Cross-layer Air Interface Design for Satellite Systems
In order to make future satellite systems meeting new services and application requirements, a complete system optimization is needed. A strict modularity and layer independence may lead to non-optimal performance in IP-based next-generation satellite communication systems. Furthermore, the growth of heterogeneous networks entails the need of adaptive actions. Such optimization is not guaranteed by the current layered protocol stack. In this framework, an optimized cross-layer approach is needed where interactions even between non-adjacent protocol layers are conceived to achieve a better adaptation to system dynamics and the highly dynamic applications demands. System efficiency is an important task in satellite communications where radio resources are costly and scarcely available. Whereas, QoS1 support is the mandatory aspect requested by end users that do not care about resource utilization, but expect a good service. System optimization and QoS support are typically conflicting needs; for instance, the best QoS condition for delay-intolerant traffic is to have a high amount of available resources, thus contrasting with system efficiency. These conflicting needs can be solved by means of a suitable cross-layer system design and by exploiting the multiplexing effect. In particular, the different layers of the OSI protocol stack should be jointly optimized or dynamically jointly adapted to find the best trade-off between resource utilization efficiency and QoS provision. The idea behind cross-layer design is that we can obtain substantial gains in performance and efficiency by jointly optimizing the behavior of different layers. This tutorial aims at describing the cross-layer framework starting from a survey of mechanisms to support it and describing the different cross-layer techniques that can be obtained by combining different protocol layers together. A wide literature overview on wireless and satellite systems will be provided and recent results will be presented in order to prove the usefulness and the potentialities of the cross-layer interface design.
Notes:
1QoS – Quality of Service – качество обслуживания.
Text 7
1. Read the text.
2. Find the information about the advantages of digital broadcast systems.
3. Write a summary of the text in English.
Digital Broadcast Systems
An important development is the digitalization of the networks for radio and television broadcasting. Once deployed, these can not only disseminate audio and visual material to the public at large but also provide new (multi-media) services with conditional access. Digital transmission allows more flexible multiplexing of different traffic streams. Hence, broadcast networks are not restricted to pure radio and television services, but also allow encryption for various purposes or watermarking of information for anti-piracy enforcement and copyright protection. Systems designed for Digital Audio Broadcasting (DAB1) in the European EUREKA2 program also appear suitable, in terms of data rates, for transmission of still pictures or data files. Elegant novel modulation techniques have been developed that allow significantly more programs to be transmitted within the same bandwidth. In particular, single-frequency networks, allowing master and relay transmitters to operate on the same carrier frequencies, will provide a spectrum efficiency that cannot be achieved with analog FM transmitters. Meanwhile, for short wave transmission, the system called Digital Radio Mondiale (DRM) has been developed.
Most broadcast systems are restricted to one-way transmission, a major drawback for interactive services, but can be augmented by using other networks for the reverse link. Future interactive services to mobile users are often highly asymmetric in their communication requirements. The bulk of data is likely to travel towards the (mobile) users, with only command and control messages traveling in the reverse direction. A broadcast network may support the high data rates required in the downlink. In the context of standardization for future Digital Video Broadcasting (DVB3), digital Terrestrial Television broadcasting (DTTB) concepts are also soon to be standardized. Such digital television systems will use MPEG-type video encoding.
Notes:
1DAB ‑ Digital Audio Broadcasting – цифровое радиовещание.
2EUREKA – a Europe-wide Network for industrial R&D – Европейская сеть исследований и разработок для индустрии, проект EUREKA.
3DVB ‑ Digital Video Broadcasting – цифровая ТВ-трансляция.
Text 8
1. Read the text.
2. Divide the text into paragraphs.
3. Express the idea of each paragraph in one sentence.
4. Write a summary of the text in English.