The Research On Non Data-aided SNR Estimation Technology In OFDM System

As the key technology of the fourth generation mobile communication system,Orthogonal Frequency Division Multiplexing(OFDM)technology is widely used in the field of communication because of its high rate of data transmission and its performance of superior anti-multipath interference.How to estimate the Signal Noise Ratio(SNR)at the receiving end in the OFDM system is a hotspot in the field of wireless communication.At present,the SNR estimation methods of OFDM system can be divided into two categories:one is based on the Data-Aided(DA)method;the other is Non Data-Aided(NDA)method which will not require to occupy additional pilots.A stable NDA SNR method in OFDM systems will be proposed in this paper.In addition,a NDA method for obtaining the unbiased estimation of noise variance under the large delay spread channel conditions will be proposed too.As we all known,in the LTE system,a large amount of control signaling needs to be transmitted,thereby increasing the burden on the system.In the actual LTE system,the insertion period of the pilots is usually redundant,so it is proposed that the control signaling bits are hidden in the pilots' transmission,without affecting the bit error rate under the improving of the system transmission effectiveness.The main contributions of the thesis are summarized as follows:Firstly,a stable method based on NDA to estimate SNR in OFDM system is proposed.Based on the correlation of the Cyclic Prefix(CP),the method obtains the stable estimation result by selecting the sampled values of the received OFDM symbols at the receiving end and using the inter-symbol interference between the symbols.Through the mathematical analysis and computer simulation,it is proved that the method can obtain the stable estimation result even when the maximum delay of the channel is longer than the CP length.And compared with other NDA methods to prove that the method has a certain performance improvement.Secondly,a NDA method for estimating noise variance is studied for OFDM systems under large delay spread channels.The method is also based on the correlation between CPs and the selection of OFDM symbol samples at the receiving end.The method selects the symbol starting points and end points to convert the received symbols into the frequency domain,and then compensates the phase.By using the independence of the symbols,the final result is obtained by mathematical derivation.The simulation results show that the method can obtain the stable noise variance estimation result when the maximum delay of the channel is equal as the CP length.Finally,a method of transmitting control signaling bit information in pilots in LTE system is researched.The study is based on the channel under normal conditions where the pilots are often in a redundant state as a prerequisite.So it can be tried to transmit control signaling bits by pilots.By studying the four resource allocation forms of Physical Downlink Control Channel(PDCCH)in different environments,different cases of control signaling implicit distribution method is designed.The simulation results show that the proposed method can improve the transmission performance of the system without affecting the bit error rate of the received signal.