Signals & Navigation

Beacon

Q: What types of RF beacons exist?

RF beacons span nearly the entire radio spectrum. Navigation beacons include NDB (Non-Directional Beacon, 190 to 535 kHz, AM, range 200+ nm) and VOR (VHF Omnidirectional Range, 108 to 118 MHz, providing bearing information). Emergency beacons include ELT (Emergency Locator Transmitter, 406 MHz, detected by COSPAS-SARSAT satellites) and EPIRB for maritime. Satellite beacons are unmodulated CW tones transmitted by communications satellites for ground station tracking and frequency reference. Wireless beacons include WiFi beacons (802.11 management frames transmitted every 100 ms by access points at 2.4 or 5 GHz) and BLE beacons (Bluetooth Low Energy advertising packets at 2.4 GHz, used for indoor positioning with 1 to 10 mW transmit power). Cellular beacons include the 5G NR SSB (Synchronization Signal Block) which carries PSS, SSS, and PBCH for cell search and beam management.

Q: How do 5G NR SSB beacons work?

The SSB (Synchronization Signal Block) is the beacon signal of 5G NR. Each SSB occupies 240 subcarriers (20 resource blocks) by 4 OFDM symbols and contains three components: PSS (Primary Synchronization Signal) for timing and sector ID (3 possibilities), SSS (Secondary Synchronization Signal) for cell ID (336 possibilities, giving 1008 total cell IDs), and PBCH (Physical Broadcast Channel) carrying the Master Information Block. At mmWave frequencies, up to 64 SSBs are transmitted in a burst period of 5 ms, each beamformed in a different direction to provide angular coverage. The UE measures RSRP on each SSB index and reports the best beams for initial access and handover. SSB periodicity is configurable: 5, 10, 20, 40, 80, or 160 ms.

Q: How is beacon signal strength used for positioning?

Beacon-based positioning uses received signal strength (RSS), time of arrival (ToA), or angle of arrival (AoA) measurements from multiple beacons to estimate a receiver's location. BLE beacons use RSS with a path loss model: distance = 10^((RSSI_ref minus RSSI) / (10 times n)), where n is the path loss exponent (2.0 in free space, 2.5 to 4.0 indoors) and RSSI_ref is the reference power at 1 meter (typically minus 59 dBm). With 3 or more beacons, trilateration estimates position to 1 to 3 meter accuracy indoors. WiFi RTT (Round-Trip Time) achieves sub-meter accuracy using time-of-flight measurements. 5G NR positioning uses DL-TDOA (Downlink Time Difference of Arrival) with SSB or PRS (Positioning Reference Signal) beacons, targeting sub-meter accuracy for industrial IoT applications.

/bee-kun/

A dedicated RF transmission enabling receivers to identify, locate, track, or synchronize with a transmitter. Beacons span every RF domain: NDB navigation (190-535 kHz), VOR bearing (108-118 MHz), emergency locators (406 MHz, COSPAS-SARSAT), satellite tracking (C/Ku/Ka-band CW), WiFi management frames (100 ms interval), BLE advertising (2.4 GHz, 1-10 mW), and 5G NR SSB (up to 64 beams for cell search and beam management). Power ranges from milliwatts (BLE) to kilowatts (NDB).

Range: kHz to mmWave

Power: mW to kW

5G SSB: Up to 64 beams

Understanding RF Beacons

The concept of a beacon is as old as radio itself: a known signal transmitted from a known location that receivers can use for reference. In aviation, Non-Directional Beacons (NDBs) have guided aircraft since the 1930s using simple AM transmissions on LF/MF frequencies that can propagate hundreds of nautical miles. Modern beacons are far more sophisticated but serve the same fundamental purpose: providing a reference for identification, timing, frequency, direction, or position.

In wireless networks, beacons perform critical management functions. A WiFi access point transmits a beacon frame every 100 ms (configurable) announcing its SSID, supported data rates, security capabilities, and timing information. This periodic broadcast enables passive scanning: a client can discover all nearby networks by listening for beacons on each channel. In 5G NR, the SSB (Synchronization Signal Block) serves as the cell's beacon, carrying synchronization signals and broadcast information swept across multiple beam directions to support beam-based access at mmWave frequencies.

Beacon Type Comparison

Beacon Type	Frequency	Power	Range	Interval	Purpose
NDB	190-535 kHz	25 W-2 kW	200+ nm	Continuous	Aviation navigation
ELT/EPIRB	406 MHz	5 W	Global (sat)	50 s burst	Emergency rescue
WiFi	2.4/5/6 GHz	100 mW	50-100 m	100 ms	Network discovery
BLE	2.4 GHz	1-10 mW	10-30 m	100-1000 ms	Indoor positioning
5G SSB	Sub-6/mmWave	Per beam	Cell radius	5-160 ms	Cell search, beam mgmt

Common Questions

Frequently Asked Questions

What types of RF beacons exist?

Navigation (NDB 190-535 kHz, VOR 108-118 MHz), emergency (ELT/EPIRB 406 MHz, COSPAS-SARSAT detection), satellite (CW tracking tones), wireless network (WiFi management frames every 100 ms, BLE advertising at 2.4 GHz), and cellular (5G NR SSB with PSS, SSS, and PBCH for cell search across up to 64 beamformed directions at mmWave).

How do 5G NR SSB beacons work?

Each SSB occupies 240 subcarriers × 4 OFDM symbols, carrying PSS (3 sector IDs), SSS (336 cell IDs, 1008 total), and PBCH (Master Information Block). At mmWave, up to 64 SSBs sweep all directions in a 5 ms burst. UEs measure RSRP per SSB index and report best beams for initial access. Periodicity: 5 to 160 ms configurable.

How is beacon signal strength used for positioning?

BLE uses RSS with path loss model: distance = 10^((RSSI_ref − RSSI)/(10n)), n = 2.0-4.0 indoor. With 3+ beacons, trilateration achieves 1-3 m accuracy. WiFi RTT measures round-trip time for sub-meter accuracy. 5G NR uses DL-TDOA with SSB/PRS beacons targeting sub-meter accuracy for industrial IoT and positioning-as-a-service.

Related Terms

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