A 3D Continuous-Space Electromagnetic Channel Model for 6G Tri-Polarized Multi-User Communications

Multi-antenna techniques capable of exploiting the elevation dimension are anticipated to be an important air-interface enhancement targeted to handle the expected growth in mobile traffic. In order to enable the development and evaluation of such multi-antenna techniques, the 3rd generation partnership project (3GPP) has recently developed a 3-dimensional (3D) channel model. The existing 2-dimensional (2D) channel models do not capture the elevation channel characteristics lending them insufficient for such studies. This article describes the main components of the newly developed 3D channel model and the motivations behind introducing them. One key aspect is the ability to model channels for users located on different floors of a building (at different heights). This is achieved by capturing a user height dependency in modelling some channel characteristics including pathloss, line-of-sight (LOS) probability, etc. In general this 3D channel model follows the framework of WINNERII/WINNER+ while also extending the applicability and the accuracy of the model by introducing some height and distance dependent elevation related parameters.

Three dimensional (3D) Multiple Input and Multiple Output (MIMO) is one of the most promising techniques for the 5th generation (5G) mobile communication system. To support its research, the property of elevation angle in 3D channel model should be accurately modeled. Conventionally, 3D channel is modeled with an assumption that the mean elevation angle of multipaths is coincided with the line-of-sight (LOS) direction. In order to investigate its authenticity and give the reliable 3D channel model, extensive 3D multiple antenna field channel measurements with 100 MHz bandwidth are conducted in three typical scenarios, including outdoor to indoor(O2I), urban microcell (UMi) and urban macrocell (UMa). The statistical characteristics and parameters are extracted and analyzed based on the measurement data. It is found that the assumption holds in the LOS condition. However, for non-line-of-sight (NLOS) condition, a difference exists between the mean elevation angle and the direction connecting transmitter and receiver, which is defined as the elevation angle offset. Then, the eigenvalue distribution and capacity are compared between the reconstructed 3D channels with and without elevation angle offset. Results show that the performance of 3D channel with angle offset fits the measurement data better whereas that without angle offset is underestimated.

Three dimensional (3D) Multiple Input Multiple Output (MIMO) is considered as one key technology for 5th Generation mobile communication systems. However, can the capacity derived from a 3D channel impulse response (CIR) better approximate the corresponding capacity derived from the measured CIR? Is there a substantial improvement in the capacity of 3D MIMO system in comparison to the classical 2D case? To answer these questions, extensive field measurements were conducted for the outdoor to indoor scenarios in China and New Zealand. Key channel parameters are extracted from the measured channel impulse response via the space-alternating generalized expectation-maximization algorithm, followed by the reconstruction of the 32 × 56 CIR according to 2D and 3D channel model. Then CIRs are used to evaluate the channel capacity and comparative simulation results demonstrate that the 3D MIMO capacity closely approximates the capacity predicted with practical CIRs. Moreover, obvious enhancements in the capacity of 3D channel is observed in comparison to 2D case. In addition, the distribution of eigenvalues and the number of contributing eigenvalues are also investigated.

The promise of future 5G networks is to provide very high capacity and ultra-reliable communication. Performance analysis of wireless systems is a key towards insightful design of current and future wireless systems. In this paper, we investigate the uplink performance of a single cell multi-user massive multiple-input multiple-output (MIMO) system over inverse-Gamma shadowing channels. Assuming perfect knowledge of the channel state information (CSI), we derive closed-form expressions for outage probability, average achievable rate and bit error rate (BER). Additionally, we obtain an approximate expression of the signal-to-interference-plus-noise ratio with imperfect CSI, and we derive the corresponding outage probability expression. The obtained expressions are assessed through numerous simulations and numerical examples that confirm the accuracy of our analysis. Furthermore, the results give a clear view on the impact of various parameter settings (including fading severity, transmit power, and the number of base station antennas) on the system’s performance.

Three dimensional (3D) Multiple Input and Multiple Output (MIMO) is one of the most promising techniques for the 5th Generation (5G) mobile communication systems. Thus there is an urgent need for one reliable 3D MIMO channel model to research and evaluate 3D MIMO techniques. In this paper, we focus on the statistic characteristics of elevation angle in urban microcell (UMi) and propose a novel elevation angle modeling methodology. In order to capture enough 3D channel characteristics, field 3D channel measurements at 3.5 GHz with 100 MHz bandwidth are conducted in UMi scenario. Based on the existing 3D channel model frame, the proposed elevation angle model is introduced and the updated 3D channel model is used to perform channel capacity analysis. Comparisons among the updated 3D channel model, the traditional two dimensional (2D) channel model and the field 3D channel data are made. The updated 3D channel model obtains obvious capacity gain compared with 2D channel model. The proposed elevation angle model and the updated 3D channel model can optimally match the channel capacity of the real 3D channel data.

Results of recent measurement campaigns demonstrate a significant increase in the degrees of freedom introduced by the elevation domain, and consequently, a large capacity gap as predicted by 3D and 2D MIMO channel models. To gain further insight into the effects of the elevation domain on MIMO system performance, we derive new spatial correlation (SC) expressions for 3D and 2D channel models, given rectangular arrays of cross-polarized antennas. The main result relates 3D SC to the 2D counterpart, allowing us to quantify the effects of the elevation domain on SC. Furthermore, our result allows us to derive the following three simple relationships between 2D and 3D correlations. We show that for a small elevation angle spread, the difference between 2D and 3D SCs grows quadratically in both vertical separation and angle spread. For the case of small vertical spacings, we derive a bound on the above correlation gap. Furthermore, we show that the elevation effects on correlation can be accurately decoupled, allowing us to express the 3D SC matrix as a Hadamard product of a 2D SC matrix and an elevation component. Collectively, our results demonstrate the need for accurate channel modeling when evaluating the performance of 3D MIMO systems.

When high power amplifiers are in OFDM transmitters employed in the area of their nonlinear characteristics, the transmitters became more energy efficient and their consumption decreases. However, transmitted signal is nonlinearly amplified and therefore subject to nonlinear distortion. When assuming perfect channel state information present at the receiver, only data symbols are nonlinearly distorted, what results in a decreased performance. However, real world devices must obtain channel state information through estimation process, which is usually based on insertion of pilot symbols into transmission and subsequent pilot symbols channel estimation. In this case, also transferred pilot symbols are subject to nonlinear amplification and distortion, which lowers the accuracy of channel estimation process, and further decreases the transmission performance. This article concerns with evaluation of channel estimation error in a situation of nonlinear amplification, and with an improvement of channel estimation error by iterative algorithm of nonlinear distortion estimation, cancellation and channel reestimation.

Reconfigurable intelligent surface (RIS) has emerged as a competitive solution to the blocking problem in millimeter wave (mmWave) communications. However, due to the passive nature of the RIS, obtaining channel state information (CSI) for RIS-assisted mmWave communication systems is rather difficult. Considering that the currently available RIS hardware cannot arbitrarily switch between the active (reflection with configurable phase response) and deactivate (absorption) modes, we suggest a new beam training method for RIS-assisted mmWave communication systems in this study. First, a predefined hierarchical codebook is created using the pattern synthesis method. Then, we provide a novel hierarchical beam training method using two multi-mainlobe codewords in each layer of the hierarchical codebook for beam sweeping. Combining the results of the beam identification in all the layers will yield the ultimate ideal beam direction. Theoretical analyses demonstrate that the suggested approach can effectively reduce training overhead while ensuring successful beam alignment. Simulation results show that the practical codebook can be created successfully, and the suggested method can achieve accurate beam alignment with reduced training overhead.

At present, the world is experiencing a significant transformation from the fifth generation (5G) wireless communication network to the sixth generation (6G) wireless communication network. An important goal is to achieve seamless global coverage of wireless signals. The combination of space network, air network and ground network has been proved to be effective, but the maritime network has not been taken into account. Therefore, how to effectively achieve the global coverage of wireless networks is a challenging topic. This paper first compares the performance of 5G and 6G, and analyzes the possibility of a wireless communication network with global coverage based on 6G technology. After that, we respectively analyze the typical characteristics of space network, air network, terrestrial network and maritime network, and then lead to the key enabling technologies to combine them. Based on the typical characteristics of the above heterogeneous networks and combined with the enabling technologies, we try to propose a 6Gsupported space-air-ground-sea integrated network (SAGSIN) architecture, to achieve seamless global wireless signal coverage. In the end, we rationally analyze a series of challenges and difficulties that may be faced in implementing the architecture.

Efficient utilization of the limited spectrum allocated for personal communication service is one of the major challenges in the wireless system design. Channel offset schemes and their applications are developed for three-dimensional frequency reuse environments. The relationships among channel reuse distance, interchannel usage distance and channel offset degree are computed. The spectral efficiency of the channel offset scheme is discussed and the result shows that compared to channel offsetless scheme, the channel offset scheme can more efficiently employ limited spectrum resource. The parameter calculation method can also be applied to the design of current two-dimensional mobile communication systems.

Printed circuits in bounded media encompass a wide range of practical structures such as discontinuities in waveguides, planar circuits embedded in shielded multilayered media or even two-dimensional printed periodic structures. The Electromagnetic (EM) modeling of printed circuits in layered bounded media is performed via an Integral Equation (IE) technique. Green's functions (GFs) are specially defined to satisfy both the Boundary Conditions (BCs) imposed by the layered media and by the transverse boundary enclosing the entire structure. Finally, a system of IEs on the equivalent sources can be solved numerically by means of the Method of Moments (MoM). Each of the problems enumerated above has already been solved by other authors using IE-MoM techniques. Nevertheless, our formulation introduces a unified approach applicable to all the aforementioned problems. Due to the symmetry presented by a bounded layered media, the GF problem can be reduced into a two-dimensional transverse boundary problem and a one-dimensional transmission line problem in the normal direction. Both problems can be treated independently. This thesis proposes and fully develops an efficient technique that encompasses different laterally bounded multilayered problems with a seamless transition between them. The method is based on a modal representation of the transverse boundary problem and on the expansion of the equivalent surface currents by zero-curl & constant-charge Basis Functions (BFs). It offers a unified and versatile approach that, on one hand eliminates redundancy in the formulation and on the other hand simplifies each particular problem to the evaluation of constant coefficients or basic line integrals. Analytical solutions can be found for the combination of linear subsectional basis functions in rectangular and circular Perfect Electric Conductor (PEC) boundaries as well as for periodic lattices. This thesis then solves the problem of transmission line model in the longitudinal direction by proposing an efficient algorithm that guarantees numerical stability under a variety of known critical conditions where other already known formulations fail. In addition, it introduces alternate equivalent expressions of this formulation that allow new interpretations of the problem. Due to its practical interest, the method is applied for the EM modeling of multilayered boxed printed circuits. This motivated the implementation of a dedicated software tool for the efficient analysis of these topologies including losses. Extensive numerical experiments have been carried out to assess the validity of the aforementioned theory and some properties of test-structures (losses, mesh, etc).

Sixth Generation (6G) research has already begun in academia and industry since 2019 which is considered as ‘year zero’ for 6G research. The technology is expected to be available for commercial deployment from 2030, following the pattern that every decade a new generation of wireless technology is introduced. Currently, i.e. from 2020, telecom operators around the world has started deploying 5G technology in their networks. There are a number of conceptual papers on 6G and its related technologies available with some research groups working actively on this new wireless communication generation. It is yet to be seen that what benefits 6G will bring for society, however, one thing is sure that Machine Learning and Artificial Intelligence in smart cities will play key roles in 6G technology. Therefore the innovative applications raise the quality of life (QoL) for the citizen by monitoring, analyzing, planning, and executing with the integration of various components. We further anticipate that the sixth generation (6G) of the wireless network should be fully autonomic to deliver the quality of services (QoS) and network performance. In this paper, we review what is the current state-of-the-art in 6G. Our aim is to provide readers a starting point in 6G research and to provide an overview of how 6G will be used to build the applications using cutting-edge technologies-SC, AI and ML. We also conceptualise and identify the role of 6G technology with its vision and future challenges. In addition, we have discussed the availability of 6G at the network and user side, along with various future potential use cases for 6G.

Elevation beamforming and Full Dimension MIMO (FD-MIMO) are currently active areas of research and standardization in 3GPP LTE-Advanced. FD-MIMO utilizes an active antenna array system (AAS), that provides the ability of adaptive electronic beam control over the elevation dimension, resulting in a better system performance as compared to the conventional 2D MIMO systems. FD-MIMO is more advantageous when amalgamated with massive MIMO systems, in that it exploits the additional degrees of freedom offered by a large number of antennas in the elevation. To facilitate the evaluation of these systems, a large effort in 3D channel modeling is needed. This paper aims at providing a summary of the recent 3GPP activity around 3D channel modeling. The 3GPP proposed approach to model antenna radiation pattern is compared with the ITU approach. A closed-form expression is then worked out for the spatial correlation function (SCF) for channels constituted by individual antenna elements in the array by exploiting results on spherical harmonics and Legendre polynomials. The proposed expression can be used to obtain correlation coefficients for any arbitrary 3D propagation environment. Simulation results corroborate and study the derived spatial correlation expression. The results are directly applicable to the analysis of future 5G 3D massive MIMO systems.

Millimeter-wave (mmW) carrier frequencies offer new opportunities to build new antenna concepts, however these high frequencies make it nearly impossible to build an omnidirectional antenna. Therefore, it is important to model the position, the rotation of the UE and the surface orientation of the connected antennas. It is also important to consider the corresponding anisotropy in the channel modeling. Especially a three-dimensional (3D) channel model taking dual polarization effects into account is required and shall be illustrated in this communication. Therefore, Radio Frequency (RF) based pattern simulation is combined with the base band link-level simulator.

Carrier Aggregation is an important feature in Long Term Evolution Advanced (LTE-A). It allows operators to provide larger operational bandwidths without the need of having a contiguous, large piece of spectrum. However, an increased bandwidth also needs a larger channel sounding to obtain channel state information (CSI), required for frequency domain scheduling and link adaptation. This constitutes a serious challenge for the uplink since wideband sounding reference signals cannot be transmitted by cell edge (power limited) users and hopped sounding requires a long time to sweep the entire transmission band, thus leading to outdated and less reliable CSI. Also, average interference and its variation in time can seriously jeopardize the CSI at the eNodeB. In this paper, we present an integration of inter cell interference coordination with CSI reporting by reducing the interference variability through controlled allocations. Results show that the entire CSI accuracy can be improved and so does the overall cell performance.