GNSS Navigation message analysis and perspectives (797930), страница 4

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New demodulation Performance methodology (3/3)• Methodology Example:* 4 satellites with 40° elevationNew MethodologyExampleHigh level operational requirementTo determine if a GPS L1C receiver cancalculate a continuous valid positionduring 4 consecutive hours, with aprobability greater than 95%Step 0: Determining MRA ( , and ) from the high level operationalneeds.MRA ( = 0,9936, = 1ℎ and = 10−2)*Step 1: Determining 0, 0, = 0,0064Step 2: Searching the favorable receptionconditions which induces 0, Messages entirely received in GOODstates of Prieto model are considered asreceived in favorable reception conditions*Step 3: Calculating the data error rateonly for the data sets of interest containedin these ‘favorable state messages’.

= 10−2 for a − 0 =26.5 − Step 4: Determining a bound on AMRA ≥ 0,953 for − 0 = 26.5- 53 -7. Code Shift Keying (CSK) modulation (1/3)CSK characteristics: Codeword source mapping• Mapping between the bits carried by a CSK symbol and the codeword bits Determines the codeword duration and the signal demodulation performance. Mapping A: Each bit mapped by a symbol belongs to a different codeword. Mapping B: All the bits mapped by a symbol belong to the same codeword.Mapping AMapping B• Mapping A provides better demodulation performance with a longer codeword duration• Mapping B has worse demodulation performance with a shorter codeword duration- 54 -7.

Code Shift Keying (CSK) modulation (2/3)CSK characteristics: Decoding• The different channel codes and its associated decoding methods will play a veryimportant role on the final signal structure design1. Determine the demodulation performance2. Determine the receiver’s complexity3.

Determine the codeword duration Final choice will be a trade-off between the previous 3 factors and the signal needs.• Couple Channel Codes/ Decoding methods:Channel CodeDecoding MethodClassical CSK decoding method (CD)GPS L1Csubframe 2 LDPC Bit-Interleaved Coded Modulation – Iterative Decoding (BICM-ID)Q-ary code:Reed-SolomonBerlekamp / Forney algorithm- 55 -7. Code Shift Keying (CSK) modulation (3/3)CSK characteristics: Demodulation performance for increased data rates in AWGN• Coherent demodulation: BER vs C/N0 and codeword duration for a CSK signal whenincreasing the data rate of a BPSK modulated signal with a PRN code of Ts = 4ms• Characteristics: Mapping A and B Channel Coding: GPS L1C subframe 2 CD and BICM-ID decoding methods Only 1 (N=1) accumulated PRN codeCodewordDuration56Bits per8symbol1112Bits persymbol5681112Map A1200∙N ∙TsMap B240∙N ∙Ts200∙N ∙Ts150∙N ∙Ts≈110∙N∙Ts100∙N∙Ts.

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