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The L*IP Satellite System developed by Joanneum Research and Graz University of Technology is a communication product hand-tailored for the Internet Protocol and its real time and non-real time applications. Video, voice and data applications can be supported via this network.
Meshed systems like the L*IP avoid the drawbacks of star topology networks, i.e., it satisfies the requirements of real-time services with only a single hop. The available satellite bandwidth is used in an optimum fashion via QoS-aware DAMA control which balances the bandwidth for all the users in the uplink as well as in the downlink. The L*IP system encapsulates IP packets based on a time granularity and not the common cell (ATM,MPEG) granularity which results in less overhead on average compared to an ATM style encapsulation.
We see our hardware architecture as another big advantage over the approach of some competitors. By using a dual Pentium platform, we have a very powerful and future-proof platform, which is not the case for a lot of embedded processors. Thus, we have a flexible hardware architecture concerning access schemes and protocol requirements. Our software radio approach is based on PC and FPGA hardware, which is flexible, relatively cheap and also available in the coming years.
We designed a satellite terminal for the meshed network market with single hop characteristic. The focus was the efficient transportation of IP traffic via satellite. This could be achieved by a low overhead encapsulation schema, an efficient codec, a low operational point of the modem and by an intelligent IP routing and IP header compression. On top of this is the operation of the Terminal at the Salve stations as well the Master station very user friendly with a JAVA based GUI. Master station and Slave station have identical hardware and can take over each others role in the network.
The L*IP System is a highly flexible platform which allows to implement various access, synchronisation, coding and modulation schemes. Because IP traffic is the major player in user traffic, we have concentrated our effort here in implementing the most efficient transportation of this sort of traffic over satellite.
In order to be prepared for future extensions and modifications, flexibility and reconfigurability have been essential aspects for the architectural design. Therefore, an open platform based on FPGA devices is realized, which allows the implementation and test of a great variety of modulation schemes, base-band shapes and synchronization algorithms. All subsequent processing, even error control coding, is carried out in pure software.
The hard real time tasks are executed on an FPGA -PCI card hosted in a dual Pentium IV (3.0 GHz) where also the tracker and codec is located. The higher layers are processed in a second PC with the same performance. With this architecture we are able to perform the processing of up to 4 Msymb/s with variable code rate (R = 1/3, 1/2, 2/3, 3/4, 4/5, 8/9), MF-TDMA access system, IP header compression, IP-optimized encapsulation, QoS-aware DAMA and a Java-based GUI for control and monitoring.
|Figure 1 shows the integrated gateway with Burst Modem PC, which hosts also the FPGA card. Further the gateway PC, the AD and DA converter box, an off the shelf L-band converter and keyboard / Monitor for both modem and gateway PC, which can be accessed with a keyboard/monitor/ mouse switch.|
Figure 1: Integrated L*IP Satellite Gateway
The architectural design of the complete system and their sub-modules was designed as the first stage of the project. Modulation, Channel codec, IP routing, IP header compression, QoS Support, DAMA, adaptive transmission and GUI for control and monitoring where then described in the detail design phase. Finally all modules where integrated and tested. All Tests passed the acceptance test.