Studies On Anti-doppler Method And Frequency Hopping Technology Based On Time Modulated Array

With the rapid development of science and technology, diversified demands ofantenna performances were put forward by the modern communication system. To improvethe stability and robustness of the antenna system, the low side lobe array pattern techniquewas adopted. Unfortunately, it’s not easy to be realized practically. So the time modulatedarray was put forward by means of introducing the time dimension in traditional antennaarray. Although the time modulated array offers an easy way to implement low side lobelevel, it also spread the radiation power to sidebands simultaneously. Previously, harmonicwaves were regard as a kind of power loss. But in some situations, the complicated signalprocessing algorithms can be realized simply in the RF part by making use of the linkbetween harmonic wave and control sequences. A potential application is high speed railcommunication system.In recent years, with the new type of trains coming into service, the speed of therailway has been improved greatly. Even though it has become one of the mostcost-efficient options in intercity traffic, the high-speed failed to perform itscommunication service synchronously. The system can’t effectively solve the Dopplereffect and the multipath effect in the high-speed mobile environment. Worse still,passengers become more attached to mobile service and multimedia service than ever withthe development of wireless network technology. Conflict between supplies and demandurges the research on finding a new solution that provide the wide band data communication services in the high speed environment.To achieve the objectives of reducing the multipath effect and the Doppler effect, andproviding multi-user with independent communication channels, a time modulated arraysystem for dual-channel frequency hopping technology and a novel self-adaptiveanti-Doppler time modulated array system are proposed in this paper. The two schemes arebased on the harmonic characteristic of the time modulated array. By applying the controlsequences to the RF switches, the array system changes the working state of each element.As the signal is modulated by the sequence, system is able to focus the first harmonic wavepattern to the desire direction and shifted the carrier frequency as designed. What’s more,the antenna array system is extended to a dual-independent channel by making use of theinterval in the time sequences, and the solution for the sequence jam is also given.The remainder of the paper is organized as follows.At first, a briefly background of time modulated array is given. And the investigationof the difficulties domestic high-speed faced with is listed. The information affirms thevalue of applying the time modulated array to the anti-Doppler technology andanti-multipath technology.Then, the time modulated array theory is introduced, able to adjust the pattern andprocess the signal in the RF part. The theory also shows that the cost and communicationsystem complexity doesn’t increase remarkably. By discussing the beam forming methodsand analyzing the communication channel model, demands for the systems are determined.Based on the previous analysis, which mainly concentrates on avoiding noise andinterference, a time modulated array system for frequency hopping is proposed in advance.Link between the sequence and the beam control is given, and sequence is optimized.Simulation results show that patterns and frequency shifts meet the expectation. Theside-lobe suppression works with the optimization sequence. The system is fabricated andtested, which verifies the response of the beam forming algorithm and the frequency shift method in real time.After study the domestic high-speed rail, the self-adaptive anti-Doppler scheme isdemonstrated with the system function, block diagram and components. Concerned withthe uncertainty, check-up algorithm is set to make the process stable. Each module isdesigned, fabricated and tested according to the demands and the simulation. Results showthat the function of each part satisfies the system needs. For the hardware implementation,the system can be realized easily. It achieves great compatibility with the currentcommunication system and takes low operation cost.