USRP Software Radio

[Yikai]

I would like to transmit my PN code as fast as I can. However, I found the maximum transmitting IQ rate I can reach is 2M. If it is larger, the error will come to be "niUSRP Write Tx Data (CDB).vi<ERR>Underflow: the Tx buffer was emptied before new data was provided.  Consider reducing the IQ rate, increasing the Write rate, or increasing the number of samples per Write."

 I have tried to increase the number of samples per write to be a very high value. However, it doesn't work.

Could anyone tell me how to increase the Tx IQ Rate efficiently?

[Sarah_Y]

Hi Yikai,

Streaming data at IQ rates of 5 or 10 MS/s should be achievable on most systems.  I have a few questions and a few suggestions for you.

Questions

• What type of computer are you using?
• What is the processor?
• What is the Ethernet chipset?  Or are you running your USRP using a PCI/PCIe gigabit Ethernet card?
• Are you using an example that came with the driver or code that you wrote yourself?

Suggestions that have worked for myself and my coworkers

• Change the computer's power setting from the default 'balanced' option to 'high performance'
• Use the built in Ethernet port if possible.  If you are using a PCI/PCIe version, make sure it is a high quality card.  The cheaper ones cause dramatically poorer performance than the slightly more expensive ones
• Turn off your virus scanner and other memory/processor intense programs
• Check the "data Streaming Performance Tips" in the NI-USRP Help document.  There is a registry key that can be changed to help improve streaming performance

There are a lot of different factors that can cause poor performance with a USRP.  Please let me know a bit more about your system and the code you are running so I can better help troubleshoot this problem. 

[Yikai]

Hi, Sarah

I use a 64-bit SONY laptop with AMD Athlon(tm) II P340 Dual-Core Processor and 4GB RAM. The Ethernet port is gigabit type. I connect the board to the laptop through Ethernet cables via a gigabit switch. An Tx example in the driver (in the attachment) is used for test.

After I take your suggestions that change the computer's power setting to "high performance", turn off the virus scanner, the rate still can't reach higher.

Yikai

[Mjsalv]

Hi Yikai,

Just wondering if you ever got this to work?

I'm having the same difficulty. What daughterboard are you using?

Thanks!

[Sarah_Y]

Hey Mjsalv,

If you have tried everything mentioned above, you should also try changing your registry key.  How to do this is described in detail in this post:

http://forums.ni.com/t5/USRP-Software-Radio/Increasing-write-rate/td-p/2165368

[Adnan_Raja]

Hi Sarah and others, 

I need to send data at 16 Ms/sec in my application. But I am having problem doing so. 

Is this possible ? I checked the various threads on this forum and can now write at 4 Msamp/sec, but I am not able to go beyond it. 

I am using:

- NI-USRP-2921

- Intel Core2 Quad CPU with 8 GB RAM

- Windows 7

- RealTek RTL8168D/8111D family PCI-E Gigabit Ethernet NIC

- I am using the "NI USRP Write Tx Data (poly)" vi

I changed the registry key to HEX2400, amde sure that the firewall is turned off, and changed the power options to high performance mode. 

When I try a Tx sampling rate of 8 Ms/s, the subCallConfigTX.vi return a Tx sampling rate of 7.69 Ms/s and I get the following error.

"niUSRP Write Tx Data (CDB Cluster).vi<ERR>Underflow: the Tx buffer was emptied before new data was provided.  Consider reducing the IQ rate, increasing the Write rate, or increasing the number of samples per Write."

I would appreciate any help. 

Thanks,

Adnan

[ORN]

Hi

If you can manage with 8 bits samples ,this would half the data sendt to the USRP,

try change the network-adapter Transmit buffer size , it may help

i manage receiving at 25 MSPS i 8 bit mode, but i have a dedicated network adapter directly to the USRP,

 it is only stable if you don't do any other network access to another network-adapter.