IPhone BLE paired to nrf52840 running at full bandwidth. How many of these systems (IPhone paired to nrf52840s) can be in one room?

RE: IPhone BLE paired to nrf52840 running at full bandwidth. How many of these systems (IPhone paired to nrf52840s) can be in one room?

Sigurd — Fri, 26 Mar 2021 15:04:52 GMT

[quote user="Markl"]I guess we really just want to know if eight device pairs is an expected number that can be supported with regard to high speed BLE data transfer, or if there is some parameters(s) we can try adjusting to improve the situation. [/quote]

If you are sending a lot of data, i.e., spending the entire connection event to send packets, and there is no "radio idle" time between connection events/intervals, and you have 8 devices that does this, the channel utilization starts to get high, packet collision can happen, and that will reduce the throughput & bandwidth. The SoftDevice will try to retransmit packets that are not ack’ed on the link layer, so if your application is continuing pushing packets to the SoftDevice, the internal SoftDevice buffer might get full. If that happens, the function sd_ble_gatts_hvx() will return NRF_ERROR_RESOURCES. Over time the central(phone in this case) might be able to set a channel map that reduces the probability of packet collisions. But the application needs to gracefully be able to handle the NRF_ERROR_RESOURCES return code. That said, it might also help to increase the SD buffer, e.g. by increasing the value of NRF_SDH_BLE_GAP_EVENT_LENGTH in sdk_config.h

RE: IPhone BLE paired to nrf52840 running at full bandwidth. How many of these systems (IPhone paired to nrf52840s) can be in one room?

Markl — Wed, 24 Mar 2021 19:49:33 GMT

Each of the 8 devices is transmitting data to the phone at max data rate (2Mbit). If we run nine or more devices simultaneously in a common space we begin to see an avalanche of packet collisions. These collisions seem to manifest in at least one of the devices' uP getting trapped in the soft device ISR, which leads to real-time failures such as watchdog timeout and starvation of other real time critical devices. One of our engineers characterized the issue as garbage collection taking a long time at highest priority ISR level, which locks out all other interrupts. I guess we really just want to know if eight device pairs is an expected number that can be supported with regard to high speed BLE data transfer, or if there is some parameters(s) we can try adjusting to improve the situation.

RE: IPhone BLE paired to nrf52840 running at full bandwidth. How many of these systems (IPhone paired to nrf52840s) can be in one room?

Sigurd — Tue, 23 Mar 2021 11:25:02 GMT

[quote user="day1ok"]The error is loss of data [/quote]

How do you measure that? If you are in a very noisy 2.4GHz environment there might be packet collision, so that some packets might need to be re-transmitted, but you should not lose the data.

Also, can you explain what you mean by "running at full bandwidth" ?

RE: IPhone BLE paired to nrf52840 running at full bandwidth. How many of these systems (IPhone paired to nrf52840s) can be in one room?

day1ok — Sun, 21 Mar 2021 16:41:36 GMT

Yes, eight iphones connected to eight nRF52840.
1) Iphone #1 paired to nrf52840 #1
2) Iphone #2 paired to nrf52840 #2
etc...

Each system (one iphone paired to 1 nrf52840) is within a few feet of each other and the room is 10'x10'.

The error is loss of data that is being transmitted from the nRF to the iphone and this only happens when we have more than eight of these systems in a room.

Yes, the iphones are also using wifi

It is an office environment and yes there are other wifi and bluetooth devices nearby no more than 10 computers, mice, phones, wireless headphones, etc.

RE: IPhone BLE paired to nrf52840 running at full bandwidth. How many of these systems (IPhone paired to nrf52840s) can be in one room?

awneil — Sat, 20 Mar 2021 00:40:13 GMT

Just to be clear: is that eight iPhones and eight nRF52840, with each iPhone connected to one nRF52840?

How big is the room?

[quote userid="102802" url="~/f/nordic-q-a/73034/iphone-ble-paired-to-nrf52840-running-at-full-bandwidth-how-many-of-these-systems-iphone-paired-to-nrf52840s-can-be-in-one-room"]I start start to get errors.[/quote]

What kinds of errors, exactly?

Presumably, these iPhones are also using WiFi?

Are there also other WiFi and/or BLE devices?