The LTE Band Challenge
With LTE, the complexity of including a reasonable number of different frequency bands in a mobile device not only for LTE but also for GSM and UMTS is once again getting trickier. Here's a how I see things from a historical point of view and where I think we are heading:
Once upon a time the wireless frequency landscape was quite simple. When GSM started in Europe, there was only a single frequency band in the 900 MHz band which all network operators used. Sure there was the legacy analog network in the 450 MHz band but nobody seriously thought about working on dual mode devices. GSM or bust! Things got a bit more complicated when the second band in the 1800 MHz range was opened for GSM at the end of the 90's and but it didn't take take device manufacturers long to come up with dual mode devices. In the US things were pretty similar but the remainder of this post continues with a Europe point of view.
Since then, things have gotten much more complicated. With UMTS, things started well for some time with 2100 MHz being 'the' 3G band around the world, except for the US. In the US, UMTS and GSM are used in the 850 and 1900 MHz ranges and these days also on the 1700/2100 MHz band combination. In Europe in the meantime, UMTS in the 900 MHz band has also taken off in some countries. I guess this was the point where the number of bands used around the world and the number of bands supported in a single mobile device really started to diverge. Today, the state of the art from a European point of view is the following combination:
- Quad band GSM support (850, 900, 1800 and 1900 MHz)
- UMTS tri-band (2100, 900 and one of the US bands)
And now with LTE just around the corner things are about to get even more complicated. Here's the bands where I think LTE will see the day of light in the next two to three years:
- In Europe LTE will likely start on 2600 MHz and potentially also on 1800 MHz and 2100 MHz
- And then there's the digital dividend band in the 800 MHz range which is likely to be used in some countries to bring broadband connectivity with LTE to rural areas.
- In Japan, LTE will be used on 2100 MHz with an additional band likely to follow.
- In the US, the situation is even more divergent. Each network operator seems to have its own band. Verizon uses a 10 MHz block in the 700 MHz range and another operator has another block in the same range but with exchanged uplink/downlink assignments. Some operators might launch LTE in the 1700/2100 MHz band combination and there are speculations of a satellite backhaul based LTE network with its own frequency range. Finally, there are rumors of Clearwire jumping from WiMAX to LTE in the 2600 MHz band but with TD-LTE.
From my point of view, this frequency diversity is far from ideal for everyone involved. For users it's an issue as global roaming capabilities of devices will get worse and worse. Also, especially in the US, it will be difficult for users to switch between networks by changing SIM cards and subscriptions while keeping the device. For network operators and device manufacturers it's also far from ideal as some will have trouble getting good devices as volumes are just too low to reach good prices. There might be multi-frequency LTE devices tailored for the US market but since almost every operator uses different legacy network technologies and frequency ranges the potential band and technology combinations for GSM, CDMA, UMTS and LTE are huge.
So what's the way out of this? To me it looks like it's in the hand of device manufacturers as the number of frequency bands will not shrink anytime soon. The question is if the ever growing number of bands and backwards compatibility combinations change the device design?
- Is it physically possible today to support so many bands? Software defined radios have been discussed for many years but as far as I know antennas and filters are not so easily to be adapted to different frequency ranges with software only.
- Or could the radio part of the device in the future be built in a way that it can easily be interchanged?
- How about exchangeable radio modules? With this approach I would in the future select a SIM, a mobile device and an RF module and maybe one or two extra for international roaming? Or will we just have to live with the situation as it grows worse?
- And then, there's still Wi-Fi which, at least so far, can be used universally around the world. Most smartphones today have Wi-Fi built there's no ubiquitous coverage and logging into foreign Wi-Fi networks automatically is still a dream.
