Why does it say that the nRF51822 has 1Mb/s and 2Mb/s data rates if it doesn't?

[westhouse]

Why does it say that the nRF51822 has 1Mb/s and 2Mb/s data rates if it doesn't?

Quote from devzone: "6 * 20 B* 1/0.0075 s = 16 kB/s = 128 kbps". And its only for S110, cause for S120 this is even less as I read.

[Håkon Alseth]

Hi,

The specification for the nRF51x22 shows the available on-air frequencies that it can operate on. the communication over-the-air is still 1Mbit rate (ie: one byte takes 8 us to transfer), but due to overhead in the RF protocol (in this case; the bluetooth protocol) the effective user data rate is therefore lowered. This has to do with the overhead in the payload that you transfer on air, and the required timing parameters of the bluetooth protocol.

Cheers, Håkon

[Eirik Aa]

The data payload thougput is not the same as the RF data rate. When using a proritary protocole the chip supports data rates over the air of 2MBit. But this is the spees each bit is transferred, not the thourgput.

In BLE applications the protocole enforces 1MBit data rates. Still this is the data rate over the air. This is usefull in reguards to how long time the chip needs to be in RX/TX mode to recieve one bit. Less time means less power used.

[westhouse]

Thanks for answer. If assume that 1Mb/s is over-the-air rate (speed of wave propagation) and real application throughput is 0.128Mb/s (official BLE protocol support up to 0.27Mb/s of app throughput), then how can I use the 2Mb/s mode in ble nRF51822 (assume that 0.128Mb/s is from 1Mb/s)?

Best regards

[westhouse]

Thanks for answer. If assume that 1Mb/s is over-the-air rate (speed of wave propagation) and real application throughput is 0.128Mb/s (official BLE protocol support up to 0.27Mb/s of app throughput), then how can I use the 2Mb/s mode in ble nRF51822 (assume that 0.128Mb/s is from 1Mb/s)?

Best regards

[kaku]

It is not possible. RF-PHY layer is capable of transmitting data at 1MBps, but until reachs RF-PHY layer from application layer, some of the overhead of protocol is piled and encapsulated. So, application throughput dramatically decreases. Purely the speed of electromagnetic wave propagation at 2.4GHz on the air is very fast, the time would be able to ignore in such wireless short range.