Multiple Channel Input and Output Operations

For multiple input multiple output (MIMO) operations, you can use multichannel radios or use single channel radios bundled together.

About MIMO Mode

You can use MIMO operations to help achieve better performance in your communications system. Space-time block coding can increase the signal-to-noise ratio (SNR). Spatial multiplexing can increase data rates.

To prepare waveforms for MIMO mode, see MIMO Techniques.

The MIMO functionality in this support package transmits signals through the TX/RX port and receives signals through the RX2 port.

Perform MIMO Operations with USRP System Objects

Transmit over Multiple Channels with SDRu System Object

Create a System object™ for a platform that supports MIMO mode. This example uses the B210 radio.

txradio = comm.SDRuTransmitter('Platform','B210','SerialNum','31B92DD')

txradio = 
  comm.SDRuTransmitter with properties:

                 Platform: 'B210'
                SerialNum: '31B92DD'
           ChannelMapping: 1
          CenterFrequency: 2.4500e+09
    LocalOscillatorOffset: 0
                     Gain: 8
                PPSSource: 'Internal'
              ClockSource: 'Internal'
          MasterClockRate: 32000000
      InterpolationFactor: 512
        TransportDataType: 'int16'
          EnableBurstMode: false

Set the ChannelMapping property to [1 2] to indicate that both channels are in use.

txradio.ChannelMapping = [1 2];

For the B210 radios only, change the master clock rate to any value up to the supported maximum of 30.72 MHz. This hardware limitation for using two-channel operations applies to the B210 radios only. For other radios, you can set the master clock rate to any of the supported values.

txradio.MasterClockRate = 16e6;

Create a comm.DSPKModulator System object to modulate the transmitted signals.

mod = comm.DPSKModulator('BitInput',true);

Transmit the data. The System object generates two signals, one for each channel.

for i = 1:5
   data1 = randi([0 1],3e4,1);
   data2 = randi([0 1],3e4,1);
   modSignal1 = mod(data1);
   modSignal2 = mod(data2);
   txradio([modSignal1 modSignal2]);
end

Release the System object.

release(txradio);

Receive from Multiple Channels with SDRu System Object

Create an SDRu Receiver System object™ for a platform that supports MIMO mode. This example uses the B210 radio.

rxradio = comm.SDRuReceiver('Platform','B210','SerialNum','31B92DD')

rxradio = 
  comm.SDRuReceiver with properties:

                 Platform: 'B210'
                SerialNum: '31B92DD'
           ChannelMapping: 1
          CenterFrequency: 2.4500e+09
    LocalOscillatorOffset: 0
                     Gain: 8
                PPSSource: 'Internal'
              ClockSource: 'Internal'
          MasterClockRate: 32000000
         DecimationFactor: 512
        TransportDataType: 'int16'
           OutputDataType: 'Same as transport data type'
          SamplesPerFrame: 362
          EnableBurstMode: false

Set the ChannelMapping property to indicate that both channels are in use.

rxradio.ChannelMapping = [1 2];

For B210 radios only, change the master clock rate to any value up to the supported maximum of 30.72 MHz. This hardware limitation for using two-channel operations applies to the B210 radios only. For other radios, you can set the master clock rate to any of the supported values.

rxradio.MasterClockRate = 16e6;

Receive the data. Because the System object uses multiple channels, the number of columns returned in data is 2.

[data,datalen] = rxradio();

Release the System object.

release(rxradio);

Perform MIMO Operations with USRP Simulink Blocks

Transmit over Multiple Channels with SDRu Transmitter Block

The SDRu Transmitter block can accept matrices at the data port. The number of columns is the same as the length of the Channel mapping parameter. If you choose to use the optional input ports for center frequency and local oscillator offset, the ports can accept scalars or row vectors of the same length as the Channel mapping parameter.

To create a waveform suitable for MIMO transmission, you can use Communications Toolbox™ blocks to create a design similar to this diagram.

To configure the SDRu Transmitter block, in the block mask:

1. Set Channel mapping to [1 2] to use both channels.

2. Set the values for the Center frequency, LO offset, and Gain parameters as two-element row vectors. To apply the same value to both channels, specify a scalar value. For multiple channels, local oscillator (LO) offset must be 0. This requirement is due to a UHD limitation. You can specify LO offset as a scalar (0) or as a vector ([0 0]).

3. For B210 radios only, change the master clock rate to any value up to the supported maximum of 30.72 MHz. This hardware limitation for using two-channel operations applies to B210 radios only.

4. Click OK.

Receive from Multiple Channels with SDRu Receiver Block

The SDRu Receiver block can output matrices at the data port. The number of columns is the same as the length of the Channel mapping parameter. If you choose to use the optional input ports for the center frequency, local oscillator offset, and gain, the ports can accept scalars or row vectors of the same length as the Channel mapping parameter.

In Simulink^®, design a model that can process multiple received channels , similar to the model in this figure.

In this example, Channel mapping in the SDRu Receiver block is defined as [1 2] to indicate that multiple channels are being used.

To configure the SDRu Receiver block, in the block mask:

1. Set Channel mapping to [1 2] to use both channels.

2. Set the values for Center frequency, LO offset, and Gain parameters as two-element row vectors. Alternatively, to apply the same value to both channels, specify a scalar value. For multiple channels, LO offset must be 0. This requirement is due to a UHD limitation. You can specify LO offset as scalar (0) or as a vector ([0 0]).

3. For B210 radios only, change the master clock rate to any value up to the supported maximum of 30.72 MHz. This hardware limitation for using two-channel operations applies to B210 radios only.

4. Click OK.

Perform MIMO Operations Bundling Multiple Radios

Bundle Multiple Radios

To perform MIMO operations involving more than two channels, you must bundle multiple N-series radios. Ettus Research™ recommends using a common external clock signal source and pulse-per-second (PPS) signal source to bundle multiple radios to act as one radio with multiple channels.

Note

USRP™ B-series radios do not support bundling of multiple radios.

This figure shows a four channel MIMO configuration realized by bundling two N200/N210 radios together on the host PC.

Receive from Multiple Radios with comm.SDRuReceiver System Object

This example shows how to bundle multiple radios for MIMO operations with a USRP Receiver System object™.

Create a comm.SDRuReceiver System object for a platform that supports MIMO mode. This example uses N210 radios.

rxRadios = comm.SDRuReceiver('Platform','N200/N210/USRP2','IPAddress','192.168.20.2,192.168.20.3')

rxRadios = 
 
  comm.SDRuReceiver with properties:
 
                       Platform: 'N200/N210/USRP2'
                      IPAddress: '192.168.20.2,192.168.20.3'
                 ChannelMapping: 1
                CenterFrequency: 2.4500e+09
          LocalOscillatorOffset: 0
                           Gain: 8
                      PPSSource: 'Internal'
                    ClockSource: 'Internal'
                MasterClockRate: 200000000
               DecimationFactor: 512
              TransportDataType: 'int16'
                 OutputDataType: 'Same as transport data type'
                SamplesPerFrame: 362
                EnableBurstMode: false

Set the channel mapping to [1 2] to indicate that two channels are in use.

rxRadios.ChannelMapping = [1 2];

Set the center frequency and gain for each channel. Display the configuration information.

rxRadios.CenterFrequency = [1 1.1]*1e9;
rxRadios.Gain = [5 6];
info(rxRadios)

Receive the data.

[data,datalen] = rxRadios();

Release the System object.

release(rxRadios);

Receive from Multiple Radios with SDRu Receiver Block

This example shows how to bundle multiple radios for MIMO operations with an SDRu Receiver block.

Note

This example uses both X310 and N210 radios. For using X310 radios, you require Wireless Testbench™ Support Package for NI™ USRP Radios

1. Open the mask of the SDRu Receiver block.

2. Set these parameters for reception on multiple N210 radios. Then, click OK.

   • Set Platform to N200/N210/USRP2.

   • Set the IP address to 192.168.20.2,192.168.20.3 or 192.168.20.2 192.168.20.3 to specify the IP addresses of the N-series radios.

   • Set Channel mapping to [1 2]. Channel mapping value 1 of the bundled radio refers to channel 1 of the radio with IP address 192.168.20.2. Channel mapping value 2 of the bundled radio refers to channel 1 of the radio with IP address 192.168.20.3.

   • Set Center frequency (Hz) to [1 1.1]. Alternatively, to apply the same value to all channels, specify a scalar value.

   • Set Gain (dB) to [5 6]. Alternatively, to apply the same receiver gain value to all channels, specify a scalar value.

   

   The SDRu Receiver block outputs a matrix at its data port. The number of columns of the output matrix equals the length of the Channel mapping parameter.

MIMO Cable Synchronization

Since R2024b

To synchronize two USRP N200/N210 radios to transmit or receive frequency, phase, and time synchronized data across multiple channels, use a MIMO cable. Connect the MIMO cable to the MIMO expansion ports of the N200/N210 radios.

MIMO cable allows to share the clock reference, timing reference, and Ethernet across two N200/N210 radios. One of the radios is referred to as the primary radio and the other will be the secondary radio. The secondary radio will synchronize its clock and timing references to the MIMO cable.

To enable MIMO cable synchronization in System objects and Simulink blocks, see EnableMIMOCableSync property and Enable MIMO Cable Sync parameter.

For Ethernet connectivity, you can use either the shared Ethernet mode or dual Ethernet mode. In shared Ethernet mode, connect the Ethernet cable to the primary radio and the IP addresses of the primary and secondary radios must be in the same subnet. Whereas, in dual Ethernet mode, you can use two different Ethernet cables to connect the radios to the host computer.

The MIMO cable shares the clock reference, time reference, and Ethernet in the shared Ethernet mode. In dual Ethernet mode, the MIMO cable shares only the clock reference and time reference.

Configure USRP System Objects for MIMO Cable Synchronization

To configure the comm.SDRuReceiver and comm.SDRuTransmitter System objects:

1. Set the Platform to 'N200/N210/USRP2'.

2. In shared Ethernet mode, the IP addresses of the primary and secondary radios must be in the same subnet. Set the IPAddress property to 192.168.20.2 192.168.20.3. If you are using the dual Ethernet mode, set the IPAddress property to 192.168.10.2 192.168.20.3

3. Set the ChannelMapping property to [1 2].

4. Set the EnableMIMOCableSync to true.

Configure USRP Simulink Blocks for MIMO Cable Synchronization

To configure the SDRu Receiver and SDRu Transmitter Simulink blocks:

1. Set the Platform to 'N200/N210/USRP2'.

2. In shared Ethernet mode, the IP addresses of the primary and secondary radios must be in the same subnet. Set the IP Address to 192.168.20.2 192.168.20.3. If you are using the dual Ethernet mode, set the IP Address to 192.168.10.2 192.168.20.3

3. Set Channel Mapping property to [1 2].

4. Enable the Enable MIMO Cable Sync parameter.

To synchronize multiple N200/N210 radios, you can use an Ettus Research OctoClock along with the MIMO cable. You can also build larger MIMO systems up to 16x16 by sharing an external reference.

Related Topics

• Single Channel Input and Output Operations
• Single- and Multiple-Channel Output