4. Signals to be measured¶
As mentioned in the previous subsection, signals from Ku-band will be received by the antenna. Ku-band is mostly used by communication satellites for fixed and broadcast satellite services. Therefore, signals from geostationary satellites covering Europe will be received. A list of geostationary satellites covering Europe is available at Lyngsat website. Most of those satellites are used to broadcast TV but also for exchange of data and internet access. As a consequence, most of the signals that will be received by the Ku-band antenna are DVB-S or DVB-S2 compliant.
Knowing the standard that is used by the received signal, it is possible to enter the required inputs for the SDR signal analyser to carry out measurements. Indeed, subsection 2. State of the art on signal analysis explained that the display of the constellation required the signal analyser to retrieve each transmitted symbol from the signal. This operation is successful only if the signal analyser correctly demodulates the information.Optimal demodulation is achieved using a matched filter at the input of the receiver to maximize the signal-to-noise ratio. Then an adapted sampling operation as explained in subsection 2. State of the art on signal analysis allows retrieving the symbols. Therefore, the following parameters should be entered as inputs:
- The shaping filter at the transmission side to define its matched filter. It is given in the standard defining the physical layer.
- The symbol rate of the link to adapt the sampling operation
- The type of modulation which is used as a reference in the computation of the phase error, magnitude error and error vector magnitude.
By using Lyngsat Website and choosing a given satellite, those 3 parameters are available for each channel the targeted satellite is transmitting.
Taking into account the bandwidth of the USRP (20 MHz), the signal analyser to be implemented will analyse signals with a symbol rate lower than 20 MHz. Some satellites are transmitting such signals, we will point at those satellites to test the SDR signal analyser.