Also known as: FLEX

FLEX is a high-speed one-way paging protocol developed by Motorola to succeed POCSAG. It uses 2- or 4-level FSK at up to 6400 bps, with robust synchronisation and interleaving that make it resilient on wide-area simulcast networks.¹

FLEX is a higher-rate paging protocol using time-multiplexed frames and multi-level FSK.

Overview

FLEX organises traffic into precisely timed frames and phases, allowing high capacity and good battery life for pagers. Its time-synchronised structure suits large simulcast paging systems covering whole regions.

Technical characteristics

Property	Value
Modulation	2-FSK or 4-FSK
Bit rates	1600, 3200, 6400 bps
Coding	BCH + bit interleaving
Framing	Time-synchronised frames/phases

History

Introduced by Motorola in the 1990s as paging demand outgrew POCSAG’s capacity; widely deployed by commercial paging carriers.¹

Deployment

Commercial wide-area paging, healthcare, and emergency notification networks.

Decoding it with GopherTrunk

FLEX shares the FSK paging family with POCSAG; see Status for current coverage and the POCSAG decoder page for the paging pipeline.

Sources

1. FLEX — Wikipedia, for Motorola’s high-speed paging protocol, its multi-level FSK rates, and time-synchronised framing. ↩ ↩²

See also

• POCSAG
• Frequency-shift keying (FSK)
• BCH code
• Interleaving

Learn it step by step

• Other signals you'll meet

From the blog

• SDR Internals, Part 10: Protocol decoders & state machines