Link Emulation » History » Version 6

GAY, Adrien, 12/15/2014 07:34 PM

1 2 Cuadro, Juan Pablo
h1. Link Emulation
2 2 Cuadro, Juan Pablo
3 2 Cuadro, Juan Pablo
4 2 Cuadro, Juan Pablo
Telecom Bretagne has resorted to SDR based channel emulation. This approach is very attractive because of its low cost and flexibility. Typically hardware-based radio channel emulators are over 100k€ and seldom affordable for academic use. 
5 2 Cuadro, Juan Pablo
6 3 Cuadro, Juan Pablo
The architecture is simple, instead of connecting both modems back to back, a VST is inserted in each link. A Vector Signal Transceiver (VST) combines a vector signal analyzer with a vector signal generator. This allows for real-time signal processing with which we will emulate channel conditions. For more information please refer to a paper published by our tutor Laurent Franck in which SDR based channel emulation is discussed: document:"COST EFFECTIVE EMULATION OF GEO SAT CHANNELS" .
7 2 Cuadro, Juan Pablo
8 2 Cuadro, Juan Pablo
On the control PC (LAB PC #4) a custom software implemented in LabVIEW handles signal processing and seeks to set the Es/N0 for a particular link. The following are screenshots of the software front panel for both forward and return links:
9 2 Cuadro, Juan Pablo
10 4 Cuadro, Juan Pablo
!{width: 80%}labviewFL.png!
11 2 Cuadro, Juan Pablo
12 4 Cuadro, Juan Pablo
!{width: 80%}labviewRL.png!
13 2 Cuadro, Juan Pablo
14 2 Cuadro, Juan Pablo
The low part of the front panel contains the following sections:
15 2 Cuadro, Juan Pablo
16 2 Cuadro, Juan Pablo
* Error Tx
17 2 Cuadro, Juan Pablo
* Error Rx
18 2 Cuadro, Juan Pablo
* Signal display
19 2 Cuadro, Juan Pablo
* VST Rx Control
20 2 Cuadro, Juan Pablo
* VST Tx Control
21 2 Cuadro, Juan Pablo
* IP Config
22 2 Cuadro, Juan Pablo
23 5 GAY, Adrien
The first two show errors such as buffer overflows and such, it is important to keep an eye on this since it maintains emulation accuracy. We should not have any messages here. The signal display simply shows the quadrature and in-phase components of both the input and output signals of the VST. The IP Config tab is important in order to determine which VST device is associated with a given link.
24 2 Cuadro, Juan Pablo
25 2 Cuadro, Juan Pablo
The rest of the front panel contains buttons and checkboxes pertaining to different parameters of the channel emulation.
26 2 Cuadro, Juan Pablo
27 6 GAY, Adrien
notice. Be sure to set the frequency, RollOffFactor and Symbol Rate fields according to whatever settings are being used in the modems.
28 2 Cuadro, Juan Pablo
 
29 2 Cuadro, Juan Pablo
notice. Maximum IQ sampling rate tested was 2,048M.
30 2 Cuadro, Juan Pablo
31 2 Cuadro, Juan Pablo
A different variant of this software is available, instead of manually defining values, an input file containing a time series of Es/N0 values is loaded.