Line-Broadcasting in Complete k-Trees

A line-broadcasting model in a connected graph $G=(V,E)$, $|V|=n$, is a model in which one vertex, called the {\it originator} of the broadcast holds a message that has to be transmitted to all vertices of the graph through placement of a series of calls over the graph. In this model, an informed vertex can transmit a message through a path of any length in a single time unit, as long as two transmissions do not use the same edge at the same time. Farley \cite{f} has shown that the process is completed within at most $\lceil \log_{2}n \rceil$ time units from any originator in a tree (and thus in any connected undirected graph). and that the cost of broadcasting one message from any vertex is at most $(n-1) \lceil \log_{2}n \rceil$. In this paper, we present lower and upper bounds for the cost to broadcast one message in a complete $k-$tree, from any vertex using the line-broadcasting model. We prove that if $B(u)$ is the minimum cost to broadcast in a graph $G=(V,E)$ from a vertex $u \in V$ using the line-broadcasting model, then $(1+o(1))n \le B(u) \le (2+o(1))n$, where $u$ is any vertex in a complete $k$-tree. Furthermore, for certain conditions, $B(u) \le (2-o(1))n$.