The intrinsic problem of hidden/exposed terminals in inter-vehicular networks may bring about communication conflicts and decrease network throughput. In this paper, we take the unidirectional feature of road into consideration, and design a single-channel transmission scheme for decreasing communication conflicts with nodes' position information and directional antennas. The scheme includes the identification and notification of relative positions among adjacent nodes, the identification of nodes' transmission state, and the scheduling of directional transmissions. By simulation experiments in NS-2, we verify that this scheme can discern hidden/exposed terminal nodes, decrease communication conflicts, and improve network performance. Keywords-inter-vehicular network; exposed terminal; hidden terminal; directional antennaAs a special type of Ad hoc network, the Inter-Vehicular Network [1] can provide convenient wireless Internet access and extended network coverage in places without communication infrastructure. With such functions as safety driving, information service and mobile office, it has become a hot research direction. However, communication conflicts are more prone to occur because of highly overlapping of nodes' coverage, and lead to the problems of hidden terminals and exposed terminals. This paper proposes a solution, i.e. Directional Optimization for Hidden and Exposed Terminal (DOHET for short), to deal with the problem and improve spatial utilization for Inter-Vehicular Network. Used in ground Geo-location RF Signal systems [2], it can identify potential communication conflicts effectively, choose appropriate time for transmission, and avoid the negative influence of hidden/exposed terminals on data transmission. Suggestion on setting proper nodes' distance is also proposed to achieve improved performance. I. DESCRIPTION OF HIDDEN/EXPOSED TERMINALS PROBLEMHidden terminals are the nodes locating within the communication range of data receiver and out of the communication range of data sender. Hidden terminals are unable to detect sender's traffic and try to communicate with the receiver, thus message conflict will happen. Exposed terminals are the nodes located within the communication range of data sender and out of the communication range of data receiver. Exposed terminals can detect sender's traffic and delay sending messages, but its transmission does not actually cause communication conflicts. So it introduces unnecessary delay and decreases the channel utilization rate.As shown in Figure 1, when node (i-1) sends messages to node i, node (i+1) locates in the coverage area of receiver i and becomes the hidden terminal. When node i sends a message to node (i-1), node (i+1) locates at the coverage area of sender i and becomes the exposed terminal. Fig. 1 Topology of one-dimensional inter-vehicular network II. RELATED WORKSCurrently there are a few research works about hiding/exposed terminals for general Ad hoc network, but few for inter-vehicular network. It is known that with single channel, t...