Slide 1

Pilot3i
CollisionAware


Slide 2

Features
• ADS-B in Receiver
• P3I Transmitter/Receiver
– Transmitter range in free space Approx 25Km

• RS232 GPS NMEA (ADS-B out)
• Bridge Connect WiFi
– WiFi enabled 3rd Party devices

• Bridge Connect RS232
– Hardwired 3rd Party devices


Slide 3

3rd Party Interfaces
• WiFi Connected Devices
– SkyDemon
– RunwayHD (TBD)

• Hardwire Connected Devices
– XC-Soar


Slide 4

P3I: Block Diagram
1090Mhz

868Mhz

2.4Ghz
ADS-B
RX
P3I
RX
P3I
TX

WiFi
Host
System

RS232
NMEA out

Transponder

RS232
traffic

Device


Slide 5

P3i: Hardware


Slide 6

P3I: 3rd Party Interface (skydemon)


Slide 7

P3I: 3rd Party Interface (xcsoar)


Slide 8

P3i: Software Requirements
• Apple IOS : OEM API Library
– Integration into 3rd Party, consistent with the
OpenP3iProtocol
– Allow overlays onto 3rd Party software
• Surrounding Aircraft
–
–
–
–
–

Position (Latitude/Longitude)
Speed
Altitude
Track
Extended info
» Pilot name,
» Flight plan (current/next leg)


Slide 9

P3i: OpenP3iProtocol
24 byte
Packet
Byte 0

sync
icao
longitude
latitude
altitude
track
msd
knots
aircraft
crc

Byte 23


Slide 10

P3i: OpenP3iProtocol
sync
24 byte
Packet

The sync character is a single character
Identifier, indicating the start of a 24 byte
Packet of data. The chosen character is
‘$’, this conforms with the GPS NMEA
Standard for a ‘$’ meaning start of line, eg
$GPGGA …


Slide 11

P3i: OpenP3iProtocol
icao
24 byte
Packet

The icao field is a 24bit value which is used
As a unique identifier over the air, this can
Be the same value used for the transponder
Or a pseudo random identifier, an example
Of an icao would be 0x40526F


Slide 12

P3i: OpenP3iProtocol
longitude/latitude
24 byte
Packet

The longitude and latitude values are encoded
As decimal degrees, encoded into a 32-bit
Floating point number, as specified by
IEEE-754 single precision
Bit[31]
- Sign
Bit[30:23] - Exponent
Bit[22:0]
- Mantissa
Note: 64-bit double number representation would be more accurate,
But in reality the inaccuracy due to a 32-bit representation, is so
Small it is not worth consideration.


Slide 13

P3i: OpenP3iProtocol
altitude
24 byte
Packet

The altitude value is encoded in metres
Above Mean Sea Level (amsl), this is represented
As an unsigned 16 bit value. There is no
Requirement for a signed value, aircraft rarely go
Underwater in normal operation!
Although the packet representation is in metres, the
Displayed value is likely to be feet, giving the
Following vertical range
range: 0ft - 215,000ft (AMSL)


Slide 14

P3i: OpenP3iProtocol
track
24 byte
Packet

The track indicates the aircrafts track vector
In degrees Relative to true north. Encoded as
an unsigned 16 bit value, this represents the
required track of 0 – 359

Note: This is a little bit of overkill as the data can represent
O – 65535, it may be worthwhile breaking this down into a
Smaller structure of
Bit[15:9]
- reserved (7 bits)
Bit[8:0]
- track (0-511) (9 bits)


Slide 15

P3i: OpenP3iProtocol
msd (message sequence data)
24 byte
Packet
msd
seq
byte0
byte1
byte2
This is a much more complicated structure than the previous fields. This
provides the ability to split a large piece of data over
Many packets of information. The seq(uence) indicator, provides an index
into an array of data for the subsequent bytes 0-2.
The sequence has a range of 0-255, meaning upto 768 bytes of
Data can be transferred over consecutive packets


Slide 16

P3i: OpenP3iProtocol
msd (message sequence data)
So what could we use an additional 768 bytes to transfer ?
Firstly bear in mind that a full packet of 768 bytes would take a long time
to transmit, so this upper limit may be unrealistic
The normal packet transmit time is 2 seconds, so for 3 bytes / second a
full message of 768 byte length would take nearly 9 minutes!
But a defined structure could be filled in much more quickly
Eg:
Route start:
latX2, lngY1
Point+1:
latX1, lngY2
Point+2:
latX1, lngY2
This is effectively 24 bytes info, which would be split across 8 packets
(24/3), and would therefore take 16 seconds to be reconstructed. But this
information does not change and would provide the receiver with
information about the pilots intended route. This kind of information is
automatically available in skydemon, airnav pro and other tools
Note: what is useful in the extended information ?


Slide 17

P3i: OpenP3iProtocol
knots
24 byte
Packet

The knots field indicates the ground speed of the
Aircraft in knots. As an unsigned 16 bit value, this
Gives a range of 0 – 65535 knots

Note: This is a little bit of overkill as the data can represent
O – 65535, it may be worthwhile breaking this down into a
Smaller structure of
Bit[15:11]
- reserved (6 bits)
Bit[9:0]
- track (0-1023) (10 bits)


Slide 18

P3i: OpenP3iProtocol
aircraft
24 byte
Packet

This field indicates the aircraft type, and has a
Range of 0-255, which means we could represent
256 types of aircraft.
Groundstation, microlight(flex), microlight(3-axis),
Helicopter, paramoter, glider, motor-glider, balloon,
Parachute, drone, model aircraft ….
Note: is there a list of types of aircraft we could encode?


Slide 19

P3i: OpenP3iProtocol
crc
24 byte
Packet

This is a simple cyclic redundancy checker
Used on the packet data from 0:22 bytes
If the CRC generated locally agrees with the
CRC at the end of the packet, the packet
Is deemed to be valid, else it is discarded


Slide 20

P3i: OpenP3iProtocol
The plan is for every plane to transmit a single packet of information at about
2 second intervals. This is at a data rate of 38.4kb/s
The greater the data rate, the less likely interference, but receiver sensitivity is
Likely reduced, consider the over the air bandwidth as a series of trains


Slide 21

P3i: OpenP3iProtocol
38400 baud
38400baud = 1bit/26uS
24 bytes = 192 bits = 5ms
2 second repeat = 2.5% of the bandwidth

2 seconds
This makes the data less likely to corruption


Slide 22

Competitive Analysis
• ADSB
– Expensive ?
– Cost prohibitive
– Limited data Routeplan, Extended Information ?

• FLARM
–
–
–
–
–

Expensive (for what you get)
Poor range
Targetted at gliders only ?
Limited data Routeplan, Extended Information ?
Bespoke (expensive) hardware – no modern standard interfaces, uses
RS232, data rate 19.2kb/s too high for Bluetooth Low Energy best case
6kb/s, and very expensive to use Bluetooth Classic (Apple MFI
program)
– No support for standard platforms
• Iphone
• Ipad
• android