USRP N310 vs N321: More RF Channels or More Bandwidth?

The USRP N310 is usually the better choice when you need four synchronized transmit and receive channels, while the USRP N321 is designed for applications that need up to 200 MHz of instantaneous bandwidth per channel and stronger multi-radio LO-distribution capabilities. In simple terms, N310 prioritises channel density; N321 prioritises per-channel bandwidth and scalable phase-coherent RF systems.

That distinction makes these two networked USRPs less interchangeable than their similar N3xx names suggest. Choosing correctly requires looking beyond frequency range and FPGA specifications to channel count, RF architecture, bandwidth, synchronization and the amount of IQ data your host system must move.

USRP N310 vs N321: quick verdict

• Choose the USRP N310 if you need four TX and four RX channels in one half-width rack unit, particularly for 4×4 MIMO, four-channel spectrum acquisition, beamforming or other multi-channel sub-6 GHz research.
• Choose the USRP N321 if two TX/RX channels are sufficient but you need up to 200 MHz of instantaneous bandwidth per channel.
• Choose the N321 for large phase-coherent multi-radio systems when its dedicated TX/RX local-oscillator distribution architecture can simplify synchronizing several radios.
• Do not choose purely by ADC or DAC bit depth. Converter resolution alone does not define receiver dynamic range, RF linearity or overall system performance.

USRP N310 vs N321 specifications

Specifications above are based on the current USRP N310 documentation, USRP N321 documentation and the Ettus N3xx UHD manual.

The main decision: four 100 MHz channels or two 200 MHz channels?

This is the fundamental difference between the N310 and N321.

The N310 provides four receive and four transmit channels, with up to 100 MHz of instantaneous bandwidth per channel.

The N321 provides two receive and two transmit channels, but increases maximum instantaneous bandwidth to 200 MHz per channel.

Neither approach is universally better.

A 4×4 MIMO experiment operating within 20, 40, 80 or 100 MHz of spectrum can benefit far more from the N310's additional channels than from doubling bandwidth that the experiment never uses.

Conversely, a two-channel radar, channel-sounding, wideband sensing or custom waveform application that genuinely occupies more than 100 MHz can make the N321's bandwidth far more valuable than two unused additional RF channels.

When the N310's four RF channels matter

The N310 integrates four complete TX/RX channels into a single networked unit.

That makes it especially attractive for:

• 4×4 MIMO research;
• multi-antenna wireless systems;
• beamforming experiments;
• four-channel spectrum acquisition;
• direction-finding research;
• distributed antenna experiments;
• multi-channel communications testbeds;
• RF sensing systems requiring more simultaneous spatial channels.

The N310 uses two AD9371 transceiver ICs. Each RFIC supplies two RF channels, giving the complete device four TX and four RX paths.

This distinction is important because “four channels” should not automatically be interpreted as four completely unrelated standalone radios. The RF channels are part of an integrated multi-channel architecture with shared timing and RF resources.

For projects that fundamentally need four simultaneous signal paths, however, having all four inside one device can be considerably simpler than building the same channel count from multiple two-channel radios.

View the USRP N310 4×4 networked SDR on SDRstore.eu.

When the N321's 200 MHz bandwidth matters

The N321 trades channel density for significantly greater per-channel bandwidth.

Each of its two RF channels supports up to 200 MHz of instantaneous bandwidth, compared with up to 100 MHz per channel on the N310.

That difference can become important for:

• wideband radar research;
• electronic-warfare research in controlled environments;
• wideband spectrum sensing;
• high-throughput RF dataset acquisition;
• wideband channel sounding;
• custom OFDM waveform research;
• carrier-aggregation experiments;
• broadband signal generation and capture;
• advanced 5G and future wireless PHY research.

If the waveform occupies only 40 or 80 MHz, purchasing an N321 simply because its headline bandwidth is 200 MHz may provide little practical benefit.

But when an experiment genuinely needs to observe or generate substantially more than 100 MHz at once, the N310 cannot substitute for the additional per-channel bandwidth.

View the USRP N321 2×2 200 MHz networked SDR on SDRstore.eu.

N310 and N321 use very different RF architectures

It is tempting to think of the N321 as simply an N310 with two channels removed and the bandwidth doubled. Internally, that is not what happened.

USRP N310

The N310 is built around two Analog Devices AD9371 integrated RF transceivers. Each AD9371 supplies two RF channels, producing the complete four-channel architecture.

Ettus refers to this RF daughterboard design as Magnesium.

USRP N321

The N320/N321 architecture instead uses discrete RF components with one RF channel per daughterboard. Ettus refers to this architecture as Rhodium.

This architecture supports higher sample rates and up to 200 MHz of usable analog bandwidth per channel.

The difference therefore affects more than the number printed in the bandwidth column. These are two distinct RF architectures optimised around different system objectives.

16-bit vs 14-bit ADC: do not choose based on bit depth alone

One specification can initially make the N310 appear superior: it uses 16-bit ADCs, while the N321 specification lists 14-bit ADCs.

The DAC specifications go in the opposite direction: N310 uses 14-bit DAC conversion while N321 lists 16-bit DACs.

Neither comparison should be used alone to declare one radio superior.

ADC bit depth is not equivalent to measured dynamic range, sensitivity, noise figure, spurious-free dynamic range or blocking performance. Those characteristics depend on the entire signal chain, including RF filters, gain stages, mixers, converters, clocking and signal level.

The practical buying decision should therefore be based primarily on the RF channels, bandwidth, synchronization architecture and performance requirements of the application rather than simply comparing converter bits.

N321 has a major synchronization advantage for large radio arrays

This is one of the most important differences for advanced laboratories and is easy to miss in a basic comparison table.

Both devices support external frequency and timing references, and both include a GPSDO. Both also support external local oscillators.

The N321 goes further by incorporating dedicated local-oscillator distribution.

Its TX and RX LO architecture can export the local oscillator through multiple outputs, allowing the same oscillator to be distributed to additional N320/N321 radios.

According to Ettus's N320/N321 LO Distribution application note, shared local oscillators are useful when channels need deterministic phase relationships and improved immunity to relative phase drift.

This is particularly relevant for:

• large MIMO arrays;
• phased-array research;
• beamforming;
• multi-channel radar;
• direction finding;
• electronic-warfare research testbeds;
• channel-sounding arrays;
• distributed phase-coherent RF measurement systems.

The N321 provides four LO distribution outputs for the relevant TX and RX paths, enabling a star-style LO distribution architecture rather than requiring every radio to have an independent external LO generator.

For a two-channel standalone system, this feature may provide little value. For a rack containing many synchronized radios, it can become one of the strongest reasons to choose N321.

Why shared LO matters beyond sharing a 10 MHz reference

Sharing a reference clock and sharing an RF local oscillator solve related but different problems.

A common 10 MHz reference can ensure that several synthesizers derive their frequencies from the same reference. It does not necessarily mean that multiple independently generated RF LOs will always have the same deterministic phase relationship after tuning.

Sharing the actual RF LO removes one level of independent synthesizer behaviour and can therefore be valuable where deterministic phase relationships are critical.

This distinction matters far more for phased arrays, coherent radar and high-channel-count measurement systems than for ordinary spectrum monitoring.

Frequency range: N321 reaches lower

The N310 has a specified operating range of 10 MHz to 6 GHz.

The N321 is specified from 3 MHz to 6 GHz.

That gives the N321 additional specified coverage between 3 and 10 MHz.

Current UHD documentation notes that the N3xx hardware may be tunable below its guaranteed operating range in some configurations, but performance is not guaranteed there. For purchasing decisions, use the manufacturer's specified operating range rather than treating unsupported tuning as equivalent to rated RF performance.

100 MHz and 200 MHz bandwidth create serious data rates

Instantaneous bandwidth is only useful if the rest of the system can transport and process the resulting samples.

Consider a simplified SC16 complex stream, where every sample contains:

• 16 bits for I;
• 16 bits for Q;
• 32 bits, or 4 bytes, per complex sample.

An illustrative four-channel N310 stream at 125 MS/s would therefore produce:

4 channels × 125,000,000 samples/s × 4 bytes = 2,000,000,000 bytes/s

That is approximately 16 Gbit/s of raw sample payload before protocol overhead.

An illustrative two-channel N321 stream at its 250 MS/s master-clock rate produces an interesting result:

2 channels × 250,000,000 samples/s × 4 bytes = 2,000,000,000 bytes/s

Again, approximately 16 Gbit/s of raw payload before overhead.

These are calculations illustrating scale rather than guaranteed host-streaming benchmarks. Actual supported streaming rates depend on FPGA configuration, sample format, Ethernet interfaces, host NICs, CPU resources, memory, UHD configuration and application processing.

The important lesson is that choosing “only two channels” does not automatically make the N321 an easy radio to stream at maximum bandwidth. Doubling per-channel sample rate can restore much of the aggregate data load removed by halving the channel count.

Networking: N321 adds QSFP+

Both radios include two SFP+ interfaces that can support network streaming configurations including 10 Gigabit Ethernet depending on the loaded FPGA image.

The N321 additionally includes a QSFP+ connector.

Current UHD documentation lists N321 FPGA configurations capable of using QSFP+ lanes for 10 Gigabit Ethernet or Aurora connections.

This additional interface exists for a practical reason: a 200 MHz-per-channel SDR can generate a large amount of IQ data.

The host PC for a high-rate N321 system should therefore be treated as part of the SDR architecture rather than as an afterthought.

For high-rate network streaming, plan for:

• suitable 10GbE or supported QSFP+ network hardware;
• compatible SFP+/QSFP+ transceivers or direct-attach cables;
• a host with sufficient PCIe bandwidth;
• adequate CPU resources;
• high sustained memory throughput;
• fast NVMe storage if samples will be recorded;
• network tuning appropriate to the chosen UHD transport.

DPDK and high-throughput streaming

For demanding network workloads, UHD supports the Data Plane Development Kit, or DPDK.

DPDK allows compatible network interfaces to move packet processing into user space and use dedicated polling threads, reducing operating-system networking overhead and helping UHD sustain higher sample rates.

Current UHD documentation notes that DPDK is available on Linux and requires appropriate NIC, IOMMU and CPU configuration.

DPDK should therefore be viewed as an advanced high-throughput deployment option, not as something every N310 or N321 user must configure before receiving a first signal.

Both radios can operate without continuously streaming everything to a host

The N310 and N321 share an important architectural advantage over simpler USB SDRs: each contains a Xilinx Zynq-7100 SoC with an ARM processor and programmable FPGA fabric.

The embedded ARM system runs Linux and the USRP Module Peripheral Manager, while the FPGA supports low-latency signal processing and RFNoC.

This allows applications to divide work among:

• the RF frontend;
• the FPGA;
• the embedded ARM processor;
• the network;
• the external host or compute server.

For systems with large raw data rates, moving suitable processing into FPGA logic can reduce the amount of information that must cross the Ethernet link.

Examples can include filtering, channelization, detection, triggering or application-specific preprocessing where a supported RFNoC or custom FPGA implementation is appropriate.

FPGA comparison: both use Zynq-7100

Both the N310 and N321 use the Xilinx Zynq-7100 SoC platform with a dual-core ARM Cortex-A9 processor.

That means this comparison is not like moving from a small FPGA radio to a radically larger FPGA platform.

However, identical SoC names should not be interpreted as identical available FPGA resources for user applications. The stock FPGA image must also implement each radio's RF interfaces, networking, DDC/DUC chains and device-specific functions.

If a project requires extensive custom RFNoC processing, verify the actual available resources in the intended FPGA image rather than making the decision from “Zynq-7100” alone.

N310 has front-panel GPIO; N321 does not

The N310 provides a front-panel GPIO interface that can be useful for experiment control, triggering or interaction with external equipment.

The N321 does not provide the same front-panel GPIO connector because its front-panel space is used for the additional LO-distribution connections.

This is a small specification until an experiment depends on external digital control. Labs planning custom triggering, switching or peripheral control should account for this difference before purchasing.

Which is better for 4×4 MIMO?

The N310 is the natural choice.

It already provides four transmit and four receive channels in a single chassis.

An N321 provides only two TX and two RX channels, so a four-channel system requires multiple devices.

The N321's LO distribution can make a multi-radio coherent system extremely capable, but if the requirement is simply four RF channels at no more than 100 MHz each, the integrated N310 architecture is considerably more direct.

Which is better for beamforming?

The answer depends on array size and bandwidth.

For a compact four-channel beamforming experiment, the N310's four integrated channels are attractive.

For a much larger array where several radios must maintain deterministic LO relationships, the N321's LO distribution architecture becomes much more important.

The choice is therefore:

• small four-channel array: N310 is often simpler;
• wideband two-channel array: N321;
• large scalable phase-coherent array: multiple N321/N320-class radios with a carefully designed synchronization architecture may be more appropriate.

Which is better for radar?

There is no single answer because radar architecture determines the RF requirements.

The N310 can be attractive where the experiment needs several simultaneous antenna channels and fits inside its 100 MHz-per-channel bandwidth.

The N321 becomes compelling where range-resolution experiments, waveform generation or wideband acquisition need significantly more instantaneous spectrum.

Its scalable LO-distribution capability can also be valuable for multi-channel coherent radar systems.

Do not select an SDR for radar solely from advertised bandwidth. Required transmit power, receiver protection, isolation, synchronization, antenna architecture, sample throughput and RF filtering can all be equally important.

Which is better for spectrum monitoring?

The N310 can monitor more simultaneous RF channels, while the N321 can observe a wider instantaneous span on each individual channel.

For example:

• four geographically, spatially or spectrally separate receive paths may favor N310;
• two very wide monitored spans may favor N321;
• a system scanning many narrow channels does not automatically require 200 MHz instantaneous bandwidth;
• a wideband signal-capture system may value N321 even if it uses only one RX channel.

The correct choice depends on whether channel count or spectrum width per channel is the limiting resource.

Which is better for 5G and 6G research?

Both can be useful research platforms, but they serve different experimental requirements.

N310 can make sense for multi-antenna sub-6 GHz work where four RF channels matter more than maximum per-channel bandwidth.

N321 is attractive for wider-bandwidth waveform research and sophisticated synchronized multi-radio testbeds.

Neither should automatically be described as a complete commercial 5G or 6G base station. The useful configuration depends on the PHY implementation, waveform bandwidth, MIMO configuration, timing requirements, FPGA processing, fronthaul architecture and external compute system.

For experiments requiring substantially greater bandwidth and processing than either device provides, newer platforms such as X410 may also be worth evaluating.

See our USRP N310 vs X410 comparison for that decision.

Application decision table

N310 vs N321 for a university or research laboratory

Before ordering either radio, define the experiment numerically.

A useful specification worksheet should include:

• required number of simultaneous TX channels;
• required number of simultaneous RX channels;
• maximum instantaneous signal bandwidth;
• frequency range;
• whether phase coherence must survive retuning;
• number of radios that may eventually be synchronized;
• expected host sample rates;
• sample format;
• network throughput;
• FPGA processing requirements;
• external reference-clock requirements;
• GPIO or trigger requirements;
• expected project lifetime and expansion path.

This usually makes the N310-versus-N321 decision much easier.

If the worksheet says “four channels, 80 MHz each,” N310 is the obvious starting point.

If it says “two channels, 160 MHz each,” N321 is the natural fit.

If it says “16 phase-coherent channels,” the design problem has moved beyond choosing one radio and should be treated as a complete synchronized RF system.

Do you actually need the N321?

The N321 is technically more capable in several areas, but that does not automatically make it the better purchase.

If your application requires:

• four channels;
• less than 100 MHz bandwidth per channel;
• standard 10GbE networking;
• no large external LO-distribution network;

then the N310 may fit the requirement more directly.

Buying bandwidth that the application cannot use can increase system cost and host-network requirements without improving the experiment.

Do you actually need four N310 channels?

The reverse is equally important.

If the application uses only two antennas and needs 150–200 MHz of instantaneous spectrum, the N310's additional two channels do not compensate for its lower maximum per-channel bandwidth.

In that scenario, N321 better matches the actual RF requirement.

What equipment should be budgeted alongside the USRP?

A complete high-end SDR system normally requires more than the radio itself.

Depending on the application, plan for:

• appropriate 10GbE or QSFP+ networking hardware;
• compatible optical transceivers or direct-attach cables;
• high-performance host NICs;
• a workstation or server with sufficient CPU and PCIe bandwidth;
• NVMe storage for sustained recording;
• 50-ohm antennas and RF cables;
• attenuators for conducted testing;
• filters and amplifiers where required;
• external timing or reference distribution hardware;
• RF splitters, couplers or switches;
• appropriate protection between transmit and receive paths.

Never connect a transmitter directly to an SDR receiver without calculating the resulting receive level and adding sufficient attenuation and isolation.

Already considering the N310?

SDRstore has several related guides that can help with the next decision.

• Read the USRP N310 Setup Guide for UHD, SFP+, networking, clocking and first-signal configuration.
• Compare the USRP N310 vs X310 if modular RF daughterboards or PCIe connectivity matter.
• Compare the USRP N310 vs X410 if you need four channels but are considering much greater bandwidth and FPGA performance.

Final recommendation

The USRP N310 and N321 solve different high-end SDR problems.

Choose the N310 when channel density is the priority. Its four TX and four RX channels make it the more direct platform for 4×4 MIMO, four-channel sensing, compact beamforming systems and other experiments where 100 MHz of instantaneous bandwidth per channel is sufficient.

Choose the N321 when bandwidth and scalable synchronization are the priority. Its two channels support up to 200 MHz each, and its dedicated LO-distribution hardware gives it an important advantage when multiple radios must operate as a phase-coherent system.

The decision can usually be reduced to three questions:

1. Do you need more than two simultaneous RF channels? Start with N310.
2. Do you need more than 100 MHz of instantaneous bandwidth on a channel? Start with N321.
3. Do you intend to build a large phase-coherent multi-radio system? Give the N321's LO-distribution architecture serious consideration.

Browse the USRP SDR range at SDRstore.eu to compare the current available configurations.

Buying USRP hardware for a laboratory, university or company?

For research laboratories, universities, telecom teams, system integrators and other organisations purchasing high-value USRP systems, a quotation can help define the complete configuration before ordering.

Use the Add to Quote control on supported product pages or the document/quote icon on product cards and include:

• required USRP model and quantity;
• intended research or engineering application;
• required channel count and bandwidth;
• antennas and RF accessories;
• networking requirements;
• synchronization hardware;
• delivery country;
• required project deadline.

This is particularly useful for N310 and N321 systems because the correct radio is only one component of the full RF, networking and synchronization architecture.

Frequently asked questions

Is the USRP N321 better than the N310?

Not universally. N321 provides twice the maximum instantaneous bandwidth per channel and advanced LO-distribution capability, while N310 provides twice as many RF channels. The better radio depends on whether your application is limited by channel count or per-channel bandwidth.

How many channels does the USRP N310 have?

The N310 provides four transmit and four receive channels. Ettus implements them using two dual-channel AD9371 RF transceivers.

How many channels does the USRP N321 have?

The N321 provides two transmit and two receive channels with up to 200 MHz of instantaneous bandwidth per channel.

Can the USRP N310 do 4×4 MIMO?

Yes. Its four TX and four RX channels make it suitable for 4×4 MIMO and other four-channel experiments when the complete system is configured and synchronized appropriately.

Can the USRP N321 do 4×4 MIMO?

One N321 provides only two TX and two RX channels. A 4×4 system therefore requires multiple radios. Its LO-distribution and synchronization architecture can be particularly valuable when building larger coherent systems.

Does the N321 have twice the total performance because it has twice the bandwidth?

No. Its maximum per-channel bandwidth is twice that of the N310, but it has half as many RF channels. Overall performance also depends on RF characteristics, synchronization, FPGA workload, networking and host processing.

Does the N310's 16-bit ADC make it better than the N321's 14-bit ADC?

Not by itself. ADC resolution is only one part of receiver design and should not be treated as measured dynamic range or RF performance. Compare the complete RF specifications and the requirements of the intended application.

Do both support GNU Radio and UHD?

Yes. Both are UHD-supported networked USRPs and can be used through GNU Radio's UHD integration. Ettus lists UHD 3.11.0 or later for N310 and UHD 3.14.0 or later for N320/N321. For a new deployment, use a current compatible UHD release unless your research software requires a specific older version.

Technical references

• Ettus Research — USRP N310
• Ettus Research — USRP N321
• Ettus Research — N300/N310 RF Specifications
• Ettus Research — N320/N321 RF Specifications
• Ettus Research — Current UHD N3xx Device Manual
• Ettus Research — N300/N310/N320/N321 Getting Started Guide
• Ettus Research — N320/N321 LO Distribution Application Note
• Ettus Research — UHD DPDK Documentation