On Circular-Shift Linear Solvability of Multicast Networks

Circular-shift linear network coding (LNC) is a class of LNC schemes with low coding complexities. However, there are explicit multicast networks whose capacities cannot be achieved by circular-shift LNC. In this work, we first extend the formulation of circular-shift LNC from over GF(2) to over GF(p), where p is an arbitrary prime. Then, in terms of scalar linear solvability, we characterize an equivalent condition on the circular-shift linear solvability of an arbitrary multicast network. Specifically, we prove that a multicast network has a circularshift linear solution over GF(p) if and only if it has a scalar linear solution over GF(p). This implies that the study of circular-shift LNC at rate smaller than 1 is inevitable. We last prove that every multicast network is asymptotically circular-shift linearly solvable over GF(p), that is, for any ϵ > 0, it has a circular-shift linear solution over GF(p) at rate larger than 1 - ϵ.