High-performance Acquisition Technique For GNSS Receiver Based On Puncture Code

With the continuous construction and development of satellite navigation system in many countries,the growing importance of satellite navigation and positioning technology has been highlighted in modern high-tech war.In order to prevent attacks and interference from enemy,and to ensure the availability,reliability and accuracy in wartime,each navigation system designs its own military signals which bring forward higher requests in structure,transmission power and other aspects,so as to prepare for the increasingly severe Navigation War situation.For example,the M-code of GPS system in USA,Military code of Compass system in China and so on.The military signal has a faster code rate and a longer pseudo-random code period which claimed to be never repeated.These features can effectively resist interference and interception from the enemy,thus has higher security.But it also brings difficulties to capture for our own side.To achieve direct acquisition of high-rate and non-periodic long codes,the U.S.military has designed the Puncture Code to help in M-code acquisition.Puncture Code is a typical time-hopping short code.Therefore,researching on the time-hopping short code acquisition technology is not only conducive to further improving the military code acquisition performance,but also can lay a foundation on military code design for our Compass system.Further more,it can help to enhance the national defense level in navigation war.This paper focuses on the acquisition technique of the puncture code in GPS system,and obtains innovations as follow:(1)Use PMF-FFT algorithm to solve the Doppler frequency and phase offset problem,and reduces coherent integration time,which can improve the tolerance of Doppler frequency offset.Therefore,it can effectively reduce the decay in the correlation peaks.Unfortunately it costs greatly more calculations.An improved algorithm is proposed in this thesis according to the aperiodic characteristic in time-hopping short code.Using FFT technique turns linear correlation into cyclic convolution,which greatly reduces the amount of computations while costing more memory in exchange.(2)Propose a parameter optimization method to minimize the total operation time,considering all the constraints between the parameters and the impact of every segment in the acquisition process.This method establishes a standard of acquisition performance,and designs the optimal parameters to shorten the acquisition time and meets the performance requirements at the same time.(3)Use the combination code to solve the problem that time-hopping short code changes in an uncertain time scale.In this method,K probable codes are added together to quickly match the receive signal simultaneously.Then shift each code to a different offset,and do the matching again to see which code is correct by the correlation-peak position offsets in thees two matches.It can be applied to fast acquisition in the environment of high SNR.Finally,this paper summarizes the achievements and puts forward the future work.