Communication chain on USRPs using QPSK » History » Version 33

PASCHOS, Alexandros, 12/15/2015 03:25 AM

1 22 PASCHOS, Alexandros
{{toc}}
2 22 PASCHOS, Alexandros
3 28 PASCHOS, Alexandros
h1. *Communication chain on USRPs using QPSK*
4 1 PASCHOS, Alexandros
5 28 PASCHOS, Alexandros
h2. *Setup*
6 1 PASCHOS, Alexandros
7 1 PASCHOS, Alexandros
To successfully connect two USRPs using the inventory mentioned earlier, it is required to have an Ethernet cable connected from the PC to one of the USRPs (in this case the Tx USRP) and then a MIMO cable that connect the Tx USRP to the Rx USRP. This way, the Rx USRP is also connected to the PC. The RF cable is connected from the USRP, using a 30dB attenuator to the Rx USRP. Below is a diagram of the setup. An update to the version of the FPGA image file might needed for LabVIEW Communications. In the NI USRP Utility an update to the images is done as demanded by the software.
8 1 PASCHOS, Alexandros
9 4 PASCHOS, Alexandros
p=. !{width: 40%}https://sourceforge.isae.fr/attachments/download/1491/setupDiagramUSRPs.png(Setup Diagram USRPs)!
10 24 PASCHOS, Alexandros
_Figure 5.1 Set-up diagram of the USRPs_
11 5 PASCHOS, Alexandros
12 28 PASCHOS, Alexandros
h2. *Transmission with QPSK*
13 5 PASCHOS, Alexandros
14 24 PASCHOS, Alexandros
The block diagram of the communication chain is shown below in Figure 5.2. An existing example of USRP communication with PSK was used for guidance.
15 6 PASCHOS, Alexandros
16 8 PASCHOS, Alexandros
p=. !{width: 40%}https://sourceforge.isae.fr/attachments/download/1492/communicationChainUSRPs.jpg(Communication Chain USRPs)!
17 24 PASCHOS, Alexandros
_Figure 5.2 Set-up Communication Chain between USRPs_
18 6 PASCHOS, Alexandros
19 6 PASCHOS, Alexandros
Bits are generated (Galois) using a PN (pseudo noise) sequence. The signal is then modulated, filtered and sent to the transmitting USRPS, which is continuously transmitting. The receiving USRP will obtain the data from the transmitting USRP, and the signal is filtered with a matched filter, demodulated, and the constellation is plotted.
20 9 PASCHOS, Alexandros
21 1 PASCHOS, Alexandros
On the front panel of the transmission there are several inputs and outputs:
22 1 PASCHOS, Alexandros
23 31 PASCHOS, Alexandros
|{background:#ddd}. Inputs/Controls|{background:#ddd}. Outputs/Indicators|=. _Figure 5.3 Set-up Front Panel Tx_|
24 13 PASCHOS, Alexandros
|- The IP address of the Tx USRP 
25 13 PASCHOS, Alexandros
- The transmission antenna of the USRP
26 13 PASCHOS, Alexandros
- Selection of a specific USRP channel
27 13 PASCHOS, Alexandros
- IQ sampling rate [Samples/sec]
28 13 PASCHOS, Alexandros
- Carrier Frequency [Hz]
29 13 PASCHOS, Alexandros
- Gain [dB]
30 13 PASCHOS, Alexandros
- PN order sequence
31 12 PASCHOS, Alexandros
Filter Parameters
32 13 PASCHOS, Alexandros
- Roll-off
33 13 PASCHOS, Alexandros
- Filter length
34 13 PASCHOS, Alexandros
- Filter Type
35 12 PASCHOS, Alexandros
 {None, Raised Cosine, Root Raised Cosine, Gaussian}
36 12 PASCHOS, Alexandros
Modulation Parameters 
37 13 PASCHOS, Alexandros
- Samples per Symbol 
38 13 PASCHOS, Alexandros
- PSK type {normal, differential}
39 13 PASCHOS, Alexandros
- Symbol Map|^. - IQ Sampling Rate [Samples/sec]
40 13 PASCHOS, Alexandros
- Carrier Frequency [Hz]
41 13 PASCHOS, Alexandros
- Gain [dB]
42 13 PASCHOS, Alexandros
- Symbol Rate [symbols/sec]
43 13 PASCHOS, Alexandros
- Frame Size [samples]
44 33 PASCHOS, Alexandros
- Constellation graph [IQ]|{background:#eaeaea}. !{width: 100%}https://sourceforge.isae.fr/attachments/download/1494/frontPanelTx.png(Front Panel Tx)!|
45 14 PASCHOS, Alexandros
46 14 PASCHOS, Alexandros
For the Receiving part of the VI, the front panel is depicted below:
47 14 PASCHOS, Alexandros
48 31 PASCHOS, Alexandros
|{background:#ddd}. Inputs/Controls|{background:#ddd}. Outputs/Indicators|=. _Figure 5.4 Set-up Front Panel Rx_|
49 15 PASCHOS, Alexandros
|- The IP address of the Rx USRP 
50 15 PASCHOS, Alexandros
Configure Signal Tab
51 15 PASCHOS, Alexandros
- The enabled USRP channel
52 15 PASCHOS, Alexandros
- The reception antenna of the USRP {RX1, RX2}
53 1 PASCHOS, Alexandros
- IQ sampling rate [Samples/sec]
54 1 PASCHOS, Alexandros
- Carrier Frequency [Hz]
55 14 PASCHOS, Alexandros
- Gain [dB]
56 15 PASCHOS, Alexandros
Configure Timing Tab
57 15 PASCHOS, Alexandros
- Acquisition Time
58 15 PASCHOS, Alexandros
- Symbol Rate [Hz]
59 15 PASCHOS, Alexandros
Configure Filter Tab
60 14 PASCHOS, Alexandros
- Roll-off
61 1 PASCHOS, Alexandros
- Filter length
62 1 PASCHOS, Alexandros
- Filter Type
63 14 PASCHOS, Alexandros
 {None, Raised Cosine, Root Raised Cosine, Gaussian}
64 14 PASCHOS, Alexandros
Modulation Parameters 
65 14 PASCHOS, Alexandros
- Samples per Symbol 
66 1 PASCHOS, Alexandros
- PSK type {normal, differential}
67 15 PASCHOS, Alexandros
- Symbol Map|^. Configure Signal Tab
68 15 PASCHOS, Alexandros
- IQ Sampling Rate [Samples/sec]
69 1 PASCHOS, Alexandros
- Carrier Frequency [Hz]
70 1 PASCHOS, Alexandros
- Gain [dB]
71 14 PASCHOS, Alexandros
- Symbol Rate [symbols/sec]
72 15 PASCHOS, Alexandros
Configure Timing
73 14 PASCHOS, Alexandros
- Frame Size [samples]
74 15 PASCHOS, Alexandros
- Constellation graph [IQ]
75 15 PASCHOS, Alexandros
Measurements
76 15 PASCHOS, Alexandros
- Frequency offset [Hz]
77 33 PASCHOS, Alexandros
- Frequency Drift [Hz]|{background:#eaeaea}. !{width: 100%}https://sourceforge.isae.fr/attachments/download/1498/frontPanelRx.png(Front Panel Rx)!|
78 19 PASCHOS, Alexandros
79 28 PASCHOS, Alexandros
h2. *Pilot Header for Synchronization*
80 19 PASCHOS, Alexandros
81 25 PASCHOS, Alexandros
Note that in the diagram, there are synchronization parameters. This is done because of the type of filtering (matched filtering) that is applied to the signal. Matched filtering is used in order to maximize the $SNR$, thus minimizing the $BER$. However, as it is well known, the output signal is delayed because of the transient response, known as filter delay. Therefore a pilot header for synchronization purposes is introduced into the bit stream previously created. This header, along with the expected location in the bit stream (bit 0) are the synchronization parameters which are to the demodulation function in order to properly decode the bits received.
82 20 PASCHOS, Alexandros
83 28 PASCHOS, Alexandros
h2. *Simulation Parameters*
84 20 PASCHOS, Alexandros
85 20 PASCHOS, Alexandros
The simulation was run with the following parameters for transmission and reception, knowing the limitations mentioned previously.
86 27 PASCHOS, Alexandros
|\6=. _Table 5.1 Simulation Parameters_ |
87 21 PASCHOS, Alexandros
|\2=. General Parameters	                |\2=. Filter Parameters	   |\2=. Modulation Parameters|
88 21 PASCHOS, Alexandros
|The IP address of the Tx USRP | 192.168.11.2   |Roll-off       |0.2	|Samples per Symbol|	8     |
89 21 PASCHOS, Alexandros
|Active antenna of the USRP    | 	TX1	| Filter length  |7	|PSK type          |	normal|
90 21 PASCHOS, Alexandros
|Channel	|Default	|Filter Type    |Root Raised Cosine	|\2=. Symbol Map              |
91 21 PASCHOS, Alexandros
|IQ sampling rate [Samples/sec] |	500k	|/4=.        |/4=.           |=.00	        | $-\sqrt{2}/2 -i\sqrt{2}/2$|
92 21 PASCHOS, Alexandros
|Carrier Frequency [Hz]         |	900MHz	                             |=.01	        |$-\sqrt{2}/2  +i\sqrt{2}/2$|
93 21 PASCHOS, Alexandros
|Gain [dB]                      |	0                                    |=.11	        |$\sqrt{2}/2  +i\sqrt{2}/2$|
94 21 PASCHOS, Alexandros
|PN order sequence              |	10                                   |=.10	        |$\sqrt{2}/2  -i\sqrt{2}/2$|