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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.
This commit is contained in:
Tom Tsou 2015-05-18 17:13:00 -07:00 committed by Alexander Chemeris
parent 6512812e43
commit 2518186b45
1 changed files with 11 additions and 13 deletions
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24
Transceiver52M/sigProcLib.cpp
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@ -44,6 +44,9 @@ using namespace GSM;
/* Clipping detection threshold */
#define CLIP_THRESH 30000.0f
/* GSM 4 sps burst length */
#define GSM_BURST_LEN_4SPS 625
/** Lookup tables for trigonometric approximation */
float cosTable[TABLESIZE+1]; // add 1 element for wrap around
float sinTable[TABLESIZE+1];
@ -697,27 +700,22 @@ static signalVector *rotateBurst(const BitVector &wBurst,
return shaped;
}
static signalVector *modulateBurstLaurent(const BitVector &bits,
int guard_len, int sps)
/*
* Laurent decomposition based GMSK modulator - 4 SPS only
*/
static signalVector *modulateBurstLaurent(const BitVector &bits)
{
int burst_len;
const int burst_len = GSM_BURST_LEN_4SPS;
const int sps = 4;
float phase;
signalVector *c0_pulse, *c1_pulse, *c0_burst;
signalVector *c1_burst, *c0_shaped, *c1_shaped;
signalVector::iterator c0_itr, c1_itr;
/*
* Apply before and after bits to reduce phase error at burst edges.
* Make sure there is enough room in the burst to accomodate all bits.
*/
if (guard_len < 4)
guard_len = 4;
c0_pulse = GSMPulse->c0;
c1_pulse = GSMPulse->c1;
burst_len = sps * (bits.size() + guard_len);
c0_burst = new signalVector(burst_len, c0_pulse->size());
c0_burst->isReal(true);
c0_itr = c0_burst->begin();
@ -826,7 +824,7 @@ signalVector *modulateBurst(const BitVector &wBurst, int guardPeriodLength,
if (emptyPulse)
return rotateBurst(wBurst, guardPeriodLength, sps);
else if (sps == 4)
return modulateBurstLaurent(wBurst, guardPeriodLength, sps);
return modulateBurstLaurent(wBurst);
else
return modulateBurstBasic(wBurst, guardPeriodLength, sps);
}