CODEWITHSUNDEEP
bluetoothbluetooth-lowenergybluetooth-gatt
Talia
Talia

Reputation: 3137

How should choose the suitable phy layer for bluetooth?

I am going to propose some solutions related to the IP for Bluetooth. I am proposing my solutions in layers of Host.

  1. My problem is that how can i select the best phy for my solution? in my approach, I need to have long rage, low power and big packet transmission.

  2. What are the main features offered with phy? what I know is that phy can impact on range, throughput, power. Is it all or is there anything else that I didn't recognize?

  3. My devices are small and working with coin batteries. I do not have audio transmission. should I go with EDR PHY, BR PHY, LE 2M PHY, LE 1M PHY or LE Coded PHY?

  4. Is it possible to use different PHY based on BL link quality to achieve specific application requirements? there is a paper entitled " Performance and Trade-offs of the new PHY Modes of BLE 5" showing that how to select the best phy based on the BL link quality.

  5. has the phy impact on the following? if so, what feature of the phy should be considered?

    a) Supported Packets Per Connection Event

    b) Maximum Supported ATT MTU Size

    c) Maximum Supported Link Layer Data Packet Size

Upvotes: 0

Views: 845

Answers (1)

Emil
Emil

Reputation: 18452

If we talk about BLE, the three different PHYs are quite similar from the radio point of view. What you need to know is that they all usually consume basically the same current (not energy) while the radio is on (with some small differences). The difference is that the radio needs to be on for longer times with shorter bitrates (and hence consume more energy in total) and shorter times with higher bitrates. Higher bitrates lead to worse delivery success rate than lower bitrates. So everything is just a tradeoff between range, speed and energy usage.

Note that a BLE radio can typically only do one radio operation at a time, so with the LE packet length extension, a maximum length Coded PHY packet can take 17 ms, which might reduce the ability for the firmware to schedule other activities, such as scanning or handle another connection. On the Link Layer, the two endpoints can negotiate the maximum time and maximum packet size, so yes, you can end up in a situation where the maximum packet length depends on the PHY used (but the link layer will segment it so it won't be any issues for the host side). You can also realise that with 2M PHY you can fit much more packets compared with other PHYs during a certain amount of time, for example one connection event with a firmware-decided deadline when it must end.

Also keep in mind that to establish a connection using Coded PHY, you need to use the new "extended advertisements", which are not backwards-compatible with devices not supporting Coded PHY, or devices that support Coded PHY but are not set up to scan using Coded PHY.

When a connection is established, you can change PHY at any time. For example if you monitor the RSSI and detect a change in signal quality you can change the PHY.

The ATT MTU is decided by the host layer and is completely separate from the link layer. Although, of course a programmer could for some reason decide to use shorter MTUs when Coded PHY is used, but I haven't heard about anyone doing so.

Don't forget that you can also change the TX power of your radio to increase the range (and current consumption) your sent packets will reach. You can also select a chip with better RX sensitivity to get better range when receiving packets. Or use an antenna amplifier.

Upvotes: 2

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