To prevent eavesdropping in Orthogonal Frequency Division Multiplexing Vehicular Ad-Hoc Network (OFDM-VANET), a cross-layer security routing protocol was presented in this paper, which includes two parts: secure routing protocol and secure frequency diversity. On the one hand, the eavesdropping of the unrelated node was prevented, by limiting its knowledge on information transmission routing. On the other hand, in the diversity of physical layer receiving, the fading difference among wireless channels, which was transparently transmitted from network layer, was utilized to identify the destination node and eavesdropping nodes. The theory analysis and simulation results illustrate that, when the vehicle on a scale of 1000 to 2000, the protocol makes instantaneous eavesdroppers only about 3. Compared to the conventional methods, it can effectively reduce the number of eavesdroppers.

When the period of objective sequence is long enough, the traditional acquisition algorithm will consume a lot of system resource. The shifted bit inverse sequential acquisition algorithm was proposed, which could be utilized to deduce the trail-and-error results of following sequence state from the previous trail-and-error result. As a result, the complicated sequence shifting calculation was avoided. Then the rule of the control state was proved, which led to the storage space reduction of the bit inverse vector and shifted bit inverse vector. Finally, an acquisition system based on the theory mentioned above was designed, which could acquire sequence with high efficiency, and the complexity decreased from conventional O(n2) to O(n).

The existing sequential acquisition methods search the correlation peak continuously in receiving signals, thus wasting a great deal of calculation resources to search correlation peak in the received signal containing no target sequence. In another case, with the sequence period increasing, the calculation resources perform exponential growth. As a result, the target sequence can be hardly got. In order to reduce the calculation resources, the paper presented a sequence core transform method to acquire the sequence. The method compressed the entire sequence information into the local sequence core, and by this sequence core, the acquiring process was divided into two steps: sequence detection and sequence acquisition. In this process, the calculation resources were reduced because the sequence acquisition only occured in the second step. Furthermore, by using the down-sampling on received signals, the sequence core transform could decrease the sequence amount needed in the acquiring process. The theoretical analysis and simulation results show that, by losing some acquiring performance, the algorithm can reduce the calculation resources to complete acquisition in one sequence period. And the reduced calculation resources increase with the sequence period.

Because of the effect of channel and noise, the effect of the traditional pilot jamming scheme will decrease because of the phase deviation. In order to avoid the problem, this paper brings forward a novel scheme based on distribution detection. Firstly, detect the phase deviation of the jamming signal by the terminal distributed in the jamming area; then the result of the detection will be sent to the jamming signal transmitter, it will drive the jamming signal phase equal to the -radian offset of the transmitted pilot tone value. Simulations prove that the scheme is effective on decreasing the phase deviation of the jamming signal.