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Burst Mode

In the Communications Toolbox™ Support Package for USRP®[1] Embedded Series Radio, if a receiver or transmitter block or System object™ cannot keep up with the radio hardware, the model or code is not processing data in real time. Burst mode enables you to buffer a set of contiguous samples without losing samples by setting the number of frames in a burst. However, lost samples can still happen between bursts, especially with large burst sizes. If your model can keep up in real time, do not use burst mode.

Determine If You Need Burst Mode

It is recommended that you enable burst mode when receive data rates exceed 500 Mbps and transmit data rates exceed 100 Mbps. Transmitting at higher rates can result in dropped samples over the Ethernet link, which can cause unpredictable results. If you do not use burst mode and the requested rate is above 100 Mbps, you receive this warning:

WARNING: Transmit rate is higher than transport link rate. 
Data may be lost. Enable burst mode for better performance.
To determine if you need burst mode, see Detect Underruns and Overruns.

Hardware-Buffered Burst Mode

When you choose a sample rate that is higher than the streaming rate supported by the Ethernet link, hardware buffering is enabled by default. You can buffer samples of up to 64 MB on the DDR3 memory of the radio hardware before transferring data to or from MATLAB® or Simulink®.

  • For the receiver, burst mode uses hardware buffering when the requested rate is above 500 Mbps (15 Msps for one channel, 7.5 Msps for two channels).

  • For the transmitter, burst mode uses hardware buffering when the requested rate is above 100 Mbps (3 Msps one channel, 1.5 Msps two channels).

Enable Burst Mode

Enable Burst Mode in Receiver and Transmitter Blocks

Each SDR block has an Enable burst mode parameter. When you select this parameter, the SDR block produces a set of contiguous frames without an overrun or underrun to the radio hardware. Enable burst mode to simulate models that cannot run in real time. Specify the amount of contiguous data using the Number of frames in burst parameter. The default number of frames in a burst is 20.

Enable Burst Mode in Receiver and Transmitter System Objects

Each SDR System object has an EnableBurstMode property. When you set this property to true, the System object produces a set of contiguous frames without an overrun or underrun to the radio hardware. For example:

rx = sdrrx('E310');
rx.EnableBurstMode = true
EnableBurstMode: true
NumFramesInBurst: 20                              

This setting can help simulate models that cannot run in real time. Specify the amount of contiguous data using the NumFramesInBurst property. The default number of frames in a burst is 20.

Burst Mode Troubleshooting

"Unable to allocate memory" error

You get this error when you specify a frame size that exceeds the maximum burst size. The maximum burst size depends on the operating system and the host due to memory constraints.

"Did not receive expected number of samples in a burst reception" error

This error occurs when MATLAB or Simulink does not receive the requested number of samples from the radio hardware.

The following are known causes of this problem:

  • On Linux® systems, the OS socket buffer size is not large enough for proper communication. Increase the socket size.

  • The Ethernet card cannot provide high-speed communication. Try using Intel® chip sets, which provide a high-quality connection in such cases.

  • The firewall or virus protection program on your system can block or slow your connection. Turn off the firewall or virus program to eliminate this problem. Keep in mind that turning off your firewall can expose your host computer to unauthorized access through the Internet.

  • Some laptops lose their Ethernet settings when the Ethernet connection is interrupted, for example, when power cycling the radio hardware. Check the Ethernet connection settings as described in Step 2 of Guided Host-Radio Hardware Setup.

See Also

Blocks

System Objects

Related Topics


[1] USRP, USRP2, UHD, and Ettus Research are trademarks of National Instruments Corp.