BLE Throughput

[kai19960504]

Hi All,

As far as I know , BLE Thrughput is basically set around a few parameters => 1. NRF_SDH_BLE_GAP_DATA_LENGTH

                                                                                                                            2. NRF_SDH_BLE_GATT_MAX_MTU_SIZE

                                                                                                                            3. NRF_SDH_BLE_GAP_EVENT_LENGTH

My question is => Does the value of NRF_SDH_BLE_GAP_EVENT_LENGTH represent the packets that can be sent in each connection interval?

According to this table : 

If the event length equal 7.5ms,does it mean that it can transmit 6 packets?

Best regards,

Kai

[Einar Thorsrud]

Hi,

The event length is a Bluetooth concept. A connection event occurs every connection interval, and the duration of it is defined by the event length. During the event length, packets can be exchanged. If the event length is as long as the connection interval, packets can be exchanged more or less continuously. This maximises throughput.

If the event length equal 7.5ms,does it mean that it can transmit 6 packets?

Yes and no. If you cant fit 6 packets, then yes. If you can fit more, then you can send more. There is no defined maximum. Note that the documentation you refer to is for an old SoftDevice. More recent SoftDevice versions does not have this bandwidth configuration, but instead just allows you to configure the event length, using NRF_SDH_BLE_GAP_EVENT_LENGTH  as you have found.

[kai19960504]

Hi Einar,

Here is my sdk_config.h setting

Now NRF_SDH_BLE_GAP_EVENT_LENGTH  is 6,so my packet will transfer total 6ms?

[Einar Thorsrud]

It means that you have 6 ms that you can spend to transfer packets, but there is no need to spend the entire 6 ms (though that is not a very long time). You can also send several short packets or a single long. Here you don't use data length extension, so you can send several short packets. This is handled by the Bluetooth stack though, so you cannot do anything other than to try to send as much data a possible so that the stack always has more data to send.

[kai19960504]

Could you please provide the latest S132 SPEC?

Else question is 1 packet have 20byte,how long will that packet take?

[Einar Thorsrud]

kai19960504 said:

Could you please provide the latest S132 SPEC?

https://infocenter.nordicsemi.com/topic/struct_nrf52/struct/s132.html

kai19960504 said:

Else question is 1 packet have 20byte,how long will that packet take?

Which exact time are you after here? If this is 20 payload bytes, you would see about 272 us on air. The SIG has a page which may be interesting for you: How Fast Can It Be?

[kai19960504]

Einar Thorsrud said:

infocenter.nordicsemi.com/.../quote]

The content of v7.3.0 is like the picture when I asked the question, I don't understand what you said "Note that the documentation you refer to is for an old SoftDevice."

[Einar Thorsrud]

Hi Kai,

That was my bad. I did not realize that you only included parts of the table. I see now that this is the upper few rows of Table 1 under Bluetooth Low Energy data throughput in the latest SoftDevice Specification.

[kai19960504]

Hi Einar,

I have checked a lot of information, and it shows that many packets can be sent, but I can only receive up to 6 packets per connection interval. Is this correct?

[Einar Thorsrud]

There is no hard limit of 6 packets per connection event. If there is more data to send, there is time left in the event, and there are no retransmissions, you can send even more packets than that per event.

[kai19960504]

So,how to interpret this picture?

[Einar Thorsrud]

Different devices may have different limitations. this shows that some different phone models have a limit of packets per connection event. This is entirely implementation specific though, and there is no such limitation in the Bluetooth specification. And for nRF devices there is no limit.

[kai19960504]

Hi Einar,

Einar Thorsrud said:

This is entirely implementation specific though, and there is no such limitation in the Bluetooth specification. And for nRF devices there is no limit.

I'm not very sure what you mean?