Peer to peer and centralized communication

[sAz-n]

Hi everyone,

I am working on a project, in which I have n nodes that communicate with each other (peer to peer communication). In addition, each node is able to communicate with another (central) node.

The peers use the nRF51822 for communication, and the central node uses the nRF24LU1+ .

Is it possible for the peers to communicate with each other and with the central unit at the same time? To be more accurate, consider the following scenario:

The peers must be aware of the position of each other. For this, each peer broadcasts its own position in turn, so they communicate among each other in round-robin fashion. In addition, the central unit sends and receives information from the peers.

In the current implementation,  peer to peer communication and peer to central node communication compete and cause packet loss. Is it possible to define one channel for peer to peer communication and another one for peer to central node communication?

[ovrebekk]

Hi 

It should not be a problem to use different RF channels for the peer to peer and the peer to central communication respectively. 

It only means that the peers need to switch between the different channels as needed. 

The main problem of this method is if the peer needs to listen for messages from other peers and the central asynchronously, since you will not be able to listen on two different channels at the same time. In this case you would have to switch channels back and forth on a timer, and accept a decent amount of packet loss. 

Best regards
Torbjørn

[sAz-n]

Hi

So does it mean that each channel uses a different frequency, but the receiving/sending components are the same, and therefore asynchronous communication is not possible?

Can a node communicate asynchronously using two different nrf51 devices? 

Best

[ovrebekk]

Hi

sAz-n said:

So does it mean that each channel uses a different frequency, but the receiving/sending components are the same, and therefore asynchronous communication is not possible?

Essentially, yes. The radio can not send and receive at the same time, nor can it receive on two different frequencies at the same time. 

In order to change from one frequency to the next you need to power the radio down and up again, which takes about 130us. 

I won't say asynchronous communication is impossible, you just have to expect that not all the packet will be received, and design the protocol accordingly (by using the retransmit feature of the ESB protocol for instance). 

sAz-n said:

Can a node communicate asynchronously using two different nrf51 devices? 

I assume you mean using two different nRF51 devices on the same board?

This is possible, then you would be able to receive on two different frequencies at the same time. Just be aware that if one of the devices are transmitting it will most likely block out reception on the other device (even if they are using different frequencies), because the two devices would be in close proximity of each other. 

Best regards
Torbjørn