Satellite-3G Hybrid Networks: Impact of ACM and ARQ on TCP Performance

The adoption of satellite systems in providing broadband transmissions to mobile users such as trains, buses and vans is expected to be an interesting solution. The scenario we considered refers to a hybrid network architecture, where a geostationary satellite forward link and a terrestrial 3G return link are used in order to exploit both the high bandwidth of a satellite channel and the lower propagation delay of a terrestrial path. The resulting round-trip delay is much shorter than that one experienced by using both the forward and return link via satellite. This is particularly appealing for overcoming the TCP efficiency degradation in high delay-bandwidth product and error prone channels. In this hybrid scenario, we used simulation results to compare the goodput of four of the most popular TCP variants, in the presence of a GOOD-BAD satellite channel, as the one experienced by mobile users. We applied an Adaptive Coding and Modulation (ACM) technique as well, and studied its impact on TCP efficiency, when used both alone and in cooperation with an Automatic Repeat reQuest (ARQ) scheme of the Selective Repeat (SR) type with low persistency. Results obtained indicate that this hybrid architecture is advantageous for TCP transmissions in terms of average goodput, and that ACM is effective only if it is jointly used with ARQ schemes

LTE Adaptation for Mobile Broadband Satellite Networks

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Coding Theory and its Applications in Communication systems

Error control coding has been used extensively in digital communication systems because of its cost-effectiveness in achieving efficient, reliable digital transmission. Coding now plays an important role in the design of modern communication systems. This paper reviews the development of basic coding theory and state-of-art coding techniques. The applications of coding to communication systems and future trends are also discussed

Computer based simulation of optical wireless communications for the development of optimized error protection and correction schemes

Commercial application of optical wireless communications is currently limited to the area of short range near ground connections, like networks between buildings over a few kilometers. For other areas of application, like data downlinks from flying platforms, demonstrations have been done, but commercial systems for long range communications over many kilometers are not yet available for general usage. The biggest challenge for reliable optical communications is to mitigate the fading of the received optical signal. A possible solution is to implement error protection and correction mechanisms for securing transmitted data. In this dissertation a simplified channel model is developed which can be used for computer based simulation. This simplified channel model is then used for the evaluation of error protection and correction mechanisms applied to the optical wireless channel. Finally generally proposed communication scenarios are evaluated if optical wireless communication is possible, based on the developed channel model. The results show that the combination of forward error correction and selective repeat automatic repeat request protocols can be used to realize reliable optical communication links in all proposed scenarios, even the most challenging ones. The back channel traffic for automatic repeat request protocols leads to a significant reduction of the transmittable user data rate in worst-case scenarios and has to be taken into account for the system design. The developed simulation approach can be used to optimize protocols for the optical wireless channel in order to reduce the load on the back channel and the over all required memory.Die kommerzielle Anwendung der optischen Freiraumkommunikation ist gegenwärtig auf den Bereich der bodennahen Kurzstreckenverbindungen mit wenigen Kilometern Länge begrenzt, beispielsweise Netzwerkverbindung zwischen Gebäuden. In anderen Anwendungsbereichen, z.B. Datendownlinks von fliegenden Plattformen, wurden zwar Technologiedemonstrationen durchgeführt, jedoch sind für solche Langstreckenverbindungen keine alltagstauglichen kommerziellen Systeme verfügbar. Die größte Herausforderung für zuverlässige optische Kommunikation ist die Kompensation der Signalschwankungen des empfangenen optischen Signals. Eine mögliche Lösung für dieses Problem ist die Implementierung von Fehlersicherungs- und Fehlerkorrekturmechanismen, um die Datenübertragung abzusichern. In dieser Dissertation wird ein vereinfachtes Kanalmodell entwickelt, welches für die Simulationen mittels Computern geeignet ist. Dieses vereinfachte Modell wird anschließend für die Bewertung von Fehlersicherungs- und Fehlerkorrekturmechanismen für den optischen Kanal verwendet. Abschliessend wird basierend auf dem entwickelten Kanalmodell der mögliche Einsatz von optischer Freiraumkommunikation in häufig vorgeschlagenen Szenarien untersucht. Die Ergebnisse zeigen, dass die Kombination von Vorwärtsfehlerkorrektur und Protokollen mit selektiver Wiederholung und automatischer Wiederholungsanfrage geeignet ist, um zuverlässige optische Kommunikationsverbindungen in allen vorgeschlagenen Szenarien zu realisieren, selbst in den anspruchsvollsten. Die Datenübertragung auf dem Rückkanal von Protokollen mit automatischer Wiederholungsanfrage führt im schlechtesten Fall zu einer signifikanten Reduzierung der übertragbaren Nutzdatenrate und muss bei der Systemauslegung berücksichtigt werden. Mit dem entwickelten Simulationsansatz können Protokolle für den optischen Funkkanal optimiert werden, um die Belastung des Rückkanals zu reduzieren und um den allgemeinen Speicherbedarf zu reduzieren

Automatic-repeat-request error control schemes

Error detection incorporated with automatic-repeat-request (ARQ) is widely used for error control in data communication systems. This method of error control is simple and provides high system reliability. If a properly chosen code is used for error detection, virtually error-free data transmission can be attained. Various types of ARQ and hybrid ARQ schemes, and error detection using linear block codes are surveyed

On-board processing satellite network architecture and control study

The market for telecommunications services needs to be segmented into user classes having similar transmission requirements and hence similar network architectures. Use of the following transmission architecture was considered: satellite switched TDMA; TDMA up, TDM down; scanning (hopping) beam TDMA; FDMA up, TDM down; satellite switched MF/TDMA; and switching Hub earth stations with double hop transmission. A candidate network architecture will be selected that: comprises multiple access subnetworks optimized for each user; interconnects the subnetworks by means of a baseband processor; and optimizes the marriage of interconnection and access techniques. An overall network control architecture will be provided that will serve the needs of the baseband and satellite switched RF interconnected subnetworks. The results of the studies shall be used to identify elements of network architecture and control that require the greatest degree of technology development to realize an operational system. This will be specified in terms of: requirements of the enabling technology; difference from the current available technology; and estimate of the development requirements needed to achieve an operational system. The results obtained for each of these tasks are presented

End-to-End Resilience Mechanisms for Network Transport Protocols

The universal reliance on and hence the need for resilience in network communications has been well established. Current transport protocols are designed to provide fixed mechanisms for error remediation (if any), using techniques such as ARQ, and offer little or no adaptability to underlying network conditions, or to different sets of application requirements. The ubiquitous TCP transport protocol makes too many assumptions about underlying layers to provide resilient end-to-end service in all network scenarios, especially those which include significant heterogeneity. Additionally the properties of reliability, performability, availability, dependability, and survivability are not explicitly addressed in the design, so there is no support for resilience. This dissertation presents considerations which must be taken in designing new resilience mechanisms for future transport protocols to meet service requirements in the face of various attacks and challenges. The primary mechanisms addressed include diverse end-to-end paths, and multi-mode operation for changing network conditions