive when the UE is close to a building without the over-rooftop diffraction, but the correlation is reversed if such a Quasi-LOS path exists. The 2-D arrival profiles of the ray clusters have been observed, and their impacts on the angular spreads are analyzed in different propagation environments. By comparing multiple candidate fitting functions, the lognormal distribution models for ASA and ESA are proposed. In addition, the channel delay spread (DS) was also measured along the streets and positive correlations among ASA, ESA, and DS have been found. This work can help to establish the 3-D spatial channel models for advanced MIMO technologies and is also valuable for future channel measurements.

Measurement and Modeling of Angular Spreads of Three-Dimensional Urban Street Radio Channels

In emerging heterogeneous networks, small-cell base stations deployed along urban streets can increase the network capacity for vehicular access significantly. To fully exploit the potential of full-dimensional multiple-input-multiple-output technologies, it is critical to understand the propagation characteristics of the small-cell vehicle-to-infrastructure (V2I) access channels. In this paper, a measurement campaign for the three-dimensional propagation with $\pm 45^\circ$ polarizations was conducted at 2.6 GHz in a typical urban street canyon environment. We utilized a sounder with two cross-polarized uniformed planar arrays. The transmitter was placed on the rooftop of a five-storey building and the receiver was placed at the 15th position along a street with the line of sight (LOS). The elevation/azimuth of arrival (EoA/AoA), power spectrum, and root-mean-square angular spread of arrival (ESA/ASA) of the multipath components were measured. We propose a dual-Laplace probability density function (PDF) model for the EoA distributions that have LOS clusters and ground reflections. We propose two models, the flat-bottom Laplace PDF and the superposed Laplace PDF, to describe the clustering behavior of the AoA distributions. We also propose the Lognormal models for the ESA and ASA distributions. Furthermore, it is found that polarization does not affect the EoA and AoA distributions, but has a significant impact on the ASA and ESA. The measurement results and channel models can help with the design and evaluation of the spatial transmission/multiplexing technologies in the small-cell V2I access.

Cross-Polarized Three-Dimensional Channel Measurement and Modeling for Small-Cell Street Canyon Scenario

To characterize multipath spatial propagations in three-dimensional space is critical in wireless channel measurements and modeling. Due to the large number of paths and the correlation among multipath signals, the direction-of-arrival (DoA) estimation for propagation paths is a challenging issue. In this letter, we propose a new multipath DoA estimation scheme, named Multipath DoA Estimation by Rotational Invariance on Array Impulse Response (MERIA), which utilizes the rotational invariance of array channel impulse response matrix and estimates the DoAs of arriving paths individually and sequentially. Simulations and field measurement experiments have demonstrated that MERIA can estimate incident angles of a large number of paths and suppress multipath interference effectively. Therefore, by using MERIA in field channel measurements, the requirements on the antenna array size and the hardware complexity of channel sounders can be reduced significantly.

Jianping Zhao

Papers

A Compact Dual-Band Dual-Polarized Antenna With Filtering Structures for Sub-6 GHz Base Station Applications

Channel Measurement and Packet-Level Modeling for V2I Spatial Multiplexing Uplinks Using Massive MIMO

Measurement and Modeling of Angular Spreads of Three-Dimensional Urban Street Radio Channels

Cross-Polarized Three-Dimensional Channel Measurement and Modeling for Small-Cell Street Canyon Scenario

Multipath DoA Estimation by Rotational Invariance on Array Channel Impulse Response