When choosing the right USRP device for your application, a good place to start is by asking a few questions related to signal parameters, size, weight, power, cost (SWaP-C), performance, and environmental application requirements.
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Question one: What center frequency and bandwidth do I require? This question is easy enough to answer, but question two is more involved: How do I plan to move signal data on or off the device?
This brings into focus the importance of data interfaces. For example, the USRP-290x models are connected to the host through USB and are limited by the maximum sustained bandwidth of that interface, whereas the Ettus USRP X440 is equipped with two 100 GbE interfaces capable of moving much more data.
To learn more about USRP interface bandwidth considerations, read about USRP Bandwidths and Sampling Rates on the Ettus Research knowledge base.
Most USRP devices have a maximum frequency up to 6 GHz and some higher; the NI Ettus USRP X420 offers the highest frequency coverage with support for up to 20 GHz. On the lower frequency end, some radios go down to 75 MHz and some as low as DC, depending on the analog chipset used. See Table 3 for a breakdown of each model.
Figure 3. The Ettus USRP X420, built on an RFSoC, is a high-frequency wideband SDR with a center frequency up to 20 GHz.
There are trade-offs to consider when choosing a USRP device—specifically, cost versus performance. If you require a radio at a great value and you do not have advanced FPGA or wide bandwidth requirements, the NI USRP 290x or Ettus Research B200mini are great options. If you need the widest bandwidth and frequencies higher than 6 GHz, the NI Ettus USRP X410 offers support up to 7.2 GHz, the OBX daughterboard for the X300 series motherboards supports up to 8.4 GHz, and the X420 supports up to 20 GHz. There are many options available in addition to these examples. Table 3 gives a full breakdown across all models.
Figure 4. USRP and USRP B200mini Low SWaP-C SDRs
If you require the widest possible instantaneous bandwidth, the NI Ettus USRP X440 may meet the need. There are many options available beyond these examples; Table 3 provides a full breakdown across all models.
Figure 5. The Ettus USRP X440 offers up to 1.6 GHz bandwidth per channel, with a direct sampling transceiver architecture.
The USRP was conceived as a computer peripheral to connect software to the electromagnetic spectrum. Applications have evolved since the first USRPs, and many require an embedded processor onboard. You may require this stand-alone configuration if your application has the SDR physically distributed from a centralized control system or deployed on its own.
If stand-alone is a key requirement, refer to Table 1 to help you to decide whether an AMD Zynq™ Multiprocessor System on Chip (MPSoC) or RF System On Chip (RFSoC) is sufficient—or if you require a powerful Intel® X86 processor onboard, as shown in Figure 6.
Radio ModelOnboard ProcessorNI USRP N320, NI USRP N321, NI USRP N310
AMD Zynq MPSoC
NI USRP E320
AMD Zynq MPSoC
NI Ettus USRP X410, NI Ettus USRP X420, NI Ettus USRP X440
AMD Zynq UltraScale+™ RFSoC ZU28DR
NI USRP
Intel Core™ i7 EQ (2 GHz quad core)
Table 1. Stand-Alone-Capable USRP Models with Onboard Processors
Figure 6. USRP Stand-Alone SDR with Built-in Intel Core i7
Although many USRPs are used in the lab, some applications require operation in outdoor or other harsh environments. If your application requires extended operating temperatures or cannot rely on air cooling, consider the Ettus Research Embedded Series for your application. Additionally, under the Ettus Research brand, you’ll find configurable options for the USRP B206mini for extended temperature range with the use of the industrial grade aluminum enclosure assembly for low SWaP operation. Alternatively, if you have extreme environmental requirements, we can help connect you with our experienced ruggedization partners; contact us to explore these options.
Figure 7. Embedded Series, USRP E320
Many applications require multiple input and multiple output (MIMO) configurations with varying levels of synchronization. Some MIMO systems simply require a shared clock for ADCs and DACs, while others require every channel to be locked to a common clock and local oscillator for a full phase coherent operation.
A common MIMO application is for communications with spatial multiplexing. As this only requires clock synchronization, most USRPs with an external 10 MHz reference clock will be sufficient. An example of such a system was built by The University of Bristol and Lund University when they broke the wireless spectral efficiency world record using an SDR-based massive MIMO system. The system used in this application is composed of NI USRP software defined radio devices with onboard FPGAs.
Figure 8. USRP N320 and N321 with Built-In LO Distribution Interfaces
When a full phase coherent operation is required, you have a few options to consider. If you require up to four channels of receive-only operation, the Ettus Research USRP X310 with two TwinRX daughterboards can be set up to share the LO and operate in a phase coherent manner. If you require up to 1 GHz of bandwidth or frequency coverage above 6 GHz, the X420 supports LO sharing and can achieve phase coherency of less than one degree root mean square (RMS). The X420 has two RF channels and can be used to build larger channel count systems. If more than four channels are required, then consider the Ettus Research USRP N320 and N321 (shown in Figure 8) or the NI Ettus USRP X440. Since the USRP X440 is built with a direct-sampling intermediate frequency (IF) architecture, synchronization can be achieved by sharing sample clocks across up to eight transmit and eight receive channels. It is prepared for multidevice synchronization to an externally provided reference clock signal.
The USRP N321 comes equipped with built-in LO distribution hardware allowing for up to 128 x 128 phase coherent operation: A 32 x 32 configuration example is shown in Figure 9.
Figure 9. USRP N320 and N321 Multichannel Phase Coherent System
In some applications, radios require synchronization but are not co-located. In these instances, a full phase coherent operation is a challenge; however, GPS-based synchronization can be used to get frequency and phase stability with a GPS disciplined oscillator (GPSDO). Many USRP models are equipped with a GPSDO from the factory. To learn more, read “Global Synchronization and Clock Disciplining with NI USRP-293x Software Defined Radio.”
Figure 10. USRP X310 with Onboard GPS Disciplined Oscillator
Some applications have processing requirements that are best suited for an onboard FPGA. These applications often have wide signal bandwidths or low/deterministic latency requirements. In these cases, picking a radio with the ability to program the FPGA is important. Many of the USB and lower-cost USRP models, such as the USRP B206mini, are built with smaller FPGA devices and do not have the space to add user code. Many of the higher-end radios come equipped with Kintex™ 7 class devices all the way up to the state-of-the-art Ettus USRP X410, X420, and X440 with the AMD Zynq UltraScale+ RFSoC. Devices built on AMD Zynq include additional cores such as onboard soft-decision forward error correction (SD-FEC), multi-Arm® processors, and built-in ADCs and DACs.
USRP ModelOnboard FPGAUSRP N320, USRP N321, USRP N310
AMD Zynq MPSoC
USRP E320
AMD Zynq MPSoC
Ettus USRP X410, USRP X420, USRP X440
AMD Zynq UltraScale+ RFSoC ZU28DR
USRP , USRP X310
AMD Kintex 7 410T
Table 2. Comparison of FPGA-Enabled USRPs
Figure 11. Comparison of FPGA Resources Across NI FPGA Products
Programmability is the key feature of an SDR, enabling a user to take a radio peripheral and turn it into an advanced wireless system. The USRP is the most open and versatile SDR on the market, helping engineers to build systems with a wide variety of software development tools on both the host and the FPGA.
As shown in Figure 2 earlier in this paper, there are a variety of options to program the host of an SDR-based system.
LabVIEW is a graphical data flow programming environment well-suited for designing and implementing communications algorithms. At the most fundamental level, LabVIEW uses the NI-USRP driver to both specify USRP hardware configuration as well as to send and receive properly formatted baseband I/Q data ready for host-side signal processing.
If LabVIEW is your preferred development environment, it should be noted that although it does have some Linux-based OS support, it’s predominantly a Microsoft Windows-based tool. Additionally, some Ettus Research USRP models and configurations may not be supported; see Table 1.
Figure 12. LabVIEW Block Diagram with the NI-USRP Driver API
Many SDR users prefer to program USRP hardware with text-based and open-source tool flows built on C/C++ and Python. All NI and Ettus Research USRP models support the USRP hardware driver (UHD), allowing for easy integration to open-source community developed tools such as GNU Radio, shown in Figure 13.
GNU Radio is an open-source tool built solely for SDR developers. While the USRP is not the only radio supported with GNU Radio, it’s the most popular and tested. To learn more about GNU Radio, visit gnuradio.org, and to see all the existing community shared IP for GNU Radio, visit cgran.org.
Figure 13. GNU Radio Companion Flow Graph
If MATLAB is your preferred tool for programming, MATLAB and MathWorks Simulink™ software connect to the USRP family of software defined radios to provide a radio-in-the-loop environment as well as support different USRP models through different add-on solutions.
USRP N3xx, X3xx, and X4xx are supported by Wireless Testbench, which offers support for testing wideband wireless systems and spectrum monitoring, featuring high-speed data transmission and capture. Wireless Testbench also enables you to integrate custom IP blocks such as filters, synchronizers, and more with RF Network-on-Chip (RFNoC™) into the signal processing chain on the USRP FPGA (with MathWorks HDL Coder™).
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USRP N2xx and B2xx devices are supported by MathWorks Communications Toolbox™, enabling the design and prototyping of SDR systems. This support enables you to transmit and receive over-the-air signals with MATLAB and Simulink, aiding transceiver design and enabling waveform testing.
USRP E310 device support is provided by Communications Toolbox, facilitating the prototyping and testing of SDR systems. This support enables HDL code generation for the E310, enabling the deployment of wireless systems on this radio.
Many USRPs come equipped with a large FPGA with sufficient free capacity that allows users to embed inline signal processing specific to their application. As described in the hardware section, some USRPs come equipped with AMD Zynq SoC devices and some with traditional fabric FPGAs such as the Kintex 7. There are two ways to gain access to the FPGA on USRPs: LabVIEW FPGA (available on select USRPs) and the RF Network on Chip (RFNoC) framework.
Unlike many FPGA development boards or COTS FPGA boards, USRPs are built on a common FPGA framework and provide a higher-level abstraction. This removes some of the complexity encountered when building an FPGA-based system from a bare-bones FPGA board support package.
LabVIEW FPGA is an add-on extension for LabVIEW that allows graphical programming of the FPGA on NI USRP RIO devices; a simple block diagram is shown in Figure 14. Although users must be familiar with FPGA concepts such as fixed-point math and clocked logic, LabVIEW abstracts hardware and data interfaces and simplifies register configuration and data movement. An advantage of LabVIEW FPGA is the ability to program both the host and FPGA with a unified development tool chain.
Do you have legacy IP you’d like to leverage? LabVIEW FPGA can import external VHDL or Verilog through Component Level IP (CLIP) nodes, allowing for non-LabVIEW IP to be imported. Additionally, LabVIEW allows for AMD Vivado project export for expert users working within the Vivado tool directly.
If LabVIEW FPGA is your tool of choice for host programming, note that it is limited to Windows-based operating systems. Many Ettus Research devices such as the USRP N300 and USRP E300 series are not supported under LabVIEW or LabVIEW FPGA. See Table 3 for a complete list.
Figure 14. Simple LabVIEW FPGA Block Diagram
For open-source USRP users, the preferred way to program the FPGA is through the RFNoC framework. RFNoC, like LabVIEW FPGA, is a data interface and command abstraction framework to simplify adding IP to your USRP without having to rebuild the entire FPGA board support package. As the name suggests, data flows through the FPGA from the radio as a compressed header network package. At the heart of the RFNoC framework is a crossbar interface allowing the user to plug new IP into the crossbar and route data to other IP blocks or to and from the host machine, as depicted in Figure 15. This network crossbar design removes the complexity of passing data and commands to and from the host.
If working in Vivado and using RFNoC is your preferred path to program the FPGA of your USRP, consider the USRP X300 series, USRP E300 series, USRP N300, or the Ettus USRP X400 series for your application.
Learn more about how you can use RFNoC, UHD, and USRP N300 devices to prototype multichannel wireless communication systems.
Figure 15. RFNoC Conceptual Block Diagram Integrated with GNU Radio
Deploy custom SDR algorithms on the FPGA of an NI USRP radio using a Simulink workflow. Run and verify your design using MATLAB objects and functions.
Table 3 shows a matrix view of different USRP hardware and supported software.
Table 3. USRP Hardware and Supported Software
USRP (Universal Software Radio Peripheral) devices are flexible, high-performance software-defined radio (SDR) platforms widely used in applications like wireless communication, research, signal processing, and prototyping. Selecting the right USRP device for your needs involves understanding several factors, such as the device's frequency range, bandwidth, sample rate, and processing capabilities. This guide will walk you through the key considerations to help you select a USRP device that meets your project’s specifications and requirements.
The first step in selecting a USRP device is understanding the specific requirements of your application. Different applications, such as LTE testing, satellite communication, academic research, and public safety communications, have unique needs. Consider the following questions:
Frequency Range: What frequency range does your application operate in? Different USRP models support different frequency ranges, from HF and VHF bands to high-frequency millimeter waves.
Bandwidth: What bandwidth is required for your signals? High-bandwidth applications require USRP models with wider instantaneous bandwidth to capture and process signals accurately.
Performance: Does your application require real-time processing? If so, you may need a model with a higher sampling rate, onboard FPGA processing, or MIMO capability.
By identifying these requirements early on, you can narrow down your options to USRP models specifically suited for your project’s demands.
USRP devices are available in a variety of frequency ranges. Each model has a base range, with some offering tunable options. Consider the following:
Low-Frequency Applications: If you need frequencies in the HF, VHF, or UHF bands (3 kHz - 3 GHz), consider models like the USRP B200 or B210, which provide coverage in these ranges and are ideal for general SDR projects.
Mid- to High-Frequency Applications: For applications above 3 GHz, such as 5G or radar testing, look into models like the USRP X310 or the USRP N310, which support higher frequency ranges and more advanced processing capabilities.
Millimeter-Wave Applications: For frequencies up to 6 GHz and above, devices like the USRP N320 or N321 are recommended. These models offer high-frequency tunability and additional processing power.
It’s essential to select a model with a frequency range that fully encompasses the spectrum required by your application.
Another critical factor to consider is the device’s bandwidth and sampling rate:
Instantaneous Bandwidth: The bandwidth of a USRP device determines the range of frequencies it can process at once. If your application requires high-bandwidth signals, such as wideband communication or spectrum monitoring, look for models like the USRP X410, which offers wide instantaneous bandwidths up to 200 MHz.
Sampling Rate: A high sampling rate is essential for capturing and processing fast-moving signals. The USRP N-series and X-series models generally offer higher sampling rates, suitable for real-time applications where accurate signal representation is needed.
Choosing a USRP model with the right bandwidth and sampling rate ensures accurate signal processing without missing any critical data.
Some applications require advanced processing capabilities, especially those involving real-time analysis or complex signal algorithms. Many USRP models come with FPGA (Field Programmable Gate Array) support, which enables high-speed processing directly on the device. Consider the following:
FPGA-Enabled Models: Models like the USRP N310 and X310 feature onboard FPGAs, which allow for accelerated processing of data, ideal for MIMO systems, real-time SDR applications, and situations requiring low-latency feedback.
Expandable Processing: For high-performance applications, the USRP X410 offers enhanced FPGA processing capabilities, which can handle complex DSP tasks without relying on external computing resources.
If your application requires custom DSP algorithms or heavy data processing, selecting a USRP model with robust FPGA support can significantly improve performance.
Portability and connectivity are essential considerations, especially for fieldwork or remote applications:
Portable Models: For portable or low-power applications, the USRP B200 series is lightweight and USB-powered, making it ideal for mobile or field-based projects.
Networked Models: Networked USRP devices, such as the N310 and N320, offer Ethernet connectivity and allow remote operation over a network, making them ideal for distributed systems and multi-device setups.
Depending on your application, selecting a device with the appropriate connectivity options and portability features can enhance usability and ease of deployment.
USRP devices vary widely in cost, so it’s important to balance performance needs with budget limitations:
Entry-Level Models: If you are new to SDR or have a limited budget, the USRP B200 or B210 offers a good balance of performance and affordability, making it suitable for most research and educational projects.
Advanced Models: For professional or high-performance needs, consider investing in models like the USRP X310 or X410, which come with more powerful FPGAs and broader bandwidth, ideal for commercial and complex applications.
While advanced models offer more features, entry-level USRP devices can often meet the needs of smaller or simpler projects effectively.
Q: Can I upgrade the frequency range of my USRP device?
A: Some USRP models allow for expansion or modules to extend the frequency range. Check the specifications of each model to see if it supports modular add-ons.
Q: Are all USRP devices compatible with GNU Radio?
A: Yes, most USRP devices are compatible with GNU Radio, a popular open-source software for SDR applications. NI also offers LabVIEW compatibility for many models.
Q: Do I need FPGA programming knowledge for USRP devices with FPGA?
A: While FPGA programming can enhance the device's performance, it is optional for many applications. Standard USRP software tools allow for operation without custom FPGA code.
Q: Can I use multiple USRP devices for MIMO applications?
A: Yes, many USRP models support MIMO configurations by synchronizing multiple devices. Models like the USRP X310 are particularly suited for MIMO setups.
Selecting the right USRP device depends on your specific application needs, including frequency range, bandwidth, processing requirements, and budget. Understanding these factors and how they relate to your project goals can help you choose a USRP model that maximizes performance and efficiency. With careful consideration of your requirements, a well-chosen USRP device can serve as a valuable tool for research, prototyping, and wireless communication development.
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