Research Of Optimal Pilot Sequence Design For OFDM Based On Cognitive Radio Systems

With the development of communication technology, the Internet and multimedia technology, the defects of spectrum resource shortage and low utilization rate of spectrum increasingly prominent, Cognitive Radio OFDM (CR-OFDM) is a spectrum efficient modulation technique which is suitable for discrete spectrum environment, and it not only has the advantages of traditional OFDM anti-multipath fading and high speed transmission, but also has strong flexibility at the aspect of the spectrum aggregation, power control and spectrum allocation. Therefore, it is considered to be one of the key transmission technologies in 4G mobile communication systems the most competitive. Because the spectrum of CR-OFDM has the characteristics of non continuous dynamic, key technology and science research resulting has become a hot research topic in related fields. Among them, the pilot sequence design can guarantee the quality of high performance wireless channel estimation accuracy and communication systems and become one of the key problems that need to be solved urgently, it has important theoretical value and practical significance to design the pilot sequences for CR-OFDM system.This paper introduces the design basic of CR-OFDM system based on pilot sequence in detail, analysis the classical algorithm of optimal pilot sequence design, for the situation of existing the inference between the licensed user and the cognitive user in CR-OFDM system, the paper put forward a kind of pilot sequence design algorithm based on channel estimation. This algorithm can effectively avoid or reduce the possibility that system deteriorates due to access for cognitive users, improve the accuracy of channel estimation, and ensure the high performance of the system.In traditional OFDM system, it thinks that equal energy and pilot uniform interval is the optimal pilot sequence. Considering the special nature of the sub-carriers in the CR-OFDM system, during designing the pilot sequence, equal power and some interval pilot sequence is used. However, the way has a high computational complexity, low utilization of the spectrum, processing delay and interference effects are significant issues. In addition the pilot sequence design of existing algorithms mostly for a single attribute, e.g. 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 puts forward a kind of pilot sequence design algorithm based on the joint optimization of pilot power and position. The first is to optimize the design of pilot position, then the design algorithm of pilot power optimal, finally feedback to the pilot position. The algorithm usage 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 sequence algorithm, it can effectively reduce the BER and MSE, thus improving the system performance as a whole.