Channel Selection Algorithm #1 (legacy) uses a simple hop increment modulo the number of used channels. CSA #2 (Bluetooth 5.0) uses a more sophisticated pseudo-random mapping that provides better channel utilization uniformity and is mandatory for BLE 5.0+ features. CSA #2 distributes hops more evenly, reducing the chance of consecutive hits on the same channel.

BLE vs Bluetooth Classic hopping?

Bluetooth Classic hops across 79 channels (1 MHz each) at 1600 hops/second. BLE hops across 37 channels (2 MHz each) at the connection event rate (1-133 hops/second depending on CI). Classic's faster hopping provides more frequency diversity but BLE's wider channels and AFH provide comparable interference robustness with much lower power consumption.

Wireless Protocols

BLE Frequency Hopping

Q: How does hopping prevent interference?

A Wi-Fi transmitter occupies a fixed 20-40 MHz band, covering approximately 10-20 BLE channels. BLE hops to a new 2 MHz channel every connection event (every 7.5 ms to 4 s). Even if some channels overlap with active Wi-Fi, the majority do not, so most packets are received cleanly. Combined with AFH (which excludes bad channels), the effective packet error rate stays below 1%.

BLE Frequency Hopping is the spread-spectrum technique where each connection event uses a different data channel (out of 37 available), selected by a pseudo-random Channel Selection Algorithm (CSA). This spreads communication across the 2400-2480 MHz ISM band, mitigating narrowband interference from Wi-Fi, microwave ovens, and other 2.4 GHz sources. Combined with Adaptive Frequency Hopping (AFH), channels with high interference are excluded from the hopping sequence.

Category: Wireless Protocols

Channels: 37 data (2 MHz each)

Understanding BLE Frequency Hopping

During a connection, both central and peripheral independently compute the next channel using the same algorithm and shared parameters (access address, channel map, event counter). CSA #1 (legacy) uses a simple modular hop; CSA #2 (BLE 5.0) uses a more sophisticated pseudo-random mapping for better uniformity across channels.

The hopping rate equals the connection event rate: at CI = 7.5 ms, the radio hops ~133 times/second. At CI = 1 s, it hops once per second. Each hop moves to a 2 MHz channel, so the signal never dwells on one frequency long enough for sustained interference to cause multiple consecutive packet losses.

Channel Selection

CSA #1 (legacy):
unmapped_ch = (last_ch + hop_increment) mod 37
If unmapped_ch is bad: remap to good channel

Hop rate: 1/CI (1-133 hops/s)
Band coverage: 37 × 2 MHz = 74 MHz

BLE vs Classic Hopping

Parameter	BLE	Bluetooth Classic
Channels	37 (2 MHz)	79 (1 MHz)
Hop rate	1-133/s (CI dependent)	1600/s
AFH	Yes (channel map)	Yes
Band	2400-2480 MHz	2402-2480 MHz
CSA version	#1 (legacy), #2 (5.0)	Basic/Adaptive

Common Questions

Frequently Asked Questions

CSA #1 vs #2?

CSA #1: simple modular hop. CSA #2 (BLE 5.0): better pseudo-random distribution for more uniform channel utilization. Mandatory for BLE 5.0+ features.

How does hopping prevent interference?

Wi-Fi occupies 10-20 fixed BLE channels. BLE hops every event; most hops land on clean channels. AFH excludes bad channels, keeping PER below 1%.

BLE vs Classic hopping?

Classic: 79 ch, 1600 hops/s. BLE: 37 ch, 1-133 hops/s. BLE's wider channels and AFH provide comparable robustness at much lower power.

Related Terms

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