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

This paper presents a novel code allocation scheme for multicasting in infrastructure-to-vehicle CDMA-based wireless networks. In a CDMA-based cellular network, to maximize the utilization of bandwidth and to minimize the overhead under varying channel conditions, the proposed scheme discusses how cellular and vehicular networks can collaborate in 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 to 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 too frequently is reduced. Simulation results show that the proposed scheme achieves better utilization of cellular network codes and vehicular network bandwidth, and proportional fairness than unicast-only or broadcast-only schemes.