throughput measurement NUS

[Martijn Jonkers]

Hi,

I have the following in my code to measure throughput over the Nordic Uart Service.

uint8_t data[244] = {'1'};
int64_t num = (sizeof(data) * 1000);

uint64_t start = k_uptime_get_32();
for( uint32_t i  = 0 ; i < 1000 ; )
{
	if( !bt_nus_send(NULL, data, sizeof(data)) )
	{
		i++;
	}
}
int64_t delta = k_uptime_delta(&start);

LOG_INF("sent %d bytes (%d KB) in %d ms at %d kbps", num, num / 1024, delta, (num * 8 / delta));

It works, but I was wondering if I am measuring correctly. I took this measurement principle from the throughput example, I also copied as much configuration as I thought were needed. But maybe the NUS implementation has a bit more overhead? Because I cannot reach the expected ~1327 kbps. I am stuck around 1050 kbps and cannot get it any faster.

I am connecting with my phone and use nrf toolbox uart to connect, maybe these speeds are expected? Is the phone app slowing me down a bit here? The speeds are high enough for me to think there really isn't anything wrong with my configuration.

[Kenneth]

Hi,

You may find some theoretical and measured values for different configurations on these two pages:
https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/ble_data_throughput/ble_data_throughput.html 
https://www.novelbits.io/bluetooth-5-speed-maximum-throughput/ 

I expect that a phone will not give one specific BLE link the entire 100% duty cycle of the radio, the max throughput will depend on the supported features, connection parameters and the phone OS/model. If you measure 1050kbps I would say that is pretty good. If you want to know more details on what is the limiting factor for this specific measurement here you will need to provide an on-air sniffer log (e.g. nrf sniffer) so we may see the features, parameters and duty cycle. I expect that if you tried this on another phone manufacturer or OS it would vary.

Kenneth

[Martijn Jonkers]

ok, thank you. I found both the pages, that is how I got to the ~1327 kbps. But to be sure, this is an expected max speed for ble using a phone / pc? The ~1327 kbps will never be reached? And my measurement method is correct?

[Kenneth]

It looks correct, though you can try for comparison the central uart example as peer for comparison.

Kenneth