When sending a file from MacBook Air to a simple phone (Nokia 130), I'm getting transfer speeds of around 40 KB/s, meaning a 60 MB file takes 20 minutes, which is ridiculous in our day and age.

My current workaround is to transfer files using the SD card, but 1) why is the transfer speed so extremely slow, and 2) what can I do to increase it?

  • Hmm. Even at 1Mbps you should probably be getting somewhere around 125kilobytes per second and I'd doubt that protocol overheads would be that high. Chances are that the processor or Bluetooth radio (or the link between the two) are just dog slow. Check the speeds to another (better) phone?
    – Mokubai
    Aug 13 '17 at 10:00

Unless both devices support Bluetooth HS (High Speed - essentially a Bluetooth negotiated WiFi connection) then Bluetooth supports anywhere from around 1Mbps to 3Mbps (EDR) depending on version. This means potentially between 128 to 384kiloBytes person second at the relevant signalling rate. The speed after protocol overheads is going to be a bit lower, but I would be surprised for it to be more than 60% of the signalling rate which seems to be what you are seeing.

There is some evidence that Bluetooth LE (low energy) has a particularly high protocol overhead and a 1mbps connection only has 256kbps of usable bandwidth. From a Digikey comparison of Bluetooth and RF technologies:

Bluetooth LE supports an over-the-air data rate of 1Mbps, which is sufficient for wireless HID applications. However, application throughput is only 256kbps due to overhead. Proprietary protocols have the advantage of limiting packet overhead as per application requirements, and hence, may be able to support higher throughput. For applications like gaming mice, audio applications, and touch applications that require an effective throughput of greater than 250kbs, implementing Bluetooth LE will fall short of proprietary standards.

L2CAP and other protocols used by Bluetooth are designed to limit protocol overheads and ensure best use of data, LE may be designed to minimise the need for packet retransmission and ensure a reliable connection which would probably account for a pretty large overhead.

I'd be surprised if your phone is forcing the use of the Low Energy protocol and limiting speed that way, but it is possible. It is possible, but not likely, that Apple chose an ultra-low-power Bluetooth chip to go in the Macbook Air in order to extend battery life.

I've tested between two (high end) devices myself and got 148kilobytes per second. Took 7.5 minutes to transfer 67 megabytes. So somewhere around the 1.5mbps area.

Out of preference you will want to use WiFi to send files to your phone, if it supports it, or you will have to connect the phone to your computer using a physical cable.

Bluetooth is designed for small device connectivity and sending small batches of information over the potentially congested 2.4GHz frequency band. It is not very good for a large scale file transfer unless the devices both support Bluetooth High Speed.

  • 1
    Impressive answer! Nothing to do about it, then. I'm just surprised that this is offered as a service at all (on the phone's side), since it's practically useless.
    – forthrin
    Aug 13 '17 at 14:20
  • It'd be okay to pass a smallish file or song between devices, but I agree that for any significant amount of data it is nearly useless and I'd only go for Bluetooth if both devices had the high speed mode which would be close to WiFi speeds. It's still a useful protocol for playing music over though, the bitrate requirements for just streaming music is a lot more in the right area for Bluetooth.
    – Mokubai
    Aug 13 '17 at 14:39
  • Trying this today from Samsung/Android phone to 2017 Macbook Air using Bluetooth and getting ~15kb/second transfer!! An estimated 5.5 hrs for 350mb file... hehe. Looks like I will need third party software to do it over wifi?
    – Drewdavid
    Dec 10 '20 at 20:55
  • @Drewdavid if you can set up Samba (SMB) file sharing on the Mac then the built-in "My files" program on Samsung phones should be able to browse to it. The app might need an update but the latest version has a "network storage" space below all the cloud accounts that can browse SMB1/SMB2 shares.
    – Mokubai
    Dec 31 '20 at 11:19

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