Harald Ernst

Measurement and Modeling of the Land Mobile Satellite Channel at Ku-Band

This paper presents the results of a measurement campaign conducted in the winter of 2002 around the city of Munich in southern Germany. The primary goal was to evaluate the link performance of the land mobile satellite channel at Ku-band and to characterize the temporal behavior of the channel to help in the evaluation of different fade mitigation techniques for future mobile satellite systems that aim at employing this frequency band. To achieve this objective, first- and second-order channel statistics will be presented, the outage probability of the channel analyzed, and a Markov-chain-based narrowband channel model proposed.

Performance analysis of CCSDS File Delivery Protocol and erasure coding techniques in deep space environments

The rising demand for multimedia services even in hazardous environments, such as space missions and military theatres, and the consequent need of proper internetworking technologies have revealed the performance limits experienced by TCP protocol over long-delay and lossy links and highlighted the importance of the communication features provided by the protocol architectures proposed by the Consultative Committee for Space Data Systems (CCSDS). This paper proposes a CCSDS File Delivery Protocol (CFDP) extension, based on the implementation of erasure coding schemes, within the CFDP itself, in order to assure high reliability to the data communication even in presence of very critical conditions, such as hard shadowing, deep-fading periods and intermittent links. Different encoding techniques are considered and various channel conditions, in terms of Bit Error Ratio and bandwidth values, are tested.

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 novel approach to model the land mobile satellite channel through reversible jump markov chain monte carlo technique

A key issue in the design of a mobile satellite communication system is an adequate knowledge of the statistical behavior of the propagation channel. To achieve this goal, the development of very accurate models plays a very important role. In contrast to traditional multi-state Markov chain based models, the novel approach proposed in this paper makes no prior assumptions on the number of states or on the statistical distributions characterizing each state. The sequence of channel states is blindly estimated using a Reversible Jump Monte Carlo Markov Chain algorithm.

Joint Application of CCSDS File Delivery Protocol and Erasure Coding Schemes over Space Communications

The rising demand for multimedia services even in hazardous environments, such as space missions and military theatres, and the consequent need of proper internetworking technologies have revealed the inapplicability of TCP/IP architectures and highlighted the importance of the communication features provided by the protocol architectures proposed by the Consultative Committee for Space Data Systems (CCSDS). This paper proposes a CCSDS File Delivery Protocol (CFDP) extension, based on the implementation of erasure coding schemes, in order to assure high reliability to the data communication even in presence of very critical conditions, such as hard shadowing, deep fading periods and intermittent links. Different encoding techniques are considered and various channel conditions, in terms of Bit Error Ratio and bandwidth values, are tested.

Ku-mobile: satellite multimedia services for cars in the Ku-band

Satellite radio for vehicles is normally hampered by the problem of the shadowing of the line of sight between satellite and receiver. In this paper, a personalized radio concept is proposed as an alternative to the streaming approach used for traditional radio: instead of transmitting a number of distinct continuous streams, individual audio and multimedia files are broadcasted. The received files are stored in a large cache located in the receiver of each mobile terminal. There, the files are sequentially played from the cache to generate a service similar to traditional radio/entertainment programs. This assembled program may depends on some user settings and does depend on the available files, which in turn depend on the reception conditions of each individual user. A continuous connection between the satellite and each receiver is therefore no longer required. Instead, it is sufficient to ensure that enough new files to generate an attractive program are available in the cache. Therefore, the aim is to reach a sufficiently high update rate for the content of the cache. A failure in the transfer of an individual file has no impact on the audible quality, since the only effect is that this file cannot be used when assembling the program. Besides its robustness, this approach opens new possibilities in terms of enhanced services, like the capability to skip or repeat part of the radio program, and to easily integrate additional data services like e.g. road and weather maps distribution or generic html content. Furthermore, this approach can be combined with the usage of satellite systems with low link margins, which are already available, for instance in the Ku-band. This results in low infrastructure costs for the deployment of such a system, together with the availability of new, personalized attractive features. An overview about the dedicated communication system being developed to support the novel concept presented above, including the status of an end-to-end demonstrator, will be given.

A fast algorithm to estimate the distance spectrum of turbo codes

The computational complexity required by the complete calculation of the distance spectrum of turbo codes, even limited to low weight input sequences, makes it too slow for practical purposes such as interleaver optimization or effective bit error rate bounding. A fast algorithm for distance spectrum estimation purposes is presented. A comparison with complete computed spectra, theoretically derived spectra and results from previous works are presented for both deterministic and uniform interleavers.

A Fast Algorithm to Estimate the Distance Spectrum of Turbo Codes and Tail-Biting Turbo Codes

The computational complexity required by the complete calculation of the distance spectrum of turbo codes, even limited to low weight input sequences, makes it too slow for practical purposes such as interleaver optimization or effective bit error rate bounding. In this paper, a fast algorithm for distance spectrum estimation purposes is presented. A comparison with complete computed spectra, theoretically derived spectra and results from previous works will be presented for both deterministic and uniform interleavers.

Achieving High Goodput Performance in Mars Missions through Application Layer Coding and Transmission Power Trading

Transferring data reliably from Mars to Earth stations is becoming an appealing challenge in the design of interplanetary networks. In this view, the use of CCSDS-based protocols along with erasure codes is a promising candidate for mitigating the performance degradation due to large propagation delays and high packet loss rates. Besides, the constraints imposed on the transmission power and on the available link bandwidth introduce further challenges to the design of the telecommunication system. In this paper, the benefits brought are investigated by tuning properly erasure code rate at the upper layers, pointing out the performance gain in terms of goodput performance and analysing power consumption and bandwidth usage issues, as well.

A comparison of the statistical properties of the land mobile satellite channel at Ku, Ka and EHF bands

This paper presents an exhaustive comparisons of the statistical properties of the land mobile satellite channel at high frequency bands, namely Ku, Ka and EHF bands. The results are obtained using models extracted from several measurement campaigns performed last decade.