On the Optimization of Local and End-to-end Forward Error Correction

Inhalt:
In this paper we investigate where best to use forward error correction if one or more mobile radio links is included on a path. On one hand, if the errors are handled locally where they appear, the knowledge of the channel conditions are better and no extra redundancy will have to traverse the other links. On the other hand, the requirements of the application are better known at the end nodes, hence the error correction can be better tuned to the needs of the application end-to-end. The first aspect investigated is the effect of a correlated error process, which is exemplified by a fading radio channel. The length of the error correcting code and the burst tolerance is essential for performance when correlation is taken into account, therefore packet level coding applied endto- end is efficient at high correlation whereas local bit error correction is more efficient at low correlation. TCP is used to exemplify the difficulties in estimating the parameters needed to implement effective coding both locally and end-to-end. Furthermore, simulation results show how the locally optimal parameters differ depending on the end-to-end path. Performance comparisons in several cases demonstrate that end-to-end forward error correction (FEC) can often be efficient to mitigate problems that are in principle local to a specific link.