外文翻譯--動(dòng)態(tài)環(huán)境下 gps 接收機(jī)跟蹤環(huán)路的優(yōu)化和靈敏度分析（英文）

1、Optimisation and sensitivity analysis of GPS receiver tracking loops in dynamic environments D.-J.Jwo Abstract: For a GPS receiver, decreasing the receiver tracking loop bandwidth reduces the probability of loss of loc

2、k if there are no vehicle dynamics. However, reduced bandwidth increases tracking errors due to dynamics. Beyond a certain limit it causes a serious degradation in the dynamic tracking performance. Therefore, there is

3、involvement of a tradeoff between two opposing considerations: narrow tracking loop bandwidths are desired for filtering noise due to thermal effects, but wide tracking loop bandwidths are desired to permit tracking of

4、 vehicle dynamics. Optimal tracking loop bandwidths, which yield the minimum errors in a certain dynamics environment, are first investigated. The linear Kalman filter is employed as the optimal estimator. The covaria

5、nce for the arbitrary gain model is solved and applied to the sensitivity analysis for investigating error growth due to incorrect noise level estimate. Theoretical results are verified by numerical simulation, and res

6、ults from both approaches are in very good agreement. 1 Introduction The tracking errors of a receivcr operating on the GPS code and carrier include two major components: noise error, caused by thermal noise; and trans

7、ient error, caused by imperfectly tracking the vehicle dynamics. Selection of the baseband processor design for a GPS receiver always involves a tradeoff between two opposing considerations. Narrow tracking-loop band

8、widths are desircd for filtering noise due to thermal effects or jamming, however, wide tracking-loop bandwidths are desired to permit tracking signal Doppler shifts induced by vehicle/user dynamics. Either the carrie

9、r loop or the code loop is usually designed to select a bandwidth which produces tracking errors under maximum dynamics approximately equal to the lock limit of the loop. When the GPS signal power is limited, the tend

10、ency would seem to make the receiver tracking-loop bandwidth narrower. However, this increases the probability that the tracking loop will lose lock owing to vehicle/user dynamics. Thus, there is a fundamental system

11、 limitation of tracking-loop threshold when consid- ering both low carrier-to-noise ratio and user dynamics at thc same time. It is therefore important to analyse the error characteristics for determining the optimal

12、loop bandwidth that minimises the total tracking error. Receiver noise models for predicting the thermal noise ,jitters have been presented, for example [l-71. Dynamics stress errors can also be accurately predicted [4

13、, 6, 71. The summation of these two major error components has a minimum value for certain carrier-to-noise ratio and user IEE. 2001 IEE Pmcerdings online no. 20010429 DUI: 10.1049/ip-rsn:20010429 Paper first received

14、23rd October 2000 and in revised form 27th March 2001 The author is with the Department of Guidance and Communications Technology, National Taiwan Ocean University, 2 Pei Ning Rd., Keelung 202-04, Taiwan, Republic of

15、China IEE Proc.-Rudu,: Sonar Nuvig,. Vol. 148, No. 4, August 2001 dynamics. Based on knowledge of the errors, the theore- tical prediction of optimal bandwidth for minimum track- ing error can be determined. The enviro

16、nment concerned is the case of limited GPS signal power or jamming for the dynamics user without other information aiding. How the incorrect parameters (i.e. departure from the design point: could be intentional or u

17、nintentional) influence the error growth, referred to as the ‘sensitivity analysis’, is consid- ered. The sensitivity analysis involves the incorrect esti- mate of received signal carrier-to-noise ratio. A theoretical

18、 approach and numerical simulation are performed for verification. 2 GPS receiver tracking loops The GPS receiver contains a code tracking loop and a carrier tracking loop for tracking the Doppler-shifted carrier. Th

19、e pseudorange obtained from the code tracking loop provides a position fix; the pseudorange rate estimate obtained from the carrier tracking loop provides a velocity fix. The receiver carrier tracking loop is more sen

20、sitive to dynamics due to the fact that it tracks a much higher frequency signal than a code tracking loop. If the carrier tracking loop loses lock during a dynamic manoeuvre, the code tracking loop will usually lose

21、 lock subsequently. Some designs use the carrier loop to track the dynamics and provide the code loop with a prior knowledge of the dynamics such that the code loop will not see the full dynamics. The external navigati

22、on source, such as inertial velocity, can also be utilised to aid the tracking loops for removing most of the dynamics stress error such that a smaller bandwidth could be used. More information regarding the inertial

23、 velocity aiding can be found in [9, lo]. The architecture of the simplified GPS receiver tracking loops is shown in Fig. I . 2.1 A generalised block diagram of a tracking loop that is applicable for analysis of both

24、 carrier and code loops is 241 Transfer functions of tracking loops u(s) = a,s“ + a,,- ,.Fl + ' ' ' + a“ c:, I , =- 2a“(l , time (PIT) in scconds, U' is the early-to-late correlator spacing norm

25、alised with respect to one chip U' = I for time-shared tau-dithcrcd early-late correlator = f for dedicated early and late correlator and clno is the carricr-to-noise ratio value clno = (SNR)(BL) (ratio-Hz) CllY,

26、= 10 log,o(c/no) (dB-Hz) The second term in parentheses is known as the 'squaring loss', Most GPS receivers employ a noncohercnt delay- lock loop (DLL) for code tracking and a Costas-type phase-lock loop (PLL)

27、 for tracking the Doppler-shifted carrier. The thermal noise jitter for the commonly used tau-dithered early-late DLL with d= I , is The P-code and CIA-code, with the chipping rate (chips per sec) of 10.23 and 1.023

28、Mbit/s, correspond to a chip width i,, of 29.305 and 293.05 m, respectively. Thermal noise for the PLL, when implemented in thc form of a Costas-type loop, is approximated by - - [x( 1 +- c/no 2Tc/no (degrees) (Xb

29、) The GPS has a 50 Hz navigation data message bit rate; the predetection integration timc is usually the period of a navigation data bit, 20 ins. The wavclcngths A ,for L, and L, carricrs, due to the link frequencies 1

30、575.42 and 1227.6 MHz, are 0.193 and 0.2442 m, respectively. IEE Pmc.-Rudur: Sonar Nuvavig.. Vol. 148, ,!Vo 4, Azrg~ist 2001 For the DLL the thermal noise is indepcndent of tracking-loop order; for the PLL, the therm

31、al noise jitter is not directly dependent on the loop order, too [4]. The C/NO s of the GPS with good signal power typically range from 35-55 dB-Hz, so tracking errors generally run on the lower end of the range. For

32、 the nominal range of C/No (35 dB-Hz and above) the squaring loss is usually consid- ered negligible. Typically, the unaided code tracking-loop bandwidths are in the range of 1-4 Hz and unaided carrier tracking-loop

33、bandwidths are in the range of 5-1 5 Hz. Fig. 5 shows one-sigma thermal jitters of the early-minus-late noncoherent DLL and the Costas-type PLL, respectively. The maxiinum bandwidths allowed for maintaining lock in v

34、arious GIN, environments arc shown in Fig. 6. 3.2 Dynamic stress errors A small steady-state crror is usually desired and is consid- ered as the criterion of good tracking performance. The transfer function representin

35、g the tracking crror is The steady-state error can be evaluated by means of the final value theorem of the Laplace transforms lirn e(t) = liin sE(s) = lim s[ 1 - H(s)] (10) t ix s+o .v+ 0 and thus The loop order

36、is sensitive to the same order of dynamics, e.g. first order to velocity stress, second order to accelera- tion stress, and third order to jerk stress. The first-order loop is suitable for a user position that varies

37、in a random walk manner (white noise velocity); the second-order loop is suitable for a user velocity that varies in a random walk manncr (white noise acceleration); the third-order loop is suitable for a user accele