The Tech Blog

Last week, I was in conversation with a friend about logistics and machinery tracking for a project, and the technologies enabling it. One tech that was talked about was Bluetooth’s PAwR, Periodic Advertising with Responses. It’s worth discussing today.

Bluetooth 5.4 introduced PAwR as a new way of enabling two-way communication between a single hub and thousands of low-power tags or sensors. These devices can communicate without having to establish individual connections, saving significant battery power. Earlier BLE standards had issues with large numbers and power efficiency. Older Bluetooth advertising was one-way. BLE 5.0 improved on this with extended advertising, but communication was always one-way. PAwR made bidirectional communication possible and standardized.

How does it work? The central hub sends periodic events. Each event contains several subevents with specific response slots. The tags/observers know exactly when to wake up, listen, and respond. This structured approach allows devices to save battery life dramatically. It can stay asleep except needed. This structured scheduling is similar TDMA (Time Division Multiple Access) used in telecom systems, where devices communicate in pre-allocated time slots. With PAwR, it’s a one to many network, with thousands of devices that can interact efficiently without establishing individual connections, ideal for scenarios like electronic shelf labels (ESLs) in retail or industrial sensor networks.
PAwR isn’t designed for real-time responses(Need to wait for the slots). Instead, it’s designed predictable battery life and scalable management of thousands of nodes. Messages are short, with larger transfers handled via temporary connections only as needed.

Using PAwR, a simple device waking briefly every 1.6 seconds can run for five full years on a tiny coin-cell battery, totalling just 8 hours of active communication over that entire span. This makes it ideal for large-scale deployments such as electronic shelf labels, price tags, and physical asset tracking.

This bit of tech was one of the most key innovations which made Bluetooth audio good. Classic Bluetooth audio sounded OK, but drained battery quickly and sometimes lagged behind video. Bluetooth Low Energy (BLE) solved power issues, but wasn’t originally built for audio. Early BLE couldn’t ensure packets arrived exactly when needed, leading to dropouts, delays, or distorted sound. We needed a reliable, low-latency audio without sacrificing battery life. That’s why Bluetooth LE Audio was introduced along with BLE v5.2 spec.

Think of Isochronous Adaptation Layer(ISOAL) as the invisible worker organizing audio packets to ensure they’re delivered precisely on time. It acts as a bridge between your audio source, like a smartphone, and the wireless radio inside your headphones/earbuds.

Before ISOAL existed, audio streams had to cram large chunks into single packets, causing inflexibility and interruptions. Synchronizing stereo earbuds was difficult because packets weren’t always perfectly timed. ISOAL fixes these issues, enabling smooth stereo playback and synchronized sound across multiple devices without lag or glitches.

So how does it actually work? When your phone streams audio, it hands complete chunks (called Service Data Units, or SDUs) to ISOAL. If these chunks are too large for transmission, ISOAL breaks them into smaller pieces. It labels each smaller piece (called Protocol Data Units, or PDUs) with precise timestamps and sequence numbers. These labels act as detailed instructions, so your earbuds know exactly when to reconstruct and play the audio smoothly.

In summary, ISOAL ensures perfect audio sync between left and right earbuds. BTW, ISOAL is implemented entirely in the controller’s firmware and doesn’t need any additional hardware or app firmware coding. Its timestamps are in the microsecond range, ensuring precision. ISOAL handles both Connected Isochronous Streams (CIS) for point-to-point audio (true-wireless earbuds) and Broadcast Isochronous Streams (BIS) for one-to-many audio.