LTE: The World Standard for 4G

So it is ironic to me that for the first time we are on the verge of having a worldwide standard for broadband services (data and then voice) yet because of the way spectrum is allocated around the world we still won’t have a true world phone on LTE anytime soon.

Recently both Clearwire and Sprint have stated that they will be moving to LTE. Sprint is using its 1900-MHz Frequency Division Duplex spectrum (FDD) and Clearwire is using its existing Time Division Duplex Spectrum (TDD). On TDD spectrum the name for LTE is TD-LTE and it is being pushed hard in China so Clearwire will be able to take advantage of that work. Add to this that some of Qualcomm’s chipsets already support both the FDD and TDD flavors of LTE and that the TDD WiMAX devices that are on the Clearwire network can be easily reworked for TDD LTE and both Sprint and Clearwire should have little trouble moving from their existing WiMAX systems to LTE. All it will take for both of them is money, which may be a big deal for Clearwire and which has some of Sprint’s shareholders jumpy, but in the end it is the correct move for both companies.

WiMAX has suffered significantly in the past two years as LTE has been adopted by more and more commercial operators around the world. It should be clear to everyone by now that LTE will be the 4G technology of choice for worldwide deployment and that for the first time in many years we are on the verge of moving toward a worldwide standard for data (first) and later voice services. Support for WiMAX has faltered since Intel pulled the plug on its program to make WiMAX a world standard 4G technology and it stopped investing millions of dollars in supporting WiMAX around the world. Will WiMAX die? Will the next generation of WiMAX ever make it out of the IEEE and be deployed? Many people still believe in WiMAX so it is too soon to pronounce it dead. It has a place as a point-to-point IP-based wireless technology but since Clearwire and Sprint are both moving to LTE the devices that support WiMAX will be few and far between in the future.

So LTE is what we will have going forward. LTE will keep getting better and more spectrally efficient, which will translate to faster data speeds and better data rates at cell edges. Before too long we will be moving into the world of LTE Advanced, which truly meets the speed goals set out by the 3GPP a few years ago for 4G networks. So all is right with the world, correct? LTE as a standard should mean devices capable of using LTE anywhere in the world and providing fast data speeds and voice (soon) with a single device. Well think again. We are a long way from where LTE in a single device will provide us with worldwide wireless communications services.

Today, both the FDD and TDD flavors of LTE are being deployed on a total (depending on who you listen to) of somewhere between 33 and 41 different portions of the radio spectrum. This spectrum runs the gamut from 700 MHz (United States, Canada) to 800, 900, 1700, 1800, 1900, 2100, and 2500 MHz, some of which is FDD spectrum and some of which is TDD spectrum. Obviously this promises to make life difficult for everyone: chip vendors, network equipment vendors, network operators, device vendors, and ultimately the customers of the service.

Today LTE phones in the United States, for example, already include 700, 800, and 1900-MHz radios and support CDMA 1X, CDMA EV-DO REV A and LTE on Verizon. On AT&T they will support 700, 800, and 1900 MHz GSM, HSPA, HSPA+, and LTE. Phones also include a GPS receiver, Bluetooth, and Wi-Fi. Soon some phones will also have to support 1700/2100 MHz (AWS-1 spectrum), and if they are to be world phones they will also have to support some of these technologies on 900, 1800, and 2100 MHz as well. That is a lot to cram into a small form factor device: lots of different antennas, lots of duplexers (used to enable transmitting and receiving on the same antenna), filters, and other RF components. We keep pushing the design engineers and they keep delivering devices that have all of this inside them. But as we move forward into the world of LTE on a global basis there will come a point where even the best engineers in the world will run out of ideas on how to make all of these bands work inside a single device while providing battery life that is acceptable to the customer.

So it is ironic to me that for the first time we are on the verge of having a worldwide standard for broadband services (data and then voice) yet because of the way spectrum is allocated around the world we still won’t have a true world phone on LTE anytime soon. The way spectrum is allocated around the world is a convoluted process controlled by the ITU, but for the most part, once it has been allocated how it is used is up to the various countries. The 700-MHz spectrum in the United States will be used by Canada and perhaps Latin America over time. Perhaps it will eventually be used for LTE in other parts of the world but that remains to be seen.

Once an LTE system is installed in a specific portion of the spectrum and devices are sold, moving LTE to another band would not only require building a new network, it would also involve replacing customer devices so they are capable of operating in the new spectrum. In other words, once a network is built out and devices are available for it, it is really difficult to move to another portion of the spectrum. But if we had a single or perhaps three spectrum bands that provided worldwide LTE coverage, the price of the devices would come down considerable because the vendors could build a single device they could sell into every market in the world. This would result in significant savings for the vendors, network operators, and customers.

But until this happens, if it ever happens, which is anyone’s guess, we will have to live with what we have, which is a worldwide standard for our wireless interface that will replace 2G and 3G networks over time. However, it will not be a world standard in the true sense of the phrase because of all of the different portions of the spectrum on which it is being deployed. Perhaps software-defined radio technology will help with this situation. However, because you can configure a radio using software does not negate the issues of filters, duplexers, and antennas.

Antennas in cell phones are not operating as efficiently as they should. This is one reason that land mobile radio systems employ external antennas or antennas mounted on vehicles. They are more efficient, radiating more of the signal generated by the device and receiving more of the signal sent from the fixed site. Antennas embedded into cell phones are very inefficient but they are good enough for the systems to work. The laws of physics for antenna design can be bent a little but not broken, and there is a relationship between antenna length for a given portion of the spectrum and its effectiveness. It is possible to use some antennas for multiple bands, it is done all the time, but if there is not a mathematical relationship between the length of the antenna and the portion(s) of the spectrum on which it must work then there is a mismatch that causes the antenna to function poorly on some of the portions of the spectrum on which it is being used.

The bottom line is that most countries are not interested in making it easy for roamers to enter their area of operations. Both the countries and their operators are more interested in taking care of local customers. In reality, only about 15% of the world wireless population ever leaves their home network for other parts of the world so it is not a priority for these countries to worry about the differences in the spectrum allocations for the various technologies. Hopefully, this could change over time but at the moment it is a fact of life. Even within the United States only 15% of the population ever moves from their home area to other parts of the country so systems such as MetroPCS and Cricket, even though they offer nationwide service, are successful by offering better pricing because most of their customers never leave their prime operating areas.

With all of the different portions of spectrum being used for LTE, the cost of the devices will remain higher than they would be if a vendor built a single LTE device that would be usable in most of the world’s markets. This would mean that the devices would be less expensive to build, would cost the network operators less to buy down (those that do), and consumers would get better pricing. The down side for operators is that it would also enable customers to quickly and easily move from one network to another without having to purchase another device. I am sure that the reason Sprint now has the iPhone 4s, in addition to its guaranteed order to Apple, is that the iPhone is already available on Verizon and therefore already capable of both CDMA 1X and CDMA EV-DO, and both Verizon and Sprint use 1900-MHz spectrum (although Verizon also uses 800-MHz spectrum).

Going forward it appears to me as though HSPA+ will be the worldwide fallback data service of choice for those who need a device capable of being used in most countries around the world. In Europe, Asia, and the Americas, HSPA+ is used on a number of different portions of the spectrum but not nearly as many as LTE. To produce an LTE-capable phone with world capabilities will mean making sure that HSPA and HSPA+ are supported on 800, 900, 1700, 1800, 1900, and 2100 MHz. Since these phones already exist it should be possible for U.S. LTE network operators to add 700-MHz LTE to the mix and still have a viable phone with decent battery life.

LTE on so many bands is problematical and it is an issue in the United States. Even in the 700-MHz band, AT&T’s and Verizon’s spectrum are separated from each other so a phone that will cover both networks will need additional filters and duplexers in order to be able to provide service on both networks. The first LTE 700-MHz phones on the market will provide service on one or the other of the networks but not both. If you add the components to cover both networks and you also want the phone to be a world phone, you have to add the other six portions of the spectrum and several different over-the-air technologies. All of this makes these phones very complex and it amazes me that the design engineers don’t simply shake their heads and walk away from the issue. Instead, they always seem to find a way to make everything work and work well.

As we approach worldwide acceptance of LTE as the 4G wireless technology of choice, we will probably still have compatibility problems for many years to come. It would be ideal if those who set spectrum policy at the ITU and then the national level would work on trying to harmonize LTE into only a few different portions of the spectrum. This would provide the best of all worlds, but as I mentioned above, since this issue affects only about 15% of the wireless population I believe it will be a long time in coming.

Andrew M. Seybold