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

h1. Simulations and results

From the method described previously, we have developed three Matlab programs enabling to compute or visualize the influence of various parameters according to what is assume known or not. 

h2. Computation of the MODCOD and (G/T) required:

Supposing that the specifications and frequency band are known (_Rb, R, f, B_ and _EIRP_ are known), we directly get all the parameters for the system design by following the method described previously.

_+f= 869,5 MHz    B= 250 kHz    PAR= 0.5 W    Rb=500 bits/s    R=50 km:+_

p=. !850M-MODCOD-GoT.png!

*Comment value (G/T): low BW so "high" modcod, high power allows low GoT, does not need a directive antenna*

_+f= 5 GHz	  B= 500 kHz	EIRP= 1 W	Rb=500 bits/s	  R=50 km:+_

p=. !5G-MODCOD-GoT.png!

*Comment value (G/T): higher BW so lower modcod, but high Got to compensate high free space loss (high freq) --> directive antenna*

h2. Influence of the bandwidth on the EIRP:

If the regulatory frequency for application is known, this tool enables to visualize the tradeoff between the EIRP and bandwidth to fulfil the specifications:

_+f= 869,5 MHz	  Rb=500 bits/s       R=50 km:+_

p=. !850M-BW_vs_EIRP.png!

Comments

_+f= 5 GHz          Rb=500 bits/s       R=50 km:+_

p=. !5G-BW_vs_EIRP.png!

Comments

h2. Influence of the distance on the bite rate:

If the required system design is too constraining for a given specification, and then not achievable, we might lower our expectations and have a tradeoff between the desired bit rate and the range

_+f= 869,5 MHz	B= 250 kHz	PAR= 0.5 W+_

p=. !850M-range_vs_Bit_rate.png!

_+f= 5 GHz	B= 500kHz	EIRP= 1 W+_

p=. !5G-range_vs_Bit_rate.png!

We can notice the bite rate is dropping quickly with the range of transmission. Then, the video transmission can be lost if the aircraft moves just a little bit too far of the limit range.