SOURCEFORGE » RALF » 2014 Dimensioning and budgeting of TM/TC link

h1. Constraints and parameters for the system design

* Required bit rate

In order to define the bit rate required for the transmission of video streams we need some input parameters, provided in the mission statement:

> # aspect ratio of the video : AR=1,78 

> # quality of the encoded video L=720p

> # frame cadence FPS=12 fps

We used the following formula

p=. Bit rate = FPS*5,0692 * L ^1,391^ /(1000*AR) 

So 

p=. *Bit rate=322 Kbps*

As the link will allow video transmission, we will need an adapted encapsulation protocol, so we must take into account extra bits: we decide to define a bit rate of 500 kbps. 

   # Network constraints

> * Frame format

The application foreseen aims at transmitting multimedia content (video on the downlink), so we choose to use the MPEG-4 coding standard. The associated frame format MP4 is particularly adapted for the encapsulation of multimedia data type.

> * Protocol stack

   # Antenna choice

> * On board antenna

The antenna placed on the aircraft must be compliant with the flight constraints listed in the introduction. Indeed, we should maintain the communication link while the aircraft is performing a turn ( +/- 15° attitude), landing or taking off ( +/- 45° inclination). Therefore, he position of the antenna must be carefully determined in order to be at LOS. 

Another constraint is the embedded 

> * Ground station antenna