Figure 2

Schematic diagram of neighborhood follow structure. The black nodes denote CHs, and the white nodes denote CMs. The arrows denote the follow relationship between two nodes. (a) shows that vehicles 1 to 9 and vehicles 10 to 20 are divided into two clusters, respectively. The hop distance between vehicle 1 and its CH vehicle 5 is 2, and the hop distance between vehicle 10 and its CH vehicle 11 is 3. (b) describes the neighborhood follow relationship for each CM, which directly follows one of its neighborhood and directly or indirectly follows its CH. For example, there is a follow chain 16 → 15 → 14 → 11, from vehicle 16 to vehicle 11.