Hermann Bischl

Packet error rate in the non-interleaved Rayleigh channel

Two analytical methods for determining the packet error rate in the non-interleaved Rayleigh fading channel are presented. The first method is an exact evaluation of the packet error rate, whereas the second method is based on a k-state digital channel model. The fading model is a nonfrequency selective Rayleigh fading with a first-order low pass spectrum for the quadrature fading components. The analytical methods are complemented by simulations. The influence of the fading bandwidth on the packet error rate and the packet throughput is discussed. Block codes as well as convolutional codes are considered. The results show that without forward error correction the throughput for slow fading is higher than for fast fading. With forward error correction the packet error rate is sensitive to the fading bandwidth. Furthermore it is shown that the convolutional code with intra packet interleaving is least sensitive to slow fading. >

Adaptive coding and modulation for satellite broadband networks: From theory to practice

This paper presents the detailed design and the key system performance results of a comprehensive laboratory demonstrator for a broadband Ka-band multi-beam satellite system exploiting the new DVB-S2 standard with adaptive coding and modulation (ACM). This complete demonstrator allows in-depth verification and optimization of the ACM techniques applied to large satellite broadband networks, as well as complementing and confirming the more theoretical or simulation-based findings published so far. It is demonstrated that few ACM configurations (in terms of modulation and coding) are able to efficiently cope with a typical Ka-band multi-beam satellite system with negligible capacity loss. It is also demonstrated that the exploitation of ACM thresholds with hysteresis represents the most reliable way to adapt the physical layer configuration to the spatial and time variability of the channel conditions while avoiding too many physical layer configuration changes. Simple ACM adaptation techniques, readily implementable over large-scale networks, are shown to perform very well, fulfilling the target packet-error rate requirements even in the presence of deep fading conditions. The impact of carrier phase noise and satellite nonlinearity has also been measured. Copyright

An adaptive MAC layer protocol for ATM-based LEO satellite networks

German aerospace center (DLR), Fraunhofer FOKUS.cats, and Tesat-Spacecom have designed a future multimedia ATM-based LEO satellite network. Part of the development was an adaptive MAC and FEC scheme which is presented in this paper. The FEC implementation switches on the fly during a connection between several FEC and modulation modes to guarantee a maximum ATM cell error rate of 10/sup -6/. In order to prevent influences of the changing FEC scheme on the user-level data rate, the MAC dynamically changes its packet lengths. Additionally, to minimize contention on the up-link, the MAC structures its TDMA frame into a fixed assigned part and a contention specific part. The boarder in between the two is dynamically altered according to the current link utilization.

Optical high-capacity satellite downlinks via high-altitude platform relays

Earth-observation (EO) satellite missions produce a large amount of data using high-resolution optical or radar sensors. During the last decades the amount of data has steadily increased due to improved sensor technologies with increased temporal resolution, sensor resolution, and pixel count. As a consequence EO satellite missions have become limited by the downlink data rates of microwave communication systems, which are inhibited by spectrum restrictions, manageable antenna sizes, and available transmit power. Optical downlinks from EO satellites with data rates of several Gbps mitigate the limiting effects of microwave communication systems; however optical links do not provide the necessary link availability through the atmosphere due to cloud blockage above the ground station. Apart from diversity concepts with several ground stations or satellite networks, a stratospheric High Altitude Platform (HAP) could act as a relay station to forward the optical communication beam over the last 20km through the atmosphere to the ground station, where short-range, high data-rate microwave systems are feasible. This paper will discuss the capabilities of HAP and GEO relay stations to increase the downlink capacities of LEO satellites. Environmental aspects for the deployment of HAP relays and regulatory/technology issues for a microwave downlink on the last 20km to the ground will be discussed.

ATM-based multimedia communication via satellite

Within the next years, a large number of new satellite systems for broadband multimedia communications will be developed, mainly for fixed terminals, but to a lesser degree also for portable and mobile terminals. The most important systems will be based on low earth orbit (LEO) satellite constellations with inter satellite links (ISLs), and will be seamlessly integrated into the environment of terrestrial broadband networks. Since most of the terrestrial broadband networks will be based on the Asynchronous Transfer Mode ATM, it is advantageous for the satellite networks to adopt the ATM transmission scheme and implement ATM switches on board the satellites. However, compared to communication in fixed networks, satellite communication is characterised by special constraints (limited bandwidth, propagation delay, transmission errors, dynamic network topology) requiring the development of a new ATM-based communication technology. In the paper, an ISL-based LEO satellite network for multimedia communication will be considered. Several relevant aspects will be discussed, such as the system architecture, the system requirements, and the protocol architecture. Since the users access the satellite network via a radio interface, an error control scheme and a multiple access scheme suitable for multimedia communication must be implemented. The aspects of TDMA- and CDMA-based medium access control are discussed. Further issues are ATM resource management, radio resource management, and ISL routing. Finally, methods for terminal antenna steering are addressed, and the demonstration of aeronautical multimedia communication via the ITALSAT satellite is described.

A Survey and Perspective on NVoD Systems for Satellite Networks

In this paper, we review different architectures for near video-on-demand (NVoD) systems on satellite networks. In many scenarios, satellites are the only available option for content distribution. On the other hand, video-on-demand (VoD) has been a topic of intense research in the past. The main problem of VoD systems is that their bandwidth requirements do not scale well with user requests. For this reason, VoD is only feasible under some constraints. In general, NVoD systems are an approximation of VoD ones. In them, downloads do not necessarily start when the request arrives, but some time later. By doing so, it is possible to bound the total required bandwidth at the cost of introducing some delay in content download.

The 60 GHz mobile-to-mobile radio channel-fading statistics and estimated packet error rates

This paper presents the results of 60 GHz mobile-to-mobile radio channel measurements which were carried out on highways, rural roads and in urban surroundings for distances up to 500 m. Fading statistics concerning the duration of fades and the distribution function of the received power are presented. Furthermore, the measured channel data were used for the simulation of a packet transmission in order to predict the packet error rates and the performance of some error control methods, i.e. time diversity, antenna diversity, forward error correction (FEC) and a code combining method. Selected results of highway measurements for distances between the transmitter and receiver from 200 m up to 500 m are presented. The probability density function of the received signal amplitude shows good agreement with a Rice/Rayleigh-lognormal density. For a transmitter power of 14 dBm, a packet length of 259 bit and BPSK-modulation with 500 kbps the estimated mean packet error rate was less than 10/sup -2/ for distances up to 300 m without additional error control. With antenna diversity as well as with the code combining method the estimated mean packet error rate was less than 10/sup -2/ even for vehicles distances up to 500 m.<<ETX>>

ATM-based multimedia communication via NGSO-satellites

Future broadband satellite networks for multimedia will be seamlessly integrated into terrestrial broadband networks which often use asynchronous transfer mode (ATM) and recently also the less complex multi protocol label switching (MPLS) technique as transmission and switching protocol. In light of this, future broadband satellite networks may adopt the ATM transmission scheme and implement ATM or ATM-like switches on board the satellites. However, as compared to communication in fixed networks, satellite communication is characterized by special constraints (e.g. signal delay, channel quality, dynamic network topology) that require novel ATM-based communication technology for satellite systems. This paper presents results from the ATM-Sat project that aims to complete this technically challenging and important R&D task in the cooperation between DLR, Fraunhofer Gesellschaft and Tesat-Spacecom. In brief the following aspects have been addressed in the ATM-Sat project: development of the concept and communication technology for a multimedia satellite system with, non-geostationary orbit (NGSO) satellites; inter satellite links (ISLs); on-board ATM switching; fixed and mobile terminals; verification of the developed communication technology with a demonstrator. In particular the ATM-Sat R&D tasks cover the system and protocol architecture, on-board processing, ISL routing, up/downlink and on board ATM resource management (including medium access control), error control, IP over satellite-ATM, and active intelligent antennas. Copyright

On Satellite Diversity and Mobile User Environment for NGSO S-PCNs

We evaluate the performance of satellite diversity under the influence of the mobile user environment. To this end, we propose a Rice-Rayleigh/lognormal channel model where the signal shadowing is represented by a two-state Markov chain which considers the elevation angle as well as the characteristics of user mobility in a given environment. For different LEO and MEO systems and for varying mobile user environments, some crucial benefits and drawbacks of satellite diversity are discussed. The conclusions are validated by numerical results from computer simulations. (Author)

The European data relay system and Alphasat to T-AOGS space to ground links, status, and achievements in 2017

The paper reports on the deployment of the first commercial optical data relay system, the European Data Relay System (EDRS), the achieved performance so far, and the progress in the characterization of optical bi-directional space to ground links performed between the Laser Communication Terminal (LCT) on the Alphasat geostationary satellite and the transportable adaptive optics ground station (T-AOGS) currently co-located with the optical ground station from the European Space Agency (ESA) at Tenerife, Spain. Uplink results using homodyne binary phase shift keying at 1064 nm from the T-AOGS were examined. The performance of a packet erasure code according to the orange book CCSDS 131.5-O-1 optimized for the conditions of a laser uplink without adaptive optics correction of the phase front is analyzed.