To mesh or not to mesh, and cheapest chip selection

[jmsartori]

I am working on a wearable design that has standalone modules distributed around the body. Each module will do the same thing, receiving commands to turn LEDs on/off or adjust their power level through PWM. My initial thought is that a mesh network would work well for this design since I want all the nodes to receive the same command and do the same thing. I also saw that mesh examples exist for lighting and dimming, which may be very close to what I want to do, but I don't know much about mesh. Can anyone advise if mesh is the best fit here?

I am also wondering what is the cheapest, smallest chip available for what I want to do. The communication distance is small, and I only need very limited functionality, so it seems to me that the cheapest, smallest chip available will best suit my needs. 

If mesh is the answer, do I need a gateway node that sends commands to the rest of the nodes, or can a phone with app accomplish that functionality, broadcasting / sending commands to all the nodes distributed around the body?

[Matt]

The mesh relay node is always ON (Nordic folks can correct me if I'm wrong here). That may pose a power drain issue for your wearables.

[Joakim Jakobsen]

Hi. 

Apologize for the long delay in response here. 

From what you describe it seems that Mesh could fit your needs. However, as mentioned below, the current consumption could be relatively high when using BLE Mesh. 
In a BLE Mesh network, you are depending on relay-nodes to relay messages to nodes that are not in direct radio contact with the sender. Also, there is no connections made between devices, they base the communication on BLE advertising/scanning. This means that the devices will need so stay in RX mode to receive data. 

There is an option to use Low Power Nodes (LPN) and Friend Nodes (FN). This way you can have a low power device which will go to sleep at given intervals and then wake up to request incoming data from it's friend node. This requires the FN to stay in RX mode and cache the incoming data (which is meant for the LPN) and then forward it to the LPN when it wakes up. The LPN will have a current consumption more similar to what we see from BLE devices. 

Using our SD you can achieve up to 20 concurrent connections, which can be an option to using BLE Mesh. 

For more information about prizing for the different devices, I suggest that you contact our regional sales manager. If you don't know who that is, you can send me your location on a PM, and I'll provide the contact information you need. Alternatively you can go through the contact form (Sales related questions) on our website: 
https://www.nordicsemi.com/About-us/Contact-Us

Best regards, 
Joakim