pi2-CBPSK, pi4-CBPSK and pi4-CQPSK modulation

Files
file	pi4cxpsk.h
	Osmocom GMR-1 pi2-CBPSK, pi4-CBPSK and pi4-CQPSK modulation support header.
file	pi4cxpsk.c
	Osmocom GMR-1 pi2-CBPSK, pi4-CBPSK and pi4-CQPSK modulation support implementation.

Data Structures
struct	gmr1_pi4cxpsk_symbol
	pi4-CxPSK symbol description More...
struct	gmr1_pi4cxpsk_modulation
	pi4-CxPSK modulation description More...
struct	gmr1_pi4cxpsk_sync
	pi4-CxPSK Synchronization sequence segment description More...
struct	gmr1_pi4cxpsk_data
	pi4-CxPSK Data segment description More...
struct	gmr1_pi4cxpsk_burst
	pi4-CxPSK Burst format description More...

Macros
#define	GMR1_MAX_SYM_EBITS   2
	Max e bits in a symbol.
#define	GMR1_MAX_SYNC   4
	Max diff. sync seqs
#define	GMR1_MAX_SYNC_SYMS   32
	Max sym in a sync seq

Functions
int	gmr1_pi4cxpsk_demod (struct gmr1_pi4cxpsk_burst *burst_type, struct osmo_cxvec *burst_in, int sps, float freq_shift, sbit_t *ebits, int *sync_id_p, float *toa_p, float *freq_err_p)
	All-in-one pi4-CxPSK demodulation method. More...
int	gmr1_pi4cxpsk_detect (struct gmr1_pi4cxpsk_burst **burst_types, float e_toa, struct osmo_cxvec *burst_in, int sps, float freq_shift, int *bt_id_p, int *sync_id_p, float *toa_p)
	Try to identify burst type by matching training sequences. More...
int	gmr1_pi4cxpsk_mod_order (struct osmo_cxvec *burst_in, int sps, float freq_shift)
	Estimates modulation order by comparing power of x^2 vs x^4. More...
int	gmr1_pi4cxpsk_mod (struct gmr1_pi4cxpsk_burst *burst_type, ubit_t *ebits, int sync_id, struct osmo_cxvec *burst_out)
	Modulates (currently at 1 sps) More...

Variables
struct gmr1_pi4cxpsk_modulation	gmr1_pi2cbpsk
	pi2-CBPSK modulation description
struct gmr1_pi4cxpsk_modulation	gmr1_pi4cbpsk
	pi4-CBPSK modulation description
struct gmr1_pi4cxpsk_modulation	gmr1_pi4cqpsk
	pi4-CQPSK modulation description
struct gmr1_pi4cxpsk_modulation	gmr1_pi2cbpsk
	pi2-CBPSK modulation description More...
struct gmr1_pi4cxpsk_modulation	gmr1_pi4cbpsk
	pi4-CBPSK modulation description More...
struct gmr1_pi4cxpsk_modulation	gmr1_pi4cqpsk
	pi4-CQPSK modulation description More...

Detailed Description

Function Documentation

gmr1_pi4cxpsk_demod()

int gmr1_pi4cxpsk_demod	(	struct gmr1_pi4cxpsk_burst *	burst_type,
		struct osmo_cxvec *	burst_in,
		int	sps,
		float	freq_shift,
		sbit_t *	ebits,
		int *	sync_id_p,
		float *	toa_p,
		float *	freq_err_p
	)

All-in-one pi4-CxPSK demodulation method.

Parameters

[in]	burst_type	Burst format description
[in]	burst_in	Complex signal of the burst
[in]	sps	Oversampling used in the input complex signal
[in]	freq_shift	Frequency shift to pre-apply to burst_in (rad/sym)
[out]	ebits	Encoded soft bits return array
[out]	sync_id_p	Pointer to sync sequence id return variable
[out]	toa_p	Pointer to TOA return variable
[out]	freq_err_p	Pointer to frequency error return variable (rad/sym)

Returns

0 for success. -errno for errors

burst_in is expected to be longer than necessary. Any extra length will be used as 'search window' to find proper alignement. Good practice is to have a few samples too much in front and a few samples after the expected TOA.

gmr1_pi4cxpsk_detect()

int gmr1_pi4cxpsk_detect	(	struct gmr1_pi4cxpsk_burst **	burst_types,
		float	e_toa,
		struct osmo_cxvec *	burst_in,
		int	sps,
		float	freq_shift,
		int *	bt_id_p,
		int *	sync_id_p,
		float *	toa_p
	)

Try to identify burst type by matching training sequences.

Parameters

[in]	burst_types	Array of burst types to test (NULL terminated)
[in]	e_toa	Expected time of arrival
[in]	burst_in	Complex signal of the burst
[in]	sps	Oversampling used in the input complex signal
[in]	freq_shift	Frequency shift to pre-apply to burst_in (rad/sym)
[out]	bt_id_p	Pointer to burst type ID return variable
[out]	sync_id_p	Pointer to sync sequence id return variable
[out]	toa_p	Pointer to TOA return variable

Returns

-errno for errors, 0 for success

The various burst types must be compatible in length and modulation !

References osmo_cxvec_sig_normalize(), and gmr1_pi4cxpsk_modulation::rotation.

gmr1_pi4cxpsk_mod()

int gmr1_pi4cxpsk_mod	(	struct gmr1_pi4cxpsk_burst *	burst_type,
		ubit_t *	ebits,
		int	sync_id,
		struct osmo_cxvec *	burst_out
	)

Modulates (currently at 1 sps)

Parameters

[in]	burst_type	Burst format description
[in]	ebits	Encoded hard bits to pack in the burst
[in]	sync_id	The sequence id to use (0 if burst_type only has one)
[out]	burst_out	Complex signal to fill with modulated symbols

Returns

0 for success. -errno for errors

burst_out is expected to be long enough to contains the resulting symbols see the burst_type structure for how long that is.

References osmo_cxvec::len, gmr1_pi4cxpsk_burst::len, osmo_cxvec::max_len, and gmr1_pi4cxpsk_burst::mod.

gmr1_pi4cxpsk_mod_order()

int gmr1_pi4cxpsk_mod_order	(	struct osmo_cxvec *	burst_in,
		int	sps,
		float	freq_shift
	)

Estimates modulation order by comparing power of x^2 vs x^4.

Parameters

[in]	burst_in	Complex signal of the burst
[in]	sps	Oversampling used in the input complex signal
[in]	freq_shift	Frequency shift to pre-apply to burst_in (rad/sym)

Returns

<0 for error. 2 for BPSK, 4 for QPSK.

Since x^4 only make sense for pi/4 variant, the pi/4 counter rotation is always applied.

References M_PIf, and osmo_cxvec_sig_normalize().

Variable Documentation

gmr1_pi2cbpsk

struct gmr1_pi4cxpsk_modulation gmr1_pi2cbpsk

Initial value:

= {
        .rotation = M_PIf/2,
        .nbits = 1,
        .syms = gmr1_piNcbpsk_syms_bits,
        .bits = gmr1_piNcbpsk_syms_bits,
}

pi2-CBPSK modulation description

gmr1_pi4cbpsk

struct gmr1_pi4cxpsk_modulation gmr1_pi4cbpsk

Initial value:

= {
        .rotation = M_PIf/4,
        .nbits = 1,
        .syms = gmr1_piNcbpsk_syms_bits,
        .bits = gmr1_piNcbpsk_syms_bits,
}

pi4-CBPSK modulation description

gmr1_pi4cqpsk

struct gmr1_pi4cxpsk_modulation gmr1_pi4cqpsk

Initial value:

= {
        .rotation = M_PIf/4,
        .nbits = 2,
        .syms = gmr1_pi4cqpsk_syms,
        .bits = gmr1_pi4cqpsk_bits,
}

pi4-CQPSK modulation description