When Master Becomes Slave and Slave Becomes Master

One of the painful things of Bluetooth Low Energy (Wibree, Bluetooth ULP) is the fighting between handsets and watches.

In the initial presentations, a Bluetooth LE system always centered on a cellphone, with the watch joining heart rate monitor and other sensors as the phone accessories. The watch displays what the cell phone tells it to display. So that system can not be without cell phone.

Of course, this model is challenged by a lot of watch centered systems already in the market. Some of the products are manufactured by the Wibree founding members, such as Suuto and Polar. Even for other watch companies, do you think they are happy to see their watch LCD displays a Nokia logo?

In the reality of a body area network(BAN), where wearable sensors and devices are around the body, both watch and handheld can be the hub to display, store and compute data. Either has its own advantages and can not be replaced by the other. "Your wrist is your beach front property", the marketing message from a watch company is so true.

So the fighting inside the Bluetooth LE SIG ground is an easy guess-out. The SIG group has been trying hard to satisfy this use case to allow the watch to be master and operate the BAN standalone. A piece of information tells that the SIG is talking about master ownership transferring in between the phone and the watch. I am inclining to believe this is true, because the frequency hopping and synchronization nature of the Bluetooth network does not allow multiple masters taking control at the same time. Transferring the master ownership seems to be the only viable approach. This is the price Bluetooth LE has to pay to be co-existing and compatible with Bluetooth.

How hard could it be? The current Bluetooth LE stack size is targeting at 90k, and the hardware manufacturers are worrying about the 128k limit could be soon reached.

However, this master-slave conversion approach still can not quite match what the proprietary solutions in the market can do today, for example, the group monitoring use case, where a phone or laptop is talking to multiple watches which in turn are the hubs for sensors on different bodies.