nRF Connect @ Android: Poor distance even with coded phy s8 (long range)

[soko]

Hi guys,

I'm researching the maximum direct connection distance between two Android phones for transfering small amount of data - which lead me to BLE Coded PHY S8 as a promising option. As a first test I used your nRF Connect Android app to do some field testing.

But I cannot get any longer distance connection via coded phy to work. After 20 meters I loose the connection. So maybe (hopefully) I'm doing something wrong or coded phy is far away from the 1000m I've read about...

I hope this is the right place to ask. If not please let me know.

Anyhow... here are the details of my test:

Phone 1 (server) is a Nokia 2.3:

I set up a GANTT server (get current time for testing purposes):

And started an advertiser:

Phone 2 (client) is a OnePlus 7 Pro:

Where I've scanned and connected to the Nokia 2.3, and read the PHY which is set to LE Coded:

But once I walk away with the client phone from the server the read/refresh of time fails and the connection gets lost after 20m or so.

The server phone is placed inside at the window sill and I'm walking away outside on the lawn with no obstacles in between.

Things I've tried:

• Changing the Tx Power Level and the interval of the Advertiser on the server phone
• Setting S8 "manually" on both phones after the connection was established via:
  

I have found a couple of threads:

https://devzone.nordicsemi.com/f/nordic-q-a/58496/advertising-phy-coded-s8-long-range-stops-at-nearly-20m-built

https://devzone.nordicsemi.com/f/nordic-q-a/70538/nrf-connect-for-mobile---does-advertiser-functionality-use-s2-or-s8-coding-for-coded-phy

https://devzone.nordicsemi.com/f/nordic-q-a/75226/how-to-set-coded-phy-rate-to-s8-or-s2-using-nrf-connect-sdk

https://devzone.nordicsemi.com/f/nordic-q-a/77411/testing-range-of-ble-coded-phy-with-nrf52833-dk

The last 3 say that S8 is used by default anyhow or are not really helpful...

The first one is exactly my issue! But as far as I can interpret the discusion there I would conclude: It does not really get better than the 20 meter.

Is that true?

Thanks guys

Soko

[soko]

Hi Torbjorn,

I was curious if the issue is hardware related or system/design related so I did an outdoor test.

Client: Oneplus 7 Pro

Server: Huawei P30 Pro

I've placed the Server on a chair on the lawn in front of my house, connected the client and started to walk away in a direction with no other wifi.

As long as both phones had line of sight the connection was stable.

"line of sight" means: My body between the phones was not an issue. But i.t. a little hill in the landscape was.

I've tested successfully 500m distance. After that my landscape dropped off so I lost line of sight.

I've repeated the test with the Nokia 2.3 as the server. I lost connection after ~200m even with line of sight.

My conclusion:

1) Bluetooth LE (long range) Coded PHY S8 is designed for non WiFi environment and line of sight

2) It also highly depends on the hardware you use

Especially point 1 is a killer for my application as I need a connection of ~100m through walls and where wifi is active.

Soko

[ovrebekk]

Hi Soko

soko said:

1) Bluetooth LE (long range) Coded PHY S8 is designed for non WiFi environment and line of sight

I wouldn't say it was designed for these situations only, but I think it is fair to say that the impact of WiFi interference on the longer coded PHY packets was underestimated when the protocol was designed. 

For situations where you need longer range indoor with a lot of interference it is probably better to add an RF frontend to the BT chipset, in order to increase TX output power and receiver sensitivity. The advantage then is that you can use the standard 1M mode for improved datarate and reduced latency, while the drawbacks are increased current consumption and BOM cost. 

soko said:

2) It also highly depends on the hardware you use

Completely agree

Best regards
Torbjørn