tinymodem::CSSConfig Struct Reference

Configuration of the chirp spread spectrum modem (CSSEncoder, CSSDecoder), which works like LoRa in the audio band: each symbol is a linear chirp over the bandwidth, which starts at one of N = 2^SF frequencies and carries SF bits (SF = spreading factor). The signal can be received far below the noise level and is robust against frequency offsets, different clocks and echoes. It is not compatible with LoRa radios. More...

#include <CSS.h>

Inheritance diagram for tinymodem::CSSConfig:

Collaboration diagram for tinymodem::CSSConfig:

Public Member Functions
	CSSConfig ()
bool	setMode (const char *mode)
int	chips () const
	chips (FFT bins) per symbol
float	symbolTime () const
	duration of a symbol in seconds
float	symbolRate () const
	symbols per second
float	lowFreq () const
	lowest frequency of the chirps in Hz
bool	isValid () const
	Checks the configuration: returns false (and logs the reason) if invalid.

Static Public Member Functions
static bool	isMode (const char *mode)
	true if the mode is a chirp spread spectrum mode

Public Attributes
int	spreading_factor = 7
float	bandwidth = 1000.0f
	bandwidth of the chirps in Hz
float	center_freq = 1500.0f
	center frequency in Hz
float	volume = 1.0f
	transmit amplitude (0.0 - 1.0)
int	preamble_symbols = 8
	transmitter: number of up chirps before the sync symbols
int	max_frame = 64
	transmitter: max number of bytes per frame (1 - 200)
int	ecc_bytes = 8
float	detect_threshold = 8.0f
bool	rx_one = false
	receiver: stop after the first frame
uint8_t	channel = 0
	receiver: input channel which is used for the decoding
float	rx_noise = 0.0f
	receiver: (testing only) amplitude of added uniform noise

Static Public Attributes
static constexpr int	MAX_FRAME = 200
	max payload of a frame
static constexpr int	HEADER_ECC = 4
	header: length byte and Reed-Solomon parity

Static Protected Member Functions
static bool	parseMode (const char *mode, int &sf, float &bw)

Detailed Description

Configuration of the chirp spread spectrum modem (CSSEncoder, CSSDecoder), which works like LoRa in the audio band: each symbol is a linear chirp over the bandwidth, which starts at one of N = 2^SF frequencies and carries SF bits (SF = spreading factor). The signal can be received far below the noise level and is robust against frequency offsets, different clocks and echoes. It is not compatible with LoRa radios.

A frame starts with preamble_symbols up chirps and 2 down chirps, followed by the header (length, Reed-Solomon protected) and the payload (CRC-16 and ecc_bytes Reed-Solomon parity bytes).

setMode() selects "css5" to "css10" (SF, 1000 Hz bandwidth) or e.g. "css7-500" or "css9-2000" (SF and bandwidth). "css" is "css7".

Copyright

GPLv3

Constructor & Destructor Documentation

CSSConfig()

tinymodem::CSSConfig::CSSConfig ( )

inline

Member Function Documentation

chips()

int tinymodem::CSSConfig::chips ( ) const

inline

chips (FFT bins) per symbol

isMode()

bool tinymodem::CSSConfig::isMode ( const char * mode )

inlinestatic

true if the mode is a chirp spread spectrum mode

isValid()

bool tinymodem::CSSConfig::isValid ( ) const

inline

Checks the configuration: returns false (and logs the reason) if invalid.

lowFreq()

float tinymodem::CSSConfig::lowFreq ( ) const

inline

lowest frequency of the chirps in Hz

parseMode()

bool tinymodem::CSSConfig::parseMode ( const char * mode, int & sf, float & bw )

inlinestaticprotected

setMode()

bool tinymodem::CSSConfig::setMode ( const char * mode )

inline

Selects e.g. "css7" or "css9-500": returns false if invalid. The other settings are kept.

symbolRate()

float tinymodem::CSSConfig::symbolRate ( ) const

inline

symbols per second

symbolTime()

float tinymodem::CSSConfig::symbolTime ( ) const

inline

duration of a symbol in seconds

Member Data Documentation

bandwidth

float tinymodem::CSSConfig::bandwidth = 1000.0f

bandwidth of the chirps in Hz

center_freq

float tinymodem::CSSConfig::center_freq = 1500.0f

center frequency in Hz

channel

uint8_t tinymodem::CSSConfig::channel = 0

receiver: input channel which is used for the decoding

detect_threshold

float tinymodem::CSSConfig::detect_threshold = 8.0f

receiver: min ratio of the peak power to the mean power of the other bins to detect the preamble

ecc_bytes

int tinymodem::CSSConfig::ecc_bytes = 8

Reed-Solomon parity bytes of the payload (2 - 64): corrects ecc_bytes / 2 wrong bytes

HEADER_ECC

int tinymodem::CSSConfig::HEADER_ECC = 4

staticconstexpr

header: length byte and Reed-Solomon parity

MAX_FRAME

int tinymodem::CSSConfig::MAX_FRAME = 200

staticconstexpr

max payload of a frame

max_frame

int tinymodem::CSSConfig::max_frame = 64

transmitter: max number of bytes per frame (1 - 200)

preamble_symbols

int tinymodem::CSSConfig::preamble_symbols = 8

transmitter: number of up chirps before the sync symbols

rx_noise

float tinymodem::CSSConfig::rx_noise = 0.0f

receiver: (testing only) amplitude of added uniform noise

rx_one

bool tinymodem::CSSConfig::rx_one = false

receiver: stop after the first frame

spreading_factor

int tinymodem::CSSConfig::spreading_factor = 7

bits per symbol (5 - 10): each step doubles the symbol duration and improves the sensitivity by about 2.5 dB

volume

float tinymodem::CSSConfig::volume = 1.0f

transmit amplitude (0.0 - 1.0)

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The documentation for this struct was generated from the following file:

• src/modem/CSS.h