Adaptive Multicasting using Common Spreading Codes in Infrastructure-to-Vehicle Communication Networks

Abstract — This paper presents a novel code allocation scheme for adaptive multicasting in infrastructure-tovehicle wireless networks. The proposed scheme discusses how cellular and vehicular networks can collaborate using spreading codes to maximize the utilization of the bandwidth during multicasting. Multiplexing is achieved by assigning a common variable rate orthogonal variable spreading factor (OVSF) code to all members of a multicast group. Because many vehicular users are expected to request the same common data ( e.g., weather and environment information) over an area of one or more cells, multicasting is often needed. But, because a multicast channel must serve all users simultaneously, the data rate cannot be adapted based on the signal quality of individual vehicular user. Instead, the data rate should be adapted based on the user with the poorest signal quality, which reduces the utilization of the codes. Therefore, this paper proposes: i) a classification scheme at cellular base station to group vehicular users into multicast groups based on their channel conditions, ii) a code assignment scheme for these multicast groups, and iii) a relaying scheme for vehicular network to rebroadcast data to users with poor channel conditions so that the overhead involved in forming multicast groups is reduced. Simulation results show that, at the expense of more control overhead, the proposed scheme achieves better code and bandwidth utilization than unicast-only or broadcast-only schemes. I