LTE Cat-1bis Devices

Even in the first version of the LTE standards (3GPP Release 8) the specs contained a device category referred to as Category-1 (CAT-1). This category was envisioned for computationally restricted devices with a maximum throughput of 10 Mbit/s. This was little compared to CAT-3 devices which was the lowest class used for smartphones, tables, USB dongles, etc. that had to support a downlink throughput of 100 Mbit/s. Nothing ever came of Cat-1 until a few years ago, when some manufacturers started producing wearable such as watches, i.e. very small devices with small batteries and little space for advanced LTE features.

For such devices Cat-1 seemed a good idea and the standard was vague enough to allow implementations with a single antenna. This was not liked by all as at the time the generally accepted gospel was that devices have to have two antennas for downlink reception for network capacity reasons. However, the standards were not quite clear about this so some companies argued that Cat-1 devices could be built with a single antenna without violating 3GPP specs. The discussion went on for some time and at a point I lost a bit of interest in it. A bit too early, as it turns out, because 3GPP Release 14 now contains the new device category Cat-1bis in TS 36.306, for which the use of a single antenna for reception is now explicitly specified!

So here we go, it looks like some companies got their way and a single antenna UE is fully legal now in the 3GPP universe! Apart from a very small number of ‘smart’ watches I haven’t seen ‘wearables’ that include LTE yet. And those that do, such as for example the Samsung Gear S3 don’t use Cat-0 according to Samsung’s product page. Instead the watch is listed as LTE Cat-4 with 75 Mbit/s which also points to a single antenna implementation, as Cat-4 with 2 RX antennas goes up to 150 Mbit/s. So much for caring about the 2 RX antenna requirement in general. But who knows, lets see if ongoing miniaturization will give rise to more LTE based wearables, this time perhaps around with Cat-1bis LTE with 10 Mbit/s.