Research Of Optimal Pilot Sequence For Sparse Channel Estimation In Cognitive Radio Systems

Orthogonal frequency division multiplexing is a multi-carrier modulation technique under wireless environment, it has multipath fading resistance, strong anti-interference ability and high spectrum efficiency, is the core of the new generation mobile communication system. Cognitive radio technology can effectively solve the problem of spectrum idle and waste of resources, the advantages of OFDM itself makes it the best way to modulation of cognitive radio technology, non contiguous orthogonal frequency division multiplexing technology of NC-OFDM arises at the historic moment, the consequent many key problems become a research hotspot. The channel estimation directly affect the quality of communication system. Based on pilot channel estimation due to its estimate of the error is small, the advantages of fast convergence rate, high transmission rate become the mainstream of the channel estimation technology, based on pilot channel estimation is restricted by the two aspects, one is the design of the channel estimator; The second is the design of the pilot sequences, so the NC-OFDM system pilot sequences design research is of great significance.OFDM system are introduced in detail in this paper the basic principle and the characteristics of wireless channel transmission, the system analyzes the optimal pilot sequences common design rules and algorithm design, according to sparse channel environment, put forward the pilot sequences of NC-OFDM system and power design method.In view of the traditional NC-OFDM channel estimation system pilot sequences design method of high computation complexity, low efficiency, low utilization rate of the data, this paper proposes a NC-OFDM sparse channel environment position of pilot sequences design method, the method with the minimum cross-correlation measurement matrix as target function, by solving an optimization problem with constraints and simplify search method to get the optimal pilot position distribution, the method not only on the channel estimation MSE is superior to the traditional interval and random search of the pilot, in the aspect of the system BER performance and computational complexity are obviously improved.Traditional OFDM system pilot power allocation methods usually consider equal power constraints limit or the total transmitted power, due to the particularity of NC-OFDM, this method cannot be directly used for NC-OFDM system pilot power allocation, therefore, this paper proposes a pilot sub-carrier power allocation algorithm for NC-OFDM system, secondary users must meet the following conditions: interference temperature, total power constraint, maximum power constraints, sub-channels power constraint. The method is based on the minimum measurement matrix cross-correlation criterion, consider more power constraints, get the optimal pilot sub-carrier power allocation, guarantee the estimation accuracy of channel, improve the utilization rate of data transmission, strengthened the transmission efficiency and reliability of the system, compared with other pilot sequences design algorithm, can effectively reduce the system BER and the channel estimation MSE, so as to improve the performance of the system on the whole.