Emmanouel T. Michailidis

The Land Mobile Earth-Space Channel

Research on mobile satellite and high-altitude platform (HAP) systems (MSHSs) has recently proliferated because of the allocation of additional spectrum, the intense standardization efforts from different international institutes, the detailed studies pursued by the European [European Space Agency (ESA)], French (CNES), and Japanese (JAXA) space agencies, and the commercial impact of some of the corresponding system implementations. A survey of mobile satellite systems is provided. Enhanced land mobile Earth-space (LMES) channels encompassing a variety of geometries, frequency bands, and propagation environments are critical for developing and assessing the performance of these new MSHS paradigms. In this article, we provide a survey of the state-of-the-art measurement campaigns, modeling approaches, and generative methods concerning the LMES channel and pinpoint future research directions. We refer to LMES since, due to the close similarities they exhibit, we present channels from both geostationary (GEO) satellites and quasi-stationary HAPs. Most of the cited models apply in both cases. General emphasis is on statistical/physical narrow-band models, which is the norm in LMES channels.

Three-Dimensional HAP-MIMO Channels: Modeling and Analysis of Space-Time Correlation

High-altitude platforms (HAPs) are one of the most promising alternative infrastructures for realizing next-generation high-data-rate wireless networks. This paper investigates the application of multiple-input-multiple-output (MIMO) techniques to HAP-based systems and proposes a 3-D geometry-based single-bounce reference model for Ricean fading channels. From this model, the space-time correlation function is derived for a 3-D nonisotropic scattering environment. The statistical properties of the reference model are analytically studied in terms of various parameters such as the elevation angle of the platform, the array configuration, the Doppler spread, and the distribution of the scatterers. Using the theoretical expressions, one can easily numerically evaluate the HAP antenna interelement spacing required to achieve uncorrelated responses in the HAP-MIMO channel matrix. The proposed model provides guidelines for the system design and performance analysis of HAP-MIMO communication systems with line-of-sight (LoS) and non-line-of-sight (NLoS) connections at the L and S frequency bands.

Three-Dimensional Modeling and Simulation of MIMO Mobile-to-Mobile via Stratospheric Relay Fading Channels

As the development of next-generation wireless communication systems envisages the synergetic integration of heterogeneous terrestrial and aerospace networks, high-altitude platforms (HAPs) could play a key role, acting as transparent relay stations in the stratosphere by transferring information from an uplink to a downlink channel. This paper deals with the 3-D modeling of multiple-input-multiple-output (MIMO) mobile-to-mobile via stratospheric relay (MMSR) fading channels in amplify-and-forward (AF) networks. A geometrical two-cylinder reference model is proposed and considers that the scatterers in the vicinity of a source mobile station and a destination mobile station are nonuniformly distributed within two separate cylinders. Both line-of-sight (LoS) and non-LoS (NLoS) propagation conditions are assumed in the transmission links from the source to the destination via the stratospheric relay. Analytical expressions are derived for the 4-D space-time correlation function (STCF), which is also used to evaluate the channel capacity of the entire link using uniform linear arrays (ULAs). Based on the reference model, a sum-of-sinusoids (SoS) statistical simulation model is developed to verify the theoretical results.

Radio Propagation Channel Measurements for Multi-Antenna Satellite Communication Systems: A Survey

For the terrestrial infrastructure, the multiple-input multiple-output (MIMO) architecture is a key technology that has brought the wireless gigabit vision closer to reality. Satellite communication systems have not been immune from this wave of innovation, and theoretical and experimental efforts have recently been devoted to the investigation of the applicability of multiple-antenna techniques to these systems. This paper intends to highlight and critically present the most important results from measurement campaigns conducted to characterize the radio channel of multi-antenna satellite systems. Emphasis is given on the viability of MIMO technology over satellite, and the potential enhancements in terms of channel capacity and link reliability that can be achieved through spatial and/or polarization diversity. The configurations under investigation range from very simple single-input multiple-output (SIMO) systems, with multiple antennas only at the terrestrial receiver, to quite complex and challenging systems, such as dual-satellite multiple-input single-output (MISO) systems, and single-satellite dual-polarized MIMO systems. The spotlight is on land mobile satellite (LMS) systems in outdoor radio propagation environments. However, satellite-to-indoor reception is also included.

Spatially Correlated 3-D HAP-MIMO Fading Channels

This paper proposes a three-dimensional (3-D) scattering model for multiple-input multiple-output (MIMO) land mobile stratospheric multipath-fading channels. Analytical and closed-form expressions for the spatial and temporal correlation functions between two arbitrary sub-channels are derived, assuming non-isotropic or isotropic scattering environments. This model can be used to estimate the required high altitude platform (HAP) antenna separation to achieve an uncorrelated HAP-MIMO channel matrix. Numerical calculations have been carried out to demonstrate theoretical derivations. The proposed model is useful to design, analyze and test future HAP-MIMO based 3G communication systems with line-of-sight (LOS) and non-line-of-sight (NLOS) components.

Statistical Simulation Modeling of 3-D HAP-MIMO Channels

High altitude platforms (HAPs) have been designated as an alternative wireless infrastructure for facilitating next generation high-speed mobile communications services. This paper deals with the design and performance evaluation of a three-dimensional (3-D) sum-of-sinusoids statistical simulation model for HAP multiple-input–multiple-output Ricean fading channels. The performance of the simulation model is investigated with respect to the temporal and spatial correlation functions. The results indicate that the simulation model accurately and efficiently approximates the statistical properties of a recently proposed non-realizable reference model.

Capacity optimized line-of-sight HAP-MIMO channels for Fixed Wireless Access

This paper proposes a design approach to construct a high rank multiple-input multiple-output (MIMO) channel matrix in line-of-sight (LoS) propagation environment, when high altitude platforms (HAPs) are involved. This approach enhances the performance of systems, which can not utilize the MIMO gain introduced by independent and identically distributed (i.i.d.) Rayleigh fading channels or require the existence of a strong LoS signal. Geometrical design recommendations are introduced, considering Ka and V frequency bands licensed for broadband communications through HAPs. In these high frequency bands, the rain has a significant effect on the quality of the link and applications, such as Fixed Wireless Access (FWA), are feasible. The results show the potential capacity gain of the optimized LoS-HAP-MIMO architecture, under clear sky and rain conditions.

Complex Envelope Second-Order Statistics in High-Altitude Platforms Communication Channels

High-altitude platforms are one of the most promising alternative infrastructures for realizing next generation high data rate wireless networks. This paper presents a three-dimensional (3-D) scattering model for land mobile stratospheric multipath-fading channel with its complex faded envelope. From the scattering model and the complex envelope second-order statistics are derived for a 3-D non-isotropic scattering environment. When we discuss on the second-order statistics we refer to the level crossing rate and the average fade duration, whichare two main parameters in describing the fading severity over time and are very important in assess system characteristics such as hand off, velocities of the transmitter and receiver and fading rate. Numerical calculations have been carried out to demonstrate theoretical derivations and the utility of the proposed model.

A three dimensional model for land mobile-HAP-MIMO fading channels

A three dimensional (3-D) cylinder scattering model is proposed for multiple-input multiple-output (MIMO) Land Mobile Stratospheric multipath fading channels. Analytical expressions for the space-time correlation function between two arbitrary sub-channels are derived in non-isotropic environments. This model can be used to estimate the required high altitude platform (HAP) antenna separation to achieve an uncorrelated HAP-MIMO channel matrix. Theoretical derivations have been derived through extensive computer simulations. Our procedure provides an important framework for designing and testing future HAP-MIMO based communication systems and studying the channel capacity of HAP-MIMO based channels, with LOS and NLOS components.

Wideband HAP-MIMO Channels: A 3-D Modeling and Simulation Approach

High-altitude platforms (HAPs) are considered as an alternative technology to provide future generation broadband wireless communications services. This paper proposes a three-dimensional (3-D) geometry-based reference model for wideband HAP multiple-input–multiple-output (MIMO) channels. The statistical properties of the channel are analytically studied in terms of the elevation angle of the platform, the antenna arrays configuration, and the angular, the Doppler and the delay spread. Specifically, the space-time-frequency correlation function (STFCF), the space-Doppler power spectrum, and the power space-delay spectrum are derived for a 3-D non-isotropic scattering environment. Finally, a sum-of-sinusoids statistical simulation model for wideband HAP-MIMO channels is proposed. The results show that the simulation model accurately and efficiently reproduces the STFCF of the reference model. The proposed models provide a convenient framework for the characterization, analysis, test, and design of wideband HAP-MIMO communications systems with line-of-sight and non-line-of-sight links.