Communication system.
Communication system requare to communicate with probe on a distances ranged
low earth orbit (200-300km), high orbit (>500km), earth-moon flight (< 400,000km).
Communication with a probe will be on 2.4GHz frequency. Core of a transmitter and
receiver will be done with a regular Bluetooth chips. Instead of an antenna transmitter
there will be a connect to power amplifier capable to 100Wt pick transmit power.
Receiver pin on chip will be connected to exit from low noise cascade amplifier
capable of 92dB gain. Both amplifiers and Bluetooth chip will be controlled by additional
microprocessor.
Protocol will support:
low
speed, medium speed 5bit/3bit with majority error correction, compatibility, and
hash protection. Mode transfer: half-duplex with hardware flow-control and each
packet with sequence number.
Portable ground stations will include 4 helical double size antennas, receiver’s
and transmitter’s amplifiers, same chip as a probe and microprocessor unit. On portable
ground station microprocessor unit will be connected to a personal computer using
a serial port. On PC special software will collect packets and send its over IP
to a central ground control station. Because of restrictions to communication on
2.4GHz band in different regions of the Earth some stations will be working in “receiver-only”
mode. 6 stations will be located around the globe to cover 24 hours communication
with probe, these stations will require a permit to operate in transmit mode. All
stations will be equipped with horizon – azimuth orientation system controlling
from the same communication software. Backup (manual) orientation assumed.
Each microprocessor unit (on probe and on ground stations) is
capable of remote software download. Each microprocessor unit can work as a regular
AT modem and as a standalone device controlling network for the probe’s internal
communications system. In normal mode of operation the probe will be accessible
as a web server with a designated IP address. Web server will be based on a main
computer module controllable by GET/PUT requests. Output of such requites will be
in XML format with telemetries readings /statuses of a probe.
Frequencies of a probe's transmitter can drift because of temperature. Testing for
temperature characteristics of a transmitter must be done and internal temperature
stabilization, temperature measurement of probe's transmitter can be used for reception's
turning. The same must be done for the on board receiver, it internal temperature
are to be recorded and used to turn frequencies of earth located transmitters.
Actually there is no guaranty that from first launch will be achieved long range
communication, In this case all failures in communication system has to be analyzed,
system can be redesigned and a second launch should be used to achieve mission goal.
Software
for a probe/craft and for ground stations
available here.
Implemented:
ATDT<ADDR>
ATA
ATH
+++
Ats9 command supports:
from ATS9=LunBMPF1F2F3 i.e.
ATS9=Lun0000020J3k
Lun
- addr
0
- 9600
0
- check sum
0
- no big preambula, not transfer to processor
02 - channel 1
frequency == 02
0J - channel 2 frequency = 0x0A
= 10
3k - channel 3 frequency = 0x3B = 59
unsigned char Config01;
0000 0000
BB -
baud rate for uart communication
00 - 9600
01 - 19200
10 - 38400
11 - 57600
M MM - mode
000 - working 250Kbit check sum 32 bytes payload + 2 bytes chek sum at the end
of data 0xff
001 - 250kBit no check sum transmit 30 bytes payload (at the end 0xff padding)
check sum calculated by rf24l01 on receive 32 bytes - to get chk sum for
processing
010 - 250kbit 3 bit data no check sum each bit converted to 3 bits (payload per
packet 10 bytes)
011 - 250kbit 5 bit data no check sum
100 - 250kbit carrier freq 1 = 1 freq 2 = 0 starting bit on freq1 followed by
freq2 stopping bit ferq1+freq2 for even (0,2,3,6,8) and freq1+freq3 for odd for
odd (1,3,5,7) P - addr == 3 byte preambula + 3 bytes preambula (01010101 6
bytes) X - transfer full received packet to processor