p25p1_heuristics.h File Reference

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Classes
struct	SymbolHeuristics
struct	P25Heuristics
struct	AnalogSignal

Macros
#define	HEURISTICS_SIZE   200

Functions
void	initialize_p25_heuristics (P25Heuristics *heuristics)
int	estimate_symbol (int rf_mod, P25Heuristics *heuristics, int previous_dibit, int analog_value, int *dibit)
void	contribute_to_heuristics (int rf_mod, P25Heuristics *heuristics, AnalogSignal *analog_signal_array, int count)
void	update_error_stats (P25Heuristics *heuristics, int bits, int errors)
float	get_P25_BER_estimate (P25Heuristics *heuristics)

Macro Definition Documentation

HEURISTICS_SIZE

#define HEURISTICS_SIZE   200

Function Documentation

contribute_to_heuristics()

void contribute_to_heuristics	(	int	rf_mod,
		P25Heuristics *	heuristics,
		AnalogSignal *	analog_signal_array,
		int	count )

This method contributes valuable information from dibits whose value we are confident is correct. We take the dibits and corresponding analog signal values to model the Gaussians for each dibit (and previous dibit if enabled).

Parameters

rf_mod	Indicates the modulation used. The previous dibit is only used on C4FM.
heuristics	Pointer to the P25Heuristics module with all the needed state information.
analog_signal_array	Sequence of AnalogSignal which contain the cleared dibits and analog values.
count	number of cleared dibits passed (= number of elements to use from analog_signal_array).

estimate_symbol()

int estimate_symbol	(	int	rf_mod,
		P25Heuristics *	heuristics,
		int	previous_dibit,
		int	analog_value,
		int *	dibit )

Important method that estimates the most likely symbol for a given analog signal value and previous dibit. This is called by the digitizer.

Parameters

rf_mod	Indicates the modulation used. The previous dibit is only used on C4FM.
heuristics	Pointer to the P25Heuristics module with all the needed state information.
previous_dibit	The previous dibit.
analog_value	The signal's analog value we want to interpret as a dibit.
dibit	Address were to store the estimated dibit.

Returns

A boolean set to true if we are able to estimate a dibit. The reason why we might not be able to estimate it is because we don't have enough information to model the Gaussians (not enough data has been passed to contribute_to_heuristics).

get_P25_BER_estimate()

float get_P25_BER_estimate

(

P25Heuristics *

heuristics

)

Returns the estimate for the BER (bit error rate).

Returns

The estimated BER. This is just the percentage of errors over the processed bits.

initialize_p25_heuristics()

void initialize_p25_heuristics

(

P25Heuristics *

heuristics

)

Initializes the heuristics state.

Parameters

heuristics

The P25Heuristics structure to initialize.

update_error_stats()

void update_error_stats	(	P25Heuristics *	heuristics,
		int	bits,
		int	errors )

Updates the estimate for the BER (bit error rate). Mind this is method is not called for every single bit in the data stream but only for those bits over which we have an estimate of its error rate, specifically the bits that are protected by Reed-Solomon codes.

Parameters

heuristics	The heuristics state.
bits	The number of bits we have read.
errors	The number of errors we estimate in those bits.