Andreas Knopp

Optimum-capacity MIMO satellite link for fixed and mobile services

This paper examines the requirements for the construction of a capacity-optimized multiple input multiple output (MIMO) line of sight (LOS) satellite channel between 2 geostationary satellites and Mr antennas placed on earth in general. It is shown that a full multiplexing gain through a geometrical optimized arrangement of the antennas can be achieved both for stationary anchor stations and mobile receivers.

Satellite System Design Examples for Maximum MIMO Spectral Efficiency in LOS Channels

MIMO satellite links have recently attracted a high interest with respect to possible link capacity enhancements. In it has been shown that especially in Line-of-Sight (LOS) satellite channels maximum multiplexing gain can be achieved via the construction of orthogonal channels by means of the geometrical arrangement of the ground terminal antennae in relation to the antennae in orbit. Based on these theoretical results, we present practically relevant design and configuration examples for satellite communication systems, involving transparent pay loads for the first time. Thus, we significantly extend the results, that have been limited to regenerative payloads. The examples cover multiple-satellite and single-satellite MIMO scenarios. The assets and drawbacks of the applications are investigated, especially highlighting system-inherent design uncertainties.

Measurements on the Impact of Sparse Multipath Components on the LOS MIMO Channel Capacity

The channel capacity of indoor line-of-sight MIMO channels is affected by the geometrical antenna setup. In theory there exist rules for the design of LOS channels with optimum channel eigenvalue profile providing maximum capacity. These prescripts are only valid in the absence of multipath signals. By measurements we investigate the relevance of such design rules in real-world MIMO channels consisting of a LOS signal component as well as multipath parts. For that purpose two new performance measures are introduced and shown to be very adequate to distinguish capacity variations which are caused by changes in receive power from those that are caused by differing eigenvalue profiles of the channel matrix. Even sparse multipath signals turn out to be capable of distinctly enhancing the measured spectral efficiency in low-rank channels, while for the high-rank case any multipath components get almost negligible. More important, the geometrical antenna setup not only affects the LOS signal, but also the remaining signal parts. Moreover, the angles of arrival determine, how multipath components affect the LOS channel capacity.

On the prospects of MIMO SatCom systems: The tradeoff between capacity and practical effort

The optimization of the channel capacity in MIMO SatCom systems predominantly requires orthogonal up- and downlink channels, which in practice are formed by distinct antenna arrangements and configurations onboard the satellite(s) as well as at the terminals on earth ground [1]. However, in many applications a significant effort has to be spent at times, not only to identify adequate antenna setups but also to preserve them when imposing practical restrictions, e.g. satellite station keeping maneuvers. This paper analyzes and quantifies any capacity degradations encountered for the case when the orthogonality of the MIMO channel is violated due to practical constraints. Furthermore, the effort for suitable countermeasures is indicated. In the end it is concluded that all potential sources for capacity shortfalls can be handled at a reasonable effort. The analysis is performed for both types of satellite payloads, the transparent as well as the regenerative transponder.

MIMO system implementation with displaced ground antennas for broadband military SATCOM

The Multiple Input - Multiple Output (MIMO) technology is applied to military satellite communication (SATCOM) systems. Superior system performance with respect to channel capacity and data rate is proven utilizing an exemplary communication setup with two antennas at both the ground stations and the geostationary satellite. Contrary to widespread discussed polarization multiplexing SATCOM systems, the approach is suited to fully exploit the multiplexing gain in the spatial domain. This goes along with a linear increase of the channel capacity and the throughput in net data rate depending upon the number of antennas used. Hence, the data rate is almost doubled for the exemplary setup in this paper without the need of higher transmit power or channel bandwidth. Moreover, the system offers improved link availability through antenna diversity. Our approach is based on two ideas: Depending upon the satellite orbit position, distinctly displaced ground antennas grant access to a MIMO channel with maximum spatial multiplexing gain. Nearly optimal data rates are then achieved through maximum likelihood equalization with a low-effort single carrier frequency domain equalizer and a zero-forcing filter. A summary on the robustness of the architecture in respect of capacity degrading influences completes the paper.

Low Complexity Two Stage Detection Scheme for MIMO Systems

This paper provides an approach to reach a near maximum likelihood performance, for MIMO systems, with a strongly reduced computational effort. This method is based on a two-step detection. The first detection step will be performed by using a MMSE equalizer and a subsequent decision unit The second step is a reduced search (RS) algorithm, that is applied only in a neighborhood of the detected symbols of the first step. For complexity reasons only the least reliable symbols are processed by the RS algorithm. The simulation results show that this MMSE RS detector outperforms the MMSE V-BLAST detector. It provides an improved performance using the same complexity.

Mimo-Capacities for Broadband In-Room Quasi-Deterministic Line-Of-Sight Radio Channels Derived from Measurements

We present broadband capacity snapshots as well as grid measurements derived with a fast 5times5 MIMO channelsounder in a typical, large-scale, non-mobile, in-room office scenario where we focus on line-of-sight (LOS) transmission channels. The accessible MIMO capacity is compared to its theoretic counterpart which would have been obtained if only the LOS signal without any reflections was considered. Our premise is to enable the user of quantifying the LOS signals impact on the overall channel capacity for the particular scenario and coinciding to demonstrate the LOSs beneficial effect for the capacity. For a huge amount the beneficial effect of the LOS signal has to be ascribed to its receive signal power increase, an advantage which can hardly be balanced by any measures in the non-LOS case. The results generally indicate the overall capacity staying fairly high even for single channel matrix realizations and widely independent from the current geometric antenna assembly. Besides, strong variations over frequency are observed. These variations are shown to be slightly reducible by rising the number of antennas, but more efficient, larger bandwidths seem to be an appropriate measure for stabilizing the overall channel capacity per bandwidth unit

Indoor LOS MIMO Channel Measurements with a Focus on Antenna Array Design

The bandwidth efficiency of Multiple Input - Multiple Output (MIMO) channels with different antenna arrays is analyzed. MIMO channels with a strong and unobstructed line-of-sight (LOS) signal component are considered, as it is the case in indoor in-room scenarios. The bandwidth efficiency of such channels is strongly dependent upon the applied antenna array and its orientation. Simulations of the pure LOS channel without multipath components are carried out to demonstrate this effect. So called polyhedron antenna arrays with antenna elements mounted on the faces of a regular polyhedron as well as the MIMO Cube deliver a bandwidth efficiency that is almost invariant from rotations of the antenna arrays. The measurement results verify this result. Polyhedron arrays appear to be a good alternative for MIMO systems, as the measured bandwidth efficiency of a polyhedron array is comparable to this of an uniform linear array (ULA), while the standard deviation is reduced to a large extend.

On the Capacity Degradation in Broadband MIMO Satellite Downlinks with Atmospheric Impairments

We investigate the impact of atmospheric impairments on the theoretical bandwidth efficiency of Multiple-Input Multiple-Output (MIMO) geostationary satellite links which are shaped to optimize the channel bandwidth efficiency. We analyze the impairments caused by precipitation, since this is the most severe atmospheric effect causing capacity degradations. By theory, the MIMO channel capacity is strongly affected by signal attenuation as well as signal phase shifts that might reduce the number and strength of spatial subchannels (eigenmodes). We will show, however, that the characteristics of the phase disturbances prevent a loss of capacity. Regarding the additional attenuation, which the signals may encounter passing through the troposphere, we will quantify outage values for several levels of link capacity degradation. Although a loss of capacity cannot be avoided in total, it still turns out that MIMO systems outperform conventional Single-Input Single-Output (SISO) designs in terms of reliability. Even in the presence of atmospheric perturbations, MIMO systems still provide enormous capacity gains and vast reliability improvements. Thus, the MIMO satellite systems presented are perfectly suited to establish the backbone network of future broadband wireless standards (e.g. DVB-SH), supporting high data rates for a variety of worldwide services.

Spatial MIMO over satellite: A proof of concept

If multiple-input multiple-output (MIMO) satellite communications (SATCOM) systems use spatial multiplexing instead of polarization multiplexing, the channel capacity depends on the geometrical conditions of the antenna setup. This theoretical result is proven and confirmed for the first time by a true-MIMO measurement campaign. We utilize two Ku-band satellites and a ground station with two antennas as a 2 × 2 MIMO SATCOM probing system. The channel capacity is estimated and compared to its theoretical prediction. Moreover, an error analysis is provided for the capacity estimation.