51822 bluetooth

RE: 51822 bluetooth

bin simon — Tue, 19 Aug 2014 03:58:55 GMT

Hi Kristin, I am working on a sensor device using S110 and I am looking for the peer central device(e.g. smartphone, tablet or PC) to which S110 can send 6 packets at each connection interval.If you do not mind, could you tell me about the peer device you used for S110 thoughput measurement as mentioned "table 15 of section 7 Radio Notification on S110 nRF51822 SoftDevice Specification v1.3".

RE: 51822 bluetooth

Paul Tay — Tue, 20 May 2014 09:47:27 GMT

Hi Kristin,

We are working on Android and iOS apps. Currently using S3 with Android 4.3 and Note to communicate with nRF51822. Baud rate of 19200bps for our serial communication.

Q1. How can we synchronize the transmission of 4 packets per connection interval? Based on sample code nRFUART, do we send out consecutively packet of 20 bytes after previous packet was sent out using writeRXCharacteristic ? Or should it pause for 10ms before sending out the next packet?

Q2. We have encountered abnormal behavior on S3 and Note after using writeRXCharacteristic at time interval of 20ms or lower. Is there a way to read transmission status in Android app before using writeRXCharacteristic to send out 20 bytes?

Q3. In our project, data size transmitted can be more than 100kbytes. Is there any further recommendation on Android and iOS app that we need to take note in order to increase data rate and avoid abnormality behavior on devices?

Thank you.

Regards, Paul

RE: 51822 bluetooth

Ole Morten — Wed, 27 Nov 2013 16:31:57 GMT

Yes, connection parameters will significantly affect the throughput. Take a a look at this question for details on what connection parameters are: https://devzone.nordicsemi.com/index.php/what-is-connection-parameters

PS: In the latest SDKs, there is a nice macro you can use instead of the SECOND_1_25_MS_UNITS define, to set the intervals like this if you want 7.5 ms: MSEC_TO_UNITS(7.5, UNIT_1_25_MS)

RE: 51822 bluetooth

Ole Morten — Wed, 27 Nov 2013 16:29:33 GMT

It is true that there is theoretically time to transfer more packets, but the S110 supports maximum six packets per event, no matter how long the interval is. This has to do with RAM usage for the internal buffers.

RE: 51822 bluetooth

Chris Lovett — Wed, 27 Nov 2013 03:17:00 GMT

note also, to get those rates you will need to set the MIN_CONN_INTERVAL and MAX_CONN_INTERVAL to something smaller than the defaults they use in the sample apps. I've used SECOND_1_25_MS_UNITS / 20 for example, to get a nice steady stream of events from my device to my phone. The defaults are set to 1/2 a second which makes for a very low bandwidth indeed.

RE: 51822 bluetooth

Wobs — Tue, 26 Nov 2013 14:45:31 GMT

Hi Kristin, I think your comment regarding the packet limit needs some clarification:

On the PHY, the max data packet size is: payload 27bytes + the 4 byte MIC + 2 byte header + 1 byte preamble + 4 byte access address + 3 byte CRC, in total this is 41bytes = 328 bits, this takes 328us on the PHY. So if both the master and the slave sends these maximum size packets back and forth in the connection event, then the maximum number of packets (x) in each direction at maximum packet has to satisfy 2 * x * (328 + 152 (max. IFS)) < connection interval [us]

Even at 7.5ms this is 7 packets, but there is no reason the LL can not send more packets than this if the connection interval is longer if I'm not mistaken.

RE: 51822 bluetooth

FormerMember — Wed, 20 Nov 2013 11:07:24 GMT

Hello,

Unfortunately, the nRF51822 does only work with BLE. Your data transfer rate is a little low, which Android version do you have?

By theory, with BLE, you can have maximum 6 packets per connection interval and minimum 7.5ms connection interval. This results the maximum throughput of (1000/7.5) * 6 * max_payload_size. Currently the nRF51822 supports max_payload_size = 20 bytes. (MTU = 23 byte, 1 byte opcode, 2 byte handle).

So the maximum data throughput that the nRF51822 can achieve is in best case = (1000/7.5) * 6 * 20 = 16 kB/s.

However, usually you will not be able to achieve this speed due to limitations on the host. On iOS and Android usually you will have maximum 4 packet per connection interval. On Android devices you can get as low as 7.5ms connection interval. On iOS device, you can get something around 20 ms connection interval.

On the test here with a Samsung S4 running Android 4.2.2, we transferred 20kB in ~1850ms (~10.8 kB/s) from the nRF51822 to the phone.

Throughput on the other direction should be very similar.

How quick the host can support depends much on the available resources on the host stack, if it have to handle several slaves which also require high bandwidth, the throughput for each will be reduced (less packets per connection interval).

Same apply for PC, not all PC BLE stack and driver support 6 packets per connection interval and 7.5ms connection interval.

Also note that with Android 4.3 on S4, the minimum connection interval is 30 ms, leading to lower data rate.

Regards, Kristin