Choosing a radio: matching the wireless technology to the product

Many products pick their radio before anyone writes down the requirements. The team knows Bluetooth, or the last product used Wi-Fi, so that becomes the plan. Sometimes it works out. Often the product ends up with a battery that drains too fast, range that falls short in the real building, an antenna that will not fit, or a certification plan that doesn’t match the markets.

There are more good options than ever, from 433 MHz links to 60 GHz radar, and each makes different trade-offs. This article covers how to narrow them down: what to ask first, the physics and rules behind the trade-offs, and where the newer options fit. It is not legal advice; radio rules depend on the product and market, and they change.

Start with what the link has to do

Before comparing radios, answer these questions:

• What is at the other end? A phone, an existing Wi-Fi network, a gateway you supply, a cellular network, or another device of yours. This one often narrows the field more than any other.
• How far, and through what? Open air, walls, floors, metal, soil, water, and people all count. Distance is rarely the whole story.
• How much data, and how often? A temperature reading every 15 minutes and a live video stream need radios several orders of magnitude apart.
• How fast must it respond? Latency matters for control, much less for logging.
• What powers it? Mains, a rechargeable battery, a coin cell meant to last years, or harvested energy.
• How much room is there? Board area, enclosure size and material, and where an antenna could go.
• Where will it sell? Frequency bands, power limits, and certification differ by region.
• Does it need to know where it is, or where something else is?
• What can it cost? Per unit, and up front for design and certification.
• How long must it be supported? Networks, standards, and chips all have lifetimes.

Write the answers down with numbers. They become the requirements every option is measured against.

The physics behind the trade-offs

Range, data rate, and power pull against each other. A receiver can hear weaker signals when it listens to a narrower bandwidth, so slower links reach farther on the same transmit power. Roughly, each halving of bandwidth buys about 3 dB of sensitivity. That is why LoRa, at a few kilobits per second, can cover kilometers on tens of milliwatts, while Wi-Fi needs far more power to carry megabits over tens of meters.

Frequency matters too. With antennas of the same gain, free-space path loss grows with frequency: a 915 MHz link loses about 8.5 dB less than one at 2.4 GHz, which works out to roughly 2.7 times the range. Lower frequencies also tend to pass through walls, foliage, and people better. Higher frequencies offer wider channels, and so more data, and smaller antennas. In free space, each doubling of distance costs 6 dB, and indoors it is usually worse. The radio range estimator works through a link budget with your own numbers.

The antenna follows the wavelength. A quarter wave is about 17 cm at 433 MHz, 8 cm at 915 MHz, 3 cm at 2.4 GHz, a little over 1 cm at 6.5 GHz, and a little over 1 mm at 60 GHz. You can shrink a low-frequency antenna, with chip antennas, meanders, or loading, but a physically small antenna at a long wavelength is inefficient. That loss eats directly into the range that drew you to the lower band.

Technology	Band	Reach	Data rate	Power	Antenna	Good fit
NFC	13.56 MHz, worldwide	A few centimeters	Up to 424 kbps	Very low; tags can be passive	Coil, sized to the read distance	Tap to pair, set up, or identify; readable by most phones
Sub-GHz (FSK, OOK)	315, 433, 868, or 915 MHz, by region	Hundreds of meters to kilometers	About 1 to 500 kbps	Low	Largest: a quarter wave is 8 cm at 915 MHz, 17 cm at 433 MHz	Simple long-range links where you control both ends
LoRa	868 or 915 MHz, by region	Kilometers; farther in open country	About 0.3 to a few tens of kbps	Very low average	As for sub-GHz	Small, infrequent messages over wide areas
Wi-Fi HaLow	Below 1 GHz, by region	About a kilometer; more in open country	150 kbps to tens of Mbps	Low to moderate	As for sub-GHz	IP networking across large sites
Bluetooth LE	2.4 GHz, worldwide	Tens of meters; more with coded PHY	125 kbps to 2 Mbps on air	Very low; coin cells are common	Small: a quarter wave is 3 cm	Phone connection, wearables, setup
Thread, Zigbee	Mostly 2.4 GHz, worldwide	Tens of meters per hop; mesh extends it	250 kbps	Very low for end devices	As for Bluetooth LE	Home and building networks; Thread carries Matter
Wi-Fi	2.4, 5, and 6 GHz; 6 GHz varies by country	Tens of meters indoors	Mbps to over a Gbps	High while active	Small; often dual-band	High data rates over existing networks
LTE-M, NB-IoT	Licensed cellular bands, by carrier	Wherever the carrier has coverage	Tens of kbps to about 1 Mbps	Low average with power-saving modes; high peaks	Must cover several bands	Devices with no local network; needs a subscription
UWB	About 6.5 and 8 GHz	Tens of meters	Several Mbps	Low to moderate	Small, but must work across a wide bandwidth	Precise distance measurement; supported by some phones
mmWave (60 GHz)	57 to 71 GHz, by region	Meters; walls and people block it	Up to several Gbps	Varies widely	Millimeters; often in the chip package	Radar sensing; short, very fast links

The options, briefly

Sub-GHz proprietary radios (FSK or OOK at 315, 433, 868, or 915 MHz) are simple, inexpensive, and reach far for their power. You design the protocol and both ends of the link, which is a strength when you need control and a burden when you need interoperability.

LoRa trades data rate for range and power, using spread-spectrum modulation that can be received below the noise floor. LoRaWAN adds a network layer, run on public networks or your own gateways. It suits small, infrequent messages from devices spread across a wide area.

Wi-Fi HaLow (802.11ah) is Wi-Fi in the sub-GHz bands: IP networking with much longer reach and lower power than conventional Wi-Fi. It is newer, with fewer chip vendors and access points, and its bands and channel widths vary sharply between regions.

Bluetooth Low Energy is the usual choice when a phone is at the other end. It runs for years on small batteries, and the coded PHY trades data rate for range. Newer versions add direction finding (angle of arrival and departure) and Channel Sounding for distance measurement.

Thread and Zigbee share the 802.15.4 radio and build low-power mesh networks. Thread carries IP traffic and is one of the transports for Matter, the smart-home standard, alongside Wi-Fi and Ethernet, with Bluetooth LE used for setup.

Wi-Fi brings high data rates and direct access to networks that already exist. The costs are power, a provisioning step to get the device onto the user’s network, and an operating environment you do not control. Wi-Fi 6 adds Target Wake Time, which helps battery devices; newer generations mostly add capacity. Some 5 GHz channels require radar detection and avoidance. The 6 GHz band is available in some countries, partly in others, and not at all in some.

Cellular IoT (LTE-M and NB-IoT) reaches devices with no local network. It needs a subscription, carrier and industry certification, and almost always a pre-certified module. Power-saving modes (PSM and eDRX) are what make multi-year battery life possible, while peak currents of hundreds of milliamps shape the battery and power design. The device must support the bands and roaming terms of the carriers in each target market. When a product needs more data than these carry, LTE Cat 1 bis and, increasingly, 5G RedCap sit between them and full-rate LTE. Not every carrier supports both LTE-M and NB-IoT, and NB-IoT coverage varies by country and carrier. Satellite connectivity for IoT devices, including cellular standards extended to satellites, is emerging for places no tower reaches.

Ultra-wideband (UWB) spreads very short pulses across about 500 MHz of bandwidth at 6.5 or 8 GHz. That bandwidth lets it measure the time of flight between devices precisely, so its main strength is distance and position rather than data. Some phones support it, which opens up phone-based uses. UWB is a particular strength of mine: I have been developing UWB products for more than a decade.

mmWave at 60 GHz is used in two ways: radar sensing, which can detect presence, motion, gestures, and even breathing without a device on the person, and short, very fast data links. Antennas are small enough to sit in the chip package, but walls and bodies block the signal.

NFC works only at a few centimeters, which is the point. It is used for tap-to-pair, setup, authentication, and reading tags that need no battery. A different technology serves longer reads: UHF RFID, around 900 MHz, reads passive tags at several meters for inventory and logistics.

The rules shape the choice

The same radio can face very different rules depending on band and market. A few that often decide things:

• Sub-GHz bands differ by region. Europe uses 868 MHz, the US 902 to 928 MHz, and Japan, Korea, China, India, and Australia each have their own plans, so a sub-GHz product usually needs regional variants with different frequency plans, antenna tuning, and sometimes hardware. In the US, 433 MHz is not an unlicensed data band as it is in Europe; it is covered by rules for remote controls and brief, periodic transmissions, which rule out continuous data.
• Airtime and power limits. Many European 868 MHz sub-bands limit each device to 0.1 to 1 percent of the time on air (one narrow sub-band allows 10 percent), unless it uses listen-before-talk with frequency agility. That sets how often a device can report. US rules for 902 to 928 MHz set no overall airtime limit, but trade power against modulation: a simple narrowband link is held to a very low power level, while higher power needs frequency hopping, with a dwell-time limit per channel, or a channel at least 500 kHz wide. That choice sets the range.
• 2.4 GHz is available almost everywhere, which is a large part of why Bluetooth and Wi-Fi dominate. It is also crowded, and like every unlicensed band, it offers no protection from interference: the product has to cope with whatever else is on the air.
• UWB transmits at very low power spectral density, and its rules are restrictive. In the US, UWB communication devices fall under rules for indoor systems or handheld devices, which restrict fixed outdoor installations. Other regions set their own bands and mitigation requirements.
• Program certifications sit on top of radio law: Bluetooth SIG listing, carrier approval plus PTCRB (North America) or GCF (elsewhere) for cellular, and Matter or Thread certification if you use those logos and ecosystems.

Compliance by market covers the approvals in each region, and Module or chip-down covers how modules change the certification work.

The antenna is half the radio

An antenna that performs in a vendor’s evaluation board can lose much of its efficiency in your enclosure, next to a battery, a display, a metal frame, or the user’s hand. It needs a ground plane of the right size, clearance from metal, and a place in the product where it can radiate. That makes it a mechanical and industrial design question as much as an electrical one, and it is easiest to settle early, before the enclosure is fixed.

Plan to tune the antenna match on assembled boards in the real enclosure, and to check radiated performance, not just the match. For lower bands, confirm early that an antenna big enough to be efficient fits at all.

Power and the radio

For battery products, the radio is often the largest consumer, and how it is used matters as much as which one it is. Connection intervals, how long the device stays on the air, retries in a weak signal, and how long a cellular modem takes to attach can each change battery life many times over. Peak current matters too: the battery and regulator must deliver the radio’s transmit bursts without the voltage dropping.

Model the radio’s duty cycle in the power budget before choosing it. Battery-powered design covers building that budget and measuring the result.

Ecosystem and lifetime

A radio is also a bet on an ecosystem. Consider:

• Who supports it at the other end. Phones support Bluetooth LE, Wi-Fi, and NFC broadly; UWB only on some models. A proprietary radio means you supply every receiver.
• Network lifetime. Products built on 2G and 3G stopped working when carriers in the US and many other countries shut those networks down. Check the operator’s commitments for any network you depend on, and plan for a product that outlives it.
• Chip supply. Prefer parts with clear lifecycle status and more than one source, especially for newer technologies with few vendors.
• Firmware updates and security. Over-the-air updates depend on the link having enough capacity and reliability to carry them. Cybersecurity for connected products covers what the rules now expect.

When the product needs location

Location is a requirement that changes the choice. The options differ widely in accuracy and in what they need around them:

• GNSS (GPS and its peers) gives a few meters outdoors with no infrastructure, and centimeters with correction services. It does not work well indoors.
• Bluetooth LE signal strength gives a rough idea of proximity, a few meters at best. Direction finding and Channel Sounding do better, with antenna arrays or newer chips.
• Wi-Fi round-trip timing can reach a meter or two where access points support it.
• UWB measures time of flight, typically to within tens of centimeters, and in good conditions about 10 cm.
• mmWave radar senses people and objects without anything attached to them.

Accuracy in a datasheet assumes good conditions. Walls, metal, and people blocking the direct path degrade every method, so test in an environment like the real one.

More than one radio

Many products combine radios: Bluetooth LE for setup alongside Wi-Fi for data, cellular alongside GNSS, or a short-range radio alongside a long-range one. Each pairing raises coexistence questions.

• Shared bands. Wi-Fi, Bluetooth LE, and 802.15.4 all use 2.4 GHz. Combination chips arbitrate between them internally; separate chips need coexistence signals wired between them and firmware that uses them.
• Neighboring bands. UWB channel 5 (about 6.5 GHz) overlaps the 6 GHz Wi-Fi band, fully in the US and partly in Europe, so the two can interfere in the same product or the same room. Channel 9 (about 8 GHz) does not overlap.
• Harmonics and desense. One transmitter’s harmonics can land in another radio’s receive band. A classic example is LTE Band 13, whose second harmonic falls next to the GPS L1 frequency.
• Antenna isolation. Antennas need spacing and orientation that keep one radio from drowning out another.
• Certification. Radios that can transmit at the same time are assessed together for RF exposure, and that can take a design outside a module’s grant.

The short version

Write down what the link must do, with numbers, before choosing a radio. Let what is at the other end, the power source, the antenna space, and the target markets narrow the field. Check the rules for each band in each market, plan the antenna with the enclosure, and test range, power, and location accuracy where the product will be used. Choosing the technology is often less about knowing every radio than about asking the right questions first.

If you are choosing a radio for a product and want a second opinion, get in touch.