Advanced global navigation satellite system receiver design (797918), страница 38

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Also equivalentloop bandwidth2 BL =1TLH–5ThereforeΣ2 →2 BL TS TC2 BL TS××=×× TSCC626N0N0H–6Further analysis finds that provided the delay time TD ≤ TS then theΣ2 =2 B L TD×× TSC6N0H–7Generalisation.Further analysis finds thatΣ2 =H.22 BLTD×CTN 0 4 ×  2 − STC× TSTD ≤ TSH–8Direct analysis for cBOC(1,1)Identify chip width TC , sub-chip width TS and half sub-chip width T = TS whereTC = 2TSH-2Derivation of exact timing formulas for sine and cosine BOCp(t)Ah(t)1TTTS∆q(t)+ ∆v(t)q(t)+ v(t)+++−TTCwhite noiseTu(t)Figure H-2, Delay line subtractor for cBOC(1,1)main peak noiseless output q(0) = 4Aat displacement T output q(T) = −AInitially choose delay line subtractor also TD = TTherefore maximum positive and negative peak in ∆q(t) = ± 5ASlope in ∆q(t) = 10A/TEquivalent difference impulse response∆h(t ) = h(t ) − h(t − T )H–9Then noise out∆v 2 =()ηη1 2η 101 + 2 2 + 0 2 + 2 2 + 12 =∆h(t )2 dt =∫22T2TH–10therefore mean square noise jitter for just one pulse (duration TC)2η 10  T ηTΣ = × × = ×2 T  10 A 2 10 A 22H–11This is reduced in a loop system of effective integration time TL toΣ2 →TηT×× C22 10 ATLH–12One can show that A2/η = C/N0 in a phase synchronised channel.

Also equivalent loopbandwidth2 BL =1TLH–13ThereforeH-3Derivation of exact timing formulas for sine and cosine BOCΣ2 →2 BL T TC2BL T× ×=× × TSCC10 210N0N0H–14Further analysis finds that provided the delay time TD ≤ TS/2 then theΣ2 =2 B L TD×× TSC10N0H–15Generalisation.Further analysis finds thatΣ2 =2 BLTD×CTN 0 4 ×  2 + STC× TSTD ≤ TS / 2H–16H-4IAltBOC(15,10) lookup tableIn Chapter 7 a simplified implementation technique for the generation of AltBOC 8PSK modulation is described. The AltBOC signal can be written as follows.  2π t  2π tS AltBOC (t ) = sgn sin + θ A  cos(θ B ) cos(ω L 5t ) + sgn sin + θ A  sin (θ B ) sin (ω L 5t )  Ts  Ts()(I–1)θ A ∈ 0, π 4 , π 2 , 3π 4 , θ B ∈ 0,± π 4 ,± π 2 ,± 3π 4 and TS is the sub-carrier period.

θ Adefines the timing of 180º phase reversals of the carrier and θ B chooses the pair ofopposite phase points which are hopped between during the chipping interval. θ A andθ B are set by the 16 possible states of the input sequences using the look-up tableshown in Table I-2. The AltBOC modulation can then be implemented as an 8-phasemodulation shown in Figure I-1. Example mapping of the phase point to 8-bit DACvalues is shown in Table I-1.Q2314I8576Figure I-1, AltBOC 8-PSK I/Q plotTable I-1, Example 8-bit DAC mappingPhase point123456788-bit I value218127360361272182558-bit Q value21825521812736036127I-1AltBOC(15,10) lookup tableTable I-2, AltBOC lookup table0123456789101112131415θAπ/2π/43π/4π/23π/400π/4π/4003π/4π/23π/4π/4π/2θBE5a data codeE5a pilot codeE5b data codeE5b pilot codeSub-carrierphase0 → Ts/8Ts/8 → Ts/4Ts/4 → 3Ts/83Ts/8 → Ts/2Ts/2 → 5Ts/85Ts/8 → 3Ts/43Ts/4 → 7Ts/87Ts/8 → TsTs → 9Ts/89Ts/8 → 5Ts/45Ts/4 → 11Ts/811Ts/8 → 3Ts/2-3π/4-1-1-1-1π-1-1-11π-1-11-13π/4-1-111-π/2-11-1-1-π/4-11-11-3π/4-111-1π/41-1-11-3π/41-11-1π/21-111-π/411-1-1011-110111-1π/41111551111555511488884444888444888844448337777333377666222266662777733337777555511115555111155551111333377773333222666622226773333777733888444488884844448888444115555111155π/2-π/2-111-11-11-1Phase point266662222666622226666222I-2.

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