Dear Wahyu Pamungkas,

As it usually happens, the answer to your question depends a lot on the overall communication system that the Doppler is present, in some cases including higher protocol layers above L1, although L1 and L2 will mainly deal with the Doppler problem. It is important to take into account the relationship between the carrier and the Doppler range, the modulation type, the exact Rx architecture and many more.

At this point I can only help you by directing you to a number of techniques that deal with Doppler in Spread Spectrum systems during the PN acquisition phase. They may give you ideas that can fit your specific problem:  so if you want visit my ResearchGate profile and download my Thesis "Receiver synchronisation techniques for CDMA mobile radio communications based on the use of a priori information". There is a chapter there about Doppler effects and how to deal with them in Spread Spectrum systems. Plenty of references as well to get you started.

Best regards,

George

Doppler shift is a carrier frequency shift because of the the relative movement of the transmitter and the receiver. Accordingly the received signal will appear as if it is frequency modulated by this Doppler shift. In case of synchronous demodulation it needs to estimate this shift and make the receiver carrier has the same frequency of the received signal to be demodulated. To accomplish this the receiver must get information on the the communication channel such that it can estimate the Doppler shift and its variation with time. So, one sends a known data as a test signal such that the receiver can estimate the channel including the frequency shift. This test signal is called a training sequence which is sent frequently to continuously estimate the doppler shift and other impairments in the channel. In OFDM pilot carriers are regularly sent within the OFDM symbol for the sake of channel estimation. If the channel is estimated one can equalize the channel. This is one of the important concepts in the advanced communication systems.

Best wishes 

the amount of dopper shift is given by =fc*v/vc

where vc is the speed of light

v-velocity of the mobile

fc is the carrier frequency

so the doppler shift is directly propotional to the speed of the mobile user.all the modern  receivers should be designed with doppler offset correction

Dear George Vardoulias, Abdelhalim Zekry, and Prasadrayi Rayi, thanks a lot to your answer to my questions. I've got the point from your answer. But, furthermore, is it right that doppler shift still become problem in VANET Performance, although so many methods has developed to combat doppler effect in user mobility?

Doppler shift cause carrier frequency offset (CFO) at the receiver. The possible solution to combat the effect of Doppler shift is to design a prober CFO estimator. This estimator usually work at the receiver side and can be divided into main categorizes: blind CFO estimator and pilot CFO aided estimators. In VANET, with carriers frequency range of 5.8–5.92 GHz and vehicles’ relative speed range of 0–120 km/h, a frequency offset due to Doppler spread within the range +232–+236 kHz might correspondingly be introduced. Fortunately, this range is within the range of frequency offsets estimated by STS using many simple approaches.(please see th papers : The Physical Layer of the IEEE 802.11 p WAVE Communication Standard: The Specifications and Challenges

or

 On channel estimation in vehicular networks)

Dear Mr Abdeldime Mohamed Salih Abdelgader, I have read your suggest about the paper The Physical Layer of the IEEE 802.11 p WAVE Communication Standard: The Specifications and Challenges, and yes ...it is realy helped me to understand about the problem. But, when i search the second paper On Channel estimation in vehicular network, it seem on non open access journal, so could you please send me that paper ? thanks.

One thing I have simulated was adaptive modulation (QAM, BPSK, etc). With the motion of one of the tranceiver, as the speed increases, the BER becomes higher. Thus by changing the modulation adaptively with the speed, you can reduce the BER. However, this is an old solution, but you can built on top of it.

Dear Massa Ndong, can you share your simulation about adaptive modulation with me?I'm courious with the graphic as the speed increase, BER becomes higher as you said...thanks a lot.