sigproc: Setup downlink bursts at 156.25 duration with 4 SPS
Instead of extending 156/157 symbol sized bursts to 624/628 when 4 samples-per-symbol are used, use a fixed size of 625 samples, or 625.25 us. This is a breaking timing change.
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@ -44,6 +44,9 @@ using namespace GSM;
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/* Clipping detection threshold */
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#define CLIP_THRESH 30000.0f
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/* GSM 4 sps burst length */
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#define GSM_BURST_LEN_4SPS 625
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/** Lookup tables for trigonometric approximation */
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float cosTable[TABLESIZE+1]; // add 1 element for wrap around
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float sinTable[TABLESIZE+1];
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@ -697,27 +700,22 @@ static signalVector *rotateBurst(const BitVector &wBurst,
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return shaped;
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}
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static signalVector *modulateBurstLaurent(const BitVector &bits,
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int guard_len, int sps)
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/*
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* Laurent decomposition based GMSK modulator - 4 SPS only
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*/
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static signalVector *modulateBurstLaurent(const BitVector &bits)
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{
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int burst_len;
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const int burst_len = GSM_BURST_LEN_4SPS;
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const int sps = 4;
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float phase;
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signalVector *c0_pulse, *c1_pulse, *c0_burst;
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signalVector *c1_burst, *c0_shaped, *c1_shaped;
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signalVector::iterator c0_itr, c1_itr;
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/*
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* Apply before and after bits to reduce phase error at burst edges.
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* Make sure there is enough room in the burst to accomodate all bits.
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*/
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if (guard_len < 4)
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guard_len = 4;
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c0_pulse = GSMPulse->c0;
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c1_pulse = GSMPulse->c1;
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burst_len = sps * (bits.size() + guard_len);
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c0_burst = new signalVector(burst_len, c0_pulse->size());
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c0_burst->isReal(true);
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c0_itr = c0_burst->begin();
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@ -826,7 +824,7 @@ signalVector *modulateBurst(const BitVector &wBurst, int guardPeriodLength,
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if (emptyPulse)
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return rotateBurst(wBurst, guardPeriodLength, sps);
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else if (sps == 4)
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return modulateBurstLaurent(wBurst, guardPeriodLength, sps);
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return modulateBurstLaurent(wBurst);
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else
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return modulateBurstBasic(wBurst, guardPeriodLength, sps);
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}
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