1Three radios, one enclosure, and no way to see them together

Coexistence faults are reported at the system level. A representative report says that the Bluetooth link drops when the modem uplink is busy, or that Wi-Fi throughput falls when the audio stream starts. A telematics unit, a medical gateway and an industrial access point share an anatomy: separate radios, one antenna structure, one ground plane, one power rail. The measurements available are per-radio, taken at different times on different instruments. Coexistence is a question about simultaneity, and it is investigated with non-simultaneous data.

Two existing methods apply, and each has a limit this paper quantifies. A faster sweep shortens the revisit interval; section 3 derives that sweeping faster shortens the dwell in exactly the proportion it shortens the revisit interval, so the fraction of a packet held intact does not improve. A longer averaging interval raises confidence on a stationary signal; section 3 also shows that the same averaging removes the one symbol that fails a slot from the reported figure.

2What the signals require

3GPP defines a scalable orthogonal frequency-division multiplexing (OFDM) numerology indexed by one integer. Fix it and every timing quantity in the frame follows:

Table 1 evaluates it. The normal cyclic prefix is 144 × 64 × 2^−μ basic units of 0.5086263 ns, which at 30 kHz is 2.34375 µs; the first symbol of each half-subframe carries 16 × 64 units more, 0.52 µs, so that fourteen symbols fill the slot exactly.

Occupied bandwidth is fixed by the resource-block allocation:

A 100 MHz FR1 carrier at 30 kHz spacing occupies 273 × 12 × 30 kHz = 98.28 MHz, leaving 0.86 MHz of guard per side. And 100 MHz is the largest single-carrier bandwidth 3GPP defines for FR1; above it, NR aggregates carriers rather than widening one. So a gap-free 100 MHz window is not only enough bandwidth for a 5G signal: it is exactly one FR1 carrier, edge to edge, under one amplitude reference. The NR synchronization signal block is placed on the synchronization raster of TS 38.101-1, which need not coincide with the carrier center, so an analyzer narrower than the carrier and tuned to its center can miss the block.

The 2.4 GHz band lands the same way. The industrial, scientific and medical allocation is 83.5 MHz wide, so one record centered at 2441.75 MHz holds all 79 Bluetooth channels, all 40 Low Energy channels and Wi-Fi 1, 6 and 11 at once.

Reading a record before demodulating it

A cyclic prefix is a copy of the end of a symbol prepended to it, so two samples separated by the useful symbol length are identical whenever the earlier lies inside a prefix. That gives the metric of van de Beek, Sandell and Börjesson:

Run it as a hypothesis test over the four lags that occur in practice, those for 15, 30, 60 and 120 kHz spacing. Only the true lag yields a regular train of peaks, as Figure 1 shows for a synthetic record. Symbol timing, the half-subframe grid and the frequency offset come with it, at a coherent gain of 10 log₁₀(288) = 24.6 dB, for one pass over the record.

3Why swept and segmented architectures fall short

A 100 MHz carrier stitched from five 20 MHz segments is five acquisitions, each with its own amplitude calibration, its own local-oscillator phase and its own trigger instant, so the composite carries five references where the signal has one. An error vector magnitude computed across a seam measures the instrument, not the transmitter. That is the second reason R1 excludes stitching, and it is independent of bandwidth.

The limit is architectural. Swept and stepped-tuned receivers, and the stitched measurement built on them, characterize stationary signals over wide spans at high dynamic range. Neither was designed for signals whose defining property is that they change.

Mechanism one, probability of intercept

Filter settling is not the binding constraint on Bluetooth; 83.5 MHz at 1 MHz resolution settles in roughly 209 µs. Dwell is. To capture a packet intact the receiver must stay on its channel for the packet's whole duration:

A sweep long enough to hold one DH1 packet needs 366 µs × 83.5 = 30.56 ms, and in that interval Bluetooth executes 1600 × 0.03056 = 48.9 hops. One was caught intact and forty-eight were not, so the best-case intercept fraction is 1/48.9 = 2.05 percent. Sweeping faster does not recover it: at a 1 ms sweep the dwell is 12 µs, 3.3 percent of a packet, a fragment with no access code and no address. Neither branch recovers the packet.

The bound under the most favorable assumptions follows. Remove the retune time, let the receiver settle instantly, and widen its instantaneous bandwidth to B. The dwell constraint becomes T_sweep = T_pkt · S/B, and the fraction of packets caught intact reduces to a single ratio:

Figure 2 draws both. Engineering moves a stepped receiver up the orange line; nothing moves it past the blue one, because coverage is set by B alone.

Figure 3 draws that arithmetic, and the same physics governs any burst: an SS/PBCH block lasts 142.7 µs and repeats every 20 ms, so it is present 0.71 percent of the time.

Mechanism two, periodic blindness

Retune dead time is not random; it repeats at the revisit period. A duplex pattern switching every 2.5 ms, watched by an analyzer revisiting five slices on a 25 ms period, is sampled at the same phase every time. If the dead time overlaps the switch, the transient is not observed on any revisit, and a longer run repeats the same phase.

Mechanism three, the composite that hides the defect

Error vector magnitude combines in root-sum-square, because device and instrument error vectors are uncorrelated:

A transmitter at the 3GPP 256QAM limit of 3.5 percent reads sqrt(12.25 + 4.00) = 4.031 percent on an instrument with a 2.0 percent residual: a wrong verdict, not a less precise one.

Averaging hides a rare symbol. Take a 70-symbol window in which 69 symbols read 2.5 percent and one, at a duplex switch, reads 15 percent. The composite is sqrt[(69 × 6.25 + 225)/70] = sqrt(9.375) = 3.06 percent, passing with margin. That symbol exceeds even the 16QAM limit of 12.5 percent, so it is undecodable and it fails the whole slot: one slot in five, a 20 percent block error rate, a throughput collapse no EVM report explains. It shows in one view only, EVM against symbol index over a contiguous record, which a segmented acquisition cannot produce.

Figure 4 plots the crossings. A receiver residual near the limit does not degrade the measurement gradually; it moves the pass boundary.

4Derived requirements

Table 2 turns those mechanisms into six numbers, each with the reason a looser value fails rather than merely degrades. Any receiver can be scored against it.

R3 turns gap-free into a throughput figure:

At 125 MSa/s with 16-bit components that is 500 MB/s, or 4.0 Gbit/s of payload. Table 3 and Figure 5 show how an instrument can carry a 100 MHz converter and still not be gap-free to storage.

5Meeting the requirements

A receiver satisfying R1 through R6 is a narrow class of instrument. The ICX-FieldHawk family meets R1 and R2 as published, and section 7 states where it does not and where it cannot be scored. Published, at 25 °C after ten minutes of warm-up with spur reject standard on: 100 MHz analysis bandwidth on the ICX-095, ICX-200 and ICX-400 handhelds, on the ICX-095R, ICX-200R and ICX-400R tablets and on the ICX-200U and ICX-400U modules, with 50 MHz standard and 100 MHz with option 50 on the 4.5, 6 and 9 GHz handhelds; IQ sample rate to 125 MSPS with decimation 1 to 4096; burst recording to 100 MHz into 128 Mbyte; continuous recording to 25 MHz.

R1 and R2 go together. A 100 MHz window holds an FR1 carrier plus both guard bands, and the whole ISM band. 125 MSPS clears the 122.88 MSa/s native rate, and 122.88/125 is exactly 3072/3125, so one polyphase stage reaches the standard's grid without interpolation. The numerator and denominator are the specification to ask any supplier for: resampler error appears as EVM attributed to the device.

Figure 6 draws the split. It matters most to anyone embedding a receiver in a product they sell: a dropped sample becomes a decode failure in the product, in code its maker cannot debug. The supplied application, SpectraCore, is at the same boundary: it is where the corrected samples surface, and it is the layer a product design is free to replace without giving up the correction underneath it.

The hopping map follows. Treating the hops as sampling channels uniformly, the expected number of hops to touch all 79 at least once is 79 × (ln 79 + 0.5772 + 1/158) = 391, or 244 ms at 1600 hops per second. The published 128 Mbyte capture memory, filled at 100 MHz with 16-bit components, holds 128 MB / 500 MB/s = 0.26 s, as Figure 7 draws.

Figure 8 is the whole 2.4 GHz band in one acquisition. The real-time engine behind it publishes the relation that makes its intercept guarantee computable: one hundred percent probability of intercept is 2 × N × D × 8 ns, 32.768 µs at 2048 points and 0.512 µs at 32. The single-slot DH1 packet worked in section 3 is eleven times the first figure and a 1 µs symbol twice the second, so neither is near the boundary. Decimation is then the storage lever: at 64, one channel records at 7.8 MB/s, turning a minute from 30 GB into 469 MB.

Decoders that already exist

None of R1 through R6 asks for a software ecosystem. Once the IQ is gap-free, corrected and on one time base, the decoders above it already exist. With the -SDR option, orderable on every current ICX model by appending -SDR to the part number, the ICX-FieldHawk presents itself through SoapySDR, the vendor-neutral hardware abstraction layer, so it appears to GNU Radio or any other SoapySDR application as an ordinary software-defined radio device. The instrument's calibration files are installed with the driver, so the samples arriving in a flowgraph are corrected before the first block sees them, and every standard measurement function of the base instrument stays installed (the ICX -SDR option datasheet).

For multi-radio work that matters more than it does anywhere else, because the protocol decoders for these three radios already exist. An 802.11a receiver, complete with packet detection, synchronization, transform, channel equalization and MAC decoding, is an existing GNU Radio flowgraph. Connecting it to a calibrated front end is a matter of changing the source block, not of writing a demodulator.

Figure 9 is the result of that substitution on a host. The -SDR option datasheet documents six chains on the same source block: AM and FM demodulation, QPSK, 16-QAM at 500 kSymbol/s received at −80 dBm, 802.11a WLAN decode at 2.412 GHz with packets exported to Wireshark or PCAP, and ADS-B aircraft tracking. What makes the path useful here is not the demodulation, which any receiver can be made to do, but that the amplitude underneath every decoded frame is still traceable. A coexistence question is settled by a PCAP file together with a calibrated power number; a PCAP file alone records the decode without the level behind it.

6Measurement practice

None of this depends on which analyzer is on the bench.

1. Prove gap-free before trusting the record. Confirm the file holds the sample rate times the duration, to the sample. Then feed a tone off center, unwrap the phase and fit a line: a dropped block of 4096 samples at 125 MSa/s is a 33 µs discontinuity. Repeat to storage for ten minutes.
2. Set the reference level from the instantaneous-power distribution, not a peak marker. Take the 0.01 percent point and add 3 dB. A peak marker never saw the OFDM peak, and clipping generates intermodulation products indistinguishable from the interference under investigation.
3. Run the cyclic-prefix autocorrelation before demodulating anything. One pass gives subcarrier spacing, symbol timing, the half-subframe grid and the frequency offset. If it disagrees with the configuration you were given, resolve that first.
4. Capture the whole 2.4 GHz band once and filter in software, and record the RF path and reference lock state with the samples. Retuning between aggressor and victim removes the one property coexistence analysis is about, and a dBm is meaningless without the path behind it.
5. Plot EVM against symbol index, not only the composite RMS. On a contiguous record it costs nothing, and it is the view that locates a single defective symbol.

Documented use

The boundary of section 5 is the one the -SDR option is built around. Its datasheet records that system integrators embed ICX receivers behind their own EMF measurement, 5G analysis and network coverage software, and that teams integrating monitoring and signal intelligence systems use the instrument as a calibrated front end and write their own application on top, in their own language and user interface. In each case the receiver supplies the bandwidth and the corrected, continuous IQ, and the protocol layer belongs to the product; no end user is named here.

7Limitations

• A 100 MHz window is not the whole problem. 802.11ax at 160 MHz, 802.11be at 320 MHz and carrier-aggregated FR1 do not fit, so cross-component behavior goes unmeasured.
• Burst and continuous recording are different specifications. The ICX-FieldHawk publishes burst recording to 100 MHz into 128 Mbyte, about 0.26 s at 16-bit I and Q, and continuous recording to a host at 25 MHz. R3 asks for 500 MB/s sustained for 60 s at full bandwidth, which is not what this instrument publishes, and the module's own interfaces are USB 2.0 bandwidth limited on the USB model and Gigabit Ethernet on the LAN model. If a measurement needs a minute of gap-free 100 MHz, this is not the instrument.
• R5 is not answered here. No residual error vector magnitude is published for this receiver at any modulation order, so the requirement Figure 4 makes the case for cannot be scored from the datasheet. Measure it on the loop described under equation (6), and treat a residual quoted without its frequency and bandwidth as unusable.
• The coexistence measurement is dynamic-range limited. R4 asks for more than a real converter delivers at these rates, and no dynamic-range figure is published. Use the proxies: display range to +20 dBm typical on the 40 GHz models, third-order input intercept +40.3 dBm at 1 GHz with the reference level at +20 dBm and +27.4 dBm with it at 0 dBm, IF flatness ±2.0 dB. Beyond that, take two captures at different attenuation.
• A conformance frequency verdict needs an external standard. The published frequency accuracy is under 1 ppm with the standard TCXO and with the option 01 OCXO alike, which is 3.5 kHz at 3.5 GHz; the OCXO's 0.15 ppm, 525 Hz at 3.5 GHz, is its temperature stability, with aging under 1 ppm a year. Against a 175 Hz base-station limit either figure serves hop tracking and neither serves adjudication. Lock the analyzer to an external 10 MHz reference through its reference input, or order the option 06 GNSS-disciplined reference clock on the ICX-FieldHawk-R or the modules, and log the lock state with every record.
• If only one radio is active at a time, a swept analyzer serves. It characterizes a stationary signal with higher dynamic range and at lower cost, and the continuity argument of section 3 does not apply.

8Summary, definitions and further reading

Table 4 collects the relations and published values with their conditions.

Selection

Where a display matters, the ICX-095, ICX-200 and ICX-400 handhelds carry 100 MHz to 9.5, 20 and 40 GHz, and the ICX-FieldHawk-R tablets carry the same three ranges in an IP68 enclosure. Embedded, the ICX-200U and ICX-400U modules give 100 MHz over USB or LAN, and the LAN interface is the one to specify where continuous streaming matters. The 4.5, 6 and 9 GHz handhelds carry 50 MHz as standard, which does not hold the 83.5 MHz ISM allocation whole; option 50 raises them to 100 MHz. Option 71 adds digital demodulation, option 01 the OCXO, and -SDR the SoapySDR and GNU Radio path.

Adaptive frequency hopping

The Bluetooth mechanism that drops congested channels from the hop sequence. A minimum number must stay in use, so a busy band forces some hops under interference.

Error vector magnitude

The root-mean-square distance between measured and ideal constellation points, normalized to the RMS reference.

Gap-free

Every sample reaches the record, with a verified count and no dropped block, for the stated duration. A claim about the path to storage, not the converter.

Probability of intercept

The minimum duration a signal must be present for its amplitude to be measured correctly.

Further reading

• 3GPP TS 38.104, NR; Base Station radio transmission and reception: 5.3.2 for channel bandwidth and resource blocks, 6.5.1 for frequency error, 6.5.2 for EVM limits; TS 38.211 4.1 to 4.4 for frame structure and prefix lengths; TS 38.101-1 5.4.3 for the synchronization raster. IEEE Std 802.11-2020, 802.11ax-2021 and 802.15.2-2003, and the Bluetooth Core Specification, cover the rest.
• J.-J. van de Beek, M. Sandell and P. O. Börjesson, "ML estimation of time and frequency offset in OFDM systems," IEEE Trans. Signal Processing, vol. 45, no. 7, 1997, and A. Peled and A. Ruiz, Proc. IEEE ICASSP, 1980, which introduced the cyclic prefix.
• The SoapySDR project, for the abstraction layer in section 5; the ICX -SDR option datasheet and the SDR Integration Handbook for the documented chains. BNC-AN-101 sets out the calibrated open-instrument argument in full; BNC-AN-102 and BNC-AN-105 cover monitoring and record and playback.

If you are specifying a front end for a multi-radio product, or settling a coexistence question with a measurement, our application engineers would be glad to work through these requirements against your own signals.