LE 1M AND LE 2M PHYs

Hello Bretley,

Well the LE 1M PHY is the standard 1 Mb/s bit rate, 1 Msym/s symbol rate. Each bit maps to a single radio symbol. The 2M PHY is double the rate, as it is being modulated at twice the speed. This comes at a small cost to range, and the throughput won't necessarily be doubled. 

You can read a bit more on what is new in advertising here.

Was this the mathematical theoretical explanation you were looking for? If not, could you expand a bit on what you are wondering about?

Regards,

Elfving

Hey Elfving,

Thanks for response.

I want to have a deep understanding of LE 1M and LE 2M phys something like mathematics or diagrammatically explanation.

Gentle Reminder 

Could you expand on what parts of the concepts you'd want a mathematical or diagrammatical explanation of, or what could be made clearer?

Could you expand on what parts of the concepts you'd want a mathematical or diagrammatical explanation of, or what could be made clearer?

Like if someone asks “What is LE 1M/ 2M Phy?”

As all blogs say LE 1m uses one bit per symbol and other uses two bits enhancing data rate!!

but how exactly is this done?

how symbols are mapped ?

how the Phy operation works actually leading to increased speed but constraint on range?

Hey Elfving, 

Gentle Reminder Please if you could help me with the LE 1m and Le 2m phys explanations at earliest please

Ridhi said:

What is LE 1M/ 2M Phy?

The new distinction between 1M and 2M PHY in Bluetooth 5 refers to the physical layer (hence the name PHY) bit rate being sent from the radio - the rate at which the electromagnetic radio signal is being sent. 1M refers to a bit rate of 1 Megabit /s.

Ridhi said:

but how exactly is this done?

Ridhi said:

how symbols are mapped ?

At this low level we are referring to literal 1s and 0s in waveform changes. These 1s and 0s are modulated on the 2.4GHz band using the GFSK modulation (the frequency is being slightly(>185kHz) shifted up or down from the band at 2.4GHz). 

We would prefer this signal to be fast and be able to travel far. However, at one point the signal will be faint, and it will make it hard to separate the signal from the noise  - increasing the bit error rate (BER). For BLE BER limit is at 0.1%. Increasing the dB the signal is sent at would also up the energy consumption that is being used, which is also something we would want to avoid. 

Ridhi said:

how the Phy operation works actually leading to increased speed but constraint on range?

With the new 2M PHY you can send the data twice as fast, which increases the throughput (as well as decreasing the time the radio antenna is in use, and therefore also the energy consumption). However, due to multiple reasons this doesn't necessarily mean doubling the throughput. Eg., when it comes to throughput we are often referring to the data, and none of the overhead. And the time it takes the radio to stop and start up again (interframe spacing) is constant. 

The issue with this faster modulation is that it is more prone to noise. At this speed we would have to increase the GFSK offset to >370kH, and increase the sensitivity. You can imagine that with an increase with a factor of two, the signal loses about 3dB of signal strength (1/sqrt(2)=~0.7). This also match what you can find in the nRF52832 spec on the difference in signal strength between the 1M and 2M versions.

For more details, you can take a look at the Bluetooth Spec.

If you could rather expand a bit on what you are trying to do? It might be easier to help you with that than explain these details.

Regards,

Elfving