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AUGER, Anne sophie, 03/22/2015 10:29 AM
DESIGN OF A TM/TC LINK BETWEEN SMALL AIRCRAFT AND GROUND STATION¶
INTRODUCTION¶
The aim of this project is the design of a Telemetry and Telecommand (TM/TC) link between small aircrafts (ie TB20) and an antenna on top of ISAE building. There are different aspects in this work:- regulatory aspects : we must pay for rights of emission on a given frequency band
- link budget aspects : some parameters can be adjusted to reach the wanted performance
- flight constraints have to be considered in the choice of the equipment to allow a full time link
To summarize the system design constraints, we can fill the mission statement below:
| Transmission content | Data (uplink and downlink | Video (downlink) |
|---|---|---|
| Quality of transmission | 50 flight parameter/frames 1 transmission/sec |
12 fps 720p display |
| Minimum range | 50 km - Line Of Sight | |
| Fligh constraints | +/-15° for attitude +/- 45° for inclination |
In order to define the video bit rate required for our application, knowing the quality of the encoded video (720p) and its frame cadence (12 fps) , we used the following formula :
Bit rate = FPS * 5,0692 * L ^1,391 / (1000 * AR)
With AR = 1,78, FPS=12 and L=720
So
p=.Bit rate=322 Kbps
As the link will allow data and video transmission, we choose to use the MPEG4 packet format, adapted for multiplexing different nature content. Therefore, we have to consider extra bits due to the encapsulation of data in MPEG4 frames, and we decide to define a bit rate of 500 kbps.