Library-encoder-decoder

Current version = 3.0

This is the encoder and decoder protocol for data broadcasting. Each package includes the following information:

Data: the actual information to be sent.
Headers: to identify the type of data.
Checksum: a simple check of corruption.
Timestamp: to indicate the time of data collection.

The decoder has one dependency which is pyserial. You can install with pip install pyserial

Data

The data is all collected as double precision floats which are 64-bit wide. Though, the protocol aims on reduceing the package size, that's why data is converted into signed integers with only the required decimal points needed, this saves space and time with no real compromises.

GPS

The GPS data consists of longitude and latitude in the following ranges:

Data	Minimum	Maximum	Integer Magnitude	Signed bit-width
LONG	-180.0000	180.0000	1,800,000	22 bit
LAT	-90.0000	90.0000	900,000	21 bit

Accelerometer

The accelerometer collects measurements on 3 axis in G's.

Data	Minimum	Maximum	Integer Magnitude	Signed bit-width
X	-40.00	40.00	4,000	13 bit
Y	-40.00	40.00	4,000	13 bit
Z	-40.00	40.00	4,000	13 bit

Barometer

The barometer collects data for pressure in mbar and temperature in celcius.

Data	Minimum	Maximum	Integer Magnitude	Signed bit-width
PRES	10.00	1200.00	120,000	18 bit
TEMP	-40.00	85.00	8,500	15 bit

Scaling Magnitudes

Each data type will be scaled with a constant magnitude to convert into an integer.

Data	Magnitude
LONG	10,000
LAT	10,000
X	100
Y	100
Z	100
PRES	100
TEMP	100

Headers

8 headers are needed.

Description	Header name	Hex	Bin
GPS Longitude	RRC_HEAD_GPS_LONG	0x00	0b000
GPS Latitude	RRC_HEAD_GPS_LAT	0x01	0b001
Accelerometer X-axis	RRC_HEAD_ACC_X	0x02	0b010
Accelerometer Y-axis	RRC_HEAD_ACC_Y	0x03	0b011
Accelerometer Z-axis	RRC_HEAD_ACC_Z	0x04	0b100
Barometer Pressure	RRC_HEAD_PRES	0x05	0b101
Barometer Temperature	RRC_HEAD_TEMP	0x06	0b110
Package Terminating	RRC_HEAD_T_END	0x07	0b111

Checksum

Each piece of data will consist of 24 bits, 4 bits of which will be copied for checksum

xxxx xxxD Bxxx xxxG Cxxx xxxF

D = LSB of highest byte
B = MSB of middle byte
G = LSB of middle byte
C = MSB of lowest byte
F = LSB of lowest byte

Timestamp

The system is expected to be running for 2 hours at a 5Hz sampling and trasmission rate (STR). With the timestamp as an integer this gives a maximum stamp of 36000 readings which is 16-bit wide.

Overall

The overall protocol will be as the following:

The largest piece of data is 22-bit wide => 24 bits will be used to pad to a whole byte.
Headers will use 3 bits of each packet, with a terminating header for the last one in a package.
Checksum will use 5 bits and will be inserted in the first packet.
Timestamp will use 20 bits giving more time of operation and/or higher STR.

Byte	Content
byte 0	`HHHC CCCC`
byte 1	`HHHD DDDD`
byte 2	`HHHD DDDD`
byte 3	`HHHD DDDD`
byte 4	`HHHD DDDD`
byte 5	`HHH0 DDDD`
byte 6	`HHHT TTTT`
byte 7	`HHHT TTTT`
byte 8	`HHHT TTTT`
byte 9	`111T TTTT`

H = Header, C = Checksum, D = Data, T = Timestamp

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