In the Communications Toolbox™ Support Package for USRP™ Radio, if the SDRu blocks or SDRu 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.
Determine If You Need Burst Mode
It is recommended that you enable burst mode when your application requires fresh samples or guaranteed contiguous samples.
To see if the transmitted or received data is contiguous for an SDRu block:
To see if the transmitted or received data is contiguous for an SDRu System object:
For more information, see Detect Underruns and Overruns.
If your model is not running in real time, you can:
Use Burst mode
Use vector-based processing
Accelerate with code generation
Any combination of these techniques may be applied to approach or achieve real-time performance.
Enable Burst Mode
Use burst mode when your model is experiencing underruns or overruns because it cannot keep up with the amount of transmitted or received data in real time. Burst mode allows you to buffer a minimum set of contiguous samples without underruns or overruns.
Overruns and underruns can still happen between bursts, especially with large burst sizes. Therefore, enabling the burst mode feature is recommended only if your model cannot keep up in real time.
The maximum burst size (in frames) is imposed by the operating system and the
USRP device UHD™. The maximum size imposed by the UHD is approximately 1 GB, or 256 megasamples. This maximum number of
samples is enforced by MATLAB®. For example, with a frame size of 4000 samples, the maximum burst
is approximately 67k frames. Depending on the memory constraints on a specific
host, a lower limit might be required. Exceeding the limit will be flagged by an
'unable to allocate memory'. For N3xx- and X3xx-
series radios , the maximum size of the burst is calculated as
NumFramesInBurst X number of frames per burst X
SamplesPerFrame, for the devices that support RFNOC . The
default burst size is
Enable Burst Mode in SDRu System objects
Receiver Burst Mode Processing
When you use the burst mode for data reception, the first SDRu receiver System object call transfers a whole burst to the host computer memory and then the SDRu receiver System object processes the first frame. Subsequent SDRu receiver System object calls process the rest of the burst, one frame at a time, from the host computer memory (not from the radio). When all the frames in the transferred data have been processed, the next SDRu receiver System object call transfers another whole burst to the host computer memory and the first frame of data is processed by the SDRu receiver System object.
For example, Set the
EnableBurstMode property to
NumFramesInBurst property to
100000. For the
first SDRu receiver System object call, a whole burst (1,00,000
samples/frame X 10 frames/burst = 1,000,000 samples/burst) is transferred
to the host computer memory and the SDRu receiver System object processes
the first frame of data. For subsequent SDRu receiver System object calls
(second through tenth calls), one frame at a time, is processed from the
host computer memory. After the whole burst has been processed, on the
eleventh SDRu receiver System object call, another whole burst is
transferred from the radio to the host computer memory and the first frame
of data is processed by the SDRu receiver System object.
Burst-Mode Buffering to Overcome Overruns at Receiver
Configure a B200 radio with serial number set to '
30FD838'. Set the radio to receive at 2.5 GHz with a decimation factor of 125 and master clock rate of 56 MHz. Enable burst-mode buffering to overcome overruns. Set number of frames in a burst to 20 and samples per frame to 37500.
Create a SDRu receiver System object to use for data reception.
rx = comm.SDRuReceiver(... 'Platform','B200', ... 'SerialNum','30FD838', ... 'CenterFrequency',2.5e9, ... 'MasterClockRate', 56e6, ... 'DecimationFactor',125, ... 'OutputDataType','double'); rx.EnableBurstMode = true; rx.NumFramesInBurst = 20; rx.SamplesPerFrame = 37500;
Capture signal data using comm.DPSKDemodulator System object.
demodulator = comm.DPSKDemodulator('BitOutput',true);
Inside a for loop, receive the data using the rx System object.
numFrames = 100; for frame = 1:numFrames [data,overrun] = rx(); if ~(overrun) demodulator(data); end end release(rx)
Transmitter Burst Mode Processing
When you use burst mode for data transmission, the data is not transferred
to the radio until the SDRu transmitter System object has been called
NumFramesInBurst times. After the SDRu transmitter System
object is called for
NumFramesInBurst times, the whole
burst is transferred to the radio and then transmitted.
Burst-Mode Buffering to Overcome Underruns at Transmitter
Configure a B200 radio with serial number set to
'30FD838'. Set the radio to transmit at
2.5 GHz with an interpolation factor of
125 and master clock rate of 56 MHz. Enable burst-mode buffering to overcome underruns. Set number of frames in a burst to
Create a SDRu Transmitter System object to use for data transmission.
tx = comm.SDRuTransmitter(... 'Platform','B200', ... 'SerialNum','30FD838', ... 'CenterFrequency',2.5e9, ... 'InterpolationFactor',125, ... 'MasterClockRate',56e6); tx.EnableBurstMode = true; tx.NumFramesInBurst = 20;
Create a DPSK modulator as the data source using
comm.DPSKModulator System object.
modulator = comm.DPSKModulator('BitInput',true); data = randi([0 1],37500,1); modSignal = modulator(data);
for loop, transmit the data using the
tx System object.
numFrames = 100; for frame = 1:numFrames underrun = tx(modSignal); end
no tx ack
Enable Burst Mode in SDRu Blocks
The SDRu Transmitter and SDRu Receiver blocks have an
Enable burst mode parameter. When you
select this parameter, the block produces a set of contiguous frames without
underruns or overruns. Enable burst mode to simulate models that cannot run in
real time. Specify the amount of contiguous data by using the Number of frames in burst parameter. The default
number of frames in a burst is