The Bluetooth SIG recently announced a new feature specifically conceived for the Electronic Shelf Label (ESL). The feature so called Periodic Advertising with Responses (PAwR) which is encapsuled in Bluetooth 5.4 standard introduces a new transmission logic that enables a single access point to conduct two-way communication with thousands of terminal nodes without established links. It aims to to bring more space for innovation to the ESL industry, not only enabling bidirectional communication between ESLs and Bluetooth hubs, but also significantly reducing their power consumption.

What is An Electronic Shelf Label

When shopping in stores or supermarkets, it is easy to find that traditional paper price tags are being replaced by electronic shelf labels. Retail giants in China and abroad such as Freshippo, Yonghui Superstores, Sam Club, and Metro have massively adopted electronic shelf labels as standard accessories. In addition, applications similar to ESLs getting adoption in other business scenarios i.e. table cards in exhibitions, venue access cards, patient cards in hospitals and BOM cards in factories, etc.

An ESL is an electronic ink display device with an embedded communication module enabling data reception. It displays basic product information, prices, barcodes or QR codes, and even other basic images. What's more, its most significant and mandatory feature is "low power consumption and long autonomy", which typically achieve a battery life of several months or even years.

ABI Research predicts that by 2027, 2.4 billion ESL devices are supposed to be installed in various retail stores. Communication protocols commonly used by ESLs are the 2.4G proprietary protocols, ZigBee, and BLE. Each protocol has its own pros and cons.  Thanks to its versatility and rich ecosystem, BLE has become more popular and is being adopted by more and more manufacturers and retail stores. Research data shows that the penetration rate of ESL in China is still below 10%. And its adoption mainly concentrates in large supermarkets. It make sense to believe that there is still huge market potential to tap in China, since middle and lower tier markets there has yet been addressed.

What is PAwR

PAwR is a communication method similar to periodic broadcast (PADVB). It allows application data to be transmitted from a broadcasting device (broadcaster) to one or more receiving devices (observers), following a one-to-many communication topology. Both PAwR and PADVB use a connectionless communication method, in which the transmission of broadcast packets is periodic, at regular intervals, without random scheduling. The difference in between: PAwR supports bidirectional communication between the broadcaster and observers; whereas, PADVB does not support  observers to send response packets to the broadcaster.

Advantages of PAwR

• Bidirectional connectionless: PAwR has the ability to achieve bidirectional connectionless communication between devices without establishing a link, which is not achieved in BLE releases prior to Bluetooth 5.4.

• Scalability: Compared to the BLE GATT connection method, PAwR adopts a more scalable, one-to-many, bidirectional topology, making it possible to support communication with thousands of nodes in both directions. In BLE GATT, however, the number of slave devices connected to a central device is very limited. And PAwR perfectly addresses that constrain.

• Low power consumption: In PAwR, a broadcaster, and an observer only need to occupy a subevent interval, so that the observer can scan only  in a small time frame specified for the broadcast. Since the subevent synchronization process are relevant to the application logic, typically the received packets are to contain data related to the observer. This low power consumption feature allows the observer device to keep operating for many years with only a button cell.

• Flexible topology and concurrent reception: PAwR adopts a flexible topology that allows broadcasted packets to be received and processed by a single observer, dedicated multiple observers, or all observers, according to different specified data synchronization logic in the application layer of the observer. Such flexibility makes PAwR extremely adaptive to different application scenarios and requirements

• Application: PAwR is suitable for scenarios where a central device communicates with other devices on a large scale. These data may be control commands, sensor data, or other messages. Among them, ESL is a very important application scenario, and PAwR has specially developed an ESL profile for it to specify the method of data transmission. However, PAwR is not suitable for scenarios with high real-time traffic. Data packets are sent periodically in a specific time slot, and the number of observers can be configured. As the number of observers increases, the time required to broadcast data also increases, resulting in delays. Therefore, when sending messages to multiple devices, there may be significant time delays, ranging from a few milliseconds to tens of seconds, depending on the configuration.

PAwR Events and Subevents

The periodic part of the PAwR refers to the periodic broadcasting of packets by a central device like an access point, which occurs at precise and regular intervals. Communication occurs in bursts of activity during periods of time called events. An event can be divided into multiple subevents.

Subevents are further divided into time slots which are used for the transmission of one packet by the central Broadcaster device, by several time slots during which to receive responses from Observer devices.

PAwR defines procedures by which Observer devices can acquire the event and subevent schedule of the Broadcaster. Other procedures define how the Observer is allocated a specific subevent during which to listen and a response slot within that subevent to use for replies. Assigning devices to specific subevents only means that they switch into receive mode infrequently, substantially increasing battery life.

PAwR is designed to accommodate data that changes at every transmission and is delivered to individuals or groups of devices. Application logic ensures that data transmitted in each subevent is relevant to the devices listening at that time, so there is little wasted energy.

PAwR is essentially stateless, and this makes it very scalable. Bi-directional, one-to-many communication involving thousands of devices like ESLs is achievable using PAwR.

New Prospects for PAwR and ESL

Automated price changing in the ESL system have improved store operational efficiency and significantly improved customer satisfaction. At the same time, the new Bluetooth technology features jointly developed by ESL industry leaders and the Bluetooth SIG indicate that a new industry standard for the electronic shelf label market is arriving. In order to expand the addressable market, the next step is to have ESL solution providers migrate their systems to standard-based wireless technology. Introducing the wireless standard for the ESL market, Bluetooth technology will help the retail industry enter the next stage of digital transformation, thereby delivering better outcomes for both stores and shoppers.

About RF-star Technology

RF-star is a high-tech company focusing on radio frequency devices and has been certified by Texas Instruments as a third-party IDH of low-power RF products for more than a decade. RF-star provides IoT wireless modules and a full set of solutions, including BLE, Wi-Fi, Matter, Wi-SUN, Sub-1G, ZigBee, Thread, etc. For more information, kindly visit the company website https://www.rfstariot.com/ or contact us at info@szrfstar.com.