The Research Of SNR Estimation Algorithms For OFDM And SC-FDE Systems

Nowadays, Orthogonal Frequency Division Multiplexing (OFDM) systems andSingle Carrier Frequency Domain Equalization (SC-FDE) systems have become thecore techniques for wireless wideband communication. In general, many othertechniques are combined with them for improving the performance, e.g. adaptivefiltering, channel coding and decoding, channel equalization, etc. As the key parameterof the above techniques, Signal-to-Noise Ratio (SNR) and its estimation algorithmappear particularly significant. Based on the OFDM and SC-FDE system models, thewireless channel models and the SNR estimators of the two kinds of systems areintroduced in the paper. Through the project from laboratory, SNR estimationalgorithms applied on synchronizing symbols and pilots for OFDM systems incomplex circumstance are proposed, which are generalized to SC-FDE systems.Through extensive literature, the following work is completed.(1) Focused on the original SNR estimation algorithms for OFDM systems, animproved algorithm in frequency-domain is proposed, which is used in meshy pilotsand Multicast Broadcast Single Frequency Network (MBSFN) transport environment.Through the new matrix formed by the pilot data, the secondary moment of adjacentpoints are utilized to estimate the noise power. Moreover, the variant formats based onother pilot structures or preambles are introduced and the method based on transportdomain is improved. MATLAB simulation results show that the mean square error ofimproved algorithm is less than the original ones and it has better robustness againstDoppler spread.(2) Based on the special structure of the OFDM synchronizing symbols, animproved time-domain SNR estimation algorithm is proposed. Symmetrical sequencesfrom the cyclic prefix and the synchronizing symbol after coarse synchronizing areused to estimate the noise power, which improves the robustness against the multipathfading. The original calculation expressions are modified to increase the accuracy. TheMATLAB simulation shows that the modified algorithm has better performance than the original ones and is not sensitive to the time offset, the multipath influence and theDoppler spread.(3) The above algorithms are generalized to the SC-FDE systems based on uniqueword (UW), which some existing algorithms for single-carrier systems are used tocompare with. Experiment results show that the proposed algorithms own remarkableperformance especially in the condition with high delay spread and Doppler effect.(4) Considering the the project from laboratory, the proposed algorithms areapplied in practical engineering to test and verify its feasibility. The working processesin Digital Signal Processer (DSP) are given in the paper and the result shows that theperformance of the algorithms becomes worse in the engineering.