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Application Note Number
AN-881
Revision History
Date Author Details -05-01 Neel Pandeya
Abstract
This AN explores the USRP family at a high level, compares devices across several primary features, and walks the reader through the process of selecting a particular device for the their application.
USRP Product Selector
The USRP Product Selector will help you choose the Ettus Research USRP Software Defined Radio products that are the best fit for your application. Based on your answers to a series of questions, the USRP Product Selector will generate a PDF price quote and it to you. The Ettus Research sales team may follow up with you to answer any additional questions that you might have. If you would like a person to talk you through the USRP product selection process, please send an to .
Overview
This guide is provided by Ettus Research to help users select the most appropriate Universal Software Radio Peripheral (USRP&#;) for their specific application. In order to make the selection process as straightforward as possible, a table showing various features is provided as a basis for the selection process.
Understanding DSP Fundamentals
If you are new to the USRP family of products, software defined radio, or digital signal processing in general, it may be useful to perform some simulation of the signals you wish to manipulate before selecting USRP hardware. Simulating signals and algorithms in software frameworks such as GNU Radio or LabVIEW will ensure a proper understanding of various concepts, such as Nyquist theorem, ADC/DAC and limitations, for example. Understanding the basics of signal theory and digital signal processing is the first step towards understanding how to make the best use of an appropriate USRP model. The Suggested Reading page provides access to several resources that may be helpful in understanding the basics.
Common Applications
Table 1 shows USRP/daughterboard combinations commonly used in various application areas. While Table 1 can serve as a starting point for selecting a USRP device, Ettus Research recommends new users evaluate their application requirements against the specifications of the USRP devices. sections of this document will assist in the selection process.
USRP Device Characteristics
Table 2 shows the key characteristics of all USRP models available from Ettus Research. The table is useful for determining the interface type, bandwidth capabilities, and synchronization mechanisms specified for each USRP model. You can use this information, and the requirements for the application in question, to select a USRP radio.
10 GigE
153.6, 125, 122.88 2 16 153.6, 125, 122.88 14 153.6, 125, 122.88 Yes Yes Yes N310 1 GigE10 GigE
153.6, 125, 122.88 2 16 153.6, 125, 122.88 14 153.6, 125, 122.88 Yes Yes Yes B200mini USB 3.0 61.44 N/A 12 61.44 12 61.44 No No Yes B205mini USB 3.0 61.44 N/A 12 61.44 12 61.44 No No Yes B200 USB 3.0 61.44 N/A 12 61.44 12 61.44 No Yes Yes B210 USB 3.0 61.44 N/A 12 61.44 12 61.44 Yes Yes Yes X300 USB 3.01 GigE
10 GigE
PCIe
200 2 14 200 16 800 Yes Yes Yes X310 USB 3.01 GigE
10 GigE
PCIe
200 2 14 200 16 800 Yes Yes Yes E310 Embedded 61.44 N/A 12 61.44 12 61.44 Yes No Yes E312 Embedded 61.44 N/A 12 61.44 12 61.44 Yes No Yes E320 Embedded1 GigE
10 GigE
61.44 N/A 12 61.44 12 61.44 Yes Yes Yes Table 2 - USRP Characteristics by Model
The following sections cover frequently asked questions in choosing a USRP device that&#;s right for your application.
Do I want to perform processing on a host PC, or operate the USRP device in a standalone fashion?
This is an obvious differentiator of the USRP Embedded Series. If you need the USRP to operate a USRP radio without a host PC, the USRP E310/E312/E320 is the most appropriate. The USRP E310/E312/E320 is ideal for applications that might require mobile transceivers or distributed RF sensors. Unless the user has a clear requirement for embedded operation, Ettus Research recommends the USRP N200, N210, B200, B210, X300, X310, N300 or N310. Developing with a host-based platform typically involves less risk and will require less effort to optimize various pieces of the software radio.
In many cases it may be easier to develop with a USRP B200/B210 or USRP N200/N210, then port the code to the USRP E310/E312/E320. The UHD (USRP Hardware Driver) enables this portability. You must also consider the different processing capabilities of the host machine and ARM processor used on the USRP E310/E312/E320.
Do I Need Synchronization and/or MIMO Capability?
Table 3 summarizes the synchronization features of each USRP device. Table 4 shows recommended solutions for MIMO systems of various sizes.
If you need MIMO capability for your application, Ettus Research recommends the USRP N200/N210, X300/X310, N300/N310 or E320. These units can be synchronized by providing a common time and frequency reference. Two USRP N200/N210s can be synchronized for MIMO operation with an Ettus Research MIMO cable. Alternatively, external 10 MHz reference and 1 PPS signals can be distributed to multiple USRP radios. With proper consideration for interface issues, it is possible to create MIMO system of arbitrary size with the USRP N200/N210, X300/X310, N300/N310 and E320.
The USRP B210, N300, E310/E312/E320 can serve a 2x2 MIMO capability because it has two integrated RF channels. When using the USRP B210 the available bandwidth is limited dependent upon the USB controller, and selected MIMO configuration. The USRP E310/E312's streaming bandwidth is limited to the 1 GigE interface to the ARM CPU. The USRP E320 supports streaming at full rate of 61.44 MS/s (SISO) or 30.72 MS/s (MIMO) via the 10 Gb interface. The USRP N300 supports streaming at 153.6 MS/s (SISO) and 125 MS/s (MIMO) via the 10Gb interface.
What Are My Bandwidth Requirements?
Many Bandwidth requirements can also be used to narrow down the USRP selection. As seen in the table, the USRP N200/N210 is capable of streaming up to 50 MS/s in each direction in 8-bit mode, and 25 MS/s in 16-bit mode. The USRP B200 is capable of streaming up to 61.44MS/s total in 16-bit, 12-bit or 8-bit modes. The USRP E320 is capable of streaming up to 61.44 MS/s in 16-bit mode. The X300/X310 is capable of streaming up to 200 MS/s per channel (400 MS/s total) with 160 MHz of usable bandwidth per channel. The N300/N310 is capable of streaming up 122.88, 125 or 153.6 MS/s per channel. The N300/N310 is limited to 2x2 operation when using a 153.6 MS/s sample rate.
However, if there is interest in transmit and/or receiving larger bandwidth signals such as 802.11, the USRP N200/N210, X300/X310, N300/N310 or E320 would be appropriate. Note these limitations are based on the data throughput provided by the corresponding interfaces. It is important to consider the performance of the processing platform, and the computational intensity of the application. The constraints of the processing platform are independent of the full capability of the Ettus Research USRP radio and UHD.
What interface do I prefer to work with?
Assuming you have narrowed the viable devices down based on bandwidth, MIMO and channel count requirements, it is possible to select a USRP device based on the interface.
In general, USB 3.0 ports are more plentiful on computers. This makes the USRP B200/B210/B200mini/B205mini slightly more usable at short ranges. The USRP N200/N210 requires a Gigabit Ethernet port and a PC typically only provides one such port. If internet access is required, the user will also need to plan for an additional network adapter. The USRP X300/X310, N300/N310 and USRP E320 all support streaming via either a 1 GigE or 10 GigE interface.
The Gigabit Ethernet interface of the USRP N200/N210 can operate over significantly longer ranges (typically up to 100ft) compared to the USB interface of the USRP B2xx. This makes it possible to operate the USRP radio it more remote locations further from the host computer. The GigE interface can be accessed via a Gigabit Ethernet switch, allowing access to multiple devices. However, Ettus Research recommends a homogeneous network without other devices, such as network routers attached.
The 10 Gigabit Ethernet interfaces of the USRP N300/N310, X300/X310 and E320 can be operated using multimode fiber optic cables with appropriate adapters which increases the distance from the host computer.
Will I develop custom IP for the USRP device&#;s FPGA?
While most users deploy their USRP devices in a stock configuration, many others customize the FPGA with their own functionality. For example, you may want to offload modulation, demodulation, or other PHY/ MAC operations to the FPGA. This reduces host processing requirements, and may allow data reduction before passing data over the host interface. A summary of the FPGAs used on each USRP model are shown in Table 5.
Highmesh contains other products and information you need, so please check it out.
The USRP N200 and USRP N210 are great, generic platforms to experiment with FPGA development. However, the important difference between these two is the FPGA size, and requirements for Xilinx development tools. The USRP N200 includes a Xilinx Spartan XC3SDA FPGA. This FPGA is optimized for DSP capability, and the logic can be modified with free Xilinx ISE tools. The USRP N210 includes a Xilinx Spartan XC3DA FPGA. This FPGA provides nearly twice the resources, but requires a licensed seat of the Xilinx development tools for development.
Do I need flexible sample clock frequencies?
Some applications may benefit from a flexible sample clock frequency. The USRP E310/E312/E320 and USRP B200/B210/B200mini/B205mini include a flexible frequency clocking solution. This flexibility allows ideal sample clock frequencies to be used for various communications standards. For example, the GSM implementations commonly use a 52 MHz sample clock.
Do I want or need a rack-mountable solution?
Generally speaking, the selection of the USRP is based on performance requirements of the electrical components. However, the convenience of a rack-mounted solution may be an attractive feature that drives your decision. The USRP N200/N210, X300/X310 and N300/N310 can all be mounted in Ettus Research rack chassis. Up to four N200/N210 USRP devices can be mounted in the 3U chassis. Up to two X300/X310 or N300/N310 USRP devices can be mounted in the 1U chassis.
Will my requirements become more demanding as I learn more about the USRP and RF systems?
One final thing to consider is how your requirements will change over time. While a lower-cost USRP device, such as the USRP B200/B200mini, may meet your immediate requirements, it is possible that the USRP N200/N210, N300/N310 or E320 would be a more appropriate platform as you continue to develop more advanced RF systems. Key improvements to note in the higher-end USRP N200/N210/X300/X310/N300/N310/E320 is the increased bandwidth, increased dynamic range, and MIMO capability.
Fortunately, UHD allows the user to develop a single application compatible with all USRP models. Within certain limitations, the code you develop to work on a USRP B2xx will generally work on any other USRP. You must still consider variables such as sample rate, host interface bandwidth, and synchronization features to ensure compatibility.
Conclusion
This application note presents the functional specifications of each USRP device sold by Ettus Research. The data from this document can be used to make an educated selection of the most appropriate USRP device for a particular user or application. If you have any additional questions, do not hesitate to contact us at .
When choosing the right USRP device for your application, a good place to start is by asking yourself a few questions related to signal parameters, size, weight, power, cost (SWaP-C), performance, and environmental application requirements. Question one: What center frequency and bandwidth do I require?
This question is easy enough to answer, but the next one 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; however, the NI Ettus USRP X410 can operate in the 7 GHz band. 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 Figure 16 for a breakdown of each model.
Figure 3: The Ettus USRP X410, built on an RFSoC, is a high-frequency wideband SDR with a center frequency up to 7.2 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 up to 7.2 GHz, the NI Ettus USRP X410 may be the best fit. There are many options available in between these two examples. Figure 15 below gives a full break down across all models.
Figure 4: USRP B200 and USRP B200mini Low SWaP-C SDRs
If you need frequencies up to 7.2 GHz, the NI Ettus USRP X410 may be the best fit. 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; Figure 16 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, you will need to decide if a Xilinx Zynq&#; Multiprocessor System on Chip (MPSoC) or RF System On Chip (RFSoC) is sufficient or if you require a powerful Intel X86 processor onboard. Table 1 provides a breakdown of various models and their onboard processors; consult USRP specification documents for more details.
Radio ModelOnboard ProcessorUSRP N320, USRP N321, USRP N310Xilinx Zynq MPSOCUSRP E31XXilinx Zynq MPSOCUSRP E320Xilinx Zynq MPSOCNI Ettus USRP X410, USRP X440Xilinx Zynq Ultrascale+ RFSOC ZU28DRUSRP 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 outdoors or in harsher environments. If your application requires extended operating temperatures or can&#;t rely on air-cooling, you may want to consider the Ettus Research branded Embedded Series for your application. Additionally, under the Ettus Research brand, there are options to configure the USRP B205mini 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 would love to 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 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, one can use GPS-based synchronization 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 B200mini or the N210, are built with smaller FPGA devices and as such 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 and X440 with the Xilinx Zynq UltraScale+ RFSoC. Devices built on Xilinx 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 N310Xilinx Zynq MPSOCUSRP E31XXilinx Zynq MPSOCUSRP E320Xilinx Zynq MPSOCEttus USRP X410, USRP X440Xilinx Zynq Ultrascale+ RFSOC ZU28DRUSRP , USRP X310Xilinx Kintex 7 410T
Table 2: Comparison of FPGA Enabled USRPs
Figure 11: Comparison of FPGA Resources across NI FPGA Products
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