/ˌeɪ ɛf ˈeɪtʃ/
n. "Dynamic channel blacklist adaptation for FHSS systems avoiding interfered frequencies in real-time."
AFH, short for Adaptive Frequency Hopping, monitors channel quality during FHSS operation and removes "bad" channels from the hop sequence—Bluetooth masters classify 1/3 of 79 channels as unusable (PER>threshold) then broadcasts reduced map (20-79 channels) via baseband packet, forcing synchronized slaves to mirror avoidance. Essential for 2.4GHz ISM coexistence with WiFi, where fixed WLAN channels create interference islands amid pseudorandom hopping.
Key characteristics of AFH include: Channel Classification RSSI/PER monitoring tags channels "bad" (used/noisy) vs "good" (unused/clean); Map Exchange master broadcasts 10-octet channel map every connection event; Hop Remapping LFSR reseeds across reduced N_channels (20-79); AFH Disable backwards compatibility with legacy slaves; Channel Assessment RSSI histograms + packet error rate tracking.
Conceptual example of AFH usage:
/* Bluetooth AFH channel map exchange */
#define NUM_CHANNELS 79
#define BAD_CHANNEL_THRESHOLD 0x20 // PER > 32/128 pkts
uint8_t channel_map; // 79 bits packed
uint8_t good_channels = 79;
uint16_t bad_channel_timer[NUM_CHANNELS];
void afh_channel_assessment(uint8_t ch) {
if (packet_error_count[ch] > BAD_CHANNEL_THRESHOLD) {
channel_map[ch/8] &= ~(1 << (ch%8)); // Mark bad
good_channels--;
}
}
void afh_map_update() {
// Master → slave baseband packet every 32 slots
l2cap_afh_packet(channel_map, good_channels);
// Slave syncs map, reseeds hop selection kernel
regenerate_hop_sequence(channel_map);
// Clear assessment counters
memset(bad_channel_timer, 0, sizeof(bad_channel_timer));
}Conceptually, AFH transforms blind FHSS into interference-aware hopping—Bluetooth piconets probe packet error rates across 2.4GHz then collaboratively blacklist WiFi-occupied channels (1,6,11), shrinking hop table from 79→20 clean channels. Periodic map exchange maintains synchronization during TDMA slots; contrasts static WiFi channels by continuous adaptation, enabling robust PAN links where traditional FHSS fails amid spectrum congestion.