Dissertation
Dissertation > Industrial Technology > Radio electronics, telecommunications technology > Wireless communications > Mobile Communications > Cellular mobile communications systems (mobile phones, mobile phone handsets )

Research of Optimal Pilot Sequence for OFDM Systems Under Rapidly Fading Time-Varying Channel

Author LiuJiEn
Tutor WangJinKuan
School Northeastern University
Course Communication and Information System
Keywords orthogonal frequency division multiplexing rapidly fading time-varyingchannel pilot clusters minimum mean square error maximum signal-to-noise ratio
CLC TN929.53
Type Master's thesis
Year 2013
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Orthogonal frequency division multiplexing is a kind of data transmission technology in a wireless environment, it uses orthogonal multi-carrier transfer information, improves the spectrum utilization, has strong anti-jamming, anti-fading ability, and it is a hot research field of a new generation of wireless communication. With the advent of high-speed railway and highway, the transmission channel of signal from the sending end to the receiving end become more complex, and due to frequency selectivity and time selectivity fading caused by time delay spread and the Doppler spread make the performance of the communication system to become further deterioration, in order to guarantee the accurate estimation of wireless channel and high quality performance of communication system, need to insert pilot sequence, while the business types and performance index of systems is different, the pilot sequence insertion requirements is different, therefore, research on the pilot sequence design is of great significance.This paper introduces the design basic of OFDM system based on pilot sequence in detail, analysis the classical algorithm of optimal pilot sequence design by the numbers, for the situation of rapidly fading time-varying channel interference between subcarriers of OFDM system, this paper put forward a kind of pilot sequence design algorithm based on cluster structure, which can effectively prevent the influence caused by Doppler frequency in rapidly fading time-varying channel, suppress the inter-carrier interference, improve the accuracy of channel estimation, ensure the high performance of the system.The traditional pilot sequence model generally adopts a single pilot insertion, it has high computational complexity, low utilization of the spectrum, treatment effect of delay and disturbance of this model are obvious, etc, in view of the above problems, this paper using pilot clusters structure mode, which is a group of pilot. In addition the pilot sequence design of existing algorithms mostly for a single attribute, e.g. quantity, power or position of the pilot of the study, this can’t satisfy the system performance to maximize the energy department in the process optimization. In order to solve this problem, this paper put forward a kind of pilot sequence design algorithm based on the joint optimization of pilot number, power and position, the algorithm according to the channel state information acquired by channel estimated in previous time, design the optimal pilot sequence for next time, then feedback to the transmitter for pilot insertion, the algorithm use of the system average BER, MSE and SNR as the performance index to optimize, improve the utilization rate of data transmission, ensure the channel estimation accuracy, strengthen the effectiveness of transmission system, and compare to other pilot (clusters) sequence algorithm, it can effectively reduce the BER and MSE, thus improving the system performance as a whole.

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