Synchronous method of orthogonal freuency division multiplex in broadband radio insertion system

Abstract

A synchronization method in OFDM broadband wireless access system includes such steps as utilizing NO.1 frame head as a delay related decision to realize rough synchronization, using the conjugate symmetry of No.2 frame head to realize accurate timing, the frame heads roughly and accurately estimate the decimal frequency deviation separately, the frequency field sequences of the two heads are used to estimate the integer frequency bias and finally synchronous tracing.

Description

technical field [0001] The invention relates to a synchronization realization scheme of Orthogonal Frequency Division Multiplexing (OFDM) especially for 802.16a broadband wireless access network, and belongs to the technical field of communication. Background technique [0002] The OFDM system has attracted more and more attention because of its advantages of strong anti-interference ability and high frequency utilization rate. The wireless broadband access system 806.16a adopts OFDM technology as one of the transmission methods of the system. However, it has very high requirements for symbol synchronization: OFDM uses orthogonal subcarriers to improve spectrum utilization, and if the timing is not synchronized, the orthogonality of subcarriers will be destroyed; frequency offset causes phase rotation and amplitude fading of useful signals, and more serious Therefore, it is very important to compensate for the system performance degradation caused by time and frequency async...

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Problems solved by technology

However, it has very high requirements for symbol synchronization: OFDM uses orthogonal subcarriers to improve spectrum utilization, and if the timing is not synchronized, the orthogonality of subcarriers will be destroyed; frequency offset causes phase rotation and amplitude fading of useful signals, and more serious It causes interference between subcarriers, and the system performance will be greatly reduced, so it is very important to compensate for the system performance degradation caused by time and frequency asynchronization

[0003] In recent years, people have conducted extensive research on OFDM synchronization, among which the typical algorithms mainly include the following: Moose gives the frequency domain maximum likelihood estimation method to estimate the frequency offset, which essentially uses the repetition of symbols to estimate the frequency domain , Moose's idea based on repeated correlation provided the basic idea for the subsequent frequency offset estimation algorithm, but because his algorithm requires the frame header to use two repeated symbols and the channel coherence time is at least greater than the duration of two symbols, so This method is not used in many practical systems now; Nogami and Nagashima use a null symbol to synchronize the frame by detecting the power drop at the receiving end, but this method is suitable for continuous structures. For burst data structures, it cannot be correct This method is not suitable for distinguishing between Null symbol and idle time; Van de Beek proposed a maximum likelihood estimation algorithm based on CP, which cannot estimate integer frequency offset and cannot provide frame synchronization information, so it is mostly used for timing and frequency offset tracking stage, considering that the synchronous tracking should ensure a simple algorithm, many literatures have proposed various improved algorithms on this basis; M.Schmidl proposed a method based on training sequences, which realized energy detection and Fine synchronization and frequency offset estimation, the algorithm is relatively simple and easy to implement; Classen also proposed a pilot-based method, the premise of which is a slow time-varying channel. This algorithm has introduced ICI when estimating the frequency offset in the frequency domain, so the performance is improved. decrease; there are also many blind estimates currently being studied, because they are based on the average of multiple symbols, requiring slow time-varying channels, and the algorithm is complex and mostly used for frequency offset tracking

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