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AE4003 Sample of Descriptive Questions(A) Signal & Systems

A.1 Random signals are non-deterministic. How do you characterize and analyse a non-deterministic random signal and system?

A.2 What is the mean square value of a random signal E[X 2(t)] in terms of itsautocorrelation function R X( ) and power spectral density function S X(f)?

A.3 How do you characterize the response of a linear system, whose transfer function isgiven by T(f), to an input random signal X(t) with the autocorrelation function R X( )?

(B) Basic Ranging Concept

B.1 In 3D ranging, there are three unknowns in the user position coordinates u(x u, yu, zu).Why do you need at least four signal emitters to resolve u uniquely, even if we assume

that there is no clock bias error for the user measurement equipment?

B.2 In 2D ranging in the horizontal plane, what is the minimum number of signal emittersto resolve the user location uniquely to a single point, assuming that there are notmeasurement errors? If there are errors in the ranging measurements, ranging circles fromeach emitter become concentric circles. Where is the expected true location of the user?

B.3 What is the difference between one-way and two-way ranging? What are theircomparative advantages and disadvantages?

(C) Satellite Based Radio Navigation System GPS)

C.1 As a one-way ranging system, how is the sending time of the GPS ranging signalprovided by the signal emitter (GPS satellite) and determined in the GPS receiver?

C.2 If the C/A code is used for the pseudorange measurement, explain why the valuerepresents the fractional milli-second equivalent of the partial pseudorange distancebetween the satellite and the user.

C.3 For pseudorange determination using the PRN code, what is the required property of the PRN sequence and why is it important for pseudorange determination?

C.4 In principle, the same PRN code with the desired autocorrelation property can beused for pseudorange measurements from all the GPS satellites. Why is it necessary touse unique and different PRN code for each satellite in the GPS? What property of thePRN codes is required besides the autocorrelation property?

C.5 What indication does the GDOP value provide to the users in GPS? Describe thepossible satellite configurations that generally give rise to good and poor GDOP?

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C.6 The ECEF coordinate system is chosen for the specification of satellite and userpositions in the GPS. What is the principal difference between the ECEF and the ECFcoordinate systems and why is the ECEF system preferred in the GPS?

C.7 What are the main features of the World Geodetic System WGS-84? Why is it

relevant and useful as a coordinate system in the GPS applications?

(D) Terrestrial Radio Navigation Systems

D.1 How is the position fix of aircrafts done in the pure VOR system? If VOR isaugmented by DME, how is the position fix accomplished and what is the advantage of the VOR/DME combination compared with the pure VOR system?

D.2 DME uses two-way ranging. Why is there a possibility of clashes in therequest/response from different users of the DME system and how can such clashes beminimized in the DME system design?

D.3 Why is LORAN-C called a Hyperbolic Radio Navigation System? How is one-wayranging accomplished in the LORAN-C system without using an elaborate method to tagthe transmitted signal with the sending time of the ranging signal?