Center Frequency Shift According to Subcarier Format in 802.11 Application Framework

Updated Oct 5, 2018

Reported In

Hardware

  • USRP-2943

Software

  • LabVIEW Communications System Design Software
  • LabVIEW Communications 802.11 Application Framework
  • LabVIEW Communications 802.11 Application Framework 1.1

Issue Details

I am using LabVIEW Communications 802.11 Application Framework 2.1 and USRP-2943R. When a signal is transmitted through 802.11 Application Framework the center frequency is different according to the Subcarrier Format. For example, I have set the center frequency to 2GHz and the bandwidth to 20MHz and tried Carrier Frequency with 20 MHz(IEEE 802.11 a)20 MHz(IEEE 802.11 ac), and 40 MHz(IEEE 802.11 a)
When I transmit the signal, I received as shown below. The center frequency was shifted to the left when 20 MHz(IEEE 802.11 ac) was selected.
Does my USRP-2943R need to be repaired?
Figure - 20 MHz(IEEE 802.11 a)
 

Figure - 20 MHz(IEEE 802.11 ac)


Figure -40 MHz(IEEE 802.11 ac)

Solution

No, you do not need to repair your USRP-2943R. This difference between Subcarrier Format is the expected results. Actually, it is working correctly as you can see below. 

Figure - Transmitting Characteristic According to Carrier Format

1. 20MHz(IEEE 802.11 a)
When 20MHz(IEEE 802.11 a) is selected, the bandwidth is 20MHz and the range is -10MHz ~ 10MHz and this range is from the DC center.

2. 20MHz(IEEE 802.11 ac)
When 20MHz(IEEE 802.11 ac) is selected, the bandwidth is -20MHz  and the range is -20MHz ~ DC center. (Primary Channel=1)

3. 40MHz(IEEE 802.11 ac)
When 40MHz(IEEE 802.11 a) is selected, the bandwidth is 40MHz and the range is -20MHz ~ 20MHz and this range is from the DC center.

Therefore this USRP and LabVIEW communication 802.11 Application Framwork work perfectly. You can select the Subcarier Format either IEEE 802.11a or IEEE 802.11ac according to your application needs. 

 

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