There is considerable pressure to define the key requirements of 5G, develop 5G standards, and perform technology trials as quickly as possible. Normally, these activities are best done in series but there is a desire to complete these tasks in parallel so that commercial deployments of 5G can begin by 2020. 5G will not be an incremental improvement over its predecessors; it aims to be a revolutionary leap forward in terms of data rates, latency, massive connectivity, network reliability, and energy efficiency. These capabilities are targeted at realizing high-speed connectivity, the Internet of Things, augmented virtual reality, the tactile internet, and so on. The requirements of 5G are expected to be met by new spectrum in the microwave bands (3.3-4.2 GHz), and utilizing large bandwidths available in mm-wave bands, increasing spatial degrees of freedom via large antenna arrays and 3-D MIMO, network densification, and new waveforms that provide scalability and flexibility to meet the varying demands of 5G services. Unlike the one size fits all 4G core networks, the 5G core network must be flexible and adaptable and is expected to simultaneously provide optimized support for the diverse 5G use case categories. In this paper, we provide an overview of 5G research, standardization trials, and deployment challenges. Due to the enormous scope of 5G systems, it is necessary to provide some direction in a tutorial article, and in this overview, the focus is largely user centric, rather than device centric. In addition to surveying the state of play in the area, we identify leading technologies, evaluating their strengths and weaknesses, and outline the key challenges ahead, with research test beds delivering promising performance but pre-commercial trials lagging behind the desired 5G targets.

5G : A tutorial overview of standards, trials, challenges, deployment, and practice

Millimeter-wave (mmWave) will be used for fifth-generation (5G) wireless systems. While many recent empirical studies have presented propagation characteristics at mmWave bands, macrodiversity and Coordinated Multipoint (CoMP) have not been carefully studied. This paper describes a large-scale mmWave base station diversity measurement campaign at 73 GHz in an urban microcell (UMi) in downtown, Brooklyn, NY, USA, and provides the first detailed analysis of CoMP and macrodiversity performance based on extensive measurements. The research employed nine different base station locations in a 200 m by 200 m area and considered 36 individual transmitter–receiver combinations for extensive co- and cross-polarized varying directional beam channel impulse response measurements. From the measured data, hypothesis testing with cross-validation shows that large-scale shadow fading of directional path loss at an RX from multiple base stations can be modeled as being independent. To consider life-like human blockage in CoMP and macrodiversity analysis, simulated human blockage traces are superimposed on the directional measurements to quantitatively show that a user that is served by multiple base stations undergoes dramatically less outage in the presence of rapid fading events, compared to a single serving base station. Moreover, the base station diversity measurements are used to determine the effectiveness of downlink precoding techniques for mmWave CoMP. While results show that the coordination can improve network performance by suppressing interference when it exists, nearly half of the 680 000 directional CoMP measurements (~43%) result in no interference for either user, meaning that macrodiversity alone may offer sufficient link and capacity improvement and that CoMP may not be necessary for interference coordination at mmWave when narrow directional beams are used.

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Millimeter-Wave Base Station Diversity for 5G Coordinated Multipoint (CoMP) Applications

With an extensive growth in user demand for high throughput, large capacity, and low latency, the ongoing deployment of Fifth-Generation (5G) systems is continuously exposing the inherent limitations of the system, as compared with its original premises. Such limitations are encouraging researchers worldwide to focus on next-generation 6G wireless systems, which are expected to address the constraints. To meet the above demands, future radio network architecture should be effectively designed to utilize its maximum radio spectrum capacity. It must simultaneously utilize various new techniques and technologies, such as Carrier Aggregation (CA), Cognitive Radio (CR), and small cell-based Heterogeneous Networks (HetNet), high-spectrum access (mmWave), and Massive Multiple-Input-Multiple-Output (M-MIMO), to achieve the desired results. However, the concurrent operations of these techniques in current 5G cellular networks create several spectrum management issues; thus, a comprehensive overview of these emerging technologies is presented in detail in this study. Then, the problems involved in the concurrent operations of various technologies for the spectrum management of the current 5G network are highlighted. The study aims to provide a detailed review of cooperative communication among all the techniques and potential problems associated with the spectrum management that has been addressed with the possible solutions proposed by the latest researches. Future research challenges are also discussed to highlight the necessary steps that can help achieve the desired objectives for designing 6G wireless networks.

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Issues, challenges, and research trends in spectrum management: A comprehensive overview and new vision for designing 6g networks

5G New Radio (NR) has attracted a large amount of interest with its foreseen improvement of user experience and capacity. To become a commercial success coverage is also an important con- sideration. The sub-6 bands are expected to provide good coverage. One such useful band is 3.5 GHz. In this paper the coverage of 3.5 GHz is studied by means of a full-scale trial with a NR testbed. With beamforming the increased propagation losses at 3.5 GHz compared to 2.1 GHz can be compensated and the coverage was demonstrated to be on par with 2.1 GHz LTE fixed antenna coverage both outdoor and indoor.

5G NR Testbed 3.5 GHz Coverage Results

The recent advancement in the 5G wireless technologies is demanding higher bandwidth, which is a challenging task to fulfill with the existing frequency spectrum i.e. below 6 GHz. It forces operators and researchers to go for higher frequency millimeter-wave (mm-wave) spectrum in order to achieve greater bandwidth. Enabling mm-wave, however, will come with various path loss, scattering, fading, coverage limitation, penetration loss and various different signal attenuation issues. Optimizing the propagation path is much essential in order to identify the behavior of channel response of the wireless channel before it is implemented in the real-world scenario. In this paper, we have analyzed the potential ability of mm-wave frequency band such as 28 and 73 GHz and compare our results with the existing 2.14 GHz LTE-A frequency band. We utilize the most current potential Alpha Beta Gama (ABG) propagation path loss model for designing urban microcell line of sight (LOS) scenario. We investigate the network performance by estimating average user throughput, average cell throughput, cell-edge user's throughput, peak user throughput, spectral efficiency and fairness index with respect to different user's capacity. The results express the significant improvement in spectrum efficiency of up to 95% for 28 GHz and 180% for 73 GHz is achieved in comparison with 2.14 GHz. It results also show that the 28 and 73 GHz frequency band is able to deliver up to 80 and 170% of enormous improvement in average cell throughput respectively as compared to currently LTE-A frequency band.

Propagation channel characterization for 28 and 73 GHz millimeter-wave 5G frequency band

This paper presents indoor and outdoor field experimental results that clarify the 4-by-8 MIMO throughput performance when applying distributed multiple-input multiple-output (MIMO) with a narrow antenna beam tracking in the 15 GHz frequency band in the downlink of a 5G cellular radio access system. The experimental results show that throughput exceeding 15 Gbps is achieved with a high average rank of 4 at an indoor office building lobby and outdoor parking area. As for the distributed MIMO gain in terms of throughput in LoS environments, we achieve throughput gain of 39 % and 105 % in the indoor office building lobby and outdoor parking area, respectively. And also throughput gain of 15 % is achieved in N-LoS environment in office building lobby in multi-path rich environment. We also observe a significant increase of throughput and rank when changing the transmission point (TP) spacing from 0.5 to 1.5 m, while only a limited performance improvement when the TP spacing exceeds 1.5 m. Finally, the throughput performance with various TP positions was tested, and the TP locations when facing each other with a TP spacing of 50 m exhibit excellent performance exceeding 10 Gpbs.

Indoor and Outdoor Experiments on 5G Radio Access Using Distributed MIMO and Beamforming in 15 GHz Frequency Band

This paper presents indoor experimental results showing the achievement of 14.5 Gbps throughput performance based on 730.5 MHz bandwidth transmission when applying carrier aggregation (CA) with 8 component carriers (CCs) and 4-by-8 single-user multiple-input multiple-output (MIMO) multiplexing in the 15 GHz frequency band in the downlink of 5G cellular radio access. Beam tracking with massive MIMO is implemented in a 5G testbed to support user mobility with a narrow beam. Experimental results in an indoor multi-path rich environment show that the peak throughput is 14.5 Gbps in a line-of-sight (LoS) environment with high mobility-reference signal received power (MRSRP) and low antenna correlation. The results also show that 12.5 Gbps is achieved behind a wall in non-LOS conditions due to ceiling reflections.

Indoor experiment on 5G radio access using beam tracking at 15 GHz band

This paper presents measurement results from different deployments with a 5G test-bed on a 15-GHz frequency band. The beam gain with a grid-of-beam solution applied to an 8x8 element antenna array is compared with a reference wide-beam power equivalent antenna. The beamforming gain in outdoor environment is found to be large, it is in the range of 10-13 dB in line-of-sight (LoS) and 7-12 dB in non-LoS. In a reflective and rich indoor environment, the gain is as expected lower but still substantial, 5-11 dB. The potential of a hybrid analog-digital solution is also assessed as an upper bound with perfect phase coherent combination of several beams. To reach an average beamforming gain of 14 dB it is sufficient with the combination of three beams in outdoor LoS, while eight beams are required in the indoor scenario.

Beamforming Gain Measured on a 5G Test-Bed

We propose a trial concept that utilizes advanced multi-antenna solutions such as beamforming and spatial multiplexing with a massive number of antenna elements for use in a previously established trial system for the fifth generation (5G) mobile broadband communications system. Furthermore, we present experimental results showing that multi-user aggregated data rates exceeding 20 Gbps are possible in a real field environment.

5G Experimental Trial Achieving over 20 Gbps Using Advanced Multi-Antenna Solutions

This paper presents outdoor field experimental results that clarify 4-by-8 multiple-input multiple-output (MIMO) in the downlink throughput performance when applying distributed MIMO in the 28 GHz frequency band of a 5G cellular radio access system. A variety of transmission point (TP) deployments with narrow antenna beam forming is evaluated in order to investigate the downlink and uplink throughput performance and appropriate TP deployment for distributed MIMO. The experimental results show that the throughput is limited to approximately 7 Gbps in the downlink and 1 Gbps in the uplink in a parking area with localized MIMO. A distributed MIMO throughput gain is achieved with various TP deployments for both the downlink and uplink using two radio units. The outdoor parking area is an open space and multipaths are not anticipated, so a distinct advantage from distributed MIMO is expected. The distributed MIMO gain of 60% in the downlink and from 50 to 200% in the uplink is achieved at the cumulative distribution function of 80%. As a result of implementing distributed MIMO, throughput exceeding 10 Gbps in the downlink and 1.9 Gpbs in the uplink is achieved in the 28-GHz frequency band.

Shoji Itoh

Papers

Indoor and Outdoor Experiments on 5G Radio Access Using Distributed MIMO and Beamforming in 15 GHz Frequency Band

Indoor experiment on 5G radio access using beam tracking at 15 GHz band

Beamforming Gain Measured on a 5G Test-Bed

5G Experimental Trial Achieving over 20 Gbps Using Advanced Multi-Antenna Solutions

Outdoor experiments on 5G radio access using distributed MIMO and beamforming in 28-GHz frequency band