Bounds on the Minimum Field Size of Network MDS Codes

We study network maximum distance separable (MDS) codes, which are a class of network error-correcting codes whose distance attains the Singleton-type bound. The minimum field size of a network MDS code is of particular interest, since it impacts the computing complexity at the network nodes. Previous constructions of network MDS codes, which are applicable to general single-source multicast networks, require large field sizes. In this paper, for two specific classes of network topologies, we derive upper and lower bounds on the minimum field size of the corresponding network MDS codes and present explicit constructions. The proposed upper bounds significantly improve upon the previous ones and differ from the lower bounds only by a small factor, which is asymptotically no more than 2. Additionally, we extend the concept of linear network error-correction coding from the scalar case to the vector case, and demonstrate a class of networks in which the minimum field size of the vector network MDS code is substantially smaller than that of the scalar case.